Department of Chemistry

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IIT Jodhpur

An efficient mild one-pot protocol for the cross-coupling of nitrones and alkynyl-magnesium compounds using a catalytic amount of 2,2,6,6- tetramethylpiperidine-N-oxyl radical (TEMPO) as an environmentally benign organic oxidant and dioxygen as terminal oxidant is described. These coupling reactions can be performed without adding any transition metal on various N-tert-butylnitrones and alkynyl-Grignard reagents. Moreover, the alkynylated nitrone products are readily transformed to regioisomerically pure 3,5-disubstituted isoxazoles. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

World University root node

Advanced Synthesis and Catalysis

Transition metal-free TEMPO-catalyzed oxidative cross-coupling of nitrones with alkynyl-grignard reagents

A mild, operationally simple cross-dehydrogenative coupling between nitrones and terminal alkynes is described by using cheap, readily available 3,3′,5,5′-tetra-tert-butyldipheno-quinone and dioxygen as oxidants. These cross-couplings can be performed on various nitrones and alkynes with good to excellent yields. Product nitrones are readily transformed to pharmaceutically important 3,5-disubstituted isoxazoles. © 2011 American Chemical Society.

Organic Letters

Zinc triflate catalyzed aerobic cross-dehydrogenative coupling (CDC) of alkynes with nitrones: A new entry to isoxazoles

Diffusion of organic dyes in neat room temperature ionic liquid (RTIL) and RTIL-mixed micelle has been studied by fluorescence correlation spectroscopy (FCS). We have selected two RTILs, 3-pentyl-1-methyl imidazolium bromide ([C5C1Im][Br]) and the corresponding tetra-fluoroborate ([C5C1Im][BF 4]). Diffusion coefficients (Dt) of three organic dyes-DCM (neutral), C480 (neutral), and C343 (anionic)-in these RTILs are ∼100 times slower compared to water. This indicates very high viscosity of the RTILs. In contrast to water, the Dt in RTIL exhibits a wide distribution which suggests the presence of heterogeneity (nanoscale organization). The presence of ions in the RTILs markedly affects diffusion in the RTILs. Dt's of C480 (neutral) and C343 (anionic) are very similar in water but in RTILs the ionic dye C343 diffuses 1.7 times slower than neutral C480. This is attributed to the electrostatic force exerted by the ions in the RTILs. In the giant (∼2-4 μm) [C5C1Im][Br]-triblock copolymer (P123) mixed micelle D t of DCM, C480, and C343 are found to be 7, 15, and 7 μm 2s-1, respectively. The results are compared with those in P123 micelle and gel. © 2011 American Chemical Society.

Journal of Physical Chemistry B

Diffusion of organic dyes in ionic liquid and giant micron sized ionic liquid mixed micelle: Fluorescence correlation spectroscopy

Journal of Organometallic Chemistry

Steric control in the reactions of 3-pyrazolecarboxylic acid with diorganotin dichlorides

The effect of a room temperature ionic liquid (RTIL) on the conformational dynamics of a protein, human serum albumin (HSA), is studied by fluorescence correlation spectroscopy (FCS). For this, the protein was covalently labeled by a fluorophore, 7-dimethylamino-3-(4-maleimidophenyl)-4-methylcoumarin (CPM). On addition of a RTIL ([pmim][Br]) to the native protein, the diffusion coefficient (Dt) decreases and the hydrodynamic radius (Rh) increases. This suggests that the RTIL ([pmim][Br]) acts as a denaturant when the protein is in the native state. However, addition of [pmim][Br] to a protein denatured by GdnHCl causes an increases in Dt and decrease in R h. This suggests that in the presence of GdnHCl addition of RTIL helps the protein to refold. In the native state, the conformational dynamics of protein is described by three distinct time constants: ∼3.6 ± 0.7, ∼29 ± 4.5, and 133 ± 23 μs. The faster components (∼3.6 ± 0.7 and ∼29 ± 4.5 μs) are ascribed to chain dynamics of the protein, while the slowest component (133 μs) is responsible for interchain interaction or concerted motion. On addition of [pmim][Br], the conformational dynamics of HSA becomes slower (∼5.1 ± 1, ∼43.5 ± 2.8, and ∼311 ± 2.3 μs in the presence of 1.5 M [pmim][Br]). The time constants for the protein denatured by 6 M GdnHCl are 3.2 ± 0.4, 34 ± 6, and 207 ± 38 μs. When 1.5 M [pmim][Br] is added to the denatured protein (in 6 M GdnHCl), the time constants become ∼5 ± 1, ∼41 ± 10, and ∼230 ± 45 μs. The lifetime histogram shows that, on addition of GdnHCl to HSA, the contribution of the shorter lifetime component decreases and vanishes at 6 M GdnHCl. The shorter lifetime component immediately reappears after addition of RTIL to unfolded HSA. This suggests recoiling of the unfolded protein by RTIL. © 2011 American Chemical Society.

