Luminescent Pt(II)(bipyridyl)(diacetylide) chromophores with pendant binding sites as energy donors for sensitised near-infrared emission from lanthanides: structures and photophysics of Pt(II)/Ln(III) assemblies

The complexes [Pt(bipy){CC-(4-pyridyl)}(2)] (1) and [Pt(tBu(2)bipy){CC-(4-pyridyl)}(2)] (2) and [Pt(tBu(2)-bipy)(CC-phen)(2)] (3) all contain a Pt(bipy)(diacetylide) core with pendant 4-pyridyl (1 and 2) or phenanthroline (3) units which can be coordinated to {Ln(diketonate)(3)} fragments (Ln = a lanthanide) to make covalently-linked Pt(II)/Ln(III) polynuclear assemblies in which the Pt(II) chromophore, absorbing in the visible region, can be used to sensitise near-infrared luminescence from the Ln(III) centres. For 1 and 2 one-dimensional coordination polymers [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) are formed, whereas 3 forms trinuclear adducts [3{Ln(hfac)(3)}(2)] (tta=anion of thenoyl-trifluoroacetone; hfac=anion of hexafluoroacetylacetone). Complexes 1-3 show typical Pt(II)-based (3)MLCT luminescence in solution at approximately 510 nm, but in the coordination polymers [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) the presence of stacked pairs of Pt(II) units with short PtPt distances means that the chromophores have (3)MMLCT character and emit at lower energy ( approximately 630 nm). Photophysical studies in solution and in the solid state show that the (3)MMLCT luminescence in [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) in the solid state, and the (3)MLCT emission of [3{Ln(hfac)(3)}(2)] in solution and the solid state, is quenched by Pt-->Ln energy transfer when the lanthanide has low-energy f-f excited states which can act as energy acceptors (Ln=Yb, Nd, Er, Pr). This results in sensitised near-infrared luminescence from the Ln(III) units. The extent of quenching of the Pt(II)-based emission, and the Pt-->Ln energy-transfer rates, can vary over a wide range according to how effective each Ln(III) ion is at acting as an energy acceptor, with Yb(III) usually providing the least quenching (slowest Pt-->Ln energy transfer) and either Nd(III) or Er(III) providing the most (fastest Pt-->Ln energy transfer) according to which one has the best overlap of its f-f absorption manifold with the Pt(II)-based luminescence.     

Characterization and deposition of various light-harvesting antenna complexes by electrospray atomization

Photosynthetic organisms have light-harvesting complexes that absorb and transfer energy efficiently to reaction centers. Light-harvesting complexes (LHCs) have received increased attention in order to understand the natural photosynthetic process and also to utilize their unique properties in fabricating efficient artificial and bio-hybrid devices to capture solar energy. In this work, LHCs with different architectures, sizes, and absorption spectra, such as chlorosomes, Fenna–Matthews–Olson (FMO) protein, LH2 complex, and phycobilisome have been characterized by an electrospray-scanning mobility particle-sizer system (ES-SMPS). The size measured by ES-SMPS for FMO, chlorosomes, LH2, and phycobilisome were 6.4, 23.3, 9.5, and 33.4?nm, respectively. These size measurements were compared with values measured by dynamic light scattering and those reported in the literature. These complexes were deposited onto a transparent substrate by electrospray deposition. Absorption and fluorescence spectra of the deposited LHCs were measured. It was observed that the LHCs have light absorption and fluorescence spectra similar to that in solution, demonstrating the viability of the process.     

Air-stable, highly fluorescent primary phosphanes

Light without fright: a synthetic route to fluorescent primary phosphanes (RPH(2)) that are resistant to air oxidation both in the solid state and in chloroform solution is described. These versatile precursors undergo hydrophosphination to give tripodal ligands and subsequently fluorescent transition-metal complexes.     

Exploring Förster electronic energy transfer in a decoupled anthracenyl-based borondipyrromethene (bodipy) dyad

An anthracenyl-Bodipy dyad containing a triazole bridge, that acts to decouple the two units in the ground state, has been synthesised and structurally characterised. Efficient electronic energy transfer occurs from the anthracenyl-based unit to the Bodipy system in toluene in around 12 ps, and becomes faster in solvents of lower refractive index. The rate of electronic energy transfer is discussed in terms of F?rster theory.     

