Premium
Theoretical and Experimental Study of the Adsorption of Neutral Glycine on Silica from the Gas Phase
Author(s) -
Lomenech C.,
Bery G.,
Costa D.,
Stievano L.,
Lambert J. F.
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200400608
Subject(s) - silanol , bathochromic shift , chemistry , moiety , amine gas treating , organosilicon , adsorption , photochemistry , inorganic chemistry , stereochemistry , organic chemistry , catalysis , physics , quantum mechanics , fluorescence
The adsorption of neutral glycine onto amorphous silica was investigated both theoretically and experimentally. DFT calculations were performed at the BLYP‐631++G** level using a cluster approach. Several possible configurations involving the formation of H bonds between glycine and one, two, or three silanol groups (SiOH) were considered. The most favorable bonding of glycine with one silanol group (45 kJ mol −1 ) occurs through the COOH moiety, thus forming a cycle in which the CO group is an H‐bond acceptor whereas the acidic OH group is an H‐bond donor. With two or three silanol groups, additional H bonds are formed between the amine moiety and the silanol groups, which leads to an increased adsorption energy (70 and 80 kJ mol −1 for two and three silanol groups, respectively). Calculated ν CO , δ HNH , and δ HCH values are sensitive to the adsorption mode. A bathochromic shift of ν CO as compared to the ν CO of free glycine (calculated in the 1755–1790 cm −1 range) is found for glycine in interaction with silanol(s). The more H bonds are formed between the COOH moiety and silanol groups, the higher the bathochromic shift. For δ HNH , no shift is found for glycine adsorbed on one and two silanol groups (where the amine is either not bound or an H‐bond donor), whereas a bathochromic shift is calculated with three silanols when the amine moiety is an H‐bond acceptor. Experimental FTIR spectra performed at room temperature for glycine adsorbed at 160 °C on Aerosil amorphous silica exhibit bands at 1371, 1423, 1630, and 1699 cm −1 . The experimental/calculated frequencies have their best correspondence for glycine adsorbed on two silanol groups. It is important to note that the forms giving the best correspondence to experimental frequencies are the most stable ones.