Biomedical subjects

Jaan Laane

Publications and source records attributed to Jaan Laane.

4 recordsLinked to original sources

PubMed2006

Spectroscopic and computational studies of the intramolecular hydrogen bonding of 2-indanol.

2-Indanol in its most stable form is stabilized by internal hydrogen bonding, which exists between the hydroxyl hydrogen atom and the pi-cloud of the benzene ring. A comprehensive ab initio calculation using the MP2/cc-pVTZ level of theory showed that 2-indanol can exist in four possible conformations, which can interchange through the ring-puckering vibration and the internal rotation of the OH group on the five-membered ring. A potential energy surface in terms of these two vibrational coordinates was calculated. Density functional theory calculations were used to predict the vibrational frequencies and to help in normal mode assignments. Fluorescence excitation spectra of 2-indanol confirm the presence of the four conformers in the electronic ground and excited states. The spectral intensities indicate that, at 90 degrees C, 82% of the molecules exist in its most stable form with the intramolecular hydrogen bonding. The other isomers are present at approximately 11, 5, and 3%. The MP2/6-311++G(d,p) calculation predicts a distribution of 70, 13, 9, and 8% at 90 degrees C, the experimental sample temperature.

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PubMed2006

Laser-induced fluorescence spectra, structure, and the ring-twisting and ring-bending vibrations of 1,4-benzodioxan in its S0 and S1(pi,pi*) states.

The laser-induced fluorescence (LIF) spectra, both the fluorescence excitation spectra (FES) and single vibrational level fluorescence spectra (SVLF) from several different vibronic states, along with the ultraviolet (UV) absorption spectra of 1,4-benzodioxan have been recorded and analyzed. A detailed energy map has been constructed for four low-frequency vibrations and their combinations for both the S(0) and S(1)(pi,pi) electronic states. These are nu(48) (ring-bending), nu(25) (ring-twisting), nu(47) (ring-flapping), and nu(24) (skeletal-twisting). Both the experimental and ab initio calculations show the molecule to be twisted in both the S(0) and S(1)(pi,pi) states with high barriers to planarity. The experimentally determined ring-twisting quantum states, which are confined to the lower regions of the potential energy surface, were used to calculate one-dimensional potential functions in terms of the twisting coordinates, and the extrapolated barriers were estimated to be 5700 and 4200 cm(-1) for the S(0) and S(1) states, respectively. Two-dimensional calculations, which included the interactions with the bending modes, gave values of 3906 and 1744 cm(-1), respectively. The S(0) value compares favorably with the ab initio value of 4095 cm(-1).

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PubMed2006

Fluorescence and ultraviolet absorption spectra and structure of coumaran and its ring-puckering potential energy function in the S1(pi,pi*) excited state.

The fluorescence excitation (jet cooled), single vibrational level fluorescence, and the ultraviolet absorption spectra of coumaran associated with its S1(pi,pi*) electronic excited state have been recorded and analyzed. The assignment of more than 70 transitions has allowed a detailed energy map of both the S0 and S1 states of the ring-puckering (nu45) vibration to be determined in the excited states of nine other vibrations, including the ring-flapping (nu43) and ring-twisting (nu44) vibrations. Despite some interaction with nu43 and nu44, a one-dimensional potential energy function for the ring puckering very nicely predicts the experimentally determined energy level spacings. In the S1(pi,pi*) state coumaran is quasiplanar with a barrier to planarity of 34 cm(-1) and with energy minima at puckering angles of +/-14 degrees. The corresponding ground state (S0) values are 154 cm(-1) and +/-25 degrees . As is the case with the related molecules indan, phthalan, and 1,3-benzodioxole, the angle strain in the five-membered ring increases upon the pi-->pi* transition within the benzene ring and this increases the rigidity of the attached ring. Theoretical calculations predict the expected increases of the carbon-carbon bond lengths of the benzene ring in S1, and they predict a barrier of 21 cm(-1) for this state. The bond length increases at the bridgehead carbon-carbon bond upon electron excitation to the S1(pi,pi*) state give rise to angle changes which result in greater angle strain and a nearly planar molecule.

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PubMed2005

S0 ring-puckering potential energy function for coumaran.

With the aid of a reported inversion splitting value, the far-infrared spectrum resulting from the ring-puckering vibration of coumaran has been reassigned and the one-dimensional potential energy function has been determined. The barrier to planarity is 155 +/- 4 cm(-1) and the dihedral angle is 25 degrees . These results agree well with the millimeter wave spectra values of 152 cm(-1) and 23 degrees , which utilized different data and a different type of potential function for the calculations. The MP2/cc-pvtz ab initio values of 238 cm(-1) and 26.5 degrees agree more poorly. If the benzene ring is assumed to remain rigid, the calculated barrier drops to 204 cm(-1). The puckering potential functions for the ring-flapping and ring-twisting vibrationally excited states were also determined and the barriers were found to be 149 and 156 cm(-1), respectively.

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