β-CD assisted dissolution of quaternary ammonium permanganates in aqueous medium

Article abstract of DOI:10.1016/j.carbpol.2014.05.046

The non-polar internal cavity of β-cyclodextrin (β-CD) has been exploited for the entrapment of the hydrophobic tails of two water insoluble quaternary ammonium permanganates (QAPs): cetyltrimethylammonium permanganate (CTAP) and tetrabutylammonium permanganate (TBAP), for solubilization in aqueous medium. The solubilization and organizational behavior of the QAPs in aqueous β-CD solution have been determined from the comparison of their rates of self-oxidation in presence and in absence of β-CD. Effect of QAP concentration on their observed rate constants (k_obs) at a fixed β-CD concentration, phase solubility analysis in varying β-CD concentration, impact of quaternary ammonium bromides (QABs) on the k _obs values of CTAP and TBAP at fixed QAP and β-CD concentrations, and the temperature effect have been reported. A scheme to explain the solvation of QAPs in aqueous β-CD has been proposed based on dynamic light scattering (DLS) analysis of the samples.

Full text of DOI:10.1016/j.carbpol.2014.05.046

Carbohydrate Polymers 111 (2014) 806–812
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
ˇ-CD assisted dissolution of quaternary ammonium permanganates
in aqueous medium
Suraj Prakash Bank, Partha Sarathi Guru, Sukalyan Dash∗
Department of Chemistry, Veer Surendra Sai University of Technology, Burla 768 018, Odisha, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The non-polar internal cavity of ˇ-cyclodextrin (ˇ-CD) has been exploited for the entrapment of the
hydrophobic tails of two water insoluble quaternary ammonium permanganates (QAPs): cetyltrimethy-
lammonium permanganate (CTAP) and tetrabutylammonium permanganate (TBAP), for solubilization in
aqueous medium. The solubilization and organizational behavior of the QAPs in aqueous ˇ-CD solution
have been determined from the comparison of their rates of self-oxidation in presence and in absence
of ˇ-CD. Effect of QAP concentration on their observed rate constants (kobs) at a fixed ˇ-CD concentra-
tion, phase solubility analysis in varying ˇ-CD concentration, impact of quaternary ammonium bromides
(QABs) on the kobs values of CTAP and TBAP at fixed QAP and ˇ-CD concentrations, and the temperature
effect have been reported. A scheme to explain the solvation of QAPs in aqueous ˇ-CD has been proposed
based on dynamic light scattering (DLS) analysis of the samples.
Received 29 October 2013
Received in revised form 30 April 2014
Accepted 14 May 2014
Available online 27 May 2014
Keywords:
Cyclodextrin
Cetyltrimethylammonium permanganate
Tetrabutylammonium permanganate
Inclusion complexation
Solubility analysis
© 2014 Elsevier Ltd. All rights reserved.
Dynamic light scattering
1. Introduction
on ˇ-CD, permanganate does not cause any notable oxidation of
this host molecule (Manhas, Mohammed, & Khan, 2007).
Quaternary ammonium permanganates (QAPs) are an estab-
lished class of phase transfer oxidants, used for the oxidation of
water-insoluble organic compounds of various classes. QAPs are
sparingly soluble in water medium; however, they show strong
solubility in several organic solvents (Dash & Mishra, 1995). The
major problem with these compounds is that they undergo a rapid
self-oxidation/dissociation in organic media (Scheme 1); hence
choosing a proper medium is generally necessary for their efficient
utilization as oxidant for organic substrates. Besides, the com-
pounds are perfectly soluble in organic media only, restricting their
utilization for the oxidation of inorganic substrates.
The present communication focuses on a model for the dis-
solution of some QAP molecules in water medium assisted by
ˇ-cyclodextrin (ˇ-CD) from the comparison of their rate constants
of self-oxidation in presence and in absence of ˇ-CD. Cyclodex-
trins are cyclic oligosaccharides composed of glucose units linked
by ˛-1,4-glycosidic bonds. These are of three types: ˛-cyclodextrin,
ˇ-cyclodextrin, ꢀ-cyclodextrin, being composed of 6, 7, and 8 ˛-
1,4-glycosidic bonds; each cyclodextrin unit having a hydrophobic
cavity, which can act as a host for a hydrophobic guest molecule
(Martin Del Valle, 2003). Despite the presence of hydroxyl groups
The most notable feature of cyclodextrins is their ability to form
inclusion complexes (host–guest complexes) with a wide range of
solid, liquid and gaseous compounds by molecular complexation.
