Experimental Setup for Observation the Bose–Einstein Condensation of Magnons in Solid Antiferromagnets CsMnF3 and MnCO3

The Bose–Einstein condensation of magnons was observed in 1984 in superfluid ³He–B. The same phenomena should exist in solid magnetic systems. We describe here a partly digital experimental setup for studying solid antiferromagnets CsMnF₃ and MnCO₃ by pulse and continuous wave nuclear magnetic resonance. With this equipment, the Bose–Einstein condensation of magnons was observed for the first time in these single crystals.     

Spatial structure of peptides determined by residual dipolar couplings analysis

The gated decoupled (13)C NMR spectra of a dipeptide (Glu-Trp) and a tetrapeptide (NAc-Ser-Phe-Val-Gly-OMe) were recorded in D(2)O and in a lyotropic alignment medium (pentaethylene glycol monododecyl ether/n-hexanol). The residual dipolar couplings were extracted as the differences between the observed couplings for the magnetic nuclei dissolved in the latter and former media. Using a computational optimization, the spatial structures of the compounds were calculated starting from their respective low energy conformations obtained on a semiempirical basis. The uniformity of each conformation was confirmed by the solid-state (13)C NMR spectra of powder samples. Differences between the starting structures and final ones, optimized when employing residual dipolar couplings, are discussed.     

Indirect detection of spectroscopically unobservable components of chemical exchange by NOESY 2D NMR

A new method for detection of intermediates in chemical exchange is suggested. It is found that the effective exchange rate constant determined from NOESY 2D NMR spectrum depends on the mixing time in the NOESY pulse sequence. The true exchange rates and relative population of the intermediates can be appreciated from this dependence. As follows from estimations, this method is applicable to detect intermediates with relative population up to 0.1% and is also useful to detect the components of exchange hidden in overlapping spectra.     

Acidic isomerization of alantolactone derivatives

A series of derivatives of the natural sesquiterpene lactones alantolactone (1) and isoalantolactone (2) was prepared. The α-methylene-γ-lactone moiety was retained in the structures of these for further modifications using reactions that affected exclusively the nonconjugated double bonds of the decalin ring. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 325–330, July–August, 2006.     

Dynamics of development of particle size distribution during styrene suspension polymerization

A variation of number particle size distribution during the suspension polymerization of styrene stabilized by poly(vinyl alcohol) has been studied. It has been disclosed that the dispersion of polymer-monomer particles plays a substantial role at the initial stage of the reaction up to a monomer conversion of ～60%. This phenomenon explains the occurrence of three peaks in the current and final distribution curves. This result provides an explanation for the previously observed polymodal particle size distribution. The typical S-shaped variation in the maximum particle diameter with time suggests a nonequilibrium dynamic character of the development of particle size distribution.     

Study of the multipositional conformational exchange in 2,2-dimethyl-1,3-dithiepin and its 5,6-benz analog by two-dimensional NMR spectroscopy

Conclusions Two-dimensional NMR spectroscopy was used to establish that the chair chair-inversion process in 2,2-dimethyl-1,3-dithiepin and its 5,6-benz derivative is a function of transitions between intermediate boat and twist structures, while the role of direct chair chair transitions is small.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1696–1699, July, 1989.