Photosensitized DNA damage and its protection via a novel mechanism

UVA, which accounts for approximately 95% of solar UV radiation, can cause mutations and skin cancer. Based mainly on the results of our study, this paper summarizes the mechanisms of UVA-induced DNA damage in the presence of various photosensitizers, and also proposes a new mechanism for its chemoprevention. UVA radiation induces DNA damage at the 5'-G of 5'-GG-3' sequence in double-stranded DNA through Type I mechanism, which involves electron transfer from guanine to activated photosensitizers. Endogenous sensitizers such as riboflavin and pterin derivatives and an exogenous sensitizer nalidixic acid mediate DNA photodamage via this mechanism. The major Type II mechanism involves the generation of singlet oxygen from photoactivated sensitizers, including hematoporphyrin and a fluoroquinolone antibacterial lomefloxacin, resulting in damage to guanines without preference for consecutive guanines. UVA also produces superoxide anion radical by an electron transfer from photoexcited sensitizers to oxygen (minor Type II mechanism), and DNA damage is induced by reactive species generated through the interaction of hydrogen peroxide with metal ions. The involvement of these mechanisms in UVA carcinogenesis is discussed. In addition, we found that xanthone derivatives inhibited DNA damage caused by photoexcited riboflavin via the quenching of its excited triplet state. It is thus considered that naturally occurring quenchers including xanthone derivatives may act as novel chemopreventive agents against photocarcinogenesis.     

Photochange in pore diameters of azobenzene-planted mesoporous silica materials

Azobenzene (Az) groups were planted on the pore wall of mesoporous silica MCM-41 (M41) by silylation of triethoxy[4-phenylazo(phenyl)]silane. The optimal surface density of Az groups was 0.9 group nm-2, and too much loading of Az induced the lowering of the efficiency of the trans-cis isomerization due to the congestion of the groups. The reversible change in the pore diameters upon UV-vis irradiation could not be confirmed by N2 adsorption at 77 K but was revealed to be ca. 1.0 nm by the shift of the UV-vis absorption band of p-N,N-dimethylaminobenzylidenemalononitrile introduced into the Az-modified pores.     

Preparation of hole transporting polymers by condensation polymerization of triphenylamine derivatives

Hole transporting polymers were prepared by condensation polymerization of triphenylamine and N,N,N',N'‐tetraphenylbenzidine (TPD) having alkyl group with aldehydes in the presence of p‐toluenesulfonic acid. The obtained polymers had molecular weight higher than 10,000 and good film formation ability. It was found that the aromatic amine monomers were connected with aldehyde monomer at the p‐position of the phenyl group. TPD‐aldehyde polymers had almost the same UV absorption and redox potentials as those of TPD monomer indicating that the electronic structure of amine unit did not change by the polymerization. The hole transporting mobility was in the range of 10⁻³‐10⁻⁶cm²/Vs. The electroluminescent device consisting of ITO/TPD polymer/Alq/Mg‐Ag had a maximum luminance of 9000 cd/m².     

Formation of Isomeric Tetrathiotungstate Clusters [{Cp*Ru(CO)}2(WS4){W(CO)4}] by the Reaction of [Cp*2Ru2S4] with [W(CO)3(MeCN)3]

Thermal and photochemical interconversion occurs between the isomeric pair of tetrathiotungstate [WS₄]²⁻ clusters 1 and 2 , which were formed by thermolysis of [Cp^*₂Ru₂S₄] and [W(CO)₃(MeCN)₃] [Eq. (1)] and then structurally characterized. During synthesis, a dramatic redistribution of ligands between the Ru and W atoms takes place without the loss of any CO and S ligands.     

