Adsorption Of Alkanethiols Research Articles

Quantum Mechanical Derived (VdW‐DFT) Transferable Lennard–Jones and Morse Potentials to Model Cysteine and Alkanethiol Adsorption on Au(111) (Adv. Mater. Interfaces 30/2024)

Quantum Mechanical Derived (VdW‐DFT) Transferable Lennard–Jones and Morse Potentials to Model Cysteine and Alkanethiol Adsorption on Au(111) (Adv. Mater. Interfaces 30/2024)

Quantum Mechanical Derived (VdW‐DFT) Transferable Lennard–Jones and Morse Potentials to Model Cysteine and Alkanethiol Adsorption on Au(111)

Quantum Mechanical Derived (VdW‐DFT) Transferable Lennard–Jones and Morse Potentials to Model Cysteine and Alkanethiol Adsorption on Au(111)

Formation and Thermal Stability of Ordered Self-Assembled Monolayers by the Adsorption of Amide-Containing Alkanethiols on Au(111).

We examined the surface structure, binding conditions, electrochemical behavior, and thermal stability of self-assembled monolayers (SAMs) on Au(111) formed by N-(2-mercaptoethyl)heptanamide (MEHA) containing an amide group in an inner alkyl chain using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) to understand the effects of an internal amide group as a function of deposition time. The STM study clearly showed that the structural transitions of MEHA SAMs on Au(111) occurred from the liquid phase to the formation of a closely packed and well-ordered β-phase via a loosely packed α-phase as an intermediate phase, depending on the deposition time. XPS measurements showed that the relative peak intensities of chemisorbed sulfur against Au 4f for MEHA SAMs formed after deposition for 1 min, 10 min, and 1 h were calculated to be 0.0022, 0.0068, and 0.0070, respectively. Based on the STM and XPS results, it is expected that the formation of a well-ordered β-phase is due to an increased adsorption of chemisorbed sulfur and the structural rearrangement of molecular backbones to maximize lateral interactions resulting from a longer deposition period of 1 h. CV measurements showed a significant difference in the electrochemical behavior of MEHA and decanethiol (DT) SAMs as a result of the presence of an internal amide group in the MEHA SAMs. Herein, we report the first high-resolution STM image of well-ordered MEHA SAMs on Au(111) with a (3 × 2√3) superlattice (β-phase). We also found that amide-containing MEHA SAMs were thermally much more stable than DT SAMs due to the formation of internal hydrogen networks in MEHA SAMs. Our molecular-scale STM results provide new insight into the growth process, surface structure, and thermal stability of amide-containing alkanethiols on Au(111).

Study ofn-Alkanethiol Self-Assembly Behavior on Iron Particles: Effect of Alkyl Chain Length and Adsorption Solvent on Resulting Iron-Based Magnetorheological Fluids

Self-assembled monolayers (SAMs) of organic molecules on metal surfaces are a type of inexpensive surface coating often used to improve metal substrate properties for sensors, electrochemistry, and nanofabrication applications. Iron, specifically, is one of the most commonly used metals, both as a pure metal and as an alloy due to its high conductivity, strong ferromagnetism, and low cost. However, magnetorheological fluids, which have shown impressive energy dampening in fields from civil infrastructure to biomedical devices utilizing iron dispersions, have suffered from low reliability and efficiency due to iron particle oxidation, corrosion, and settling. To understand the effect of self-assembled monolayers on iron and both the adsorbed particle's resistance against aggregation and performance impact, this work performs an in-depth study on alkanethiol-based self-assembled monolayers on iron particles. Adsorption of alkanethiols and the generation of SAMs on micron-sized iron particles were evaluated as a function of adsorption solvent polarity and alkanethiol chain length. Maximum alkanethiol loading, determined from appropriate isotherms, was found to strongly be a function of both parameters. Alkanethiol adsorption increased with increasing alkyl chain length and increasing solvent log P values in polar solvents. With respect to magnetorheologically relevant parameters, alkanethiol adsorption did not show any significant effect on both the magnetic properties of iron (as particles) and fluid on-state yield stress. The colloidal stability of n-alkanethiol adsorbed iron-based magnetorheological fluids (MRFs) was a function of both n-alkanethiol chain length and the iron particle adsorption solvent. MRFs composed of hexadecanethiol adsorbed iron prepared in polar solvents like methanol and ethanol showed excellent sedimentation stability compared to all other MRFs prepared in this study.

