Extractive Spectrophotometric Determination of Titanium in Silicate Rocks, Soils and Columbite–Tantalite Minerals

2,3-Dihydroxynaphthalene forms a strong chelate with titanium over the pH range 4 to 9. At pH 4–5, titanium is extracted into ethyl acetate along with iron, leaving behind V, Nb, Mo, and a host of elements present in complex matrices of rock samples. In the extract, titanium is easily separated from iron after raising the pH of the medium and re-extracting. The method is free from any interference. The sensitivity of the method is 3.2×10⁴ L·mol^–1cm^–1. The method has been applied to a number of diverse samples including rocks and minerals. The precision of the Ti method is excellent. This method has been compared with tiron, chromotropic acid, diantipyrilmethane (DAM) and other existing spectrophotometric methods used in the analysis of rocks, ores and minerals. The proposed method has definite advantages over most spectrophotometric methods in terms of sensitivity, selectivity, reproducibility and simplicity.     

On the optical properties of the imidazolium ionic liquids

Room-temperature ionic liquids, particularly those based on substituted imidazolium cations, are currently being extensively studied for a variety of applications. Herein, we explore the suitability of several imidazolium salts in optical applications by carefully examining the electronic absorption and fluorescence behavior of these substances, generally believed to be transparent in most of the UV region and fully transparent in the visible region. It is shown that all imidazolium ionic liquids are characterized by significant absorption in the entire UV region and a long absorption tail that extends into the visible region. These absorption characteristics are attributed to the imidazolium moiety and its various associated structures. When excited in the UV or early part of the visible region, these liquids exhibit fluorescence, which covers a large part of the visible region and shows dramatic excitation wavelength dependence. The excitation wavelength dependent shift of the fluorescence maximum has been rationalized taking into consideration the existence of the various associated structures of the ionic liquids and the inefficiency of the excitation energy-transfer process between them. The results imply that these liquids may have serious drawbacks in some of the optical studies.     

Structural modifications of aqueous ionic micelles in the presence of denaturants as studied by DLS and viscometry

Hydrophobic interactions control the morphologies of both surfactant aggregates and proteins. Globular proteins "denature" upon addition of excess amounts of denaturants such as urea. Understanding the microscopic basis of the urea effect on proteins or supramolecular aggregates such as micelles has always been a debated issue. Inspired by this need, the effect of urea (U), thiourea (TU), monomethylurea (MMU), dimethylurea(DMU), tetramethylurea (TMU), dimethylthiourea (DMTU), and tetramethylthiourea (TMTU) on the structural transition (spherical micelles to rod-shaped micelles, s --> r) in the sodium dodecylbenzenesulfonate (SDBS)-1-pentanol system has been investigated through dynamic light scattering(DLS) and viscosity measurements at 25 degrees C. 1-Pentanol, at 0.14 M, is found to promote s --> r in this system (0.2 M SDBS). The presence of the additives causes, in almost all cases, a decrease and increase in this 1-pentanol concentration depending upon the concentration and nature of the additive. These effects are explained in terms of an increased dielectric constant of the solvent medium due to the presence of additives and increased micellar hydration due to the repulsion of charged monomers caused by adsorption of the additives. Taken together, the data signal the exposure of biological assemblies to water at higher [additive], which causes a decrease in hydrophobic interactions responsible for compact structure formation (i.e., native protein).     

Aziridine carboxylate from D-glucose: synthesis of polyhydroxylated piperidine, pyrrolidine alkaloids and study of their glycosidase inhibition

The D-glucose derived aziridine carboxylate 5 was obtained from (E)-ethyl-6-bromo-1,2-O-isopropylidene-3-O-benzyl-5-deoxy-alpha-D-xylo-5-eno-heptofuranuronate 4 through conjugate addition of benzylamine and in situ intramolecular nucleophilic expulsion of bromine. The regioselective aziridine ring-opening, using water as a nucleophile, resulted in the alpha-hydroxy-beta-aminoester 6, which was exploited in the synthesis of six and five membered azasugars 1b/1c and 2b/2c, respectively. The glycosidase inhibitory activity of the title compounds was evaluated.     

