H. Bissig, S. Romer, L. Cipelletti, V. Trappe, P. Schurtenberger
We investigate the slow dynamics of strongly aggregated particle gels by diffusing wave spectroscopy (DWS) using a charge coupled device (CCD) camera as a multispeckle detector. The evolution of the slow dynamics after the gel-point is followed using two different techniques, the multispeckle method and a novel correlation scheme, time resolved correlation (TRC), which allows us to obtain time resolved information on the dynamics of the gel. We find that the intensity autocorrelation function measured by multispeckle DWS exhibits an ultraslow relaxation, whose characteristic time strongly depends on the age of the gel. An analysis of the TRC data reveals that the slow dynamics is intermittent. We propose that the intermittency is due to rare disruptions or formations of bonds affecting the elastic backbone of the network, which lead to sudden long range rearrangements of the particle position and thus to a sudden change of the speckle pattern.
{"title":"Intermittent dynamics and hyper-aging in dense colloidal gels","authors":"H. Bissig, S. Romer, L. Cipelletti, V. Trappe, P. Schurtenberger","doi":"10.1039/B211806H","DOIUrl":"https://doi.org/10.1039/B211806H","url":null,"abstract":"We investigate the slow dynamics of strongly aggregated particle gels by diffusing wave spectroscopy (DWS) using a charge coupled device (CCD) camera as a multispeckle detector. The evolution of the slow dynamics after the gel-point is followed using two different techniques, the multispeckle method and a novel correlation scheme, time resolved correlation (TRC), which allows us to obtain time resolved information on the dynamics of the gel. We find that the intensity autocorrelation function measured by multispeckle DWS exhibits an ultraslow relaxation, whose characteristic time strongly depends on the age of the gel. An analysis of the TRC data reveals that the slow dynamics is intermittent. We propose that the intermittency is due to rare disruptions or formations of bonds affecting the elastic backbone of the network, which lead to sudden long range rearrangements of the particle position and thus to a sudden change of the speckle pattern.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2003-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90620871","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}
We give a selective review of quantum mechanical methods for calculating and characterizing resonances in small molecular systems, with an emphasis on recent progress in Chebyshev and Lanczos iterative methods. Two archetypal molecular systems are discussed: isolated resonances in HCO, which exhibit regular mode and state specificity, and overlapping resonances in strongly bound HO2, which exhibit irregular and chaotic behavior. Future directions in this field are also discussed.
{"title":"Quantum dynamical characterization of unimolecular resonances","authors":"Hong Zhang, Sean C. Smith","doi":"10.1039/B300284P","DOIUrl":"https://doi.org/10.1039/B300284P","url":null,"abstract":"We give a selective review of quantum mechanical methods for calculating and characterizing resonances in small molecular systems, with an emphasis on recent progress in Chebyshev and Lanczos iterative methods. Two archetypal molecular systems are discussed: isolated resonances in HCO, which exhibit regular mode and state specificity, and overlapping resonances in strongly bound HO2, which exhibit irregular and chaotic behavior. Future directions in this field are also discussed.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2003-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72813702","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}
Low temperature fluorescence line-narrowing (FLN) and spectral hole-burning experiments (SHB) were performed in the 2E←4A2 spin–flip transition of [Cr(2,2′:6′,2″-terpyridine)2]3+ in frozen ethylene glycol/water (2 ∶ 1) and DMSO/water (2 ∶ 1) glasses. In the FLN experiments an average 2E splitting of 23 cm−1 is observed. It is concluded that the interaction with water molecules in pockets provided by the ligands is most likely to be responsible for the relatively efficient non-photochemical hole-burning. Fast spectral diffusion and spontaneous hole-filling prevent the observation of holes above 20 K. The FLN and SHB experiments were performed by using a diode laser.
