PCCP Blog

Spanish scientists have established how natural products protect plants from sun damage. The compounds could be used as active ingredients in sunscreens.

Using computational techniques on palythine – a compound found in coral – as a model compound, Diego Sampedro at the University of La Rioja, Logroño, investigated what happens to the molecule after it absorbs UV light.

Sampedro found that when UV light was shone on palythine, the molecule rapidly dissipated the light energy into heat energy without forming reactive, harmful, photoproducts. He looked at the mechanism in detail on both the protonated and neutral forms of palythine, as scientists were unsure which form was active in the coral. He found that both forms underwent a bond rotation to transform light into heat energy, but the protonated form was responsible for the main absorption of the radiation.

Mike Robb of Imperial College, London, an expert in computational chemistry, praises the timeliness of the study. “MAAs are already being studied as industrial photostabilisers. Understanding the details of the mechanism should help in the design of such species”.

Want to find out more?

Read the rest of the Chemistry World story by Yuandi Li

Or view the PCCP article by Diego Sampedro:
Computational exploration of natural sunscreens
Diego Sampedro, Phys. Chem. Chem. Phys., 2011
DOI: 10.1039/c0cp02901g

Monomer, clusters, liquid: an integrated spectroscopic study of methanol condensation

US scientists have combined static pressure, spectroscopic temperature, Fourier transform infrared spectroscopy (FTIR), and small angle x-ray scattering (SAXS) measurements to develop a detailed picture of methanol condensing from a dilute vapor-carrier gas mixture under the highly supersaturated conditions present in a supersonic nozzle.

This is significantly more than is predicted by a model that describes the vapour phase as an equilibrium mixture of methanol monomer, dimer, and tetramer. An energy balance suggests that a significant fraction of the cluster population is larger than the tetramer, while preliminary SAXS measurements suggest that these clusters contain, on average, 6 monomers.

In their experiments, methanol condensation can be divided into three stages as the gas mixture expands in the nozzle. In the first stage, as the temperature decreases rapidly, small methanol n-mers (clusters) form, increase in concentration, and evolve in size. In the second stage, the temperature decreases more slowly, and the n-mer concentrations continue to rise. Thermodynamic and FTIR experiments cannot, however, definitively establish if the average cluster size is constant or if it continues to increase. Finally, when the vapor becomes supersaturated enough, liquid droplets form via nucleation and growth, consuming more monomer and reducing the concentration of clusters. At the point where liquid first appears, cluster formation has already consumed up to 30% of the monomer.

Read the article in full for free:

Monomer, clusters, liquid: An integrated spectroscopic study of methanol condensation
H Laksmono, S Tanimura, H C Allen, G Wilemski, M S Zahniser, J H Shorter, D D Nelson, J B McManus and B E Wyslouzil
Phys. Chem. Chem. Phys., 2011, DOI: 10.1039/c0cp02485f

‘HOT’ article – UV laser removal of varnish on tempera paints

Painting conservation using laser ablation has been the subject of many recent studies – exploring both the possibilities and limitations of the technique.

In this study, two laser cleaning approaches using UV laser pulses of femtosecond (fs) and nanosecond (ns) durations allow controlled micrometric layer removal of varnish on coloured temperas. These results widen the choice of laser conditions for painting restoration.

UV laser removal of varnish on tempera paints with nanosecond and femtosecond pulses
Mohamed Oujja, Ana García, Carolina Romero, Javier R. Vázquez de Aldana, Pablo Moreno and Marta Castillejo
Phys. Chem. Chem. Phys., 2011, DOI: 10.1039/C0CP02147D