Diastereoselective Mukaiyama aldol reaction of (N-alkyl) isatins with 2-(trimethylsilyloxy)furan by using lanthanum triflate

An efficient vinylogous Mukaiyama aldol reaction (VMAR) of 2-(trimethylsilyloxy)furan with various (N-alkyl)isatins is described in the presence of lanthanum(III) triflates (5 mol %). The reaction proceeds rapidly and affords the corresponding 3-hydroxy-(5-oxo-2,5-dihydrofuran-2-yl)indolin-2-one in high yields with good diastereoselectivities (threo:erythro ratio up to ≤95:5).     

Ratiometric and simultaneous estimation of Fe and Cu ions: 1,3,5-substituted triethylbenzene derivatives coupled with benzimidazole

We synthesized a novel 1,3,5-substituted triethylbenzene derivative with a benzimidazole moiety as a binding and signalling subunit. The triethylbenzene platform was judiciously incorporated into the receptor design such that all the fluorophores are in close proximity to each other in order to facilitate stacking. The advantage of this approach lies in the fact that the receptor will offer a dual channel emission for the multiple ratiometric determination of metal ions. The sensor was tested in a CH₃CN/H₂O (7:3, v/v, pH 7.1) HEPES buffered solution and successfully developed for the ratiometric and simultaneous estimation of Fe³⁺ and Cu²⁺ ions in aqueous samples.     

Fine tuning of a solvatochromic fluorophore for selective determination of Fe: a new type of benzimidazole-based anthracene-coupled receptor

We synthesized a novel benzimidazole-based, anthracene-coupled fluorescent receptor capable of recognizing and estimating the concentrations of Fe³⁺ in semi-aqueous solution by ratiometric estimation. Our sensor can be made highly selective for Fe³⁺ over other metal ions by changing the solvent composition.     

Enantioselective organocatalytic aldol reaction of unactivated ketones with isatins

Enantioselective organocatalytic direct aldol reaction of unactivated ketones with various isatin derivatives was developed using cinchonine based urea ligand employing a noncovalent catalysis mechanism. Using this protocol we can access functionalized 3-alkyl-3-hydroxyindolin-2-ones in high yields with good to excellent enantioselectivities.     

Metabolite identification by liquid chromatography-mass spectrometry

Metabolite identification (Met ID) is important during the early stages of drug discovery and development, as the metabolic products may be pharmacologically active or toxic in nature. Liquid chromatography-mass spectrometry (LC-MS) has a towering role in metabolism research.This review discusses current approaches and recent advances in using LC-MS for Met ID. We critically assess and compare various mass spectrometers, highlighting their strengths and limitations. Citing appropriate examples, we cover recent LC and ion sources, isotopic-pattern matching, hydrogen/deuterium-exchange MS, data dependent analyses, MS^E, mass defect filter, 2D and 3D approaches for the elucidation of molecular formula, polarity switching, and background-subtraction and noise-reduction algorithms. A flow chart outlines a comprehensive strategy for Met ID, including a focus on reactive metabolites.     

Mathematical modeling of solvent extraction of uranium from sulphate media employing 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A) and its mixture with trioctylphosphine oxide (TOPO) as extractants

The extraction of U(VI) from sulphate medium with 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A, H₂A₂ in dimeric form) in n-dodecane has been investigated under varying concentrations of sulphuric acid and uranium. Slope analysis of uranium (VI) distribution data as a function of PC88A concentration suggests the formation of monomeric species, viz. UO₂(HA₂)₂. This observation was further supported by the mathematical expression obtained during non-linear least square regression analysis of U(VI) distribution data correlating the percentage extraction (%E) and the acidity (H _i). A mathematical model correlating the experimental distribution ratio values of U(VI) (D _U) with initial acidity (H _i) and initial uranium concentrations (C _i) was developed: D_\textU = 12.98( ±0.90)/{ C_\texti ^{- 0.75( ±0.05)} ×[ H_\texti ]² } D_{\text{U}} = 12.98( \pm 0.90)/\left\{ {C_{\text{i}}^{ - 0.75( \pm 0.05)} \times \left[ {H_{\text{i}} } \right]^{2} } \right\} . This expression can be used to predict the concentration of uranium in organic as well as in aqueous phase at any C _i and H _i. The extraction data were used to calculate the conditional extraction constant (K _ex) values at different acidities (2–7 M H⁺), uranium (0.02–0.1 M) and PC88A (0.2–0.6 M) concentrations. These studies were also extended for the extraction of U(VI) using synergistic mixtures of PC88A and TOPO from sulphate medium.     

Kinetics of copper(II)‐catalyzed oxidation of S(IV) by atmospheric oxygen in ammonia buffered solutions

To understand the chemistry of Cu(II)–NH₃–S(IV)–O₂ system, the kinetics of the oxidation of sulfur(IV) catalyzed by amminecopper(II) complexes has been studied in the ammonia‐buffered solutions. Sulfur(IV) is oxidized to sulfate. The complexes, Cu(NH₃)²⁺, Cu(NH₃)₂²⁺, and Cu(NH₃)²⁺₃ appear to be equally reactive and Cu(NH₃)₄²⁺ appears to be unreactive. The kinetics obey the rate law: where α₁ and γ₁ are the rate constants for O₂‐dependent and O₂‐independent pathways, respectively, for Cu(NH₃)²⁺, Cu(NH₃)²⁺₂, and Cu(N H₃)₃²⁺ complexes, which appear to be equally reactive. The values of α₁ and γ₁ were found to be (1.32 ± 0.21) × 10⁶ L² mol^?2 s^?1 (1.74 ± 0.40) × 10⁹ L³ mol^?3 s^?1respectively at 30°C. The reaction rate is not influenced by the presence of ethanol—a free radical scavenger, so a nonradical mechanism has been proposed. The results of this study are useful in understanding the atmospheric chemistry of aqueous phase autoxidation of dissolved sulfur dioxide in copper(II)–ammonia–sulfur(IV)–oxygen system at high pH. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 379–392, 2011     