The lipophilic cavity of cyclodextrin molecules provides a microen-
vironment into which appropriately sized non-polar moieties can
enter to form inclusion complexes (Loftsson & Brewster, 1996). This
property is useful for solubilizing and stabilizing highly hydropho-
bic molecules in water. No hydrogen bonds are formed or broken
during the formation of such host-guest complexes (Singh, Sharma,
& Banerjee, 2002). Solubilization may also occur through the forma-
tion of micellar types of aggregate in aqueous solutions (Loftsson,
Jarho, Masson, & Jarvinen, 2005). The main driving force of com-
plex formation is the release of enthalpy-rich water molecules from
the cavity. Water molecules are displaced by more hydrophobic
guest molecules present in the solution to attain an apolar–apolar
association and decrease the cyclodextrin ring strain resulting in a
more stable lower energy state (Szetjli, 1998). The binding of guest
molecules within the host cyclodextrin is not fixed or permanent;
rather, it is in the state of a dynamic equilibrium.
The ability of cyclodextrin to form an inclusion complex with
a guest molecule is a function of two key factors such as steric
factor and critical factor. The steric factor depends on the relative
size of the cyclodextrin to the size of the guest molecule or cer-
tain key functional groups within the guest and the critical factor
represents the thermodynamic interactions between the different
∗
Corresponding author. Tel.: +91 9438640496; fax: +91 6632430204.
E-mail address: sukalyan dash@yahoo.com (S. Dash).
http://dx.doi.org/10.1016/j.carbpol.2014.05.046
0144-8617/© 2014 Elsevier Ltd. All rights reserved.

S.P. Bank et al. / Carbohydrate Polymers 111 (2014) 806–812
807
create new functionalized oxidant, therefore, will become highly
important in the years to come.
2. Materials and methods
2.1. Materials
CTAP and TBAP were synthesized in the laboratory as per the
standard procedures (Chidambaram, Sonavane, de la, & Sasson,
2007; Dash et al., 1995). Quaternary ammonium bromides (QAB)
such as cetyltrimethylammonium bromide (CTAB) and tetrabutyl-
ammonium bromide (TBAB) were procured from Merck, India, and
were recrystallized using methanol solution and their purity was
checked from physical constants. ˇ-CD (Merck, India) was used as
received and triple distilled water was used throughout the exper-
iments.
2.2. Methods
2.2.1. Preparation of solutions
ˇ-CD (8.0 mmol) was dissolved in 500 ml triple distilled water
through slight warming, filtered through a cotton plug to prepare
the stock solution of 15 mM concentration, which was used for
the preparation of a range of solutions of ˇ-CD of concentra-
tions 1.5–15 mM. Freshly prepared solutions of CTAP and TBAP
(0.5–0.9 mM) in aqueous ˇ-CD medium maintained within the
above concentration range, were prepared and filtered by cotton
plug to obtain clear solutions of CTAP and TBAP.
2.2.2. Absorption spectral analysis
Solutions having appropriate concentrations of the QAPs and
ˇ-CD were transferred to the sample cuvette of a pair of matched
quartz cells to measure the rates of self-oxidation/dissociation of
QAPs by a thermostated Hitachi U-3010 double beam UV–vis spec-
trophotometer at 22.0 1 ◦C at four different wavelengths (ꢁmax
)
of 568, 546, 528, and 486 nm. The measurements were done for
40 min in each case with 2 min time interval. All the calculations
have been done at a standard ꢁmax of 528 nm and the rate constant
values (kobs) have been calculated using Eq. (1) (Dash et al., 1995).
