Echinosulfonic acid D: an ESI MSn evaluation of a new cytotoxic alkaloid from the New-Caledonian sponge Psammoclemma sp

A new bromoindolesulfonic acid derivative, echinosulfonic acid D (1) was isolated from the New-Caledonian sponge Psammoclemma sp. in a minute quantity. The structure of the alkaloid was established by spectroscopic methods and, in particular, by ESI MSn experiments. Echinosulfonic acid D was cytotoxic to KB cells (IC50 2 microg/mL).     

Cover Feature: The Role of Common Alcoholic Sacrificial Agents in Photocatalysis: Is It Always Trivial? (Chem. Eur. J. 64/2021)

Photocatalytic hydrogen production is proposed as a sustainable energy source. Simultaneous reduction and oxidation of water is a complex multistep reaction with high overpotential. Photocatalytic processes involving semiconductors transfer electrons from the valence band to the conduction band. Sacrificial substrates that react with the photochemically formed holes in the valence band are often used to study the mechanism of H₂ production, as they scavenge the holes and hinder charge carrier recombination (electron-hole pairs). Here, we show that the desired sacrificial agent is one forming a radical that is a fairly strong reducing agent, and whose oxidized form is not a good electron acceptor that might suppress the hydrogen evolution reaction (HER). In an acidic medium, methanol was found to fulfill both these requirements better than ethanol and propan-2-ol in the TiO₂-(M⁰-NPs) (M=Au or Pt) system, whereas in an alkaline medium, the alcohols exhibit a reverse order of activity. Moreover, we report that CH₂(OH)₂ is by far the most efficient sacrificial agent in a nontrivial mechanism in acidic media. Our study provides general guidelines for choosing an appropriate sacrificial substrate and helps to explain the variance in the performance of alcohol scavenger-based photocatalytic systems.     

无机非铅钙钛矿Cs3Bi2I9的电子和光学性质

有机-无机卤化钙钛矿材料因具有优异的光电性质而被广泛应用于太阳电池中,然而材料及器件的稳定性及含铅问题却严重制约其生产发展.与杂化钙钛矿相比,无机非铅钙钛矿Cs₃Bi₂I₉因具有更强的稳定性和环境友好性受到人们的广泛关注.Cs₃Bi₂I₉具有单斜、三角和六方3种晶型,目前,对Cs₃Bi₂I₉的理论和实验研究主要集中在六方相.本文基于密度泛函理论的第一性原理对Cs₃Bi₂I₉单斜、三角和六方相的电子性质、载流子有效质量(m~*)、稳定性和光学性质进行了理论研究.结果表明,3种晶相具有相近的稳定性,三角相因具有较小的直接带隙(1.21 eV)性质成为最具研究潜力的对象.3种晶相的m~*均具有沿a,b方向相同和沿c方向不同的特点,三角相的电子有效质量最小、且沿a方向的电子有效质量小于c方向.相比单斜和六方相,三角相Cs_3<...     

Wall friction effects and viscosity reduction of gel propellants in conical extrusion

Influence of wall friction on mean apparent viscosity reduction of gel propellants in conical radial flow extrusion is investigated analytically and numerically. A parametric study has been conducted to evaluate the effects of injector geometry, rheological constants, wall friction factor and volumetric flow rate on fluid viscosity profile. Gel propellants were modeled by the non-Newtonian power law constitutive relation. The influence of wall friction on the mean apparent viscosity, on wall slip and on pressure gradient is found to be substantial. Central results are supported by asymptotic analysis for small cone angles and low wall friction. Contact is made with lubrication type flow pattern.     

Experimental investigation of magneto-rheological droplet impact on a smooth surface

We present an experimental investigation of the impact of magneto-rheological droplets on a smooth surface. The experimental setup consists of a syringe pump with capillary tube of 1.6 mm diameter located perpendicularly above a dry smooth quartz surface assembled above an electromagnetic module, which enables magnetic flux density control up to 7.8 G. Free surface flow patterns generated during the impact of droplets of 2.2 mm diameter, Reynolds number in the range 15-125 were recorded using a digital high-speed camera. The materials used in this study were commercial ferro-fluids, (hydrocarbon-based fluid containing micron-sized magnetizable particles). These fluids were characterized using a rotational rheometer modified by an electromagnetic module. The results show an up to 40% reduction in maximum spread diameters as well as reductions in spread velocities for droplets subjected to a magnetic field.     

Sensitivity analysis for inference with partially identifiable covariance matrices

In some multivariate problems with missing data, pairs of variables exist that are never observed together. For example, some modern biological tools can produce data of this form. As a result of this structure, the covariance matrix is only partially identifiable, and point estimation requires that identifying assumptions be made. These assumptions can introduce an unknown and potentially large bias into the inference. This paper presents a method based on semidefinite programming for automatically quantifying this potential bias by computing the range of possible equal-likelihood inferred values for convex functions of the covariance matrix. We focus on the bias of missing value imputation via conditional expectation and show that our method can give an accurate assessment of the true error in cases where estimates based on sampling uncertainty alone are overly optimistic.     

Hooked extended Langford sequences of small and large defects

It is shown that for m = 2d +5, 2d+6, 2d+7 and d ≥ 1, the set {1, …, 2m + 1} ? {k} can be partitioned into differences d, d + 1, …, d + m ? 1 whenever (m, k) ≡ (0, 1), (1, d), (2, 0), (3, d+1) (mod (4, 2)) and 1 ≤ k ≤ 2m+1. It is also shown that for m = 2d + 5, 2d + 6, 2d + 7, and d ≥ 1, the set {1, …, 2m + 2} ? {k, 2m + 1} can be partitioned into differences d, d + 1, … …, d + m ? 1 whenever (m, k) ≡ (0, 0), (1, d + 1), (2, 1), (3, d) (mod (4, 2)) and k ≥ m + 2. These partitions are used to show that if m ≥ 8d + 3, then the set {1, … …, 2m+2}?{k, 2m+1} can be partitioned into differences d, d+1, …, d+m?1 whenever (m, k) ≡ (0, 0), (1, d+1), (2, 1), (3, d) (mod (4, 2)). A list of values m, d that are open for the existence of these partitions (which are equivalent to the existence of Langford and hooked Langford sequences) is given in the conclusion.