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PubMed2002

Oxygen permeability of hydrogel contact lenses with organosilicon moieties.

Oxygen transport through two extended wear (day and night) hydrogel contact lenses that contain organosilicon moieties (balafilcon A and lotrafilcon A) was studied in the hydrate (hydrogel) and dry (xerogel) states. The water uptake increased the oxygen permeability [(Dk)app] and transmissibility [Dk/L(av)] coefficients of the dry materials by about 70%. The (Dk)app for the hydrated lenses was determined following the so-called stack procedure. The values obtained were 107 +/- 4 barrer for balafilcon A and 141 +/- 5 barrer for lotrafilcon A, about 5-10 times larger than those previously reported for conventional (without organosilicon moieties) extended wear hydrogels contact lenses. The Dk/L(av) for -3.00 diopter lenses (harmonic average thickness, L(av) = 75 +/- 2 microm for lotrafilcon, and 85 +/- 2 microm for balafilcon) was 123 +/- 6 barrer/cm for balafilcon A and 183 +/- 8 barrer/cm for lotralicon A. The minimum oxygen transmissibility 87 barrer/cm stipulated by Holden and Mertz to avoid corneal edema with extended wear contact can be easily achieved with lotrafilcon and balafilcon lenses of diverse dioptric powers if the central and peripheral thickness of the lenses are kept below the critical level of oxygen transmissibility.

Contact Lenses, Hydrophilic↗
PubMed2004

Poly(decyl methacrylate)-based fluorescent PEBBLE swarm nanosensors for measuring dissolved oxygen in biosamples.

150-250 nm Poly(decyl methacrylate)(PDMA) fluorescent ratiometric nanosensors for dissolved oxygen have been developed. Platinum octaethylporphine ketone (PtOEPK), the oxygen-sensitive dye, and octaethylporphyrin (OEP), the oxygen-insensitive dye, have been incorporated into PDMA nanoparticles to make the sensors ratiometric. Based on the corresponding Stern-Volmer plot, these nanosensors exhibit almost complete linearity over the whole range of dissolved molecular oxygen from 0 to 42.5 ppm (deoxygenated to pure oxygen-bubbled water). The overall quenching response is up to 97.5%, the best so far for all dissolved oxygen optical sensors. These PEBBLE nanosensors also show very good reversibility and stability to leaching and photobleaching, as well as very short response times and no perturbation by proteins. In human plasma they demonstrate a robust oxygen sensing capability, little affected by light scattering and autofluorescence. Potential applications include intracellular oxygen imaging and microresolved pressure profiles in biological and other heterogenous environments.

Fluorescent Dyes↗
PubMed1991

Theoretical studies on the mechanism of conversion of androgens to estrogens by aromatase.

Semiempirical molecular orbital calculations (AM1) were used to model several possible reaction mechanisms for the third oxidation of the aromatase-catalyzed conversion of androgens to estrogens. The reaction mechanisms considered are based on the assumption that the third oxidation is initiated by 1 beta-hydrogen atom abstraction. Homolytic cleavage of the C10-C19 bond was modeled for both the 3-keto and 2-en-3-ol forms of the androgen 1-radicals. The addition of a protein nucleophile to the 19-oxo intermediate was also considered, and -OCH3, -SCH3, and -NHCH3 were used to represent the Ser, Cys, and Lys adducts. The transition states were estimated and optimized from the reaction coordinates obtained by constraining and increasing the C10-C19 bond lengths. The enthalpies of activation range from 14 to 21 kcal and are approximately 2 kcal lower for cleavage of the enol form. Given the tendency for AM1 to overestimate activation energies, all reactions may be energetically accessible. Other reactions modeled include a homolytic cleavage reaction from a thioether radical cation and the direct additions of oxygen radical compounds to the carbonyl of the 1-radical-2-en-3-ol-19-oxo androgen. A mechanism is proposed in which the 19-oxo intermediate is subject to initial nucleophilic attack by the protein. Since rotation of the 19-carbonyl can bring the oxygen within 2.1 A of the 2 beta-hydrogen, the formation of a tetrahedral intermediate can occur with concomitant removal of the 2 beta-proton. Enolization activates the C1-position for hydrogen atom abstraction, since the resulting radical is resonance stabilized.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgens↗
PubMed2002

Proton-transfer dynamics in the activation of cytochrome P450eryF.

