PhysChemComm

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 Crank-Nicholson method. The mean square displacement shows a transition from sub-diffusive (exponent $\alpha \sim$ 0.43) to a super-diffusive (exponent $\alpha \sim$ 1.75) behavior with time and ultimately to a diffusive dynamics. The decay of self intermediate scattering function ($F_{s}(k,t)$) 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 dynamics of water in protein and micellar hydration shell. The present analysis provides a simple microscopic explanation for the transition from the sub-diffusivity and super-diffusivity. {\em The super-diffusive behavior is due to escape from the well near the surface and the sub-diffusive behavior is due to return of quasi-free molecules to form the bound state again, after the initial escape}

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.

In this paper, we discuss the synthesis of cadmium sulfide (CdS) quantum dots within thermally evaporated sodium bis(2-ethylhexyl) sulfosuccinate (AOT) thin films. This procedure uses electrostatic interactions to entrap positively charged cadmium ions into thin films of the anionic surfactant AOT by a simple immersion of the film in electrolyte solution. Thereafter, the composite film is treated with (HS)-S-2 gas/Na2S solution resulting in the in-situ formation of CdS nanoparticles in the quantum size regime. It is believed that the ability of AOT molecules in the thermally evaporated thin films to form reverse micelles is responsible for the CdS nanoparticle size control observed. Investigation of the entrapment of cadmium ions in the AOT film and subsequent quantum dot synthesis was carried out by quartz crystal microgravimetry (QCM), UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) measurements.

The intermolecular free-length is evaluated by making use of thermoacoustical parameters followed by a comparative study. To achieve this objective, thermoacoustical parameters of four ternary and two quaternary liquid mixtures have been computed. These parameters have been utilized to calculate the available volume (V-a), which in turn has been used to compute intermolecular free-length (L-f) for the systems under investigation. The computed values of L-f have then been compared with the values estimated from well-established thermodynamic and ultrasonic methods. To the best of our knowledge, this investigation is a pioneering attempt in evaluation of intermolecular free-length involving multicomponent liquid mixtures by making use of thermoacoustical parameters.

The Fukui function f(k)(+) and local softness s(k)(+) are assigned as reactivity parameters for nucleophilic addition reaction in acrolein, methylacrylate, methylmethacrylate, acryloylchloride, cinnamaldehyde and cinnamoylchloride. All calculations were performed at the HF level of theory using 6-31G, 6-31G** and TZV basis sets. The condensed local softness calculated using a Lowdin population is compared with the local softness calculated from a Mulliken population. The most probable sites for nucleophilic attack on the alpha,beta-unsaturated carbonyl compounds are determined from local reactivity descriptors: they are quite reliable to predict the reactivity relative to atomic charges.

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.

Low temperature fluorescence line-narrowing (FLN) and spectral hole-burning experiments (SHB) were performed in the E-2<--(4)A(2) 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 E-2 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.

Carbon nanotubes (CNTs) are widely considered as promising materials both in nanochemistry and nanoelectronics. (1-3) New generations of composite materials, semiconductor circuits or TV screens based upon CNT technology are under construction and very near to being realized. (4) However, in order to appear on the market and later in the households, these products as well as their components must be cheap enough.In contrast to the laser ablation(5) and arc discharge(6) techniques catalytic chemical vapour deposition (CCVD) is able to produce nanotubes in industrial quantities. In the laboratory scale C2H2 or C2H4 as carbon sources, cobalt, iron or nickel as catalyst particles, and high surface area SiO2, Al2O3 or zeolite supports are commonly used for the synthesis of multiwalled nanotubes (MWNTs). (7-11) After the synthesis process nanotubes must be removed from the catalyst. This means strong acidic (HF in the case of zeolites) or basic ( concentrated NaOH in the case of Al2O3 and SiO2) treatment in most of the cases. Applying a water soluble catalyst support could make the purification step easier controllable, more economical, and environmentally friendly.

Theoretical studies of the electronic properties of three confined aromatic molecules—benzene, naphthalene and anthracene—have been presented in support of the electronic confinement effect. The confined space of the cavities has been modeled using a mica sheet with the molecule–surface distance in the range of 1.5–4.0 Å. Evidence of the confinement has been revealed by semiempirical calculations, which are theoretically interpreted by means of the Hückel molecular orbital theory. It has been found that the HOMO has been predicted to be more sensitive to the confinement than the LUMO and the overall effect is a reduction on the band gap of the frontier molecular orbitals when the molecule–surface distance is less than ca. 2.5 Å. The variations of the frontier orbital energies and band gaps are correlated with the increase of both Coulomb integral, α, and resonance integral, β. The order of magnitude of the energy increment of Δα and Δβ values is evaluated from data of the above semiempirical calculations. It is also found that the confinement effect is associated with the conjugated system of the aromatic molecules. The theoretical evaluations here prove that confining organic molecules in the cavities is sufficient to alter their electronic properties as a consequence of changes in the molecular orbital energies and band gaps.

