Vitamin A Vitamin A is a group of unsaturated nutritional organic compounds, that includes retinol, retinal, retinoic acid, and several provitamin A carotenoids, among which  beta-carotene  is the most important. Vitamin A has multiple functions: it is important for growth and development, for the maintenance of the immune system and good vision. Vitamin A is needed by the  retina  of the eye in the form of retinal, which combines with protein opsin to form rhodopsin, the light-absorbing molecule necessary for both low-light (scotopic vision) and  color vision. Vitamin A also functions in a very different role as retinoic acid (an irreversibly oxidized form of retinol), which is an important hormone-like growth factor  for  epithelial  and other cells. Vitamin A is involved in immune function, vision, reproduction, and cellular communication [1,4,5]. Vitamin A is critical for vision as an essential component of rhodopsin, a protein that absorbs light in the retinal receptors, and because it supports the normal differentiation and functioning of the conjunctival membranes and cornea [2-4]. Vitamin A also supports cell growth and differentiation, playing a critical role in the normal formation and maintenance of the heart, lungs, kidneys, and other organs. - Molecular Weight: 286.4516 [g/mol] - Molecular Formula: C20H30O - Boiling Point: 137-138 deg C at 1X10-6 mm Hg - Melting Point: 62-64 deg C - Solubilities: Practically insoluble in water or glycerol; soluble in absolute alcohol, methanol, chloroform, ether, fats and oils. Sol in ethanol and acetone and benzene Vitamin D Vitamin D refers to a group of fat-soluble secosteroids responsible for enhancing intestinal absorption of calcium, iron, magnesium,phosphate  and  zinc. In humans, the most important compounds in this group are vitamin D3 (also known as  cholecalciferol) and vitamin D2 (ergocalciferol). Cholecalciferol and ergocalciferol can be ingested from the diet and from supplements.[1][2][3] The body can also synthesize vitamin D (specifically cholecalciferol) in the skin, from cholesterol, when sun exposure is adequate (hence its nickname, the "sunshine vitamin"). Vitamin D promotes calcium  absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent hypocalcemic tetany. It is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts [1,2]. Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults [1]. Together with calcium, vitamin D also helps protect older adults from osteoporosis. Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation.   - Molecular Weight: 384.63766 [g/mol] - Molecular Formula: C27H44O - Melting Point: 84-85 deg C - Solubilities: Sol in the usual org solvents; slightly sol in vegetable oils. In water, 1.3X10-5 mg/L at 25 deg C (est) Vitamin E Vitamin E is found naturally in some foods, added to others, and available as a dietary supplement. "Vitamin E" is the collective name for a group of fat-soluble compounds with distinctive antioxidant activities [1]. Naturally occurring vitamin E exists in eight chemical forms (alpha-, beta-, gamma-, and delta-tocopherol and alpha-, beta-, gamma-, and delta-tocotrienol) that have varying levels of biological activity [1]. Alpha- (or α-) tocopherol is the only form that is recognized to meet human requirements. Vitamin E has many biological functions, the  antioxidant  function being the most important and best known.[23]  Other functions include  enzymatic activities, gene expression, and neurological function(s). The most important function of vitamin E has been suggested to be in cell signaling  (and it may not have a significant role in antioxidant metaboli