Roberto Fornasier

Very strong binding and mode of complexation of water-soluble porphyrins with a permethylated β-cyclodextrin

Abstract Heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin in a pH=7.0 aqueous solution binds meso -tetrakis(4-carboxyphenyl) porphyrin and its zinc complex to yield 2:1 complexes with exceptionally high binding constants. The mode of binding, involving the inclusion of two opposite aryl groups in the cyclodextrin cavity, is clearly defined by a detailed NMR analysis.

Functional micellar catalysis. Part 3. —Quantitative analysis of the catalytic effects due to functional micelles and comicelles

The kinetic treatment of reactions catalysed by functional micelles and comicelles made up of chemically inert and functional surfactants, based on the pseudophase separation approach, allows the evaluation of the parameters defining the catalytic phenomena. The rate enhancements of activated ester hydrolysis due to cationic micelles of previously described functional surfactants, when compared to those due to analogous non-micellar model compounds, can be mainly accounted for by concentration and electrostatic effects. Desolvation and other medium effects on anionic micellar functions are not a relevant source of rate enhancement. The merits of comicellar solutions for the analysis under standard conditions of the catalytic effectiveness of a variety of functional surfactants are also presented.

Electrochemical reduction of carbonyl compounds in aqueous media in the presence of β-cyclodextrin. Reduction of acetophenone and p-methoxyacetophenone in alkaline solution

Abstract The electrochemical reduction of acetophenone, 1, and 4-methoxy-acetophenone, 2, has been investigated in aqueous alkaline solutions, on mercury electrode, in the absence and in the presence of β-cyclodextrin (β-CD). Macroelectrolyses afforded mixtures of d,l and meso pinacols (head-to-head dimers) as preferential products and, in the case of 1, also head-to-tail dimers. These dimers showed some optical activity (enantiomeric excess of ca 24% for each diastereoisomer) when obtained by reduction in the presence of β-CD, whereas d,l pinacols did not. The same results were obtained by reduction of pre-formed 1:1 complexes with β-CD. A mechanism involving dimerization of radical anions is proposed for the formation of both type of dimers, and the asymmetric induction observed in the head-to-tail dimerization products is attributed to chiral effects exerted by β-CD on the guest molecules in this particular process.

Synthesis, characterization and chemisorption on gold of a β-cyclodextrin–lipoic acid conjugate

Abstract Mono-6-lipoyl-amido-2,3,6- O -permethyl-β-cyclodextrin, TMβCDLA, was synthesized in 79% isolated yield by coupling the mono-6-amino-permethyl-β-cyclodextrin with lipoic acid in the presence of 1-(3-dimethylamino)ethyl carbodiimide. The identity of cyclodextrin–lipoic acid conjugate was confirmed by NMR spectroscopy and electrospray mass spectrometry. Chemiadsorption of TMβCDLA on colloidal gold was shown to occur by colloid flocculation test analysis.

Capillary electrophoresis behavior of water-soluble anionic porphyrins in the presence of β-cyclodextrin and its O-methylated derivatives

The electrophoretic behavior of water‐soluble anionic porphyrins, such as meso‐tetrakis(4‐carboxyphenyl) porphyrin (TCPP), meso‐tetrakis(4‐sulfonatophenyl) porphyrin (TSPP) and its zinc(II) and copper(II) complexes (ZnTSPP and CuTSPP, respectively) has been studied by capillary zone electrophoresis using fused‐silica capillaries. The selectivity of the separation is strongly dependent on the type and concentration of β‐cyclodextrin (βCD) or the O‐methylated derivatives added to the background electrolyte. CuTSPP and TSPP can be separated using a pH 2.5 aqueous sodium phosphate buffer in the presence of 1 mM βCD. Resolution is poorer or absent employing alkylated βCDs, such as the heptakis (2, 6‐di‐O‐methyl)‐β‐cyclodextrin or the heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin, as additives. On the other hand, separation of TSPP from its copper and zinc complexes has been achieved using a pH 7.0 aqueous sodium phosphate buffer, in the presence of 0.75 mM βCD and 20% dimethyl sulfoxide (DMSO) as organic modifier. Under such conditions, the calibration curve for quantitative analysis of copper(II) was obtained. A rationale for the observed behavior will be presented and discussed on the basis of binding and protonation equilibria and a simple mathematical model.

Synthesis and spectroscopic properties of a water-soluble porphyrin-modified β-cyclodextrin compound

Abstract Reductive amination of 6-deoxy-6-formyl-β-cyclodextrin, 1 , with 5-( p -aminophenyl)-10,15,20-tris( p -sulfonatophenyl)porphyrin, 2 , in the presence of an excess of sodium cyanoborohydride, affords the water-soluble compound 3 (23% yield) as confirmed by NMR spectroscopy and mass spectrometry techniques.

Highly enantioselective cleavage of α-amino acid p-nitrophenyl esters by chiral metallomicelles

Chiral CuII-chelating micelles of 2-[hexadecyl-N,N-(2-hydroxypropyl)aminomethyl]pyridine are effective and remarkably enantioselective catalysts for the hydrolytic cleavage of p-nitrophenyl esters of α-amino acids.

Functional micellar catalysis. Part 8. Catalysis of the hydrolysis of p-nitrophenyl picolinate by metal-chelating micelles containing copper(II) or zinc(II)

The kinetic analysis of the esterolysis of p-nitrophenyl picolinate in neutral aqueous solutions of Cu2+ and Zn2+ in the presence of co-micelles made up of cetyltrimethylammonium bromide and either 6-(myristoylamido) methylpyridine-2-carboxylic acid (1) or 6-(myristoylamido)methyl-2-hydroxymethyl-pyridine (2) is reported. The results strongly indicate the formation of reactive micellar ternary complexes composed of metal ion, (1) or (2), and the substrate. The higher reactivity observed with co-micelles of (2) than that with those of (1) suggests that the metal ion in the ternary complex with (2) acts as a template for an intracomplex nucleophilic attack of the activated hydroxy function of (2) on the carbonyl of p-nitrophenyl picolinate.

Asymmetric induction in the borohydride reduction of carbonyl compounds by means of chiral phase-transfer catalysts. Part 2

Reaction of carbonyl compounds with sodium borohydride in a two-phase system, in the presence of chiral ammonium salts containing a secondary hydroxy-group affords the corresponding carbinols with 0–32% enantiomeric excess. The optical yields are higher when the hydroxy group is β to the ‘onium’ function and the catalyst is conformationally more rigid.

The crystal structure of the 1:1 inclusion complex of β-cyclodextrin with squaric acid

The crystal and molecular structure of the 1:1 inclusion complex of beta-cyclodextrin (cyclomaltoheptaose) with squaric acid (3,4-dihydroxycyclobutene-1,2-dione) was determined by X-ray diffraction. The complex crystallizes in the monoclinic P2(1) space group and belongs to the monomeric cage-type, characterized by a herringbone-like packing motif. Co-crystallized water molecules are present on seven sites, of which six are fully occupied. The guest molecule is placed inside the beta-cyclodextrin cavity, perpendicular to the plane defined by the glycosidic O-4n atoms, and held in place by direct and water-mediated hydrogen bonds mainly involving symmetry-related beta-cyclodextrin molecules. The accommodation of the planar guest molecule into the beta-cyclodextrin cavity determines a significant distortion of the latter from the sevenfold symmetry.