Study on functionalization of metal surfaces. III. Photopolymerization of monomer films on metal surfaces

The three kinds of monomer films on metal surfaces were deposited by adsorption from a solution of 6-polymerizable substituents-1,3,5-triazine-2,4-dithiol monosodium salts (RTDN); the polymerizable substituents such as cis-9-octadecenylamino, di(cis-9-octadecenyl)amino, and p-vinylbenzyl(cis-9-octadecenyl)amino groups were selected in view of the polymerization activity of unsaturated groups in the substituents and the packing degree of monomer molecules. The monomer films were estimated to consist of mainly 6-substituents-1,3,5,-triazine-2,4-dithione (3H, 5H) and to be multimolecular layers that are considerably cross-packed and ordered. The monomer films on metal surfaces were polymerizable under a UV light irradiation in air atmosphere to give polymer films. In the photopolymerization, azobis(isobutyronitrile) (AIBN) was very effective for increasing the monomer conversion and the polymerization rate. The optimum concentration of AIBN in monomer films was very small, about 0.025 mol %. The monomer conversion was influenced by the kind of monomers, namely, the polymerization activity and the packing degree. The effect of the packing degree was especially remarkable. The monomer conversion decreased with an increase in the thickness of monomer films. This is because the polymerization was initiated by oxygen and AIBN, which were diffused into the inner of monomer films. The possibility of polymerization of the unsaturated groups and the thione groups in monomer molecules under UV light irradiation is discussed.     

Molecular-level functionalization of electrode surfaces

An ultra-thin film of functional molecule(s) can be deposited on an electrode, which then serves as a device to amperometrically monitor compounds of biological interest. The methods of surface functionalization, mostly on tin oxide (SnO₂) electrodes, include: chemical modification (covalent bond formation between the surface OH group with a functional group of a molecule); the Langmuir-Blodgett technique, where the NH₂ group of a long-chain alkylamine is bound to an enzyme via a small dialdehyde molecule as spacer; and electropolymerization of pyrrole in an electrolyte containing a single enzyme or a sequentially operating bienzyme system. The results of such investigations by the author’s group are presented.     

Single-step covalent functionalization of polylactide surfaces

A single-step, nondestructive, and versatile technique for the grafting and chemical surface modification of biodegradable polymers such as polylactide is described. The substrates are subjected to the vapor phase of any of three investigated vinyl monomers: acrylamide, maleic anhydride, and N-vinylpyrrolidone, and grafting is induced by photoinitiation of benzophenone under solvent free conditions. The modified surfaces exhibit higher wettability, and the grafting is verified by X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform IR, contact-angle measurements, and scanning electron microscopy. The graft-chain pendant groups remain functional and can subsequently be modified so that a tailor-made surface with desired properties may be achieved.     

Monolayer-derivative functionalization of non-oxidized silicon surfaces

This article describes a variety of monolayers anchored directly onto silicon surfaces without an oxide interlayer, their formation mechanisms, their technological applications, and our personal views on the future prospects for this field. The chemical modification of non-oxidized silicon surfaces utilizing monolayers was first reported in 1993. The basic finding that a non-oxidized silicon surface could be neutralized with alkyl chains through direct covalent linkage, i.e., silicon-carbon, has offered chemical scientists ease of handling even in an ambient environment and, thus, research has been predictably focused on forming anti-stiction coating films for nano- and micro-electromechanical systems (NEMS/MEMS). Such surface reforming has also been achieved by using other monolayers, which form interfacial bonds, e.g., silicon-nitrogen and silicon-oxygen. The resultant monolayer surfaces are useful for silicon-based applications including molecular electron transfer films, monolayer templates, molecular insulators, capsulators, and bioderivatives. Such monolayers are applicable not only for surface modification, but also for manipulating individual nanomaterials. By modifying the terminal groups of monolayers with nanomaterials including nanocrystals and biomolecules, the nanomaterials can remarkably be immobilized directly onto non-oxidized silicon surfaces based on the formation mechanisms of the monolayer. Such immobilizations will revolutionize the analysis of the specific features and capabilities of individual nanomaterials. Furthermore, the path will be opened for the development of more advanced monolayer-derived chip technology. To achieve this goal, it is extremely important to thoroughly understand the functionalization processes on silicon, since the resultant internal structures and properties of monolayer-derivative silicon may strongly depend on their course of formation.     

