Synthesis of 2-phenoxy-2-phenylethyl acrylate and copolymerization with 2-phenylethyl acrylate: Estimation of monomer reactivity ratios,thermal and optical properties

A new aromatic based monomer 2-phenoxy-2-phenylethyl acrylate (PPEA) was synthesized. Copolymers of PPEA with 2-phenylethyl acrylate (PEA) were prepared by free radical polymerization. The reactivity ratios were estimated using various graphical methods. Structural parameters of the copolymers were obtained by calculating the dyad monomer sequence fractions and the mean sequence length. Optical properties of polymers such as refractive indices and UV-Visible absorption were investigated. The glass transition temperature and thermal degradation behavior of the copolymers were studied. Combined with the RI, transparency and thermal properties, prepared copolymers hold great promise as materials for intraocular lens applications.     

PNA versus DNA: effects of structural fluctuations on electronic structure and hole-transport mechanisms

The effects of structural fluctuations on charge transfer in double-stranded DNA and peptide nucleic acid (PNA) are investigated. A palindromic sequence with two guanine bases that play the roles of hole donor and acceptor, separated by a bridge of two adenine bases, was analyzed using combined molecular dynamics (MD) and quantum-chemical methods. Surprisingly, electronic structure calculations on individual MD snapshots show significant frontier orbital electronic population on the bridge in approximately 10% of the structures. Electron-density delocalization to the bridge is found to be gated by fluctuations of the covalent conjugated bond structure of the aromatic rings of the nucleic bases. It is concluded, therefore, that both thermal hopping and superexchange should contribute significantly to charge transfer even in short DNA/PNA fragments. PNA is found to be more flexible than DNA, and this flexibility is predicted to produce larger rates of charge transfer.     

Thermodynamic stability of novel boron sheet configurations

Thermodynamic stability together with the vibrational spectrum of several structural motifs of the pristine 2D boron sheet are investigated. The results suggest that the nature of the chemical bonding, rather than thermal effects, appears to be the prime factor in determining the stability of atomic monolayers of boron. The most stable configuration is predicted to be composed of a hybrid of triangular and hexagonal configuration. A boron sheet composed of either perfect triangular or perfect hexagonal motifs is unlikely to be synthesized. The distinctive features predicted in vibrational and thermodynamic properties for boron sheet configurations are expected to exhibit their signatures in the corresponding pristine nanotubes and crystalline bundles.     

Interaction of metallic nanoparticles with a biologically active molecule, dopamine

We present the results of first-principles molecular orbital calculations describing the interaction of metallic nanoparticles, represented by Mn(13), Ag(13), and Al(13) atomic clusters, with a biologically active molecule, dopamine. The interaction strength, determined in terms of the nanoparticle-molecule complex binding energy, is found to be higher for Mn than either Ag or Al and can be explained in terms of the degree of the hybridization of the (metal) atomic orbitals with the molecular orbitals in the complex. Furthermore, smaller interaction strength of these metallic nanoparticles with water compared to that with dopamine predicts the preference of forming a complex of dopamine with the metallic nanoparticles in the aqueous solution. The calculated results may therefore suggest that the presence of these metallic nanoparticles could induce different levels of dopamine depletion in solution.     

Concentration and temperature polarization effects during osmotic membrane distillation

Pineapple juice is one of the popular fruit juice due to its pleasant aroma and flavor. Concentration of clarified pineapple juice was carried out by osmotic membrane distillation in a plate and frame membrane module. Concentration and temperature polarization effects are found to have significant role on flux reduction during osmotic membrane distillation process. The contribution of these polarization effects on reduction of the driving force (in turn the flux) at various process conditions such as osmotic agent concentration (2–10 mol/kg (1 molality = 1 mol/kg)), flow rate (25–100 ml/min) of feed and osmotic agent are studied. Concentration polarization has more significant effect on flux reduction when compared to temperature polarization. The experimental fluxes were in good agreement with theoretical fluxes when calculated by considering both concentration and temperature polarization effects. The pineapple juice was concentrated up to a total soluble solids content of 62°Brix at ambient temperature.     

Detection and relative quantification of proteins by surface enhanced Raman using isotopic labels

Accurate quantification of protein content and composition has been achieved using isotope-edited surface enhanced resonance Raman spectroscopy. Synthesis of isotopomeric Rhodamine dye-linked bioconjugation reagents enabled direct labeling of surface lysines on a variety of proteins. When separated in polyacrylamide gels and stained with silver nanoparticles. The spectral signatures reflect the expected statistical distribution of isotopomeric labels on the labeled proteins in the gel matrix format without interference from protein features.     

