Chemistry in the Bioactivity of Chlorophylls: An Overview.

BACKGROUND: In addition to the considerable number of different chlorophyll structures originated naturally, prominent research is made to produce new specific semisynthetic structures. The final target is to obtain chlorophyll derivatives with even better bioactive properties than those of the natural parent compounds. METHOD: A detailed, extensive and critic literature search has been made in Web of Science™. RESULTS: Great efforts are applying to optimize the function of chlorophyll-based photosensitizers, to understand the molecular mechanisms of the antioxidant and antigenotoxic properties of chlorophyll derivatives and, lastly, to investigate new biological actions of them. However, the fundamental physiological functions of the chlorophylls are their physicochemical properties. CONCLUSION: This review aims to reflect the chemical grounds of the healthy and/or medical features of chlorophylls, including the consequences, advantages or even new actions that modifications over the chlorophyll structure introduce. Finally, new perspectives in the functionality of chlorophylls at molecular level are discussed.

[Cyanobacterial Phycobilisomes and Phycobiliproteins].

In cyanobacteria, phycobilisomes (PBS) act as antennae of the photosynthetic pigment apparatus. They contain brightly colored phycobiliproteins (PBP) and form giant supramolecular complexes (up to 3000-7000 kDa) containing 200 to 500 phycobilin chromophores covalently bound to the proteins. Over ten various PBP are known, which fall into three groups: phycoerythrins, phycocyanins, and allophycocyanins. Hollow disks of PBP trimers and hexamers are arranged into cylinders by colorless linker proteins; the cylinders are then assembled into PBS. Typical semidiscoid PBS consist of a central nucleus formed by three allophycocyanin cylinders and of six lateral cylinders consisting of other PBP and attached as fans to the nucleus. The PBS number, size, and pigment composition in cyanobacteria depend on illumination and other ambient factors. While PBS have certain advantages compared to other antennae, these pigment-protein complexes require more energy than the chlorophyll a/b- and chlorophyll a/c-proteins of oxygenic photosynthetic organisms.

[Ultrastructure and pigment composition of Sagittaria sagittifolia L. leaves].

Comparative analysis of the cellular ultrastructure and pigment content of both submerged and above-water Sagittaria sagittifolia leaves with transmission electron microscopic and biochemical methods were realized. Essential distinctions of S. sagittifolia ultrastructure of photosynthesizing cells in submerged leaves were revealed during the comparison with those in mesophyll cells of above-water leaves. The changes of chloroplast ultrastructure in submerged leaves are examined as the adaptative signs of photosynthesizing cells under influence of altered environment.

Demetalation kinetics of chlorophyll derivatives possessing different substituents at the 7-position under acidic conditions.

Conversion of the formyl group at the 7-position in chlorophyll (Chl) b to the methyl group via the hydroxymethyl group is biologically important in Chl b degradation. To clarify the effects of the 7-substituents on demetalation properties of chlorophyllous pigments in the early process of Chl b degradation, we report demetalation kinetics of the zinc Chl derivative possessing a 7-hydroxymethyl group, which is a good model compound of the intermediate molecule in the early process of Chl b degradation, under acidic conditions, and compare its properties with those of zinc Chl derivatives possessing a methyl and a formyl group, which are model compounds of Chls a and b, respectively. Demetalation rate constants of 7-hydroxymethyl zinc chlorin were much larger than those of 7-formyl zinc chlorin, but were slightly smaller than those of 7-methyl zinc chlorin. The activation energy for demetalation reaction of 7-formyl zinc chlorin was larger than those of other derivatives. Demetalation rate constants of 7-deformyl-7-hydroxymethyl Chl b were also larger than those of Chl b, and were similar to those of Chl a. These indicate that the 7-hydroxymethyl group in the chlorin macrocycle has a smaller effect on demetalation compared with the 7-formyl group.

Applying and comparing two chemometric methods in absorption spectral analysis of photopigments from Arctic microalgae.

Pigment absorption property of two arctic microalgae species (Skeletonema marinoi and Chlorella sp.) cultured at three temperatures (0, 4 and 8°C) was analyzed. Carotenoids and chlorophyll (Chl) c were positive factors to the high cell activities and primary productivities of S. marinoi at 4°C and 0°C, respectively; whereas Chl a had a positive effect on Chlorella sp. at all three temperatures, and carotenoids had a relatively high effect at 0°C. The absorption locations of photopigments were analyzed in detail using both fourth derivative and Symlet-6 wavelet analysis. Both methods precisely detected pigments with a relative large content; the fourth derivative analysis specifically detected the existence of a Chl a peak at about 410 nm and showed better differentiation of diatoxanthin, whereas the wavelet analysis distinctively indicated the existence of chlorophyllide a, ß-carotene, and Chl c. The separation limit to pigment peaks of the fourth derivative spectra (4 nm) was 1 nm higher than that of the wavelet high-frequency spectra (3 nm). The wavelet high-frequency spectra were more stable in detecting pigment locations and were more effective in discriminating microalgae. Small algebraic difference of 10(-16) between the reconstructed absorption spectra obtained by the inverse wavelet transform and their corresponding original spectra also showed the validity of Symlet-6 wavelet in the detection of pigments. Another specific discovery of this research is the existence of a Chl a allomer in Chlorella sp., which was detected by both methods.

