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At least 343 records · Page 19Linked to original sources
PubMed2006

Effect of crude extract and fractions from Vitex megapotamica leaves on hyperglycemia in alloxan-diabetic rats.

The effect of the crude extract, ethyl acetate and n-butanol fractions from Vitex megapotamica (Spreng) Moldenke on glycemia was investigated in diabetic rats. Oral administration of crude extract significantly reduced serum glucose levels in both normal and diabetic animals. In normal rats, serum glucose lowering was observed with 400 and 800 mg/kg at 2 and 2-3h, respectively after oral crude extract treatment. Nevertheless, the hypoglycemic effect of Vitex megapotamica in diabetic rats was evident at 1 and 2h and from 1 to 3h after treatment with 400 and 800 mg/kg, respectively. The ethyl acetate as well as n-butanol fractions were able to diminish glycemia in diabetic animals. The ethyl acetate fraction (400 and 800 mg/kg) produced the maximum hypoglycemic effect (28 and 20%, respectively) in diabetic rats and the same dose of the n-butanol fraction reduced the hyperglycemia only by 11% at 1h after treatment. Additionally, in hyperglycemic normal rats neither crude extract nor ethyl acetate fraction modified the glucose tolerance and the known tolbutamide effect on insulin release was clearly observed in this group. Thus, this study shows that Vitex megapotamica has an anti-hyperglycemic action, is able to ameliorate the diabetic state and, probably, is a source of hypoglycemic compounds.

Acetates↗
PubMed2005

Spectroscopic properties and Judd-Ofelt theory analysis of erbium chelates.

Erbium chelates including tris(acetylacetonato) erbium(III) monohydrate, tris(acetylacetonato)(1,10-phenanthroline) erbium(III) and tris(trifluoroacetylacetonato)(1,10-phenanthroline) erbium(III) are synthesized. Judd-Ofelt theory is employed on basis of the UV-Vis-NIR absorption spectra of erbium chelates dissolved in methanol. Judd-Ofelt parameters of erbium chelates are determined by a least square fitting and dealt with the chemical structure of erbium chelates. Photoluminescence characteristics of erbium chelates are investigated upon excitation at 488 nm by an Ar(+) laser. The qualitative correlation of Judd-Ofelt parameters with photoluminescence properties for erbium chelates is also discussed. It is found that larger Omega(6) value for erbium chelate is and larger photoluminescence intensity at 1.54 microm is, and Omega(2) value should contribute to the photoluminescence full width at half maximum (FWHM) at 1.54 microm. The changes of Judd-Ofelt parameters result from the introduction of the second ligand phenathroline or the substitution of electron-drawing group CF(3) in beta-diketone for erbium chelates.

Chelating Agents↗
PubMed2006

Density functional theory study of vibronic structure of the first absorption Qx band in free-base porphin.

Harmonic vibrational frequencies and vibronic intensities in the first S(0)-->S(1) (pipi( *)) absorption band of free-base porphin (H(2) P) are investigated by hybrid density functional theory (DFT) with the standard B3LYP functional. The S(0)-S(1) transition probability is calculated using time-dependent DFT with account of Franck-Condon (FC) and Herzberg-Teller (HT) contributions to the electric-dipole transition moments including displacements along all 108 vibrational modes. Two weak wide bands observed in the gas phase absorption spectra of the H(2) P molecule at 626 and 576 nm are interpreted as the 0-0 band of the X(1) A(g)-->1B(3u) transition and the 0-1 band with largest contributions from the nu(10)(a(g))=1610 cm(-1) and nu(19)(b(1g))=1600 cm(-1) modes, respectively, in agreement with previous tentative assignments. Both bands are induced by the HT mechanism, while the FC contributions are negligible. A number of fine structure bands, including combination of two vibrational quanta, are obtained and compared with available spectra from supersonic jet and Shpolskij matrices. Both absorption and fluorescence spectra are interpreted on ground of the linear coupling model and a good fulfillment of the mirror-symmetry rule.

Chemical Phenomena↗
PubMed2006

Similarities and differences between azomethines and ketimines: synthesis, materials characterization and structure of novel imines compounds.

Imines (ketimines and azomethines) derived from p-dibenzoylbenzene (DB) and terephthalic aldehyde (TA) and two aromatic amines: aniline and 2,6-dimethylaniline have been investigated. Compounds were synthesized via condensation of amines with carbonyl monomers in DMA or amine solution. When using DMA as a solvent, azomethines with high yields were obtained. On the other hand, the amines used as a monomers served also as an effective solvent for the synthesis of the ketanils. This different reactivity of the aldehyde and ketone groups in DMA and in amine depends on the dehydration mechanism being dominated by a kinetic process or thermodynamic one. On the basis of FTIR, 13C and 1H NMR, UV-vis spectra, thermal characteristic and theoretical calculations conclusions are drawn regarding the similarities and differences between azomethines and ketimines.

