Chinese Journal of Chemistry, 2006, 24, 923—928 Full Paper * E-mail: yfzhao@mail.tsinghua.edu.cn; Tel.: 0086-010-64413899; Fax: 0086-010-64451572 Received April 13, 2005; revised July 29, 2005; accepted March 30, 2006. Project supported by the National Natural Science Foundation of China (Nos. 20132020, 20572008). © 2006 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Electrospray Ionization Mass Spectral Characteristics of Polyamide Containing 1,4,7,10-Tetraazacyclododecane QIAO, Ren-Zhong a,b (乔仁忠) ZHANG, Zhen a (张祯) JU, Yong a (巨勇) XIA, Chuan-Qin c (夏传琴) YU, Xiao-Qi c (余孝其) ZHAO, Yu-Fen* ,a (赵玉芬) a The Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China b Department of Pharmaceutical Engineering, Beijing University of Chemical Technology, Beijing 100029, China c Department of Chemistry, Sichuan University, Chengdu, Sichuan 610064, China The study of the fragmentations of the protonated molecular species [M＋H] ＋ and selected fragment ions al- lowed proposals for the main fragmentation pathways of the title compound. In order to better understand the frag- mentation pathways, the MS 3 and MS 4 spectra of the title compound were obtained. The main fragmentation path- ways occur by the cleavage of the C—CO bonds between N-methylpyrrole and carbonyl groups, CO—NH amide bonds, NH — C bonds between the NH groups and the N-methylpyrrole rings, and N — C bonds in 1,4,7,10-tetraazacyclododecane. Electrospray ionization was proven to be a good method for the structural charac- terization and identification of this kind of compound. Keywords polyamide, 1,4,7,10-tetraazacyclododecane, mass spectrometry Introduction Polyamides containing N-methylpyrrole have at- tracted considerable attention of biological chemists because they can permeate living cell membranes and have the potential to control specific gene expression. 1,2 The properties of azacrowns such as 1,4,7,10-tetraaza- cyclododecane (cyclen) have been studied intensively over the last few years. The compounds were used as ligands for very stable metal complexes in medicinal applications. 3,4 Some zinc complexes of azamacrocycles showed dynamic anion recognition in water and proper- ties mimicking enzyme, and this has been used to achieve self assembly under physiological conditions 5,6 and even to control gene expression in vivo. 7 The new compound (NO 2 Py 4 γ-cyclen) has been synthesized by connecting the polyamide (NO 2 Py 4 γ) with cyclen in our laboratory, where Py ＝N-methylpyrrole, cyclen ＝1,4, 7,10-tetraazacyclododecane, γ ＝ NH 2 CH 2 CH 2 CH 2 CO- OH. This paper describes the mass spectral fragmenta- tion mechanisms of this compound, investigated by electrospray ionization with tandem mass spectrometry (ESI-MS 2 ). Experimental Preparation of the polyamine amide Compound 3 (NO 2 Py 4 γ-cyclen) was prepared by di- cyclohexylcarbodiimide/1-hydroxybenzotriazole (DCC/ HOBt) mediated coupling reaction (Scheme 1), which has been characterized by elemental analyses, 1 H NMR and 13 C NMR. Mass spectrometry Mass spectra were acquired in positive ion mode us- ing a Bruker Esquire LC-MS TM ion trap spectrometer equipped with a gas nebulizer probe, capable of analyz- ing ions up to m/z 6000. Nitrogen was used as drying gas with a flow rate of 4 L/min and the nebulizer pres- sure was 48.23 kPa. The capillary was typically held at 4 kV and the source temperature was maintained at 300 . The instrument was operated at unit ℃ -mass resolution, and calibration of m/z was performed using a standard ES-tuning-mix. Five scans were averaged for each spectrum. The samples dissolved in methanol were ion- ized by electrospray ionization and continuously infused into the ESI chamber at a flow rate of 4 μL/min by a Cole-Parmer 74900 syringe pump (Cole-Parmer In- strument Co.). Results and discussion Positive-ion ESI-MS of the compound 3 displays [M＋H] ＋ ion m/z 776.5 as indicated in Figure 1. The observed fragmentation modes of the mass spec- tra of the compound 3 can be rationalized by the a n and b n cleavages (n＝1—5) proposed in Scheme 2. Because of the introduction of cyclen into the polyamide, the most striking feature of the MS 2 of the [M＋H] ＋ ion of the compound is the fragment ions m/ z 647 and