S. Asen

Co-pigmentation of anthocyanins in plant tissues and its effect on color

Glycosides of the 6 common anthocyanidins all formed co-pigment complexes with flavonoids and other compounds at pHs ranging from 2 to 5. The formation of co-pigment complexes resulted in a bathochromic shift in the visible λmax of the anthocyanins and a large increase in extinction at pH 3 and higher. These complexes apparently formed with both the red flavylium salts and the purple anhydro bases. The increase in extinction at pHs 3 to 5 was attributed to the stabilizing effect co-pigmentation had on the anhydro bases. The degree of co-pigmentation was a function of the concentration of the anthocyanins and the molar ratio of co-pigments to anthocyanins. Co-pigmentation offers an explanation for the infinite color variations that occur in flowers in a pH range where anthocyanins alone are virtually colorless.

The formation of metal and “co-pigment” complexes of cyanidin 3-glucoside

Abstract Quercitrin, chlorogenic acid, and methyl gallate have no measurable effect on the color, spectra, or stability of cyanidin 3-glucoside in aq. solutions at pH 3–6·5. In acetate buffer solutions (pH 5·45) containing aluminum salts, however, quercitrin and chlorogenic acid form highly colored co-ordination complexes with the anthocyanin (anhydro base). The chlorogenic acid complex is blue and insoluble in water. In these properties it distinctly differs from the cerise aluminum chelate of cyanidin 3-glucoside which forms in the absence of chlorogenic acid or other co-pigments. The formation of these co-pigment-aluminum-anthocyanin complexes depends not only on pH but also on the type of organic acids which constitute the buffering system. Thus, complexes do not form in citrate buffers at pH 5·45, since citric acid itself preferentially complexes with the metal and thus makes it unavailable for reaction with the co-pigment and anthocyanin.

Anthocyanin, flavonol copigments, and pH responsible for larkspur flower color

Abstract The anthocyanin and flavonol glycosides in Larkspur flowers (cv. Dark Blue Supreme) are delphinidin 3-di( p -hydroxybenzoyl)glucosylglucoside, kaempferol 3-robinobioside-7-rhamnoside (robinin), kaempferol 3-rutinoside, kaempferol 7-rhamnoside, and kaempferol 3-(caffeylgalactosylxyloside)-7-rhamnoside. As young flowers age the pH of epidermal tissue increases from 5·5 to 6·6 and the color of many of the cells changes from moderate reddish-purple to light purplish-blue. Many of the older cells also contain blue crystals. Visible absorption spectra of moderate reddish-purple and light purplish-blue cells were simulated with a solution of the anthocyanin (10 −2 M) plus robinin (5 × 10 −3 M) at pH 5·6 and 7·1, respectively. Changes in the absorption spectra of living tissue with heating or cooling and of concentrated solutions of the anthocyanin with dilution or moderate heat, indicate that in the natural state the pigment is present in an associated form.

Co-pigmentation effect of quercetin glycosides on absorption characteristics of cyanidin glycosides and color of Red Wing azalea

Abstract A quercetin 5-methyl ether and five quercetin glycosides were isolated from flowers of Red Wing azalea1 but were found only in trace amounts in an orange sport of this cultivar. The anthocyanins (cyanidin glycosides) extracted from the orange and red flowers were identical, even though the absorption spectra of the intact cells differed. The absorption spectrum of the orange sport was simulated with a 10−3 M aqueous solution of cyanidin 3,5-diglucoside at the pH of the tissue, 2·8. The absorption spectrum of Red Wing was matched with cyanidin 3,5-diglucoside at the same concentration and pH, co-pigmented with the 3-rhamnoside or galactoside of quercetin.

A stable blue non-metallic co-pigment complex of delphanin and C-glycosylflavones in Prof. Blaauw Iris

Abstract The pigment of Prof. Blaauw Iris is a stable blue non-metallic co-pigment complex of C -glycosylflavones and the anhydro-base of delphanin [delphinidin 3-( p -coumaroylrutinoside)-5-glucoside]. At a concentration comparable to that within the plant cell the reconstituted complex is stable and has an absorption spectrum matching that of the intact cell. The blue pigment is associated with a pectin and the co-pigment C -glycosylflavones are 6- C -β- d -glucopyranosylgenkwanin (swertisin), O -xylosylswertisin, 8- C -β- d -glucopyranosylapigenin (vitexin), 6- C -β- d -glucopyranosylluteolin (iso-orientin) and 6- C -β- d -glucopyranosyl-7- O -methylluteolin (swertiajaponin).

