NMR spectroscopy and MALDI-TOF MS characterisation of end-functionalised PVP oligomers prepared with different esters as chain transfer agents

Ester-functionalised poly(1-vinylpyrrolidin-2-one) (PVP) oligomers obtained by radical polymerisation in methyl propionate, diethyl malonate and diethyl 2-methylmalonate were characterised by NMR spectroscopy, and MALDI-TOF mass spectrometry. The chain-transfer constants were determined as 5.54 x 10(-4), 1.22 x 10(-3) and 1.70 x 10(-2), respectively, by measuring the variation of the number-average molecular weight on conversion. These values were compared with those of methyl isobutyrate (1.65 x 10(-3)) and ethyl lactate (1.03 x 10(-2)), which had been previously determined. A clear dependence was found on the reactivity of the mobile hydrogen atoms alpha with the ester group. All of the macromolecules carried a single ester function. Therefore, the re-initiation step by the CTA-derived radicals overwhelmingly prevailed over initiation by the primary radicals.     

Changes in ultraviolet absorbance and hence in protective efficacy against lipid peroxidation of organic sunscreens after UVA irradiation

Owing to the spectral distribution of solar UV, the UVA component of sunlight is now believed to be the main cause of photoaging and photocarcinogenesis and is much more effective than UVB in inducing peroxidative damage. Consequently, most skin care cosmetic products now include UVA filters in their formulations along with UVB filters. These modern sunscreens should provide and maintain their initial absorbance, hence protection, throughout the entire period of exposure to sunlight. However, not all UVA and UVB filters are sufficiently photostable. In this study, we examine the correlation between the photochemical degradation of sunscreen agents under UVA irradiation, with particular reference to the UVA-absorber 4-tert-butyl-4'-methoxydibenzoylmethane, alone and in combination with other organic UV filters (2-ethylhexyl 4 methoxycinnamate and 2-ethylhexyl 2-cyano-3,3-diphenylacrylate) and their ability to prevent UVA-induced lipid peroxidation. Since antioxidants are also added to formulations to deactivate free radicals generated during UVA exposure, vitamin E and the synthetic antioxidant, bis(2,2,6,6-tetramethyl-1-oxyl-piperidine-4-yl)sebacate, a nitroxide derivative, were also included in this study. By using simple in vitro tests, the results show that a decrease in spectral absorbance of the UV filters correlates in most cases with increased UVA-induced lipid peroxidation; this depends on the specific UV absorber analysed and also on whether they are alone or in combination. Furthermore, the combined presence or absence of antioxidants has a profound effect on this oxidative event. In particular, the nitroxide appears to be a more efficient photo-antioxidant than vitamin E. Similar experiments were also performed under natural sunlight and the results obtained did not differ substantially from those performed under UVA. The results presented and discussed in this work may help in understanding the effects of UVA/UVB absorbers and antioxidants upon the level of UV-induced ROS generated under UVA exposure and in natural sunlight which could be relevant for improving the photoprotection and efficacy of skin care cosmetic formulations.     

Implementing tandem mass spectrometry as a routine tool for characterizing the complete purine and pyrimidine metabolic profile in urine samples

Purines and pyrimidines are the basic constituents of DNA and RNA and constitute the basis of at least 50 other important compounds that serve equally vital but separate roles as integral components of intracellular mononucleotide pools. They maintain the supply of these basic components to the different nucleotide pools through an extremely efficient mechanism involving the degradation and recycling of the daily waste products of normal cell turnover. We have developed an LC-MS/MS diagnostic and routine monitoring method for known defects due to both purine and pyrimidine metabolism in a single analysis. Precision tests were made by spiking several urine samples with different creatinine concentrations. For nonspiked low-creatinine urine, intraday precision was in the range of 0.1-9.8% and interday precision was between 1.6 and 14.1%. For nonspiked high-creatinine urine, intraday precision was in the range 0.5-17.2% and interday precision was between 1.5 and 29%. Limit-of-detection (LOD) was in the range 0.1-10 micromol/l and limit-of-quantification (LOQ) in the range of 0.2-15 micromol/l. The current 'dilute and shoot' approach monitors many metabolites, and utilizes a reverse phase chromatographic analysis with a detection requiring 17 min of analysis time. Tandem mass spectrometry and isotope dilution technique enable the accurate quantitation of more than 30 metabolites in one analysis.     

Influence of Intermolecular Vibrations on the Electronic Coupling in Organic Semiconductors: The Case of Anthracene and Perfluoropentacene

We have performed classical molecular dynamics simulations and quantum‐chemical calculations on molecular crystals of anthracene and perfluoropentacene. Our goal is to characterize the amplitudes of the room‐temperature molecular displacements and the corresponding thermal fluctuations in electronic transfer integrals, which constitute a key parameter for charge transport in organic semiconductors. Our calculations show that the thermal fluctuations lead to Gaussian‐like distributions of the transfer integrals centered around the values obtained for the equilibrium crystal geometry. The calculated distributions have been plugged into Monte‐Carlo simulations of hopping transport, which show that lattice vibrations impact charge transport properties to various degrees depending on the actual crystal structure.     

