Relaxation (NMR)

About: Relaxation (NMR) is a research topic. Over the lifetime, 29342 publications have been published within this topic receiving 689851 citations.

Quantum dynamics simulations of interfacial electron transfer in sensitized TiO2 semiconductors.

Abstract: Ab initio DFT molecular dynamics simulations are combined with quantum dynamics calculations of electronic relaxation to investigate the interfacial electron transfer in catechol/TiO2-anatase nanostructures under vacuum conditions. It is found that the primary process in the interfacial electron-transfer dynamics involves an ultrafast (τ1 ≃ 6 fs) electron-injection event that localizes the charge in the Ti4+ surface ions next to the catechol adsorbate. The primary event is followed by charge delocalization (i.e., carrier diffusion) through the TiO2-anatase crystal, an anisotropic diffusional process that can be up to an order of magnitude slower along the [−101] direction than carrier relaxation along the [010] and [101] directions in the anatase crystal. It is shown that both the mechanism of electron injection and the time scales for interfacial electron transfer are quite sensitive to the symmetry of the electronic state initially populated in the adsorbate molecule. The results are particularly releva...

Vibrational dephasing and frequency shifts of polyatomic molecules in solution

Abstract: A theory for the effects of repulsive and spatially slowly varying attractive forces on the vibrational frequency and dephasing of polyatomic molecular liquids is developed. Thermodynamic state dependence of these features is of particular interest because of the competition between the two types of forces. Solvent shifts of vibrational lines are computed. Proper separation of the rapidly and slowly varying branches of the intermolecular potentials leads to a separation of time scales that allows the dephasing relaxation to be computed using a combination of binary collision and mean field ideas. The question of homogeneous vs inhomogeneous broadening of the isotropic Raman line is addressed. The theory is applied to several polyatomic fluids with special emphasis on the isothermal density dependence of the spectral features. Agreement with experiment is good. The slowly varying attractive forces are found to play a significant role in determining the Raman linewidth for all the systems studied. Comparison with previous theories is made.

Rotational diffusion studied by passage saturation transfer electron paramagnetic resonance

Abstract: A comprehensive description is given of instrumental and theoretical methods employed to make accurate measurements of rotational correlation times using passage saturation transfer electron paramagnetic resonance (ST–EPR). Saturation transfer methods extend by several orders of magnitude the sensitivity of EPR to very slow motion; for example, for nitroxide spin labels, correlation times as long as 10−3 sec become accessible to measurement. Two ST–EPR detection schemes are discussed in detail: dispersion, detected 90° out of phase with respect to the 100 kHz field modulation, and absorption, detected 90° out of phase with respect to the second harmonic of the 50 kHz field modulation. The sensitivities of these configurations are illustrated with experimental spectra obtained from a system obeying isotropic Brownian rotational diffusion; namely, maleimide spin labeled human oxyhemoglobin in aqueous glycerol solutions. Two theoretical approaches, one employing coupled Bloch equations and the other utilizing the stochastic Liouville equation for the density matrix with the orientation variables treated by transition rate matrix or orthogonal eigenfunction expansion methods, are in excellent agreement with each other and with model system spectra. Both experimental and theoretical spectra depend on a number of relaxation processes other than rotational diffusion; consequently, considerable care must be taken to ensure the accuracy of measured rotational correlation times. Although the absorption method is currently the more sensitive and convenient one to apply with most conventional (commercial) spectrometers, the dispersion ST–EPR method is potentially more powerful, providing strong motivation for future technological efforts to decrease noise levels in dispersion experiments.

DNA-Based Magnetic Nanoparticle Assembly Acts as a Magnetic Relaxation Nanoswitch Allowing Screening of DNA-Cleaving Agents

Abstract: Monodisperse magnetic nanoparticles conjugated with complementary oligonucleotide sequences self-assemble into stable magnetic nanoassemblies resulting in a decrease of the spin−spin relaxation times (T2) of neighboring water protons. When these nanoassemblies are treated with a DNA cleaving agent, the nanoparticles become dispersed, switching the T2 of the solution back to original values. These qualities render the developed nanoparticles and their nanoassemblies as magnetic relaxation switches capable of screening for DNA-cleaving compounds by magnetic resonance methods such as MRI and NMR.