Bio-inspired surfactants capable of generating plant volatiles

Article abstract of DOI:10.1039/c5sm00157a

Plants are able to synthesize, store and release lipophilic organic molecules known as plant volatiles (PVs) utilizing specific biological pathways and different enzymes which play vital roles in the plant's defence and in dealing with biotic and abiotic stress situations. The process of generation, storage and release of PVs by plants acquired during the course of evolution is a very complex phenomenon. Bio-inspired molecular design of farnesol-based surfactants facilitates similar production, storage and release of PVs. The designed molecules adsorb at air-water interface and self-aggregate into micelles in aqueous system. The structural design of the molecules allows them to self-activate in water via intramolecular cation-π interactions. The activated molecules undergo molecular rearrangements generating volatile organic molecules both at interface and inside the micelle core. The molecules adsorbed at the interface initially release the formed volatile molecules creating vacant space at interface, thus thermodynamically directing the micelle to release the manufactured volatile products. This journal is

Full text of DOI:10.1039/c5sm00157a

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Bio-inspired surfactants capable of generating
plant volatiles†
Cite this: DOI: 10.1039/c5sm00157a
Avinash Bhadani,a Jayant Rane,b Cristina Veresmortean,a Sanjoy Banerjeeb
a
*
and George John
Plants are able to synthesize, store and release lipophilic organic molecules known as plant volatiles (PVs)
utilizing specific biological pathways and different enzymes which play vital roles in the plant's defence and
in dealing with biotic and abiotic stress situations. The process of generation, storage and release of PVs by
plants acquired during the course of evolution is a very complex phenomenon. Bio-inspired molecular
design of farnesol-based surfactants facilitates similar production, storage and release of PVs. The
designed molecules adsorb at air–water interface and self-aggregate into micelles in aqueous system.
The structural design of the molecules allows them to self-activate in water via intramolecular cation-p
interactions. The activated molecules undergo molecular rearrangements generating volatile organic
molecules both at interface and inside the micelle core. The molecules adsorbed at the interface initially
release the formed volatile molecules creating vacant space at interface, thus thermodynamically
directing the micelle to release the manufactured volatile products.
Received 20th January 2015
Accepted 26th February 2015
DOI: 10.1039/c5sm00157a
www.rsc.org/softmatter
debated topic of research.10–12 Volatile isoprenoids provide
protection to plants against several abiotic stresses including
Introduction
light, temperature, drought and oxidizing conditions of the
atmosphere.13 Among the various PVs generated and emitted by
the plants the bulk of them belong to the terpene family and
almost all plants have the potential to manufacture terpenes for
certain essential physiological functions.14 However, the
importance and function of the numerous terpenes remains
underexplored and investigations are lagging behind, especially
to understand the chemistry of plant volatiles, and their prac-
tical application in medicine, agriculture and industry. To best
of our knowledge, no chemical systems have been discovered
that mimic the in situ synthesis, storage and release of PVs.
Since PVs are important signaling molecules, the deciphering of
the chemical signals may be useful for designing new sustain-
able methods for pest and environmental control.15
In recent years the area of surfactant science has witnessed
robust progress and researchers have been successful in
designing several category of stimuli responsive surfactants
which response to change in pH, temperature, CO2, light and
magnetic eld.16 Here-in, unique set of new surfactants capable
of generating and releasing variety of volatile organic molecules
in aqueous system has been developed. We in the past have
designed several biobased/biocompatible molecules/materials
taking clue from the working pattern in nature.17–19 In contin-
uation of our work we have designed series of farnesol-based
heterocyclic cationic surfactants capable of self-activating
themselves when dissolved in water via intramolecular cation-p
interactions. The activated molecules undergo hydrolysis and
rearrangements generating and releasing volatile organic
Nature has always inspired mankind to develop future tech-
nologies based on its simple but efficient working pattern and
many designs in nature are oen based on the concept of self-
assembly.1 The process of evolution has enriched living systems
with incomparable levels of design, which is maintained by the
encoded information in their genetic material. Plants are
unique in this regard. Despite the extremely limited locomotion
capability they have the ability to control their surroundings by
releasing important PVs, which inuence the behavior of other
living organism nearby.2 Plants are able to synthesize, store and
release PVs which play vital roles in their defense, tritrophic
interactions, plant–plant communication and in dealing with
biotic and abiotic stress situations.3 When attacked by herbi-
vores they release specic herbivore-induced PVs4 or charac-
teristic terpenoids to attract carnivorous enemies of the
herbivores.5,6 Plant can be chemically provoked to release PVs
for defense.7 Furthermore, genetically modied plants capable
of releasing increased levels of herbivore-induced volatiles
demonstrate a greater ability to attract carnivorous predators,
thereby increasing the plant defenses.8,9 The long distance
signaling among plants with the help of PVs is still a well
aThe City College Center for Discovery and Innovation & Department of Chemistry, The
City University of New York, New York, NY 10031, USA. E-mail: john@sci.ccny.cuny.
