Publications

Crystalline suspensions of monoclonal antibodies (mAbs) have great potential to improve drug substance isolation
and purification on a large scale and to be used for drug delivery via high-concentration formulations. Crystalline mAb suspensions
are expected to have enhanced chemical and physical properties relative to mAb solutions delivered intravenously, making them
attractive candidates for subcutaneous delivery. In contrast to small molecules, the development of protein crystalline suspensions is
not a widely used approach in the pharmaceutical industry. This is mainly due to the challenges in finding crystalline hits and the
suboptimal physical properties of the resulting crystallites when hits are found. Modern advances in instrumentation and increased
knowledge of mAb crystallization have, however, resulted in higher probabilities of discovering crystal forms and improving their
particle properties and characterization. In this regard, physical, analytical characterization plays a central role in the initial steps of
understanding and later optimizing the crystallization of mAbs and requires careful selection of the appropriate tools. This
contribution describes a novel crystal structure of the antibody pembrolizumab and demonstrates the usefulness of small-angle X-ray
scattering (SAXS) for characterizing its crystalline suspensions. It illustrates the advantages of SAXS when used to (i) confirm
crystallinity and crystal phase of crystallites produced in batch mode; (ii) confirm crystallinity under various conditions and detect
variations in crystal phases, enabling fine-tuning of the crystallizations for phase control across multiple batches; (iii) monitor the
physical response and stability of the crystallites in suspension with regard to filtration and washing; and (iv) monitor the physical
stability of the crystallites upon drying. Overall, this work highlights how SAXS is an essential tool for mAb crystallization
characterization. Less |Related Solutions: SONICC^®

This research delves into the early nucleation stages of phycocyanin, a protein pivotal for its fluorescent properties and crystalline stability and holding considerable potential for biotechnological applications. The paper contrasts traditional crystallization methods with the innovative Langmuir–Blodgett nanotemplate approach, aiming to enhance molecular assembly and nucleation processes. The study employs Langmuir–Blodgett nanotemplates alongside second-order nonlinear imaging of chiral crystal (SONICC) spectroscopy. This combination is designed to orderly organize phycocyanin molecules and provide a sensitive visualization of early-stage crystal formation, capturing the intricate dynamics of protein crystallization. The experiments were conducted under controlled conditions, where surface pressure was maintained at 26 mN/m and barrier speed at 70 cm/min to optimize the monolayer formation at the air–water interface. The Langmuir–Blodgett method, compared to traditional vapor diffusion techniques, shows improvements in the uniformity and efficiency of nucleation. The sensitivity of SONICC spectroscopy significantly enhances the visualization of the nucleation process, revealing a more structured and uniform crystalline assembly in the early stages of formation. This method demonstrates a substantial improvement in nucleation dynamics, leading to a more orderly growth process and potentially larger, well-ordered crystals. Integrating Langmuir–Blodgett nanotemplates with SONICC spectroscopy offers a significant step in understanding protein crystallization processes with insights into the nucleation and growth of protein crystals and broad implications for refining crystallography methodologies of protein-based biomaterials, contributing to the advancement of structural biology and materials science. Less |Related Solutions: SONICC^®

Spatial heterogeneity is ubiquitous across life and the universe; the same is true for phase separating pharmaceutical formulations, cells, and tissues. To interrogate these spatially-varying complicated samples, simple analysis techniques such as fluorescence recovery after
photobleaching (FRAP) can provide information on molecular transport. Conventional FRAP
approaches localize analysis to small spots, which may not be representative of trends across the full field of view. Taking advantage of strategies used for structures illumination, an approach has been developed to use patterned illumination in combination with FRAP for probing large fields of view while representatively sampling. Patterned illumination is used to establish a concentration
gradient across a sample by irreversibly photobleaching fluorophores, such as with the simple comb pattern photobleach presented in Chapters 1 and 4. Patterned photobleaching allows spatial Fourier-domain analysis of multiple spatial harmonics simultaneously. In the spatial FT-domain the real-space photobleach signal is integrated into puncta, greatly increasing the signal to noise ratio compared to conventional point-bleach FRAP. The order of the spatial harmonic is directly related to the length scale of translational diffusion measured, with a series of harmonics accessing
diffusion over many length scales in a single experiment. Measurements of diffusion at multiple length scales informs on the diffusion mechanism by sensitively reporting on deviations away from normal diffusion. Complementing the physical hardware for inducing patterned illumination, this dissertation
introduces novel algorithms for reconstructing spatially-resolved diffusion maps in heterogeneous materials by combining Fourier domain analysis with patterned photobleaching. FT-FRAP is introduced in Chapter 1 for interrogating phase-separating samples using beam-scanning instrumentation for comb-bleach illumination. This analysis allowed disentangling separate contributions to diffusion from normal bulk diffusion and an interfacial exchange mechanism only available due to multi-harmonic analysis. The introduction of a dot-array bleach pattern using widefield microscopy is presented in Chapter 2 for high-throughput detection of mobility in simple binary systems as well as for segmentation in phase-separating pharmaceutical formulations. The analysis becomes more complicated as more components are added to the system such as a surfactant. Introduced in chapter 3, FT-FRAP with dot-array photobleaching was shown to be
useful for characterizing diffusion of phase-separating micro-domain smaller than a single pixel of the camera. Supported by simulations, a biexponential fitting model was developed for
quantification of diffusion by multiple species simultaneously. Chapter 4 introduces imaging
inside of 3D particles comprised of an active pharmaceutical ingredient (API) in
microencapsulated agglomerates which exhibited strong interfacial exchange. Multi-photon excited fluorescence enabled imaging a small focal volume within the particles. Less |Related Solutions: SONICC^®

For optimal bioperformance, the drug in an amorphous solid dispersion (ASD) should ideally not undergo crystallization in the solid dosage form during storage or from the supersaturated solution generated upon dissolution. Incomplete processing during hot melt extrusion (HME) can lead to residual crystallinity. Commonly, residual crystallinity is evaluated using techniques such as powder X-ray diffraction (pXRD). However, residual crystallinity at levels below the detection limit of pXRD can be detrimental to the ASD performance. The goal of this study was to evaluate the impact of different levels of residual crystallinity in an ASD containing the fast-crystallizing drug posaconazole (PCZ) and hydroxypropyl methylcellulose acetate succinate (HPMCAS) on dissolution and additional crystallization. ASDs with and without residual crystallinity at 10, 25, and 50 wt % drug loadings were prepared using HME, processing at temperatures below and above the critical temperature, which was calculated using the Flory–Huggins theory. Some of the ASDs contained levels of residual crystallinity that were below the quantification limit of pXRD, requiring the use of second harmonic generation (SHG) imaging. The impact of residual crystallinity on dissolution was studied by using two-stage dissolution. Additional characterization in support of dissolution measurements included SHG imaging and particle size evolution with focused beam reflectance measurement (FBRM) using pH-shift experiments. The 10 wt % ASD processed below the critical solution temperature contained residual crystallinity of 0.3%, which promoted rapid crystallization when the ASD was in a solution environment. Real-time monitoring of both the solid and solution phases revealed that PCZ in ASDs containing residual crystals underwent crystallization both in the matrix and from solution. The study supports the need to select a sufficiently sensitive crystallinity estimation technique, a suitable discriminatory dissolution technique, and appropriate HME processing conditions in order to optimize and achieve successful performance of ASDs of fast-crystallizing drugs. Less |Related Solutions: SONICC^®

