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Two isomers of methanocarba (MC) thymidine are used to determine whether kinases and polymerases discriminate between their substartes on the basis of sugar conformation. A combined solid-state and solution conformational analysis of both compounds, coupled with the direct measurement of mono suggests that kinases prefer substrates that adopt the S sugar conformation.

Results demonstrate that alpha-fluro-dideoxynucleosideATP in its north conformational form is the potent inhibitor of HIV-1 reverse transcriptase whereas the south conformational beta-fluro-dideoxynucleosideATP has to be converted to the alpha form before it can react with the enzyme.

Research has been conducted on the adenosine deaminase (ADA). The study of the ADA binding efficiencies and synthetic adenosine analogue deamination kinetics is presented.

Low-energy excitations and optical absorption spectrum of C[sub 60] are computed by using time-dependent (TD) Hartree–Fock, TD-density functional theory (TD-DFT), TD DFT-based tight-binding (TD-DFT-TB), and a semiempirical Zerner intermediate neglect of diatomic differential overlap method. A detailed comparison of experiment and theory for the excitation energies, optical gap, and absorption spectrum of C[sub 60] is presented. It is found that electron correlations and correlation of excitations play important roles in accurately assigning the spectral features of C[sub 60], and that the TD-DFT method with nonhybrid functionals or a local spin density approximation leads to more accurate excitation energies than with hybrid functionals. The level of agreement between theory and experiment for C[sub 60] justifies similar calculations of the excitations and optical absorption spectrum of a monomeric azafullerene cation C[sub 59]N[sup +], to serve as a spectroscopy reference for the characterization of carborane anion salts. Although it is an isoelectronic analogue to C[sub 60], C[sub 59]N[sup +] exhibits distinguishing spectral features different from C[sub 60]: (1) the first singlet is dipole-allowed and the optical gap is redshifted by 1.44 eV; (2) several weaker absorption maxima occur in the visible region; (3) the transient triplet–triplet absorption at 1.60 eV (775 nm) is much broader and the decay of the triplet state is much faster. The calculated spectra of C[sub 59]N[sup +] characterize and explain well the measured ultraviolet–visible (UV–vis) and transient absorption spectra of the carborane anion salt [C[sub 59]N][Ag(CB[sub 11]H[sub 6]Cl[sub 6])[sub 2]] [Kim et al., J. Am. Chem. Soc. 125, 4024 (2003)]. For the most stable isomer of C[sub 48]N[sub 12], we predict that the first singlet is dipole-allowed, the optical gap is redshifted by 1.22 eV relative to that of C[sub 60], and optical absorption maxima occur at 585, 528, 443, 363, 340, 314, and 303 nm. We point out that the characterization of the UV–vis and transient absorption spectra of C[sub 48]N[sub 12] isomers is helpful in distinguishing the isomer structures required for applications in molecular electronics. For C[sub 59]N[sup +] and C[sub 48]N[sub 12] as well as C[sub 60], TD-DFT-TB yields reasonable agreement with TD-DFT calculations at a highly reduced cost. Our study suggests that C[sub 60], C[sub 59]N[sup +], and C[sub 48]N[sub 12], which differ in their optical gaps, have potential applications in polymer science, biology, and medicine as single-molecule fluorescent probes, in photovoltaics as the n-type emitter and/or p-type base of a p–n junction solar cell, and in nanoelectronics as fluorescence-based sensors and switches. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The conformations of three 2',3'-difluoro uridine nucleosides are studied in order to define the roles that the two vicinal fluorine atoms has played in the puckering preferences of the furanose ring. The studies have shown that both gauche and antiperiplanar effects are operative to maintain a pseudodiaxial arrangement of the C2' and C3' vicinal fluorine atoms.

A systematic survey of the complete set of isomers of fullerences C38, C40, C42, C44, C46, C48, C50, and azafullerene C44N6 is reported. The C NMR chemical shifts and nucleus-independent chemical shifts (NICS) for the stable isomers of each fullerence are presented.