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At least 307 records · Page 17Linked to original sources
PubMed2003

Zonal organization of the vestibulocerebellum in pigeons (Columba livia): I. Climbing fiber input to the flocculus.

Previous studies in pigeons have shown that the neurons in the medial column of the inferior olive respond best to patterns of optic flow resulting from self-rotation. With respect to the axis of rotation, there are two functional groups: rVA neurons prefer rotation about the vertical axis, whereas rH45 neurons respond best to rotation about an horizontal axis oriented at 45 degrees ipsilateral azimuth. The rVA and rH45 neurons are located in the caudal and rostral margins of the medial column, respectively. These olivary neurons project as climbing fibers to the contralateral flocculus. In this study, injections of anterograde tracers into the medial column were used to investigate the zonal organization of the climbing fiber input to the flocculus of pigeons. Iontophoretic injections of either cholera toxin subunit-B or biotinylated dextrin amine were made into the medial column of the inferior olive at locations responsive to rVA or rH45 rotational optic flow. Anterogradely labeled climbing fibers in the flocculus showed a clear zonal organization. There were four parasagittal bands spanning both folia IXcd and X consisting of two rVA zones interdigitated with two rH45 zones. These findings are compared with the zonal organization of the flocculus in mammalian species.

Action Potentials↗
PubMed1989

Modelling studies of solvent effects on the conformational stability of agarobiose and neoagarobiose and their relationship to agarose.

The conformational equilibria of the low energy conformers of the repeating units of agarose, i.e. neoagarobiose and agarobiose have been studied theoretically in five solvents. The structure of each individual conformer has been refined by molecular mechanics calculations, from the distinct low-energy regions determined from potential energy surfaces. The stability of the conformers in dilute solution has been evaluated through consideration of the relaxed intramolecular energy including electrostatic, dispersion and cavity terms. For each disaccharide, the calculated abundance of conformers is practically independent of the solvent. Dipole moments and linkage rotation have been calculated for each of the low energy conformers. The calculated molar fractions of the stable conformers were used to model the optical rotation values measured for a single strand of agarose chain in its disordered state, and a satisfactory agreement has been reached (lambda cal = -133 degrees, lambda obs = -145 degrees). For the agarose molecule in the solid state, a left-handed threefold single helix, repeating in 2.85 nm is predicted. Such a helix, which represents the calculated stable conformation for a single strand of agarose, should be considered in descriptions of the molecular basis of sol-gel transition of agarose.

Carbohydrate Conformation↗
PubMed2001

Enantioselective synthesis of imperanene, a platelet aggregation inhibitor.

Both enantiomers of imperanene, a platelet aggregation inhibitor, have been synthesized in 82-90% ee. The key step of establishing the chiral center was achieved through stereoselective alkylation with benzyl chloromethyl ether using Enders' RAMP/SAMP chiral auxiliary method. The natural product was determined to be the (S)-enantiomer through comparison of optical rotation data. Reaction: see text.

Alkylation↗
PubMed1975

Structural studies of the capsular polysaccharide of Klebsiella type 28.

The capsular polysaccharide from Klebsiella type 28 has been studied by methylation analysis, a modified Smith-degradation procedure, and uronic acid degradation with subsequent oxidation and elimination of the substituents of the oxidized residue. The polysaccharide contained the hexasaccharide repeating-unit shown below. The terminal D-glucopyranose residue was hydrolysed by emulsin, indicating a beta linkage. The anomeric natures of other glycosidic linkages were determined by characterization of fragments obtained during the degradative studies. The D-galactopyranose residue was not present in any fragment, but is assumed to be alpha-linked from optical-rotation considerations. (see article)

Chemical Phenomena↗
PubMed1977

Microbial conversion of DL-2-amino-delta2-thiazoline-4-carboxylic acid to L-cysteine and L-cystine: screening of microorganisms and identification of products.

