Search results for "molecule"
showing 10 items of 5162 documents
“Through-space” nuclear spin–spin couplings in ferrocenyl polyphosphanes and diphosphino cavitands: A new way of gathering structural information in …
2009
Abstract Nuclear magnetic resonance is an invaluable technique for investigating a variety of important issues ranging from the determination of molecular structure to therapeutic medical imaging. In this respect, the indirect nuclear spin–spin coupling involving common nuclei such as 1 H, 13 C or 31 P provides, via the J constant, conclusive data for compound characterization in solution. This electron-mediated nuclear spin coupling is usually regarded as being transmitted by covalently bonded magnetic atoms. However, several experimental and theoretical studies, first focused on constrained organofluorides, and more recently devoted to phosphane ligands highlighted the existence of very i…
One-bond 1 J (15 N,H) coupling constants at sp2 -hybridized nitrogen of Schiff bases, enaminones and similar compounds: A theoretical study
2020
1 J(15 N,H) coupling constants for enaminones and NH-forms of intramolecularly hydrogen-bonded Schiff bases as model compounds for sp2 -hybridized nitrogen atoms are evaluated using density functional theory (DFT) to find the optimal functionals and basis sets. Ammonia is used as a test molecule and its one-bond coupling constant is compared with experiment. A methylamine Schiff base of a truncated molecule of gossypol is used for checking the performance of selected B3LYP, O3LYP, PBE, BHandH, and APFD density functionals and standard, modified, and dedicated basis sets for coupling constants. Both in vacuum and in chloroform, modeled by the simple continuum model of solvent, the modified b…
New constraints on axion-mediated P , T -violating interaction from electric dipole moments of diamagnetic atoms
2018
The exchange of an axionlike particle between atomic electrons and the nucleus may induce electric dipole moments (EDMs) of atoms and molecules. This interaction is described by a parity- and time-reversal-invariance-violating potential which depends on the product of a scalar ${g}^{s}$ and a pseudoscalar ${g}^{p}$ coupling constant. We consider the interaction with the specific combination of these constants, ${g}_{e}^{s}{g}_{N}^{p}$, which gives significant contributions to the EDMs of diamagnetic atoms. In this paper, we calculate these contributions to the EDMs of $^{199}\mathrm{Hg}$, $^{129}\mathrm{Xe}$, $^{211}\mathrm{Rn}$, and $^{225}\mathrm{Ra}$ for a wide range of axion masses. Com…
Simulated annealing with restrained molecular dynamics using a flexible restraint potential: Theory and evaluation with simulated NMR constraints
1996
A new functional representation of NMR-derived distance constraints, the flexible restraint potential, has been implemented in the program CONGEN (Bruccoleri RE, Karplus M, 1987, Biopolymers 26:137-168) for molecular structure generation. In addition, flat-bottomed restraint potentials for representing dihedral angle and vicinal scalar coupling constraints have been introduced into CONGEN. An effective simulated annealing (SA) protocol that combines both weight annealing and temperature annealing is described. Calculations have been performed using ideal simulated NMR constraints, in order to evaluate the use of restrained molecular dynamics (MD) with these target functions as implemented i…
Role of Disorder on the Dynamics of a Nonlinear Model for DNA Thermal Denaturation
1992
The dynamics of thermal denaturation of DNA is a good example in which nonlinearity coexits with disorder. The amplitude of the motions is so high that bonds break and the base sequence is inhomogeneous since it contains the genetic code. Using a simple nonlinear model, we study the role of local inhomogeneities or of extended disorder on the dynamics of the localized excitations and on the denaturation rate by numerical simulations at constrained temperature. Approximate analytical results are obtained for the trapping of the breatherlike excitations by isolated defects and the statistical mechanics of the disordered molecule.
ChemInform Abstract: “Through-Space” Nuclear Spin-Spin Couplings in Ferrocenyl Polyphosphanes and Diphosphino Cavitands: A New Way of Gathering Struc…
2010
Abstract Nuclear magnetic resonance is an invaluable technique for investigating a variety of important issues ranging from the determination of molecular structure to therapeutic medical imaging. In this respect, the indirect nuclear spin–spin coupling involving common nuclei such as 1 H, 13 C or 31 P provides, via the J constant, conclusive data for compound characterization in solution. This electron-mediated nuclear spin coupling is usually regarded as being transmitted by covalently bonded magnetic atoms. However, several experimental and theoretical studies, first focused on constrained organofluorides, and more recently devoted to phosphane ligands highlighted the existence of very i…
Frequency conversion of propagating surface plasmon polaritons by organic molecules
2008
We demonstrate frequency conversion of surface plasmon polaritons (SPP) by utilizing the coupling between organic dye molecules and SPP. Launching of SPPs into a plasmonic waveguide is done in two ways: by optically excited molecules and by quantum dots (QDs). QDs are demonstrated to overcome the major problem of bleaching occurring with molecules. The SPP propagates tens of micrometers and clear frequency conversion is observed in the SPP spectrum after passing an area of converter molecules. The use of molecules and QDs as elements of all-plasmonic devices has the potential for high integration and use of self-assembly in fabrication. Peer reviewed
Chemical and Structural Trends in the Spin-Admixture Parameter of Organic Semiconductor Molecules
2019
Spin mixing in organic semiconductors is related to spin–orbit coupling (SOC). However, a detailed study analyzing the dependence of the spin-admixture parameter (γ) on structural and material para...
Force probe simulations using a hybrid scheme with virtual sites.
2017
Hybrid simulations, in which a part of the system is treated with atomistic resolution and the remainder is represented on a coarse-grained level, allow for fast sampling while using the accuracy of atomistic force fields. We apply a hybrid scheme to study the mechanical unfolding and refolding of a molecular complex using force probe molecular dynamics (FPMD) simulations. The degrees of freedom of the solvent molecules are treated in a coarse-grained manner while atomistic resolution is retained for the solute. The coupling between the solvent and the solute is provided using virtual sites. We test two different common coarse-graining procedures, the iterative Boltzmann inversion method an…
Benchmark Thermochemistry of the Hydroperoxyl Radical
2004
A theoretical estimation of the enthalpy of formation for the hydroperoxyl radical is presented. These results are based on CCSD(T)/aug-cc-pCV5Z calculations extrapolated to the basis-set limit with additional corrections. Anharmonic vibrational zero-point energies, scalar relativistic, spin -orbit coupling, and diagonal BornOppenheimer corrections are further used to correct the extrapolated term energies, as well as various empirical corrections that account for correlation effects not treated at the CCSD(T) level. We estimate that ¢fH° ) 3.66 ( 0.10 kcal mol -1 (¢fH° ) 2.96 ( 0.10 kcal mol -1 ) using several reaction schemes. Significantly, it appears to be necessary to include effects o…