Characterization of poly[(R)-3-hydroxybutyrate-co-epsilon-caprolactone] copolymers by matrix-assisted laser desorption/ionization time-of-flight and electrospray ionization mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) of narrowly dispersed molecular weight gel permeation chromatography (GPC) fractions was used to characterize random and microblock poly[(R)-3-hydroxybutyrate-co-epsilon-caprolactone] [P(HB-co-CL)] copolymers obtained via the acid-catalyzed transesterification of the corresponding homopolymers, poly([(R)-3-hydroxybutyrate] (PHB) and poly(epsilon-caprolactone) (PCL). High-quality mass spectra were obtained, which made it possible to establish the nature of the polymer end groups. Besides the carboxylic termination, two other moieties were found: alcoholic and tosyl end groups. MALDI mass spectra of CL-rich samples possessed mostly tosyl end groups, while HB-rich samples possessed mostly alcoholic end groups, showing that the tosyl moiety is linked prevalently to CL terminal units. The higher resolution of electrospray ionization (ESI) mass spectra of lower molecular weight GPC fractions permitted the identification of the different oligomer species hypothesized in the assignment of the corresponding MALDI mass spectra. Partial methanolysis of these copolymers was explored as a method of producing mixed HB-CL oligomers to be utilized as new synthons, possessing a minor number of chiral centers from those obtained from hydrolysis of biotechnologically synthesized poly(hydroxyalkanoates) (PHAs).     

Facile light-triggered one-step synthesis of small and stable platinum nanoparticles in an aqueous medium from a beta-cyclodextrin host-guest inclusion complex

It is shown, for the first time, that small (ca. 2 nm) and stable platinum nanoparticles can be easily obtained in one step through visible light irradiation of a host-guest inclusion complex between beta-cyclodextrin and platinum acetylacetonate in a water solution. The exclusive control of the reaction by an external trigger, the removal of the undesired reaction products without any manipulation of the sample, and the absence of ionic repulsions between the metal nanoparticles represent the main remarkable advantages offered by this synthetic methodology.     

Direct mass spectrometry of polymers. XIII.. Thermal fragmentation processes in copoly-α-amino acids

The thermal fragmentation processes in L-Proline—Sarcosine and in L-Proline—L-Alanine copolymers have been investigated by direct pyrolysis—mass spectrometry. The mass spectral data show that proline—sarcosine copolymers decompose in three steps, yielding cyclic oligomers. The first step is characterized by the presence of the Sar—Sar, Sar—Pro, and Pro—Pro cyclic dimers. In the second step the formation of several series of cyclic oligomers up to nonamers—decamers can be observed, while the third step of thermal decomposition process leads to the almost exclusive formation of Pro—Pro cyclic dimer. The proline—alanine copolymers, instead, show a single-step thermal degradation process leading to the formation both of cyclic oligomers and compounds with olefin and nitrile end-groups. Our results show that the thermal decompostion of alanine units is affected by the neighboring units along the polymer chain. Sarcosine units act as thermally labile probes, causing the selective thermal cleavage of the Pro—Sar copolymer.     

pH Effects on the Spectroscopic and Photochemical Behavior of Enoxacin: A Steady-State and Time-Resolved Study

The spectroscopic and photochemical behavior of Enoxacin (ENX), 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-1,8-naphthyridine-3-carboxylic acid, has been investigated in aqueous solutions between pH 3.5 and pH 12. The absorption and emission properties of ENX are strongly affected by pH. The fluorescence quantum yield, 4 x 10⁻³ at pH 3.5, increases by a factor of two on going to neutral pH while a strong reduction is observed at alkaline pH. The photodegradation quantum yield also depends on pH, being maximum in neutral conditions ( ca 0.04). Nanosecond flash photolysis experiments confirm that the yield of absorbing transients is maximum at neutral pH while it decreases to zero at acid and alkaline pH. These results indicate that both the dissociation of the carboxylic group and the protonation of the piperazinyl residues are key steps for the formation of the photochemically active form of ENX. Loss of F⁻ by heterolytic cleavage of the C–F bond is proposed to occur from the triplet state of the zwitterion with formation of a carbocation. A path for the evolution of this intermediate to the final product is also proposed.     

