The reaction of OH radical with cis- and trans-HONO has been investigated by ab initio molecular orbital and variational transition-state theory calculations. The overall mechanism has been elucidated and found to be quite complex. The bimolecular rate constants for the major reaction paths have been calculated and compared with existing, conflicting kinetic data. The total rate constant for the production of H2O and NO2 was concluded to have noticeable negative temperature dependence below 1000 K. The following two expressions are recommended for atmosphere and combustion modeling applications: k1 = 4.12 x 1012 (T/300)-0.8 cm3 mol-1 s-1, 200-500 K; k1 = 1.77 x 107T1.5 exp [+1260/T] cm3 mol-1 s-1, 500-2000 K. The predicted rate constant for the low-temperature regime agrees quantitatively with the result of Burkholder et al. (Int. J. Chem. Kinet., 1992, 24, 711) measured at 298 < T < 373 K
{"title":"Ab initio MO/statistical theory prediction of the OH + HONO reaction rate: evidence for the negative temperature dependence","authors":"W. Xia, M. Lin","doi":"10.1039/B007803O","DOIUrl":"https://doi.org/10.1039/B007803O","url":null,"abstract":"The reaction of OH radical with cis- and trans-HONO has been investigated by ab initio molecular orbital and variational transition-state theory calculations. The overall mechanism has been elucidated and found to be quite complex. The bimolecular rate constants for the major reaction paths have been calculated and compared with existing, conflicting kinetic data. The total rate constant for the production of H2O and NO2 was concluded to have noticeable negative temperature dependence below 1000 K. The following two expressions are recommended for atmosphere and combustion modeling applications: k1 = 4.12 x 1012 (T/300)-0.8 cm3 mol-1 s-1, 200-500 K; k1 = 1.77 x 107T1.5 exp [+1260/T] cm3 mol-1 s-1, 500-2000 K. The predicted rate constant for the low-temperature regime agrees quantitatively with the result of Burkholder et al. (Int. J. Chem. Kinet., 1992, 24, 711) measured at 298 < T < 373 K","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"49 1","pages":"71-78"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84100055","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 complexation of various 'normal' tetracyclines and anhydrotetracycline with Mg2+ and Ca2+ was investigated under physiological conditions (aqueous Tris buffer at pH 7.0 and 8.5) by spectrometric titration. The generated sets of UV-Vis absorption and fluorescence spectra were analysed by two techniques, namely (i) classical evaluation which relies on the occurrence of isosbestic points and (ii) multivariate fitting employing the program Specfit. The latter yields not only the conditional binding constants, but also, for each tested kinetic scheme, the absorption or emission spectra of the individual metal?tetracycline complexes. It was found that absolute values of binding constants and deduced spectra are in all cases in favour of a consecutive metal ion complexation yielding 1 : 1 and 2 : 1 metal?tetracycline ion complexes
{"title":"Spectroscopic investigation of complexation between various tetracyclines and Mg2+ or Ca2+","authors":"M. Schmitt, S. Schneider","doi":"10.1039/B005722N","DOIUrl":"https://doi.org/10.1039/B005722N","url":null,"abstract":"The complexation of various 'normal' tetracyclines and anhydrotetracycline with Mg2+ and Ca2+ was investigated under physiological conditions (aqueous Tris buffer at pH 7.0 and 8.5) by spectrometric titration. The generated sets of UV-Vis absorption and fluorescence spectra were analysed by two techniques, namely (i) classical evaluation which relies on the occurrence of isosbestic points and (ii) multivariate fitting employing the program Specfit. The latter yields not only the conditional binding constants, but also, for each tested kinetic scheme, the absorption or emission spectra of the individual metal?tetracycline complexes. It was found that absolute values of binding constants and deduced spectra are in all cases in favour of a consecutive metal ion complexation yielding 1 : 1 and 2 : 1 metal?tetracycline ion complexes","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"29 1","pages":"42-55"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73204484","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}
Two models have recently been proposed to explain the electrokinetic properties of surfaces with electrostatically deposited particles (R. A. Hayes, Colloids Surf., A, 1999, 146, 89, and M. Zembala and Z. Adamczyk, Langmuir, 2000, 16, 1593). However, supporting experimental data is sparse. In this study, the effects of particle size, particle coverage and ionic strength on the electrokinetic behaviour of positively charged surfaces with negatively charged particles deposited were investigated by streaming current measurements. Results confirm that deposition of oppositely charged particles decreases the magnitude of the zeta potential of the underlying surface. Reversal of the zeta potential was observed at all particle sizes with larger particles reversing the potential at lower coverages. The results presented are fitted to the respective models, and the relative merits of each are discussed
最近提出了两个模型来解释静电沉积颗粒表面的电动力学性质(R. A. Hayes, Colloids Surf)。M. Zembala和Z. Adamczyk, Langmuir, 2000,16, 1593)。然而，支持实验数据是稀疏的。在本研究中，通过流电流测量研究了颗粒大小、颗粒覆盖率和离子强度对沉积有负电荷颗粒的正电荷表面的电动力学行为的影响。结果证实，相反带电粒子的沉积降低了下垫面zeta电位的大小。在所有粒径的粒子上都观察到zeta电位的逆转，较大的粒子在较低的覆盖率下逆转电位。将所得结果拟合到各自的模型中，并讨论了每种模型的相对优点
