Application of 57Co emission Mössbauer spectroscopy to studying biocomplexes in frozen solutions

Emission Mössbauer spectroscopy with the ⁵⁷Co isotope was used to study very dilute rapidly frozen aqueous solutions of cobalt(II) complexes with low-molecular-weight biomolecules (aromatic amino acids – anthranilic acid and L-tryptophan) and within a sophisticated biopolymer, bacterial glutamine synthetase, a key enzyme of nitrogen metabolism. The appearance of after-effects of the ⁵⁷Co→⁵⁷Fe nuclear transformation as well as the coordination properties of the cation and the ligands in the complexes are discussed on the basis of their Mössbauer parameters.     

Dynamic Modes of One Seismic-Damping Mechanism with Frictional Bonds

The possible states of a system of interacting solids with rolling friction and unilateral sliding friction bonds are analyzed. The system can be used for seismic isolation of buildings. The structures (modes) of motion are established. The basic analytical relations are derived, which are needed to construct a dynamic model of variable structure     

Liquid-phase epitaxy of multicomponent layer-based porous coordination polymer thin films of [M(L)(P)0.5] type: importance of deposition sequence on the oriented growth

The progressive liquid-phase layer-by-layer (LbL) growth of anisotropic multicomponent layer-based porous coordination polymers (PCPs) of the general formula [M(L)(P)(0.5)] (M: Cu(2+), Zn(2+); L: dicarboxylate linker; P: dinitrogen pillar ligand) was investigated by using either pyridyl- or carboxyl-terminated self-assembled monolayers (SAMs) on gold substrates as templates. It was found that the deposition of smooth, highly crystalline, and oriented multilayer films of these PCPs depends on the conditions at the early growth cycles. In the case of a two-step process with an equimolar mixture of L and P, growth along the [001] direction is strongly preferred. However, employing a three-step scheme with full separation of all components allows deposition along the [100] direction on carboxyl-terminated SAMs. Interestingly, the growth of additional layers on top of previously grown oriented seeding layers proved to be insensitive to the particular growth scheme and full retention of the initial orientation, either along the [001] or [100] direction, was observed. This homo- and heteroepitaxial LbL growth allows full control over the orientation and the layer sequence, including introduction of functionalized linkers and pillars.     

Spin-glass behavior in LaFe(x)Co(2-x)P2 solid solutions: interplay between magnetic properties and crystal and electronic structures

To explore the evolution of magnetic properties from ferromagnetic LaCo(2)P(2) to paramagnetic LaFe(2)P(2) (both of ThCr(2)Si(2) structure type) a series of mixed composition LaFe(x)Co(2-x)P(2) (x ≤ 0.5) has been comprehensively investigated by means of single-crystal and powder X-ray and neutron diffraction, magnetization and heat capacity measurements, M?ssbauer spectroscopy, and electronic band structure calculations. The Curie temperature decreases from 132 K in LaCo(2)P(2) to 91 K in LaFe(0.05)Co(1.95)P(2). The ferromagnetic ordering is suppressed at higher Fe content. LaFe(0.1)Co(1.9)P(2) and LaFe(0.2)Co(1.8)P(2) demonstrate spin-glass-like behavior, which was also confirmed by the absence of characteristic features of long-range magnetic ordering, namely, a λ-type anomaly in the heat capacity, a hyperfine splitting in the M?ssbauer spectrum, and magnetic reflections in the neutron diffraction pattern. Finally, both LaFe(0.3)Co(1.7)P(2) and LaFe(0.5)Co(1.5)P(2) exhibit paramagnetic behavior down to 1.8 K. The unit cell parameters of the mixed compounds do not follow the Vegard behavior as the increase in the Fe content results in the decrease of average M-M distances (M = Fe, Co). Quantum-chemical calculations and crystal orbital Hamiltonian population analysis reveal that upon aliovalent (nonisoelectronic) substitution of Fe for Co the antibonding character of M-M interactions is reduced while the Fermi level is shifted below the DOS peak in the 3d metal subband. As the result, at higher Fe content the Stoner criterion is not satisfied and no magnetic ordering is observed.     

X-ray diffraction study of the complexes of SAICAR synthase with adenosinetriphosphate

The three-dimensional structures of two enzyme-substrate complexes of SAICAR synthase from the yeast Saccharomyces cerevisiae with adenosinetriphosphate (ATP) prepared under different conditions were studied by X-ray diffraction analysis and then refined. An enzyme molecule was shown to contain two binding sites of ATP. One of these sites is located in the central cavity of the enzyme molecule and apparently binds the ATP molecule directly involved in the enzymatic reaction. In the complexes, the phosphate groups of ATP occupying this site adopt different conformations depending on the Mg²⁺ concentration. The functional role of the second binding site located at a distance of approximately 15 Å from the first site away from the central enzyme cavity has not been understood as yet. It might be that the second site perform the regulatory role in enzyme functioning.     

Charge transfer states in GeO2-doped silicate fiber-optic waveguides and their role in second-harmonic generation

The concentration dependence of the broad-band luminescence arising in GeO₂-doped silicate fiber-optic waveguides is measured and interpreted. The spectra obtained show that electronic excitations of a new type that are absent in pure silicate glass — charge transfer excitons — arise in the doped system. Under the action of light an electron can be transferred both from a Ge center into the host and between Ge centers. Self-organization of these excitations in the field of a light wave (orientational ordering of their dipole moments) results in the appearance of a macroscopic electric field that destroys the initial centrosymmetry of the system and allows second-harmonic generation. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 737–740 (25 November 1998)     

Lipidated ras and rab peptides and proteins--synthesis, structure, and function

Chemical biology can be defined as the study of biological phenomena from a chemical approach. Based on the analysis of relevant biological phenomena and their structural foundation, unsolved problems are identified and tackled through a combination of chemistry and biology. Thus, new synthetic methods and strategies are developed and employed for the construction of compounds that are used to investigate biological procedures. Solid-phase synthesis has emerged as the preferred method for the synthesis of lipidated peptides, which can be chemoselectively ligated to proteins of the Ras superfamily. The generated peptides and proteins have solved biological questions in the field of the Ras-superfamily GTPases that are not amendable to chemical or biological techniques alone.