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At least 541 records · Page 30Linked to original sources
PubMed2003

Direct observation of triplet state emission of single molecules: single molecule phosphorescence quenching of metalloporphyrin and organometallic complexes by molecular oxygen and their quenching rate distributions.

Single molecules are detected through the phosphorescence emission of their triplet states. Emission of the triplet states of single molecules of Pt octabutoxycarbonyl porphyrin (PtOBCP) and ruthenium(II)-tris-4,7-diphenyl-1,10-phenanthroline dichloride (Ru(dpp)(3)Cl(2)) is reported. The single molecule phosphorescence is very sensitive to molecular oxygen. Each molecule has its own characteristic quenching rate by oxygen, and the distribution of these rates is measured for (Ru(dpp)(3)Cl(2)) on a quartz surface. The large variance of this distribution is presumed to be caused by fluctuations in the pseudobimolecular rate coefficient and the local oxygen concentration. The possibility of creating a quantitative single oxygen molecule sensor is suggested.

Luminescent Measurements↗
PubMed2006

Sensitive single-layered oxygen-sensing systems: polypyridyl ruthenium(II) complexes covalently attached or deposited as langmuir-blodgett monolayer on glass surfaces.

Oxygen-sensing elements containing single-layered structures of luminescent indicators of ruthenium(II) bipyridyl complexes on glass surfaces prepared by covalent attachment and LB deposition are described. They are capable of detecting gaseous oxygen concentration by luminescence quenching of the indicator with reproducible and large quenching efficiencies that are comparable to the best quenching efficiencies obtained by other ruthenium(II) polypyridine based complexes immobilized in matrixes. The large quenching efficiencies for both films imply that the probe complexes are effectively quenched by oxygen, which is probably due to the thin single-layered structures with large surface-to-area ratio and short distance between the probe complexes and oxygen.

Electrochemistry↗
PubMed1999

A new metal ion interaction in the Tetrahymena ribozyme reaction revealed by double sulfur substitution.

The Tetrahymena ribozyme is a metalloenzyme that catalyzes cleavage of oligonucleotide substrates by phosphoryl transfer. Thiophilic metal ions such as Mn2+, Zn2+ or Cd2+ rescue the >10(3)-fold inhibitory effect of sulfur substitution of the 3'-oxygen leaving group but do not effectively rescue the effect of sulfur substitution of the nonbridging pro-Sp phosphoryl oxygen. We now show that the latter effect can be fully rescued by Zn2+ or Cd2+ using a phosphorodithioate substrate, in which both the 3'-oxygen and the pro-Sp oxygen are simultaneously substituted with sulfur. These results provide the first functional evidence that metallophosphotransferases can mediate catalysis via metal ion coordination to both the leaving group and a nonbridging oxygen of the scissile phosphate.

Animals↗
PubMed1977

Examination of the filterability of oxygenated erythrocytes (containing normal, trait or sickle cell disease type hemoglobins) in the presence of L-epinephrine, D,L-isoproterenol or prostaglandins (PG) A1, A2, E1, E2, F1alpha or F2alpha.

These studies were directed toward determining effects of selected vasoactive compounds on oxygenated erythrocytes. Considering the major circulatory effects that small changes in blood flow might initiate in sickle cell anemia patients, erythrocytes from individuals with this disease and from one person with the trait condition were included. PGA1, PGE1, and PGE2 significantly increase filtration times in normal erythrocytes (AA-type hemoglobin) at 10(-11) M by this method. From studies of the effects of L-epinephrine, D,L-isoproterenol, PGA1, PGA2, PGE1, PGE2, PGF1alpha and PGF2alpha on red blood cell filterabilities, the following observations and conclusions appear to hold: (1) Erythrocytes from different individuals (or from the same individual at different times) vary greatly in responses to these compounds. Effects of vasoactive compounds upon red cell filterability may be positive, negligible or negative. Decreased filterability (positive effect) was seen more frequently than increased. (2) Effects are observed with all compounds on some erythrocyte preparation at every concentration tested (10(-5), 10(-7), 10(-9), 10(-11) M). (3) Where epinephrine showed significant positive effect, PGA2 and PGE2 did also when tested. The reverse was not always true. (4) For PGA and PGE analogs, the subscript 2 analogs affected filterability more frequently. (5) When significant average effects for a group of donors were produced by a given compound at a particular concentration, these effects were positive for the donors studied.

