Intermolecular Interactions in Mixed Self‐Assembled Monolayers of Ferrocene

Electrochemical characterization of mixed self‐assembled monolayers (SAMs) of 6‐ferrocenyl‐1‐hexanethiol (FcH) and mercaptoundecanoic acid tyrosinamide (MUATyr) on gold is reported. Single‐component SAMs of FcH presented repulsive intermolecular interactions (vGθ_T=?1.12), while mixed SAMs of FcH/MUATyr (1 : 1) exhibited attractive interactions (vGθ_T=+0.20), with a homogeneous distribution of both components. Electrochemical kinetic determinations on mixed SAMs of FcH/MUATyr, indicated a secondary electron transfer pathway between the redox centers of both components. Higher amounts of FcH in the mixed SAMs lowered the observed rate of electron transfer of MUATyr. The oxidation of FcH caused an anodic shift of 160 mV in the voltammetric wave of MUATyr.     

Electron Transfer Behavior through Densely Packed Self‐Assembled Monolayers of a Novel Heteroaromatic Thiol Derivative onto the Gold Surface

This article is describing the electrical characteristics of the self‐assembled monolayers (SAMs) formed during spontaneous chemical adsorption of a recently synthesized heteroaromatic thiol 2‐(2‐mercaptophenylnitrilomethylidyne)‐phenol ( L ). Some surfactants were used to regulate the electron transfer through the resulting SAMs, as investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results revealed that the surface structure is approximately complete and fractional coverage is very close to unity. The use of surfactants clearly improved the electron transfer properties. Furthermore, complementary experiments were carried out to investigate the electron transfer from modified surface to cytochrome C (cyt‐C), as a biological iron containing protein, which exists in living cells with important life roles. It was found that cyt‐C is able to interact with the modified surface so that it can be used as a scaffold to study the electrochemical characteristics of sensitive biological compounds like proteins. The voltammetric behavior of the redox protein on the resulting SAMs was found to be highly reproducible, emphasizing the fact that the protein denaturation is greatly suppressed.     

Voltammetric Determination of Surface‐Confined Biomolecules with N‐(2‐Ethyl‐ferrocene)maleimide

A thiol‐specific electroactive cross‐linker, N‐(2‐ethyl‐ferrocene)maleimide (Fc‐Mi), has been used to tag surface‐confined peptides containing cysteine residues or oligodeoxynucleotides (ODNs) whose 3′ ends have been modified with thiol groups. The peptides studied herein include both the oxidized and reduced forms of glutathione and a hexapeptide. Cyclic voltammograms (CVs) of the Fc‐Mi groups attached to the surfaces were used to quantify the total number of cysteine residues that are tagged and/or can undergo facile electron transfer reactions with the underlying electrodes. A quartz crystal microbalance was used in conjunction with CV to estimate the total number of cysteine groups labeled by Fc‐Mi per peptide molecule. By comparing to mass spectrometric studies, it is confirmed that not all of the Fc‐Mi linked to the cysteine groups can participate in the electron transfer reactions. The methodology is further extended to the determination of ODN samples in a sandwich assay wherein the thiol linker on the 3′ end can be tagged with Fc‐Mi. The analytical performance was evaluated through determinations of a complementary ODN target and targets with varying numbers of mismatching bases. ODN samples as low as 10 fmol can be detected. Such a low detection level is remarkable considering that no signal amplification scheme is involved in the current method. The approach is shown to be sequence‐ and/or structure‐specific and does not require sophisticated instrumentation and complex experimental procedure.     

Electrochemical Deposition onto Self‐Assembled Monolayers: New Insights into Micro‐ and Nanofabrication

Pattern transfer with high resolution is a frontier topic in the emerging field of nanotechnologies. Electrochemical molding is a possible route for nanopatterning metal, alloys and oxide surfaces with high resolution in a simple and inexpensive way. This method involves electrodeposition onto a conducting master covered by a self‐assembled alkanethiolate monolayer (SAMs). This molecular film enables direct surface–relief pattern transfer from the conducting master to the inner face of the electrodeposit, and also allows an easy release of the electrodeposited film due their excellent anti‐adherent properties. Replicas of the original conductive master can be also obtained by a simple two‐step procedure. SAM quality and stability under electrodeposition conditions combined with the formation of smooth electrodeposits are crucial to obtain high‐quality pattern transfer with sub‐50 nm resolution.     

