Cs[Si3O6(OH)] and Rb[Si2O4(OH)]: two novel phyl­losilicates

The crystal structures of two novel phyl­losilicates with compositions Cs[Si₃O₆(OH)] (caesium hydroxo­hexa­oxotetra­otri­silicate) and Rb[Si₂O₄(OH)] (rubidium hydroxo­hexa­oxotetrao­di­silicate) have been characterized by X‐ray diffraction. The topology of the caesium phyl­losilicate silica sheet consists of interconnected four‐ and six‐membered rings and thus differs from all of the previously reported phyl­losilicates. The topology of the rubidium phyl­losilicate silica sheet consists of six‐membered rings only, in boat conformations, resulting in a corrugated sheet similar to that observed in δ‐Na₂Si₂O₅. Both of the title compounds exhibit the characteristic sandwich structure of sheet silicates, with the Cs atom ninefold coordinated and the Rb atom eightfold coordinated to the framework O atoms.     

A Statistical Journey through the Topological Determinants of the β2 Adrenergic Receptor Dynamics

Activation of G-protein-coupled receptors (GPCRs) is mediated by molecular switches throughout the transmembrane region of the receptor. In this work, we continued along the path of a previous computational study wherein energy transport in the β2 Adrenergic Receptor (β2-AR) was examined and allosteric switches were identified in the molecular structure through the reorganization of energy transport networks during activation. In this work, we further investigated the allosteric properties of β2-AR, using Protein Contact Networks (PCNs). In this paper, we report an extensive statistical analysis of the topological and structural properties of β2-AR along its molecular dynamics trajectory to identify the activation pattern of this molecular system. The results show a distinct character to the activation that both helps to understand the allosteric switching previously identified and confirms the relevance of the network formalism to uncover relevant functional features of protein molecules.     

Possible Transmission Flow of SARS-CoV-2 Based on ACE2 Features

Angiotensin-converting enzyme 2 (ACE2) is the cellular receptor for the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) that is engendering the severe coronavirus disease 2019 (COVID-19) pandemic. The spike (S) protein receptor-binding domain (RBD) of SARS-CoV-2 binds to the three sub-domains viz. amino acids (aa) 22–42, aa 79–84, and aa 330–393 of ACE2 on human cells to initiate entry. It was reported earlier that the receptor utilization capacity of ACE2 proteins from different species, such as cats, chimpanzees, dogs, and cattle, are different. A comprehensive analysis of ACE2 receptors of nineteen species was carried out in this study, and the findings propose a possible SARS-CoV-2 transmission flow across these nineteen species.     

Negative refraction

Light bends the wrong way in materials where both ε and μ are negative as was pointed out in 1968, but the absence of natural materials with this property led to neglect of the subject until 1999 when it was shown how to make artificial materials, metamaterials, with negative μ. The rapid advance of the subject since that date, both in theory and experiment, is reflected in the exponential growth of publications now at the 200 per year level and still growing. This interest is explained by the sudden availability of a qualitatively different class of electromagnetic materials combined with the quite startling properties which these materials appear to have; all of which provokes debate as each new facet of their behaviour is revealed. Experiment has been vital to resolution of controversy and has chiefly been in the microwave region of the spectrum though there is potential in the optical region currently being explored by several groups.     

(K4Li4)Al8Ge8O32·8H2O: an Li+‐exchanged potassium aluminogermanate with the zeolite gismondine (GIS) topology

The title compound, lithium potassium dialuminium di­ger­man­ium octaoxide dihydrate, (K,Li)‐(Al,Ge)‐GIS (GIS is gismondine), is the result of a 50% Li⁺ exchange into the K‐(Al,Ge)‐GIS structure. The (K,Li)‐(Al,Ge)‐GIS structure was determined from a 4 × 4 × 2 µm octahedral single crystal at the ESRF synchrotron X‐ray source. The ion exchange results in a symmetry transformation from I2/a for K‐(Al,Ge)‐GIS to C2/c for (K,Li)‐(Al,Ge)‐GIS. The structural change is due to disordering of K⁺ ions with Li⁺ ions along the [001] channel and ordering of water molecules in the [101] channels. The distance between sites partially occupied by K⁺ ions increases from 2.19 (3) Å in K‐(Al,Ge)‐GIS to 2.94 (3) Å in (K,Li)‐(Al,Ge)‐GIS. The Li⁺ ions occupy positions along the twofold axis at the intersection of the eight‐membered‐ring channels in a twofold coordination with water mol­ecules. For the four closest framework O²⁻ anions, the Li⃛O distances are 3.87 (4) Å.     

