SERRS spectra of cationic free-base porphyrin species adsorbed on laser ablated Ag colloids modiﬁed by mercaptoacetate spacers P. S ˇ mejkal a , B. Vlc ˇkova ´ a, * , M. Procha ´zka b , P. Mojzes ˇ b , J. Pﬂeger c a Department of Physical and Macromolecular Chemistry, Charles University, Hlavova 2030, 12840 Prague, Czech Republic b Institute of Physics, Charles University, Ke Karlovu 5, 12116 Prague 2, Czech Republic c Institute of Macromolecular Chemistry, Academy of Sciences of Czech Republic, Heyrovsky ´ sq. 2, 162 06 Prague 6, Czech Republic Received 24 August 1998; accepted 30 September 1998 Abstract Sodium mercaptoacetate and mercaptoacetic acid were tested as prospective spacers between the surface of Ag colloidal particles (prepared by laser ablation) and a chromophoric cationic adsorbate. Time-evolution of the SERRS signal, a cationic free base porphyrin, 5,10,15,20-tetrakis(1-methyl-4-pyridiniumyl)porphine (H 2 TMPyP) attached to the surface of laser-ablated Ag colloidal particles modiﬁed by adsorption of either sodium mercaptoacetate (MA), or mercaptoacetic acid (MAA) was measured on a 2 h time-scale and analyzed. Both MA and MAA either prevent or hinder the rapid conversion of H 2 TMPyP into AgTMPyP surface complex (spectrally identical with its synthetic analogue) observed upon adsorption of H 2 TMPyP on bare surfaces of laser-ablated Ag colloidal particles. A complete preservation of the native structure of H 2 TMPyP was achieved for systems with 1 × 10 -4 M MA and a several hours time-delay between the preparation of Ag colloid/MA system and addition of H 2 TMPyP. Modiﬁcation of the colloid by MAA prevents porphyrin metalation, however, it induces another kind of perturbation of the native structure of H 2 TMPyP.  1999 Elsevier Science B.V. All rights reserved. Keywords: SERS and SERRS spectroscopy; Laser-ablated Ag colloids; Spacers; Porphyrins 1. Introduction Modiﬁcation of Ag colloids by spacers is an efﬁ- cient way of obtaining SERRS spectra of the chemi- cally unperturbed chromophoric species [1]. Mercaptoalkanoic acids were successfully employed as spacers for the adsorption of cytochrome c [2], and mercaptoethanol for b -carotene [3]. In this study, we use a relatively simple cationic chromophoric adsor- bate, 5,10,15,20-tetrakis(1-methyl-4-pyridiniumyl)- porphine which was shown to undergo a rapid and complete metalation upon adsorption on a bare surface of the laser-ablated colloidal particles [4], as a probe of efﬁciency of sodium mercaptoacetate- and mercaptoacetic acid-based anionic spacers. 2. Experimental 2.1. Materials Sodium mercaptoacetate, (MA, 96%, Aldrich), mercaptoacetic acid (MAA, p.a., MERCK) and 5,10,15,20-tetrakis(1-methyl-4-pyridiniumyl)por- phine tosylate (H 2 TMPyP) (Aldrich) were employed. Deionized distilled water was used as solvent. Journal of Molecular Structure 482–483 (1999) 225–229 0022-2860/99/$ - see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0022-2860(98)00646-2 * Corresponding author. E-mail address: vlc@prfdec.natur.cuni.cz (B. Vlc ˇkova ´)