First‐principles based theoretical investigation of the adsorption of alkanethiols on the iron surface: A DFT-D3 study

The search for novel corrosion inhibitors is a never-ending and challenging task. Computational studies are fundamental to assessing the interaction of inhibitor molecules with metals, thus opening the way to design new inhibitors with specific characteristics. Herein, first-principles DFT-D3 calculations were performed to simulate the bonding of three alkanethiols, namely 11-mercaptoundecanoic acid (MDA), decanethiol (DT), hexanethiol (HT) with the iron surface Fe(110). The interaction energies obtained from different adsorption systems predicted this adsorption strength: MDA > DT > HT. The perpendicular adsorption geometries were found to be more stable than other adsorption modes. However, all adsorption configurations showed covalent interactions between sulfur atom and iron surface. Electron density difference (EDD) plots and projected density of states (PDOS) further confirmed the electron-donation and back-donation synergic interactions between interactive systems. This study showed that alkanethiols with a long carbon chain and an end-functional group had increased charge transfer and bonding with the bare iron surface, i.e., Fe(110).

Interplays of Dipole and Charge‐Transfer‐Plasmon Modes in Capacitively and Conductively Coupled Dimer with High Aspect Ratio Nanogaps

AbstractCharge transfer plasmons (CTPs) in coupled plasmonic cavities have gained attention for their interesting resonance mechanisms and potential applications in sensing. The authors present the first investigation of the CTP mode in top‐down fabricated tall plasmonic nanostructures with deep nanogaps, whose excitation becomes possible by the interaction of transversal and longitudinal plasmonic modes. Hybridization of dipole and CTP modes at different parts of the plasmonic nanostructures, for both capacitively coupled dimer of sub‐5 nm gap and conductively coupled dimer with junction bridge is extensively studied. Importantly, the authors demonstrate the conditional emergence of a hybrid dimer‐CTP mode based on the cladding refractive index and analyte thickness, which can present an opportunity for highly specific surface sensing applications. The sensing performances of these modes are evaluated, showing a figure‐of‐merit of ≈18.4 and Q ≈ 44 for the hybrid dimer‐CTP mode in the visible spectrum. Surface sensing based on alkanethiol adsorption shows surface sensitivity as high as ≈3.2 nm/carbon‐chain for this mode, which is higher than the typical values obtained by LSP structures.

Facile Preparation of Functional Group Gradient Surfaces by Desorption and Re -Adsorption of Alkanethiols on Gold

Facile Preparation of Functional Group Gradient Surfaces by Desorption and <i>Re</i> -Adsorption of Alkanethiols on Gold

Self-Assembled Monolayers on Ferromagnetic Metals Prepared By an Electrochemical Method

Self-assembled monolayers on ferromagnetic metals are of interest, both because they can protect the surface from oxidation and because they are of potential use in spintronic devices. We have studied the adsorption of alkanethiols on Ni and Co from aqueous solutions under potential control using a renewable micro-electrode and an electrochemical quartz crystal microbalance. Monolayers of both octanethiol and dodecanethiol have been prepared and characterized. Potential control enables us to maintain the metal surface free of oxide, and initial electrochemical studies show that this method is more effective at blocking Ni dissolution than the standard method of immersion in an ethanolic solution of dodecanethiol as well as giving better protection to the Ni surface against oxidation.

Using QCM and SPR for the Kinetic Evaluation of the Binding Between A New Recombinant Chimeric Protein and Specific Antibodies of the Visceral Leishmaniasis.

