one micelle to another occurs by means of collisions and is a very fast process. Like
in other immobilization methods, the catalytic activity of enzymes may be altered
through entrapment in micelles. For instance, the activity [520–522] and the
temperature stability [523] is often enhanced; in some cases also the specificity is
changed [524, 525]. From a preparative point of view, it is important that compounds which are sparingly soluble in water (e.g., steroids) can be converted at
much higher rates than would have been possible in aqueous media [526]. The
disadvantages encountered when using micelles on a preparative scale are considerable operational problems during (extractive) workup, caused by the presence of a
considerable amount of surfactant, which behaves like a soap.
Synthetic Membranes A practical alternative to the use of sensitive biological
matrices is the use of synthetic membranes [527, 528] based on polyamide or
polyethersulfone (Fig. 3.9).
10 They have long been employed for the purification
Enz
Enz
6 - 40 nm
= surfactant
= enzyme
Vesicle/Liposome
Reverse Micelle
aqueous medium
organic solvent
water pool
surfactant
Enz
Fig. 3.8 Entrapment of enzymes in reversed micelles and vesicles
OH
O
n-C 8 H 17
N +
O
SO 3
-
O
O
O
9
Triton X-100 (non-ionic)
Bis(2-ethylhexyl)sodium sulfosuccinate (AOT, anionic)
Cetyltrimethyl ammonium bromide (CTAB, cationic)
Surfactant
polar
head
non-polar tail
Br -
Na
+
Scheme 3.49 Commonly employed surfactants
10 A popular membrane from daily life is Gore-Tex™.
376
3 Special Techniques
in other immobilization methods, the catalytic activity of enzymes may be altered
through entrapment in micelles. For instance, the activity [520–522] and the
temperature stability [523] is often enhanced; in some cases also the specificity is
changed [524, 525]. From a preparative point of view, it is important that compounds which are sparingly soluble in water (e.g., steroids) can be converted at
much higher rates than would have been possible in aqueous media [526]. The
disadvantages encountered when using micelles on a preparative scale are considerable operational problems during (extractive) workup, caused by the presence of a
considerable amount of surfactant, which behaves like a soap.
Synthetic Membranes A practical alternative to the use of sensitive biological
matrices is the use of synthetic membranes [527, 528] based on polyamide or
polyethersulfone (Fig. 3.9).
10 They have long been employed for the purification
Enz
Enz
6 - 40 nm
= surfactant
= enzyme
Vesicle/Liposome
Reverse Micelle
aqueous medium
organic solvent
water pool
surfactant
Enz
Fig. 3.8 Entrapment of enzymes in reversed micelles and vesicles
OH
O
n-C 8 H 17
N +
O
SO 3
-
O
O
O
9
Triton X-100 (non-ionic)
Bis(2-ethylhexyl)sodium sulfosuccinate (AOT, anionic)
Cetyltrimethyl ammonium bromide (CTAB, cationic)
Surfactant
polar
head
non-polar tail
Br -
Na
+
Scheme 3.49 Commonly employed surfactants
10 A popular membrane from daily life is Gore-Tex™.
376
3 Special Techniques