Analytical theory is proposed predicting remarkably large and fully electric-dipole-allowed circular dichroism (CD) in electronic ultraviolet-visible (UV-vis) absorbance spectroscopy of uniaxial surface assemblies. Partial depolarization of the transmitted beam provides a pathway for surface-specific and chiral-specific dissymmetry parameters that are orders of magnitude greater than those from analogous measurements of isotropic systems. Predictions of the model generated using ab initio quantum chemical calculations with no adjustable parameters agreed with UV-vis absorbance CD measurements of naproxen microcrystals prepared on hydrophilic substrates. Notably, these calculations correctly predicted (i) the key spectroscopic features, (ii) the relative magnitudes of chiral-specific peaks in the CD spectrum, (iii) the absolute CD sign, and (iv) the reciprocal CD sign inversion arising from sample reorientation in the instrument. These results connect the molecular structure and orientation to large CD observable in oriented thin-film assemblies, with the potential for further extension to broad classes of chiral-specific spectral analyses. Less |Related Solutions: SONICC^®

Vision is initiated by the rhodopsin family of light-sensitive G protein-coupled receptors (GPCRs)1. A photon is absorbed by the 11-cis retinal chromophore of rhodopsin, which isomerizes within 200 femtoseconds to the all-trans conformation2, thereby initiating the cellular signal transduction processes that ultimately lead to vision. However, the intramolecular mechanism by which the photoactivated retinal induces the activation events inside rhodopsin remains experimentally unclear. Here we use ultrafast time-resolved crystallography at room temperature3 to determine how an isomerized twisted all-trans retinal stores the photon energy that is required to initiate the protein conformational changes associated with the formation of the G protein-binding signalling state. The distorted retinal at a 1-ps time delay after photoactivation has pulled away from half of its numerous interactions with its binding pocket, and the excess of the photon energy is released through an anisotropic protein breathing motion in the direction of the extracellular space. Notably, the very early structural motions in the protein side chains of rhodopsin appear in regions that are involved in later stages of the conserved class A GPCR activation mechanism. Our study sheds light on the earliest stages of vision in vertebrates and points to fundamental aspects of the molecular mechanisms of agonist-mediated GPCR activation. Less |Related Solutions: SONICC^®

Subcutaneous (SC) administration is a desired route for monoclonal antibodies (mAbs). However, formulating mAbs for small injection volumes at high concentrations with suitable stability and injectability is a significant challenge. Here, this work presents a platform technology that combines the stability of crystalline antibodies with injectability and tunability of soft hydrogel particles. Composite alginate hydrogel particles are generated via a gentle centrifugal encapsulation process which avoids use of chemical reactions or an external organic phase. Crystalline suspension of anti-programmed cell death protein 1 (PD-1) antibody (pembrolizumab) is utilized as a model therapeutic antibody. Crystalline forms of the mAb encapsuled in the hydrogel particles lead to stable, high concentration, and injectable formulations. Formulation concentrations as high as 315 mg mL−1 antibody are achieved with encapsulation efficiencies in the range of 89–97%, with no perceivable increase in the number of antibody aggregates. Bioanalytical studies confirm superior maintained quality of the antibody in comparison with formulation approaches involving organic phases and chemical reactions. This work illustrates tuning the alginate particles’ disintegration by using partially oxide alginates. Crystalline mAb-laden particles are evaluated for their biocompatibility using cell-based in vitro assays. Furthermore, the pharmacokinetics (PK) of the subcutaneously delivered human anti-PD-1 mAb in crystalline antibody-laden alginate hydrogel particles in Wistar rats is evaluated. Less |Related Solutions: SONICC^®

Biological macromolecules, such as proteins and nucleic acids, are composed of linked monomers and play an important role in biological functions based on their three-dimensional (3D) structures. Proteins are composed of one or more polypeptide chains of different amino acid residues. These polypeptide chains fold into a 3D structure to constitute a functional protein. The 3D structure information of proteins can be applied to analyze protein-ligand processes and interactions. Furthermore, the 3D structure information of proteins can serve as the basis for structure-based target selection for drug discovery research. As it is not possible for protein 3D structures to be seen even under the most advanced light microscope, other methods are employed to determine their 3D structures. Since proteins can form crystals, X-ray crystallography can be used to solve the 3D structures of these proteins. In the deposited protein data bank (PDB), nearly 90% of protein structures are solved through X-ray crystallography. As a result, X-ray crystallography is the fundamental method for characterizing the atomic structure of proteins.
Notably, the primary and oldest method of X-ray crystallography is single-crystal X-ray diffraction. The major challenge of using this method is obtaining well-ordered crystals with a suitable size for crystallographic data collection. The demand for larger and well-ordered protein crystals has introduced difficulties for those proteins which cannot grow to larger dimensions.
With the development of synchrotron radiation, the brilliant beams achieved through synchrotron radiation have decreased the necessary protein crystal size for conventional X-ray diffraction crystallography. A free-electron laser (FEL) uses a much brighter beam, which decreases the dimensions of protein crystals that are required for diffraction data collection. Consequently, today micro-sized and nano-sized protein crystals are preferred. This preference for small crystals creates a strong demand to develop and establish new methods and instrumentation to identify, detect and analyze protein nano- and micro-crystals.
Current methods to detect micro-sized and nano-sized protein crystals mainly include bright-field imaging, ultraviolet fluorescence (UV) imaging, second harmonic generation (SHG) imaging and X-ray powder diffraction. However, each of these imaging methods has its own limitations. Because of this, a reliable and advanced imaging method is required.
The present work describes an in-house developed multi-modalities multiphoton instrument that is composed of three imaging methods, which are third-harmonic generation (THG), second-harmonic generation (SHG) and three-photon excited ultraviolet fluorescence (3PEUVF). To analyze the feasibility and detection sensitivity of the multimodal MPM system, different protein crystals and salt crystals were prepared with different symmetries. The combined effect of THG, SHG and 3PEUVF imaging is precise, as the system is able to identify nano- or micro-sized protein crystals and can distinguish between protein crystals, salt crystals and amorphous aggregates.
During the testing process, a detailed study of the angular-dependent SHG polarization response was conducted. The results demonstrated that the SHG polarization response of the crystal is highly sensitive to the lattice orientation of crystals. As a result, SHG polarization can extend its potential for protein crystal detection and characterization.
To better compare the differences between commercial imaging instruments and MPM system instruments, the in vitro nanocrystal samples were simultaneously tested with dynamic light scattering (DLS), depolarized dynamic light scattering (DDLS), transmission electron microscopy (TEM) and X-ray powder diffraction. For second-order nonlinear optical imaging of chiral crystals (SONICC) and MPM imaging instrument, the experimental results illustrate that the MPM imaging instrument processes a non-invasive detection method and high detection sensitivity to detect in vitro and in vivo protein nanocrystals. Notably, the nano-sized or sub-micro-sized protein crystals can be detected efficiently through the MPM system. For in vitro protein crystals, the MPM system reduces the risk of obtaining false-negative and false-positive results in crystal detection through providing a higher signal sensitivity. Moreover, the MPM imaging system offers the possibility for in vivo crystals to be detected. Furthermore, weak SHG signals from centrosymmetric crystals are also observed with the MPM system. Less |Related Solutions: SONICC^®

