We report on the novel protocol for enzyme immobilization into gel of siloxanes using water-organic mixtures with the high content of organic solvent as a reaction medium. Hydrolysis of alkoxysilanes carried out without excessive dilution with water resulted in more active and stable enzyme containing membranes. Immobilization of an inherently labile lactate oxidase according to the proposed sol-gel protocol over Prussian Blue modified electrode resulted in an advanced lactate biosensor characterized with a sensitivity of 0.18 A M(-1) cm(-2) in the flow injection analysis (FIA) mode over a wide dynamic range. A comparison with the known sensors has shown that analytical performances of the elaborated lactate biosensor are advantageous over both published systems and commercialized devices. The biosensor shows an appropriate stability and is suitable for clinical analysis (including noninvasive diagnostics) and food quality control.

New stereoregular cyclic polysilanols of the general formula [PhSi(O)OH]n (n = 6 and 12) have been selectively obtained in high yields by the reaction of cagelike oligophenylmetallasiloxanes with dilute solutions of hydrochloric acid at low temperatures. An alternative method was used to prepare cis-[PhSi(O)OH](4) from sodium phenylsiloxanolate, cis-[(Na(+))(4)[PhSi(O)O(-)](4)].(1-butanol)(x). All compounds were fully characterized by NMR and IR spectroscopy and molecular weight determinations. The structure of cis-[PhSi(O)OH](6) was confirmed by single-crystal X-ray analysis. Furthermore, a series of stereoregular cyclosiloxanes containing triorganylsiloxy groups at each silicon atom was prepared by the reactions of the cyclic polysilanols with triorganylchlorosilanes Me(3)SiCl, Me(2)ViSiCl, and Me(2)(CH(2)Cl)SiCl.

The magnetic behavior of the clusters [(PhSiO(2))(6)Cu(6)(O(2)SiPh)(6)].6EtOH (1), Na(4)[(PhSiO(2))(12)Cu(4)].8(n)()BuOH (2), and K(4)[(C(2)H(3)SiO(2))(12)Cu(4)].6(n)()BuOH (3) has been investigated by combined magnetic susceptibility measurements and variable-temperature EPR techniques (9.25 and 245 GHz). The six copper(II) ions in the core of 1, which approaches 6/mmm symmetry, are ferromagnetically coupled as a result of the geometry at the bridging siloxanolate oxygen atoms (Cu-O-Cu = 91.5-94.6 degrees; J = -42 cm(-)(1) with H = J S(i)().S(i)()(+1), S(7) = S(1)). The ground S = 3 spin state is split in zero field mainly due to anisotropic exchange contributions (D = 0.30 cm(-)(1)). Notably, both the magnitude and the sign of the zero-field splitting parameter have been determined from HF-EPR spectra. Large antiferromagnetic Cu-Cu interactions (J approximately 200 cm(-)(1)) and an S = 0 ground state have been detected in the tetranuclear clusters 2 and 3 as a consequence of the larger Cu-O-Cu angles. The results presented in the paper are relevant to the search for new molecule-based magnetic materials.

No abstract

Two different synthetic routes for the formation of sodium phenylsiloxanolate (SPS) have been developed: (i) the cleavage of oligo(phenylsilsesquioxane), OPSSO, by NaOH in n-butyl alcohol and (ii) the reaction of phenyltri-n-butoxysilane, PhSi(n-BuO) 3 , and NaOH in n-butyl alcohol in the presence of water. From both reactions, (i) and (ii), crystalline sym-cis-{(Na + ) 4 -[PhSi(O)O -] 4 }‚8n-BuOH (A) was the product isolated and characterized by X-ray diffraction. Reaction of SPS with Me 3 SiCl resulted in the formation of the corresponding sym-cistetraphenyltetrakis(trimethylsiloxy)cyclotetrasiloxane, [PhSi(O)OSiMe 3 ] 4 . Under anhydrous conditions, PhSi(n-BuO) 3 and NaOH reacted to give sodium phenyldi-n-butoxysilanolate, PhSi(ONa)(n-BuO) 2 . Subsequent treatment with Me 3 SiCl led to the formation of phenyl-(trimethylsiloxy)di-n-butoxysilane, PhSi(n-BuO) 2 (OSiMe 3 ).

No abstract

No abstract

No abstract