Vibrational dephasing and hydrodynamic effects on vibrational relaxation rates in acetophenone: Raman bandshape analysis

The isotropic component of Raman band for C=O stretching mode of acetophenone in solution was analyzed by estimating the correlation coefficient with reference to Lorentzian lineshape. In the intermediate region of solute/solvent concentration there is a sharp decrease in the correlation coefficient and there appears to be a transition from non-Lorentzian to Lorentzian lineshape. The vibrational relaxation rates have been estimated from the isotropic component of Raman band in different solvents. The rate is shown to be dependent on several macroscopic as well as microscopic properties of the solute-solvent system and intermolecular interactions. The hydrodynamic and dispersion forces appear to play a major role in determining the vibrational relaxation rate and the broadening of the bands.     

Amino Acid based cationic surfactants in aqueous solution: physicochemical study and application of supramolecular chirality in ketone reduction

The present study provides a molecular understanding of the origin of the chirality in aqueous micelles and its correlation with the proficiency of stereoselective ketone reduction. The effects of varied headgroup architecture on the surface-active properties as well as on other microstructural parameters were studied and correlated to the structural differences of these naturally occurring amino acid containing surfactants (1-4). Micropolarity sensed by pyrene showed that the micelles prepared using 1-4 are mostly hydrated; particularly large headgroup size surfactant produces more polar environment. A theoretical study was done to quantify the varied spatial dissymmetry for all four surfactants. Asymmetric reduction of prochiral ketones was carried out at the aqueous micellar interface of these chiral amphiphiles by exploiting the supramolecular chirality as evidenced from a circular dichroism study. The enantioselectivity of the reduction process is rationally improved through increase in spatial dissymmetry and steric constraint imposed at the micellar interface by the polar head of surfactants.     

Sulfone coupling and double-elimination strategy for carotenoid synthesis

[Reaction: see text]. A highly efficient synthetic method of carotenoid compounds has been developed on the basis of the sulfone coupling and double-elimination strategy. This method highlighted the sulfone-mediated coupling with the novel C(10) dialdehyde, 2,7-dimethyl-4-octenedial, which was easily prepared and efficiently utilized in the synthesis of the conjugated polyene chains.     

An efficient synthesis of the constrained peptidomimetic 2-oxo-3-(N-9-fluorenyloxycarbonylamino)-1-azabicyclo[4.3.0]nonane-9-carboxylic acid from pyroglutamic acid

[reaction: see text] Azabicyclo[X.Y.0]alkane amino acids are rigid dipeptide mimetics that are useful tools for structure-activity studies in peptide-based drug discovery. Herein, we report an efficient synthesis of three diastereomers of 9-tert-butoxycarbonyl-2-oxo-3-(N-tert-butoxycarbonylamino)-1-azabicyclo[4.3.0]nonane (3S,6S,9S, 3S,6R,9R, and 3S,6R,9S). Methyl N-Boc-pyroglutamate is cleaved with vinylmagnesium bromide to produce an acyclic gamma-vinyl ketone. Michael addition of N-diphenylmethyleneglycine tert-butyl ester produces the N-Boc-delta-oxo-alpha,omega-diaminoazelate intermediate, which, on hydrogenloysis, gives the fused ring system. Acidolytic deprotection followed by Fmoc-protection provided building blocks suitable for solid-phase synthesis.     

Regioselective haloaromatization of 1,2-bis(ethynyl)benzene via halogen acids and PtCl2. Platinum-catalyzed 6-pi electrocyclization of 1,2-bis(1'-haloethenyl)benzene intermediates

[reaction: see text] Treatment of 1,2-bis(ethynyl)benzene (1) with aqueous HX (X = Br, I) in hot 3-pentanone (100-105 degrees C, 2 h) afforded 1,2-bis(1'-haloethenyl)benzene species 2-Br and 2-I in 98% and 95% yields, respectively. The hydrochlorination of endiyne 1 failed to proceed at elevated temperature but was implemented efficiently by PtCl2 (5 mol %) in hot 3-pentanone (100 degrees C, 2 h) to give 1,2-bis(1'-chloroethenyl)benzene 2-Cl in 80% yield. In the presence of PtCl2 (5 mol %), these halides 2-Cl,2-Br, and 2-I were subsequently converted to 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in the mother solution via sequential 6-pi electrocyclization and dehalogenation reactions. PtCl2 (5 mol %) also effected direct haloaromatization of endiyne 1 with HX (X = Cl, Br, I) and gave 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in 64-71% yields. This investigation reports the scope and the regioselectivity of haloaromatization of various enediynes catalyzed by PtCl2.