Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2020 Jul 1;5(27):16628–16634. doi: 10.1021/acsomega.0c01453

Molecular Description of Grafted Supramolecular Assemblies on Gold Surfaces: Effect of Grafting Points and Chain Lengths

Ludovic Garnier 1, Christine Bonal 1,*, Patrice Malfreyt 1
PMCID: PMC7365550  PMID: 32685829

Abstract

graphic file with name ao0c01453_0007.jpg

The association of 4 aminoazobenzene (4AA) with two different water-soluble hosts, β-cyclodextrins (β-CD) and calixarenesulfonates (CnS), was studied in heterogeneous conditions using molecular simulations. This situation is achieved by immobilization of macrocycles onto a gold Au(111) surface. Several factors that can influence the binding properties are investigated here through the chain length of alkylthiols spacer of the surface-immobilized host and the number of attachment points to the surface. A conformational change of β-CD as a function of the chain length is evidenced upon grafting on the gold surface, whereas CnS does not show any changes. It is then possible to tune the thermodynamic properties of β-CD by changing the grafted chain length and forming a larger hydrophobic region. The mechanisms of insertion of guests into the cavities are similar to those obtained in a homogeneous system. 4AA is included longitudinally in the β-CD cavity, and it interacts rather with the sulfonate groups of the CnS located at the outer edge of the cavity.

1. Introduction

Supramolecular chemistry is based on all types of intermolecular interactions that include noncovalent interactions such as electrostatics, hydrogen bonding, van der Waals, and hydrophobic interactions. A large body of work has been reported in this field over the past thirty years (since the 1987 Nobel Prize1−3). Macrocycle hosts and suitable hosts can form host–guest inclusion complexes with high binding affinities in aqueous solution. The families of cyclodextrins (CDs)4 and calixarenes5 are among the most important organic supramolecular hosts. Cyclodextrin derivatives are mainly used for drug solubilization and delivery thanks to their properties such as inexpensiveness, availability on an industrial scale, and safety.6 Calixarenes can be easily modified and consequently are used mainly for building functional supramolecular architectures.7 Azobenzene is a guest molecule of particular importance for obtaining driven molecular machines8,9 such as photoregulated host–guest macroscopic objects using the differential affinities of hosts for trans-azobenzene and cis-azobenzene10

More recently, we have investigated the association of water-soluble macrocyclic hosts with 4-aminoazobenzene (4AA) in water using both experimental and atomistic simulation approaches.11,12 Using UV–visible spectroscopy, we have obtained whole thermodynamical characterization of the association between hosts (β-cyclodextrins and calixarenesulfonates) with 4AA guest. These thermodynamic studies have been developed by molecular dynamic simulations using the potential of the mean force technique. Our combined approach has provided a structural and energetic characterization of these complexes in solution.

The passage of host–guest chemistry from solution to a solid surface becomes a fundamental requirement for the development of applications in various fields including biology, nanotechnology, and environmental and energy technologies.13 However, many molecular devices operate well in solution but are no longer effective when transferred onto a solid surface.14−16 As an example, the photocontrolled molecular shuttles formed from host–guest chemistry between alpha-CD and azobenzene derivatives exhibit such behavior.10 Moreover, it is now accepted that the association process of supramolecular assemblies17 can be different between homogeneous (free in solution) and heterogeneous conditions (host or guest grafted on surface) in water. Concerning the association between CDs and some guests totally inserted into the host cavity, a higher association constant at the surface than in solution was typically measured.18−21 The same conclusions have been drawn with the association of ferrocenemethanol with gold confined CD by using molecular simulations. The larger negative enthalpy change obtained for the surface was attributed to the wider opening of the surface confined CD, leading to an insertion of a larger number of atoms.21 Clearly, changing the surrounding environment of operation from solution to the solid surface affects the structure of assemblies of molecules and therefore the binding properties.

