Theoretical study on the hydrophobic and hydrophilic hydration on large solutes: The case of phthalocyanines in water

A theoretical study on the hydration phenomena of three representative Phthalocyanines (Pcs): the metal-free, H2Pc, and the metal-containing, Cu-phthalocyanine, CuPc, and its soluble sulphonated derivative, [CuPc(SO3)4]4−, is presented. Structural and dynamic properties of molecular dynamics trajectories of these Pcs in solution were evaluated. The hydration shells of the Pcs were defined by means of spheroids adapted to the solute shape. Structural analysis of the axial region compared to the peripheral region indicates that there are no significant changes among the different macrocycles, but that of [CuPc(SO3)4]4−, where the polyoxoanion presence induces a typically hydrophilic hydration structure. The analyzed water dynamic properties cover mean residence times, translational and orientational diffusion coefficients, and hydrogen bond network. These properties allow a thorough discussion about the simultaneous existence of hydrophobic and hydrophilic hydration in these macrocycles, and indicate the trend of water structure to well define shells in the environment of hydrophobic solutes. The comparison between the structural and dynamical analysis of the hydration of the amphipathic [CuPc(SO3)4]4− and the non-soluble Cu–Pc shows a very weak coupling among the hydrophilic and hydrophobic fragments of the macrocycle. Quantitative results are employed to revisit the iceberg model proposed by Frank and Evans, leading to conclude that structure and dy- namics support a non-strict interpretation of the iceberg view, although the qualitative trends pointed out by the model are supported.Junta de Andalucía P11-FQM7607Ministerio de Ciencia e Innovación CTQ2008-0527

Modeling the interactions of phthalocyanines in water: From the Cu(II)-tetrasulphonate to the metal-free phthalocyanine

A quantum and statistical study on the effects of the ions Cu2+ and SO3− in the solvent structure around the metal-free phthalocyanine (H2Pc) is presented. We developed an ab initio interaction potential for the system CuPc–H2O based on quantum chemical calculations and studied its transferability to the H2Pc–H2O and [CuPc(SO3)4]4−–H2O interactions. The use of the molecular dynamics technique allows the determination of energetic and structural properties of CuPc, H2Pc, and [CuPc(SO3)4]4− in water and the understanding of the keys for the different behaviors of the three phthalocyanine (Pc) derivatives in water. The inclusion of the Cu2+ cation in the Pc structure reinforces the appearance of two axial water molecules and second-shell water molecules in the solvent structure, whereas the presence of SO3− anions implies a well defined hydration shell of about eight water molecules around them making the macrocycle soluble in water. Debye– Waller factors for axial water molecules have been obtained in order to examine the potential sensitivity of the extended x-ray absorption fine structure technique to detect the axial water molecules.Ministerio de Ciencia e Innovación de España-CTQ2008-0527