EFFECT OF BASICITY AND STRUCTURE ON THE HYDRATION OF PROTONATED MOLECULES, PROTON-BOUND DIMER AND CLUSTER FORMATION: AN ION MOBILITY-TIME OF FLIGHT MASS SPECTROMETRY AND THEORETICAL STUDY
堿性和結(jié)構(gòu)對(duì)質(zhì)子化分子水化，質(zhì)子結(jié)合的二聚體和團(tuán)簇形成的影響：離子遷移-飛行時(shí)間質(zhì)譜和理論研究
Younes Valadbeigi,1 Vahideh Ilbeigi,2
Bartosz Michalczuk,3 Martin Sabo,3 Stefan Matejcik3
1Department of Chemistry, Faculty of Science, Imam Khomeini International University, Qazvin, Iran
2TOF Tech. Pars Company, Isfahan Science & Technology Town, Isfahan, Iran
3Department of Experimental Physics, Comenius University, Mlynska dolina F2, 84248, Bratislava, Slovak Republic
Abstract
Protonation, hydration, and cluster formation of ammonia, formaldehyde, formic acid, acetone, butanone, 2-ocatanone, 2-nonanone, acetophenone, ethanol, pyridine, and its derivatives were studied by IMS-TOFMS technique equipped with a corona discharge ion source. It was found that tendency of the protonated molecules, MH+, to participate in hydration or cluster formation depends on the basicity of M. The molecules with higher basicity were hydrated less than those with lower basicity. The mass spectra of the low basic molecules such as formaldehyde exhibited larger clusters of MnH+(H2O)n, while for compounds with high basicity such as pyridine, only MH+ and MH+M peaks were observed. The results of DFT calculations show that enthalpies of hydrations and cluster formation decrease as basicities of the molecules increases. Using comparison of mass spectra of formic acid, formaldehyde, and ethanol, effect of structure on the cluster formation was also investigated. Formation of symmetric (MH+M) and asymmetric proton-bound dimers (MH+N) was studied by ion mobility and mass spectrometry techniques. Both theoretical and experimental results show that asymmetric dimers are formed more easily between molecules (M and N) with comparable basicity. As the basicity difference between M and N increases, the enthalpy of MH+N formation decreases.
通過配備電暈放電離子源的IMS-TOFMS技術(shù)研究了氨，甲醛，甲酸，丙酮，丁酮，2-辛酮，2-壬酮，苯乙酮，乙醇，吡啶及其衍生物的質(zhì)子化，水合和團(tuán)簇形成。已發(fā)現(xiàn)質(zhì)子化分子MH +參與水化或團(tuán)簇形成的趨勢(shì)取決于M的堿度。具有較高堿度的分子的水合程度低于具有較低堿度的分子的水合程度。低堿性分子(例如甲醛)的質(zhì)譜表現(xiàn)出較大的M n H +(H 2 O)n簇，而對(duì)于高堿性的化合物(例如吡啶)，只有MH + 和MH +觀察到M個(gè)峰。DFT計(jì)算的結(jié)果表明，隨著分子堿度的增加，水合焓和簇形成焓降低。通過比較甲酸，甲醛和乙醇的質(zhì)譜，還研究了結(jié)構(gòu)對(duì)團(tuán)簇形成的影響。通過離子遷移率和質(zhì)譜技術(shù)研究了對(duì)稱的(MH + M)和不對(duì)稱的質(zhì)子結(jié)合二聚體(MH + N)的形成。理論和實(shí)驗(yàn)結(jié)果均表明，在具有相當(dāng)堿性的分子(M和N)之間更容易形成不對(duì)稱二聚體。隨著M和N之間的堿度差增加，MH + N形成的焓降低。
Keywords:Proton affinity, Clustering, Hydration, Proton-bound dimer, Mass spectrometry
關(guān)鍵詞：質(zhì)子親和力、團(tuán)簇、水合作用、質(zhì)子結(jié)合二聚體、質(zhì)譜
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