Inversion of acoustic diffraction fields in anisotropic solids

We show that the fast Fourier transform (FFT) technique provides a computationally efficient method of calculating 2D amplitude and phase images of complex wave fields generated and measured in elastically anisotropic solids by phase sensitive acoustic microscopy. Further, we discuss how this technique can be used to treat inverse problems such as source reconstruction, image quality assessment, and the determination of elastic constants.     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.     

Isolation of NO(3)(-)-N as 1-phenylazo-2-naphthol (Sudan-1) for measurement of delta(15)N

The conversion of nitrate (NO(3)(-)) to 1-phenylazo-2-naphthol (Sudan-1) has been examined as a method for natural abundance measurement of delta(15)N of NO(3)(-). The reaction results in dilution of NO(3)(-)-N with only one reagent-derived N and the product is readily concentrated from dilute samples by reverse phase chromatography. There is systematic isotopic fractionation during the reaction, but this can be allowed for by analysing known NO(3)(-) standards along with each sample set. Sudan-1 prepared from surface water samples containing approximately 50 &mgr;g NO(3)(-)-N can be analysed by automated continuous flow isotope ratio mass spectrometry with a precision of 0.2 per thousand (one standard deviation) and the accuracy is not affected by interference from other nitrogenous species in the sample or reagents. Copyright 1999 John Wiley & Sons, Ltd.     

Island formation and manipulation of prochiral azobenzene derivatives on Au(111)

Based on previous work with very similar azobenzene derivatives, this study of para-TBA (2,2',5,5'-tetra-tert-butylazobenzene) molecules aims to identify single intact molecules and investigate their adsorption behavior on a Au(111) surface. The molecules are found to be mobile on the surface at the deposition temperature, leading to highly ordered and enantiomerically pure molecular islands. Voltage pulses between the surface and the tip of a scanning tunneling microscope are used to change the chirality of the adsorbate molecules. On the Cu(111) surface instead, single molecules are found on the terraces, which points to a stronger molecule-substrate interaction.     

Racemic and chiral expanded salen-type complexes derived from biphenol and binaphthol: Salbip and salbin

The reaction of 2-fluoronitrobenzene with 2,2′-biphenol or (R)-binaphthol, followed by reduction and subsequent reaction of the resulting diamine with two equivalents of a salicylaldehyde, affords expanded salen-type ligands having backbones based on biphenol or binaphthol: salbipH₂, (R)-salbinH₂ and (R)-salbin(t-Bu)₄H₂. Deprotonation of these ligands with sodium methoxide or potassium hydride, followed by metallation with M(OAc)₂ (M = Mn, Co, Ni, or Cu), affords the corresponding metal complexes in good yield (61-85%). The species containing Mn, Co, and Ni all have distorted octahedral geometry, as determined by X-ray crystallography. The ethereal oxygen atoms occupy two coordination sites with metal-oxygen distances ranging from 2.19 to 2.36 Å. The imine nitrogen atoms are trans to each other in the solid state, an impossible geometry in traditional salen-type complexes. The species containing Cu are distorted square planar and show much longer metal-ethereal oxygen distances ranging from 2.79 to 3.22 Å. The manganese complexes are competent catalysts for the epoxidation of olefins.     

Contacting a single molecular wire by STM manipulation

The Lander molecule (C₉₀H₉₈) consists of a long polyaromatic molecular wire and four lateral di-tert-butyl-phenyl spacer groups, designed to maintain the molecular wire parallel above the substrate. It represents a model system for investigating the electronic contacts of a molecular wire to a nanoscale metallic electrode. In this article, some recent manipulation experiments of single Lander molecules by low temperature scanning tunneling microscopy (LT-STM) are presented. The selective adsorption of the molecule, the molecule-induced reconstruction of copper substrates, and their application to the investigation of contacts between molecules and nanostructures or between molecules are discussed. Manipulation experiments are reported, where the molecular wire part of a Lander molecule is contacted to a monoatomic step and to a two-atom-wide metallic nanostructure. The contact is characterized by the apparent height of the contact point in STM images and, in case of the Cu(111) substrate, by the perturbation observed in the electronic standing wave patterns. PACS 68.37.Ef; 72.80.Le; 68.65.La; 85.65.+h     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

An ion-exchange procedure for quantifying biologically active copper in sea water

An ion-exchange column method is described for determining the dissolved inorganic copper concentration and copper(II) ion activity in sea water. The method is based on the assumption that the amount of copper sorbed by a sulfonic-acid cation exchanger is related to the activities of the cationic forms of copper in solution. This assumption was tested in artificial sea water containing copper and the organic ligands EDTA, NTA, histidine and glutamic acid. A correlation was also observed between the inorganic copper fraction determined by the ion-exchange procedure and the toxic fraction of copper quantified by a diatom bioassay (Thalassiosira pseudonana). These results demonstrate the potential of such a technique for determining the concentration of biologically active trace metals in marine and estuarine environments.