To enhance the bioavailability of poorly soluble therapeutics, enabling formulations that generate supersaturation are currently of great interest. There is limited knowledge of how the gastrointestinal environment can influence the complex phase behavior of these systems, in particular, crystallization. Simulated media are generally used to mimic physiologically relevant fluids, although their predictability remains unknown for crystallizing systems since they are simplified models of the gastrointestinal fluids. The purpose of this study was to evaluate and compare how different simulated media, as well as aspirated intestinal fluid, impact the phase behavior of supersaturated solutions of two poorly soluble compounds, atazanavir and posaconazole, in fasted-state conditions. The onset of nucleation and progression of crystallization were found to be highly medium dependent. In the aspirated fluid, the crystallization kinetics for both compounds was significantly reduced compared to commercial simulated media. The use of simple buffers or current simulated fluids as surrogates for intestinal fluids appears to require further verification when attempting to predict crystallization kinetics of supersaturated solutions, based on the observed lack of correlation between commercial media and human fluids. The findings highlight the importance of carefully considering the composition of in vitro testing media for assessing crystallization kinetics, particularly in the context of supersaturating formulations. Less |Related Solutions: SONICC^®

Unique challenges in formulating the next generation of active pharmaceutical ingredients (APIs) into stable formulations demand analytical tools not currently available using common benchtop methods. Herein, we review approaches to address some of these challenges through leveraging nonlinear optical (NLO) interactions between light and matter. Applications in dissolution testing, polymorphism, and accelerated stability testing highlight the breadth of these methods. The specificity of second harmonic generation (SHG) to chiral crystals supports rapid polymorphism analysis at the limit of individual crystals and informs formulations designs to address solubility challenges common in emerging drug candidates. Coherent anti-Stokes Raman spectroscopy (CARS) and stimulated Raman spectroscopy (SRS) provide vibration-specific microscopy of final dosage forms to inform composition at video-rate acquisition speeds and ~1 μm spatial resolution. Recent results are reviewed to illustrate challenges in designing formulations for emerging drug candidates and opportunities for the development of NLO tools tailored to meet them. Less |Related Solutions: SONICC^®

The unique crystallization properties of the antenna protein C-phycocyanin (C-PC) from the thermophilic cyanobacterium Thermosynechococcus elongatus are reported and discussed. C-PC crystallizes in hundreds of significantly different conditions within a broad pH range and in the presence of a wide variety of precipitants and additives. Remarkably, the crystal dimensions vary from a few micrometres, as used in serial crystallography, to several hundred micrometres, with a very diverse crystal morphology. More than 100 unique single-crystal X-ray diffraction data sets were collected from randomly selected crystals and analysed. The addition of small-molecule additives revealed three new crystal packings of C-PC, which are discussed in detail. The high propensity of this protein to crystallize, combined with its natural blue colour and its fluorescence characteristics, make it an excellent candidate as a superior and highly adaptable model system in crystallography. C-PC can be used in technical and methods development approaches for X-ray and neutron diffraction techniques, and as a system for comprehending the fundamental principles of protein crystallography. Less |Related Solutions: SONICC^®

Monoclonal antibodies are therapeutic molecules known for their high specificity and versatility in the treatment of cancer and autoimmune disorders, but dosage forms are typically limited to low concentrations and large fluid volumes due to formulation challenges. Hydrogel microsphere formulations offer a route to quicker, patient-friendly dosing regimens for monoclonal antibodies with high loading and favorable flow properties needed for injection through a narrow syringe needle under moderate applied force. Crystals of an intact monoclonal antibody are prepared as a concentrated suspension (>300 mg mL−1) which is then encapsulated within hydrogel microspheres with diameters as small as 30 µm. The hydrogel microspheres contain up to 56 wt% (dry basis) monoclonal antibody and release within 4 days under in vitro dissolution conditions. The hydrogel microspheres are concentrated into densely packed suspensions containing up to 300 mg mL−1 monoclonal antibody to evaluate their flow. These hydrogel formulations shear-thin and have lower viscosity when compared to both liquid and suspended crystal forms of the monoclonal antibody, demonstrating the potential of hydrogel microsphere encapsulants as a carrier which can mask undesirable flow properties of concentrated antibody therapeutics. Less |Related Solutions: SONICC^®

There is an increasing demand for rapid, effective methods to identify and detect protein micro- and nano-crystal suspensions for serial diffraction data collection at X-ray free-electron lasers or high-intensity micro-focus synchrotron radiation sources. Here, we demonstrate a compact multimodal, multiphoton microscope, driven by a fiber-based ultrafast laser, enabling excitation wavelengths at 775 nm and 1300 nm for nonlinear optical imaging, which simultaneously records second-harmonic generation, third-harmonic generation and three-photon excited ultraviolet fluorescence to identify and detect protein crystals with high sensitivity. The instrument serves as a valuable and important tool supporting sample scoring and sample optimization in biomolecular crystallography, which we hope will increase the capabilities and productivity of serial diffraction data collection in the future. Less |Related Solutions: SONICC^®

