Diffusion constant of a nonspecifically bound protein undergoing curvilinear motion along DNA

The mechanism of a protein's diffusion along a DNA segment is a subject of much current interest because of the involvement of this diffusion in numerous biological processes, including the recognition of DNA sequences and chemical modifications of DNA. In this work we present a theoretical derivation of the diffusion coefficient of a nonspecifically bound protein, assuming that the protein follows a helical track along the DNA. It is shown that, for protein-sized molecules, the principal contribution to the total translational friction comes from the curvilinear motion along the helix, and this contribution is given by 6pietaRR(oc)(2) + 8pietaR(3), where R is the protein radius, ROC is the distance of separation between the center of mass of the protein and the helical axis of DNA, and eta is the viscosity of the medium. The translational diffusion of the protein along the helical track of DNA is thus predicted to have a nearly R(-3) size dependence, not the R(-1) dependence characterizing simple translational diffusion. It is shown that this expression gives rather good estimates of the translational diffusion coefficient measured in single molecule experiments.     

Wurtzite CuGaS2 with an In-Situ-Formed CuO Layer Photocatalyzes CO2 Conversion to Ethylene with High Selectivity

We present surface reconstruction-induced C−C coupling whereby CO₂ is converted into ethylene. The wurtzite phase of CuGaS_2. undergoes in situ surface reconstruction, leading to the formation of a thin CuO layer over the pristine catalyst, which facilitates selective conversion of CO₂ to ethylene (C₂H₄). Upon illumination, the catalyst efficiently converts CO₂ to C₂H₄ with 75.1 % selectivity (92.7 % selectivity in terms of R_electron) and a 20.6 μmol g⁻¹ h⁻¹ evolution rate. Subsequent spectroscopic and microscopic studies supported by theoretical analysis revealed operando-generated Cu²⁺, with the assistance of existing Cu⁺, functioning as an anchor for the generated *CO and thereby facilitating C−C coupling. This study demonstrates strain-induced in situ surface reconstruction leading to heterojunction formation, which finetunes the oxidation state of Cu and modulates the CO₂ reduction reaction pathway to selective formation of ethylene.     

Vibrational phase relaxation of O–H stretch in bulk water: Role of large amplitude angular jumps and negative cross-correlations among the forces on the O–H bond

The ultrafast vibrational phase relaxation of O–H stretch in bulk water is investigated in molecular dynamics simulations. The dephasing time (T₂) of the O–H stretch in bulk water calculated from the frequency fluctuation time correlation function (C_ω(t)) is in the range of 70–80 femtosecond (fs), which is comparable to the characteristic timescale obtained from the vibrational echo peak shift measurements using infrared photon echo [W.P. de Boeij, M.S. Pshenichnikov, D.A. Wiersma, Ann. Rev. Phys. Chem. 49 (1998) 99]. The ultrafast decay of C_ω(t) is found to be responsible for the ultrashort T₂ in bulk water. Careful analysis reveals the following two interesting reasons for the ultrafast decay of C_ω(t). (A) The large amplitude angular jumps of water molecules (within 30–40 fs time duration) provide a large scale contribution to the mean square vibrational frequency fluctuation and gives rise to the rapid spectral diffusion on 100 fs time scale. (B) The projected force, due to all the atoms of the solvent molecules on the oxygen (F_O(t)) and hydrogen (F_H(t)) atom of the O–H bond exhibit a large negative cross-correlation (NCC). We further find that this NCC is partly responsible for a weak, non-Arrhenius temperature dependence of the dephasing rate.     

Spectroscopic study of association of a hemicyanine dye in mixed aqueous binary solvents

Electronic absorption and steady state emission properties of a hemicyanine dye [4-[4-(dimethylamino)styryl]-1-docosylpyridinium bromide], have been studied in several pure solvents and two mixed binary solvents (water+ethanol and water+acetonitrile). In pure solvents the band-width of the absorption spectrum correlates well with the Stoke's shift. In mixed aqueous solvents two different molecular forms of the solute, viz. the monomer and the dimer of the solute exists in equilibrium. Thermodynamic parameters (e.g. the Delta G degrees and Delta H degrees ) characterizing the equilibrium have been determined. While the value of Delta G degrees changes very slightly with the composition of the binary mixture, the value of Delta H degrees has been observed to depend significantly with solvent composition.     