Alanine↗
PubMed2006

Spectral and optical studies of 2-amino-5-nitropyridinium dihydrogen phosphate: a semiorganic nonlinear optical material.

2-Amino-5-nitropyridinium dihydrogen phosphate (2A5NPDP) was synthesized and the molecular structure was elucidated by FT-IR, FT-Raman and FT-NMR. The proton and carbon configurations of 2A5NPDP was confirmed through FT-NMR technique. UV-vis-NIR spectrum was recorded and the optical transmittance region was identified as 350 nm. Single crystals were grown from ethanol by slow evaporation technique at 35 degrees C and the unit cell constants were determined. Bulk and powder second harmonic generation (SHG) measurements were carried out using Nd:YAG laser (lambda=1064 nm) and its phase matching condition was determined.

Aminopyridines↗
PubMed2006

Synthesis, spectral studies of salicylidine-pyridines: crystal and molecular structure of 2-[(1E)-2-aza-2-(5-methyl(2-pyridyl)ethenyl)]-4-bromobenzen-1-ol.

Schiff bases derived from different meta-substituted salicylaldehyde and 5-methylaminopyridine have been synthesized and characterized by elemental analysis, FT-IR, NMR and UV-vis techniques. NMR assignments were made using (1)H, (13)C NMR and aided by 2D HETCOR and HMBC heteronuclear correlation techniques. The UV-vis spectra of the compounds were found useful in understanding the existence of tautomeric equilibria [phenol-imine (O-H...N) and keto-amine (O...H-N) forms] in polar and non-polar solvents. In order to rationalize the stabilization of tautomer in solid state, X-ray structure of 2-[(1E)-2-aza-2-(5-methyl(2-pyridyl)ethenyl)]-4-bromobenzen-1-ol (6) was determined. According to our crystallographic result, it has enol-imine tautomeric form.

Aldehydes↗
PubMed2000

Mucoadhesive drug carriers based on complexes of poly(acrylic acid) and PEGylated drugs having hydrolysable PEG-anhydride-drug linkages.

We have designed a new mucoadhesive drug delivery formulation based on H-bonded complexes of poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMAA) with the poly(ethylene glycol) (PEG), of a (PEG)-drug conjugate. The PEGylated prodrugs are synthesized with degradable PEG-anhydride-drug bonds for eventual delivery of free drug from the formulation. In this work we have used indomethacin as the model drug which is PEGylated via anhydride bonds to the PEG. The complexes are designed first to dissociate as the formulation swells in contact with mucosal surfaces at pH 7.4, releasing PEG-indomethacin, which then hydrolyses to release free drug and free PEG. We found that as MW of PAA increases, the dissociation rate of the complex decreases, which results in decreased rate of release of the drug. On the other hand, the drug release from PEG-indomethacin alone and from solid mixture of PEG-indomethacin+PAA was much faster than that from the H-bonded complexes. Due to the differences in the thermal stability, PMAA complex exhibited slightly faster drug release than that of the PAA complex of comparable MW. These H-bonded complexes of degradable PEGylated drugs with bioadhesive polymers should be useful for mucosal drug delivery.

Acrylic Resins↗
PubMed2003

Dendrimers conjugates for colonic delivery of 5-aminosalicylic acid.

The water-soluble polyamidoamine (PAMAM) dendrimer conjugates for colonic delivery of 5-aminosalicylic acid (5-ASA) were designed. The drug was bound to the dendrimer using two different spacers containing azo-bond, p-aminobenzoic acid (PABA) and p-aminohippuric acid (PAH). Incubation of PAMAM dendrimer conjugates containing PABA and PAH spacers with rat cecal contents at 37 degrees C gradually released 5-ASA with time and the amount of drug released was 45.6 and 57.0% of the dose in 24 h, respectively. The release of the drug from the commercial prodrug, sulfasalazine was significantly faster than both conjugates (80.2% of the dose in 6 h). No 5-ASA was detected from the incubation of dendrimer conjugates with the homogenate of the stomach or phosphate buffer, pH 1.2 and 6.8. Only a small amount of 5-ASA was found after incubation of both conjugates with the homogenate of the small intestine for 12 h. It appears that this PAMAM dendrimer can be developed for use as a carrier for colon-specific drug delivery.