The vast majority of biomolecular structural information is derived from macromolecular X-ray crystallography
methods, which serve as a foundation for structural biology and account for nearly 90% of the more than 165,000
biomolecular structures available in the PDB. Crystallography requires high-quality, well-diffracting crystals;
coaxing biomolecules into crystalline form is a rate-limiting step in structure determination. Searching for
conditions in which a biomolecule will crystallize often entails screening multiple different constructs against
thousands of crystallization conditions, requiring large sample amounts and many person-hours in a typical
laboratory set-up. In recent circumstances due to the COVID-19 pandemic, being physically in the laboratory for
setting up crystallization screening has become even more difficult. The Crystallization Center at HWI has been in
continuous operation as a crystallization resource for 20 years providing mail-in crystallization and remote access
to crystal growth monitoring. These services have become even more critical in the face of restrictions due to
COVID-19. The Crystallization Center is a high-throughput facility that provides expertise and access to state-ofthe-
art instrumentation to facilitate efficient and cost-effective crystallization. We have extensive robotics for
automated sample handling with very small sample volumes integrated with advanced imaging and a Formulatrix
Rock Imager with SONICC for rapid detection of crystal growth. The current pipeline in the Crystallization Center
screens for 1,536 conditions in one experimental plate and employs a robust imaging schedule, all of which is then
accessible remotely. Here, we will present details about the current capacity for high-throughput crystal growth
screening. We will also discuss innovations we are developing and opportunities for enhanced crystallization
services that will further facilitate crystallization for biomolecular structure determination, including scale up and
optimization, in situ diffraction experiments and enhanced imaging for crystal detection. Less |Related Solutions: SONICC^®

μNS is a 70 kDa major nonstructural protein of avian reoviruses, which cause significant economic losses in the poultry industry. They replicate inside viral factories in host cells, and the �NS protein has been suggested to be the minimal viral factor required for factory formation. Thus, determining the structure of �NS is of great importance for understanding its role in viral infection. In the study presented here, a fragment consisting of residues 448-605 of �NS was expressed as an EGFP fusion protein in Sf9 insect cells. EGFP-�NS(448-605) crystallization in Sf9 cells was monitored and verified by several imaging techniques. Cells infected with the EGFP-�NS(448-605) baculovirus formed rod-shaped microcrystals (5-15 �m in length) which were reconstituted in high-viscosity media (LCP and agarose) and investigated by serial femtosecond X-ray diffraction using viscous jets at an X-ray free-electron laser (XFEL). The crystals diffracted to 4.5 � resolution. A total of 4227 diffraction snapshots were successfully indexed into a hexagonal lattice with unit-cell parameters a = 109.29, b = 110.29, c = 324.97 �. The final data set was merged and refined to 7.0 � resolution. Preliminary electron-density maps were obtained. While more diffraction data are required to solve the structure of �NS(448-605), the current experimental strategy, which couples high-viscosity crystal delivery at an XFEL with in cellulo crystallization, paves the way towards structure determination of the �NS protein. Less |Related Solutions: SONICC^®

Amorphous solid dispersions (ASDs) are single-phase amorphous systems, where drug molecules are molecularly dispersed (dissolved) in a polymer matrix. The molecular dispersion of the drug molecules is responsible for their improved dissolution properties. Unambiguously establishing the phase behavior of the ASDs is of utmost importance. In this paper, we focused on the complementary nature of (modulated) differential scanning calorimetry ((m)DSC) and X-ray powder diffraction (XRPD) to elucidate the phase behavior of ASDs as demonstrated by a critical discussion of practical real-life examples observed in our research group. The ASDs were manufactured by either applying a solvent-based technique (spray drying), a heat-based technique (hot melt extrusion) or mechanochemical activation (cryo-milling). The encountered limiting factors of XRPD were the lack of sensitivity for small traces of crystallinity, the impossibility to differentiate between distinct amorphous phases and its impossibility to detect nanocrystals in a polymer matrix. In addition, the limiting factors of (m)DSC were defined as the well-described heat-induced sample alteration upon heating, the interfering of residual solvent evaporation with other thermal events and the coinciding of enthalpy recovery with melting events. In all of these cases, the application of a single analytical technique would have led to erroneous conclusions, whilst the combination of (m)DSC and XRPD elucidated the true phases of the ASD. Less |Related Solutions: SONICC^®

Crystallization processes have been widely used in the pharmaceutical industry for the manufacture, storage, and delivery of small-molecule and small protein therapeutics. However, the identification of crystallization processes for biologics, particularly monoclonal antibodies, has been prohibitive due to the size and the flexibility of their overall structure. There remains a challenge and an opportunity to utilize the benefits of crystallization of biologics. The research laboratories of Merck Sharp & Dome Corp. (MSD) in collaboration with the International Space Station (ISS) National Laboratory performed crystallization experiments with pembrolizumab (Keytruda�) on the SpaceX-Commercial Resupply Services-10 mission to the ISS. By leveraging microgravity effects such as reduced sedimentation and minimal convection currents, conditions producing crystalline suspensions of homogeneous monomodal particle size distribution (39 �m) in high yield were identified. In contrast, the control ground experiments produced crystalline suspensions with a heterogeneous bimodal distribution of 13 and 102 �m particles. In addition, the flight crystalline suspensions were less viscous and sedimented more uniformly than the comparable ground-based crystalline suspensions. These results have been applied to the production of crystalline suspensions on earth, using rotational mixers to reduce sedimentation and temperature gradients to induce and control crystallization. Using these techniques, we have been able to produce uniform crystalline suspensions (1�5 �m) with acceptable viscosity (<12 cP), rheological, and syringeability properties suitable for the preparation of an injectable formulation. The results of these studies may help widen the drug delivery options to improve the safety, adherence, and quality of life for patients and caregivers. Less |Related Solutions: SONICC^®

Purpose
The overall goal of this study was to investigate the dissolution performance and crystallization kinetics of amorphous solid dispersions (ASDs) of a weakly basic compound, posaconazole, dispersed in a pH-sensitive polymeric matrix consisting of hydroxypropyl methylcellulose acetate succinate (HPMC-AS), using fasted-state simulated media.

Methods
ASDs with three different drug loadings, 10, 25 and 50 wt.%, and the commercially available tablets were exposed to acidic media (pH 1.6), followed by transfer to, and dissolution in, intestinal media (pH 6.5). Parallel single stage dissolution experiments in only simulated intestinal media were also performed to better understand the impact of the gastric stage. Different analytical methods, including nanoparticle tracking analysis, powder x-ray diffraction, second harmonic generation and two-photon excitation ultraviolet fluorescence microscopy, were used to characterize the phase behavior of these systems at different stages of dissolution.