Molecular dynamic simulations has demonstrated that it can access the structure of host–guest systems in heterogeneous conditions in water. We take the route of investigating two hosts: a β-cyclodextrin (CD) and a p-sulfonatocalixarenes (C4S and C6S) (see Figure 1). These hosts are then grafted on a gold surface through sulfur atoms, as shown in Figure 1. The gold surface was chosen because this metal substrate is the most widely studied for self-assembled monolayer (SAM) preparation and offers a large spectrum of applications in nanoscience and nanotechnology22 such as chemical sensors, lubricating layers, or corrosion inhibitors. At the gold–sulfur interface, the covalent interaction requires the formation of gold–thiolate (RS–Au) bond(s). Sulfur-metal interfacial chemistry has been investigated by numerous techniques such as scanning tunneling microscopy, low-energy electron diffraction, and X-ray spectroscopic techniques, and first-principles calculations.23,24 The reader is redirected to significant works in this field.22,25−28 Different binding modes have been suggested for the S–Au bond:25,26 a classical view involving monothiolate bonding on an Au atom of the Au(111) surface, a disulfide bonding, a complex involving an Au adatom and a thiolate (Au–SR), and a polymeric chain structure where monothiolates are bridging Au adatoms. In addition, the transport of Au adatoms at the interface leads to the breaking and making of Au–S bonds.24

Figure 1.

Figure 1

Open in a new tab

Representation of (a) free β-CD, (b) a protonated 4AA, (c) p-sulfonatocalix[4]arene, and (d) grafted β-CD.

Because the sulfur–gold chemistry is complex in terms of diversity of the adsorption sites, binding, presence, and transport of Au adatoms, we take the route of defining a model system: an Au(111) gold surface in which only the chain length of alkylthiols spacer of the surface-immobilized host and the number of grafting points involving the formation of covalent thiolate–Au (S–Au) bonds with the substrate will vary. We assume that the variety of Au–S bonding will be implicitly considered through the number of grafting points. Actually, it has been reported that the inclusion properties can depend of these key parameters. Previous work has indeed shown that difference in the heterogeneous binding of Mg2+, Ca2+, and Sr2+ ions has been obtained for similar ligands that are differently attached onto a Au(111) surface through one or two arms.29

Inspired by these results, herein, we report the structure of the complexes in heterogeneous conditions as a function of both the chain length linked to the surface (i.e., symbolized in the paper by the letter l) and the number of anchors points (symbolized by a). Thus, an inclusion complex of (2a7l) corresponds to a system with two attachment points and a chain length of seven. We only investigate the protonated form of 4AA because it was shown from experiments11,30 and simulations11,12 that stable complexes with calixarene were found at acidic pH and no inclusion of the guest into the calixarene at neutral pH. For β-cyclodextrin, the association was identical at two pH conditions. As a conclusion, the simulations reported here are performed in acidic solutions.

2. Results and Discussion

In order to deeply examine the architectures of these complexes grafted onto the gold surface at the molecular scale as a function of the number of attachments points and length of the grafted chains, we first examined the displacements in the x and y directions of the chains attached to the Au surface. For clarity, we focus only on (β-CD, 4AA). Plots of displacements for all others systems are given in Supporting Information (see Figure S4). Figures 2a,b represent the displacement of β-CD for 2 (2a) and 7 (7a) anchor points as a function of the grafted chain length (from 1l to 7l).

Figure 2.

Figure 2

Open in a new tab

(a,b) Mean displacement of β-Cd on the gold surface along x and y coordinates as a function of both the number of anchor points (a) and the length of the grafted chains (l). Representations of β-Cd grafted with (c) 2 anchor points and (d) 7 anchor points.

As expected for a given chain length, we observe that the mobility of the chain decreases as the number of interaction points increases. Actually, for the largest chain investigated here (7l), the grafted host can sample a region of 20 Å in the x and y directions with 2 anchor points (see Figure 2a). This sampled space in the x and y directions is reduced to 10 Å with 7 anchor points (see Figure 2b). The chain length also impacts on the mobility. Indeed, increasing the chain length from (1l) to (7l) leads to increase the displacements in the x and y directions by a factor 4 (see Figures 2a,b).

