Catálogo de publicaciones - libros

The central importance of (bacterio)chlorophyll as a major photosynthetic pigment arises from its ability to both harvest the sunlight and perform ultrafast electron transfer (ET) reactions. The main function of the reaction center (RC) is to convert the photoexcitation in order to generate a trans-membrane potential in a series of ET steps. In bacterial RCs it is possible to relate molecular structure and biological function by exploring the early events after photoexcitation. In a series of ultrafast time resolved experiments with native and modi- fied samples, the details of the primary photosy nthetic reactions become visible, information on the relevant electron transfer parameters (free energy, reorganization energy and electronic coupling) can be deduced. This leads to a better understanding of architectural principles in photosynthetic RCs and optimization strategies in photosynthesis.

Photodynamic therapy (PDT) has proved to be a viable and interesting alternative to currently used less selective methods for palliative care of cancer and, in a limited number of cases, for curative treatment. Still, in spite of impressive progress and a few approvals for clinical applications, the great potential of PDT has not yet been fully realized because of current deficiencies of applied sensitizers and of applied treatment strategies. Introduction of chlorophyll- and bacteriochlorophyll-derived sensitizers is expected to markedly change this situation in the coming decade. In this and the following chapter we provide an updated summary of these new sensitizers, their syntheses, relevant characteristics and pharmaceutical activity in vitro and in vivo. The first chapter is focused on the general principles of photodynamic therapy with particular emphasis on the vascular-targeted approach to treatment. A general introduction is followed by a comprehensive description of chlorophyll based sensitizers. The following chapter (Chapter 33) is focused on the use of bacteriochlorophyll derivatives.

Recent progress in the bioproduction and chemical manipulation of bacteriochlorophyll (BChl) has opened the way for utilization of highly potent sensitizers in photodynamic therapy. Although less stable than their chlorin analogues in their native form, BChl derivatives provide a superior optical and biophysical profile for the generation of reactive oxygen species (ROS). In fact this pigment family probably represents the most ef- ficient light collectors and radical generators in nature. Here we describe a recent development of this exciting family of drugs, with particular emphasis on vascular targeted therapy (VTP).

Chromophore molecules have fascinated scientists for decades. As early as 1903, chlorophylls were analyzed by chromatography, a newly introduced technique at that time (Tswett, 1906). Ever since, porphyrins and hydroporphyrins and their metal complexes, such as chlorophylls and bacteriochlorophylls, have been studied extensively in the context of their roles in photosynthesis, as biological model systems, and recently, as promising sensitizers for photodynamic therapy. When increasing ring saturation from the porphyrin macrocycle symmetry to the less symmetrical hydroporphyrins (together with an additional isocyclic ring), a wealth of possibilities for experimental observations of increasing complexity and detail became available. The synergistic link between theoretical and experimental approaches has advanced not only the understanding of various (bacterio)chlorophyll functions, but has also provided tools for exploring other complex electronic systems.

Transients of chlorophyll (Chl) fluorescence emission are widely used to estimate kinetics, yield and regulation of photosynthetic processes in intact plants. In this chapter, we introduce concepts and terms required for a qualified application of the technique. An overview of relevant processes that occur on different timescales, from picoseconds to organism lifetime, is provided as a reference framework for description of approximations and models connecting physiologically relevant photosynthetic parameters and the fluorescence data. Reaching beyond the conventional analysis, we also describe models including Photosystem II heterogeneity and short-living radicals that can affect plant-Chl fluorescence emission. Current state-of-the-art and future prospects for Chl-fluorescence instrumentation are described at the end of the chapter.

Detecting and measuring, from space, the chlorophyll (Chl) content within the upper layer of the ocean, where the concentration is so low and the Chl-bearing phytoplanktonic cells are so small, can appear to be an impossible task. Further, a satellite-borne sensor directed towards the ocean captures the dominant atmospheric signal, due to light scattered by air molecules and aerosols, so that the marine signal must be extracted from this invasive background. Ocean color sensors, however, have been developed and now provide, on a daily basis, maps of the Chl distribution over the oceans of the world. This chapter explains how this challenge was faced and finally solved. These solutions involved the so-called ‘bio-optical’ properties of open ocean waters; namely, the existence in these waters of empirical relationships between the whole biogenic material, which governs the bulk optical properties, and a single component, the Chl content which can be detected and estimated from space by ocean color sensors. With newly developed sensors, it is now also possible to detect natural sun-stimulated Chl a fluorescence of phytoplankton which also provides a new promising approach to derive information about the physiological state of algal populations. The method of retrieving the marine signal and making the ‘atmospheric correction’ is briefly described. Paradoxically, this correction itself provides highly valuable information on the atmospheric aerosols, a crucial component of the radiative budget of our planet.

In spite of intensive studies over more than 70 years, the geochemistry of tetrapyrrole pigments still presents numerous challenges. Recent studies have focused on functionalized precursors of sedimentary porphyrins, making extensive use of developments in analytical capabilities. Many new structures have been characterized, confirming the Treibs hypothesis linking chlorophyll to the major sedimentary porphyrin, deoxophylloerythroetioporphyrin, and revealing a number of alternative transformation pathways. Functionalized transformation products of chlorophylls , , and and of bacteriochlorophylls and have all been recognized indicating that all primary producer communities are represented in the sedimentary record. It is evident that redox status, grazing pressure and secondary reactions can all influence the fate of chlorophyll, and that the variety of transformation products present in natural sedimentary environments contains a wealth of information pertaining to the conditions present at the time of sediment deposition. Several entirely novel pigment transformation products have been identified and others represent viable precursors for sedimentary porphyrin structures previously of uncertain origin. As a direct result of the advances in analytical methods it is now possible to perform on-line analysis at very high stratigraphic resolution. At cm and mm scale resolution pigment profiles can show a significant degree of variation, indicating that the pigments are highly sensitive markers of environmental change. Thus, in addition to providing information on the source organisms present in past environments, chlorophyll derivatives have great potential for use in a range of paleoenvironmental proxies.