R. Bisby, Steven A. Johnson, A. Parker, S. Tavender
The literature contains conflicting evidence regarding the protonation state of the carbonate radical, a species which now appears to be of biological significance. The time-resolved resonance Raman spectrum of CO3- has been observed. The radical was produced by oxidation of bicarbonate and carbonate using sulfate radicals at pH values from 7.5 to 12.3. The resonance Raman spectrum was found to be invariant with pH and contains a strongly polarised and intense band at 1062 cm-1. The spectrum is consistent with the radical having C2v symmetry, indicating some distortion from the predicted D3h structure. The data suggest that the carbonate radical (CO3-) formed by one-electron oxidation of bicarbonate and carbonate does not undergo protonation to the conjugate acid, HCO3, as previously suggested with a pKa of 9.6. Some biochemical consequences of this are discussed.
{"title":"Time-resolved resonance Raman spectroscopy of the carbonate radical","authors":"R. Bisby, Steven A. Johnson, A. Parker, S. Tavender","doi":"10.1039/A801239C","DOIUrl":"https://doi.org/10.1039/A801239C","url":null,"abstract":"The literature contains conflicting evidence regarding the protonation state of the carbonate radical, a species which now appears to be of biological significance. The time-resolved resonance Raman spectrum of CO3- has been observed. The radical was produced by oxidation of bicarbonate and carbonate using sulfate radicals at pH values from 7.5 to 12.3. The resonance Raman spectrum was found to be invariant with pH and contains a strongly polarised and intense band at 1062 cm-1. The spectrum is consistent with the radical having C2v symmetry, indicating some distortion from the predicted D3h structure. The data suggest that the carbonate radical (CO3-) formed by one-electron oxidation of bicarbonate and carbonate does not undergo protonation to the conjugate acid, HCO3, as previously suggested with a pKa of 9.6. Some biochemical consequences of this are discussed.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"76 1","pages":"2069-2072"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86546748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The temperature dependence of the excess heat capacity and evaluation of thermodynamic parameters of bovine α-lactalbumin has been studied by high-sensitivity micro differential scanning calorimetry in the presence of 4-chlorobutan-1-ol, n-butanol, 3-chloropropan-1-ol, 3-chloropropan-1,2-diol, propan-1,2-diol, n-propanol, 2,2,2-trifluoroethanol, and ethanol at neutral pH. The chlorosubstituted alcohols are observed to be more effective destabilisers of α-lactalbumin compared with their normal alcohols in the order: 4-chlorobutan-1-ol > n-butanol > 3-chloropropan-1-ol > n-propanol > 2,2,2-trifluoroethanol > 3-chloropropan-1,2-diol > ethanol > propan-1,2-diol. A reversible two-state approximation for the unfolding of the protein has been shown in the absence and presence of these alcohols. A second, smaller, endothermic transition, 23°C beyond the main endotherm was observed only in the presence of 0.125 to 0.250 mol dm-3 3-chloropropan-1-ol. Concentrations higher than 25 mmol dm-3 4-chlorobutan-1-ol resulted in total loss of an observable endotherm. Thermal destabilisation of the protein in these solvent systems is explained on the basis of competing patterns of interactions of the cosolutes with the native versus unfolded states of the protein during the nativedenatured reaction. These results are supported by intrinsic fluorescence, energy transfer and UV difference measurements.
