Studies on the Stereochemistry of 2-(Nitromethylidene)-Heterocycles

The ¹H-NMR spectra of 2-(nitromethylidene)pyrrolidine ( 7 ), 1-methyl-2-(nitromethylidene)imidazolidind ( 10 ) and 3-(nitromethylidene)tetrahydrothiazine ( 11 ) in CDCl₃ and (CD₃)₂SO indicate that these compounds have the intramolecularly H-bonded structures (Z)- 7 , (E)- 10 and (Z)- 11 while the N-methyl derivative 8 of 7 is (E)-configurated in both solvents. 1-Benzylamino-1-(methyltio)-2-nitroehtylene ( 13 ), an acylic model, has the H-bonded configuration (E)- 13 in CDCl₃ and in (CD₃)₂SO. 2-(Nitromethylidene)thiazolidine ( 3 ) has the (E)-configuration in CDCl₃ but exists in (CD₃)₂SO as a mixture of (Z)- and (E)-isomers with the former predominating. Both species are detected to varying proportions in a mixture of the two solvents. ¹⁵N-NMR spectroscopy of 3 ruled out unambiguously the nitronic acid structure 6 and the nitromethyleimine structure 5 . The N-methyl derivative 4 of 3 is (Z)-configurated in (CD₃)₂SO. Comparison of the olefinic proton shifts of (Z)- 3 and (Z)- 4 with those of analogues and also of 1,1-bis(methylti)-2-nitroethylene ( 12 ) shows decreased conjugation of the lone pair of electrons of the ring N-atom in (Z)- 3 and (Z)- 4 . This is also supported by ¹³C-NMR studies. Plausible explanations for the phenomenon are offered by postulating that the ring N-atoms are pyramidal in (Z)- 3 and (Z)- 4 and planar in other cases or, alternatively, that the conjugated nitroenamine system gets twisted due to steric interaction between the NO₂-group and the ring S-atom. Single-crystal X-ray studies of 3 and 8 show that the former exists in the (Z)-configuration and the latter in (E)-configuration; the ring N-atom in the former has slightly more pyramidal character than in the latter.     

A potent and highly selective sulfotransferase inhibitor

In the present work, we have used a newly developed, fluorescence-based assay to screen a library of >30 000 compounds as potential beta-arylsulfotransferase-IV inhibitors. A total of 11 inhibitors were discovered. Most of the compounds discovered showed low micromolar inhibition, but one of the compounds showed potent inhibition (Ki = 96 nM). The most potent of these inhibitors was tested against a variety of other purine binding enzymes and showed remarkable specificity.     

DNA recognition interfaces: the influence of interfacial design on the efficiency and kinetics of hybridization

The effect of the surface chemistry of DNA recognition interfaces on DNA hybridization at a gold surface was investigated using both electrochemistry and the quartz crystal microbalance (QCM) technique. Different DNA recognition interfaces were prepared using a two-component self-assembled monolayer consisting of thiolated 20-mer probe single-stranded DNA (ss-DNA) containing either a 3'-mercaptopropyl or a 3'-mercaptohexyl linker group and an alcohol-terminated diluent layer with 2-, 6-, or 11-carbon length. The influence of the interfacial design on the hybridization efficiency, the affinity constant (Ka) describing hybridization, and the kinetics of hybridization was assessed. It was found that the further the DNA was above the surface defined by the diluent layer the higher the hybridization efficiency and Ka. The kinetics of DNA hybridization was assessed using both a QCM and an electrochemical approach to ascertain the influence of the interface on both the initial binding of target DNA to the surface and the formation of a complete duplex. These measurements showed that the length of the diluent layer has a large impact on the time taken to form a perfect duplex but no impact on the initial recognition of the target DNA by the immobilized probe DNA.     

Behavior of plutonium isotopes in the marine environment of Enewetak atoll

There continue to be reports in the literature that suggest a difference in the behavior of^239+240Pu and²³⁸Pu in some aquatic environments. Plutonium isotopes have been measured in marine samples collected over 3 decades from Enewetak atoll, one of the sites in the Marshall Islands used by the United States between 1946 and 1958 to test nuclear devices. The plutonium isotopes originated from a variety of complex sources and could possibly coexist in this environment as different physical-chemical species. However results indicate little difference in the mobility and biological availability of^239+240Pu and²³⁸Pu.     

ANALYSIS OF MICROSECOND FLUORESCENCE YIELD AND DELAYED LIGHT EMISSION CHANGES AFTER A SINGLE FLASH IN PEA CHLOROPLASTS: EFFECTS OF MONO- AND DIVALENT CATIONS

