Chlorophylls a and

This experiment demonstrates how control charts and an analysis of variance can be used to evaluate the quality of results in a quantitative analysis for chlorophyll a and b in plant material. 

Chlorophyll b [519-62-0] M 907.52, sinters at 86-92 , sinters at 170 , dec at 160-170 , m 183-185 , 190-195 , [alj, -267 (Me2CO + McOH), [a] j-133 (McOH + Pyridine 95 5). See purification of chlorophyll a, and is separated from "a" by chromatography on sucrose [UV, IR Stoll and Weidemann Helv Chim Acta 42 679, 681 7959]. It forms red-black hexagonal bipyramids or four sided plates from dilute EtOH and has been recrystd from CHCl3-MeOH. It is soluble in MeOH, EtOH, EtOAc and insoluble in pet ether. [J Am Chem Soc 88 5037 1966.]... 

Chlorophyll, as extracted from plants, is actually made up of two closely related compounds, chlorophyll A and chlorophyll B. These differ slightly in molecular structure and can be separated because they have different tendencies to be adsorbed on a finely divided solid (such as powdered sugar). 

Although phthalocyanines are structurally similar to porphyrins such as hemoglobin, chlorophyll a and vitamin B12, they do not occur in nature. Formally, phthalocyanines can be regarded as tetrabenzotetraazaporphyrins and as the condensation products of four iso-indoline units. 

Photoautotrophic organisms, such as algae, cyanobacteria, and plants, all contain chlorophyll a and obtain energy by a process known as oxygenic photosynthesis. The overall chemical reaction of this process is ... 

Flowever, many photosynthetic bacteria, such as purple sulfur and green sulfur bacteria contain special bacteriochlorophyll compounds (not chlorophyll a) and carry out anoxygenic photosynthesis without producing oxygen ... 

The typical isocyclic ring E present in chlorophylls is susceptible to a number of different modifications such as epimerization, which produces stereoisomers by inversion of the configuration at C-13 of their parent pigments. These 13 -epichlorophylls, known as chlorophylls a and b, are minor pigments. They are considered artifacts produced in the course of handling plant extracts and sometimes are also found in small amounts in heated and deep-frozen vegetables, hi the old Fischer systan of nomenclature that can still be found in some literature, these epimers were named 10-epichlorophylls. 

From these stractural features it is interesting to note that each molecule of chlorophylls a and b consists of a hydrophilic part (tetrapyrrole macrocycle) and a hydrophobic portion (long terpenoid chain of phytol esterifying the acid group at C-17). Figure 2.1.2 shows the structures and nomenclature of chlorophylls a and b and their major breakdown derivatives. 

Whereas the biosynthesis of chlorophylls a and b in higher plants has been described in detail, the synthesis and regulation of related substances found in less well-known algal groups and lower plants are largely unknown and will be areas of scientific interest in the future. Different and new types of chlorophylls and related substances have been reported and little is known about their possible biological... 

Rudiger, W., Biosynthesis of chlorophylls a and b the last steps, in Chlorophylls and Bacteriochlorophylls Biochemistry, Biophysics, Functions and Applications, 25, Grimm, B. et al., Eds., Springer, Dordrecht, 2006, chap. 14. 

Lafferty, J., Truscott, T.C., and Land, E.J., Electron transfer reactions involving chlorophylls a and b and carotenoids, J. Chem. Soc. Farad. Trans., lA, 2760, 1978. Burri, B.J., Clifford, A.J., and Dixon, Z.R., Beta-carotene depletion and oxidative damage in women, in Natural Antioxidants and Anticarcinogens in Nutrition, Health and Disease, Kumulainen, J.T. and Salonen, J.T., Eds., Royal Society of Chemistry, Stockholm, 1999, 231. 

Despite the ubiquitous distribution of chlorophylls in all photosynthetic plants, quantitative information exists only for a few vegetables. The most common edible plants lack definitive data and consequently no information is available about chlorophyll distribution in current food composition tables. Still more difficult is to find analytical data in literature about the individual amounts of chlorophyll a and b and their respective derivatives. 

The wide distribution of chlorophylls throughout the plant kingdom facilitates the scrutiny of chlorophyll-rich vegetables for human nutrition with a view to their direct consumption. However, until now, little standardized information was available in the literature regarding the absolute total chlorophyll contents and the ratios of chlorophylls a and b in raw materials. The different analytical methods of extraction and quantification and the lack of data about moisture contents (that may vary considerably among varieties and preparations) can also influence the final contents of pigments. These factors have largely contributed to the discrepancies found in similar food samples. 

Liu, M.H. and Chen, B.H., Relationship between chlorophyll a and (3-carotene in a lipid-containing model system during heating, Food Chem., 61, 41, 1998. 

Chen, B.H. and Huang, J.H., Degradation and isomerization of chlorophyll a and (3-carotene as affected by various heating and illumination treatments, Food Chem., 62, 299, 1998. 

Because a chlorophyll molecule contains a closed circuit of ten conjugated double bounds to absorb light, spectrophotometric (UV-Vis) and fluorometric measurements are satisfactory to identify and estimate amounts of chlorophyll a and chlorophyll b, usually the only ones present in fresh plant extracts. The basis of numerous spectrophotometric determinations reported in literature is that chlorophylls strongly absorb at 500 to 700 nm in the visible region and show a large typical band around 400 nm. 

Chlorophyll a and chlorophyll b are distinguishable by their typical spectral properties (Figure 6.1.lA). Each one shows a specific absorbance coefficient and E... 

In 1941, Mackinney ° published the first specific absorption coefficients for chlorophyll a and chlorophyll b in 80% acetone, quickly followed by other reports citing different solvents. Chlorophylls form aggregates in various organic solvent-water mixtures that may interfere strongly with the absorbance maximum wavelength and the shapes of spectra. 

Amotf was the first to develop a set of equations for acetone to simultaneously calculate chlorophyll a and chlorophyll b in 1949. Several authors later proposed different new equations based on more adjusted and accurate extinction coefficients due to the development of higher resolution spectrophotometers adapted to each special condition. Moreover, besides 80% acetone, coefficients for diethyl ether and ethanol were also established and their respective equations developed, as reviewed by Schwartz and Lorenzo and Eder. Solvents chosen should be those for which specific absorbance coefficients have been published to derive equations and updates should be carefully tracked for new values. 

The equations (1 through 3 below) of the official method for total chlorophyll, chlorophyll a, and chlorophyll b analysis of plants published as Method 942.04 by... 

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