Uncharged Water-Soluble Co(II)−Porphyrin:  A Receptor for Aromatic α-Amino Acids

Abstract

Changes in the UV-vis spectra and induced circular dichroism (ICD) signals observed, in correspondence with the porphyrin Soret region, for aqueous solutions of achiral 5,10,15,20-tetrakis{p-[omega-methoxy poly(oxy-ethylene)]phenyl}porphyrin cobalt (II) (Co-P) and aromatic alpha-L-amino acids (Trp and Phe) give direct evidence for the coordination between the Co-P and amino acids. Considering that Co-P, besides the Co atom (one-fixation-point system), does not contain in the molecule active ligand groups and that no ICD signals have been observed in the case of Co-P/Ala, it has been concluded that hydrophobic interactions or stacking interactions between the aromatic rings of the porphyrin and those of Trp or Phe, acting as further amino acid (AA) fixation points, can strongly reduce the mobility of the chiral guest, thus permitting the generation of ICD signals. The effects of changes of both pH (in the range 2-9) and amino acid structure on the ICD phenomenon have also been investigated. In particular, the following have been observed: (i) strong ICD signals for all of the Co-P/N-acetyl amino acid aqueous solutions at pH 7, (ii) an unexpected ICD band with a bisignate form for the Co-P/Ala solution at pH 9 after long aging, and (iii) an opposite ICD signal when alpha-D-Phe and alpha-D-Trp enantiomers have been used. The data reported in this paper show how the binding mechanism between receptor and AAs changes by modulating properly the pH or the molecular structures and indicate that in these aqueous solutions the coordination Co-N is not the fundamental mechanism giving rise to the formation of the complexes and that the binding can be driven by hydrophobic interactions. These occurrences, through the analysis of the spectroscopic response (and, in particular, the form of the ICD band), can allow the recognition of AAs.

Uncharged Water‐Soluble Metal‐Bis‐Porphyrins Like Molecular Tweezers for Amino Acids

“…As an example, Soret and Q regions of the spectra of aqueous (at pH 7) and THF solutions of pure (H 2 P)-CH 2 -(H 2 P) and of its Co and Zn metal derivatives are shown in Figure 3(a) and 3(b), respectively (other pertinent values are reassumed in Table S2 of Supporting Information). As previously reported for monoporphyrin compounds, [24] UV-vis spectra indicate an evident change in the position, shape and intensity of the Soret band as a function of the metal inserted in the porphyrin core. Also the spectral regions of the Q-bands are significantly modified with the disappearance of some signals and the shift of the maximum absorption wavelengths (l max ) of the remaining peaks.…”

“…Molecular aggregation of these compounds in aqueous solutions [22,23] and modification of their spectroscopic properties (NMR, UV-vis and circular dichroism (CD) in correspondence with the porphyrin Soret band) upon treatment with aliphatic and aromatic a-L-AAs, oligopeptides and/or proteins have been studied. [24,25] In the present work, a similar synthetic procedure was adopted to prepare uncharged water-soluble bisporphyrins I whose use as molecular receptor of AAs has also been studied.…”

Phthalocyanine‐Cored Star‐Shaped Polystyrene for Nano Floating Gate in Nonvolatile Organic Transistor Memory Device

“…[ 1 ] One of the most promising emerging trends is organic fi eldeffect transistor (OFET) memory, which has a nondestructive read-out memory cell system with multi-bit storage and an arm polymers, possesses unique properties derived from the 3D topology and has attracted much attention in materials science. [ 28 ] In particular, aromatic macrocycles, such as porphyrins and phthalocyanines (Pcs), have been incorporated as functional cores in star polymers owing to their attractive optical and electrical properties, [ 28,29 ] and they have investigated for applications in sensors, [ 30 ] optoelectronic devices, [ 31,32 ] photodynamic therapy, [ 33 ] and drug delivery. [ 34 ] In such star polymers, functional cores can be isolated and dispersed in various media through the surrounding polymer materials.…”

A new water soluble Zn‐salophen derivative as a receptor for α‐aminoacids: Unexpected chiral discrimination

“…Although the presence of free charges does not seem to influence the general properties of these compounds, it is to be expected that anionic pendants or anionic counterions would compete with the target species for binding at the metal center. For this reason, it seemed more desirable to look for derivatives in which the presence of uncharged hydrophilic 18 and biocompatible units can achieve the goal of making them hydrosoluble.…”