Theoretical Study of Hydration of Cyanamide and Carbodiimide

Tordini, Francesco; Bencini, Alessandro; Bruschi, Maurizio; Gioia, Luca De; Zampella, Giuseppe; Fantucci, Piercarlo

doi:10.1021/jp026535r

Cited by 65 publications

(67 citation statements)

References 67 publications

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“…These can be considered as conservative estimates, which also account for the approximations made and for neglecting higher-order correlation effects. From Tables 1, 2, 3, 4 and 5, it is evident that all isomers considered have been previously studied at different levels of theory [11,[41][42][43][44][45][46][47][48], but we report the first systematic investigation of their molecular structure. As in most cases the method and/or the basis set used are inferior to ours, a detailed comparison of these results to ours is not too meaningful.…”

Section: Molecular Structurementioning

confidence: 99%

A theoretical study on CH2N2 isomers: structure and energetics

Puzzarini

Gambi

2012

Theor Chem Acc

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Five CH2N2 isomers, namely cyanamide, carbodiimide, diazomethane, isocyanamide and nitrilimine, have been investigated at a high level of accuracy. The singles and doubles coupled-cluster method including a perturbational correction for connected triple excitations, CCSD(T), in conjunction with correlation-consistent basis sets ranging in size from triple to quintuple zeta have been employed. Extrapolation to the complete basis set limit has been used with treatments of core-valence correlation effects in order to accurately predict structures, relative energies as well as N-H and C-H bond dissociation energies. The latter required to also investigate the HNNC radical with the same methodology used for CH2N2 isomers, while HCNN and HNCN data are available in the literature by the same authors (Puzzarini and Gambi in J Chem Phys 122:064316, 2005). For all the species studied, harmonic vibrational frequencies have also been evaluated at the CCSD(T) level in order to obtain zero-point corrections to total energies

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Section: Molecular Structurementioning

confidence: 99%

A theoretical study on CH2N2 isomers: structure and energetics

Puzzarini

Gambi

2012

Theor Chem Acc

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“…We found that an amidine with a 74-like structure does not correspond to a minimum and, instead, rotation about the C2-N3 bond via transitionstate structure 74 results in amino-group transfer along the down path from 74 to 75. tautomer of carbodiimides 9 and 9= and of cyanoimines 10 and 10=. In the gas phase, the activation barrier for the isomerization between the prototypical carbodiimide and cyanamide is over 330 kJ/mol [53]. The tautomerization of 95 to 10= requires an activation enthalpy of ⌬H act H ϭ 162.71 kJ/mol but even this low barrier apparently does not allow for competition with decarbonylation and 1,2-Hshift to 96 (m/z 107).…”

Section: Esi-ms Of Guanosinementioning

confidence: 99%

Ammonia elimination from protonated nucleobases and related synthetic substrates

Qian

Yang

et al. 2007

J. Am. Soc. Mass Spectrom.

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The results are reported of mass-spectrometric studies of the nucleobases adenine 1h (1, R ϭ H), guanine 2h, and cytosine 3h. The protonated nucleobases are generated by electrospray ionization of adenosine 1r (1, R ϭ ribose), guanosine 2r, and deoxycytidine 3d (3, R ϭ deoxyribose) and their fragmentations were studied with tandem mass spectrometry. In contrast to previous EI-MS studies of the nucleobases, NH 3 elimination does present a major path for the fragmentations of the ions [1h ϩ H] ϩ , [2h ϩ H] ϩ , and [3h ϩ H] ϩ . The ion [2h ϩ H Ϫ NH 3 ] ϩ also was generated from the acyclic precursor 5-cyanoamino-4-oxomethylenedihydroimidazole 13h and from the thioether derivative 14h of 2h (NH 2 replaced by MeS). The analyses of the modes of initial fragmentation is supported by density functional theoretical studies. Conjugate acids 15-55 were studied to determine site preferences for the protonations of 1h, 2h, 3h, 13h, and 14h. The proton affinity of the amino group hardly ever is the substrate's best protonation site, and possible mechanisms for NH 3 elimination are discussed in which the amino group serves as the dissociative protonation site. The results provide semi-direct experimental evidence for the existence of the pyrimidine ring-opened cations that we had proposed on the basis of theoretical studies as intermediates in nitrosative nucleobase deamination. [1,2]. This chemistry has been studied extensively because of the dietary and environmental exposure of humans to these substances [3][4][5]. Toxicological studies of deamination became more significant when it was recognized that endogenous nitric oxide [6,7] causes nitrosation [8,9], and that this process is accelerated by chronic inflammatory diseases [10,11]. It has been known for a long time that deamination of adenine 1, guanine 2, and cytosine 3 (Scheme 1) results in the formation of hypoxanthine, xanthine, and uracil, respectively, and these products are thought to result from DNA base diazonium ions 4-6, respectively, by direct nucleophilic dediazoniation. The discovery of oxanine formation [12][13][14] in the nitrosative deamination of guanine challenged the generality and completeness of this mechanism. Theoretical studies revealed that unimolecular dediazoniation of guaninediazonium ion 5 is accompanied or immediately followed by pyrimidine ringopening [15,16] and that cytosine-catalysis promotes the process [17,18]. The resulting 5-cyanoimino-4-oxomethylene-4,5-dihydroimidazole is a highly reactive intermediate and undergoes acid-catalyzed 1,4-addition via cyano-N or imino-N protonated 5-cyanoimino-4-oxomethylene-4,5-dihydroimidazoles, 9 and 10, respectively [19].Labeling studies support this reaction mechanism for oxanine formation [20]. Moreover, we synthesized 5-cyanoamino-4-imidazolecarboxamide and studied its cyclization chemistry [21] and its proficiency for cross-link formation [22]. The unimolecular dediazoniation of the diazonium ions of adenine and cytosine can proceed without ring-opening but the cations 7 and 11 formed in this...

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“…A possible reason is that hydrolysis side reaction of cyanamide occurred during the guanidinylation reaction. 25 …”

Section: Characterization Of Guanidinylated Chitosanmentioning

confidence: 99%

Guanidinylation: A simple way to fabricate cell penetrating peptide analogue‐modified chitosan vector for enhanced gene delivery

Zhai

Sun

Luo

et al. 2011

J of Applied Polymer Sci

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In view of the analogous transmembrane function to cell penetrating peptides, guanidine group was incorporated into chitosan by chemical modification to enhance the transfection performance of chitosan vectors. Guanidinylated chitosan (GCS) was shown to be well soluble in neutral aqueous solution. The interaction between GCS with plasmid DNA was characterized by agarose retardation experiment and ethidium bromide displacement assay. GCS formed more stable complexes with DNA under physiological pH than chitosan. The transfection efficiency of GCS was evaluated employing COS-7 cell line-GCS polyplexes demonstrated higher transfection efficiency and lower cytotoxicity relative to chitosan. The optimum efficiency of GCS was achieved in the vicinity of the critical complexing ratio. The results of flow cytometry indicated that guanidinylation promoted an eightfold increase in the cell uptake. The study revealed that guanidinylated chitosan is a promising candidate as an effective nonviral vector for in vivo gene delivery.

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Theoretical Study of Hydration of Cyanamide and Carbodiimide

Cited by 65 publications

References 67 publications

A theoretical study on CH2N2 isomers: structure and energetics

A theoretical study on CH2N2 isomers: structure and energetics

Ammonia elimination from protonated nucleobases and related synthetic substrates

Guanidinylation: A simple way to fabricate cell penetrating peptide analogue‐modified chitosan vector for enhanced gene delivery

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