In the present study, the surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) techniques were employed to kinetically evaluate the binding affinity of a new recombinant chimeric protein (CP10) toward anti-Leishmania infantum antibodies for the immunodiagnostics of the visceral leishmaniasis (VL). This chimeric protein was formed by the union in a same artificial coding DNA of ten different peptides, which showed themselves reactive toward positive canine serum for VL. Using the CP10 in enzyme-linked immunosorbent assays (ELISA), it was possible to detect 80% of the asymptomatic infected dogs. After this, SPR and QCM immunosensors were constructed by the covalent immobilization of the CP10 on a self-assembled monolayer (SAM) formed by adsorption of alkanethiol on gold substrates. The thickness (6.80 nm) and the refractive index (1.475) of the protein on the SAM were simultaneously determined through SPR curves measured in different wavelengths (670 and 785 nm). Interactions between the CP10 and its specific IgGs (anti-CP10 antibodies) were characterized by the electrochemical impedance spectroscopy, SPR and QCM techniques. The equilibrium dissociation constant obtained by SPR (K(D) = 8.27 x 10(-10) mol.L(-1)) and QCM (K(D) = 2.42 x 10(- 10) mol.L(-1)) demonstrated high binding affinity of the CP10 toward anti-CP10 antibodies. In this sense, this work quantitatively proves the strong antigenic character of a new recombinant chimeric protein, giving evidence to potential contribution for the use of this protein in programs of control of the VL.

Thiol Adsorption on the Au(100)-hex and Au(100)-(1 × 1) Surfaces

Alkanethiol adsorption on the Au(100) surfaces is studied by using scanning tunneling microscopy, X-ray photoelectron spectroscopy, and electrochemical techniques. Adsorption of hexanethiol (HT) on the Au(100)-hex surface results in the formation of elongated Au islands following the typical stripes of the reconstruction. Ordered molecular arrays forming hexagonally distorted square patterns cover the stripes with surface coverage ≈0.33. On the other hand, HT adsorption on the Au(100)-(1 × 1) surface shows the absence of the elongated island and the formation of square molecular patterns with a surface coverage ≈0.44. The core level shift of thiolates adsorbed on the Au(100)-(1 × 1) and Au(111) is only 0.15 eV, suggesting that chemistry rather than surface sites determines the binding energy of the S 2p core level. These results are also important to complete our knowledge of the chemistry and surface structure for small thiolated AuNPs where the Au(100) together with the Au(111) are the dominant faces.

Change of cobalt magnetic anisotropy and spin polarization with alkanethiolates self-assembled monolayers

We demonstrate that the deposition of a self-assembled monolayer of alkanethiolates on a 1 nm thick cobalt ultrathin film grown on Au(111) induces a spin reorientation transition from in-plane to out-of-plane magnetization. Using ab initio calculations, we show that a methanethiolate layer changes slightly both the magnetocrystalline and shape anisotropy, both effects almost cancelling each other out for a 1 nm Co film. Finally, the change in hysteresis cycles upon alkanethiolate adsorption could be assigned to a molecular-induced roughening of the Co layer, as shown by STM. In addition, we calculate how a methanethiolate layer modifies the spin density of states of the Co layer and we show that the spin polarization at the Fermi level through the organic layer is reversed as compared to the uncovered Co. These results give new theoretical and experimental insights for the use of thiol-based self-assembled monolayers in spintronic devices.

Hydrogen Abstraction Probability in Reactions of Gas-Phase NO3 with an OH-Functionalized Organic Surface

Interfacial collisions between gas-phase nitrate radicals and a model organic surface have been investigated to determine the initial reaction probability. Model surfaces were created by the spontaneous adsorption of HO-terminated alkanethiols (HS(CH2)15CH2OH) at a polycrystalline gold substrate. The experimental approach employed in situ reflection–absorption infrared spectroscopy (RAIRS) to monitor bond rupture and formation, while a well-characterized effusive flux of NO3 impinges on the organic surface. The surface reaction kinetics derived from RAIRS measurements revealed that the consumption of the terminal hydroxyl groups was strongly correlated to the formation of a surface-bound nitrate species. The reaction rate and RAIR spectral assignments suggest that the reaction between NO3 and the HO-SAM is initiated by hydrogen abstraction at the terminal −CH2OH groups. The initial reaction probability for hydrogen abstraction at the terminal groups was determined to be (6 ± 1) × 10–3. This rate is approx...

