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At least 235 records · Page 13Linked to original sources
PubMedDate not supplied

Diastereoisomeric glucuronides of oxazepam. Isolation and stereoselective enzymic hydrolysis.

Oxazepam glucuronide isolated from swine urine by previously published methods was separated into its diastereoisomers by ion-exchange chromatography on a preparative scale. Quantitative high-performance liquid chromatography was used to monitor the separation. The two isomers were obtained in analytically pure form and then characterized by elemental analysis, oxazepam content, mass spectrometry, ultraviolet spectroscopy, optical rotation and optical rotatory dispersion-circular dichroism. The latter permitted the assignment of the dextrorotatory and the levorotatory isomers to the (S)- and (R)- configurations, respectively. Rates of enzymic hydrolysis depend on the configuration of the substrate as well as on the enzyme preparation used. Rate of cleavage was highest with the (S)-(+)-glucuronide and beta-glucuronidase from Escherichia coli. This enzyme possesses the highest degree of stereoselectivity; it hydrolyzes the (S)-(+)-isomer more than 400 times faster than the (R)-(-)-form. Bovine liver glucuronidase is less stereoselective, whereas glucuronidase preparations of molluscan origin exhibit little stereoselectivity. The ready hydrolysis of one of the glucuronides by an enzyme from an intestinal microorganism may play a role in the enterohepatic circulation of oxazepam.

Animals↗
PubMed2005

Layer-scale optical chirality of liquid-crystalline phases.

We present a model for the optical chirality of layered liquid-crystalline phases. The model demonstrates that uniform stacking of chiral layers can lead to significant collective optical rotation, even in the absence of a superlayer helix. We predict the optical rotation of the B2 phases of bent-core liquid crystals, which can have optical rotation as large as 1000 times the molecular optical activity.

Journal Article↗
PubMed1975

Identification of d- or dl-alpha-tocopherol in pharmaceuticals, food supplements, or feed supplements: a collaborative study.

A collaborative study was conducted to evaluate a method for identifying d- or dl-alpha-tocopherol in pharmaceuticals, food supplements, or feed supplements. The sample is extracted and saponified, the extraneous color is removed by chromatography, and the sample is assayed for vitamin E. Optical rotations are determined before and after formation of the ferricyanide oxidation product. The specific optical rotation of the oxidation product is negligible for the dl-form and +25.5 degrees for the d-form. Statistical analysis of the data reported by 8 collaborators for the standard d-alpha-tocopheryl acetate and for 6 unknown samples indicates a significant interaction between laboratories and samples. The mean coefficients of variation among laboratories for the determinations of the corrected specific optical rotation of the standard and the rotation ratio for the unknown samples containing d-alpha-tocopherol were 11.7 and 21.6%, respectively, for all laboratories and 5.8 and 11.8%, respectively, for experienced laboratories. This identification test for vitamin E is acceptable for determining the form of vitamin E as either d or dl, but is not acceptable for accurately determining mixtures of the 2 forms. The method has been adopted as official first action for the identification of d- or dl-alpha-tocopherol.

Animal Feed↗
PubMedDate not supplied

Constrained optimization of Drude's equations eliminates effects of confounding molecules for the polarimetric measurement of glucose.

Common confounding factors for polarimetric concentration measurements include additional optical rotations from unknown optically active molecules, linear birefringence of the medium, and path length variability. We show that by approximating Drude's equation and taking several measurements from the same sample at different wavelengths, the error due to confounding rotations in the measurements can theoretically be canceled. The analysis is developed with regard to glucose sensing in aqueous humor. First, we show that the optical rotatory dispersions of the known molecules in bovine aqueous humor could be represented by Drude's equations. Then, the total optical rotation is approximated by a function combining Drude's equations for the major contributors in the sample, i.e., glucose, glutamine, fructose, and phenylalanine. The concentration-related unknown coefficients in the approximating function are found by constrained nonlinear optimization of the function at different wavelengths. This technique is tested on a published data set and four alterations of those data: (1) concentrations randomly varied within narrow limits, (2) similar to alteration 1 but with significantly elevated glucose concentration, (3) similar to alteration 1 but with significantly decreased glucose concentration, and (4) concentrations randomly varied within wider limits than alteration 1. The method produces very accurate glucose-concentration estimates in all of these data sets. The relative error was smaller than 1% in all except the low-glucose sample (1.4%). This method may prove useful in noninvasive glucose measurement in humans.

