Multiphoton ionization detected by fourier-transform mass spectrometry

Ions produced by multiphoton ionization (MPI) of naphthalene, fluoranthene and triphenylene have been detected by Fourier-transform mass spectrometry (FT MS). Paret ions are produced very efficiently at 250 and 222 nm with pulse energies as low as 1 mJ. With FT MS a complete, high-resolution mass spectrum is obtained for each laser pulse.     

Rational design of an inhibitor of dethiobiotin synthetase; interaction of 6-hydroxypyrimindin-4(3H)-one with the adenine base binding site

Modelling of the H-bonding interactions involved in the binding of the adenine base component of ATP to E. coli dethiobiotin synthetase (DTBS) suggested that 6-hydroxypyrimidin-4(3H)-one (6-HP4) should selectively bind to this site in the enzyme. Kinetic studies show that 6-HP4 is a competitive inhibitor of DTBS and x-ray crystallography shows that 6-HP4 binds specifically in the purine base binding site of the enzyme.     

Electronic spectra of gas phase ions. An equilibrium perturbation approach

A method is proposed by which the electronic absorption of an ion may be obtained by perturbation of a chemical equilibrium established in an ion cyclotron resonance spectrometer.     

A general approach to triphenylenes and azatriphenylenes: total synthesis of dehydrotylophorine and tylophorine

A convergent and flexible synthesis of substituted triphenylenes, azatriphenylenes, and the cytotoxic alkaloids dehydrotylophorine and tylophorine has been developed.     

Applications of He neutron spin filters at the NCNR

At the NIST Center for Neutron Research (NCNR), we have applied ³He neutron spin filters (NSFs) to the instruments where ³He NSFs are advantageous, such as thermal triple-axis spectrometry, small-angle neutron scattering, and diffuse reflectometry. We present the status of our development and application of this method, including polarized gas production by spin-exchange optical pumping, magnetostatic cavities for storage of the polarized gas on the beam line, and nuclear magnetic resonance (NMR)-based, on-line monitoring and reversal of the ³He polarization. We present the status of developing user-friendly interfaces incorporated into the instrument software to handle these ³He neutron spin filters while taking data and performing data analysis. Finally we discuss the status of development of a polarization capability on the multi-axis crystal spectrometer, which requires polarization analysis over a 220° angular range.     

Modular chiral polyether podands and their lanthanide complexes

A novel series of modular chiral polyether podands derived from enantiomerically pure hydrobenzoin and binaphthol has been prepared using a NaH/15-crown-5 mediated Williamson ether synthesis. These new homochiral ligands form catalytically active complexes with lanthanide triflates, two of which have been characterised by X-ray diffraction.     

Diffraction by a rigid barrier with a soft or perfectly absorbent end face

The reduction of noise levels in the shadow region of a rigid barrier of finite thickness is considered when the end face of the barrier is lined with either a soft or a perfectly absorbent material. Solutions, obtained by the method of matched asymptotic expansions, are given for both a semi-infinite barrier and for a finite length barrier placed on a rigid plane. Comparisons are made with existing solutions for barriers that have a rigid end face.