Nonionic Cyclodextrin Based Binary System with Upper and Lower

Jun 9, 2014 - Critical Solution Temperature Transitions via Supramolecular. Inclusion ... ABSTRACT: A nonionic binary aqueous interaction system...
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Nonionic Cyclodextrin Based Binary System with Upper and Lower Critical Solution Temperature Transitions via Supramolecular Inclusion Interaction Zhen Yang, Xiaodong Fan,* Wei Tian,* Dan Wang, Haitao Zhang, and Yang Bai The Key Laboratory of Space Applied Physics and Chemistry, Ministry of Education and Shaanxi Key Laboratory of Macromolecular Science and Technology, School of Science, Northwestern Polytechnical University, Xi’an 710072, P. R. China S Supporting Information *

ABSTRACT: A nonionic binary aqueous interaction system consisting of β-cyclodextrin trimer (β-CD3) and naphthaleneterminated poly(ethylene glycol) (PEG-NP2), which has tunable upper critical solution temperature (UCST) behavior around room temperature and lower critical solution temperature (LCST) behavior at high temperature, was investigated. In the UCST transition, gel-like aggregates form because of supramolecular inclusion complexation between β-CD3 and PEG-NP2. During LCST transition, PEG-NP2 becomes insoluble in water, which results in its precipitation. The effects of concentration, stoichiometry of the two components, and electrolyte on UCST behavior are discussed. This study provides a new nonionic thermoresponsive material.

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INTRODUCTION Polymeric supramolecular complexes based on reversible noncovalent interactions between multiple components are considered dynamic equilibrium systems that initiate responses to external stimuli when the surrounding environment changes.1−3 Cyclodextrin (CD) could form supramolecular host/guest inclusion complex with many guest molecules, such as adamantine,4 naphthalene,5 and ferrocene.6 If the molecular structures of the guest molecules are subjected to external stimuli, such as variations in pH,7 redox reagents,8 and exposure to UV rays,9 the inclusion complex disassociates. Compared with the stimulus-responsive properties restricted to a limited species of guest molecules that can tolerate structural changes under certain stimuli, the thermosensitivity of the CD inclusion complex is more extensive because no structural change is needed and the stability of the inclusion complex is intrinsically related to temperature. Therefore, the CD inclusion complex is useful for constructing thermoresponsive materials,10−13 especially those that exhibit an upper critical solution temperature (UCST) in aqueous solutions14,15 and are water insoluble at low temperatures and become soluble above a critical temperature. This phenomenon has long interested researchers because materials that exhibit UCST in water are potentially useful in drug delivery systems and wastewater treatment applications. These materials are also highly desirable because studies on thermoresponsive materials are overwhelmingly focused on materials with lower critical solution temperatures (LCSTs).16 Through inclusion complexation between β-CD-conjugated poly(ε-lysine) and 3-trimethysilylpropionic acid, Yui et al. © 2014 American Chemical Society

prepared a zwitterionic system featuring rapid UCST transition.14 Similarly, Ritter et al. found that CD-containing poly(pseudobetaines) exhibit the UCST phenomenon;15 by copolymerizing different thermoresponsive blocks with LCST, the obtained copolymers exhibited insoluble−soluble−insoluble transition behavior.17 These systems exhibit UCST because a large number of CD inclusion complexes are formed at low temperatures, acting as physical cross-linkers and thereby constructing insoluble hydrogels. In previous reports, zwitterionic interactions were considered and served as physical crosslinkers, and unfortunately, the UCST behavior could be suppressed when additional salt is added to the system. Furthermore, homopolymers exhibiting both tunable LCST and UCST in aqueous solution are notably rare.17,18 Generally, to confer LCST and UCST behaviors to a polymer, different thermoresponsive blocks must be copolymerized,19−21 which requires a complicated preparation process. In this study, we aim to construct a nonionic thermoresponsive supramolecular system based on a CD inclusion complex and thermoresponsive polymer that could show a clear transition from UCST to LCST in a considerably convenient manner. To fulfill this goal, a supramolecular system based on β-CD trimer (β-CD3) and naphthalene-terminated poly(ethylene glycol) (PEG-NP2) was prepared. We report and analyze the thermoresponsive properties of the proposed Received: April 3, 2014 Revised: June 7, 2014 Published: June 9, 2014 7319

