A test for unsaturated compounds in which potassium per­manganate is used. Alkenes, for ex­ample, are oxidised to glycols, and the permanganate loses its colour: 3R2C=CR2 + 2KMnO4 + 4H2O → 2MnO2 + 2KOH + 3R2COHR2COH

A membrane­ bound protein of the halophilic (salt­resistant) bacterium Halobacterium halobium. When activated by light, it pumps protons out of the cell; this creates a concentration gradient, which enables ATP to be synthesized. Bacteriorhodopsin is composed of seven a-helix segments, which span the membrane and are joined to­gether by short amino-acid chains. It contains the

back titration : A technique in vol­umetric analysis in which a known excess amount of a reagent is added to the solution to be estimated. The unreacted amount of the added reagent is then determined by titra­tion, allowing the amount of sub­stance in the original test solution to be calculated.   بوسترات (لوحات) كيميائية بدقة