To further analyze the structural properties, we also examine in Figure 3 the size of the wide (upper) and narrow (lower) rims of the grafted macrocycle as a function of the length of the grafting chains and number of anchor points. Clearly, the length of the grafted chains impacts the conformation of the β-CD to a greater extent than CnS (Figure 3a). We observe a large distortion of the narrower rim of β-CD with a change in the size of about 1 Å for the shortest chain length (1l). For this latter system, the size of the lower rim is larger than that of the upper rim. β-CD therefore undergoes a significant deformation. The size of the lower rim becomes comparable again to that obtained in homogeneous medium when the length of the grafted chain is large, here (7l). Finally, the number of grafting points has little influence on the shape of β-CD.

Figure 3.

Figure 3

Open in a new tab

Cavity radius of the wider and narrower rims of hosts depending of the length of grafted chains in (a) β-CD, (b) C4S, and (c) C6S. The blue and red lines correspond to the size of the wider and narrower rims of the macrocycles in a homogeneous phase.

The fact that few changes are observed as a function of the chain length with CnS is evidenced in Figure 3b. Indeed, we obtain the same value of the cavity radius for all chain lengths for a given value of anchor point. Nevertheless, the size of C4S cavity seems to be dependent on the value of a. In the case of (C4S, 4AA) with two anchoring points, the size of the upper rim is larger than that obtained in homogeneous conditions. For the same system with four anchoring points, the sizes of both rims are increased significantly. Note that this dependence is less marked in C6S (see Figure 3c).

In summary, all these results about the conformational change of the cavities highlight that the passage of host–guest chemistry from solution to a solid surface has a greater effect on β-CD than on CnS. This is in line with the expected greater flexibility of β-CD and a deeper insertion of 4AA helped by a larger cavity size. This aspect should have an important role in the insertion of the guest.

In order to address the aspect of insertion, we show in Figures 4a,b two typical conformations of inclusion (β-CD, 4AA) complexes for two chain lengths (1l and 7l) and the largest number of grafted points (7a). Figure 4c shows an insertion rate ranging from 40 to 60% into the β-CD cavity. This type of insertion does not seem to be too impacted by the key-parameters of this study, that is, the number of grafting points and the chain length. The comparison with the insertion rate calculated in a bulk water phase confirms this conclusion. However, when we consider the insertion no longer in the cavity of β-CD but in the hydrophobic region extended to the grafted chains, the values of insertion are significantly changed, as illustrated in a conformation in Figure 4b and quantified in Figure 4d.

Figure 4.

Figure 4

Open in a new tab

Conformations of (β-CD, 4AA) for (a) 7a1l and (b) 7a7l. Percentage of 4AA atoms inserted (c) into the β-CD cavity and (d) into the cage composed of the cavity and the region of grafted chains. The red lines correspond to the insertion calculated in a bulk water phase.

Interestingly, increasing the grafted chain length changes significantly the insertion of the guest into the region delimited by the cavity and the grafted chains. Insertion rates of the order of 90–100% are obtained for the longest chains, demonstrating that the insertion in β-CD of 4AA is largely favored with longer grafted chains. Because the association in inclusion complexes is proportional to the number of inserted atoms, we can expect a more favorable association when increasing the grafted chain length. A grafted chain length of seven carbons is optimal to obtain a total insertion of the guest. For this grafted chain length, the host–guest van der Waals interaction is about −130 kJ mol–1 against −90 kJ mol–1 in homogeneous conditions, whereas the electrostatic contribution is about −40 kJ mol–1 for both cases. In the case of two anchoring points (2a) and the longest chain length (7l), we observe that the percentage found is lower than in other cases. In fact, with few number of attachment points on the surface, the macrocycle has more freedom of movement. Consequently, it can move along the x, y, and z axes. The chain can then tilt toward the surface which drastically hinders the insertion of 4AA into the host cavity. A representation of this case is given in Supporting Information (see Figure S5).