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Scheme 1. Preparation Routes for the Binary Supramolecular System

spectra were obtained using a Thermo Fisher Scientific Nicolet iS10. Samples analyzed were cast into thin films on KBr. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDITOF-MS) was utilized to determine the monomer’s molecular weight using a Bruker Ultraflex TOF mass spectrometer. 2D NOESY NMR spectra at 25 °C were obtained with a Bruker AVANCEIII 500 spectrometer using D2O as the solvent. Samples were prepared by mixing the D2O solutions of both PEG-NP2 (1 mM) and β-CD3 (0.74 mM). Fluorescence emission spectroscopy was applied through a Hitachi F-4600 instrument thermostated with a circulating water bath. Mixture solutions containing different stoichiometries were first stabilized at a fixed temperature with a thermostatic oscillator for at least 4 h. Afterward, the solution was measured with the spectrophotometer, and fluorescence emission spectra were recorded at an excitation wavelength of 283 nm. The LCST and UCST of the supramolecular system were determined through turbidity measurements using a UV−vis spectrometer (Shimadzu UV-2550 model) within the temperature range of 15−75 °C. Before conducting measurements, the aqueous polymer solution or mixture solution was placed in the spectrophotometer (path length, 1 cm) thermostated with a circulating water bath. The temperature ramp was 1 °C/min. The transmittance data of the solution at λ = 500 nm were recorded at temperature intervals of 0.5 °C. The temperature corresponding to the onset of transmittance reduction was defined as the UCST-type or LCST-type cloud point. Images of the different morphologies of the supramolecular system corresponding to the temperature were obtained by TEM using a Hitachi H-600 electron microscope. For sample preparation, a 200mesh copper grid was first placed in the mixed solution and then slowly moved into a constant-temperature incubator at a fixed temperature. After 10 min, the copper grid was quickly removed from the solution and then quenched in liquid nitrogen. After freeze-drying of the copper grid for 4 h, images were taken with an acceleration voltage of 75 kV. The assembly behavior of the supramolecular system was also revealed by dynamic light scattering (DLS) using a Malvern Zetasizer Nano ZS instrument at different temperatures. The particle size distribution was determined by the general mode included in the DTS software.

system according to inclusion interactions between the two components.

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MATERIALS AND METHODS

Mono-(6-azido-6-desoxy)-β-cyclodextrin (β-CD-N3) was synthesized according to our previously reported method.22 Tripropargylamine (TPA) (98%) and 2-naphthoyl chloride (NPC) (98%) were purchased from J&K Chemistry. Bromotris(triphenylphosphine)copper (98%) and poly(ethylene glycol)-1500 (PEG-1500, molecular weight = 1500) (BioUltra) were purchased from Sigma-Aldrich. Dialysis bags were purchased from Spectrumlabs (MWCO 2.0 kDa). The other reagents were analytical grade and produced by Tianjin Kermel Chemical Reagents Development Center (Tianjin City, China). All purchased chemical were used as received without further purification. β-CD3 was synthesized via click reaction between TPA and β-CDN3 according to the literature with several changes.23 Briefly, TPA (0.187 g, 1.43 mmol) and β-CD-N3 (5.5 g, 4.74 mmol) were dissolved in N,N-dimethylformamide (DMF). After bubbling with nitrogen gas for 30 min, bromotris(triphenylphosphine)copper (0.618 g, 4.31 mmol) was added to the mixture. After bubbling with nitrogen gas for another 20 min, the mixture was allowed to react at 100 °C for 12 h. The resulting product was precipitated with 200 mL of acetone to obtain a pale yellow solid. The crude product was dissolved in 5 mL of deionized water and dialyzed in a dialysis bag (MWCO 2.0 kDa) with deionized water for 5 days to remove the unreacted β-CD-N3. After removal of water from the product through freeze-drying, a white solid was obtained (2.0 g, yield 40%). 1H NMR (D2O, 400 MHz): δ H (ppm) = 2.74 (d, 3H), 3.02 (d, 3H), 3.20 to 4.00 (m, 120H), 4.08 (t, 3H), 4.50 (t, 3H), 4.90 (m, 21H), and 7.85 (s, 3H). MALDI-TOF-MS of β-CD3: calculated for [M + H]+: 3611.21, found m/z: 3611.30 [M + H]+. PEG-NP2 was synthesized via condensation reaction between poly(ethylene glycol) and NPC. Poly(ethylene glycol) and dry pyridine were dissolved in anhydrous THF, and NPC was slowly added to this mixture. The solution was subsequently cooled to 0 oC in an ice bath. The temperature of the solution was increased to 40 °C and stirred for 24 h. After completion of the reaction, the product was filtered and precipitated with cold diethyl ether twice. The resulting white crude product was repeatedly dissolved in alcohol and kept at 4 o C for recrystallization. 1H NMR (D2O, 400 MHz): δ H (ppm) = 3.50 to 3.62 (m, 67H), 3.81 (t, 2H), 4.47 (t, 2H), 7.61 to 7.68 (m, 2H), 8.01 (m, 3H), 8.16 (d, 2H), and 8.63 (s, 1H). To construct a supramolecular system, β-CD3 and PEG-NP2 were first separately dissolved in an equal volume of deionized water. The PEG-NP2 solution was then added dropwise to the β-CD3 solution with supersonic vibration. 1 H NMR spectra were obtained with a Bruker Avance 300 spectrometer operating at 400 MHz (1H) in DMSO-d6 or D2O. FT-IR

