Pyrazines are omnipresent in nature and have their occurrence in plants, microbes, food supplies, marine arenas. The present studies aimed at aquatic speciation of the neptunyl ion (NpO₂⁺) with two pyrazine compounds namely pyrazine monocarboxylic acid (PMC) and pyrazine dicarboxylic acid (PDC). Absorption spectrophotometry was used to probe the stability, speciation and spectral properties for the complexation process. NpO₂⁺ forms a more stable complex with PMC than PDC for 1:1 (ML), while for 1:2 (ML₂) the opposite trend is observed. The extent of shift in λ_max, which is also an indicator for the strength of complexation, reflected similar trends for the complexation process. Isothermal titration calorimetry was employed to determine the enthalpies of complex formation, which is found to be endothermic. The complexation process is entropy driven. Linear free energy correlations were established to retrieve the coordination modes of the complexes. The variation in peak potentials (the cyclic voltammograms) with change in pH and metal to ligand ratio were explored to understand redox speciation, electron transfer kinetics and Eh-pH characteristics for the interaction of NpO₂⁺ with pyrazine carboxylate ligands. Density functional theory calculations were employed to optimize the geometries and to calculate the bond distances and partial charges on key atoms of the optimized geometries. The theoretical calculations helped to reveal the contributions from two different configurations of the same geometry towards the optical absorption. The bond distances and partial charges estimated theoretically helped to understand the aqueous interactions at the molecular level.

吡嗪在自然界无处不在，并存在于植物，微生物，食品，海洋场所。本研究的目的是与两种吡嗪化合物即吡嗪单羧酸（PMC）和吡嗪二羧酸（PDC）进行水合的壬基离子（NpO ₂ ⁺）水生物种形成。吸收分光光度法用于检测络合过程的稳定性，形态和光谱性质。对于1：1（ML），NpO ₂ ⁺与PMC形成比PDC更稳定的络合物，而对于1：2（ML ₂），则观察到相反的趋势。_λmax的偏移程度_，这也是复合强度的指标，反映了复合过程的相似趋势。用等温滴定热法测定复合物形成的焓，发现该复合物是吸热的。络合过程是由熵驱动的。建立线性自由能相关性以检索配合物的配位模式。研究了峰电位（循环伏安图）随pH和金属配体比的变化而变化，以了解NpO ₂ ⁺相互作用的氧化还原形态，电子转移动力学和Eh-pH特性。与吡嗪羧酸酯配体。使用密度泛函理论计算来优化几何形状，并计算优化几何形状的关键原子上的键距和部分电荷。理论计算有助于揭示相同几何形状的两种不同配置对光吸收的贡献。理论上估计的键距和部分电荷有助于理解分子水平上的水相互作用。