We now turn our attention to the association between C4S and the protonated 4AA guest. The equilibrium conformations of these structures at four grafting points are represented in Figures 5a,b for the smallest (4a1l and largest 4a7l) grafted chains. In Figure 5c, we have represented the total energy contributions (sum of the Lennard-Jones and electrostatic energy parts) between the host and the guest molecules. The red curve represents the same contribution in homogeneous systems.12 The total energy values may be either identical or significantly more favorable to those obtained in the homogeneous system. The decomposition into the Lennard-Jones (LJ) and electrostatic contributions are given in Supporting Information in Figure S6. Contrary to what we have observed for the association between β-CD and 4AA, the LJ contribution is less favorable, but the electrostatic contributions are much more favorable by ranging from −600 to −1200 kJ mol–1 (see Figure S6b). As confirmed in Figure S6a in Supporting Information by the insertion rate, this indicates that the insertion of 4AA is much less marked and that 4AA interacts more strongly with the sulfonate groups of C4S through electrostatic interactions. The association between C4S and 4AA is mainly governed by the electrostatic interactions.

Figure 5.

Figure 5

Open in a new tab

Conformations of the complex formed by C4S and protonated 4AA for four grafting points and two grafted chain lengths (a) l = 1 and (b) l = 7; (c) total energy (kJ mol–1) between C4S and 4AA; (d) electrostatic contributions (kJ mol–1) between 4AA and water molecules within a radius of 14 Å.

In addition, significant differences in the total energy contributions (and consequently in the electrostatic interactions) are observed in Figure 5c as a function of the number of grafting points. For instance, for 2a5l, the total energy between C4S and 4AA is about −600 kJ mol–1, whereas the same contribution is in the order of −1100 kJ mol–1 for 4a5l. This result reveals two modes of inclusion of the host that are energetically equivalent. Indeed, we can see in Figure 5d that the total energy contribution between C4S and 4AA is counterbalanced by the electrostatic contributions between 4AA and water molecules. To characterize these two modes of binding, we have calculated a parameter α that specifies the position of the amine function of 4AA with respect to phenyl groups of C4S (the definition of α is given in Supporting Information in Figure S7). The value of α < 1 corresponds to the insertion of the phenyl group, whereas α > 1 corresponds to that of the protonated amine. The results obtained for α for different values of a and l are given in Figure 6a. For the same chain length, α can be greater or smaller than 1, indicating thus that two inclusion modes occur. Let us recall that for the same system in homogeneous conditions, a privileged penetration of the phenyl part of 4AA rather than the amino group has been established.12 However, note that a scan of the literature data regarding water-soluble calixarenes and quaternary ammonium cations also reports a non-selective insertion of the aromatic derivative or ammonium cations into the cavity.31

Figure 6.

Figure 6

Open in a new tab

(a) α coefficient values in the (C4S, 4AA) complex as a function of grafted chain length and the number of grafting points; (b) number of hydrogen bonds between water and the 4AA amine group; (c) number of hydrogen bonds between sulfonate groups of C4S and the amine group of 4AA.

Because favorable electrostatic interactions between C4S and 4AA may be partly related to the possibility of forming hydrogen bonds between the two species, we have investigated the formation of these H-bonds. The H-bonds between water and the 4AA amine group have been reported in Figure 6b and those between sulfonate groups and the 4AA amine group in Figure 6c. As expected, the insertion of the phenyl group into the host cavity (α < 1) prevents any possibility of H-bonds (Figure 6c) between the protonated amine and the sulfonate groups because of the large separation distance. However, this situation allows us to enhance the hydrophobic interactions of the guest with C4S. It is noteworthy that this orientation of the guest upon complexation leads to a less favorable electrostatic term between C4S and 4AA counterbalanced by a less unfavorable electrostatic contribution between 4AA and water molecules (see Figures 5c and 6a). In contrast, the electrostatic term is largely negative for α > 1, corresponding to the penetration of the protonated group into the host cavity. This results in loss of H-bonds between 4AA and water and more unfavorable (4AA. water) electrostatic contributions (see Figure 5d).

3. Conclusions

The association between two grafted macrocyclic hots (β-CD and C4S) and the protonated 4AA has been investigated in terms of the dependences of the insertion rate and energy contributions on the number of grafting points and grafted chain length. The results were compared with the associations in bulk water phases. First, an in-depth analysis of the association process at the molecular level has shown that the grafted chain length can impact the insertion rate of 4AA into β-CD and as a consequence the strength of the interaction between the host and guest. Actually, the longest chain length of alkylthiols spacer of the surface-immobilized host induces a large expansion of the hydrophobic zone and consequently allows a more deep insertion of 4AA into the host cavity. On the other hand, for the shortest chain length, the association will probably be less favorable than in the homogeneous phase because of the presence of the surface. Second, the association of 4AA with C4S is much weaker with a very weak dependence of grafting parameters on the association. We establish a non-selective insertion of 4AA into the host cavity (by the aromatic moities or by the protonated amine). The 4AA interacts with C4S via two modes of binding which are energetically equivalent.

