The balance of flexibility and rigidity in the active site residues of hen egg white lysozyme

The crystallographic temperature factors （B factor） of individual atoms contain important information about the thermal motion of the atoms in a macromolecule. Previously the theory of flexibility of active site has been established based on the observation that the enzyme activity is sensitive to low concentration denaturing agents. It has been found that the loss of enzyme activity occurs well before the disruption of the three-dimensional structural scaffold of the enzyme. To test the theory of conformational flexibility of enzyme active site, crystal structures were perturbed by soaking in low concentration guanidine hydrochloride solutions. It was found that many lysozyme crystals tested could still diffract until the concentration of guanidine hydrochloride reached 3 M. It was also found that the B factors averaged over individually collected data sets were more accurate. Thus it suggested that accurate measurement of crystal temperature factors could be achieved for medium-high or even medium resolution crystals by averaging over multiple data sets. Furthermore, we found that the correctly predicted active sites included not only the more flexible residues, but also some more rigid residues. Both the flexible and the rigid residues in the active site played an important role in forming the active site residue network, covering the majority of the substrate binding residues. Therefore, this experimental prediction method may be useful for characterizing the binding site and the function of a protein, such as drug targeting.

Topology and Photoluminescence Property of a Neodymium-carboxylate Coordination Polymer Based on a Tripodal Flexible Ligand

A new metal-organic coordination polymer {[Nd（tci）（H2O）2]·2H2O}n（1） has been synthesized based on the flexible tricarboxylate ligand tris（2-carboxyethyl）isocyanuric acid（H3tci） and structurally characterized by single-crystal X-ray diffraction analyses, elemental analysis, infrared spectra（IR）, powder X-ray diffraction（PXRD） and thermogravimetric analysis（TGA）. Complex 1 crystallizes in triclinic, space group P1 with a = 9.1648（11）, b = 9.3326（12）, c = 12.440（2） , C（12）H（20）N3O（13） Nd, Mr = 558.55, V = 886.9（2） 3, Z = 2, Dc = 2.092 g·cm-3, μ = 3.006 mm-1, F（000） = 554, 2.56〈θ〈25.00°, λ（Mo Kα） = 0.71073 , T = 293（2） K, the final R = 0.0662 and w R = 0.2071. X-ray diffraction analysis reveals that complex 1 is a two-dimensional layer, which is further assembled into a three-dimensional supramolecular architecture through hydrogen bonding interactions. The structure of complex 1 can be simplified as a rare 2-periodic uninodal {48·62} topology and a non-interpenetrating kgd topology. Furthermore, the thermal stability and photoluminescence property of 1 were investigated.

Electrohydrodynamic lithography of metallic mesh for optically transparent flexible and conformal antennas

The optically transparent antenna is becoming a very attractive proposition for various applications, such as wearable devices and vehicle radars. The fabrication of transparent flexible/conformal antennas is a long-lasting interest in academia and industry.However, the preparation of radio-frequency radiators with excellent conductivity and optical transmittance is still quite challenging. Herein, we introduce a facile approach to directly fabricate optically transparent flexible and conformal coplanar waveguide-fed antennas using programmable electrohydrodynamic lithography. Metallic meshes with transmittance above 90%have been successfully created based on the conformal electrohydrodynamic printing of high-viscosity photoresist masks, and the corresponding sheet resistance can be tuned down to ~2 Ω/□. Then, the geometrical structure of the proposed transparent antenna has been systematically optimized because of the basic radio frequency components, including the radiator, feeder line,ground plane, and size of metallic meshes. Optically transparent flexible and conformal antennas are finally obtained, presenting an optical transmittance of 92% and 55%, respectively. The simulated and measured results demonstrate that the transparent antennas with a good optoelectronic performance indeed exhibit a nice electromagnetic behavior. We believe that this newly developed conformal electrohydrodynamic lithography method can be utilized to fabricate a variety of other transparent electronic devices, such as transparent electromagnetic shielding meshes on aircraft canopies, in the future.

Phenylboronic acids in crystal engineering:Utility of the energetically unfavorable syn,syn-conformation in co-crystal design

Phenylboronic acids can exist, in principle, in three different conformers （syn, syn; syn, anti and anti, anti） with distinct energy profiles. In their native state, these compounds prefer the energetically favored syn, anti-conformation. In molecular complexes, however, the functionality exhibits conformational diversity. In this paper we report a series of co-crystals, with N-donor compounds, prepared by a design strategy involving the synthons based on the syn, syn-conformation of the boronic acid functionality. For this purpose, we employed compounds with the 1,2-diazo fragment （alprazolam, 1H-tetrazole, acetazolamide and benzotriazole）, 1,10-phenanthroline and 2,2＇-bipyridine for the co-crystallization experiments. However, our study shows that the mere presence of the 1,2-diazo fragment in the coformer does not guarantee the successful formation of co-crystals with a syn, syn-conformation of the boronic acid.