Pyrimidinone: Versatile Trojan horse in DNA photodamage?

(6-4) Photolesions between adjacent pyrimidine DNA bases are prone to secondary photochemistry. It has been shown that singlet excited (6-4) moieties form Dewar valence isomers as well as triplet excitations. We here report on the triplet state of a minimal model for the (6-4) photolesion, 1-methyl-2(1H)-pyrimidinone. Emphasis is laid on its ability to abstract hydrogen atoms from alcohols and carbohydrates. Steady-state and time-resolved experiments consistently yield bimolecular rate constants of ∼104 M−1 s−1 for the hydrogen abstraction. The process also occurs intramolecularly as experiments on zebularine (1-(β-D-ribofuranosyl)-2(1H)-pyrimidinone) show

Identification of charge separated states in thymine single strands

UV excitation of the DNA single strand (dT)(18) leads to electronically excited states that are potential gateways to DNA photolesions. Using time-resolved infrared spectroscopy we characterized a species with a lifetime of similar to 100 ps and identified it as a charge separated excited state between two thymine bases

Identification of charge separated states in thymine single strands

UV excitation of the DNA single strand (dT)(18) leads to electronically excited states that are potential gateways to DNA photolesions. Using time-resolved infrared spectroscopy we characterized a species with a lifetime of similar to 100 ps and identified it as a charge separated excited state between two thymine bases

A comparative analysis of the UV/Vis absorption spectra of nitrobenzaldehydes.

In a joint experimental and theoretical study, the UV/Vis absorption spectra of the three isomers (ortho, meta, para) of nitrobenzaldehyde (NBA) were analyzed. Absorption spectra are reported for NBA vapors, cyclohexane and acetonitrile solutions. All spectra are poor in vibronic structure and hardly affected in shape by the surroundings (vapor or solution). Moderate solvatochromic shifts of [similar]−0.2 eV are measured. For all isomers vertical transition energies, oscillator strengths, and excited state dipole moments were computed using the MS-CASPT2/CASSCF and CC2 methods. Based on these calculations the experimental transitions were assigned. The spectra of all isomers are characterized by weak (εmax ≈ 100 M−1 cm−1) transitions around 350 nm (3.6 eV), arising from nπ* absorptions starting from the lone pairs of the nitro and aldehyde moieties. The next band of intermediate intensity peaking around 300 nm (4.2 eV, εmax ≈ 1000 M−1 cm−1) is dominated by ππ* excitations within the arene function. Finally, strong absorptions (εmax ≈ 10 000 M−1 cm−1) were observed around 250 nm (5.0 eV) which we ascribe to ππ* excitations involving the nitro and benzene groups

High magnetic fields in chemistry

Recent applications of large (∼ 1 T ∼ 30 T) magnetic fields in modern chemical research are reviewed. Magnetic field effects of chemical relevance appear on the levels of quantum mechanics, thermodynamics, and macroscopic forces. Quantum mechanical magnetic field effects are governed by the Zeeman interaction and are borne out as static and dynamic effects in spectroscopy and in chemical kinetics. Magnetic circular dichroism (MCD) spectroscopy and magnetic fluorescence quenching in the gas phase serve to illustrate the former, while radical pair spin chemistry is representative of the latter. The principles of the radical pair mechanism are outlined and highfield applications are illustrated in some detail for photo-induced electron transfer reactions of some transition metal complexes. Thermodynamic effects concern the magnetization of chemical samples, which is the focus of magnetochemistry or more modern molecular magnetism, and the equilibrium of chemical reactions. Representative examples of both aspects are described. Finally, the exploitation of orientational forces caused by the magnetic anisotropy of larger particles (from macromolecules to micro-crystals) is exemplified. Crystal growth in a magnetic field may hold a potential for achieving better control of the quality of protein crystals for structural analysis

Ultrashort Laser Pulses in Biology and Medicine

Sources of ultrashort laser pulses are nowadays commercially available and have entered many areas of research and development. This book gives an overview of biological and medical applications of these laser pulses. The briefness of these laser pulses permits the tracing of the fastest processes in photo-active bio-systems, which is one focus of the book. The other focus is applications that rely on the high peak intensity of ultrashort laser pulses. Examples covered span non-linear imaging techniques, optical tomography, and laser surgery

Magnetic field effect on the photooxidation efficiency of ferrocene

The cage escape efficiency νce of radicals in the electron transfer quenching of triplet methylene blue by ferrocene in acetonitrile was found to be sensitive towards an external magnetic field. The field dependence of the effect corresponding to a monotonic decrease of νce was determined in a field range from 0.0 to 3.2T, where it reaches a value of −20.7%. The effect is analyzed in terms of a spin chemical model wherein the effective rate of geminate reverse electron transfer, regenerating the singlet ground state of the reactants, becomes magnetic field dependent due to magnetic mixing of non-uniformly reactive spin sublevels by the anisotropic Zeeman interaction. From the analysis, the absolute values of the rate constants of spin-allowed reverse electron transfer (605 ns−1), cage escape (15 ns−1, and electron spin relaxation in the ferricenium cation (154 ns−1) could be determined