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Results for “Optical Rotatory Dispersion”

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At least 469 records · Page 26Linked to original sources
PubMed1978

Polar corticosteroids in human neonatal urine; synthesis and gas chromatography-mass spectrometry of ring A reduced 6-hydroxylated corticosteroids.

This report describes the synthesis of 3alpha,6beta,11beta,17alpha,21-pentahydroxy-5beta-pregnane-20-one, 3alpha,6beta,11beta,17alpha,21-pentahydroxy-5beta-pregnane-20-one, 3alpha,6alpha,11beta,17alpha,21-pentahydroxy-5alpha-pregnane-20-one, 3alpha,6beta,17alpha,21-tetrahydroxy-5beta-pregnane-11,20-dione, 3alpha,6beta,17alpha,21-tetrahydroxy-5alpha-pregnane-11,20-dione, 3alpha,6alpha,17alpha,21-tetrahydroxy-5beta-pregnane-11,20-dione and 3alpha,6alpha,17alpha,21-tetrahydroxy-5alpha-pregnane-11,20-dione. The gas chromatographic-mass spectrometric properties of these compounds are given. Proof of structure was accomplished using gas chromatography-mass spectrometry, microchemical reactions, optical rotatory dispersion and nuclear magnetic resonance spectroscopy.

Chromatography, Gas↗
PubMed1997

Fast natural and magnetic circular dichroism spectroscopy.

The addition of circular or, more generally, elliptical polarization state detection to fast optical absorption spectroscopy can increase the amount of electronic and nuclear conformational information obtained about transient molecular species. To accomplish this, fast circular dichroism methods have emerged over the past decade that overcome the millisecond limit on time resolution associated with conventional modulation techniques and enable structural studies of excited states and kinetic intermediates. This article reviews techniques for time-resolved natural and magnetic circular dichroism spectroscopy covering the picosecond to millisecond time regimes and their applications, with particular emphasis on quasi-null ellipsometric techniques for nanosecond multichannel measurements of circular dichroism. Closely related quasi-null polarimetric techniques for nanosecond optical rotatory dispersion and linear dichroism measurements are also discussed.

Artifacts↗
PubMed1976

Sedimentation equilibrium studies on protein from kookaburra beak.

Fractionated samples of the soluble S-carboxymethyl proteins from kookaburra beak (Frenkel and Gillespie 1976) were examined by equilibrium sedimentation. The molecular weight was found to be 11,300 when the photoelectric scanning absorption optical system was employed and 13,700 when Rayleigh interference optics were used. Possible explanations for this difference are considered and it is concluded that it must arise from heterogeneity of the protein. Optical rotatory dispersion measurements indicate that the proteins probably exist as random coils in dilute aqueous buffer.

Animals↗
PubMed1975

Drug-biomolecule interactions: interactions of mononucleotides and polybasic amino acids.

Histones and ribosomal proteins are basic proteins that participate in gene regulation and protein synthesis, respectively. How these proteins interact with nucleic acids is not yet clear, although specificities in these interactions have been observed. Study of the interaction of mononucleotides with basic polyamino acids is one approach to understanding such interactions. The results of studies with the mononucleotides can help elucidate the normal molecular processes in biological systems and also shed light on some effects of drugs, such as puromycin and tubericidin, that are nucleotide derivatives. A review of studies on the interaction of mononucleotides and basic polyamino acids such as polylysine and polyarginine is presented. In addition, a short review of the self-associative properties of mononucleotides is given. Studies of the mononucleotide-polyamino acid interaction have involved a wide variety of techniques including equilibrium dialysis, NMR, optical rotatory dispersion, circular dichroism, and precipitate analysis.

Amino Acids↗
PubMed1972

Influence of magnesium and manganese on some biological and physical properties of tetracycline.

Accumulation of (3)H-tetracycline in nonproliferating cells of susceptible and resistant strains of Escherichia coli and Staphylococcus aureus in tris(hydroxymethyl)aminomethane (Tris) buffer (10 mm, pH 7.5) was significantly decreased in the presence of 5 to 40 mm MgCl(2) and increased in the presence of 5 to 10 mm MnCl(2). When the bacteria first accumulated (3)H-tetracycline in plain Tris.HCl, and the metal salts were thereafter added, a prompt decrease or increase in radioactivity of the cells was observed after the addition of Mg(2+) or Mn(2+), respectively. In phosphate buffer (10 mm, pH 7.5), the effect of Mg(2+) was delayed. Three minutes after addition of (3)H-tetracycline, uptake was as in the control cell suspension, but thereafter it dropped rapidly. When (3)H-tetracycline was incubated with Mg(2+) before addition to the bacterial suspension, uptake was scarcely measurable. The addition of Mg(2+) to growing cultures of S. aureus and E. coli caused a marked decrease in susceptibility; in contrast, no increase in susceptibility could be demonstrated when Mn(2+) was added. It was also demonstrated that Mg(2+) and Mn(2+) had distinct influences on the absorption spectrum, the optical rotatory dispersion, the circular dichroism, and the lipid solubility of tetracycline.

