Konrad Szaciłowski

S-NITROSOTHIOLS: MATERIALS, REACTIVITY AND MECHANISMS

The article provides a comprehensive view of S-nitrosothiols, chemical behaviour, the pathways leading to their synthesis, their spectral properties, analytical methods of detection and determination, chemical and photochemical reactivity, kinetic aspects and suggested mechanisms. The structure parameters of S-nitrosothiols and the parent thiols are analysed with respect to their effect on the strengthening or weakening the S–NO bond, and in consequence on the S-nitrosothiol stability. This depends also on the ease of S–S bond formation in the product disulphide. These structural features seem to be crucial both to spontaneous as well as to Cu-catalysed decomposition. Principal emphasis is given here to the S-nitrosothiols’ ability to act as ligands and to the effect of coordination on the ligand properties. The chemical and photochemical behaviours of the complexes are described in more detail and their roles in chemical and biochemical systems are discussed. The aim of the article is to demonstrate that the contribution of S-nitrosothiols to chemical and biochemical processes is more diverse than supposed hitherto. Nevertheless, their role is predictable and, based on the correlation between structure and reactivity, many important mechanisms of biochemical processes can be interpreted and various applications designed.

Nanoscale optoelectronic switches and logic devices

The photoelectrochemical photocurrent switching (PEPS) effect, in the beginning regarded as a scientific curiosity, has become a field of extensive study for numerous research groups all over the world. This unique effect can be utilized for nanoscale switching and information processing, furthermore, is can serve as an interface between molecular information processing and macroscopic electronics. This review summarizes recent efforts in understanding photocurrent switching effects and their application for the construction of nanoscale switches and logic devices. Furthermore, some future prospects concerning the development of electronic/optoelectronic devices based on photoactive semiconducting hybrid materials are presented.

Ligand and medium controlled photochemistry of iron and ruthenium mixed-ligand complexes: prospecting for versatile systems

Abstract Selected Fe and Ru systems, whose photochemical behaviour is sensitive to numerous parameters, are presented. These systems, containing multiple species in equilibrium, are versatile enough to be adapted to special tasks and may also be used to model the phenomena and mechanisms occurring in nature. The role of various parameters is analysed and principal emphasis is given to the ligand sphere influence on the nature of the excited state and thereby on the photochemical mode. This is crucial in the case of Fe(II) complexes of the type [Fe(CN) 5 L] n − , whereas in the carbolyl–cyclopentadienyl complexes, represented by [cpRu(CO) 2 ] 2 , the nature of the excited state is of less importance than for pentacyanoferrates(II). The photochemistry of the carbonyl–cyclopentadienyl complexes is more susceptible to the impact of the medium and the role of the secondary processes is more significant.

Synthesis, structure and photoelectrochemical properties of the TiO2–Prussian blue nanocomposite

The nanocomposite comprising of two simple components – titanium dioxide and Prussian blue – have been synthesized and used for photoelectrode construction. Switching of the photocurrent direction in semiconducting systems upon changes of the electrode potential has been observed. The nanocomposite was characterized by optical spectroscopy and electrochemistry. The structure of the surface complex was modeled using simple quantum chemical models. The behaviour of the photoelectrode was simulated by an adequate electronic circuit. Possible applications of the composite material have been presented.

