Unravelling RNA–Substrate Interactions in a Ribozyme‐Catalysed Reaction Using Fluorescent Turn‐On Probes

The Diels–Alder reaction is one of the most important C?C bond‐forming reactions in organic chemistry, and much effort has been devoted to controlling its enantio‐ and diastereoselectivity. The Diels–Alderase ribozyme (DAse) catalyses the reaction between anthracene dienes and maleimide dienophiles with multiple‐turnover, stereoselectivity, and up to 1100‐fold rate acceleration. Here, a new generation of anthracene‐BODIPY‐based fluorescent probes was developed to monitor catalysis by the DAse. The brightness of these probes increases up to 93‐fold upon reaction with N‐pentylmaleimide (NPM), making these useful tools for investigating the stereochemistry of the ribozyme‐catalysed reaction. With these probes, we observed that the DAse catalyses the reaction with >91 % de and >99 % ee. The stereochemistry of the major product was determined unambiguously by rotating‐frame nuclear Overhauser NMR spectroscopy (ROESY‐NMR) and is in agreement with crystallographic structure information. The pronounced fluorescence change of the probes furthermore allowed a complete kinetic analysis, which revealed an ordered bi uni type reaction mechanism, with the dienophile binding first.     

Chiral recognition in solution and the gas phase. Experimental and theoretical studies of aromatic D- and L-amino acid–Cu(II)–chiragen complexes Jennifer L. Seymour František Tureček Andrei V. Malkov Pavel Kočovský Journal of Mass Spectrometry 2004; 39: 1044–1052

The original article to which this Erratum refers was published in Journal of Mass Spectrometry 2004; 39: 1044–1052.     

Simple one-dimensional interaction systems with superexponential relaxation times

Finite one-dimensional random processes with local interaction are presented which keep some information of a topological nature about their initial conditions during time, the logarithm of whose expectation grows asymptotically at least asM ³, whereM is the size of the setR _M of states of one component. ActuallyR _M is a circle of lengthM. At every moment of the discrete time every component turns into some kind of average of its neighbors, after which it makes a random step along this circle. All these steps are mutually independent and identically distributed. In the present version the absolute values of the steps never exceed a constant. The processes are uniform in space, time, and the set of states. This estimation contributes to our awareness of what kind of stable behavior one can expect from one-dimensional random processes with local interaction.Partially supported by NSF grant #DMS-932 1216.     

Quantum decay of supercurrent in thin superconducting wires

Quantum fluctuations cause a decay of the supercurrent in thin superconducting wires making them resistive even at very low temperatures. We derive a microscopic effective action formalism that goes beyond the usual TDGL approach and study quantum fluctuations of the superconducting order parameter at all temperatures belowT _C . We calculate the quantum phase slip rate in thin superconducting wires, demonstrate the importance of dissipation in a quantum phase slip process, and evaluate the resistanceR(T) of the wire. In very thin wires the effect is well observable, even at zero temperature.