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RESULTS AND DISCUSSION To obtain a supramolecular system exhibiting both UCST and LCST transitions, β-CD trimer and PEG-NP2 were designed and synthesized, as presented in Scheme 1. β-CD3 was synthesized via a 1,3-dipolar cycloaddition reaction between β-CD-N3 and TPA in DMF solution using bromotris(triphenylphosphine)copper as the catalyst. Figure S1 (see 7320

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Figure 1. 2D-NOESY NMR spectrum of the binary system mixture at 25 °C.

Figure 2. 1/(I − I0) as a function of [CD]−1 at T = 25 °C; concentration of PEG-NP2 is 2 × 10−5 M.

Supporting Information) shows the 1H NMR spectrum of the β-CD3 compound. The proton peak of H-1,2,3 triazole evidently appears at 7.92 ppm, and the area ratio of this peak to the proton peak of 2,3-OH at β-CD ranging from 5.5 to 6.0 ppm is 14, which suggests that each TPA molecule reacts with three β-CD-N3 molecules. Completion of the cycloaddition reaction was also confirmed by the disappearance of the characteristic absorption bands of the azido group at 2104 cm−1 and alkynyl group at 2118 cm−1 from the FTIR spectrum (Figure S2). Moreover, Figure S3 shows a single mass peak at m/z = 3611.30 in the MALDI-TOF-MS spectrum, which indicates successful β-CD3 preparation. PEG-NP2 could be precisely synthesized through a condensation reaction between NPC and poly(ethylene glycol) according to our previous design. Figure S4 shows that the area ratio of peak 1 to peak 8 is about 2, which demonstrates that each chain terminal of the polymer is linked to a naphthalene molecule. The numberaverage molecular weight of PEG-NP2 was determined to be

1890 kDa from integral calculation of its 1H NMR spectrum. In the FTIR spectrum of PEG-NP2 presented in Figure S5, the characteristic absorptions of the hydroxyl group at 3433 cm−1 and acyl chloride group at 1752 cm−1 disappeared as a new absorption band for an ester group appeared at 1717 cm−1. All data soundly suggest that the condensation reaction performed for this polymer was successful. When aqueous solutions of β-CD3 and PEG-NP2 were mixed under a specific concentration and stoichiometry at 25 °C, the mixture solution suddenly became cloudy, which indicates the occurrence of certain supramolecular interactions. To investigate the detailed interaction between β-CD3 and PEG-NP2, 2D-NOESY NMR measurements in D2O at 25 °C were conducted, as presented in Figure 1. The partial contour plots of the 2D-NOESY NMR spectrum indicated that the naphthalene protons were correlated to H-3 and H-5, which are located at the cavity of β-CD. This result suggested that naphthalene molecules in PEG-NP2 are enclosed by β-CD 7321

