PAMAM-Based Dendrimers with Different Alkyl Chains Self-Assemble

Article Cite This: J. Phys. Chem. B XXXX, XXX, XXX−XXX

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PAMAM-Based Dendrimers with Different Alkyl Chains SelfAssemble on Silica Surfaces: Controllable Layer Structure and Molecular Aggregation Minghui Zhang,†,‡ Hui Yang,*,† Shujuan Wang,† Wei Zhang,† Qingfeng Hou,§ Donghong Guo,§ Fanghui Liu,† Ting Chen,† Xu Wu,∥ and Jinben Wang†

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†

CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China ‡ University of Chinese Academy of Sciences, Beijing 100049, P. R. China § Key Laboratory of Oilfield Chemistry, Research Institute of Petroleum Exploration and Development (RIPED), CNPC, Beijing 100083, P. R. China ∥ Department of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006, Guangdong, P. R. China S Supporting Information *

ABSTRACT: Amphiphilic poly(amidoamine) (PAMAM) dendrimers are a well-known dendritic family due to their remarkable ability to self-assemble on solid surface. However, the relationship between molecular conformation (or adsorption kinetics) of a self-assembled layer and molecular amphiphilicity of such kind of dendrimer is still lacking, which limits the development of modulating self-assembling structures and surface functionality. With this in mind, we synthesized a series of amphiphilic PAMAM-based dendrimers, denoted as G1Cn, with different alkyl chains (n = 8, 12, and 16), and investigated the molecular aggregation on silica surfaces by means of quartz crystal microbalance with dissipation, atomic force microscopy, and contact angle. After rinsing, remaining adsorption amounts of G1C12 were higher than those of G1C8 at high concentrations, suggesting that G1C12 adlayers were more stable due to the stronger intermolecular hydrophobic interactions, whereas it preferred to adopt the intramolecular hydrophobic interactions for G1C16, with low adsorption amounts and unstable adlayers. Bilayer-like structures were inferred in G1C8 and G1C12 adlayers with loose conformation, whereas monolayer structures were likely to exist in the sparse adsorption film of G1C16. Our results provided more detailed understanding of the effect of molecular structure on the self-assembled structures of amphiphilic dendrimers on solid surfaces, shedding light on the controlled microstructure and wettability of functional surface by modulating the length of hydrophobic chains of dendrimers and a potential application of dendrimer−substrate combinations.

1. INTRODUCTION

(caprolactone) dendrimers were successfully prepared and assessed as a potential drug delivery system. However, to date, systematic investigations on the molecular conformation, adsorption kinetics, or morphology of a self-assembled layer of amphiphilic dendrimers are still lacking, which limits the development of modulating self-organizing structures and interface properties. Molecular dynamics simulation studies proposed that the hydrophobic tail and dendron generation have critical impacts on the properties of self-organized bilayers, such as generating electrostatic interaction or Hbond network.21,22 In our previous study, a decrease in adsorption mass occurred in high generation of amphiphilic PAMAM dendrimer, depending on the balance of hydrophobic interaction and electrostatic repulsion.23 And we found that the

Dendrimers, owning compact and symmetrical structures, are a class of macromolecules, which have been increasingly employed for many applications, including drug delivery, gene diagnosis, cancer targeting therapy, ultrasensitive sensors, etc.1−7 Amphiphilic dendrimers, as an important branch of dendrimer family, have been successfully designed through introducing amphiphilic balance by appropriate modification of hydrophobic tails. Compared with conventional dendrimers, amphiphilic ones show a talent for forming a large variety of self-assembled structures in bulk and at surface,8−12 such as bilayer structure, pancakelike structure, scattered islandlike film, and so on.13−17 These various self-assembly behaviors make amphiphilic dendrimers charming candidates for the development of new types of layer structures, possessing potential applications in controlled-release delivery systems, biosensors, etc.18−20 For example, micellar and vesicular aggregates formed by poly(amidoamine) (PAMAM)-poly© XXXX American Chemical Society

Received: March 15, 2018 Revised: June 13, 2018 Published: June 13, 2018 A

DOI: 10.1021/acs.jpcb.8b02534 J. Phys. Chem. B XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry B

Figure 1. Chemical structures of G1Cn (n = 8, 12, 16, representing carbon number).