Results
Results revealed that all ASDs exhibited some degree of drug release upon suspension in acidic media, and were also vulnerable to matrix crystallization. Upon transfer to intestinal media conditions, supersaturation was observed. This was short-lived for some dispersions due to the release of the crystals formed in the acid immersion stage which acted as seeds for crystal growth. Lower drug loading ASDs also exhibited transient formation of amorphous nanodroplets prior to crystallization.

Conclusions
This work emphasizes the significance of assessing the impact of pH change on dissolution and provides a fundamental basis of understanding the phase behavior kinetics of ASDs of weakly basic drugs when formulated with pH sensitive polymers. Less |Related Solutions: SONICC^®

Second harmonic generation (SHG) microscopy and Raman microscopy were used for
qualitative and quantitative analysis of pharmaceutical materials. Prototype instruments and
algorithms for sampling strategies and data analyses were developed to achieve pharmaceutical
materials analysis with low limits of detection and short measurement times.
Manufacturing an amorphous solid dispersion (ASD), in which an amorphous active
pharmaceutical ingredient (API) within polymer matrix, is an effective approach to improve the
solubility and bioavailability of a drug. However, since ASDs are generally metastable materials,
they can often transform to produce crystalline API with higher thermodynamic stability.
Analytical methods with low limits of detection for crystalline APIs were used to assess the
stability of ASDs. With high selectivity to noncentrosymmetric crystals, SHG microscopy was
demonstrated as an analytical tool, which exhibited a limit of detection of 10 ppm for ritonavir
Form II crystals. SHG microscopy was employed for accelerated stability testing of ASDs, which
provided a four-decade dynamic range of crystallinity for kinetic modeling. An established model
was validated by investigating nucleation and crystal growth based on SHG images. To achieve in
situ accelerated stability testing, controlled environment for in situ stability testing (CEiST) was
designed and built to provide elevated temperature and humidity, which is compatible with a
commercial SHG microscope based on our research prototype. The combination of CEiST and
SHG microscopy enabled assessment of individual crystal growth rates by single-particle tracking
and nucleation rates for individual fields of view with low Poisson noise. In addition, SHG
microscopy coupled with CEiST enabled the study of heterogeneity of crystallization kinetics
within pharmaceutical materials.
Polymorphism of APIs plays an important role in drug formulation development. Different
polymorphs of identical APIs may exhibit different physiochemical properties, e.g., solubility,
stability, and bioavailability, due to their crystal structures. Moreover, polymorph transitions may take place during the manufacturing process and storage. Therefore, analytical methods with high
speed for polymorph characterization, which can provide real-time feedback for the polymorphic
transition, have broad applications in pharmaceutical materials characterization. Raman
spectroscopy is able to determine the API polymorphism, but is hampered by the long
measurement times. In this study, two analytical methods with high speed were developed to
characterize API polymorphs. One is SHG microscopy-guided Raman spectroscopy, which
achieved the speed of 10 ms/particle for clopidogrel bisulfate. Initial classification of two different
polymorphs was based on SHG images, followed acquisition of Raman spectroscopy at the
selected positions to determine the API crystal form. Another approach is implementing of
dynamic sampling into confocal Raman microscopy to accelerate Raman image acquisition for 6-
folds. Instead of raster scanning, dynamic sampling algorithm enabled acquiring Raman spectra at
the most informative locations. The reconstructed Raman image of pharmaceutical materials has
<0.5% loss of image quality with 15.8% sampling rate. Less |Related Solutions: SONICC^®

With the advent of X-Ray free electron lasers (FELs), the field of serial femtosecond crystallography (SFX) was borne, allowing a stream of nanocrystals to be measured individually and diffraction data to be collected and merged to form a complete crystallographic data set. This allows submicron to micron crystals to be utilized in an experiment when they were once, at best, only an intermediate result towards larger, usable crystals. SFX and its variants have opened new possibilities in structural biology, including studies with increased temporal resolution, extending to systems with irreversible reactions, and minimizing artifacts related to local radiation damage. Perhaps the most profound aspect of this newly established field is that �molecular movies,� in which the dynamics and kinetics of biomolecules are studied as a function of time, are now an attainable commodity for a broad variety of systems, as discussed in Chaps. 11 and 12. However, one of the historic challenges in crystallography has always been crystallogenesis and this is no exception when preparing samples for serial crystallography methods. In the following chapter, we focus on some of the specific characteristics and considerations inherent in preparing a suitable sample for successful serial crystallographic approaches. Less |Related Solutions: SONICC^®

A statistical model enables auto-calibration of second harmonic generation (SHG) images for quantifying trace crystallinity within amorphous solid dispersions (ASDs) over a wide dynamic range of crystallinity. In this paper, we demonstrate particle-counting approaches for quantifying trace crystallinity, combined with analytical expressions correcting for particle overlap bias in higher crystallinity regimes to extend the continuous dynamic range of standard particle-counting algorithms through to the signal averaging regime. The reliability of the values recovered by these expressions was demonstrated with simulated data as well as experimental data obtained for an amorphous solid dispersion formulation containing evacetrapib, an Eli Lilly and Company compound. Since particle counting independently recovers the crystalline volume and the SHG intensity, the average SHG intensity per unit volume can be used as an internal calibrant for quantifying crystallinity at higher volume fractions, for which particle counting is no longer applicable. Less |Related Solutions: SONICC^®

Liquid microjets are a common means of delivering protein crystals to the focus of X-ray free-electron lasers (FELs) for serial femtosecond crystallography measurements. The high X-ray intensity in the focus initiates an explosion of the microjet and sample. With the advent of X-ray FELs with megahertz rates, the typical velocities of these jets must be increased significantly in order to replenish the damaged material in time for the subsequent measurement with the next X-ray pulse. This work reports the results of a megahertz serial diffraction experiment at the FLASH FEL facility using 4.3 nm radiation. The operation of gas-dynamic nozzles that produce liquid microjets with velocities greater than 80 m s-1 was demonstrated. Furthermore, this article provides optical images of X-ray-induced explosions together with Bragg diffraction from protein microcrystals exposed to trains of X-ray pulses repeating at rates of up to 4.5 MHz. The results indicate the feasibility for megahertz serial crystallography measurements with hard X-rays and give guidance for the design of such experiments. Less |Related Solutions: SONICC^®

