Presence Of Trifluoroacetic Acid Research Articles

Synthesis and Properties of Bicyclo[2.2.2]octadiene- and Benzene-Fused Bis(thiaporphyrin)s

Abstract In this study, a benzene-fused bis(thiaporphyrin) was synthesized by the retro-Diels–Alder reaction of a bicyclo[2.2.2]octadiene (BCOD)-fused bis(thiaporphyrin) precursor. This precursor was prepared by the double [3+1] porphyrin synthesis of the BCOD-fused dipyrrole with thiatripyrrane. The ultraviolet–visible (UV–vis) spectrum of benzene-fused bis(thiaporphyrin) in dichloromethane was extremely different from that of the corresponding benzene-fused bis(porphyrin). In contrast, extremely similar spectra were obtained in the presence of trifluoroacetic acid. The similar electronic structures in the protonated states were supported by X-ray analysis and time-dependent density-functional theory (TD-DFT) calculations.

Anion-Redox Mechanism of MoO(S2)2(2,2'-bipyridine) for Electrocatalytic Hydrogen Production.

Redox processes of molybdenum-sulfide (Mo-S) compounds are important in the function of materials for various applications from electrocatalysts for the hydrogen evolution reaction (HER) to cathode materials for batteries. Our group has recently described a series of Mo-S molecular HER catalysts based on a MoO(S2)2L2 structural motif. Herein, reductive pathways of MoO(S2)2bpy (Mo-bpy) (bpy = 2,2'-bipyridine) are presented from both experimental and theoretical studies. We tracked chemical reduction of Mo-bpy with UV-vis spectroscopy using sodium napthalenide (NaNpth) as the reducing agent and found that Mo-bpy undergoes anionic persulfide reduction to form the tetragonal Mo(VI) complex [MoOS3]2-. We also identified silver mercury amalgam as an inert working electrode (WE) for spectroectrochemical (SEC) studies. UV-vis spectra in the presence of trifluoroacetic acid with an applied potential confirmed that Mo-bpy maintains its structure during catalytic cycling. Finally, theoretical catalytic reaction pathways were explored, revealing that Mo=O may function as a proton relay. This finding together with the observed anion reduction as the redox center is of broad interest for amorphous Mo-S (a-MoSx) electrocatalytic materials and anion-redox chalcogel battery materials.

Acid-catalyzed reaction of phenols with N-(4,4-diethoxybutyl)sulfonamides – a new method for the synthesis of 2-aryl-1-sulfonylpyrrolidines

We have developed a new method for the synthesis of 2-aryl-1-sulfonylpyrrolidines on the basis of reactions between various phenols and N-(4,4-diethoxybutyl)sulfonamides in the presence of trifluoroacetic acid. The structures of the obtained products were confirmed by 1H and 13C NMR spectroscopy, IR spectroscopy, and X-ray structural analysis.

Synthesis and characterisation of heterotrinuclear transition metal complexes for biomimetic proton reduction

Selected structural, spectroscopic, electrochemical and photochemical properties of novel heterotrinuclear [FeFe]-hydrogenase enzyme model compounds carrying a catalytic iron sulfur cluster site directly coupled to different transition metal subunits are reported. Typical metal-to-ligand charge transfer (MLCT) chromophores based on electron donating copper(I), rhenium(I) and tungsten(0) complex fragments were selected to provide both long-wavelength spectral sensitization and photoredox activity. Photoinduced one-electron transfer from the MLCT donor subunit to the diiron acceptor site could be observed with an efficient steady-state accumulation of the corresponding charge-separated state. The reduced iron site of these deeply coloured heterotrinuclear [FeFe]-hydrogenase model systems has been shown to be electrocatalytically active for proton reduction in the presence of trifluoroacetic acid (TFA). However, a successful visible-light powered system for catalytic hydrogen release in homogeneous solution could not be achieved, and the reaction remained stoichiometric with all of the systems investigated.

The modulator driven polymorphism of Zr(IV) based metal-organic frameworks.

