Terminal Ethynyl Groups Research Articles

Complex isomerism influencing the textural properties of organometallic [Cu(salen)] porous polymers: paramagnetic solid-state NMR characterization and heterogeneous catalysis.

Although organometallic porous polymer networks are recognized as promising heterogeneous catalysts, the relationship between ligand/monomer geometry and network parameters is usually not well understood due to the lack of atom-resolved characterization methods for the amorphous network matrix. In this work, a series of copper(II) salen-type metal complexes was synthesized, using trans- and cis-1,2-diaminocyclohexane segments, and thoroughly characterized by single-crystal X-ray diffraction and solution- and solid-state NMR spectroscopy. Terminal ethynyl groups of the complexes were then transformed into polyacetylene chains by coordination chain-growth homopolymerization, resulting in highly porous (458-655 m2 g-1) organometallic polymer networks with a copper(II) ion content of about 12 wt%. The presence of paramagnetic copper(II) moieties in these complexes and respective polymer networks required the application of tailored NMR techniques, which together with X-ray crystallography and DFT calculations of the paramagnetic NMR shifts made it possible to investigate the differences in the complex geometry in liquid, powder and crystalline form and compare it with the complex geometry in polymer networks. All prepared organometallic polymer networks were also tested as heterogeneous catalysts for styrene oxidation with uncommonly high substrate conversions and compared with their low-molecular-weight analogues. The high reusability of such heterogeneous polymer-based catalysts was also proven.

3D hybrid materials based on zinc and cobalt phthalocyanine derivatives bearing terminal ethynyl substituents as active layers for chemiresistive gas sensors

Porous 3D hybrid materials (SWCNT/CoPc and SWCNT/ZnPc) were prepared by the reaction between single walled carbon nanotubes (SWCNT) functionalized with azido groups and ZnPc or CoPc phthalocyanines containing 16 terminal ethynyl groups and characterized by various physical methods. It was shown by thermogravimetric analysis (TGA) that the number of CoPc molecules attached on the SWCNT surface was one CoPc molecule per 115 carbon atoms, which is larger than in the case of the SWCNT/ZnPc (one ZnPc molecule per 312 carbon atoms). The prepared hybrids were studied as active layers of chemiresistive sensors for the detecting gaseous H2S at low concentrations (0.1–50 ppm). It was found that the sensor response of SWCNT/CoPc was about 4 times higher than in the case of SWCNT/ZnPc, which correlated well with the larger number of CoPc molecules on the SWCNT surface. The prepared hybrids are promising materials for the creation of fully reversible sensors for the detection of H2S at room temperature. The calculated LOD (3σ/m) of H2S was 18 and 65 ppb for SWCNT/CoPc and SWCNT/ZnPc, respectively.

Coumarin bearing asymmetrical zinc(II) phthalocyanine functionalized SWCNT hybrid nanomaterial: Synthesis, characterization and investigation of bifunctional electrocatalyst behavior for water splitting

A novel asymmetrical zinc(II) phthalocyanine (Coum-Pc) bearing three 7-ethynyl-3-(3,4,5-trimethoxyphenyl) coumarin and one ethyloxy azido groups was synthesized and characterized for the first time. This novel asymmetric Coum-Pc was covalently attached to single walled carbon nanotube (SWCNT) containing terminal ethynyl groups via the azide-alkyne Huisgen cycloaddition (Click) reaction for preparation of coumarin bearing zinc(II) phthalocyanine functionalized SWCNT hybrid nanomaterial (SWCNT-Coum-Pc). Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalyst for water splitting behavior of SWCNT-Coum-Pc hybrid nanomaterial were evaluated. The SWCNT-Coum-Pc hybrid reduced the onset potential required for HER by approximately 200 mV compared to SWCNT catalyst in acidic medium. The SWCNT-Coum-Pc catalyst reduced the HER overpotential of 570 mV at a current density of 10 mA cm−2 in alkaline medium. It also exhibited outstanding activity in OER, required only an overpotential of 330 mV at a current density of 10 mA cm−2. Heterogeneous rate constants of the electrodes from impedance analysis were used to calculate the value of charge transfer resistance and the conductivity of the composite film. The presence of Coum-Pc groups on the SWCNT surface increased for both the conductivity and electron transfer rate of the SWCNT. Therefore, SWCNT-Coum-Pc hybrid significantly improved the performance of OER and HER for water splitting. The present work provided a promising ground for the of SWCNT-Coum-Pc hybrid as a bifunctional electrocatalyst for water splitting.

