Recent Advances In Structural Characterization Research Articles

Recent advances in structural characterization of biomacromolecules in foods via small-angle X-ray scattering.

Small-angle X-ray scattering (SAXS) is a method for examining the solution structure, oligomeric state, conformational changes, and flexibility of biomacromolecules at a scale ranging from a few Angstroms to hundreds of nanometers. Wide time scales ranging from real time (milliseconds) to minutes can be also covered by SAXS. With many advantages, SAXS has been extensively used, it is widely used in the structural characterization of biomacromolecules in food science and technology. However, the application of SAXS in charactering the structure of food biomacromolecules has not been reviewed so far. In the current review, the principle, theoretical calculations and modeling programs are summarized, technical advances in the experimental setups and corresponding applications of in situ capabilities: combination of chromatography, time-resolved, temperature, pressure, flow-through are elaborated. Recent applications of SAXS for monitoring structural properties of biomacromolecules in food including protein, carbohydrate and lipid are also highlighted, and limitations and prospects for developing SAXS based on facility upgraded and artificial intelligence to study the structural properties of biomacromolecules are finally discussed. Future research should focus on extending machine time, simplifying SAXS data treatment, optimizing modeling methods in order to achieve an integrated structural biology based on SAXS as a practical tool for investigating the structure-function relationship of biomacromolecules in food industry.

Probing Structural Variation and Dynamics in the HIV-1 Env Fusion Glycoprotein.

Recent advances in structural characterization of the HIV envelope glycoprotein (Env) have provided a high-resolution glimpse of the architecture of this target for neutralizing antibodies and the machinery responsible for mediating receptor binding and membrane fusion. These structures primarily capture the detailed organization of the receptor-naive, prefusion conformation of Env, but under native solution conditions Env is highly dynamic, sampling multiple conformational states as well as exhibiting local protein flexibility. Special emphasis is placed on the use of biophysical methods, including single-molecule fluorescence microscopy and hydrogen/deuterium-exchange mass spectrometry. Using novel biophysical approaches, striking isolate-specific differences in Env's dynamic profile have been revealed that appear to underlie phenotypic differences of the viral isolates such as neutralization sensitivity and CD4 receptor reactivity. Structural studies are complemented by novel biophysical investigations that enable visualization of the dynamics of HIV-1 Env under native conditions. These approaches will also enable us to gain new insights into the mechanisms of action of antibodies and drugs.

Recent Advances in Structural Characterization of Natural Rubber

Abstract Structural characterization of rubber from Hevea brasiliensis (NR) has been carried out to elucidate the biosynthesis mechanism of rubber molecule as well as to find the relationship between physical properties characteristic of NR and its structure. Recent advances of structural studies have provided a series of new information on the structure of long-chain branching based on the result of selective decomposition of branch-points by chemical and enzymatic treatments as well as physical treatment such as polar solvent treatments and washing of NR latex by centrifugation in the presence of a surfactant. The measurement of the resulting rubber with NMR, FTIR, SEC and dilute solution viscosity provided confirming evidence that the initiating terminal (ω-terminal) with an unidentified functional group and phosphate terminal (α-terminal) form branch-points by hydrogen bond, ionic bond or micelle formation of phospholipids linked to both terminal groups. Based on these results, the origin of green properties characteristic of NR has been explained and a new mechanism of storage hardening has been proposed. The purification method by saponification of NR latex developed for the structural characterization has been applied to produce purified NR latex free from Type I allergic reaction. Instantaneous coagulation of saponified latex by the use of a flocculant and formic acid has provided solid saponified NR having good green and cured rubber properties.

Phase contrast imaging and diffraction-space mapping of periodic inversion domains in LiNbO3 with advanced x-rays

This paper presents some recent advances in structural characterization of periodic inversion domains in ferroelectric nonlinear optical crystals using novel techniques such as diffraction-space mapping, diffuse scattering imaging and phase-contrast imaging. The great advantages of using both highly coherent hard x-ray photons delivered by the third-generation synchrotron source and the well-defined x-ray beam provided by state-of-the-art laboratory diffractometer are addressed in terms of investigation of periodically domain-inverted LiNbO3 crystals. The microstructural characteristics of the periodic inversion domains in LiNbO3 are discussed, with an indication of their differences from naturally-occurring inversion domains.