edu
bDepartment of Chemical Engineering, The City College of the City University of New
York, New York, NY 10031, USA
† Electronic supplementary information (ESI) available: Experimental procedures,
supplementary gures, and characterization data. See DOI: 10.1039/c5sm00157a
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molecules as displayed in nature by plants. The mechanistic
strategy adopted to stimulate these molecules in aqueous
system consists of activating the double bond present at b
position of farnesyl chain adjacent to ester functional group of
designed molecule by a heterocyclic cationic system present
within the molecule, thus directing them to generate reactive
intermediate species capable of undergoing rearrangements
generating PVs.
Results and discussion
The farnesyl pyrophosphate (diphosphate) is the precursor for
the production of large array of PVs in the plants. The diphos-
phate dissociation from the enzyme-bound acyclic farnesyl
diphosphate generates an allylic carbocation that electrophili-
cally attacks double bond of terpene chain which further
undergo rearrangements producing several cyclic and acyclic
sesquiterpenes in plants.20
Farnesyl diphosphate can be considered an amphiphilic
molecule containing both hydrophobic and hydrophilic moie-
ties within same molecule (Fig. 1). Taking cue from this natu-
rally occurring molecule we designed a series of amphiphilic
molecules (Scheme 1) capable of self-activating, undergoing
rearrangements, producing and subsequently releasing volatile
organic molecules.
These amphiphilic molecules typically behave as surfactants
when dissolved in water as they diffuse to the air–water inter-
face and reduce the surface tension of the water. The migration
process of the surfactants to the air–water interface and the
corresponding decrease in surface tension value of water
continues until the air–water interface becomes fully occupied
by surfactant molecules and no vacant space is available at the
interface.21 At this point the farnesol-based surfactants begin to
Fig. 2 Surface tension vs. log C plot of the farnesol-based surfactants.
form micelle in an aqueous system and there is no further
decrease in surface tension value. Farnesol based cationic
surfactants are able to form micelles at this point is known as
the critical micelle concentration (cmc).
Fig. 2 shows the plot of surface tension versus log of
concentration for farnesol based cationic surfactants. The break
point in the graph corresponds to the cmc value of individual
surfactant. Far[Py]Br was able to form micelles at 5.90 mM
concentration and have the lowest cmc value among the series
of surfactants investigated, however Far[Im]Br has been found
to reduce the surface tension of water to a greater extent when
compared to other farnesol based surfactants. The cmc values
of these surfactants have also been investigated by conductivity
method.22,23 The results of conductivity experiments further
conrmed the ability of farnesol based cationic surfactants to
form micelles in aqueous solution (Fig. 3). Physical parameters
of farnesol-based surfactants have been calculated from the
data obtained from surface tension and conductivity experi-
ments (Table 1).
The calculated free energy of micellization (DGmicꢀ) of these
farnesol based cationic surfactants has been found to be
negative which suggests that micellization is a thermodynami-
cally favourable and spontaneous process for these molecules
when all the interface is occupied by surfactant monomers.24
The degree of counterion binding (b%) shows the bromide
counterions present in the stern layer of micelle to counter-
balance the electrostatic force which opposes micelle forma-
tion.25 The b value indicates the ability of counterion to bind
Fig. 1 Structure of farnesyl pyrophosphate. The molecule contains
both hydrophobic carbon chain (farnesyl moiety) and a hydrophilic
head group (diphosphate moiety).
Scheme 1 Synthesis of farnesol-based surfactants.
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Fig. 3 Specific conductivity vs. concentration plot of farnesol-based
surfactants.
micelles which has been found to be maximum for Far[Im]Br.