Electrochemical Aziridination of Tetrasubstituted Alkenes with Ammonia

Ammonia (NH3) is an ideal nitrogen source in terms of availability, reactivity, safety, atom economy, environmental compatibility, and ease of isolation. However, its utility for amine synthesis is...

A synergetic and sensitive physostigmine pesticide sensor using copper complex of 3D zinc (II) phthalocyanine-SWCNT hybrid material

2,3,9,10,16,17,23,24-Octakis (4-methyl-2,6-bis((prop-2-yn-1-yloxy)methyl)phenoxy) phthalocyaninato zinc(II) (Pc) bearing sixteen terminal ethynyl groups was synthesized and attached to SWCNT (Single-walled carbon nanotube) covalently to obtain three dimensional porous hybrid material (SWCNT-Pc 3D) and its copper complex (Cu-SWCNT-Pc 3D). The structural characterization and electrochemical sensor features of the Cu-SWCNT-Pc hybrid towards to physostigmine pesticide were performed. A fast, direct and suitable determination method for physostigmine detection was offered. The designed sensor, Cu-SWCNT-Pc 3D/GCE (glassy carbon electrode) shows sensitivity ca 1.8, 4.3 and 2.8 times more than that of SWCNT/GCE, SWCNT-Pc-noncovalent/GCE and SWCNT-Pc 3D/GCE in terms of peak heights while bare and Pc/GCE had almost no voltammetric response to 2 μM physostigmine in PBS at a pH of 7.0. The limit of detection and quantification of physostigmine determination with Cu-SWCNT-Pc 3D/GCE were found to be 53 and 177 nM in the range of 0.1–4.8 μM, respectively. This study demonstrated that the modification of the GCE with Cu-SWCNT-Pc 3D as an electrochemical sensor was acted as catalytic role toward physostigmine presence of other interfering pesticides as high sensitivity and selectivity. The electrochemical determination of physostigmine in real samples was performed under the optimized conditions, also accuracy of the electrochemical determination method was evaluated with HPLC as a standard determination method.

1,4‐Diethynylbenzene‐Bridged [Cp*(dppe)Fe]n+ Units: Effect of 2,5‐Ethynyl Groups on the Chemical and Electronic Properties

The bis(ironvinylidene) complex [1,4‐{Cp*(dppe)Fe=C=CH}2‐2,5‐(C≡CH)2‐C6H2](PF6)2 ([2–2H](PF6)2) was prepared from 1,2,4,5‐tetraethynylbenzene and two equiv. of Cp*(dppe)FeCl in 87 % yield. The reaction is very selective and [2–2H](PF6)2 is the unique organoiron species to be formed. Deprotonation of [2–2H](PF6)2 provided the target complex 2 (66 % yield) and subsequent oxidation gave the monocationic and dicationic complexes 2(PF6) and 2(PF6)2. The new complexes were characterized by ESI‐mass spectrometry, IR, multinuclear NMR, ESR and Mössbauer spectroscopy, and XRD analyses on single crystals for [2–2H](PF6)2 and 2(PF6)2. The magnetic properties of 2(PF6)2 were investigated by VT 1H NMR. The data were analyzed with the support of quantum chemistry calculations. The terminal ethynyl groups on the aromatic ring of the bridge modify the population of the bridge‐oxidized state, weaken the electronic communication (Hab ≈ 601 cm–1) and strengthen magnetic coupling interactions (J = –530 cm–1) compared to the unsubstituted species (Hab = 1700 cm–1 and J = –340 cm–1, respectively).