Tailor-made functionalization of silicon nitride surfaces

This communication presents the first functionalization of a hydrogen-terminated silicon-rich silicon nitride (Si3Nx) surface with a well-defined, covalently attached organic monolayer. Properties of the resulting monolayers are monitored by measurement of the static water contact angle, X-ray photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRRAS). Further functionalization was performed by reaction of Si3Nx with a trifluoroethanol ester alkene (CH2=CH-(CH2)8CO2CH2CF3) followed by basic hydrolysis to afford the corresponding carboxylic acid-terminated monolayer with hydrophilic properties. These results show that Si3Nx can be functionalized with a tailor-made organic monolayer, has highly tunable wetting properties, and displays significant potential for further functionalization.     

A citric acid-derived ligand for modular functionalization of metal oxide surfaces via "click" chemistry

Citric acid is a widely used surface-modifying ligand for growth and processing of a variety of nanoparticles; however, the inability to easily prepare derivatives of this molecule has restricted the development of versatile chemistries for nanoparticle surface functionalization. Here, we report the design and synthesis of a citric acid derivative bearing an alkyne group and demonstrate that this molecule provides the ability to achieve stable, multidentate carboxylate binding to metal oxide nanoparticles, while also enabling subsequent multistep chemistry via the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The broad utility of this strategy for the modular functionalization of metal oxide surfaces was demonstrated by its application in the CuAAC modification of ZnO, Fe(2)O(3), TiO(2), and WO(3) nanoparticles.     

Transition metal mediated functionalization of o-carboranes

<正>Carboranes are a class of boron hydride clusters in which one or more of the BH vertices are replaced by CH units.Unlike small boranes, carboranes are kinetically and thermodynamically very stable as well as relatively chemically inert, which are often called three-dimensional relatives of benzenes. They are finding many applications in medicine as boron neutron capture therapy(BNCT) agents, in nanomaterials/supramolecular design as building blocks, and as ligands for transition metals [1]. However, their unique structures make derivatization difficult, which limits their application scope. To this end, there is a need to develop     

Protein-resistant surfaces through mild dopamine surface functionalization

The synthesis and evaluation of new dopamine-based catechol anchors coupled to poly(ethylene glycol) (PEG) for surface modification of TiO(2) are reported. Dopamine is modified by dimethylamine-methylene (7) or trimethylammonium-methylene (8) groups, and the preparation of mPEG-Glu didopamine polymer 11 is presented. All these PEG polymers allow stable adlayers on TiO(2) to be generated through mild dip-and-rinse procedures, as evaluated both by variable angle spectroscopic ellipsometry and X-ray photoelectron spectroscopy. The resulting surfaces substantially reduced protein adsorption upon exposure to full human serum.     

Photochemical functionalization of polymer surfaces for microfabricated devices

Herein we report the topochemical modification of polymer surfaces with perfluorinated aromatic azides. The aryl azides, which have quaternary amine or aldehyde functional groups, were linked to the surface of the polymer by UV irradiation. The polymer substrates used in this study were cyclic olefin copolymer and poly(methyl methacrylate). These substrates were characterized before and after modification using reflection-absorption infrared spectroscopy, sessile water contact angle measurements, and X-ray photoelectron spectroscopy. Analysis of the surface confirmed the presence of aromatic groups with aldehyde or quaternary amine functionality. Enzyme immobilization and patterning onto polymer surfaces were studied using confocal microscopy. Enzymatic digests of protein were carried out on modified probes manufactured from thermoplastic substrates, and the resulting peptide analysis was completed using matrix-assisted laser desorption/ionization mass spectrometry. The use of functionalized perfluorinated aromatic azides allows the surface chemistry of thermoplastics to be tailored for specific lab-on-a-chip applications.     

