GenLocDip: A Generalized Program to Calculate and Visualize Local Electric Dipole Moments

Local dipole moments (i.e., dipole moments of atomic or molecular subsystems) are essential for understanding various phenomena in nanoscience, such as solvent effects on the conductance of single molecules in break junctions or the interaction between the tip and the adsorbate in atomic force microscopy. We introduce Gen Loc Dip , a program for calculating and visualizing local dipole moments of molecular subsystems. Gen Loc Dip currently uses the Atoms‐In‐Molecules (AIM) partitioning scheme and is interfaced to various AIM programs. This enables postprocessing of a variety of electronic structure output formats including cube and wavefunction files, and, in general, output from any other code capable of writing the electron density on a three‐dimensional grid. It uses a modified version of Bader's and Laidig's approach for achieving origin‐independence of local dipoles by referring to internal reference points which can (but do not need to be) bond critical points (BCPs). Furthermore, the code allows the export of critical points and local dipole moments into a POVray readable input format. It is particularly designed for fragments of large systems, for which no BCPs have been calculated for computational efficiency reasons, because large interfragment distances prevent their identification, or because a local partitioning scheme different from AIM was used. The program requires only minimal user input and is written in the Fortran 90 programming language. To demonstrate the capabilities of the program, examples are given for covalently and non‐covalently bound systems, in particular molecular adsorbates. © 2016 Wiley Periodicals, Inc.     

巧用“唯一法”速算反应热

介绍了一种与常规解法不同的利用盖斯定律求算反应热的方法：观察目标反应,找出在所给的多个反应中仅出现1次的物质,以此来确定目标反应的反应热表达式。从实际调查反馈的情况来看,该方法能明显提高学生的解题速度和正确率。     

Total Synthesis of Farnesin through an Excited-State Nazarov Reaction

The asymmetric total synthesis of farnesin, a rearranged ent-kaurenoid, was achieved through a convergent approach involving photo-Nazarov and intramolecular aldol cyclizations to build the syn-syn-syn hydrofluorenol ABC ring system and bicyclo[3.2.1]octane CD ring system in the first application of a UV-light-induced excited-state Nazarov cyclization of a non-aromatic dicyclic divinyl ketone in a total synthesis. Unlike the conventional acid-promoted ground-state Nazarov reaction, the excited-state Nazarov reaction enables stereospecific formation of the highly strained syn-syn-syn-fused hydrofluorenone scaffold through a disrotatory cyclization.     

A Computer Program for the Evaluation of Non-isothermal Kinetic Parameters

A program for the evaluation of non-isothermal kinetic parameters is presented. The program allows evaluation of the kinetic parameters under constant heating rate or constant reaction rate conditions. The simulation of temperature vs. conversion curves is also possible. A regression method is included, which allows a discrimination between various conversion functions and also evaluation of the activation parameters. The program was tested with various simulated decomposition curves and the non-isothermal decomposition curves of calcium oxalate. The program is written in Visual BASIC 4.0 and can be run under Windows 95 ©.     

A General Approach to O-Sulfation by a Sulfur(VI) Fluoride Exchange Reaction

O-sulfation is an important chemical code widely existing in bioactive molecules, but the scalable and facile synthesis of complex bioactive molecules carrying O-sulfates remains challenging. Reported here is a general approach to O-sulfation by the sulfur(VI) fluoride exchange (SuFEx) reaction between aryl fluorosulfates and silylated hydroxy groups. Efficient sulfate diester formation was achieved through systematic optimization of the electronic properties of aryl fluorosulfates. The versatility of this O-sulfation strategy was demonstrated in the scalable syntheses of a variety of complex molecules carrying sulfate diesters at various positions, including monosaccharides, disaccharides, an amino acid, and a steroid. Selective hydrolytic and hydrogenolytic removal of the aryl masking groups from sulfate diesters yielded the corresponding O-sulfate products in excellent yields. This strategy provides a powerful tool for the synthesis of O-sulfate bioactive compounds.     

