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Biomedical subjects

Nicholas J Turro

Publications and source records attributed to Nicholas J Turro.

61 records · Page 4Linked to original sources
PubMed2002

Supramolecular organic photochemistry: control of covalent bond formation through noncovalent supramolecular interactions and magnetic effects.

Supramolecular organic photochemistry, a field concerned with the interaction of light with supramolecular assemblies of organic molecules, has been inspired by the remarkable structural and dynamic features of guest@host chemistry, particularly as exemplified by enzymes. Exemplars of supramolecular organic photochemistry from soft-matter hosts (micelles) and hard-matter hosts (porous solids) are discussed with an emphasis on how noncovalent interactions, which are at the heart of supramolecular chemistry, can be systematically exploited to control the catalytic and magnetic effects on the formation of covalent bonds from photochemically produced pairs of radicals.

Binding Sites↗
PubMed2002

Damage control of DNA in nucleosome core particles: when a histone's loving, protective embrace is just not good enough.

Packaging DNA into nucleosome core particles generally offers protection from damage by molecules diffusing in solution. However, on page 403 of this issue, Barton and coworkers report that although noncovalently bound, activated Rh (Rhodium) does not readily bind within nucleosomal DNA, activated Rh that is covalently tethered to the 5' terminus of a histone-associated oligonucleotide oxidizes guanine bases from a distance of up to 24 base pairs, demonstrating that histones do not protect DNA from long-range damage from the transport of charge through stacked bases. This implies that oxidative damage generated on DNA in vivo may spread from an initially damaged site to distal sites. Once created, such sites may persist and be resistant to repair because of the protective packaging by histones; they thus may result in permanent mutations.

Animals↗
PubMed2002

Inhibition of lipid peroxidation in synaptosomes and liposomes by nitrates and nitrites.

NO is produced endogenously from arginine by the action of NO synthase, and exogenously by nitrovasodilators, including organic nitrates and nitrites. NO has been proposed as a cytotoxic and cytoprotective agent. There is strong evidence that NO acts as an apparent antioxidant in inhibiting lipid peroxidation, via chain termination, and interestingly lipid nitrates and nitrites have been proposed to be products of this chain termination. Both pro- and antioxidant mechanisms may be drawn for nitrates and nitrites; therefore, their effects on lipid peroxidation were measured in two systems, using tocopherol, thiol, and an NO donor for comparison: (1) rat cerebrocortical synaptosomes with Fe(II)-induced lipid peroxidation measured by thiobarbituric acid reactive substances (TBARS), and (2) phospholipid liposomes with an azo-initiator induction system, quantified by a fluorescent probe of peroxide formation. In contrast to the classical nitrate nitroglycerin, novel nitrates which release NO on reaction with thiols and two novel nitrates which spontaneously generate NO in aqueous solution inhibited lipid peroxidation. i-Amyl nitrite inhibited lipid peroxidation, and its properties were further studied with ESR spectroscopy. The data show that classical nitrites and novel nitrates are not prooxidants, but inhibit lipid peroxidation.

Amyl Nitrite↗
PubMedDate not supplied

Two-photon excitation induced fluorescence of a trifluorophore-labeled DNA.

Two-photon excitation of a trifluorophore (6-carboxyfluorescein, N,N,N',N'-tetramethyl-6-carboxyrhodamine and cyanine-5 monofunctional dye) labeled DNA, which has a scaffold of 26 nucleotides, was achieved using focused laser light of a Q-switched Nd-YAG laser (1064 nm). The observed fluorescence signature (emission ratio from the three fluorophores) of the labeled DNA after two-photon excitation is very different from the fluorescence signatures produced by one-photon excitation at different wavelength. The additional fluorescence signatures produced by two-photon excitation of the fluorescent oligonucleotides will facilitate their use as combinatorial fluorescence energy transfer tags for multiplex genetic analysis.

DNA↗
PubMedDate not supplied

Control of chirality by cations in confined spaces: Photooxidation of enecarbamates inside zeolite supercages.

On photooxygenation of the optically active Z/E enecarbamates 1 (X = i-Pr) and 2 (X = Me) equipped with the oxazolidinone chiral auxiliary in methylene-blue (MB)-incorporated, alkali-metal (M = Li, Na, K, Cs, Rb), exchanged Y-type zeolites (MY-MB), oxidative cleavage of the alkenyl functionality releases the enantiomerically enriched methyldesoxybenzoin (MDB) product. The extent (%ee) and/or the sense (R or S) of the stereoselectivity in the formation of the MDB product depends on the choice of the alkyl substiuent (i-Pr or Me) at the C-4 position of the oxazolidinone chiral auxiliary, the Z/E configuration of the alkene functionality in the enecarbamates, and the type of alkali metal in the zeolite. Most significantly-the highlight of this study-is the reversed sense (R or S) in the stereoselection when the photooxygenation is run in CDCl3 solution versus inside the MY-MB zeolite. As a mechanistic rationale for this novel stereochemical behavior, we propose the combined action of spatial confinement and metal-ion coordination (assessed by density-functional calculations) of the substrate within the zeolite supercage, both of which greatly reduce the freedom of the substrate and entropically manipulate the stereochemical outcome.

Journal Article↗
PubMedDate not supplied

Superoxidation of retinoic acid.

Atmospheric pressure chemical ionization mass spectroscopy (APCI-MS) was used to examine the light-induced oxidation products of retinoic acid under conditions that favor and preclude its aggregation. We observed that in conditions that favor aggregation, i.e. in aqueous solutions, retinoic acid undergoes superoxidation to yield highly oxidized species. Oxidation is limited, however, in the absence of such communication, i.e. when the polyene is fully solvated. From a comparison of the measured MS with that obtained from chemical oxidation of retinoic acid under conditions that promote radical oxidation and singlet oxygen-mediated oxidation, we conclude that superoxidation is mediated by reactive oxygen species other than singlet oxygen.

Mass Spectrometry↗