Synthesis of luminescent gold(I) and gold(III) complexes with a triphosphine ligand

We have synthesized and characterized a series of trinuclear gold(I) complexes [(AuX)(3)(mu-triphos)] (triphos = bis(2-diphenylphosphinoethyl)phenylphosphine; X = Cl 1, Br 2, I 3, C(6)F(5) 4) and di- and trinuclear gold(III) complexes [[Au(C(6)F(5))(3)](n)(mu-triphos)] (n = 2 (5), 3 (6)). The crystal structure of 6 [[Au(C(6)F(5))(3)](3)(mu-triphos)] has been determined by X-ray diffraction studies, which show the triphosphine in a conformation resulting in very long gold-gold distances, probably associated with the steric requirements of the tris(pentafluorophenyl)gold(III) units. Complex 6 crystallizes in the triclinic space group P(-1) with a = 12.7746(16) A, b = 18.560(2) A, c = 21.750(3) A, alpha = 98.215(3) degrees, beta = 101.666(3) degrees, gamma = 96.640(3) degrees, and Z = 2. Chloride substitutions in complex 1 afford trinuclear gold(I) complexes [(AuX)(3)(mu-triphos)] (X = Fmes (1,3,5-tris(trifluoromethyl)phenyl) 7, p-SC(6)H(4)Me 8, SCN 9) and [Au(3)Cl(3)(-)(n)()(S(2)CNR(2))(n)(mu-triphos)] (R = Me, n = 3 (10), 2 (12), 1 (14); R = CH(2)Ph, n = 3 (11), 2 (13), 1 (15)). The luminescence properties of these complexes in the solid state have been studied; at low temperature most of them are luminescent, including the gold(III) derivative 6, with the intensity and the emission maxima being clearly influenced by the nature and the number of the ligands bonded to the gold centers.     

Thermolysis and Chemiluminescence of Monocyclic 1,2,4-Trioxan-5-ones

The 3,6-substituted 1,2,4-trioxan-5-ones 11 – 14 , on heating to 170–200°, underwent unimolecular thermolysis to generate electronically excited singlet ketones with an efficiency of ca. 0.2%. The chemiluminescence quantum yields (?oS_CL) depended on the nature of the 6-substitutents and increased linearly with temperature. The Arrhenius activation energies were obtained by measuring the rate of decay of luminescence and determined as 22.9, 30.4, 35.6, and 34.2 kcal/mol for 11 – 14 , respectively. Step analysis of the chemiluminescence of 14 afforded an average activation energy of 44.3 kcal/mol. This latter result is explicable in terms of two decomposition paths, higher and lower in energy, leading to excited and ‘dark’ products, respectively. The thermolysis of trioxanones 12 – 14 lacking a H-atom at the 6-position is interpreted as involving successive rupture of the peroxide bond, excision of ketone at the 3-substituted end, and loss of CO₂, to finally produce ketone originating from the 6-position (see Scheme 4).     

Hydrolysis of new phthalimide-derived esters catalyzed by immobilized lipase

The last step of the production of four phthalimide-derived acids, designed to act as antiasthma drugs, was performed by enzymatic hydrolysis of the respective methyl or ethyl esters. The esters 4-ethyl-[2-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)]-phenoxyacetic methyl ester (PHT-MET), 4-ethyl-[2-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)]-phenoxyacetic ethyl ester, 4-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)-phenoxyacetic ethyl ester, and 2-(1,3-dioxo-1, 3-dihydro-2-isoindoylyl)-phenoxyacetic ethyl ester were hydrolyzed by immobilized lipase. The enzymatic reaction could be used only to produce the desired 4-substituted compounds. The best result that was found to hydrolysis of PHT-MET, and, therefore, that ester was selected for optimization experiments in a three-phase system. Reactions were performed with solid biocatalyst (Lipozyme® RM IM), organic solvent phase (ethyl acetate), and aqueous phase (saturated Na₂CO₃ solution). To optimize the reaction conditions, an experimental design optimization procedure was used. The variables studied were the amount of enzyme, the temperature, and the volume of the aqueous solution. Time course experiments were then performed for different initial enzyme concentrations (0.5, 0.9, and 1.4 U_H/mL of solvent). The optimized reaction conditions found were 20 mg of Lipozyme (0.9 U_H/mL_solvent) and 5.0 mL of Na₂CO_3(sat) at 40°C for 6 h.     

