新水解速率常数揭示氰化物在低温中性水体中存续时间最长
New Hydrolysis Rate Constants Reveal Longest Cyanide Persistence in Cool, Neutral Waters
AI总结：
本研究测定了不同温度、pH及盐类条件下氰化氢的水解速率与不确定度，发现其在低温中性水体中存续最久，为评估地内外生命前分子浓度上限提供了关键依据。
AI中文摘要：
氰化氢（HCN）是生命前化学中的关键分子，其在水中的可利用性受水解作用限制。本研究估算了HCN的水解速率，重点分析了速率相关误差随温度、pH值以及亚硫酸盐、硫化物和磷酸盐类盐存在时的变化规律。对于纯水体系，我们测得0℃下酸催化水解速率常数为$\n (k^+_{273}/1\\,{\rm M^{-1} s^{-1}}) = -12.7 \pm 1.12$，活化能为$67.1 \\, {\rm kJ \\, mol^{-1}}$；0℃下碱催化速率常数为$\n (k_{273}^-/1\\,{\rm M^{-1} s^{-1}}) = -9.0 \pm 1.27$，活化能为$89.5 \\, {\rm kJ \\, mol^{-1}}$。在pH>8的条件下，这些数值与文献估算值在我们的不确定度范围内一致，但在较低pH下与文献值存在差异。盐存在时，酸性条件下的水解反应被加速，速率是无盐时酸催化速率的6–14倍；而在${\rm pH \gtrsim 8}$的条件下，亚硫酸盐和硫化物会使水解速率减慢2.5倍。这些结果表明，在限定地球及其他行星自然水体中生命前分子可达到的最高浓度时，估算速率相关的不确定度至关重要。
英文摘要：
Hydrogen cyanide (HCN) is a key molecule in prebiotic chemistry, and its availability in water is limited by hydrolysis. In this work, we estimate the hydrolysis rates of \ce{HCN}, particularly the errors associated with the rates as a function of temperature, pH and in the presence of salts containing sulfite, sulfide and phosphate. For pure water, we find an acid-catalyzed hydrolysis rate constant at ${\rm 0 ^{\circ}C}$ of $\ln (k^+_{273}/1\,{\rm M^{-1} s^{-1}}) = -12.7 \pm 1.12$ with an activation energy of $67.1 \, {\rm kJ \, mol^{-1}}$. We find a base-catalyzed rate constant of $\ln (k_{273}^-/1\,{\rm M^{-1} s^{-1}}) = -9.0 \pm 1.27$ at ${\rm 0^{\circ}C}$ with an activation energy of $89.5 \, {\rm kJ \, mol^{-1}}$. These values are consistent with estimates from the literature within our uncertainties at ${\rm pH} > 8$ but diverge from literature values at lower pH. In the presence of salts, hydrolysis is accelerated under acidic conditions to 6--14$\times$ the acid-catalyzed rate without salts. However, at ${\rm pH \gtrsim 8}$ hydrolysis rates become $2.5\times$ times slower with sulfite and sulfide. These results demonstrate the importance of estimating uncertainties associated with rates when constraining the maximum concentrations of prebiotic molecules attainable in natural waters on the Earth and other planets.
