Unreactive Substrates Research Articles

Phosphoric acid and various transition metal salt solutions as a combined etchant and activator prior to the use of an anaerobic adhesive

Objectives. The objectives of this experiment were to determine whether various transition metal salts in 37% o-phosphoric acid could both activate and etch an enamel surface prior to the use of an anaerobic adhesive. Method. Stainless steel attachments were bonded to human enamel using an anaerobic adhesive. In each case, the enamel was etched and activated using a solution of 37% o-phosphoric acid containing various transition metal sulfates and chlorides. After bench curing, the specimens were shear bond tested to failure and the load at debond recorded in each case. Results. The results were analyzed using mean force to debond (N) and 95% confidence intervals. Kaplan–Meier survival probabilities and log-rank tests were also performed. Conclusions. Under the conditions of this experiment, the sulfate and chloride of copper in acid were the most effective etching/activating solutions. There was no significant difference in the mean force to debond between the copper (II) sulfate and copper (II) chloride. The chloride in acid was, however, the only one of the two to produce a conventional etch pattern on the surface of the enamel. Significance. It is possible to render the enamel surface both retentive and active towards anaerobic adhesives, such that relatively unreactive substrates can be bonded to enamel using such adhesives.

Biomedical coatings by the covalent immobilization of polysaccharides onto gas-plasma-activated polymer surfaces

As the surface properties of polymeric biomaterials play an important role in the performance of biomedical devices, highly hydrophilic, ultrathin coatings were applied onto hydrophobic, perfluorinated and organosilicon polymers by the covalent immobilization of polysaccharides using a reductive amination reaction. Gas plasma (r.f. glow discharge) methods were employed to equip the surfaces of these normally unreactive polymeric substrates with chemical groups capable of reacting with polysaccharides in aqueous solution. In one variant, ammonia plasmas were used to introduce into the polymer surfaces a submonolayer of amine groups. Alternatively, an n-heptylamine process vapour was used to deposit a thin plasma polymer film that possessed surface amine groups. The polysaccharides were activated for covalent immobilization by periodate oxidation, which produced hemiacetal structures, as revealed by NMR and XPS. The hemiacetal structures in the polysaccharide chains were reacted with the surface amine groups on the polymers. The resulting Schiff base linkages were stabilized by reduction to secondary amine linkages using sodium cyanoborohydride. Detailed surface analysis is important for verification that the intended chemistries have indeed been achieved in such multilayer coating schemes. X-ray photoelectron spectroscopy provided a thickness estimate of 1 ± 0.3 nm for the polysaccharide coatings in the dehydrated state. Copyright © 2000 John Wiley & Sons, Ltd.

Impurity-suppressed sintering in copper nanophase materials

Abstract We use an ultrahigh-vacuum in-situ transmission electron microscope to study the behaviour of copper nanoparticles formed by inert-gas condensation onto unreactive substrates. We show that copper nanoparticles ‘instantaneously’ sinter upon contact in vacuo but that trace oxygen exposure slows this sintering and alters particle structures. These results support a picture where particles grow primarily by Brownian coagulation to produce a self-similar distribution. The model confirms the role of oxygen in inhibiting surface diffusion. The size distribution approaches the commonly reported log-normal distribution. Impurities such as oxygen may be desirable to limit agglomeration and to permit dense nanoparticle compact formation.

Polymerization of C-Si Films on Metal Substrates: Potential Adhesion/Diffusion Barriers for Microelectronics

ABSTRACTCarbon-Silicon polymeric films have been formed by electron beam bombardment (500eV) of molecularly adsorbed vinyl silane precursors under ultra-high vacuum (UHV) conditions. Temperature programmed desorption (TPD) studies show that polymerization is occurring via the vinyl groups, while Auger spectra show that the polymerized films have compositions very similar to the starting precursors; vinyltrichlorosilane (VTCS) or vinyltrimethylsilane(VTMS). VTCSderived films ˜ 100 Å thick show no reaction with Cu substrates and no diffusion of Cu until temperatures greater than 700 K, while Cu deposited on VTMS films on Al substrates show no diffusion prior to Al reaction/decomposition at 600 K. Auger and TPD studies also show that fluorocarbon precursors, such as perfluorobenzene can be incorporated into the films by e-beaminduced reactions, a first step in the controlled growth of adherent polymer films on unreactive substrates such as Cu.

