Electronic structure of porphyrins. All-valence-electron SCF MO CI calculations of the spectra of dianion and free base porphin

All-valence-electron SCF MO CI calculations of the spectra of dianion and free base porphin were performed. Comparisons are made with other SCF MO CI calculations and with experiment. The results obtained are seen to be in reasonable agreement with experiment. Characteristics of the calculated band between the usual L and M bands are also discussed.     

Space-time microstructure and singularity-free quantum field theory

It is shown that the dynamical consistency requirements of quantum field theory and the Lorentz-invariant character of particle kinematics and wave equations are compatible with the postulate that physical space is a complex manifold with Euclidean-Gaussian measure in the small. Such a postulate for the microstructure of space introduces a fundamental length(10^–16 cm) and leads to-functions that are analytic on the light-cone for a free field, and hence to self-energies and renormaiization constants that are finite for interacting fields.Work supported by a National Science Foundation grant.     

Index of refraction in ‘dirty’ displacive ferroelectrics

We report measurements of the optic index of reflection as a function of temperature, n(T), for several highly disordered ferroelectrics: PLZT ceramic [Pb_1?xLa_x(Zr_0.65Ti_0.35)_1?x/4O₃ where x = 0.08] and single crystals of Pb₃(MNb₂)O₉ where M = Zn and Mg. The results are qualitatively different from the unusual displacive ferroelectric behavior and the difference is clearly due to local disorder.     

Rheo-optical studies of concentrated polystyrene solutions subjected to transient simple shear flow

Concentrated polystyrene solutions were investigated on the inception and cessation of simple shear flow by means of the technique of two-color flow birefringence. Both monodisperse solutions of various molecular weights and bimodal mixtures were studied. The molecular weight affected both the amount of overshoot in the birefringence and the response time on the inception of shear flow. Large overshoots in birefringence, up to 250%, and undershoot in the orientation angle were observed. The shear stress and the first normal stress difference were calculated by using the stress–optical rule. The amount of strain at the peaks in the stress growth curves are presented along with the steady-state viscosity and primary normal stress coefficient. The experimental results are compared qualitatively with theoretical predictions of various molecular models.     

Discovery of structurally diverse natural product antagonists of chemokine receptor CXCR3

The chemokines (CXCL9, CXCL10 and CXCL11) and associated CXCR3 receptor are expressed during the inflammatory process from multiple sclerosis, atherosclerosis or organ transplantation resulting in the recruitment of lymphocytes leading to tissue damage. It is hypothesized that blocking of the ligand/CXCR3 receptor interaction has potential to provide opportunity for development of agents that would block tissue rejection. In this paper, four classes of natural product inhibitors (IC₅₀ ranging 0.1–41 M) have been described that block the CXCR3 receptor interaction of IP-10 ligand. These include a cyclic thiopeptide (duramycin), polyketide glycosides (roselipins), steroidal glycosides (hypoglausin A and dioscin) and a novel alkyl pyridinium alkaloid that were isolated by bioassay-guided fractionation of the organic extracts derived from actinomycete, fungal, plant and marine sources and discovered using ¹²⁵ I IP-10/CXCR3 binding assay. Duramycin was the most potent with an IC₅₀ of 0.1 M. Roselipins 2A, 2B and 1A showed IC₅₀ values of 14.6, 23.5, and 41 M, respectively. Diosgenin glycosides dioscin, hypoglaucin A and kallstroemin D exhibited IC₅₀ values of 2.1, 0.47 and 3 M, respectively. A novel cyclic 3-alkyl pyridinium salt isolated from a sponge displayed a binding IC₅₀ of 0.67 M.     

Synthesis and biological testing of aminoxyls designed for long-term retention by living cells

Owing to recent advances in electron paramagnetic resonance (EPR) imaging methodologies, it is now potentially possible to track and image, in real time in vivo, cells that had been tagged with aminoxyl spin probes. We had previously reported that living cells can accumulate 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl [1] to high (millimolar) intracellular concentrations through passive incubation with the corresponding acetoxymethyl (AM) ester [2]. In the present study, we show that under physiological conditions aminoxyl [1] is rapidly extruded by cells through an organic anion transport mechanism, resulting in an intracellular exponential lifetime (t(1/e) or tau) of just 9.84 min at 37 degree C. Through successive rational structural modifications, we arrived at (2,2,5,5-tetramethylpyrrolidin-1-oxyl-3-ylmethyl)amine-N,N-diacetic acid [10], which can still be accumulated by cells to high intracellular concentrations, but which, with an intracellular exponential lifetime of tau]= 114 min, is well retained by cells for long periods of time, where one expects 14% retention even after 5 h. These results suggest that it should be feasible to use EPR imaging to perform in vivo tracking of populations of cells that have accumulated high intracellular levels of aminoxyls.     

Summarizing complexity in high dimensions

High-dimensional, multispectral data on complex physical systems are increasingly common. As the amount of information in data sets increases, the difficulty of effectively utilizing it also increases. For such data, summary information is required for understanding and modeling the underlying dynamics. It is here proposed to use an extension of computational mechanics [C. R. Shalizi and J. P. Crutchfield, J. Stat. Phys. 104, 817 (2001)] to arbitrary spatiotemporal and spectral dimension, for providing such summary information. An example of the use of these tools to identify state evolution in the brain, an archetypal, complex biophysical system, serves as an illustration.