4. Computational Methods

The simulation boxes contain one protonated 4AA molecule (Figure 1b), one host molecule (C4S or β-CD), a Au(111) gold surface, and 2000 water molecules. The grafted hosts are immobilized on a five-layer Au(111) surface through the seven sulfur atoms. Because the system is nonperiodic along the direction normal to the surface (z axis), the simulation cell is closed by an additional gold layer. To keep applying the periodic conditions in three dimensions and a three-dimensional method for the calculation of long-range electrostatic interactions (PPPM 3D), we add a void of 248 Å above the top gold layer.32 The boxlengths along x, y, and z directions are 40, 40, and 300 Å, respectively. In acidic solution, all the sulfonate groups located on the upper rim are deprotonated.11 Depending on the host, some ions such as Cl– or Na+ can be added to maintain the neutrality of the simulation box. The details of the grafting methodology are given in Supporting Information S1.

Concerning the force fields, we chose the TIP4P2005 model for water molecules33 and the General AMBER Force Field (GAFF) for hosts and guests molecules.34 However, for the guest molecule, the dihedral angle C–N=N–C was taken from the work of Heinz et al.35 and the force field for the S–Au bond was taken from ref (36).

MD simulations were performed with the LAMMPS package.37 To constrain H-based bonds and the HOH angle for water, we used the SHAKE algorithm.38 The Lennard-Jones crossing parameters were calculated using Lorentz–Berthelot rules (i.e., Inline graphic and Inline graphic, where i and j refer to the force centers and ε and σ are the energy parameter and diameter of atoms of types i and j, respectively). Our simulations were carried in the constant NVT ensemble with the velocity-verlet integrator and a timestep of 2 fs. The Langevin39,40 thermostat was used with a relaxation time of 2 ps to keep the temperature at 300 K. Both long-range electrostatic interactions and long-range dispersion-repulsion tail correction41 were considered. PPPM style (particle–particle particle-mesh) with a relative error force of 10–4 was used to calculate the long-range electrostatic interactions. This method maps atom charge to a 3D mesh.42,43

As mentioned in the introduction, the chain length (l) and the number of anchor points (a) are the two key parameters under investigation in this paper. This implies that several simulations were performed to study various anchor points and chain lengths. In the Table 1, we summarized these parameters. Each simulation was composed of a relaxation phase (NVE ensemble) of 10 ps and an equilibrium phase (NVT ensemble) of 1.4 ns. Finally, the thermodynamic and structural properties were averaged over 20 ns of the acquisition phase in the NVT statistical ensemble.

Table 1. Parameters for the Grafted Hosts.

association Nb of anchor points chain length
(β-Cd, 4AA) 2, 4 and 7 1, 3, 5 and 7
(C4S, 4AA) 2 and 4 1, 3, 5 and 7
(C6S, 4AA) 2, 4 and 6 1, 3, 5 and 7
Open in a new tab

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c01453.

  • Methodology of grafting the chains onto the gold surface, typical conformations of the different complexes, mean displacements, insertion rates, energy contributions, and the definition of the α coefficient (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao0c01453_si_001.pdf (1MB, pdf)