The low limits of detection afforded by second harmonic generation (SHG) microscopy coupled with image analysis algorithms enabled quantitative modeling of the temperature-dependent crystallization of active pharmaceutical ingredients (APIs) within amorphous solid dispersions (ASDs). ASDs, in which an API is maintained in an amorphous state within a polymer matrix, are finding increasing use to address solubility limitations of small-molecule APIs. Extensive stability testing is typically performed for ASD characterization, the time frame for which is often dictated by the earliest detectable onset of crystal formation. Here a study of accelerated stability testing on ritonavir, a human immunodeficiency virus (HIV) protease inhibitor, has been conducted. Under the condition for accelerated stability testing at 50 �C/75%RH and 40 �C/75%RH, ritonavir crystallization kinetics from amorphous solid dispersions were monitored by SHG microscopy. SHG microscopy coupled by image analysis yielded limits of detection for ritonavir crystals as low as 10 ppm, which is about 2 orders of magnitude lower than other methods currently available for crystallinity detection in ASDs. The four decade dynamic range of SHG microscopy enabled quantitative modeling with an established (JMAK) kinetic model. From the SHG images, nucleation and crystal growth rates were independently determined. Less |Related Solutions: SONICC^®

The purpose of this work was to evaluate the impact of polymer(s) on the dissolution rate, supersaturation and
precipitation of indomethacin amorphous solid dispersions (ASD), and to understand the link between precipitate characteristics and redissolution kinetics. The crystalline and amorphous solubilities of indomethacin
were determined in the absence and presence of hydroxypropylmethyl cellulose (HPMC) and/or Eudragit � EPO
to establish relevant phase boundaries. At acidic pH, HPMC could maintain supersaturation of the drug by
effectively inhibiting solution crystallization while EPO increased both the crystalline and amorphous solubility
of the drug, but did not inhibit crystallization. The HPMC dispersion dissolved relatively slowly without undergoing crystallization while the supersaturation generated by rapid dissolution of the EPO ASD was short-lived
due to crystallization. The crystals thus generated underwent rapid redissolution upon pH increase, dissolving
faster than the reference crystalline material, and at a comparable rate to the amorphous HPMC dispersion. A
ternary dispersion containing both EPO and HPMC dissolved rapidly, generating an apparent drug concentration
that exceeded the amorphous solubility of indomethacin, leading to the formation of a new nanosized droplet
phase. These nanodroplets dissolved virtually immediately when the pH was increased. In conclusion, the
concentration-time profiles achieved from indomethacin ASD dissolution are a complex interplay of drug release
rate, precipitation kinetics and outcome, and precipitate redissolution rate, whereby each of these processes is
highly dependent on the polymer(s) employed in the formulation. Less |Related Solutions: SONICC^®

Various techniques have been used to detect crystallization in amorphous solid dispersions (ASD). However, most of these techniques do not enable the detection of very low levels of crystallinity (<1%). The
aim ofthe current study was to compare the sensitivity of second harmonic generation (SHG) microscopy
with powder X-ray diffraction (XRPD) in detecting the presence of crystals in low drug loading amorphous solid dispersions. Amorphous solid dispersions of the poorly water soluble compounds, flutamide
(FTM, 15 wt.% drug loading) and ezetimibe (EZT, 30 wt.% drug loading) with hydroxypropyl methylcellulose acetate succinate (HPMCAS) were prepared by spray drying. To induce crystallization, samples
were subsequently stored at 75% or 82% relative humidity (RH) and 40 ?C. Crystallization was monitored
by XRPD and by SHG microscopy. Solid state nuclear magnetic resonance spectroscopy (ssNMR) was
used to further investigate crystallinity in selected samples. For flutamide, crystals were detected by
SHG microscopy after 8 days of storage at 40 ?C/82% RH, whereas no evidence of crystallinity could be
observed by XRPD until 26 days. Correspondingly, for FTM samples stored at 40 ?C/75% RH, crystals were
detected after 11 days by SHG microscopy and after 53 days by XRPD. The evolution of crystals, that is
an increase in the number and size of crystalline regions, with time could be readily monitored from the
SHG images, and revealed the formation of needle-shaped crystals. Further investigation with scanning
electron microscopy indicated an unexpected mechanism of crystallization, whereby flutamide crystals
grew as needle-shaped projections from the surface of the spray dried particles. Similarly, EZT crystals
could be detected at earlier time points (15 days) with SHG microscopy relative to with XRPD (60 days).
Thus, SHG microscopy was found to be a highly sensitive method for detecting and monitoring the evolution of crystals formed from spray dried particles, providing much earlier detection of crystallinity than
XRPD under comparable run times. Less |Related Solutions: SONICC^®

Second harmonic generation (SHG) was integrated with Raman spectroscopy for the
analysis of pharmaceutical materials. Particulate formulations of clopidogrel bisulphate were
prepared in two crystal forms (Form I and Form II). Image analysis approaches enable
automated identification of particles by bright field imaging, followed by classification by SHG.
Quantitative SHG microscopy enabled discrimination of crystal form on a per particle basis with
99.95% confidence in a total measurement time of ~10 ms per particle. Complementary
measurements by Raman and synchrotron XRD are in excellent agreement with the
classifications made by SHG, with measurement times of ~1 minute and several seconds per
particle, respectively. Coupling these capabilities with at-line monitoring may enable real-time
feedback for reaction monitoring during pharmaceutical production to favor the more
bioavailable but metastable Form I with limits of detection in the ppm regime. Less |Related Solutions: SONICC^®

Riboswitches are structural RNA elements that are generally located in the 5' untranslated region of messenger RNA. During regulation of gene expression, ligand binding to the aptamer domain of a riboswitch triggers a signal to the downstream expression platform1�3. A complete understanding of the structural basis of this mechanism requires the ability to study structural changes over time4. Here we use femtosecond X-ray free electron laser (XFEL) pulses5,6 to obtain structural measurements from crystals so small that diffusion of a ligand can be timed to initiate a reaction before diffraction. We demonstrate this approach by determining four structures of the adenine riboswitch aptamer domain during the course of a reaction, involving two unbound apo structures, one ligand-bound intermediate, and the final ligand-bound conformation. These structures support a reaction mechanism model with at least four states and illustrate the structural basis of signal transmission. The three-way junction and the P1 switch helix of the two apo conformers are notably different from those in the ligand-bound conformation. Our time-resolved crystallographic measurements with a 10-second delay captured the structure of an intermediate with changes in the binding pocket that accommodate the ligand. With at least a 10-minute delay, the RNA molecules were fully converted to the ligand-bound state, in which the substantial conformational changes resulted in conversion of the space group. Such notable changes in crystallo highlight the important opportunities that micro- and nanocrystals may offer in these and similar time-resolved diffraction studies. Together, these results demonstrate the potential of �mix-and-inject� time-resolved serial crystallography to study biochemically important interactions between biomacromolecules and ligands, including those that involve large conformational changes. Less |Related Solutions: SONICC^®

