A simple and effective synthesis of activated vinylphosphonates from 3-methoxy-2-diethoxyphosphorylacrylate

A facile, efficient and general one-step procedure for the synthesis of 3-substituted 2-diethoxyphosphorylacrylates from 3-methoxy-2-diethoxyphosphorylacrylate 1b and nitrogen, carbon and phosphorus nucleophiles is presented. Reaction of 1b with 3,5-dimethoxyphenol in the presence of trifluoromethanesulfonic acid yields 3-diethoxyphosphoryl-5,7-dimethoxychromen-2-one.     

Geometric changes around an N atom due to a urethane‐type bis(tert‐butoxycarbonyl) substituent

Two crystal structures of urethane‐protected derivatives of aspartic acid dimethyl ester are presented, namely dimethyl (2S)‐2‐[(tert‐butoxycarbonyl)amino]butanedioate, C₁₁H₁₉NO₆, and dimethyl (2S)‐2‐{bis[(tert‐butoxycarbonyl]amino}butanedioate, C₁₆H₂₇NO₈. The geometry at the N atom is discussed and compared with similar structures. The analysis of singly and doubly N‐substituted derivatives reveals an elongation of all bonds involving the N atom and conformational changes of the amino acid side chain due to steric interactions with two bulky substituents on the amino group.     

Trans‐A2B‐corroles Bearing a Coumarin Moiety ‐ From Synthesis to Photophysics

Four dyads comprised of corrole and coumarin units have been synthesised. Three coumarincarboxaldehydes were synthesized and transformed into the corresponding trans‐A₂B‐corroles by reaction with 5‐(pentafluorophenyl)dipyrromethane. It has been proven that this type of direct condensation can lead to the corresponding corroles in moderate yields. The reaction of hydroxybenzaldehydes with vinylphosphonium salts has been identified as the most general method for the preparation of formyl‐coumarins with various patterns of substituents. The dyad consisting of ketobiscoumarin and corrole was synthesized by Sonogashira coupling. Spectroscopic and photophysical investigations revealed that there is an efficient energy transfer from the coumarin moiety to corrole in all four dyads. Energy transfer can be clearly ascribed to a dipole–dipole mechanism (Förster) for all dyads that contain luminescent coumarins and to an electron exchange mechanism (Dexter) for the dyad with the non‐luminescent one. In the case of the dyad that bears coumarin with a hydroxy group at position 5, an electron‐transfer was detected from corrole to coumarin. The latter process is possible because of the suitably low reduction potential of coumarins of this type.     

Obtaining the two-body density matrix in the density matrix renormalization group method

We present an approach that allows to produce the two-body density matrix during the density matrix renormalization group (DMRG) run without an additional increase in the current disk and memory requirements. The computational cost of producing the two-body density matrix is proportional to O(M3k2+M2k4). The method is based on the assumption that different elements of the two-body density matrix can be calculated during different steps of a sweep. Hence, it is desirable that the wave function at the convergence does not change during a sweep. We discuss the theoretical structure of the wave function ansatz used in DMRG, concluding that during the one-site DMRG procedure, the energy and the wave function are converging monotonically at every step of the sweep. Thus, the one-site algorithm provides an opportunity to obtain the two-body density matrix free from the N-representability problem. We explain the problem of local minima that may be encountered in the DMRG calculations. We discuss theoretically why and when the one- and two-site DMRG procedures may get stuck in a metastable solution, and we list practical solutions helping the minimization to avoid the local minima.     

Effect of thermal treatment on potato starch evidenced by EPR,XRD and molecular weight distribution

Effect of heating of the potato starch on damages of its structure was investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy, X‐ray diffraction and determination of the molecular weight distribution. The measurements were performed in the temperature range commonly used for starch modifications optimizing properties important for industrial applications. Upon thermal treatment, because of breaking of the polymer chains, diminishing of the average molecular weights occurred, which significantly influences generation of radicals, evidenced by EPR. For the relatively mild conditions, with heating parameters not exceeding temperature 230 °C and time of heating equal to 30 min a moderate changes of both the number of thermally generated radicals and the mean molecular weight of the starch were observed. After more drastic thermal treatment (e.g. 2 h at 230 °C), a rapid increase in the radical amount occurred, which was accompanied by significant reduction of the starch molecular size and crystallinity. Experimentally established threshold values of heating parameters should not be exceeded in order to avoid excessive damages of the starch structure accompanied by the formation of the redundant amount of radicals. This requirement is important for industrial applications, because significant destruction of the starch matrix might annihilate the positive influence of the previously performed intentional starch modification. Copyright © 2015 John Wiley & Sons, Ltd.