Electrical bias dependent photochemical functionalization of diamond surfaces

Diamond is an excellent substrate for many sensing and electronic applications because of its outstanding stability in biological and aqueous environments. When the diamond surface is H-terminated, it can be covalently modified with organic alkenes using wet photochemical methods that are surface-mediated and initiated by the ejection of electrons from the diamond. To develop a better understanding of the photochemical reaction mechanism, we examine the effect of applying an electrical bias to the diamond samples during the photochemical reaction. Applying a 1 V potential between two diamond electrodes significantly increases the rate of functionalization of the negative electrode. Cyclic voltammetry and electrochemical impedance measurements show that the 1 V potential induces strong downward band-bending within the diamond film of the negative electrode. At higher voltages a Faradaic current is observed, with no further acceleration of the functionalization rate. We attribute the bias-dependent changes in rate to a field effect, in which the applied potential induces a strong downward band-bending on the negative electrode and facilitates the ejection of electrons into the adjacent fluid of reactant organic alkenes. We also demonstrate the ability to directly photopattern the surface with reactant molecules on length scales of <25 microm, the smallest we have measured, using simple photomasking techniques.     

Molecular-level functionalization of electrode surfaces. An overview

Electrochemical reactions occur at electrode/electrolyte interfaces. Hence, manipulation and design of electrochemical interfaces accompanied by surface modifications have assumed vital importance. Molecular level modification, either at the monolayer or multilayer level of electrode surfaces and leading to functionalization of electrodes, is being actively pursued by researchers. Modification based on the self-assembled monolayer approach has enabled electrodes to acquire molecular recognition and molecular electronic characteristics. Functionalization of electrode surfaces using polymeric materials and enzymes has facilitated electrodes in exhibiting properties like catalysis, molecular recognition, electrochromism and birefringence. The results of such molecular level functionalization studies of electrode surfaces carried out recently in our laboratories are presented in this overview. Besides, some representative results reported from elsewhere are also included.     

Activation and functionalization of molecular nitrogen by metal complexes

Molecular nitrogen is intrinsically unreactive, so much so that it has confounded chemists for decades in attempts to functionalize this abundant diatomic molecule. While biological systems and industrial processes can fix nitrogen to form ammonia, the challenge is to discover a process that involves a homogeneous catalyst that can utilize N(2) as a feedstock to generate higher value organonitrogen materials. In this review, the activation of molecular nitrogen by transition metal complexes is reviewed with the view to present new kinds of transformations for coordinated dinitrogen. Moreover, some reaction types that are as yet unknown are outlined to try and stimulate further research in this area.     

A peptide-based catalyst approach to regioselective functionalization of carbohydrates

Two small peptide libraries (150 members and 36 members) have been subjected to screening experiments to evaluate their potential for regioselective (i.e. site-selective) acylation of carbohydrate monomers. Two substrates, one diol derived from N-acetyl glucosamine and one tetraol derived from glucose, have served as the test cases. In each case, the inherent regioselection of catalyzed acylation was defined as that derived from the reaction where N-methylimidazole (NMI) is used as the catalyst. With both substrates, peptides were found to perturb the inherent selectivities from those observed with NMI. From the libraries, the catalysts that provide the largest deviation from NMI were subjected to optimization studies. The work sets the groundwork for studies of expanded peptide libraries and development of structure-selectivity relationships to obtain catalysts that can selectively derivatize the unique sites in stereochemically complex polyols.     

Chemical functionalization of polyethylene surfaces by plasma-assisted carbene insertion

Controlled surface modification of PE is achieved by an efficient and facile approach via plasma-assisted carbene insertion generated using diazo chemistry. The combination of plasma and carbene insertion shows a synergistic effect, which leads to an obvious enhancement of surface grafting, as shown qualitatively by a combination of IR and UV reflectance spectroscopy, and XPS analysis. The chemical modification may be observed spectroscopically, and the approach provides an opportunity for the convenient modification of low surface energy materials.     

