Sunday, 5 July 2009

Wet-type earwax fluoresces weakly under ultraviolet (UV or "black") light. One of the ways of testing the authenticity of amber is to pass it under a fluorescent light - amber should fluoresce. The crystalline structure of dried urine causes it to fluoresce a dull yellow color under UV light.

The hardness of amber varies from 1-3, and it is transparent to opaque, with the cloudy turbidity due to air bubbles and inclusions. It has no cleavage, conchoidal fracture, and is tough to brittle (Baltic amber tends to be tough, while Dominican amber, brittle). The luster is resinous and amber fluoresces bluish-white, yellow-green, or blue (more fluorescence with higher sulfur content). The color of amber varies, with white, yellow, and orange common, as well as red, brown, green, "black" (deep shades of other colors), and bluish colors possible.

Blue amber can be found, predominately in the Dominican Republic. It is also found in the Baltic. An amber researcher Sawkiewicz determined that Baltic blue amber was formed through the optical effect of closely concentrated bubbles of the same size, 0.00007 mm.The author has in his possession a tiny piece which shows some blue colouring and is pictured here. Green fossil resin can be found, again from the Dominican Republic and also in copal from Colombia. Burmite from Burma has a deep red colour.

Chlorophyll will fluoresce in the red part of the spectrum and also give off heat. Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Chlorophyll is the molecule that absorbs sunlight and uses its energy to synthesise carbohydrates from CO2 and water. This process is known as photosynthesis and is the basis for sustaining the life processes of all plants.

Chlorophyll molecules are specifically arranged in and around pigment protein complexes called photosystems which are embedded in the thylakoid membranes of chloroplasts. Light energy absorbed by chlorophyll molecules in a leaf can undergo one of three fates: it can be used to drive photosynthesis, excess energy can be dissipated as heat, or it can be re-emitted as light - chlorophyll fluorescence. The spectrum of fluorescence is different to that of absorbed light, with the peak of fluorescence emission being of longer wavelength than the absorption.

Light energy absorbed initially by the antenna and transferred to the reaction centers is channeled by a number of different processes including photochemistry, photo-protective heat dissipation, other heat dissipation and about 3%-9% of the light energy absorbed by chlorophyll pigments is re-emitted as fluorescence. The emission peak is of a longer wavelength than the excitation energy. This effect was first observed more than 100 years ago, when N.J.C. Müller (1874) by visually using colored glass filters. He also noted that fluorescence changes that occur in green leaves are correlated with photosynthetic assimilation. Lack of appropriate technical equipment prevented a more detailed investigation of this phenomenon. The light energy drives photosynthetic electron transport through PSII and PSI leading to the oxidation of water, oxygen evolution, the reduction of NADP+ to NADPH, membrane proton transport and ATP synthesis.

Lutein and zeaxanthin belong to the class of carotenoids known as xanthophylls and both contain hydroxyl groups. In photosynthetic plants lutein and zeaxanthin are located in chloroplasts where they are integrated with light-harvesting chlorophyll proteins. Lutein and zeaxanthin are phytochemicals found most often in leafy green vegetables, but also in other fruits and vegetables. Chicken egg yolks are a rich food source of lutein and zeaxanthin. Lutein is only obtained through the diet, while zeaxanthin can be produced by conversion from lutein in the eye.

Xanthophylls serve as accessory light-gathering pigments and to protect these organisms against the toxic effects of ultra-violet radiation and oxygen. Both lutein and zeaxanthin absorb blue light (peak absorption is 446 nm) The absorption of blue light protects plants from damage but does not prevent photosynthesis. Absorption of blue light is responsible for the colour of lutein and zeaxanthin, causing yellow pigmentation at low concentrations and orange-red at high concentrations. The name lutein is derived from Latin for "yellow".

Lutein and zeaxanthin are two dietary carotenoids which accumulate in the ‘yellow spot’ or macula lutea of the retina. The macula is located roughly in the center of the retina, temporal to the optic nerve. It is a small and highly sensitive part of the retina responsible for detailed central vision. The fovea is the very center of the macula. The macula allows us to appreciate detail and perform tasks that require central vision such reading. It is interesting to note that lutein and zeaxanthin are the only carotenoids known to concentrate specifically in the eye tissues.

Macular pigment has been implicated as a risk factor in age-related macular degeneration (AMD), the most prevalent cause of vision loss in the elderly. Vision loss in AMD is due to the irreversible death of photoreceptors and/or the invasion of leaky, unwanted blood vessels into the retina. At advanced stages of this progressive disease, everyday activities such as reading, driving, or even seeing the face of a loved one become impossible.

In the short-term study, reported in the November 2002 issue of Investigative Ophthalmology and Visual Science (IOVS), the team divided the carotenoid-deficient quail into two groups, and for one week preceding light damage, they fed one group zeaxanthin-supplemented diet. The study established that photoprotection was strongly correlated with the concentration of zeaxanthin in the retinas of the quail. Retinas with low concentrations of zeaxanthin had suffered severe light damage, as evidenced by a very high number of apoptotic photoreceptor cells, while the group with high zeaxanthin concentrations had minimal damage. Apoptosis is programmed cell death, the final common pathway for photoreceptor death in retinal degeneration.

The macular pigment acts like "sunglasses" by protecting the critically important central sight from damaging light waves. The distribution of lutein and zeaxanthin in the eye may indicate they have different functions. Zeaxanthin is the dominant component in the center of the macula, while lutein dominates at the outer edges. The eye is selective and preferentially places dietary zeaxanthin in the very center of the macula, the most critical area for central vision with the greatest need for protection. This selective uptake of zeaxanthin occurs even though lutein is more available in the diet by a 20:1 ratio.

Previous investigations may have obscured evidence of zeaxanthin's greater protective role by looking at the two carotenoids together, rather than separately. Although both of these carotenoids protect the retina, zeaxanthin has been shown to be a better photoprotector and a recent animal study supports the photoprotective activity of zeaxanthin. Additionally, zeaxanthin's chemical structure makes it a much more effective antioxidant than lutein.

The human study concluded that decreased blood plasma zeaxanthin, but not blood plasma lutein, is significantly associated with the risk of age-related macular degeneration. This correlation strongly indicates that a high level of dietary zeaxanthin intake may directly affect the risk of developing macular degeneration. Increasing intake through diet or supplementation may help to slow down or stop vision loss with those who have been diagnosed with AMD.

Many thanks:

Safety of Dietary Supplements for Horses, Dogs, and Cats By National Research Council (U.S.)

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