The experimental results of the self-aggregation studies of far-
nesol-based surfactants revealed that the nature of hydrophilic
head group greatly inuences the aggregation behavior of each
individual surfactant in aqueous system.
Fig. 4 Time dependent 1H NMR studies of 50 mM solution of Far[Py]Br
in D2O. The NMR spectra shown at different time interval: 0 hour, after
6 hours, 12 hours, 24 hours and 48 hours respectively at 25 ꢀC. The
surfactants solution were kept at 25 ꢀC. The surfactant starts to
degrade after 6 hours and completely degrades in 48 hours (degra-
dation time determined by recording NMR on short time interval).
The aqueous solutions of farnesol-based surfactants were
further investigated above their cmc values by time dependent
1H NMR spectroscopy. The results provided further insight into
solution chemistry of these molecules. The activated farnesol
based surfactants undergo time dependent isomerization and
hydrolysis in the aqueous solution. 1H NMR studies further
established that different surfactants isomerize and hydrolyze
at different rates and the process is dependent upon the nature
of the hydrophobic head group attached to the farnesyl moiety.
Far[Im]Br starts to hydrolyze aer 36 hours and completely
hydrolyzes in 144 hours (Fig. S1†). By contrast, the pyridinium
analogue (Far[Py]Br) undergoes very fast isomerization and
hydrolysis as it start to hydrolyze aer 6 hours and is completely
hydrolyzed by 48 hours (Fig. 4). Far[Trop]Br starts to isomerize
and hydrolyze by 18 hours (Fig. S2†) and the process is
completed in 110 hours.
Surface studies established that these farnesol based
surfactants self-aggregate to form micelles at different concen-
trations depending upon the nature of the cationic hydrophilic
head present in the molecule. The calculated surface parame-
ters and thermodynamic parameters also differ for different
surfactants under investigation. Correspondingly different
surfactants have different levels of self-activation when dis-
solved in water. Interestingly, the rst-hand macroscopic
observation was that we noticed the odorless surfactant
assemblies generate mild pleasant smell (fragrance-like) aer
certain time in water at ambient conditions. Further, the
changes evident from the time dependent 1H NMR spectroscopy
encouraged us to investigate the solution chemistry in detail by
headspace GC-MS analysis by analyzing the type of volatile
components being generated in the aqueous solution inside the
micelle core. Since different surfactants undergo isomerization
and hydrolysis at different rates, each individual system was
investigated at different time intervals depending on the
information available by time dependent 1H NMR spectroscopy.
The initial analysis of air samples withdrawn from the
headspace of each individual surfactant solution shows 5 main
peaks. These peaks corresponds to (Z)-nerolidol, (E)-nerolidol,
two of their activated derivatives, and an undetermined peak by
hydrolyzed heterocyclic ionic liquid derivative. The two isomers
of nerolidol are formed by rearrangement and hydrolysis at the
interface of the aqueous system. However, when the samples
Table 1 Surface properties of farnesol based cationic surfactant at 25 ꢀ
C
cmca
(mM)
cmcb
(mM)
gcmc
(mN mÀ1
106 Gmax
Amin
DGmic
ꢀ
ꢀ
DGads
Surfactant
b%
)
(mol mÀ2
)
(nm2)
(kJ molÀ1
)
(kJ molÀ1
)
Far[Im]Br
Far[Trop]
Br
6.77
6.20
6.85
6.79
60
55
28.8
29.2
1.47
1.38
1.13
1.20
À35.7
À34.6
À65.1
À65.6
Far[Py]Br
5.90
5.96
48
31.9
1.35
1.23
À33.5
À63.2
Determined by pendent drop method. b Determined by conductivity method.
