Chlorophyll spectrum

FIGURE 1 The optical absorption spectrum of chlorophyll as a plot of percentage absorption against wavelength. Chlorophyll a is shown in red, chlorophyll b in blue. 

Carotenoids also assist chlorophylls in harvesting light. Carotenoids absorb wavelengths of blue light which chlorophylls do not. The energy that carotenoids harvest in the blue range of the spectrum and transfer to chlorophyll contributes... 

Since the function of most of the chlorophyll and the accessory pigments is thought to be the harvesting of light, one would expect the action spectrum... 

In order to obtain nearly absolute purity of the spectra of these xanthophylls, it was necessary to calculate the difference Raman spectra. Therefore, for zeaxanthin, two spectra of samples, one containing violaxanthin and the other enriched in zeaxanthin, were measured at 514.5 nm excitation. After their normalization using chlorophyll a bands at 1354 or 1389 cm-1, a deepoxidized-minus-epoxidized difference spectrum has for the first time been calculated to produce a pure resonance Raman spectrum of zeaxanthin in vivo (Figure 7.10b). A similar procedure was used for the calculation of the pure spectrum for violaxanthin. The only difference is that the 488.0nm excitation wavelength and epoxidized-minus-deepoxidized order of spectra have been applied in the calculation. The spectra produced using this approach have remarkable similarity to the spectra of xanthophyll cycle carotenoids in pure solvents (Ruban et al., 2001). The v, peaks of violaxanthin and zeaxanthin spectra are 7 cm 1 apart and in correspondence to the maxima of this band for isolated zeaxanthin and violaxanthin, respectively. The v3 band for zeaxanthin is positioned at 1003 cm-1, while the one for violaxanthin is upshifted toward 1006 cm-1. 

Fig. 3. Photokinetic action spectrum (circles and solid line) and in vivo absorption spectrum (long dashed line) of Phormidium ambiguum. Absorption spectrum of chlorophyll a (short dashed line). Abscissa wavelength in nm Ordinates relative response and absorbance respectively (modified after103 )...

While phototactic action spectra measured in some Phormidium species indicate that chlorophyll a is not involved in the absorption of phototactically active light (see below), the phototactic action spectrum of Anabaena variabilis106) shows slight activity around 440 nm and a distinct peak at around 670 nm, both indicating chlorophyll a. Since blockers of the photosynthetic electron transport, such as DCMU andDBMIB, (see below) do not affect phototactic orientation, the active light seems not to be utilized via the photosynthetic electron transport chain (for further information see below). 

Phototactic action spectra of Phormidium autumnale and Phormidium uncinatum, measured by Nultsch86>89), show prominent maxima in the absorption range of C-phycoerythrin and smaller, but distinct, peaks in the absorption range of C-phyco-cyanin. Red light absorbed by chlorophyll a is not active, while in the blue range absorbedby the Soret band, the action spectrum shows aminimum(Fig. 6). Nultsch87) concluded that biliproteins are photoreceptors of phototaxis, but independently of the photosynthetic electron transport and phosphorylation. 

The chlorophyll molecule (309) is involved in initiating photosynthesis in green plants and contains magnesium coordinated to a partially reduced porphyrin (namely, a chlorin derivative). Life relies ultimately on the unique redox and electron transfer abilities of the chlorophylls which are necessary for the conversion of light to chemical energy. Chlorophyll mainly absorbs light from the far red region of the spectrum... 

This is an interesting result, as with an absorption maximum in the blue-green part of the spectrum that is close to but not coincident with an absorption maximum in the spectrum for chlorophyll (see Figure 2.2). 

Figure 2.2 Absorption spectrum of chlorophyll overlaid with the energy flux from the Sun...

Taking into account the most likely pigment compositions of the phytoplankton in most seawater samples, a simplified set of equations was obtained. As the quantum efficiency of chlorophyll c appears to be very high, its emission spectrum is very little affected by interference from the emissions of other pigments. 

Using the individual solvents as blanks, acquire a visible absorption spectrum of each sample. Superimpose the four spectra, and determine which solvent is the most effective solvent for extracting chlorophyll from spinach leaves. 

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