Influence of dissociation of tris(2,2′-bipyridyl)iron(II) cations on the time dependence of currents in clay-modified electrodes

The time dependence of the voltammetric waves of [Fe(bpy)₃]²⁺ adsorbed in clay-modified electrodes (CMES) differed greatly from those of [Ru(bpy)₃]²⁺ and [Os(bpy)₃]²⁺. The currents obtained with the ruthenium and osmium cations were essentially constant in the first 2 h that the CME spent in the blank electrolyte. For [Fe(bpy)₃]²⁺, the maximum currents were twice as large. After a sharp rise in the first few scans, they decreased rapidly to less than half of their maximum values after 40 min. The decrease was more rapid when the potential was scanned continuously or when the pH of the electrolyte was increased. Coulometry shows that a larger fraction of the adsorbed [Fe(bpy)₃] ²⁺ cations were oxidized and that they were oxidized much more rapidly than the other two cations. The unique behaviour of [Fe(bpy)₃]²⁺ is attributed to its dissociation in the CME. UV—visible spectroscopy shows that significant dissociation of this cation occurred on the time-scale of the electrochemical measurements. Much larger currents were also found for CMEs containing cis- or trans-[Ru(bpy)₂(H₂O)₂] ²⁺, and these are attributed to the greater mobility of adsorbed bis-bipyridyl cations.     

Gliadin effect on fluctuation properties of phospholipid giant vesicles

Gliadin is a fraction of wheat gluten, a protein supramolecular complex known for its remarkable and biotechnologically relevant viscoelastic properties. Very high molecular mass characterise these systems, thus hindering high-resolution structural investigations. It is known, however, that these proteins comprise rather extended, extensively interassociated structures, which respond for their peculiar mechanical behaviour. Besides these properties, some of gluten's fractions, such as gliadin, are also known to be involved in a nutritionally relevant pathology of auto-immune character, the celiac disease, supposedly related to some unusual structural features of the protein. Despite its medical relevance, however, the role played by gliadin in the etiology of the celiac disease is not sufficiently understood to date. In this work, we investigated the role of gliadin on mechanical properties of a membrane model of dioleoylphosphatidylcholine (DOPC) giant unilamellar vesicles. The technique of micropipette aspiration, coupled to videomicroscopy, was applied. The microvesicles, produced by electric field pulsing over metal-covered plates, were suctioned into the micropipettes under varying applied pressures. A significant increase in the values of the bilayer curvature constant, k(c), was observed, with a saturation effect being verified at around 0.02-0.03 gliadin/DOPC mass ratio, indicating that the membrane becomes less elastic in the presence of the protein. Possible correlations between the observed membrane fluctuation properties and the celiac disease etiology are suggested and discussed.     

Emission energies and photophysical properties of ladder oligo(p-aniline)s

Emission properties and the photophysics of three ladder oligo(p-aniline)s; namely 5,11-diethyl-6,12-dimethylindolo[3,2-b]carbazole (DIMER 2P), 14-ethyl-5,8-dihydro-diindolo[3,2-b:2′,3′-h]carbazole (TRIMER 2P), and 5,8,14-triethyl-diindolo[3,2-b:2′,3′-h]carbazole (TRIMER 3P) are presented. The optimization (relaxation) of the first singlet excited electronic state (S₁) has been done using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. The excitation to the S₁ state does not cause important changes in the geometrical parameters of the compounds, as is experimentally corroborated by the small Stokes shifts. Emission energies from the relaxed excited states have been obtained from TDDFT calculations performed on the S₁ optimized geometries and have been correlated with the corresponding fluorescence spectra of the derivatives dissolved in dichloromethane. A good agreement has been found between TDDFT emission energies and the (0,0) fluorescence bands. As predicted from theoretical calculations, all compounds exhibit small Stokes shift, which testify the rigidity of these ladder compounds. Moreover, this theoretical approach provides a good evaluation of the bathochromic shifts caused by the increase in the conjugation length or by the presence of alkyl chains on the nitrogen atoms. Finally, the fluorescence quantum yield and lifetime of the compounds in dichloromethane have been obtained. From these data, the radiative and nonradiative rate constants of the deactivation of the S₁ state have been determined.     