Molecular dynamics simulations are combined with quantum chemistry calculations of instantaneous proton-transfer energy profiles to investigate proton-transfer events in the transient pathway of cytochrome P450eryF (6-deoxyerythronolide B hydroxylase; CYP107A1), from the oxyferrous species to the catalytically active ferryl oxygen species (compound I). This reaction is one of the most fundamental unresolved aspects in the mechanism of oxidation that is common to all cytochrome P450s. We find that this process involves an ultrafast proton transfer from the crystallographic water molecule W519 to the distal oxygen bound to the heme group, and a subsequent proton-transfer event from W564 to W519. Both proton-transfer events are found to be endothermic in the oxyferrous state, suggesting that the oxyferrous reduction is mechanistically linked to the proton-transfer dynamics. These findings indicate that the hydrogen bond network, proximate to the O(2)-binding cleft, plays a crucial functional role in the enzymatic activation of P450s. Our results are consistent with the effect of mutations on the enzymatic efficacy.

Bacterial Proteins↗
PubMed1984

Effect of oxygen radical scavengers on K-cell cytolysis.

We have shown that the hydroxyl radical scavengers sodium benzoate, phenol, dimethyl sulfoxide, sodium formate, and mannitol protect chicken erythrocyte (Ec) target cells from lysis by K-cells in plaque assays. The protection afforded by benzoate, phenol, mannitol, and dimethyl sulfoxide was abrogated if the target cells were pretreated with sodium chromate. Neither superoxide dismutase nor catalase protected Ec target cells, indicating that superoxide and H2O2 are not involved in lysis. The lysis obtained on chromium-treated Ec target cells in the presence of benzoate, phenol, and mannitol is likely due to singlet oxygen, because 1,4-diazabicyclo[2.2.2]octane and bilirubin, singlet oxygen scavengers, protected chromium-treated Ec target cells in the presence of phenol. Ec target cells not treated with chromium were not protected by either of the singlet oxygen scavengers.

Adult↗
PubMed1997

MR imaging of renal function.

MR imaging has advantages over both computed tomography and nuclear scintigraphy for assessing renal function, because it combines high spatial resolution with information on perfusion and function. A further advantage is the lack of ionizing radiation. Quantitation of flow rate by phase contrast in the renal arteries and veins has the potential to provide estimation of renal blood flow, which could prove useful in a number of clinical situations, especially for studying renal vascular disorders and the effects of treatment, and for assessing renal transplants. Evaluation of renal perfusion with MR imaging has become feasible with the development of rapid data acquisition techniques, which provide adequate temporal resolution to monitor the rapid signal changes during the first passage of the contrast agents in the kidneys. More recently, magnetically labeling water protons in blood flowing into kidneys has been used to noninvasively quantitate regional measurement of cortical and medullary perfusion. Other techniques being investigated with MR imaging for assessment of renal function include diffusion imaging GFR estimation and blood oxygenation level dependent imaging to evaluate intrarenal oxygenation levels.

Animals↗
PubMedDate not supplied

[Effect of diethylene-triaminopentamethylphosphonic acid complex on various hematologic and biochemical indicators in experimental animals].

A successive triple introduction of organophosphorus complexon DTPP (sodium-dicalcium salt of diethylene-triaminopentamethylphosphonic acid) in a dose of 500 mg/kg to albino male rats did not produce any marked effect on the composition of the peripheral blood. Some shortening of the initial period in blood coagulation process was noted. DTPP produced a moderate stimulation of the iron-containing enzymes (catalase, peroxidase, cytochroxidase) which led to an increased oxygen consumption. The blood serum and urine potassium, sodium and calcium content did not undergo any significant changes, while the magnesium concentration in the blood serum dropped by 37 pc and in the urine rose by as much as twice as compared to controls. This bears evidence to an elevated discharge of magnesium from the organism following the action of the DTPP complexon.

Adenosine Triphosphatases↗
PubMed2006

Sulfide removal by moderate oxygenation of anaerobic sludge environments.

Introduction of a limited amount of oxygen to anaerobic bioreactors is proposed as a simple technique to lower the level of sulfide in the biogas. This paper presents the results of a bioreactor study and of batch experiments that were performed to obtain better insight into the fate of sulfur compounds and oxygen during micro-aerobic sulfide oxidation. Introduction of a low airflow (0.7-0.9 m(3)m(-3)d(-1), corresponding to an O(2)/S molar ratio of 8-10) to a fluidized bed reactor fed with low-sulfate vinasse was sufficient to reduce the biogas H(2)S-content to an undetectable level. Sulfide was initially oxidized to elemental sulfur, thiosulfate and - most probably - polysulfide. Significant sulfate production did not occur. Bioreactor sludge sampled from the reactor after three weeks' micro-aerobic operation was much faster in oxidizing sulfur than bioreactor sludge sampled during fully anaerobic reactor operation. The reaction proceeded faster with increasing O(2)/sulfide ratios.