The Effect of Sound Frequency and Intensity on Yeast Growth,Fermentation Performance and Volatile Composition of Beer

This study investigated the impact of varying sound conditions (frequency and intensity) on yeast growth, fermentation performance and production of volatile organic compounds (VOCs) in beer. Fermentations were carried out in plastic bags suspended in large water-filled containers fitted with underwater speakers. Ferments were subjected to either 200–800 or 800–2000 Hz at 124 and 140 dB @ 20 µPa. Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was used to identify and measure the relative abundance of the VOCs produced. Sound treatment had significant effects on the number of viable yeast cells in suspension at 10 and 24 h (p < 0.05), with control (silence) samples having the highest cell numbers. For wort gravity, there were significant differences between treatments at 24 and 48 h, with the silence control showing the lowest density before all ferments converged to the same final gravity at 140 h. A total of 33 VOCs were identified in the beer samples, including twelve esters, nine alcohols, three acids, three aldehydes, and six hop-derived compounds. Only the abundance of some alcohols showed any consistent response to the sound treatments. These results show that the application of audible sound via underwater transmission to a beer fermentation elicited limited changes to wort gravity and VOCs during fermentation.     

Electronic Structure and Substitution and Redox Reactivity of Imidazolate-Bridged Complexes of Pentacyanoferrate and Pentaammineruthenium

The mixed-valence compound [(NC)(5)Fe(II)-Im-Ru(III)(NH(3))(5)](-),M(i), was prepared in solution and as a solid sodium salt from [Fe(CN)(5)H(2)O](3)(-) and [Ru(NH(3))(5)Im](2+). The binuclear complex shows two bands at 366 nm (epsilon = 3350 M(-)(1) cm(-)(1)) and 576 nm (epsilon = 1025 M(-)(1) cm(-)(1)), assigned as LMCT transitions, as well as a near-IR band at 979 nm (epsilon = 962 M(-)(1) cm(-)(1)) associated with an intervalence transition. By calculation of the Hush model parameters alpha(2) and H(ab) (delocalization and electronic coupling factors, respectively), the complex is defined as a valence-trapped Fe(II)-Ru(III) system; this is confirmed by the measured redox potentials at -0.20 V and 0.30 V, associated with redox processes at the ruthenium and iron center, respectively. The formation stability constant of the mixed-valence ion was obtained through independent measurements of k(f) and k(d), the formation and dissociation specific rate constants, respectively. The stabilization of M(i) with respect to disproportionation into the isovalent states, as well as toward the formation of the electronic isomer, Fe(III)-Im-Ru(II), was also estimated. The fully reduced (R(i)) and fully oxidized (O(i)) binuclear complexes were prepared in solution and characterized by UV-vis spectroscopy. The kinetics of the reactions of R(i) and M(i) with peroxydisulfate were measured and a mechanistic analysis was performed, showing the relevance of electronic isomerization in completing the full conversion to O(i), through the assistance of the Ru(II)(NH(3))(5)(2+) center in the oxidation of the neighboring Fe(II)(CN)(5)(3)(-) moiety. The latter results are compared with those obtained with related complexes comprising different X(5)M-L moieties bound to Ru(II)(NH(3))(5)(2+). A linear correlation is displayed by plotting ln k(et) against E degrees (Ru), associated with the intramolecular oxidation rate constant of Ru(II) in the ion pair (binuclear species + peroxydisulfate) and the reduction potential of the corresponding Ru(III,II) couple in the ion pair.     

Experimental investigations of the nuclear level density by using heavy ion reactions

The transition of the level density parameter a _off from the low excitation energy value a _off=A/8 MeV⁻¹ to the Fermi gas value a _FG ∼ A/15 MeV⁻¹ was discovered a few years ago studying particle spectra evaporated from hot compound systems of A∼ 160. A number of experiments have been recently performed to confirm the earlier findings and extend the investigation to other mass regions and to higher excitation energies. Furthermore, precision coincidence experiments have been done in the lead region in which evaporation residues are tagged by low energy gammarays. Those experiments open the possibility of a detailed study of the level densities in nuclei where the shell effects are important.     

Network rigidity in GeSe2 glass at high pressure

Acoustic measurements using synchrotron radiation have been performed on glassy GeSe2 up to pressures of 9.6 GPa. A minimum observed in the shear-wave velocity, associated anomalous behavior in Poisson's ratio, and discontinuities in elastic moduli at 4 GPa are indicative of a gradual structural transition in the glass. This is attributed to a network rigidity minimum originating from a competition between two densification mechanisms. At pressures up to 3 GPa, a conversion from edge- to corner-sharing tetrahedra results in a more flexible network. This is contrasted by a gradual increase in coordination number with pressure, which leads to an overall stiffening of the glass.