References

  1. Pedersen C. J. The Discovery of Crown Ethers (Noble Lecture). Angew. Chem. 1988, 27, 1021–1027. 10.1002/anie.198810211. [DOI] [Google Scholar]
  2. Cram D. J. The Design of Molecular Hosts, Guests, and Their Complexes (Nobel Lecture). Angew. Chem., Int. Ed. 1988, 27, 1009–1020. 10.1002/anie.198810093. [DOI] [PubMed] [Google Scholar]
  3. Lehn J.-M. Supramolecular Chemistry—Scope and Perspectives Molecules, Supermolecules, and Molecular Devices (Nobel Lecture). Angew. Chem., Int. Ed. 2018, 89–112. 10.1002/anie.198800891. [DOI] [Google Scholar]
  4. Szejtli J. Introduction and General Overview of Cyclodextrin Chemistry. Chem. Rev. 1998, 98, 1743–1754. 10.1021/cr970022c. [DOI] [PubMed] [Google Scholar]
  5. Guo D.-S.; Liu Y. Supramolecular Chemistry of p-Sulfonatocalix[n]arenes and Its Biological Applications. Acc. Chem. Res. 2014, 47, 1925–1934. 10.1021/ar500009g. [DOI] [PubMed] [Google Scholar]
  6. Ma D.; Hettiarachchi G.; Nguyen D.; Zhang B.; Wittenberg J. B.; Zavalij P. Y.; Briken V.; Isaacs L. Acyclic Cucurbit[n]uril Molecular Containers Enhance the Solubility and Bioactivity of Poorly Soluble Pharmaceuticals. Nat. Chem. 2012, 4, 503–510. 10.1038/nchem.1326. [DOI] [PubMed] [Google Scholar]
  7. Böhmer V. Calixarenes, Macrocycles with(Almost) Unlimited Possibilities. Angew. Chem., Int. Ed. 1995, 34, 713–745. 10.1002/anie.199507131. [DOI] [Google Scholar]
  8. Patra D.; Zhang H.; Sengupta S.; Sen A. Dual Stimuli-Responsive, Rechargeable Micropumps via ″Host-Guest″ Interactions. ACS Nano 2013, 7, 7674–7679. 10.1021/nn402173w. [DOI] [PubMed] [Google Scholar]
  9. Yamaguchi H.; Kobayashi Y.; Kobayashi R.; Takashima Y.; Hashidzume A.; Harada A. Photoswitchable Gel Assembly Based on Molecular Recognition. Nat. Commun. 2012, 3, 603. 10.1038/ncomms1617. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Yang H.; Yuan B.; Zhang X.; Scherman O. A. Supramolecular Chemistry at Interfaces: Host-Guest Interactions for Fabricating Multifunctional Biointerfaces. Acc. Chem. Res. 2014, 47, 2106–2115. 10.1021/ar500105t. [DOI] [PubMed] [Google Scholar]
  11. Garnier L.; Sarraute S.; Israëli Y.; Bonal C.; Malfreyt P.. Associations of Water-Soluble Macrocyclic Hosts with 4-Aminoazobenzene: Impact of pH. J. Phys. Chem. B 2018, [DOI] [PubMed] [Google Scholar]
  12. Garnier L.; Bonal C.; Malfreyt P. Thermodynamics of Supramolecular Associations with Macrocyclic Water-Soluble Hosts. ACS Omega 2019, 4, 16899–16905. 10.1021/acsomega.9b02136. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Yang Y.-W.; Sun Y.-L.; Song N. Switchable Host-Guest Systems on Surfaces. Acc. Chem. Res. 2014, 47, 1950–1960. 10.1021/ar500022f. [DOI] [PubMed] [Google Scholar]
  14. Wang P.; Hill E. H.; Zhang X. Interfacial Supramolecular Chemistry for Stimuli-Responsive Functional Surfaces. Prog. Chem. 2012, 24, 1–7. [Google Scholar]
  15. Kim H. J.; Lee M. H.; Mutihac L.; Vicens J.; Kim J. S. Host-guest sensing by calixarenes on the surfaces. Chem. Soc. Rev. 2012, 41, 1173–1190. 10.1039/c1cs15169j. [DOI] [PubMed] [Google Scholar]
  16. Ludden M. J. W.; Reinhoudt D. N.; Huskens J. Molecular printboards: versatile platforms for the creation and positioning of supramolecular assemblies and materials. Chem. Soc. Rev. 2006, 35, 1122–1134. 10.1039/b600093m. [DOI] [PubMed] [Google Scholar]
