Acetal formation from formylthiophene-2-carboxylic acids and recalculation of σI and σR substituent constants of the acetal group by 13C NMR chemical shifts

A uv-visible, ¹H and ¹³C nmr study has been carried out to show that 4-, 1, and 5-formylthiophene-2-carboxylic acids, 2, give acetals in methanol. The ms data have confirmed the acetal formation, which has been studied kinetically by the uv technique. The substituent chemical shifts induced on the carboxy carbon atom and on the endocyclic carbon atoms in the acetals formed from 1 and 2 and in the corresponding anions have been used to recalculate σ_I and σ_R values by means of a dual substituent parameter treatment of data.     

Linear free energy ortho-correlations in the thiophene series. Part IX . Kinetics of esterification with diazodiphenylmethane of some 3-, 4-, and 5-substituted thiophene-2-carboxylic acids in methanol

The rate constants for the esterification of some 3-, 4-, and 5-substituted thiophene-2-carboxylic acids with diazodiphenylmethane in methanol at 25° have been measured. The reactivity of some para- and ortho-substituted benzoic acids has also been determined. Logarithmic kinetic constants for ortho-, meta-, and para-like substituted thiophene-2-carboxylic acids furnish an excellent linear free energy relationship when plotted versus Δpk_a (β 0.89, r 0.989, C.L. > 99.9%, n 18, i 0.04), thus confirming the peculiar behaviour of five-membered ring derivatives. The correlation with σ^H values offers an additional proof of the hyper-ortho character of the 2,3-relation in thiophene derivatives. para- and ortho-Substituted benzoic acids show the usual behaviour of six-membered ring derivatives.     

Density functional theory study of the trans-trans-cis (TTC)-->trans-trans-trans (TTT) isomerization of a photochromic spiropyran merocyanine

Density Functional Theory (DFT) calculations have been performed on the TTC-->TTT isomerization reaction of the open forms of the 1',3'-dihydro-8-bromo-6-nitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-(2H)indole (8-Br-6-nitro-BIPS) system. The calculations were carried out in vacuo and in methylene chloride solution at different temperatures. Results are compared with the available experimental values of free energy difference and activation energy in solution.     

On the characterization of some [bmim][X]/co-solvent binary mixtures: a multidisciplinary approach by using kinetic, spectrophotometric and conductometric investigations

In order to study the intrinsic characteristics and to evaluate the structural variations determined by the addition of a co-solvent to 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) we examined the behaviour of some probes in [bmim][BF₄]/co-solvent binary mixtures. The rate constants of the piperidino-catalyzed rearrangement of the Z-phenylhydrazone of the 3-benzoyl-5-phenyl-1,2,4-oxadiazole into the relevant 4-benzoylamino-2,5-diphenyl-1,2,3-triazole as well as the spectrometric properties of pyrene and Nile Red were evaluated. With the same purpose also ¹H NMR and conductivity measurements were carried out. By comparison the behaviour of 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonylimide)/1,4-dioxane mixtures has been analyzed. The whole of data confirms the presence of weak interactions that determine a partially preorganized structure for [bmim][X]. This is perturbed at some degrees by quantity and nature of guest molecules. For example conductivity measurements support the idea that different charged aggregates are present in the [bmim][X]/co-solvent binary mixtures.     

Activity of Candida rugosa lipase immobilized on gamma-Fe2O3 magnetic nanoparticles

We report the stability and enzymatic activity of Candida rugosa Lipase (E.C.3.1.1.3) immobilized on gamma-Fe2O3 magnetic nanoparticles. The immobilization strategies were either reacting the enzyme amine group with a nanoparticle surface acetyl, or amine groups. In the former, the enzyme was attached through a C=N bond, while in the latter it was connected using glutaraldehyde. AFM images show an average particle size of 20 +/- 10 nm after deconvolution. The enzymatic activity of the immobilized lipase was determined by following the ester cleavage of p-nitrophenol butyrate. The covalently immobilized enzyme was stabile and reactive over 30 days.     

1H NMR metabolite fingerprinting as a new tool for body fluid identification in forensic science

In this feasibility study, we propose, for the first time, ¹H NMR spectroscopy coupled with mathematical strategies as a valid tool for body fluid (BF) trace identification in forensic science. In order to assess the ability of this approach to identify traces composed either by a single or by two different BFs, samples of blood, urine, saliva, and semen were collected from different donors, and binary mixtures were prepared. ¹H NMR analyses were carried out for all samples. Spectral data of the whole set were firstly submitted to unsupervised principal component analysis (PCA); it showed that samples of the same BF cluster well on the basis of their characterizing molecular components and that mixtures exhibit intermediate characteristics among BF typologies. Furthermore, samples were divided into a training set and a test set. An average NMR spectral profile for each typology of BF was obtained from the training set and validated as representative of each BF class. Finally, a fitting procedure, based on a system of linear equations with the four obtained average spectral profiles, was applied to the test set and the mixture samples; it showed that BFs can be unambiguously identified, even as components of a mixture. The successful use of this mathematical procedure has the advantage, in forensics, of overcoming bias due to the analyst's personal judgment. We therefore propose this combined approach as a valid, fast, and non‐destructive tool for addressing the challenges in the identification of composite traces in forensics. Copyright © 2013 John Wiley & Sons, Ltd.     

Low-loading asymmetric organocatalysis

Asymmetric organocatalysis is now recognized as the third pillar of asymmetric synthesis. Recent years have witnessed increasing interest towards the use of highly active and stereoselective organocatalysts. This critical review documents the advances in the development of chiral organocatalysts which are systematically used in ≤3 mol% loading in all the sub-areas of the field, namely aminocatalysis, Br?nsted acids and bases, Lewis acids and bases, hydrogen bond-mediated catalysis, phase transfer and N-heterocyclic carbene catalyses (194 references).     

Room temperature ionic liquids structure and its effect on the mononuclear rearrangement of heterocycles: an approach using thermodynamic parameters

The kinetics of the rearrangement of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole (1) into the relevant 4-benzoylamino-2,5-diphenyl-1,2,3-triazole (2) induced by amines have been studied in five room-temperature ionic liquids (RTILs) at different temperatures. The kinetic data collected show that both cationic and anionic parts of RTILs significantly influence the reactivity of the title reaction. The calculated activation parameters allow us to advance hypotheses about the weak interactions operating in RTIL solutions.     

Synthesis of diazahexathia-24-crown-8 derivatives and structures of Ag+ complexes

Diazahexathia-24-crown-8 (2) has been isolated from the reaction mixture during the preparation of monoazatrithia-12-crown-4 (1). When N-Boc protected bis(2-chloroethyl)amine was employed as a starting material, N-Boc protected monoazatrithia-12-crown-4 (3) and N-Boc protected diazahexathia-24-crown-4 (4) were separated easily. Double-armed diazahexathia-24-crown-8 having two 3',5'-dichlorobenzyl groups (5a) or two 2-phenylethyl groups (5b) were also prepared using reductive amination. The stoichiometry and detailed structures of the Ag+ complexes with and were investigated by 1H NMR titration experiments and X-ray crystallography.