Efficient Synthesis of Muramic and Glucuronic Acid Glycodendrimers as Dengue Virus Antagonists.

Carbohydrates are involved in many important pathological processes, such as bacterial and viral infections, by means of carbohydrate-protein interactions. Glycoconjugates with multiple carbohydrates are involved in multivalent interactions, thus increasing their binding strengths to proteins. In this work, we report the efficient synthesis of novel muramic and glucuronic acid glycodendrimers as potential Dengue virus antagonists. Aromatic scaffolds functionalized with a terminal ethynyl groups were coupled to muramic and glucuronic acid azides by click chemistry through optimized synthetic strategies to afford the desired glycodendrimers with high yields. Surface Plasmon Resonance studies have demonstrated that the compounds reported bind efficiently to the Dengue virus envelope protein. Molecular modelling studies were carried out to simulate and explain the binding observed. These studies confirm that efficient chemical synthesis of glycodendrimers can be brought about easily offering a versatile strategy to find new active compounds against Dengue virus.

Anodic Oxidation of Ethynylferrocene Derivatives in Homogeneous Solution and Following Anodic Deposition onto Glassy Carbon Electrodes

AbstractEight ferrocene derivatives linked by either an ether, amine, or phenylacetylene moiety to a terminal ethynyl group were covalently deposited on glassy carbon electrodes by anodic electrochemical methods. The lithio activation method, in which the terminal hydrogen of the ethynyl group is replaced by a lithium atom before anodic oxidation, was successfully employed in all cases. Direct oxidation of the inactivated ethynyl group also resulted in surface deposition. Surface coverages between 1×10−10 mol cm−2 and 14×10−10 mol cm−2 were achieved. Cyclic voltammetry scans of the modified electrodes in pure electrolytes differed depending on the size of the supporting electrolyte anion, as little as half the current being measured for a [B(C6F5)4]− vs. [PF6]− solution, suggesting differences in ion transport near the electrode surface. An ether‐linked ethynylferrocenium ion (5+) was isolated after electrolytic and chemical oxidation of 5 and characterized by X‐Ray crystallography as its [SbCl6]− salt.

A novel application of terminal alkynes as the homogeneous catalysts for acetalization and esterification

The theoretical study focused on the possible use of low-molecular-weight mono-as well as multifunctional terminal alkynes as catalysts for two reactions, which are known to be typically acid catalyzed - acetalization and esterification, is presented in this study. Multifunctional terminal alkynes [(diethynylbenzenes, triethynylbenzene, and tetrakis(4-ethynylphenyl)methane] were significantly more active than the monofunctional ones (cyclopropylacetylene, phenylacetylene, 3-cyclohexylprop-1-yne, 1-ethynyl-2-fluorobenzene, 1-ethynyl-4-fluorobenzene, 4-ethynyltoluene, 4-tert-butylphenylacetylene, and 2-ethynyl-α,α,α-trifluorotoluene), this fact can be partly explained by the higher amount of ethynyl groups per alkyne molecule. We confirmed that terminal ethynyl groups in low-molecular-weight alkynes can successfully act as acid catalytic centers for acetalization as well as for esterification.

Effect of different SWCNT-BODIPY hybrid materials for selective and sensitive electrochemical detection of guanine and adenine

In this study; the synthesis, structural characterization and electrochemical sensor properties of SWCNTs covalently functionalized with different BODIPY derivatives toward guanine and adenine were investigated. The target SWCNTs-BODIPY hybrids (CB, CB1 and CB2) were synthesized by the reaction of azido functionalized SWCNT with the BODIPY derivatives containing terminal ethynyl group via the Click reaction. Structural characterization of SWCNT-BODIPY hybrid materials was performed by Raman, UV–visible, FTIR spectroscopies and thermogravimetric analysis. The surface morphologies of the new hybrids were evaluated by SEM and TEM. The sensing behavior of these hybrid materials was investigated to detect guanine and adenine in PBS. CB1 hybrid material showed the better sensor properties with the detection limits of 1.07μM and 2.91μM for guanine (G) and adenine (A), respectively. The quantification limits were found to be 3.21μM for guanine and 18.6μM for adenine in PBS. The applicability of the modified electrode for the detection of G and A in DNA from calf thymus was demonstrated with the standard addition method.