a
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were analyzed for the volatile components aer it had under- (DGadsꢀ) is always greater (more negative) than the free energy of
gone complete hydrolysis, several different fractions of PVs were micellization (DGmicꢀ), which is also true for the farnesol-based
detected (Fig. 5). The initial results of headspace analysis of the surfactants under investigation (Table 1), the micelles break
samples seem quite obvious because during the initial stages down releasing the manufactured organic volatile as well as
when the surfactants are dissolved in the water, the molecules surfactant monomers in the aqueous solution. The released
tend to migrate to the air–water interface due to their surfactant surfactant monomers migrate to the air–water interface to
nature and subsequently when the interface is completely occupy the vacant space created by the hydrolyzing and isom-
occupied the surfactant monomers start to form micelles. The erizing surfactant molecules at the interface. The generated
molecules present at the air–water interface experience a organic molecule remains in water while some escapes into the
different chemical environment compared to molecules that are air. The calculated thermodynamic parameters support this
part of the micelle. The hydrophobic farnesyl chain of the hypothesis. This process continues until the entire micelle is
surfactant molecules at the interface is slightly exposed to an consumed generating the volatile organic molecules. A gradual
aqueous environment, while those parts of the micelles that change in turbidity of the aqueous solution can be observed
remain inside the hydrophobic micellar core are parts of the over time, as most of the volatile organic molecules formed are
hydrophobic environments. The results of headspace sample practically insoluble in water, although they remain as an
analysis conrmed that initial changes occurring at the air– emulsion due to the emulsifying nature of surfactants present
water interface rather than in the bulk solution. Two probable in the solution.
mechanisms can be conceived for the synthesis of PVs starting
During the changes occurring at the air–water interface and
from farnesol based cationic surfactants. One occurs at the inside the micelle core the hydrophilic head group dissociates
interface in an aqueous environment and the other occurs from the parent surfactant molecule to form heterocyclic ionic
inside the hydrophobic environment in the micelle core.
liquids in the solution. Most of the generated ionic liquids move
Isomerization and hydrolysis of monomeric molecules at the out to the aqueous solution as head groups are present at
interface generate volatile organic molecule and an ionic liquid. periphery of micelle, however some may be able to penetrate
However, the activated surfactant monomers, which are the part into the micelle core and catalyze the formation of different
of the micelle, continue to generate and store PVs inside the types of products. This assumption is based on the volatile
micelle core and the consistency and structure of micelle molecules detected from the headspace GC-MS (Fig. 6). The
structure is preserved because all molecules do not undergo major volatile organic molecules generated inside the micelle
1
structural changes at the same time (as observed by H NMR core are: (Z)-b-farnesene, (E)-b-farnesene, (Z,E)-a-farnesene,
spectroscopy).
(E,E)-a-farnesene, (E,Z)-a-farnesene, (Z,Z)-a-farnesene, b-bisa-
The changes occurring at the interface create vacant empty bolene, a-bisabolene, a-bisabolol, (E)-nerolidol, (Z)-nerolidol,
spaces at the air–water interface. Since free energy of adsorption isopulegol acetate and a-bergamotene. However the generated
Fig. 5 Headspace analysis of 50 mM aqueous solution of Far[Trop]Br. Headspace was collected after 110 h. The main components were
identified by mass spectra of computerized libraries. The chemical structure of major molecules generated inside the micelle core are 2:
germacrene B, 3: (Z)-b-farnesene, 4: (E)-b-farnesene, 5: (Z,E)-a-farnesene, 6: (Z,Z)-a-farnesene, 7: (E,Z)-a-farnesene, 8: (E,E)-a-farnesene, 9: b-
bisabolene, 10: a-bergamotene, 11: isopulegol acetate, 12: (Z)-nerolidol, 13: b-bisabolene, 14: (E)-nerolidol, 15: a-bisabolol. Peak 1 corresponds
to unidentified hydrolyzed tropine based ionic liquid derivative.
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Fig. 6 Volatile organic molecules generated at the air–water interface and inside the micelle core in aqueous solution as determined by
headspace GC-MS analysis.
imidazolium ionic liquids in case of Far[Im]Br may be able to
The hydrogen attached to C2 carbon of imidazolium cation
catalyse formation of other organic volatiles i.e. 5-isopropyl-2- in citronellol-based amphiphile is strongly acidic and
methyl-2-vinyltetrahydrofuran, oxepine, (Z)-3,4-dimethylpent-2- undergoes exchange with deuterium when dissolved in D2O
ene, (Z)-4,8-dimethylnona-3,7-dien-2-one, 4,8-dimethylnona- (Fig. 7a). In contrast, the hydrogen attached to C2 carbon of
3,8-dien-2-one and (Z)-linalool oxide (Fig. S3†), which were not imidazolium cation in the case of Far[Im]Br does not undergo
detected in case of other structural analogues. Similarly, the exchange with deuterium. It is evidenced that in case of citro-
dissociated tropine based ionic liquids are able to catalyse the nellol based amphiphile, formation of cation-p complex does
formation of germacrene B in the case of Far[Trop]Br (Fig. S4†) not occur, while it do occur in case of farnesol-based surfactant
not detected in case of Far[Im]Br and Far[Py]Br. Currently we are leading to compensation of the concentrated positive charge on
investigating the role of dissociated ionic liquids for their role the C2 carbon of the imidazolium cation thereby making the
as catalyst in the formation of different volatile component.