A New Enantioselective Total Synthesis of Natural Vincamine via an Intramolecular Mannich Reaction of an Silyl Enol Ether

Natural Vincamine ( 1 ) has been synthesized in an enantioselective manner starting from the ethylpentenal 7 . In the key step a mixture of the diastereoisomeric racemates, 14 and 15 , was directly obtained from the silyl enol ether 11 and the dihydro-β-carboline 12 by the way of an intramolecular Mannich reaction of the intermediate 13 (Scheme 4). The undesired stereoisomers, 14 and 15b , were recycled to 15a using the related reversible Mannich reaction 18 ? 14 + 15 , followed by crystallization of the salt from 15a and (+)malic acid. 15a was converted to natural vincamine ( 1 ) in several steps including the known transformation 20→1 .     

滴定分析终点误差的通用高效计算策略

终点误差是滴定分析的核心内容之一,现行教材中众多导出公式致使终点误差的计算过于复杂。本文提出了一种通用高效的计算策略,统一了酸碱滴定、配位滴定以及氧化-还原滴定的终点误差计算;此外,还将准确滴定判别统一到终点误差的计算中。各种实例显示,这种策略不要求记忆任何导出公式即可完成计算,而且运算强度低。公式的统一性以及运算的便捷性极大地简化了终点误差的计算,在教学中能够显著减轻学生的记忆和运算负担,提升学习兴趣,从而能够将学习重点放在滴定体系的分析和处理上。本研究作为当前形势下分析化学教学改革的一个尝试,对传统课程内容进行优化,去冗存精,使其简明凝练,重点突出,定量分析的主旨更加明晰。     

Dithioacetal Exchange: A New Reversible Reaction for Dynamic Combinatorial Chemistry

Reversibility of dithioacetal bond formation is reported under acidic mild conditions. Its utility for dynamic combinatorial chemistry was explored by combining it with orthogonal disulfide exchange. In such a setup, thiols are positioned at the intersection of both chemistries, constituting a connecting node between temporally separated networks.     

Deuteration as an aid to the high-temperature gas chromatography—mass spectrometry of steryl fatty acyl esters

A method is presented for reducing degradative losses of steryl fatty acyl esters bearing polyunsaturated fatty acyl moieties during high-temperature gas chromatography (GC) and combined high-temperature GC—mass spectrometry (MS). The method employs selective deuteration of the double bonds in the fatty acyl moiety using a homogeneous catalyst (Wilkinson's catalyst). The Δ⁵ double bond, which occurs in the most commonly occurring plant and animal sterols, is not deuterated under the conditions described. In addition to improving GC behaviour, the method has the advantage of preserving structure information by labelling each double bond present in the original unsaturated fatty acyl moiety. The carbon number and degree of unsaturation of the labelled fatty acyl moiety are readily revealed by combined GC—MS employing negative-ion ammonia chemical ionisation. Two applications of the method are demonstrated in the analysis of steryl fatty acyl esters isolated from a rape seed oil and ovary tissue of the marine prawn Penaeus monodon.     

Metal-Free and NBS-Mediated Direct Thiol-Disulfide Exchange Reaction to Access Unsymmetrical Disulfides

A metal-free and N-Bromosuccinimide (NBS)-mediated direct thiol-disulfide exchange reaction at room temperature is developed. A variety of unsymmetrical disulfides have been prepared with good to excellent yields. Efficient late-stage modification of amino acids and drugs demonstrates the utility of this strategy. In addition, easy to operate, broad substrate scope and good functional group tolerance further demonstrate that this reaction provides an essential complementary route to access unsymmetrical disulfides.     

Total Synthesis of Farnesin through an Excited‐State Nazarov Reaction

The asymmetric total synthesis of farnesin, a rearranged ent‐kaurenoid, was achieved through a convergent approach involving photo‐Nazarov and intramolecular aldol cyclizations to build the syn‐syn‐syn hydrofluorenol ABC ring system and bicyclo[3.2.1]octane CD ring system in the first application of a UV‐light‐induced excited‐state Nazarov cyclization of a non‐aromatic dicyclic divinyl ketone in a total synthesis. Unlike the conventional acid‐promoted ground‐state Nazarov reaction, the excited‐state Nazarov reaction enables stereospecific formation of the highly strained syn‐syn‐syn‐fused hydrofluorenone scaffold through a disrotatory cyclization.     