{"title":"The effect of deposition of negatively charged particles on the electrokinetic behaviour of oppositely charged surfaces","authors":"A. Michelmore, R. Hayes","doi":"10.1039/B001277G","DOIUrl":"https://doi.org/10.1039/B001277G","url":null,"abstract":"Two models have recently been proposed to explain the electrokinetic properties of surfaces with electrostatically deposited particles (R. A. Hayes, Colloids Surf., A, 1999, 146, 89, and M. Zembala and Z. Adamczyk, Langmuir, 2000, 16, 1593). However, supporting experimental data is sparse. In this study, the effects of particle size, particle coverage and ionic strength on the electrokinetic behaviour of positively charged surfaces with negatively charged particles deposited were investigated by streaming current measurements. Results confirm that deposition of oppositely charged particles decreases the magnitude of the zeta potential of the underlying surface. Reversal of the zeta potential was observed at all particle sizes with larger particles reversing the potential at lower coverages. The results presented are fitted to the respective models, and the relative merits of each are discussed","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"113 1","pages":"24-28"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86426413","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. Frumin, S. Peltek, S. Bukshpan, V. V. Chasovskikh, G. Zilberstein
A strong drift velocity non-linearity of the (doublestranded) DNA molecules vs. the electric field was discovered in gel electrophoresis. The non-linear drift velocity of the longer molecules is higher than that of the short ones, depending on the molecular size in a complex fashion. This behavior contrasts with that of the ordinary, linear, drift velocity where short molecules move faster than the long ones. The molecular size dependence of the non-linear velocity or the non-linear mobility has a non-monotonous wave-like character. The non-linear mobility offers possibilities of manipulating the drift velocity at will?the DNA fragments of different size can be made to move in opposite directions in pulsed field gel electrophoresis
{"title":"Anomalous size dependence of the non-linear mobility of DNA","authors":"L. Frumin, S. Peltek, S. Bukshpan, V. V. Chasovskikh, G. Zilberstein","doi":"10.1039/B007756I","DOIUrl":"https://doi.org/10.1039/B007756I","url":null,"abstract":"A strong drift velocity non-linearity of the (doublestranded) DNA molecules vs. the electric field was discovered in gel electrophoresis. The non-linear drift velocity of the longer molecules is higher than that of the short ones, depending on the molecular size in a complex fashion. This behavior contrasts with that of the ordinary, linear, drift velocity where short molecules move faster than the long ones. The molecular size dependence of the non-linear velocity or the non-linear mobility has a non-monotonous wave-like character. The non-linear mobility offers possibilities of manipulating the drift velocity at will?the DNA fragments of different size can be made to move in opposite directions in pulsed field gel electrophoresis","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"72 1","pages":"61-63"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84330956","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}
Re-oxidation of reduced oxide surfaces is a fundamental step in catalysis and related fields. This paper reports the first study of the re-oxidation, at elevated temperature, of crystallographic shear planes (CSPs) occurring on the non-stoichiometric rutile TiO2(110) surface by scanning tunnelling microscopy (STM). The re-oxidation occurs by the reaction of interstitial Tin+ ions dissolved in the crystal bulk with oxygen at the surface to re-grow new TiO2 layers on the surface. The CSPs act as nucleation centres for the re-growth and are, in general, preserved during the early stages of the re-oxidation. CSPs appear in pairs on the surface and sandwich a layer of rutile that is displaced by one half an atomic step height from the original terrace. Each step edge of the pair shows markedly different structure and growth rate. The growth of the surface also takes place on the displaced region between CSP pairs
{"title":"The re-oxidation of the substoichiometric TiO2(110) surface in the presence of crystallographic shear planes","authors":"R. Bennett","doi":"10.1039/B001938K","DOIUrl":"https://doi.org/10.1039/B001938K","url":null,"abstract":"Re-oxidation of reduced oxide surfaces is a fundamental step in catalysis and related fields. This paper reports the first study of the re-oxidation, at elevated temperature, of crystallographic shear planes (CSPs) occurring on the non-stoichiometric rutile TiO2(110) surface by scanning tunnelling microscopy (STM). The re-oxidation occurs by the reaction of interstitial Tin+ ions dissolved in the crystal bulk with oxygen at the surface to re-grow new TiO2 layers on the surface. The CSPs act as nucleation centres for the re-growth and are, in general, preserved during the early stages of the re-oxidation. CSPs appear in pairs on the surface and sandwich a layer of rutile that is displaced by one half an atomic step height from the original terrace. Each step edge of the pair shows markedly different structure and growth rate. The growth of the surface also takes place on the displaced region between CSP pairs","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"284 1","pages":"9-14"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86743602","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}