The reaction of ZrCl4 and 2,5-thiophenedicarboxylic acid (H2tdc) in the presence of trifluoroacetic acid (Htfa) as modulator results in the formation of the new metal-organic framework (MOF) named DUT-126 (DUT = Dresden University of Technology). The nature and concentration of modulators are found to be decisive synthetic parameters affecting the topology of the formed product. DUT-126 ( HBR: ) extends the series of polymorphs differing in topology, namely DUT-67 ( REO: ), DUT-68 ( BON: ) and DUT-69 ( BCT: ) to four, where DUT-67 and DUT-68 show the same eight-connected secondary building units as in DUT-126. In DUT-126, linker molecules have a peculiar orientation, resulting in HBR: topology, which is described for the first time in this work for MOFs. DUT-126 contains three pore types, including two micropores surrounding mesoporous channels. DUT-126 is stable against hydrolysis and features permanent porosity with a specific surface area of 1297 m2 g-1 and a total pore volume of 0.48 cm3 g-1, calculated from the nitrogen physisorption isotherm measured at 77 K.This article is part of the themed issue 'Coordination polymers and metal-organic frameworks: materials by design'.

Single step fabrication of CuO–MnO–2TiO2 composite thin films with improved photoelectrochemical response

CuO–MnO–2TiO2 composite thin film having a photocurrent density of 2.21 mA cm−2 at +0.7 V has been deposited from a homogeneous mixture of acetates of Cu and Mn and (Ti(O(CH2)3CH3)4) in the presence of trifluoroacetic acid in THF via AACVD at 550 °C.

Red emitting triphenylamine based rhodamine analogous with enhanced Stokes shift and viscosity sensitive emission

Four novel structural hybrid analogues of Rhodamine B and Rhodamine 101 are synthesized by condensing N-substituted amino phenols with keto-acids of N-substituted phenols in presence of trifluoroacetic acid and are characterized by spectroscopic methods. Triphenylamine based derivatives show large Stokes shift (47 nm–69 nm) and red shifted emission (close to Near Infrared region) as compared to parent Rhodamine B and Rhodamine 101. These N-phenyl substituted dyes exhibited negative solvatochromism and pronounced viscosity sensitivity (14–24 folds increase in emission intensity) as compared to parent rhodamines. Polarity graphs and mathematically calculated charge transfer descriptors are in good correlations with observed trends. Computed values obtained by Density Functional Theory are in good agreement with the experimental results.

Palladium-Catalyzed Intramolecular Fujiwara-Hydroarylation: Synthesis of Benzo[a]phenazines Derivatives.

An atom-economical Pd-catalyzed approach for the synthesis of benzophenazine derivatives using substituted 2-aryl-3-(aryl/alkylethynyl) quinoxaline in the presence of trifluoroacetic acid at 65 °C has been described. The chemistry involves in situ generation of cationic Pd(II) species, which functionalized the aromatic C-H bonds via electrophilic metalation followed by concomitant intramolecular trans-insertion of C-C triple bond to aryl-Pd complex. The results were supported by various control experiments including with electron-deficient arenes and deuterium labeling studies. The deuterium labeling studies supports electrophilic palladation of aromatic C-H over activation of C-C triple bond of alkyne. The structure of synthesized compounds was further confirmed by X-ray crystallography studies. This catalytic protocol has been efficiently applied for novel synthesis of highly functionalized benzo fused phenazines.

Hemilabile Bridging Thiolates as Proton Shuttles in Bioinspired H2 Production Electrocatalysts.

Synthetic analogues and computationally assisted structure-function analyses have been used to explore the features that control proton-electron and proton-hydride coupling in electrocatalysts inspired by the [NiFe]-hydrogenase active site. Of the bimetallic complexes derived from aggregation of the dithiolato complexes MN2S2 (N2S2 = bismercaptoethane diazacycloheptane; M = Ni or Fe(NO)) with (η5-C5H5)Fe(CO)+ (the Fe' component) or (η5-C5H5)Fe(CO)2+, Fe″, which yielded Ni-Fe'+, Fe-Fe'+, Ni-Fe″+, and Fe-Fe″+, respectively, both Ni-Fe'+ and Fe-Fe'+ were determined to be active electrocatalysts for H2 production in the presence of trifluoroacetic acid. Correlations of electrochemical potentials and H2 generation are consistent with calculated parameters in a predicted mechanism that delineates the order of addition of electrons and protons, the role of the redox-active, noninnocent NO ligand in electron uptake, the necessity for Fe'-S bond breaking (or the hemilability of the metallodithiolate ligand), and hydride-proton coupling routes. Although the redox active {Fe(NO)}7 moiety can accept and store an electron and subsequently a proton (forming the relatively unstable Fe-bound HNO), it cannot form a hydride as the NO shields the Fe from protonation. Successful coupling occurs from a hydride on Fe' with a proton on thiolate S and requires a propitious orientation of the H-S bond that places H+ and H- within coupling distance. This orientation and coupling barrier are redox-level dependent. While the Ni-Fe' derivative has vacant sites on both metals for hydride formation, the uptake of the required electron is more energy intensive than that in Fe-Fe' featuring the noninnocent NO ligand. The Fe'-S bond cleavage facilitated by the hemilability of thiolate to produce a terminal thiolate as a proton shuttle is a key feature in both mechanisms. The analogous Fe″-S bond cleavage on Ni-Fe″ leads to degradation.