Experimental Study of Hydrogen Bonding Potentially Stabilizing the 5′‐Deoxyadenosyl Radical from Coenzyme B12

Coenzyme B₁₂ can assist radical enzymes that accomplish the vicinal interchange of a hydrogen atom with a functional group. It has been proposed that the Co? C bond homolysis of coenzyme B₁₂ to cob(II)alamin and the 5′‐deoxyadenosyl radical is aided by hydrogen bonding of the corrin C19? H to the 3′‐O of the ribose moiety of the incipient 5′‐deoxyadenosyl radical, which is stabilized by 30 kJ mol^?1 (B. Durbeej et al., Chem. Eur. J. 2009 , 15, 8578–8585). The diastereoisomers (R)‐ and (S)‐2,3‐dihydroxypropylcobalamin were used as models for coenzyme B₁₂. A downfield shift of the NMR signal for the C19? H proton was observed for the (R)‐isomer (δ=4.45 versus 4.01 ppm for the (S)‐isomer) and can be ascribed to an intramolecular hydrogen bond between the C19? H and the oxygen of CHOH. Crystal structures of (R)‐ and (S)‐2,3‐dihydroxypropylcobalamin showed C19? H???O distances of 3.214(7) Å (R‐isomer) and 3.281(11) Å (S‐isomer), which suggest weak hydrogen‐bond interactions (?ΔG<6 kJ mol^?1) between the CHOH of the dihydroxypropyl ligand and the C19? H. Exchange of the C19? H, which is dependent on the cobalt redox state, was investigated with cob(I)alamin, cob(II)alamin, and cob(III)alamin by using NMR spectroscopy to monitor the uptake of deuterium from deuterated water in the pH range 3–11. No exchange was found for any of the cobalt oxidation states. 3′,5′‐Dideoxyadenosylcobalamin, but not the 2′,5′‐isomer, was found to act as a coenzyme for glutamate mutase, with a 15‐fold lower k_cat/K_M than 5′‐deoxyadenosylcobalamin. This indicates that stabilization of the 5′‐deoxyadenosyl radical by a hydrogen bond that involves the C19? H and the 3′‐OH group of the cofactor is, at most, 7 kJ mol^?1 (?ΔG). Examination of the crystal structure of glutamate mutase revealed additional stabilizing factors: hydrogen bonds between both the 2′‐OH and 3′‐OH groups and glutamate 330. The actual strength of a hydrogen bond between the C19? H and the 3′‐O of the ribose moiety of the 5′‐deoxyadenosyl group is concluded not to exceed 6 kJ mol^?1 (?ΔG).     

Coupling external cavity mid-IR quantum cascade lasers with low loss hollow metallic/dielectric waveguides

We report on the optical coupling between hollow core waveguides and external cavity mid-IR quantum cascade lasers (QCLs). Waveguides with 1000???m bore size and lengths ranging from 2 to 14?cm, with metallic (Ag)/dielectric (AgI or polystyrene) circular cross-section internal coatings, have been employed. Our results show that the QCL mode is perfectly matched to the hybrid HE₁₁ waveguide mode, demonstrating that the internal dielectric coating thickness is effective to suppress the higher losses TE-like modes. Optical losses down to 0.44?dB/m at 5.27???m were measured in Ag/polystyrene-coated waveguide with an almost unitary coupling efficiency.     

Chiral salen ligands designed to form polymetallic complexes

Chiral salen ligands capable of forming polymetallic complexes have been designed. The ligands possess substituents in the 4,4′-positions, but have no substituent in the 3,3′-positions to allow a second metal ion access to the salen oxygen atoms. Ligands in which a polyether chain links the 4,4′-positions were prepared and complexed to copper. In addition, acyclic ligands with potential metal coordinating substituents in the 4,4′-positions were prepared and complexed to copper and cobalt. The crystal structure of one of the cobalt complexes shows it to be a trimetallic complex in which a Co(II)(OAc)₂ group coordinates to the salen oxygen atoms of two Co(III)(salen)(OAc) units. In contrast, the crystal structure of a Co(salen) complex with tert-butyl groups attached to the 3,3′-positions is found to be mononuclear. All of the complexes were tested as asymmetric phase transfer catalysts for the asymmetric alkylation of an alanine methyl ester, forming (R)-α-methyl phenylalanine methyl ester with up to 85% ee.     

Quantitative determination of chlorpromazine and thioridazine by high-performance thin layer chromatography

An assay for quantitation of chlorpromazine and thioridazine in patient plasma is developed. The procedure utilizes high-performance thin layer chromatography for separation and in situ absorption densitometry for quantitation. Depending upon the HPTLC plate size, 30 to 60 samples may be processed in less than 6 hr, with an intra-assay coefficient of variation of less than 4%. The procedure can be used to measure as little as 10 ng/ml of drug in plasma, well below expected concentrations in patients receiving these medications. Investigations of extraction procedures, sample application procedures, chromatographic conditions, sample derivatization, and in situ absorption densitometry are described.     

The -automorphism method and noninvariant classes of degrees

A set of nonnegative integers is computably enumerable (c.e.), also called recursively enumerable (r.e.), if there is a computable method to list its elements. Let denote the structure of the computably enumerable sets under inclusion, . Most previously known automorphisms of the structure of sets were effective (computable) in the sense that has an effective presentation. We introduce here a new method for generating noneffective automorphisms whose presentation is , and we apply the method to answer a number of long open questions about the orbits of c.e. sets under automorphisms of . For example, we show that the orbit of every noncomputable ( i.e., nonrecursive) c.e. set contains a set of high degree, and hence that for all the well-known degree classes (the low c.e. degrees) and (the complement of the high c.e. degrees) are noninvariant classes.