Microorganisms able to form L-cysteine from DL-2-amino-delta2-thiazoline-4-carboxylic acid (DL-ATC), a chemical intermediate in the synthesis of DL-cysteine, were isolated from soil samples and classified as Pseudomonas sp., Pseudomonas cohaerens, P. desmolytica, and P. ovalis. Thirteen L-cysteine-producing bacteria were also found in among 463 stock cultures representing 37 genera. These were Achromobacter delmarvae. Alcaligenes denitrificans, Bacillus brevis, Brevibacterium flavum, Enterobacter aerogenes, Erwinia carotovora, Escherichia coli, Micrococcus sodonensis, Myocoplana dimorpha, Sarcina lutea, Serratia marcescens, Flavobacterium acidoficum, and Pseudomonas ovalis. In the presence of intact cells of Pseudomonas sp. AJ 3854, 6.1 mg of L-cysteine and/or L-cystine per ml was produced from 10 mg of DL-ATC-3H2O per ml in a molar yield of 100%. This finding suggests that racemization and asymmetric hydrolysis occurred simultaneously in this incubation mixture. After the complete oxidation of cysteine to cystine by aeration in the presence of ferrous ion, crystalline cystine was isolated; its configuration was the L isomer based on data from X-ray diffraction, microbioassay, and optical rotation studies.

Bacteria↗
PubMed1997

Synthesis of polylactides with different molecular weights.

The synthesis of poly(lactic acid) through polycondensation of the lactic acid monomer gave weight average molecular weights (Mw) lower than 1.6 x 10(4), whereas ring-opening polymerization of lactides in bulk at 130 degrees C for 72 h using stannous octoate as catalyst in the concentration range from 0.003 to 0.8 wt% produced polylactides with viscosity average molecular weight (Mv) ranging from 2 x 10(4) to 6.8 x 10(5). The monomer conversion and Mv showed a maximum at a catalyst concentration around 0.05 wt%. The monomer conversion and Mv increased almost linearly with polymerization time up to a monomer conversion of 80%, but both the conversion and Mv decreased after passing through a maximum, when the polymerization reaction was allowed to proceed for longer periods of time. This time dependence was pronounced at higher polymerization temperatures. The decrease in Mv at prolonged polymerization and higher polymerization temperatures was attributed to thermal depolymerization of resultant polylactides, but no significant optical rotation of poly(L-lactide) was noticed.

Biocompatible Materials↗
PubMed2006

[Temperature-dependent optical activity and birefringence study of D-alanine single crystal].

The measurement of the anisotropy of optical acitivity and birefringence is one of the most important clues to studying physical properties of a biaxial crystal of D-alanine. In order to investigate a second-order phase transition predicted by A. Salam between two states of D-alanine, the behavior of birefringence and optical activity is useful for the phenomenological approach to the transition mechanism. The optical activity as a peculiar quantity can respond to the modulation of the crystal lattice and to the change in the bonding nature of constituent atoms. In the present paper, the authors use the PEM-90 photoelastic modulator to study the conformation change of D-alanine at the temperature ranging from 220 to 290 K. The temperature dependence of I(2f)/I(dc) showed that the conformation of D-alanine molecule in single crystal changed around 250 K. The obtained results provide an obvious evidence of optical rotation phase transition predicted by Salam.

Alanine↗
PubMed1985

Synthesis of protected peptides with the sequence 8-13-1-3 and 4-13-1-3 of mycobacillin and their analogs.

We have synthesized both a protected nonapeptide of the mycobacillin 8-13-1-3 amino acid sequence and a protected tridecapeptide of the 4-13-1-3 sequence, which are a fragment and a open chain analog of this antibiotic, respectively. Some of their analogs with a reversed configuration of the amino acids at fixed positions have also been synthesized. The nonapeptides were obtained by coupling partially protected mycobacillin fragments with the sequence 8-10 and 11-13-1-3 while the tridecapeptides were synthesized by coupling partially protected fragments 4-7 and 8-13-1-3. Configuration analogs of these fragments were also used. The coupling methods applied were DCCI/HONSu or DCCI/HOBt. The purification of the synthesized peptides was achieved by means of recrystallization or column chromatography on silica gel. They were characterized mainly by m.p., degree of optical rotation, elemental and amino acid analysis.

