Environmental Engineering Reference
In-Depth Information
A simple nonaqueous method for the preparation of carboxymethyl
(CM) derivatives of galactomannans and other biopolymers has been developed
[
76
]. In a typical reaction, weighed samples (0.1-1 g) of galactomannan and finely
powdered NaHCO
3
(1-5 g) are mixed well manually using a pestle and mortar and
then, are added 0.1-0.2 ml of ethanol (100 % for surface wetting), and solid
monochloroacetic acid (0.5-2 g). The reaction is carried out at ambient or elevated
temperature (60, 80, 98
C) for 2 h, with intermittent manual mixing with a glass
rod, followed by the addition of dilute acetic acid to phenolphthalein end point. The
salts formed are removed by repeated washings with 70 % aqueous ethanol
followed by 100 % ethanol and solvent exchange drying. A number of CM
derivatives of differing degree of substitution (DS) values (0.065-0.675) can be
prepared by varying the ratio of catalyst and the reagent.
Polysaccharides that do not possess ionic gelling ability such as xanthan gum,
guar gum, locust bean gum, pullulan, etc., can also be converted into their sodium
carboxymethyl derivative by wet method [
77
]. The polysaccharides (2 g) are
dispersed for 30 min in 6.72 ml of ice-cold deionized water containing 3.024 g of
sodium hydroxide. Monochloroacetic acid (1.5 g) dissolved in 3.33 ml of deionized
water was added slowly for a period of 1 h in the above mixture maintained at 15-
18
C. The temperature of the mixture is raised slowly to 60-65
C and stirred for at
least another 1 h. The wetted mass is washed with 80 % methanol for 15 min. The
pH of the suspension is adjusted to neutrality with glacial acetic acid. Finally, it is
washed with methanol and kept for drying at 50-60
C until two consecutive
weights were the same.
Once hydrophilic character has been imparted into the polysaccharides, these are
further tailored chemically with hydrophobic counterparts to give amphiphilic
character. This is achievable by any of the above synthetic pathways.
16.6 Future Directions
A lot of international publications and patents exists that deals with the polymeric
micelles for drug delivery and targeting applications. In most of the cases, the
copolymer contains poly(ethylene oxide) (also known as polyethylene glycol) as
the hydrophilic component and poly(amino acids), poly(
D
-,
L
- and
DL
-lactic acids),
poly(
-caprolactone), poly(glycolic acid) as the hydrophobic component. In addi-
tion, most of the work focused mostly on micelles formed from commercially
available Pluronic
®
triblock copolymers. Hitherto, the research efforts on
polysaccharide-based micelles for drug delivery are limited in the scientific litera-
ture. Hence, there is a lot of opportunity to exploit the natural polysaccharides for
their drug delivery potentials by decorating their chemical structures via simple
chemistry.
Minimizing drug use would significantly reduce effective cost of drug which
would give financial relief to the patients. Delivery systems increase commercial
opportunity by distinguishing a drug from competitive threats posed by “me to”
ʵ
