Dynamic Covalent Nanoparticle Building Blocks

Rational and generalisable methods for engineering surface functionality will be crucial to realising the technological potential of nanomaterials. Nanoparticle‐bound dynamic covalent exchange combines the error‐correcting and environment‐responsive features of equilibrium processes with the stability, structural precision, and vast diversity of covalent chemistry, defining a new and powerful approach for manipulating structure, function and properties at nanomaterial surfaces. Dynamic covalent nanoparticle (DCNP) building blocks thus present a whole host of possibilities for constructing adaptive systems, devices and materials that incorporate both nanoscale and molecular functional components. At the same time, DCNPs have the potential to reveal fundamental insights regarding dynamic and complex chemical systems confined to nanoscale interfaces.     

核磁共振研究二茂铁硒铂配合物构象交换热焓

The intramolecular conformational exchange thermodynamics of cis-PtCl[1,1'bis(undecenylseleno)ferrocene](B11SeFcPt) in CDCl3 solution was studied by one dimensional proton NMR． The chemical equilibrium constants were obtained directly from the integration of the 1H NMR spectra and the enthalpy as a function of temperature for the conformational exchange of B11SeFcPt was calculated from the equilibrium constant.     

Scanning force microscopy of polyester: surface structure and adhesive properties

Scanning force microscopy has been used to characterize the surface structure and properties of poly(ethylene terephthalate) (PET) films. Two types of biaxially oriented film have been studied: one (Melinex O) is free of additives while the other (Mylar D) contains particulate additives at the surface. Contact mode characterization of both materials provide clear images of the polymer surface and (in the case of Mylar D) the additives. Phase images reveal substantial nanoscale morphological detail, including small features thought to be crystallites. To model the adhesive properties of polymer surfaces, mixed self‐assembled monolayers containing polar and methyl terminated adsorbates were studied using chemical force microscopy. It was found that the strength of the tip‐sample adhesion increased with the fraction of polar terminated adsorbates at the surface when a carboxylic acid terminated tip was employed, while the trend was reversed when a methyl terminated tip was used. Adhesion forces measured for plasma treated PET increased with treatment time, and linearly with the cosine of the water contact angle, illustrating the chemical selectivity of chemical force microscopy. However, friction forces were found to vary in a non‐linear fashion, indicating that changes to the polymer surface mechanical properties following treatment were important.     

Novel halogen and interhalogen adducts of nanoscale magnesium oxide

The difference in the adsorption properties of magnesium oxide in two different physical forms--large micron-sized crystals (CM-MgO) and nanoscale crystals (AP-MgO)--is described. The highly energetic surface of the nanoparticles is significantly more active than the bulk surface in adsorption of nonpolar halogens (Cl(2), Br(2), and I(2)) and dipole interhalogen molecules (ICl, IBr, and ICl(3)). The nanocrystalline and microcrystalline MgO adducts with halogens and interhalogens were characterized by thermogravimetric analysis (TGA), UV-vis and Raman spectroscopies, and transmission electron microscopy (TEM). The bonds of the adsorbates were considerably strained upon adsorption on the nanocrystalline MgO without a molecular dissociation. The results presented in the paper explain the enhanced reactivities of the nanoscale MgO, halogen adducts as halogenating agents of organic molecules and their noticeable biocidal activity.     

Modeling adsorbate‐induced property changes of carbon nanotubes

Because of their potential for chemical functionalization, carbon nanotubes (CNTs) are promising candidates for the development of devices such as nanoscale sensors or transistors with novel gating mechanisms. However, the mechanisms underlying the property changes due to functionalization of CNTs still remain subject to debate. Our goal is to reliably model one possible mechanism for such chemical gating: adsorption directly on the nanotubes. Within a Kohn–Sham density functional theory framework, such systems would ideally be described using periodic boundary conditions. Truncating the tube and saturating the edges in practice often offers a broader selection of approximate exchange–correlation functionals and analysis methods. By comparing the two approaches systematically for NH₃ and NO₂ adsorbates on semiconducting and metallic CNTs, we find that while structural properties are less sensitive to the details of the model, local properties of the adsorbate may be as sensitive to truncation as they are to the choice of exchange–correlation functional, and are similarly challenging to compute as adsorption energies. This suggests that these adsorbate effects are nonlocal. © 2017 Wiley Periodicals, Inc.     

