Determination of Vardenafil in Pure and Dosage Forms by Spectrophotometry

Journal of Applied Spectroscopy - Three simple, sensitive, precise, and rapid spectrophotometric methods are developed and optimized for the assay of vardenafil in pharmaceutical formulations. The...     

Structure and properties of the mesophase of syndiotactic polystyrene. VIII. Solvent sorption behavior of syndiotactic polystyrene/p‐chlorotoluene mesophase membranes

A crystalline δ form of a syndiotactic polystyrene (sPS) membrane was prepared from a solution of sPS (1 wt %) and p‐chlorotoluene (p‐CT) by a solution‐casting method. The mesophase (δ empty form) of sPS was obtained by the extraction of the guest solvent from the δ form of sPS by a stepwise solvent‐extraction method. The sPS/p‐CT mesophase membrane [p‐CT (A‐M)] was used for the sorption of 1 mol % p‐CT for different times and for the sorption of different concentrations of p‐CT, chlorobenzene (CB), p‐xylene (p‐X), toluene, and chloroform for 48 h. The presence of solvents in the sPS membrane was confirmed by IR analysis. A thermal study revealed that the sorption amount of 1 mol % p‐CT increased with increasing immersion time, and the sorption amounts of different solvents increased with increasing solvent concentration. Differential scanning calorimetry results showed that the desorption peak temperature increased as the amount of the solvent increased in the clathrated sPS membrane. Wide‐angle X‐ray diffraction results showed that 2θ at 8.25° was slightly shifted toward 8°, and there was no change in the peak position at 10° for p‐CT (A‐M), which was immersed in different solvents (1 mol %); however, the intensity of 2θ at 10° was not similar for all the samples. Among the solvents used for the sorption studies at 1 mol %, p‐CT (A‐M) could sorb more p‐CT and CB than p‐X, toluene, and chloroform. The solvent sorption isotherm was the Langmuir sorption mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3439–3446, 2004     

Imino Diels–Alder adducts. XII. Two pyrano[3,2‐c]quinolines

The crystal structures of pyrano­quinolines 9‐fluoro‐5‐phenyl‐3,4,4a,5,6,10b‐hexa­hydro‐2H‐pyrano[3,2‐c]quinoline, C₁₈H₁₈FNO, and 9‐methyl‐5‐phenyl‐3,4,4a,5,6,10b‐hexa­hydro‐2H‐pyrano­[3,2‐c]quinoline, C₁₉H₂₁NO, are isomorphous. In both structures, the pyran ring is exo to the six‐membered N‐heterocyclic ring formed in the cyclo­addition step. The torsion angles across the phenyl linkage for the two structures are −91.2 (1) and −88.3 (2)°. The striking feature in both crystal packings is that they do not contain the expected conventional hydrogen bonds, in spite of the presence of good hydrogen‐bonding functionalities. Possible C—H⋯π inter­actions are, however, observed.     

Role of micro-crystalline parameters in the physical properties of cotton fibers

Karnataka state in India is very well known for its cotton cultivation and there are innumerable varieties of these cotton fibers. Although, the yield and other types of characterization have been carried out on these fibers, the structure-property relation is not well studied till today. We have examined four different raw cotton fibers using Wide Angle X-ray Scattering (WAXS) technique and also we have computed micro-crystalline parameters. This study brings out the structure-property relation in cotton fibers.     

Novel deoxygenation reaction of epoxides by indium

[reaction: see text] A novel, mild, ecofriendly protocol for the deoxygenation of epoxides to alkenes using indium metal and indium(I) chloride or ammonium chloride in alcohol has been developed. It was necessary for the presence of good radical-stabilizing groups adjacent to the oxirane ring for the deoxygenation reaction to occur. It is proposed that this reaction occurs through an SET process with indium as an electron donor.     

Diastereoselective intermolecular Pauson-Khand reactions of chiral cyclopropenes

In this Letter, it is demonstrated that the unusual reactivity of cyclopropenes can increase the scope and utility of intermolecular Pauson-Khand reactions. The well-defined chiral environment of cyclopropenes has a powerful influence on the diastereoselectivity of the reactions and leads to the production of a single cyclopentenone in each of the described cases. The cyclopropane ring strongly influences the stereochemistry of reactions at the enone, and the three-membered ring can subsequently be cleaved under mild conditions. [reaction: see text]     

Cracking in drying latex films

Thin films of latex dispersions containing particles of high glass transition temperature generally crack while drying under ambient conditions. Experiments with particles of varying radii focused on conditions for which capillary stresses normal to the film deform the particles elastically and generate tensile stresses in the plane of the film. Irrespective of the particle size, the drying film contained, simultaneously, domains consisting of a fluid dispersion, a fully dried packing of deformed spheres, and a close packed array saturated with water. Interestingly, films cast from dispersions containing 95-nm sized particles developed tensile stresses and ultimately became transparent even in the absence of water, indicating that van der Waals forces can deform the particles. Employing the stress-strain relation for a drying latex film along with the well-known Griffith's energy balance concept, we calculate the critical stress at cracking and the accompanying crack spacing, in general agreement with the observed values.     

Synthesis of pyrene and benzo[a]pyrene adducts at the exocyclic amino groups of 2'-deoxyadenosine and 2'-deoxyguanosine by a palladium-mediated C-N bond-formation strategy

Single-electron oxidation of the carcinogenic hydrocarbon benzo[a]pyrene (BaP) is thought to result in a radical cation intermediate and this species has been proposed to cause alkylation at the nitrogens of the purine nucleobases. Although several different nucleoside adducts have been isolated as arising from this mode of metabolic activation, there are no selective, total syntheses of the stable exocyclic amino group adducts formed by the single-electron oxidation of any hydrocarbon with the purine 2'-deoxynucleosides to date. In this paper we disclose the synthesis of the model adducts N(6)-(1-pyrenyl)-2'-deoxyadenosine and N(2)-(1-pyrenyl)-2'-deoxyguanosine as well as the first synthesis of the carcinogen-linked nucleoside derivatives N(6)-(6-benzo[a]pyrenyl)-2'-deoxyadenosine and N(2)-(6-benzo[a]pyrenyl)-2'-deoxyguanosine via a palladium-mediated C-N bond formation. Two different coupling strategies were attempted: coupling of an aryl bromide with a suitably protected nucleoside and the coupling of an arylamine with a suitable halonucleoside. The former had somewhat limited applicability in that only N(6)-(1-pyrenyl)-2'-deoxyadenosine was prepared by this method; on the other hand, the latter was more general. However, there are noteworthy differences in the amination reactions at the C-6 and C-2 positions. Reactions at the C-6 resulted in the competing formation of a 1:2 amine-nucleoside adduct in addition to the desired monoaryl nucleoside. Such a dimer formation was not observed at the C-2. The C-2 adducts, however, displayed an interesting conformational behavior.