Deuteration effect in auto-oscillation chemiluminescence of the Belousov-Zhabotinskii reaction

It has been established that substitution of H₂O by D₂O in the auto-oscillation system of malonic acid+bromate+catalyst (Ce^{3+ 4+}, Ru(bipy) ₃ ^{2+, 3+} ) not only changes the parameters of oscillations recorded according to the chemiluminescence intensity, but can also lead to their complete disappearance. The step that is responsible for the D₂O effect on chemiluminescent oscillation reactions is the deuteration of the methylene group of malonic acid.

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, H₂O D₂O — — (Ce^3+,4+, Mn^2+,3+, Ru(bipy) ₃ ^2+,3+ ) , , . , D₂O , .

     

A Computer Program for the Selection of Gradient Elution in High Performance Liquid Chromatography

Abstract

A computer program is presented for the selection of a gradient mobile phase that will give the same resolution for all the component pairs in the mixture. Each pair is treated as a separate experiment. The computer is used to compile these experiments and to recommend an optimum gradient.     

A Novel Attempt to Calculate the Velocity Correlation Coefficients in Ternary Electrolyte Solution

This work gives estimated values of the velocity correlation coefficients VCCs for ternary electrolyte solutions (the system may have a tracer ion as one of the components), utilizing available measured transport coefficients. The VCCs originate from linear response theory and give a deeper insight into the microdynamic structure of complex ionic solutions. By assuming Onsager’s relation to be valid, ten sets of velocity correlation coefficients were calculated for a ternary system and were used to calculate the VCCs for ¹³⁴Cs⁺ ion (present in trace amount) transport in aqueous solutions of CsCl and KCl at 25^○C.     

A Computer Program for Identifying Anomalous Peaks in Automated Amino Acid Analyses

Abstract

In automated ion-exchange chromatography of amino acids utilizing spectrophotometric measurement., the ratio of the areas under the 40 mμ; and 570 mμ; absorption peak tracings has been shown to be specific for each amino acid. Symmetrical, but impure peaks have ratios deviating from these norms. A simple computer program for the rapid identification of these anomalous peaks has been designed. It is proposed as an addendum to any computer program now in use with amino-acid analyzers.     

The Impact of the Mukaiyama Aldol Reaction in Total Synthesis

Four decades since Mukaiyama’s first reports on the successful application of silicon and boron enolates in directed aldol reactions, the ability of this highly controlled carbon–carbon bond‐forming method to simultaneously define stereochemistry, introduce complexity, and construct the carbon skeleton with a characteristic 1,3‐oxygenation pattern has made it a powerful tool for natural product synthesis. This Minireview highlights a number of representative total syntheses that demonstrate the impact of the Mukaiyama aldol reaction and discusses the underlying mechanistic rationale that determines the stereochemical outcomes.     

Kinetics of Heterogeneous Isotopic Exchange Reaction in Finite Bath

A general method to find the rate constant and particle self-diffusion coefficient is suggested for a heterogeneous isotopic exchange reaction which is controlled by surface mass reaction or controlled by a combination of surface mass reaction and intraparticle diffusion. The values of the kinetic parameter, ξ₁ (ratio of the forward surface mass reaction rate to the intraparticle diffusion rate), particle self-diffusion coefficient D and rate constant k are obtained by the proposed method for the isotopic exchange reaction systems CaCO₃(s)/Ca²⁺(aq) and CaC₂O₄(s)/Ca²⁺(aq).     

A Fortran II Computer Program for Calculation of Concentration-Dependent Sedimentation Coefficients

A computer program for calculation of concentration-dependent sedimentation coefficients is presented. Provision is made for rejection of outlying experimental points. The method yields extremely rapid and precise results from original data without any intermediate steps.     

A Total Synthesis of α-Kainic Acid by an Intramolecular Ene Reaction. Preliminary communication

The neurotoxin α-kainic acid ( 7 ) was synthesized from 1 via the thermal key step 5 → 6 in 41% overall yield.