Nanoscale Biomolecular Structures on Self‐Assembled Monolayers Generated from Modular Pegylated Disulfides

A solid‐phase synthetic strategy was developed that uses modular building blocks to prepare symmetric oligo(ethylene glycol)‐terminated disulfides with a variety of lengths and terminal functionalities. The modular disulfides, composed of alkyl amino groups linked by an amide group to oligoethylene chains were used to generate self‐assembled monolayers (SAMs), which were characterised to determine their applicability for biomolecular applications. X‐ray photoelectron spectroscopy (XPS) of the SAMs obtained from these molecules demonstrated improved stability towards displacement by 16‐hexadecanethiol, while surface plasmon resonance (SPR) analyses of SAMs prepared with the hydroxy‐terminated oligoethylene disulfide showed equal resistance to non‐specific protein adsorption in comparison to 11‐mercaptoundecyl tri(ethylene glycol). SAMs made from these adsorbates were amenable to nanoscale patterning by scanning near‐field photolithography (SNP), facilitating the fabrication of nanopatterned, protein‐functionalised surfaces. Such SAMs may be further developed for bionanotechnology applications such as the fabrication of nanoscale biological arrays and sensor devices.     

Chiral Organoborane Lewis Pairs Derived from Pyridylferrocene

In an effort to develop a new class of redox‐active chiral Lewis pairs, pyridine and borane moieties with different steric and electronic properties were introduced onto a planar chiral 1,2‐disubstituted ferrocene framework. Metathesis of lithiated, stannylated, or mercuriated pyridylferrocenes with boron halides afforded (pR)‐2‐[bis(pentafluorophenyl)boryl]‐1‐(3,5‐dimethylpyrid‐2‐yl)ferrocene ( 4‐Pf ), (pR)‐2‐[dimesitylboryl]‐1‐(3,5‐dimethylpyrid‐2‐yl)ferrocene ( 4‐Mes ), (pS)‐2‐(bis(pentafluorophenyl)boryl)‐1‐(2‐trimethylsilylpyrid‐6‐yl)ferrocene ( 5‐Pf ), or (pS)‐2‐[dimesitylboryl]‐1‐(2‐trimethylsilylpyrid‐6‐yl)ferrocene ( 5‐Mes ). The borylated products were analyzed by multinuclear NMR spectroscopy, HRMS, and single‐crystal X‐ray diffraction. Chiral HPLC and optical‐rotation measurements were employed to assess the stereoselectivity of the borylation process and to establish the correct stereochemical assignments. The strength of the B–N interactions were investigated in solution and in the solid state. Compounds 4‐Pf and 4‐Mes formed robust ‘closed’ B?N heterocyclic systems that proved to be perfectly stable to air and moisture, whereas 5‐Pf established a dynamic equilibrium, in which the B?N heterocycle was observed exclusively at room temperature, but opened up at high temperature according to ¹⁹F NMR exchange spectroscopy data. As a consequence, 5‐Pf reacted readily with a molecule of water to generate a ring‐opened pyridinium borate. The combination of bulky borane and bulky pyridyl groups in 5‐Mes led to a completely ‘open’ frustrated Lewis pair system with uncomplexed pyridine and borane groups, even at room temperature. Electrochemical studies were performed and the effect of preparative ferrocene oxidation on the structural features was also explored.     

Synthesis and catalytic performance of ferrocene‐based compounds as burning rate catalysts

To overcome migration problems of ferrocene‐based burning rate catalysts and to enhance burning rate of ammonium perchlorate (AP)‐based propellants, eleven ferrocene‐based compounds ( 1 – 11 ) were synthesized by the condensation reaction of ferrocenecarbonyl chloride with corresponding amines and alcohols. The synthesis of 1 – 11 was confirmed using ¹H NMR, Fourier transform infrared and UV–visible spectroscopy. Their electrochemical properties were analyzed using cyclic voltammetry. The compounds showed redox behavior due to the presence of ferrocene. Their catalytic behavior in the thermal decomposition of AP was investigated using thermogravimetry (TG) and differential TG (DTG). In the presence of 5 wt% 1 – 11 , the thermal decomposition temperature of AP was significantly decreased. TG and DTG analyses showed that 1 – 11 had a good catalytic effect in the thermal decomposition of AP. Anti‐migration studies showed that migration of 1 – 11 was slower than that of 2,2‐bis(ethylferrocenyl)propane (catocene) and ferrocene. The effect of the presence of polar elements like oxygen and nitrogen on anti‐migration behavior of small ferrocene‐based compounds was also investigated. Oxygen‐containing compounds showed better anti‐migration behavior than nitrogen‐containing compounds.     

