Influence of hydrogen on delayed fracture of RPV steels

Different factors, such as irradiation, cyclic and thermal stresses, hydrogen embrittlement and static load can cause degradation of properties of reactor pressure vessel steels.The hydrogen embrittlement of low alloy ferritic steels has been investigated in dependence on the electrolytic hydrogen charging parameters. It was observed that the degradation of plastic properties appears over critical value 2.5 p.p.m. of hydrogen. In a test under constant load of notched specimens the lower threshold stress was ascertained as a function of cathodic hydrogen charging parameters.     

Semiconductor quantum dots for photodynamic therapy

The applicability of semiconductor QDs in photodynamic therapy (PDT) was evaluated by studying the interaction between CdSe QDs with a known silicon phthalocyanine PDT photosensitizer, Pc4. The study revealed that the QDs could be used to sensitize the PDT agent through a fluorescence resonance energy transfer (FRET) mechanism, or interact directly with molecular oxygen via a triplet energy-transfer process (TET). Both mechanisms result in the generation of reactive singlet oxygen species that can be used for PDT cancer therapy.     

Oxo-tricyano complexes of molybdenum(IV) and tungsten(IV) with bidentate Schiff bases

Summary The reaction of [M(CN)₄O(OH₂)]^2– (M = Mo or W) with 2-acetylpyridine and methyl-or butyl-amine in a water-MeOH mixture gave [M(CN)₃O(L-L)]^- (L-L= Schiff base ligand), isolated as [AsPh₄]⁺ salts. The complexes have been characterized by elemental analysis, and electronic, i.r. and¹H-n.m.r. spectroscopy. The Schiff base ligands complex in a bidentate manner through the two nitrogen atoms giving mixed-ligand compounds similarly to 2,2-bipyridyl or 1,10-phenanthroline.On leave from the Faculty of Chemistry, Jagiellonian University, Kraków.     

Mössbauer spectroscopy in studies of photosynthesis

Photosynthesis is a process occurring in certain species of bacteria, algae and higher plants. It transforms solar energy into various forms of energy-rich organic molecules. Photosystem II (PSII) is the “heart” of the photosynthetic apparatus because it delivers electrons and protons for further steps of the light-driven phases of photosynthesis. There are two enigmatic iron binding structures within the core of photosynthetic apparatus, which play an important role in the electron transfer within PSII. Many investigations focus on the determination of their function which is the key to the understanding of the molecular mechanism of the energy and electron transfer within PSII. Among many methods used in this research field, the Mössbauer spectroscopy is a unique one, which gives the possibility to study changes of the valence and spin states of those two iron sites and the dynamical properties of their protein matrix in the presence of various physiological and stress conditions.     

Collective behavior of electronic fireflies

A simple system composed of electronic oscillators capable of emitting and detecting light-pulses is studied. The oscillators are biologically inspired, there are designed for keeping a desired light intensity, W, in the system. From another perspective, the system behaves like modified integrate and fire type neurons that are pulse-coupled with inhibitory type interactions: the firing of one oscillator delays the firing of all the others. Experimental and computational studies reveal that although no direct driving force favoring synchronization is considered, for a given interval of W phase-locking appears. This weak synchronization is sometimes accompanied by complex dynamical patterns in the flashing sequence of the oscillators.     

X-ray spectroscopic study of the electronic structure of visible-light responsive N-, C- and S-doped TiO2

The electronic origins of the visible-light response of N-, C- and S-doped TiO₂ have been studied using X-ray absorption, X-ray emission, and X-ray photoelectron spectroscopies. New electronic states are observed in the bulk band gap, above the valence band edge of pure TiO₂, which can be directly related to the visible-light absorption of the N-, C- and S-doped TiO₂ materials.     

Reaction force decomposition of activation barriers to elucidate solvent effects

The reaction force F(Rc) of a chemical or physical process is given by the negative derivative of the potential energy V(Rc) along the intrinsic reaction coordinate Rc. F(Rc) unambiguously and naturally divides the activation barrier in each direction into two contributions, one of which has been found to reflect preparative structural factors, Eact,prep, and the other corresponds to the first part of the transition to products, Eact,trans. We have analyzed F(Rc) for an SN2 substitution reaction in both the gas and aqueous phases. Although the overall forward and reverse activation barriers are significantly lowered by the solvent, the Eact,trans are very little affected. Thus the increased rates that are predicted for this process in aqueous solution can be attributed to the solvent facilitating the structural effects in the preparative stages, decreasing the Eact,prep. This example shows how the reaction force decomposition of activation barriers can help to elucidate the roles played by external factors, e.g., solvents.     

Exploring a reaction mechanism for acetato ligand replacement in paddlewheel tetrakisacetatodirhodium (II,II) complex by ammonia: computational density functional theory study

This study focuses on the first step of interaction between DNA and the paddle-wheel dirhodium complex. The ammonia molecule was used to model the oligonucleotide sequence. The reaction was considered in neutral and acidic conditions, in gas phase, and in solvent, using the COSMO model. Molecular structures of the complexes were optimized in both models at the B3PW91/6-31G(d) level. The B3LYP functional and aug-cc-pvdz basis set were employed for single-point energy determination and electron distribution analyses. It was shown that in neutral solution the replacement of axial aqua ligand is mildly exoergic. The reaction is characterized by a relatively low activation barrier (10-12 kcal/mol), and, according to Eyring transition state theory, it proceeds very quickly. The breaking of the Rh-O(ac) bond in neutral solution is mildly endoergic (less than 1 kcal/mol) with an activation barrier of about 21 kcal/mol. However, this process can occur much more spontaneously (ΔG of -14 kcal/mol) when the dirhodium complex is protonated at the acetyl oxygen in remote position.     

Formation of a Thymine‐HgII‐Thymine Metal‐Mediated DNA Base Pair: Proposal and Theoretical Calculation of the Reaction Pathway

A reaction mechanism that describes the substitution of two imino protons in a thymine:thymine (T:T) mismatched DNA base pair with a Hg^II ion, which results in the formation of a (T)N3‐Hg^II‐N3(T) metal‐mediated base pair was proposed and calculated. The mechanism assumes two key steps: The formation of the first Hg^II? N3(T) bond is triggered by deprotonation of the imino N3 atom in thymine with a hydroxo ligand on the Hg^II ion. The formation of the second Hg^II? N3(T) bond proceeds through water‐assisted tautomerization of the remaining, metal‐nonbonded thymine base or through thymine deprotonation with a hydroxo ligand of the Hg^II ion already coordinated to the thymine base. The thermodynamic parameters ΔG_R=?9.5 kcal mol^?1, ΔH_R=?4.7 kcal mol^?1, and ΔS_R=16.0 cal mol^?1 K^?1 calculated with the ONIOM (B3LYP:BP86) method for the reaction agreed well with the isothermal titration calorimetric (ITC) measurements by Torigoe et al. [H. Torigoe, A. Ono, T. Kozasa, Chem. Eur. J. 2010 , 16, 13218–13225]. The peculiar positive reaction entropy measured previously was due to both dehydration of the metal and the change in chemical bonding. The mercury reactant in the theoretical model contained one hydroxo ligand in accord with the experimental pK_a value of 3.6 known for an aqua ligand of a Hg^II center. The chemical modification of T:T mismatched to the T‐Hg^II‐T metal‐mediated base pair was modeled for the middle base pair within a trinucleotide B‐DNA duplex, which ensured complete dehydration of the Hg^II ion during the reaction.