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Title: 1H NMR Spectroscopic and Quantum Chemical Studies on a Poly(ester amide) Model Compound: Nα-Benzoyl-l-Argininate Ethyl Ester Chloride. Structural Preferences for the Isolated Molecule and in Solution
Authors: Fonseca, A. C. 
Jarmelo, S. 
Carvalho, R. A. 
Fausto, R. 
Gil, M. H. 
Simões, P. N. 
Issue Date: Apr-2010
Publisher: American Chemical Society
Serial title, monograph or event: J. Phys. Chem. B,
Volume: 114
Abstract: The molecular structure of the l-arginine derivative, Nα-benzoyl-l-argininate ethyl ester chloride (BAEEH+·Cl−), was characterized by combining quantum chemical methods and 1H NMR spectroscopy. A conformational search on the potential energy surfaces of the three lowest-energy tautomers of BAEEH+ [A: R−N+H═(NH2)2; B: R−NH−C(═NH)N+H3; C: R−N+H2−C(═NH)NH2; R = C6H5C(═O)NH−CH(COOCH2CH3)CH2CH2CH2−] was carried out using the semiempirical PM3 method. The lowest-energy conformations obtained using this method were then optimized at the DFT(B3LYP)/6-31++G(d,p) level of theory. For all tautomers, it was found that all low-energy conformers present folded structures, in which a H-bond interaction between the guanidinium group and the amide carbonyl oxygen atom appears to be the most relevant stabilizing factor. 1H NMR spectra of BAEEH+·Cl− in DMF-D7 were acquired in the temperature range [−55 to 75 °C], providing information about the rotational motions in the guanidinium group and showing that the tautomeric form of BAEEH+ that exists in solution is tautomer A. The interpretation of the experimental findings was supported by 1H NMR chemical shifts obtained theoretically at the DFT(B3LYP)/6-31++G(d,p) level of approximation, using both the polarized continuum model and a BAEEH+−water complex model.
DOI: 10.1021/jp9114749
Rights: openAccess
Appears in Collections:FCTUC Química - Artigos em Revistas Internacionais

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