  17. Ghoufi A.; Bonal C.; Morel J. P.; Morel-Desrosiers N.; Malfreyt P. Structures and Energetics of Complexes of thep-Sulfonatocalix[4]arene with Ammonium, Alkylammonium, and Tetraalkylammonium Cations in Water Using Molecular Dynamics Simulations. J. Phys. Chem. B 2004, 108, 5095–5104. 10.1021/jp037411x. [DOI] [Google Scholar]
  18. Domi Y.; Yoshinaga Y.; Shimazu K.; Porter M. D. Characterization and Optimization of Mixed Thiol-Derivatized β-Cyclodextrin/Pentanethiol Monolayers with High-Density Guest-Accessible Cavities. Langmuir 2009, 25, 8094–8100. 10.1021/la900586e. [DOI] [PubMed] [Google Scholar]
  19. Rojas M. T.; Koeniger R.; Stoddart J. F.; Kaifer A. E. Supported Monolayers Containing Preformed Binding Sites. Synthesis and Interfacial Binding Properties of a Thiolated .beta.-Cyclodextrin Derivative. J. Am. Chem. Soc. 1995, 117, 336–343. 10.1021/ja00106a036. [DOI] [Google Scholar]
  20. Kitano H.; Taira Y.; Yamamoto H. Inclusion of Phthalate Esters by a Self-Assembled Monolayer of Thiolated Cyclodextrin on a Gold Electrode. Anal. Chem. 2000, 72, 2976–2980. 10.1021/ac000074t. [DOI] [PubMed] [Google Scholar]
  21. Filippini G.; Bonal C.; Malfreyt P. Why is the Association of Supramolecular Assemblies Different Under Homogeneous and Heterogeneous Conditions?. Phys. Chem. Chem. Phys. 2012, 14, 10122–10124. 10.1039/c2cp41661a. [DOI] [PubMed] [Google Scholar]
  22. Pensa E.; Cortés E.; Corthey G.; Carro P.; Vericat C.; Fonticelli M. H.; Benítez G.; Rubert A. A.; Salvarezza R. C. The Chemistry of the Sulfur-Gold Interface: In Search of a Unified Model. Acc. Chem. Res. 2012, 45, 1183–1192. 10.1021/ar200260p. [DOI] [PubMed] [Google Scholar]
  23. Torres E.; Biedermann P. U.; Blumenau A. T. The Role of Gold Adatoms in Self-Assembled Monolayers of Thiol on Au(111). Int. J. Quantum Chem. 2009, 109, 3466–3472. 10.1002/qua.22055. [DOI] [Google Scholar]
  24. Paulius D.; Torres D.; Illas F.; Archibald W. E. A study on adatom transport through (√3 × √3)-R30°-CH3S self-assembled monolayers on Au(111) using first principles calculations. Phys. Chem. Chem. Phys. 2014, 16, 23067–23073. 10.1039/c4cp03074e. [DOI] [PubMed] [Google Scholar]
  25. Whetten R. L.; Price R. C. CHEMISTRY: Nano-Golden Order. Science 2007, 318, 407–408. 10.1126/science.1150176. [DOI] [PubMed] [Google Scholar]
  26. Häkkinen H. The gold-sulfur interface at the nanoscale. Nat. Chem. 2012, 4, 443–455. 10.1038/nchem.1352. [DOI] [PubMed] [Google Scholar]
  27. Zojer E.; Taucher T. C.; Hofmann O. T. The Impact of Dipolar Layers on the Electronic Properties of Organic/Inorganic Hybrid Interfaces. Adv. Mater. Interfaces 2019, 6, 1900581. 10.1002/admi.201900581. [DOI] [Google Scholar]
  28. Rissner F.; Rangger G. M.; Hofmann O. T.; Track A. M.; Heimel G.; Zojer E. Understanding the Electronic Structure of Metal/SAM/Organic–Semiconductor Heterojunctions. ACS Nano 2009, 3, 3513–3520. 10.1021/nn9010494. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Burshtain D.; Mandler D. The effect of surface attachment on ligand binding: studying the association of Mg2+, Ca2+and Sr2+by 1-thioglycerol and 1,4-dithiothreitol monolayers. Phys. Chem. Chem. Phys. 2006, 8, 158–164. 10.1039/b511285k. [DOI] [PubMed] [Google Scholar]