(DCAT 21, DataPhysics, Germany). The standard deviation of surface tension measurements was less than 0.2 mN/m. Sample solutions were put into a constant-temperature bath at a set temperature of 25.0 °C. Sets of measurements were taken at certain intervals until the change in the surface tension was less than 0.01 mN/m every 60 s. Each surface tension value was obtained by averaging at least five consistent measured values. The critical micelle concentration (cmc) values were determined according to the breakpoint of the static surface tension versus log of the bulk concentration. The platinum ring was cleaned by burning under an alcohol flame to obliterate the residual dendrimer before each measurement. 2.3. Quartz Crystal Microbalance with Dissipation (QCM-D). The adsorption behavior of amphiphilic dendrimers was studied using QCM-D (Q-Sense E1, Gothenburg, Sweden). The Q-Sense sensor-coated with a SiO2 layer (QSX303) was used after thorough cleaning with plasma for 10 min. The flow rate used in this work was 0.1 mL/min. All experiments were carried out at a constant temperature of 25 °C. A shift in the resonance frequency (f) corresponds to a mass change of the substrate. When dendrimer molecules adsorbed on the SiO2 surface, the frequency decreased with an increase of weight. If the layer is rigid, homogeneous, and evenly distributed, the adsorbed mass should be converted according to the Sauerbrey equation (eq 1)24

adsorption layer thickness and the molecular orientation mainly rely on the dendrimer generation,13 while the contribution of hydrophobic tail of amphiphilic dendrimer to the adsorption and the conformation is far from being understood, in which molecular structure seems to be responsible for developing more desirable organized films. To address the above outlined knowledge gap, a designed series of ionic amphiphilic dendrimers based on PAMAM dendrimers with different alkyl chains as shown in Figure 1, denoted as G1Cn (n = 8, 12, 16), were synthesized in this work. To explore the structure of adsorption films formed by these specific molecules and the molecular aggregation mechanism, quartz crystal microbalance with dissipation (QCM-D), atomic force microscopy (AFM), and contact angle (CA) methods were employed. The effects of hydrophobic chain length and solution concentration on the adsorption processes and the mechanisms of the amphiphilic dendrimers were revealed, providing an insight into the balance of hydrophobic and electrostatic interactions involved in wide application fields of engineering flexible interfacial materials.

2. MATERIALS AND METHODS 2.1. Materials. A series of G1Cn (n = 8, 12, 16) with different chains were synthesized and purified by our group. Details of the preparation procedures and 1H NMR data are presented in Scheme S1 and Figures S1−S3. Milli-Q water with a conductivity of 18.2 Ω cm was used for the preparation of sample solutions. The silica substrates were activated with piranha solution (H2SO4: 30% H2O2 = 3:1 v/v) at 80 °C for 40 min, rinsed with distilled water and acetone three times successively, and finally dried under a nitrogen atmosphere. 2.2. Surface Tension Measurement. The surface tension measurements were performed using the DuNoüy ring method

Δm = −

ρq tq Δf Δf = −C f0 n n

(1)

where Δm is the adsorbed amount, Δf is the change in resonance frequency, n is the overtone number, and C is the mass sensitivity constant, which can be calculated according to the following eq 225 B


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The Journal of Physical Chemistry B C=−

A ρq μq 2f0 2

(2)

where f 0 is the resonant frequency (Hz), A is the active crystal area (50 mm2), ρq is the density of quartz (2.648 g/cm3), and μq is the shear modulus of the AT cut quartz crystal (2.947 × 1011 g cm−1 s−2). For a resonance frequency of 5 MHz, the value of C is 0.177 mg m−2 Hz−1. The dissipation factor (D) was measured to investigate the viscoelasticity of the adsorbed layer. In the QCM-D system, the dissipation factor is defined by the relation of the energy dissipation and the energy stored as follows (eq 3)26−28 D=

Ediss 2πEstore

(3) Figure 2. Surface tension curves of G 1 C n plotted against concentrations.

where Ediss refers to the total dissipated energy during one oscillation cycle and Estore refers to the total energy stored in the oscillation system. The QCM-D measurement was performed according to the following three steps: (i) a stable baseline was obtained through injecting water; (ii) dendrimer solutions were injected into the fluid cell for at least 1 h; and (iii) water was reinjected to remove unstable adsorbed layers. Δf and ΔD selected from the third overtone were used to evaluate the data basically due to its stability. Δm was interpreted base on the Sauberey model using Q-tools software. Each test was repeated more than 3 times. 2.4. Atomic Force Microscopy (AFM) Imaging. Surface topography was characterized through AFM (FASTSCAN, Bruker Instruments) with tapping mode. Standard silicon AFM probes (FASTSCAN-B) with cantilever spring constants of 4 N/m and resonance frequencies of around 400 kHz were used. The root-mean-square roughness of adsorbed layers was evaluated and determined using Nanoscope Analysis software. 2.5. Contact Angle Measurements. Water contact angles of the films were measured at 25 °C with a contact angle instrument (SL-200B Theta, Biolin, Sweden). Ten microliters of water was gently dispensed onto the surface, and the measurement time was less than 10 s. At least three measurements on different film locations were averaged for data analysis.

