Bilirubin, the end product of heme catabolism in mammals, is generally regarded as a potentially cytotoxic, lipid-soluble waste product that needs to be excreted. However, it is here that bilirubin, at micromolar concentrations in vitro, efficiently scavenges peroxyl radicals generated chemically in either homogeneous solution or multilamellar liposomes. The antioxidant activity of bilirubin increases as the experimental concentration of oxygen is decreased from 20% (that of normal air) to 2% (physiologically relevant concentration). Furthermore, under 2% oxygen, in liposomes, bilirubin suppresses the oxidation more than alpha-tocopherol, which is regarded as the best antioxidant of lipid peroxidation. The data support the idea of a "beneficial" role for bilirubin as a physiological, chain-breaking antioxidant.

http://science.sciencemag.org/content/sci/235/4792/1043.full.pdf

Bilirubin is an antioxidant of possible physiological importance

III. Foldamer Research 3910 A. Overview 3910 B. Motivation 3910 C. Methods 3910 D. General Scope 3912 IV. Peptidomimetic Foldamers 3912 A. The R-Peptide Family 3913 1. Peptoids 3913 2. N,N-Linked Oligoureas 3914 3. Oligopyrrolinones 3915 4. Oxazolidin-2-ones 3916 5. Azatides and Azapeptides 3916 B. The â-Peptide Family 3917 1. â-Peptide Foldamers 3917 2. R-Aminoxy Acids 3937 3. Sulfur-Containing â-Peptide Analogues 3937 4. Hydrazino Peptides 3938 C. The γ-Peptide Family 3938 1. γ-Peptide Foldamers 3938 2. Other Members of the γ-Peptide Family 3941 D. The δ-Peptide Family 3941 1. Alkene-Based δ-Amino Acids 3941 2. Carbopeptoids 3941 V. Single-Stranded Abiotic Foldamers 3944 A. Overview 3944 B. Backbones Utilizing Bipyridine Segments 3944 1. Pyridine−Pyrimidines 3944 2. Pyridine−Pyrimidines with Hydrazal Linkers 3945

A field guide to foldamers.

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Ranging from the physics of elementary particles to the structure of viruses, the subject matter of this book stresses the importance of optical activity and chirality in modern science and will be of interest to a wide range of scientists. Using classical and quantum methods with a strong emphasis on symmetry principles, the volume develops the theory of varied optical activity and related phenomena from the perspective of molecular scattering of polarized light. First Edition Hb (1983): 0-521-24602-4

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Molecular Light Scattering and Optical Activity

Hydrogen bonds are like human beings in the sense that they exhibit typical grouplike behavior. As an individual they are feeble, easy to break, and sometimes hard to detect. However, when acting together they become much stronger and lean on each other. This phenomenon, which in scientific terms is called cooperativity, is based on the fact that 1+1 is more than 2. By using this principle, chemists have developed a wide variety of chemically stable structures that are based on the reversible formation of multiple hydrogen bonds. More than 20 years of fundamental studies on these phenomena have gradually developed into a new discipline within the field of organic synthesis, and is nowadays called noncovalent synthesis. This review describes noncovalent synthesis based on the reversible formation of multiple hydrogen bonds. Starting with a thorough description of what the hydrogen bond really is, it guides the reader through a variety of bimolecular and higher order assemblies and exemplifies the general principles that determine their stability. Special focus is given to reversible capsules based on hydrogen-bonding interactions that exhibit interesting encapsulation phenomena. Furthermore, the role of hydrogen-bond formation in self-replicating processes is actively discussed, and finally the review briefly summarizes the development of novel materials (nanotubes, liquid crystals, polymers, etc.) and principles (dynamic libraries) that recently have emanated from this intriguing field of research.

Noncovalent synthesis using hydrogen bonding

Typical linear and porphyrin-like structure representations of bilirubin give an incorrect impression of its actual shape and expected solution properties. Conformational alnalysis of bilirubin, assisted by molecular dynamics computations, indicates that (i) nonbonded intramolecular steric interactions are minimized in a ridge-tile shape conformation lying at a global energy minimum on the conformational energy map and (ii) considerable additional stabilization is achieved though a network of intramolecular hydrogen bonds. The linear and porphyrin-like conformations are computed to lie some 37-48 kcal/mol above the isoenergetic global minimum energy conformations, which correspond to superimposable (identical) or to nonsuperimposable (enantiomeric) mirror image intramolecularly hydrogen-bonded ridge-tile conformers

Bilirubin conformational analysis and circular dichroism

Cyclohexane and Cyclohexanone. Optical Activity. The Octant Rule. Conformational Analysis of Substituted Cyclohexanones. Other Cycloalkanones. Saturated Bicyclic Ketones. Saturated Polycyclic Ketones. Isotopically Perturbed Ketones. Diketones. Unsaturated and Cyclopropyl Ketones. Dienes. Biaryls and Helicenes. Exciton Coupling and Exciton Chirality. Indexes.

Organic conformational analysis and stereochemistry from circular dichroism spectroscopy

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.

https://science.sciencemag.org/content/sci/208/4440/145.full.pdf

Blue Light and Bilirubin Excretion

Four different hexahelicenes, 5-aza-hexahelicene (1), hexahelicene (2), 2-methyl-hexahelicene (3), and 2-bromo-hexahelicene (4), were prepared and their enantiomers, which are stable at r.t., were separated. Vibrational circular dichroism (VCD) spectra were measured for compound 1; for all the compounds, electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) spectra were recorded. Each type of experimental spectrum was compared with the corresponding theoretical spectrum, determined via Density Functional Theory (DFT). Following the recent papers by Nakai et al., this comparison allowed to identify some features related to the helicity and some other features typical of the substituent groups on the helical backbone. The Raman spectrum of compound 1 is also examined from this point of view.

Helical Sense-Responsive and Substituent-Sensitive Features in Vibrational and Electronic Circular Dichroism, in Circularly Polarized Luminescence, and in Raman Spectra of Some Simple Optically Active Hexahelicenes

David A. Lightner

Papers

Bilirubin conformational analysis and circular dichroism

Organic conformational analysis and stereochemistry from circular dichroism spectroscopy

Blue Light and Bilirubin Excretion

Helical Sense-Responsive and Substituent-Sensitive Features in Vibrational and Electronic Circular Dichroism, in Circularly Polarized Luminescence, and in Raman Spectra of Some Simple Optically Active Hexahelicenes

Complementarity and chiral recognition: enantioselective complexation of bilirubin