Fluorescence quenching in fluid solution by the external heavy-atom effect usually follows simple Stern?Volmer kinetics, and the quenching effect is gauged by the magnitude of the bimolecular quenching rate constant. However, it is the increased unimolecular S1→Tn intersystem crossing rate constant of the perturbed fluorophore in the perturber?fluorophore complex that can be directly compared with that of the unperturbed fluorophore. From a simple model for external heavy atom quenching in fluid solution, the decay law is predicted to be singly exponential for all quencher concentrations, and a new expression for the unimolecular S1→Tn intersystem crossing rate constant of the perturbed fluorophore is obtained. The same problem, but in rigid solution, is also discussed for the first time. The model now predicts a nonexponential fluorescence decay law, from which the unimolecular S1→Tn intersystem crossing rate constant of the perturbed fluorophore can be directly determined.
{"title":"External heavy-atom effect on fluorescence kinetics","authors":"M. Santos","doi":"10.1039/B002307H","DOIUrl":"https://doi.org/10.1039/B002307H","url":null,"abstract":"Fluorescence quenching in fluid solution by the external heavy-atom effect usually follows simple Stern?Volmer kinetics, and the quenching effect is gauged by the magnitude of the bimolecular quenching rate constant. However, it is the increased unimolecular S1→Tn intersystem crossing rate constant of the perturbed fluorophore in the perturber?fluorophore complex that can be directly compared with that of the unperturbed fluorophore. From a simple model for external heavy atom quenching in fluid solution, the decay law is predicted to be singly exponential for all quencher concentrations, and a new expression for the unimolecular S1→Tn intersystem crossing rate constant of the perturbed fluorophore is obtained. The same problem, but in rigid solution, is also discussed for the first time. The model now predicts a nonexponential fluorescence decay law, from which the unimolecular S1→Tn intersystem crossing rate constant of the perturbed fluorophore can be directly determined.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"68 1","pages":"18-23"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87659512","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}
Thiol-functionalized MCM-41 mesoporous materials with a well-defined pore size of 40 A may be used to discriminate between colloidal gold and silver particles in a mixture. More specifically, the thiol-functionalized MCM-41 material selectively entraps colloidal gold particles (size 35 A) in the pores from a mixture of the gold and silver particles of size 70 A. The gold particles are held in the matrix via thiolate linkages and this process has been studied using UV-vis spectroscopy and thermogravimetry/differential thermal analysis. This approach is promising for application in bioseparation methodologies as well as in the generation of one-dimensional superstructure assemblies
{"title":"Size discrimination of colloidal nanoparticles by thiol-functionalized MCM-41 mesoporous molecular sieves","authors":"Priyabrata Mukherjee, M. Sastry, R. Kumar","doi":"10.1039/B002419H","DOIUrl":"https://doi.org/10.1039/B002419H","url":null,"abstract":"Thiol-functionalized MCM-41 mesoporous materials with a well-defined pore size of 40 A may be used to discriminate between colloidal gold and silver particles in a mixture. More specifically, the thiol-functionalized MCM-41 material selectively entraps colloidal gold particles (size 35 A) in the pores from a mixture of the gold and silver particles of size 70 A. The gold particles are held in the matrix via thiolate linkages and this process has been studied using UV-vis spectroscopy and thermogravimetry/differential thermal analysis. This approach is promising for application in bioseparation methodologies as well as in the generation of one-dimensional superstructure assemblies","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"84 1","pages":"15-17"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83459963","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}
Through well-established methods of group theory, we suggest how to construct new basis sets in the four-dimensional system of bending modes in acetylene. A novel, comprehensive family of vibrational modes is found allowing one to improve the partial analyses available for this molecule in terms of local/normal quantum numbers. We provide the general features of our technique for future extensions to other, more complex systems of current interest
{"title":"Quantum representations of dynamical systems: new bending modes of acetylene","authors":"J.-M. Champion, M. A. Temsamani, S. Oss","doi":"10.1039/B001934H","DOIUrl":"https://doi.org/10.1039/B001934H","url":null,"abstract":"Through well-established methods of group theory, we suggest how to construct new basis sets in the four-dimensional system of bending modes in acetylene. A novel, comprehensive family of vibrational modes is found allowing one to improve the partial analyses available for this molecule in terms of local/normal quantum numbers. We provide the general features of our technique for future extensions to other, more complex systems of current interest","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"03 1","pages":"5-8"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86046614","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 rotational spectrum of the pyridazine(((Ne complex, a species observable in supersonic expansions, has been measured by free jet absorption millimeter wave spectroscopy. The equilibrium configuration, dynamics and dissociation energy have been deduced from the spectroscopic constants. The equilibrium distance of Ne with respect to the center of mass of the molecule is 3.26 A, with the Ne atom tilted by 5.8° from the perpendicular to the center of mass of the ring towards the mid-point of the two nitrogen atoms. The dissociation energy is estimated, from the centrifugal distortion constant DJ, to be ca. 0.8 kJ mol?1.
