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Crystalline, amorphous, and crystalline–amorphous materials have become three important electrode materials for the bottleneck oxygen‐evolving reaction (OER) in the promising hydrogen‐producing technology of water splitting. With the rapid development of in situ/ex situ characterizations, the understanding of active sites in electrocatalysts has been deepened via the structure–activity/stability relationships extracted from the observations on catalysts during/after the OER. Herein, the origins of changes in initial crystalline, amorphous, and crystalline–amorphous materials during/after the OER are systematically analyzed and the underlying variation effects on catalyst activity and stability are discussed based on recent representative studies, aiming at guiding OER catalyst design in the future. Crystalline, amorphous, and crystalline–amorphous materials have been explored for catalyzing the oxygen‐evolving reaction (OER). However, a systematic insight into the origins and effects of the behaviors on initial crystalline, amorphous, and crystalline–amorphous materials during/after the OER is still absent. Herein, it is attempted to offer a systematic viewpoint on these issues to guide the rational design of electrocatalysts.

This paper examines the effect of mechanical activation on the amorphization of starch having different types of crystalline structure (A-type corn starch; B-type potato starch; and C-type tapioca starch). Structural properties of the starches were studied by X-ray diffraction analysis. Mechanical activation in a planetary ball mill reduces the degree of crystallinity in proportion to pretreatment duration. C-type tapioca starch was found to have the highest degree of crystallinity. Energy consumed to achieve complete amorphization of the starches having different types of crystalline structure was measured. The kinetic parameters of the process (the effective rate constants) were determined. The rate constant and the strongest decline in the crystallinity degree after mechanical activation change in the following series: C-type starch, A-type starch, and B-type starch.

Polymer electrets are increasingly getting application in a very wide range. However, its charge trapped mechanism is still poorly understood. It is always challenging how to improve its charge trapped ability and to enhance its performance stability. In this study, a charge trapped mechanism, quasi-dipole model, is proposed for semi-crystalline polymer electrets. Every grain of crystallite is viewed as a dipole based on the polarisation effect between crystalline and amorphous region when charged. The energy level of the charge trap has a dependence on the crystallite structure. The more regular the crystallite grain structure the better charge stability is. The melt-blown polypropylene (MBPP) electret fabrics with α or mesomorphic crystallite are used as the model material to verify the rationality of the mechanism. The experiment results from thermally stimulating discharge and X-ray diffraction proved that the charge-trapped stability could be improved by means of transformation from meso-crystalline to α crystalline structure. The MBPP fabric containing α-crystallite shows much better charge trapped performance than one containing mesomorphic-crystallite because of more regular structure in α crystallite. The findings not only present new insight into charge-trapped phenomena in polymer electrets, but also provide innovation for the processing technology of polymer electret materials.

G-protein-coupled receptors have a major role in transmembrane signalling in most eukaryotes and many are important drug targets. Here we report the 2.7 Å resolution crystal structure of a β 1 -adrenergic receptor in complex with the high-affinity antagonist cyanopindolol. The modified turkey ( Meleagris gallopavo ) receptor was selected to be in its antagonist conformation and its thermostability improved by earlier limited mutagenesis. The ligand-binding pocket comprises 15 side chains from amino acid residues in 4 transmembrane α-helices and extracellular loop 2. This loop defines the entrance of the ligand-binding pocket and is stabilized by two disulphide bonds and a sodium ion. Binding of cyanopindolol to the β 1 -adrenergic receptor and binding of carazolol to the β 2 -adrenergic receptor involve similar interactions. A short well-defined helix in cytoplasmic loop 2, not observed in either rhodopsin or the β 2 -adrenergic receptor, directly interacts by means of a tyrosine with the highly conserved DRY motif at the end of helix 3 that is essential for receptor activation. G-protein-coupled receptors: Binding commitment The adrenalin stress hormone receptor (β 1 adrenergic receptor or β 1 AR) regulates heart rate and blood pressure and is the target for β-blockers. Like other members of the G-protein-coupled receptor family, it is difficult to purify. But the form of the enzyme found in the turkey is more stable than the human equivalent, and by using that, and mutagenesis to thermostabilize the receptor, β 1 AR has been crystallized bound to the β-blocker cyano-pindolol. The structure reveals insights into the G-protein-binding interface.

Structural analysis of G-protein-coupled receptors (GPCRs) for hormones and neurotransmitters has been hindered by their low natural abundance, inherent structural flexibility, and instability in detergent solutions. Here we report a structure of the human β 2 adrenoceptor (β 2 AR), which was crystallized in a lipid environment when bound to an inverse agonist and in complex with a Fab that binds to the third intracellular loop. Diffraction data were obtained by high-brilliance microcrystallography and the structure determined at 3.4 Å/3.7 Å resolution. The cytoplasmic ends of the β 2 AR transmembrane segments and the connecting loops are well resolved, whereas the extracellular regions of the β 2 AR are not seen. The β 2 AR structure differs from rhodopsin in having weaker interactions between the cytoplasmic ends of transmembrane (TM)3 and TM6, involving the conserved E/DRY sequences. These differences may be responsible for the relatively high basal activity and structural instability of the β 2 AR, and contribute to the challenges in obtaining diffraction-quality crystals of non-rhodopsin GPCRs. A tough structure to crack Most hormones and neurotransmitters — and therefore many drugs — work via G protein-coupled receptors, or GPCRs. With the one exception of rhodopsin, the most stable GPCR known, structural data for these proteins are hard to come by. Now several collaborating research groups, publishing in this issue of Nature and also in Science , have exploited a raft of different techniques, including the use of the inverse agonist carazolol to stabilize the receptor structure, to determine the crystal structure of the human β 2 AR adrenaline receptor. Its structure contrasts markedly with that of 'dark' rhodopsin, which helps explain why it is so hard to prepare diffraction-quality crystals of most GPCRs. High resolution structural information for G protein-coupled receptors has so far been limited to rhodopsin; here a crystal structure of the β 2 AR adrenaline receptor is presented.

