Chemical characterization of the smallest S-nitrosothiol, HSNO; cellular cross-talk of H2S and S-nitrosothiols

Dihydrogen sulfide recently emerged as a biological signaling molecule with important physiological roles and significant pharmacological potential. Chemically plausible explanations for its mechanisms of action have remained elusive, however. Here, we report that H(2)S reacts with S-nitrosothiols to form thionitrous acid (HSNO), the smallest S-nitrosothiol. These results demonstrate that, at the cellular level, HSNO can be metabolized to afford NO(+), NO, and NO(-) species, all of which have distinct physiological consequences of their own. We further show that HSNO can freely diffuse through membranes, facilitating transnitrosation of proteins such as hemoglobin. The data presented in this study explain some of the physiological effects ascribed to H(2)S, but, more broadly, introduce a new signaling molecule, HSNO, and suggest that it may play a key role in cellular redox regulation.     

Stabilization through precipitation in a system of colloidal iron(III) pyrophosphate salts

The ionic strength of a solution decreases during the precipitation of an insoluble salt, which can cause an initially unstable colloidal system to stabilize during its formation. We show this effect in the precipitation and aging of colloidal iron(III) pyrophosphate, where we observe two distinct stages in the aggregation process. The first stage is the formation of nanoparticles that immediately aggregate into clusters with sizes on the order of 200 nm. In the second stage these clusters slowly grow in size but remain in dispersion for days, even months for dialyzed systems. Eventually these clusters become macroscopically large and sediment out of dispersion. Noting the clear instability of the nanoparticles, it is interesting to find two stages in their aggregation even without the use of additives such as surface active molecules. This is explained by accounting for the rapid decrease of ionic strength during precipitation, rendering the nanoparticles relatively stable when precipitation is complete. Calculating the interaction potentials for this scenario we find good agreement with the experimental observations. These results indicate that coupling of ionic strength to aggregation state can be significant and should be taken into account when considering colloidal stability of insoluble salts.     

Random field forward interest rate models,market price of risk and their statistics

In this paper we consider discrete time forward interest rate models. In our approach, unlike in the classical Heath–Jarrow–Morton framework, the forward rate curves are driven by a random field. Hence we get a general interest rate structure. Our aim is to give an overview of our results in such a model on the following questions: no-arbitrage conditions, maximum likelihood estimation of the volatility, as well as the joint estimation of the parameters and the asymptotic behaviour of the estimators, relationship with continuous models. Finally we give discussion on the practical problems of the estimation and we show several numerical results on the statistics of such models. This research has been supported by the Hungarian Scientific Research Fund under Grants No. OTKA–F046061/2004 and OTKA–T048544/2005.     

A diamond anvil cell for the study of fluid mixtures at high temperatures

Abstract

A new diamond anvil cell has been developed to study the phase behavior of fluid mixtures at high temperature. Special care has been taken to achieve good temperature stability and small temperature gradients. Preliminar experiments show that the cell performs well.     

The potential energy surface for the [C2H2O]+˙ system: The ketene radical cation [CH2CO]+˙ and its isomers

Ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence electron correlation have been employed to examine the [C₂H₂O]^+˙ potential energy surface. Four [C₂H₂O]^+˙ isomers have been identified as potentially stable, observable ions. These are the experimentally well-known ketene radical cation, [CH₂?C?O]^+˙ (a), and the presently unknown ethynol radical cation, [CH₂?C? OH]^+˙ (b), the oxirene radical cation (c) and an ion resembling a complex of CO with [CH₂]^+˙, (d). The calculated energies of b, c and d relative to a are 189, 257 and 259 kJ mol^?1, respectively. Dissociation of ions a and d is found to occur without reverse activation energy.     

Unanimous Model for Describing the Fast Bioluminescence Kinetics of Ca2+‐regulated Photoproteins of Different Organisms

Upon binding their metal ion cofactors, Ca²⁺‐regulated photoproteins display a rapid increase of light signal, which reaches its peak within milliseconds. In the present study, we investigate bioluminescence kinetics of the entire photoprotein family. All five recombinant hydromedusan Ca²⁺‐regulated photoproteins—aequorin from Aequorea victoria, clytin from Clytia gregaria, mitrocomin from Mitrocoma cellularia and obelins from Obelia longissima and Obelia geniculata—demonstrate the same bioluminescent kinetics pattern. Based on these findings, for the first time we propose a unanimous kinetic model describing the bioluminescence mechanism of Ca²⁺‐regulated photoproteins.     

Flash vacuum thermolysis of spirocyclohexadienones

In an attempt to prepare short-bridged hydroxymetacyclophanes $\text{1b-d}$, the spirocyclohexadienones $\text{2b-d}$ were pyrolyzed by flash vacuum thermolysis (FVT). Instead of $\text{1b-d}$, variable amounts of 4-(5-hexenyl)phenol ($\text{4b}$), β-hydroxybenzocycloalkenes ($\text{5b-d}$) and 4-(trans-1-alkenyl) phenols ($\text{6c-d}$) were obtained. The formation of these products is explained by invoking cleavage of a spiro bond in $\text{2}$ under formation of the intermediate diradical $\text{3}$ which, depending on the length of the aliphatic chain and on the temperature, has several pathways open for isomerization to spin-paired products.