adsorbing onto solid surfaces at the third overtone. Four stages of the whole adsorption process can be distinguished: (i) the frequency of baseline was obtained when the quartz crystal was immersed in buffer solution; (ii) a sharp decrease in Δf was observed after dendrimer solution was introduced in the measurement chamber, due to the adsorption of material on the surface of the sensor; (iii) the adsorption process ended (Δf = constant) because of the arrival of saturation adsorption; (iv) weakly bound molecules were removed from the surfaces after being rinsed by buffer. In the presence of G1C8, when the dendrimer concentration increases from 1 × 10−6 to 1 × 10−3 mol/L, Δf decreases from −10 to −17.5 Hz before rinse and ΔD increases from 0.48 to 3.4 × 10−6 (Table S1). It suggests a rapid adsorption of dendrimers, in accordance with a previous report on the efficient adsorption of G1QPAMC12 depending on the surfactant concentration.19 There are negative charges on the silica substrate that aid the adsorption, and thus the electrostatic interaction between adsorption sites and cationic polar headgroups in each branch plays an important part in the adsorption process.31−33 To further characterize the adsorption kinetics, a one-step model is employed to fit the initial adsorption period, reflecting the initial adsorption rate at each concentration.34

3. RESULTS AND DISCUSSION 3.1. Critical Micelle Concentration (cmc). The surface tensions of G1Cn (n = 8, 12, 16) were determined at 25 °C as a function of concentration, as shown in Figure 2. For the series of dendrimers, the surface tension decreases as the concentration increases and reaches a clear breakpoint that is considered as cmc. With the alkyl chain length of dendrimer increasing from C8 to C16, cmc values decrease from 8 × 10−5 to 3 × 10−6 mol/L, which are 2 orders of magnitude lower than that of alkyltrimethylammonium bromide (CnTAB, n = 8, 12, 16) as one branch of the corresponding dendrimer.29 It suggests an excellent micelle-forming ability of the amphiphilic dendrimers. In addition, it is found that an increase in the alkyl chain length for G1Cn brought in an efficient reduction in the surface tension, indicating that the dendrimers with longer chains tend to widely adsorb and pack tightly at the air−water interface due to the strong hydrophobic interaction.30 3.2. Adsorption Behaviors on Solid Surfaces. 3.2.1. Adsorption Kinetics. Figure 3 showed the shifts both in frequency (Δf) and dissipation (ΔD) for G1C8, G1C12, and G1C16

q = q0 − kt

(4)

where q and q0 are constants, represent the adsorption amounts at time t and at equilibrium, respectively. k is the rate constant, which represents the adsorption process of molecules from bulk solution to the interface and the rearrangement of the adsorbed molecules. As can be seen in Table 1, the values of rate constant k exhibit an increased tendency as the concentration increases, indicating that more dendrimer molecules (below cmc) or aggregates (above cmc) adsorb onto silica surfaces at higher concentration in short time due to the dendrimer-surface interaction. Additionally, hydrophobic tails play a critical role in the adsorption process. A sharp decrease is shown in k values from C8 to C16 at the same concentration, indicating that longer hydrophobic tails hinder the adsorption rate of amphiphilic dendrimers onto the hydrophilic silica surface.35 Besides the electrostatic attraction of dendrimer surface, the “physical affinity” of dendrimersurface interaction is also associated with the adsorbate degree of hydration.36,37 For amphiphilic dendrimers, long hydroC


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Figure 3. Shifts in frequency and dissipation for G1Cn adsorbed on silica surfaces at different concentrations at the third overtone.

