Electronically-coupled MM quadruply-bonded complexes of molybdenum and tungsten

The reaction of M2(O2CBu(t))4 (M = Mo, W) with a dicarboxylic acid in toluene yields compounds of general formula [M2]-O2C-X-CO2-[M2] ([M2] = M2(O2CBu(t))3; X = conjugated spacer). The M2 units are electronically coupled via interactions between the M2 delta and dicarboxylate pi* orbitals, and the magnitude of this coupling is revealed by electronic structure calculations and spectroscopic data. These compounds show intense metal to ligand charge transfer (MLCT) absorptions in the visible region of the electronic spectrum that are temperature and solvent dependent. Evidence of electronic coupling is seen in their cyclic voltammograms, which show two successive one-electron oxidations. The extent of electronic coupling in the mixed valence radical cations [M2]-O2C-X-CO2-[M2]+, generated by oxidation with one equivalent of AgPF6 or FeCp2PF6, is evaluated by EPR and UV-vis-NIR spectroscopic data, and delocalized behavior is observed in compounds with W2 units separated by up to 13.6 angstroms. The simplicity of the frontier M2 orbital interactions with the bridge pi orbitals provides a convenient system with which to study electron transfer in mixed valence systems, as compared to the extensively studied, but more complicated, dinuclear t(2g)6/t(2g)5 mixed valence compounds. Oligomeric and polymeric compounds incorporating M2 units have also been synthesized, having general formula [M2(O2CR)2(O2C-Thio-CO2)]n (Thio = n-hexyl substituted ter- and quinque-thiophenes). They can be deposited as thin films by spin coating, and show photoluminescence and electroluminescence. These metallo-polythiophenes show potential for application in electronic materials. (     

Crystal Structure and Packing of Isocyclosporin A

The crystal structure of isocyclosporin A ( 1 ), a rearrangement product of the immunosuppressant drug cyclosporin A, has been determined at 193 (2) K. Crystals are orthorhombic with cell dimensions a = 26.684 (7), b = 26.936 (3) Å, c = 28.549 (7) Å, space group C222₁. The structure was solved by direct methods and refined by full-matrix least-squares methods to a conventional R value of 0.110. In contrast to the structure of cyclosprin A in solution and in the crystal, isocyclosporin A ( 1 ) has no regular secondary structural elements. The backbone adopts an open, irregular conformation with cis amide bonds between residue 2 and 3, and 3 and 4, respectively. All the other amide bonds and the ester linkage are trans. Contrary to crystal structures of cyclosporin derivatives, this crystal structure is stabilized by two transannular and four intermolecular H-bonds.     

Synthesis of substituted 3-amino[6,5-b]triazinoindoles

4-[(9-Methyl-as-triazino[6,5-b]indol-3-yl)amino]-2-methyl-2-butanol ( 13 ) and the corresponding 2-methyl-3-imino derivative 12 were synthesized and tested in vitro against Rhino 2 virus. The two compounds were more active than the known triazino[5,6-b]indole 4 . 2,9-Dimethyl-3-methoxy-9H-as-triazino[6,5-b]indolium tosylate ( 21 ) and the related 3-methylthio compound 9 were prepared. Quaternary 21 formed a pseudo base, 22a , whereas quaternary 9 did not form a pseudo base.     

PHOTODYNAMIC THERAPY INDUCED ULTRASTRUCTURAL ALTERATIONS IN MICROVASCULATURE OF THE RAT CREMASTER MUSCLE

Abstract— Photodynamic therapy disrupts blood flow to tumors and produces tumor necrosis. These effects may be due to a localized generation of singlet oxygen. The current studies used direct observations of the rat cremaster microvasculature to examine the vascular effects of PDT. The objective of the morphological examination was to delineate the structural basis for the altered blood flow in photodynamic therapy. Dihematoporphyrin ether given 30 min or 48 h prior to the experiment was activated with green light (wavelength530–560 nm, 120 J/cm²). After the in vivo activation the tissues were prepared for electron microscopy. Light alone induced little or no change in the luminal content or vessel wall. On exposure to activating light both acute (30 min) and long term (48 h) dihematoporphyrin ether pretreated samples displayed formation of luminal aggregates, granulocyte margination and migration, and endothelial cell and smooth muscle cell damage. The latter was more pronounced in the arterioles than the venules. Perivascular changes included interstitial edema and damage to striated myocytes. Some of the alterations such as interstitial edema may be transient; however, smooth and skeletal muscle cell injury are important in normal and tumor tissue necrosis after photodynamic therapy.     

Raman spectrum of n-C23H48 and n-C44H90 at high pressures: Fermi resonance between the CH2 deformation and bending modes

Resonance interaction in the deformation (1400 to 1500 cm^?1) region of the Raman spectrum of n-C₂₃ H₄₈ and n-C₄₄H₉₀ at high pressures are reported. Implications of these results concerning the interpretation of the corresponding bands of the Raman spectrum of crystalline polyethylene are discussed.     