{"title":"Non-photochemical spectral hole-burning mediated by water molecules in interligand pockets of [Cr(terpy)2]3+","authors":"H. Riesen, L. Wallace","doi":"10.1039/B209460F","DOIUrl":"https://doi.org/10.1039/B209460F","url":null,"abstract":"Low temperature fluorescence line-narrowing (FLN) and spectral hole-burning experiments (SHB) were performed in the 2E←4A2 spin–flip transition of [Cr(2,2′:6′,2″-terpyridine)2]3+ in frozen ethylene glycol/water (2 ∶ 1) and DMSO/water (2 ∶ 1) glasses. In the FLN experiments an average 2E splitting of 23 cm−1 is observed. It is concluded that the interaction with water molecules in pockets provided by the ligands is most likely to be responsible for the relatively efficient non-photochemical hole-burning. Fast spectral diffusion and spontaneous hole-filling prevent the observation of holes above 20 K. The FLN and SHB experiments were performed by using a diode laser.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2003-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79328590","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}
Experimental and simulation studies have reported the presence of a transition in the internal dynamics of proteins at 220 K. This transition has been correlated with the onset of activity in several proteins. The role of the solvent in the dynamical transition has been the subject of increased attention. Here simulation techniques are used to distinguish dynamical features inherent to the protein energy landscape from those induced by the surrounding solvent. The present results indicate that the protein dynamical transition primarily affects the side-chains on the outer layers of the protein. Moreover, the results indicate that the solvent restrains protein motions at low temperatures.
{"title":"Solvent caging of internal motions in myoglobin at low temperaturesThis paper was originally presented as a poster at the Faraday Discussion 122 meeting.","authors":"A. Tournier, Jiancong Xu, Jeremy C. Smith","doi":"10.1039/b209839c","DOIUrl":"https://doi.org/10.1039/b209839c","url":null,"abstract":"Experimental and simulation studies have reported the presence of a transition in the internal dynamics of proteins at 220 K. This transition has been correlated with the onset of activity in several proteins. The role of the solvent in the dynamical transition has been the subject of increased attention. Here simulation techniques are used to distinguish dynamical features inherent to the protein energy landscape from those induced by the surrounding solvent. The present results indicate that the protein dynamical transition primarily affects the side-chains on the outer layers of the protein. Moreover, the results indicate that the solvent restrains protein motions at low temperatures.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2003-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77946767","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}
G. Louit, A. Hocquet, M. Ghomi, M. Meyer, J. Sühnel
The interaction of guanine tetrads with various alkaline, alkaline earth and transition metal ions has been studied by means of an AIM topological analysis of the electronic density based on density functional calculations. The interaction between metal ion and ligand has been characterized in terms of the Laplacian of the electronic density, the Hamiltonian kinetic energy density and the Lagrangian kinetic energy density. The influence of the metal ion–ligand interaction on tetrad hydrogen bonding is also discussed.
{"title":"Guanine tetrads interacting with metal ions. An AIM topological analysis of the electronic density","authors":"G. Louit, A. Hocquet, M. Ghomi, M. Meyer, J. Sühnel","doi":"10.1039/B210911E","DOIUrl":"https://doi.org/10.1039/B210911E","url":null,"abstract":"The interaction of guanine tetrads with various alkaline, alkaline earth and transition metal ions has been studied by means of an AIM topological analysis of the electronic density based on density functional calculations. The interaction between metal ion and ligand has been characterized in terms of the Laplacian of the electronic density, the Hamiltonian kinetic energy density and the Lagrangian kinetic energy density. The influence of the metal ion–ligand interaction on tetrad hydrogen bonding is also discussed.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2003-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85379432","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}
Diffusion of a tagged particle near a constraining biological surface is examined numerically by modeling the surface-water interaction by an effective potential. The effective potential is assumed to be given by an asymmetric double well constrained by a repulsive surface towards r → 0 and unbound at large distances. The time and space dependent probability distribution P(r,t) of the underlying Smoluchowski equation is solved by using the Crank–Nicholson method. The mean square displacement shows a transition from sub-diffusive (exponent α ≈ 0.46) to a super-diffusive (exponent α ≈ 1.75) behavior with time and ultimately to diffusive dynamics. The decay of self intermediate scattering function (Fs(k,t)) is non-exponential in general and shows a power law behavior at the intermediate time. Such features have been observed in several recent computer simulation studies on the dynamics of water in proteins and micellar hydration shells. The present analysis provides a simple microscopic explanation for the transition from the sub-diffusivity and super-diffusivity. The super-diffusive behavior is due to escape from the well near the surface and the sub-diffusive behavior is due to the return of quasi-free molecules to form the bound state again, after the initial escape.
