W. M. Keck Laboratories, California Institute of Technology, Pasadena, California 91125, USA.
J Phys Chem A. 2010 May 13;114(18):5817-22. doi: 10.1021/jp1019729.
Reactive gas uptake on environmentally realistic aqueous surfaces is expected to be affected by a combination of multiple interactions. This issue is herein explored in experiments where the formation of Me(3)NH(+) on neat and doped water microjets exposed to Me(3)N(g) is monitored within <1 ms by online electrospray ionization mass spectrometry as a function of pH of the bulk liquid (pH(BLK)). Notably, Me(3)N(g) is protonated on the surface of neat water microjets below pH(BLK) approximately 4, rather than at pH(BLK) less than or approximately pK(A)(Me(3)NH(+)) = 9.8 as in bulk water. Me(3)N(g) uptake is significantly enhanced by anionic surfactants and fulvic acid (a surrogate of complex natural organic matter) above pH(BLK) approximately 4, uniformly depressed by cationics (which otherwise counteract FA effects), and unaffected by n-octanol. The direct hydrogen isotope effects associated with enhanced uptake of Me(3)N(g) on H(2)O/D(2)O microjets implicate a process controlled by proton transfer from interfacial donors whose coverage is electrostatically modulated by ionic headgroups. The finding that the combined effect of fulvic acid and tetrabutylammonium bromide closely matches the geometric mean of their separate effects on TMA uptake is evidence of strong dopant interactions.
在实际的环境水相表面上，反应性气体的吸收预计会受到多种相互作用的共同影响。本文通过实验探索了这一问题，实验中使用在线电喷雾电离质谱法在 <1 ms 的时间内监测到纯水滴射流和掺杂水滴射流暴露于 Me(3)N(g) 时 Me(3)NH(+) 的形成，其函数为本体液体的 pH 值 (pH(BLK))。值得注意的是，Me(3)N(g)在 pH(BLK)约为 4 以下的纯水滴射流表面上发生质子化，而不是在本体水中的 pH(BLK)小于或约为 pK(A)(Me(3)NH(+)) = 9.8 时发生质子化。在 pH(BLK)约为 4 以上，阴离子表面活性剂和富里酸（复杂天然有机物的替代物）显著增强 Me(3)N(g)的吸收，阳离子则均匀抑制（否则会抵消 FA 的影响），而正辛醇则不受影响。与 Me(3)N(g)在 H(2)O/D(2)O 微射流上增强吸收相关的直接氢同位素效应表明，这是一个由界面供体的质子转移过程控制的，其覆盖度受离子头基的静电调制。富里酸和四丁基溴化铵的综合效应与它们对 TMA 吸收的单独效应的几何平均值非常吻合，这证明了掺杂剂之间存在强烈的相互作用。
