Divergent synthetic routes to biologically relevant types of compounds: chiral polyfunctional γ-lactams and amino acids

Divergent and versatile synthetic routes leading to the title compounds are described. They start from a common chiral precursor derived from (−)-(S)-verbenone and afford polyfunctional γ-lactams and γ- and ε-amino acids. The cyclobutane moiety in these molecules acts as a chiral and polyfunctional platform providing stereogenic centres with unambiguous absolute configuration that control the chirality of the newly produced asymmetric carbons. Furthermore, it affords functional groups and carbon chains suitable not only to create the basic skeleton of the desired products but additional functional groups. These features confer on these derivatives a great versatility for further uses in the development of new drugs and as synthetic building blocks.     

Unravelling Enzymatic Features in a Supramolecular Iridium Catalyst by Computational Calculations

Non-biological catalysts following the governing principles of enzymes are attractive systems to disclose unprecedented reactivities. Most of those existing catalysts feature an adaptable molecular recognition site for substrate binding that are prone to undergo conformational selection pathways. Herein, we present a non-biological catalyst that is able to bind substrates via the induced fit model according to in-depth computational calculations. The system, which is constituted by an inflexible substrate-recognition site derived from a zinc-porphyrin in the second coordination sphere, features destabilization of ground states as well as stabilization of transition states for the relevant iridium-catalyzed C−H bond borylation of pyridine. In addition, this catalyst appears to be most suited to tightly bind the transition state rather than the substrate. Besides these features, which are reminiscent of the action modes of enzymes, new elementary catalytic steps (i. e. C−B bond formation and catalyst regeneration) have been disclosed owing to the unique distortions encountered in the different intermediates and transition states.     

Controlling the leader-laggard dynamics in delay-synchronized lasers

We study experimentally the collective dynamics of two delay-coupled semiconductor lasers. The lasers are coupled by mutual injection of their emitted light beams, at a distance for which coupling delay times are non-negligible. This system is known to exhibit lag synchronization, with one laser leading and the other one lagging the dynamics. Our setup is designed such that light travels along different paths in the two coupling directions, which allows independent control of the two coupling strengths. A comparison of unidirectional and bidirectional coupling reveals that the leader-laggard roles can be switched by acting upon the coupling architecture of the system. Additionally, numerical simulations show that a more extensive control of the network architecture can also lead to changes in the dynamics of the system. Finally, we discuss the relevance of these results for bidirectional chaotic communications.     

<Emphasis Type="Italic">N</Emphasis>-Methyl-D-aspartic Acid (NMDA) in the nervous system of the amphioxus <Emphasis Type="Italic">Branchiostoma lanceolatum</Emphasis>

Background  

NMDA (N-methyl-D-aspartic acid) is a widely known agonist for a class of glutamate receptors, the NMDA type. Synthetic NMDA elicits very strong activity for the induction of hypothalamic factors and hypophyseal hormones in mammals. Moreover, endogenous NMDA has been found in rat, where it has a role in the induction of GnRH (Gonadotropin Releasing Hormone) in the hypothalamus, and of LH (Luteinizing Hormone) and PRL (Prolactin) in the pituitary gland.     

The Chemical Bond: When Atom Size Instead of Electronegativity Difference Determines Trend in Bond Strength

We have quantum chemically analyzed element−element bonds of archetypal H_nX−YH_n molecules (X, Y=C, N, O, F, Si, P, S, Cl, Br, I), using density functional theory. One purpose is to obtain a set of consistent homolytic bond dissociation energies (BDE) for establishing accurate trends across the periodic table. The main objective is to elucidate the underlying physical factors behind these chemical bonding trends. On one hand, we confirm that, along a period (e. g., from C−C to C−F), bonds strengthen because the electronegativity difference across the bond increases. But, down a period, our findings constitute a paradigm shift. From C−F to C−I, for example, bonds do become weaker, however, not because of the decreasing electronegativity difference. Instead, we show that the effective atom size (via steric Pauli repulsion) is the causal factor behind bond weakening in this series, and behind the weakening in orbital interactions at the equilibrium distance. We discuss the actual bonding mechanism and the importance of analyzing this mechanism as a function of the bond distance.     

