The Betalains are indole-derived pigments replacing anthocyanin pigments in plants belonging to the
Caryophyllanes and in higher-order fungi. The deep colours of Beets (and other cultivars of
Beta vulgaris), Bougainvillea, Amaranth and many cacti owe their deep colours to these compounds. There are two categories of Betalains: BetaCyanins (which are not present in Marvel-of-Peru) and BetaXanthins (which are). Betalain pigments and AnthoCyanin pigments are mutually exclusive,- no plant ever produces both, but sometimes those producing Betalain pigments also produce
AnthoXanthins. Most members of the Caryophyllanes produce betalain pigments; only two families within the Caryophyllanes produce AnthoCyanins instead of Betalains, namely the Caryophyllaceae (Carnation) family and the Molluginaceae family. The production (or not) of Betalains is now used diagnostically in Taxonomy.
The colour of all Betalains is due to the oscillatory twisting of the C=N double bond which induces larger rotations about the C=C bond just beneath it in the structural formulae diagrams. Your Author wonders if this might mean that MiraXanthin I and MiraXanthin II are not coloured by this resonance, seeing as both these lack the requisite C=N bond (being replaced by a C-N bond, which is therefore free to rotate continuously rather than twist clockwise and anticlockwise like a clock escapement with hairspring balance wheel).
Betalains perform a photoregulation and hormone control role in plants.
These are yellow to orange coloured Betalain pigments and include
IndicaXanthine and Portulaxanthin (present in species belonging to the Portulaca genus), only the latter compound has not been found in Marvel-of-Peru. Betaxanthines cannot be hydrolysed by acid to strip them of any sugar moiety without also fundamentally changing their chemical structures. They are shown here as the aglycones, without their sugar moieties.
The BetaXanthines are based upon a Betalamic Acid moiety.
Indicaxanthin is a powerful anti-oxidant present in Beets (Beta vulgaris spp), in Marvel-of-Peru and in cacti such as
Prickly Pear (Opuntia genus). It has charge-separation on the 4-valent nitrogen atom, and is therefore a zwitterion as are many betalaines.
Indicaxanthin was first found in the dye extracted from the fruits of
Barbary Fig aka
Prickly Pear Opunti ficus-indica, a species of cactus which has long been domesticated in semi-arid parts of the world as a crop plant. Barbary Fig has orange, yellow or white flowers, but the colour of the fruits the dye is extracted from are bright red to purple or yellow to white. The juice of the fruit, which is red in colour, contains both Betanin and Indicaxanthin.
The colour of the mixture of Indicaxanthin (yellow-orange) and Betanin (purple) is highly dependant upon the pH (as you might expect for a Zwitterion with separated positive and negative charges). Dying at pH 4 yields optimum results. Various metal salts added as mordant improve light-fastness, but un-mordanted wool already has good water and washing fastness.
There are five Vulgaxanthines known, I to V, but only VulgaXanthin-I has been reported to occur in Marvel-of-Peru.
MiraXanthines are dyes present in plants belonging to the
Miraxanthine V and Miraxanthin III are closely related to each other; both contain a Dopamine (aka 3,4-DiHydroxyPhenylEthylAmine) moiety in their structure. Dopamine is one of the main neurotransmitters in the mammalian brain out of the dozens that have now been found operating within it. Dopamine itself is found within the petals of the flower.
The structure of Miraxanthin IV is not certain, because it does not occur in sufficient quantities to determine. Instead of the Dopamine moiety in Miraxanthin V and III, Miraxanthin IV, as depicted, has a 3,4-DiHydroxyPhenylMethylAmine moiety attached to it. This moiety is also an important neurotransmitter of the Catecholamine type in the mammalian brain.