4-Aminobenzoic Acid↗
PubMed2000

Macromolecular prodrugs. VIII. Synthesis of polymer-gemfibrozil conjugates.

Gemfibrozil is covalently linked to two similar polymers: poly[alpha,beta-(N-2-hydroxyethyl-DL-aspartamide)] and poly[alpha,beta-(N-3-hydroxypropyl-DL-aspartamide)]. The synthesised polymer drug conjugates differ in average molecular mass, type of covalent bonding, length of spacer, drug-loading and solubility.

Gemfibrozil↗
PubMed2002

Flow injection analysis with multiple on-line spectroscopic analysis (UV, IR, 1H-NMR and MS).

Studies on the capabilities of flow injection analysis (FIA) combined with on-line characterisation of model compounds via a combination of diode array UV, 1H-NMR, FT-IR spectroscopy and mass spectrometry are described. Using this combination of spectrometers enabled the on-flow collection of UV, 1H-NMR, IR and MS for a range of model compounds. Samples were introduced into the system as solutions in deuterium oxide in concentrations ranging from 1.4 to 8.4 mg ml(-1). A sample volume of 100 microl was used for FIA at a flow rate of 1 ml min(-1). From these studies a practical working quantity of ca. 140 microg/sample of analyte was determined which provided characteristic spectra.

4-Aminobenzoic Acid↗
PubMed2002

High-throughput analytical techniques for reaction optimization.

This review describes recent developments in approaches to high-throughput reaction optimization, as well as the associated analytical techniques. The studies discussed include the use of UV-visible, IR-thermographic and mass spectrometric methods for application in catalyst development, process optimization and materials science. Other methods of potential use in a high-throughput format are also discussed.

Combinatorial Chemistry Techniques↗
PubMed2005

Role for the alpha-helix in aberrant protein aggregation.

Is the alpha-helix structure capable of triggering the formation of aberrant protein aggregates? To answer this question, we investigate the in vitro aggregation of tau protein in the presence of the helix-inducing agent TFE. Tau is a natively unfolded protein that binds to microtubules and forms aggregates in Alzheimer's disease. We find that full-length tau has residual alpha-helix structure, which is further enhanced by three mutations involved in genetic neurological disorders. TFE concentrations matching an alpha-helical content of 40% in full-length tau and the triple mutant induce the formation of aggregates that are morphologically and structurally heterogeneous. A simple dilution experiment reveals that heterogeneity results from the competition between alpha-helical fibrillar aggregates and more classical amyloid-like aggregates. The alpha-helical aggregates are more resilient to dilution and have the spectroscopic features of alpha-helical coiled coils. We propose a general mechanism by which intrinsically stable alpha-helices can associate into aggregates with only coarse coiled-coil symmetry. In tau, high intrinsic alpha-helix stability and coarse coiled-coil symmetry could be byproducts of its biological function.

Binding Sites↗
PubMed2001

Hydroxo-bridged Cubane-type tetrairon(II) clusters supported by sterically-hindered carboxylate ligands.

A series of hydroxo-bridged cubane-type tetrairon(II) clusters, [Fe(4)(mu-OH)(4)(mu-O(2)CAr(4)(-)t(BuPh))(2)(mu-OTf)(2)L(4)] (L = C(5)H(5)N (1), 4-(t)BuC(5)H(4)N (2), 3-FC(5)H(4)N (3)), were synthesized by using a sterically hindered carboxylate ligand, 2,6-di(4-tert-butylphenyl)benzoate (Ar(4)(-)t(BuPh)CO(2)(-)). Three different bridging units that mediate weak antiferromagnetic coupling interactions between the metal centers support the unprecedented cubane-type [Fe(4)(mu-OH)(4)](4+) cores in 1-3. The solution structures of 1 and 3 probed by FT-IR and (19)F NMR spectroscopy are consistent with the solid-state geometry determined by X-ray crystallography. Zero-field Mössbauer spectra of 1-3 at 4.2 K are characteristic of high-spin iron(II) centers in nearly identical coordination environments. Compound 1 undergoes two irreversible oxidation processes at ca -10 and +880 mV (vs Fc/Fc(+)), the former approaching quasi-reversible behavior with increased scan rates and a narrow potential sweep range. Comparisons are made with analogous known [Fe(4)X(4)](n)()(+) (X = O, S) units, and the structural integrity of tetrairon fragments upon a change in oxidation state is discussed together with some possible biological implications.

Algorithms↗
PubMed2002

Nitric oxide photorelease from ruthenium salen complexes in aqueous and organic solutions.

