Hydrangea

Hydrangea umbellata Rheder (Saxifragaceae). A Chinese anti-malarial drug said to contain several crystalline alkaloids. (Jang, Fu, Huang, Wang, Nature, 1948, 161, 401.)... 

Hordenine (Anhaline), 154, 155, 161, 633 Hunnernanrtia fuTrumoefolia, 173 hunnemannine, 173, 302 Hydrangea umbeUata, 781 Hydrastal hydrastic acid, 164, 165 Hydrastine, 162, 209, 210, 328 constitution, 163 formula, 166-7... 

The color change of hydrangeas is exactly the opposite of that for litmus. 

Influence of acidic or basic soil. Hydrangeas grown in strongly acidic soil (below pH 5) are blue. When they are grown in neutral or basic soil, the flowers are rosy pink. 

You may be surprised to learn that many metal cations act as weak acids in water solution. A 0.10 M solution of A12(S04)3 has a pH close to 3 you can change the color of hydrangeas from red to blue by adding aluminum salts to soil At first glance it is not at all obvious how a cation such as Al3+ can make a water solution addic. However, the aluminum cation in water solution is really a hydrated species, A1(H20)63+, in which six water molecules are bonded to the central Al3+ ion. This spedes can transfer a proton to a solvent water molecule to form an H30+ ion ... 

There are many naturally occurring indicators. For instance, a single compound is responsible for the colors of red poppies and blue cornflowers the pH of the sap is different in the two plants. The color of hydrangeas also depends on the acidity of their sap and can be controlled by modifying the acidity of the soil (Fig. 11.11). 

FIGURE 11.11 The color of these hydrangeas depends on the acidity of the soil in which they are growing acid soil results in blue flowers, alkaline soil results in pink flowers. 

Hiroshima, 721 histidine, 443, 774 hole, 195 homeostasis, 386 HOMO, 126, 580 homogeneous alloy, 202 homogeneous catalyst, 565 homogeneous equilibria, 362 homogeneous mixture, F53 homolytic dissociation, 80 homonuclear diatomic molecule, 103 Hooke s law, 92 hormone, 670 horsepower, A4, 791 hour, A4 HPLC, 354 HRF products, 723 HTSC, 192 Humphreys series, 51 Hund, F 35 Hund s rule, 35, 37 Hurricane Rita, 144 hyaluronic acid, 344 hybrid orbital, 109 hybridization bond angle, 131 molecular shape, 111 hydrangea color, 463 hydrate, F32 hydrate isomer, 676 hydration, 178 hydrazine, 627... 

The colors of flowering plants such as hydrangeas are highly sensitive to soil acidity. At pH > 6.5, these showy flowers are deep pink, but at pH < 5, the blossoms are vivid blue. The chemistry of these changes involves complexation of aluminum by pigments that have acidic groups, as the structures show. 

If gardeners want blue flowers, they often add aluminum sulfate [AI2(S04)3] or sulfur to the soil to reduce the pH to 5.5. For people who prefer pink, lime (a base) is used to bring the pH to 6.5 or above. Occasionally, a hydrangea bush will produce purple flowers. This color is difficult to obtain, however. Purple flowers only come about when the pH is between... 

Figure 3.2 A hydrangea bush s flowers turn blue if it is being grown in acidic soil the flowers are pink if the soil is alkaline, or basic. Purple flowers grow in soil that is in a narrow midrange between acidic and basic.

Knox, Gary. French hydrangea for gardens in North and Central Florida, University of Florida, Institute of Food and Agricultural Sciences Web site. Available online. URL http //edis.ifas. ufl.edu/EP330. Accessed on March 13, 2008. 

Why do hydrangeas vary in color when grown in dry versus wet regions See p. 122. 

Why Do Hydrangeas Vary in Color When Grown in Dry versus Wet Regions ... 

Hydrangeas are popular summer flowers as a consequence of their vivid color that persists throughout the season. Large blooms of pink and blue colors are common, but the predominant color varies with a number of environmental factors. What role does chemistry play in determining the hue of these magnificent flowers ... 

Certain varieties of hydrangeas are extremely popular for their ability to vary in color from blue to pink with growing conditions (see color Fig. 9.4.1). Research has determined that the actual mechanism for color variation is determined by the concentration of aluminum compounds in the flowersJ J In the presence of aluminum, blue flowers result in the absence of aluminum compounds, pink flowers predominate. 

Many gardening books will state that the acidity of the soil affects the color of certain varieties of hydrangeas. The soil pH affects the availability of aluminum in the soil and thereby indirectly affects the flower color. A low pH or acidic conditions will yield blue blooms pink blossoms will be favored by a higher pH or alkaline conditions. A purple color is the result of a more moderate pH level. Potting soils with a high level of peat moss will produce blue hydrangeas. Areas... 

The plant pigments responsible for the variable coloration in hydrangeas is the class of pigments known as the red and blue anthocyanins. The anthocyanins are water soluble and display a color dependent on the acidity of their environment in the flower petal vacuoles. In acidic solution, the general structure of an anthocyanin is given by Fig. 9.4.2, with a formal charge on one oxygen atom and... 

Figure 9.4.2 General structure of an anthocyanin pigment molecule in hydrangeas.

Hydrangea Hydrangea macrophylla. Michigan State University Extension, http //www.msue.msu.edu/msue/imp/mod10/10000171. html... 

Figure 9.4.1 The blue and pink colors of hydrangeas that result from growing in soil with different degrees of acidity. From Masterton and Hurley, Chemistry Principles and Reactions, 4th edition. Orlando Harcourt, 2001. Photo courtesy of Charles D. Winters. 

AKIYAMA, T SHIBUYA, M., LIU, H.M., EBIZUKA, Y. p-Coumaroyltriacetic acid synthase, a new homologue of chalcone synthase, from Hydrangea macrophylla var. thunbergii, Eur. J. Biochem., 1999, 263, 834-839. 

Why do some hydrangea bushes look red and others blue ... 

The name hydrangea derives from classical Greek mythology, in which the hydra was a beast with many heads. 

The chromophore in hydrangeas is delphinidin (X), which is a member of the anthrocyanidin class of compounds. Compound X reminds us of phenol (VII), indicating that delphinidin is also a weak acid. In fact, all pH indicators are weak acids or weak bases, and the ability to change colour is a visible manifestation of the indicator s ability to undergo reversible changes in structure. In the laboratory, only a tiny amount of the pH indicator is added to the titration solution, so it is really just a probe of the solution pH. It does not participate in the acid-base reaction, except insofar as its own structure changes with the solution pH. 

The hydroxyl group placed para to the anthracene core is protonated in acidic solutions (i.e. when the hydrangea sap is slightly acidic). The proton is abstracted in alkaline sap, causing molecular rearrangement to form the quinone moiety. 

In addition to lupines, poison-hemlock and Nicotiana spp., other plant species of the genera Genista, Prosopis, Lobelia, Cytisus, Sophora, Pinus, Punica, Duboisia, Sedum, Withania, Carica, Hydrangea, Dichroa, Cassia, Ammondendron, Liparia, and Colidium contain potentially toxic and teratogenic piperidine alkaloids. Many plant species or varieties from these genera may be included in animal and human diets (Keeler and Crowe, 1984). 

If out baek hard to a stubby framework eaeh year, this less familiar hydrangea bears the biggest flower elusters. 

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