Kinetic features of the formation of poly(epoxy isocyanurate) networks

A new method is developed for the synthesis of branched and network polymers that give rise to poly(epoxy isocyanurate) matrices during thermal curing. Matrix polymers are prepared on the basis of polyethers (poly(propylene glycol) or poly(tetramethylene glycol)), diisocyanate, and an epoxy oligomer. The chemistry of formation of networks is studied by NMR and IR spectroscopy. Formation of structures with different topologies is analyzed, and optimum conditions for the formation of gradient networks that are complex structural organizations are ascertained. It is shown that, during microphase separation of a three-component system whose components differ appreciably in surface energy and other parameters, the composition of microphases may be estimated. Optimum conditions of the curing process that provide formation of the perfect structure of networks are found, and their chemical structure is investigated.     

Ruthenium bis(phosphinite) pincer complexes

Resorcinol-based ruthenium bis(phosphinite) complexes were synthesized. Complexes RuCl(CO)[2,6-(Bu^t ₂PO)₂C₆H₃] (9) and RuH(CO)[2,6-(Bu^t ₂PO)₂C₆H₃] (10) were obtained by cyclometallation of 1,3-(Bu^t ₂PO)₂C₆H₃ with RuCl₂(DMSO)₄ in 2-methoxyethanol in the presence of Hünig’s base. The interconversion of complexes 9 and 10 was studied. The addition of carbon monoxide to complexes 9 and 10 yielded 18e adducts, RuCl(CO)₂[2,6-(Bu^t ₂PO)₂C₆H₃] (11) and RuH(CO)₂[2,6-(Bu^t ₂PO)₂C₆H₃] (12), respectively. In the case of complex 9, this reaction is reversible. Reaction of complex 10 with trifluoroacetic acid resulted in complex Ru(CF₃COO)(CO)[2,6-(Bu^t ₂PO)₂C₆H₃] (13), which reacted with carbon monoxide to give complex Ru(CF₃COO)(CO)₂[2,6-(Bu^t ₂PO)₂C₆H₃] (14). Based on the IR spectral data, the TFA ligand in complexes 13 and 14 is bound in a bi- and monodentate fashion, respectively. The structure of compound 9 was determined by X-ray diffraction analysis.     

Conformations of 1,3,3,5-tetrabromopentane in the solid state and in solutions

When estimating the¹³C NMR spectrum for 1,3,3,5-tetrabromopentane according to the topological increment scheme for polybromoalkanes, the discrepancy relative to the experimental values of the chemical shifts is significantly greater than the allowable error [1]. Using the methods of PMR,¹³C NMR in the solid phase, IR spectros-copy, and x-ray diffraction, we have shown that this discrepancy is due to realization in solution of predominantly one conformation. 1,3,3,5-Tetrabromopentane in the crystalline state has the planar zigzag conformation tttt, which is also predominant in solution (50–60%), where the conformations tgtt and tggt are also present.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2228–2234, October 1989.     

Synthesis, spectral characteristics, and crystal structure of the hexanuclear complex MeSi[η1,η5-C5H4(CO)2Fe(η1,η5-C5H5)Mn(CO)3]3

The reaction of MeSiCl₃ with 3 equivalents of LiC₅H₄(CO)₂Fe(η¹,η⁵-C₅H₄)Mn(CO)₃ afforded the hexanuclear complex MeSi[η¹,η⁵-C₅H₄(CO)₂Fe(η¹,η⁵-C₅H₅)Mn(CO)₃]3. The structure of the resulting complex was established by¹H and¹³C NMR and IR spectroscopy and by X-ray diffraction analysis. Dedicated to the memory of Academician M. I. Kabachnik on his 90th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2056–2061, October, 1998.     