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units, thereby forming inclusion complexes in aqueous solution at 25 °C. To confirm the results of 2D-NOESY NMR analyses, fluorescence emission spectroscopy was utilized, and the results are shown in Figure 2. When the PEG-NP2 concentration was maintained at 2 × 10−5 M, the fluorescence intensity markedly increased with increasing β-CD concentration. Thus, naphthalene moieties in PEG-NP2 presumably act as fluorophores and move into the hydrophobic cavity of β-CD to reduce fluorescence quenching. 24 To determine the inclusion stoichiometry between the naphthalene moiety and β-CD, the double reciprocal plot was utilized through the modified Hidebrand−Benesi equation, shown as follows:25 1 1 1 = + I − I0 k Δε[NP][CD] Δε[NP]

where I0 denotes the fluorescence intensity in pure water, I denotes the fluorescence intensity, Δε denotes the molar extinction coefficient between the host and host−guest complex, and NP denotes the PEG-NP2 naphthalene moiety. The plot of 1/(I − I0) versus 1/[β-CD] clearly presents a straight line, and the correlation coefficient R2 was equal to 0.995. These results indicate an inclusion relationship with a stoichiometry of 1:1 between naphthalene and β-CD.26 Interestingly, when a triple molar concentration of sodium adamantane-1-carboxylate (Ada-COONa) was added to the system, the solution, which was originally cloudy, became clear within several minutes. These results were not observed with addition of the same amount of NaCl or Na2SO4. Considering that complexation of β-CD and adamantine is substantially stronger than that of β-CD with naphthalene,24,28 the insoluble aggregates were definitely from the inclusion interaction between PEG-NP2 and β-CD3. The solution’s transition from cloudy to transparent was caused by replacement of PEG-NP2 with adamantine in the β-CD cavities. The above observation again indicates that the mechanism of this supramolecular interaction may be described in Scheme 1, wherein the inclusion complexes are constructed via a 1:1 stoichiometry between naphthalene and β-CD. When the cloudy binary solution was heated, the solution presented insoluble−soluble−insoluble transition as the temperature increased. To study this phase transition, turbidity tests with cooling and heating rates of 1 °C/min were performed. Figure 3 shows that when the temperature gradually decreases from 70 to 10 °C, two marked phase transitions may be observed. The first transition started from 64 °C and was terminated at about 57 °C; during this transition, the solution showed typical LCST behavior and changed from cloudy to clear. The second transition occurred from 23 to 16 °C, during which a second cloud point was observed and the solution showed UCST behavior. Upon heating, the solution first became clear after passing 32 °C and then became cloudy again at 60 °C. This finding suggests that the entire transition process is reversible. In addition, pronounced hysteresis was observed between heating and cooling. To inspect the morphologies of the supramolecular complex at different temperatures, TEM was applied and the results are shown in Figure 4. The supramolecular aggregates were gel-like below the UCST-type cloud point (Figure 4a). Compared with the TEM image of the supramolecular complex obtained below its UCST-type cloud point, the system appeared as nanoscaled aggregates at 40 °C (Figure 4b). As the temperature increased to 65 °C above its LCST-type cloud point, the binary system

Figure 3. Typical turbidity−temperature curves of a mixture solution of PEG-NP2 (1 mM) and β-CD3 (0.74 mM) upon cooling (square) and heating (cycle). The lines are a guide to the eye.

presented relatively large dotted associations, as shown in Figure 4c. The morphological changes observed with increasing temperature imply that binary system interactions are evidently affected by temperature. A detailed study of the probable mechanism of transition at the molecular level is presented in the succeeding section. To investigate the UCST behavior of the system, a plot of binary solution concentration versus UCST-type cloud point is presented in Figure 5. By maintaining the stoichiometry at 1.35 (PEG-NP2:β-CD3 = 1.35:1), the UCST-type cloud point increased with the concentration of the mixture solution. At solution concentrations of 1.74, 2.61, and 3.48 mM, corresponding cloud points of 23, 32, and 39 °C were respectively obtained. When the concentration of the mixture solution was below 1.31 mM at the same stoichiometry, no phase transition occurred. Similar phenomena could also be observed at other stoichiometries. This finding shows that, at high concentrations, gel-like aggregates easily form because these aggregations tend to decompose into smaller particles when the temperature increases. Inclusion complex formation is a process of achieving thermodynamic equilibrium that is affected not only by temperature but also by CD and guest molecule concentrations. When the concentration increases, the complexation equilibrium shifts toward complex formation and more inclusion complexes are formed.28,29 Therefore, gellike aggregation could be constructed at elevated temperatures and the UCST-type cloud point could increase. This type of change for the cloud point could also be explained by an increase in the percentage of intermolecular over intramolecular host−guest links because of increasing solution concentration.14 Besides the substantial influence of the system’s concentration on its UCST behavior, we found that the stoichiometry of the two system components also has an important role in the UCST-type cloud point. To explore this factor, we first fixed the PEG-NP2 content at 1 mM and then varied the β-CD3 content to generate different stoichiometries between PEG-NP2 and β-CD3. These results show that UCST behavior only exists in a fixed range of stoichiometries. When the stoichiometry of the two components is higher than 1.80 or lower than 0.22, the UCST-type cloud point is not observed even if the surrounding temperature decreases to 4 °C. Figure 6 shows that, compared 7322

