Simple one-flask method for the preparation of hydroxamic acids

[reaction: see text] A one-step conversion of carboxylic acids to hydroxamic acids under very mild conditions is described. This simple and efficient method has been applied for the synthesis of enantiopure hydroxamate of alpha-amino acids and peptides.     

Pelseneeriol-1 and -2: new furanosesquiterpene alcohols from porostome nudibranch Doriopsilla pelseneeri

The paper reports the first chemical study of the porostome nudibranch Doriopsilla pelseneeri collected off the Portuguese coast (Atlantic Ocean). Two new furanosesquiterpene alcohols, pelseneeriol-1 (1) and pelseneeriol-2 (2), have been isolated together with known compounds, 15-acetoxy-ent-pallescensin-A (5), and dendocarbin-A (6), from the mantle of the nudibranch, whereas euryfuran (3) and drimane ester mixture 4 were identified in the extract of the internal glands. The structures of 1 and 2 have been determined by extensive spectroscopic studies as well as by comparison with literature model compounds. In order to assess the relative stereochemistry of 1 and 2, full NMR assignment of related sponge metabolite microcionin-2 (8) and of co-occurring sesquiterpenes 9-11, that have been re-isolated from the Mediterranean sponge Fasciospongia cavernosa, has been also conducted. In particular, the relative stereochemistry of tricyclic sesquiterpene microcionin-1 (9) has now been rigorously assigned by detailed analysis of NOE difference experiments.     

N-Hydroxy-o-benzenedisulfonimide: A Misunderstood Selective Oxidizing Agent

N-Hydroxy-o-benzenedisulfonimide (now an easily accessible reagent) is a useful selective oxidizing agent; this is contrary to what was previously believed. The oxidation reactions of aldehydes to acids, benzyl alcohols to aldehydes, thiols to disulfides, and sulfides to sulfoxides were investigated (18 examples).     

Ring B functionalization of scalarane sesterterpenes by radical relay halogenation

The functionalization of the B-ring of the scalarane framework has been achieved for the first time by a radical relay halogenation (RRH) synthetic method. The known scalaranic methyl ester, which was prepared by a procedure with an overall yield higher than those reported in the literature, has been used as the starting substrate. Some theoretical considerations explaining the course of RRH reaction are also presented.     

Absolute continuity of the law for the two dimensional stochastic Navier–Stokes equations

We consider the two dimensional Navier–Stokes equations in vorticity form with a stochastic forcing term given by a gaussian noise, white in time and colored in space. First, we prove existence and uniqueness of a weak (in the Walsh sense) solution process $\xi$ and we show that, if the initial vorticity ${\xi }_0$ is continuous in space, then there exists a space–time continuous version of the solution. In addition we show that the solution $\xi (t,x)$ (evaluated at fixed points in time and space) is locally differentiable in the Malliavin calculus sense and that its image law is absolutely continuous with respect to the Lebesgue measure on $\mathbb{R}$.     

Two New Polyhydroxylated Steroids from the Hainan Soft Coral Sinularia sp.

Two new polyhydroxylated steroids, (2β,3β,4α,5α,8β,11β)‐4‐methylergost‐24(28)‐ene‐2,3,8,11‐tetrol‐( 1 ) and (3β,5α,6β)‐ergosta‐22,24(28)‐diene‐3,5,6,19‐tetrol ( 3 ), together with the six known related steroids 2 and 4 – 8 , were isolated from the Hainan soft coral Sinularia sp. Their structures were elucidated on the basis of spectroscopic analysis and by comparison with previously reported data. The structure of the known compound 9 (hyrtiosterol) was revised as 2 by extensive analysis of the ROESY data and by the NOE difference experiment.     

Hydrogel-filled micropipette contact systems for solid state electrochemical measurements

This paper reports on the use of a novel microcapillary system for solid contact electrochemical measurements. The probe is made of moveable micropipettes, with orifice of 1–30-μm radii, filled with a conducting hydrogel, which forms a thin-gelled meniscus at the pipette end. The hydrogel is made of 2 % (w/v) agarose and water solutions, containing KCl or KNO₃ as supporting electrolytes. The micropipette can be brought in contact with a conducting substrate to form a microcell, which allows performing voltammetric measurements confined within limited contact regions. The suitability of the proposed probe for local electrochemical measurements are tested using two electroactive species, dissolved in the hydrogel, namely [Fe (CN₆)]^4- and Ag⁺ ions. Mass transport characteristics of the two species, in bulk hydrogel and at micropipette meniscuses of different radii, are examined in detail in the frame of existing theory. For comparison, voltammetric measurements are also performed with micropipettes filled with the corresponding aqueous solutions. It is shown that the gel-filled micropipette, at variance with the aqueous one, prevents the spreading and leakage of solution on the sample surface. The microprobe developed here can be useful to perform electrochemical measurements on surfaces, which suffer from direct contact with liquid electrolytes. A proof-of-concept hydrogel-capillary measurement is performed to distinguish the presence of metallic silver deposited on a graphite-on-paper–based material, realized through simple pencil strokes.

Graphical abstract

     

Localization for a Nonlinear Sigma Model in a Strip Related to Vertex Reinforced Jump Processes

We study a lattice sigma model which is expected to reflect Anderson localization and delocalization transition for real symmetric band matrices in 3D, but describes the mixing measure for a vertex reinforced jump process too. For this model we prove exponential localization at any temperature in a strip, and more generally in any quasi-one dimensional graph, with pinning (mass) at only one site. The proof uses a Mermin–Wagner type argument and a transfer operator approach.