Wetting transition on grain boundaries in Al contacting with a Sn-rich melt

The contact angle at the intersection of a grain boundary in Al bicrystals with the solid Al/liquid Al–Sn interphase boundary has been measured for two symmetric tilt <011> {001} grain boundaries with tilt angles of 32° and 38.5°. The temperature dependencies (T) present the evidence of the grain boundary wetting phase transition at T_w. The observed hysteresis is consistent with the assumption that the wetting transition is of first order. The determined discontinuity in the temperature derivative of the grain boundary energy is–5.6 J/m²K (T w1=617°C) for the boundary with a low energy (=38.5°) and –17 J/m²K (T w2=604°C) for the grain boundary with a high energy (=32°).     

Driving force and electronic coupling effects on photoinduced electron transfer in a fullerene-based molecular triad

Tuning thermodynamic driving force and electronic coupling through structural modifications of a carotene (C) porphyrin (P) fullerene (C60) molecular triad has permitted control of five electron and energy transfer rate constants and two excited state lifetimes in order to prepare a high-energy charge-separated state by photoinduced electron transfer with a quantum yield of essentially unity (> or = 96%). Excitation of the porphyrin moiety of C-P-C60 is followed by a combination of photoinduced electron transfer to give C-P(.+)-C60.- and singlet-singlet energy transfer to yield C-P-1C60. The fullerene excited state accepts an electron from the porphyrin to also generate C-P(.+)-C60.-. Overall, this initial state is formed with a quantum yield of 0.97. Charge shift from the carotenoid to yield C(.+)-P-C60.- is at least 60 times faster than recombination of C-P(.+)-C60.-, leading to the overall quantum yield near unity for the final state. Formation of a similar charge-separate species from the zinc analog of the triad with a yield of 40% is also observed. Charge recombination of C(.+)-P-C60.- in 2-methyltetrahydrofuran yields the carotenoid triplet state, rather than the ground state. Comparison of the results for this triad with those for related triads with different structural features provides information concerning the effects of driving force and electronic coupling on each of the electron transfer steps.     

Photonic switching of photoinduced electron transfer in a dithienylethene-porphyrin-fullerene triad molecule

A dithienylethene (DTE)-porphyrin (P)-fullerene (C(60)) triad molecule in which intramolecular photoinduced electron transfer is controlled by the photochromic DTE moiety has been prepared. Irradiation of the molecule with visible light gives the open form of the dithienylethene (DTEo). Excitation of the porphyrin gives DTEo-(1)P-C(60), which undergoes photoinduced electron transfer with a time constant of 25 ps to generate DTEo-P(.+)-C(60)(.-). Irradiation with ultraviolet light produces the closed form of the dithienylethene (DTEc). Excitation of DTEc-P-C(60) yields DTEc-(1)P-C(60), whose porphyrin first excited singlet state is quenched in 2.3 ps by singlet-singlet energy transfer to DTEc, generating (1)DTEc-P-C(60) and precluding significant photoinduced electron transfer. Such highly reversible photonically controlled intramolecular photoinduced electron transfer may eventually be useful in the design of photonic or optoelectronic devices.     

ENERGY TRANSFER FROM CAROTENOID POLYENES TO PORPHYRINS: A LIGHT-HARVESTING ANTENNA

Carotenoid to porphyrin singlet-singlet energy transfer has been observed in a new covalently linked carotenoid-porphyrin ester. Nuclear magnetic resonance studies reveal that the relatively high energy transfer efficiency (? 25%) is a result of a stacked conformation in which the 26 π electron carotenoid chromophore resides ?4–5 Å above the mean porphyrin plane. Substantial quenching of porphyrin fluorescence was also observed. Implications for the mechanism of energy transfer and possible applications to synthetic solar energy conversions systems are discussed.     

1,3-Diphenylpropane-1,3-diamines,X: Synthesis and biochemical evaluation of highly substituted 1,3-diphenylpropane-1,3-diamines and preparation of their Pt(II) complexes

Summary The ligands of the title complexes1 and2 were prepared from the pertinent chalcone5 and hydrazine hydrate, followed by N-N cleavage. The estrogenic activity of the diamines11 and12 was determined by measuring the RBA values (calf uterine cytosol) and by a luciferase test in MCF 7-2a cells. The compounds are by far less active thanSchönenberger's most active compound ([meso-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethane-1,2-diamine]dichloro-platinum(II),3).Dedicated with kind regards to Prof. Dr.G. Seitz, Marburg/Germany, on the occasion of his 60^th birthday     