Highly selective and ultra-sensitive electrochemical sensor behavior of 3D SWCNT-BODIPY hybrid material for eserine detection

In this work, 4,4-difluoro-8-(4-hydroxyphenyl)− 2,6-diethynly-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY) having double terminal ethynyl groups was synthesized. Three dimensional single walled carbon nanotube (SWCNT)-BODIPY hybrid material (3D SWCNT-BODIPY) was synthesized by the reaction of BODIPY bearing double terminal ethynyl groups with azido containing SWCNTs via “Click” reaction. The structural properties and electrochemical detection of eserine (a pesticide) on BODIPY functionalized SWCNTs as a three dimensional (3D) material were investigated. A glassy carbon electrode (GCE) was modified by 3D SWCNT-BODIPY hybrid material for the determination of eserine in the range of 0.25–2.25 μM. In the study by the square wave voltammetry (SWV), the bare GCE showed no response, while the new peak at − 0.6 V appeared in the case of the modified electrode. The detection limit and quantification were determined as 160 nM and 528 nM for eserine on the 3D SWCNT-BODIPY modified electrode, respectively. Eserine was also determined with a standard addition method in different brands of orange juices, and the recovery of eserine was obtained to be in the range of 102.09% and 103.22%. This study clearly indicates that the 3D SWCNT-BODIPY modified electrode tested as an electrochemical sensor was found to be highly selective and sensitive to eserine.

Click histochemistry for whole-mount staining of brain structures

Labeling of the replicating DNA with synthetic thymidine analogs is commonly used for marking the dividing cells. However, until now this method has only been applied to histological sections. A growing number of current approaches for three-dimensional visualization of large tissue samples requires detection of dividing cells within whole organs. Here we describe a method for labeling dividing cells with 5-ethynyl-2'-deoxyuridine (EdU) and their further detection in whole brain structures (for example, hippocampus) using the Cu (I) -catalyzed [3 + 2] cycloaddition reaction (so-called click-reaction). The presented method can be used for brain neurogenesis studies as well as for whole-mount staining of any preparations in which the terminal ethynyl group has been introduced.•New click histochemistry method based on Cu (I) -catalyzed [3 + 2] cycloaddition reaction allows whole-mount staining of brain structures and other tissues.•Our whole-mount click histochemistry method allows to visualize dividing cells in 3D and can be used in neurogenesis studies, i.e. for birthdating dividing early progenitors and further tracking of proliferation, survival, migration, differentiation, and fate of their progeny.•Our whole-mount click histochemistry staining demonstrates high staining specificity, high signal intensity, and low background levels in young and adult mouse brain tissue.

Hyper-Cross-Linked Polyacetylene-Type Microporous Networks Decorated with Terminal Ethynyl Groups as Heterogeneous Acid Catalysts for Acetalization and Esterification Reactions.

Heterogeneous catalysts based on materials with permanent porosity are of great interest owing to their high specific surface area, easy separation, recovery, and recycling ability. Additionally, porous polymer catalysts (PPCs) allow us to tune catalytic activity by introducing various functional centres. This study reports the preparation of PPCs with a permanent micro/mesoporous texture and a specific surface area SBET of up to 1000 m2 g-1 active in acid-catalyzed reactions, namely aldehyde and ketone acetalization and carboxylic acid esterification. These PPC-type conjugated hyper-cross-linked polyarylacetylene networks were prepared by chain-growth homopolymerization of 1,4-diethynylbenzene, 1,3,5-triethynylbenzene and tetrakis(4-ethynylphenyl)methane. However, only some ethynyl groups of the monomers (from 58 to 80 %) were polymerized into the polyacetylene network segments while the other ethynyl groups remained unreacted. Depending on the number of ethynyl groups per monomer molecule and the covalent structure of the monomer, PPCs were decorated with unreacted ethynyl groups from 3.2 to 6.7 mmol g-1 . The hydrogen atoms of the unreacted ethynyl groups served as acid catalytic centres of the aforementioned organic reactions. To the best of our knowledge, this is first study describing the high activity of hydrogen atoms of ethynyl groups in acid-catalyzed reactions.

