Über die Chemie der Oberfläche des Titandioxids. IV. Austausch von Hydroxidionen gegen Fluoridionen

On reaction of anatase of high surface area with NaF solutions, OH groups of the TiO₂ surface were replaced by F^?. Only half the surface OH groups were exchanged in unbuffered solutions or at a pH at or slightly above the zero point of charge (pH 6.6). These are the OH groups exhibiting basic character. The remaining OH groups of acidic character exchange H⁺ for Na⁺ concurrently. They too, are replaced by fluorine in more acidic solutions (pH 4.6).     

Highly Electron‐Deficient and Air‐Stable Conjugated Thienylboranes

Introduced herein is a series of conjugated thienylboranes, which are inert to air and moisture, and even resist acids and strong bases. X‐ray analyses reveal a coplanar arrangement of the thiophene rings, an arrangement which facilitates p–π conjugation through the boron atoms despite the presence of highly bulky 2,4,6‐tri‐tert‐butylphenyl (Mes*) or 2,4,6‐tris(trifluoromethyl)phenyl (^FMes) groups. Short B???F contacts, which lead to a pseudotrigonal bipyramidal geometry in the ^FMes species, have been further studied by DFT and AIM analysis. In contrast to the Mes* groups, the highly electron‐withdrawing ^FMes groups do not diminish the Lewis acidity of boron toward F^? anions. These compounds can be lithiated or iodinated under electrophilic conditions without decomposition, thus offering a promising route to larger conjugated structures with electron‐acceptor character.     

A colorimetric anion receptor containing the <Emphasis Type="Italic">cis</Emphasis>-Ru(bipy)<Subscript>2</Subscript><Superscript>2+</Superscript> group

When one or more nitro groups are incorporated into an anion receptor, intramolecular proton transfer from nearby –NH groups often takes place and is a significant obstacle for the construction of supramolecular systems. In this paper, by employing an intramolecular hydrogen bond between –NH and nitro groups in order to reduce the acidity of the amide group, we were able to construct a receptor that formed stable supramolecular systems. The receptor forms a 1:2 supramolecular compound with fluoride, whereas 1:1 complexes were formed with AcO⁻ and H₂PO₄ ⁻ in DMSO solution. Using this system, an easy-to-prepare test paper for the detection of F⁻ in low concentration at (10⁻⁴ M) in water was developed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Zur Frage der Deprotonierung primärer und sekundärer Aminogruppen beim Kobaltieren von o-Hydroxy-o′-amino (bzw. alkyl-amino)-azofarbstoffen vom Typus Phenyl-azonaphtalin

Phenyl-azo naphthalene dyestuffs, which are substituted in o and in o′ position by hydroxy and amino (or alkylamino) groups, have been metallised with agents releasing either Co^II ions or Co^III ions, the 1:2 complexes formed being examined by means of electrophoresis and alkalimetric titrations. The amino or alkylamino groups are deprotonised only if they are in the naphthalene radical, or, if present in the benzene radical they are acidified by electrophilic substituents. Metallising with Co^II ions yielded usually 1:2 Co^III complexes. With one particular dyestuff, however, a 1:2 Co^II complex was obtained; it is assumed that this is due to a relatively lower oxidation potential of this dyestuff.     

Selenium-77 NMR chemical shifts of five-membered selenium and sulphur heterocycles with CSe,CS,and CO groups

This paper reports the ⁷⁷Se NMR chemical shifts of 1,3-dithiole-, 1,3-thiaselenole- and 1,3-diselenole-2-ones, -thiones and -selones, of the corresponding saturated compounds 1,3-diselenolane-2-one, -thione and -selone, and the 1,3-thiaselenolium tetrafluoroborates, either unsubstituted or substituted by morpholino, ethylthio or ethylseleno groups in the 2-position. The ⁷⁷Se chemical shift values of the ring selenium and the C?Se groups are compared with the ¹³C chemical shift values of neighbouring carbon atoms. The relationships between the ⁷⁷Se chemical shifts of the C?Se groups and the wavelengths of their n→* absorption in the UV-visible spectrum are discussed with respect to the significance of the δE term in the contribution of the paramagnetic screening and the electron density distribution.     

