Acylation of Amines with 5-Phenyltetrazol-2-ylacetyl Chloride

The acylation of primary and secondary amines by 5-phenyltetrazol-2-ylacetyl chloride leads to the corresponding tetrazolylacetamides irrespective of the nature of the substituent in the structure of the amine.     

Structural Transformations in Polydisperse Ferrofluids

Real polydisperse ferrofluid is modeled by a bidispersed magnetic colloid composed of large and small particles. It is assumed that the energy of magnetodipole interaction for small particles is much lower and that of large particles is substantially higher than their thermal energy. Therefore, large particles can combine into the chain and droplet aggregates that are present in a sea of small particles. The influence of small particles on the structurization in the ensemble of large particles is studied. It is shown that small particles can either prevent or stimulate these structural transformations depending on the parameters of a medium.     

Electron capture dissociation of polypeptides using a 3 Tesla Fourier transform ion cyclotron resonance mass spectrometer

Electron capture dissociation (ECD) of polypeptides has been demonstrated using a commercially available 3 Tesla Fourier transform ion cyclotron resonance (FTICR) instrument. A conventional rhenium filament, designed for high-energy electron impact ionisation, was used to effect ECD of substance P, bee venom melittin and bovine insulin, oxidised B chain. A retarding field analysis of the effective electron kinetic energy distribution entering the ICR cell suggests that one of the most important parameters governing ECD for this particular instrument is the need to employ low trapping plate voltages. This is shown to maximise the abundance of low-energy electrons. The demonstration of ECD at this relatively low magnetic field strength could offer the prospect of more routine ECD analysis for the wider research community, given the reduced cost of such magnets and (at least theoretically) the greater ease of electron/ion cloud overlap at lower field.     

Dissociative recombination cross section and branching ratios of protonated dimethyl disulfide and N-methylacetamide

Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD.     

The Schwinger variational principle for the rearrangement collisions

The Lippmann-Schwinger equations were rewritten in the form of Faddeev equations. The number of equations is determined by the number of open channels. On the basis of the Schwinger variational principle the approximate one-dimensional equations for the rearrangement collisions are obtained.Submitted to the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.In conclusion the authors wish to thank V. B. Belyaev for useful discussions and interest in this work.     

N-Terminal Peptide Sequence Repetition Influences the Kinetics of Backbone Fragmentation: A Manifestation of the Jahn-Teller Effect?

Analysis of large (>10,000 entries) databases consisting of high-resolution tandem mass spectra of peptide dications revealed with high statistical significance (P?<?1?10^–3) that peptides with non-identical first two N-terminal amino acids undergo cleavages of the second peptide bond at higher rates than repetitive sequences composed of the same amino acids (i.e., in general AB- and BA- bonds cleave more often than AA- and BB- bonds). This effect seems to depend upon the collisional energy, being stronger at lower energies. The phenomenon is likely to indicate the presence of the diketopiperazine structure for at least some b₂ ⁺ ions. When consisting of two identical amino acids, these species should form through intermediates that have a symmetric geometry and, thus, must be subject to the Jahn-Teller effect that reduces the stability of such systems.

Diffusion and magnetotransport in ferrofluids containing chain-shaped aggregates

The effect of chain structures on particle diffusion in nanodisperse ferrofluids subjected to external magnetic fields is studied. It is shown that the chain formation imparts very strong anisotropy to the diffusion properties of ferrofluids: the diffusion coefficient along a field appears to be approximately two orders of magnitude higher than that in the transverse direction. The presence of the chains changes the particle magnetophoresis coefficient significantly.     

Equilibrium configurations of a jet of an ideally conducting liquid in an external nonuniform magnetic field

Possible equilibrium configurations of the free surface of a jet of an ideally conducting liquid placed in a nonuniform magnetic field are considered. The magnetic field is generated by two thin wires that are parallel to the jet and bear oppositely directed currents. Equilibrium is due to a balance between capillary and magnetic forces. For the plane symmetric case, when the jet deforms only in the plane of its cross section, two one-parameter families of exact solutions to the problem are derived using the method of conformal mapping. According to these solutions, a jet with an initially circular cross section deforms up to splitting into two separate jets. A criterion for jet splitting is derived by analyzing approximate two-parameter solutions.