Antifungal Agents↗
PubMed1986

Synthesis of methyl pyranosides and furanosides of 3-deoxy-D-manno-oct-2-ulosonic acid (KDO) by acid-catalysed solvolysis of the acetylated derivatives.

Treatment of methyl 2,4,5,7,8-penta-O-acetyl-3-deoxy-alpha-D-manno-oct- 2-ulopyranosonic acid, or its methyl ester, with refluxing methanolic 0.1 M hydrogen chloride for 16 h gave 95% of methyl (methyl 3-deoxy-alpha-D-manno-oct-2-ulopyranosid)onate. Acetylation of the methyl ester of 3-deoxy-D-manno-oct-2-ulosonic acid (KDO) gave mainly methyl 2,4,6,7,8-penta-O-acetyl-3-deoxy-alpha,beta-D-manno-oct-2-ulofuranoso nate. Treatment of this mixture with methanolic 0.02 M hydrogen chloride at room temperature gave methyl (methyl 3-deoxy-alpha, beta-D-manno-oct-2-ulofuranosid)onate and the corresponding 4-acetates which were isolated by reverse-phase column chromatography of their 7,8-O-isopropylidene derivatives. Confirmation of the position of the isopropylidene group was obtained by acetylation to give methyl (methyl 4,6-di-O-acetyl-3-deoxy-7,8-O-isopropylidene-alpha,beta-D-manno-oct-2-ul ofuranosid)onate. The furanose anomers were differentiated primarily by J3,4 values (alpha approximately 6.1 Hz, beta approximately 2.2 Hz). The anomeric configuration in the furanose series has been assigned on the basis of optical rotation.

Bordetella pertussis↗
PubMed1977

Structural analysis of nine oligosaccharides isolated from the urine of a blood group O, nonsecretor, woman during pregnancy and lactation.

Nine oligosaccharides have been isolated from urine collected from an O(H), Le(a+ b-), nonsecretor, woman during her pregnancy and subsequent lactation. One of them is a new hexasaccharide denoted lacto-N-neo-difucohexaose II: beta-D-Gal-(1 leads to 4)-[alpha-L-Fuc-(1 leads to 3)]-beta-D-GlcNAc-(1 leads to 3)-beta-D-Gal-(1 leads to 4)-[alpha-L-Fuc-(1 leads to 3)]-D-Glc. Seven of the remainder were identified as the milk oligosaccharides lacto-N-difucohexaose II, lacto-N-fucopentaose II and III, lacto-N-tetraose, 6'-galactosyllactose, 3-fucosyllactose, and lactose. The ninth component is a glucose-containing tetrasaccharide, alpha-D-Glc-(1 leads to 6)-alpha-D-Glc-(1 leads to 4)-alpha-D-Glc-(1 leads to 4)-D-Glc, previously found in normal human urine. The oligosaccharides were isolated by gel chromatography, preparative zone electrophoresis, and paper chromatography. The structures were determined by sugar and methylation analyses. Sequence analysis of tri- and tetra-saccharides was carried out by gas-liquid chromatography-mass spectrometry of reduced and permethylated oligosaccharide derivatives. The monosaccharide sequence in penta- and hexasaccharides was deduced from gas chromatographic-mass spectrometric studies of di- and trisaccharides obtained from partial acid hydrolysis of the parent compound. Anomeric configurations were deduced from the optical rotation.

ABO Blood-Group System↗
PubMed1999

Triple helical stabilities of guest-host collagen mimetic structures.