{"title":"Origin of the sub-diffusive behavior and crossover from sub-diffusive to super-diffusive dynamics near a biological surface","authors":"A. Mukherjee, B. Bagchi","doi":"10.1039/B212786E","DOIUrl":"https://doi.org/10.1039/B212786E","url":null,"abstract":"Diffusion of a tagged particle near a constraining biological surface is examined numerically by modeling the surface-water interaction by an effective potential. The effective potential is assumed to be given by an asymmetric double well constrained by a repulsive surface towards r \u0000→ 0 and unbound at large distances. The time and space dependent probability distribution P(r,t) of the underlying Smoluchowski equation is solved by using the Crank–Nicholson method. The mean square displacement shows a transition from sub-diffusive (exponent α \u0000≈ 0.46) to a super-diffusive (exponent α \u0000≈ 1.75) behavior with time and ultimately to diffusive dynamics. The decay of self intermediate scattering function (Fs(k,t)) is non-exponential in general and shows a power law behavior at the intermediate time. Such features have been observed in several recent computer simulation studies on the dynamics of water in proteins and micellar hydration shells. The present analysis provides a simple microscopic explanation for the transition from the sub-diffusivity and super-diffusivity. The super-diffusive behavior is due to escape from the well near the surface and the sub-diffusive behavior is due to the return of quasi-free molecules to form the bound state again, after the initial escape.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80007387","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 diffusion of superoxide radical anions on the surface of TiO2 catalysts is theoretically considered as an important step in the kinetics of photocatalytic oxidation of toxic pollutants. A detailed analysis is performed to discriminate the effects of rotation, anion and adsorption bonds vibrations on the diffusion coefficient. A resonant dependence of the diffusivity on the lattice parameters of the TiO2 surface is discovered showing that the most rapid diffusion takes place when the lattice parameters are twice larger than the bond length of the superoxide radical anions. Whereas the rotation and vibrations normal to the catalyst surface are important, the anion bond vibrations do not affect the diffusivity due to their low amplitudes as compared to the lattice parameters.
{"title":"Surface diffusion control of the photocatalytic oxidation in air/TiO2 heterogeneous reactors","authors":"Roumen Tsekov, E. Evstatieva, P. Smirniotis","doi":"10.1039/B207965H","DOIUrl":"https://doi.org/10.1039/B207965H","url":null,"abstract":"The diffusion of superoxide radical anions on the surface of TiO2 catalysts is theoretically considered as an important step in the kinetics of photocatalytic oxidation of toxic pollutants. A detailed analysis is performed to discriminate the effects of rotation, anion and adsorption bonds vibrations on the diffusion coefficient. A resonant dependence of the diffusivity on the lattice parameters of the TiO2 surface is discovered showing that the most rapid diffusion takes place when the lattice parameters are twice larger than the bond length of the superoxide radical anions. Whereas the rotation and vibrations normal to the catalyst surface are important, the anion bond vibrations do not affect the diffusivity due to their low amplitudes as compared to the lattice parameters.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88651779","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}
Available volumes in pure liquids and binary liquid mixture at varying temperature have been computed using thermoacoustical parameters and the values thus obtained are compared with the values obtained from a thermodynamic relation of the available volume. Fairly good agreement between the values from the two methods proves the applicability of thermoacoustical parameters for the computation of the available volume in pure liquids and liquid mixtures.