Patterned polyfluorene surfaces by functionalization of nanoimprinted polymeric features

A new procedure is described for surface grafting polymer brushes by step-growth polymerization from initiator-embedded polymeric thin films and micron- and nanometer-scale patterns. An imprint lithographic process, nanocontact molding, was used to prepare thin patterned cross-linked polyacrylate network films on silicon wafers that incorporated 4-bromostyrene in the networks. These networks present reactive 4-bromophenyl functionality at the surface that act as attachment sites for the subsequent Ni(0)- mediated step-growth condensation polymerization of 2,7-dibromo-9,9-dihexylfluorene The step-growth polymerization medium consisted of 2,7-dibromo-9,9-dihexylfluorene, Ni(0)-catalyst, and bipyridine in a toluene/dimethylformamide solvent mixture. The resulting growth of polydihexylfluorene brushes from the patterned surface was monitored by contact angle, optical spectrometry, surface profilometry and AFM. Brush growth was conducted from patterned features ranging from 100 microm to 100 nm in width and 50 nm in height. The optical and fluorescence behavior of the polyfluorene brushes was similar to that of thin polyfluorene films made by spin coating.     

Chemical functionalization of diamond surfaces by reaction with diaryl carbenes

A rapid route to the chemical functionalization of hydrogen-terminated diamond surfaces deposited by chemical vapor deposition involving their reaction with substituted diaryl carbenes has been investigated. To avoid difficulties in the handling of highly reactive compounds, the carbene is generated in situ from the thermal decomposition at 400 K of a thin film of the corresponding diaryl diazomethane precursor deposited at the diamond interface. X-ray photoelectron spectroscopy (XPS) has been used to verify that surface functionalization using two starting compounds, bis(4-iodophenyl) diazomethane and bis(4-nitrophenyl) diazomethane, can be achieved using this approach in agreement with recent theoretical studies. The surface grafting density is measured to be around 10(14) cm(-2) in each case. The chemistry observed is found to be insensitive to the detailed properties of the diamond film and to the presence of oxygen contamination at the hydrogen-terminated diamond surface. We further demonstrate the utility of the approach, in the case of the bound nitrophenyl compound, by its reduction to the corresponding primary amine followed by reaction with fluorescein isothiocyanate to achieve fluorescent tagging of the diamond interface.     

Transition metal compound surfaces

Studies of transition metal compound surfaces using modern surface science techniques are reviewed. Studies of the surface structure and composition of model transition metal compound surfaces are emphasized. The growth of the transition metal compound surface from a chemisorbed layer is used as an introduction to investigations of the surface properties of macroscopic single crystals of transition metal compounds. Examples of both binary and tenary compound systems are examined in relation to chemisorbed layer studies. Although only a few systems are chosen to illustrate work in this field, extensive references to other studies and other systems are included.     

One-step photochemical attachment of NHS-terminated monolayers onto silicon surfaces and subsequent functionalization

N-Hydroxysuccinimide (NHS)-ester-terminated monolayers were covalently attached in one step onto silicon using visible light. This mild photochemical attachment, starting from omega-NHS-functionalized 1-alkenes, yields a clean and flat monolayer-modified silicon surface and allows a mild and rapid functionalization of the surface by substitution of the NHS-ester moieties with amines at room temperature. Using a combination of analytical techniques (infrared reflection absorption spectroscopy (IRRAS), extensive X-ray photoelectron spectroscopy (XPS) in combination with density functional theory calculations of the XPS chemical shifts of the carbon atoms, atomic force microscopy (AFM), and static contact angle measurements), it was shown that the NHS-ester groups were attached fully intact onto the surface. The surface reactivity of the NHS-ester moieties toward amines was qualitatively and quantitatively evaluated via the reaction with para-trifluoromethyl benzylamine and biotin hydrazide.