{"title":"Thermodynamics of the interaction of some chloro- and fluoro-substituted alcohols with bovine α-lactalbumin","authors":"N. Kishore, B. Sabulal","doi":"10.1039/A708066B","DOIUrl":"https://doi.org/10.1039/A708066B","url":null,"abstract":"The temperature dependence of the excess heat capacity and evaluation of thermodynamic parameters of bovine α-lactalbumin has been studied by high-sensitivity micro differential scanning calorimetry in the presence of 4-chlorobutan-1-ol, n-butanol, 3-chloropropan-1-ol, 3-chloropropan-1,2-diol, propan-1,2-diol, n-propanol, 2,2,2-trifluoroethanol, and ethanol at neutral pH. The chlorosubstituted alcohols are observed to be more effective destabilisers of α-lactalbumin compared with their normal alcohols in the order: 4-chlorobutan-1-ol > n-butanol > 3-chloropropan-1-ol > n-propanol > 2,2,2-trifluoroethanol > 3-chloropropan-1,2-diol > ethanol > propan-1,2-diol. A reversible two-state approximation for the unfolding of the protein has been shown in the absence and presence of these alcohols. A second, smaller, endothermic transition, 23°C beyond the main endotherm was observed only in the presence of 0.125 to 0.250 mol dm-3 3-chloropropan-1-ol. Concentrations higher than 25 mmol dm-3 4-chlorobutan-1-ol resulted in total loss of an observable endotherm. Thermal destabilisation of the protein in these solvent systems is explained on the basis of competing patterns of interactions of the cosolutes with the native versus unfolded states of the protein during the nativedenatured reaction. These results are supported by intrinsic fluorescence, energy transfer and UV difference measurements.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"15 1","pages":"905-911"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87593238","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The substrate-generation–tip-collection (SG–TC) mode of the scanning electrochemical microscope (SECM) is used as a new approach to investigate the kinetics of EC processes. Under the conditions of interest, a species O is generated at a macroscopic substrate (generator) electrode, with potential-step control, through the diffusion-limited electrolysis of a solution species R (E step). As O diffuses away from the generator, it undergoes a first order chemical reaction in solution (C step). A fraction of O is collected by electrolysis back to R at an externally biased ultramicroelectrode (UME), positioned directly over the substrate. This promotes the diffusional feedback of R to the substrate. Theory for the problem, relating the time-dependent tip current response to the rate constant for the C step and the tip–substrate electrode separation is developed numerically. Results of the calculations illustrate how the characteristic features of the tip current transients: peak current, peak time and post-half-peak time, depend on the kinetics of the C step and the inter-electrode separation. It is shown that both the kinetics and tip–substrate separation can be determined independently from a single transient by simply measuring the peak current and peak time. The theoretical results are validated experimentally through model studies of the oxidative deamination of N,N,-dimethyl-p-phenylenediamine (DMPPD) in aqueous solution at high pH. The effective second-order rate constant for the deamination step is in excellent agreement with values measured by alternative methods.
{"title":"Scanning electrochemical microscopy Kinetics of chemical reactions following electron-transfer measured with the substrate-generation–tip-collection mode","authors":"Rachel D. Martin, P. Unwin","doi":"10.1039/A707984B","DOIUrl":"https://doi.org/10.1039/A707984B","url":null,"abstract":"The substrate-generation–tip-collection (SG–TC) mode of the scanning electrochemical microscope (SECM) is used as a new approach to investigate the kinetics of EC processes. Under the conditions of interest, a species O is generated at a macroscopic substrate (generator) electrode, with potential-step control, through the diffusion-limited electrolysis of a solution species R (E step). As O diffuses away from the generator, it undergoes a first order chemical reaction in solution (C step). A fraction of O is collected by electrolysis back to R at an externally biased ultramicroelectrode (UME), positioned directly over the substrate. This promotes the diffusional feedback of R to the substrate. Theory for the problem, relating the time-dependent tip current response to the rate constant for the C step and the tip–substrate electrode separation is developed numerically. Results of the calculations illustrate how the characteristic features of the tip current transients: peak current, peak time and post-half-peak time, depend on the kinetics of the C step and the inter-electrode separation. It is shown that both the kinetics and tip–substrate separation can be determined independently from a single transient by simply measuring the peak current and peak time. The theoretical results are validated experimentally through model studies of the oxidative deamination of N,N,-dimethyl-p-phenylenediamine (DMPPD) in aqueous solution at high pH. The effective second-order rate constant for the deamination step is in excellent agreement with values measured by alternative methods.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"7 1","pages":"753-759"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87790456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Kuo, C. Chiang, Jenwei Yu, K. Peck, Ta-Chau Chang
The satellite holes in hole burned (HB) spectra have been used to study the binding modes of chromophore–oligonucleotide interactions. Substantial differences of several distinct satellite holes of 4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-propionic acid, succinimidyl ester (BODIPY591) chemically bound to an oligonucleotide of ten bases ofthymidine deoxyribonucleotides, d(T10), doped in glycerol–water (Gl–H2O) glass are observed. Normal mode calculations fordipyrrometheneboron difluoride (BODIPY) and an HB study of the BODIPY591 derivative have been conducted to help with vibrational mode assignments. The lack of appreciable perturbations on the vibrations of the diene chain and the phenyl group implies that these groups are much less perturbed upon interacting with d(T10). However, significant frequency differences for several N2BF2 modes indicate that the geometry of the N2BF2 moiety is dramatically perturbed upon interacting with d(T10). Our results suggest that the central ring of the BODIPY moiety is the main binding site and the electrostatic interaction between the BF2 group of BODIPY591 and the NH group of d(T10), as well as the stacking of the aromatic rings between BODIPY and thymine, are the most probable binding mechanisms.