An integrated study for mapping the moisture distribution in an ancient damaged wall painting

An integrated study of microclimate monitoring, IR thermography (IRT), gravimetric tests and portable unilateral nuclear magnetic resonance (NMR) was applied in the framework of planning emergency intervention on a very deteriorated wall painting in San Rocco church, Cornaredo (Milan, Italy). The IRT investigation supported by gravimetric tests showed that the worst damage, due to water infiltration, was localized on the wall painting of the northern wall. Unilateral NMR, a new non-destructive technique which measures the hydrogen signal of the moisture and that was applied directly to the wall, allowed a detailed map of the distribution of the moisture in the plaster underlying the wall panting to be obtained. With a proper calibration of the integral of the recorded signal with suitable specimens, each area of the map corresponded to an accurate amount of moisture. IRT, gravimetric tests and unilateral NMR applied to investigate the northern wall painting showed the presence of two wet areas separated by a dry area. The moisture found in the lower area was ascribed to the occurrence of rising damp at the bottom of the wall due to the slope of the garden soil towards the northern exterior. The moisture found in the upper area was ascribed to condensation phenomena associated with the presence of a considerable amount of soluble, hygroscopic salts. In the framework of this integrated study, IRT investigation and gravimetric methods validated portable unilateral NMR as a new analytical tool for measuring in situ and without any sampling of the distribution and amount of moisture in wall paintings.     

Non-sinusoidal wall oscillation for drag reduction

The drag reducing properties of wall flows under non-sinusoidal oscillations are analyzed in the present work. The dependency of the drag reduction rate, R, and of the power spent to move the walls, P_in, with respect the shape of the wall motion are investigated. This preliminary work highlights a significant role of the oscillation shape for turbulence control suggesting more research efforts in the field with possible repercussions for practical applications. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The interaction of the antitoxin DM43 with a snake venom metalloproteinase analyzed by mass spectrometry and surface plasmon resonance

DM43 is a circulating dimeric antitoxin isolated from Didelphis aurita, a South American marsupial naturally immune to snake envenomation. This endogenous inhibitor binds non-covalently to jararhagin, the main hemorrhagic metalloproteinase from Bothrops jararaca snake venom, and efficiently neutralizes its toxicity. The aim of this study was to apply mass spectrometry (MS) and surface plasmon resonance (SPR) to improve the molecular characterization of this heterocomplex. The stoichiometry of the interaction was confirmed by nanoelectrospray ionization-quadrupole-time-of-flight MS; from native solution conditions, the complex showed a molecular mass of ~94 kDa, indicating that one molecule of jararhagin (50 kDa) interacts with one monomer of DM43 (43 kDa). Although readily observed in solution, the dimeric structure of the inhibitor was barely preserved in the gas phase. This result suggests that, in contrast to the toxin-antitoxin complex, hydrophobic interactions are the primary driving force for the inhibitor dimerization. For the real-time interaction analysis, the toxin was captured on a sensor chip derivatized with the anti-jararhagin monoclonal antibody MAJar 2. The sensorgrams obtained after successive injections of DM43 in a concentration series were globally fitted to a simple bimolecular interaction, yielding the following kinetic rates for the DM43/jararhagin interaction: k(a) = 3.54 ± 0.03 × 10(4) M(-1) s(-1) and k(d) = 1.16 ± 0.07 × 10(-5) s(-1), resulting in an equilibrium dissociation constant (K(D) ) of 0.33 ± 0.06 nM. Taken together, MS and SPR results show that DM43 binds to its target toxin with high affinity and constitute the first accurate quantitative study on the extent of the interaction between a natural inhibitor and a metalloproteinase toxin, with unequivocal implications for the use of this kind of molecule as template for the rational development of novel antivenom therapies.     

Methacrylic Polymers Bearing in the Side-Chain an Optically Active Moiety Linked to the trans-4-Azobenzene Chromophore: Chiroptical Properties of Poly[(S)-(+)-N-methyl-(2-methacryloyloxypropanoyl)-4-aminoazobenzene]

The synthesis by radical homopolymerization of a novel optically active methacrylic polymer containing a side-chain chiral moiety linked to a photochromic chromophore has been carried out starting from the related monomer trans-(S)-(+)-N-methyl-(2-methacryloyloxypropanoyl)-4-aminoazobenzene. The chiroptical properties in solution of the polymer have been investigated by circular dichroism and compared with those of the corresponding low molecular weight model compound, trans-(S)-(+)-N-methyl-(2-pivaloyloxypropanoyl)-4-aminoazobenzene. The optical activity displayed by the polymer is discussed in terms of extent of chiral conformations assumed by the macromolecules as a consequence of dipole-dipole interactions between the azoaromatic chromophores.