Materials showing long-range two-dimensional hexagonal order (called SBA-15 in the literature) were produced by templating a silica precursor (TEOS) with two Pluronic copolymers, EO x PO y EO x , of nearly the same x/y (0.3) ratio but different y values (x ) 18, y ) 60 and x ) 20, y ) 70, respectively). These materials were hydrothermally treated to increase the condensation of silicate species around the Pluronic aggregates and calcined to liberate the hexagonal array of mesopores. All materials, i.e., before and after hydrothermal treatment and calcination, were investigated by X-ray diffraction (XRD), and all calcined samples were further characterized by transmission electron microscopy and N 2 sorption experiments. The large number and narrow width of the XRD powder diffraction lines demonstrate the good crystallographic quality of the materials. This allows us to quantitatively exploit the XRD reflection intensities and to show that simple structural models of the silica lattice cannot account for them. This means that SBA-15 materials cannot be regarded as an ideal hexagonal lattice of pores imbedded in a uniform silica matrix. The structure of the silica walls is more complex and shows a "corona" region of lower density around the cylindrical organic aggregates. This corona becomes microporous upon calcination, and we suggest that it arises from the partial occlusion of the PEO chains in the silica matrix. Modeling the XRD intensities allows us, for all the solids of this series, to derive estimates of pore diameters, corona, and wall thicknesses and to examine the influence on these structural parameters of the hydrothermal treatment.

1. Isolated rat liver and heart mitochondria incubated in 150 mM-KSCN or sucrose medium in the presence of respiratory-chain inhibitors showed a large increase in swelling when exposed to 250 microM-Ca2+. Swelling was inhibited by bongkrekic acid and cyclosporin A in both media and by ADP in KSCN medium; the effect of ADP was reversed by carboxyatractyloside. These results demonstrate that this is a suitable technique with which to study the opening of the Ca2(+)-induced non-specific pore of the mitochondrial inner membrane and implicate the adenine nucleotide carrier in this process. 2. Titration of the rate of swelling with increasing concentrations of cyclosporin showed the number of cyclosporin-binding sites (+/- S.E.M.) in liver and heart mitochondria to be respectively 113.7 +/- 5.0 (n = 9) and 124.3 +/- 11.2 (n = 10) pmol/mg of protein, with a Ki of about 5 nM. 3. Liver and heart mitochondrial-matrix fractions were prepared free of membrane and cytosolic contamination and shown to contain cyclosporin-sensitive peptidyl-prolyl cis-trans isomerase (cyclophilin) activity. Titration of isomerase activity with cyclosporin gave values (+/- S.E.M.) of 110.6 +/- 10.1 (n = 5) and 165.4 +/- 15.0 (n = 3) pmol of enzyme/mg of liver and heart mitochondrial protein respectively, with a Ki of 2.5 nM. The similarity of these results to those from the swelling experiments suggest that the isomerase may be involved in the Ca2(+)-induced swelling. 4. The rapid light-scattering change induced in energized heart mitochondria exposed to submicromolar Ca2+ [Halestrap (1987) Biochem. J. 244, 159-164] was inhibited by ADP and bongkrekic acid, the former effect being reversed by carboxyatractyloside. These results suggest an interaction of Ca2+ with the adenine nucleotide carrier when the 'c' conformation. 5. A model is proposed in which mitochondrial peptidyl-prolyl cis-trans isomerase interacts with the adenine nucleotide carrier in the presence of Ca2+ to cause non-specific pore opening. The model also explains the involvement of the adenine nucleotide translocase in the PPi-mediated cyclosporin-insensitive increase in K+ permeability described in the preceding paper [Davidson & Halestrap (1990) Biochem. J. 268, 147-152]. 6. The physiological and pathological implications of the model are discussed in relation to reperfusion injury and cyclosporin toxicity.

