A highly emissive Cu2N2 diamond core complex supported by a [PNP]- ligand

A Cu2N2 diamond core structure, {(PNP)CuI}2 (2), supported by a [PNP]- ligand (1) ([PNP]- = bis(2-(diisobutylphosphino)phenyl)amide) has been prepared. 2 is highly emissive at ambient temperature in both the solid and solution states and is characterized by a relatively long-lived excited state (tau > 10 mus) and an unusually high quantum yield (phi > 0.65). These observations are consistent with a low degree of structural reorganization between the ground state of 2 and its excited state *2, and also with a high degree of steric protection of the two copper centers of 2 afforded by the bulky [PNP]- ligand. An estimate for the excited-state reduction potential of *2 (ca. -3.2 V vs Fc+/Fc), and the availability of two well-separated and reversible ground-state redox processes, suggests that bimetallic copper systems of these types may be interesting candidates to consider for photochemically driving multielectron redox transformations.     

Chromatographic Detection of Trimetoquinol (Inolin®) and its Major Urinary Metabolites in the Horse: A Preliminary Report

Trimetoquinol (TMQ) (1-(3,4,5-trimethoxybenzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, m.w. 345) is the prototype tetrahydroisoquinoline pharmaceutical. TMQ is marketed as a bronchodilator in human medicine; in horse racing, TMQ is listed as an Association of Racing Commissioners International (ARCI) class 3 foreign substance. As such, TMQ is considered to have the potential to affect racing performance in horses, and a validated qualitative confirmatory method is required to regulate its use in racing. We selected 8 g kg^–1 of TMQ IV as a safe and effective dose for studies on its metabolism and analytical detection in horses. We developed a solid phase extraction method for recovery of TMQ and its metabolites from equine urine, identified suitable high performance liquid chromatographic conditions for these substances and our internal standard, papaverine, and developed a highly sensitive ESI(+)-LC-MS-MS method (estimated LOD, 100 pg mL^–1) for TMQ and its major metabolites in equine urine. Multiple Reaction Monitoring (MRM) analysis of unhydrolyzed post-administration urine showed small amounts of unchanged TMQ, along with glucuronide, methylated, and sulfated metabolites, with glucuronide metabolites predominating. Following glucuronidase hydrolysis, recovered parent TMQ peaked at relatively high concentrations (>300 ng mL^–1) within 1 h of administration and thereafter declined. The methylated metabolites of TMQ peaked later and at comparable total concentrations, and thereafter declined more slowly. These data suggest that glucuronide hydrolysis of post-administration urine samples will allow recovery of readily identifiable quantities of parent TMQ. These findings, combined with the highly sensitive LC-MS-MS detection of parent TMQ described herein suggest that glucuronide hydrolysis of post-administration urine, followed by LC-MS-MS or other analysis, will allow effective regulatory control of this agent in racing horses.Published as # 351 from the Equine Pharmacology, Therapeutics and Toxicology Program at the Maxwell H. Gluck Equine Research Center and Department of Veterinary Science, University of Kentucky. Published as Kentucky Agricultural Experiment Station Article # 04-14-048 with the approval of the Dean and Director, College of Agriculture and the Kentucky Agricultural Experimental Station.Revised: 8 June and 12 July 2004     

Overtone spectroscopy of some benzaldehyde derivatives

Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm⁻¹ region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined. We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed in these distances is an indication of the substitution effect. It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the case of o-disubstituted benzenes it is only 80% of the para-substituted shift.     

