Biomedical subjects
Publications and source records attributed to Zdenek Slanina.
We show here that La@C72 has a non-IPR cage, unique electronic properties, and high reactivity by the spectroscopic and X-ray crystallographic analysis and the theoretical study. The isolation of La@C72 as a stable derivative might constitute an important stepping-stone on the way to isolation of these unknown metallofullerenes and open new material science of metallofullerenes.
The La2@C72 and Sc2@C72 metallofullerenes have been characterized by systematic density functional computations. On the basis of the most stable geometry of 39 C72 hexaanions and the computed energies of the best endofullerene candidates, the experimentally isolated La2@C72 species was assigned the structure coded #10611. The good agreement between the computed and the experimental 13C chemical shifts for La2@C72 further supports the literature assignment (Kato, H.; Taninaka, A.; Sugai, T.; Shinohara, H. J. Am. Chem. Soc. 2003, 125, 7782). The geometry, IR vibrational frequencies, and 13C chemical shifts of Sc2@C72 were predicted to assist its future experimental characterization.
Reported herein are computations on the relative concentrations of the two experimentally known isomers of Sc3N@C80 , that is, those produced by encapsulation of Sc3N in two particular C80 cages that obey the isolated-pentagon rule, namely, with I(h) and D(5h) symmetries. The calculations are based on density functional methods and have been carried out using the Gibbs energy over a broad temperature interval. It has been computed that, if a relatively free motion of the encapsulate inside the cages is allowed, the observed populations of 10 and 17 % for the D(5h) Sc3N@C80 species are reached at temperatures of 2100 and 2450 K, respectively. The inclusion of the entropy term is essential as, if it is neglected, the D(5h) Sc3N@C80 population at a temperature of 2100 K would be a mere 1 %, owing to the relatively large interisomeric separation potential energy of 19 kcal mol(-1).
The push-pull conjugated molecules 2,7-bis-(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine (BPN) and 2,7-bis(1H-indol-2-yl)ethynyl-1,8-naphthyridine (BIN) adopting daad relays of proton donors (d) and acceptors (a) form multiple hydrogen-bonding complexes with various monosaccharides that possess complementary adda sequences. Although the free BPN emits blue light at lambda(max) = 475 nm in CH(2)Cl(2), its complexation with octyl beta-d-glucopyranoside gives green fluorescence at lambda(max) = 535 nm. The excellent photophysical properties make BPN a highly sensitive probe for monitoring glucopyranoside to a detection limit of approximately 100 pM. On the other hand, the CD-silent BIN molecule binds with monosaccharides to form the CD-active multiple hydrogen-bonding complexes, which exhibit the remarkable chirality dependent helicities consistent with the prediction by the ab initio approaches. On the basis of the similar daad cleft and hence the binding property, the fluorescence and CD absorption methods in BPN and BIN, respectively, are complementary, which, in combination with computational molecular modeling, not only give a detailed insight into the structures of the receptor-saccharide complexes in solution, but also differentiate octyl beta-d-glucopyranoside from its enantiomer and other monosaccharides.
Relative concentrations of nine isomers of Ca at C82 derived from the C82 isolated-pentagon-rule satisfying cages are computed in a wide temperature interval. The computations are based on the Gibbs energy constructed from partition functions supplied with molecular parameters from density functional theory calculations. Five structures show significant populations at higher temperatures: C2v > Cs > C2 > C3v > Cs. The computed relative stabilities agree well with available observations.
En route to conformationally restricted analogues of nicotine and anabasine, a novel synthetic route to bridged anabasines is described that hinges on a domino intramolecular [4 + 2]-cycloaddition/ring opening-elimination sequence of 3-amino-substituted furo[3,4-c]pyridines. Extension of this route to bridged nicotines, however, proved abortive, even when the dienophile tether is activated by a p-tolylsulfonyl group or when the diene moiety is activated by an electron-releasing methoxy substituent. A detailed density functional theoretical study (B3LYP/6-31+G) was undertaken to provide insight into the factors that facilitate an intramolecular Diels-Alder reaction in the former case.
New type of carbon nanotubes-narrow nanotubes-has recently been observed with diameters of 4-5 A. It has been postulated that the narrow nanotubes are closed by fullerene fragments of C(20) and C(36). This paper presents computational results on related model nanotubes with stoichiometries such as C(80), C(84), C(96), C(108), or C(120). The computations were carried out at the PM3, AM1, SAM1, HF/3-21G, HF/4-31G, and B3LYP/6-31G(*) levels. Two C(36) fullerenes were considered, D(6h) and D(2d). At the PM3 level and with the C(84) nanotube stoichiometry, the D(2d) cage closure gave a lower energy (by 185 kcal/mol and a diameter of 5.42 A). There is another possible candidate, a C(32) cage with D(4d) symmetry (two four-membered rings). At the PM3 level and with the C(96) nanotube stoichiometry, the D(4d) closure (with a diameter of 5.43 A) had energy lower by 210 kcal/mol than that of the D(6h) nanotube closure. On the other hand, four-membered rings should not play a significant role for narrow nanotubes with a diameter of 4 A, where the dodecahedron-related closure should be exclusive. Still narrower nanotubes are briefly discussed.
[structure: see text] A push-pull conjugated molecule, 2,7-bis(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine (BPN), has been designed to bind selectively with octyl glucopyranoside (OGU). The BPN/OGU quadruple hydrogen-bonding complex adopts a rigid BPN conformation in which the proton donor (d) and acceptor (a) relays (daad) are resonantly conjugated through the ethynyl bridge, inducing pi-electron delocalization, i.e., a charge transfer effect. The excellent photophysical properties make BPN a highly sensitive probe for monitoring glucopyranoside to a detection limit of approximately 100 pM.