The use of model probes for assessing in depth modifications induced during laser cleaning of modern paintings

The cleaning of over-paint layers is a usual requirement to be met in the conservation of modern paintings. In most cases, acrylics or other related compounds must be removed without affecting the original painting. The elucidation of the extent of any photochemical or structural modification induced to the substrate following laser irradiation is a crucial challenge for the broader implementation of such laser cleaning strategies into the conservation practice. To achieve this, a methodology based on the use of a sensitive photochemical and photomechanical model system is introduced. A probe consisting of a polymeric material (e.g., Paraloid B72) doped with aromatic photo-sensitizers (e.g., POPOP) of known photochemistry and coated with uniform acrylic layer effectively simulates the real case scenario. Following laser irradiation, a variety of spectroscopic techniques including single or multiphoton laser-induced fluorescence and third-harmonic generation are employed for the assessment of any photochemical and structural modification induced in the bulk material. Practical issues related to the laser parameters employed will be presented, and the potential for a more general applicability of this methodology in the laser cleaning of modern paintings will be discussed.     

The Effects of Photosensitizing Dyes Fagopyrin and Hypericin on Planktonic Growth and Multicellular Life in Budding Yeast

Naphthodianthrones such as fagopyrin and hypericin found mainly in buckwheat (Fagopyrum spp.) and St. John’s wort (SJW) (Hypericum perforatum L.) are natural photosensitizers inside the cell. The effect of photosensitizers was studied under dark conditions on growth, morphogenesis and induction of death in Saccharomyces cerevisiae. Fagopyrin and hypericin induced a biphasic and triphasic dose response in cellular growth, respectively, over a 10-fold concentration change. In fagopyrin-treated cells, disruptions in the normal cell cycle progression were evident by microscopy. DAPI staining revealed several cells that underwent premature mitosis without budding, a striking morphological abnormality. Flow Cytometric (FC) analysis using a concentration of 100 µM showed reduced cell viability by 41% in fagopyrin-treated cells and by 15% in hypericin-treated cells. FC revealed the development of a secondary population of G1 cells in photosensitizer-treated cultures characterized by small size and dense structures. Further, we show that fagopyrin and the closely related hypericin altered the shape and the associated fluorescence of biofilm-like structures. Colonies grown on solid medium containing photosensitizer had restricted growth, while cell-to-cell adherence within the colony was also affected. In conclusion, the photosensitizers under dark conditions affected culture growth, caused toxicity, and disrupted multicellular growth, albeit with different efficiencies.     

Cytotoxic Evaluation and Determination of Organic and Inorganic Eluates from Restorative Materials

Over the last years, diverse commercial resin-based composites have dominated as dental filling materials. The purpose of the present study was to determine organic and inorganic eluates from five restorative materials using GC/MS and ICP–OES and to compare the effect on cell survival of human gingival fibroblasts of a conventional and a bioactive resin. Five commercially available restorative materials were employed for this study: Activa^TM Bioactive Restorative, ENA HRi, Enamel plus HRi Biofunction, Fuji II LC Capsule, and Fuji IX Capsule. Disks that were polymerized with a curing LED light or left to set were immersed in: 1 mL methanol or artificial saliva for GC/MS analysis, 5mL deionized water for ICP–OES, and 5mL of culture medium for cell viability. Cell viability was investigated with a modified staining sulforhodamine B assay.The following organic substances were detected: ACP, BHT, BPA, 1,4-BDDMA, CQ, DBP, DMABEE, HEMA, MCE, MeHQ, MOPA, MS, TMPTMA, and TPSb and the ions silicon, aluminum, calcium, sodium, and barium. Activa Bioactive Restorative was found to be biocompatible. Elution of organic substances depended on material’s composition, the nature of the solvent and the storage time. Ions’ release depended on material’s composition and storage time. The newly introduced bioactive restorative was found to be more biocompatible.     

Multisensor Hot Wire Vorticity Probe Measurements of the Formation Field of Two Corotating Vortices

Experimental evidence is reported, regarding the formation of a pair of co-rotating tip vortices by a split wing configuration, consisting of two half wings at equal and opposite angles of attack. Simultaneous measurements of the three-dimensional vector fields of velocity and vorticity were conducted on a cross plane at a downstream distance corresponding to 0.3 cord lengths (near wake), using an in-house constructed 12-sensor hot wire anemometry vorticity probe. The probe consists of three closely separated orthogonal 4-wire velocity sensor arrays, measuring simultaneously the three-dimensional velocity vector at three closely spaced locations on a cross plane of the flow filed. This configuration makes possible the estimation of spatial velocity derivatives by means of a forward difference scheme of first order accuracy. Velocity measurements obtained with an X-wire are also presented for comparison. In this near wake location, the flow field is dictated by the pressure distribution established by the flow around the wings, mobilizing large masses of air and leading to the roll up of fluid sheets. Fluid streams penetrating between the wings collide, creating on the cross plane flow a stagnation point and an “impermeable” line joining the two vortex centres. Along this line fluid is directed towards the two vortices, expanding their cores and increasing their separation distance. This feeding process generates a dipole of opposite sign streamwise mean vorticity within each vortex. The rotational flow within the vortices obligates an adverse streamwise pressure gradient leading to a significant streamwise velocity deficit characterizing the vortices. The turbulent flow field is the result of temporal changes in the intensity of the vortex formation and changes in the position of the cores (wandering).     