Total Syntheses of (+)-Ricinelaidic Acid Lactone and of (−)-Gloeosporone Based on Transition-Metal-Catalyzed C−C Bond Formations

Total syntheses of the macrolides (R)-(+)-ricinelaidic acid lactone (6) and (−)-gloeosporone (7), a fungal germination self-inhibitor, are presented, which are distinctly shorter and more efficient than any of the previous approaches to these targets reported in the literature. Both of them benefit from the remarkable ease of macrocyclization of 1,ω-dienes by means of ring-closing olefin metathesis (RCM) using the ruthenium carbene 1a as catalyst precursor. The diene substrates are readily formed via the enantioselective addition of dialkylzinc reagents to aldehydes in the presence of catalytic amounts of Ti(OiPr)4 and bis-triflamide 18 and/or the stereoselective allylation of aldehydes developed by Keck et al. using allyltributylstannane in combination with a catalyst formed from Ti(OiPr)4 and (S)-(−)-1,1‘-bi-2-naphthol. Comparative studies show this latter procedure to be more practical than the stoichiometric allylation reaction employing the allyltitanium−α,α,α‘,α‘-tetraaryl-1,3-dioxolane-4,5-dimethanol complex 3b. Finally, a method for the efficient ring closure of 4-pentenoic acid esters by RCM is presented that relies on the joint use of 1a and Ti(OiPr)4 as a binary catalyst system. These results not only expand the scope of RCM to previously unreactive substrates but also provide additional evidence for the important role of ligation of the evolving ruthenium carbene center to a polar relay substituent on the substrate which constitutes the necessary internal bias for the RCM-based macrocyclization process.

A nuclear paramagnetic relaxation study of the interaction of the cyclopentanedione substrate with chloroperoxidase

Association of the physiological substrate cyclopentanedione (CPDO) with chloroperoxidase (CPO) was confirmed from both line-width and longitudinal relaxation time measurements of the proton NMR signals of CPDO. A dissociation constant of 33 mM for the enzyme-substrate complex was calculated from proton NMR relaxation experiments. Chloride ion does not affect the stability of the complex, but iodide ion greatly decreased the stability of the CPO-CPDO complex. Binding of cyanide ion to the heme iron center of CPO also decreased the stability of the CPO-CPDO complex. This result indicates the critical influence of perturbation in the heme active site on the affinity of CPO toward its substrate. Titration of CPO with CPDO revealed that CPDO does not bind directly to the heme iron of CPO. A distance of 7.1 Å between the heme center of CPO and the protons of bound CPDO is deduced from the Solomon-Bloembergen relationship. This distance is 1 to 3 Å shorter than those reported for the complexes formed between CPO and organic sulfide and unreactive phenol substrates, but the distance approximates that for reactive phenol substrates.

ChemInform Abstract: Nickel‐Catalyzed Addition of Grignard Reagents to Oxabicyclic Compounds. Ring‐Opening Reactions with Previously Unreactive Substrates and Nucleophiles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Identification of Cu+ as the effective reagent in nitric oxide formation from S-nitrosothiols (RSNO)