{"title":"Applicability of thermoacoustical parameters for the computation of available volume in liquid systems","authors":"J. D. Pandey, R. Dey, Bishan Datt Bhatt","doi":"10.1039/B109599D","DOIUrl":"https://doi.org/10.1039/B109599D","url":null,"abstract":"Available volumes in pure liquids and binary liquid mixture at varying temperature have been computed using thermoacoustical parameters and the values thus obtained are compared with the values obtained from a thermodynamic relation of the available volume. Fairly good agreement between the values from the two methods proves the applicability of thermoacoustical parameters for the computation of the available volume in pure liquids and liquid mixtures.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74946677","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}
Shawna S. York, Scott E. Boesch, R. Wheeler, R. Frech
An experimental and computational investigation of the structures and vibrational frequencies of N,N′-dimethylethylenediamine–lithium triflate (DMEDA–LiTf; Tf – = CF 3 SO 3 – ) has been done using a combination of hybrid Hartree–Fock/density functional calculations and Raman and IR spectroscopy. Band assignments for DMEDA–LiBr were made by comparing the experimental Raman and IR spectra of a 5 ∶ 1 DMEDA–LiBr sample with the calculated vibrational frequencies of the DMEDA–Li + and DMEDA–LiBr complexes. Band assignments for DMEDA–LiTf were made by comparing the experimental spectra of samples over a composition range of 20 ∶ 1 to 1.5 ∶ 1 with calculations done on the DMEDA–LiTf complexes. The effect of the lithium cation and lithium triflate on the geometries and vibrational frequencies of the DMEDA will be examined. The combined experimental data and computational results clearly show that the intramolecular hydrogen bonding in pure DMEDA is broken upon addition of lithium bromide or lithium triflate.
{"title":"The effect of lithium triflate and lithium bromide on the vibrational frequencies of DMEDA","authors":"Shawna S. York, Scott E. Boesch, R. Wheeler, R. Frech","doi":"10.1039/B204103K","DOIUrl":"https://doi.org/10.1039/B204103K","url":null,"abstract":"An experimental and computational investigation of the structures and vibrational frequencies of N,N′-dimethylethylenediamine–lithium triflate (DMEDA–LiTf; Tf – = CF 3 SO 3 – ) has been done using a combination of hybrid Hartree–Fock/density functional calculations and Raman and IR spectroscopy. Band assignments for DMEDA–LiBr were made by comparing the experimental Raman and IR spectra of a 5 ∶ 1 DMEDA–LiBr sample with the calculated vibrational frequencies of the DMEDA–Li + and DMEDA–LiBr complexes. Band assignments for DMEDA–LiTf were made by comparing the experimental spectra of samples over a composition range of 20 ∶ 1 to 1.5 ∶ 1 with calculations done on the DMEDA–LiTf complexes. The effect of the lithium cation and lithium triflate on the geometries and vibrational frequencies of the DMEDA will be examined. The combined experimental data and computational results clearly show that the intramolecular hydrogen bonding in pure DMEDA is broken upon addition of lithium bromide or lithium triflate.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80480966","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}
Some unexpected properties of the ionic conductor, silver iodide, when heated by 2.45 GHz microwave radiation are investigated using temperature-resolved, in-situ powder X-ray diffraction. The lowering of the phase transition temperature can be explained by multi-phonon interactions with the microwaves and low-lying transverse optic modes.
{"title":"Temperature-resolved, in-situ powder X-ray diffraction of silver iodide under microwave irradiation","authors":"G. Robb, A. Harrison, A. G. Whittaker","doi":"10.1039/B207258K","DOIUrl":"https://doi.org/10.1039/B207258K","url":null,"abstract":"Some unexpected properties of the ionic conductor, silver iodide, when heated by 2.45 GHz microwave radiation are investigated using temperature-resolved, in-situ powder X-ray diffraction. The lowering of the phase transition temperature can be explained by multi-phonon interactions with the microwaves and low-lying transverse optic modes.","PeriodicalId":20106,"journal":{"name":"PhysChemComm","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80989293","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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