Study of the binding of Eu3+ and Tb3+ to L-phenylalanine and L-tryptophan

Abstract

Os íons európio e térbio trivalentes possuem raios iônicos semelhantes àquele do Ca 2+ . Em função disto, eles são usados como sondas de sítios de ligação de cálcio em moléculas de seres vivos. Tais íons possuem características espectroscópicas muito úteis ao seu estudo, particularmente uma luminescência intensa. Em proteínas contendo estes íons lantanídios a elas ligados, emissão de luz pode ser observada quando radiação no UV é absorvida por seus resíduos de aminoácidos aromáti-cos, indicando que há transferência de energia para o íon lantanídio. O presente trabalho foi feito com o objetivo de definir os sítios de ligação do Eu 3+ e do Tb 3+ nos complexos com os aminoácidos aromáticos L-fenilalanina e L-triptofano. As técnicas utilizadas foram as espectroscopias no infravermelho e de ressonância magnética nuclear de 13 C. Foi verificado que európio e térbio trivalentes interagem com o grupo carboxilato de ambos os aminoácidos. Com o L-triptofano o grupo imino do anel indólico também se liga ao lantanídio, representando um segundo ponto de coordenação.Trivalent europium and terbium ions have ionic radii similar to that of Ca 2+ . So they are employed as probes of calcium binding sites in biological molecules. These ions exhibit very useful spectroscopic characteristics, chiefly a pronounced luminescence. In protein bound lanthanide, visible light emission from the lanthanide excited states can be observed when UV light is absorbed by aromatic amino acids. Subsequently, the energy is transferred to the lanthanide ion. The present work was carried out to define the binding sites of Eu 3+ and Tb 3+ in complexes with the aromatic amino acids L-phenylalanine and L-tryptophan. The techniques utilized were infrared and 13 C nuclear magnetic resonance spectroscopies. It was found that trivalent europium and terbium interact with the carboxylate group of both amino acids. With L-tryptophan, the imino group of the indole ring is also involved representing another coordination site.

Ferrocenoyl-amino acids: redox response towards di- and trivalent metal ions

“…The amide carbonyl and carbons of ferrocene showed shifts of less than 1.0 ppm indicating that they do not participate in binding of the metal ions. Such magnitudes of shifts have been reported for Asp and Glu, Phe and glutathione, with Pd 2+ [48] and Ln 3+ [5,8,49]. The downfield shifts of the carbonyl chemical shifts are consistent with complexation with the metals since it causes a decrease of the electron density around the corresponding carbon atom [49].…”

Synthesis, spectroscopic and electrochemical characteristics of a novel Schiff-base from saccharin and tryptophan

“…5. This spectrum accords with that previously reported for L-tryptophan [42]. As can be seen in Fig.…”

“…As can be seen in Fig. 5, tryptophan has the IR absorption peak of the carboxylic acid group at 1675 cm -1 [43,44] and the deformation vibrations in the region between 700 and 500 cm -1 [42]. In Fig.…”

LaF3 nanoparticles surface modified with tryptophan and their optical properties

“…Strong chemical bonding of Trp to the surface is supported by the fact that it is not eliminated after numerous washings. Trp complexes can be formed with participation of carboxyl [28,33], amino group [34][35][36], and -electron system of indole [27,37,38]. Coordination of Trp through carboxyl group seems more possible in surface complexes, with protonated ␣-amino group oriented to the solution and thus stabilizing the nanoparticle.…”