Excited-state intramolecular proton transfer distinguishes microenvironments in single- and double-stranded DNA

Herein, the efficient interaction of an environment-sensitive fluorophore that undergoes excited-state intramolecular proton transfer (ESIPT) with DNA has been realized by conjugation of a 3-hydroxychromone (3HC) with polycationic spermine. On binding to a double-stranded DNA (dsDNA), the ratio of the two emission bands of the 3HC conjugates changes up to 16-fold, so that emission of the ESIPT product increases dramatically. This suggests an efficient screening of the 3HC fluorophore from the water molecules in the DNA complex, which is probably realized by its intercalation into dsDNA. In sharp contrast, the 3HC conjugates show only moderate changes in the dual emission on binding to a single-stranded DNA (ssDNA), indicating a much higher fluorophore exposure to water at the binding site. Thus, the 3-hydroxychromone fluorophore being conjugated to spermine discriminates the binding of this polycation to dsDNA from that to ssDNA. Consequently, ESIPT-based dyes are promising for monitoring the interaction of polycationic molecules with DNA and probing the microenvironment of their DNA binding sites.     

Piezoelectric effect in GaAs nanowires: experiment and theory

The anomalous piezoelectric effect in GaAs nanowires was detected (the piezoelectric strain coefficient up to d₃₃ ≈ 26 pC/N) that is 12 times larger than the theoretically estimated value. This result is explained by the dominant content of the phase with the wurtzite‐type crystal structure in GaAs nanowires and an increased pressing force by the contact layer on the nanowire. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Synthesis and structural investigation of new isothiochromen-4-one 2,2-dioxide derivatives

This article presents a combined experimental and computational study of novel isothiochromene 2,2-dioxide derivatives, which were synthesized by the electrophilic substitution reactions. The compounds have been studied by NMR, IR spectroscopy and single-crystal X-ray analysis. According to X-ray diffraction data, the six-membered ring of 6 adopts a distorted half-chair conformation, but in case of compounds 7 and 8, we have a twist-boat conformation of the six-membered ring with deviation of the S1 and C8 atoms from the mean plane of the remaining atoms of the ring, respectively. Results of quantum-chemical calculations of possible isomers and tautomers of the isolated oxime 8 and azo compounds 10 at the B3LYP/aug-cc-pVDZ level indicate that the oxime-oxo tautomer (8a) is more stable than the nitroso-hydroxy tautomer (8b) in agreement with the crystal data and that the keto tautomer (II) is more stable than the hydroxyl tautomer (I) and zwitterion tautomer (III), because of a strong intramolecular hydrogen bond N–H···O.

     

Mechanistic study on rearrangement cascades starting from annulated 2-aza-hepta-2,4-dienyl-6-ynyl anions: formation of aniline and azepine derivatives

Deprotonation of benzothiophene-derived alkynyl imine 11 with lithium diisopropylamide (LDA) and subsequent transmetalation with ZnCl2 etherate furnished azepine 12 upon aqueous workup. Similarly, alkynyl benzaldimine 1a gave a mixture of benzazepine 13 and naphthylamine 14. Allylic benzonitriles 15 a,b reacted to produce naphthylamine 16 upon deprotonation with LDA at room temperature. In an analogous manner, imino benzonitrile 17 may be converted into 4-amino isoquinoline 18 by means of an intramolecular nucleophilic attack on the nitrile function upon treatment with LDA. The allylic benzonitriles 19 a,b were prepared by LDA treatment of alkynyl imine 11. They were further converted to amino dibenzothiophene 20 by LDA deprotonation and aqueous workup. These various transformations represent the key steps of a multistep reaction cascade, which was previously postulated on the basis of quantum chemical calculations. Thus, all features of this complex rearrangement mechanism could now be confirmed experimentally. DFT calculations support the lower reactivity of zinc species in the ring-opening step compared to the lithium intermediates. All new compounds were completely characterized by spectroscopic data, including X-ray diffraction studies for the key compounds 12, 19 a, and 20.     

Design of new imidazole derivatives with anti-HCMV activity: QSAR modeling,synthesis and biological testing

Journal of Computer-Aided Molecular Design - The problem of designing new antiviral drugs against Human Cytomegalovirus (HCMV) was addressed using the Online Chemical Modeling Environment (OCHEM)....     

Unraveling the Guest-Induced Switchability in the Metal-Organic Framework DUT-13(Zn)**

The switching mechanism of the flexible framework Zn₄O(benztb)_1.5 (benztb=N,N,N’,N’-benzidine tetrabenzoate), also known as DUT-13, was studied by advanced powder X-ray diffraction (PXRD) and gas physisorption techniques. In situ synchrotron PXRD experiments upon physisorption of nitrogen (77 K) and n-butane (273 K) shed light on the hitherto unnoticed guest-induced breathing in the MOF. The mechanism of contraction is based on the conformationally labile benztb ligand and accompanied by a reduction in specific pore volume from 2.03 cm³ g⁻¹ in the open-pore phase to 0.91 cm³ g⁻¹ in the contracted-pore phase. The high temperature limit for adsorption-induced contraction of 170 K, determined by systematic temperature variation of methane adsorption isotherms, indicates that the DUT-13 framework is softer than other mesoporous MOFs like DUT-49 and does not support the formation of overloaded metastable states required for negative gas-adsorption transitions.     

Metal-organic frameworks for energy-related applications

Current micro review describes the recent progress in the energy-related MOF applications. The most outstanding research papers and reviews, which report the application of Metal-Organic Frameworks for gas storage, adsorption heat transformation, solar cells, fuel cells, hydrogen evolution reaction and supercapacitors are highlighted.     

Koszul Duality for Semidirect Products and Generalized Takiff Algebras

We obtain Koszul-type dualities for categories of graded modules over a graded associative algebra which can be realized as the semidirect product of a bialgebra coinciding with its degree zero part and a graded module algebra for the latter. In particular, this applies to graded representations of the universal enveloping algebra of the Takiff Lie algebra (or the truncated current algebra) and its (super)analogues, and also to semidirect products of quantum groups with braided symmetric and exterior module algebras in case the latter are flat deformations of classical ones.     

Self-assembly of the unique heterotrimetallic Cu/Co/M complexes possessing triangular antiferromagnetic {Cu2CoPb}2 and linear ferromagnetic {Cu2CoCd2} cores

Two novel heterotrimetallic octa-[Cu2CoPbCl4(L)4]2 (1) and pentanuclear [Cu2CoCd2Cl6(L)4(HOMe)2] (2) complexes have been prepared in one-pot reactions of zerovalent copper with metal chlorides in a methanol (for 1) or acetonitrile (for 2) solution of 2-(dimethylamino)ethanol (HL) in open air. The crystal structures of both compounds consist of discrete centrosymmetric heterotrimetallic molecules revealing triangular (1) and unique consecutive (2) arrangements of magnetic CuII(2)CoII cores. The complex 1 can be viewed as a dimer made up of tetranuclear Cu2CoPbCl4(L)4 units linked through the two micro(2)-Cl atoms. The molecular structure of 2 is a pentanuclear assembly containing the previously unknown Cu(micro-O)(2)Co(micro-O)(2)Cu core. The magnetic studies of 1 revealed an antiferromagnetic coupling (J(CoCu) = 37 cm(-1) and J(CuCu) = 87 cm(-1)) while 2 exhibits a weak ferromagnetic behavior (J(CoCu) = -3.2 cm(-1) and J(CuCu) = -14.2 cm(-1)). The correlations between magnetic behaviour and structures as well as synthetic features are also discussed.