ꢀ
ꢁ
ꢀ
ꢁ
2.303
t
ODo
ODt
kobs
=
log
(1)
Scheme 1. Self-oxidation of CTAP in chloroform medium.
where ODo = optical density at ‘0’ time, ODt = optical density at time
‘t’.
components of the system (cyclodextrin, guest, solvent) (Martin
Del Valle, 2003). For a complex to form there must be a favorable net
energetic driving force that pulls the guest into the cyclodextrin. In
general, there are four energetically favorable interactions that help
shift the equilibrium to form the inclusion complex (Martin Del
Valle, 2003): (a) the displacement of polar water molecules from
the apolar cyclodextrin cavity, (b) the increased number of hydro-
gen bonds formed as the displaced water returns to the larger pool,
(c) a reduction of the repulsive interactions between the hydropho-
bic guest and the aqueous environment, and (d) an increase in the
hydrophobic interactions as the guest inserts itself into the apo-
lar cyclodextrin cavity. However, host cyclodextrin molecules are
also known to form non-inclusion complexes. (Loftsson, Masson, &
Brewster, 2004; Loftsson, Magnusdottir, Masson, & Sigurjonsdottir,
2002).
The solution behavior of cetyltrimethylammonium perman-
ganate (CTAP) and tetrabutylammonium permanganate (TBAP)
containing C16 and C4 chains respectively in water medium in pres-
ence of ˇ-CD have been studied to understand the ˇ-CD-QAP inclu-
sion complexation, their stability and self-oxidation/dissociation
properties as well as their oxidizing capabilities of various sub-
strates in that medium. The combination of ˇ-CD and QAPs to
The results reported are an average of three runs with an error
of ( ) 6.0%.
2.2.3. Dynamic light scattering analysis
Dynamic light scattering measurements were made on the fixed
scattering angle Zetasizer Nano-ZS system (Malvern, UK) equipped
with a He–Ne laser beam at 658 nm. The instrument was used for
sizing (dynamic light scattering, DLS) to determine the z-average
molecular “size” in terms of the hydrodynamic diameter dH in solu-
tion, a parameter inversely related to the z-average translational
diffusion coefficient, D (Eq. (2)) in solution.
kBT
D =
(2)
3ꢂꢃdH
Samples, filtered through cotton plug, were measured at
22.0 1 ◦C and the light scattering was detected at 173◦ and
collected in automatic mode, typically requiring a measurement
duration of 120 s.
2.2.4. Phase solubility analysis
Phase–solubility analysis of ˇ-CD on the QAPs has been carried
out after constructing a phase-solubility diagram by plotting the

808
S.P. Bank et al. / Carbohydrate Polymers 111 (2014) 806–812
0.0025
total molar concentration of the QAPs on the y-axis and the total
molar concentration of ˇ-CD on the x-axis and the profile of the
change has been recorded to determine the type of complexation,
stability constant (Ky:x) and the complexation efficiency of ˇ-CD
with QAP molecules (Higuchi & Connors, 1965).
TBAP
CTAP
0.002
For a linear profile of the plot (AL), which represents a 1:1 com-
plexation (Eq. (3)), the stability constant (K1:1) of the complex has
been calculated from the slope of the plot, according to Eq. (4).
0.0015
0.001
Guest + ˇ-CD = Guest − ˇ-CD
(3)
(4)
slope
K1:1
=
So(1 − slope)
where So = Intrinsic solubility of guest molecules in aqueous
complexation medium (i.e. guest molecule solubility when no
cyclodextrin is present).
The complexation efficiency (CE) for 1:1 inclusion complex has
been calculated from the slope of the plot using Eq. (5).
0.0005
0.000
0.005
0.010
0.015
0.020
[β-CD] in mM
[Guest − ˇ-CD]
[ˇ-CD]
slope
CE =
= So · K1:1
=
(5)
(1 − slope)
Fig. 1. Variation of [ˇ-CD] in mM with [QAP] in mM in aqueous medium at
22.0 1 ◦C.
3. Results and discussion
that potentially forms inclusion complex with the number of sub-
strate molecules have been done form the CE value. In case of CTAP,
the number of substrate molecules is calculated to be 1 in every 11
number of ˇ-CD molecules, and in case of TBAP, the number of
substrate molecules is 1 in every 21 number of ˇ-CD molecules
(Loftsson, Hreinsdı´ottir, & Mı´asson, 2005).