Nucleation and crystallization of globular proteins — what we know and what is missing

Recently, much progress has been made in understanding the nucleation and crystallization of globular proteins, including the formation of compositional and structural crystal defects. Insight into the interactions of (screened) protein macro-ions in solution, obtained from light scattering, small angle X-ray scattering and osmotic pressure studies, can guide the search for crystallization conditions. These studies show that the nucleation of globular proteins is governed by the same principles as that of small molecules. However, failure to account for direct and indirect (hydrodynamic) protein interactions in the solutions results in unrealistic aggregation scenarios. Microscopic studies of numerous proteins reveal that crystals grow by the attachment of growth units through the same layer-spreading mechanisms as inorganic crystals. Investigations of the growth kinetics of hen-egg-white lysozyme (HEWL) reveal non-steady behavior under steady external conditions. Long-term variations in growth rates are due to changes in step-originating dislocation groups. Fluctuations on a shorter timescale reflect the non-linear dynamics of layer growth that results from the interplay between interfacial kinetics and bulk transport. Systematic gel electrophoretic analyses suggest that most HEWL crystallization studies have been performed with material containing other proteins at percent levels. Yet, sub-percent levels of protein impurities impede growth step propagation and play a role in the formation of structural/compositional inhomogeneities. In crystal growth from highly purified HEWL solutions, however, such inhomogeneities are much weaker and form only in response to unusually large changes in growth conditions. Equally important for connecting growth conditions to crystal perfection and diffraction resolution are recent advances in structural characterization through high-resolution Bragg reflection profiling and X-ray topography.

Recent Advances in Structural Characterization of Elastomers

Abstract One of the main targets of the structural characterization of elastomers so far has been the correlation of the polymerization conditions with the properties of the resulting polymers. The first step is the analysis of polymer structure, such as the chemical composition of copolymers, isomeric structure of diene polymers, degree of branching, extent of modification, functionality of end groups, amounts of abnormal groups, tacticity, and so on. Progress in nuclear magnetic resonance spectroscopy (NMR) makes possible the second step, which is the structural characterization of polymer chains, such as the sequence distribution of comonomer units in copolymer, isomeric units in diene polymers, configurational sequences in vinyl polymers, head and tail arrangement of monomer units. Recent development of FT-NMR spectroscopy, high-field spectroscopy from 300 MHz to 600 MHz at 1H-NMR, solid-state 13C-NMR, and two-dimensional NMR has facilitated a more detailed analysis of these structural features. The complexity of the structure of elastomers, which is derived from highly controlled copolymerization processes, leads to the widespread application of modern FT-NMR spectroscopy. It may reasonably be said that a fair number of structural problems in elastomers has been solved by NMR analysis. The high sensitivity of Fourier-transform infrared spectroscopy (FT-IR) has enabled one to determine trace structural changes in elastomers. Coupled on-line techniques such as gas-chromatography-mass-spectrometry combined with pyrolysis, liquid chromatography-NMR, and gel permeation chromatography-FT-IR will be powerful tools for the characterization of elastomers. Progress in analytical instruments has stimulated the development of high-performance elastomers, the synthesis of new speciality elastomers, and the elucidation of mechanisms for property enhancements. The use of modern instruments and a combination of ordinary methods of structural analysis have satisfied needs to some extent. However, a newer method of structural characterization is always desired in order to achieve higher orders of information. for example, the characterization of inhomogeneity along the polymer chain and between the polymer chains has become an important problem, especially in polymer blend systems. As to the former problem, spectroscopic methods provide only limited information. Although the NMR and FT-IR spectroscopies are very powerful tools for the analysis of short sequence distributions, it is difficult to characterize the distribution of long sequences and hybrid systems containing random and blocked sequences along the polymer chain. Gel permeation chromatography (GPC) is one of the most popular techniques for the analysis of molecular-weight distribution. However, it provides complicated information including molecular-weight distribution and chemical-composition distribution in the case of copolymers. Recent progress of high-performance liquid chromatography (HPLC) has provided a new powerful tool for the structural characterization of copolymers. It is appropriate to review the recent advances in structural characterization of elastomers, especially the characterization of microstructure of polymer chains, from the viewpoints of methodology and applicability of new methods. As to the NMR analysis of elastomers, reviews are available. Here, considerable attention is focused on the procedures for the assignment of signals, because the applicability of a NMR method is based on the reliability of the signal assignments. The other topics are selected to provide direct information for polymer synthesis or polymer properties.