Synthesis of 1-(arenesulfonyl)-2-arylpyrrolidines by reaction of N-(4,4-diethoxybutyl)-4-methylbenzene-sulfonamide with phenols

New 1-(arenesulfonyl)-2-arylpyrrolidines were synthesized by reactions of several phenols with N-(4,4-diethoxybutyl)-4-methylbenzenesulfonamide in the presence of trifluoroacetic acid.

Influence of the Acetamide from Acetonitrile Hydrolysis in Acid-Contained Mobile Phase on the Ultraviolet Detection in High Performance Liquid Chromatography

The paper presents the influence of acetamide on ultraviolet detection after generation of acetonitrile by hydrolysis in the presence of trifluoroacetic acid in the HPLC mobile phase. The acetonitrile, with added varying contents of trifluoroacetic acid and water, was determined by GC–MS at various times. The results showed that the concentration of acetamide increased approximately linearly with time. Using a mixed standard sample solution and a model mobile phase of acetonitrile-water-tri-fluoroacetic acid (25:75:0.3, v/v) after 0, 24 and 48 h, the influence of the hydrolyzate acetamide on HPLC detection was investigated at the wavelength of 205–220 nm. The results showed that the limit of detection (LOD) of standard sample lost about 30 % after the mobile phase was placed 48 h. It is suggested that the acid-containing mobile phase was placed no more than 24 h for HPLC trace analysis at the wavelength of 205–220 nm.

Specific features of oxidation of ferrocenylmethanol with hydrogen peroxide in acidic media

Two types of transformations (the metal complex protonation and oxidation) have been revealed in the ferrocenylmethanol–Н2О2–НХ system (HX = HClO4, CF3COOH) by means of electronic spectroscopy. The efficiency of protonation has been determined from the intensity of the FcCH2+ carbocation absorption band (λmax = 600 nm); it depends on the acid strength and relative concentration as well as the solvent nature. Kinetics of ferrocenylmethanol oxidation in dioxane has been studied in the presence of trifluoroacetic acid. Two alternative reaction mechanisms have been proposed, differing in the coordination type of the reagents.

Synthesis of 2-arylpyrrolidines by reaction of γ-ureidoacetals with benzene-1,3,5-triol

New 2,2′-(2,4,6-trihydroxybenzene-1,3-diyl)dipyrrolidine derivatives have been synthesized by reaction of benzene-1,3,5-triol (phloroglucinol) with γ-ureidoacetals in the presence of trifluoroacetic acid as catalyst.

Cyclization of 1-(4,4-diethoxybutyl)-3-aryl(thio)ureas to 2-arylpyrrolidines and 2,3´-bipyrrole derivatives

A reaction of 1-(4,4-diethoxybutyl)-3-phenylthiourea with resorcinol, 2-methylresorcinol, pyrogallol, and hydroquinone in chloroform in the presence of trifluoroacetic acid leads to 2-aryl-1-(N-phenylcarbamothioyl)pyrrolidines. 1-(4,4-Diethoxybutyl)-3-arylureas and 1-(4,4diethoxybutyl)-3-arylthioureas in the presence of an acid catalyst undergo intramolecular cyclization and dimerization with the formation of 1,1´-bis(N-arylcarbamo(thio)yl)-2,3´-bipyrrole derivatives.

Synthesis and evaluation of multitopic bisbenzothiazolyl calix[4]arenes for ionic toxicants

Two new benzothiazolyl calix[4]arene-based multitopic molecular receptors L-1 and L-2 have been synthesised and evaluated for recognition of ionic toxicants. The receptors selectively interact with copper, silver and fluoride ion toxicants as assessed through UV-visible, NMR and colorimetric techniques. The stability of L-1:Cu+2 and L-2:Cu+2 complexes was found to be higher than that of complexes formed with Ag+ and F– complexes in the presence of trifluoroacetic acid. Superiority of L-1 over L-2 for analysis of identified toxicants has been determined by measurement of binding constants.

