Energy spectra for decaying 2D turbulence in a bounded domain

We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T(K) and the specific heat in the low temperature phase.     

Enantioselective conjugate addition nitro-Mannich reactions: solvent controlled synthesis of acyclic anti- and syn-β-nitroamines with three contiguous stereocenters

We report an enantioselective conjugate addition nitro-Mannich reaction protocol which combines dialkylzinc, aromatic nitro alkene and imine to form two C-C bonds and three contiguous stereocenters in one reaction vessel. Absolute stereochemistry was controlled from the initial 1,4-addition of dialkylzinc to aromatic nitroalkenes by known copper-chiral ligand catalysts. The choice of solvent dictated the formation of either the syn,anti or syn,syn diastereoisomers, two of the four possible diastereoisomers. The syn,syn isomer is a rare example of a syn-selective nitro-Mannich reaction. The diastereoselectivity is dependent upon the presence or not of Zn(O(2)CCF(3))(2) in the reaction mixture and empirical transition state models are proposed to account for the observed stereochemical course of the two reaction conditions. The extent of enantioselectivity and structural diversity of the process is limited by current methodology for the catalytic asymmetric addition of dialkylzincs to nitrostyrenes. The synthetically versatile products are the most complex β-nitro amines prepared using the nitro-Mannich reaction and are formed in high yield and enantioselectivity.     

Stereoselective synthesis of densely functionalized pyrrolidin-2-ones by a conjugate addition/nitro-Mannich/lactamization reaction

Copper-catalyzed conjugate addition of diorgano zinc reagents to nitroacrylate 1 followed by a subsequent nitro-Mannich reaction and in situ lactamization leads to an efficient one-pot synthesis of 1,3,5-trisubstituted 4-nitropyrrolidin-2-ones (5). The versatility of the reaction is shown for a wide range of N-p-(methoxy)phenyl protected aldimines 3 derived from alkyl, aryl, and heteroaryl aldehydes. The densely functionalized pyrrolidin-2-ones 5 are isolated as single diastereoisomers (40 examples, 33-84% yield). An enantioselective copper-catalyzed conjugate addition of diethylzinc led to highly crystalline products that could be recrystallized to enantiopurity in high yield. A range of successful chemoselective transformations were investigated, which widens the applicability of the pyrrolidn-2-ones as stereochemically pure building blocks for further organic synthesis.     

Diastereoselective reductive nitro-Mannich reactions

A range of nitroalkenes 1 and imines 3 derived from alkyl, aryl, and heteroaryl aldehydes underwent a tandem 1,4-hydride addition nitro-Mannich reaction to afford anti-rich β-nitroamines 4. The crude anti-β-nitroamines 4 could be converted to the corresponding anti-β-nitroacetamides 5 (33 examples) to allow purification in good yield from the parent nitroalkenes (60-87%), and with a high diastereomeric ratio (90:10 to mostly >95:5). A representative selection of anti-β-nitroacetamides 5 (five examples) were reduced to vicinal diamines 7 with zinc hydrochloride; concomitant acyl migration provided differentially protected vicinal diamines 7 in good yield (80-91%).     

Electrochemical processes in electrospray ionization mass spectrometry

Editorial Comment Last month we presented, as a Special Feature, a set of five articles that constituted a Commentary on the fundamentals and mechanism of electrospray ionization (ESI). These articles produced some lively discussion among the authors on the role of electrochemistry in ESI. Six authors participated in a detailed exchange of views on this topic, the final results of which constitute this month's Special Feature. We particularly hope that younger scientists will find value in this month's Special Feature, not only for the science that it teaches but also what it reveals about the processes by which scientific conclusions are drawn. To a degree, the contributions part the curtains on these processes and show science in action. We sincerely thank the contributors to this discussion. The give and take of intellectual debate is not always easy, and to a remarkable extent this set of authors has maintained good humor and friendships, even when disagreeing strongly on substance. Graham Cooks and Richard Caprioli Copyright 2000 John Wiley & Sons, Ltd.     

Derivatization for electrospray ionization-mass spectrometry. 4. Alkenes and alkynes

A survey of derivatization strategies and prospective derivatization reactions for conversion of simple alkenes and alkynes to 'electrospray-active' species is presented. General synthetic strategies are discussed and illustrative examples of prospective derivatives prepared from model compounds are presented along with their electrospray ionization (ES) mass spectra. The identified derivatives of these neutral, nonpolar analytes are either ionic or are ionizable in solution through Bronsted acid/base chemistry, by Lewis acid/base chemistry, or by chemical or electrochemical electron-transfer chemistry. Once ionized, the derivatives are expected to be amenable to detection by electrospray ionization-mass spectrometry. Derivatives are identified for positive and negative ion analysis of both alkenes and alkynes. Copyright 2000 John Wiley & Sons, Ltd.     

The neglected pillar of material computation

Many novel forms of computational material have been suggested, from using slime moulds to solve graph searching problems, to using packaging foam to solve differential equations. I argue that attempting to force such novel approaches into the conventional Universal Turing computational framework will provide neither insights into theoretical questions of computation, nor more powerful computational machines. Instead, we should be investigating matter from the perspective of its natural computational capabilities. I also argue that we should investigate nonbiological substrates, since these are less complex in that they have not been tuned by evolution to have their particular properties. Only then we will understand both aspects of computation (logical and physical) required to understand the computation occurring in biological systems.