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At least 19 recordsLinked to original sources
PubMed1992

[Determination of the protonation constants of pipecuronium bromide on the basis of optical rotation as a function of pH values].

Pipecuronium bromide molecule contains two slightly basic nitrogen atoms in its two piperazine rings. Their pK values are quite similar to each other in consequence of their almost equivalent surroundings. Although the potentiometric titration used mostly for determination of pK values of organic compounds can be performed in this case too, but the polarimetric titration applied by us is more advantageous. Change of pH considerably influences the values of optical rotation; consequently, the curve obtained in this way is more utilizable than that of potentiometric titration. Protonation of two nitrogen atoms one after the other changes the optical rotation of the molecule in opposite direction. Consequently, a minimum can be seen on the curve of optical rotation versus pH value. The exact pK values were determined on the basis of the estimated parameters of a curve established corresponding to an equation and fitted to the measuring points. The sequence of deprotonation of nitrogen atoms could only be ascertained on the basis of the curves of polarimetric titration of compounds containing one piperazine ring; on the basis of the pK values and of the changing direction of optical rotation.

Androstane-3,17-diol↗
PubMed1975

[Studies on the magneto-optical rotation of porphyrins, hemins and methemoglobin compounds].

Using the method of magneto-optical rotation (MOR) various porphyrin derivatives, hemin and heme compounds, and a number of methemoglobin complexes were investigated. The spectra were recorded from 450-600 nm; with methemoglobin also in the Soret region. 1. The metalfree porphyrin derivatives (deutero-, meso-, hemato- and protoporphyrins) were measured in strongly acidic aqueous solution. The derivatives thus present as di-cations yield highly resolved MORspectra, where the Q-bands (Oo leads to; Oo leads to 1) originated from the pi-pi transitions of the porphyrin display the curve shape characteristic of an A-term, this proving the presence of the D4h symmetry. An exception is the protoporphyrin, in which the pi-electron system of the porphyrin is perturbed by the influence of pi-electrons of the vinyl group, causing poor resolution, line broadening, and shift of the Q-bands into the lower-energy spectral region. 2. With iron porphyrins (hemin, heme and their complexes) the charge of the iron and the nature of axial ligands determine the position and intensity of the O-bands in the MOR spectrum. Low-spin complexes have a higher symmetry than the high-spin complexes. Whereas with hemin (S = 5/2), the iron located outside the heme plane strongly disturbs the porphyrin pi-system, the high symmetry of porphyrin is greatly retained in the case of heme. This can be explained by the enhanced binding distance between the bivalent iron and the porphyrin to great for a strong coupling between the microsymmetry of the iron and the macrosymmetry of the porphyrin pi-system.

Heme↗
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↗
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↗
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↗
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↗
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↗
PubMed1990

Determination of enantiomeric purity of ephedrine and pseudoephedrine by high-performance liquid chromatography with dual optical rotation/UV absorbance detection.

A reversed-phase high-performance liquid chromatography (HPLC) method with dual optical rotation/UV absorbance detection has been developed for the determination of enantiomeric purity of ephedrine hydrochloride and pseudoephedrine hydrochloride using an achiral column. The method gave a correlation coefficient of 0.9997 for the plot of log(optical rotation response) versus log (concentration) over the range of 0.06-10 mg ml(-1) of (+)-ephedrine hydrochloride (20 microliters injection). The limit of detection was 1.0 micrograms. Enantiomeric purity is shown to be most readily determined by measuring optical rotation, alpha, and absorbance, A, responses for standard and unknown samples, and using the equation (alpha/A)u/(alpha/A)s = (2xu - 1)/(2xs - 1), where x is the mole fraction of one of the enantiomers and subscripts s and u refer to standard and unknown, respectively. In blind trials using unknown mixtures of (+)- and (+/-)-ephedrine hydrochloride and a (+)-ephedrine hydrochloride standard, enantiomeric purities were determined to +/- 0.4% (95% confidence level) with five or six replicate 50 micrograms injections. The method has also been applied to the determination of the enantiomer mole fraction of (+)-pseudoephedrine hydrochloride in a cough linctus, giving xu = 0.99 +/- 0.01 with seven replicate injections of 20-fold diluted linctus samples containing 7.5 micrograms of the chiral compound being assayed. Unlike conventional polarimetry, the method does not require chemically-pure samples and can be orders of magnitude more economical in material.

Antitussive Agents↗
PubMed1976

Stereospecific inversion of l-alpha-methylfluorene-2-acetic acid to its d-enantiomer in the dog.

1. After administration of dl-alpha-methylfluorene-2-acetic acid to dogs, the optical rotation of the drug in blood increased with time. Of the total drug in blood, the d-enantiomer increased from 61 to 80% between 3 and 24 h after administration; by 384 h it was 100%. 2. Both l- and d-enantiomers had plasma half-lives and excretion characteristics similar to those of the dl-racemic mixture, indicating that the increase in the proportion of the d-enantiomer was not due to more rapid excretion of the l-enantiomer. 3. Studies of optical rotation and circular dichroism demonstrated that the l-enantiomer was converted to the d-enantiomer in the blood of the dog, but the d-enantiomer remained unchanged. After administration of the l-enantiomer, the d-enantiomer increased from 26 to 71% of the total drug in blood between 0-3 and 2 days after administration; 14 days after dosing, almost all of the drug was present as the d-enantiomer. 4. Isomerization of l-alpha-methylfluorene-2-acetic acid to its d-enantiomer also occurs in rat, monkey and man.

Acetates↗