用自由射流吸收毫米波光谱法测定了在超音速膨胀中可观测到的吡嗪(Ne)配合物的旋转光谱。从光谱常数推导出了平衡构型、动力学和解离能。Ne原子相对于分子质心的平衡距离为3.26 A, Ne原子从与环质心的垂直方向向两个氮原子的中点倾斜5.8°。根据离心畸变常数DJ，估计离解能约为0.8 kJ mol?1。
{"title":"Bonding energies of rare gases with aromatic molecules: rotational spectrum and dynamics of pyridazine?neon","authors":"W. Caminati, S. Melandri, A. Dell'Erba, P. Favero","doi":"10.1039/A909649C","DOIUrl":"https://doi.org/10.1039/A909649C","url":null,"abstract":"The rotational spectrum of the pyridazine(((Ne complex, a species observable in supersonic expansions, has been measured by free jet absorption millimeter wave spectroscopy. The equilibrium configuration, dynamics and dissociation energy have been deduced from the spectroscopic constants. The equilibrium distance of Ne with respect to the center of mass of the molecule is 3.26 A, with the Ne atom tilted by 5.8° from the perpendicular to the center of mass of the ring towards the mid-point of the two nitrogen atoms. The dissociation energy is estimated, from the centrifugal distortion constant DJ, to be ca. 0.8 kJ mol?1.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"73 1","pages":"1-4"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91104676","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 luminescence spectra of the tetragonal trans-ReO2(vinylimidazole)4+ complex and the square planar Pd(SCN)42? and Pt(SCN)42? complexes all show vibronic progressions in two predominant vibrational modes. In the first complex, the vibronic progressions involve high-frequency and low-frequency metal?ligand modes. In the square planar complexes, the two vibrational modes have similar frequencies. At the intermediate resolution, often observed experimentally, these compounds provide an example of the missing mode (or MIME) effect. Wavepacket dynamics on two-dimensional surfaces explain in a visual and intuitively appealing way the spectroscopic features. The distinct effects are caused by the different frequency ratios between the two modes of the two-dimensional models describing each complex. The emitting state structure determined from the spectra reveals similar changes along a bending normal coordinate for Pd(SCN)42? and Pt(SCN)42?
{"title":"Vibronic structure in the luminescence spectra of tetragonal d2 and d8 complexes analyzed by wavepacket dynamics on two-dimensional potential surfaces","authors":"M. Triest, S. Masson, J. Grey, C. Reber","doi":"10.1039/B008386K","DOIUrl":"https://doi.org/10.1039/B008386K","url":null,"abstract":"The luminescence spectra of the tetragonal trans-ReO2(vinylimidazole)4+ complex and the square planar Pd(SCN)42? and Pt(SCN)42? complexes all show vibronic progressions in two predominant vibrational modes. In the first complex, the vibronic progressions involve high-frequency and low-frequency metal?ligand modes. In the square planar complexes, the two vibrational modes have similar frequencies. At the intermediate resolution, often observed experimentally, these compounds provide an example of the missing mode (or MIME) effect. Wavepacket dynamics on two-dimensional surfaces explain in a visual and intuitively appealing way the spectroscopic features. The distinct effects are caused by the different frequency ratios between the two modes of the two-dimensional models describing each complex. The emitting state structure determined from the spectra reveals similar changes along a bending normal coordinate for Pd(SCN)42? and Pt(SCN)42?","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":"33 1","pages":"64-70"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77272901","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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