Preparation and characterization of polymers with oxadiazole on the side chain

Three styrene-type monomers having an oxadiazole group were prepared. The monomers were polymerized by a radical initiator into high molecular weight polymer. Polymers were soluble in many organic solvents such as chloroform, benzene and tetrahydrofuran. Polymer films were amorphous and transparent and showed no change after several months of preparation. The polymer had two reduction potentials around −2 V versus Ag/AgCl electrode. The polymer film dispersed with N,N,N′, N-tetraphenyldiaminobiphenyl (TPD) showed electroluminescence due to the exciplex with TPD. © 1997 John Wiley & Sons, Ltd.     

Oxidative coupling polymerization of 4‐methyltriphenylamine

4‐Methyltriphenylamine was oxidatively polymerized in chloroform (CL) or propylene carbonate (PC) in the presence of ferric chloride (FeCl₃) at 50°C. Polymerization proceeded more rapidly and the molecular weight of the resulting polymer was higher in CL than in PC due to the higher oxidation potential of the solution. The linear structure was confirmed by ¹³C NMR, and the resulting polymer exhibited high thermal stability and electrochemical activity.     

Liquid chromatographic analysis of cinchona alkaloids in beverages

A method for the determination of Cinchona extract (whose main components are the alkaloids cinchonine, cinchonidine, quinidine, and quinine) in beverages by liquid chromatography was developed. A beverage with an alcohol content of more than 10% was loaded onto an OASIS HLB solid-phase extraction cartridge, after it was adjusted to pH 10 with 28% ammonium hydroxide. Other beverages were centrifuged at 4000 rpm for 5 min, and the supernatant was loaded onto the cartridge. The cartridge was washed with water followed by 15% methanol, and the Cinchona alkaloids were eluted with methanol. The Cinchona alkaloids in the eluate were chromatographed on an L-column ODS (4.6 mm id x 150 mm) with methanol and 20 mmol/L potassium dihydrogen phosphate (3 + 7) as the mobile phase. Cinchona alkaloids were monitored with an ultraviolet (UV) detector at 230 nm, and with a fluorescence detector at 405 nm for cinchonine and cinchonidine and 450 nm for quinidine and quinine (excitation at 235 nm). The calibration curves for Cinchona alkaloids with the UV detector showed good linearity in the range of 2-400 microg/mL. The detection limit of each Cinchona alkaloid, taken to be the concentration at which the absorption spectrum could be identified, was 2 microg/mL. The recovery of Cinchona alkaloids added at a level of 100 microg/g to various kinds of beverages was 87.6-96.5%, and the coefficients of variation were less than 3.3%. A number of beverage samples, some labeled to contain bitter substances, were analyzed by the proposed method. Quinine was detected in 2 samples of carbonated beverage.     

Relationship between Muscle Flexibility and Characteristics of Muscle Contraction in Healthy Women during Different Menstrual Phases

Objective: Skeletal muscle function is vital for preventing injury during exercise. It has been reported that skeletal muscle function fluctuates with the menstrual cycle and is considered one of the causes of injury. This study aimed to clarify the relationship between muscle flexibility and muscle contraction characteristics and their changes with the menstrual cycle. Methods: The subjects were healthy women who voluntarily participated in the study through recruitment posters. Muscle flexibility was measured with the passive knee extension (PKE) test, isokinetic knee flexor strength, and the maximum muscle strength exertion angle under two conditions of 60°/s and 120°/s in dominant hamstrings. Additionally, their correlations were analyzed and compared between the menstrual and ovulatory phases. Results: Sixteen subjects (mean age: 20.56 ± 0.73 years; body mass index: 20.21 ± 1.60) participated in the study. Correlation analysis showed a significant negative correlation between PKE and the maximum muscle strength exertion angle under the condition of 60°/s during the menstrual phase (r = –0.54; p = 0.03). No significant difference was observed in the two-group comparison of the variables measured during the menstrual and ovulatory phases. Conclusion: This study confirmed that the more flexible muscles generate the maximum strength at a more contracted position during the menstrual phase in women. In the future, it is necessary to examine the relationship between the results of this study and exercise performance and injury occurrence.