State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Xianlin Campus, Nanjing University, Nanjing 210046, PR China.
Sci Total Environ. 2012 Jan 1;414:404-16. doi: 10.1016/j.scitotenv.2011.10.063. Epub 2011 Nov 25.
Polyhydroxylated dibenzo-p-dioxins (PHODDs) are important metabolic and synthetic products of polychlorinated dibenzo-p-dioxins (PCDDs). Two types of hydrogen bonds exist in PHODD molecules: one between a hydroxyl group (HO) and an oxygen atom of the ether bond, and the other between two ortho hydroxyls of a benzene ring. By fully optimized calculation with density functional theory (DFT), their bond energies were ascertained to be approximately 9-14 kJ/mol and 15-19 kJ/mol respectively by the comparison of standard Gibbs energy of formation (Δ(f)G(θ)) between different molecules, which was experimentally verified. The two types of hydrogen bonds affect the hydrophilicity and stability of the molecules. The torsional potential of hydroxyls and the orientation making the congener most stable were obtained. The octanol-water partition coefficients (logK(ow)s) were calculated based on the group contribution method, and the standard state entropy (S(θ)), standard enthalpy (Δ(f)H(θ)) of formation and Δ(f)G(θ) were obtained from the combination of DFT calculation and isodesmic reaction for the stable PHODD congeners. The number and position of hydroxyl substitution (N(PHOS)) were employed as descriptors to establish quantitative structure-property relationship (QSPR) models. Although the hydrophilicity of PHODDs increases with the number of hydroxyl groups, it is impaired by the intramolecular hydrogen bonds. The logK(ow)s of PHODDs are much smaller than those of PCDDs, and the variation trend with the number of substituents is different. In addition, the relative stability order of PHODD congeners was theoretically proposed, which is quite different from that of PCDDs. Considering the ionization in water, first-order ionization constants of PHODDs were calculated according to the results of SMD method of Self-Consistent Reaction Field Theory (SCRF), and they were influenced by the hydrogen bonds.
多羟基二苯并对二噁英（PHODD）是多氯二苯并对二噁英（PCDD）的重要代谢和合成产物。PHODD 分子中存在两种氢键：一种是羟基（HO）与醚键氧原子之间的氢键，另一种是苯环两个邻位羟基之间的氢键。通过密度泛函理论（DFT）的全优化计算，通过比较不同分子的标准生成吉布斯自由能（Δ(f)G(θ)），确定其键能分别约为 9-14 kJ/mol 和 15-19 kJ/mol，这在实验中得到了验证。这两种氢键影响分子的亲水性和稳定性。得到了羟基的扭转势能和使同系物最稳定的取向。基于基团贡献法计算了辛醇-水分配系数（logK(ow)s），并通过 DFT 计算和等电子反应组合获得了标准状态熵（S(θ)）、标准生成焓（Δ(f)H(θ)）和Δ(f)G(θ)，用于稳定的 PHODD 同系物。羟基取代的数量和位置（N(PHOS)）被用作描述符来建立定量构效关系（QSPR）模型。尽管 PHODD 的亲水性随羟基数量的增加而增加，但它会受到分子内氢键的影响。PHODD 的 logK(ow)s 远小于 PCDD 的 logK(ow)s，且取代基数量的变化趋势不同。此外，还从理论上提出了 PHODD 同系物的相对稳定性顺序，与 PCDD 有很大不同。考虑到水中的电离，根据自洽反应场理论（SCRF）的 SMD 方法的结果计算了 PHODD 的一级电离常数，它们受氢键的影响。
