Finiteness obstructions and cocompact actions onS m×ℝn

Partially supported by the National Science Foundation under grant number DMS88-03149.     

Almost Complex Structures Which Are Compatible with Kähler or Symplectic Structures

In this note we prove that half of all homotopy classes of almost complex structures on M is not compatible with any symplectic structure for a certain class of oriented compact 4-manifolds M. In particular, half of all homotopy classes of almost complex structures on an oriented 4-manifold is not compatible to any Kähler structure.     

FLUORESCENCE PROPERTIES OF C-PHYCOCYANIN ISOLATED FROM A THERMOPHILIC CYANOBACTERIUM

Abstract The fluorescence lifetime of purified C-phycocyanin from the thermophilic cyanobacterium, Phormidium laminosum (strain OH-1-p. Cl 1), was measured as 1.48 ± 0.06 ns using the technique of time-correlated single-photon counting under very weak excitation pulses. The natural radiative lifetime (∼6.1 ns) of the pigment was calculated by integrating the absorption spectrum using the Strickler–Berg equation. From these two lifetimes we calculate a fluorescence quantum yield of ∼0.24 which is very close to the value ∼0.22 which we measure relative to the known value of cresyl violet in methanol. Both the fluorescence lifetime and the quantum yield of the pigment from this organism are lower than most previous values reported in the literature. We conclude that our lower values are not due to high light intensity, pH, buffer, concentration, instrumentation artifacts, aggregation effects or the thermophilic nature of the organism. Instead, we suggest that the photophysical properties of C-phycocyanin are species dependent, perhaps due to the specific molecular environment of the tetrapyrrole.     

MS-Xα calculations on boron trihalides and comparison with their photoelectron spectra

The multiple-scattering Xα model has been applied to the sequence of boron trihalides BX₃ where X = F.C1. Br, and I. Transition state calculations show good agreement with the experimental ionization potentials measured by photoelectron spectra.     

Biogenetic-type synthesis of vepridimerines A–D

A simple synthesis of vepridimerines A–D based on thermolysis of veprisine is presented. In addition, the structure of a novel synthetic veprisine dimer is reported. Since veprisine has been previously synthesized, this report constitutes the first total synthesis of the vepridimerines.     

Evodulone,a new tetranortriterpenoid from carapa procera

Hexane extraction of the ground seeds of $\text{Carapa procera}$ followed by chromatography afforded a new tetranortritepenoid for which the structure (II) is proposed on the basis of spectroscopic evidence.     

Triterpenoids

This review covers the isolation and structure determination of triterpenoids including squalene derivatives, lanostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleannes, friedelanes, ursanes, hopanes, isomalabaricanes and saponins. The literature from January to December 2002 is reviewed and 221 references are used.     

Explicit hydrogen molecular dynamics simulations of hexane deposited onto graphite at various coverages

We present results of molecular dynamics (MD) computer simulations of hexane (C6H14) adlayers physisorbed onto a graphite substrate for coverages in the range 0.5 < or = rho < or = 1 monolayers. The hexane molecules are simulated with explicit hydrogens, and the graphite substrate is modeled as an all-atom structure having six graphene layers. At coverages above about rho congruent with 0.9 the low-temperature herringbone solid loses its orientational order at T(1) = 140 +/- 3 K. At rho = 0.878, the system presents vacancy patches and T(1) decreases to ca. 100 K. As coverage decreases further, the vacancy patches become larger and by rho = 0.614 the solid is a connected network of randomly oriented islands and there is no global herringbone order-disorder transition. In all cases we observe a weak nematic mespohase. The melting temperature for our explicit-hydrogen model is T(2) = 160 +/- 3 K and falls to ca. 145 K by rho = 0.614 (somewhat lower than seen in experiment). The dynamics seen in the fully atomistic model agree well with experiment, as the molecules remain overall flat on the substrate in the solid phase and do not show anomalous tilting behavior at any phase transition observed in earlier simulations in the unified atom (UA) approximation. Energetics and structural parameters also are more reasonable and, collectively, the results from the simulations in this work demonstrate that the explicit-hydrogen model of hexane is substantially more realistic than the UA approximation.