Absorption↗
PubMed1970

Optical activity of bovine neurophysins and their peptide complexes in the near ultraviolet.

Circular dichroism studies of the bovine neurophysins in the near ultraviolet show a strong negative band at 280 nm and a strong positive band at 248 nm, both of which are attributable almost exclusively to disulfide transitions. The ellipticities per disulfide bond of the unresolved bands in neurophysin-II are -2900 deg cm(2)/decimole and +2300 deg cm(2)/decimole at 280 nm and 248 nm, respectively. Binding of oxytocin, vasopressin, or the peptide S-methyl-L-cysteinyl-L-tyrosyl-L-phenylalanine amide lead to large changes in optical activity in the near and far ultraviolet. Of these circular dichroism changes above 290 nm are attributed to changes in the optical activity of neurophysin disulfides, while changes elsewhere are more generally ascribed to changes in either disulfide, tyrosine, or peptide bond transitions. Optical rotatory dispersion studies show that calcium ion, at concentrations of 0.01 M, has only trivial effects on the affinity of bovine neurophysins for oxytocin.

Animals↗
PubMed1964

SONIC ENERGY EFFECTS IN BOVINE SERUM ALBUMIN SOLUTIONS.

Bovine serum solutions exposed to high-frequency sound were examined by ultracentrifugal, electrophoretic, viscometric, conductivity, light scattering, and optical rotatory dispersion procedures. Parameters determined with treated material were the same as those determined with untreated albumin solutions except for slight differences in rotation, the dispersion constant, and in weight-average molecular weight.

Animals↗
PubMed1998

Applications of chiroptical spectroscopy for the characterization of pharmaceutical compounds.

Many pharmaceutical compounds contain one or more centers of dissymmetry, thus presenting a unique series of regulatory and compendial requirements. Although most often characterized using chiral chromatography, these molecules can be effectively studied using the various techniques of chiroptical spectroscopy. Techniques which have been found to be very useful for such work include polarimetry, optical rotatory dispersion, circular dichroism, and circularly polarized luminescence. The principles underlying each effect will be briefly outlined, and the application of each illustrated through the inclusion of appropriate examples.

Chemistry, Pharmaceutical↗
PubMed1969

Some optical properties of diadenosine-5'-phosphates.

The absorption spectra, optical rotatory dispersion, and circular dichroism of a series of diadenosine-5'-phosphates, differing in the length of the phosphate bridge, indicate that in this set of compounds the adenine residues form an intramolecular stacked conformation. The differences in the optical properties suggest that this arrangement is different from that deduced by others for diadenosine-3',5'-monophosphate (ApA(3',5')) but is of comparable stability.

Adenine Nucleotides↗
PubMed1975

Temperature dependence of the optical activity of human serum low density lipoprotein. The role of lipids.

Low density lipoprotein (LDL) (1.024-1.045 G/cm3) was prepared by ultracentrifugal flotation from serum of normal fasting subjects. Circular dichroism (CD) and optical rotatory dispersion (ORD) spectra in the ultraviolet region were measured at 2, 25, and 37 degrees on LDL, lipid extracted from LDL, and on pure component lipids. All exhibit reversible, temperature-dependent optical activities. Sphingomyelin has a strong negative CD band around 195 nm. Cholesterol and cholesteryl esters have a CD minimum at 208 nm. They have positive CD bands around 201 and 198 nm which decrease sharply and become negative at 198 and 193 nm, respectively. The CD of the total lipid extract of LDL is negative and drops monotonically below 200 nm. Thus, the lipid moiety could account for the increasing negativity of the CD of LDL below 195 nm. After subtraction of the ellipticity corresponding to amounts of lipids in organic solvents equivalent to those found in LDL, the 208-210 nm trough of LDL diminishes markedly. This is accompanied by a blue-shift of the extrema from 195-196 to 193 nm and an increase in the magnitude of the positive ellipticity. The fractions of helix and of beta form in the protein, determined by the method of Y. H. Chen, J. T. Yang, and K. H. Chau ((1974), Biochemistry 13, 3350), in the wavelength interval of 250-240 nm, remain essentially unchanged between 2 and 37 degrees. These observations suggest that a substantial part of the thermal change in the CD spectrum of LDL between 208 and 210 nm may be attributable to lipids.