A new approach is described to screen for protein nanocrystals based on the reversibility of crystallization. Methods to characterize nanocrystals are in strong need to facilitate sample preparation for serial femtosecond X-ray nanocrystallography (SFX). SFX enables protein structure determination by collecting X-ray diffraction from nano- and microcrystals using a free electron laser. This technique is especially valuable for challenging proteins as for example membrane proteins and is in general a powerful method to overcome the radiation damage problem and to perform time-resolved structure analysis. Nanocrystal growth cannot be monitored with common methods used in protein crystallography, as the resolution of bright field microscopy is not sufficient. A high-performance method to screen for nanocrystals is second order nonlinear imaging of chiral crystals (SONICC). However, the high cost prevents its use in every laboratory, and some protein nanocrystals may be �invisible� to SONICC. In this work using a crystallization robot and a common imaging system precipitation comprised of nanocrystals and precipitation caused by aggregated protein can be distinguished. Less |Related Solutions: SONICC^®

Protein crystallization is a major bottleneck of structure determination by X-ray crystallography, hampering the process by years in some cases. Numerous matrix screening trials using significant amounts of protein are often applied, while a systematic approach with phase diagram determination is prohibited for many proteins that can only be expressed in small amounts. Here, we demonstrate a microfluidic nanowell device implementing protein crystallization and phase diagram screening using nanoscale volumes of protein solution per trial. The device is made with cost-effective materials and is completely automated for efficient and economical experimentation. In the developed device, 170 trials can be realized with unique concentrations of protein and precipitant established by gradient generation and isolated by elastomeric valving for crystallization incubation. Moreover, this device can be further downscaled to smaller nanowell volumes and larger scale integration. The device was calibrated using a fluorescent dye and compared to a numerical model where concentrations of each trial can be quantified to establish crystallization phase diagrams. Using this device, we successfully crystallized lysozyme and C-phycocyanin, as visualized by compatible crystal imaging techniques such as bright-field microscopy, UV fluorescence, and second-order nonlinear imaging of chiral crystals. Concentrations yielding observed crystal formation were quantified and used to determine regions of the crystallization phase space for both proteins. Low sample consumption and compatibility with a variety of proteins and imaging techniques make this device a powerful tool for systematic crystallization studies. Less |Related Solutions: SONICC^®

X-ray transparent Microfluidics for Protein Crystallization and Biomineralization A dissertation presented to the Faculty of the Graduate School of Arts and Sciences of Brandeis University, Waltham, Massachusetts by Achini Opathalage Protein crystallization demands the fundamental understanding of nucleation and applying techniques to find the optimal conditions to achieve the kinetic pathway for a large and defect free crystal. Classical nucleation theory predicts that the nucleation occurs at high supersaturation conditions.In this dissertation we sought out to develop techniques to attain optimal supersaturation profile to a large defect free crystal and subject it to in-situ X-ray diffraction using microfluidics. We have developed an emulsion-based serial crystallographic technology in nanolitre-sized droplets of protein solution encapsulated in to nucleate one crystal per drop. Diffraction data are measured, one crystal at a time, from a series of room temperature crystals stored on an X-ray semi-transparent microfluidic chip, and a 93% complete data set is obtained by merging single diffraction frames taken from different un-oriented crystals. As proof of concept, the structure of Glucose Isomerase was solved to 2.1 �. We have developed a suite of X-ray semi-transparent micrfluidic devices which enables; controlled evaporation as a method of increasing supersaturation and manipulating the phase space of proteins and small molecules. We exploited the inherently high water permeability of the thin X-ray semi-transparent devices as a mean of increasing the supersaturation by controlling the evaporation. We fabricated the X-ray semi-transparent version of the PhaseChip with a thin PDMS membrane by which the storage and the reservoir layers are separated, and studies the phase transition of amorphous CaCO3. Less |Related Solutions: SONICC^®

Crystallization of biological macromolecules such as proteins implies several prerequisites, for example, the presence of one or more initial nuclei, sufficient amounts of the crystallizing substance and the chemical potential to provide the free energy needed to force the process. The initiation of a crystallization process itself is a stochastic event, forming symmetrically assembled nuclei over kinetically preferred protein-dense liquid clusters. The presence of a spatial repetitive orientation of macromolecules in the early stages of the crystallization process has so far proved undetectable. However, early identification of the occurrences of unit cells is the key to nanocrystal detection. The optical properties of a crystal lattice offer a potential signal with which to detect whether a transition from disordered to ordered particles occurs, one that has so far not been tested in nanocrystalline applications. The ability of a lattice to depolarize laser light depends on the different refractive indices along different crystal axes. In this study a unique experimental setup is used to detect nanocrystal formation by application of depolarized scattered light. The results demonstrate the successful detection of nano-sized protein crystals at early stages of crystal growth, allowing an effective differentiation between protein-dense liquid cluster formation and ordered nanocrystals. The results are further verified by complementary methods like X-ray powder diffraction, second harmonic generation, ultraviolet two-photon excited fluorescence and scanning electron microscopy. Less |Related Solutions: SONICC^®

The second-harmonic generation (SHG) activity of protein crystals was found to be enhanced by up to ~1000-fold by the intercalation of SHG phores within the crystal lattice. Unlike the intercalation of fluorophores, the SHG phores produced no significant background SHG from solvated dye or from dye intercalated into amorphous aggregates. The polarization-dependent SHG is consistent with the chromophores adopting the symmetry of the crystal lattice. In addition, the degree of enhancement for different symmetries of dyes is consistent with theoretical predictions based on the molecular nonlinear optical response. Kinetics studies indicate that intercalation arises over a timeframe of several minutes in lysozyme, with detectable enhancements within seconds. These results provide a potential means to increase the overall diversity of protein crystals and crystal sizes amenable to characterization by SHG microscopy. Less |Related Solutions: SONICC^®

Rhodopsin is a membrane protein from the G protein-coupled receptor family. Together with its ligand retinal, it forms the visual pigment responsible for night vision. In order to perform ultrafast dynamics studies, a time-resolved serial femtosecond crystallography method is required owing to the nonreversible activation of rhodopsin. In such an approach, microcrystals in suspension are delivered into the X-ray pulses of an X-ray free-electron laser (XFEL) after a precise photoactivation delay. Here, a millilitre batch production of high-density microcrystals was developed by four methodical conversion steps starting from known vapour-diffusion crystallization protocols: (i) screening the low-salt crystallization conditions preferred for serial crystallography by vapour diffusion, (ii) optimization of batch crystallization, (iii) testing the crystal size and quality using second-harmonic generation (SHG) imaging and X-ray powder diffraction and (iv) production of millilitres of rhodopsin crystal suspension in batches for serial crystallography tests; these crystals diffracted at an XFEL at the Linac Coherent Light Source using a liquid-jet setup. Less |Related Solutions: SONICC^®

