Complexation of a crown-substituted naphthalimide derivative with heavy metals in Langmuir monolayers

Russian Chemical Bulletin - It was demonstrated that, in contrast to a solution in an organic solvent, the relaxation of the excited state of a fluorophore moiety proceeds mainly radiationless upon...     

Optimal use of components of a dyadic wavelet representation

In practice, one may encounter linear transforms whose result is important for a certain set of vector components only. In particular this relates to vector components restored from its dyadic wavelet representation. In this paper we study optimization of the index set of the dyadic wavelet representation which can be used to restore required original vector components.     

On the Deductive Security of Queries to Databases with Multi-Bit Records

One of the priority problems in the development and use of databases is that of information security. It becomes substantially more complicated when databases are implemented in cloud computing systems. In our previous paper we studied this problem for the simple case of databases with one-bit records; we offered a criterion of deductive security for queries to such databases, proved the hardness of its checking, and showed that for some classes of queries deductive security can be verified relatively easy. In this paper these results are generalized for the case of more complex databases with multi-bit records.     

Electrochemically controlled multistability of ultrathin films of double-decker cerium phthalocyaninates

The spectral and electrochemical properties of Langmuir-Blodgett (LB) films of homoleptic double-decker cerium bis-[tetra-15-crown-5]-phthalocyaninate Ce[R₄Pc]₂ and its heteroleptic analog [Pc]Ce[R₄Pc] were studied. It was shown that during formation of Langmuir monolayers upon contact of both complexes solutions with water subphase the metal center with valent state IV in the solution transforms into one with the valent state III in the monolayer. Upon cyclic compression-expansion of these monolayers, orientation-induced reversible intramolecular transfers of electron from 4f orbital of cerium ion to the phthalocyanine macrocycle (compression) and in reverse direction (expansion) occur in a planar supramolecular system. Scheme of reversible electrochemical transformations occurring in ultrathin films of double-decker cerium crown-phthalocyaninates, one of which is associated with the Ce⁺³/Ce⁺⁴ redox-transition of metal center of the complex, was proposed and substantiated using the results of spectro-electrochemical investigations. It was shown that one of these transformations is associated with the Ce⁺³/Ce⁺⁴ redox transition of metal center of the complex and upon change of metal center oxidation state its size changes, and, consequently, the distance between the decks of the complex also changes. This change in the distance can lead to a substantial (13–15%) modulation of the linear size of molecular assemblies with a large number of molecules in stack. On the basis of this effect the supramolecular device that can perform mechanical work can be developed. Using surface plasmon resonance technique we have demonstrated that a step change in electrode potential in region of 200–1000 mV induces a corresponding optical response reflected in a step change of the resonance angle. High operation speed and reversibility of switching between stable states can serve as a basis for development of optoelectronic switching systems.     

Ultrathin film sensory system based on resonance energy transfer between the monolayers consisting of non-covalently linked fluorophores

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On the deductive security of queries to confidential databases in cloud computing systems

We study certain simple models of confidential databases in cloud computing systems. In the framework of these models we introduce a concept of deductive security for queries to such databases, find necessary and sufficient conditions of deductive security, and describe some classes of queries which satisfy these requirements.     

Orientation-induced redox transformations in Langmuir monolayers of double-decker cerium bis[tetra-(15-crown-5)-phthalocyaninate] and multistability of its Langmuir-Blodgett films

The spectral, electrochemical, and optical properties of Langmuir-Blodgett films (LBFs) and cast films from a solution of new double-decker cerium bis[tetra-(15-crown-5)-phthalocyaninate] (Ce(R₄Pc)₂) are studied. Based on analysis of compression isotherms and quantum-chemical calculations, schemes of the organization of Ce(R₄Pc)₂ molecules at different states of its monolayers are proposed. Correlation dependences are determined in order to relate the optical and electrochemical characteristics of monolayers and LBFs of sandwich-type lanthanide phthalocyaninates to the ionic radii of their metal centers. The valent state of Ce ions in a monolayer-forming complex is determined, and a sequence of redox transformations occurring in LBF uppon appliance of a potential is proposed, one of the transformations being associated with the Ce³⁺/Ce⁴⁺ redox transition. Orientation-induced intramolecular electron transfer is revealed in the planar supramolecular system. It is shown that, during the formation of a monolayer from a Ce(R₄Pc)₂ solution, a tetravalent metal center passes to a trivalent state. Monolayer compression to a high surface pressure reverts the complex to the electronic state typical of the solution. The reversible transformations observed upon the monolayer compression result from intramolecular electron transfer from the 4f-orbital of Ce to the phthalocyanine ring and backwards. The high operation rate and the reversibility of switching between the stable states, which are determined by means of the surface plasmon resonance technique, upon a stepwise change in the electrode potential within the range of 200?C850 mV may underlie the development of optoelectronic systems. With a large number of molecules in a stacking aggregate, changes in the distance between the decks of the complex that occur with changes in the oxidation level of the metal center can substantially modulate the sizes of molecular ensembles. A supramolecular device capable of performing mechanical work can be developed based on this effect.