腈菌唑的热容和热力学性质

通过小样品精密自动绝热热量计测定了自己合成并提纯的腈菌唑 (C₁₅H₁₇ClN₄) 在78 ～ 368K温区的低温摩尔热容。量热实验发现, 该化合物在363 ~ 372 K温区, 有一固-液熔化相变过程, 其熔化温度为 (348.800±0.06)K, 摩尔熔化焓、摩尔熔化熵及化合物的纯度分别为：(30931±11) J•mol^-1、(88.47±0.02) J•mol^-1•K^-1和0.9941(摩尔分数)。用差示扫描量热(DSC) 技术对该物质的固-液熔化过程作了进一步研究，结果与绝热量热法一致。     

Rapid estimation of charge distribution. II. Heteroatoms

A rapid method for estimating CNDO charges in large data bases using a reparameterized Del Re method has been described previously. In this article the method is extended to saturated compounds containing B, N, O, F, Si, P, S, and Cl. Good results are obtained by forcing the Del Re δ^o parameter for each element to be linearly related to its Pauling electronegativity, but with the slopes and intercepts being different for second- and third-row elements. With a test set of 17 compounds and 71 atoms, the CNDO charge was reproduced with an average deviation of ±0.03. The largest deviations, up to ±0.2, were observed for carbons having multiple F or Cl substituents and for sterically hindered atoms. © 1992 by John Wiley & Sons, Inc.     

Synthesis of optically active polymers bearing amino acid moieties by atom transfer radical polymerization

We report here an approach toward the synthesis of optically active polyacrylamide bearing amino acid moieties, poly[N- methacryloyl L-leucine methyl ester] (PMALM), with controlled average number molecular weight (Mn) and relatively narrow polydispersity index (PDI, Mw/Mn < 1.3) by atom transfer radical polymerization (ATRP) using initiating system methyl 2- bromopropionate/CuBr/tris(2-dimethylaminoethyl) amine. The optical properties of the resulting polymers were evaluated fromspecific optical rotation value and CD spectra.     

A study on application of impregnated synthetic peptide TLC stationary phases for the screening of 5-HT1A ligands. Part 2

Six extended analogues of the recently described peptides (LDVL, ADVL) were designed and synthesized on a solid support, and then impregnated on TLC stationary phases. The impact of the impregnated peptide sequence modifications on the chromatographic retard, Delta R(f) (difference in the migration of tested compound on control and impregnated plates), of 42 arylpiperazine 5-HT(1A) receptor ligands was studied. None of the new models tested made a better prediction of 5-HT(1A) affinity than that utilizing ADVL tetrapeptide. Further validation of the ADVL model on a set of 22 structurally differentiated 2-methoxy-phenylpiperazine derivatives confirmed its effectiveness in the affinity discrimination of a coherent group of 5-HT(1A) receptor ligands.     

Fluorimetric determination of alkaline phosphatase in solid and fluid dairy products

A new assay has been developed for measuring residual alkaline phosphatase (ALP) activity in a wide variety of dairy products. The method proposed is simple, rapid and directly applicable to solid and liquid dairy samples. ALP in the test sample hydrolyzes a non fluorescent substrate, trifluoromethyl-β-umbelliferone phosphate, to its highly fluorescent phenolate product. The assay is performed in a reverse micellar medium composed of mixed buffer (2-amino-2-methyl-1-propanol buffer pH 9.0 and borate buffer pH 9.0) in AOT/isooctane, at a temperature of 38 °C. Total test time is 450 s. Reaction rates are linear (except for butter) up to 8.5 and 11% (v/v) raw milk, for whole milk and chocolate milk, respectively. The detection limits are 0.04, 0.4 and 0.22% (v/v) raw milk, for whole milk, chocolate milk and butter, respectively. The precision of the fluorimetric method was assessed by repeated analysis of a pasteurized milk sample spiked with mixed herd raw milk. The accuracy of the method was evaluated by comparison with an official colorimetric assay using p-nitrophenylphosphate as ALP substrate.     

A novel approach to the use of graph theory in structure–activity relationship studies. Application to the qualitative evaluation of mutagenicity in a series of nonfused ring aromatic compounds

In this article we describe a novel approach to the application of graph theory in structure–activity relationship studies. An information–theoretical topological index for the vertices of a molecular graph has been used for the qualitative evaluation of the mutagenic activity of a series of nonfused ring aromatic compounds. The use of a vertex index contrasts with the conventional approach of using a topological index for the entire molecule. The idea is to identify regions, or substructures in the molecules (molecular graphs) which may be used to determine certain biological activity of chemical compounds. The results obtained in this paper indicate that the present approach is capable of classifying the mutagenic activity of the compounds under consideration and may find useful application in structure–activity relationship studies of diverse bioactive compounds.     

Structural characterization and gas‐transport properties of brominated matrimid polyimide

The commercial polyimide Matrimid was modified by bromination for the purpose of improving its membrane‐transport properties as a gas‐separation material and providing functional group reactivity for further modifications. The unmodified and brominated polymers were characterized by elemental analysis and one‐dimensional and two‐dimensional NMR, which revealed that one bromine atom per repeat unit was incorporated regioselectively onto the indane aromatic ring. The thermal and physical properties of the polymers before and after bromination were also investigated. The gas‐transport properties of the unmodified and brominated polymers were compared. © 2002 Government of Canada. Exclusive worldwide publication rights in the article have been transferred to Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4193–4204, 2002