Decomposition of S-nitrosothiols (RSNO) in aqueous solution at pH 7.4 is brought about by copper ions, either present as an impurity or specifically added. The primary products are nitric oxide and the disulfide. In the presence of the specific Cu+ chelator, neocuproine, reaction is progressively inhibited as the [neocuproine] is increased, the reaction eventually stopping completely. The characteristic UV–VIS spectrum of the Cu+ adduct can be obtained from the reaction solutions. This shows clearly that Cu+ and not Cu2+ is the effective catalyst. Two limiting kinetic conditions can be identified for a range of S-nitrosothiols at specific copper ion concentrations (a) a first-order dependence and (b) a zero-order dependence upon [RSNO]. Normally both situations also have a short induction period. This induction period can be removed by the addition of the corresponding thiol RSH. A mechanism is proposed in which Cu+ is formed by reduction of Cu2+ by thiolate anion via an intermediate, possibly RSCu+. Loss of nitric oxide from RSNO is then brought about by Cu+, probably via another intermediate in which Cu+ is bound to the nitrogen atom of the NO group and another electron-rich atom (such as nitrogen from an amino group, or oxygen from a carboxylate group) involving a six-membered ring. As well as NO this produces both RS– and Cu2+ which then are part of the cycle regenerating Cu+. Thiolate ion is oxidised to RS˙ which dimerizes to give the disulfide. Depending on the structure (and hence reactivity) of RSNO either Cu+ formation or its reaction with RSNO can be rate-limiting. Computer modelling of the reaction scheme allows the generation of absorbance time plots of the same forms as those generated experimentally, i.e. first- or zero-order, both with or without induction periods. We suggest that the thiolate ion necessary to bring about Cu2+ reduction is either present as a thiol impurity or is generated in small quantities by partial hydrolysis of the nitrosothiol, which results in an induction period. Addition of small quantities of thiol removes the induction period and leads to catalysis but larger quantities bring about a rate reduction by, it is suggested, complexation of the Cu2+. For two very unreactive substrates, S-nitrosoglutathione and S-nitroso-N-acetylcysteine very large induction periods were observed, typically three hours. This results, we suggest, from competitive re-oxidation of Cu+ to Cu2+ by the dissolved oxygen. Experiments carried out anaerobically confirm this, since there is then no induction period. Addition of hydrogen peroxide extends the induction period ever further. The results are discussed in terms of the biological properties of S-nitrosothiols which are related to nitric oxide release.

Nickel-Catalyzed Addition of Grignard Reagents to Oxabicyclic Compounds. Ring-Opening Reactions with Previously Unreactive Substrates and Nucleophiles.

Nickel-Catalyzed Addition of Grignard Reagents to Oxabicyclic Compounds. Ring-Opening Reactions with Previously Unreactive Substrates and Nucleophiles.

Silica Gel Catalyzed Eschenmoser Reaction

Silica gel has been shown to be an effective catalyst for the ring opening of α,β-epoxycycloalkanones with p-toluene-sulfonohydrazide (the Eschenmoser reaction). The reaction conditions are extremely mild and excellent yields of acetylenic-carbonyl compounds (6-heptyn-2-ones and 2-(3-butynyl)-cycloalkanones) are obtained even with unreactive substrates.

Glycosylation of unreactive substrates

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGlycosylation of unreactive substratesDaniel Kahne, Suzanne Walker, Yuan Cheng, and Donna Van EngenCite this: J. Am. Chem. Soc. 1989, 111, 17, 6881–6882Publication Date (Print):August 1, 1989Publication History Published online1 May 2002Published inissue 1 August 1989https://doi.org/10.1021/ja00199a081RIGHTS & PERMISSIONSArticle Views3235Altmetric-Citations425LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (252 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Schottky barrier formation by silicon deposition on unreactive and reactive metal substrates

We compare the interface Fermi-level positions in the Si gap, obtained from photoemission studies of Si overlayers on Al(110) and Cu(111), and of Al overlayers on Si(111). These positions are similar to each other, and consistent with the predictions of a corrected midgap-energy approach.

Activation of methylenetriphenylphosphorane by reaction with [formula omitted]-butyl- or [formula omitted]-butyllithium

Experimental details are provided to support a previous report that α-methylenetriphenylphosphorane ( 1 ) may be activated for reaction with unreactive substrates such as epoxides and hindered ketones by α-metallation to 2 .