3D SWCNTs-coumarin hybrid material for ultra-sensitive determination of quercetin antioxidant capacity

The novel 7-propinyloxy-3-(p-propinyloxyphenyl) coumarin having terminal ethynyl groups was synthesized for the first time. This coumarin has been successfully bounded covalently to single walled carbon nanotubes (SWCNTs) via the azide-alkyne Huisgen cycloaddition (Click) reaction for the preparation of a 3D hybrid material. Glassy carbon electrode was modified with the 3D SWCNTs-coumarin hybrid material for the determination of quercetin antioxidant. The proposed modified electrode is nearly 10-fold more sensitive than the bare electrode by applying the differential pulse stripping voltammetry (DPSV). In addition, the parameters of DPSV measurements such as accumulation time, accumulation potential and pH were optimized as 20 s, 200 mV and pH 2 Britton-Robinson buffer solutions in 1 μM quercetin, respectively. In the optimized conditions, the linear working range from 0.25 to 3 μM was determined. The detection and quantification limits of quercetin were found to be 20 nM and 66 nM by DPSV on the modified electrode, respectively. The DPSV procedure was also applied to test different brand tea real samples and quercetin was determined by a standard addition method with the recovery between 97.00 and 103.10.

Theoretical Studies of the Spin-Dependent Electronic Transport Properties in Ethynyl-Terminated Ferrocene Molecular Junctions.

The spin-dependent electron transport in the ferrocene-based molecular junctions, in which the molecules are 1,3-substituted and 1,3′-substituted ethynyl ferrocenes, respectively, is studied by the theoretical simulation with nonequilibrium Green’s function and density functional theory. The calculated results suggest that the substitution position of the terminal ethynyl groups has a great effect on the spin-dependent current-voltage properties and the spin filtering efficiency of the molecular junctions. At the lower bias, high spin filtering efficiency is found in 1,3′-substituted ethynyl ferrocene junction, which suggests that the spin filtering efficiency is also dependent on the bias voltage. The different spin-dependent transport properties for the two molecular junctions originate from their different evolutions of spin-up and spin-down energy levels.

Synthesis of novel dimeric subphthalocyanines via azide-alkyne Huisgen 1,3-dipolar cycloaddition and palladiumcatalyzed Glaser–Hay coupling reactions

In this study, the monomeric subphthalocyanines bearing azido (2) and terminal ethynyl (3) groups were synthesized. These subphthalocyanines were converted to their dimeric derivatives using azide-alkyne Huisgen cycloaddition and palladium-catalyzed Glaser–Hay coupling reactions subphthalocyanine (4) and (5), respectively. The novel subphthalocyanines were fully characterized by elemental analysis and general spectroscopic methods such as MALDI-TOF mass, FT-IR, UV-vis and [Formula: see text]H-NMR. All synthesized subphthalocyanines showed quite good solubility in the most of common organic solvents. The fluorescence measurements were conducted for these subphthalocyanines to estimate their fluorescence quantum yields. The singlet oxygen generation abilities were also examined to investigate their photosensitizer properties.

On the Importance of Electronic Symmetry for Triplet State Delocalization.

The influence of electronic symmetry on triplet state delocalization in linear zinc porphyrin oligomers is explored by electron paramagnetic resonance techniques. Using a combination of transient continuous wave and pulse electron nuclear double resonance spectroscopies, it is demonstrated experimentally that complete triplet state delocalization requires the chemical equivalence of all porphyrin units. These results are supported by density functional theory calculations, showing uneven delocalization in a porphyrin dimer in which a terminal ethynyl group renders the two porphyrin units inequivalent. When the conjugation length of the molecule is further increased upon addition of a second terminal ethynyl group that restores the symmetry of the system, the triplet state is again found to be completely delocalized. The observations suggest that electronic symmetry is of greater importance for triplet state delocalization than other frequently invoked factors such as conformational rigidity or fundamental length-scale limitations.