Cholesterol↗
PubMed1971

Location of aromatic amino acids and belix content in Escherichia coli ribonucleic acid polymerase.

1. The perturbing effect of glycerol on the direct spectrum of Escherichia coli DNA-dependent RNA polymerase has been studied. 2. By comparison with model compounds and with the unfolded polymerase in 3.8m-urea it was possible to determine the ratio of tyrosine and tryptophan residues present. On reduction of the urea-treated enzyme with 2-mercaptoethanol, no further change in the difference spectrum occurred. 3. The amino acid composition of the enzyme is given. 4. In the intact protein approx. 30% of the tryptophan and 54% of the tyrosine residues were exposed. In conjunction with the extinction value and molecular weight this corresponded to 7 tryptophan residues and 57 tyrosine residues on the surface and 16 tryptophan residues and 48 tyrosine residues ;buried'. 5. The optical rotatory dispersion of the enzyme was unaffected by 20% glycerol. 6. The helix content calculated from Moffit plots over 560-300nm was 13%, and from the 233nm trough 13%.

Amino Acids↗
PubMed2001

Determining absolute configuration in flexible molecules: a case study.

Assigning absolute configuration of molecules continues to be a major problem. Determining absolute configuration in conformationally flexible systems is challenging, even for experts. Here, we present a case study in which we use a combination of molecular modeling, solution NMR, and X-ray crystallography to illustrate why it is difficult to use solution methods alone for configuration assignment. For the case examined, a comparison of calculated and experimental optical rotatory dispersion (ORD) data provides the most straightforward way to assign the absolute configuration.

Benzoates↗
PubMed1975

The tyrosyl residues in creatine kinase. Modification by iodine.

The effect of the iodination of tyrosyl residues in creatine kinase from rabbit muscle has been investigated at alkaline pH after reversible masking of the reactive thiol groups. The conversion of 4-5 tyrosyl residues to monoiodotyrosines as measured by spectrotitration and by radioactive iodine labelling resulted in almost total loss of enzymic activity. The modified enzyme was unable to bind its nucleotide substrates but no significant conformational change was revealed by optical rotatory dispersion or Stokes radius measurements. However, change in the reactivity of some non-essential thiol groups, presumably those located near the active thiol groups, was observed.

Amino Acids↗
PubMed1974

Denaturation: an example of a catastrophe.

We show that a "phase diagram" for the conformational states of proteins can be constructed using the mathematical theory of singularities of functions developed recently by René Thom. For proteins subjected to the disruptive influences of temperature and/or concentration of denaturing agent, this theory can be used as a predictive tool to account for the shape, sense, and changes in the curves that result when the optical rotatory dispersion is plotted as a function of these two constraints. The mathematical model is found to be in accord with known experimental data on collagen, lysozyme, and ribonuclease.

Calcium Chloride↗
PubMed1976

Physico-chemical characterization of the spectrin tetramer from bovine erythrocyte membranes.

The tetramer of bovine spectrin has been purified and characterized in terms of its hydrodynamic and optical properties. (1) The molecular weight, from both sedimentation equilibrium and sedimentation velocity/diffusion measurements, is close to one million. (2) The hydrodynamic properties suggest a highly expanded but basically symmetrical molecule of Stokes radius 200 A. (3) Optical rotatory dispersion measurements indicate a high degree of order in the tertiary structure of the molecule. These results are not consistent with the assumption that is often made, that the spectrin molecule is a long fibrous rod.

Animals↗
PubMed1976

Conformational aspects of the interaction of polyanions with liganded beta chains of human hemoglobin.

