The infrared spectra of pyridine N-oxide complexes of transition metal perchlorates in relation to their structures

The infrared spectra of the complexes [M(pyO)₆](ClO₄)₂ (pyO = pyridine N-oxide; M = Mn, Fe, Co, Ni, Zn) are discussed. Assignments of v(M-O) and other significant vibrations are based on the band shifts induced by deuteration of the heterocyclic ring and the effects of metal ion substitution. Earlier spectroscopic evidence suggesting distortion from regular octahedral site symmetry is discounted by the far-infrared spectra. In agreement with recent crystallographic evidence for O_h site symmetry in these complexes, one infrared-active v(M-O) band is expected and observed. The effects on the spectra of structural distortion in the 6-coordinate Cu^II complex [Cu(pyO)₆](ClO₄)₂, reduced coordination number in the 4-coordinate complex [Cu(pyO)₄](C1O₄)₂, and increased cationic charge in the Ga^III complex [Ga(pyO)₆](C1O₄)₃are discussed.     

An instrument for measuring branching ratios in photoionizing processes

An instrument using photo-electron spectrometry has been developed to measure branching ratios and relative partial cross-sections for photoionizing processes in gases, with particular emphasis given to measuring variation of these parameters as a continuous function of wavelength. The instrument is described together with a consideration of sources of errors and a method of calibration.     

Fracture and secondary flow of elastic liquids

Summary In the absence of disturbances at the free surfaces, secondary flow due to elastic forces occurs in elastic liquids sheared in cone-and-plate rheometers but not in parallel-plate rheometers. In both types of apparatus an instability is observed. Using a theory based on a fracture mechanism, the critical normal stress differences for the onset of the instability can be correctly predicted for both types of apparatus. It is concluded that the fracture instability is a distinctly different effect from the secondary flow considered.     

Rapid,Traceless, AgI‐Promoted Macrocyclization of Peptides Possessing an N‐Terminal Thioamide

Peptide macrocyclization is often a slow process, plagued by epimerization and cyclodimerization. Herein, we describe a new method for peptide macrocyclization employing the Ag^I‐promoted transformation of peptide thioamides. The Ag^I has a dual function: chemoselectively activating the thioamide and tethering the N‐terminal thioamide to the C‐terminal carboxylate. Extrusion of Ag₂S generates an isoimide intermediate, which undergoes acyl transfer to generate the native cyclic peptide, resulting in a rapid, traceless macrocylization process. Cyclic peptides are furnished in high yields within 1 hour, free of epimerization and cyclodimerization.     

Preparation of diazabicyclo[4.3.0]nonene-based peptidomimetics

Several functionalized diazabicyclo[4.3.0]nonenes and other heterocycles have been prepared as potential peptidomimetic scaffolds. A novel and efficient method has been developed for the preparation of N-substituted gamma-lactams 13. Preparation of amidine-containing 1,5-diazabicyclo[4.3.0]nonenes 43 and 44 has been achieved through Hg-mediated cyclization of the precursor N-aminopropyl-gamma-thiolactams and subsequent functional group manipulation. Bicycle 43 represents a novel scaffold for potential peptide turn mimetics, whereas 44 could potentially be employed as an alpha-helix template attached to the C-terminus of peptides. These compounds are novel additions to the current range of small-molecule constrained peptidomimetics.     

Experience in making rheological measurements at high pressures

Summary We review the difficulties encountered in the design and operation of apparatus for rheological studies on liquids at pressures up to 900 MN m^–2 and temperatures from –30 to 120°C. Such rheological information is required in connection with elastohydrodynamic lubrication in which high pressures and shear rates are encountered.With 3 figures     

Simulating a low-temperature Maxwellian plasma using SH-HtscEBIT

This paper reports an experimental realization of a low-temperature quasi-Maxwell–Boltzmann plasma in an electron beam ion trap (EBIT) by employing a special energy sweep technique. A Maxwellian C IV plasma with electron temperatures in the range 10–40?eV is simulated in the Shanghai high-temperature superconducting EBIT (SH-HtscEBIT), which requires stable performance of the EBIT under the extreme condition of ultralow electron beam energy. The C IV spectra are obtained by an extreme ultraviolet spectrometer in the wavelength region 290–400?Å. The measured spectral line intensity ratios are compared with the results of calculations using a collisional-radiative model. The mean difference between the experimental and theoretical results in the simulated temperature region is about 14%.