Isoprene-Derived Organosulfates: Vibrational Mode Analysis by Raman Spectroscopy, Acidity-Dependent Spectral Modes, and Observation in Individual Atmospheric Particles
Isoprene-Derived Organosulfates: Vibrational Mode Analysis by Raman Spectroscopy, Acidity-Dependent Spectral Modes, and Observation in Individual Atmospheric Particles
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DOI：
10.1021/acs.jpca.7b10587
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发表时间：
2018-01-11
影响因子：
2.9
通讯作者：
Ault, Andrew P.
中科院分区：
文献类型：
--
作者：
Bondy, Amy L.;Craig, Rebecca L.;Ault, Andrew P.
异戊二烯是大气中最丰富的生物挥发性有机化合物（BVOC），其低挥发性氧化产物导致二次有机气溶胶（SOA）的形成。由异戊二烯氧化产物与颗粒相中的硫酸盐反应形成的异戊二烯衍生的有机硫酸盐是SOA的重要组分，并且可以水解形成多元醇。尽管通过质谱进行表征，但其基本结构和光谱性质仍然知之甚少。在此，拉曼显微光谱和密度泛函理论（DFT）计算（CAM-B3 LYP水平的理论）相结合，以分析关键的有机硫酸酯，3-甲基四醇硫酸酯（两种异构体的外消旋混合物），外消旋2-甲基甘油酸硫酸酯，和水解产物，2-甲基四醇和2-甲基甘油酸的振动模式。确定了两个强振动模式，v（RO-SO 3）（846 +/- 4 cm（-1））和v（s）（SO 3）（1065 +/- 2 cm（-1）），沿着较低强度的δ（SO 3）模式（586 +/- 2 cm（-1））。对于2-甲基甘油酸及其硫酸酯，当pH值高于pg a时，羧酸的去质子化降低了羰基伸缩频率（1724 cm（-1）），而对于v（s）（COO-）和v（a）（COO-），羧酸酯模式分别在1413和1594 cm（-1）（，）处增长。v（RO-SO 3）和v（s）（SO 3）模式在个别大气颗粒物中观察到，并可用于未来的研究复杂的SOA混合物，以区分有机硫酸盐从无机硫酸盐或水解产物。
Isoprene, the most abundant biogenic volatile organic compound (BVOC) in the atmosphere, and its low-volatility oxidation products lead to secondary organic aerosol (SOA) formation. Isoprene-derived organosulfates formed from reactions of isoprene oxidation products with sulfate in the particle phase are a significant component of SOA and can hydrolyze forming polyols. Despite characterization by Mass spectrometry, their basic structural and spectroscopic properties remain poorly understood. Herein, Raman microspectroscopy and density functional theory (DFT) calculations (CAM-B3LYP level of theory) were combined to analyze the vibrational modes of key organosulfates, 3-methyltetrol sulfate esters (rac&nic mixture of two isomers), and racemic 2-methylglyceric acid sulfate ester, and hydrolysis products, 2-methyltetrols, and 2-methylglyceric acid. Two intense vibrational modes were identified, v(RO-SO3) (846 +/- 4 cm(-1)) and v(s)(SO3) (1065 +/- 2 cm-(1)), along with a lower intensity delta(SO3) mode (586 +/- 2 cm(-1)). For 2-methylglyceric acid and its sulfate esters, deprotonation of the carboxylic acid at pH values above the pg a decreased the carbonyl stretch frequency (1724 cm(-1)), while carboxylate modes grew in for v(s)(COO-) and v(a)(COO-) at 1413 and 1594 cm-(1)(,) respectively. The v(RO-SO3) and v(s) (SO3) modes were observed in individual atmospheric particles and can be used in future studies of complex SOA mixtures to distinguish organosulfates from inorganic sulfate or hydrolysis products.