Search results for "molecule"

Comparison of epimeric methyl lithocholate and methyl iso-lithocholate molecules: single crystal X-ray structure of methyl lithocholate, ab initio HF…

2003

Abstract 13 C NMR chemical shifts have been measured and assigned for epimeric methyl 3α/β-hydroxy-5β-cholan-24-oates (methyl lithocholate [3α-OH epimer] and methyl iso-lithocholate [3β-OH epimer]). Their molecular dynamics simulations suggest that for both epimers there exists two predominant gas phase conformations, which have been further forwarded for ab initio/HF optimizations and DFT/GIAO based 13 C NMR chemical shift calculations. Excellent linear relationships have been observed between experimental and calculated 13 C NMR chemical shifts for both epimers. For methyl lithocholate (MeLC), the other minimum energy conformation equates very well with the single crystal X-ray structure …

Corrigendum to “Comparison of epimeric methyl lithocholate and methyl iso-lithocholate molecules: Single crystal X-ray structure of methyl lithochola…

2003

DFT calculations of structures, 13C NMR chemical shifts, and Raman RBM mode of simple models of small-diameter zigzag (4,0) carboxylated single-walle…

2012

Linearly conjugated benzene rings (acenes), belt-shaped molecules (cyclic acenes), and models of single-walled carbon nanotubes (SWCNTs) with one carboxylic group at the open end were fully optimized at the B3LYP/6-31G* level of theory. These models were selected to obtain some insight into the nuclear isotropic changes resulting from systematically increasing the basic building units of open-tip-monocarboxylated SWCNTs. In addition, the position of radial breathing mode (RBM), empirically correlated with the SWCNT diameter, was directly related with the radius of model cyclic acene rings. A regular convergence of selected structural, NMR, and Raman parameters with the molecular system size…

Alkyloxy modified pyrene fluorophores with tunable photophysical and crystalline properties

2019

Novel alkyloxy modified 2,7-di-tert-butyl-4,5,9,10-tetra(arylethynyl)pyrenes were prepared through a straightforward Sonogashira coupling approach. Optical properties such as quantum yields and absorption/emission spectra of the fluorophores were investigated by UV/Vis and fluorescence measurements. Aggregation induced excimer formation of the chromophores in polar solvents and in the solid state was proved by the presence of a characteristic bathochromically shifted emission band and a decrease of the emission capability. These results strongly indicate the unexpected observation that the excimer formation of adjacent pyrene rings is not prevented by the introduction of bulky tert-butyl su…

Single Molecule Spectroscopy: Methodological Developments and Experiments at Low Temperature

2001

Interacting induced dipoles polarization model for molecular polarizabilities. Reference molecules, amino acids and model peptides

1999

Abstract We outline a method for the calculation of molecular dipole ( μ ) and quadrupole ( Θ = ) moments and dipole–dipole polarizabilities ( α = ) which we have successfully applied to a series of reference molecules, amino acids and model peptides. The results for μ are in line with CPHF reference calculations. In particular, the calculated positive value of CO is in agreement with both experimental and CI calculations. The computation of ( α = ) has been performed by the interacting induced dipoles polarization model that calculates tensor effective anisotropic point polarizabilities (method of Applequist et al.). The POLAR program cannot be used as a black box. Some tests should be per…

A MRCI PS and CASSCF study of the ground state MgO dissociation energy

1991

Abstract Ab initio calculations at CASSCF and MRCI PS levels are used to determine the dissociation energy for the X 1 Σ + state of MgO, which adiabatically dissociates to the ground state 1 S g of magnesium and to the excited 1 D g state of oxygen, as well as other spectroscopic parameters. Emphasis is placed upon the problem of properly selecting an adequate active space in CASSCF calculations and upon the improvements obtained in MRCI by selecting perturbatively the most important contributions to the total wavefunction and evaluating the remaining ones only by perturbational method. Through a procedure based on stabilizing the computed dissociation energy, values of 3.87 eV (MRCI PS) an…

A mutliconfigurational study of low-lying electronic states of KO

1992

Abstract Potential energy curves and spectroscopic parameters of several electronic states of the KO molecule have been calculated using multi-configurational methods. The KO B 2Π state, first time theoretically described, presents a strong avoided crossing with the A 2Π state, and allows for the explanation of the observed fluorescence of the KO molecule. Eleven electronic states have been studied at all the internuclear distances. Effects of complete active space and basis set selections on the results are also analyzed.

Determination of association constants towards carbon nanotubes

2015

Single-walled carbon nanotubes (SWNTs) are one of the most promising nanomaterials and their supramolecular chemistry has attracted a lot of attention. However, despite well over a decade of research, there is no standard method for the quantification of their noncovalent chemistry in solution/suspension. Here, we describe a simple procedure for the determination of association constants (Ka) between soluble molecules and insoluble and heterogeneous carbon nanotube samples. To test the scope of the method, we report binding constants between five different hosts and two types of SWNTs in four solvents. We have determined numeric values of Ka in the range of 1–104 M−1. Solvent effects as wel…

CASSCF/CASPT2 analysis of the fragmentation of H2 on a Pd4 cluster

2009

Two reactive pathways are described for the dissociative adsorption of a hydrogen molecule on a Pd4 pyramidal cluster, by using DFT/B3LYP and CASSCF/CASPT2 computational methods. Because of the different spin multiplicities of the cluster in the initial and final states, the reaction proceeds through a spin multiplicity change, which occurs close to the transition states. The activation energy values are very similar when the DFT method is used, whereas the CASPT2 calculations predict that the concerted mechanism is disfavored. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010