Novel ferrocenyl polyene derivatives and their binding to unmodified cyclodextrins

Two new ferrocene derivatives, 7-ferrocenyl-2,4,6-heptatrienal (1) and 7-ferrocenyl-2,4,6-heptatrienol (2), were synthesized and characterized. These two compounds possess a rigid triene chain conjugated to one of the cyclopentadienyl rings of the ferrocene residue, and as a result, they exhibit very stiff structures. The electronic absorption and electrochemical properties of these compounds were utilized to investigate their host-guest binding interactions with the receptors alpha-cyclodextrin (alpha-CD) and beta-cyclodextrin (beta-CD) in aqueous solution. From electronic absorption measurements binding constants in the range 790-12900 M(-)(1) were obtained; beta-CD formed more stable complexes than alpha-CD with both guests. Electrochemical measurements suggest some degree of site selectivity in the complexation processes, with beta-CD binding preferentially to the ferrocene moiety while alpha-CD interacts with the unsaturated chain.     

Ferrocenylundecanethiol self-assembled monolayer charging correlates with negative differential resistance measured by conducting probe atomic force microscopy

Electrical and mechanical properties of metal-molecule-metal junctions formed between Au-supported self-assembled monolayers (SAMs) of electroactive 11-ferrocenylundecanethiol (FcC(11)SH) and a Pt-coated atomic force microscope (AFM) tip have been measured using a conducting probe (CP) AFM in insulating alkane solution. Simultaneous and independent measurements of currents and bias-dependent adhesion forces under different applied tip biases between the conductive AFM probe and the FcC(11)SH SAMs revealed reversible peak-shaped current-voltage (I-V) characteristics and correlated maxima in the potential-dependent adhesion force. Trapped positive charges in the molecular junction correlate with high conduction in a feature showing negative differential resistance. Similar measurements on an electropassive 1-octanethiol SAM did not show any peaks in either adhesion force or I-V curves. A mechanism involving two-step resonant hole transfer through the occupied molecular orbitals (MOs) of ferrocene end groups via sequential oxidation and subsequent reduction, where a hole is trapped by the phonon relaxation, is proposed to explain the observed current-force correlation. These results suggest a new approach to probe charge-transfer involving electroactive groups on the nanoscale by measuring the adhesion forces as a function of applied bias in an electrolyte-free environment.     

Supramolecular effects on the potential of redox units-nanoscaffolds internally functionalised with ferrocene units

Redox-active nanoscale racks and nanoladders were prepared as proof of principle in a directional heteroleptic approach towards internally functionalised aggregates. Using the HETTAP concept, zinc(ii) phenanthroline terpyridine nanoladder and nanorack structures with internal ferrocene units were prepared. Proximal effects exerted by the ferrocene units in the nanoladders could be read out by comparison of their redox potentials with those of nanorack R1 and of the parent ligand. The increasing compression of the ferrocene units when going from the larger nanoladder L1 to the smaller aggregate L2 manifested itself in an enlarged anodic shift. Thus, the redox potential series (vs. DMFc: E(1/2) = 0.462 V for R1, 0.480 V for L1 and 0.491 V for L2) reveals convincingly the supramolecular effect on a redox transition. At cathodic potentials the zinc(II) phenanthroline terpyridine complexes were decomposed due to a reduction of the ligands, as could be detected from an evaluation of the ferrocene redox potential.     

Comprehensive SPHYB and B3LYP‐DFT Studies of Two Types of Ferrocene

Structural and optoelectronic properties of ferrocene (FeC₁₀H₁₀) using various exchange correlation potentials including Spin Polarized Generalized Gradient Approximation (SPGGA), Hybrid Density Functional Theory (SPHYB‐DFT), and hybrid density functional Becke3LYP are investigated. Obtained bandgap by the SPHYB‐DFT and SPGGA methods show consistency with the experiment, that are indirect and direct, respectively. The cell size effects on physical properties of ferrocene studied about two types of its lattice parameters ( I and II ). The calculated results reveal that the cell size and the lattice parameters have a remarkable effect on optoelectronic and magnetic properties of ferrocene. However, there is no significant difference between I and II within molecular, structural and charge transitions in calculating UV/Vis spectrum. The calculated electronic absorption spectrum is in good agreement with experiment, in which two major electron‐transition bands derived from d–d (n → n*) and n → π* metal to ligand. NBO analyses show that there are strong donor‐acceptor interactions between central Fe atoms and cyclopentadienyl (Cp) rings that these results are in close agreement with contour plots of charge densities for prediction of the strong covalent bond between C and Fe. The optoelectronic properties of ferrocene predict that it can be efficiently used in the semiconductor devices.     