Kinetic aspects of the Diels-Alder reaction between poly(styrene-co-furfuryl methacrylate) and bismaleimide

The crosslinking Diels-Alder reaction between styrene-furfuryl methacrylate copolymer samples (poly(ST-co-FM)) and bismaleimide (BM) at 25 °C in chloroform was studied by following the decay in UV absorbance of the maleimide (MI) group at 320 nm. Reaction conditions were changed by using copolymers with different mole fraction of FM, F_FM, and by employing different initial molar ratios of reactants (furan group within FM and MI group within BM). Second order kinetics were obeyed. ¹³C NMR spectra showed that, even when all reactants had been converted to an insoluble crosslinked network, unreacted MI groups remained, presumably in the form of singly reacted pendant BM molecules. The fractions of MI groups remaining unreacted were found to be 0.49, 0.34 and 0.22 for FM:MI mole ratios in the initial mixture of 2, 1 and 0.5 respectively, when using a copolymer of F_FM=0.1354. An attempt was also made to follow the kinetics of network formation by ¹³C NMR spectroscopy, using the peak areas for reacted and unreacted MI and FM groups, but many of the findings were subject to some uncertainty for reasons, which are discussed. However, because the peak areas were considered reliable for unreacted MI groups, the rate constant, k, was evaluated, thereby. Overall using UV and NMR the values of k lay within the interval (0.8-3.6) × 10⁻⁵ dm³ mol⁻¹ s⁻¹.     

An improved algorithm to locate critical points in a 3D scalar field as implemented in the program MORPHY

A new algorithm for location of the critical points in general scalar fields is described. The new method has been developed as part of an on-going process to exploit the topologic analysis of general 3D scalar fields. Part of this process involves the use of topologic information to seed the critical point search algorithm. The continuing move away from topologic studies of just the electron density requires more general algorithms and the ability to easily "plug in" new functions, for example, the Laplacian of the electron density ( triangle down (2)rho), the Electron Localisation Function (ELF), the Localised Orbital Locator (LOL), the Lennard-Jones function (LJF), as well as any new functions that may be proposed in the future. Another important aspect of the current algorithm is the retention of all possible intermediate information, for example, the paths describing the connectivity of critical points, as well as an ability to restart searches, something that becomes increasingly important when analysing larger systems. This new algorithm represents a core part of a new local version of the MORPHY code. We distinguish nine universal types of gradient paths.     

[2,6‐Bis(3,5‐dimethylpyrazol‐1‐ylmethyl)pyridine]iodocopper(I) dichloromethane solvate

The title compound, [CuI(C₁₇H₂₁N₅)]·CH₂Cl₂, contains a tetracoordinate Cu^I centre with an unusual distorted tetrahedral stereochemistry, which has also been observed in other Cu^I complexes containing this tridentate ligand. This distortion is probably a result of intermolecular steric contacts between the I^? ligand and a neighbouring CH₂Cl₂ mol­ecule.     

Thermotropic copolyesters. II. Synthesis and characterization of liquid-crystal copolyesters containing the bicyclo[2.2.2]octane ring system

The syntheses and characterizations of poly(oxy-trans-1,4-cyclohexyleneoxycarbonyl-1,4-bicyclo[2.2.2]octylenecarbonyl) (I) and poly(oxy-trans-1,4-cyclohexyleneoxycarbonyl-1,4-bicyclo[2.2.2]octylenecarbonyl-co-oxy-trans-1,4-cyclohexyleneoxysebacoyl) (II) are described. The polymer systems were characterized by infrared spectroscopy, proton magnetic resonance spectroscopy, solution viscosity, and differential scanning calorimetry. The random copolyester prepared from 1:0.65:0.35 mol of trans-1,4-cyclohexanediol, bicyclo[2.2.2]octane-1,4-dicarbonyl chloride, and sebacoyl chloride, respectively, formed a birefringent fluid state in the melt.     

SEASONAL TRENDS IN ERYTHEMAL and CARCINOGENIC ULTRAVIOLET RADIATION AT MID-SOUTHERN LATITUDES1989–1991

A network of solar carcinogenic/erythemal ultraviolet radiometers has been established in New Zealand. Daily integrated irradiances of this biologically harmful ultraviolet radiation for 1989, 1990 and 1991 are reported from radiometers located at Wellington (41°S) and Christchurch (43.5°S) and for 1990 and 1991 from the Auckland (37°S) radiometer. Although the monitoring program has not been running sufficiently long to discern any long-term changes in levels of solar ultraviolet radiation, shorter term trends are apparent, which are attributed to a seasonal cycle in levels of ozone at midlatitudes and changes in atmospheric aerosols.