Unexpected reactivity of trifluoromethylated olefins with indole: a mechanistic investigation

Several trifluoromethylated compounds were reacted with indole sodium salt, leading to monofluorinated compounds. The unexpected products formation was rationalized by DFT calculations.     

Hydrogen‐bonding controls the solid‐state and enantiomeric comformations of the amino alcohol ligand 2‐[(2‐hydroxyethyl)amino]cyclohexanol

The crystal structure of the title compound, C₈H₁₇NO₂, consists of (R,R) and (S,S) enantiomeric pairs packed in adjacent double layers which are characterized by centrosymmetric hydrogen‐bonded dimers, generated via N—H...O and O—H...O interactions, respectively. Intermolecular interactions, related to acceptor and donor molecule chirality, link the achiral double layers into tubular columns, which consist of a staggered hydrophilic inner core surrounded by a hydrophobic cycloalkyl outer surface and extend in the [011] direction.     

Chirped fibre Bragg grating based multiplexer and demultiplexer for DWDM applications

A multiplexer/demultiplexer for 100 GHz channel spacing based on chirped fibre Bragg gratings with different bandwidths and optical circulators is presented. The spectral characteristics, specifications and operation of these passive devices are described, showing its potential use in dense wavelength division multiplexing (DWDM) applications.     

Structure Determination of Hydroxytrypargine: A New Tetrahydro‐β‐Carboline Toxin from the Venom of the Spider Parawixia bistriata

A new, highly active tetrahydro‐β‐carboline toxin from the spider Parawixia bistriata, the most‐common species of social spider occurring in Brazil, was isolated. The new toxin was identified as 1,2,3,4‐tetrahydro‐6‐hydroxy‐β‐carboline (=N‐[3‐(2,3,4,9‐tetrahydro‐6‐hydroxy‐1H‐pyrido[3,4‐b]indol‐1‐yl)propyl]guanidine; 3 ). This type of alkaloid, not common among spider toxins, was found to be the most‐potent constituent of the spider's chemical weaponry to kill prey. When P. bistriata catch arthropods in their web, they apparently attack their prey in groups of many individuals injecting their venoms. In vivo toxicity assays with 3 demonstrated a potent lethal effect to honeybees, giving rise to clear neurotoxic effects (paralysis) before death. The compound's toxicity (LD₅₀ value) was determined to be ca. 8 ng/g of honeybee. The investigation of the pharmacological properties and neurotoxic actions of 3 may be used in the future for the development of new drugs to be applied for pest control in agriculture.     

类氖钛X射线激光实验研究

在“星光”装置上采用预脉冲技术和透-反射线聚焦系统成功地进行了类氛钛x射线激光实验.测量了TiXⅢ,3s-3p,J=0～1激光线的增益系数.首次实验研究了预脉冲能量不同时,激光线强度随泵浦激光能量的变化及其发散角和偏转角.     

On the singularity of Green's tensor for a perfectly conducting semi-infinite cone

This paper is intended to clarify a misunderstanding concerningthe source singularity of the electric Green's tensor for aperfectly conducting semi-infinite cone of circular cross-section.Tai's series expansion of the Green's tensor is known to lacka singular term at the source region. Jones has reconstructedthe solution to this problem and has pointed out the differencebetween his result and that of Tai. The aim of our paper isto demonstrate that, although Jones's closed-form solution iscorrect, there is a mistake in his comparison with Tai's seriessolution. We conclude that one of the two additional singularterms that Jones claims as missing from Tai's formula must beomitted. Besides, we compare Jones's closed-form solution withSmyshlyaev's solution to the very same problem. We concludethat the magnetic field expressions given by Jones and Smyshlyaevcoincide, but a singular term is missing from Smyshlyaev's expressionfor the electric field.     

On the limiting profile arising from orthonormalizing shifts of exponentially decaying functions

It is shown that, under certain conditions, orthonormalizingthe positive integer shifts of an exponentially decaying functionon the half line by the Gram-Schmidt process leads to a limitingprofile given by orthonormalizing all their integer shifts onthe whole line. These results derive from properties of Choleskyfactorization of bi-infinite and semi-infinite matrices. Anexample is provided by the negative exponential function andconjectures are given, supported by numerical evidence, forthe Gaussian and Lorentz function.     

Enantioselective heterogeneous catalytic production of alpha-amino acids

Summary In the present paper the heterogeneous catalytic preparation of alpha-amino acids by hydrogenation of the dehydroamino acids catalyzed by palladium is described. Enantiomeric excess of up to 26% was achieved when the hydrogenation was carried out in ethanol at 0.5 MPa, 298 K with substrate concentration kept at 80 mmol L^-1, 50 mol% cinchonidine as modified and triethylamine as addictive.</o:p>     

Modulated Taylor-Couette Flow: Onset of Spiral Modes

The linear stability of the flow between concentric cylinders, with the inner cylinder rotating at a constant angular velocity and the outer cylinder with an angular velocity varying harmonically about a zero mean, is addressed. The bifurcations of the base state are analyzed using Floquet theory, paying particular attention to non-axisymmetric bifurcations which are dominant in significant regions of parameter space. In these regions the spiral modes of the unforced system become parametrically excited and dominant. This is typical behavior of parametrically forced extended systems, where some modes are stabilized, but others are simultaneously excited. The flow structure of the bifurcated states are examined in detail, paying particular attention to the dynamic implications of their symmetries, and in particular how and when subsequent period doublings are inhibited. Received 5 November 2001 and accepted 29 March 2002 Published online: 2 October 2002 RID="*" ID="*" This work was supported by NSF Grants INT-9732637 and CTS-9908599 (U.S.A.) and MCYT Grants PB97-0685 and BFM2001-2350 (Spain). Communicated by H.J.S. Fernando