Dipole strengths of the Qy(0,0) bacteriochlorophyll c transition

The absorption spectra of bacteriochlorophyll (BChl) c solutions in two mixtures of two solvents (acetonitrile with pyridine and dimethylsulfoxide with methanol) exhibiting different refractive indices were measured and deconvoluted into Gaussian components. The refractive index of mixed solvents was changed by the change in the ratio of the volumes of the liquids used in the mixture. Using the Qy(0,0) band half widths and absorption coefficient, based on the simplified formula proposed by Knox, the dipole strengths of the Qy(0,0) BChl c transition for various values of solvent refractive index were calculated and compared with values given by Knox and Spring. For both investigated combinations of two liquids, the dependence of Qy(0,0) transition dipole strength of the BChl c on solvent refractive index was almost linear. The slopes of the lines obtained from the experimental absorption bands were different for two investigated solvent mixtures. More accurate linear dependence and similar slopes of lines for both solvent mixtures were obtained using half widths and absorption coefficients of the Gaussian components of Qy(0,0) transition. It is explained by the superposition of the contributions from other electronic and vibronic transitions of BChl c monomers or possibly also from transitions of the pigments involved in some complexes with solvent molecules in the absorption region investigated. The results show that the formula proposed by Knox can be successfully applied also for BChl c, after elimination of the overlapped contributions from the other transitions, by applying Gaussian analysis to select only contribution from Qy(0,0) pigment transition.     

NanoFAST: structure-based design of a small fluorogen-activating protein with only 98 amino acids

One of the essential characteristics of any tag used in bioscience and medical applications is its size. The larger the label, the more it may affect the studied object, and the more it may distort its behavior. In this paper, using NMR spectroscopy and X-ray crystallography, we have studied the structure of fluorogen-activating protein FAST both in the apo form and in complex with the fluorogen. We showed that significant change in the protein occurs upon interaction with the ligand. While the protein is completely ordered in the complex, its apo form is characterized by higher mobility and disordering of its N-terminus. We used structural information to design the shortened FAST (which we named nanoFAST) by truncating 26 N-terminal residues. Thus, we created the shortest genetically encoded tag among all known fluorescent and fluorogen-activating proteins, which is composed of only 98 amino acids.

We solved the structure of a fluorogen-activating protein FAST and synthesized the library of potential fluorogens. Using these data, we designed the shortest genetically encoded fluorescent tag among all known.     

Kinetics of oxidation of vanadyl acetylacetonate by oxygen in methanolic solution

The kinetics of oxidation of vanadyl acetylacetonate to VO(OH)(OMe)(acac) by molecular O2 in MeOH have been studied spectrophotometrically. The reaction, which is pseudo first-order with respect to [VO(acac)2] and [O2], is inhibited by Hacac and a vanadium(V) complex. The rate data were used to calculate the thermodynamic activation parameters. A mechanism for the reaction is discussed.     

Metal complexes of the flavonoid quercetin: antibacterial properties

Two types of complexes were obtained when quercetin (L) was reacted with metal ions in EtOH. The compounds [M(L)Cl₂(H₂O)₂] (M = Mn^II or Co^II) and the semi-oxidized complexes [M(L)₂CL₂] · 2H₂O (M = Cd^II or Hg^II) were characterized by elemental analysis., conductivity and magnetic susceptibility measurements, i.r., u.v.–vis. and e.p.r. spectroscopy. The (C=O) stretching mode located on the C ring of the ligand and the complexes remains in the same range, showing that this oxygen atom does not participate in coordination to the metal ions. Magnetic susceptibilities and e.p.r. spectra of powdered samples indicated that the monomeric form of the complexes in the solid state, and the paramagnetic nature of the Cd^II and Hg^II complexes is attributable to the semiquinone character of the ligand. The antibacterial activity of the metal complexes were tested against five bacterial strains and compared with penicillin activity.     

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.     

Limit Cycles Near Homoclinic and Heteroclinic Loops

In the study of near-Hamiltonian systems, the first order Melnikov function plays an important role. It can be used to study Hopf, homoclinic and heteroclinic bifurcations, and the so-called weak Hilbert’s 16th problem as well. The form of expansion of the first order Melnikov function at the Hamiltonian value h ₀ such that the curve defined by the equation H(x, y) = h ₀ contains a homoclinic loop has been known together with the first three coefficients of the expansion. In this paper, our main purpose is to give an explicit formula to compute the first four coefficients appeared in the expansion of the first order Melnikov function at the Hamiltonian value h ₀ such that the curve defined by the equation H(x, y) = h ₀ contains a homoclinic or heteroclinic loop, where the formula for the fourth coefficient is new, and to give a way to find limit cycles near the loops by using these coefficients. As an application, we consider polynomial perturbations of degree 4 of quadratic Hamiltonian systems with a heteroclinic loop, and find 3 limit cycles near the loop. Dedicated to Professor Zhifen Zhang on the occasion of her 80th birthday     

The level-rank duality for non-abelian theta functions

We prove that the strange duality conjecture of Beauville–Donagi–Tu holds for all curves. We establish first a more extended level-rank duality, interesting in its own right, from which the standard level-rank duality follows by restriction.     

Electrical conductivity in solid solutions and in two-phase regions of the silver halide-bivalent metal (cadmium,cobalt, zinc) halide systems

Electrical conductivity of solid systems AgX-MX₂ (where M=Cd, Co, Zn and X=Cl, Br) were measured in a large range of temperature and compositions. Activation energies and conductivity values vs. composition are presented and discussed in relation to phase equilibria in the respective systems. Maximum of the conductivity value and stabilization of the activation energy have been found for silver halides doped heavily with divalent cation e.g. in the systems forming solid solutions on the silver halide side. Disorder in AgBr on the approach to melting, expected to be higher than in AgCl, has been shown by means of original DSC curves presented for both halides.     

Thermodynamics and phase equilibrium studies of silver halide-cobalt(II) halide systems

Phase diagrams for the systems AgCl-CoCl₂ and AgBr-CoBr₂ were determined by differential scanning calorimetry. The systems are of the eutectic type. Eutectic points are at 271±2 K, 19.5 mol% CoCl₂ and 653±2 K, 17.0 mol% CoBr₂, respectively. The solid solubility does not exceed 2 and 4 mol% in the systems AgCl-CoCl₂ and AgBr-CoBr₂, respectively. Thermodynamic activities of components in molten mixtures and molar free enthalpies of mixing were determined for both systems on the basis of liquidus curves. Deviations from ideality were not found to be considerable.