The peptoid Nleu (N-isobutylglycine) has been successfully incorporated into a series of collagen mimetics composed of Gly-Pro-Nleu and Gly-Nleu-Pro sequences and has been able to maintain triple helices in appropriate structures. The achiral trimeric sequence Gly-Nleu-Nleu as a guest sequence in structures such as Ac-(Gly-Pro-Hyp)3-(Gly-Nleu-Nleu)3-(Gly-Pro-Hyp)3-NH2 retains triple helicity. As an extension of this study, we report, in this paper, on a series of guest-host collagen mimetic structures in which Gly-Nleu-Pro sequences are employed as the host. The guest sequences for these guest-host structures include Gly-Nleu-Nleu and Gly-Nx-Pro sequences where Nx is composed of a variety of alkyl and aralkyl peptoid residues. From these guest-host collagen mimetic structures, we are able to elucidate the contributions of hydrophobic and steric effects on triple helix formation. The Gly-Nleu-Pro sequences have been shown to be effective in inducing triple helicity. Conformational characterization of the guest-host collagen mimetic structures was established by techniques such as temperature-dependent optical rotation measurements and circular dichroism (CD) spectroscopy.

Amino Acid Sequence↗
PubMed2005

Synthesis of eupomatilone-6 and assignment of its absolute configuration.

[Reaction: see text]. The Zn-mediated Barbier reaction of the biarylaldehyde 8 with crotyl bromide followed by hydroboration and oxidation provided the gamma-butyrolactones 4 and 5. The stereoselective installation of methyl group at C-3 by using LiHMDS and MeI completed the synthesis of racemic eupomatilone-6 (2) and its diastereomer 3. The spectroscopic data of 2 was in full agreement with reported spectra of natural product, thus confirming the revised relative configuration of eupomatilone-6. Similarly, an optically active (3R,4R,5S)-isomer of eupomatilone-6 (23) was prepared in which the aldol reaction with thiazolidinethione as a chiral auxiliary was employed as a key step. On the basis of the spectroscopic data and optical rotation values of 23, the absolute configuration of eupomatilone-6 was proposed.

Benzofurans↗
PubMed1979

Chemical synthesis of three 14 alpha-hydroxymethyl cholestenols.

Reported herein are chemical syntheses of 14 alpha-hydroxymethyl-5 alpha-cholest-8-en-3 beta-ol, 14 alpha-hydroxymethyl-5 alph-cholest-7-en-3 beta-ol, and 14 alpha-hydroxymethyl-5 alpha-cholest-6-en 3 beta-ol. These compounds were obtained in pure form after repeated medium-pressure column chromatography of the mixture obtained by treatment of 3 beta-acetoxy-7 alpha,32-epoxy-14 alpha-methyl-5 alpha-cholestane with pyridine hydrochloride in refluxing acetic anhydride followed by reduction with lithium aluminum hydride. The compounds were characterized by their chromatographic properties and by the results of infrared, optical rotation, nuclear magnetic resonance, and low and high resolution mass spectral studies.

Cholestenes↗
PubMed1983

The lack of effectiveness of (-)-epicatechin against alloxan induced diabetes in Wistar rats.

(-)-Epicatechin, a naturally occurring flavonoid, has been reported to protect pancreatic beta cells from alloxan-induced diabetes (1) and to stimulate beta cell regeneration when given after alloxan administration (2,3). However, in the present study, we have not been able to confirm these findings. Administration of (-)-epicatechin (100 mg/kg/day for 15 days) beginning three days after alloxan administration (140 mg/kg) had no significant effect on blood glucose levels when compared to alloxan control animals. Another study which failed to demonstrate an antidiabetic effect of (-)-epicatechin (4) has been criticized for not using fresh solutions of (-)-epicatechin because of its instability in aqueous solution (5). We have found, however, that (-)-epicatechin is stable for at least five days based on thin-layer chromatographic analysis and optical rotation measurements.

Animals↗
PubMed1977

Structural analysis of oligosaccharides isolated from the urine of a blood group A, secretor, woman during pregnancy and lactation.