Extension of pi-conjugation length along the Qy axis of a chlorophyll a derivative for efficient dye-sensitized solar cells.

A chlorophyll a derivative was synthesized and used for dye-sensitized solar cells with a solar energy-to-electricity conversion efficiency of 6.5%.

FTIR difference spectroscopy in combination with isotope labeling for identification of the carbonyl modes of P700 and P700+ in photosystem I.

Room temperature, light induced (P700(+)-P700) Fourier transform infrared (FTIR) difference spectra have been obtained using photosystem I (PS I) particles from Synechocystis sp. PCC 6803 that are unlabeled, uniformly (2)H labeled, and uniformly (15)N labeled. Spectra were also obtained for PS I particles that had been extensively washed and incubated in D(2)O. Previously, we have found that extensive washing and incubation of PS I samples in D(2)O does not alter the (P700(+)-P700) FTIR difference spectrum, even with approximately 50% proton exchange. This indicates that the P700 binding site is inaccessible to solvent water. Upon uniform (2)H labeling of PS I, however, the (P700(+)-P700) FTIR difference spectra are considerably altered. From spectra obtained using PS I particles grown in D(2)O and H(2)O, a ((1)H-(2)H) isotope edited double difference spectrum was constructed, and it is shown that all difference bands associated with ester/keto carbonyl modes of the chlorophylls of P700 and P700(+) downshift 4-5/1-3 cm(-1) upon (2)H labeling, respectively. It is also shown that the ester and keto carbonyl modes of the chlorophylls of P700 need not be heterogeneously distributed in frequency. Finally, we find no evidence for the presence of a cysteine mode in our difference spectra. The spectrum obtained using (2)H labeled PS I particles indicates that a negative difference band at 1698 cm(-1) is associated with at least two species. The observed (15)N and (2)H induced band shifts strongly support the idea that the two species are the 13(1) keto carbonyl modes of both chlorophylls of P700. We also show that a negative difference band at approximately 1639 cm(-1) is somewhat modified in intensity, but unaltered in frequency, upon (2)H labeling. This indicates that this band is not associated with a strongly hydrogen bonded keto carbonyl mode of one of the chlorophylls of P700.

Lipophilic pigments from the benthos of a perennially ice-covered Antarctic lake.

The benthos of a perennially ice-covered Antarctic lake, Lake Hoare, contained three distinct 'signatures' of lipophilic pigments. Cyanobacterial mats found in the moat at the periphery of the lake were dominated by the carotenoid myxoxanthophyll; carotenoids: chlorophyll a ratios in this high light environment ranged from 3 to 6.8. Chlorophyll c and fucoxanthin, pigments typical of golden-brown algae, were found at 10 to 20 m depths where the benthos is aerobic. Anaerobic benthic sediments at 20 to 30 m depths were characterized by a third pigment signature dominated by a carotenoid, tentatively identified as alloxanthin from planktonic cryptomonads, and by phaeophytin b from senescent green algae. Pigments were not found associated with alternating organic and sediment layers. As microzooplankton grazers are absent from this closed system and transformation rates are reduced at low temperatures, the benthos beneath the lake ice appears to contain a record of past phytoplankton blooms undergoing decay.

Lipophilic pigments from cyanobacterial (blue-green algal) and diatom mats in Hamelin Pool, Shark Bay, Western Australia.

Lipophilic pigments were examined in microbial mat communities dominated by cyanobacteria in the intertidal zone and by diatoms in the subtidal and sublittoral zones of Hamelin Pool, Shark Bay, Western Australia. These microbial mats have evolutionary significance because of their similarity to lithfied stromatolites from the Proterozoic and Early Paleozoic eras. Fucoxanthin, diatoxanthin, diadinoxanthin, beta-carotene, and chlorophylls a and c characterized the diatom mats, whereas cyanobacterial mats contained myxoxanthophyll, zeaxanthin, echinenone, beta-carotene, chlorophyll a and, in some cases, sheath pigment. The presence of bacteriochlorophyll a within the mats suggest a close association of photosynthetic bacteria with diatoms and cyanobacteria. The high carotenoids : chlorophyll a ratios (0.84-2.44 wt/wt) in the diatom mats suggest that carotenoids served a photoprotective function in this high light environment. By contrast, cyanobacterial sheath pigment may have largely supplanted the photoprotective role of carotenoids in the intertidal mats.