706
S.M. Shaban et al. / Journal of Molecular Liquids 212 (2015) 699–707
Table 4
where they can be used as antibiotic against the tested bacteria (Gram
positive and negative), but they don't have any effect on the tested
fungi (Aspergillus flavus and Candida albicans).
Biocidel effect of the prepared compounds against sulfate reducing bacteria, SRB.
Conc.
Compound
The obtained result showed that the activity of prepared double
tailed cationic surfactant increases by increasing the length of the hy-
drophobic tail till maximum inhibition efficiency at chain length of
twelve carbon atom (II), then it decreases again at sixteen carbon
atom chain length (III), this behavior is known by cut-off effect [48–50].
There are some parameters effect on that phenomenon like, critical
micelle concentration of the used surfactant antibiotic, the change in
the free energy of adsorption on the cell membrane of bacteria, and
the size of diffused surfactant and the hydrophobicity of surfactant.
The net effect is the magnitude of all the previous parameters. Increas-
ing the chain length accompanied by decreasing the CMC, and so the
concentration at surface be lower, consequently the activity of
I ˃ II ˃ III, at the same time increasing the hydrophobic character, the
rate of adsorption at membrane interface be higher as discussed previ-
ously, so it predicted that III ˃ II ˃ I. Other theory return the cut-off effect
to a decrease in the perturbation of the membrane at higher alkyl tail,
assuming that the longer chain, the better mimic molecule in the lipid
layer, leading to disruption in the membrane. From the data recorded
in Table 3, it was found that the prepared double tailed cationic surfac-
tants with tail of twelve carbon atom has the maximum effect on Gram
positive and Gram negative bacteria [51–54].
Sulfate reducing bacteria (SRB) is one of the sources of H2S, which
increases the corrosiveness of brine and causing metals to crack and
blister especially in petroleum industry. The strategies to mitigate and
control the microbial induced corrosion by SRB in the petroleum com-
pany are to use biocide capable of reducing the growth of this type of
bacteria. The prepared double tailed surfactants have been tested
against sulfate reducing bacteria, using the serial dilution technique,
the contaminated water by SRB were supplied from AGIBA petroleum
company and subject to growth to 107 bacteria cell/ml. The obtained re-
sults were listed in Table 4, where the prepared surfactants have good
activity and can suppress the growth of bacteria and the prepared sur-
factants I, was found to have maximum efficiency as shown in Table 4.
The structure of bacteria cytoplasmic membrane of Gram-positive
and Gram-negative bacteria is shown in Fig. 9. The main composition of
the membrane is phospholipid and protein. The phosphatidylethanol-
amine (almost neutral at physiological pH) is a major component present
in the bacterial cytoplasmic membrane and that phosphatidylglycerol
1 ∗ 10−3
(M)
1 ∗ 10−4
(M)
5 ∗ 10−5
(M)
1 ∗ 10−5
(M)
Blank
I
II
III
107
10
102
103
103
103
103
103
103
103
103
102
103
cationic head be in contact with polar medium. The previous two
behaviors decrease the energy of the system, so the change in the
free energy of the prepared surfactant-solvent system will be de-
creased and increased in the negative direction.
(b) Increasing the temperature of surfactant aqueous system causes
a decrease of hydration around the hydrophilic group, so the hy-
drophobicity of the system increases and accompanied by in-
creasing the energy of the system, so molecules of surfactant
tend to adsorb and form micelle to decrease the energy of the
system.
By comparing ΔGomic and ΔGoads in Table 2, we note that the change
in the free energy of adsorption at certain temperature higher than the
change in free energy of micellization which indicate that the prepared
amidoamine double-tailed cationic surfactants favor adsorption at air–
water interface first till maximum surface saturation then the mono-
mers in bulk aggregates in clusters. The change in the entropy of both
micellization ΔSmic and adsorption ΔSads values were listed in Table 2,
and it found to be positive values indicating the disruption of water
structure around the double tailed hydrocarbon when they transfer
from the aqueous bulk to the air–water interface or to the micellar inte-
rior. The change in the entropy of adsorption ΔSads is more positive than
that of micellization ΔSmic, this reflect the greater freedom of hydropho-
bic part through motion to the interface than to form micelle [46–47].
3.7. Antimicrobial activity
The effect of prepared aminoamine double tailed cationic surfactants
on the bacteria and fungi has been determined and recorded in Table 3,
Fig. 9. Structure of the bacterial cell walls.