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D A Lightner

Publications and source records attributed to D A Lightner.

At least 37 records · Page 2Linked to original sources
PubMed1993

Structure of 6-(3,3-dimethyl-2-oxo-2,3-dihydro-5-furanyl)-2-pyridone at 145 K.

C11H11NO3, M(r) = 205.21, triclinic, P1, a = 5.725 (1), b = 9.038 (1), c = 10.401 (2) A, alpha = 101.37 (1), beta = 102.63 (1), gamma = 102.83 (1) degrees, V = 494.7 (3) A3, Z = 2, Dx = 1.38 g cm-3, lambda (Mo K alpha) = 1.7107 A, mu = 0.62 cm-1, F(000) = 216, T = 145 K, R = 0.049, wR = 0.063 for 2386 unique observed reflections. The molecules, which are self-associating in solution, are arranged in the crystal in centrosymmetric dimers joined by N--H...O bonds between the amide functional groups. Analysis of displacement parameters indicates that the furanyl and pyridone groups are independently quite rigid, with the furanyl group librating with respect to the hydrogen-bonded pyridone.

Crystallization↗
PubMed1992

Conformation inversion of bilirubin formed by reduction of the biliverdin-human serum albumin complex: evidence from circular dichroism.

As shown by circular dichroism spectroscopy, biliverdin preferentially adopts an M-helicity conformation on human serum albumin in aqueous buffer, pH 7.5, whereas biliverdin exhibits only a weak preference for the P-helicity conformation on bovine serum albumin at the same pH. Upon rapid reduction of the complexes with sodium borohydride, P-helicity bilirubin-IX alpha is obtained on the human albumin complex, and M-helicity bilirubin-IX alpha is obtained on the bovine serum albumin complex. Thus, biliverdin in effect undergoes an inversion of chirality upon reduction. Since the reduction did not afford a rubin with the same helicity as that of the verdin, the observations point to a hitherto undetected conformational mobility of albumin-bound bilirubin.

Bilirubin↗
PubMed1992

Effect of volatile anesthetics on the circular dichroism of bilirubin bound to human serum albumin.

The characteristic circular dichroism of bilirubin bound to human serum albumin undergoes a remarkable sign inversion on addition of halothane, chloroform and other volatile anesthetics. This sign inversion, which is completely reversed by removal of the anesthetic, reflects a pronounced conformational change of the bound ligand; probably a complete inversion of chirality. The observation suggests that association of volatile anesthetics with proteins can markedly alter the internal topography of receptor sites and potentially influence the stereoselectivity of ligand binding.

Anesthetics↗
PubMed1991

Resonance Raman spectroscopy of bilirubins: band assignments and application to bilirubin/lipid complexation.

Resonance Raman spectra of bilirubins IX alpha, III alpha, and XIII alpha and mesobilirubin XIII alpha in alkaline aqueous and chloroform solutions are reported. Partial band assignments of bilirubin IX alpha are proposed. The model compounds confirm assignments of bands of the Raman spectrum of bilirubin IX alpha to each of the two different pyrromethenones. Resonance Raman spectra of mesobilirubin IV alpha, vinylneoxanthobilirubinic acid, and vinylisoneoxanthobilirubinic acid in alkaline aqueous solution and of the tetra-n-butylammonium salt of bilirubin IX alpha are used to define markers for the presence or absence of internal hydrogen bonds. Interaction of bilirubin dianion and sphingomyelin liposomes is studied. The Raman evidence suggests that in the bilirubin dianion/liposome complex the intramolecular hydrogen bonds between the propionate groups and the lactam NH/CO are ruptured. It is proposed that in the complex the bilirubin propionates form ion pairs with the quaternary ammonium ion of the choline moiety of sphingomyelin.

Bilirubin↗
PubMed1988

Circular dichroism of bilirubin-amine association complexes: insights into bilirubin-albumin binding.

Bichromophoric (4Z, 15Z)-bilirubin-IX alpha, the yellow-orange cytotoxic pigment of jaundice, adopts either of two intramolecularly hydrogen-bonded enantiomeric conformations that are in dynamic equilibrium in solution. The addition of optically active amines induces the pigment solutions to exhibit intense bisignate circular dichroism in the region of the bilirubin long wavelength uv-visible absorption band. The most intense circular dichroism Cotton effects, (delta epsilon) approximately equal to 130, are induced by beta-arylamines and are comparable to those exhibited by bilirubin complexes with serum albumin and other proteins. Like serum albumin and other proteins, the optically active base acts as a chiral complexation agent to induce an asymmetric transformation of bilirubin, whose induced bisignate circular dichroism Cotton effect is characteristic of exciton splitting of the component pyrromethenone chromophores. The amines thus serve as chiral templates for molecular recognition, and the complementary action of the amine complexation sites provides insight into the binding forces important in protein-bilirubin heteroassociation.

Amines↗
PubMed1986

On the structure of albumin-bound bilirubin. Selective binding of intramolecularly hydrogen-bonded conformational enantiomers.

