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W2NCl7 has been prepared by the reaction of tungsten pentachloride with the bromide of Millon's base, [Hg2N]Br, in boiling CCl4. The product forms a dark brown, moisture sensitive crystal powder (μeff = 0.7 B.M. at 21 °C). With phosphoryl chloride, the complex W2NCl7·2 POCl3 is formed. The reaction with chlorine leads to the mixed-valenced W(V)/W(VI) complex W2NCl8 (μeff = 0.5 B.M. at 22 °C), which reacts with tetraphenylphosphonium chloride in CH2Cl2 to form (PPh4)2[W2NCl10] ·2CH2Cl2. The reactions of W2NCl7 with PPh4Cl in molar ratios in CH2Cl2 solution lead to several complexes; one of them was identified bv X-ray diffraction methods to be (PPh4)2[W3Cl9(μ3-N)(0)(μ2-NCl)]2 ·1,5 CH2Cl2, which forms black crystals. The compound crystallizes monoclinically in the space group P21/n with two formula units per unit cell (7318 observed, independent reflexions, R = 0.083). The lattice dimensions are (20 °C): a = 994.4; b = 2673; c = 1518.2 pm; β = 101.00°. The compound consists of PPh4⊕ cations and centrosymmetric anions [W3Cl9(μ3-N)(O)(μ2-NCl)]22⊕. The tungsten atoms form a scalene triangle with WW bond lengths of 282 and 278 pm, respectively. The hypothenuse of this triangle is a nearly linear W - N -W bridge with WN distances of 199 and 182 pm. One of the WW edges is bridged by a μ-NCI group with WN bond lengths of 196 und 189 pm. respectively.
[Na-15-Crown-5][MoF5(NCl)] has been prepared as yellow crystals by the reaction of NaF with MoF4(NCl) in the presence of 15-crown-5 in acetonitrile solution. The compound was characterized by its IR and 19F NMR spectra as well as by an X-ray structure determination. Crystal data: space group P21/n, Z = 4 (3736 observed, independent reflexions, R = 0.034). Lattice dimensions at -70 °C: a = 823.5(4). b = 1612.2(9), c = 1383.4(8), β = 99.35(3)°. The compound forms ion pairs, in which the sodium ion is seven-coordinated by the oxygen atoms of the crown ether molecule and by two fluorine ligands of the [MoF5(NCl)]- unit with Na-F distances of 228.3 and 249.6 pm. The Mo=N-Cl group of the anion is nearly linear (bond angle 175.8°) with bond lengths MoN = 172.9 and NCl = 161.8 pm.
[Na-15-crown-5][WF5(NCl)] has been prepared as yellow crystals by the reaction of NaF with WC14(NCl) in the presence of 15-crown-5 in acetonitrile solution. The compound was characterized by its IR spectrum as well as by an X-ray structure determination. Crystal data: space group P 21/n, Z = 4 (2945 observed, independent reflexions, R = 0.035). Lattice dimensions at - 65 °C: a = 827.2(8); b = 1617.3(13); c = 1372.2(10) pm; β = 99.42(5)°. The com pound forms ion pairs, in which the sodium ion is seven-coordinated by the oxygen atoms of the crown ether m olecule, and by two fluorine ligands of the [WF5(NCl)]- unit with Na -F distances of 228.3(6) and 251.3(6) pm. The W ≡ N-Cl group of the anion is nearly linear (bond angle 176.1(5)°) with bond lengths WN = 173.3(6) and NCI = 162.2(7) pm.
WCl4(NCl) has been prepared as a red-brown crystal powder by the reaction of tungsten hexacarbonyl with excess nitrogen trichloride in boiling CCl4. The complex is associated via chloro bridges, forming dimeric units, according to the IR spectrum. Thermal decomposition at 200 °C leads to tungsten nitride trichloride, WNCl3,. With acetonitrile, WCl4(NCl) reacts with formation of the monomeric complex [CH,CN-WCl4(NCl)], which was characterized by its IR spectrum as well as by an X-ray structure determination. Crystal data: space group P21/m, Z = 2 (1387 independent observed reflexions, R = 0.07). Lattice dimensions at 20 °C: a = 590.4(3), b = 729.0(3), c = 1124.6(4) pm, β = 100.63(2)°. The complex forms monomeric molecules, in which the tungsten atom has a distorted octahedral environment of four chlorine atoms in equatorial positions, and the acetonitrile molecule in trans-position to the group. Bond lengths WN = 172 and NCI = 161 pm; bond angle WNCl = 175.5°.
Kristallstruktur von 1,1-Dichlor-3,5-diphenyl-4-H-1,2,4,6-λ4-selenatriazin, SeCl2C2N3H(C6H5)2
(1989)
The title compound has been prepared as a byproduct of the reaction of Se2Cl2 with Ν,Ν,N′-Tris(trimethylsilyl)benzamidine in CH2Cl2 solution. [SeCl2(HNC2N2Ph2)]2 was characterized by an X-ray structure determination. Space group P21/n, Z = 2, 2979 observed independent reflexions, R = 0.032. Lattice dimensions (-65 °C): a = 1050.1(4), b = 1018.9(4), c = 1402.1(6) pm; β = 99.78(3)°. The compound forms centrosymmetric dimeric molecules with SeCl2Se bridges (bond lengths 241.6(1) and 339.3(1) pm), the selenium atoms being members of nearly planar [xxx] selenatriazine rings with Se—N bond lengths of 182.2(2) and 181.5(2) pm.
