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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.|
Carvalho, R. A.
Gil, M. H.
Simões, P. N.
|Publisher:||American Chemical Society|
|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.|
|Appears in Collections:||FCTUC Química - Artigos em Revistas Internacionais|
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|J.Physical Chemistry B, 114 (2010) 6156.pdf||279.6 kB||Adobe PDF||View/Open|
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