Absorption flattening as one cause of distortion of circular dichroism spectra of Delta-RuPhen(3) . H(2)TPPS complex

To extend the model that explains why and how much absorption flattening (AF) influences circular dichroism (CD) signals, we have investigated the interesting case of exciton CD in the Soret region of a noncovalent complex formed by (DRuPhen3) 21 and the tetraanionic porphyrin H2TPPS. Different concentrations have been studied by using an AF emulator and spectra simulation. The CD spectra of this compound occasionally show distortions in the solution sampling mode with the increase of concentration; the inhomogeneous distribution in the cell volume is due to aggregation and is the source of the AF effect. On the basis of these results, we conclude that AF is an important cause of distortions in CD spectra for D-RuPhen3 H2TPPS complexes and might affect the CD bands of other aggregated systems as wel

Single-Stranded Nucleic Acids As Templates For Porphyrin Assembly Formation

Resonance light scattering (RLS) and circular dichroism (CD) spectroscopies have been used to investigate the interactions of several cationic porphyrins with poly(dA) and poly(rA). Neither tetrakis(N-methylpyridinium-4-yl)porphin nor its zinc(II) derivative (H₂T4 and ZnT4) show any tendency to form extended porphyrin assemblies in the presence of poly(dA). However, the poly(dA) complex of CuT4 involves considerable porphyrin self-stacking. In the presence of poly(rA), only ZnT4 of these three porphyrin derivatives, fails to assemble. Differences in the interactions of trans-bis(N-methyl-pyridinium-4-yl)diphenylporphine (t-H₂Pagg) with these two single-stranded nucleic acid polymers are described. Whereas the porphyrin is capable of forming extended assemblies with either poly(dA) or poly(rA), increasing the salt concentration in the latter system results in a reversal of the induced circular dichroism spectrum in the Soret region indicating a conformational change of the porphyrin assembly

Kinetic investigation of porphyrin interaction with chiral templates reveals unexpected features of the induction and self-propagation mechanism of chiral memory

Kinetics of the porphyrin aggregation leading to a chiral memory system shows a remarkable "catalytic" effect of the noncovalent templates explaining their self-replication ability

Hierarchical self-assembly of water-soluble porphyrins

Hierarchy is a powerful and promising tool to rationally synthesize non-covalent complex species. In this paper we show two different examples of hierarchically driven aggregation processes allowing for the control of aggregation state or "shape" of the final species. In the first case we propose that water-soluble porphyrins presenting various protonation steps can follow kinetic routes alternative to the thermodynamic pathway; namely for each protonation step is allowed, in principle, an alternative kinetically driven homo-self-aggregation process. Our results indicate that the thermodynamic route leads to a monomeric, protonated final state, but the kinetic pathway ends with self-assemblies of the title porphyrin. The bias between the two final states can be easily pre-determined by going quickly or slowly throughout the thermodynamic-kinetic junction. The second case deals with the so-called "chiral memory" phenomenon. Also in this case the role of the kinetic control over the assembly process is remarkable. In particular, we have observed that self-aggregation of opposite charged, achiral porphyrins does not lead to induced chirality even if a chiral template is added after their aggregation. The final aggregates are kinetically inert, mostly because stabilized by a network of electrostatic interactions between net charges. However, if the two supramolecular components are mixed in the presence of a chiral template, then an induced circular dichroism signal (ICD) appears in the Soret region (the main absorption feature of porphyrins in the visible region whose maximum and intensity are strongly affected by the aggregation state). Removal of the template does not significantly affect the intensity of the ICD: the inert aggregates have memorized the chiral template shape. Remarkably, these species - now inherently chiral - act as very efficient templates for self-aggregation of additional non-chiral porphyrins. © 2004 Elsevier B.V. All rights reserved

Assembly of positively charged porphyrins driven by metal ions: A novel polymeric arrangement of cationic metalloporphyrin

Crystallization and crystal structure analysis of chlorohydrates of either tri- or tetracationic copper porphyrins, namely copper(5,-10,15-tris(N-methyl- pyridinium-4-yl)-20-pyridine-porphyrinato) (1) and copper(5,10,15,20-tetrakis(N- methyl-pyridinium-4-yl)-porphyrinato), respectively, have been performed. Two crystalline forms, 2 and 3, of the latter have been obtained under different preparation conditions. A novel kind of slipped stack chains of these cationic porphyrins has been detected. The pronounced saddle conformation of the porphyrin reveals π-like interactions between the peripheral pyrrole C b-Cb "double bond" and the metal center. DFT calculations on the isolated porphyrins clearly show the HOMO orbitals with the correct topology to yield a bonding interaction among the stacked porphyrin units. To our knowledge, a slipped stack chain of positively charged porphyrins has never been previously reported, if the arrangement of faced units of monocationic metalloporphyrins or phthalocyanins is excluded

Noncovalent synthesis in aqueous solution and spectroscopic characterization of multi-porphyrin complexes

The interactions of the tetracationic meso-tetrakis(N-methyl-4-pyridyl)porphyrin (H(2)TMPyP) and its metallo derivatives (MTMPyP) (where M=copper(II), zinc(II), and gold(III) with the octa-anionic form (at neutral pH) of 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(hydroxycarbonylmethoxy)calix[4]arene (C(4)TsTc) lead to a series of complex species whose stoichiometry and porphyrin sequence can be easily tuned. Crystallographic, spectroscopic, and diffusion NMR studies converge towards a common picture in which a central 1:4 porphyrin/calixarene unit serves as a template for the formation of more complex species. These species arise by successive, stepwise addition of single porphyrin molecules above and below the plane of the 1:4 central core to ultimately give a 7:4 complex. Noticeably, the stoichiometry of the various complex species corresponds to the actual concentration ratio of porphyrins and calixarenes in solution allowing the stoichiometry of these species to be easily tuned. This behavior and the remarkable stability of these species allow homo-porphyrin and hetero-(metallo)porphyrin species to be formed with control of not only the stoichiometry but also the sequence of the porphyrin array. The flexibility and ease of this approach permit, in principle, the design and synthesis of porphyrin arrays for predetermined purposes. For example, we have shown that it is very easy to design and obtain mixed porphyrin species in which a foreseen photoinduced electron-transfer is indeed observed