Effect of gold deposition onto titanium on the adsorption of alkanethiols as the protein linker functionalizing the metal surface

A new method to enhance the biofunctionalization of Ti materials was developed by the immersion of Au-sputtered titanium plates into a solution of alkanethiol with a carboxy group end (HS-C11-COOH). X-ray photoelectron spectroscopy (XPS) analysis showed that the gold content increased with the Au sputtering time and reached over 98 at% after 100 s. The content of the characteristic alkanethiol elements (S, C, and O) in the immersed Ti specimens increased with the Au sputtering time, which indicates that the binding of alkanethiol molecules is enhanced by the Au modification on the Ti surface. Qualitative analysis of XPS (Au-S, COO(-), and OH(-) species) and FTIR spectra (peaks assignable to an aliphatic carboxylic acid) for the sample after immersion also supported this. A strong positive correlation between the S and Au content confirms that Au sputtering is an effective method to control the alkanethiol treatment of Ti substrates.

First-Principles Density Functional Theory (DFT) Study of Gold Nanorod and Its Interaction with Alkanethiol Ligands

The structure and mechanical properties of gold nanorods and their interactions with alkenthiolate self-assembled monolayers have been determined using a novel first-principle density functional theory simulation approach. The multifaceted, 1-dimensional, octagonal nanorod has alternate Au100 and Au110 surfaces. The structural optimization of the gold nanorods was performed with a mixed basis: the outermost layer of gold atoms used double-ζ plus polarization (DZP), the layer below used double-ζ (DZ), and the inner layers used single-ζ (SZ). The final structure compares favorably with simulations using DZP for all atoms. Phonon dispersion calculations and ab initio molecular dynamics (AIMD) were used to establish the dynamic and thermal stability of the system. From the AIMD simulations it was found that the nanorod system will undergo significant surface reconstruction at 300 K. In addition, when subjected to mechanical stress in the axial direction, the nanorod responds as an orthotropic material, with uniform expansion along the radial direction. The Young's moduli are 207 kbar in the axial direction and 631 kbar in the radial direction. The binding of alkanethiolates, ranging from methanethiol to pentanethiol, caused formation of surface point defects on the Au110 surfaces. On the Au100 surfaces, the defects occurred in the inner layer, creating a small surface island. These defects make positive and negative concavities on the gold nanorod surface, which helps the ligand to achieve a more stable state. The simulation results narrowed significant knowledge gaps on the alkanethiolate adsorption process and on their mutual interactions on gold nanorods. The mechanical characterization offers a new dimension to understand the physical chemistry of these complex nanoparticles.

Atomistic Simulations of the Surface Coverage of Large Gold Nanocrystals

Here, the adsorption of alkanethiols (from ethane to dodecanethiol) on icosahedral gold nanocrystals with diameters up to 10 nm is studied by molecular dynamics simulations in a vacuum. The surface coverage of the nanocrystals obtained in the simulations is in good agreement with experimental data. We show that the average surface per adsorbed thiol does not markedly depend on the nanocrystal size and ligand and is only about 10% lower than the value observed on a flat Au(111) surface. We observe two different molecular organizations of the thiolates on the edges and in the centers of the nanocrystal facets. The incompatibility between both organizations explains the fact that the formation of self-assembled monolayers usually observed on flat Au(111) surfaces is hindered for nanocrystals smaller than 6 nm. We also show that the organization of thiolates on the edges is at the origin of the lower average surface per adsorbed thiol found for the nanocrystal.

Adsorption of Alkanethiols on Gold Surfaces: PM-IRRAS Study of the Influence of Terminal Functionality on Alkyl Chain Orientation

The present paper focuses on a simplified method to study the orientation and the anisotropy of two different alkanethiols self-assembled monolayers on gold surfaces. The alkanethiols of interest vary only by their terminal functionalities (COOH and COOCH3), thus allowing one to highlight the influence of these ending chemical groups on the final orientation of the adsorbed molecules. 11-Mercaptoundecanoic acid [HS-(CH2)10-COOH] and the methyl-11-mercaptoundecanoate [HS-(CH2)10-COOCH3] were grafted under adequate conditions to obtain a high grafting density on gold substrates. These latter, before and after the alkanethiol adsorption, were analyzed mainly by the polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) technique to access orientation angles, and by atomic force microscopy (AFM) to check the homogeneity of the grafted layer. By applying an original PM-IRRAS simplified method, the results showed an orientation closer to the normal of the surface plane in the case of the acid thiol compared with the ester one, which is probably because of the lateral hydrogen bonds established between the adjacent COOH functions. This method offers a direct and simple way to quantify the orientation angles in the alkanethiol nanofilms.

