The Effect of Solvent and Fiber Treatment on the Deposition of Organic Silane Solutions Using THF and Acetone

To facilitate the deposition of gamma-ureidopropyltrimethoxysilane monomer onto E-glass fibers, anhydrous acetone and THF were used as carrier solvents. Untreated industrial E-glass fibers and cold water plasma treated E-glass fibers were used. Cold water plasma treatment of the fibers increased the hydrophobicity of the surface by increasing the number of hydroxyl groups at the surface; additionally, the amount of aluminium and calcium at the surface was increased. The silane was found to deposit in bilayers with an external surface due to condensed siloxane; aluminium and calcium were also condensed into the network when acetone was used as a deposition solvent. The bilayers were strongly hydrogen bonded via the ureido functional groups. When THF was used as a carrier solvent, a ureido functional surface was obtained due to the THF interfering with the condensation of the silane. The silane was deposited in conical patches of varying heights. Copyright 2001 Academic Press.     

Prins cyclization for the preparation of 2-isobutyl-4-methyl-tetrahydro-<Emphasis Type="Italic">2H</Emphasis>-pyran-4-ol using supported heteropoly acids

The selective preparation of 2-isobutyl-4-methyl-tetrahydro-2H-pyran-4-ol (also called Florosa or Florol) was performed. Prins cyclization of isoprenol and isovaleraldehyde was used for the preparation of this important fragrant compound. Heteropoly acids (phosphotungstic and phosphomolybdic) were used as a catalyst in homogeneous and also in heterogeneous arrangements (after their immobilization). The only solvent necessary for the reaction was water that enables the increase of the selectivity to the desired product by hydrolysis of catalyst-carbocation intermediates. In a flow, both heteropoly acids were successfully anchored on siliceous MCM-41 and resultant materials were characterized by XRF, XRD, SEM, FTIR, UV–Vis, and nitrogen adsorption. Heterogenization was performed in water as a solvent. Anchored heteropoly acids were used in Prins cyclization under the same conditions (addition of water), and the selectivity was even higher (96 %), comparing the homogeneous arrangement. No leaching of catalyst from solid was observed. Moreover, the catalyst may be reused without loss of activity and selectivity at least four times.     

Excited‐State Proton Transfer and Intramolecular Charge Transfer in 1,3‐Diketone Molecules

The photophysical signature of the tautomeric species of the asymmetric (N,N‐dimethylanilino)‐1,3‐diketone molecule are investigated using approaches rooted in density functional theory (DFT) and time‐dependent DFT (TD‐DFT). In particular, since this molecule, in the excited state, can undergo proton transfer reactions coupled to intramolecular charge transfer events, the different radiative and nonradiative channels are investigated by making use of different density‐based indexes. The use of these tools, together with the analysis of both singlet and triplet potential energy surfaces, provide new insights into excited‐state reactivity allowing one to rationalize the experimental findings including different behavior of the molecule as a function of solvent polarity.     

Characterization of green copper phase pigments in Egyptian artifacts with X-ray absorption spectroscopy and principal components analysis

The characterization of materials in historical artifacts can contribute significantly to their preservation and understanding; however, sampling and characterization are ideally performed using non-destructive approaches. The analysis of green pigments from Egyptian artifacts presents a further challenge as responses to laboratory based techniques have proven unsuccessful in many cases. An alternative approach is the use of non-destructive X-ray absorption near-edge structure spectroscopy, which was performed on a reference set of copper-containing green minerals and other compounds. Data projection using principal component analysis was used to explore the spectral data structures and to illustrate the relationship between the spectra and copper speciation, resulting in a calibration or training set of the reference materials used. Data from the training set were compared with samples from Egyptian artifacts. The combination of X-ray absorption spectroscopy with principal components analysis provides a novel approach in archeometry and the characterization of objects of cultural heritage.     

Kinetic and Product Study of the S-oxidation vs HAT Chemoselectivity in Reactions Promoted by Nonheme Iron(IV)-oxo Complex/NHPI Mediator System

