Conformational analysis of 1,4-disilabutane and 1,5-disilapentane by combined application of gas-phase electron diffraction and ab initio calculations and the crystal structure of 1,5-disilapentane at low temperatures

Mitzel NW, Smart BA, Blake AJ, Robertson HE, Rankin DWH. Conformational analysis of 1,4-disilabutane and 1,5-disilapentane by combined application of gas-phase electron diffraction and ab initio calculations and the crystal structure of 1,5-disilapentane at low temperatures. JOURNAL OF PHYSICAL CHEMISTRY. 1996;100(22):9339-9347.The gas-phase structures of the conformers of 1,4-disilabutane and 1,5-disilapentane have been analyzed from electron-diffraction data augmented by flexible restraints derived from ab initio calculations. This allowed the simultaneous refinement of 22 and 29 parameters for 1,4-disilabutane and 1,5-disilapentane, respectively. 1,4-Disilabutane has been found to be present in the vapour predominantly in the anti (A) form (76(2)% from the experiment, 83% predicted by theory). Consistency in the geometries is found between theoretical predictions and experimental findings, except for the torsion angle angle(SiCCSi) of the gauche (G) conformer [exptl 78.5(21)degrees, theor 68.0 degrees]. The AA conformer of 1,5-disilapentane was always found to be the lowest energy structure, while some doubt still remains about the ordering of the AG and G(+)G(-) conformers. The AA conformer is found to be the sole form present in the crystal [C2/c, a = 15.585(8), b = 4.704(3), c = 9.895(6) Angstrom, beta = 95.77(4)degrees, Z = 4]. Good agreement is found for geometrical parameters determined experimentally in the gas phase and solid state and calculated by nb initio methods. The following values represent the most important distances (r(g)/Angstrom) and angles (angle(g)/deg) found for the gas phase and crystal structures. 1,4-Disilabutane GED (A/G, esd's correspond to 1 sigma): r(CSi) 1.882(1)/1.885(1), r(CC) 1.563(5)/1.563(5), r(SiH) both 1.499(3), angle(CCSi) 110.7(2)/114.4(5), angle(SiCCSi) 180.0/78.5(21). 1,5-Disilapentane GED [AA/G(+)G(-)]: r(CSi) 1.886(1)/1.888(1), r(CC) 1.537(2)/1.539(2), r(SiH) both 1.487(4), angle(CCC)114.8(7)/118.8(7), angle(CCSi)114.1(4)/116.8(7), angle(SiCCC) 180.0/60.9(10); X [%, AA/AG/G(+)G(-)] 28(4)/40(5)/26(6). 1,5-Disilapentane XRD: r(CSi) 1.868(2), r(CC) 1.527(2), angle(CCC) 113.8(2), angle(CCSi) 115.2(1), angle(siCCC) 180.0(1)

Prenatal exposure to TCDD and atopic conditions in the Seveso second generation: a prospective cohort study

Abstract Background 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a toxic environmental contaminant that can bioaccumulate in humans, cross the placenta, and cause immunological effects in children, including altering their risk of developing allergies. On July 10, 1976, a chemical explosion in Seveso, Italy, exposed nearby residents to a high amount of TCDD. In 1996, the Seveso Women’s Health Study (SWHS) was established to study the effects of TCDD on women’s health. Using data from the Seveso Second Generation Health Study, we aim to examine the effect of prenatal exposure to TCDD on the risk of atopic conditions in SWHS children born after the explosion. Methods Individual-level TCDD was measured in maternal serum collected soon after the accident. In 2014, we initiated the Seveso Second Generation Health Study to follow-up the children of the SWHS cohort who were born after the explosion or who were exposed in utero to TCDD. We enrolled 677 children, and cases of atopic conditions, including eczema, asthma, and hay fever, were identified by self-report during personal interviews with the mothers and children. Log-binomial and Poisson regressions were used to determine the association between prenatal TCDD and atopic conditions. Results A 10-fold increase in 1976 maternal serum TCDD (log10TCDD) was not significantly associated with asthma (adjusted relative risk (RR) = 0.93; 95% CI: 0.61, 1.40) or hay fever (adjusted RR = 0.99; 95% CI: 0.76, 1.27), but was significantly inversely associated with eczema (adjusted RR = 0.63; 95% CI: 0.40, 0.99). Maternal TCDD estimated at pregnancy was not significantly associated with eczema, asthma, or hay fever. There was no strong evidence of effect modification by child sex. Conclusions Our results suggest that maternal serum TCDD near the time of explosion is associated with lower risk of eczema, which supports other evidence pointing to the dysregulated immune effects of TCDD

Structure-based evaluation of the resonance interactions and effectiveness of the charge transfer in nitroamines

Structural data for five nitroamines of general formula Me₂N–G–NO₂ show effectiveness of the ground-state charge transfer to be most and least efficient in N,N-dimethylnitramine and in 4-N,N-dimethylamino-β-nitrostyrene, respectively. Electron-donor power of the amino nitrogen atom in the latter compound is less than that in 4-nitro-β-N,N-dimethylaminostyrene (these two compounds are isomers). Natural population analysis shows that the charge transfer from the amino to the nitro oxygen atoms is most effective in N,N-dimethylnitramine, Me₂N–NO₂. The nitro oxygen atoms are not the only acceptors of the negative charge lost by the amino nitrogen atom. The nitro group in two substituted nitrobenzenes studied was found to be independent on substituent (nitro group attached to the benzene ring withdraws a constant electron density regardless the substitution).peerReviewe