Self‐Assembled Monolayers of Cobalt and Iron Phthalocyanine Complexes on Gold Electrodes: Comparative Surface Electrochemistry and Electrocatalytic Interaction with Thiols and Thiocyanate

The self‐assembling of the octa(hydroxyethylthio)‐metallophthalocyanine {MOHETPc (M=Co and Fe)} complexes and their similar analogues, octabutylthiometallophthalocyanine {MOBTPc (M=Co and Fe)} complexes on gold electrodes are investigated. Comparative surface voltammetric insights into their distinct self‐assembling properties with respect to the passivation of Faradaic processes and surface coverages, including their solution electrochemistry, suggest different orientations and non‐cleavage of their C? S bonds. In the pH 2?9 range, the reversible [M^(III)Pc(?2)]⁺ / [M^(II)Pc(?2)] redox couples show potential shifts close to ?59 mV / pH. The gold electrodes modified with the SAMs of these species show electrocatalytic activity towards the oxidation of thiols (L ‐cysteine, homocysteine and penicillamine) and thiocyanate in acidic media with detection limits in the region of 10^?7–10^?6 mol dm^?3. These monolayers are stable and easily reproducible.     

Robust Self‐Assembled Monolayers of RuII and OsII Polypyridines on Gold Surfaces: Exploring New Potentials

Functional monolayers : Ru^II and Os^II bis‐terpyridine complexes have been attached through a piperazine‐supported dithiocarbamate to a gold substrate (see picture). The robust tether, and the favourable reduction in oxidation potential induced by the electron‐rich piperazine result in self‐assembled monolayers with excellent reversible redox behaviour and exceptional stability.

     

Study on the Electrochemical Behavior of Dopamine and Uric Acid at a 2‐Amino‐5‐mercapto‐[1,3,4] Triazole Self‐Assembled Monolayers Electrode

Selected from a series of structurally related heteroaromatic thiols, a newly synthesized reagent 2‐amino‐5‐mercapto‐[1,3,4] triazole (MATZ) was used to fabricate self‐assembled monolayers (SAMs) on gold electrode for the first time. The MATZ/Au SAMs was characterized by electrochemical methods and scanning electronic microscopy (SEM). In 0.04 mol/L Britton–Robinson buffer solution (pH 5), the electrochemical behavior of dopamine showed a quasireversible process at the MATZ/Au SAMs with an electrode kinetic constant 0.1049 cm/s. However, the electrochemical reaction of uric acid at the SAMs electrode showed an irreversible oxidation process, the charge‐transfer kinetics of uric acid was promoted by the SAMs. By Osteryoung square‐wave voltammetry (OSWV), the simultaneous determination of dopamine and uric acid can be accomplished with an oxidation peak separation of 0.24 V, the peak current of dopamine and uric acid were linearly to its concentration in the range of 2.5×10^?6–5.0×10^?4 mol/L for dopamine and 1×10^?6–1×10^?4 mol/L for uric acid with a detection limit of 8.0×10^?7 mol/L for dopamine and 7.0×10^?7 mol/L for uric acid. The MATZ/Au SAMs electrode was used to detect the content of uric acid in real urine and serum sample with satisfactory results.     

Self‐Assembled Monolayers into the 21st Century: Recent Advances and Applications

The modification of an interface on a molecular level with more than one molecular ‘building block' is essentially an example of the ‘bottom–up' fabrication principle of nanotechnology. The fabrication of such integrated molecular systems in electrochemistry has seen rapid progress in recent years via the development of sensing interfaces fabricated using self‐assembled monolayers (SAMs). This review outlines recent advances and applications of self‐assembled monolayers for modifying electrodes with an emphasis on the development of integrated molecular systems. First, some basic issues regarding fabricating integrated molecular systems, such as the role of the surface topography of the electrode and patterning surfaces, are discussed. Subsequently an overview of recent developments in pH, inorganic and bio sensing involving the use of SAMs is given. Finally emerging trends in using molecular building blocks in the fabrication of integrated molecular systems, such as nanotubes, dendrimers and nanoparticles, are reviewed.     

