Document Detail

Evidences of deprotonation of aromatic acids and amides adsorbed on silver colloids by Surface-Enhanced Raman Scattering.
MedLine Citation:
PMID:  22268552     Owner:  NLM     Status:  Publisher    
The Surface-Enhanced Raman Scattering (SERS) of benzoic acid/benzamide and salicylic acid/salicylamide on silver colloids show important wavenumber shifts with respect to the Raman spectrum of the band assigned to mode 1;ring when adsorbed on the metal surface (ca. +50 cm-1). In the case of the acids, this shift is originated by the deprotonation of the carboxylic group in agreement with the well known fact that aromatic acids are adsorbed on silver as carboxylates. However, the main conclusion of this work is that a similar behaviour is found for the respective amides that do not behave as acids in water solution. The here studied aromatic amides are adsorbed as azanions on silver nanoparticles even at pH 7 and link to the metal through the nitrogen and oxygen atoms of the ionized carboxamide group. This is a very surprising result given that amides are not significantly ionized even at pH 13-14. The deprotonation of these amides is not determined exclusively by the pH but it is mainly caused by the strong affinity of the anionic species to the metal. Therefore, the SERS must be cautiously used as a universal pH sensor if the adsorption occurs through the ionizable group. In order to support this conclusion, theoretical DFT force field calculations have been carried out, confirming that deprotonated benzamide and salicylamide interact with the metallic surface.
Jose Luis Castro; María Rosa López Ramírez; Juan Francisco Arenas; Juan Soto; Juan C Otero
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-1-23
Journal Detail:
Title:  Langmuir : the ACS journal of surfaces and colloids     Volume:  -     ISSN:  1520-5827     ISO Abbreviation:  -     Publication Date:  2012 Jan 
Date Detail:
Created Date:  2012-1-24     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9882736     Medline TA:  Langmuir     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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