Fluorophenyl Bilirubins: Synthesis and Stereochemistry

Summary.  Analogs of bilirubin with vinyl groups replaced by symmetrically-disposed o-fluorophenyls (1, bis-exo, and 2, bis-endo) were synthesized and characterized spectroscopically. Their ¹H NMR spectra and NOE data are consistent with an intramolecularly hydrogen-bonded ridge-tile conformation where each propionic acid group embraces an opposing dipyrrinone. Like bilirubin, 1 and 2 exhibit negative chirality induced circular dichroism (ICD) Cotton effects in chloroform containing quinine. Unlike bilirubin, however, in aqueous buffer containing human serum albumin, 2 exhibits a negative exciton chirality ICD, whereas that of 1 is positive. Received May 22, 2001. Accepted May 29, 2001     

On the Molecularity of Bilirubins and their Esters and Anions in Chloroform Solution

Summary.  Bilirubins with propionic acids at C-8 and C-12 engage in intramolecular hydrogen bonding and are thought to be monomeric in solution, although the latter is unproven. In contrast, their dimethyl esters and etiobilirubin analogs (with the C-8 and C-12 propionic acids replaced by alkyl residues) favor intermolecular hydrogen bonding and are thought to be dimeric in nonpolar solvents. There is little information on the molecularity of the bilirubin dianion in solution. In this work, vapor pressure osmometry studies of chloroform solutions of bilirubins, their dimethyl esters, and etio-analogs clearly indicate that the diacids and dianions are monomeric, whereas the diesters and dialkyls are dimeric. However, the presence of a C-10 gem-dimethyl group causes the ester and the etiobilirubin to become monomeric. Received May 9, 2000. Accepted May 19, 2000     

Nearly isotropic propagation of spatially discretized waves

The effect of spatial discretization on the isotropy of propagating waves is investigated. A general criterion is given for minimizing the numerical anisotropy and dispersion caused by spatial discretization, and specific discretizations in two and three space dimensions are derived which give, in a well-defined sense, optimally isotropic propagation. We establish the group-theoretic connection between the properties of the spatial discretization and the symmetries of the underlying computational grid. The discretization technique, described here in the context of the scalar wave equation, may also be applied to other partial differential equations containing the Laplacian or gradient operators.     

Hadron scattering in two-dimensional QCD: (I). Formalism and leading order calculations

Two-dimensional quantum chromodynamics in the 1/N_c expansion is explored as a model for hadronic interactions. In meson-meson scattering, order 1/N_c terms exhibit embryonic “Regge” behaviour, with the crossed channel factorization, signature and exchange degeneracy properties found in dual Regge models. “Regge” intercepts are additive in the quark quantum numbers exchanged, and have a lower limit for large quark masses. Residues also factorize in the direct channel. An analogue for fixed angle scattering is presented which has deviations from dimensional counting rules related to form factors and Regge intercepts.     

Critical exponents for the Reggeon quantum spin model

The Reggeon quantum spin (RQS) model on the transverse lattice in D dimensional impact parameter space has been conjectured to have the same critical behaviour as the Reggeon field theory (RFT). Thus from a high “temperature” series of ten (D = 2) and twenty (D = 1) terms for the RQS model we extrapolate to the critical temperature T = T_c by Padé approximants to obtain the exponents η=0.238±0.008, z=1.16±0.01, v=1.271±0.007 for D=2 and η=0.317±0.002, z=1.272±0.007, v=1.736±0.001, λ=0.57±0.03 for D=1. These exponents naturally interpolate between the D=0 and D=4?ε results for RFT as expected on the basis of the universality conjecture.     

Measurement of the Hall dynamo effect during magnetic reconnection in a high-temperature plasma

The fluctuation-induced Hall electromotive force, [deltaJ x deltaB]/nee, is experimentally measured in the high-temperature interior of a reversed-field pinch plasma by a fast Faraday rotation diagnostic. It is found that the Hall dynamo effect is significant, redistributing (flattening) the equilibrium core current near the resonant surface during a reconnection event. These results imply that effects beyond single-fluid MHD are important for the dynamo and magnetic reconnection.     

Control of density fluctuations and electron transport in the reversed-field pinch

Contrary to what has been observed thus far collision-induced light scattering (CILS) can be completely polarized. This exceptional behavior characterizes the very far wing of the binary CILS spectrum by gaseous helium. This conclusion is drawn from an experimental study of the depolarization ratio of He (2) in a much extended, previously unexplored, spectral domain. Our analysis shows that this property, unique thus far, is mainly due to an almost perfect cancellation between polarization and exchange pair polarizability contributions to the depolarized spectrum, taking place at internuclear distances shorter than the atomic diameter.     

Electron paramagnetic resonance and relaxation of amorphous silicon below 1 K

Amorphous silicon, generated within crystalline Si by ²⁸Si⁺ ion implantation, exhibits an electron spin relaxation rate which varies with temperature as T^2.37 between 0.3 and 4.2 K. These results exclude the current model of a phonon-limited, direct relaxation mechanism in a-Si. A relaxation process, consistent with the known temperature variation, is outlined. EPR signal strengths, relative to a known paramagnet at temperatures near 1.2 and 0.4 K, put limits on an antiferromagnetic Curie-Weiss temperature of 0?θ?0.06 K.     

The external field problem for QCD

In lattice gauge theory, many computations such as the strong coupling expansions, mean field theory, or the few plaquette models require the evaluation of the one-link integral in the presence of an arbitrary N × N complex matrix source (J). For SU(N) gauge theories, we express our general solution to the external field problem as an integral over the maximal abelian subgroup [U(1)]^N?1

where S₀ = 2Σ_kz_k cos(φ_k ? θ), z_j are eigenvalues of √JJ⁺, e^2iNθ=detJ/detJ⁺, and G is an appropriate jacobian determinant. Our explicit solution follows from differential Schwinger-Dyson equations cast in a separable form by using fermionic variables, and the special cases of N = 2, 3 and ∞ agree with earlier derivations.     

Plasma diagnostic applications on the TEXT tokamak using a high power, twin frequency optically pumped far-infrared laser

A high-power, twin-frequency, optically-pumped, far-infrared (FIR) laser has been developed at UCLA for diagnostic application on the TEXT tokamak. The source is operated at 245 GHz (=1.22 mm) for heterodyne scattering measurements and 694 GHz (=432 m) for high resolution interferometry. Future plans include a 30 channel interferometer/polarimeter operating at 694 GHz to accurately determine current profiles.