Synthesis and ring‐opening (co)polymerization of L‐lysine N‐carboxyanhydrides containing labile side‐chain protective groups

This contribution describes the synthesis and ring‐opening (co)polymerization of several L ‐lysine N‐carboxyanhydrides (NCAs) that contain labile protective groups at the ?‐NH₂ position. Four of the following L ‐lysine NCAs were investigated: N^?‐trifluoroacetyl‐L ‐lysine N‐carboxyanhydride, N^?‐(tert‐butoxycarbonyl)‐L ‐lysine N‐carboxyanhydride, N^?‐(9‐fluorenylmethoxycarbonyl)‐L ‐lysine N‐carboxyanhydride, and N^?‐(6‐nitroveratryloxycarbonyl)‐L ‐lysine N‐carboxyanhydride. In contrast to the harsh conditions that are required for acidolysis of benzyl carbamate moieties, which are usually used to protect the ?‐NH₂ position of L ‐lysine during NCA polymerization, the protective groups of the L ‐lysine NCAs presented here can be removed under mildly acidic or basic conditions or by photolysis. As a consequence, these monomers may allow access to novel peptide hybrid materials that cannot be prepared from ?‐benzyloxycarbonyl‐L ‐lysine N‐carboxyanhydride (Z‐Lys NCA) because of side reactions that accompany the removal of the Z groups. By copolymerization of these L ‐lysine NCAs with labile protective groups, either with each other or with γ‐benzyl‐L ‐glutamate N‐carboxyanhydride or Z‐Lys NCA, orthogonally side‐chain‐protected copolypeptides with number‐average degrees of polymerization ≤20 were obtained. Such copolypeptides, which contain different side‐chain protective groups that can be removed independently, are interesting for the synthesis of complex polypeptide architectures or can be used as scaffolds for the preparation of synthetic antigens or protein mimetics. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1167–1187, 2003     

LC-MS<Superscript><Emphasis Type="BoldItalic">n</Emphasis></Superscript> Analysis of Isomeric Chondroitin Sulfate Oligosaccharides Using a Chemical Derivatization Strategy

Improved methods for structural analyses of glycosaminoglycans (GAGs) are required to understand their functional roles in various biological processes. Major challenges in structural characterization of complex GAG oligosaccharides using liquid chromatography-mass spectrometry (LC-MS) include the accurate determination of the patterns of sulfation due to gas-phase losses of the sulfate groups upon collisional activation and inefficient on-line separation of positional sulfation isomers prior to MS/MS analyses. Here, a sequential chemical derivatization procedure including permethylation, desulfation, and acetylation was demonstrated to enable both on-line LC separation of isomeric mixtures of chondroitin sulfate (CS) oligosaccharides and accurate determination of sites of sulfation by MS ⁿ . The derivatized oligosaccharides have sulfate groups replaced with acetyl groups, which are sufficiently stable to survive MS ⁿ fragmentation and reflect the original sulfation patterns. A standard reversed-phase LC-MS system with a capillary C18 column was used for separation, and MS ⁿ experiments using collision-induced dissociation (CID) were performed. Our results indicate that the combination of this derivatization strategy and MS ⁿ methodology enables accurate identification of the sulfation isomers of CS hexasaccharides with either saturated or unsaturated nonreducing ends. Moreover, derivatized CS hexasaccharide isomer mixtures become separable by LC-MS method due to different positions of acetyl modifications.     

Nickel‐Catalyzed Site‐Selective Amidation of Unactivated C(sp3)H Bonds

Intramolecular dehydrogenative cyclization of aliphatic amides was achieved on unactivated sp³ carbon atoms by a nickel‐catalyzed C?H bond functionalization process with the assistance of a bidentate directing group. The reaction favors the C?H bonds of β‐methyl groups over the γ‐methyl or β‐methylene groups. Additionally, a predominant preference for the β‐methyl C?H bonds over the aromatic sp² C?H bonds was observed. Moreover, this process also allows for the effective functionalization of benzylic secondary sp³ C?H bonds.     

Stabilization of <Emphasis Type="Italic">n</Emphasis>-aminopropyl silica gel against hydrolysis by blocking silanol groups with TiO<Subscript>2</Subscript> or ZrO<Subscript>2</Subscript>

Silanol groups of n-aminopropyl silica gel (APSG) were blocked with TiO₂ or ZrO₂ to produce Ti-APSG and Zr-APSG, respectively. The silica materials were characterized by infrared, Raman spectra, thermogravimetric, elemental analyses, magic angle spinning ¹³C-nuclear magnetic resonance, specific surface area measurements, pH-metric titration and inductively coupled plasma—optical emission spectrometry—monitored silica hydrolysis. The stability of APSG against hydrolysis was found to be mainly affected by the specific surface area and the basicity of the n-aminopropyl groups which acquire additional strength from their intramolecular interaction with the silanol groups. The hydrolysis of silica in Ti-APSG and Zr-APSG remarkably decreased in the range of pH 1.0–9.1 due to the interruption of that intramolecular interaction. The hydrolyzed silica of Ti-APSG and Zr-APSG was decreased to 22.7 and 29.9%, respectively, of that of APSG at pH 4.5. Capacity and stability of Ti-APSG and Zr-APSG were improved in comparison with APSG upon application in the extraction of Cu²⁺ for 20 cycles of extraction and regeneration.     