Vibrational spectra and structure of “staircase” carbonyl π-complexes of transition metals

FTIR spectra have been studied for staircase cyclopentadienyl complexes comprising two or three metal carbonyl fragments bound by the metal-carbon bond Cp(CO)₂Fe-CpmMn(CO)₃ (1), Cp(CO)₂Fe-CpmFe(CO)₂CH₂Ph (2), Cp(CO)₂Fe-Cpm(CO)₂Fe-CpmMn(CO)₃ (3), Cp(CO)₂Mo-Cpm(CO)₂Fe-CpmMn(CO)₃ (4), Cp(CO)₃W- Cpm(CO)₂Fe-CpmMn(CO)₃ (5), Cp(CO)₂Fe-Cpm(CO)₂Fe-BmCr(CO)₃ (6), Cr(CO)₃Bm-CpmFe(CO)₂CH₂Ph (7), where Cp = ⁵-C₅H₅, Cpm = ¹⁵-C₅H₄, Bm = ¹⁶-C₆H₅, as well as mononuclear model complexes Cp(CO)₂Fe(CH)₂Ph (8), CpMn(CO)₃ (9), and (⁶-C⁶H⁶)Cr(CO)³ (10). The spectra were interpreted on the basis of the local symmetry of each metal carbonyl center. The positions of vCOs are determined by the mutual electronic effect of each center. CpmM(CO)_n groups are strong electron acceptors and cause an increase in vCOs of adjacent M(CO)_n groups. Cp(CO)_nM groups, being electron donors, cause a decrease in the frequencies of neighboring groups. In trinuclear complexes, the frequencies of the central Fe(CO)₂ group are not changed much due to the compensation of donor and acceptor influences of two neighboring substituents.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1948–1951, November, 1994.This project was supported by the Russian Foundation for Basic Research (project code No. 93-03-18592).     

Nuclear orbiting and anomalies in nuclear reactions

In this paper, we report our measurements of back-angle oxygen and carbon particle yields from ¹⁶O+⁸⁹Y, ¹²C+⁹³Nb reactions forming the same compound nucleus ¹⁰⁵Ag at the same excitation energy and spin distribution. We find anomalously large oxygen yield and entrance channel dependence at high excitation energies from ¹⁶O+⁸⁹Y reaction implying formation of a dinuclear orbiting complex. Possible connection between nuclear orbiting and fast fission is also discussed.     

Metal-sensitive and thermostable trypsin from the crevalle jack (<Emphasis Type="Italic">Caranx hippos</Emphasis>) pyloric caeca: purification and characterization

Background

Over the past decades, the economic development and world population growth has led to increased for food demand. Increasing the fish production is considered one of the alternatives to meet the increased food demand, but the processing of fish leads to by-products such as skin, bones and viscera, a source of environmental contamination. Fish viscera have been reported as an important source of digestive proteases with interesting characteristics for biotechnological processes. Thus, the aim of this study was to purify and to characterize a trypsin from the processing by-products of crevalle jack (Caranx hippos) fish.

Results

A 27.5 kDa trypsin with N-terminal amino acid sequence IVGGFECTPHVFAYQ was easily purified from the pyloric caeca of the crevalle jack. Its physicochemical and kinetic properties were evaluated using N-α-benzoyl-_DL-arginine-p-nitroanilide (BApNA) as substrate. In addition, the effects of various metal ions and specific protease inhibitors on trypsin activity were determined. Optimum pH and temperature were 8.0 and 50°C, respectively. After incubation at 50°C for 30 min the enzyme lost only 20% of its activity. K _m , k_cat, and k _cat /K _m values using BApNA as substrate were 0.689 mM, 6.9 s^-1, and 10 s^-1 mM^-1, respectively. High inhibition of trypsin activity was observed after incubation with Cd²⁺, Al³⁺, Zn²⁺, Cu²⁺, Pb²⁺, and Hg²⁺ at 1 mM, revealing high sensitivity of the enzyme to metal ions.

Conclusions

Extraction of a thermostable trypsin from by-products of the fishery industry confirms the potential of these materials as an alternative source of these biomolecules. Furthermore, the results suggest that this trypsin-like enzyme presents interesting biotechnological properties for industrial applications.

     

Synthesis and characterization of complexes η5,η5-(CO)3Mn(C5H4-C5H4)(CO)2Fe-η1,η5-C5H4Mn(CO)3 and μ-(C≡C)[C5H4(CO)2Fe-η1,η5-C5H4Mn(CO)3]2

The complex η⁵,η⁵-(CO)₃Mn(C₅H₄-C₅H₄)(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ was synthesized by the reaction of η⁵-Cp(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ with BuⁿLi (THF, ?78 °C) and then with anhydrous CuCl₂. The complex μ-(C≡C)[C₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃]₂ was prepared by the reaction of η⁵-IC₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ with Me₃SnC≡CSnMe₃ (2:1) in the presence of Pd(MeCN)₂Cl₂.