Microscopy of large-scale porphyrin aggregates formed from protonated TPP dimers in water – organic solutions Alexander V. Udal’tsov a, * , Masatoshi Tosaka b , Gerd Kaupp c a Institute of Biology, Komi Science Center, UrB RAS, Russian Federation b Institute for Chemical Research, Kyoto University, Japan c Organic Chemistry I, University of Oldenburg, Germany Received 30 August 2002; revised 20 May 2003; accepted 12 June 2003 Abstract Properties of porphyrin aggregates were investigated by absorption spectroscopy (UV – Vis and IR) in water – tetrahydrofuran (THF) solutions in the presence of different concentrations of HCl. The morphology of the aggregates was observed by scanning electron microscopy (SEM) and atomic force microscopy in thin films. A new protonated meso-tetraphenylporphine (TPP) form that shows characteristic absorptions in the UV – Vis spectra was found in the aggregated porphyrin in the presence of 2N HCl. Two types of changes with time were observed in these spectra, one of which is due to sticking together of the porphyrin aggregates. The second is associated with the formation of complexes between the protonated TPP dimer with l max ¼ 465 nm and metal ions that are probably leached out from the support by the acid. IR spectra of porphyrin aggregates prepared in the presence of different concentrations of HCl show huge water contents in the thin films and different characteristics of the water bound in the aggregates. Porphyrin aggregates prepared at different concentrations of HCl exhibited different surface properties. TPP aggregates prepared in the presence of 0.4N HCl and observed by SEM exhibit smooth surfaces over ranges of several micrometers. TPP aggregates prepared in the presence of 2N HCl form a continuous thin layer with 3 – 5 mm wide domains that consist of submicroscopic grains. These appear to be the result of 200 – 400 nm wide spherical particles that stick together. q 2003 Elsevier B.V. All rights reserved. Keywords: Protonated porphyrin; Dimers; Aggregates; Scanning electron microscopy; Atomic force microscopy 1. Introduction Atomic force microscopy (AFM) is widely used for the investigation of various biological and chemical objects and their surface structures [1–9]. Sometimes the study of a polymer surface can be a little difficult as in the case of polyethylene because the surface is soft apparently due to water adsorbed to the polymer. Large-scale porphyrin aggregates and water form unstable structures that are surrounded by a solvate cover. This type of aggregation was recently found in solution by absorption spectroscopy and the porphyrin aggregates were observed by scanning electron microscopy (SEM) in thin films [10]. It was proposed that porphyrin aggregates were formed from protonated meso-tetraphenylporphine (TPP) dimers in water – organic solutions when the hydrophobic 0022-2860/03/$ - see front matter q 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0022-2860(03)00412-5 Journal of Molecular Structure 660 (2003) 15–23 www.elsevier.com/locate/molstruc * Corresponding author. Address: Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, Moscow 119899, Russian Federation. Fax: þ7-95-939-4658. E-mail address: alevet@rol.ru (A.V. Udal’tsov).