Preparation of pentahalophenyl p-tolylisocyanide complexes of gold(I) and their reactions with amines,ammonia and alcohols

(Pentahalophenyl) (p-tolylisocyanide)gold(I) complexes were prepared by treating Au(C₆X₅) (tetrahydrothiophen) (X = F, Cl or Br) with p-MeC₆H₄NC. Their reactivity toward nucleophiles was studied and found to decrease in the sequence: primary amines > ammonia > secondary amines > aromatic amines > alcohols; the effects of the various C₆X₅ groups were less pronounced, but decreased according to C₆F₅ > C₆Cl₅ > C₆Br₅.Twenty-five novel gold(I) carbene derivatives were isolated.     

Determination of trace levels of mercury in water samples based on room temperature phosphorescence energy transfer

A novel method has been developed for the sensitive determination of mercury in aqueous media by room temperature phosphorescence (RTP). The measurement principle is based on the energy transfer (ET) from a phosphor molecule (acting as a donor) to a Hg-sensitive dye (acceptor). To our acknowledgment this is the first RTP method for mercury measurement developed so far. α-Bromonaphthalene (BrN) was selected as the phosphorescent donor molecule (BrN can produce significant RTP emission in aqueous media in a β-cyclodextrin rigid microenvironment without deoxygenation).The absorption spectrum of the complex formed between mercury and the dithizone dye possesses a desirable spectral overlap with the RTP emission spectrum of the donor (BrN), giving rise to a nonradiative ET from the phosphor molecules to the mercury complex. An increase in the concentration of Hg(II) causes an increase on the concentration of the dithizone complex (acceptor) with the subsequent increase of the absorbance and, therefore, resulting in a decrease of the RTP emission. Both, RTP intensities and triplet lifetimes of the BrN decreased with increases on the Hg(II) concentration.Possible interferences present in natural waters, including different cations and anions, which could affect the analytical response, were evaluated and the analytical performance characteristics investigated. The use of phosphorescence measurements (low background noise signals) resulted in an improvement on the sensitivity of the Hg(II) detection higher than five times as compared to the molecular absorption spectrophotometric method for Hg(II) detection based on dithizone as Hg-indicator. A detection limit (D.L.) of 14 ng ml⁻¹ of Hg(II) was obtained by RTP with a precision of ±4.8% for five replicates of 300 ng ml⁻¹ of Hg(II). The usefulness of the method was successfully evaluated by the determination of Hg(II) in spiked natural water samples.     

Phase transitions in the tantalum-hydrogen system observed by PAC

The perturbation felt by¹⁸¹Hf probes in a¹⁸¹HfTa lattice loaded with 30 at% hydrogen was observed by PAC as a function of temperature. Three different interactions were identified: 1) Ν_Q1=433 (6) MHz, η=0.45 2) Ν_Q2=142 (9) MHz, η=0.9, and 3) Ν_Q?0, σ=4–14 Μ^?1 which are attributed to the Β^?, ε^? and α-phase in TaH system, respectively.     

Singlet fission in a hexacene dimer: energetics dictate dynamics

Singlet fission (SF) is an exciton multiplication process with the potential to raise the efficiency limit of single junction solar cells from 33% to up to 45%. Most chromophores generally undergo SF as solid-state crystals. However, when such molecules are covalently coupled, the dimers can be used as model systems to study fundamental photophysical dynamics where a singlet exciton splits into two triplet excitons within individual molecules. Here we report the synthesis and photophysical characterization of singlet fission of a hexacene dimer. Comparing the hexacene dimer to analogous tetracene and pentacene dimers reveals that excess exoergicity slows down singlet fission, similar to what is observed in molecular crystals. Conversely, the lower triplet energy of hexacene results in an increase in the rate of triplet pair recombination, following the energy gap law for radiationless transitions. These results point to design rules for singlet fission chromophores: the energy gap between singlet and triplet pair should be minimal, and the gap between triplet pair and ground state should be large.

