Analyses of the complex proton NMR spectra: determination of anisotropic proton chemical shifts of oriented molecules by a two dimensional experiment

NMR spectra of molecules oriented in the liquid crystalline media provide information on the molecular structure and order parameter. However, the numerical iterative analysis of the proton spectra of strongly coupled spins is difficult and time consuming. Such analysis is simplified if nearly accurate starting parameters are available. One such parameter is the chemical shift which in the oriented media is very different from the isotropic values due to anisotropic contributions. In this study, we have explored the possibility of obtaining chemical shifts in the oriented phase to aid the analysis of the spectra. A two dimensional experiment in which FSLG decoupling employed during the t1 period eliminates the homonuclear dipolar couplings and retains only the chemical shifts has been implemented. Experiments on the molecule cis,cis-mucononitrile demonstrate that the chemical shifts obtained by this procedure are nearly the same as the chemical shifts derived by iterative analysis of the one dimensional spectrum of the molecule following the standard procedure. The method has also been used to analyse the spectrum of 1-iodopropane using the chemical shifts obtained from the proposed experiment as the starting parameters.     

Tandem C-C coupling--intramolecular acetylenic Schmidt reaction under Pd/C-Cu catalysis

A new one-pot reaction for the regioselective construction of a six-membered fused N-heterocyclic ring leading to isoquinolones under Pd/C-Cu catalysis is described.     

Investigation of the synthetic and mechanistic aspects of the highly stereoselective transformation of alpha-thioamides to alpha-thio-beta-chloroacrylamides

Treatment of a series of alpha-thioamides with N-chlorosuccinimide results in efficient transformation to the analogous alpha-thio-beta-chloroacrylamides. The mechanistic pathway has been established through isolation and characterisation of intermediate compounds. The scope of the transformation has been explored-aryl and alkylthio substituents, primary, secondary and tertiary amides can be employed. In most instances, the chloroacrylamides are formed exclusively as the Z-stereoisomer; however, with tertiary propanamides or with amides derived from butanoic or pentanoic acid a mixture of E- and Z-stereoisomers is formed.     

Energetic Ordering of Hydrogen Bond Strengths in Methanol-Water Clusters: Insights via Molecular Tailoring Approach

In this work, we examine the strength of various types of individual hydrogen bond (HB) in mixed methanol-water M_nW_m, (n+m=2 to 7) clusters, with an aim to understand the relative order of their strength, using our recently proposed molecular tailoring-based approach (MTA). Among all the types of HB, it is observed that the O_M−H…O_W HBs are the strongest (6.9 to 12.4 kcal mol⁻¹). The next ones are O_M−H…O_M HBs (6.5 to 11.6 kcal mol⁻¹). The O_W−H…O_W (0.2 to 10.9 kcal mol⁻¹) and O_W−H…O_M HBs (0.3 to 10.3 kcal mol⁻¹) are the weakest ones. This energetic ordering of HBs is seen to be different from the respective HB energies in the dimer i. e., O_M−H…O_M (5.0 to 6.0 kcal mol⁻¹)>O_W−H…O_M (1.5 to 6.0 kcal mol⁻¹)>O_M−H…O_W (3.8 to 5.6 kcal mol⁻¹)>O_W−H…O_W (1.2 to 5.0 kcal mol⁻¹). The plausible reason for the difference in the HB energy ordering may be attributed to the increase or decrease in HB strengths due to the formation of cooperative or anti-cooperative HB networks. For instance, the cooperativity contribution towards the different types of HB follows: O_M−H…O_W (2.4 to 8.6 kcal mol⁻¹)>O_M−H…O_M (1.3 to 6.3 kcal mol⁻¹)>O_W−H…O_W (−1.0 to 6.5 kcal mol⁻¹)>O_W−H…O_M (−1.2 to 5.3 kcal mol⁻¹). This ordering of cooperativity contribution is similar to the HB energy ordering obtained by the MTA-based method. It is emphasized here that, the interplay between the cooperative and anti-cooperative contributions are indispensable for the correct energetic ordering of these HBs.     

Design and Synthesis of New Biprivileged Molecular Scaffolds: Indolo‐Fused Benzodiazepinyl/quinoxalinyl benzimidazoles

The present article describes the design and synthesis of new biprivileged molecular scaffolds with diverse structural features. Commercially available, simple heterocyclic building blocks such as 4‐fluoro‐3‐nitrobenzoic acid, 2‐chloro‐3‐nitrobenzoic acid, and indoline were utilized for the synthesis of the novel heterocycles. Pictet–Spengler‐type condensation was used as a key step to construct tetracyclic indolo‐benzodiazepines and indolo‐quinoxalines linked with substituted benzimidazoles. Analysis of single crystals of representative compounds showed that these molecular skeletons have the potential to present various substituents with distinct three‐dimensional orientations.     

Adsorption of Glucose Oxidase to 3-D Scaffolds of Carbon Nanotubes: Analytical Applications

This study is the first to focus on the potential use of carbon nanotube (CNT) scaffolds as enzyme immobilization substrates for analytical purposes. Besides all the well-known advantages of CNT, three-dimensional scaffolds can significantly increase the amount of enzymes adsorbed per unit area, preserve the catalytic activity of the adsorbed molecules, and allow effective exposure to substrates present in the adjacent medium. Additionally, our results indicate that the sensitivity of analytical probes based on enzyme-loaded CNT scaffolds is proportional to the thickness of the scaffold providing 3-fold sensitivity improvements with respect to the control surfaces.     

A Comparative Evaluation of Nitrogen Compounds in Petroleum Distillates

Although the concentration of nitrogen compounds in crude oil is relatively low, they can become more concentrated in petroleum distillates and poison the catalysts used in refining processes. They cause undesirable deposits, color formation and odor in products; they also contribute to air pollution and some are highly carcinogenic. The poisoned catalyst becomes deactivated for hydrodesulfurization and unable to remove sulfur from middle distillates. In order to understand the effect on catalytic processes, it is desirable to identify the nitrogen compounds in various petroleum distillates. This paper compares the nitrogen species profiles in different petroleum distillates using a nitrogen chemiluminescence detector. In addition, four different petroleum distillate samples from different refineries were analyzed to find the variation in their nitrogen profiles. The nitrogen compounds in petroleum distillate samples were identified as anilines, quinolines, indoles, and carbazoles and their alkyl derivatives. Quantitation was carried out against known reference standards. The quantitative data were compared to the total nitrogen content determined by elemental analysis.     

Energy transfer from Sm3+ to Er3+ in zinc phosphate glass

A study of energy transfer from samarium to erbium ions in zinc phosphate glass has been performed for a range of donor (1.0 wt% fixed) and acceptor concentrations ranging from 0.2 wt% to 1.2 wt%. The intensity of emission spectra of Sm³⁺ ions in the presence of Er³⁺ ions shows an overall decrease, thereby suggesting a non radiative energy transfer from Sm³⁺ ions to Er³⁺ ions. The interaction mechanism between the donor and acceptor ions is found to be mainly electric dipole-dipole in nature. The parameters required for the quantitative study of energy transfer e.g. energy transfer efficiencies, transfer probabilities, critical transfer distances have been computed.     

RuCl3-TBHP mediated allylic oxidation of Δ lanosterol derivatives

A variety of Δ⁸⁽⁹⁾-lanosterol derivatives were converted into 7,11-dienones using t-butyl hydroperoxide in the presence of ruthenium chloride (RuCl₃) in good yields.