30 No. 1
“Photochemistry for A Better Life”*
A special issue of L’Actualité Chimique, May/June 2007, edited by E. Amouyal and T.H. Tran-Thi
reviewed by Marie-Laure Viriot, Bernard Valeur, and Thu-Hoa Tran-Thi
“Photochemistry for a Better Life” was the theme of the June 2007 special issue of L’Actualité Chimique, the official journal of the French Chemical Society that is aimed at popularizing chemistry. For this issue, the journal editor offered the French Group of Photochemistry the opportunity to write about the multiple applications of photochemistry in everyday life. The result is an issue covering four main themes: Light and Life; Photons for Lighting, Detection, and Analysis; Light for the Protection of the Environment; and Solar Energy: Energy for the Future?
“How does light interact with living organisms?” is the question addressed by the authors of the Light and Life section. Five major topics are discussed, with the central idea that light is a tool with which to observe, analyze, and understand the chemical reactions in living organisms, but with the caveat that light can be harmful and beneficial at the same time.
UV radiation for instance provokes “DNA Photodamage.” Under this topic, the main DNA lesion routes induced by UV radiation are described, in particular those involving the formation of pyrimidine dimers and guanine oxidation. The approaches used for the elucidation of the mechanisms involved in their formation include the synthesis and photochemical studies of model compounds, as well as experiments performed by time resolved spectroscopy. The role of UV radiation is also considered in the topic “Amino Acids and Proteins in Photochemistry,” which focuses on protein photo-fragmentation and protein photo-inactivation by ruthenium complexes. In the chapter on “Cellular Photoperception and Photoactive Proteins,” the authors show how real-time laser spectroscopy allows the characterization of the crucial photochemical steps in light-induced intracellular energy transduction. The proteins presented are involved in vision (bacteriorhodopsin), microorganism photomotility (yellow protein and oxyblepharismin), and plant phototropism (cryptochrome), and can also be used as a temporal probe (green fluorescent protein).
The beneficial role of light is pointed out in “Photodynamic Therapy,” which targets the destruction of carcinogenic tissues by combining the actions of a photoactive drug or photosensitizer with light and oxygen. Additional topics discussed include the search for new efficient and selective photoactive compounds, the photosensitization mechanism at the molecular level, and the main applications in therapy.
In “UV and Skin: Mechanism and Photoaging Treatment,” aspects of the skin aging process are described, and different approaches for its prevention and treatment are discussed.
Sustainable energy production based upon renewable resources is achievable. This is the message conveyed by the authors of “Solar Energy: Energy for the Future?” A strategy for converting visible light into electrical current is described in “New Nanocrystalline Solar Cells,” with examples of credible devices able to produce electricity from sunlight with an overall efficiency of 11.1%. Another strategy described in this section involves new methods for efficiently splitting water into H2 and O2 without using noble metals as catalysts. Many bio-inspired artificial systems elaborated for light harvesting, energy transfer, and charge separation, including a hybrid photobiofuel cell, are reviewed in the section “Bio-Inspired Constructs for Sustainable Energy Production and Use.” In “Water Photolysis by Molecular Biomimetics,” the authors describe recent progress and findings on the structure of the water oxidizing enzyme of natural photosynthesis.
“Light for the Protection of the Environment” covers four topics. A rapid survey of the treatment and disinfection of spring water with UV and V-UV, and also of air treatment using V-UV irradiation, is given in “Photons Can Directly Destroy Pathogens and Pollutants.” In “Solar Light to Eliminate Pollutants,” the focus is on the solar-induced transformation of organic pollutants present in the upper layer of water surfaces, and on the surfaces of soil or leaves, which can lead to stable and more or less toxic compounds. To illustrate the photo-transformation of the pollutants, three examples are given. In “Detecting the Pollutants in Air and in Water,” the authors show the large panoply of tools and methods (LIDARs, chemiluminescence, fluorescence) developed for the analysis and detection of pollutants (particulates, nitrogen oxides, formaldehyde, heavy ions) in various environments. In section on “Photocatalysis for the Elimination of Pollutants,” the main concepts of photocatalysis are described and the latest research developments in the field are reviewed. A special focus is on the strategies aimed at improving the efficiency of TiO2, such as the use of dopant, surface treatments, coupling of TiO2 with dyes absorbing in the visible, and modifications of the structure and morphology of the photocatalyst. Also reviewed are the principal commercial and industrial applications for water and air depollution or disinfection.
Under the theme “Photons for Lighting, Detection, and Analysis,” the main “Lighting Sources” are first described: incandescent lamps, discharge lamps, and light emitting diodes (LED). Future prospects are presented with special attention to environmental concerns. Fluorescent lighting is of particular interest, and current efforts focus on “Phosphors for Fluorescent Lighting,” with the aim of finding more efficient materials in which “cascades of photons” occur. The second section deals with the use of light as a tool of detection in the field of security. For instance, “The Detection of Explosives” is of major importance in preventing terrorist attacks and facilitating mine clearance. Polymer-based fluorescent sensors show much promise in this respect. In the article “Light to Fight Counterfeiting,” various marking techniques are discussed that concern not only bank notes and artwork, but also more common commercial products. “Light and Trace in Police Inquiry” are strongly associated: Fluorescence and chemiluminescence for are currently used at crime scenes.
The third theme concerns light and art. In the article “Optics for a Better Knowledge of Works of Art,” various techniques and applications are presented: identification of pigments by diffuse reflectance, identification of varnishes by fluorescence under UV illumination, and distinction of different artistic techniques by goniophotometry and colorimetry. “Dating by Luminescence” is the subject of the last article. The energy accumulated by minerals with time, as a result of the natural radioactivity, can be released in the form of light with heating (thermoluminescence) or with light irradiation (optically stimulated luminescence), with the amount of light proportional to the elapsed time.
This issue can be ordered online through the website of L’Actualité Chimique. A second special issue on “Photochemistry to Transform Matter” is scheduled in 2008.
Marie-Laure Viriot <firstname.lastname@example.org>, Département de Chimie Physique des Réactions, France; Bernard Valeur <email@example.com>, Laboratoire de Chimie Générale, CNAM, France; and Thu-Hoa Tran-Thi <firstname.lastname@example.org>, Laboratoire Francis Perrin, CEA / CNRS, Saclay, France.
* This review was first published in the June 2007 Newsletter of the European Photochemistry Association <www.unibas.ch/epa> and is reprinted with permission.
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