Methyl group dynamics in a confined glass

We present a neutron scattering investigation on methyl group dynamics in glassy toluene confined in mesoporous silicates of different pore sizes. The experimental results have been analysed in terms of a barrier distribution model, such a distribution following from the structural disorder in the glassy state. Confinement results in a strong decreasing of the average rotational barrier in comparison to the bulk state. We have roughly separated the distribution for the confined state in a bulk-like and a surface-like contribution, corresponding to rotors at a distance from the pore wall respectively larger and smaller than the spatial range of the interactions which contribute to the rotational potential for the methyl groups. We have estimated a distance of 7 Amstrong as a lower limit of the interaction range, beyond the typical nearest-neighbour distance between centers-of-mass (4.7 Amstrong).Comment: 5 pages, 3 figures. To be published in European Physical Journal E Direct. Proceedings of the 2nd International Workshop on Dynamics in Confinemen

Lattice Knots in a Slab

In this paper the number and lengths of minimal length lattice knots confined to slabs of width $L$, is determined. Our data on minimal length verify the results by Sharein et.al. (2011) for the similar problem, expect in a single case, where an improvement is found. From our data we construct two models of grafted knotted ring polymers squeezed between hard walls, or by an external force. In each model, we determine the entropic forces arising when the lattice polygon is squeezed by externally applied forces. The profile of forces and compressibility of several knot types are presented and compared, and in addition, the total work done on the lattice knots when it is squeezed to a minimal state is determined

Acid-Catalyzed Hydration of 1-Methylcycloheptene and Methylenecycloheptane. Construction of the Complete Free Energy Profile for Olefin-Alcohol Interconversion in the 1-Methylcycloheptyl System

Rates of the reversible hydration of 1-methylcycloheptene (ENDO) to 1- methylcycloheptanol (ROH) and the essentially irreversible hydration of ethylenecycloheptane (EXO) to ROH, plus the position of equilibrium between ENDO and ROH, were determined in concentrated aqueous perchloric acid solution at 25 °C. The results, together with a literature value of the ENDO : EXO equilibrium ratio, allow dissection of the experimental data into hydronium-ion catalytic coefficients for the following individual processes: ENDO-> ROH, *H+ = 102 x 10~3 NT1 s"1; EXO-ROH, *„ + = 3.53 x 1CT3 NT1 s_1; ROH-ENDO, *H+ = 2.17 x lCT5 M\u271 s\u271, and ROH-EXO, *H+ = 1.01 x 10~6 M-1 s"1. Combination of these results with a previous estimate of the barrier to reaction of tertiary carbocations with water leads to a complete free energy profile for this system

Synthesis of Mesoporous Silica@Co–Al Layered Double Hydroxide Spheres: Layer-by-Layer Method and Their Effects on the Flame Retardancy of Epoxy Resins

Hierarchical mesoporous silica@Co–Al layered double hydroxide (m-SiO2@Co–Al LDH) spheres were prepared through a layer-by-layer assembly process, in order to integrate their excellent physical and chemical functionalities. TEM results depicted that, due to the electrostatic potential difference between m-SiO2 and Co–Al LDH, the synthetic m-SiO2@Co–Al LDH hybrids exhibited that m-SiO2 spheres were packaged by the Co–Al LDH nanosheets. Subsequently, the m-SiO2@Co–Al LDH spheres were incorporated into epoxy resin (EP) to prepare specimens for investigation of their flame-retardant performance. Cone results indicated that m-SiO2@Co–Al LDH incorporated obviously improved fire retardant of EP. A plausible mechanism of fire retardant was hypothesized based on the analyses of thermal conductivity, char residues, and pyrolysis fragments. Labyrinth effect of m-SiO2 and formation of graphitized carbon char catalyzed by Co–Al LDH play pivotal roles in the flame retardance enhancement