Algorithms↗
PubMed1976

Single-tablet enantiomeric purity assay of amphetamine by rotation enhancement.

Enhancement of the optical rotation of dextroamphetamine by production of an optically active chromophore through reaction with 1-fluoro-2,4-dinitrobenzene to give alpha-methPYL-N-(2,4-dinitrophenyl)-beta-phenylethylamine is reported. This reaction forms the basis of an assay for both the content and optical purity of dextroamphetamine sulfate at single-dose levels (5 mg). Results of assays of standard solutions and of commercial tablets demonstrate the suitability of the method for the determination of enantiomeric purity and amphetamine content.

Dextroamphetamine↗
PubMed1993

Temperature-induced conformational transition in xanthans with partially hydrolyzed side chains.

The conformational properties of xanthans with partially hydrolyzed side chains were investigated by optical rotation, CD, and differential scanning calorimetry (DSC). All variants displayed the well-known temperature-driven, cooperative order-disorder transition, and both optical rotation and DSC showed that the transition temperature was essentially independent of the content of terminal beta-mannose. It was found that up to 80% of the changes in the specific optical rotation accompanying the transition reflects conformational changes linked to the terminal beta-mannose in the side chains. Modification of the side chains also affected the CD when xanthan was in the ordered state, but in this case the data suggest that the glucuronic acid is the major component determining the magnitude of the CD signal. DSC measurements showed that the transition enthalpy (delta Hcal) increased linearly with the fraction of beta-mannose, again indicating that a significant part (up to 80%) of delta Hcal reflects conformational changes in the side chains. The conformational transition of the xanthan variants generally showed a higher degree of cooperativity (sharper transition) than unmodified, pyruvated xanthan. Calculation of the cooperativity parameter sigma by means of the Zimm-Bragg theory (OR data) or from the ratio between delta Hcal and the van't Hoff enthalpy (delta HvH) using DSC data showed a correlation between sigma and the content of beta-mannose, but the two methods gave different results when the content of beta-mannose approached 100%. The ionic strength dependence of the transition temperature, expressed as d (log I)/d(T-1m), was nearly identical for intact xanthan and a sample containing only 6% of the terminal beta-mannose. Application of the Manning polyelectrolyte theory does not readily account for the observed delta Hcal values, neither does it provide new information on the nature of the ordered and disordered conformations in xanthan.

Calorimetry, Differential Scanning↗
PubMed2005

Soliton spiraling in optically induced rotating Bessel lattices.

We address soliton spiraling in optical lattices induced by multiple coherent Bessel beams and show that the dynamic nature of such lattices makes it possible for them to drag different soliton structures, setting them into rotation. We can control the rotation rate by varying the topological charges of lattice-inducing Bessel beams.

Journal Article↗
PubMed1987

Change in optical activity of a lobster nerve associated with excitation.

