Calix-arene silver nanoparticles interactions with surfactants are charge, size and critical micellar concentration dependent

Article abstract of DOI:10.1039/c2cc34670b

The interactions of silver nanoparticles capped by various calix[n]arenes bearing sulphonate groups at the para and/or phenolic faces with cationic, neutral and anionic surfactants have been studied. Changes in the plasmonic absorption show that only the calix[4]arene derivatives sulphonated at the para-position interact and then only with cationic surfactants. The interactions follow the CMC values of the surfactants either as simple molecules or mixed micelles.

Full text of DOI:10.1039/c2cc34670b

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COMMUNICATION
Calix-arene silver nanoparticles interactions with surfactants are charge,
size and critical micellar concentration dependentw
Yannick Tauran,ab Arnaud Brioude,a Patrick Shahgaldian,c Alessandro Cumbo,c
Beomjoon Kim,bd Florent Perret,e Anthony W. Coleman*a and Imed Montasserf
Received 29th June 2012, Accepted 8th August 2012
DOI: 10.1039/c2cc34670b
The interactions of silver nanoparticles capped by various
calix[n]arenes bearing sulphonate groups at the para and/or
phenolic faces with cationic, neutral and anionic surfactants
have been studied. Changes in the plasmonic absorption show
that only the calix[4]arene derivatives sulphonated at the para-
position interact and then only with cationic surfactants. The
interactions follow the CMC values of the surfactants either as
simple molecules or mixed micelles.
and assembly properties9 have been widely studied. They are
known to complex a wide range of organic cations,10 including
alkyl ammonium,11 and alkylated pyridinium12 salts. Amphiphilic
calix[n]arenes have been demonstrated to form various types
of assembly in aqueous media. One minor drawback is
that calix[n]arenes require very considerable modification to
introduce reporter groups, with the possible perturbation of
the complexation properties. The discovery by Xiong et al.
that para-sulphonato-calix[n]arenes can cap silver nanoparticles
and that the plasmon resonance bands of the hybrid colloids
show strong spectral shifts upon selective interaction with
histidine introduces the needed reporter functions.13 Recently
we have shown that the hybrid nanoparticles interact with
nucleic bases in a similar manner and that the interactions
can lead to aggregation of the colloids.14
Micelles are formed by the aggregation of surfactants having a
cone like geometry,1 they are characterised by the critical
micellar concentration (CMC), above which no free surfactant
molecules go into solution.2 The CMCs can be determined by
a quite large number of physical measurements of which the
surface tension is the most widely used.3 Micelles are used in a
vast range of applications varying from soaps and detergents,4
through butter or margarine5 to the extraction of membrane
proteins.6 Such applications as the last require detailed knowledge
of the micellar aggregations whereas the former applications are
dependent on a subjective feeling by a consumer. It is the field of
membrane protein biochemistry that the use of supramolecular
surfactants is starting to make an impact.
In the present work we report the interactions of three types
of sulphonato-calix[n]arene silver nanoparticles with various
cationic, neutral and anionic surfactants. The measured spectral
shifts can be used as a novel way to determine CMC values for
cationic surfactants. Moreover this behaviour can be used to study
the highly non-ideal behaviour of mixed surfactant assemblies.
The chemical structures of the various calix[n]arenes are
given in Scheme 1 and those of the surfactants in Scheme 2.
The calix[n]arenes are one of the most widely studied classes of
organic host molecules, their biological,7 solid-state complexation8
a LMI CNRS UMR 5615, Univ. Lyon 1, Villeurbanne, F69622,
France. E-mail: antony.coleman@adm.univ-lyon1.fr;
Tel: +33 4 4243 1027
b LIMMS/CNRS-IIS (UMI 2820), University of Tokyo, Tokyo,
Japan
c Fachhochschule Nordwestschweiz, Hochschule fur Lifesciences,
Grundenstrasse 40, 4132 Muttenz, Switzerland.
¨
¨
E-mail: patrick.shahgaldian@fhnw.ch
d CIRMM, Institute of Industrial Science, University of Tokyo,
Tokyo, Japan. E-mail: bjoonkim@iis.u-tokyo.ac.jp
e ICBMS, UMR 5246, Univ. Lyon 1, Villeurbanne, F69622, France.
E-mail: florent.perret@univ-lyon1.fr; Tel: +33 4 2623 4404
f Institut National de Recherche et d’Analyse physico-chimique
Technopoˆle de Sidi Thabet, Tunisia.
E-mail: imed.montasser@inrap.rnrt.tn
w Electronic supplementary information (ESI) available: Full details
of the syntheses, along with electrospray mass spectrometry and
1H NMR spectral details, preparation of the hybrid nanoparticles
via sodium borohydride reduction, full details of the visible spectro-
metric characterisation of the formation and stability of the hybrid
nanoparticles and the spectrometric titrations. See DOI: 10.1039/
c2cc34670b
Scheme 1 Structures of the sulphonato calix[n]arenes studied. SC(n)a,
SC(n)b and SC(n)c correspond, respectively, to para-sulphonato-
calix[n]arene, O-propyl sulphonate calix[n]arene and O-propyl para-
sulphonato-calix[n]arene; with (n) corresponding to the number of
phenolic units in the macrocycle.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 9483–9485 9483

