Understanding the folding process of synthetic polymers by small-molecule folding agents

Two acceptor containing polyimides PDI and NDI carrying pyromellitic diimide units and 1,4,5,8-naphthalene tetracarboxy diimide units, respectively, along with hexa(oxyethylene) (EO6) segments as linkers, were prepared from the corresponding dianhydrides and diamines. These polyimides were made to fold by interaction with specifically designed folding agents containing a dialkoxynaphtha-lene (DAN) donor linked to a carboxylic acid group. The alkali-metal counter-ion of the donor carboxylic acid upon complexation with the EO6 segment brings the DAN unit in the right location to induce a charge-transfer complex formation with acceptor units in the polymer backbone. This two-point interaction between the folding agent and the polymer backbone leads to a folding of the polymer chain, which was readily monitored by NMR titrations. The effect of various parameters, such as structures of the folding agent and polymer, and the solvent composition, on the folding propensities of the polymer was studied.

Structural studies of the hen's egg lipovitellins. NMR and fluorescence investigations

The pH dependent reversible association-dissociation reaction of α- and β-lipovitellins from egg yolk has been studied by 1H NMR and fluorescence probe methods. Increased mobility of the choline methyl groups has been demonstrated on dissociation. The lipid methylene resonance of β-lipovitellin shows clear doublet character suggesting that the fatty acid chains exist in distinct environments. The high field component increases with temperature but is suppressed on treatment with pronase, suggesting a significant role for proteins in maintaining the differences in lipid environments. 1-Anilino-8-naphthalene sulfonate has been shown to bind less effectively to the monomeric lipovitellins. This is in agreement with earlier results suggesting that dissociation may be accompanied by increased hydration and conformational changes.

Dipole moments and molecular structure of picrates of aromatic hydrocarbons and heterocyclic amines

Dipole moment measurements have been made in the case of a few aromatic hydrocarbon picrates, the values obtained being 2·18, 2·25, 2·97 (all in Debye units) for picrates of naphthalene, acenaphthene and phenanthrene respectively and the results discussed in terms of Mulliken's theory. Measurements have also been extended to include a few salt-like heterocyclic amine picrates.

A spectroscopic study of the interaction of isoflavones with human serum albumin

Genistein and daidzein, the major isoflavones present in soybeans, possess a wide spectrum of physiological and pharmacological functions. The binding of genistein to human serum albumin (HSA) has been investigated by equilibrium dialysis, fluorescence measurements, CD and molecular visualization. One mole of genistein is bound per mole of HSA with a binding constant of 1.5 +/- 0.2 X 10(5) m(-1). Binding of genistein to HSA precludes the attachment of daidzein. The ability of HSA to bind genistein is found to be lost when the tryptophan residue of albumin is modified with N-bromosuccinimide. At 27 degrees C (pH 7.4), van't Hoff's enthalpy, entropy and free energy changes that accompany the binding are found to be -13.16 kcal.mol(-1), -21 cal.mol(-1)K(-1) and -6.86 kcal.mol(-1), respectively. Temperature and ionic strength dependence and competitive binding measurements of genistein with HSA in the presence of fatty acids and 8-anilino-1-naphthalene sulfonic acid have suggested the involvement of both hydrophobic and ionic interactions in the genistein-HSA binding. Binding measurements of genistein with BSA and HSA, and those in the presence of warfarin and 2,3,5-tri-iodobenzoic acid and Forster energy transfer measurements have been used for deducing the binding pocket on HSA. Fluorescence anisotropy measurements of daidzein bound and then displaced with warfarin, 2,3,5-tri-iodobenzoic acid or diazepam confirm the binding of daidzein and genistein to subdomain IIA of HSA. The ability of HSA to form ternery complexes with other neutral molecules such as warfarin, which also binds within the subdomain IIA pocket, increases our understanding of the binding dynamics of exogenous drugs to HSA.