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Figure 4. TEM images of binary system at (a) 4, (b) 40, and (c) 65 °C (PEG-NP2 1 mM plus β-CD3 0.74 mM).

negatively correlated with temperature,34 the number of complexes formed would decrease when the temperature is elevated. Therefore, when the system is heated above its UCST-type cloud point, the phase transition is happened because the gel-like aggregates break into smaller fragments, as shown in Figure 4b. Poly(ethylene glycol) is regarded to be soluble in water because its LCST is higher than 100 °C in most cases.35 However, when we reacted naphthalene in both terminals of PEG-1500, the cloud point of resulting polymer was only 44.5 °C if the concentration of PEG-NP2 was 1 mM, as shown in Table 1. This phenomenon may be caused by the lower PEG molecular weight and the attached naphthalene molecules, which enhances the hydrophobic property of the polymer. Interestingly, when β-CD3 was added to the solution, the system’s LCST-type cloud point dramatically increased to 57 °C. Figure S7 shows that the LCST-type cloud point of the mixture solution is positively correlated with the amount of added β-CD3. Because the LCST for a water-soluble polymer can definitely increase when this polymer is covalently or noncovalently bonded to a hydrophilic compound,36,37 the increase in LCST-type cloud point of PEG-NP2 after addition of β-CD3 may be caused by the inclusion complexation between PEG-NP2 and β-CD3 at high temperatures. To confirm this argument, a sufficient amount of Ada-COONa was added to the mixed solution. Surprisingly, upon addition of Ada-COONa, the LCST-type cloud point of the binary system of PEG-NP2 and β-CD3 dramatically decreased to 44.5 °C, which was the original cloud point of pure PEG-NP2. As adamantine can replace naphthalene in the β-CD cavity because of its high association constant, the LCST behavior of the binary solution conclusively came from the intrinsic property of PEG-NP2; however, the existing β-CD3 could form an inclusion complex with PEG-NP2 even at elevated temperatures. To obtain more information on the aggregation processes occurring above the LCST-type cloud point, DLS measurements of the binary solution were conducted at different temperatures, as presented in Figure S8. The z-average size sharply increased from about 200 nm to the micrometer scale when the temperature increased to the LCST-type cloud point. This result agrees with the TEM images of supramolecular aggregates above the LCST-type cloud point. The micrometerscale size of the aggregates indicates that, although β-CD3 helps improve the hydrophilicity of PEG-NP2, it fails to prevent the PEG-NP2 from precipitating out of the solution. As the inclusion complex of β-CD3 and PEG-NP2 exists not only below the UCST but also above the LCST of the system, the inclusion complex was also formed between the two critical

Figure 5. UCST-type cloud point as a function of binary aqueous solution concentration during cooling. The X-axis refers to the total concentration of initial PEG-NP2 and β-CD3 in the solution. The stoichiometry of PEG-NP2:β-CD3 was maintained at 1.35. The lines are a guide to the eye.

with the gel-like aggregates with stoichiometries of 1.35 (Figure 6b) to 0.30 (Figure 6e) at 4 °C, only nanoscaled micelles could be observed at stoichiometries of 1.80 (Figure 6a) and 0.22 (Figure 6f). This result is similar to the conventional polymerization model of A2 plus B3 monomer; that is, when a monomer’s functional groups number is more than that of the other, excessive functional groups act as end-capping reagents, leading to lower molecular weights in the resulting polymer and effectively preventing the monomers from gelation during polymerization.30 To study the influence of the electrolyte on the UCST behavior of the system, different amounts of NaCl and Na2SO4 were added to the mixture solution. Figure 7 shows that increasing NaCl or Na2SO4 concentrations cause a steady increase in the UCST-type cloud point, which indicates that gel-like aggregates easily form under these conditions. This result contrasts those of ion-containing systems, in which the cloud point is suppressed or disappears upon addition of an electrolyte.31 This phenomenon may be caused by increases in the association constant between β-CD and naphthalene following addition of an electrolyte.32,33 An explanation is given of the phase transition during the UCST behavior of the system. Aggregation of this system below its UCST-type cloud point has been proved to be initiated by inclusion interactions between β-CD and naphthalene. Moreover, as the association constant is generally 7323