Ideal rate of collision of cylinders in simple shear flow

The collision of particles influences the behavior of suspensions through the formation of aggregates for adhesive particles or through the contributions of solid-body contacts to the stress for nonadhesive particles. The simplest estimate of the collision rate, termed the ideal collision rate, is obtained when particles translate and rotate with the flow but have no hydrodynamic or colloidal interactions. Smoluchowski calculated the ideal collision frequency of spherical particles in 1917. So far, little work has been done to understand rate of collision for nonspherical particles. In this work, we calculate the ideal collision rate for cylindrical particles over a broad range of particle aspect ratios r defined as the ratio of length to diameter. Monte Carlo simulations are performed with initial relative positions and orientations that model the rate of approach of noninteracting particles following Jeffery orbits with several choices of the orbit distribution. The role of rotational motion of particles on collision frequency is elucidated by comparing the ideal collision rate calculations with similar calculations for nonrotating particles. It is shown that the ratio of the collision rate of cylinders to that of spheres that circumscribe the cylinders is proportional to 1/rr(e) for r ? 1 and r(e) for r ? 1. Here, r(e) is the effective aspect ratio defined as the aspect ratio of a spheroid having the same period of rotation as the cylinder. The effective aspect ratio of the cylindrical particles was determined using finite element calculations of the torque on nonrotating cylinders with their axes parallel to the velocity and velocity gradient directions. In addition to deriving the total collision rate, we categorize collisions as side-side, edge-side, and face-edge based on the initial point of contact. Most collisions are found to be side-edge for r ? 1 and face-edge for r ? 1, suggesting that nonlinear aggregates will develop if particles stick at the point of first contact.     

Interaction and solubilization of some phenolic antioxidants in Pluronic® micelles

The solubilization of four phenolic antioxidants, namely p-hydroxybenzoic acid (PHBAA), syringic acid, sinapic acid, and quercetin in micelles of an ethylene oxide (EO)–propylene oxide (PO) triblock copolymer Pluronic^® P104 (EO₂₇–PO₆₁–EO₂₇, PPO mol wt = 3540, % PEO = 40) was examined at different temperatures, pHs, and in the presence of sodium chloride. The nano-size core–shell micelles of P104 characterized by dynamic light scattering had hydrodynamic diameter of about 18–20 nm with low polydispersity. Antioxidants induced micellization and micellar growth were observed. The critical micellar concentration (CMC), critical micellar temperature (CMT), cloud point (CP) of P104 decreased due to solubilization and interactions of antioxidants. The solubilization was favored at higher temperature, pH and in the presence of salt and follows the order PHBA > syringic acid > sinapic acid > quercetin which corresponds to the trend in their aqueous solubility. The location of antioxidant in micelles observed from NOESY spectra. Structure and hydrophobicity of antioxidants were found to be governing factors for their interaction and location in the micelles.     

Intermolecular hydrogen bonding in the binary mixture [(C2H5)2CO + CH3OH] probed by polarized Raman measurements and DFT calculations

The Raman spectra of neat (C₂H₅)₂CO (pentanone) and its binary mixtures with hydrogen donor solvent (CH₃OH), [(C₂H₅)₂CO + CH₃OH] having different mole fractions of the reference system, (C₂H₅)₂CO in the range 0.1-0.9 at a regular interval of 0.1 were recorded in the CO stretching region. In neat liquid, the Raman peak appears asymmetric. The asymmetric nature of the peak has been attributed to the CO stretching mode of the two conformers of (C₂H₅)₂CO having C₂ and C_2v point groups and the corresponding bands at ∼1711 and ∼1718 cm⁻¹, respectively. A careful analysis of the I_iso (isotropic component of the Raman scattered intensity) at different concentrations reveals that upon dilution with methanol, at mole fraction C = 0.6, an additional peak in the CO stretching region is observed at ∼1703 cm⁻¹ which is attributed to the hydrogen bonding with methanol. A peculiar feature in this study is that upon dilution, the peak at ∼1718 cm⁻¹ shows a minimum at C = 0.6, but on further dilution it shows a blue shift. However, the other peak at ∼1711 cm⁻¹ shows a continuous red shift with dilution as well as a maximum at C = 0.7 in the linewidth vs. concentration plot, which is essentially due to competition between motional narrowing and diffusion phenomena. A significant amount of narrowing in the Raman band at ∼1718 cm⁻¹ can be understood in terms of caging effect of the reference molecule by the solvent molecules at high dilution. A density functional theoretic (DFT) calculation on optimized geometries and vibrational frequencies of two conformers of neat (C₂H₅)₂CO in C₂ ad C_2v forms and the complexes with one and two CH₃OH molecules with both the conformers was performed. The experimental results and theoretical calculations together indicate a co-existence of two conformers as well as hydrogen bonded complex with methanol in the binary mixture, [(C₂H₅)₂CO + CH₃OH] at intermediate concentrations.