The Evolution of High-Throughput Macromolecular Crystallography at Synchrotrons

On May 11 and 12, 2000, the Stanford Synchrotron Radiation Laboratory, as it was then known, hosted a “Workshop on Techniques for Automated Mounting, Viewing and Centering Pre-Cooled Protein Crystals” [1 http://www-ssrl.slac.stanford.edu/conferences/workshops/px-robotics/. [Google Scholar], 2 E. Abola, Nature Structural Biology 7, 973–977 (2000).[Crossref], [PubMed] , [Google Scholar]]. The 12 presentations during the meeting all focused on the impact that automation could have on the performance of synchrotron beamlines and thus on research in structural biology. Two principal themes ran through the workshop: (1) robotics to mount crystals on a diffractometer; and (2) methods to place a crystal in the X-ray beam. Five conceptual and prototype robotic systems for automated mounting were described—the original ACTOR from Abbott Laboratories, later modified and marketed by Rigaku/MSC, and the systems which in final form become the ALS [3 G. Snell, Structure 12, 537–545 (2004).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], EMBL/ESRF SC3 [4 F. Cipriani, Acta Cryst. D62(10), 1251–1259 (2006). [Google Scholar]], APS/SBC [5 D. Shu, AIP Conference Proceedings 705(1), 1201–1204 (2004).[Crossref] , [Google Scholar]], and SSRL SAM robots [6 A. E. Cohen, J. Appl. Cryst. 5(6), 720–726 (2002).[Crossref], [Web of Science ®] , [Google Scholar]]. By December of that year, the ACTOR had been installed for testing at Sector 32 of the Advanced Photon Source (Figure 1). Within three years, by the end of 2003, several of these robots, plus the commercial MARcsc from MAR Research, had been deployed to handle frozen protein crystals at beamlines for macromolecular crystallography (MX). Currently, at least 13 distinct robot types, not including variants of the ALS automounter, are employed at synchrotron beamlines to transfer crystals from storage to beam position.     

Supramolecular Water Oxidation with Ru–bda‐Based Catalysts

Extremely slow and extremely fast new water oxidation catalysts based on the Ru–bda (bda=2,2′‐bipyridine‐6,6′‐dicarboxylate) systems are reported with turnover frequencies in the range of 1 and 900 cycles s^?1, respectively. Detailed analyses of the main factors involved in the water oxidation reaction have been carried out and are based on a combination of reactivity tests, electrochemical experiments, and DFT calculations. These analyses give a convergent interpretation that generates a solid understanding of the main factors involved in the water oxidation reaction, which in turn allows the design of catalysts with very low energy barriers in all the steps involved in the water oxidation catalytic cycle. We show that for this type of system π‐stacking interactions are the key factors that influence reactivity and by adequately controlling them we can generate exceptionally fast water oxidation catalysts.     

Interfacial Chiral Selection by Bulk Species

A chiral selection process in a self‐assembled soft monolayer of an achiral amphiphile as a consequence of its interaction with chiral species dissolved in the aqueous subphase, is reported. The extent of the chiral selection is statistically measured in terms of the enantiomorphic excess of self‐assembled submillimeter domains endowed with well‐defined orientational chirality that is unambiguously resolved using optical microscopy. Our results show that the emergence of chirality is mediated by electrostatic interactions and significantly enhanced by hydrophobic effects. This chiral chemical effect can be suppressed and even reversed by opposing a macroscopic physical influence, such as vortical stirring. This result gives evidence for the crucial role of hydrodynamic effects in supramolecular aggregation.     

S=1/2 One‐Dimensional Random‐Exchange Ferromagnetic Zigzag Ladder,Which Exhibits Competing Interactions in a Critical Regime

The synthesis, crystal structure, and magnetic properties (from a combined experimental and First‐Principles Bottom‐Up theoretical study) of the new compound catena‐dichloro(2‐Cl‐3Mpy)copper(II), 1 , [2‐Cl‐3Mpy=2‐chloro‐3‐methylpyridine] are described and rationalized. Crystals of 1 present well isolated magnetic 1D chains (no 3D order was experimentally observed down to 1.8 K) and magnetic frustration stemming from competing ferromagnetic nearest‐neighbor (J_NN) interactions and antiferromagnetic next‐nearest neighbor (J_NNN) interactions, in which α=J_NNN/J_NN <?0.25. These magnetic interactions give rise to a unique magnetic topology: a two‐leg zigzag ladder composed of edge‐sharing up‐down triangles with antiferromagnetic interactions along the rails and ferromagnetic interactions along the zigzag chain that connects the rails. Crystals of 1 also present a random distribution of the 2‐Cl‐3Mpy groups, which are arranged in two different orientations, each with a 50 % occupancy. This translates into a random static structural disorder within each chain by virtue of which the value of the J_NN magnetic interactions can randomly take one of the following three values: 53, 36, and 16 cm^?1. The structural disorder does not affect the J_NNN value, which in all cases is approximately ?9 cm^?1. A proper statistical treatment of this disorder provides a computed magnetic susceptibility curve that reproduces the main features of the experimental data.