Twenty different oligosaccharides have been isolated from urine collected from an A, Le(a- b+), secretor woman during her pregnancy and subsequent lactation. Nine of these have been found previously in the milk of Le (a- b+) individuals. Three new fucose-containing oligosaccharides denoted lacto-N-neotrifucoheptaose II (alpha-L-Fuc-(1 leads to 2)-beta-D-Gal-(1 leads to 4)-[alpha-L-Fuc-(1 leads to 3)]-beta-D-GlcNAc-(1 leads to 3)-[alpha-L-Fuc-(1 leads to 2)]-beta-D-Gal-(1 leads to 4)-D-Glc), lacto-N-neodfucohexaose I (alpha-L-Fuc-(1 leads to 2)-beta-D-Gal-(1 leads to 4)-[alpha-L-Fuc-(1 leads to 3)]beta-D-GlcNAc-(1 leads to 3)-beta-D-Gal-(1 leads to 4)-D-Glc), and lacto-N-difucohexaose IV (alpha-L-Fuc-(1 leads to 2)-beta-D-Gal-(1 leads to 3)-beta-D-GlcNAc-(1 leads to 3)-[alpha-L-Fuc-(1 leads to 2)]-beta-D-Gal-(1 leads to 4)-D-Glc) are described. Three new myo-inositol-containing oligosaccharides which are characteristic for pregnancy have also been isolated. Their structures are: alpha-D-GalNAc-(1 leads to 3)-[alpha-L-Fuc-(1 leads to 2)]-beta-D-Gal-(1 leads to 0)-[alpha-L-Fuc-(1 leads to 0)]-myo-inositol; alpha-L-Fuc-(1 leads to 2)-beta-D-Gal-(1 leads to 0)-[alpha-D-Fuc-(1 leads to 0)]myo-inositol; and alpha-L-Fuc-(1 leads to 2)-beta-D-Gal-(1 leads to 0)-myo-inositol, respectively. Three oligosaccharides containing only glucose were found and partially characterized. In addition, two oligosaccharides described previously (a glucose tetrasaccharide (Hallgren, P., Hansson, G., Henriksson, K.-G., Häger, A., Lundblad, A., and Svensson, S. (1974) Eur. j. clin. Invest. 4, 429-433) and a urine A pentasaccharide (Lundblad, A., and Svensson, S. (1973) Carbohyd. Res. 30, 187-189) were also isolated and characterized. The isolation procedure included ultrafiltration, gel chromatography on Sephadex G-25, and preparative paper chromatography, Structural determination involved sugar and methylation analyses. Tri- and tetrasaccharides were investigated by combined gas-liquid chromatography-mass spectrometry. Sequence analyses of larger oligosaccharides were performed by combined gas-liquid chromatography-mass spectrometry of di- and trisaccharides obtained after partial acid hydrolysis of the parent compound. Anomeric configurations were deduced from optical rotations and by comparison with authentic samples.

ABO Blood-Group System↗
PubMed2003

Phase chirality and stereo-selective swelling of cholesteric elastomers.

Cholesteric elastomers possess a macroscopic "phase chirality" as the director n rotates in a helical fashion along an optical axis z and can be described by a chiral order parameter alpha. This parameter can be tuned by changing the helix pitch p and the elastic properties of the network at formation. The cholesterics also possess a local nematic order, changing with temperature or during solvent swelling. In this paper, by measuring the power of optical rotation d upsilon /dz , we discover how these two parameters vary as functions of temperature or solvent adsorbed by the network. The main result is a finding of pronounced stereo-selectivity of cholesteric elastomers, demonstrating itself in the retention of the "correct" chirality component of a racemic solvent. It has been possible to quantify the amount of such stereo-separation, and the basic dynamics of the effect.

Calorimetry, Differential Scanning↗
PubMed2002

Total synthesis of cis-solamin.

[structure: see text] A convergent total synthesis of cis-solamin and its diastereomer was accomplished using VO(acac)2-catalyzed diastereoselective epoxidation followed by cyclization of bis-homoallylic alcohol as the key step. By comparison of the optical rotation of two possible diastereomers, it is suggested that the absolute configuration of natural cis-solamin is 1a.

Annonaceae↗