LIGHT-DRIVEN REDOX PROCESSES IN FUNCTIONAL MICELLAR UNITS—III. Zn-TETRAPHENYLPORPHYRIN SENSITIZED REACTIONS IN METHYL VIOLOGENE SURFACTANT ASSEMBLIES

Abstract— The photoreduction of methyl viologene by ZnTPP triplet excited states was studied in mixed micelles containing the functional surfactant JV-dodecyl, N -methyl viologene (C₁₂MV²⁺) as one and Cetyltrimethylammoniumchloride (CTAC) as the other component. Using the laser photolysis technique the kinetics of the redox reaction were studied at various CTAC/C₁₂MV²⁺ ratios. The average time for the electron transfer decreases linearly with the C₁₂MV²⁺ occupancy. The back transfer from C₁₂MV²⁺ to ZnTPP²⁺ can be intercepted if a donor such as NADH is cosolubilized in the micelle. In such a system irreversible methyl viologene reduction is achieved which in the presence of a suitable redox catalyst can be used to produce hydrogen from water.     

Quantitative differential thermal analysis of the reduction of uranyl fluoride

The enthalpy of the reduction of UO₂F₂ with hydrogen was obtained from quantitative DTA measurements with a linear heating rate and under isothermal conditions, and the thermodynamic data on UO₂F, formed as a stable intermediate in the reduction of UO₂F₂ to UO₂, are also presented. The advantages of isothermal DTA in the reduction of U₃O₈ to UO₂ could be demonstrated.     

THE REACTIVITY OF CITRONELLOL and α-THUJENE WITH SINGLET OXYGEN. RATE CONSTANTS OF CHEMICAL REACTION and PHYSICAL QUENCHING*

The quantum yields of Rose Bengal sensitized photooxidation of citronellol and α-thujene have been determined as a function of added acceptor and compared with those of furfuryl alcohol as a standard. The results permitted the calculation of the corresponding rate constants of chemical reaction (k_T) and physical quenching (K_q) of singlet oxygen. The sum (k_T+ k_q) has been verified independently by a Stern-Volmer analysis of the singlet oxygen luminescence quenching. α-Thujene reacts faster with singlet oxygen than citronellol, physical quenching being negligible in both cases.     

Efficient search for all low energy conformations of polypeptides by Monte Carlo methods

The Metropolis Monte Carlo method has been added to the program FANTOM for energy refinement of polypeptides and proteins using a Newton–Raphson minimizer in torsion angle space. With this extension, different strategies for global minimization of the semiempirical energy function ECEPP/2 by various temperature schedules and restriction of conformational space were tested for locating local minimum conformations with low energy of the pentapeptide Met-enkephalin. In total, 1881 conformations below ?10 kcal/mol were found. These conformations could be represented by 77 nonidentical conformations which were analysed for their pattern of hydrogen bonds, types of tight turn, pairwise root-mean-square-deviation (rmsd), Zimmermann codes and side chain conformations. All low energy conformations below ?10.4 kcal/mol show strong similarity to the global minimum conformation in the backbone structure.     

Activation and Coordination of Ammonia at [Cp*Ir(H)2]: NMR and Matrix Isolation Studies

¹H NMR exchange spectroscopy of a reaction mixture of [Cp*Ir(H)₄] ( 1 ; Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) and ammonia suggests an exchange of hydrogen atoms between the hydrido ligands and ammonia. Treatment of 1 with ND₃ led to an H/D exchange between ND₃ and the hydrido ligands of 1 . Subsequent studies showed that photolysis of 1 isolated in frozen argon matrices leads to the formation of the iridium compounds [Cp*Ir(H)₂] ( 2 ) and [Cp*Ir(H)₃] ( 4 ), as it was confirmed by IR spectroscopy. In the presence of water the aqua complex [Cp*Ir(H)₂(OH₂)] ( 3 ) was generated simultaneously. Accordingly, photolysis of 1 in an argon matrix doped with ammonia gave rise to the ammine complex [Cp*Ir(H)₂(NH₃)] ( 5 ). IR assignments were supported by calculations of the gas‐phase IR spectra of 1 – 5 by DFT methods.