The effect of nH(2)O (n = 1-3) on the association energies of H2O complexes and on the barriers for the formation of O-3 in the self-reaction of HO2 reaction has been investigated by ab initio molecular orbital calculations at the modified Gaussian-2 (G2M) level of theory. The results show that H2O can affect the complex and O-3 formation processes: the more H2O molecules participating in the reaction, the higher stability of the association complexes and the greater the lowering of the O-3 elimination barrier becomes. For the isomers of the reactions, more hydrogen bonds being formed in the complexes enhances their stabilities. A preliminary kinetic calculation shows that below room temperature, H2O may enhance the formation of O-3 noticeably.

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.

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.

The one-dimensional algebraic model is applied to analyze infrared spectra of n-alkane molecules. We consider CH stretching vibrations in both fundamental (v = 1) and first overtone (v = 2) energy regions. We show that a relatively small set of well-defined parameters leads to a very good agreement with observed data. Both CH2 and CH3 vibrations are accounted for. In particular, we suggest that first overtone infrared spectra can be fairly well described without adding complex anharmonic (Fermi) interactions. Their inclusion is required however to obtain a closer agreement with the available experimental spectra.

By using the ab initio norm-conserving pseudopotential method, the lithium intercalations in AlSb, GaSb and InSb have been studied. The formation energies, changes of volumes, electronic structures and charge densities of the lithium interactions in zinc blende-type antimonides LixMSb (M = Al, Ga, In) are presented. Our calculations show that during lithium insertion in MSb the lithium intercalation formation energy per lithium atom are all around 2.0 eV. The volume expansions of AlSb, GaSb and InSb due to lithium insertions are relatively large, which might imply that the limit of Li intercalation in antimonides should be small.

This article reports on the generation of [Mm-phenyl]− (M = Mn–Cu) complexes, which are very rare cases in chemistry. Experimental results showed that the typical cation products for the reactions of all 3d transition metal clusters (Sc–Cu) with benzene were different [Mm(C6H6)n]+ (M = Sc–Cu) species, while the typical anion products for the late 3d transition metals were [Mm–C6H5]− (M = Mn–Cu) complexes. Their formation mechanisms, which involve anion metal clusters inducing a selective benzene C–H cleavage in the gas phase, were proposed.

Theoretical studies of the electronic properties of three confined aromatic molecules-benzene, naphthalene and anthracene-have been presented in support of the electronic confinement effect. The confined space of the cavities has been modeled using a mica sheet with the molecule-surface distance in the range of 1.5-4.0 Angstrom. Evidence of the confinement has been revealed by semiempirical calculations, which are theoretically interpreted by means of the Huckel molecular orbital theory. It has been found that the HOMO has been predicted to be more sensitive to the confinement than the LUMO and the overall effect is a reduction on the band gap of the frontier molecular orbitals when the molecule-surface distance is less than ca. 2.5 Angstrom. The variations of the frontier orbital energies and band gaps are correlated with the increase of both Coulomb integral, alpha, and resonance integral, beta. The order of magnitude of the energy increment of Deltaalpha and Deltabeta values is evaluated from data of the above semiempirical calculations. It is also found that the confinement effect is associated with the conjugated system of the aromatic molecules. The theoretical evaluations here prove that confining organic molecules in the cavities is sufficient to alter their electronic properties as a consequence of changes in the molecular orbital energies and band gaps.

The second-order polarizabilities and the UV-vis-IR spectra of a transition-metal complex Co(NH3)(2)(L-ala-gly-gly) have been studied by using the MP2 and TDHF methods. The complex has a maximum beta component in the direction from the N(alanyl) group to the N( glycyl) groups. A transparent optical spectrum region from 0.55 to 5.5 mum was found, which offers potential applications as an optical material. The alkyl substitution of the glycyl group only slightly affected the beta value and retained the IR transparent region but may cause the molecules to have a favorite packing fashion in the bulk crystal that leads to larger second-order nonlinear optical coefficients.

Visible light emission from metal-water interfaces at laser-induced breakdown (LIB) has been observed for aluminium, titanium and platinum. The spectra are found to consist of broadband continuum without any discrete atomic lines, which may be useful as a pulsed light source for spectroscopy. A simple thermal diffusion model combined with blackbody radiation is described, the numerical result of which agrees fairly well with the observed spectra.

This perspective reviews experiments in which spectroscopy rather than scattering is used to probe reactive potential energy surfaces. The application of negative ion photodetachment to the transition state spectroscopy of benchmark reactions is described, followed by a brief description of recent transition state spectroscopy experiment starting from clustered precursor anions that probe the effects of solvation on transition state spectroscopy and dynamics. Experiments on the spectroscopy of open-shell "pre-reactive" complexes are also discussed.

Novel self-organized carbon nanoropes consisting of three helically coiled multi-wall nanotubes with a remarkable constant pitch over several microns were grown by the lanthanide oxide-catalyzed decomposition of gaseous acetylene on aluminophosphate (AlPO4-5) support. Direct characterization by the stereo transmission electron microscope and scanning electron microscope has convincingly shown that these three strands entwine with each other helically, which are presumably kept together by both the spontaneous curvature and van der Waals (vdW) attraction.