Protein crystals obtained in initial screens typically require optimization before they are of X-ray diffraction quality. Seeding is one such optimization method. In classical seeding experiments, the seed crystals are put into new, albeit similar, conditions. The past decade has seen the emergence of an alternative seeding strategy: microseed matrix screening (MMS). In this strategy, the seed crystals are transferred into conditions unrelated to the seed source. Examples of MMS applications from in-house projects and the literature include the generation of multiple crystal forms and different space groups, better diffracting crystals and crystallization of previously uncrystallizable targets. MMS can be implemented robotically, making it a viable option for drug-discovery programs. In conclusion, MMS is a simple, time- and cost-efficient optimization method that is applicable to many recalcitrant crystallization problems. Less |Related Solutions: SONICC^®

Studies were undertaken to assess the merits and limitations of second-harmonic generation (SHG) for the selective detection of protein and polypeptide crystal formation, focusing on the potential for false positives from SHG-active salts present in crystallization media. The SHG activities of salts commonly used in protein crystallization were measured and quantitatively compared with reference samples. Out of 19 salts investigated, six produced significant background SHG and 15 of the 96 wells of a sparse-matrix screen produced SHG upon solvent evaporation. SHG-active salts include phosphates, hydrated sulfates, formates and tartrates, while chlorides, acetates and anhydrous sulfates resulted in no detectable SHG activity. The identified SHG-active salts produced a range of signal intensities spanning nearly three orders of magnitude. However, even the weakest SHG-active salt produced signals that were several orders of magnitude greater than those produced by typical protein crystals. In general, SHG-active salts were identifiable through characteristically strong SHG and negligible two-photon-excited ultraviolet fluorescence (TPE-UVF). Exceptions included trials containing either potassium dihydrogen phosphate or ammonium formate, which produced particularly strong SHG, but with residual weak TPE-UVF signals that could potentially complicate discrimination in crystallization experiments using these precipitants. Less |Related Solutions: SONICC^®

Traditional macroscale protein crystallization is accomplished non-trivially by exploring a range of protein concentrations and buffers in solution until a suitable combination is attained. This methodology is time consuming and resource intensive, hindering protein structure determination. Even more difficulties arise when crystallizing large membrane protein complexes such as photosystem I (PSI) due to their large unit cells dominated by solvent and complex characteristics that call for even stricter buffer requirements. Structure determination techniques tailored for these �difficult to crystallize� proteins such as femtosecond nanocrystallography are being developed, yet still need specific crystal characteristics. Here, we demonstrate a simple and robust method to screen protein crystallization conditions at low ionic strength in a microfluidic device. This is realized in one microfluidic experiment using low sample amounts, unlike traditional methods where each solution condition is set up separately. Second harmonic generation microscopy via Second Order Nonlinear Imaging of Chiral Crystals (SONICC) was applied for the detection of nanometer and micrometer sized PSI crystals within microchannels. To develop a crystallization phase diagram, crystals imaged with SONICC at specific channel locations were correlated to protein and salt concentrations determined by numerical simulations of the time-dependent diffusion process along the channel. Our method demonstrated that a portion of the PSI crystallization phase diagram could be reconstructed in excellent agreement with crystallization conditions determined by traditional methods. We postulate that this approach could be utilized to efficiently study and optimize crystallization conditions for a wide range of proteins that are poorly understood to date. Less |Related Solutions: SONICC^®

Structure elucidation of large membrane protein complexes still comprises a considerable challenge yet is a key factor in drug development and disease combat. Femtosecond nanocrystallography is an emerging technique with which structural information of membrane proteins is obtained without the need to grow large crystals, thus overcoming the experimental riddle faced in traditional crystallography methods. Here, we demonstrate for the first time a microfluidic device capable of sorting membrane protein crystals based on size using dielectrophoresis. We demonstrate the excellent sorting power of this new approach with numerical simulations of selected sub-micrometer beads in excellent agreement with experimental observations. Crystals from batch crystallization broths of the huge membrane protein complex photosystem I were sorted without further treatment, resulting in a high degree of monodispersity and crystallinity in the ~ 100 nm size range. Microfluidic integration, continuous sorting, and nanometer-sized crystal fractions make this method ideal for direct coupling to femtosecond nanocrystallography. Less |Related Solutions: SONICC^®

The potential of second-harmonic generation (SHG) microscopy for automated crystal centering to guide synchrotron X-�ray diffraction of protein crystals was explored. These studies included (i) comparison of microcrystal positions in cryoloops as determined by SHG imaging and by X-ray diffraction rastering and (ii) X-ray structure determinations of selected proteins to investigate the potential for laser-induced damage from SHG imaging. In studies using �2 adrenergic receptor membrane-protein crystals prepared in lipidic mesophase, the crystal locations identified by SHG images obtained in transmission mode were found to correlate well with the crystal locations identified by raster scanning using an X-�ray minibeam. SHG imaging was found to provide about 2 �m spatial resolution and shorter image-acquisition times. The general insensitivity of SHG images to optical scatter enabled the reliable identification of microcrystals within opaque cryocooled lipidic mesophases that were not identified by conventional bright-field imaging. The potential impact of extended exposure of protein crystals to five times a typical imaging dose from an ultrafast laser source was also assessed. Measurements of myoglobin and thaumatin crystals resulted in no statistically significant differences between structures obtained from diffraction data acquired from exposed and unexposed regions of single crystals. Practical constraints for integrating SHG imaging into an active beamline for routine automated crystal centering are discussed. Less |Related Solutions: SONICC^®

Second-order nonlinear optical imaging of chiral crystals (SONICC) is an emerging technique for crystal imaging and characterization. We provide a brief overview of the origin of second harmonic generation signals in SONICC and discuss recent studies using SONICC for biological applications. Given that they provide near-complete suppression of any background, SONICC images can be used to determine the presence or absence of protein crystals through both manual inspection and automated analysis. Because SONICC creates high-resolution images, nucleation and growth kinetics can also be observed. SONICC can detect metastable, homochiral crystalline forms of amino acids crystallizing from racemic solutions, which confirms Ostwald�s rule of stages for crystal growth. SONICC�s selectivity, based on order, and sensitivity, based on background suppression, make it a promising technique for numerous fields concerned with chiral crystal formation. Less |Related Solutions: SONICC^®