  30. Liu Y.; Guo D.-S.; Zhang H.-Y.; Ma Y.-H.; Yang E.-C. The Structure and Thermodynamics of Calix[n]arene Complexes with Dipyridines and Phenanthroline in Aqueous Solution Studied by Microcalorimetry and NMR Spectroscopy. J. Phys. Chem. B 2006, 110, 3428–3434. 10.1021/jp0545703. [DOI] [PubMed] [Google Scholar]
  31. Arena G.; Casnati A.; Contino A.; Lombardo G. G.; Sciotto D.; Ungaro R. Water-Soluble Calixarene Hosts that Specifically Recognize the Trimethylammonium Group or the Benzene Ring of Aromatic Ammonium Cations: A Combined1H NMR, Calorimetric, and Molecular Mechanics Investigation. Chem.—Eur. J. 1999, 5, 738–744. . [DOI] [Google Scholar]
  32. Goujon F.; Bonal C.; Limoges B.; Malfreyt P. Molecular Simulations of Grafted Metal-Chelating Monolayers: Methodology, Structure and Energy. Mol. Phys. 2008, 106, 1397–1411. 10.1080/00268970802235557. [DOI] [Google Scholar]
  33. Abascal J. L. F.; Vega C. A General Purpose Model for the Condensed Phases of Water: TIP4P/2005. J. Chem. Phys. 2005, 123, 234505. 10.1063/1.2121687. [DOI] [PubMed] [Google Scholar]
  34. Wang J.; Wolf R. M.; Caldwell J. W.; Kollman P. A.; Case D. A. Development and Testing of a General Amber Force Field. J. Comput. Chem. 2004, 25, 1157–1174. 10.1002/jcc.20035. [DOI] [PubMed] [Google Scholar]
  35. Heinz H.; Vaia R. A.; Koerner H.; Farmer B. L. Photoisomerization of Azobenzene Grafted to Layered Silicates: Simulation and Experimental Challenges. Chem. Mater. 2008, 20, 6444–6456. 10.1021/cm801287d. [DOI] [Google Scholar]
  36. Rai B.; Sathish P.; Malhotra C. P.; Pradip; Ayappa K. G. Molecular Dynamic Simulations of Self-Assembled Alkylthiolate Monolayers on an Au(111) Surface. Langmuir 2004, 20, 3138–3144. 10.1021/la0357256. [DOI] [PubMed] [Google Scholar]
  37. Plimpton S. Fast Parallel Algorithms for Short-Range Molecular Dynamics. J. Comput. Phys. 1995, 117, 1–19. 10.1006/jcph.1995.1039. [DOI] [Google Scholar]
  38. Ryckaert J.-P.; Ciccotti G.; Berendsen H. J. C. Numerical Integration of the Cartesian Equations of Motion of a System with Constraints: Molecular Dynamics of n-Alkanes. J. Comput. Phys. 1977, 23, 327–341. 10.1016/0021-9991(77)90098-5. [DOI] [Google Scholar]
  39. Schneider T.; Stoll E. Molecular-Dynamics Study of a Three-Dimensional One-Component Model for Distortive Phase Transitions. Phys. Rev. B: Condens. Matter Mater. Phys. 1978, 23, 1302. 10.1103/PhysRevB.17.1302. [DOI] [Google Scholar]
  40. Dünweg B.; Paul W. Brownian Dynamics Simulations Without Gaussian Random Numbers. Int. J. Mod. Phys. C 1991, 02, 817. 10.1142/S0129183191001037. [DOI] [Google Scholar]
  41. Sun H. COMPASS: An ab Initio Force-Field Optimized for Condensed-Phase ApplicationsOverview with Details on Alkane and Benzene Compounds. J. Phys. Chem. B 1998, 102, 7338–7364. 10.1021/jp980939v. [DOI] [Google Scholar]
  42. Hockney R. W.; Eastwood J. W.. Computer Simulation Using Particles; CRC Press, 1988. [Google Scholar]
  43. Pollock E. L.; Glosli J. Comments on P3M, FMM, and the Ewald Method for Large Periodic Coulombic Systems. Comput. Phys. Commun. 1996, 95, 93–110. 10.1016/0010-4655(96)00043-4. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao0c01453_si_001.pdf (1MB, pdf)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES