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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The acidity and lipophilicity of the fluorinated arylalkylsulphonamides are determined by the nature of the substituents on their aromatic rings. Herbicidal and anti-inflammatory effects of these compounds appear to increase with their lipophilicity. According to Mitchell's chemiosmotic theory, lipophilic weak-acid uncoupling agents act by transporting protons across the inner mitochondrial membrane and thus destroying the proton-electrochemical potential gradient required for ATP synthesis and ion transport. 1:1:1-Trifluoro-N-[2-methyl-4-(phenylsulphonyl) phenyl]methanesulphonamide (Perfluidone), a pre- and post-emergence herbicide (at 20 microM concentration), in isolated rat-liver mitochondria caused (1) a 2-fold stimulation of metabolic state-4 respiration, (2) a reduction of respiratory control ratio (RCR) by at least 50%, (3) an enhancement of latent ATPase activity by 40%, (4) a significant passive swelling of mitochondria in 0.15 N NH4Cl(delta A520 = -0.46 +/- 0.003), (5) proton intrusion during state-4 respiration (356 ng H+/min/mg protein; ng H+/min/mg protein with 5 microM perfluidone), and (6) at least 100% stimulation of oligomycin-inhibited respiration. These profiles are qualitatively comparable with those of the classical lipophilic weak-acid uncoupler, carbonylcyanide-trifluoro-methoxyphenylene hydrazone (FCCP), which acts by promoting the electrogenic transport of H+ ions across mitochondrial membrane.
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PMID:Protonophoric properties of fluorinated arylalkylsulfonamides. Observations with perfluidone. 299 24

The protonophoric activity through liposomal membranes was measured and compared with the uncoupling activity with the oxidative phosphorylation of rat-liver mitochondria for 19 substituted phenols. Quantitative analyses of the protonophoric activity of the phenols in terms of physicochemical molecular parameters showed that the activity was mostly decided by two factors: the partition coefficient between the liposome and aqueous buffer phases and the acid dissociation constant. Correlation was excellent between protonophoric and uncoupling activities when the difference in the effect of acidity of phenols between liposomal and mitochondrial membranes was taken into account. The results were further evidence for the shuttle-type of mechanism of weakly acidic uncouplers based on the Mitchell chemiosmotic hypothesis.
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PMID:Quantitative relationship between protonophoric and uncoupling activities of substituted phenols. 382 29

It is shown that neither the set of directly determined blood-brain concentration ratios (BB) of Young and Mitchell nor the set of indirectly obtained values of Abraham and Weathersby are suitable for the construction of a general equation for the interpretation and prediction of log BB values. However, combination of both sets leads to the general equation log BB = -0.038 + 0.198R2 - 0.687 pi H2 - 0.715 alpha H2 - 0.698 beta H2 + 0.995Vx (n = 57, rho = 0.9522, sd = 0.197, F = 99.2), where the solute descriptors are R2, an excess molar refraction; pi H2, the dipolarity/polarizability, alpha H2 and beta H2, the effective or summation hydrogen-bond acidity and basicity; and Vx, the characteristic volume of McGowan. Thus solute dipolarity/polarizability, hydrogen-bond acidity, and hydrogen-bond basicity favor blood, and solute size, as Vx, favors brain. Methods are given for the estimation of solute descriptors through fragment schemes, so that log BB values themselves may be obtained simply from knowledge of solute molecular structure.
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PMID:Hydrogen bonding. 33. Factors that influence the distribution of solutes between blood and brain. 783 Feb 42

It is shown that the octanol-water partition coefficient (Poct) cannot be used to predict blood brain distribution (BB) rectilinearly, but can be combined with Abraham solute descriptors to yield a predictive regression equation, eq (15), in which the solute descriptors sigma alpha H2 and sigma beta H2 are the overall summation hydrogen-bond acidity and basicity respectively. It is also demonstrated that of the various predictive models now available, that of Abraham, Chadha and Mitchell, eq (14), still yields the best results on a new test set of drug molecules; where the other solute descriptors are: R2, an excess molar refraction; pi H2, the dipolarity/polarisability; and Vx the characteristic volume of McGowan. Thus, solute dipolarity/polarizability, hydrogen-bond acidity and hydrogen-bond basicity favour blood, and solute size favours brain. logBB = +0.055 + 0.203logPoct - 0.507 sigma alpha H2 - 0.500 sigma beta H2 n = 49 rho = 0.9491 sd = 0.201 F = 136.1 (15) logBB = -0.038 + 0.198R2 - 0.607 pi H2 - 0.715 alpha H2 - 0.698 beta H2 + 0.995Vx n = 57 rho = 0.9522 sd = 0.197 F = 99.2 (14)
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PMID:Hydrogen-bonding. Part 36. Determination of blood brain distribution using octanol-water partition coefficients. 887 56

On the basis of the earlier proposed model of electron transport, which takes into account the Mitchell Q-cycle, stationary values for the fluxes of electrons Je along the electron transport chain and of protons JH across the thylakoid membrane were obtained, which are calculated now as the functions of photoexcitation of reaction centers and the medium acidity inside and outside of the thylakoid, pHin and pHout. In the framework of the model, the stoichiometric ratio JH/Je is determined virtually only by the time of reduction of plastoquinone (tau B) on the B site of photosystem II and restoration of plastoquinone (tau C) on the C site to the b/f complex.
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PMID:[A model of electron transport in chloroplasts taking into account the Mitchell Q-cycle. Calculation of J(e) and J(H) fluxes in steady state]. 1206 5

The physical and chemical climatology of high elevation (> 1500 m) spruce-fir forests in the southern Appalachian mountains was studied by establishing a weather and atmospheric chemical observatory at Mt Mitchell State Park in North Carolina (35 degrees 44' 05" N, 82 degrees 17' 15"W). Data collected during the summer and autumn (May-October) of 1986, 1987, and 1988 are reported. All measurements were made on or near a 16.5 m walk-up tower extending 10 m above the forest canopy on Mt Gibbes (2006 m msl), which is located approximately 2 km SW of Mt Mitchell. The tower was equipped with standard meteorological instrumentation, a passive cloud water collector, and gas pollutant sensors for O3, SO2, NOx. The tower and nearby forest canopy were immersed in clouds 25 to 40% of the time. Non-precipitating clouds were very acidic (pH 2.5-4.5). Precipitating clouds were less acidic (pH 3.5-5.5). The dominant wind directions were WNW and ESE. Clouds from the most common wind direction (WNW) were more acidic (mean pH 3.5) than those from the next most common wind direction (ESE, mean pH 5.5). Cloud water acidity was related to the concentration of SO4(2-), and NO3- ions. Mean concentration of H+, NH4+, SO4(2-), and NO3- ions in the cloud water varied from 330-340, 150-200, 190-200 and 120-140 micromol litre(-1) respectively. The average and range of O3 were 50 (25-100) ppbv (109) in 1986, 51 (26-102) ppbv in 1987, and 66 (30-140) during the 1988 field seasons, respectively. The daily maximum, 1-h average, and 24-h average concentrations were all greatest during June through mid-August, suggesting a correlation with the seasonal temperature and solar intensity. Throughfall collectors near the tower were used to obtain a useful estimate of deposition to the forest canopy. Between 50-60% of the total deposition of SO4(2-) was due to cloud impact.
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PMID:Chemical climatology of high elevation spruce-fir forests in the southern Appalachian mountains. 1509 54