The structural design of the farnesol based heterocyclic
cationic surfactants enables them to self-activate in aqueous
solution by forming cation-p complex. The double bond at the b
position of the farnesyl moiety adjacent to ester functional
group interacts with the positive charge on the hydrophilic
cationic head group of the surfactant molecule. The activated
molecules are able to isomerize and form different type of
volatile organic molecules.
To understand the interaction of farnesol-based surfactants
in the aqueous system we synthesized a reference citronellol
based cationic amphiphile (ESI†) and investigated both farnesol
and citronellol based amphiphile by NMR spectroscopy using
D2O as solvent. The –NCHN– proton of imidazolium cation is
strongly deshielded. Imidazolium cation across the front (i.e.
–N–C2–N–) can be described by delocalized three center 4eÀ
component. The hydrogen at C2 position is more acidic because
imidazolium cation forms C]N p bond, leaving the C2 carbon
Fig. 7 1H NMR spectra of (a) citronellol based amphiphile and (b)
with concentrated positive charge and electron decient
farnesol based cationic surfactant in D2O. The imidazolium –NCHN–
proton do not undergo D2O exchange in case of (b) due to presence of
(Fig. 7).26
cation-p interactions.
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proton attached to it less acidic. This structural feature is Several new molecules can be designed capable of generating,
prevalent in aqueous system when both a cation and a p system storing and controlled releasing fragrance molecules. Such new
are present in close proximity.27 A closely related system to our fragrance release technology combined with detergency can be
designed cation-p system is the indole-3-acetic acid choline utilized in both consumer and industrial applications.
ester model investigated by Aoki et al.28
An important factor regulating the rate at which the volatile
organic molecules are formed is controlled by the extent of the
Acknowledgements
cation-p interaction.29 Each individual heterocyclic moiety have This work was partially supported by the GoMRI Grant # SA 12-
different magnitude of the cation-p interactions. The imidazo- 05/GoMRI-002 (subcontract TUL-626-11/12). GJ thank Tokyo
lium cation interacts with p-electrons of the double bond b to University of Science (TUS), where part of this manuscript was
the farnesyl ester group through a delocalized positive charge written, for a TUS President Award 2014 and the visiting
distributed across the –N–C2–N– front region, while the pyr- Professorship.
idinium cation probably interacts with the delocalized positive
charge on its ring with a larger sphere of positive charge and
tropine with a positive charge centered on the quaternary
Notes and references
nitrogen atom. However, apart from activation through forma-
tion of a cation-p complex structural arrangement of molecules
also plays an important role. Far[Im]Br is able to form tighter
packing at the air–water interface as evident from the calculated
Amin value (the area per molecule at the interface), this ability
decreases in the order as Far[Im]Br > Far[Trop]Br > Far[Py]Br.
Consequently, Far[Im]Br undergoes a slow isomerization and
hydrolysis compared to the others which have higher Amin
values. Since a tighter packing at the interface restricts the
movement of molecules principally involved in rearrangement,
Far[Im]Br undergoes a slow isomerization and hydrolysis at the
interface compared to others.
1 G. M. Whitesides and B. Grzybowski, Science, 2002, 295,
2418–2421.
2 N. Dudareva, F. Negre, D. A. Nagegowda and I. Orlova, Crit.
Rev. Plant Sci., 2006, 25, 417–440.
3 E. Pichersky, J. P. Noel and N. Dudareva, Science, 2006, 311,
808–811.
4 A. Kessler and I. T. Baldwin, Science, 2001, 291, 2141–2144.
5 M. Dicke, J. J. A. van Loon and R. Soler, Nat. Chem. Biol.,
2009, 5, 317–324.
6 T. C. J. Turlings and J. H. Tumlinson, Proc. Natl. Acad. Sci. U.
S. A., 1992, 89, 8399–8402.
7 J. S. Thaler, Nature, 1999, 399, 686–688.
8 I. F. Kappers, A. Aharoni, T. W. J. M. van Herpen,
L. L. P. Luckerhoff, M. Dicke and H. J. Bouwmeester,
Science, 2005, 309, 2070–2072.