Anaerobiosis↗
PubMed1993

Successful treatment of life-threatening propionitrile exposure with sodium nitrite/sodium thiosulfate followed by hyperbaric oxygen.

Propionitrile, a substituted aliphatic nitrile commonly used in the chemical manufacturing industry, is capable of generating cyanide. However, there are few reports of human intoxication involving propionitrile. We report two workers at an organic chemical manufacturing plant who were overcome by fumes while treating a waste slurry into which unreacted propionitrile was discharged by mistake. One victim was comatose, acidotic, and hypotensive; his blood cyanide level was later measured at 5.0 micrograms/ml. He responded to sodium nitrite/sodium thiosulfate therapy by regaining consciousness. Continued symptoms were treated with hyperbaric oxygen at 2 atmospheres for a total of 4 hours. The second victim, who complained only of nausea, dizziness, and headache and who never lost consciousness, was treated with sodium nitrite/sodium thiosulfate. His measured blood cyanide concentration was 3.5 micrograms/ml. The ambient concentration of propionitrile in air samples at the work site shortly after the exposure was 77.5 mg/m3. In occupational situations in which workers exhibit rapidly progressive symptoms of headache, dizziness, collapse, and coma, and where substituted nitriles are known to be on site, acute cyanide poisoning should be strongly considered. Because of continued endogenous generation of cyanide from the metabolism of the parent compound, hyperbaric oxygen may be a valuable adjunctive therapy to consider, in addition to the immediate use of the cyanide antidote kit, in cases of poisoning by propionitrile or other substituted nitrile compounds. We urge the Occupational Safety and Health Administration to adopt workplace standards for the maximum ambient air concentrations for propionitrile.

Adult↗
PubMed1987

Two beta-adrenergic pharmacophores on the same molecule. A set of agonist-antagonist combinations.

A series of compounds containing combinations of one or two pharmacophores of the agonist type (isoproterenol) or the antagonist type (propranolol or alprenolol) on the same molecule were prepared. The pharmacophores were connected by a derivative of polyethylene glycol with an average length of six atoms (carbon and oxygen). Furthermore, compounds containing two alprenolol residues, separated by chains of average lengths of 70 or 145 atoms, were synthesized. The abilities of these compounds to interact with beta-adrenoceptors of rat heart and lung tissues were examined by measuring the following parameters: competitive binding with [3H]dihydroalprenolol, activation of adenylate cyclase, and inhibition of isoproterenol-stimulated adenylate cyclase. The affinity of the compound with two isoproterenol pharmacophores for receptor was about the same as that with one isoproterenol pharmacophore and between 30 and 200 times weaker than that of (+/-)isoproterenol. Both mono- and bis-pharmacophore compounds partially stimulated catecholamine sensitive adenylate cyclase and at high concentrations inhibited the stimulation produced by (-)isoproterenol. The affinity of the compound with antagonist (propranolol) and agonist (isoproterenol) pharmacophores on the same molecule was intermediate between that of propranolol and isoproterenol. The compound was only able to inhibit adenylate cyclase activity. Compounds containing two antagonist (alprenolol) pharmacophores bound to receptors with affinities from an order of magnitude lower to about equal to that of the compound containing one pharmacophore. When membranes were preincubated with compounds containing two antagonist pharmacophores and then washed extensively, there were persistent effects of all of these compounds on the binding constants of [3H]dihydroalprenolol. All of these compounds were only able to inhibit adenylate cyclase activity and none exhibited any subtype selectivity at beta-adrenoceptors. The results suggest that, in the beta-adrenergic system, compounds with agonist and antagonist substituents on the same molecule exhibit properties of the substituent with the higher affinity for beta-adrenoceptor, and no agonist activity is evident when two antagonist pharmacophores are linked on the same molecule. All of the above results may be explained without recourse to cross-linking of beta-adrenoceptors with two pharmacophores, a phenomenon cited in similar studies of receptors for opiates and gonadotropin-releasing hormone.

