J Surfact Deterg
absorbance data of the dose–response curves. The IC50
values (in lM) were expressed as the average of two
independent experiments.
followed by neutralization with aqueous NaOH solution.
The isolated yields were in the range of 81–96 %.
Characterization of Alkyl Lactates
Antimicrobial Activity
Spectral Data of Some Important Alkyl Lactates
Antimicrobial activity of lactic acid-based anionic surfac-
tants was determined using the modified broth dilution
method as described previously [24]. The target strains
used for screening the antimicrobial activities were Mi-
crococcus luteus MTCC 2470, Staphylococcus aureus
MTCC 96, S. aureus MLS16 MTCC 2940, Bacillus subtilis
MTCC 121, Escherichia coli MTCC 739, Pseudomonas
aeruginosa MTCC 2453, Klebsiella planticola MTCC 530
and Candida albicans MTCC 3017. These strains were
procured from the Microbial Type Culture Collection and
Gene Bank (CSIR-Institute of Microbial Technology,
Chandigarh, India).
1-Octyl lactate (1a): Colorless liquid; FT-IR (cm-1,
CHCl3): 3480 (br.m, –O–H symmetric mode), 2927, 2858
(s, alkyl chain –C–H symmetric mode), 1738 (s, –C = O
symmetric mode), 1460 (m, –C–H scissoring mode), 1212
(m, –C–O symmetric mode), 1131 (s, –O–C = O asym-
metric mode); 1H-NMR (CDCl3, 500 MHz, d in ppm): 4.26
(1H, q, J = 6.9 Hz), 4.18 (2H, m), 2.99 (brs, OH), 1.66
(2H, m), 1.41 (3H, d, J = 6.9 Hz), 1.39–1.22 (10H, m),
0.88 (3H, brt); 13C-NMR (CDCl3, 75 MHz, d in ppm):
175.8, 66.7, 65.7, 31.7, 29.1 (2 9 CH2), 28.5, 25.7, 22.5,
20.4, 13.9; M.W: 202.29. ESI–MS m/z: 225.21
(M? ? Na?). HRMS (m/z) calculated for C11H22O3Na is
225.1461, found at 225.1461 (M? ? Na).
The pathogenic reference strains were seeded on the
surface of the media Petri plates, containing Muller–Hinton
agar with 0.1 ml of previously prepared microbial sus-
pensions individually containing 1.5 9 108 cfu mL-1
(equal to 0.5 McFarland standards). Wells of 6.0 mm
diameter were prepared in the media plates using a cork
borer and the synthesized compounds dissolved in 10 %
DMSO at a dose range of 125–0.97 lg were added to each
well under sterile conditions in a laminar air flow chamber.
Standard antibiotic solutions of Neomycin at a dose range
of 125–0.97 lg well-1, served as positive controls, while
the well containing DMSO served as a negative control.
The plates were incubated for 24 h at 30 °C and the well
containing the least concentration showing the inhibition
zone is considered as the minimum inhibitory concentra-
tion. All experiments were carried out in duplicate and
mean values are represented.
2-Octyl lactate (1 h): Colorless liquid; FT-IR (cm-1
,
CHCl3): 3491 (br.m, –O–H symmetric mode), 2930, 2868
(s, alkyl chain –C–H symmetric mode), 1742 (s, –C = O
symmetric mode), 1464 (m, –C–H scissoring mode), 1253
(m, –C–O symmetric mode), 1130 (s, –O–C = O asym-
metric mode); 1H-NMR (CDCl3, 500 MHz, d in ppm):
5.02–4.94 (1H, m), 4.26–4.19 (1H, m), 2.99 (brs, OH),
1.67–1.47 (2H, m), 1.40 (3H, d, J = 6.1 Hz), 1.36–1.20
(11H, m), 0.88 (3H, brt); 13C-NMR (CDCl3, 75 MHz, d in
ppm): 175.4, 72.7, 66.8, 35.7, 31.6, 28.9, 25.2, 22.5, 20.4,
19.8, 13.9; M.W: 202.29. ESI–MS m/z: 225.46
(M? ? Na). HRMS (m/z) calculated for C11H22O3Na is
225.1461, found at 225.1457 (M? ? Na).
3,7-Dimethyl 1-octyl lactate (1i): Colorless Liquid; FT-
IR (cm-1, CHCl3): 3467 (br.m, –O–H symmetric mode),
2955, 2927 (s, alkyl chain –C–H symmetric mode), 1738
(s, –C = O symmetric mode), 1471 (m, –C–H scissoring
mode), 1245 (m, –C–O symmetric mode), 1133 (s, –O–
Results and Discussion
Synthesis
1
C = O asymmetric mode); H-NMR (CDCl3, 500 MHz, d
in ppm): 4.29–4.24 (1H, m), 4.23–4.16 (2H,m), 2.89 (brs,
OH), 1.74–1.64 (1H, m), 1.58–1.47 (3H, m), 1.41 (3H, d,
J = 6.9 Hz), 1.35–1.21 (3H, m), 1.18–1.09 (3H, m), 0.91
(3H, d, J = 5.999 Hz), 0.87 (6H, d, J = 6.9 Hz); 13C-
NMR (CDCl3, 75 MHz, d in ppm): 175.8, 66.7, 64.2, 39.1,
37.1, 35.4, 29.7, 27.9, 24.5, 22.6, 22.5, 20.4, 19.4; M.W:
230.34, ESI–MS m/z: 253.43 (M? ? Na?). HRMS (m/z)
calculated for C13H26O3Na is 253.1774, found at 253.1772
(M? ? Na).
In the present study, a series of lactic acid-based anionic
surfactants (Fig. 2) were synthesized by a two-step proce-
dure. In the first step, alkyl lactates were synthesized by a
simple and efficient chemical method using different
straight chain, branched chain and unsaturated fatty alco-
hols and lactic acid employing PTSA as the catalyst. When
10 % PTSA was used as the catalyst, the yields were low
(71–75 %). However, after 6 h, the addition of one drop of
concentrated H2SO4 to the reaction mixture increased the
product yields to 81–95 %. In the second step, sulfated
sodium salts of alkyl lactates resulted from treatment of
corresponding alkyl lactates with chlorosulfonic acid
2-Penta nonyl lactate (1j): Colorless Liquid; FT-IR
(cm-1, CHCl3): 3467 (br.m, -O–H symmetric mode), 2962,
2874 (s, –C–H symmetric mode), 1736 (s, –C = O sym-
metric mode), 1463 (m, –C–H scissoring mode), 1212 (m,
–C–O symmetric mode), 1131 (s, –O–C = O asymmetric
123