Structure determination of proteins and other macromolecules has historically required the growth of high-quality crystals sufficiently large to diffract x-rays efficiently while withstanding radiation damage. We applied serial femtosecond crystallography (SFX) using an x-ray free-electron laser (XFEL) to obtain high-resolution structural information from microcrystals (less than 1 micrometer by 1 micrometer by 3 micrometers) of the well-characterized model protein lysozyme. The agreement with synchrotron data demonstrates the immediate relevance of SFX for analyzing the structure of the large group of difficult-to-crystallize molecules.

Structural data show that the light atom at the center of the nitrogenase active site cofactor is a carbon. The identity of the interstitial light atom in the center of the FeMo cofactor of nitrogenase has been enigmatic since its discovery. Atomic-resolution x-ray diffraction data and an electron spin echo envelope modulation (ESEEM) analysis now provide direct evidence that the ligand is a carbon species.

The crystalline structure of silk fibroin Silk I is generally considered to be a metastable structure; however, there is no definite conclusion under what circumstances this crystalline structure is stable or the crystal form will change. In this study, silk fibroin solution was prepared from B. Mori silkworm cocoons, and a combined method of freeze-crystallization and freeze-drying at different temperatures was used to obtain stable Silk I crystalline material and uncrystallized silk material, respectively. Different concentrations of methanol and ethanol were used to soak the two materials with different time periods to investigate the effect of immersion treatments on the crystalline structure of silk fibroin materials. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman scattering spectroscopy (Raman), Scanning electron microscope (SEM), and Thermogravimetric analysis (TGA) were used to characterize the structure of silk fibroin before and after the treatments. The results showed that, after immersion treatments, uncrystallized silk fibroin material with random coil structure was transformed into Silk II crystal structure, while the silk material with dominated Silk I crystal structure showed good long-term stability without obvious transition to Silk II crystal structure. α-chymotrypsin biodegradation study showed that the crystalline structure of silk fibroin Silk I materials is enzymatically degradable with a much lower rate compared to uncrystallized silk materials. The crystalline structure of Silk I materials demonstrate a good long-term stability, endurance to alcohol sterilization without structural changes, and can be applied to many emerging fields, such as biomedical materials, sustainable materials, and biosensors.

G protein coupled receptors (GPCRs) exhibit a spectrum of functional behaviours in response to natural and synthetic ligands. Recent crystal structures provide insights into inactive states of several GPCRs. Efforts to obtain an agonist-bound active-state GPCR structure have proven difficult due to the inherent instability of this state in the absence of a G protein. We generated a camelid antibody fragment (nanobody) to the human β 2 adrenergic receptor (β 2 AR) that exhibits G protein-like behaviour, and obtained an agonist-bound, active-state crystal structure of the receptor-nanobody complex. Comparison with the inactive β 2 AR structure reveals subtle changes in the binding pocket; however, these small changes are associated with an 11 Å outward movement of the cytoplasmic end of transmembrane segment 6, and rearrangements of transmembrane segments 5 and 7 that are remarkably similar to those observed in opsin, an active form of rhodopsin. This structure provides insights into the process of agonist binding and activation. β-adrenergic receptor structures Two papers by Brian Kobilka and colleagues describe the X-ray crystal structure of the human β 2 adrenergic receptor (β 2 AR) bound to various agonists. β 2 AR is a member of the G protein coupled receptor (GPCR) family of membrane-spanning receptors that sense molecules outside the cell and activate internal signalling pathways. With a ubiquitous role in human physiology, GPCRs are prime targets for drug discovery. A third paper by Christopher Tate and his team describes crystal structures of a similar GPCR, the turkey β 1 -adrenergic receptor (β 1 AR), bound to full and partial agonists. Together, these new structures reveal the subtle structural changes that accompany agonist binding, showing how binding events inside and outside the cell membrane stabilize the receptor's active state. Agonist binding to β 1 AR is shown to induce a contraction of the catecholamine-binding pocket relative to the antagonist-bound receptor, and molecular-dynamics simulations of the β 2 AR agonist complex suggest that the agonist-bound active state spontaneously relaxes to an inactive-like state in the absence of a G protein. The X-ray crystal structure of the human β 2 adrenergic receptor, a G-protein-coupled receptor, in an agonist-bound 'active' state is solved. Comparison of this structure with a previously published structure of the same GPCR in an inactive state indicates that minor changes in the binding pocket of the protein lead to major changes elsewhere — there is a large outward movement of the cytoplasmic end of one of the transmembrane segments and rearrangements of two other transmembrane segments. This structure provides insights into the process of agonist binding and activation.

In macromolecular x-ray crystallography, refinement R values measure the agreement between observed and calculated data. Analogously, R merge values reporting on the agreement between multiple measurements of a given reflection are used to assess data quality. Here, we show that despite their widespread use, R merge values are poorly suited for determining the high-resolution limit and that current standard protocols discard much useful data. We introduce a statistic that estimates the correlation of an observed data set with the underlying (not measurable) true signal; this quantity, CC*, provides a single statistically valid guide for deciding which data are useful. CC* also can be used to assess model and data quality on the same scale, and this reveals when data quality is limiting model improvement.