The high hydroxyl content of mesoporous silicates makes it possible to use them as anchors for the attachment of transition-metal species. In the present study, three different samples corresponding to atomic V/Si ratio of 0.01, 0.05, and 0.10 have been prepared by reacting a silica-based mesoporous matrix of the cubic MCM-48 structure, with dry hexane solutions of OdV(OiPr) 3 . Bulk structural characterization (X-ray diffraction and BET) shows that the cubic structure is maintained during the impregnation process. In the presence of V centers, a noticeable decrease of the main-pore diameter and of the a unit-cell parameter is observed. Thus, a strong interaction between the mesoporous walls and the V centers is suggested. The microstructural configuration of V centers has been investigated further by 51 V NMR and UV-vis spectroscopies. Both techniques reveal that, in the absence of water, pseudotetrahedral O 3/2 VdO centers, probably coordinated by three (Si-O-V) bridges, are grafted to the mesoporous walls. The presence of these functional groups and their particular reactivity toward entering ligands such as water impart a number of unique properties to the bulk V/MCM-48, including color changes from white to orange in the presence of moisture.

No abstract

No abstract

No abstract

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) originated from Wuhan, China in December 2019, and rapidly spread to other areas worldwide. Since then, COVID-19 has reached pandemic proportions with more than 570,000 deaths globally by mid-July 2020. The magnitude of the outbreak and the potentially severe clinical course of COVID-19 has led to a burst of scientific research on this novel coronavirus and its host receptor, angiotensin converting enzyme-2 (ACE2). ACE2 is a homolog of the angiotensin-I converting enzyme (ACE) that acts on several substrates in the renin-angiotensin system. With unprecedented speed, scientific research has solved the structure of SARS-CoV-2 and imaged its binding with the ACE2 receptor. In SARS-CoV-2 infection, the viral spike (S) protein receptor binding domain (RBD) binds to ACE2 to enter the host cell. ACE2 expression in the lungs is relatively low, but it is present in type II pneumocytes, a cell type also endowed with transmembrane protease serine 2 (TMPRSS2). This protease is critical for priming the SARS-CoV-2 S protein to complex with ACE2 and enter the cells. Herein, we review the current understanding of the interaction of SARS-CoV-2 with ACE2 as it has rapidly unfolded over the last months. While it should not be assumed that we have a complete picture of SARS-CoV-2's mechanism of infection and its interaction with ACE2 much has been learned with clear therapeutic implications. Potential therapies aimed at intercepting SARS-CoV-2 from reaching the full-length membrane-bound ACE2 receptor using soluble ACE2 protein and other potential approaches are briefly discussed as well.

An original preparation method, called “two solvents” method, allows the production of MnO2 nanowires patterned by SBA-15 silicas under mild conditions, with a preserved two-dimensional hexagonal structure, a 97% filling of the porosity by oxide nanowires, and a controlled microstructure. A comparison is made with Mn-loaded SBA-15 prepared by more conventional adsorption methods. In the latter case, MnO x particles inside and outside the silica grains, empty and filled mesopores, and several Mn oxides (MnO2, Mn2O3, and Mn3O4) were identified. Once the preparation method of Mn-loaded SBA-15 optimized, various X-ray scattering and adsorption techniques using synchrotron radiation were used to observe salient features of the MnO2 nanowires crystallization in situ upon calcination. X-ray absorption at the Mn K edge shows that the oxidation state of manganese increases from (II) to (IV) between 80 and 120 °C. The oxidation of the Mn(II) salt occurs at a temperature lower than that necessary for bulk manganese nitrate (200 °C), which confirms its confinement within the SBA-15 pores. β-MnO2 nanowires of defective pyrolusite type are identified by wide-angle diffraction. The comparison between diffraction results and simulations demonstrates that the nanowire diameter is similar to the mesopore diameter of the silica host. A small contraction of unit-cell parameters occurs upon the crystallization of β-MnO2 nanowires. A parallel overall intensity increase observed in small-angle X-ray diffraction is the fingerprint of a homogeneously filled porosity.