The intramolecular external heavy atom effect in bromo-, benzo-, and naphthonorbornenes

A theoretical analysis of the external heavy atom effect of a halogen atom on the radiative rate constant of phosphorescence is examined as a function of position of a bromine atom or atoms relative to a naphthalene or a benzene chromophore for a series of mono- and dibromo-, naphtho-, and benzonorbornenes. The theoretical results are then compared to experimentaldata and lead to the conclusion that the enhancement of the phosphorescence process takes place through the second-ordermixing of the triplet states of the chromophore with the singlet charge transfer states arising primarily from an electron transferfrom the orbitals of the heavy atom perturber to the unfilled x* orbitals of the chromophore.

Physicochemical behaviour of polyperoxide

Polymeric peroxides are equimolar alternating copolymers formed by the reaction of vinyl monomers with oxygen. Physicochemical studies on the microstructure and chain dynamics of poly(styrene peroxide) PSP were first carried out by Cais and Bovey. We have found that polyperoxides are formed as main intermediates in solid-propellant combustion by the interaction of the monomer and oxygen generated by the decomposition of the polymeric binder and the oxidizer ammonium perchlorate. The experimentally determined heat of degradation and that calculated from thermochemical considerations reveal that polyperoxides undergo highly exothermic primary degradation, the rate-controlling step being the O-O bond dissociation. A random-chain scission mechanism for the thermal degradation of polyperoxides has been proposed. The prediction of unusual exothermic degradation of polyperoxides has resulted in the discovery of an interesting new phenomenon of 'autopyrolysability' in polymers. Several new polyperoxides based on vinyl naphthalene have been synthesized. We have also found that PSP, in conjunction with amines, can be used as initiator at ambient temperature for the radical polymerization of vinyl monomers.

Time-Resolved Resonance Raman Studies on Proton-Induced Electron-Transfer Reaction from Triplet Excited State of 2-Methoxynaphthalene to Decafluorobenzophenone

In this paper time-resolved resonance Raman (TR3) spectra of intermediates generated by proton induced electron-transfer reaction between triplet 2-methoxynaphthalene ((ROMe)-R-3) and decafluorobenzophenone (DFBP) are presented The TR3 vibrational spectra and structure of 2-methoxynaphthalene cation radical (ROMe+) have been analyzed by density functional theory (DFT) calculation It is observed that the structure of naphthalene ring of ROMe+ deviates from the structure of cation radical of naphthalene

Folding of a Donor-Containing Ionene by Intercalation with an Acceptor

Cationic ionenes that bear electron-rich 1,5-dialkoxynaphthalene (DAN) units within the alkylene segment were allowed to interact with different types of electron-deficient, acceptor-containing molecules in an effort to realize intercalation-induced folding of the ionenes; the collapse of the chains was expected to occur in such a way that the donor and acceptor units become arranged in an alternating fashion. Several acceptor-bearing molecules were prepared by the derivatization of pyromellitic dianhydride and naphthalene tetracarboxylic dianhydride with two different oligoethylene glycol monomethyl ether monoamines. This yielded acceptor molecules with different water solubility and allowed the examination of solvophobic effects in the folding process. UV/Vis spectroscopic studies were carried out by using a 1:1 mixture of the DAN-ionenes and different acceptor molecules in water/DMSO solvent mixtures. The intensity of the charge-transfer (CT) band was seen to increase with the water content in the solvent mixture, thereby suggesting that the intercalation is indeed aided by solvophobic effects. The naphthalene diimide (NDI) bearing acceptor molecules consistently formed significantly stronger CT complexes when compared to the pyromellitic diimide (PDI) bearing acceptor molecules, which is a reflection of the stronger pi-stacking tendency of the former. AFM studies of drop-cast films of different ionene-acceptor combinations revealed that compact folded structures are formed most effectively under conditions in which the strongest CT complex is formed.