1. To record the change in optical rotation of a nerve fibre associated with excitation, an optical apparatus was constructed using a polarizer, a photo-elastic modulator, an analyser and a lock-in amplifier. The apparatus was calibrated with the sucrose solution as the standard. 2. When a lobster leg nerve was dissected and mounted on the sample stage of the apparatus, stimulation elicited a transient change in the lock-in amplifier output. The signal (here called the 'R-signal') had a rapid time course, formed a peak during the rising phase of the birefringence signal, and often quickly returned to the base line, but sometimes showed a long-lasting later phase. 3. The R-signal arose at about the time when the compound action potential of slowly conducting fibres passed through the window of the chamber for the optical experiment, suggesting that it originates mainly in the smaller fibres. 4. The R-signal reversed its sign when the azimuth of the polarizer was changed by 90 deg, indicating that the R-signal was not due to electrical artifacts. Simultaneously recorded changes in the intensity of the transmitted light had a different time course and an amplitude too small to explain the appearance of the R-signal. 5. When the azimuth of the nerve was changed, the later phase of the R-signal changed its amplitude and direction, but the initial phase of the R-signal was much less influenced, suggesting that the birefringence signal was a component of the later phase. 6. The later phase of the R-signal could be reconstructed as a sum of an R-signal at a different azimuth and the birefringence signal, if the amplitude and direction of the latter were adjusted by multiplication of a factor. 7. Assuming that the nerve is a homogeneous, linearly and circularly birefringent and linearly and circularly dichroic material, the lock-in output was described by mathematical equations. From one of them the birefringence signal could be deduced from a series of R-signals observed at various nerve azimuths. The time course of the calculated birefringence signal agreed well with that of the experimentally recorded birefringence signals. 8. Utilizing the same equations, the contribution of the birefringence change to the R-signal was estimated and subtracted. The remaining part was independent of the nerve azimuth, and could be regarded as representing the time course of the change in optical rotation of the nerve.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1978

[Changes in the conformation of myo-inositol residues in triphosphoinositides].

Dependency of optical rotation of di- and triphosphoinositide water solutions on pH is investigated. The inversion of myo-inosite ring in triphosphoinositide molecule is found to take place at pH range corresponding to the transition of phosphomonoesters from monoanionic into dianionic form. Stabilization of optical rotation is observed at pH range, where one monoester phosphate group is in monoanionic form and the other--in dianionic form. Probably, triphosphoinositide is in the conformation (distorted boat) at this pH range. Diphosphoinositide does not change its optical rotation under pH changes of water or organic solutions. A contribution is estimated of free conformational energy into standard free energy of splitting triphosphoinositide phosphate group depending on pH value. It is concluded that low energy phosphate bond becomes high energy bond due to the free electrostatic interaction of dianionic phosphate group with other negatively charged group in sin-clynal conformation.

Hydrogen-Ion Concentration↗
PubMedDate not supplied

Noninvasive glucose monitoring of the aqueous humor of the eye: Part II. Animal studies and the scleral lens.

We have discussed the nature of a scleral lens that will allow us to follow changes in aqueous humor glucose levels in animals by a method based on optical rotation and a technique described in an earlier paper. We have shown how this lens can be micro-miniaturized and can be used in humans as a non-invasive glucose monitor. We have described preliminary experiments designed to show the correlation between the blood glucose assay (BGA) and the aqueous humor glucose concentration as determined by chemical assay (AGA) and by optical rotation determination (ARD). The last mentioned has been obtained by paracentesis directly into a microcell used in conjunction with instrumentation capable of measuring optical rotations as low as 0.0013 degrees (4.5") corresponding to 20 mg/dl glucose with a sensitivity of 0.0001 degrees (0.36"). The variability among normal rabbits as a function of individuality and diurnal changes is described, and the correlation between AGA and ARD shown to be essentially 1.0. Such rabbits are examined when undergoing very rapid decreases in BGA (insulin treatment) or very rapid increases in BGA (bolus of glucose). The AGA and ARD are shown to lag behind the BGA, and this is discussed in terms of the rate of change of BGA with respect to time and its concomitant change in AGA/ARD as well as a simple procedure that would materially reduce this lag.

Animals↗
PubMed2006

Polarization squeezing by optical faraday rotation.

We show that it is possible to generate continuous-wave fields and pulses of polarization squeezed light by sending classical, linearly polarized laser light twice through an atomic sample which causes an optical Faraday rotation of the field polarization. We characterize the performance of the process and we show that an appreciable degree of squeezing can be obtained under realistic physical assumptions.

Journal Article↗
PubMedDate not supplied

The composition and optical rotary dispersion of bovine aqueous humor.