From the kinetics study it is evident that concentration of
cyclodextrin is directly related to the first order rate constant
(Fig. 2).
3.1. Analysis of phase-solubility
Variation of optical density and rate constant of dissociation of
QAP with concentration of ˇ-CD has been analyzed to study the
phase-solubility analysis of the QAPs. The molar concentration of
both CTAP and TBAP have been calculated from their optical densi-
ties in their 0.5 mM solution in aqueous ˇ-CD solutions of variable
concentrations (1.5–15 mM) using the well-known Beer–Lambart
equation (Eq. (6)).
When the number of cyclodextrin molecule increases for a
fixed number of guest molecules, the later finds more option
to be encapsulated, either due to inclusion and/or non inclu-
sion type complexation and aggregation. Besides, an increase in
the rate constant is indicative of the shifting of the equilibrium
toward right, thereby leading to the enhanced stability of the
guest after complexation. The stability of the 1:1 inclusion com-
plex can also be deciphered from the dissociation constant value.
The lower value for the dissociation kinetics indicates the stronger
host–guest complexation (Loftsson & Brewster, 2012). The slope
for variation of rate constant of CTAP dissociation (SlCTAP = 4.84)
OD = ε.c.l
(6)
where OD = optical density, ε = extinction coefficient of perman-
ganate (2300 M−1 cm−1), c = molar concentration of the substrate,
and l = path length of the quartz cell (1 cm).
The plots of molar concentrations of CTAP and TBAP with the
concentration of ˇ-CD represent the solution phase-solubility pro-
file for the ˇ-CD induced dissolution of CTAP and TBAP from
aqueous medium and are found to be of AL type (i.e. a linear increase
in the solubility of CTAP and TBAP as a function of ˇ-CD concen-
tration), which is indicative of the formation of soluble inclusion
complexes (Fig. 1).
The slopes of the phase-solubility profile for CTAP and TBAP are
found to be 0.0894 and 0.0483 respectively, which are less than
unity, suggesting a probability of formation of 1:1 inclusion com-
plexes, thus enhancing the solubility of the quaternary ammonium
ions in aqueous ˇ-CD medium. However, beside the formation of
inclusion complexes, formation of some non-inclusion complexes
cannot completely be excluded.
Intrinsic solubilities of CTAP (So CTAP) and TBAP (So TBAP) in
aqueous complexation medium (i.e. QAP solubility when no
cyclodextrin is present) are found to be 0.9 ␮g/mL in both the cases.
The stability constants (K1:1) for CTAP and TBAP are found to be
109.1 and 56.4 M−1 indicating the formation of stable inclusion
complexes between ˇ-CD and each of the QAP solute (Connors,
1997).
Complexation efficiency (CE) value for CTAP (CECTAP = 0.1) is
found to be 50% more than that of TBAP (CETBAP = 0.05). A higher
CE value for CTAP than that for TBAP suggest that CTAP is more
susceptible for being trapped into the hydrophobic microenviron-
ment of the ˇ-CD since it is hydrophobic due to the presence of
long hexadecyl chain. This assumption is also supported by a higher
stability constant (K1:1) for the CTAP-ˇ-CD inclusion complex than
the TBAP-ˇ-CD inclusion complex. Quantification of ˇ-CD molecule
TBAP
CTAP
100
80
60
40
20
0
0
5
10
15
20
[β-CD] in mM
Fig. 2. Variation of [ˇ-CD] in mM with rate constants of self-oxidation/dissociation
of QAPs in aqueous medium at 22.0 1 ◦C.

S.P. Bank et al. / Carbohydrate Polymers 111 (2014) 806–812
809
80
90
85
80
75
70
65
60
55
50
TBAP
CTAP
TBAP
CTAP
75
70
65
60
55
50
4
5
6
7
8
9
10
0
1
2
3
4
[QAP] in mM
[CTAB] in mM
Fig. 3. Variation of [QAP] in mM with rate constants of self-oxidation/dissociation
at a fixed ˇ-CD concentration of 9.0 mM in aqueous medium at 22.0 1 ◦C.