Table 1. Kinetics Rate k of Adsorption for G1Cn at the Silica-Water Surface

the slope of the profiles is bigger in the subsequent regime than the initial, which suggests that the adlayers become more viscoelastic when the adsorption amount increases due to the accumulation of aggregates. However, the slope becomes smaller with lengthening of the hydrophobic tails at the same frequency, suggesting that the adlayers are more rigid and flatten with longer hydrophobic tails, probably because the water content of adlayer is lower in the presence of dendrimers with longer hydrophobic tails. The self-assembly and rearrangement of amphiphilic molecules occur mainly through hydrophobic interaction due to the entropy-driven tendency,38−40 in which more water molecules can be repulsed outside for longer hydrophobic tails. It seems that the repulsion of water makes the molecular conformation become more flat for dendrimers with longer hydrophobic tails (Figure 5). After rinsing, ΔD/Δf increases and adsorbed mass decreases in all dendrimer systems, indicating that weakly adsorbed molecules are removed and stable adlayers remain. Significantly, the amounts removed at high concentration are more than those at low concentration. This is because the dominant individual molecules adsorbed are easier to self-assemble compared with primary aggregates adsorbed at high concentrations, which is consistent with our previous investigations.23 However, the tendencies of adsorption with bulk concentration are different compared with that before the rinse, as shown in Figure 4b. For G1C8, frequency and dissipation change to the range of −4 to −8.2 Hz and (0.12−0.24) × 10−6, respectively, which indicates an appearance of conformation rearrangement

kinetics rate k concentration (mol/L) 1 1 1 1

× × × ×

10−6 10−5 10−4 10−3

G1C8

G1C12

G1C16

0.007 79 0.0334 0.0998 0.135

0.0106 0.0157 0.0464 0.112

0.000 395 0.003 24 0.0242 0.0787

phobic tails can reduce the hydration degree and therefore weaken the molecular adsorption, especially for G1C16, although molecular self-assembly can be facilitated to some extent through intermolecular hydrophobic interaction. 3.2.2. Adsorption Amounts. In the case of adsorption before rinse, an upward trend in the adsorption amount was observed with increasing concentration, as shown in Figure 4a. For example, in the presence of G1C8 and G1C12, ΔD/Δf value decreases to about −0.1 to −0.3 × 10−6 and adsorbed mass increases to about 200−300 ng/cm2 as the concentration rises (Table S1), due to the accumulated adsorption of aggregates at higher concentration. In addition, the adsorption amount decreases with lengthening hydrophobic tails due to the decrease of affinity between surface and dendrimer molecules. From the profiles of ΔD/Δf in Figure 4c−e, it can be seen that the slope increases with increasing concentration, especially for G1C8, indicating that more loose and soft adlayers are formed at higher concentrations. In addition, the profiles are divided into two regimes at the highest concentration of 10−3 mol/L; D


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Figure 4. Adsorption isotherms of G1Cn before rinse (a) and after rinse (b); D−f plot of G1C8 (c), G1C12 (d), and G1C16 (e) adsorbed on the silica surface; (f) water droplet contact angle of silica surface with adsorbed G1Cn at different concentrations after rinsing.

3.3. Adsorption Mechanisms. To speculate the microstructures of adlayers, the theoretical adsorption amounts of the saturated monolayer are calculated from the theoretic length of hydrophobic tails. The theoretical adsorption amount of the monolayer is obtained according to the following

and the formation of stable adlayers. It is found that when more unstable adsorbed molecules are washed away, the remaining adsorption amounts decrease largely at higher concentration. Interestingly, we can see that remaining adsorption amounts of G1C12 are approachable and bigger than those of G1C8 at the concentration range except at 1 × 10−6 mol/L, due to the original adsorption at a low level. It is speculated that the stronger intermolecular hydrophobic interactions in the process of self-assembly and rearrangement exist in G1C12 system with longer hydrophobic tails. Because there is a certain repulsive interaction between adsorbed molecules according to the “three-body model” theory,41−43 the self-assembly and rearrangement of the adlayer occurred mainly through intermolecular hydrophobic interaction. However, in the case of G1C16, most of the adsorbed molecules are washed away, implying that the adlayers are not well self-assembled and reorganized. This is because the hydrophobic tails of G1C16 are so long that they can form intramolecular hydrophobic microdomains within a single molecule but reduce the intermolecular hydrophobic interactions, which is proposed to be the main driven force for selfassembly and rearrangement of the adlayer.