Molecular switches controlled by light

The photochemical processes of singlet-singlet energy transfer and photoinduced electron transfer are important not only in natural and artificial photosynthetic energy conversion, but also in a variety of other scientific and technological applications. Controlling these functions at the molecular level using outside stimuli is an interesting scientific challenge. Photochromes, organic molecules that are isomerized by light between two stable forms, can be covalently linked to other chromophores, and changes in their properties resulting from photoisomerization used to switch electron and energy transfer on or off. Simple single- and double-throw molecular switches have been constructed, as well as Boolean logic gates. Such molecules are potentially useful in light-controlled molecular data processing and storage applications.     

Enzyme-assisted reforming of glucose to hydrogen in a photoelectrochemical cell

Hydrogen gas has been produced by reforming glucose in a hybrid photoelectrochemical cell that couples a dye-sensitized nanoparticulate wide band gap semiconductor photoanode to the enzyme-based oxidation of glucose. A layer of porphyrin sensitizer is adsorbed to a TiO2 nanoparticulate aggregate sintered to a conducting glass substrate to form the photoanode. Excitation of the porphyrin results in electron injection into the TiO2, and migration to a microporous platinum cathode where hydrogen is produced by hydrogen ion reduction. The oxidized sensitizer dye is reduced by NADH, regenerating the dye and poising the NAD+/NADH redox couple oxidizing. The NAD+ is recycled to NADH by the enzyme glucose dehydrogenase, which obtains the necessary electrons from oxidation of glucose. The reforming of glucose produces gluconolactone, which hydrolyzes to gluconate; the electrochemical potential necessary to overcome thermodynamic and kinetic barriers to hydrogen production by NADH is provided by light. The quantum yield of hydrogen is approximately 2.5%.     

Porphyrin-sensitized nanoparticulate TiO2 as the photoanode of a hybrid photoelectrochemical biofuel cell

Porphyrin-sensitized nanoparticulate TiO(2) on conducting glass has been investigated as a photoanode material for a new cell that converts light energy into electricity. The cell is a hybrid of a dye-sensitized nanoparticulate semiconductor photoelectrochemical solar cell, and a biofuel cell that oxidizes glucose. Porphyrin molecules excited by light inject electrons into the photoanode, from where they enter the external circuit. The resulting porphyrin radical cations are reduced by NADH in aqueous buffer, ultimately regenerating the photoanode and producing NAD(+). Glucose dehydrogenase oxidizes glucose, and in the process recycles NAD(+) back to NADH. The photoanode is coupled with a suitable cathode to make a functioning cell (Hg/Hg(2)SO(4) was employed for evaluation purposes). The cell produces 1.1 V at open circuit and has a fill factor of 0.61. These values are both significantly higher than those for a previously reported cell of a similar type based on an SnO(2) electrode.     

Dichlorobis(cycloalkylamine)platinum(II) complexes structure activity relationship on the human MDA-MB-231 breast cancer cell line

Summary The syntheses of dichlorobis(cycloalkylamine)platinum(II) complexes withcis andtrans cycloalkylamine ligands [cis-PtCl₂(C₃H₅NH₂)₂ tocis-PtCl₂(C₈H₁₅NH₂)₂ (3–8) andtrans-PtCl₂(C₇H₁₃NH₂)₂ (9) andtrans-PtCl₂(C₈H₁₅NH₂)₂ (10)] are described. The distinction betweencis andtrans isomers was achieved by¹H-NMR spectroscopy. The antitumor activity was determined on the cell proliferation of the human MDA-MB-231 breast cancer cell line during long-term drug exposure. The complexes with small cycloalkylamine ligands (3–6) were inferior, those with large cycloalkylamine ligands were comparable (7) or superior (8) to cisplatin. Surprisingly, thecis/trans isomers7/9 and8/10 were equally active. All cycloalkylamine ligands were inactive. IR-spectroscopic studies showed that the size of the cycloalkylamine ring does not lead to significant differences in the Pt-Cl binding strength. Therefore it is assumed that the markedly stronger antitumor activity of the higher homologues,7–10, is not the result of a faster reaction with bionucleophils such as DNA. A possible explanation of the high activity of7–10 is the strong lipophilicity of the complexes. This assumption was confirmed by toxicity tests against confluent cultures.In memory of Professor Dr. Günter Gliemann, late director of the Institut für Physikalische und Theoretische Chemie, Universität Regensburg.