Novel mercury(II) complexes of porphyrins

Treatment of octa-alkylporphyrins (e.g. 1–3) with mercury(II) acetate in methylene chloride and tetrahydrofuran affords novel complexes (4) containing two porphyrin rings layered between three Hg atoms. A new type of stereoisomerism in regularly substituted porphyrins (e.g. 1a, 2a) is identified; it is observed by NMR spectroscopy and occurs because two forms of the complex (4) are possible, depending upon which faces of the porphyrin molecule are turned in towards the central Hg atom. The NMR spectra also indicate that in concentrated solution the double sandwich complexes (4) are stable towards disproportionation and recombination. On the basis of the inherent geometrical arrangements in the complex (4), an efficient NMR method for unambiguous identification of the four primary type isomers of the aetio- and copro-porphyrin series is described.

In very dilute solution, or in mixtures containing nucleophilic solvents such as pyridine, methanol, dioxan, or tetrahydrofuran (in the absence of excess mercury(II) acetate), the double sandwich complexes (4) are destroyed to afford normal 1:1 metalloporphyrins.     

Operator stable laws: Series representations and domains of normal attraction

LetX,X ₁,X ₂,... be i.i.d. random vectors in ^d. The limit laws that can arise by suitable affine normalizations of the partial sums,S _n=X ₁+...+X _n, are calledoperator-stable laws. These laws are a natural extension to ^d of the stable laws on. Thegeneralized domain of attraction of [GDOA()] is comprised of all random vectorsX whose partial sums can be affinely normalized to converge to . If the linear part of the affine transformation is restricted to take the formn ^–B for some exponent operatorB naturally associated to thenX is in thegeneralized domain of normal attraction of [GDONA()]. This paper extends the theory of operator-stable laws and their domains of attraction and normal attraction.     

Metal-containing triarylboron compounds for optoelectronic applications

Triarylboranes have recently emerged as a powerful new class of electron acceptors with great potential as optoelectronic materials. The empty p(z) orbital on the boron centre promotes strong charge-transfer transitions, leading to highly luminescent compounds with colors spanning the entire visible spectrum. Due to intense research efforts over the past decade, many examples now exist of organic molecules based on this structural motif. Only recently, however, have transition metal-containing triarylboranes been closely investigated. These compounds are capable of bright luminescence from a triplet excited state, and have been developed as efficient emissive materials for organic light-emitting diodes (OLEDs) as a result. In addition, their long-lived phosphorescence gives these materials potential as highly selective chemical sensors for small anions using time-gated detection, eliminating interference from background fluorescence. The research of the past several years has now led to a better understanding of the impact of the triarylboron group on the photophysical properties of metal complexes, which we expect will provide many opportunities for research into this class of functional phosphorescent materials.     

Additions of enantiopure alpha-sulfinyl carbanions to (S)-N-sulfinimines: asymmetric synthesis of beta-amino sulfoxides and beta-alphamino alcohols

The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported.     

Synchronization Analysis of Coupled Noncoherent Oscillators

We present two different approaches to detect and quantify phase synchronization in the case of coupled non-phase coherent oscillators. The first one is based on the general idea of curvature of an arbitrary curve. The second one is based on recurrences of the trajectory in phase space. We illustrate both methods in the paradigmatic example of the R?ssler system in the funnel regime. We show that the second method is applicable even in the case of noisy data. Furthermore, we extend the second approach to the application of chains of coupled systems, which allows us to detect easily clusters of synchronized oscillators. In order to illustrate the applicability of this approach, we show the results of the algorithm applied to experimental data from a population of 64 electrochemical oscillators.     

Science Teacher Supply in the United States

The purpose of this study was to describe the supply and potential shortages of science teachers in the United States. Ninety-six percent of the State Science Consultants of the 50 State Boards of Education responded to a 1992 survey to assess the supply of science teachers. This survey was modeled after Howe and Gerlovich's 1982 study to provide an assessment of changes in science teacher supply over the last 10 years. Although there were improvements in the supply of science teachers, shortages were reported in all science subjects and were particularly critical in physics, chemistry, and earth science. In addition to providing a needed update on science teacher supply, this study analyzed 45 previous studies of science teacher supply and found convincing evidence to support the hypothesis that there is a persistent but fluctuating long term shortage of science teachers. This shortage is attributed to competition with business and industry. To alleviate critical shortages of science teachers, it is recommended that salaries be raised to be more competitive with industry and a national database be established to facilitate monitoring the supply of science teachers.     

THE ANTI-HIV ACTIVITIES OF PHOTOACTIVE TERTHIOPHENES

Abstract— Various synthetic analogues of the naturally occurring terthiophene, α-terthienyl (αT), were evaluated for anti-human immunodeficiency virus (HIV) activity. The compounds were incubated individually with a known amount of the virus, with or without UVA radiation (long-wavelength ultraviolet) and residual virus was monitored for its ability to produce cytopathic effects in cell culture and the production of virus-specific protein (p24). The basic terthiophene structure was essential for good anti-HIV activity, although various side chains, such as alcohols, bromo, methyl, thiomethyl and trimethylsilyl groups, permitted retention of maximum activity. Under optimum conditions, as little as 12 ng/mL of these compounds ( i.e approximately 3 × 10⁻⁸ M ) could inactivate 10³ infectious virions. None of the compounds however were more active than αT itself. In all cases, UVA radiation was essential. Several side chains decreased the antiviral efficacy, and some side chains abrogated the activity.     

Higher order Ito product formula and generators of evolutions and flows

A simple combinatorial formula is found for the product of two iterated quantum stochastic integrals, and used to find conditions that such an integral represent a unitary-valued or^*-algebra homomorphism-valued process.