The concentration of over 20 biochemicals in bovine aqueous humor was determined by conventional means, and the contribution of each to the observed optical rotation was estimated. Of those studied, only glucose and the total proteins made a significant contribution. However, other unidentified chemicals apparently also contribute to the optical activity since it was not possible to reconstruct the actual aqueous humor optical rotation based on the chemicals included. Alternative experimental approaches that may yield more complete results are discussed. With further work, optical rotation might be used as the basis of a noninvasive sensor for measuring the glucose concentration of aqueous humor in the intact eye.

Animals↗
PubMed1984

Mechanism and dynamics of conformational ordering in xanthan polysaccharide.

The thermally induced order-disorder transition of xanthan (extracellular bacterial polysaccharide from Xanthomonas campestris) has been investigated by optical rotation, differential scanning calorimetry, stopped-flow reaction kinetics and low-angle laser light scattering, and the results have been analysed in terms of Zimm -Bragg helix-coil transition theory. The reciprocal of the transition midpoint temperature (Tm) varies linearly with the logarithm of cation (K+) the salt dependence of Tm, is in agreement with Manning polyelectrolyte theory the ordered structure. The associated increase in cation binding, calculated from the salt dependence of tm, is in agreement with the Manning polyelectrolyte theory for one of the candidate structures from X-ray diffraction, a 5(1) single helix stabilized by packing of side-chains along the polymer backbone, but not for the alternative double-helix structure that has also been proposed. At each salt concentration, the two fundamental parameters of the Zimm -Bragg theory, s and sigma, were calculated. The equilibrium constant for growth of the ordered structure (s) is derived directly from calorimetric measurement of transition enthalpy (delta Hcal ), and sigma, which quantifies the relative instability of the helix nucleus, is derived from the ratio of delta Hcal to the apparent transition enthalpy (delta Happ ) obtained by van't Hoff analysis of the optical rotation data. The temperature course of conformational ordering calculated theoretically is in good quantitative agreement with experimental results from both optical rotation and scanning calorimetry. The calculated average length of stable, ordered chain-sequences increases with decreasing temperature, but equals or exceeds the total chain length from light scattering only at temperatures more than approximately equal to 70 K below Tm, suggesting that ordered and disordered regions may co-exist within the same xanthan molecule. Consistent with this interpretation, the observed rate of conformational ordering increases sharply under conditions where the starting solution for dynamic measurements is partially ordered, suggesting that ordered sequences within each chain may act as helix nuclei for adjacent disordered regions, so that helix growth, rather than the slower nucleation process, becomes rate limiting.

Calorimetry, Differential Scanning↗
PubMed1976

Conformation of the extracellular polysaccharide of Xanthomonas campestris.

The solution conformation of the extracellular polysaccharide of the bacterium Xanthomonas campestris is examined by optical rotation, viscometry, and potentiometric titration. Measurements of optical rotation vs. temperature for solutions of the polysaccharide at low ionic strength reveal a sharp transition to a denatured structure which is reversible if sufficient salt is present. The temperature Tm at the transition midpoint increases as log (Na+) or log (Ca2+). Viscosity-temperature profiles substantiate a structural change of the polysaccharide at Tm. The intrinsic viscosity of the native molecule at zero shear rate exceeds 5000 ml/g. This high figure is indicative of a stiff chain. The viscosity of the native molecule is relatively insensitive to salt, whereas the denatured molecule collapses if salt is present. Hydrogen-ion titration shows that the pKapp of the COO- groups of the polymer decreases from 3.2 in 0.01 M NaC1 to 2.6 in 0.2 M NaC1. All these data suggest that the native polysaccharide possesses ordered secondary structure stabilized by nonionic interactions outweighing the repulsion between adjacent COO- groups.

Hydrogen-Ion Concentration↗
PubMed1975

The pH jump study of enzyme proteins. I. Liquefying alpha-amylase from Bacillus subtilis.

