Complex formation of Zn-, Ni-, and Pd-derivatives of purpurin-18 with serum albumin

We analyzed the spectral characteristics of the complexes of Zn²⁺, Ni²⁺, and Pd²⁺ derivatives of purpurin-18 with human serum albumin (HSA) in aqueous buffer at pH 7.0. Pd²⁺ in the coordination sphere of purpurin-18 decreased the affinity to HSA compared to the respective complexes of zinc and nickel derivatives. Since the formation of complexes with HSA is an important parameter of photodynamic activity of tetrapyrrolic compounds, the differential affinity of metal derivatives of purpurin-18 to this protein should be considered for the optimization of photosensitizers.     

The influence of the generation number of liquid-crystalline polypropyleneimine dendrimers on the sorption of low-molecular-weight compounds

The thermodynamic characteristics of ultimately dilute solutions of n-alkanes and n-alkanols in columnar and isotropic poly(propyleneimine) dendrimer phases of three generations (G1-G3) were studied by reversed-phase gas chromatography. The influence of the structure of dendrimers and the chemical nature and the size of nonmesogen molecules on their ability to be dissolved in liquid crystalline phases is discussed. It was found that the compatibility of low-molecular-weight compounds with anisotropic phases increased as the number of dendrimer generation grew.     

Investigation of the thermal diffusion during the formation of a quasicrystalline phase in thin Al-Pd-Re films

The layer mixing during the formation of the Al₇₀Pd₂₀Re₁₀ icosahedral quasicrystalline phase in thin (55 nm) Al-Pd-Re layered film systems subjected to vacuum annealing has been studied. It is shown that a combined layer of Pd and Al atoms (with the Al₃Pd₂ phase dominating) is formed in the first stage (at 350°C), while the rhenium layer remains invariable. In the second annealing stage (at 450°C), the β′-AlPd phase is formed and the Re layer is diffused. In the third stage (700°C), Pd and Re atoms are uniformly distributed throughout the film with the formation of a quasicrystalline phase.     

A new approach for studying fast biological reactions involving nitric oxide: generation of NO using photolabile ruthenium and manganese NO donors

Nitric oxide (NO) is recognized as one of the major players in various biochemical processes, including blood pressure, neurotransmission and immune responses. However, experimental studies involving NO are often limited by difficulties associated with the use of NO gas, including its toxicity and precise control over NO concentration. Moreover, the reactions of NO with biological molecules, which frequently occur on time scales of microseconds or faster, are limited by the millisecond time scale of conventional stopped-flow techniques. Here we present a new approach for studying rapid biological reactions involving NO. The method is based on designed ruthenium and manganese nitrosyls, [Ru(PaPy3)(NO)](BF4)2 and [Mn(PaPy3)(NO)](ClO4) (PaPy3H = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide), which upon photolysis produce NO on a fast time scale. The kinetics of the binding of the photogenerated NO to reduced cytochrome c oxidase (CcO) and myoglobin (Mb) was investigated using time-resolved optical absorption spectroscopy. The NO was found to bind to reduced CcO with an apparent lifetime of 77 micros using the [Mn(PaPy3)(NO)]+ complex; the corresponding rate is 10-20 times faster than can be detected by conventional stopped-flow methods. Second-order rate constants of approximately 1 x 10(8) M(-1) s(-1) and approximately 3 x 10(7) M(-1) s(-1) were determined for NO binding to reduced CcO and Mb, respectively. The generation of NO by photolysis of these complexes circumvents the rate limitation of stopped-flow techniques and offers a novel alternative to study other fast biological reactions involving NO.     

Photoreactions of cytochrome C oxidase

The photoreduction of oxidized bovine heart cytochrome c oxidase (CcO) by visible and UV radiation was investigated in the absence and presence of external reagents. In the former case, the quantum yields for direct photoreduction of heme A (heme a + heme a(3)) were 2.6 +/- 0.5 x 10(-3), 4 +/- 1 x 10(-4), and 4 +/- 2 x 10(-6) with pulsed laser irradiation at 266, 355 and 532 nm, respectively. Within experimental uncertainty, the quantum yields did not depend on pulse energy, implying that the mechanism is monophotonic. Irradiation with 355 nm light resulted in spectral changes similar to those produced independently by reduction with dithionite, whereby the low-spin heme a and Cu(A) are reduced first. Extended illumination at 355 and 532 nm yielded substantial amounts of reduced heme a(3). Heme decomposition was noted with 266 nm light. In the presence of formate and cyanide ions, which bind at the binuclear heme a(3)/copper center in CcO, irradiation at 355 nm caused selective reduction of only the low-spin heme a and Cu(A). The addition of ferrioxalate ion dramatically increased the efficiency of cytochrome c oxidase photoreduction. The quantum efficiency for heme A reduction was found to be near unity, significantly greater than for other known methods of photoreduction. The active reductant is most likely ferrous iron, and its reduction of the enzyme is thermodynamically driven by the reformation of ferrioxalate in the presence of excess oxalate ion. Other metalloenzymes with redox potentials similar to those of cytochrome c oxidase should be amenable to indirect photoreduction by this method.     

Exponential decay for semilinear wave equation with localized damping in the hyperbolic space

In this paper, we study the exponential decay of the energy associated to an initial value problem involving the wave equation on the hyperbolic space ${\mathbb{B}}^N$. The space ${\mathbb{B}}^N$ is the unit disc of ${\mathbb{R}}^N$ endowed with the Riemannian metric g given by $g_{ij}=p^2{\delta }_{ij}$, where $p(x)=\frac{2}{1-{|x|}^2}$ and ${\delta }_{ij}=1$, if $i=j$ and ${\delta }_{ij}=0$, if $i\ne j$. Making an appropriate change, the problem can be seen as a singular problem on the boundary of the open ball endowed with the euclidean metric. The proof is based on the multiplier techniques combined with the use of Hardy's inequality, in a version due to the Brezis–Marcus, which allows us to overcome the difficulty involving the singularities.