Modified-Pore-Filled-PVDF-Membrane Electrolytes for Direct Methanol Fuel Cells

The polyvinylidene fluoride (PVDF) membrane is modified by the chemical etchant-route employing a sodium naphthalene charge-transfer complex followed by impregnation with Nafion ionomer or polyvinyl alcohol (PVA)-polystyrene sulfonic acid (PSSA) polymeric blend solutions by a dip-coating technique to form pore-filled-membrane electrolytes for application in direct methanol fuel cells (DMFCs). The number of coatings on the surface-modified PVDF membrane is varied between 5 and 15 and is found to be optimum at 10 layers both for Nafion and PVA-PSSA impregnations for effective DMFC performance. Hydrophilicity of the modified-membrane electrolytes is studied by determining average contact angle and surface-wetting energy. Morphology of the membranes is analyzed by a cross-sectional scanning electron microscope. The modified PVDF membrane electrolytes are characterized for their water-methanol sorption in conjunction with their mechanical properties, proton conductivity, and DMFC performance. Air permeability for the modified membranes is studied by a capillary-flow porometer. Methanol crossover flux across modified-PVDF-membrane electrolytes is studied by measuring the mass balance of methanol using a density meter. DMFCs employing membrane electrode assemblies with the modified PVDF membranes exhibit a peak power-density of 83 mW/cm(2) with Nafion impregnation and 59 mW/cm(2) for PVA-PSSA impregnation, respectively. Among the membranes studied here, stabilities of modified-pore-filled PVDF-Nafion and PVDF-PVA-PSSA membranes with 10-layers coat are promising for application in DMFCs. (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3518774] All rights reserved.

The variants of the protein toxins abrin and ricin A useful guide to understanding the processing events in the toxin transport

Kinetic data on inhibition of protein synthesis in thymocyte by three abrins and ricin have been obtained. The intrinsic efficiencies of A chains of four toxins to inactivate ribosomes, as analyzed by k1-versus-concentration plots were abrin II, III > ricin > abrin I. The lag times were 90, 66, 75 and 105 min at a 0.0744 nM concentration of each of abrin I, II, III and ricin, respectively. To account for the observed differences in the dose-dependent lag time, functional and structural variables of toxins such as binding efficiency of B chains to receptors and low-pH-induced structural alterations have been analyzed. The association constants obtained by stopped flow studies showed that abrin-I (4.13 × 105 M−1 s−1) association with putative receptor (4-methylumbelliferyl-α-D-galactoside) is nearly two times more often than abrin III (2.6 × 105 M−1 s−1) at 20°C. Equillibrium binding constants of abrin I and II to thymocyte at 37°C were 2.26 × 107 M−1 and 2.8 × 107 M−1 respectively. pH-induced structural alterations as studied by a parallel enhancement in 8-anilino-L-naphthalene sulfonate fluorescence revealed a high degree of qualitative similarity. These results taken with a nearly identical concentration-independent lag time (minimum lag of 41–42 min) indicated that the binding efficiencies and internalization efficiencies of these toxins are the same and that the observed difference in the dose-dependent lag time is causally related to the proposed processing event. The rates of reduction of inter-subunit disulfide bond, an obligatory step in the intoxication process, have been measured and compared under a variety of conditions. Intersubunit disulfide reduction of abrin I is fourfold faster than that of abrin II at pH 7.2. The rate of disulfide reduction in abrin I could be decreased 1 I-fold by adding lactose, compared to that without lactose. The observed differences in the efficiencies of A chains, the dose-dependent lag period, the modulating effect of lactose on the rates of disulfide reduction and similarity in binding properties make the variants a valuable tool to probe the processing events in toxin transport in detail.