Stability-Indicating LC Determination of Nitazoxanide in Bulk Drug and in Pharmaceutical Dosage Form

A novel stability-indicating high-performance liquid chromatographic assay method was developed and validated for quantitative determination of nitazoxanide in bulk drugs and in pharmaceutical dosage form in the presence of degradation products generated from forced decomposition studies. An isocratic, reversed phase LC method was developed to separate the drug from the degradation products, using an Ace5- C18 (250 mm × 4.6 mm, 5 μm) column, and 50 mM ammonium acetate (pH 5.5 by acetic acid) and acetonitrile (55:45 v/v) as a mobile phase. The detection was carried out at a wavelength of 240 nm. The nitazoxanide was subjected to stress conditions of hydrolysis (acid, base), oxidation, photolysis and thermal degradation. Degradation was observed for nitazoxanide in base, acid and in 30% H₂O₂ conditions. The drug was found to be stable in the other stress conditions attempted. The degradation products were well resolved from the main peak. The percentage recovery of nitazoxanide was from (100.55 to 101.25%) in the pharmaceutical dosage form. The developed method was validated with respect to linearity, accuracy (recovery), precision, system suitability, specificity and robustness. The forced degradation studies prove the stability indicating power of the method.     

Bile pigment studies-VII New syntheses of biliverdin-IXα dimethyl ester and two related mono-vinyl-mono-ethyl isomers

Using the recently developed route through di-t-butyl b-bilene-1,19-dicarboxylates, new syntheses of biliverdin-IXα dimethyl ester (1) and two related mono-vinyl-mono-ethyl isomers (2) and (3), are described. The two dihydro-derivatives of (1) are important in connection with biosynthetic studies of the origin of algal biliproteins.     

Diagnosing infeasibilities in network flow problems

We consider the problem of finding a feasible flow in a directed networkG = (N,A) in which each nodei N has a supplyb(i), and each arc(i,j) A has a zero lower bound on flow and an upper boundu _ij . It is well known that this feasibility problem can be transformed into a maximum flow problem. It is also well known that there is no feasible flow in the networkG if and only if there is a subsetS of nodes such that the net supplies of the nodes inS exceeds the capacity of the arcs emanating fromS. Such a setS is called awitness of infeasibility (or, simply, awitness) of the network flow problem. In the case that there are many different witnesses for an infeasible problem, a small cardinality witness may be preferable in practice because it is generally easier for the user to assimilate, and may provide more guidance to the user on how to identify the cause of the infeasibility. Here we show that the problem of finding a minimum cardinality witness is NP-hard. We also consider the problem of determining aminimal witness, that is, a witnessS such that no proper subset ofS is also a witness. In this paper, we show that we can determine a minimal witness by solving a sequence of at mostn maximum flow problems. Moreover, if we use the preflow-push algorithm to solve the resulting maximum flow problems and organize computations properly, then the total time taken by the algorithm is comparable to that of solving a single maximum flow problem. This approach determines a minimal cardinality witness in O(n ² m ^1/2) time using simple data structures and in O(nm logn) time using the standard implementation of the dynamic tree data structures. We also show that the recognition version of the minimal witness problem is equivalent to a recognition version of a related problem known as theminimum rooted cut problem. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.Corresponding author.     

CARBON-14 LABELING AND BIOLOGICAL ACTIVITY OF THE TUMOR-LOCALIZING DERIVATIVE OF HEMATOPORPHYRIN

Abstract— Carbon-14-labeled hematoporphyrin ([¹⁴C]HP) was synthesized by two methods, (i) Using an in vitro avian whole-blood system, [¹⁴C]protoheme was obtained biosynthetically by incorporating [⁴C]aminolevulinic acid into the porphyrin ring structure. Subsequently, the [¹⁴C]protoheme was converted to [⁴C]HP by standard procedures, (ii) By adopting several well-characterized chemical reactions, deuteroporphyrin was treated with [¹⁴C]acetyl chloride, giving [¹⁴C]diacetyl deuteroporphy-rin which was readily reduced and hydrolyzed to [¹⁴C]HP (with thecarbon–14 label on the hydroxyethyl side-chains). These two methods are simple and afford good yields of [¹⁴C]HP with moderate to high specific activities. The [¹⁴C]HP was then treated with acetic acid/sulfuric acid followed by sodium hydroxide to give [¹⁴C]HPD. Upon gel- and ultra-filtration, the [¹⁴C]HPD was enriched in the so-called tumor-localizing fraction of HPD, giving [¹⁴C]PII with specific activities of 0.4 Ci/mol (biosynthesis) and 10 Ci/mol (chemical synthesis). These [¹⁴C]PII preparations were equivalent with respect to chromatographic and spectrophotometric characteristics, as well as tumoricidal photodynamic activity in the DBA/2 Ha-DD mouse: SMT-F tumor system, to the unlabeled commercial product Photofrin^? II. The distribution of [¹⁴C]PII in mouse tissues was in close agreement to that previously reported, after adjustment for dose, for [¹⁴C]HPD biosynthetically labeled in vivo (Gomer and Dougherty, 1979), as well as for Photofrin^? II, where tissue levels were determined spectrophotometrically after extraction (Dougherty and Mang, unpublished).