![]() The spectra obtained by the researchers using this method show negligible dependence on the nature of the tag cation. Excitation of the molecules by laser light leads to the dissociation of chlorophylls and tags, thus allowing the measurement of the chlorophyll spectra for different cations. Then, dissolved mixtures of chlorophyll and tags are electrosprayed into a vacuum within a spectrometer. positively charged ions – with no mobile protons, so that in each case the distance between the chlorophyll and the electric charge is known. The method consists in tagging the chlorophyll a and b molecules with three different ammonium cations – i.e. Now, Angel Rubio and his colleagues have developed a method to measure the true color of chlorophyll in the absence of perturbations from its environment. The problem with this method is that these solvents have an effect on the electronic structure of the chlorophyll molecule, namely on the electron cloud at the porphyrin, thus modifying its optical behavior. This has already been done with different solvents. You might think that it is as simple as preparing a solution of chlorophyll and use a spectrometer to get the answer. This is not an easy question to answer, though. This is very important if we are ever going to understand how photosynthesis works and if we want to use this knowledge to build truly efficient photovoltaic devices. To know how much this microenvironment affects the visible color, we first need to know what the true color of chlorophyll is. It is this interaction with the surrounding microenvironment what fine-tunes chlorophylls to cover as much of the visible spectrum as possible. Photosynthetic chlorophyll pigments are not alone in the leaf cells they are usually in a protein pocket. They only differ in a substituent of the porphyrin ring. Molecular structures of chlorophyll a ( left) and b ( right). Furthermore, chlorophyll a and b only differ in a substituent of the porphyrin, for chlorophyll a it is a methyl group (-CH 3) and for chlorophyll b it is an aldehyde group (-CHO) in the C7 position, but it is sufficient to significantly alter the absorption spectrum of the molecule. A slight change of the molecular structure leads to a change of the optical behavior. a proton – and the color changes from bright green to the dull color of overcooked broccoli. If you boil a leaf in water, this magnesium ion gets replaced by a hydrogen ion – i.e. Since there are no other strong pigments present in leaves, that is the whole story.Ĭhlorophyll molecules have a ring shape at one end – called a porphyrin – with a magnesium ion in the center. However, none of them absorbs green, so the leaf looks green because that light is reflected to our eyes instead of being absorbed by the leaf. They both also absorb light of other wavelengths with less intensity. Chlorophyll b absorbs mostly blue and yellow light. © Wikimedia Commons / Daniele Pugliesi, M0ttyĬhlorophyll a absorbs violet and orange light the most. ![]()
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