5,20‐Bis(ethoxycarbonyl)‐Substituted Antiaromatic [28]Hexaphyrin and Its Bis‐NiII and Bis‐CuII Complexes

5,20‐Bis(ethoxycarbonyl)‐[28]hexaphyrin was synthesized by acid catalyzed cross‐condensation of meso‐diaryl‐substituted tripyrrane and ethyl 2‐oxoacetate followed by subsequent oxidation. This hexaphyrin was found to be a stable 28π‐antiaromatic compound with a dumbbell‐like conformation. Upon oxidization with PbO₂, this [28]hexaphyrin was converted into an aromatic [26]hexaphyrin with a rectangular shape bearing two ester groups at the edge side. The [28]hexaphyrin can incorporate two Ni^II or Cu^II metals by using the ester carbonyl groups and three pyrrolic nitrogen atoms to give bis‐Ni^II and bis‐Cu^II complexes with essentially the same dumbbell‐like structure. The antiaromatic properties of the [28]hexaphyrin and its metal complexes have been well characterized.     

Intramolecular Metal‐Free Oxidative Aryl–Aryl Coupling: An Unusual Hypervalent‐Iodine‐Mediated Rearrangement of 2‐Substituted N‐Phenylbenzamides

Hypervalent‐iodine‐mediated oxidative coupling of the two aryl groups in either 2‐acylamino‐N‐phenyl‐benzamides or 2‐hydroxy‐N‐phenylbenzamides, with concomitant insertion of the ortho‐substituted N or O atom into the tether, has been described for the first time. This unusual metal‐free rearrangement reaction involves an oxidative C(sp²)? C(sp²) aryl–aryl bond formation, cleavage of a C(sp²)? C(O) bond, and a lactamization/lactonization. Furthermore, unsymmetrical diaryl compounds can be easily obtained by removing the tether within the cyclized product.     

Über Oberflächenverbindungen von Übergangsmetallen. X [1]. Zum Stöchiometrie-Problem der Bindung von Oberflächen-Chrom(II) an Silicagel

On Surface Compounds of Transition Metals. X. The stoichiometry Problem of Fixation of Surface Chromium (II) on Silicagel. Thermogravimetric analysis of a reduced Philips catalyst (support: silicagel “Merck 7733”) shows that the metal is bound prediminantly (if not only) in chromate-like units up to a concentration of 2,8% Cr^II. At higher Cr^II contents. up to the maximum of 3.5%, the additionally fixed chromium does not consume further OH^s, within the scope of the thermogravimetric method formation of polychromatelike structures and/or use of not-neighbouring OH groups. The analysis further demonstrates that not all the Si? Oh groups comprised by the method are able to accommodate surface chromium. The fixation of the metal seems to proceed most likely by reaction with the vicinal pairs of Si? OH, as a correlation of our data with silica models shows.     

Nickel‐Catalyzed Csp2Csp3 Bond Formation by CarbonFluorine Activation

We report herein a general catalytic method for Csp²?Csp³ bond formation through C?F activation. The process uses an inexpensive nickel complex with either diorganozinc or alkylzinc halide reagents, including those with β‐hydrogen atoms. A variety of fluorine substitution patterns and functional groups can be readily incorporated. Sequential reactions involving different precatalysts and coupling partners permit the synthesis of densely functionalized fluorinated building blocks.     

Bioligand carriers based on methyl methacrylate copolymers with <Emphasis Type="Italic">N</Emphasis>-vinylformamide or glycidyl methacrylate

Emulsifier-free emulsion copolymerization of methyl methacrylate with N-vinylformamide and glycidyl methacrylate initiated by a cationic or anionic azoinitiator in the presence of dextran is used to produce monodisperse polymer particles with a developed multifunctional surface. As a result, monodisperse particles are obtained with a diameter of 350–660 nm, the surface layer of which contains, in addition to carboxyl groups, amino or epoxy groups. The conditions are determined for the formation of multifunctional hydrophilic particle surface via the hydrolysis of comonomer units and residual groups of initiators. The limiting values of bovine serum albumin chemisorption (2.4 and 1.0 mg/m² on the particles of methyl methacrylate copolymers with glycidyl methacrylate or N-vinyl formamide, respectively) indicate that the obtained particles have sufficient sorption capacity to be applied as carriers for immunoreagents.     