equation n =

1 cm 2 23 , πR2 × NA

assuming the dendrimer molecules are

fully stretched. The theoretical molecular radius R with different hydrophobic tails C8, C12, and C16 is 1.10, 1.70, and 2.20 nm, respectively, according to a previous report.10 For G1C8, it is found that the adsorption amount at a series of concentrations is 2-fold higher than the theoretical adsorption amount of the saturated monolayer (Table 2), indicating that there are probably bilayer-like structures existing in adlayers. The hydrophobicity of the silica surface modified by G1C8 is enhanced at higher concentration, demonstrated by the value of contact angle (Figure 4f), along with the decrease of adsorption amounts (Figure 4b) and increase of surface roughness (Figure 5) after rinsing. The contact angle increased with the increasing surface roughness, suggesting that the detachment of dendrimers leads to the exposure of hydrophobic chains. So, schematic adsorption mechanisms of G1C8 on solid surfaces speculate that polar headgroups adsorb at E


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Figure 5. AFM topography for G1C8 (a1−d1), G1C12 (a2−d2), and G1C16 (a3−d3) at different concentrations of 1 × 10−6, 1 × 10−5, 1 × 10−4, and 1 × 10−3 mol/L adsorbed onto silica surfaces.

adsorbed dendrimers QPAMCm at water−air interface.44 Hydrophilicity increases with the reduced adsorption amount and surface roughness, so it can be concluded that lacking the dendrimer coverage increases the exposure of hydrophilic silica surface and enhances the surface hydrophilicity to some extent. A compact conformation forms with flexible hydrophobic endgroups of G1C16 toward the flowing water and finally results in relatively low adsorption amount and high hydrophilicity.

Table 2. Adsorption Amount after Rinsing in nmol/cm2 of G1Cn Adsorbed Layers at Different Concentrations adsorption amount (nmol/cm2) concentration (mol/L) 1 × 10−6 1 × 10−5 1 × 10−4 1 × 10−3 theoretical adsorption amount of saturated monolayer

G1C8

G1C12

G1C16

0.10 0.094 0.063 0.051 0.043

0.053 0.072 0.068 0.060 0.018

0.0032 0.015 0.014 0.011 0.011

4. CONCLUSIONS By use of QCM-D, AFM, and CA methods, we investigated the adsorption behaviors of a series of amphiphilic dendrimers with different alkyl chain lengths on silica surfaces. Experimental results showed that the hydrophobic tails were not in favor of the adsorption rate, suggesting that the adsorption kinetics were dominated by the synergistic effect of electrostatic interaction and hydration degree of amphiphilc dendrimers. Additionally, the difference of hydrophobic tail lengths led to intermolecular interaction for G1C8 and G1C12 and intramolecular interaction for G1C16, resulting in interesting adlayer microstructures. Upon adsorption, G1C8 and G1C12 formed loose layers with bilayer-like structures on solid surfaces, while the absorbed film was in the form of a

surface due to the electrostatic interaction and dendrimer alkyl chains from the second layer interact with the alkyl chains in the first layer due to the hydrophobic interaction (Figure 6a), resulting in a pancakelike conformation. Similar conformation of bilayer-like structures can be deduced in the G1C12 system (Figure 6b), mainly because the lowest adsorption amount brings in the highest hydrophobicity. In the presence of G1C16, most of the adsorption amounts are smaller than the theoretical adsorption amounts of a saturated monolayer, suggesting that monolayer structures are likely to exist in the adlayers (Figure 6c), agreeing with the physical models of