An FCS study of unfolding and refolding of CPM-labeled human serum albumin: Role of ionic liquid

A simple and efficient biomimetic synthesis of pyrrolo[1,2-a]indoles using a highly stereo- and regioselective [3 + 2] reaction cascade was developed and then further applied in the first total synthesis of flinderoles B and C, which proceeded in 17.2% yield over the longest linear sequence of 11 steps. © 2011 American Chemical Society.

Journal of the American Chemical Society

Biomimetic total syntheses of flinderoles B and C

In a previous article (Phys. Chem. Chem. Phys.2010, 12, 4435), nonequilibrium molecular dynamics (MD) simulations of heat transfer from a hot Au{111} substrate to an alkylthiolate self-assembled monolayer (H-SAM) were presented. The simulations were performed for an H-SAM chain length of eight carbon atoms, and a qualitative agreement with the experiments of Wang et al. (Science2007, 317, 787) was found. Here, simulation results are presented for heat transfer to H-SAM surfaces with carbon chain lengths of 10-20 carbon atoms. Relaxation times for heat transfer are extracted, compared with experiment, and a qualitative agreement is obtained. The same relaxation time is found from either the temperature of the H-SAM or the orientational disorder of the H-SAM versus time. For a simulation model with the Au substrate thermally equilibrated, the relaxation times determined from the simulations are approximately a factor of 4 larger than the experimental values. © 2011 American Chemical Society.

Journal of Physical Chemistry C

Effect of carbon chain length on the dynamics of heat transfer at a gold/hydrocarbon interface: Comparison of simulation with experiment

Algorithms are presented for sampling quantum microcanonical ensembles for a potential energy minimum and for the conical intersection at the minimum energy crossing point of two coupled electronic states. These ensembles may be used to initialize trajectories for chemical dynamics simulations. The unimolecular dynamics of a microcanonical ensemble about a potential energy minimum may be compared with the dynamics predicted by quantum Rice-Ramsperger-Kassel-Marcus (RRKM) theory. If the dynamics is non-RRKM, it will be of particular interest to determine which states have particularly long lifetimes. Initializing a microcanonical ensemble for the electronically excited state at a conical intersection is a model for electronic nonadiabatic dynamics. The trajectory surface-hopping approach may be used to study the ensuing chemical dynamics. A strength of the model is that zero-point energy conditions are included for the initial nonadiabatic dynamics at the conical intersection. © 2011 American Chemical Society.

Journal of Physical Chemistry A

Algorithms for sampling a quantum microcanonical ensemble of harmonic oscillators at potential minima and conical intersections

The origin of ultraslow component of solvation observed in an aqueous protein solution is studied by femtosecond up-conversion. It has been observed that solvation dynamics in hen egg lysozyme and lysozyme- cetyltrimethylammonium bromide (CTAB) aggregate exhibits a nearly twofold slowing down when the solvent H 2O is replaced by D 2O. The deuterium isotope effect suggests that water is the main polar species responsible for the observed ultrafast solvation dynamics in the aqueous protein solution.

Current Science

Deuterium isotope effect on solvation dynamics in lysozyme and lysozyme-CTAB aggregate: A femtosecond study

The study was designed with an aim to evaluate the protective effects of reduced glutathione on cyclophosphamide induced lipid peroxidation and also changes in cholesterol content. Goat liver and white New Zealand rabbit were used as lipid source for the models. Lipid peroxidation study was performed by measuring the malon-dialdehyde, 4-hydroxy-2-nonenal, reduced glutathione and nitric oxide content of tissue homogenates or rabbit blood. In the cholesterol profile total cholesterol and high density lipoprotein cholesterol content of rabbit blood was determined. The data presented in this work demonstrate the lipid peroxidation induction potential of cyclophosphamide and the antiperoxidative potential of reduced glutathione on cyclophosphamide-induced lipid peroxidation. It was also observed that reduced glutathione has protective effect on cyclophosphamide-induced changes in cholesterol content. A significant correlation was also found between malondialdehyde, 4-hydroxy-2-nonenal with total cholesterol as well as between reduced glutathione and nitric oxide with HDL cholesterol. These findings from both in vitro as well as in vivo models indicate the lipid peroxidation induction potential of cyclophosphamide which may be related to its toxic potential. The results also suggest the antiperox-idative effects of reduced glutathione and demonstrate its potential to reduce cyclophosphamide-induced lipid peroxidation and thus to increase therapeutic index of the drug by way of reducing toxicity that may be mediated through free radical mechanisms.