engleski

Self-assembly of weakly acidic photoactive dyes in aqueous solution at varied pH and ionic strength

The amphiphilic photoactive molecules self-assembled in aqueous medium have drawn significant attention in the past years due to their unique photophysical properties both in biological and functional materials sciences. Such compounds have been investigated in a variety of application fields such as solar cell production, development of pharmaceutical formulations and biomedical applications (e.g. photodynamic therapy) [1-3]. However, the formation of aggregates changes their figures of merit, and in the first place the photophysical properties by affecting their ability to absorb and emit electromagnetic radiation. Therefore, it is important to investigate the relationship between the aggregation state of the self-assemblies (size and type), and the electrostatic charge at their surface which depends on the pK of the compound, the bulk solution pH and ionic strength. The poster presents an experimental methodology for the assessment of charge-structure relationship in the case of self-assembled weakly acidic or basic amphiphilic dyes. The studied molecules were synthesized by introduction via esterification of an aliphatic chain to some commercially available compounds that mimic the photoactive dyes: rhodamine B and Orange II. The size of the nanoparticles prepared by self-assembly of those molecules was measured by means of dynamic light scattering (DLS), as a function of pH, ionic strength and dye concentration. The critical micellization concentration (CMC) was measured in the pendant drop experiments for varied pH and ionic strength. The protonation speciation and surface charge was determined form the experimental proton binding isotherms measured in potentiometric and spectrophotometric titrations, also at varied ionic strengths. The interpretation of these measurements is proposed in terms of the established models for the self-assembly of ionic surfactants [4], whereby the obtained results should facilitate an evaluation of such dyes for the above mentioned applications. Acknowledgements: This work was supported by the European Fund for Regional Development and the Ministry of Science, Education and Sports of the Republic of Croatia under the project Research Infrastructure for Campus-based Laboratories at the University of Rijeka (grant numberRC.2.2.06-0001) [1] K. Hosomizu, M. Oodoi, T. Umeyama, Y. Matano, K. Yoshida, S. Isoda, M. Isosomppi, N. V. Tkachenko, H. Lemmetyinen, and H. Imahori, J. Phys. Chem. B, 2008, 112 (51), 16517. [2] H. Tajalli, A. Ghanadzadeh Gilani, M. S. Zakerhamidi, and M. Moghadam, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc., 2009, 72 (4), 697. [3] S. Svenson, Curr. Opin. Colloid Interface Sci., 2004, 9, (3–4), 201. [4] D. F. Evans and H. Wennerström, The colloidal domain : where physics, chemistry, biology, and technology meet. Wiley-VCH, 1999.

multivariate regression ; pK, model ; spectrophotometry ; UV/VIS ; porphyrin ; dye ; amphiphilic

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