(a)
is found to be lower than that for variation of rate constant of
TBAP dissociation (SlTBAP = 5.16) indicating a stronger host–guest
complexation in case of CTAP. As the cyclodextrin concentration
increases, the cyclodextrin molecules and their complexes self-
assemble to form aggregates that often ranges in size between
20 and 100 nm in diameter. The aggregation and the size of the
aggregates increase with increasing cyclodextrin concentration
(Messner, Kurkov, Jansook, Loftsson, 2010; Jansook, Kurkov, &
Loftsson, 2010; Messner, Kurkov, Brewster, Jansook, & Loftsson,
2011; Messner, Kurkov, Flavia-Piera, Brewster, & Loftsson, 2011;
Messner, Kurkov, Palazon, et al., 2011; Rao & Geckeler, 2011).
85
80
75
70
65
60
55
50
TBAP
CTAP
3.2. Variation of CTAP and TBAP concentration in fixed ˇ-CD
concentration
Keeping the concentration of ˇ-CD at an optimum value of
9.0 mM within the concentration range of 1.5–15 mM, the inclu-
sion complexation and/or non-inclusion complexation leading to
the stability of CTAP and TBAP as well as the possibility of self-
oxidation/dissociation of both the QAPs were enumerated. The
possible self-oxidation/dissociation of both the QAPs was also com-
pared with the data obtained in absence of ˇ-CD. The pseudo-first
order rate constants (kobs) determined from their kinetic study at
22.0 1 ◦C are found to increase with concentration of both the
QAPs up to 0.8 mM, beyond which they decrease. In case of CTAP,
the slope of the increasing arm of the plot is 0.472 and that of
decreasing arm is −0.636, whereas in case of TBAP, the slope of
the increasing arm of the plot is 0.546 and that of decreasing arm is
−2.65 (Fig. 3). A sharper change of rate constant in TBAP solutions
is indicated from the slopes of both the arms.
With the increase in the concentration of CTAP up to 0.8 mM in
aqueous ˇ-CD medium there occurs an increase in the rate constant
(kobs) of self-oxidation, a phenomenon which is in sharp contrast
with the previous observations during its self oxidation in neat
organic solvents, where the rate constant values go on decreasing
with concentration rise of CTAP (Dash et al., 1995). The reverse
dependence of rate constants on the concentration of CTAP in neat
organic medium was proposed to be due to reverse micellization
phenomenon of CTAP, which helps in decreasing the self-oxidation
of CTAP due to the increase in the extent of aggregation with the rise
in the concentration of CTAP (Dash & Mishra, 1997; Dash, Nayak,
Sahu, Patel, & Mishra, 2008; Patel & Mishra, 2006). In the present
case, the increase in the kobs values for both the QAPs up to a concen-
tration of 8 × 10−4 M, thus indicates the absence of any micellar or
reverse micellar aggregation; rather it is an indication of inclusion
0
1
2
3
4
[TBAB] in mM
(b)
Fig. 4. Effect of [CTAB] in mM (a) and [TBAB] in mM (b) on rate constants of CTAP
and TBAP at a fixed ˇ-CD concentration of 9.0 mM in aqueous medium at 22.0 1 ◦C.
complexation with the inner non-polar cavity of ˇ-CD molecules
present in the aqueous medium. In other words, the possibility
of micellar aggregation of free QAP molecules up to the above-
mentioned concentration in each case are potentially overcome by
inclusion complexation with ˇ-CD. Beyond the concentration of
0.8 mM, a sharp decrease in the kobs values for both the QAPs may
be due to the aggregation of ˇ-CD inclusion complexes.
3.3. Effect of QAB (CTAB and TBAB)
The effects of CTAB and TBAB have been studied on the
self-oxidation/dissociation of CTAP and TBAP at an optimum
concentration of 0.5 mM in 9.0 mM ˇ-CD aqueous solution at
22.0 1 ◦C. The rate constants (kobs) for the self-oxidation of CTAP
show a decreasing trend with the increased concentrations of CTAB
and TBAB, whereas a reverse trend is observed in case of TBAP
(Fig. 4).