Copolymerization of ethylene with linear α‐olefins by 2‐phosphinophenolate nickel catalysts

2‐Dicyclohexyl‐ and 2‐diphenylphosphinophenol, CCHH and PPHH , react with Ni(1,5‐COD)₂ to form catalysts for polymerization of ethylene in or copolymerization with α‐olefins. The more P‐basic CCHH/Ni catalyst allows concentration‐dependent incorporation of olefins to give copolymers with isolated side groups and higher molecular weights, whereas the PPHH/Ni catalyst undergoes mainly stabilizing interactions with the olefins and leads to ethylene oligomers with no or marginal olefin incorporation. Pressure–time plots of the batch reactions show that the ethylene conversion is usually slower by catalysis with CCHH/Ni than by PPHH/Ni . The microstructure of the copolymers was determined by ¹³C NMR spectra, the number of side groups per main chain was estimated by ¹H NMR analyses. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 258–266, 2009     

Complex Formation of d‐Metal Ions at the Interface of TbIII‐Doped Silica Nanoparticles as a Basis of Substrate‐Responsive TbIII‐Centered Luminescence

The complex formation of d‐metal ions at the interface of Tb^III‐doped silica nanoparticles modified by amino groups is introduced as a route to sensing d‐metal ions and some organic molecules. Diverse modes of surface modification (covalent and noncovalent) are used to fix amino groups onto the silica surface. The interfacial binding of d‐metal ions and complexes is the reason for the Tb^III‐centered luminescence quenching. The regularities and mechanisms of quenching are estimated for the series of d‐metal ions and their complexes with chelating ligands. The obtained results reveal the interfacial binding of Cu^II ions as the basis of their quantitative determination in the concentration range 0.1–2.5 μM by means of steady‐state and time‐resolved fluorescence measurements. The variation of chelating ligands results in a significant effect on the quenching regularities due to diverse binding modes (inner or outer sphere) between amino groups at the interface of nanoparticles and Fe^III ions. The applicability of the steady‐state and time‐resolved fluorescence measurements to sense both Fe^III ions and catechols in aqueous solution by means of Tb^III‐doped silica nanoparticles is also introduced.     

Synthesis and characterization of phosphonate‐containing polysiloxanes

Phosphonate‐functionalized polysiloxanes have been prepared with a new siloxane/phosphonate monomer. The reaction of 3‐chloropropylmethyldimethoxysilane with trimethylphosphite or triethylphosphite produces several new monomers containing pendant phosphonate groups. Copolymerization with dimethyldimethoxysilane has produced polymers soluble in most organic solvents. The acid hydrolysis of the phosphoryl esters has produced hydrophilic siloxane polymers containing phosphonic acid groups. The thermal properties of the polymers and several related small molecules have been compared with thermogravimetric analysis. Both the monomers and the resulting polymers have been characterized with ¹H, ¹³C, ³¹P, and ²⁹Si NMR. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 48–59, 2003     

New organic picolylamine-type ligands and electrochemical study of their complexation with Cu(MeCN)<Subscript>4</Subscript>ClO<Subscript>4</Subscript>

A series of novel organic ligands with dipicolylamine and disulfide groups connected by polymethylene, alkylaryl, alkoxyaryl, or alkoxycarbonyl linker was synthesized. The electrochemical study by cyclic voltammetry was carried out for two synthesized ligands, and the formation of the complexes with Cu(MeCN)ClO₄ in the solution or on the gold electrode surface was established. The complex of Cu^I with 1,24-bis[N,N-bis(2-pyridylmethyl)-glycinoyloxy]-12,13-dithiatetracosane chemisorbed on the Au electrode is capable of binding molecular oxygen from solution.     

Solvent‐Dependent Truxene‐Based Nanostructures

Three truxene derivatives functionalized with alkyl chains, either attached directly or distanced by linking phenyl or ethynyl groups, self‐assemble in solution and induce the gelation of different solvents in spite of not being endowed with groups able to establish strong directional interactions. A ¹H NMR study points to face‐to‐face alternating π‐stacked motifs at the origin of nucleation. Solvents play an important role in modulating the aggregation of these derivatives giving rise to fibrous or spherical superstructures. Analysis of the influence of different solvents on the morphology of the aggregates provides a better understanding of the various stages of the hierarchical self‐assembly. The way in which alkyl chains are attached to the central core also strongly affects the self‐assembling properties and gelation ability of this series. Phenyl spacers present the highest association constants in solution and give rise to gelation in a broader range of solvents. This behavior has been rationalized by means of ¹H NMR spectroscopy, X‐ray powder diffraction, SEM, and photophysical measurements. Interestingly, it was found that these compounds in the gel state exhibit unusual emission properties most likely arising from the formation of excimers, which evidences that π–π interactions also occur in the excited state.     

Palladium‐Catalyzed Direct Thiolation of Aryl CH Bonds with Disulfides

A catalytic variant of the direct thiolation of arenes, bearing directing groups, with disulfides or thiols has been developed under palladium and copper co‐catalysis. Both sulfenyl moieties of the disulfide could be incorporated into the thiolated products, therefore, the reactions reached completion with only half an equivalent of disulfide, with respect to the starting arene. Experimental evidence suggested that the reaction proceeds through a Pd^II/Pd^IV mechanism.