Photophysical Properties of Rufloxacin in Neutral Aqueous Solution

The photophysical properties of rufloxacin, 9-fluoro-2_r3-dihydro-10-(4-methyl-l-pyrazinyl)-7-oxo-7-H-pyri-do[l,2,3-de]-l,4-benzothiazin-6-carboxylic acid, a fluoroquinolone antibacterial drug exhibiting photosensitizing action toward biological substrates, were studied in aqueous solutions at neutral pH. The lowest excited electronic states of the zwitterion were characterized by both experimental techniques and theoretical methods. Steady-state and time-resolved emission, triplet-state absorption and singlet oxygen production were investigated. The results indicate that the lowest excited singlet is a fluorescent, relatively long-lived state (φ_r= 0.075, T_r? 4.5 ns) with an efficient intersystem crossing to the triplet manifold (φ_isc? 0-⁷)- The lowest triplet is a long-lived state (T_T? 10 μs at 295 K in 0.01 M phosphate buffer), with properties that make it a good candidate for being the precursor of the photodecarboxylation of the drug. It is quenched by oxygen at a rate of 1.7 times 10⁹M^-1 s-¹ and singlet oxygen is formed with a quantum yield of 0.32 in air-saturated solutions.     

Coordination properties of 3-functionalized beta-cyclodextrins. Thermodynamic stereoselectivity of copper(II) complexes of the A,B-diamino derivative and its exploitation in LECE

The bis-amino AB derivative of beta-cyclodextrin on the secondary rim was synthesised and spectroscopically characterised by different techniques. Its binary systems both with protons and copper(II) were thermodynamically characterised by pH-metric potentiometry. In addition the ternary systems with each of the enantiomers of tryptophan and alanine were investigated. A thermodynamic stereoselectivity was observed for the tryptophan enantiomers and this was exploited to separate them by capillary electrophoresis through a ligand exchange mechanism (LECE). LECE separation of racemates of phenylalanine and tyrosine was also obtained.     

Photochemical synthesis of copper nanoparticles incorporated in poly(vinyl pyrrolidone)

The effect of the presence of poly(vinyl pyrrolidone) (PVP) on the copper nanoparticle formation, obtained by UV irradiation of ethanol solution of Cu(acac)₂ (acac = 2,4-pentanedionato), was investigated. At 254 nm, in conditions of light completely absorbed by complex, the PVP exhibited protective and stabilizing effects, as shown by the formation of a colloidal copper solution and by a block of the heterogeneous process, which leads to thin film formation on the quartz walls. The colloidal solution was tested for several months by plasmon position and it was found that it remained unaltered in inert atmosphere, but returned to the starting complex on contact with air. The PVP ability to control the particle size was investigated by carrying out photoreduction sensitized by Hacac at 254 and 300 nm, in the presence of PVP concentration varying from 0 to 0.2 M. In this range it was possible to obtain copper nanoparticles of dimensions decreasing from 30 to 4 nm. Besides this, the PVP (0.005–0.05 M) role as sensitizer was investigated by irradiating solutions of Cu(acac)₂ at 300 nm which is an inactive wavelength for copper reduction by direct light absorption. It was found that the PVP was an efficient sensitizer of the copper photoreduction. The nanoparticles were characterized by plasmon band, Trasmission Electron Microscope (TEM) as well as Dynamic Light Scattering (DSL) analysis. The overall results evidence the advantages of the PVP use in the nanoparticle copper formation through the photochemical technique such as the exclusive formation of colloidal copper, their size control, stable colloidal solution and complete return to the starting complex.     

Human proteome enhancement: high-recovery method and improved two-dimensional map of colostral fat globule membrane proteins.

The human milk fat globule membrane protein composition is still largely unknown, although it counts for 2-4% of the total milk protein content and contains several important biologically active components. The aim of this work was to create a two-dimensional electrophoresis (2-DE) map of the human milk fat globule membrane proteins, both integral and membrane-associated, and to identify and characterize as many protein components as possible. A new protocol for the solubilization and extraction of the human milk fat globule membrane proteins with a double extraction procedure is presented, and the results compared with the extraction methods reported in the literature. The proteins were separated, in the first dimension, by isoelectric focusing (IEF) in the pH range 3-10 on strips of 13 cm length and, in the second dimension, by Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) on 11.5% T homogeneous gels. A reproducible 2-DE map of integral and membrane-associated proteins was obtained and the first 23 spots, representing the major components, were identified by matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometric analysis and/or by amino acid sequencing.