{"title":"Satellite hole investigation of binding mechanism of dipyrrometheneboron difluoride derivative and oligonucleotide in glycerol–water glass","authors":"C. Kuo, C. Chiang, Jenwei Yu, K. Peck, Ta-Chau Chang","doi":"10.1039/A800325D","DOIUrl":"https://doi.org/10.1039/A800325D","url":null,"abstract":"The satellite holes in hole burned (HB) spectra have been used to study the binding modes of chromophore–oligonucleotide interactions. Substantial differences of several distinct satellite holes of 4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-propionic acid, succinimidyl ester (BODIPY591) chemically bound to an oligonucleotide of ten bases ofthymidine deoxyribonucleotides, d(T10), doped in glycerol–water (Gl–H2O) glass are observed. Normal mode calculations fordipyrrometheneboron difluoride (BODIPY) and an HB study of the BODIPY591 derivative have been conducted to help with vibrational mode assignments. The lack of appreciable perturbations on the vibrations of the diene chain and the phenyl group implies that these groups are much less perturbed upon interacting with d(T10). However, significant frequency differences for several N2BF2 modes indicate that the geometry of the N2BF2 moiety is dramatically perturbed upon interacting with d(T10). Our results suggest that the central ring of the BODIPY moiety is the main binding site and the electrostatic interaction between the BF2 group of BODIPY591 and the NH group of d(T10), as well as the stacking of the aromatic rings between BODIPY and thymine, are the most probable binding mechanisms.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"85 1","pages":"1989-1994"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87404247","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kinetics and equilibria in aqueous 1:1 chelation of iron(III) by 2-acetylcyclohexanone have been investigated spectrophotometrically in aqueous solution at 25°C and 0.5 mol dm-3 NaClO4. In conjunction with earlier work, the results suggest that the deprotonation rate of the keto tautomer of 2-acetylcyclohexanone has a minimum value when compared with 1,3-dicarbonylic ligands of similar structure. The mechanism proposed to account for the kinetic data involves pathways in which both Fe3+ and Fe(OH)2+ react with the enol tautomer of the ligand. The relative rates of complex formation are shown to depend not only on the metal species involved but also on ligand structure factors such as steric hindrances, ring strain and intramolecular hydrogen bonding.
{"title":"Rate constants and equilibria of monochelate formation of iron(III) with 2-acetylcyclohexanone","authors":"C. Blanco, Antonio Rojas","doi":"10.1039/A800521D","DOIUrl":"https://doi.org/10.1039/A800521D","url":null,"abstract":"Kinetics and equilibria in aqueous 1:1 chelation of iron(III) by 2-acetylcyclohexanone have been investigated spectrophotometrically in aqueous solution at 25°C and 0.5 mol dm-3 NaClO4. In conjunction with earlier work, the results suggest that the deprotonation rate of the keto tautomer of 2-acetylcyclohexanone has a minimum value when compared with 1,3-dicarbonylic ligands of similar structure. The mechanism proposed to account for the kinetic data involves pathways in which both Fe3+ and Fe(OH)2+ react with the enol tautomer of the ligand. The relative rates of complex formation are shown to depend not only on the metal species involved but also on ligand structure factors such as steric hindrances, ring strain and intramolecular hydrogen bonding.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"61 1","pages":"1447-1450"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88303449","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
It has been demonstrated experimentally that the focusing effect can appear in a multicomponent (polydisperse in size) colloidal particle dispersion at sedimentation equilibrium. Consequently, an equilibrium concentration distribution of sedimenting colloidal particles of different sizes cannot be a simple convolution (or superposition) of the corresponding distributions of uniform size components of the dispersion. Although an extensive theoretical approach considering the microscopic scale interactions of the molecules or colloidal particles of the complex, gradient forming, liquid is needed to elucidate the macroscopically observed phenomena, the experimental results, reproduced several times, prove incontrovertibly the emergence of isoperichoric focusing (which is the more accurate term, compared with isopycnic focusing, describing the observed phenomena).