The complexes [Ru(salen)(NO)Cl] and [Ru(salen)(NO)(H(2)O)](+) were shown to release the nitrosyl ligand as nitric oxide upon exposure to visible light in organic and aqueous solutions respectively, by means of UV-visible, EPR, and FTIR spectroscopies. The former was prepared by a new synthetic route and had its structure determined by single-crystal X-ray diffraction. A crystal of the dichloromethane solvate is orthorhombic, space group Fdd2 (No. 43) and formula C(16)H(14)ClN(3)O(3)Ru.CH(2)Cl(2), with Z = 16 and cell parameters a = 25.489(4), b = 33.435(4), and c = 9.3716(9) A. The electronic absorption spectra of the complexes were calculated using the INDO/S method. The water-soluble complex is a potential drug for antitumoral phototreatment.

Crystallography, X-Ray↗
PubMed2006

Fast catalytic hydroxylation of hydrocarbons with ruthenium porphyrins.

Ruthenium porphyrin complexes such as carbonylruthenium(II) tetrakispentafluorophenylporphyrin [Ru(II)(TPFPP)(CO)] were found to be efficient catalysts for the hydroxylation of alkanes in the presence of 2,6-dichloropyridine N-oxide as the oxidant under mild, nonacidic conditions. Up to 14 800 turnovers (TO) and rates of 800 TO/min were obtained for the hydroxylation of adamantane. The hydroxylation of cis-decalin afforded cis-9-decalol and cis-decalin-9,10-diol, exclusively, thus, excluding a long-lived radicals mechanism. The kinetics of product evolution in a typical catalytic oxygenation showed an initial induction period followed by a fast, apparently zero-order phase with maximum rates and high efficiencies. Deuterium isotope effects (kH/kD) in the range of 4.2-6.4 were found for the hydroxylation of alkanes. A Hammett treatment of the data for the oxidation of para-substituted toluene derivatives showed a linear correlation with a highly negative rho+ value of -2.0. On the basis of kinetic and spectroscopic evidence, Ru(VI)(TPFPP)(O)2, Ru(II)(TPFPP)(CO), and Ru(IV)(TPFPP)Cl2 observed during catalysis were ruled out as candidates for the active catalyst responsible for the high efficiencies and turnover rates in the oxidation reactions. The fastest rates of adamantane hydroxylation with 2,6-dichloropyridine N-oxide were achieved by the reductive activation of Ru(IV)(TPFPP)Cl2 with a zinc amalgam. This redox activation is consistent with the formation of an active Ru(III) intermediate in situ by a one-electron reduction of the Ru(IV) porphyrin. EPR spectra characteristic of Ru(III) have been observed upon the reduction of Ru(IV)(TPFPP)Cl2 with a zinc amalgam. In the adamantane oxidation mediated with Ru(III)(TPFPP)(OEt), it was found that, during this process, the Ru(III) porphyrin was gradually converted to a dioxoRu(VI) porphyrin. Concomitant with this conversion, the reaction rates decreased. Catalyst activation was also stimulated by autoxidation of the solvent CH2Cl2. On the basis of these data, a mechanism is proposed that incorporates a "fast" cycle involving metastable Ru(III) and oxoRu(V) intermediates and a "slow" oxidation cycle, mediated by oxoRu(IV) and trans-dioxoRu(VI) porphyrin complexes.

Adamantane↗
PubMed2001

Prenylated benzophenone derivatives from Clusia havetiodes var. stenocarpa.

Extracts of the fruit of Clusia havetiodes var. stenocarpa have yielded three new prenylated benzophenone derivatives, 28,29-epoxyplukenetione A (1), 33-hydroperoxyisoplukenetione C (2), and 15,16-dihydro-16-hydroperoxyplukenetione F (3), as well as four which have been previously described, plukenetiones C, F, and G and sampsonione G.

Benzophenones↗
PubMed2001

Chemical constituents from Drypetes littoralis.

Chemical investigation of Drypetes littoralis yielded three new tricyclic diterpenes, drypetenones A, B, and C (1--3), and one new xanthone (4). Spectral analyses and chemical correlations established the structures as 10S-12-hydroxy-11-methoxy-13-methylpodocarpa-1,5,8,11,13-pentaene-3,7-dione, (1), 10S-12-hydroxy-11-methoxy-13-methylpodocarpa-5,8,11,13-tetraene-3,7-dione (2), 10S-12-hydroxy-6,11-dimethoxy-13-methylpodocarpa-1,5,8,11,13-pentaene-3,7-dione (3), and 1-hydroxy-7-hydroxymethyl-6-methoxyxanthone (4). Complete (13)C NMR assignment of boehmenan D (5) is also made.

Antineoplastic Agents, Phytogenic↗