Sequential solid-phase fabrication of bifunctional anchors on gold nanoparticles for controllable and scalable nanoscale structure assembly

This letter reports a serial solid-phase placement approach to synthesize anisotropically or symmetrically functionalized gold nanoparticles (AuNPs), in which the functionality and directionality (i.e., numbers, locations, and orientations) of the functional ligands are controlled. The solid-phase ligand exchange methodology using highly rigid filter papers enabled us to produce two types of bifunctionalized (bif-) AuNPs in a site-specific manner with increased yield and accuracy: (1) homobif-AuNPs with two carboxyl groups at approximately 180 degrees (para configuration) and (2) heterobif-AuNPs with one carboxyl and one amine functional groups at less than 180 degrees but greater than 90 degrees (meta configuration). Their chemical functionality was validated by 1H nuclear magnetic resonance as well as cyclic voltammetry after ferrocene ethylamine coupling reactions. The directional assemblies of 1D chains with homobif-AuNPs and 2D rings with heterobif-AuNPs were demonstrated through diamine and imidization coupling reactions, respectively, further validating their highly functional and directional selectivity, which is critical to realizing the practical nanoscale assembly.     

Analytical method for parameterizing the random profile components of nanosurfaces imaged by atomic force microscopy

The functional properties of many technological surfaces in biotechnology, electronics, and mechanical engineering depend to a large degree on the individual features of their nanoscale surface texture, which in turn is a function of the surface manufacturing process. Among these features, the surface irregularities and self-similarity structures at different spatial scales, especially in the range of 1 to 100 nm, are of high importance because they greatly affect the surface interaction forces acting at a nanoscale distance. An analytical method for parameterizing the surface irregularities and their correlations in nanosurfaces imaged by atomic force microscopy (AFM) is proposed. In this method, flicker noise spectroscopy--a statistical physics approach--is used to develop six nanometrological parameters characterizing the high-frequency contributions of jump- and spike-like irregularities into the surface texture. These contributions reflect the stochastic processes of anomalous diffusion and inertial effects, respectively, in the process of surface manufacturing. The AFM images of the texture of corrosion-resistant magnetite coatings formed on low-carbon steel in hot nitrate solutions with coating growth promoters at different temperatures are analyzed. It is shown that the parameters characterizing surface spikiness are able to quantify the effect of process temperature on the corrosion resistance of the coatings. It is suggested that these parameters can be used for predicting and characterizing the corrosion-resistant properties of magnetite coatings.     

Diffusion of metal complexes inside of silica-surfactant nanochannels within a porous alumina membrane

The present paper describes diffusivities of a series of metal complexes inside of silica-surfactant nanochannels (channel diameter = 3.4 nm), which were formed within a porous alumina membrane by a surfactant-templated method using cetyltrimethylammonium bromide (CTAB) as a template surfactant. The metal complexes used in this study were Fe(CN)6(3-), Ru(NH3)6(3-), ferrocenecarboxylic acid (Fc-COO-), (ferrocenylmethyl)-trimethylammonium (Fc-NMe3+), N,N-(dimethylamminomethyl)ferrocene (Fc-NMe2), and ferrocene methanol (Fc-OH). Apparent diffusion coefficients of these metal complexes were estimated by measuring their mass transports through the silica-surfactant nanochannels. The estimated apparent diffusion coefficients were on the order of 10(-11) cm2 s(-1) for Fe(CN)6(3-) and Ru(NH3)6(3-), and these values were five orders of magnitude smaller than those in a bulk aqueous solution. For the ferrocene derivatives, the apparent diffusion coefficients of charged ferrocene derivatives are almost the same (5.3 x 10(-11) cm2 s(-1) for Fc-COO- and 5.4 x 10(-11) cm2 s(-1) for Fc-NMe3+), whereas neutral ferrocene derivatives (Fc-NMe2 and Fc-OH) show faster diffusion than the charged species. In addition, the apparent diffusion coefficient of Fc-NMe2 (27 x 10(-11) cm2 s(-1)) was about three times larger than that of Fc-OH (10 x 10-11 cm2 s(-1)). The difference in these diffusion coefficients is discussed by considering the mesostructure of the silica-surfactant nanochannels, that is, an ionic interface with cationic head groups of CTA and their counteranions, a hydrophobic interior of the micellar phase, and a silica framework. As a result, it is inferred that the slow diffusivities of the charged metal complexes are due to the electrostatic interaction between the charged species and the ionic interface, whereas less interaction between neutral ferrocenes and the ionic interface causes distribution of metal complexes into the hydrophobic micellar phase, which is a less viscous medium compared to the ionic interface, resulting in the faster diffusivities of the neutral species.     

