Biliverdin (BV) structure was analyzed by using NMR techniques and unrestricted density function theory simulations to explain the incapacity of BV to build coordination complex(es) with Cu2+ in dimethyl sulfoxide, which was confirmed by UV-Vis, EPR and NMR spectroscopy. NMR showed that N atoms are protonated in all four pyrrole rings. The structure is stabilized by two hydrogen bonds between NH moieties and carbonyl oxygens from opposite terminal pyrrole rings, and by the bending of propionyl chain with carboxyl group out of the plain toward central position of BV. The simulations of deprotonated BV, which builds copper complexes in water and chloroform as described previously, showed a different conformation and organization of hydrogen bonds. Taking into account that deprotonation represents a critical step in coordinate bonds formation, the protonation of an additional N atom may represent a key difference between the interactions of BV with copper in different solvents.

中文翻译：

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二甲亚砜中胆绿素的构象：对与铜配位的影响

通过使用 NMR 技术和无限制密度函数理论模拟分析了胆绿素 (BV) 结构，以解释 BV 无法与二甲基亚砜中的 Cu2+ 构建配位络合物，这已通过 UV-Vis、EPR 和 NMR 光谱证实。NMR 显示所有四个吡咯环中的 N 原子都被质子化。该结构通过 NH 部分和来自相反末端吡咯环的羰基氧之间的两个氢键以及通过带有羧基的丙酰基链从平面向 BV 的中心位置弯曲而稳定。如前所述，去质子化 BV 在水和氯仿中构建铜络合物的模拟显示了不同的氢键构象和组织。考虑到去质子化是配位键形成的关键步骤，