Emilio Scamporrino

Synthesis and Characterization of Uncharged Water-Soluble Star Polymers Containing a Porphyrin Core

Uncharged water-soluble porphyrins were prepared by reaction between tetrakis(p-hydroxy-phenyl)porphyrin and chlorinated poly(ethylen glycol) methyl ethers of different molecular weights. Water-solubility was achieved by binding four poly(ethylene glycol) branches to a porphyrin core to give star polymers with molecular weights in the range 2000-21 000 Da. Structural characterization of these star polymers was performed by means of gel permeation chromatography, NMR spectroscopy, and MALDI-TOF analysis.

Effect of combined changes in delayed extraction time and potential gradient on the mass resolution and ion discrimination in the analysis of polydisperse polymers and polymer blends by delayed extraction matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Data reported here show that, in the delayed extraction matrix-assisted laser desorption/ionization time-of-flight (DE-MALDI-TOF) mass spectrometric analysis of synthetic polydisperse polymers, different experimental conditions of spectral recording are required to optimize the signal in all the m/z regions of the spectrum. The effect of combined changes in delay time and grid voltage % values on both mass resolution and mass accuracy of DE spectra of a polyethylene glycol sample (PEG(mix), with a well-defined molar distribution of its components) is discussed. The necessity of a compromise between the values of these two parameters is shown. Furthermore, the occurrence of analyte discrimination, which can invalidate the composition analysis especially in the case of polymer blends, is demonstrated. Copyright 1999 John Wiley & Sons, Ltd.

A NEW PROCEDURE FOR QUANTITATIVE CORRECTION OF MATRIX-ASSISTED LASER DESORPTION/IONIZATION TIME-OF-FLIGHT MASS SPECTROMETRIC RESPONSE

A simple procedure for the correction of the decreasing detection response in a Matrix-assisted laser desorption/Ionization time-of-flight (MALDI-TOF) mass spectrum with increasing ion mass is reported. On the basis of the experimental MALDI-TOF mass spectrum of a mixture of four polymethylmethacrylate (PMMA) standards (molecular masses in the range 4–100 kDa), present in equal molar abundance, an equation describing the MALDI-TOF response has been derived. This equation has been used to correct any subsequently recorded MALDI spectrum. As an example, the procedure has been applied here to normalize the MALDI-TOF mass spectrum of a 1,20-di(bisphenoxy-A)eicosane based copolyformal (I) containing porphyrin units in the main chain. # 1998 John Wiley & Sons, Ltd.

Role of the hydrogen-bond in porphyrin J-aggregates

J-aggregates of conjugated molecules are known to be the result of π–π stacking and hydrophobic and electrostatic interactions with hydrogen bonding providing stabilization. The present study on porphyrin derivatives, thanks to the absence of chargeable groups, helps to focus the attention on the effect of the hydrogen-bonding interactions. Moreover, the aqueous medium, causing a competitive effect for the formation of H-bonds with porphyrins, strengthens the role of the inter-porphyrin hydrogen bonding contribution in the self-assembly. Herein it is proven, through UV-vis and time-resolved fluorescence measurements, that the presence of peripheral OH groups, able to form hydrogen bonds with the nitrogen atoms of the macrocycle, has an important role in driving towards the formation of J-type aggregates rather than having only a stabilization effect. Indeed, although the porphyrin derivative with peripheral OH-to-OCH2CH3 group substitution gives rise to aggregates with almost comparable size, as indicated by dynamic light scattering, in the resulting structures porphyrins take an H-type arrangement.

Uncharged water-soluble porphyrin tweezers as a supramolecular sensor for α-amino acids

The binding between uncharged cobalt porphyrin tweezers and L-amino acids in aqueous solutions is studied by means of UV–vis and circular dichroism spectroscopy. By varying the length of the aliphatic bridge between the two porphyrin units, the number of cobalt ions in the porphyrin cores and the pH of the solution, the chirality induction phenomenon has been investigated. The binding of the amino acid to the porphyrin seems to occur via a coordination mechanism between the metal and the nitrogen of the amino group; the steric, hydrophobic and π–π interactions operate to stabilize the complexes. The chirogenesis displays an opposite behaviour in the presence of aromatic guests with respect to the non-aromatic ones. Moreover, the UV–vis and the induced circular dichroism spectral changes suggest that the amino acid arrangement in the tweezers is determined by many factors, so that, unlike in organic solvent, the porphyrin tweezers in aqueous solution allow for two different arrangements of the same aromatic amino acid. The experimental findings indicate that the porphyrins tweezers reported in the paper are promising in opening perspectives toward their application as a selective molecular sensor in aqueous solutions directly.

Identification of pyrolysis products of polysulphides by collisionally activated decomposition linked scanning mass spectrometry

Abstract Collisionally activated decomposition (CAD) linked scan mass spectra have been used in the identification of pyrolysis products obtained by the direct pyrolysis of some polysulphides in a mass spectrometer. Structures were determined by comparing the CAD spectra of the pyrolysis products with those of authentic compounds. The results are of help in elucidating the thermal degradation mechanisms that occur in the pyrolysis of the polysulphides investigated.

Synthesis and structural characterization by fast-atom bombardment mass spectrometry of exactly alternating copolyesters containing photolabile units in the main chain

Abstract Polycondensation between bis(2-hydroxymethylenephenyl)adipate, bis(3-hydroxypropylene)terephthalate and bis(2-hydroxyethylene)terephthalate with α-truxilloyl chloride were performed to obtain exactly alternating copolyesters containing photoreactive cyclobutane units in the main chain. The resulting copolyesters were characterized by fast-atom bombardment (f.a.b.) mass spectrometry, and the structure of the oligomers detected in the f.a.b.(+) and f.a.b.(−) mass spectra allowed confirmation of the alternating sequence present in the copolymers.

Thermal decomposition processes in alphatic-aromatic polysulphides investigated by electron impact and chemical ionization mass spectrometry

Abstract The thermal degradation of four aliphatic-aromatic polysulphides was investigated by direct pyrolysis in the ion source of a mass spectrometer operating both in electron impact and chemical ionization modes. The overall evidence indicates that the primary thermal decomposition processes of these polysulphides yield cyclic sulphides or disulphides according to a backbiting process initiated at the SH ends. A β-CH hydrogen transfer process occurring in parallel with the former produces compounds with both olefin and SH end-groups.

Reading of Protein Surfaces in the Native State at Micromolar Concentrations by a Chirogenetic Porphyrin Probe

The recognition of some globular proteins was carried out in aqueous solution, at micromolar concentrations, by using an uncharged symmetrical cobalt-porphyrin (Co-P). By means of UV/Vis, induced circular dichroism, and fluorescence spectroscopy techniques, it was ascertained that the interactions between specific amino acid residues and Co-P occurred on the protein surface. In particular, spectroscopic evidence showed the formation of supramolecular complexes without disruption of the native structure of the proteins and, furthermore, that signal changes were characteristic of each Co-P/protein system, so that they could be used as a highly sensitive analytical tool for protein recognition. The relative association constants were proportional to the protein molecular masses (and then to the number of amino acid residues).

Copper(II) assisted self-Assembly of functionalized β-Cyclodextrins with β-Alanyl-l-histidine

Abstract A combined UV–visible, CD and ESI-MS spectroscopic approach has been followed to obtain the speciation and the bonding details of copper(II) complexes with β-cyclodextrins functionalized by means of the bio-active peptide β-alanyl- l -histidine (carnosine). A new metal-assisted self-assembled system of bifunctionalized β-cyclodextrins has been shown to exist.