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C6H12O6 =2C2H60+2CO2.
These enzymes have an extremely specific See also:action, producing, for instance, the See also:change in See also:ordinary natural See also:glucose, but not at all in its artificial antipode, and so they are often valuable means of isolating an antipode from the inactive mixtures or racemic compounds; this method has indeed been used for the See also:isolation of the glucose-antipode from the artificial racemic See also:form. The fundamental fact here is due once more to See also:Pasteur, but Emil See also:Fischer added that sugars are acted upon by zymase in an analogous way if their configuration shows a certain amount of identity. For example yeast acts on
d-Glucose d-Mannose d-See also:Fructose
HCO HCO H2COH
HCOH HOCIIH CO
HOH HOH HOCH
HCOH HCOH HOH
HCOH HCOH HCOH
H2OH H2COH I-I2COH,
and we observe that the three formulae agree indeed in the See also:lower four-See also:carbon See also:chain. This particular behaviour led Fischer to the expression that the See also:enzyme-action on given substances needs a corresponding feature as " See also:lock and See also:key." There are indications that in the See also:synthesis by enzymes, of which examples have been realized in fats, sugars, glucosides and albuminoids, an analogous behaviour prevails.
6. Mutual Transformation of See also:Antipodes.—Thus far we have
supposed the See also:molecule to be See also:stable with atoms in fixed places, as may be the See also:case at See also:absolute zero; in reality, at ordinary temperatures, atoms probably are endowed with See also:movement, and this may be supposed to take See also:place along the fixed places just mentioned as centres, which movement can go so far as to See also:lead to See also:total trans-formation, the one stereo-isomer changing over into the other. These cases may be considered now.
As a See also:general See also:rule the liquid, gaseous or dissolved antipode is it itself unstable, tending to be transformed into inactive complexes Temperature may accelerate this, and, as a rule, sufficient See also:heat will. produce the loss of See also:optical activity, See also:half of the See also:original See also:compound: having changed over into its optical antipode. This transformation has been often used for preparing the latter, as was first done by Le See also:Bel with the optically active amyl See also:alcohol, HC(See also:CH3)(See also:C2H6)(See also:CH2OH), rendering it inactive by sufficient See also:heating, and separating from the obtained complex the stereo-isomer. See also:Walden found that in some cases analogous transformations take place at ordinary temperature, as for instance with d-phenylbromacetic See also:acid, which within three years totally lost its considerable rotative See also:power; this transformation has been termed " autoracemization." It explains that till now the most See also:simple compounds with See also:asymmetric carbon have not yet been obtained in antipodes; active CHCIBrF might be obtained by treating chlorobromofiuoracetic acid with potash, but autoracemization, which especially shows itself when See also:halogens are linked to the asymmetric carbon, might, without See also:special precautions, lead to an inactive mixture of antipodes.
When two asymmetric carbons are See also:present, four stereo-isomers are possible, which may be represented by:
(i) A-I-B, (2) —(A+B), (3) A—B, (4) —(A—B),
(I) and (2), as well as (3) and (4), being antipodes. The stable form will be in this case also the inactive mixture, corresponding in the solid See also:state either to (I), (2) or (3), (4). In the last case, suppose the See also:primitive compound is (I), the first step towards stability may be the See also:production of (3), so that practically
one stereo-isomer changes over into another See also:Ito of a different type.
End of Article: C6H12O6
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