The PE spectra of the nitrogen-rich title compounds cyanogen azide NC-N3, azodicarbonitrile NC - N = N - CN, azidoacetonitrile NC - H2C - N3, tetrazolo[1,5-a]pyridine (H4C5N)(N )3 and trimethylenetetrazole (H2C)3(CN4) are presented and assigned by radical cation state comparison with related compounds or by Koopmans’ correlation with MNDO eigenvalues. In a low pressure flow system the compounds decompose at higher temperatures, with elimination of the thermodynamically favorable N2 molecule. PE-spectroscopic real-time analysis reveals as further products: NC - N3 → C∞, NC - N = N - CN → NC - CN , NC - H2C - N3 → 2HCN (+ traces NC - HC = NH?) and (H2C)3(CN4) → H2C = N - CN + H2C = CH2. For tetrazolo[1,5-a]pyridine, a preceding ring opening to the corresponding 2-azidopyridine is observed.
Crystal and molecular structure analysis of the electron rich title compound exhibits an undistorted, yet sterically shielded tetra(primary alkyl)-substituted double bond system with alternating anti-periplanar CH2SiMe3 substituents. The diastereotopic methylene protons have been located and their position correlated to the 1HNMR data and to the ESR hyperfine coupling constants of the corresponding radical cation. In contrast to the highly inert all-carbon derivative, tetraneopentylethene, the more electron-rich and more flexible organosilicon title compound reacts with bromine. Close to orthogonal arrangement between the C-C(H2)-Si planes and the ethene plane ensures effective, fourfold σ/π-hyperconjugation.
In order to determine the influence of OH and O2H-radicals on proteins, bovine serum albumin (BSA) in aqueous solution was treated with Fenton’s reagent [Fe(II)SO4+EDTA+H2O2] and with ultraviolet light (λ > 2800 Å) in the presence of H2O2. The action of free radicals produced in this way did not change the properties of the native protein with respect to the sedimentation in the ultracentrifuge or optical rotatory dispersion and electrophoresis under normal conditions. Ampèrometric titration indicated partial oxidation of SH-groups and of 3—5 SS-groups which are not reducible by NaBH4.
Heat aggregation investigated by means of light-scattering was suppressed at pH 7.5 and strongly accelerated at pH 4.6 (range of coagulation), the latter being a result of increased entropy of activation of coagulation velocity.
The difference spectrum against native BSA had positive values of Δε and two maxima at 2480 and 2950 Å.
Ultracentrifugation at room temperature in phosphate buffer (pH 7.3, μ=0.18) furnishes a molecular weight of 63 300. In a solution of 8 M urea and borate buffer (pH 9, μ=0.05) fragments with molecular weights between 25 000 and 37 000 were observed while in phosphate buffer (pH 7.3, without urea) at temperatures higher than 46 °C an anomalous behaviour of the concentration gradient indicated an effect which possibly depends on a dissociation equilibrium.
As a consequence oxygen radicals seem to attack not only SH- and SS-groups but at least one covalent bond of the peptide chain. Some experiments of heat aggregation with BSA treated with γ-rays (60Co) gave the same results as BSA treated with Fenton’s reagent or UV-light+H2O2.
Diluted aqueous solutions of some proteins (bovine serum albumin, β-Lactoglobubin, Peroxidase) show weak phosphorescence lasting over several minutes after they have been irradiated with light in the range 3500-4200 A. Addition of Eosin after the irradiation amplifies in some cases the intensity of luminescence to a value of about hundred. If Eosin is present at the irradiation process the excitation to phosphorescence is possible with light of the wavelength 5460 A.
After denaturation processes which destroy the configuration of proteins (Urea, Guanidine-HCI. detergents, heat at higher pH) the ability of phosphorescence disappears altogether; likewise after blocking the SH-groups by benzochinone or a total oxidation or reduction of the SS-groups which causes an complete unfolding of the peptide chain.
In solutions of bovine serum-albumin irradiated with 3650 Å at room temperature and afterwards frozen to -178°C no radicals could be observed by measurements of electron-spin-resonance but they were detectable if the irradiation took place in the presence of H2O2.
The reactions Xanthinoxidase-Xanthine-O2, Peroxidase-H2O2 and bovine serum-albumin-H2O2-Fe (II) EDTA are accompanied by chemiluminescence. By comparison with the behaviour of oxidised serum-albumin it could be shown that the chemical reaction produces an excited state of the native protein.
The observations lead to the conclusion that the weak phosphorescence of long duration originates from a triplet-state which is sufficiently populated only as the consequence of cooperative phenomena attending the undisturbed α-Helix-structure of the protein.