The intramolecularly hydrogen-bonded bichromophoric tetrapyrrole pigments, bilirubin-IX alpha and mesobilirubin-XIII alpha, adopt either of two folded, intramolecularly hydrogen-bonded, enantiomeric conformations which are in dynamic equilibrium in solution. Added human serum albumin binds preferentially, although not necessarily exclusively, to one conformational enantiomer, and the solutions exhibit bisignate circular dichroism Cotton effects in the region of the pigment's long wavelength electronic transition. In contrast, the bichromophoric tetrapyrrole pigment mesobilirubin-IV alpha, which is incapable of adopting intramolecularly hydrogen-bonded folded conformations, and the monochromophoric pyrromethenone, xanthobilirubic acid, show only monosignate induced circular dichroism Cotton effects under the same conditions. Application of exciton coupling theory indicates a preference for complexation of the right-handed (or positive) chirality conformational enantiomer of bilirubin-IX alpha or mesobilirubin-XIII alpha to human serum albumin at physiologic pH.

Bilirubin↗
PubMed1985

'Like a shrivelled blood orange'--bilirubin, jaundice, and phototherapy.

The biochemistry of bilirubin is reviewed with particular reference to newborn infants. The formation, properties, and metabolism of bilirubin are summarized and the importance of molecular shape, hydrogen-bonding, and polarity on the biologic disposition of bilirubin is emphasized. The chemical basis for the subtle influence of visible (blue) light on bilirubin structure and metabolism is explained, and recent concepts of the mechanism of phototherapy are presented. A glossary of current jargon is appended.

Bilirubin↗
PubMed1984

Bilirubin photooxidation products in the urine of jaundiced neonates receiving phototherapy.

Bilirubin-IX alpha photooxidation products were detected by high performance liquid chromatography in the urine of neonates undergoing phototherapy for hyperbilirubinemia. The in vivo photoproducts were identified by chromatographic comparison with authentic synthetic standards using two complementary methods. Bilirubin photooxidation products were not detected in urine from jaundiced infants not receiving phototherapy. The specific photoproducts identified in the urine include propentdyopents, hematinic acid imide and its hydrolysis product (3-carboxy-2-methyl-2-hexenedioic acid), and the hydrolysis product (2-vinyl-3-methyl-maleic acid) of methylvinylmaleimide. Their total urinary concentrations were low (0.2-0.9 mg/dl) during phototherapy. These observations show that photooxidation of bilirubin clearly does occur during phototherapy. They are consistent with the view that, although photooxidation is not the major photochemical event associated with phototherapy, it can and clearly does occur concurrently with photoisomerization.

Bilirubin↗
PubMed1980

Action spectra for bilirubin photodisappearance.

The excitation wavelength dependence of bilirubin photodestruction, as measured by quantum yields, has been determined in benzene, chloroform-1% ethanol, chloroform-1% hexane, methanol-1% concentrated ammonia, pH 8.5 aqueous buffer and pH 7.4 aqueous buffer with added albumin. The results show that in the visible spectrum the 370-490 nm excitation wavelength region is very effective in the photodestruction, but excitation in the UV-region (lambda less than 320 nm) is even more effective.

Animals↗
PubMed1980

Blue light and bilirubin excretion.

Blue light converts bilirubin in the skin of jaundiced rats to metastable geometric isomers that are transported in blood and excreted in bile. The same reaction probably occurs in jaundiced babies exposed to light, particularly during treatment with phototherapy. Excretion of unisomerized bilirubin is prevented by intramolecular hydrogen bonding, and the pigment has to be metabolized to more polar derivatives to be excreted efficiently.

Animals↗
PubMed1980

The octant rule VIII. Variable temperature circular dichroism spectra of alpha-methyl- and methoxyl-substituted 5 alpha-cholestan-2- and -3-ones.

2 alpha- and 2 beta-Methyl- and methoxy-5 alpha-cholestan-3-ones and 3 alpha- and 3 beta-methyl- and methoxy-5 alpha-cholestan-2-ones have been synthesized and their variable temperature circular dichroism spectra obtained and analyzed. Rotatory strength (R) values for alpha-axial and equatorial CH3 and OCH3 groups are determined by difference measurements with the parent ketone. The (small) equatorial CH3 R-values do not consistently follow the Octant Rule. Axial OCH3 groups do not obey the Octant Rule ("anti-octant" behavior) and impose a bathochromic shift on the C = O n-pi transition. Equatorial OCH3 groups do not consistently follow octant or "anti-octant" behavior.

Chemical Phenomena↗
PubMed1979

Photobilirubin: an early bilirubin photoproduct detected by absorbance difference spectroscopy.

Absorption of light converts bilirubin-IXalpha in solution to a mixture of what are probably cis-trans geometric isomers. This reaction is much faster than other photochemical reactions of bilirubin and reaches photoequilibrium before losses due to photooxidation are significant. At room temperature in the dark in the presence of trifluoroacetic acid or iodine or simply on standing, the photoproducts revert to the natural isomer. They also revert under visible light. Their formation and reversion can be followed by chromatography on polyamide and by absorbance difference spectroscopy.

Bilirubin↗