Reactions of the [Fe(CN)5NO]2− complex with biologically relevant thiols

Reactions of the [Fe(CN)5NO]2− complex with biologically relevant thiols (HnRS = cysteine, N-acetylcysteine, ethyl cysteinate and glutathione) are initiated by the nucleophilic attack of a thiolate (RSn−) on the N atom of the NO+ ligand in the complex to form [Fe(CN)5N(O)SR](n+2)−. The N–S bond in the latter complex is, however, weak and can undergo both heterolytic and homolytic splitting. The former process makes the synthesis reaction reversible, whereas the latter is responsible for the spontaneous redox decomposition: [Fe(CN)5N(O)SR](n+2)− → [FeI(CN)5NO]3− + RS˙(n−1)−. The rate of the monomolecular reaction is controlled by an inductive effect in the thiol with an additional stabilisation coming from formation of a six-membered ring in the case of the N-acylated compounds. In the presence of thiolate excess, the RS˙(n−1)− radicals are transformed into the more stable RSSR˙(2n−1)− radicals, which are scavenged by both [Fe(CN)5N(O)SR](n+2)− and [Fe(CN)5NO]2−. The former reaction initiates, whereas the latter terminates, chain reactions of the catalysed redox decomposition. The catalytic decomposition (in the thiol excess) is much faster than the spontaneous decay (in the nitroprusside excess) but leads to the same final products. The Fe(I) reduction product is identified by UV/Vis, IR, electrochemical and EPR methods. The effect of molecular oxygen is investigated and explained. The mechanism is interpreted in terms of intermediate [Fe(CN)5N(O)(SR)2](2n+2)− complex formation via nucleophilic attack and its decay mainly via homolytic splitting of the N–S bond. To verify the mechanism, a simple reaction model is constructed, based on the assumption that the RSNO(n−1)− ligands are mostly responsible for the [Fe(CN)5N(O)(SR)](n+2)− reactivity and their electronic properties are discussed within the DFT framework.

Molecular switches based on cyanoferrate complexes

Abstract A new system able to play the role of a molecular switch has been characterised. The system consists of the [Fe(CN) 5 NO] 2− –[Fe(CN) 5 N(O)SR] 3− complexes in equilibrium. The constituent complexes differ considerably in electronic absorption (especially in the visible region) and undergo photochemical reactions proceeding in distinct spectral ranges and yielding different products. The equilibrium can be shifted by several physical and chemical stimuli changing thereby absorption and/or modifying the photochemical behaviour of the system. To the stimuli belong: pH, thiol concentration, ion strength, nature and concentration of cations, temperature and pressure. All these features make the system suitable for switching purposes and for different kinds of signal processing in digital, analogue and integrating circuits. As the [Fe(CN) 5 NO] 2− –[Fe(CN) 5 N(O)SR] 3− system photochemically produces NO-donors and/or nitric oxide, its phototherapeutic application is considered.

Photochemistry of the [Fe(CN)5N(O)SR]3- complex : A mechanistic study

Photochemical behaviour of the title complex (RS − = mercaptosuccinate) was defined as photodissociation and photooxidation–

Arithmetic Device Based on Multiple Schottky-like Junctions

Photoelectrodes containing cadmium sulfide deposited as powders and crystalline thin layers combined with semi-solid ionic liquid electrolyte behave like Schottky photodiodes. Appropriate connection of these devices results in simple optoelectronic logic gates (AND, XOR) and enables construction of an optoelectronic binary half-adder.

Towards 'Computer-on-a-Particle' Devices: Optoelectronic 1:2 Demultiplexer Based on Nanostructured Cadmium Sulfide

Nanocrystalline sulfur-doped cadmium sulfide (CdS) prepared by microwave synthesis was investigated. Photoelectrochemical and optical characteristics of sulfur-doped CdS exhibit the photoelectrochemical photocurrent switching effect. Depending on the wavelength and applied bias, the anodic and/or cathodic photocurrent was observed. The unusual behaviour of nanocrystalline CdS allowed the construction of a combinatorial logic system from this material.

BixLa1−xVO4 solid solutions: tuning of electronic properties via stoichiometry modifications

BixLa1-xVO4 solid solutions were obtained in the form of fine powder via a microwave-assisted hydrothermal route. The presence of a solid solution in the studied system was confirmed using X-ray diffraction (XRD) and optical spectroscopy techniques. Pure BiVO4 and LaVO4 were obtained in the monoclinic form, whereas solid solutions in the tetragonal, zircon-type structure. The optical band gap dependence on the composition of the solid solution is parabolic, thus there is a possibility to tune this parameter in a wide concentration range, from 2.4 to 4.0 eV. An absorption coefficient maximum is also concentration-dependent, possibly, due to the structural disorder of the samples. Solid solutions with Bi(3+) concentration between 11.94 and 32.57 at.% exhibit intense, green luminescence. This indicates the presence of Bi-originated electronic states within the band gap. The value of the conduction band edge potential, measured by both electrochemical impedance spectroscopy and work function measurements, is concentration-independent. Moreover, solid solutions exhibit a photoelectrochemical photocurrent switching effect, thus they may be promising materials for molecular electronics and as dioxygen activators.