Conclusion
Bio-inspired farnesol-based surfactants capable of self-acti-
9 E. Pennisi, Science, 2005, 309, 1976.
vating and self-aggregating in aqueous system have been 10 E. E. Farmer, Nature, 2001, 411, 854–856.
designed. These surfactants are able to adsorb at air–water 11 I. T. Baldwin, R. Halitschke, A. Paschold, C. C. Von Dahl and
interface and self-assemble as micelles in aqueous solution.
The micelle core acts as center for generation and storage of 12 J. B. Runyon, M. C. Mescher and C. M. De Moraes, Science,
volatile organic molecules where the activated aggregated 2006, 313, 1964.
molecules rearrange to form several organic volatile molecules. 13 C. E. Vickers, J. Gershenzon, M. T. Lerdau and F. Loreto, Nat.
The molecules at the air–water interface undergo rearrange- Chem. Biol., 2009, 5, 283–291.
ment and hydrolysis creating new vacant space at interface thus 14 J. Gershenzon and N. Dudareva, Nat. Chem. Biol., 2007, 3,
thermodynamically directing the micelle to release surfactant 408–414.
molecules as well as the manufactured products. The rate of 15 M. E. Maffei, J. Gertsch and G. Appendino, Nat. Prod. Rep.,
generation of volatile organic molecules formed inside the 2011, 28, 1359–1380.
micelle core as well as the types of the volatile molecule formed 16 P. Brown, C. P. Buttsa and J. Eastoe, So Matter, 2013, 9,
can be controlled by varying the type of heterocyclic cationic 2365–2374.
moiety attached to the parent farnesyl chain. Since each indi- 17 A. L. M. Reddy, S. Nagarajan, P. Chumyim, S. R. Gowda,
C. A. Preston, Science, 2006, 311, 812.
vidual cationic system activates and function in a specic
P. Pradhan, S. R. Jadhav, M. Dubey, G. John and
manner it is possible to control the rate at which the volatiles
P. M. Ajayan, Sci. Rep., 2012, 2, 960.
are generated. During the physicochemical changes taking 18 V. S. Balachandran, S. R. Jadhav, P. Pradhan, S. De Carlo and
effect in the aqueous solution the detaching/hydrolyzing G. John, Angew. Chem., Int. Ed., 2010, 49, 9509–9512.
cationic head group forms heterocyclic ionic liquids that 19 A. Kumar, P. K. Vemula, P. M. Ajayan and G. John, Nat.
further catalyze the formation of different organic volatiles Mater., 2008, 7, 236–241.
inside the micelle core in each individual system under 20 C. M. Starks, K. Back, J. Chappell and J. P. Noel, Science,
investigation.
1997, 277, 1815–1819.
The current research ndings open new door in the eld of 21 A. Bhadani, T. Endo, S. Koura, K. Sakai, M. Abe and H. Sakai,
surfactant science and in investigating the chemistry of PVs. In Langmuir, 2014, 30, 9036–9044.
nature, plants are able to generate, store and release volatile 22 C. Pucci, L. Perez, C. L. Mesa and R. Pons, So Matter, 2014,
´
organic molecules including many types of volatile fragrances.
10, 9657–9667.
Soft Matter
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View Article Online
Paper
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23 S. D. Choudhury, N. Barooah, V. K. Aswal, H. Pal, 27 P. C. Kearney, L. S. Mizoue, R. A. Kumpf, J. E. Forman,
A. C. Bhasikuttan and J. Mohanty, So Matter, 2014, 10,
3485–3493.
A. McCurdy and D. A. Dougherty, J. Am. Chem. Soc., 1993,
15, 9907–9919.
24 A. Bhadani and S. Singh, Langmuir, 2009, 25, 11703–11712. 28 K. Aoki, K. Murayama and H. Nishiyama, J. Chem. Soc.,
25 A. Bhadani and S. Singh, Langmuir, 2011, 27, 14033–14044. Chem. Commun., 1995, 2221–2222.
26 P. A. Hunt, B. Kirchner and T. Welton, Chem.–Eur. J., 2006, 29 A. S. Mahadevi and G. N. Sastry, Chem. Rev., 2013, 113, 2100–
12, 6762–6775.
2138.
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