Studies with trialkylsilyltriflates: new syntheses and applications

Syntheses and applications are described for three useful reagents for silylation of unreactive substrates, tert -butyldimethylsilyl, triisopropylsilyl, and octadecyldimethylsilyl triflate.

Molecular complex formation between positronium and organic molecules in solutions

Evidence is presented which supports the reversible formation of molecular complexes between Ps atoms and a series of nitrobenzene derivatives and p-benzoquinone in solution. The activation energy for the forward reaction step I (Ps + M (II) reversible PsM (I)) is generally very small; E/sub A/ approximately 1 kcal/mol. $delta$H/sub EQ/, the enthalpy of the overall process, ranges from almost zero, in the case of very unreactive substrates, such as toluene or heptane, to -8 kcal/mol for dinitrobenzene or p-benzoquinone. The reactivities of the various substrate molecules toward Ps follow trends as observed in conventional molecular complex formation. Furthermore an attempt was made to assess the role of the solvent upon the stability of the molecular complexes. (auth)

Horseradish Peroxidase. XVII. Reactions of Compounds I and II with p-Aminobenzoic Acid in Deuterium Oxide

The kinetics of reactions of horseradish peroxidase compounds I and II (HRP-I and HRP-II, respectively) with p-aminobenzoic acid have been studied in ordinary water and in deuterium oxide solution over a pH (pD) range 3–10, at 25° and at an ionic strength of 0.11. Under the conditions of the experiments the rate of reaction is first order both in substrate concentration and in enzyme concentration in both solvents. An analysis of the pH dependence of the second order rate constant in H2O confirms the presence of two acid dissociation groups on the enzyme with pKa' of 8.6 and ∼0 for HRP-II, whereas for HRP-I the data suggest a pKa of 5.1 on the enzyme and reveal, as previously shown, the influence of the ionization of the substituted ammonium group of the substrate. In deuterium oxide the pD profiles are similar to those in water but significant shifts for both kinetic and acid dissociation constants are observed for both compounds.The numerical values of the isotope effects taken together with previous results in general confirm that with labile substrates the group of pKa 8.6 in H2O on HRP-II is involved in general acid catalysis. p-Aminobenzoic acid is intermediate between labile and somewhat unreactive substrates and behaves similarly to the ferrocyanide ion in that both acid dissociation groups (pKa's 8.6 and ∼0) are influential in the catalysis of substrate oxidation by HRP-II. The kinetic isotope effect for the HRP-I reaction with p-aminobenzoic acid at high pH (pD) is consistent with a rate determining proton transfer but the group of pKa 5.1 in H2O remains unidentified.

Solvolysis of highly unreactive substrates using the trifluoromethanesulfonate (triflate) leaving group

Solvolysis of highly unreactive substrates using the trifluoromethanesulfonate (triflate) leaving group

Non-conventional paths in electrophilic aromatic reactions. Part VI. Chlorination of 3,5-dichloro-2,4,6-trimethylanisole and related compounds

The electrophilic chlorination of some hexa-substituted benzenes has been investigated. Both 3,5-dichloro-2,4,6-trimethylanisole and the parent phenol lead to cyclohexadienone formation. The isomer composition of the product depends on the solvent as well as on the substrate. In trifluoroacetic acid the anisole derivative probably undergoes primary attack of the electrophile on the 4-position. The reaction kinetics show that the methyl-group transfer to the solvent occurs in a fast step subsequent to the slow formation of the intermediate benzenium ion. 2,4,6-Trichloro-3,5-dimethyl-1-R-benzenes (R Me or OMe) were found to be highly unreactive substrates. The implications of these results in connection with the mechanisms of the electrophilic side-chain chlorination of methylbenzenes and of certain demethylation reactions of anisoles are discussed.