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Scheme 2 Structures of cationic and neutral surfactants. CPB, CTAB
and NOG correspond, respectively, to cetyl pyridium bromide, cetyl
trimethyl ammonium bromide and N-octyl glucopyranoside.
The calix[n]arenes carrying O-propylsulphonate groups at
the phenolic functions were synthesised by treating the parent
calix[n]arenes with butyl sultone and a large excess of sodium
hydride in tetrahydrofuran as per the method of Shinkai
et al.15,16 The reaction was followed using electrospray mass
spectrometry and further additions of the reactants were
continued until total substitution was achieved.
Suspensions of nine calix[n]arene capped silver nano-
particles at a concentration of 10À3 M were titrated against
five surfactants; with CPB and CTAB as cationics; Triton
X-100 and NOG as neutral; and SDS as an anioinic.
Fig. 2 Maximum absorbance of calix[n]arene capped silver nano-
particles (Ag_NP_Calix[n]arene) as a function of cationic surfactant
concentration. (A) With CPB and (B) with CTAB. is Ag_NP_SC4a;
Of the calix[n]arenes only for SC4a, SC4b and SC4c were
there changes in the visible spectra, see ESIw, with both
intensity changes and small changes in maximum wavelength,
Fig. 1. The shifts in the plasmon resonance paeks are in
accordance with interactions but not aggregation. Thus the
presumed cone conformation of these molecules on the surface
of the silver nanoparticles is important for complexation.
The work was extended for SC4a to cover a range of
surfactant concentrations up to ten times the CMC values,
shown in Fig. 1. Here there is a clear differentiation between
cationic and anionic or neutral surfactants. Measuring the
absorbance at 390 nm corresponding to the maximum absorbance
in the absence of surfactants or using the maximum absorbance
is Ag_NP_SC4b;
is Ag_NP_SC4c.
shows identical behaviour. Extending further to all calix[4]arene
derivatives, for SC4a and SC4c there is a minimum in the
absorbance at the CMC value for both CPB and CTAB, Fig. 2.
Interestingly with SC4b the behaviour is totally different. Here a
decrease in the absorbance to reach a plateau is observed. Such
behaviour seems more typical of a molecular interaction
independent of the micellisation process. DLS and electron
microscopy indicate a lack of aggregation up to surfactant to
nanoparticle ratios of 5 : 1, see ESI.w However for SC4b the
observed DLS values are almost invariant. In the electron
microscopy it was observed that at the CMC concentration
there is a large degree of variation in the geometry of the
objects. Intriguingly for SC4c at 1 : 1 and 5 : 1 ratios, there is
formation of small crystallites. Such behaviour might have
an impact on nucleation of bio-macromolecules. Thus the
presence of the sulphonate group in the para-position is
required for CMC dependent interactions.
We have demonstrated how capped nanoparticles can be
used as probes for CMC determination in the case of cationic
surfactants.
Applications of micellar suspensions often involve the use of
mixtures of two or more surfactants, as for example in the
extraction of membrane proteins. Here one detergent is used
to remove the protein from its lipid bilayer environment and
then the first surfactant is stripped away by a stabilising
detergent.17 Obviously while the CMC values of the pure
detergents are known, the effects of surfactant protein and
how CMC values will change as a function of mole fractions of
the various components are non-trivial problems.
Fig. 1 Maximum absorbance of para-sulphonato-calix[4]arene
capped silver nanoparticles (Ag_NP_SC4a) as a function of surfactant
concentration. is CPB; is CTAB; is NOG; is Triton X 100;
is SDS.
c
9484 Chem. Commun., 2012, 48, 9483–9485
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function of the surfactant mole fractions are given in Fig. 3.
For comparison the values obtained by Kharitonova are given
as insets. It can be clearly seen that values obtained here parallel
those previously observed using surface tension isotherms as the
analytical tool.
In conclusion we have shown that hybrid silver nano-
particles capped by para-sulphonato-calix[4]arene derivatives
interact in a critical micellar concentration dependent manner
with cationic surfactants. Intensity changes in the plasmon
resonance absorption spectral peak intensity can be used to
determine the CMC. More importantly the method can be applied
directly to the determination of critical micellar concentrations in
mixed micellar systems. The method generates a new means of
studying critical micellar concentrations in media containing
proteins and in particular membrane proteins, work is underway
to confirm this application.
This work was funded in part by the ANR PiriBio program,
grant number ANR-09-PIRI-0002.
Notes and references
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Fig. 3 Dependencies of the maximum absorbance of Ag_NP_SC4a
mixed with a neutral–cationic surfactant mixture on the molar fraction
of Triton X100. (A) With CPB and (B) with CTAB. Inset: Dependencies
of the CMC of the cationic surfactant Triton X100 mixture required to
reach surface pressure on the molar fraction of Triton X100 in solution.
(1) refers to the calculation for the ideal system and (2) denotes
experimental data. See ref. 18.
10 F. Perret and A. W. Coleman, Chem. Commun., 2011, 47,
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11 Y. J. Lee, S. W. Ko, H. M. Yeo, H. Jeong and K. C. Nam, Bull.
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A study by Kharitonova et al.18 on the behaviour of CTAB/
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that there was a very strong non-ideal behaviour of the CM (CMC
of a mixture). Diminutions of a factor of ten between the ideal
behaviour and the experimental values were found. The measure-
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12 K. Araki, H. Shimuzu and S. Shinkai, Chem. Lett., 1993, 205–208.
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´ ´
17 R. Matar-Merheb, M. Rhimi, A. Leydier, F. Huche, C. Galian,
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of the CM values by using various mole fractions of the mixture
in the 96 titre well visible spectrometer. Such measurements
require only a few minutes and indeed sample preparation is
more time consuming in the experiments. The spectra are given
in the ESIw, and the variations of the maximum absorbance as a
E. Desuzinges-Mandon, D. Ficheux, D. Flot, N. Aghajari, R. Kahn,
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c
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Chem. Commun., 2012, 48, 9483–9485 9485