Figure 6. Schematic adsorption mechanism of G1Cn on the silica surface. F


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(7) Cahill, B. P.; Papastavrou, G.; Koper, G. J. M.; Borkovec, M. Adsorption of poly(amido amine) (PAMAM) dendrimers on silica: Importance of electrostatic three-body attraction. Langmuir 2008, 24, 465−473. (8) Raghupathi, K. R.; Guo, J.; Munkhbat, O.; Rangadurai, P.; Thayumanavan, S. Supramolecular Disassembly of Facially Amphiphilic Dendrimer Assemblies in Response to Physical, Chemical, and Biological Stimuli. Acc. Chem. Res. 2014, 47, 2200−2211. (9) Sikwal, D. R.; Kalhapure, R. S.; Govender, T. An Emerging Class of Amphiphilic Dendrimers for Pharmaceutical and Biomedical Applications: Janus Amphiphilic Dendrimers. Eur. J. Pharm. Sci. 2017, 97, 113−134. (10) Zhang, P.; Zhang, L.; Zhou, J.; Wang, J.; Yan, H.; et al. Dilational Properties of Novel Amphiphilic Dendrimers at Water-Air and Water-Heptane Interfaces. J. Phys. Chem. B 2012, 116, 12760− 12768. (11) Wang, X.; Ma, X.; Zang, D. Aggregation Behavior of Polystyrene-b-Poly(acrylic acid) at the Air-Water Interface. Soft Matter 2013, 9, 443−453. (12) Su, A.; Tan, S.; Thapa; Flanders, P. B. N.; Ford, W. T. Highly Ordered Langmuir-Blodgett Films of Amphiphilic Poly(propylene imine) Dendrimers. J. Phys. Chem. C 2007, 111, 4695−4701. (13) Ito, M.; Imae, T.; Aoi, K.; Tsutsumiuchi, K.; Noda, H.; Okada, M. In Situ Investigation of Adlayer Formation and Adsorption Kinetics of Amphiphilic Surface-Block Dendrimers on Solid Substrates. Langmuir 2002, 18, 9757−9764. (14) Weener, J.-W.; Meijer, E. W. Photoresponsive Dendritic Monolayers. Adv. Mater. 2000, 12, 741−746. (15) Schenning, A. P. H. J.; Elissen-Roman, C.; Weener, J.-W.; Baars, M. W. P. L.; van der Gaast, S. J.; Meijer, E. W. Amphiphilic Dendrimers as Building Blocks in Supramolecular Assemblies. J. Am. Chem. Soc. 1998, 120, 8199−8208. (16) Tan, S.; Su, A.; Ford, W. T. Aggregation of a Hydrophobically Modified Poly(propylene imine) Dendrimer. Eur. Phys. J. E 2008, 27, 205−211. (17) Nummelin, S.; Selin, M.; Legrand, S.; Ropponen, J.; Seitsonen, J.; Nykanen, A.; Koivisto, J.; Hirvonen, J.; Kostiainen, M. A.; Bimbo, L. M. Modular Synthesis of Self-Assembling Janus-Dendrimers and Facile Preparation of Drug-Loaded Dendrimersomes. Nanoscale 2017, 9, 7189−7198. (18) Avila-Salas, F.; Pereira, A.; Rojas, M. A.; Saavedra-Torres, M.; Montecinos, R.; Bonardd, S.; Quezada, C.; Saldías, S.; Díaz, D. D.; Leiva, A.; Radic, D.; Saldías, C. An Experimental and Theoretical Comparative Study of the Entrapment and Release of Dexamethasone From Micellar and Vesicular Aggregates of PAMAM-PCL Dendrimers. Eur. Polym. J. 2017, 93, 507−520. (19) Wu, Y.; Zhang, L.; Cui, C.; Cansiz, S.; Liang, H.; Wu, C.; Teng, I. T.; Chen, W.; Liu, Y.; Hou, W.; Zhang, X.; Tan, W. Enhanced Targeted Gene Transduction: AAV2 Vectors Conjugated to Multiple Aptamers via Reducible Disulfide Linkages. J. Am. Chem. Soc. 2018, 140, 2−5. (20) Sarazen, M. L.; Jones, C. W. Insights into Azetidine Polymerization for the Preparation of Poly(propylenimine)-Based CO2 Adsorbents. Macromolecules 2017, 50, 9135−9143. (21) Márquez-Miranda, V.; Araya-Duran, I.; Camarada, M. B.; Comer, J.; Valencia-Gallegos, J. A.; Gonzalez-Nilo, F. D. SelfAssembly of Amphiphilic Dendrimers: The Role of Generation and Alkyl Chain Length in siRNA Interaction. Sci. Rep. 2016, 6, No. 29436. (22) Wang, L.; Hu, Y.; Liu, R.; Liu, J.; Sun, W. Synergistic Adsorption of DDA/Alcohol Mixtures at the Air/Water Interface: A Molecular Dynamics Simulation. J. Mol. Liq. 2017, 243, 1−8. (23) Zhang, M.; Wang, J.; Zhang, P. Controllable Self-Assembly of Amphiphilic Dendrimers on a Silica Surface: The Effect of Molecular Topological Structure and Salinity. J. Phys. Chem. B 2016, 120, 10990−10999. (24) Zhao, Z.; Ji, X.; Dimova, R.; Lipowsky, R.; Liu, Y. Viscoelasticity of Poly(ethylene glycol) Solutions on Supported

monolayer of G1C16, because the coiled alkyl chains mainly adopt intramolecular hydrophobic interaction. Reasonable physical models were proposed to reveal the adsorption mechanisms of amphiphilic dendrimers onto solid−liquid interface, providing guidance for designing controlled surfaces or functional materials.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcb.8b02534.