Abstract. New results are presented on the effects of mono- and divalent cations on concurrent changes in the microsecond yields and kinetics of chlorophyll a fluorescence and delayed light emission, and the light saturation curve for the latter at 100 μs, following a 10 ns flash at 337 nm. (1) The fluorescence yield increases exponentially from 3 to 30 μs (lifetime, τ, 6.4 ± 0.6/μs), and decays biphasically between 50 and 800μs. (2) The delayed light emission decays biphasically with two exponential phases: fast phase, T= 7–10μs, and slow phase, T= 33–40μs. (3) The light saturation curve for 100μs delayed light emission is satisfactorily represented by a one-hit Poisson saturation curve. (4) Addition of 5 mM NaCl to salt-depleted chloroplasts decreases (by as much as 40%) the yields of μs fluorescence and delayed light emission, and the subsequent addition of 5mM MgCl₂ increases the yields (≤2 × over samples with only NaCl). (5) The fluorescence yield rise and delayed light emission decay kinetics are independent of low concentrations of cations. The lifetime of the fast phase of fluorescence decay changes from ?90μs to ?160μs, when Na⁺ or Na⁺+ Mg²⁺ are added. Based on a detailed analysis presented in this paper, the following conclusions regarding the effects of low concentrations (few mM) of mono-and divalent cations in sucrose-washed chloroplasts at room temperature are made: (a) Na⁺ decreases (?6%) and Mg²⁺ increases (? 20% compared with the Na⁺ sample) the sensitization of photosystem II photochemistry: this effect is small, but significant. (b) Na⁺ increases and Mg²⁺ decreases the efficiency for radiationless transitions in singlet excited Chl a in the antenna and closed reaction center of PS II; this includes non-radiative energy transfer to PS I, intramolecular intersystem crossing and internal conversion. The ratio of the sum of the rate constants for radiationless transitions to that for fluorescence increases by ? 2-fold upon the addition of Na⁺, and is completely reversed by the addition of Mg²⁺. (c) The rate constant for the re-oxidation of Q^- decreases (about 50%) in the presence of Na⁺ or Na⁺+ Mg²⁺. These conclusions imply that cations produce multiple changes in the primary photoprocesses of PS II at physiological temperatures. It is proposed that these changes are mutually independent and can co-exist.     

Molecular mechanics (MM2) calculations and cone angles of phosphine ligands

Molecular mechanics (MM2) calculations were performed on 54 conformations of 18 phosphines (PH₃; PH_3−nR_n, where n = 1,…3, and R = Me and Et, n = 1 or 2 and R =ⁱPr, and n = 1 and R =^tBu, PMe₂Et, PMeEt₂, and PPhMe₂, and PPh₂R where R = Me, Et, ⁱPr, ^tBu and Ph). The results are compared to those previously obtained from MINDO/3 and MNDO calculations, and to experimental data. Single conformer cone angles and weighted average cone angles were calculated from MM2 optimized geometries employing Tolman's general definition, and they are compared to Tolman's values, MINDO/3 results, and T.L. Brown's E_R values. Of the cone angle definitions used, the weighted average values are suggested as the best single representation of phosphine ligand sizes. The steric parameters (cone angle and E_R values) alone, and in conjunction with electronic parameters, are correlated with experimental data.     

Aromatic polyethers,polysulfones, and polyketones as laminating resins. IV. Polymers with p-cyclophane units for crosslinking

1,3-Bis(p-phenoxybenzenesulfonyl)benzene, 4,4′-bis(p-phenoxybenzenesulfonyl)diphenyl ether, and 4,4′-diphenoxydiphenyl sulfone were polymerized with isophthaloyl or terephthaloyl chlorides in Friedel-Crafts type polymerizations. These polymers had [2,2]p-cyclophane units in the backbone, introduced by employing 3,9-bis(p-phenoxybenzoyl) [2.2]p-cyclophane as part of the polyaryl ether component. Thermolysis of the dimethylene bridge of the [2.2]p-cyclophane monomer produced diradicals which combined across polymer chains to provide crosslinks. p-Cyclophane polymers with 1,3-bis-(p-phenoxybenzenesulfonyl)benzene showed potential as high performance, thermally stable laminating resins.     

Pre-irradiation treatments for CR-39 detectors

The production of track-spots in CR-39 detectors for alpha particles and the subsequent optical counting of the detectors are often influenced by foreign substances deposited on the surface of the detectors. The removal of these substances can be achieved using chemicals for pre-irradiation treatment. Two methods of pre-irradiation treatment were studied in the present experiments. One of them involves the dipping of the detectors in ethanol. In the other method, the detectors were treated in 6N KOH etchant prior to exposure. It was found that prolonged treatment could only produce a reduction in the track density of less than 20%.     

Spectroscopic fingerprints of valence and spin states in manganese oxides and fluorides

We performed a systematic study of soft X-ray absorption spectroscopy in various manganese oxides and fluorides. Both Mn L-edges and ligand (O and F) K-edges are presented and compared with each other. Despite the distinct crystal structure and covalent/ionic nature in different systems, the Mn-L spectra fingerprint the Mn valence and spin states through spectral lineshape and energy position consistently and evidently. The clear O- and F-K pre-edge features in our high resolution spectra enable a quantitative definition of the molecular orbital diagram with different Mn valence. In addition, while the binding energy difference of the O-1s core electrons leads to a small shift of the O-K leading edges between trivalent and quadrivalent manganese oxides, a significant edge shift, with an order of magnitude larger in energy, was found between divalent and trivalent compounds, which is attributed to the spin exchange stabilization of half-filled 3d system. This shift is much enhanced in the ionic fluoride system. This work provides the spectroscopic foundation for further studies of complicated Mn compounds.