Effect of molecular structure on spin-dependent electron transport in biferrocene-based molecular junctions: a first-principles study

The spin-dependent electronic transport properties in the molecular junctions based on ethynyl-connected biferrocene are investigated by density functional theory combined with nonequilibrium Green’s function. The calculated results show that the transport properties can be affected by the molecular structure of ethynyl-connected biferrocene. The linkage mode of the terminal ethynyl groups plays an important role on the spin-dependent currents, the spin polarization, and the total currents of the molecular junctions. The spin polarization value of the two molecules in this work is dependent on the applied bias. The difference of electron transport properties between the molecular junctions is related to the different electronic structures of the two isolated molecules.

Copolymerization of N -(prop-1-yne-3-yl)-4-(piperidine-1-yl)-1,8-naphthalimide with Arylacetylenes into Fluorescent Polyacetylene-Type Conjugated Polymers

N-(prop-1-yne-3-yl)-4-(piperidine-1-yl)-1,8-naphthalimide (PNPr), i.e., the monomer with a terminal ethynyl group and 1,8-naphthalimide fluorophore, has been successfully copolymerized with a series of monoethynylarenes into well-soluble high-molecular-weight (Mw up to 210 000) linear polyacetylene-type copolymers containing from 14 to 51 mol% units derived from PNPr. The copolymerization of PNPr with bifunctional 4,4′-diethynylbiphenyl provides polyacetylene-type micro/mesoporous fluorescent network containing 8 mol% PNPr units and exhibiting the Brunauer–Emmett–Teller surface of ≈1000 m2 g−1. The copolymerizations (catalyzed with acetylacetonato(norborna-2,5-diene)rhodium complex, [Rh(nbd)acac]) proceed smoothly despite the fact that the homopolymerization of PNPr fails. The fluorescence of PNPr (emission at ≈ 510 nm) has been retained after the incorporation of PNPr into the copolymers. The fluorescence of the copolymers can be induced by a direct excitation of PNPr units or via an energy transfer mechanism. In the latter case, the comonomeric units with aromatic hydrocarbon fluorophores (e.g., of the biphenyl-type) emitting at 380–400 nm (after irradiation with 300 nm UV radiation) serve as energy donors for fluorescent PNPr acceptors. The difference between the wavelengths of the primary absorbed radiation and the finally emitted radiation is 210 nm.

Synthesis, thermal properties, and ceramization of a novel ethynylaniline-terminated polysilazane

A novel ethynylaniline-terminated polysilazane (PCSN) was synthesized from the ammonolysis reaction of dichloromethylsilane (MeSiHCl2) and p-phenylenediamine, by which terminal ethynyl groups were introduced into the resultant PCSN. Different average molecular weight PCSNs obtained with adjusting the molar ratios between p-phenylenediamine and MeSiHCl2 were used to investigate the influence of average molecular weights and contents of terminal ethynyl groups on thermal properties and ceramic conversions of PCSNs. The structure of PCSN was characterized using Fourier transform infrared, proton, carbon-13, and silicon-29 nuclear magnetic resonance spectroscopies. Among all the PCSN precursors, PCSN-4 has the lowest curing temperature (237.1°C) and the highest enthalpy (863.0 J g−1) because of its highest content of terminal ethynyl groups, improving its cross-linking. The thermal properties of cured PCSN were studied by means of thermogravimetric analysis under nitrogen atmosphere. The collaborative effect from both the average molecular weight and the contents of terminal ethynyl groups gave PCSN-3 the best thermal stability. The temperature of 5% mass loss was 564°C and the residual mass at 900°C was 84.4%. After sintering at 1450°C in argon atmosphere, PCSN-3 thermoset turned into black solids composited of β-silicon carbide (β-SiC), α-silicon nitride, α-SiC, and free carbon with a yield of 78.4%, indicating PCSN had the potential to be used as ceramic precursors.