Electrografting of calix[4]arenediazonium salts to form versatile robust platforms for spatially controlled surface functionalization

An essential issue in the development of materials presenting an accurately functionalized surface is to achieve control of layer structuring. Whereas the very popular method based on the spontaneous adsorption of alkanethiols on metal faces stability problems, the reductive electrografting of aryldiazonium salts yielding stable interface, struggles with the control of the formation and organization of monolayers. Here we report a general strategy for patterning surfaces using aryldiazonium surface chemistry. Calix[4]tetra-diazonium cations generated in situ from the corresponding tetra-anilines were electrografted on gold and carbon substrates. The well-preorganized macrocyclic structure of the calix[4]arene molecules allows the formation of densely packed monolayers. Through adequate decoration of the small rim of the calixarenes, functional molecules can then be introduced on the immobilized calixarene subunits, paving the way for an accurate spatial control of the chemical composition of a surface at molecular level.

Alkanethiol Adsorption on Platinum: Chain Length Effects on the Quality of Self-Assembled Monolayers

The adsorption of butanethiol (BT), hexanethiol (HT), and dodecanethiol (DT) on Pt from ethanolic solutions has been studied by electrochemical techniques, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. XPS data show two main S 2p components at 162.3 and 163.4 eV. The barrier properties estimated by double-layer capacitance and the blockage of the electron transfer from a redox couple in solution are markedly improved for self-assembled monolayers (SAMs) of the longer DT molecule. While the behavior of DT monolayers on Pt is comparable to that found for those grown on Au, HT and BT SAMs on Pt are more defective, are less blocking, and have a slightly lower thiolate coverage than their Au counterparts. The chain length dependent quality of these SAMs is explained based on DFT and thermodynamics calculations. It is demonstrated that a lying down (LD) surface structure dominates the stability diagram for the shorter chain thiols, while the standing up (SU) phase is more important for DT. We propose that the poor quality observed for SAMs of short chain thiolates results from an easier C–S bond scission of the thioalkyl radical in a LD configuration.

Surface Interactions for Controlling the Microfluidic Separation of Polymeric Microspheres

ABSTRACTApplications of self-assembled monolayers (SAMs) formed by the adsorption of alkanethiols onto gold surfaces have had a widespread growth in adhesion investigations, interfacial interaction investigations and other interfacial phenomena in recent years. As computational modelling showed that modified surfaces can segregate compliant microspheres, a microfluidic flow cell was designed to roll polymeric microcapsules on surfaces with different chemistries, in order to obtain experimental data to validate previous results. Particle image velocimetry showed that rolling speed of microcapsules is affected by surface chemistry. The velocity of vesicles rolling on thiol surfaces with positive of negative charged head groups was significantly lower than vesicles rolling on thiol surfaces with a hydrocarbon chain head group and pure gold surface respectively. Since fabrication of patterned SAMs with different thiol surfaces is possible through oxidation by UV light, our results point to a facile method for carrying out a continuous separation process.

Adsorption of Long-Chain Alkanethiols on Au(111): A Look from the Substrate by High Resolution X-ray Photoelectron Spectroscopy

The structure of the interface between a self-assembled monolayer (SAM) of alkanethiolates (AT) and the underlying Au(111) substrate is a longstanding puzzle in surface science. To cast further light on this problem, we took SAMs of hexanethiolate and dodecanethiolate on Au(111) as test systems and studied them by a combination of synchrotron-based high resolution X-ray photoelectron spectroscopy (HRXPS) and scanning tunneling microscopy (STM). The emphasis of the HRXPS characterization was put on the Au 4f emission of the substrate, which could be decomposed into the components related to the bulk and surface. The behavior of the surface component upon formation of hexanethiolate and dodecanethiolate SAMs was monitored in detail. We observed both a shift of this component and its branching into two independent emissions, which can be associated with two groups of Au atoms differently affected by the adsorption. This behavior, along with the relative intensity of both surface emissions, was correlated wit...