8-(3-methylphenoxy)-16H-dinaphtho[2,1-d;1',2'-g][1,3,2]dioxaphosphocine 8-oxide

In the title compound, C28H21O4P, the eight-membered heterocyclic dioxaphosphocine ring has a distorted boat conformation, with the phosphoryl O atom axial and the phenoxy group equatorial. The P=O distance is 1.451 (1) Angstrom and the average length of the three P-O bonds is 1.573 (1) Angstrom. The phenyl ring is nearly perpendicular to both naphthalene planes, making dihedral angles of 91.30 (3) and 97.65 (5)degrees with them. The angle between the two naphthalene planes is 67.73 (3)degrees. The crystal structure is stabilized by van der Waals interactions.

Oxidation of substituted benzylic hydrocarbons and naphthalenes by peroxydisulphate in the presence of metal ions

Oxidations of various substituted benzylic hydrocarbons with peroxydisulphate in the presence of metal ion catalysts like iron, nickel, copper, cobalt, silver and cerium were examined. Among the metal ions copper (II) catalysed reaction gives products in excellent yield, whereas oxidation of naphthalene and substituted naphthalenes gives low to moderate yield of the products with peroxydisulphate- copper (II).

In vitro micropropagation of scented geranium (Pelargonium graveolens L. Her. ex Ait: syn P. roseum willd)

The objective of this study was to develop a rapid and efficient system for regenerating shoots from nodal explants of scented geranium (Pelargonium graveolens L. Her. ex Ait: syn. P. roseum willd). Single node stem explants were inoculated in MS media containing different combinations of 6-benzylaminopurine (BAP) with indole-3-acetic acid (IAA) or naphthalene acetic acid (NAA) (0, 0.5, 1.0, 2.0 mg/l) in a 4x4 factorial experiment. Multiple shoots were induced in media supplemented with BAP and IAA, Maximum number of shoots (56 per explant) were observed in the medium containing BAP and IAA at 1 mg/l each, 30 days after inoculation. Micro shoots were subcultured once in every four weeks. Adventitious shoots were induced from in vitro grown leaves and petioles. Several regenerated shoots were rooted on MS half-strength medium supplemented with 0.5 mg/l indole-3-butyric acid (IBA) and the plantlets were hardened in the growth chamber. This micropropagation system could be used for rapid and large-scale production of scented geranium.

In vitro regeneration from immature cotyledon explant and protein profile changes during organogenesis in groundnut (Arachis hypogaea L.)

Complete plants were regenerated from in vitro cultured immature cotyledon segments of groundnut (Arachis hypogaea L. cv. TMV-7) by organogenesis. Callus cultures were best Initiated from immature cotyledon segments on MS (Murashige and Skoog) salts containing B5 vitamins supplemented with indole-3-acetic acid (IAA) and alpha -naphthalene acetic acid (NAA; 4.0 mg L-1) and kinetin (KIN; 0.5 L-1). Calluses were transferred to a medium containing KIN (2.0 mg L-1) and IAA and NAA (0.5 mg L-1) for shoot Initiation. The regenerated shoots were transferred to a medium containing Indole-3-butyric acid (IBA; 2.0 mg L-1) and KIN (0.2 mg L-1) for developing roots. In vitro produced plantlets developed sucessfully, matured, and set seed. The protein profiles [sodium dodecyl sulphate - polyacrylamide gel electrophoresis (SDS-PAGE)] of callus, callus with shoot, and callus with shoot and root showed differences.

Is O-1(2) alone sufficient for DNA cleavage? Possible involvement of paramagnetic intermediates

It is proposed that singlet dioxygen reacting with guanosine or deoxyguanosine part of nucleotides does not, by itself, cause DNA cleavage. The strand break originates at the endoperoxide stage whenever this link evolves into a O-centered radical. The O-centered radical is then in a good spatial position to abstract an hydrogen intramolecularly from the ribose or desoxyribose part of the nucleotide. The carbon centered radical thus formed on the sugar part may lead to strand break either by a p-scission mechanism or by an homolytically induced solvolysis. High pH could also induce cleavage after the endoperoxide stage via a base catalyzed ring chain protomerism.