Rapid conformational changes due to pH jump were studied kinetically at 25 degrees mainly by the stopped-flow method using liquefying alpha-amylase from Bacillus subtilis [EC 3.2.1-.1, liquefying]. First, the conformational change due to a pH jump produced by mixing with alkali was monitored as a function of time at 245 nm through the ionization of phenolic hydroxyl groups of tyrosine residues which were originally buried and finally become exposed due to the pH jump. Three distinct phases of conformational change were clearly recognized by this method by varying the final pH values. Each phase involved the exposure of an essentially definite number of tyrosine residues, whose rate constant was crucially dependent on pH. Second, these phases of conformational change were subjected to examination in terms of the optical rotation change at 411 nm and the reversibility upon reverse pH jump with respect to conformational reconstitution, as observed through the protonation ofphenolic hydroxyl groups of ionized tyrosine residues and the enzyme activity. The first phase, which occurs above pH 12.5, involves no change in the optical rotation and is reversible as observed by the above two monitoring methods. In contrast, the other two phases, which are observed above pH 12.7, are accompanied by an optical rotation change and no appreciable reversibility was detected by these methods.

Amylases↗
PubMed2002

Single-isomer science: the phenomenon and its terminology.

Single-isomer drugs are of great importance in modern therapeutics. In this article, the basics of the underlying phenomenon are explained. Some molecules are chiral, ie, their mirror image is not superposable on the original. The most common element producing molecular chirality is a chiral center, typically a carbon atom carrying four different groups. The mirror-image molecules are termed enantiomers, but the less specific terms stereoisomers and isomers are also used. A substance consisting of only one of the two enantiomers is a single enantiomer or single isomer, and the 1:1 mixture of the enantiomers is the racemic mixture or racemate. A graphical convention that conveys the three-dimensional aspects of chiral molecules drawn in two dimensions, as well as two nongraphical conventions, based on optical rotation and configuration, are used to identify enantiomers. Optical rotation is a physical property of single enantiomers and involves rotation of the plane of plane-polarized light, each pure enantiomer rotating with equal magnitude but in the opposite direction (dextro and levo). Configuration is the actual arrangement in space of the atoms of chiral molecules. Two systems of indicating configuration are in use. One employs D and L to denote the respective enantiomers, and is applicable only to a-amino acids and carbohydrates. The other is a universal system using R and S as descriptors for the two possible arrangements, respectively, of the atoms around the chiral center. Interest in chiral drugs stems from the frequently observed biological differences between enantiomers. Such enantioselectivity is the result of different interactions of the drug enantiomers with target receptors that are themselves chiral and single-enantiomeric.

Journal Article↗
PubMed1974

Effects of dilute HCl on yeast tRNAPhe and E. coli tRNA1fMet.

HCl treatment of yeast tRNA(Phe) under conditions generally used for excision of ;Y' base results in structure and conformation changes as monitored by line widths in the PMR spectra at 220 MHz and by optical rotation. Like exposure of E. coli tRNA(fMet) (1) causes similar changes in the PMR spectra and optical rotation although no residues are eliminated. Electrophoresis in polyacrylamide gels provides evidence for aggregation in HCl-treated tRNA(fMet) (1). One must thus consider a general effect of HCl exposure as well as possible residue removal in assessing induced structural and conformation changes in tRNA.

Computers↗
PubMed2003

The absolute configuration of (+)-oxopropaline D by theoretical calculation of specific rotation and asymmetric synthesis.

The specific optical rotations of (R)-oxopropaline D calculated by two ab initio MO methods were +52+/-31 degrees and +61+/-29 degrees, respectively, and (+)-oxopropaline D (3) was presumed to have an R-configuration. On the basis of this theoretical result, the reaction of 1-litio-beta-carboline with (R)-glyceraldehyde acetonide followed by oxidation with MnO(2) gave (R)-oxopropaline D acetonide (4a), which was consistent with the previously synthesized (+)-oxopropaline D acetonide (4) in all respects. From the results of theoretical calculations and the experimental synthesis, we determined that natural (+)-oxopropaline D (3) has an R-configuration.

Carbolines↗