1.Carbohydrate-aromatic interactions: vibrational spectroscopy and structural assignment of isolated monosaccharide complexes with p-hydroxy toluene and N-acetyl l-tyrosine methylamide.
Stanca-Kaposta EC1, Carçabal P, Cocinero EJ, Hurtado P, Simons JP. J Phys Chem B. 2013 Jul 11;117(27):8135-42. doi: 10.1021/jp404527s. Epub 2013 Jun 28.
The nature of carbohydrate binding first to p-hydroxy toluene and then the capped amino acid, N-acetyl l-tyrosine methyl amide (AcTyrNHMe), has been investigated in a solvent-free environment under molecular beam conditions. A combination of double resonance IR-UV spectroscopy and quantum chemical calculations has established the structures of complexes with the α and β anomers of methyl d-gluco- and d-galacto- and l-fucopyranosides (α/βMeGlc, MeGal, MeFuc). The new results, when combined with dispersion-corrected DFT calculations, reveal gas phase structures which are dominated by hydrogen bonding but also with evidence of CH-π bonded interactions in complexes with α/βMeGal. These adopt stacked intermolecular structures in marked contrast to those with α/βMeGlc; p-OH → O bonds linking AcTyrNHMe, or p-hydroxy toluene, to the carbohydrate provide an anchor that facilitates further binding, both through OH → O and NH → O hydrogen bonds to the peptide backbone and through CH-π dispersion interactions with the aromatic side group.
2.Ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine and N-acetyltryptophan in aqueous solution: proton-coupled electron transfer versus electron transfer.
Zhang Y1, Yuan S, Lu R, Yu A. J Phys Chem B. 2013 Jun 20;117(24):7308-16. doi: 10.1021/jp404466f. Epub 2013 Jun 11.
We studied the ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine (AcTyr) and N-acetyltryptophan (AcTrp) in aqueous solution with femtosecond transient absorption spectroscopy. We found that the charge-transfer rate between Atto655 and AcTyr is about 240 times smaller than that between Atto655 and AcTrp. The pH value and D2O dependences of the excited-state decay kinetics of Atto655 in the presence of AcTyr and AcTrp reveal that the quenching of Atto655 fluorescence by AcTyr in aqueous solution is via a proton-coupled electron-transfer (PCET) process and that the quenching of Atto655 fluorescence by AcTrp in aqueous solution is via an electron-transfer process. With the version of the semiclassical Marcus ET theory, we derived that the electronic coupling constant for the PCET reaction between Atto655 and AcTyr in aqueous solution is 8.3 cm(-1), indicating that the PCET reaction between Atto655 and AcTyr in aqueous solution is nonadiabatic.