{"title":"Emergence of isoperichoric focusing in multicomponent colloidal particle dispersion at sedimentation equilibrium","authors":"J. Janča, N. Caron, N. Gospodinova","doi":"10.1039/A804997A","DOIUrl":"https://doi.org/10.1039/A804997A","url":null,"abstract":"It has been demonstrated experimentally that the focusing effect can appear in a multicomponent (polydisperse in size) colloidal particle dispersion at sedimentation equilibrium. Consequently, an equilibrium concentration distribution of sedimenting colloidal particles of different sizes cannot be a simple convolution (or superposition) of the corresponding distributions of uniform size components of the dispersion. Although an extensive theoretical approach considering the microscopic scale interactions of the molecules or colloidal particles of the complex, gradient forming, liquid is needed to elucidate the macroscopically observed phenomena, the experimental results, reproduced several times, prove incontrovertibly the emergence of isoperichoric focusing (which is the more accurate term, compared with isopycnic focusing, describing the observed phenomena).","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"45 1","pages":"2961-2964"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89069969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Paduano, R. Sartorio, G. D’Errico, V. Vitagliano
Mutual diffusion coefficients have been measured, at 25 °C, for binary systems of some ethylene glycol oligomers in aqueous solution over the whole mole fraction range. The results have been combined with activity and intradiffusion data to calculate the velocity cross-correlation coefficients (VCCs). An attempt has been made to explain the results in terms of molecular interactions.
{"title":"Mutual diffusion in aqueous solution of ethylene glycol oligomers at 25 °C","authors":"L. Paduano, R. Sartorio, G. D’Errico, V. Vitagliano","doi":"10.1039/A803567I","DOIUrl":"https://doi.org/10.1039/A803567I","url":null,"abstract":"Mutual diffusion coefficients have been measured, at 25 °C, for binary systems of some ethylene glycol oligomers in aqueous solution over the whole mole fraction range. The results have been combined with activity and intradiffusion data to calculate the velocity cross-correlation coefficients (VCCs). An attempt has been made to explain the results in terms of molecular interactions.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"1 1","pages":"2571-2576"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83467205","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Encapsulated vanadium picolinic complexes have been synthesized by treatment of a dehydrated form of VO2+-NaY zeolite with molten picolinic acids and characterized by X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), EPR, FTIR and UV–VIS spectroscopies, and XRD. It was suggested by XRD and XPS that the complexes were located in the zeolite cavities. Differences in the spectroscopic properties of encapsulated and impregnated samples were explained in terms of coordination of vanadium complexes with zeolite –OH groups. The stability of VO(pic)2 and its adduct with pyridine depended strongly on the complex location. The encapsulated vanadium picolinate complex retained solution-like activity in the liquid-phase oxidation of hydrocarbons and alcohols with hydrogen peroxide.
{"title":"Vanadium(IV) complexes with picolinic acids in NaY zeolite cages Synthesis, characterization and catalytic behaviour","authors":"A. I. Kozlov, K. Asakura, Y. Iwasawa","doi":"10.1039/A706679A","DOIUrl":"https://doi.org/10.1039/A706679A","url":null,"abstract":"Encapsulated vanadium picolinic complexes have been synthesized by treatment of a dehydrated form of VO2+-NaY zeolite with molten picolinic acids and characterized by X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), EPR, FTIR and UV–VIS spectroscopies, and XRD. It was suggested by XRD and XPS that the complexes were located in the zeolite cavities. Differences in the spectroscopic properties of encapsulated and impregnated samples were explained in terms of coordination of vanadium complexes with zeolite –OH groups. The stability of VO(pic)2 and its adduct with pyridine depended strongly on the complex location. The encapsulated vanadium picolinate complex retained solution-like activity in the liquid-phase oxidation of hydrocarbons and alcohols with hydrogen peroxide.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"37 1","pages":"809-816"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79159438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ryōji Takahashi, Shoichi Takenaka, S. Sato, T. Sodesawa, K. Ogura, K. Nakanishi
A mesoporous titania was prepared from titanium tetraisopropoxide and stearic acid (STA). The pore size of the titania increases linearly from ca. 5 to 15 nm with increase in the STA/Ti ratio (X) for X 1.5. A mol equivalent of STA coordinates with Ti atom forming a bidentate carboxy group and excess STA forms propyl stearate. Upon calcination, the propyl stearate is removed at a lower temperature by vaporization, and does not affect the pore structure of the titania. The Ti–STA precursor has the layered structure of the Ti–STA complex, whose interplanar distance increases with increasing STA content, while the mesoporous titania is composed of aggregates of crystallites of anatase. During calcination of the precursor, decomposition of the complex and crystallization of anatase occur concurrently. The crystallization process is considered to be affected by the interplanar distance of the layered structure in the precursor, so that both the pore size and the pore volume increase with increase in the STA/Ti ratio.
