Photodimerization Process Research Articles

Infrared reflection absorption spectroscopic study on photodimerization process of stilbazoles in Langmuir-Blodgett films

Infrared reflection absorption (IRA) spectroscopy was applied to the study of photodimerization process induced by irradiation (at 340 nm) of N-(1-octadecyl)-4-stilbazolium cation incorporated in the Langmuir-Blodgett films of perdeuterated arachidic acid (CD 3(CD 2) 18COOH).

Infrared reflection absorption spectroscopic study on the photodimerization process of a stilbazolium cation embedded in Langmuir-Blodgett films

Infrared reflection absorption (IRA) spectroscopy was applied to photodimerization process induced by irradiation (at 340 nm) of N-(1-octadecyl)-4-stilbazolium cations (C 18 S) incorporated in the Langmuir-Blodgett films of perdeuterated arachidic acid (CD 3 (CD 2 ) 18 COOH, A). The IRA spectra proved that the main process proceeds through cyclobutane ring formation of the stilbazolium cations in a syn head-to-head arrangement

Steady-state and time-resolved fluorescence anisotropy study of phospholipid molecular motion in the gel phase using 1-palmitoyl-2-[9-(2-anthryl)-nonanoyl] -sn-glycero-3-phosphocholine as probe.

1-Palmitoyl-2-[9-(2-anthryl)-nonanoyl]-sn-glycero-3-phosphocholine (Anthr-PC), a non-perturbing phospholipid probe [de Bony, J. and Tocane, J. F. (1983) Chem. Phys. Lipids 32, 105-121], has been designed in order to obtain insight into the membrane lipid organization at a 'microscopic' level, in terms of lateral distribution both in model and in natural membranes [de Bony, J. et al. (1984) Eur. J. Biochem. 143, 373-379; FEBS Lett. 174, 1-6]. In the present study, the molecular motions of this new fluorescent probe embedded in a lipid matrix have been investigated by fluorescence anisotropy techniques in steady-state and time-resolved modes. The results indicate that long axis rotation, monitored by the out-of-plane mode of rotation of the fluorophore, is fast even in the phospholipid gel state. It is moderately sensitive to the phase transition. The data suggest that this rotation is anisotropic. Cholesterol exhibits little effect on this rotation. The rotation of the long axis itself is sensitive to the transition. It is hindered as inferred from measurements at wavelength where both the in-plane and out-of-plane motions contribute to the depolarization of the emitted fluorescence light. Cholesterol restricts this motion. The behaviour of the free 9-(2-anthryl)-nonanoic acid is not significantly different from that of Anthr-PC. These results are discussed with respect to the influence of orientational constraints on the photodimerization process when this lipid probe is used to monitor phospholipid lateral distribution.

Structure and dynamics of a new phase of anthracene

A new triclinic phase of anthracene (II), which cannot be isolated in the pure state, has been identified by analysis of the intensities and symmetry of the electron diffraction patterns (recorded at low temperature) exhibited by stressed specimens of the monoclinic, thermodynamically stable form (I). A number of trial structures were derived on the basis of both packing calculations (using the “atom–atom” approach) and observed topotactic relationships between II and I. Lattice dynamical computations were used to refine the structure and, in particular, it was possible to compute the i.r. and Raman active vibrations of the two forms. The atomic coordinates and temperature factors of the new structure (Ptext-decoration:overline1, a= 8.342 A, b= 5.892 A, c= 11.282 A, α= 123.34°, β= 96.70°, γ= 85.91°, z= 2, V= 460.07 A3) are given and so are some of the thermodynamic properties, also computed, of the phase II. The influence of temperature and pressure upon phase II (which has a cohesive energy only 2 kJ mol–1 less than that of I), along with its importance in the solid-state photodimerization process, is also discussed.

ChemInform Abstract: WATER PARTICIPATION IN THE CRYSTALLINE‐STATE PHOTODIMERIZATION OF CINNAMIC ACID DERIVATIVES. A NEW TYPE OF ORGANIC PHOTOREACTION

AbstractDie Bestrahlung von Kristallen der Zimtsäure (I) in Wasser führt zum Truxinsäurederivat‐monohydrat (II), das bei Erwärmen auf 100‐110°C in das wasserfreie, kristalline Dimere (II) übergeht.

Water-Participation in the Crystalline-State Photodimerization of Cinnamic Acid Derivatives. A New Type of Organic Photoreaction

Abstract A new type of organic photoreaction, a water-participation reaction in the crystalline state, has been investigated. The photoirradiation of p-formylcinnamic acid (p-FCA) crystals in the presence of water leads to 4,4′-diformyl-β-truxinic acid (p-FCA dimer) which has one molecule of crystal water. A comparison of the photodimerization carried out in the presence/absence of water revealed the effects of the water molecule on the reaction. That is, the water molecule is incorporated into the p-FCA dimer during the photodimerization process. Furthermore, the water accelerates the reaction rate of photodimerization, leading to the formation of the crystalline dimer, whereas only the water-free amorphous dimer results in the absence of water. In addition, by heating at 100–110 °C, the p-FCA dimer with a water molecule is converted into a water-free crystalline dimer, which is not attainable from a water-free amorphous dimer. The photodimerization of several β-form crystals of cinnamic acid derivatives has been examined from the viewpoint of water-participation: p-nitro, p-chloro, and 3,4-dichlorocinnamic acid were found to photodimerize in the same manner as p-FCA.

A spectroscopic study of the photodimerization of anthracene sandwich dimers in dianthracene

The photodimerization of anthracene sandwich pairs embedded in dianthracene single crystals has been studied by absorption and fluorescence spectroscopy over a wide range of temperature (6–295 K). An excimer state has been found to be the intermediate state in the formation of the dianthracene. The fluorescence efficiency of the sandwich pair is unity at very low temperature while the quantum yield for the dimerization process is unity at high temperatures. The thermal activation energy for the photodimerization process has been determined directly as well as from temperature dependence measurements of the fluorescence intensity. The two methods yield 590 ± 25 cm-1 and 611 ± 20 cm-1 respectively for this energy. Corresponding measurements were also carried out with the perdeuterated anthracene sandwich dimer. These show a marked deuterium effect.

THE MECHANISM FOR FROZEN AQUEOUS SOLUTION IRRADIATION OF PYRIMIDINES*

Summary Upon freezing an aqueous solution, the formation of crystalline ice forces the solute molecules into solid aggregates. Therefore, identical photodimerimtion of pyrimidines occur in either frozen aqueous solutions or dry solid films. No photodimerization of pyrimidines was evidenced in a homogeneous glycerol glass. Upon freezing an aqueous solution containing solute and a small percentage of organic solvent, the solute molecules together with some organic solvent form ‘puddles’. Therefore, a photochemical reaction in this organic solvent was observed. Only those pyrimidines having an α,β‐unsaturated keto group in their structure undergo photodimerization. The mechanism through which the cyclobutyl ring is formed most probably involves a diradical intermediate. The unstable thymine monohydrate crystal has the most favorable orientation for two thymine molecules to form dimer. Therefore, the photodimerization process for thymine is less favored in dry solid film than in frozen aqueous solution because the thymine monohydrate crystalline lattice collapses under low humidity.