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Synthesis pathway of amphiphilic dendrimer G1C8 (Scheme S1); typical 1H NMR spectrum of G1C8, G1C12, and G1C16 in CDCl3, respectively (Figures S1− S3); exhibiting Δf, ΔD, Δm, and ΔD/Δf of G1Cn at different concentrations obtained from QCM-D measurements (Table S1) (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +8610-62523395. Fax: +8610-62523395. ORCID

Hui Yang: 0000-0001-6750-4551 Xu Wu: 0000-0002-8907-6073 Jinben Wang: 0000-0002-6360-9572 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was funded by the National Natural Science Foundation of China (21603240 and 21406040), the Important National Science and Technology Specific Project of China (2017ZX05013-003), the Foundation Projects of Basic Research, Strategic Reserve Technology from Research Institutes of Petro China (2017D-5008-03), and the Strategic Priority Research Program of CAS (XDB22030102). We thank Dr. Min Wang from Biolin Scientific AB for the help in QCM measurements.

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REFERENCES

(1) Caminade, A. M.; Ouali, A.; Laurent, R.; Turrin, C. O.; Majoral, J. P. The Dendritic Effect Illustrated with Phosphorus Dendrimers. Chem. Soc. Rev. 2015, 44, 3890−3899. (2) Wong, P. T.; Choi, S. K. Mechanisms of Drug Release in Nanotherapeutic Delivery Systems. Chem. Rev. 2015, 115, 3388− 3432. (3) Ye, R.; Zhukhovitskiy, A. V.; Deraedt, C. V.; Toste, F. D.; Somorjai, G. A. Supported Dendrimer-Encapsulated Metal Clusters: Toward Heterogenizing Homogeneous Catalysts. Acc. Chem. Res. 2017, 50, 1894−1901. (4) Stiriba, S.-E.; Frey, H.; Haag, R. Dendritic Polymers in Biomedical Applications:From Potential to Clinical Use in Diagnostics and Therapy. Angew. Chem., Int. Ed. 2002, 41, 1329−1334. (5) Xuan, F.; Fan, T. W.; Hsing, I.-M. Electrochemical Interrogation of Kinetically-Controlled Dendritic DNA/PNA Assembly for Immobilization-Free and Enzyme-Free Nucleic Acids Sensing. ACS Nano 2015, 9, 5027−5033. (6) Mureşan, L.; Maroni, P.; Popa, I.; Porus, M.; Longtin, R.; Papastavrou, G.; Borkovec, M. Conformational Changes of Polyamidoamine (PAMAM) Dendrimers Adsorbed on Silica Substrates. Macromolecules 2011, 44, 5069−5071. G


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Importance of Electrostatic Three-Body Attraction. Langmuir 2008, 24, 465−473. (43) Ramon, P.-C.; Georg, P.; Borkovec, M. Atomic Force Microscopy Study of the Adsorption and Electrostatic SelfOrganization of Poly(amidoamine) Dendrimers on Mica. Langmuir 2004, 20, 3264−3270. (44) Zhang, P.; Xu, X.; Zhang, M.; Wang, J.; Bai, G.; Yan, H. SelfAggregation of Amphiphilic Dendrimer in Aqueous Solution: The Effect of Headgroup and Hydrocarbon Chain Length. Langmuir 2015, 31, 7919−7925.

