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Spontaneous Reactions (spontaneous + reaction)
Selected AbstractsKinetics and thermodynamics of nick sealing by T4 DNA ligaseFEBS JOURNAL, Issue 21 2003Alexey V. Cherepanov T4 DNA ligase is an Mg2+ -dependent and ATP-dependent enzyme that seals DNA nicks in three steps: it covalently binds AMP, transadenylates the nick phosphate, and catalyses formation of the phosphodiester bond releasing AMP. In this kinetic study, we further detail the reaction mechanism, showing that the overall ligation reaction is a superimposition of two parallel processes: a ,processive' ligation, in which the enzyme transadenylates and seals the nick without dissociating from dsDNA, and a ,nonprocessive' ligation, in which the enzyme takes part in the abortive adenylation cycle (covalent binding of AMP, transadenylation of the nick, and dissociation). At low concentrations of ATP (< 10 µm) and when the DNA nick is sealed with mismatching base pairs (e.g. five adjacent), this superimposition resolves into two kinetic phases, a burst ligation (, 0.2 min,1) and a subsequent slow ligation (, 2 × 10,3 min,1). The relative rate and extent of each phase depend on the concentrations of ATP and Mg2+. The activation energies of self-adenylation (16.2 kcal·mol,1), transadenylation of the nick (0.9 kcal·mol,1), and nick-sealing (16.3,18.8 kcal·mol,1) were determined for several DNA substrates. The low activation energy of transadenylation implies that the transfer of AMP to the terminal DNA phosphate is a spontaneous reaction, and that the T4 DNA ligase,AMP complex is a high-energy intermediate. To summarize current findings in the DNA ligation field, we delineate a kinetic mechanism of T4 DNA ligase catalysis. [source] Guidance on Safety/Health for Process Intensification including MS Design; Part I: Reaction HazardsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2009O. Klais Abstract The implementation of process intensification by multiscale equipment will have a profound impact on the way chemicals are produced. The shift to higher space-time yields, higher temperatures, and a confined reaction volume comprises new risks, such as runaway reactions, decomposition, and incomplete conversion of reactants. Simplified spreadsheet calculations enable an estimation of the expected temperature profiles, conversion rates, and consequences of potential malfunction based on the reaction kinetics. The analysis illustrates that the range of optimal reaction conditions is almost congruent with the danger of an uncontrolled reaction. The risk of a spontaneous reaction with hot spots can be presumed if strong exothermic reactions are carried out in micro-designed reactors. At worst, decomposition follows the runaway reaction with the release of noncondensable gases. Calculations prove that a microreactor is not at risk in terms of overpressure as long as at least one end of the reactor is not blocked. [source] The Identity of European Law: Mapping Out the European Legal SpaceEUROPEAN LAW JOURNAL, Issue 2 2000Christopher Harding The main purpose of this discussion is to supply some content to the concept of the ,European legal space' at the turn of the twentieth century. The term ,legal space' is used in preference to ,legal system' or ,systems' in order to convey a sense of the complex, non-hierarchical, overlapping, interlocking and evolutionary character of contemporary European legal phenomena. A number of evident legal orders may be identified within the overall European space: those of the EC, the EU, the EEA, the Council of Europe and the OSCE, although to refer to some of these as ,orders' may be misleading, by implying too much in terms of a centrally determined structure. It is also possible to point to less evident legal ordering, such as the process of norm exportation contained in the Europe Agreements concluded between the EU and individual non-Member States, or the kind of order resulting from transatlantic co-operation in fields such as criminal justice (which also challenges the description of ,European'). In juristic terms, the argument here confronts the primacy traditionally accorded to the sovereign state in the field of law-making, and draws upon two non-juridical models of analysis: that of multi-level governance, as used by political scientists to indicate a shift away from the exclusive authority and legitimacy claimed by sovereign states; and the biological model of catalytic closure, used to indicate evolution through a process of spontaneous reactions within a body. Both models may be usefully employed to probe the dynamics of European legal ordering at the close of the Twentieth Century. [source] Organic and polymer chemistry of electrophilic tri- and tetrasubstituted ethylenesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2004H. K. Hall Jr. Abstract A survey of the spontaneous reactions of electrophilic olefins and nucleophilic olefins is presented as an area in which organic chemistry merges with polymer chemistry. The products include both small molecules and polymers, arising via tetramethylene biradical zwitterions that can cyclize or initiate polymerizations. Electrophilic tri- and tetrasubstituted olefins are particularly useful in delineating the transition from radical chemistry to ionic chemistry. A periodic table embodying these results enables predictions. Charge-transfer complexes, although observed in many of these reactions, play no significant role. Various aspects arising from these investigations include new cationic initiators, Lewis acid catalysis, quinodimethane chemistry, and photochemistry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2845,2858, 2004 [source] On the electrodetection threshold of aquatic vertebrates with ampullary or mucous gland electroreceptor organsBIOLOGICAL REVIEWS, Issue 3 2007Rob C. Peters Abstract Reinterpretation of research on the electric sense in aquatic organisms with ampullary organs results in the following conclusions. The detection limit of limnic vertebrates with ampullary organs is 1 ,Vcm,1, and of marine fish is 20 nVcm,1. Angular movements are essential for stimulation of the ampullary system in uniform d.c. fields. Angular movements in the geomagnetic field also generate induction voltages, which exceed the 20 nVcm,1 limit in marine fish. As a result, marine electrosensitive fish are sensitive to motion in the geomagnetic field, whereas limnic fish are not. Angular swimming movements generate a.c. stimuli, which act like the noise in a stochastic resonance system, and result in a detection threshold in marine organisms as low as 1 nVcm,1. Fish in the benthic space are exposed to stronger electric stimuli than fish in the pelagic space. Benthic fish scan the orientation plane for the maximum potential difference with their raster of electroreceptor organs, in order to locate bioelectric prey. This behaviour explains why the detection threshold does not depend on fish size. Pelagic marine fish are mainly exposed to electric fields caused by movements in the geomagnetic field. The straight orientation courses found in certain shark species might indicate that the electric sense functions as a simple bisensor system. Symmetrical stimulation of the sensory raster would provide an easy way to keep a straight course with respect to a far-field stimulus. The same neural mechanism would be effective in the location of a bioelectric prey generating a near-field stimulus. The response criteria in conditioning experiments and in experiments with spontaneous reactions are discussed. [source] | ||||||||||