The interaction of carbon monoxide beta chains with two allosteric effectors, namely inositol hexaphosphate and benzenehexacarboxylate, was studied. The sedimentation coefficient (s20,w) of the liganded beta chains was measured to be the same both in the presence and absence of the two effectors suggesting that the protein exists as a tetramer under the conditions of our titration and optical studies. The binding of benzenehexacarboxylate to the liganded beta chains was investigated by potentiometric titration in the pH range 6.7-8.0. The results at pH 7.4 showed a binding of 2 mol of benzenehexacarboxylate per tetramer, with an association constant of 1.26 X 10(4) 1. mol-1 at 20 degrees C. The Hill coefficient for the binding was determined to be 0.73. Similar experiments on the interaction of inositol hexaphosphate with the beta chains showed a binding of 2 mol of the effector per tetramer with identical Hill coefficient (0.737) and comparable association constants (0.88 X 10(4)1. mol-1). The value below unity of the Hill coefficient, found for the binding of the two effectors to the protein, probably reflected an anticooperativity produced by the different net electric charges of the free protein and the protein-effector complex. The difference in protons bound per mole of heme by the beta subunits in the presence and absence of benzenehexacarboxylate appeared consistent with the proposal that two groups per chain changed their pK from 6.6 to 7.4 upon the interaction. In the presence of benzenehexacarboxylate, the protonation of these groups appeared to be cooperative, suggesting a conformational change of the protein upon the binding. The absorption spectra of carbon monoxide beta chains in the Soret region was markedly altered by benzenehexacarboxylate and inositol hexaphosphate. The features in the difference spectra of the protein obtained with the two effectors were qualitatively identical and indicated changes in the heme environment produced by the interaction of the effectors with the beta chains. Concomitant changes in circular dichroism and optical rotatory dispersion of the liganded beta chains caused by the addition of the two effectors provided supporting evidence for the conformational change in the protein produced by the binding of the effectors.

Binding Sites↗
PubMedDate not supplied

Experiments of the origins of optical activity.

Two recent reports claim that (1) aqueous L-aspartic acid polymerizes faster than D-Asp in the presence of kaolin at 90 degrees, and (2) L-phenylalanine is adsorbed by kaolin more extensively than D-Phe at pH 4(the reverse being true at pH2). The novelty of these observations and their potential significance for the origin of optical activity has prompted us to duplicate these experiments using more sensitive methods. L- and D, L-Asp in 0.01 M solution were incubated with kaolin at 90 degrees for 8 days. Careful examination of the aqueous residues from such experiments failed to demonstrate any preferential polymerization of L-Asp over D-Asp, or indeed any significant gross polymerization of Asp at all. In other experiments 0.001 M solutions of D, L-Phe at pH 6 and pH 2 were stirred with large excesses of kaolin for 24 hr, and the aqueous extracts from these mixtures were examined for gross adsorption using the amino acid analyzer. No significant gross adsorption was noted. We then looked for asymmetric adsorption in the aqueous residues using optical rotatory dispersion, gas chromatography and thin layer chromatography. By none of these analytical criteria could we find any evidence whatsoever for the preferential adsorption of D- versus L-Phe from either pH 6 or pH 2 solutions. Finally, in experiments bearing on the origin of optical activity by parity violation during beta-decay, we have irradiated solid samples of D-, L- and D,L-leucine in a 61700 Ci Sr-90 source at Oak Ridge National Lab. for 1.34 yr (total dose: 4.2 x 10(8) rad). Gas chromatographic examination of the (appropriately derivitized) recovered samples showed that the L-Leu was 16.7% decomposed, the D-Leu 11.4% and theD,L-Leu 13.8% decomposed. The recovered D,L-Leu sample had a gas-chromatographically determined enantiomeric composition of 50.8% D-leu and 49.2% L-Leu. These data, though very close to experimental error, may indicate a slight preferential radiolysis of L-Leu compared to D-Leu by the Bremsstrahlung from Sr-90 beta-decay. These high intensity irradiation experiments are being continued on a prolonged basis in order to reach more definitive conclusions.

Adsorption↗
PubMed1971

The specificity of combination between ristocetins and peptides related to bacterial cell wall mucopeptide precursors.

The affinity of ristocetin B for analogues of the C-terminal tripeptide sequence of bacterial cell wall mucopeptide precursors resembles that of vancomycin. Complex-formation requires a d-configuration in the two amino acid residues of the C-terminal dipeptide, an l-configuration is preferred in the preceding amino acid residue and positive charges on the peptide molecule decrease its affinity. The specificity of ristocetin B, however, differs from that of vancomycin in the requirements for the size of the side chains on the C-terminal dipeptide. These differences may explain the observed differences in antibiotic behaviour of vancomycin and ristocetin with particular micro-organisms. The optical rotatory dispersion and u.v.-absorption characteristics of the ristocetins are very different from those of vancomycin but nearly identical with those of ristomycin A. Aglycones prepared from ristomycin A were antibiotically active and also combined with a specific peptide.

Amino Acid Sequence↗