Syntheses and properties of two-dimensional, dicationic nonlinear optical chromophores based on pyrazinyl cores

Six new dicationic 2D nonlinear optical (NLO) chromophores with pyrazinyl-pyridinium electron acceptors have been synthesized by nucleophilic substitutions of 2,6-dichloropyrazine with pyridyl derivatives. These compounds have been characterized as their PF(6)(-) salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Large red shifts in the intense, π → π* intramolecular charge-transfer (ICT) transitions on replacing -OMe with -NMe(2) substituents arise from the stronger π-electron donor ability of the latter. Each compound shows a number of redox processes which are largely irreversible. Single crystal X-ray structures have been determined for five salts, including two nitrates, all of which adopt centrosymmetric packing arrangements. Molecular first hyperpolarizabilities β have been determined by using femtosecond hyper-Rayleigh scattering at 880 and 800 nm, and depolarization studies show that the NLO responses of the symmetric species are strongly 2D, with dominant "off-diagonal" β(zyy) components. Stark (electroabsorption) spectroscopic measurements on the ICT bands afford estimated static first hyperpolarizabilities β(0). The directly and indirectly derived β values are large, and the Stark-derived β(0) response for one of the new salts is several times greater than that determined for (E)-4'-(dimethylamino)-N-methyl-4-stilbazolium hexafluorophosphate. These Stark spectroscopic studies also permit quantitative comparisons with related 2D, binuclear Ru(II) ammine complex salts.     

Metabolism linked synthesis of fluorinated anti-tumour drug the fluorine - deuterium gambit

Metabolism studies of the known anti-tumour agents 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (C C N u), 4-[4-bis(2-chloroethyl)amino phenyl]butyric acid (chloroambucil) and [2-bis(2-chloroethyl)amino]tetrahydro-2H-1,3,2 oxazaphosphorine-2-oxide (cyclophosphamide) and their polydeuterio derivatives have led to an understanding of their mode of action, deactivation and ultimate excretion.In an attempt to modify or halt these processes, with the object of improving drug design and potency we have synthesised analogues of these drugs with fluorinated substituents in strategic positions within the molecules as indicated by metabolism data.The synthesis of each set of derivatives will be described with emphasis on the overcoming of problems of isomer distribution.Biological test results will be presented.     

Coordinate measurement in 2-D and 3-D geometries using frequency scanning interferometry

Frequency Scanning Interferometry (FSI) has been developed for robust precise distance measurements. We present the reconstruction of two and three dimensional geodetic grids, using simultaneous FSI measurements between grid nodes.The shape of the particle physics tracker inside the ATLAS experiment (currently under construction for the Large Hadron Collider at CERN) will be monitored using a geodetic grid of 842 remotely measured, fibre-coupled interferometers. The challenge is to make precise distance measurements in the hostile, high radiation environment and combine them to reconstruct node coordinates and hence the grid shape in quasi real time to a three dimensional precision of around .Two and three dimensional prototype grids with adjustable geometries have been measured, demonstrating shape reconstruction to a precision of around . Error propagation through these grids was studied with different reconstruction models. Grid redundancy allowed the agreement between software models and node coordinate reconstruction to be verified.     

Polyfluoro-1,2-epoxy alkanes and cycloalkanes. Part IV [1]. Thermal reactions of the epoxides of the pentamer and hexamer oligomers of tetrafluoroethene

Oxirans (1) and (2), derived respectively from the pentamer and hexamer oligomers of tetrafluoroethene, were pyrolysed over pyrex glass at 300–500° alone and in the presence of cyclohexene, bromine and toluene. Thus, oxiran (1), pyrolysed alone, afforded perfluoro-2-methylbut-1-ene (3), perfluoro-2,3-dimethylpent-2-ene (4) and (E) and (Z) perfluoro-2,3-hex-3-ene (TFE tetramer) (5a, 5b). Co-pyrolysis of (1) with bromine afforded (E) and (Z) 2-bromoperfluoro-3-methylpent-2-ene (6a, 6b), whilst with toluene, (E) and (Z) 2H-perfluoro-3-methylpent-2-ene (7a, 7b) were obtained: (1) with excess cyclohexene also gave (7a, 7b). The oxiran (2), on pyrolysis alone, gave only (3). In the presence of bromine, (2) gave an equimolar mixture of 1-bromoperfluoro-3-methylpentan-2-one (8) and 3-bromoperfluoro-3-methylpentane (9). Co-pyrolysis of (2) with toluene yielded (3) and 3H-perfluoro-3-methylpentane (10). Pyrolysis of (2) with cyclohexene at 175° gave perfluoro-3-methyl-2-(1-methylpropyl)pent-2-en-1-oylfluoride (11), pentafluoroethylcyclohexane (12) and perfluoro[(1-ethyl-1-methylpropyl) (1-methylpropyl)]ketne (13).     