Adult↗
PubMed1985

Use of digitonin fractionation to determine mitochondrial transmembrane ion distribution in cells during anoxia.

A method to determine intracellular distribution of ions and metabolites under conditions of low oxygen concentration was developed. The technique involves rapid digitonin fractionation and addition of cyanide to inhibit reoxygenation. Applicability of the procedure was examined by studying the distribution of the lipophilic ion triphenylmethylphosphonium, the weak acid 5,5-dimethyloxazolidine-2,4-dione, and adenine nucleotides.

Adenine Nucleotides↗
PubMed1982

[Role of SH-groups in the pharmacology of the action of novurite and ethacrynic acid].

In experiments in vivo the mercuric diuretic, novurite, and ethacrynic acid in therapeutic doses (25 and 50 mg/kg, respectively) do not block the respiration and active transport of calcium in the kidney mitochondria. The diuretic effect of these substances is not prevented by cystein (50 mg/kg), the donator of sulphydryl groups. In vitro novurite (3 mM) and ethacrynic acid (1 mM) block the systems of ionic transport inthe kidney epithelium cells and in concentrations of 0.2 and 0.5 mM, respectively, disturb the oxygen uptake and oxidative phosphorylation in the kidney mitochondria. A preliminary administration of cystein (5 mM) into the incubation medium prevents these effects. Novurite and ethacrynic acid manifest the typical thyol toxins of general cell effect in doses considerably exceeding the therapeutic ones. A specific "kidneys" effect of these substances is not connected with their ability to block SH-group of biologically active substances.

Alkylmercury Compounds↗
PubMedDate not supplied

The German Environmental Survey 1990/92 (GerES II): sources of personal exposure to volatile organic compounds.

In the framework of the second German Environmental Survey carried out in the Western part of Germany in 1990/91 (GerES IIa) 113 adults aged 25-69 years were selected at random from the total study population of about 2500 to investigate personal exposure to about 70 volatile organic compounds (VOCs). Each subject wore a diffusive badge-type sampler for 1 week. The VOCs determined included alkanes, aromatics, aliphatic halocarbons, terpenes, and oxygen-containing compounds. Multivariate regression analysis was carried out to determine and quantify the major sources of personal exposure to various VOCs. In this paper, results are given for benzene, and C8- and C9-aromatics. Being subject to environmental tobacco smoke was found to be the most important determinant of benzene exposure, but automobile-related activities such as driving a car or refuelling, were also associated with significantly increased levels of benzene. The major determinant of C8- and C9-aromatics concentrations was occupational exposure. Emissions from paints, lacquers, newspapers, magazines and print-works were also important contributors to C8-aromatics exposure. Renovation, painting and smoking were associated with a significant increase of the exposure to C9-aromatics.

Adult↗
PubMed1990

Non-ohmic proton conductance of the mitochondrial inner membrane in hepatocytes.

The mitochondrial membrane potential in isolated hepatocytes was measured using the distribution of the lipophilic cation triphenylmethylphosphonium (TPMP+) with appropriate corrections for plasma membrane potential, cytoplasmic and mitochondrial binding of TPMP+, and other factors. The relationship between mitochondrial membrane potential and respiration rate in hepatocytes was examined as the respiratory chain was titrated with myxothiazol in the presence of oligomycin. This relationship was nonproportional and similar to results with isolated mitochondria respiring on succinate. This shows that there is an increased proton conductance of the mitochondrial inner membrane in situ at high values of membrane potential. From the respiration rate and mitochondrial membrane potential of hepatocytes in the absence of oligomycin, we estimate that the passive proton permeability of the mitochondrial inner membrane accounts for 20-40% of the basal respiration rate of hepatocytes. The relationship between log[TPMP+]tot/[TPMP+]e and respiration rate in thymocytes was also nonproportional suggesting that the phenomenon is not peculiar to hepatocytes. There is less mitochondrial proton leak in hepatocytes from hypothyroid rats. A large proportion of the difference in basal respiration rate between hepatocytes from normal and hypothyroid rats can be accounted for by differences in the proton permeability characteristics of the mitochondrial inner membrane.

Animals↗
PubMed1999

Biochemical characterization of S-nitrosohemoglobin. Mechanisms underlying synthesis, no release, and biological activity.