810
S.P. Bank et al. / Carbohydrate Polymers 111 (2014) 806–812
Table 1
-14.9
Size distribution of QAPs and QAP + QABs in aqueous ˇ-CD medium, [ˇ-CD] = 9.0 mM.
TBAP
CTAP
-14.85
-14.8
Samplesa
Mean intensity percent at various size range
0–100 nm
100–1000 nm
1000–3000 nm
-14.75
-14.7
1
2
3
4
5
6
13
52
80
07
08
09
65
60
62
35
16
11
–
–
–
-14.65
-14.6
11
05
09
-14.55
-14.5
a
Sample 1: [CTAP] = 0.5–0.9 mM, Sample 2: [TBAB] = 0.0–0.4 mM, [CTAP] = 0.5 mM
(Constant), Sample 3: [CTAB] = 0.0–0.4 mM, [CTAP] = 0.5 mM (Constant), Sample 4:
[TBAP] = 0.5–0.9 mM, Sample 5: [TBAB] = 0.0–0.4 mM, [TBAP] = 0.5 mM (Constant),
Sample 6: [CTAB] = 0.0–0.4 mM, [TBAP] = 0.5 mM (Constant).
-14.45
-14.4
0.00325
0.0033
0.00335
0.0034
1/T (k-1)
Increase in the CTAP and TBAP concentration in the aque-
ous solution with a constant ˇ-CD concentration increases the
rate constant up to a concentration of 0.8 mM of the QAPs, since
up to that concentration the inclusion complexes of ˇ-CD–QAP
exist in monomeric form. Beyond this concentration, aggregation
has been proposed resulting in a decrease in the rate constant
values. In the present case, prior to the addition of QABs, the ˇ-
CD–QAP inclusion complexes continue to remain in monomeric
form; however, addition of QABs change the rate constants of self-
oxidation/dissociation of CTAP as well as TBAP.
With CTAP as the substrate, addition of both the QABs decrease
the rate constants, which may be due to aggregation of ˇ-CD–CTAP
and ˇ-CD–QAB inclusion complexes. However, when TBAP is taken
as the substrate, which possesses a shorter hydrophobic cleft,
such an aggregation among the inclusion complexes becomes
improbable, rather both the inclusion complexes (ˇ-CD–TBAP
and ˇ-CD–QAB) may be existing in monomeric forms in the
solution, resulting in an increase in the rate constant of self-
oxidation/dissociation.
The above outcome was confirmed from the dynamic light
scattering experiments of the solution containing CTAP, TBAP,
CTAP + TBAB, CTAP + CTAB, TBAP + TBAB, and TBAP + CTAB in 9.0 mM
ˇ-CD solution. The mean intensity percent versus size (r) in nm
for all the samples have been analyzed within three size ranges
(Table 1).
The DLS analyses show that (i) the solutions containing CTAP
do not show any peak in the range of 1000–3000 nm, whereas
a peak in this range is definitely obtained for all the solutions
containing TBAP, (ii) solutions containing only CTAP, as well
as those with TBAB and CTAB along with CTAP show much
higher intensities at all ranges compared to the solutions with
TBAP at comparable size range, (iii) solutions containing CTAP
only, CTAP + TBAB, and CTAP + CTAB show clear enhancements of
percent intensity in the size range of 0–100 nm in the order,
CTAP < CTAP + TBAB < CTAP + CTAB; however, in the size range of
100–1000 the percent intensity remains almost a constant, and
(iv) in case of the solutions containing TBAP only, TBAP + TBAB, and
TBAP + CTAB, the intensities in each of the size range does not show
any remarkable change.
Fig. 5. Plot of ln(kobs/T) versus 1/T at a fixed ˇ-CD concentration of 9.0 mM in aque-
ous medium.
These observations fully corroborate the explanations from
kinetic data: the aggregation of CTAP molecules occurring in the
ˇ-CD solution are further enhanced by the addition of quaternary
ammonium bromide salts and this enhancement increases in order
of the addition of TBAB and CTAB. However, TBAP molecules or
any of the quaternary ammonium bromides along with TBAP in the
ˇ-CD solution do not trigger the formation of aggregated organiza-
tions (Supplementary Fig. 1 (a)–(f)).
