Mean field theory-based calculation of FLC polarization

Mean field theory and Monte Carlo sampling are applied to the calculation of the spontaneous polarization density of ferroelectric liquid crystals by the ensemble averaging of single molecules confined in mean field potentials reflecting the SmC environment. Molecules are modelled with atomistic detail, using intramolecular interaction potentials derived from ab initio quantum mechanical calculations. This technique is applied to thirteen members of a family of novel fluoro ether-based compounds. Comparison with experiment shows that the observed variation of polarization density with chemical structure is well reproduced in most cases, but that the observed temperature dependence of polarization density is not captured by our model. The features of molecular organization responsible for the discrepancies between theory and experiment are discussed.     

Montmorillonite K10/ZnCl2 Catalyzed Alkyl Disulfide Substitution Reactions: Preparation of Thiomethyl Derivatives for the Synthesis of Organic Conducting Materials

Experiments are described detailing a method for the direct introduction of thiomethyl groups into activated benzenes, thiophene and benzo[b]thiophene using an activated mesoporous clay to promote thiomethyl substitution. Elaboration of 2,3-dithiomethylbenzo[b]thiophene, a product of the clay-catalyzed reaction of benzo[b]thiophene with dimethyl disulfide, to a tetrathiafulvalene derivative is described.     

From 1 to 6: A Finer Analysis of Perturbed Branching Brownian Motion

The logarithmic correction for the order of the maximum for two-speed branching Brownian motion changes discontinuously when approaching slopes , which corresponds to standard branching Brownian motion. In this article we study this transition more closely by choosing and . We show that the logarithmic correction for the order of the maximum now smoothly interpolates between the correction in the i.i.d. case , and when . This is due to the localization of extremal particles at the time of speed change, which depends on α and differs from the one in standard branching Brownian motion. We also establish in all cases the asymptotic law of the maximum and characterize the extremal process, which turns out to coincide essentially with that of standard branching Brownian motion. © 2020 the Authors. Communications on Pure and Applied Mathematics published by Wiley Periodicals LLC     

Metal‐Templated,Tight Loop Conformation of a Cys‐X‐Cys Biomimetic Assembles a Dimanganese Complex

With the goal of generating anionic analogues to MN₂S₂ ? Mn(CO)₃Br we introduced metallodithiolate ligands, MN₂S₂^2? prepared from the Cys‐X‐Cys biomimetic, ema^4? ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=Ni^II, [V^IV≡O]²⁺ and Fe^III) to Mn(CO)₅Br. An unexpected, remarkably stable dimanganese product, (H₂N₂(CH₂C=O(μ‐S))₂)[Mn(CO)₃]₂ resulted from loss of M originally residing in the N₂S₂^4? pocket, replaced by protonation at the amido nitrogens, generating H₂ema^2?. Accordingly, the ema ligand has switched its coordination mode from an N₂S₂^4? cavity holding a single metal, to a binucleating H₂ema^2? with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH₂‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn₂ product. By computational studies we compared the conformations of “linear” ema^4? to ema^4? frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H₂ema^2? that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state.     

A Heteroleptic Ferrous Complex with Mesoionic Bis(1,2,3‐triazol‐5‐ylidene) Ligands: Taming the MLCT Excited State of Iron(II)

Strongly σ‐donating N‐heterocyclic carbenes (NHCs) have revived research interest in the catalytic chemistry of iron, and are now also starting to bring the photochemistry and photophysics of this abundant element into a new era. In this work, a heteroleptic Fe^II complex ( 1 ) was synthesized based on sequentially furnishing the Fe^II center with the benchmark 2,2′‐bipyridine (bpy) ligand and the more strongly σ‐donating mesoionic ligand, 4,4′‐bis(1,2,3‐triazol‐5‐ylidene) (btz). Complex 1 was comprehensively characterized by electrochemistry, static and ultrafast spectroscopy, and quantum chemical calculations and compared to [Fe(bpy)₃](PF₆)₂ and (TBA)₂[Fe(bpy)(CN)₄]. Heteroleptic complex 1 extends the absorption spectrum towards longer wavelengths compared to a previously synthesized homoleptic Fe^II NHC complex. The combination of the mesoionic nature of btz and the heteroleptic structure effectively destabilizes the metal‐centered (MC) states relative to the triplet metal‐to‐ligand charge transfer (³MLCT) state in 1 , rendering it a lifetime of 13 ps, the longest to date of a photochemically stable Fe^II complex. Deactivation of the ³MLCT state is proposed to proceed via the ³MC state that strongly couples with the singlet ground state.     

Chemistry of ascorbic acid and sulfur dioxide as an antioxidant system relevant to white wine

The impact of the combined ascorbic acid and sulfur dioxide antioxidants on white wine oxidation processes was investigated using a range of analytical techniques, including flow injection analysis for free and total sulfur dioxide and two chromatographic methods for ascorbic acid, its oxidative degradation products and phenolic compounds. The combination of different analytical techniques provided a fast and simultaneous means for the monitoring of oxidation processes in a model wine system. In addition, the initial mole ratio of sulfur dioxide to ascorbic acid was varied and the model wine complexity was increased by the inclusion of metal ions (copper(II) and iron(II)). Sulfur dioxide was found not to be a significant binder of ascorbic acid oxidative degradation products and could not prevent the formation of certain phenolic pigment precursors. The results provide a detailed insight into the ascorbic acid/sulfur dioxide antioxidant system in wine conditions.