Search

Rotationally resolved S[sub 1]-S[sub 0] fluorescence excitation spectra of ethylbenzene, two conformers of n-propylbenzene, and two conformers of n-butylbenzene have been observed and assigned. The data obtained provide information about the equilibrium properties of each molecule, including their geometries in the S[sub 1]-S[sub 0] states, their electronic distributions, and their dynamical behavior following the absorption of light. Trans structures are found to have S[sub 1] states that are [sup 1]L[sub b] in character with relatively long fluorescence lifetimes. Gauche structures are found to have S[sub 1] states that are mixed ([sup 1]L[sub b]/[sup 1]L[sub a]) in character with relatively short fluorescence lifetimes. Possible reasons for these differences in properties are discussed. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A combination of vibrational spectroscopy was conducted under molecular beam conditions and quantum chemical calculation to establish the intrinsic three-dimensional structures of the cellulose disaccharide and the critical [beta]1,4-linkage at the nonreducing end of the growing cellulose polymer, its C-4' epimer. The results obtained could have significant implications for the structure and insolubility of native cellulose polymers.

The intrinsic, global minimum secondary structure of the glycosylation-compatible consensus peptide sequon NGS has resembled QGS, but it is much less tightly bound. The structural changes involving interactions with the carboxamide side chain has provided evidence for the operation of structural constraints and a potential insight into the unique reactivity of the asparagine side chain toward enzymatic glycosylation.

The intrinsic conformational preferences and structures of the branched trimannoside, [alpha]-phenyl 3,6-di-O-([alpha]-D-mannopyranosyl)-[alpha]-D-mannopyranoside and its singly hydrated complex, are examined in the gas phase isolated at low temperature in a molecular beam expansion. The creation of a water pocket motif localized at the bisecting axis of the trimannoside is similar to the structure of more complex N-glycans in water, indicating a general role for the bisecting OH4 group in the central mannose unit.

The conformational structures of protonated polyalanine peptides, [Ala.sub.n][H.sup.+] are investigated in the gas phase. Results show that the peptide [Ala.sub.3][H.sup.+] exhibits an unfolded shape with likely dynamic interconversion between different conformations.

Infrared ion-dip spectroscopy coupled with DFT and ab initio calculations are employed to establish the intrinsic conformational preference of the basic structural unit of a peptide mimic, a cis-tetrahydrofuran-based 'carbopeptoid' (amide-sugar-amide) isolated at low temperature in the gas phase. The cis-tetrathydrofuran-based carbopeptoid units form a [beta]-turn-type structure, which is stabilized by an intramolecular NH->O[double bond]C hydrogen bond across the sugar ring, consequently forming a 10-membered, [C.sub.10] turn.

While probing benzyl lactoside isolated in the gas phase using UV and IR ion-dip, it is found that the disaccharide unit adopts only a single, rigid structure. The biological implications of this discovery are discussed.

Partially resolved ultraviolet rotational band contours associated with the S1

The isotopmer selected N = 2 CH chromophore absorption of (super 12)C(sub 6)H(sub 6) and (super 13)C(super 12)C(sub 5)H(sub 6) near 6000 cm(super -1) at natural abundance are recorded. The (super 12)C(sub 6)H(sub 6) spectrum is compatible with a proposed model of intramolecular vibrational redistribution with a distinct hierarchy of time scales.

Rotationally resolved fluorescence excitation spectra of the N2 van der Waals complex of p-difluorobenzene (pDFB-N2) are recorded in the collision free environment. The data obtained provide information about the structure and internal motion of pDFB-N2 in its ground (S0) and excited (S1) electronic states.

The kinetics of CF3CFHO radical reactions was studied at 20 and 35 Torr and from 259 to 297 K by flash photolysis with time-resolved mass spectrometry. Ab initio molecular orbital calculations for optimized geometries, vibrational frequencies, and total energies of CF3CFHO, the reaction products, and the C-C bond-breaking transition state were made.

The structural investigation of a hydrated monosaccharide, phenyl beta-D-glucopyranoside (PhebetaGlc), in the gas phase is presented. It is reported that despite the potentially large set of possible binding sites and conformations, only two singly hydrated complexes are formed in the free jet expansion.