We report the synthesis and photophysical characterization of highly exoergic singlet fission in a hexacene dimer revealing exciton dynamics that follow the energy gap law.     

Salt Stress Proteins Identified by a Functional Approach in Yeast

We have performed functional genomics of salt stress by overexpression of gene libraries in yeast and selection for salt tolerance. Thirty halotolerance genes were isolated from yeast, Arabidopsis, and sugar beet. The results indicate that Na⁺ transport (uptake, efflux, and compartmentation), sulfate activation, RNA processing, and protein synthesis are crucial for salt tolerance.     

Organic tellurium compounds—VIII Di-aryl tellurides as dehalogenation agents —the reduction of metallic salts by DI-p-tolyl telluride

The reaction of di-p-tolyltelluride with ferric, cupric and mercuric chloride, performed in glacial acetic acid, effects the reduction of the metallic salts giving rise to di-p-tolyltellurium dichloride. In toluene solution only the ferric chloride was reduced and the anhydride of di-p-tolyltellurium hydroxychloride formed, due to the hydrolysis of the tellurium dichloride. The reaction of the mentioned telluride and benzoyl chloride gave rise to a mixture of the dichloride and the dibenzoate. The mechanism of this reaction is discussed.     

Reduction of (imine)Pt(IV) to (imine)Pt(II) complexes with carbonyl-stabilized phosphorus ylides

A novel method is reported for generation of the difficult-to-obtain (imine)Pt(II) compounds that involves reduction of the corresponding readily available Pt(IV)-based imines by carbonyl-stabilized phosphorus ylides, Ph3P=CHCO2R, in nonaqueous media. The reaction between neutral (imino)Pt(IV) compounds [PtCl4[NH=C(Me)ON=CR1R2]2] [R1R2 = Me2, (CH2)4, (CH2)5, (Me)C(Me)=NOH], [PtCl4[NH=C(Me)ONR2]2] (R = Me, Et, CH2Ph), (R1 = H; R2 = Ph or C6H4Me; R3 = Me) as well as anionic-type platinum(IV) complexes (Ph3PCH2Ph)[PtCl5[NH=C(Me)ON=CR2]] [R2 = Me2, (CH2)4, (CH2)5] and 1 equiv of Ph3P=CHCO2R (R = Me, Et) proceeds under mild conditions (ca. 4 h, room temperature) to give selectively the platinum(II) products (in good to excellent isolated yields) without further reduction of the platinum center. All thus prepared compounds (excluding previously described Delta4-1,2,4-oxadiazoline complexes) were characterized by elemental analyses, FAB mass spectrometry, IR and 1H, 13C[1H], 31P[1H] and 195Pt NMR spectroscopies, and X-ray single-crystal diffractometry, the latter for [PtCl2[NH=C(Me)ON=CMe2]2] [crystal system tetragonal, space group P4(2)/n (No. 86), a = b = 10.5050(10) A, c = 15.916(3) A] and (Ph3PCH2CO2Me)[PtCl3(NCMe)] [crystal system orthorhombic, space group Pna2(1) (No. 33), a = 19.661(7) A, b = 12.486(4) A, c = 10.149(3) A]. The reaction is also extended to a variety of other Pt(II)/Pt(IV) couples, and the ylides Ph3P=CHCO2R are introduced as mild and selective reducing agents of wide applicability for the conversion of Pt(IV) to Pt(II) species in nonaqueous media, a route that is especially useful in the case of compounds that cannot be prepared directly from Pt(II) precursors, and for the generation of systematic series of Pt(II)/Pt(IV) complexes for biological studies.