Determination of hydrogen peroxide by using a flow injection system with immobilized peroxidase and long pathlength capillary spectrophotometry

The development of a highly sensitive method for the determination of nanomolar concentrations of hydrogen peroxide in the liquid phase is described. This paper demonstrates for the first time a flow injection analysis (FIA) system with immobilized enzyme reactor combined with a total internal reflective cell (a liquid waveguide capillary cell (LWCC)) and spectrophotometric detection, for the development of an improved procedure for the determination of hydrogen peroxide. Moreover, the newly synthesized 4-aminopyrazolone derivative, 4-amino-5-(p-aminophenyl)-1-methyl-2-phenyl-pyrazol-3-one (DAP), is used as a color coupler in its oxidative condensation with the sodium salt of N-ethyl-N-sulphopropylaniline sodium salt (ALPS) which acts as a hydrogen donor. Immobilization of peroxidase is achieved by coupling the periodate-treated enzyme to aminopropyl controlled-pore glass (CPG) beads. The determination of hydrogen peroxide is carried out in a 0.1 M phosphate buffer and the product is monitored at 590 nm with a charge-coupled device (CCD) detector equipped with fiber optics in a fully computerized system. The interference of different species, mainly ionic, was investigated.The method permits detection down to 4 nmol l⁻¹ hydrogen peroxide (signal-to-noise ratio=3). A linear calibration graph was obtained over the range 20-700 nmol l⁻¹. The relative standard deviation (R.S.D.) at 300 nmol l⁻¹ H₂O₂ is 1.7% (n=7). The method was successfully applied for the determination of hydrogen peroxide in samples from a vat-cleaning process.     

Stereoselective synthesis of (3-aminodecahydro-1,4-methanonaphthalen-2-yl)methanols targeted to the C1 domain of protein kinase C

Protein kinase C (PKC) is a widely studied molecular target for the treatment of cancer and other diseases. We have approached the issue of modifying PKC function by targeting the C1 domain in the regulatory region of the enzyme. By using the X-ray crystal structure of the PKCδ C1b domain combined with molecular modeling, we discovered (3-aminodecahydro-1,4-methanonaphthalen-2-yl)methanol as a novel C1 domain ligand. The stereoselective synthesis of this tricyclic γ-amino alcohol was based on two successive Diels-Alder reactions to construct the six continuous stereocenters of the key intermediate.     

Rapid access to the tricyclic spirotetronic core of abyssomicins

[reaction: see text] Abyssomicins, a novel class of polyketide antibiotics, are characterized by an unprecedented spirotetronic tricyclic subunit in their structure. In this letter, a short synthesis of a suitably functionalized tricyclic precursor of abyssomicins is reported. Key steps of the synthesis are (i) the highly stereoselective Al(III)-tethered Diels-Alder reaction and (ii) the tandem Dieckmann cyclization/TBS trapping of the C9 hydroxyl group followed by a regioselective intramolecular epoxide opening for the assembly of the target tricyclic structure.     

Particle localization and hyperuniformity of polymer‐grafted nanoparticle materials

The properties of materials largely reflect the degree and character of the localization of the molecules comprising them so that the study and characterization of particle localization has central significance in both fundamental science and material design. Soft materials are often comprised of deformable molecules and many of their unique properties derive from the distinct nature of particle localization. We study localization in a model material composed of soft particles, hard nanoparticles with grafted layers of polymers, where the molecular characteristics of the grafted layers allow us to “tune” the softness of their interactions. Soft particles are particular interesting because spatial localization can occur such that density fluctuations on large length scales are suppressed, while the material is disordered at intermediate length scales; such materials are called “disordered hyperuniform”. We use molecular dynamics simulation to study a liquid composed of polymer‐grafted nanoparticles (GNP), which exhibit a reversible self‐assembly into dynamic polymeric GNP structures below a temperature threshold, suggesting a liquid‐gel transition. We calculate a number of spatial and temporal correlations and we find a significant suppression of density fluctuations upon cooling at large length scales, making these materials promising for the practical fabrication of “hyperuniform” materials.     

d- and l-Erythrose as sources of chiral quaternary carbon centers. Total synthesis of (−)-malyngolide and (+)-tanikolide

A highly efficient and versatile approach was applied for the total synthesis of the marine natural products (−)-malyngolide and (+)-tanikolide from isopropylidene l- and d-erythrose, using a common strategy.