title: Metal Complex Pigment Involved in the Blue Sepal Color Development of Hydrangea.
abstract: Anthocyanins exhibit various vivid colors from red through purple to blue and are potential sources of food colorants. However, their usage is restricted because of their instability, especially as a blue colorant. The blue sepal color of Hydrangea macrophylla is due to a metal complex named "hydrangea-blue complex" composed of delphinidin 3-O-glucoside, 1, 5-O-caffeoylquinic acid, 2, and/or 5-O-p-coumaroylquinic acid, 3, as copigments, and Al(3+) in aqueous solution at approximately pH 4.0. However, the ratio of each component ins not stoichiometric, but is fluctuates within a certain range. The hydrangea-blue complex exists only in aqueous solution, exhibiting a stable blue color, but attempts at crystallization have failed; therefore, the structure remains obscure. To clarify the basis of the character of the hydrangea-blue pigment and to obtain its structural information, we studied the mixing conditions to reconstruct the same blue color as observed in the sepals. In highly concentrated sodium acetate buffer (6 M, pH 4.0) we could measure (1)H NMR of both the hydrangea-blue complex composed of 1 (5 mM), 2 (10 mM), and Al(3+) (10 mM) and a simple 1-Al(3+) complex. We also recorded the spectra of complexes composed with structurally different anthocyanins and copigments. Comparison of those signals indicated that in the hydrangea-blue complex 1 might be under equilibrium between chelating and nonchelating structures having an interaction with 2.
authors.affiliation: Research Center for Materials Science and ‡Graduate School of Information Science, Nagoya University , Chikusa, Nagoya 464-8601, Japan.
authors.forename: Kin-ichi
authors.initials: K
authors.lastname: Oyama
authors.affiliation: Research Center for Materials Science and ‡Graduate School of Information Science, Nagoya University , Chikusa, Nagoya 464-8601, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Yamada
authors.affiliation: Research Center for Materials Science and ‡Graduate School of Information Science, Nagoya University , Chikusa, Nagoya 464-8601, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ito
authors.affiliation: Research Center for Materials Science and ‡Graduate School of Information Science, Nagoya University , Chikusa, Nagoya 464-8601, Japan.
authors.forename: Tadao
authors.initials: T
authors.lastname: Kondo
authors.affiliation: Research Center for Materials Science and ‡Graduate School of Information Science, Nagoya University , Chikusa, Nagoya 464-8601, Japan.
authors.forename: Kumi
authors.initials: K
authors.lastname: Yoshida
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D000872:Anthocyanins / Q000737:chemistry*; D002726:Chlorogenic Acid / Q000031:analogs & derivatives / Q000737:chemistry; D003116:Color; D035264:Flowers / Q000737:chemistry*; D005960:Glucosides / Q000737:chemistry; D031966:Hydrangea / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D011801:Quinic Acid / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D000535:Aluminum; D000872:Anthocyanins; D002726:Chlorogenic Acid; D005960:Glucosides; D011801:Quinic Acid; C494120:delphinidin 3-O-glucopyranoside; C473200:5-caffeoylquinic acid
keywords: 5-O-caffeoylquinic acid; Hydrangea macrophylla; aluminum complex; blue sepal color; delphinidin 3-O-glucoside