Lipid Bilayers via Quartz Crystal Microbalance with Dissipation. Macromolecules 2015, 48, 1824−1831. (25) Shoaib, T.; Nalam, P. C.; He, Y.; Chen, Y.; Espinosa-Marzal, R. M. Assembly, Morphology, Diffusivity, and Indentation of HydrogelSupported Lipid Bilayers. Langmuir 2017, 33, 7105−7117. (26) Yang, G.; Chen, T.; Zhao, J.; Yu, D.; Liu, F.; Wang, D.; Fan, M.; Chen, W.; Zhang, J.; Yang, H.; et al. Desorption Mechanism of Asphaltenes in the Presence of Electrolyte and the Extended Derjaguin-Landau-Verwey-Overbeek Theory. Energy Fuels 2015, 29, 4272−4280. (27) Wang, T.; Long, Y.; Liu, L.; Wang, X.; Craig, V. S.; Zhang, G.; Liu, G. Cation-Specific Conformational Behavior of Polyelectrolyte Brushes: From Aqueous to Nonaqueous Solvent. Langmuir 2014, 30, 12850−12859. (28) Yang, H.; Duan, H.; Wu, X.; Wang, M.; Chen, T.; Liu, F.; Huang, S.; Zhang, W.; Chen, G.; Yu, D.; Wang, J. Self-Assembly Behavior of Ultrahighly Charged Amphiphilic Polyelectrolyte on Solid Surfaces. Langmuir 2016, 32, 11485−11491. (29) Petek, A.; Krajnc, M.; Petek, A. Study of Host-Guest Interaction Between ß-Cyclodextrin and Alkyltrimethylammonium Bromides in Water. J. Inclusion Phenom. Macrocyclic Chem. 2016, 86, 221−229. (30) Le Tirilly, S.; Tregouet, C.; Reyssat, M.; Bone, S.; Geffroy, C.; Fuller, G.; Pantoustier, N.; Perrin, P.; Monteux, C. Interfacial Rheology of Hydrogen-Bonded Polymer Multilayers Assembled at Liquid Interfaces: Influence of Anchoring Energy and Hydrophobic Interactions. Langmuir 2016, 32, 6089−6096. (31) Hyltegren, K.; Nylander, T.; Lund, M.; Skepo, M. Adsorption of the Intrinsically Disordered Saliva Protein Histatin 5 to Silica Surfaces. A Monte Carlo Simulation and Ellipsometry Study. J. Colloid Interface Sci. 2016, 467, 280−290. (32) Lowe, B. M.; Skylaris, C. K.; Green, N. G. Acid-Base Dissociation Mechanisms and Energetics at the Silica-Water Interface: An Activationless Process. J. Colloid Interface Sci. 2015, 451, 231−244. (33) Mivehi, L.; Bordes, R.; Holmberg, K. Adsorption of cationic gemini surfactants at solid surfaces studied by QCM-D and SPR Effect of the presence of hydroxyl groups in the spacer. Colloids Surf., A 2013, 419, 21−27. (34) Penfold, J.; Thomas, R. K.; Li, P.; Xu, H.; Tucker, I. M.; Petkov, J. T.; Sivia, D. S. Multivalent-Counterion-Induced Surfactant Multilayer Formation at Hydrophobic and Hydrophilic Solid-Solution Interfaces. Langmuir 2015, 31, 6773−6781. (35) Mivehi, L.; Bordes, R.; Holmberg, K. Adsorption of Cationic Gemini Surfactants at Solid Surfaces Studied by QCM-D and SPREffect of the Presence of Hydroxyl Groups in the Spacer. Colloids Surf., A 2013, 419, 21−27. (36) Biswas, S. C.; Chattoraj, D. K. Kinetics of Adsorption of Cationic Surfactants at Silica-Water Interface. J. Colloid Interface Sci. 1998, 205, 12−20. (37) Fairclough, J. P. A.; Norman, A. I.; Shaw, B.; Nace, V. M.; Heenan, R. K. Small Angle Neutron Scattering Study of the Structure and Hydration of Polyoxyethylene-Block-Polyoxybutylene in Aqueous Solution. Polym. Int. 2006, 55, 793−797. (38) Rokach, S.; Ottaviani, M. F.; Shames, A. I.; Aserin, A.; Garti, N. Behavior of PPI-G2 Dendrimer in a Microemulsion. J. Phys. Chem. B 2017, 121, 2339−2349. (39) Dai, C.; Du, M.; Zhao, M.; You, Q.; Guan, B.; Wang, X.; Liu, P. Study of Micelle Formation by Fluorocarbon Surfactant N-(2hydroxypropyl)perfluorooctane Amide in Aqueous Solution. J. Phys. Chem. B 2013, 117, 9922−9928. (40) Cai, B.; Dong, J.; Cheng, L.; Jiang, Z.; Yang, Z.; Li, X. Adsorption and Micellization of Gemini Surfactants with Pyrrolidinium Head Groups: Effect of the Spacer Length. Soft Matter 2013, 9, 7637−7646. (41) Schapotschnikow, P.; Vlugt, T. J. Understanding Interactions Between Capped Nanocrystals: Three-Body and Chain Packing Effects. J. Chem. Phys. 2009, 131, No. 124705. (42) Cahill, B. P.; Papastavrou, G.; Koper, G. J. M.; Borkovec, M. Adsorption of Poly(amido amine) (PAMAM) Dendrimers on Silica: H


PAMAM-Based Dendrimers with Different Alkyl Chains Self-Assemble

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