MICROSPECTROPHOTOMETRIC MEASUREMENT OF PH AND PH EFFECT ON COLOR OF PETAL EPIDERMAL-CELLS

Abstract A microspectrophotometric method has been developed for calorimetric pH determination using indicator dyes. Tissue samples as small as five cells were used. Measurements of standard buffered solutions of known pH were within a standard error of less than ± 0.04 pH units. Validity of the technique has previously been established by matching the pH values and absorption spectra of several model systems to that of living cells. A method for spectrophotometric pH determination of single cells is suggested. The pH change seemed to be the major factor in the color change in aging flowers. The epidermal pH, the absorption spectra of living tissue, the anthocyanidins, flavonols, and flavones present in more than 250 plants of many families were determined. These data indicate that pH is only one of numerous parameters determining flavonoid color in the living cell.

Anthocyanin and pH in the color of ‘Heavenly Blue’ morning glory

Abstract The major anthocyanin in blue morning glory flowers, peonidin 3-(dicaffeylsophoroside)- 5-glucoside, is stable in a neutral aqueous solution and is solely responsible for the color of the flowers. Co-ocurring flavonols based on quercetin at the pHs of epidermal cells have no effect on the color of the anthocyanin. Deep or strong reddish-purple buds change to moderate or light blue open flowers within a 4 hr period, and during this time the pH of epidermal tissue increases from ca 6.5 to 7.5.

The constitution of a crystalline, blue cornflower pigment

Abstract A new, crystalline, deep blue pigment has been isolated from cornflowers ( Centaurea cyanus L.). The pigment is an iron complex of 4 molecules of cyanidin 3,5-diglucoside and 3 molecules of a “bisflavone” glucoside. The “bisflavone” glucoside is liberated on acid decomposition of the blue pigment, and chromatographic examination indicates that it is a single substance. On acid hydrolysis, however, it yields 7- O -methylapigenin and a second flavone which appears to be new and has not yet been positively identified. It is spectrally identical with 7- O -methylapigenin, and on the basis of its R f values it may be the 7- O -methyl derivative of vitexin. The reported properties of commelinin, the blue pigment of Commelina communis L., are strikingly similar to those of the cornflower pigment and suggest that these two pigments have an essentially identical type of structure.

High pressure liquid chromatographic analysis of flavonoid chemical markers in petals from Gerbera flowers as an adjunct for cultivar and germplasm identification

Abstract Flavonoids present in petals from Gerbera flowers were resolved and quantitated by high pressure liquid chromatography (HPLC). The anthocyanins isolated from 18 cultivars, ranging in color from orange through lavender, were pelargonidin and cyanidin 3-malonylglucosides accompanied by smaller amounts of pelargonidin and cyanidin 3-glucosides. Related flavonoid copigments were apigenin and luteolin 4′-glucosides and 7-glucosides, apigenin 7-malonylglucoside, kaempferol and quercetin 3-glucosides, 4′-glucosides and 3-malonylglucosides. Both qualitative and quantitative differences in these flavonoid chemical markers distinguished cultivars with very similar colors. Malonyl esters of anthocyanins are easily degraded by HCl and conventional extraction and purification procedures were adjusted to preserve their natural state.

Absorption spectra and color of aluminium-cyanidin 3-glucoside complexes as influenced by pH

Abstract The effects of pH on the color and the absorption spectra of a solution of cyanidin 3-glucoside (3·5×10 −5 M) complexed with AlCl 3 .6H 2 O (7×10 −4 M) were determined. Increasing pH from 2·21 to 6·16 influenced the type of aluminium-anhydro base complex formed and greatly affected the wavelength of maximum absorption of the sample. The color of the solution changed from red to blue-violet as pH increased. The color change was most pronounced in the pH range of 3·00–3·50.