Enantiomeric Enrichments via the Self‐Disproportionation of Enantiomers (SDE) by Achiral,Gravity‐Driven Column Chromatography: a Case Study Using N‐(1‐Phenylethyl)acetamide for Optimizing the Enantiomerically Pure Yield and Magnitude of the SDE

This work explores the self‐disproportionation of enantiomers (SDE) via achiral, gravity‐driven column chromatography as typically used in laboratory settings for the purpose of enantiomeric enrichment using N‐(1‐phenylethyl)acetamide (PEA) as a case study. The major finding of this work is the very large magnitude of the SDE for PEA across a variety of conditions and broad range of starting ee values, thereby facilitating a simple, reliable, and predictable means of obtaining enantiomerically pure samples. For example, starting with a sample of PEA of ee as low as 28%, a single column run yielded an enantiomerically pure sample (>99.9% ee) from the first fractions and a significantly enantiomerically depleted sample (<17% ee) from the final fractions. An assessment of SDE via achiral, gravity‐driven column chromatography was also rendered with regard to the differing objectives that workers might target – a large magnitude of the SDE, obtaining an optimum sample of desired ee, or preparative‐scale separation of the excess enantiomer. Overall, it can be considered that the SDE phenomenon via achiral, gravity‐driven column chromatography – readily applicable in the usual laboratory settings – is a simple and convenient method for enantiomeric enrichment with a high degree of proficiency. Advantages of SDE via achiral, gravity‐driven column chromatography over conventional fractional recrystallization for the enantiomeric enrichment of amides/amines, and applicable also to many other classes of compounds as well, are discussed.     

A series of (E)‐5‐(arylideneamino)‐1‐tert‐butyl‐1H‐pyrrole‐3‐carbonitriles and their reduction products to secondary amines: syntheses and X‐ray structural studies

An efficent access to a series of N‐(pyrrol‐2‐yl)amines, namely (E)‐1‐tert‐butyl‐5‐[(4‐chlorobenzylidene)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₆H₁₆ClN₃, (7a), (E)‐1‐tert‐butyl‐5‐[(2,4‐dichlorobenzylidene)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₆H₁₅Cl₂N₃, (7b), (E)‐1‐tert‐butyl‐5‐[(pyridin‐4‐ylmethylene)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₅H₁₆N₄, (7c), 1‐tert‐butyl‐5‐[(4‐chlorobenzyl)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₆H₁₈ClN₃, (8a), and 1‐tert‐butyl‐5‐[(2,4‐dichlorobenzyl)amino]‐1H‐pyrrole‐3‐carbonitrile, C₁₆H₁₇Cl₂N₃, (8b), by a two‐step synthesis sequence (solvent‐free condensation and reduction) starting from 5‐amino‐1‐tert‐butyl‐1H‐pyrrole‐3‐carbonitrile is described. The syntheses proceed via isolated N‐(pyrrol‐2‐yl)imines, which are also key synthetic intermediates of other valuable compounds. The crystal structures of the reduced compounds showed a reduction in the symmetry compared with the corresponding precursors, viz. Pbcm to P from compound (7a) to (8a) and P2₁/c to P from compound (7b) to (8b), probably due to a severe change in the molecular conformations, resulting in the loss of planarity observed in the nonreduced compounds. In all of the crystals, the supramolecular assembly is controlled mainly by strong (N,C)—H…N hydrogen bonds. However, in the case of (7a)–(7c), C—H…Cl interactions are strong enough to help in the three‐dimensional architecture, as observed in Hirshfeld surface maps.     

Synthesis and Crystal Structures of the Molybdenum(II) Complexes with the N,N‐dimethylthiocarbamoyl Containing Ligand: Crystal Structures of β [Mo(CO)2{η2‐S2P(OEt)2}(η2‐SCNMe2)(PPh3)] and [Mo(CO)2(η3‐Tp)(η2‐SCNMe2)(PPh3)]

Reactions of the thiocarbamoyl‐molybdenum complex [Mo(CO)₂(η²‐SCNMe₂)(PPh₃)₂Cl] 1 , and ammonium diethyldithiophosphate, NH₄S₂P(OEt)₂, and potassium tris(pyrazoyl‐1‐yl)borate, KTp, in dichloromethane at room temperature yielded the seven coordinated diethyldithiophosphate thiocarbamoyl‐molybdenum complexe [Mo(CO)₂{η²‐S₂P(OEt)₂}(η²‐SCNMe₂)(PPh₃)] β‐3 , and tris(pyrazoyl‐1‐yl)borate thiocabamoyl‐molybdenum complex [Mo(CO)₂(η³‐Tp)(η²‐SCNMe₂)(PPh₃)] 4 , respectively. The geometry around the metal atom of compounds β‐3 and 4 are capped octahedrons. The α‐ and β‐isomers are defined to the dithio‐ligand and one of the carbonyl ligands in the trans position in former and two carbonyl ligands in the trans position in later. The thiocabamoyl and diethyldithiophosphate or tris(pyrazoyl‐1‐yl)borate ligands coordinate to the molybdenum metal center through the carbon and sulfur and two sulfur atoms, or three nitrogen atoms, respectively. Complexes β‐3 and 4 are characterized by X‐ray diffraction analyses.