{"title":"Structural study of mesoporous titania and titanium–stearic acid complex prepared from titanium alkoxide","authors":"Ryōji Takahashi, Shoichi Takenaka, S. Sato, T. Sodesawa, K. Ogura, K. Nakanishi","doi":"10.1039/A804984J","DOIUrl":"https://doi.org/10.1039/A804984J","url":null,"abstract":"A mesoporous titania was prepared from titanium tetraisopropoxide and stearic acid (STA). The pore size of the titania increases linearly from ca. 5 to 15 nm with increase in the STA/Ti ratio (X) for X 1.5. A mol equivalent of STA coordinates with Ti atom forming a bidentate carboxy group and excess STA forms propyl stearate. Upon calcination, the propyl stearate is removed at a lower temperature by vaporization, and does not affect the pore structure of the titania. The Ti–STA precursor has the layered structure of the Ti–STA complex, whose interplanar distance increases with increasing STA content, while the mesoporous titania is composed of aggregates of crystallites of anatase. During calcination of the precursor, decomposition of the complex and crystallization of anatase occur concurrently. The crystallization process is considered to be affected by the interplanar distance of the layered structure in the precursor, so that both the pore size and the pore volume increase with increase in the STA/Ti ratio.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"88 1 1","pages":"3161-3168"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83926072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A Taylor dispersion tube has been used to measure binary mutual diffusion in aqueous solutions of partially dissociated maleic acid (H2MH++HM-). The diffusion coefficients of the molecular acid and the hydrogen maleate ion are estimated from the results. To investigate the effects of added salt on the transport of a weak electrolyte, quaternary mutual diffusion coefficients are reported for aqueous maleic acid+NaCl solutions. The cross-diffusion coefficients for this system indicate that the gradient in maleic acid drives large coupled flows of NaCl and HCl components. Nernst–Planck equations are used to interpret these results. The analysis shows that the addition of NaCl leads to a dramatic increase in the rate of diffusion of H+ ions because they are no longer required to diffuse at the same speed as the less-mobile HM- ions to maintain electroneutrality. Also, the electric field generated by the diffusing acid drives a large counter-current coupled flow of Na+ ions and a large co-current coupled flow of Cl- ions. Each mole of diffusing maleic acid co-transports up to 5 mol HCl and counter-transports up to 1.5 mol NaCl. The results for the aqueous maleic acid+NaCl solutions provide a guide to the diffusion behaviour of the environmentally important SO2+seawater system.
{"title":"Diffusion of weak acids in salt solutions Maleic acid+NaCl+water","authors":"S. Wright, D. G. Leaist","doi":"10.1039/A800424B","DOIUrl":"https://doi.org/10.1039/A800424B","url":null,"abstract":"A Taylor dispersion tube has been used to measure binary mutual diffusion in aqueous solutions of partially dissociated maleic acid (H2MH++HM-). The diffusion coefficients of the molecular acid and the hydrogen maleate ion are estimated from the results. To investigate the effects of added salt on the transport of a weak electrolyte, quaternary mutual diffusion coefficients are reported for aqueous maleic acid+NaCl solutions. The cross-diffusion coefficients for this system indicate that the gradient in maleic acid drives large coupled flows of NaCl and HCl components. Nernst–Planck equations are used to interpret these results. The analysis shows that the addition of NaCl leads to a dramatic increase in the rate of diffusion of H+ ions because they are no longer required to diffuse at the same speed as the less-mobile HM- ions to maintain electroneutrality. Also, the electric field generated by the diffusing acid drives a large counter-current coupled flow of Na+ ions and a large co-current coupled flow of Cl- ions. Each mole of diffusing maleic acid co-transports up to 5 mol HCl and counter-transports up to 1.5 mol NaCl. The results for the aqueous maleic acid+NaCl solutions provide a guide to the diffusion behaviour of the environmentally important SO2+seawater system.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"37 1","pages":"1457-1463"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86161292","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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