A Minimal Model of Metabolism Based Chemotaxis

Since the pioneering work by Julius Adler in the 1960's, bacterial chemotaxis has been predominantly studied as metabolism-independent. All available simulation models of bacterial chemotaxis endorse this assumption. Recent studies have shown, however, that many metabolism-dependent chemotactic patterns occur in bacteria. We hereby present the simplest artificial protocell model capable of performing metabolism-based chemotaxis. The model serves as a proof of concept to show how even the simplest metabolism can sustain chemotactic patterns of varying sophistication. It also reproduces a set of phenomena that have recently attracted attention on bacterial chemotaxis and provides insights about alternative mechanisms that could instantiate them. We conclude that relaxing the metabolism-independent assumption provides important theoretical advances, forces us to rethink some established pre-conceptions and may help us better understand unexplored and poorly understood aspects of bacterial chemotaxis

SMPD4 regulates mitotic nuclear envelope dynamics and its loss causes microcephaly and diabetes

Biallelic loss-of-function variants in SMPD4 cause a rare and severe neurodevelopmental disorder with progressive congenital microcephaly and early death. SMPD4 encodes a sphingomyelinase that hydrolyses sphingomyelin into ceramide at neutral pH and can thereby affect membrane lipid homeostasis. SMPD4 localizes to the membranes of the endoplasmic reticulum and nuclear envelope and interacts with nuclear pore complexes (NPC). We refine the clinical phenotype of loss-of-function SMPD4 variants by describing five individuals from three unrelated families with longitudinal data due to prolonged survival. All individuals surviving beyond infancy developed insulin-dependent diabetes, besides presenting with a severe neurodevelopmental disorder and microcephaly, making diabetes one of the most frequent age-dependent non-cerebral abnormalities. We studied the function of SMPD4 at the cellular and organ levels. Knock-down of SMPD4 in human neural stem cells causes reduced proliferation rates and prolonged mitosis. Moreover, SMPD4 depletion results in abnormal nuclear envelope breakdown and reassembly during mitosis and decreased post-mitotic NPC insertion. Fibroblasts from affected individuals show deficient SMPD4-specific neutral sphingomyelinase activity, without changing (sub)cellular lipidome fractions, which suggests a local function of SMPD4 on the nuclear envelope. In embryonic mouse brain, knockdown of Smpd4 impairs cortical progenitor proliferation and induces premature differentiation by altering the balance between neurogenic and proliferative progenitor cell divisions. We hypothesize that, in individuals with SMPD4-related disease, nuclear envelope bending, which is needed to insert NPCs in the nuclear envelope, is impaired in the absence of SMPD4 and interferes with cerebral corticogenesis and survival of pancreatic beta cells.</p

Molecular Clusters in Mesoporous Materials as Precursors to Nanoparticles of a New Lacunar Ternary Compound PdxMoyP

Bimetallic clusters of composition Pd2Mo2(g5-C5H5)2(l3-CO)2(l2-CO)4 (PR3)2 (R = ethyl or phenyl) were incorporated by impregnation from solution into two different silica matrices, amorphous xerogels and ordered SBA-15, and a study of their thermal decomposition under a reducing atmosphere is reported. With both matrices, a suitable thermal treatment afforded nanoparticles of a new bimetallic phosphide. Although nanoparticles of composition PdxMoyP, isostructural with Mo3P, were formed in both matrices, they were more uniformly distributed in the SBA-15 framework and showed a narrower size distribution. The samples have been characterized by powder XRD, chemical analysis, FT-IR spectroscopy, TEM and electron tomography (3D TEM)

Nanoscale Confinement and Fluorescence Effects of Bacterial Light Harvesting Complex LH2 in Mesoporous Silicas

Many key chemical and biochemical reactions, particularly in living cells, take place in confined space at the mesoscopic scale. Toward understanding of physicochemical nature of biomacromolecules confined in nanoscale space, in this work we have elucidated fluorescence effects of a light harvesting complex LH2 in nanoscale chemical environments. Mesoporous silicas (SBA-15 family) with different shapes and pore sizes were synthesized and used to create nanoscale biomimetic environments for molecular confinement of LH2. A combination of UV-vis absorption, wide-field fluorescence microscopy, and in situ ellipsometry supports that the LH2 complexes are located inside the silica nanopores. Systematic fluorescence effects were observed and depend on degree of space confinement. In particular, the temperature dependence of the steady-state fluorescence spectra was analyzed in detail using condensed matter band shape theories. Systematic electronic-vibrational coupling differences in the LH2 transitions between the free and confined states are found, most likely responsible for the fluorescence effects experimentally observed