Supplementary material related to this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.carbpol.
2014.05.046.
A model consistent with the above discussions with reference
to the impact of QAB concentration on the trend of rate constants
of self-oxidation/dissociation of CTAP and TBAP in ˇ-CD aqueous
phase has been presented in Scheme 2.
3.4. Temperature effect
Activation parameters for self-oxidation/dissociation of the
QAPs in ˇ-CD aqueous phase were calculated from the plots of ln
(kobs/T) versus 1/T, which are found to be linear (Fig. 5) and the data
are presented in Table 2.
The thermodynamic parameters are dependent not only on the
extent of self-oxidation/dissociation of QAPs, but also on the impact
of complexation induced by ˇ-CD. ꢄH# values are found to be sig-
nificantly higher than the TꢄS# values, indicating the complexation
process to be enthalpy driven. Besides, the higher ꢄH# value of
CTAP compared to TBAP shows a better inclusion complexation of
the former, due to its longer hydrophobic cleft. The ꢄG# values in
both the QAPs increase with temperature, which indicate better
complexation with the ˇ-CD host molecules at a lower tempera-
ture condition. The negative values of ꢄS# for both the QAPs show
lower randomness and higher stabilization of the systems in the
aqueous ˇ-CD medium.
Table 2
Thermodynamic parameters of pseudo-first order kinetics of self- oxidation/dissociation of QAPs in aqueous medium, [QAP] = 0.5 mM, [ˇ-CD] = 9.0 mM.
QAP
kobs × 105 (s−1
)
T (K)
ꢄG# (kJ/mol)
ꢄH# (kJ/mol)
−ꢄS# (J/mol/K)
57.8
65.2
83.7
295
300
305
94.6
95.8
97.0
CTAP
25.2
235.3
67.3
75.8
86.9
295
300
305
94.2
95.5
96.8
TBAP
16.6
263.0

S.P. Bank et al. / Carbohydrate Polymers 111 (2014) 806–812
811
4
6
CTAB
CTAB
CTAP
TBAP
2
1
3
TBAB
TBAB
5
7
= -CD
= CTAP
= TBAP
= CTAB
= TBAB
Scheme 2. Impact of CTAB and TBAB on CTAP and TBAP dissolved in ˇ-CD aqueous phase (1: ˇ-CD aqueous phase, 2: CTAP dissolved in ˇ-CD aqueous phase, 3: TBAP dissolved
in ˇ-CD aqueous phase, 4: partitioning of CTAP to CTAP-CTAB micellar submicro phase, 5: partitioning of CTAP to CTAP-TBAB micellar submicro phase, 6: CTAB-enhanced
inclusion complexation of TBAP, 7: TBAB-enhanced inclusion complexation of TBAP).
4. Conclusion
increase in the concentration of CTAP, a competition seems to
occur between ˇ-CD-CTAP complexation and micellar aggregation
of CTAP molecules, whereas, with an increase in the concentration
of TBAP, an increased ˇ-CD-TBAP complexation might be occurring.
The work will stem further research on the oxidation of various
water-soluble inorganic and organic substrates using quaternary
ammonium permanganate oxidants.
An attempt has been initiated to solubilize QAP molecules in
water medium for their further oxidizing applications. ˇ-CD has
been found to enhance the solubilization and stabilization of these
molecules in water medium through inclusion-complex forma-
tion. The impact of chain-length of CTAP and TBAP are the chief
deciding factor in their solubilization and stabilization. The reverse
micellization phenomenon observed during the oxidation of sub-
strates by QAP molecules in neat organic media during the course
of several previous works does not exist in the ˇ-CD aqueous
phase. Dynamic light scattering experiments show that with an
Acknowledgement
SD acknowledges the financial help extended by AICTE, New
Delhi, through a RPS project to set up the laboratory.

812
S.P. Bank et al. / Carbohydrate Polymers 111 (2014) 806–812
Loftsson, T., Magnusdottir, A., Masson, M., & Sigurjonsdottir, J. F. (2002). Self-
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