The electrochemical behaviour of ferrocene in a photocurable poly(methyl methacrylate-co-2-hydroxylethyl methacrylate) film for a glucose biosensor

A single-step fabrication of a glucose biosensor with simultaneous immobilization of both ferrocene mediator and glucose oxidase in a photocurable methacrylic film consisting of poly(methyl methacrylate-co-2-hydroxylethyl methacrylate) was reported. The entrapped ferrocene showed reversible redox behaviour in the photocured film and no significant leaching of both entrapped ferrocene and enzyme glucose oxidase was observed because of the low water absorption properties of the co-polymer films. From electrochemical studies, ferrocene entrapped in the co-polymer film demonstrated slow diffusion properties. A linear glucose response range of 2-11 mM was obtained at low applied potential of +0.25 V. The glucose biosensor fabricated by this photocuring method yielded sensor reproducibility and repeatability with relative standard deviation of <10% and long-term stability of up to 14 days. The main advantage of the use of photocurable procedure is that biosensor membrane fabrication can be performed in a single step without any lengthy chemical immobilization of enzyme.     

Truncated ditetragonal gold prisms as nanofacet activators of catalytic platinum

We report a facile, seed-mediated method to synthesize nanoscale gold truncated ditetragonal nanoprisms (TDPs) enclosed by 12 high-index {310} facets. The method leads to the formation of nanoparticles with high size and shape monodispersity and allows for easy surfactant removal. The dependence of particle shape on the synergetic contribution of metallic ions, halide ions, and surfactant adsorbates during synthesis is described. The resulting high-index nanoparticle facets were demonstrated as efficient activators of a supported catalytic material (platinum). A Pt monolayer deposited onto the Au TDP nanofacets with sharp electrochemical signatures exhibits an enhanced catalytic activity.     

二茂铁亚甲基三氮唑配合物的合成、晶体结构及性能研究

以二茂铁亚甲基三氮唑为配体,通过与金属离子的自组装得到了两个新的二茂铁基功能配合物：[Cd(tmf)2(SCN)2]n (1) 和 [Ni(tmf)4(SCN)2] (2) (tmf =二茂铁亚甲基三氮唑)。其中,配合物1呈一维链状结构;配合物2是一个通过氢键作用而形成的二维超分子。三阶非线性光学性质测试结果表明,配合物1（n2 = 2.11 × 10-11 esu）和2（n2 = 1.92 × 10-11 esu）的三阶非线性光学折射效应与配体tmf（n2 = 2.49 ×10-11 esu）接近,说明配合物1和2的三阶非线性光学性质主要受配体控制。循环伏安法(CV)测试结果显示,这两个配合物在电极上的氧化还原过程是受扩散控制的。计时电流法(CA)和计时电量法(CC)测得配合物1的扩散系数比配合物2的扩散系数小。     

Electrochemical detection of nanoscale phase separation in binary self-assembled monolayers

Developing methods to probe the nature and structure of nanoscale environments continues to be a challenge in nanoscience. We report a cyclic voltammetry investigation of the internal, hydrogen-bond-driven phase separation of amide-containing thiols and alkanethiols. Amide-containing thiols with a terminal ferrocene carboxylate functional group were investigated in two binary monolayers, one homogeneously mixed and the other phase separated. The electrochemical response of the ferrocene probe was used to monitor adsorbate coverage, environment, and phase separation within each of these monolayers. The results demonstrate that the behavior of ferrocene-containing monolayers can be used to probe nanoscale organization.