S-Nitrosohemoglobin (SNO-Hb) has been suggested to act as an endogenous NO donor and physiological regulator of blood pressure. However, the mechanisms responsible for the formation of SNO-Hb and those underlying the release of NO and subsequent biological activity have yet to be elucidated. In the present study, a number of nitrosated oxyhemoglobin (HbO(2)) derivatives have been synthesized and characterized. HbO(2) can be nitrosated at up to three distinct residues, one in the alpha-globin chain and two in the beta-chain. A beta-chain mononitrosated species (designated "SNO-Hb"), generated by the reaction of HbO(2) and S-nitrosoglutathione, released NO via a thiol-dependent mechanism involving nucleophilic attack at the nitrosated thiol functionality of SNO-Hb; in the case of glutathione, this process was associated with the formation of a mixed disulfide. In contrast, multinitrosated hemoglobin species released NO and relaxed vascular smooth muscle by a thiol-independent mechanism. HbO(2) scavenged potently NO released from SNO-Hb and inhibited its vasorelaxant properties. These data show that the predominant vasoactive species released from SNO-Hb is NO, with HNO a putative intermediate; the presence of a low molecular weight thiol is a prerequisite for this process. Such observations have important implications for the generation, metabolic fate, and biological activity of S-nitrosothiols.

2,3-Diphosphoglycerate↗
PubMed1985

Photoinduced reactions of anthraquinone antitumor agents with peptides and nucleic acid bases: an electron spin resonance and spin trapping study.

The photoexcitation (lambda = 313 +/- 10 nm) of adriamycin, daunomycin, and mitoxantrone in the presence of peptides or pyrimidine nucleic acid bases was investigated. In air-saturated and air-free solutions, peptides are decarboxylated by the photoexcited drug molecules. The decarboxylation reactions were shown to occur specifically at the C-terminal amino acid of the peptide. The decarboxylated peptide radicals were spin-trapped using 2-methyl-2-nitrosopropane (MNP) and identified by electron spin resonance (ESR). In air-free solutions, nucleic acid bases are oxidized by the photoexcited drug molecules predominantly generating C(5)-carbon-centered radicals in the pyrimidine rings of uracil, cytosine, and thymine. However, spin adducts of MNP and thymine were also obtained at the N(1) or N(3) positions of the pyrimidine ring. In air-saturated adriamycin and daunomycin solutions, the spin adducts of MNP with uracil or thymine are similar to those obtained following hydroxyl radical reactions with these pyrimidines. This suggests that in the presence of oxygen, the photoexcited adriamycin and daunomycin transfer an electron to oxygen generating the superoxide anion radicals (O2-.), which are precursors of hydroxyl radicals. O2-. was also formed when O2-saturated DNA solutions were photoirradiated (lambda = 313 +/- 10 and 438 +/- 10 nm) in the presence of adriamycin and daunomycin, indicating that the photodegradation of DNA in the presence of these drugs caused by hydroxyl radicals is mediated by dissolved oxygen.

Anthraquinones↗
PubMed1984

[The efficacy of gammaphos in whole-body irradiation during normal oxygenation and hypoxia].

The authors showed the absence of differences in the value of a protective effect of gammaphos at doses of 0.25 and 0.5 mM/kg (67 and 134 mg/kg) evaluated by the survival of mice irradiated in the air and while breathing a gaseous mixture containing 10% O2; the dose modifying factor (DMF) was 1.15 and approximately equal to 1.3, respectively. During irradiation of mice under conditions of normal oxygenation and while breathing hypoxic gaseous mixtures containing 10 and 8% O2 no differences were found in the level of an antiradiation effect of gammaphos at a dose of 1mM/kg (268 mg/kg); the DMF of gammaphos in all the cases was 1.6. During a short-term hard hypoxia (6.5% O2, DMF = 2.01), the protective effect of gammaphos is somewhat lower (DMF = 1.41) perhaps as a result of the modification limits in radiosensitivity because the DMF in the combination of both factors (gammaphos + 1 min. of 6.5% O2) equals 2.84. The DMF of gammaphos under the conditions of 20 min hypoxia (6.5% O2) producing a lesser radioprotective effect (DMF-1.48) equals 1.6, i. e. the value of the gammaphos protective effect in this case does not differ from that during irradiation of mice in the air. The data obtained lead to a conclusion of the independence of the value of the gammaphos protective effect on the level of the oxygenation of cells and tissues of irradiated objects.

Amifostine↗