The chemoselectivity between S-oxidation and hydrogen atom transfer (HAT) from C−H bonds has been investigated in the oxidations of a series of aryl sulfides, alkyl aromatic compounds and benzylic alcohols promoted by the iron(IV)-oxo complex [(N4Py)Fe^IV(O)]²⁺ (N4Py: N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)-methylamine) either alone or in the presence of the N-hydroxyphthalimide (NHPI) mediator via kinetic and product studies. Kinetic analyses indicate a generally higher reactivity of [(N4Py)Fe^IV(O)]²⁺ for S-oxidation process while HAT is favored in the reactions promoted by phthalimide-N-oxyl radical (PINO) deriving from NHPI oxidation. Product analysis in intermolecular competitive oxidations confirms the kinetic results with sulfoxides obtained as major products in the oxidation promoted by [(N4Py)Fe^IV(O)]²⁺. Conversely, when NHPI is employed as a mediator, significant differences in terms of chemoselectivity are observed, and HAT-derived products are obtained in higher yields which translate into an inversion of selectivity in the case of the substrates containing activated C−H bonds like diphenylmethane, triphenylmethane and benzylic alcohols. A similar change of chemoselectivity is also observed in the oxidation of aromatic substrates containing both a sulfur atom and α to OH benzylic C−H bonds, with the sulfoxide product more abundant in the absence of NHPI and carbonyl products prevailing with the [(N4Py)Fe^IV(O)]²⁺/NHPI system.     

Concepts and recent advances in microchip electrophoresis coupled to mass spectrometry: Technologies and applications

The online coupling of microchip electrophoresis (ME) as a fast, highly efficient, and low-cost miniaturized separation technique to mass spectrometry (MS) as an information-rich and sensitive characterization technique results in ME–MS an attractive tool for various applications. In this paper, we review the basic concepts and latest advances in technology for ME coupled to MS during the period of 2016–2021, covering microchip materials, structures, fabrication techniques, and interfacing to electrospray ionization (ESI)–MS and matrix-assisted laser desorption/ionization–MS. Two critical issues in coupling ME and ESI–MS include the electrical connection used to define the electrophoretic field strength along the separation channel and the generation of the electrospray for MS detection, as well as, a miniaturized ESI-tip. The recent commercialization of ME–MS in zone electrophoresis and isoelectric focusing modes has led to the widespread application of these techniques in academia and industry. Here we summarize recent applications of ME–MS for the separation and detection of antibodies, proteins, peptides, carbohydrates, metabolites, and so on. Throughout the paper these applications are discussed in the context of benefits and limitations of ME–MS in comparison to alternative techniques.     

Oxidation of Sanguinarine and Its Dihydro‐Derivative at a Pyrolytic Graphite Electrode Using Ex Situ Voltammetry. Study of the Interactions of the Alkaloids with DNA

This study describes the oxidation of sanguinarine (SG) and its metabolite dihydrosanguinarine (DHSG) on the surface of a basal‐plane pyrolytic graphite electrode (PGE). Since both alkaloids strongly adsorb onto the surface of pyrolytic graphite, measurements were performed using ex situ voltammetric methods, adsorptive transfer (AdT) cyclic voltammetry (CV) and square‐wave voltammetry (SWV). Oxidation peaks of SG (peak A) and DHSG (peak A*) were observed around the potential of +0.7 V (vs. Ag/AgCl/3 M KCl), depending on the experimental conditions. The voltammetric peaks A and A* are probably related to the oxidation of N‐methylphenanthridine nitrogenous heterocycle of SG and oxidation of DHSG back to SG, respectively. The electrochemical results and optimized AdT SWV were subsequently applied to the study of the interactions of SG and DHSG with DNA in vitro. Analysis of the alkaloid/DNA interactions was based on observing heights of oxidation peaks A and A* after incubation of SG and/or DHSG with supercoiled (sc) DNA [pBSK_(?)]. Electrochemical study of the interactions was supported and complemented with measurements using gel electrophoresis (Topoisomerase I scDNA relaxation assay) and steady‐state and time‐resolved fluorescence spectroscopy. The results suggest that SG intercalates into the double‐stranded structure of scDNA (the SG/base pair ratio is max. 1/4) while increased binding affinity was observed for quaternary cation (SG⁺). DHSG which, unlike SG⁺, does not possess a strictly planar molecular structure, did not show intercalative DNA binding in any of the three methods applied.     

Organocatalytic synthesis of α-quaternary amino acid derivatives via aza-Friedel-Crafts alkylation of indoles with simple α-amidoacrylates

The first (organo)catalytic method for regio- and chemoselective aza-Friedel-Crafts (FC) alkylation of indoles and pyrroles with commercially available methyl α-acetamidoacrylates has been discovered. It minimizes/eliminates common competing reactions that occur due to the high and multiatom-nucleophilic character of indole and pyrrole. Diverse quaternary α-amino acids were successfully prepared in good yield and high selectivity using low catalyst loading. The enantioselective variant using BINOL-derived phosphoric acids was also explored with indole providing the desired F-C alkylation product with moderate enantioselectivities.