Adrenergic beta-Agonists↗
PubMed1995

Photodissociation of a (mu-peroxo)(mu-hydroxo)bis[bis(bipyridyl)-cobalt(III)] complex: a tool to study fast biological reactions involving O2.

Upon photolysis at 355 nm, dioxygen is released from a (mu-peroxo)(mu-hydroxo)bis[bis(bipyridyl)cobalt-(III)] complex in aqueous solutions and at physiological pH with a quantum yield of 0.04. The [Co(bpy)2(H2O)2]2+ (bpy = bipyridyl) photoproduct was generated on a nanosecond or faster time scale as determined by time-resolved optical absorption spectroscopy. A linear correspondence between the spectral changes and the oxygen production indicates that O2 is released on the same time scale. Oxyhemoglobin was formed from deoxyhemoglobin upon photodissociation of the (mu-peroxo) (mu-hydroxo)bis[bis(bipyridyl)cobalt(III)] complex, verifying that dioxygen is a primary photoproduct. This complex and other related compounds provide a method to study fast biological reactions involving O2, such as the reduction of dioxygen to water by cytochrome oxidase.

Electron Spin Resonance Spectroscopy↗
PubMed1996

[Effect of efonidipine hydrochloride (NZ-105), a dihydropyridine derivative with calcium antagonistic action, on myocardial oxygen tension in anesthetized dogs].

Effect of efonidipine hydrochloride (efonidipine) on myocardial oxygen tension (PO2) was investigated in open-chest anesthetized dog and compared with those of nifedipine and nisoldipine. PO2 was measured by a membrane-coated platinum wire, which was inserted into the myocardium. Intravenous administration of efonidipine (10 and 30 micrograms/kg) decreased mean blood pressure to a similar extent to that induced by nifedipine (1 and 3 micrograms/kg) or nisoldipine (1 and 3 micrograms/kg). Efonidipine increased coronary blood flow (CBF) and decreased the double product (DP) dose-dependently. Similar results were observed in nisoldipine-treated animals. Nifedipine produced a transient increase in CBF and a transient decrease in DP. The duration of action of efonidipine on CBF was longer than that of nifedipine or nisoldipine. Efonidipine increased PO2, and the effect was more pronounced in the endocardial region than in the epicardial region. Nifedipine had no significant effect on the PO2, while nisoldipine significantly increased PO2 in the endocardial region. The effect of efonidipine on the PO2 was greater than that of nisoldipine and the duration of action of efonidipine was longer than that of nisoldipine. These results suggest that efonidipine may increase PO2 by mediating, at least in part, a long-lasting increase in oxygen supply and a decrease in oxygen demand in dog heart.

Animals↗
PubMed1995

Kinetics of nitrosation of thiols by nitric oxide in the presence of oxygen.

Nitrosothiols are powerful vasodilators. They act by releasing nitric oxide, which activates the heme protein guanylate cyclase. We have studied the kinetics of nitrosothiol formation of glutathione, cysteine, N-acetylcysteine, human serum albumin, and bovine serum albumin upon reaction with nitric oxide (NO) in the presence of oxygen. These studies have been made at low pH as well as at physiological pH. At pH 7.0, contrary to published reports, nitric oxide by itself does not react with thiols to yield nitrosothiol. However, formation of nitrosothiols is observed in the presence of oxygen. For all thiols studied, the rates of nitrosothiol formation were first order in O2 concentration and second order in NO concentration and at lower concentrations (< 5 mM thiol) also depended on thiol concentrations. Analysis of the kinetic data indicated that the rate-limiting step was the reaction of NO with oxygen. Analysis of the reaction products suggest that the main nitrosating species is N2O3: RSH+N2O3-->RSNO+NO2- + H+. Rate constants for this reaction for glutathione and several other low molecular weight thiols are in the range of 3-1.5 x 10(5) M-1 s-1, and for human and bovine serum albumins 0.3 x 10(5) M-1 s-1 and 0.06 x 10(5) M-1 s-1, respectively. The data further indicate that the reaction rate of the nitrosating species N2O3 with thiols is competitive with its rate of hydrolysis. At physiological concentrations nitrosoglutathione formation represents a significant metabolic fate of N2O3, and at glutathione concentrations of 5 mM or higher almost all of N2O3 formed is consumed in nitrosation of glutathione. Implications of these results for in vivo nitrosation of thiols are discussed.

Animals↗