Den Marsh'schen Arsennachweis

Ohne Zusammenfassung     

Structural snapshots of a flexible Cu2P2 core that accommodates the oxidation states Cu(I)Cu(I), Cu1.5Cu1.5, and Cu(II)Cu(II)

The phosphido-bridged dicopper(I) complex {(PPP)Cu}2 has been synthesized and structurally characterized ([PPP]- = bis(2-di-iso-propylphosphinophenyl)phosphide). Cyclic voltammetry of {(PPP)Cu}2 in THF shows fully reversible oxidations at -1.02 V (Cu1.5Cu1.5/CuICuI) and -0.423 V (CuIICuII/Cu1.5Cu1.5). Chemical oxidation of {(PPP)Cu}2 by one electron yields the class III mixed-valence species [{(PPP)Cu}2]+ (EPR, UV-vis). Structural data establish an unexpectedly large change (0.538 A) in the Cu...Cu distance upon oxidation state. Oxidation of {(PPP)Cu}2 by two electrons yields the dication [{(PPP)Cu}2]2+, an antiferromagnetically coupled dicopper(II) complex. Maintenance of a pseudotetrahedral geometry that is midway between a square plane and an ideal tetrahedron at the copper centers, along with a high degree of flexibility at the phosphide hinges, allows for efficient access to CuICuI, Cu1.5Cu1.5, and CuIICuII redox states without the need for ligand exchange, substitution, or redistribution processes.     

Alpha-synuclein structures probed by 5-fluorotryptophan fluorescence and 19F NMR spectroscopy

Alpha-synuclein, the main protein component of fibrillar deposits found in Parkinson's disease, is intrinsically disordered in vitro. Site-specific information on the protein conformation has been obtained by biosynthetic incorporation of an unnatural amino acid, 5-fluorotryptophan (5FW), into the recombinant protein. Using fluorescence and 19F NMR spectroscopy, we have characterized three proteins with 5FW at positions 4, 39, and 94. Steady-state emission spectra (maxima at 353 nm; quantum yields approximately 0.2) indicate that all three indole side chains are exposed to the aqueous medium. Virtually identical single-exponential excited-state decays (tau approximately 3.4 ns) were observed in all three cases. Single 19F NMR resonances were measured for W4, W39, and W94 at -49.0 +/- 0.1 ppm. Our analysis of the spectroscopic data suggests that the protein conformations are very similar in the regions near the three sites.     

Amido-bridged Cu2N2 diamond cores that minimize structural reorganization and facilitate reversible redox behavior between a Cu1Cu1 and a class III delocalized Cu1.5Cu1.5 species

A novel Cu(2)N(2) diamond core structure supported by an [SNS](-) ligand (1) ([SNS](-) = bis(2-tert-butylsulfanylphenyl)amido) has been prepared. This dicopper system exhibits a fully reversible one-electron redox process between a reduced Cu(1)Cu(1) complex, [[SNS][Cu]](2) (2), and a class III delocalized Cu(1.5)Cu(1.5) state, [[[SNS][Cu]](2)][B(3,5-(CF(3))(2)C(6)H(3))(4)] (3). Structural snapshots of both redox forms have been obtained to reveal remarkably little overall structural reorganization. The Cu...Cu bond distance nonetheless undergoes an appreciable compression (approximately 0.13 A) upon oxidation, providing a Cu...Cu distance of 2.4724(4) A in the mixed-valence state that is virtually identical to the Cu...Cu distance observed in the reduced form of the Cu(A) site of thiolate-bridged cytochrome c oxidase. Despite the low structural reorganization evident between 2 and 3, the [SNS](-) ligand is quite flexible. For example, square-planar geometries can prevail for divalent copper ions supported by [SNS](-) as evident from the crystal structure of [SNS]CuCl (4). Physical characterization for the mixed valence complex 3 includes electrochemical, magnetic (SQUID), EPR, and optical data. The complex has also been examined by density functional methods. An attempt was made to measure the rate of electron self-exchange k(s) between the Cu(1)Cu(1) and the Cu(1.5)Cu(1.5) complexes 2 and 3 by NMR line-broadening analysis in dichloromethane solution. While the system is certainly in the fast-exchange regime, the exchange process is too fast to be accurately measured by this technique. The value for k(s) can be bracketed with a conservative lower boundary of > or =10(7) M(-1) s(-1), a value that appears to be larger than other low molecular weight copper model complexes for which similar data is available. The unusually large magnitude of k(s) likely reflects the minimal structural reorganization that accompanies Cu(1)Cu(1) <--> Cu(1.5)Cu(1.5) interchange.