Two-dimensional infrared investigation of N-acetyl tryptophan methyl amide in solution

The linear infrared and two-dimensional infrared (2D IR) spectra in the amide-I region of N-acetyl tryptophan methyl amide (NATMA) in solvents of varying polarity are reported. The two amide-I transitions have been assigned unambiguously by using 13C isotopic substitution of the carbonyl group. The amide unit at the amino end shows a lower transition frequency in CH2Cl2 and methanol, while the acetyl end has a lower transition frequency in D2O. Multiple conformers exist in CH2Cl2 and methanol, but only one conformer is evident in D2O. The 2D IR cross peaks from the intermode coupling yield off-diagonal anharmonicities 2.5 +/- 0.5, 3.25 +/- 0.5, and 3.0 +/- 0.5 cm(-1) in CH2Cl2, methanol, and D2O, respectively, which by simple matrix diagonalization yield the coupling constants 8.0 +/- 0.5, 8.0 +/- 1.0, and 5.5 +/- 1.0 cm(-1). The major conformer in CH2Cl2 corresponds to a C7 structure, in agreement with that found in the gas phase [Dian, B. C.; Longarte, A.; Mercier, S.; Evans, D. A.; Wales, D. J.; Zwier, T. S. J. Chem. Phys. 2002, 117, 10688-10702] with intramolecular hydrogen bonding between the acetyl end C=O and the amino end N-H. The backbone dihedral angles (phi, psi) are determined to be in the ranges of (-55 +/- 5 degrees , 30 +/- 5 degrees ), (120 +/- 10 degrees , -20 +/- 10 degrees ), and (+/-160 +/- 10 degrees , +/-75 +/- 10 degrees ) in CH2Cl2, methanol, and D2O, respectively.     

Comparative study of temperature dependent orientational relaxation in a model thermotropic liquid crystal and in a model supercooled liquid

Recent optical Kerr effect experiments have revealed a power law decay of the measured signal with a temperature independent exponent at short-to-intermediate times for a number of liquid crystals in the isotropic phase near the isotropic-nematic transition and supercooled molecular liquids above the mode coupling theory critical temperature. In this work, the authors investigate the temperature dependence of short-to-intermediate time orientational relaxation in a model thermotropic liquid crystal across the isotropic-nematic transition and in a binary mixture across the supercooled liquid regime in molecular dynamics simulations. The measure of the experimentally observable optical Kerr effect signal is found to follow a power law decay at short-to-intermediate times for both systems in agreement with recent experiments. In addition, the temperature dependence of the power law exponent is found to be rather weak. As the model liquid crystalline system settles into the nematic phase upon cooling, the decay of the single-particle second-rank orientational time correlation function exhibits a pattern that is similar to what has been observed for supercooled liquids.     

Multifunctional polymers as multi-role materials for photonics

Multifunctional polymers can play multi-roles such as laser light source, passive interconnects, optical signal processing and optical data storage in the development of photonics technology. In this paper, two approaches to achieve nanostructure control to introduce multifunctionality at both molecular and bulk levels are presented. A novel concept of multiphasic nanostructured composites is discussed. Various applications of a specific multifunctional property introduced by strong two-photon absorption and efficient fluorescence are presented. The combined action of these two functions produces upconverted emission. Specific applications discussed are upconversion lasing, optical data storage, confocal microscopy, and photodynamic therapy.     

Gamma radiation dose rate in indoor, outdoor and underground atmosphere around Tehri dam project, Uttarakhand, India

The natural pollution level due to gamma radiation was measured in about 22 residential houses around the Tehri Dam Project in Uttarakhand state by using Environmental Radiation Dosimeter. Both urban and rural houses were selected for the measurements. The recorded gamma dose rate in indoor atmosphere was found to vary from 25.1 μR/h to 67 μR/h with a mean value 38.6 μR/h whereas in traditional rural houses the obtained values varied from 42.6 μR/h to 83.5 μR/h with mean value 60.3 μR/h. In outdoor atmosphere, it was found to vary from 25.1 μR/h to 60 μR/h with an average value 35.8 μR/h. It is observed that the dose rates are higher in rural houses than that in modern houses. Efforts have also been made to observe deviation of dose rate in the underground (Power House) atmosphere of Tehri Dam Project in vertical and horizontal mode. It was observed that dose rate remain almost same in horizontal mode, but a significant variation has been found in the vertical mode. In addition, the variation of dose rate with type of building material, trend and mode of construction of houses and the age of houses are also discussed in detail.