Quadratic and cubic nonlinear optical properties of salts of diquat-based chromophores with diphenylamino substituents

A series of chromophoric salts has been prepared in which 4-(diphenylamino)phenyl (Dpap) electron donor groups are connected to electron-accepting diquaternized 2,2'-bipyridyl (diquat) units. The main aim is to combine large quadratic and cubic nonlinear optical (NLO) effects in potentially redox-switchable molecules with 2D structures. The chromophores have been characterized as their PF(6)(-) salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. The visible absorption spectra are dominated by intense π → π* intramolecular charge-transfer (ICT) bands, and all of the compounds show two reversible or quasireversible diquat-based reductions and partially reversible Dpap oxidations. Single crystal X-ray structures have been obtained for one salt and for the precursor compound (E)-4-(diphenylamino)cinnamaldehyde, both of which adopt centrosymmetric space groups. First hyperpolarizabilities β have been measured by using hyper-Rayleigh scattering (HRS) with a 800 nm laser, and Stark (electroabsorption) spectroscopy of the ICT bands affords estimated static first hyperpolarizabilities β(0). The directly and indirectly derived β values are large and generally increased substantially for the bis-Dpap derivatives when compared with their monosubstituted analogues. Polarized HRS studies show that the NLO responses of the disubstituted species are dominated by "off-diagonal" β(zyy) components. Lengthening the diquaternizing alkyl unit lowers the electron-acceptor strength and therefore increases the ICT energies and decreases the E(1/2) values for diquat reduction. However, compensating increases in the ICT intensity prevent significant decreases in the Stark-based β(0) responses. Cubic NLO properties have been measured by using the Z-scan technique over a wavelength range of 520-1600 nm, revealing relatively high two-photon absorption cross-sections of up to 730 GM at 620 nm for one of the disubstituted chromophores.     

fac,trans‐[(2,2′‐Bipyridine‐N,N′)tricarbonylrhenium(I)]‐μ‐(4,4′‐bipyridine)‐N:N′‐{chlorobis[1,2‐phenylenebis(dimethylarsine)]ruthenium(II)} bis(hexafluorophosphate) diacetone solvate

The crystal structure of the heterobimetallic title compound, [ReRuCl(C₁₀H₁₆As₂)₂(C₁₀H₈N₂)₂(CO)₃](PF₆)₂·2C₃H₆O, is described. Both metal centres have pseudo‐octahedral coordination geometries, with a facial arrangement of the carbonyl ligands at Re^I and a trans disposition of the diarsine ligands at Ru^II. The dihedral angle between the pyridyl rings of the 4,4′‐bi­pyridine bridging ligand is 13.9 (6)°.     

Large Molecular Quadratic Hyperpolarizabilities in Donor/Acceptor-Substituted trans-Tetraammineruthenium(II) Complexes

A series of new Ru(II) complex salts trans-[Ru(NH(3))(4)(L(1))(L(2))](PF(6))(n) [n = 2, L(1) = 4-acetylpyridine (4-acpy) and L(2) = 4-(dimethylamino)pyridine (dmap) (1), 4-(dimethylamino)benzonitrile (dmabn) (2), 4-picoline (4-pic) (3), or 1-methylimidazole (1-MeIm) (4); n = 3, L(1) = N-methyl-4,4'-bipyridinium (MeQ(+)) and L(2) = dmap (6), dmabn (7), 1-MeIm (8), 4-acpy (9), or phenothiazine (PTZ) (10); n = 2, L(1) = dmap and L(2) = 4-pyridinecarboxaldehyde (pyca) (12) or ethyl isonicotinate (isne) (13)] have been synthesized and fully characterized. These complexes display intense, visible metal-to-ligand charge-transfer (MLCT) absorptions which are highly solvatochromic. An X-ray crystal structure determination has been carried out for trans-[Ru(NH(3))(4)(MeQ(+))(PTZ)](PF(6))(3).Me(2)CO (10.Me(2)CO). This salt, empirical formula C(26)H(38)F(18)N(7)OP(3)RuS, crystallizes in the hexagonal system, space group P6(3), with a = b = 17.853(4) ?, c = 21.514(6) ?, and Z = 6. The MeQ(+) ligand adopts an almost planar conformation, with a torsion angle of 9.6 degrees between the two pyridyl rings. The dipolar cations exhibit a strong projected component along the z axis, but crystal twinning precludes second-harmonic generation. Measurements of the first hyperpolarizability beta by using the hyper-Rayleigh scattering technique at 1064 nm yield very large values in the range (232-621) x 10(-30) esu, the largest being for trans-[Ru(NH(3))(4)(MeQ(+))(dmabn)](PF(6))(3) (7). These beta values are resonance enhanced via the MLCT excitations. A correlation between beta and the MLCT absorption energy confirms that this excitation is the primary contributor to beta. The two-level model yields static hyperpolarizabilities beta(0) in the range (10-130) x 10(-30) esu, with trans-[Ru(NH(3))(4)(MeQ(+))(dmap)](PF(6))(3) (6) having the largest. The beta(0) values of the complexes of the bipyridyl ligand MeQ(+) are larger than those of their analogues containing monopyridyl ligands because of extended conjugation. beta(0) correlates with the MLCT energy only when the MLCT absorption is sufficiently far from the second harmonic at 532 nm.     

Determination of methylcyclopentadienylmanganesetricarbonyl by gas chromatography—atomic absorption spectrometry at ng m-3 levels in air samples

A procedure is given for the determination of methylcyclopentadienylmanganese tricarbonyl (MMT) at ng m^-3 concentrations in air. The method involves trapping of MMT in a small segment of gas chromatographic column and then determination by gas chromatography with an electrothermal atomic absorption detector. The detection limit of the procedure is 0.05 ng m^-3. Air samples from an underground car-park (when MMT was detected) were found to contain between 0.1 and 0.3 ng m^-3 MMT. MMT was not detected in any of the street air samples taken.     

Solution-phase combinatorial chemistry

The use of solution phase techniques has been explored as an alternative to solid-phase chemistry approaches for the preparation of arrays of compounds in the drug discovery process. Solution-phase work is free from some of the constraints of solid-phase approaches but has disadvantages with respect to purification. This article will also illustrate some of the advances made in recent years in solution phase array chemistry including using supported reagents and simple extractive protocols for the effective preparation of high quality samples.