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Figure 6. TEM images of the mixture solution at different stoichiometries of PEG-NP2 to β-CD3 at 4 °C: (a) 1.80 (a), (b) 1.35, (c) 0.9, (d) 0.45, (e) 0.30, and (f) 0.22. The PEG-NP2 concentration was fixed at 1 mM.

peak corresponding to particles with a mean size of 4.25 nm can be observed in Figure 8b; Figure 8c shows peaks corresponding to particles with a mean size of 2.5 nm in the β-CD3 solution. We can speculate that a supramolecular “oligomer”, which may be formed by several PEG-NP2 and βCD3 molecules, is the prevalent form of supramolecular aggregates between the two types of cloud points. In summary, gel-like aggregates formed as a 1:1 inclusion complex below the UCST-type cloud point. When the temperature increased to over the UCST-type cloud point but below the LCST-type cloud point, the inclusion aggregates partially disassociated into smaller inclusion complexes, most of which may form supramolecular “oligomers”. When the temperature increased above the LCST-type cloud point, the PEG-NP2 component became hydrophobic and relatively weaker supramolecular complexes aggregated into insoluble precipitates.

Figure 7. UCST-type cloud points of the binary solution versus ionic strengths for different types of salt. The PEG-NP2 and β-CD3 concentrations were set to 1 and 0.74 mM, respectively. The lines are a guide to the eye.

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CONCLUSIONS A nonionic aqueous system with UCST and LCST transitions could be prepared by mixing a solution of β-CD trimer and PEG-NP2. The UCST behavior, which shows electrolyte resistance, could be adjusted by changing the solution concentration and stoichiometry of the two components. UCST behavior was presumably caused by the formation of more inclusion complexes between β-CD3 and naphthalene at

temperatures. As a typical example, the size distribution by intensity and volume of the binary solution at 40 °C is presented in Figure 8. The peak around 500 nm in Figure 8a corresponds to particles with sizes of around hundreds of nanometers that appear in Figure 4b. However, only a single

Table 1. LCST-Type Cloud Point Data for Pure PEG-NP2, Binary System, and Binary System with Ada-COONa

solution systems

PEG-NP2 (1 mM)

PEG-NP2 (1 mM) β-CD3 (0.74 mM)

PEG-NP2 (1 mM) β-CD3 (0.74 mM) Ada-COONa (4 mM)

PEG-NP2 (1 mM) β-CD3 (0.7 mM) Ada-COONa (8 mM)

LCST-type cloud point under cooling (oC)

44.5

57

43.5

44.5

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ASSOCIATED CONTENT

S Supporting Information *

Figures S1−S8. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (X.F.). *E-mail [email protected] (W.T.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Science Foundations of China (No. 21274116 and No. 21374088). W.T. thanks the grant from the Program for New Century Excellent Talents of Ministry of Education (NCET-13-0476), the Program of Youth Science and Technology Nova of Shaanxi Province of China (2013KJXX-21), and the Program of New Staff and Research Area Project of NPU (13GH014602).

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REFERENCES

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Figure 8. Size distributions in (a, b) aqueous solutions of PEG-NP2 (1 mM) and β-CD3 (0.74 mM) at 40 oC and (c) an aqueous solution of β-CD3 (0.74 mM) at 40 oC.

low temperatures, while LCST behavior was caused by the decrease in hydrophilicity of the PEG-NP2 component, which is affected by the formation of the inclusion complex between βCD3 and naphthalene moieties. As thermosensitivity is prevalent in supramolecular complex, the facile implementation of UCST and LCST transition in this study may inspire interest in a class of new nonionic thermoresponsive materials. 7325

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dx.doi.org/10.1021/la501278n | Langmuir 2014, 30, 7319−7326