Brønsted Acid Cocatalysis in Copper(I)-Photocatalyzed α-Amino C–H Bond Functionalization

We have exploited a bis(1,10-phenanthroline)copper(I) visible light photocatalyst (VLP), [Cu(dap)2]+, to effect the direct α-C–H functionalization of amines. To our knowledge, this represents the first example of the oxidation of amines that are ultimately incorporated into synthetic targets by a copper(I) VLP. We have utilized this approach to rapidly prepare unprecedented octahydroisoquinolino[2,1-a]pyrrolo[3,4-c]quinoline frameworks and exploited this process to synthesize a novel aglycone analogue of the natural product incargranine B. Most significantly, our studies suggest that the presence of trifluoroacetic acid (TFA) is crucial in mediating the aerobic oxidative quenching of a putative photoexcited copper(I) species involved in the catalytic cycle.

Condensation of 2-Ethoxyvinylphosphonic Acid Dichloroanhydride with 2,3,5-Trimethylphenol. Novel Method for Preparation of Phosphacoumarins

GRAPHICAL ABSTRACT

Dual Emissions of Salicylidene-5-chloroaminepyridine Due to Excited State Intramolecular Proton Transfer: Dynamic Photophysical and Theoretical Studies

In this study, the photophysical properties of N-salycilidene-5-chloroaminopyridine were evaluated. This molecule presented dual emission from the keto* and enol* species, depending on the solvent used (DMSO or methanol in the absence and presence of trifluoroacetic acid). This molecule was synthesized through a dehydration reaction of salicylaldehyde under sonication and characterized using FTIR, cyclic voltammetry, mass spectrometry, and single-crystal X-ray diffraction, yielding the molecular structure. Theoretical calculations were performed under the DFT framework and its time-dependent counterpart. Our results suggest the occurrence of excited state proton transfer, ESIPT, in the aprotic solvent, leading to a keto*–enol* balance, which is confirmed by the emission bands observed at 425 and 545 nm, respectively. However, in a protic environment (methanol or DMSO with trifluoroacetic acid), only the enol form is emissive due to the hydrogen bonding between the iminic group and the solvent. Molecules with double emissions are potentially useful for white light emitting diodes.

Molecular co-catalyst accelerating hole transfer for enhanced photocatalytic H2 evolution.

In artificial photocatalysis, sluggish kinetics of hole transfer and the resulting high-charge recombination rate have been the Achilles' heel of photocatalytic conversion efficiency. Here we demonstrate water-soluble molecules as co-catalysts to accelerate hole transfer for improved photocatalytic H2 evolution activity. Trifluoroacetic acid (TFA), by virtue of its reversible redox couple TFA·/TFA−, serves as a homogeneous co-catalyst that not only maximizes the contact areas between co-catalysts and reactants but also greatly promotes hole transfer. Thus K4Nb6O17 nanosheet catalysts achieve drastically increased photocatalytic H2 production rate in the presence of TFA, up to 32 times with respect to the blank experiment. The molecular co-catalyst represents a new, simple and highly effective approach to suppress recombination of photogenerated charges, and has provided fertile new ground for creating high-efficiency photosynthesis systems, avoiding use of noble-metal co-catalysts.

Combined method of immunoaffinity membrane within tubes and MALDI-TOF MS for capturing and analyzing amyloid beta.

Amyloid beta 1-40 peptide was specifically isolated and analyzed from human plasma spiked with amyloid beta using a combined method of biotinylated anti-amyloid beta antibody binding to membrane-immobilized avidin (immunoaffinity membrane) and matrix-assisted laser desorption /ionization time-of-flight mass spectrometry (MALDI-TOF MS). A solution of 10μL containing 13.6ng to 2.9μg of amyloid beta peptide was examined in this method. After the isolated amyloid beta peptide from the spiked human plasma containing 2.9μg of amyloid beta peptide was incubated in the presence of trifluoroacetic acid, fibrillization of the peptides was observed using a thioflavin T assay. Furthermore, an immunoaffinity membrane present on the inner wall of a tube (diameter 2mm) captured the amyloid beta peptide from the spiked human plasma. Our results indicate that the combination of the immunoaffinity membrane procedure and MALDI-TOF MS can be used to capture and analyze the target antigens such as amyloid beta in micro-spaces.