Electro-withdrawing Group Research Articles

A sequencing electroreduction-electrooxidation system driven by atomic hydrogen for enhancing 2,4-dichloronitrobenzene removal from wastewater

The sequencing electroreduction-electrooxidation process has emerged as a promising approach for the degradation of the chloronitrobenzenes (CNBs) due to its elimination of electro-withdrawing groups in the reduction process, facilitating further removal in the subsequent oxidation process. Herein, we developed a cathode consisting of atom Pd on a Ti plate, which enabled the electro-generation of atomic hydrogen (H*) and the efficient electrocatalytic activation of H2O2 to hydroxyl radical (•OH). Cyclic voltammetry (CV) curves and electron spin resonance (ESR) spectra verified the existence of H* and •OH. The electroreduction-electrooxidation system achieved 94.7% of 20 mg L−1 2,4-DCNB removal with a relatively low H2O2 addition (5 mM). Moreover, the inhibition rate of Photobacterium phosphoreum in the effluent decreased from 95% to 52% after the sequencing electroreduction-electrooxidation processes. It was further revealed that the H* dominated the electroreduction process and triggered the electrooxidation process. Our work sheds light on the effective removal of electron-withdrawing groups substituted aromatic contaminants from water and wastewater.

End-capped modeling of dithienopicenocarbazole based derivatives for high-performance photovoltaic cells with optoelectronic response over 900 nm

Dithienopicenocarbazole (DTPC), as the inner core in the A-D-A configuration, has been recognized for its exceptionally small energy loss, narrow energy gap, and excellent power conversion efficiency. In this work, a series of six novel dithienopicenocarbazole-based molecules with wide absorption and remarkable opto-electrical properties, were designed as the new electron-donating materials for organic photovoltaic devices. (DI1-DI6) were derived by substituting end-capped moieties attached to the middle core (DTPC) with highly conjugated and electro withdrawing groups and insertion of π spacer between the donor part and the newly attached acceptor part. The findings demonstrated that the modified molecules had smaller excitation energies (Ex), a decreased energy gap (Eg), and have higher absorption (λmax) values in comparison to the DIR (reference structure). The greatest λmax (980 nm), smallest Ex (1.21 eV), and shortest Eg (1.63 eV) were all displayed by the DI4 molecule. In addition, due to its lowest RE value for the electron, DI4 might have best electron carrier ability among all. Furthermore, upon coupling each examined molecule with a PC61BM acceptor, the value of open circuit voltage (VOC) was computed. DI4 displayed the most suitable outcomes for the VOC (1.45 V), FF (0.91178) and normalized VOC (56.14). Therefore, all the altered structures, with special reference DI4, are strongly recommended to synthesize organic photovoltaic cells with exceptional optoelectronic and photovoltaic applications.

The influence and mechanism of ligand steric hindrance and electronic effects on the ring-opening metathesis polymerization of polycyclopentene under tungsten complex

Polycyclopentene rubber has attracted attention due to its unique ring-opening metathesis polymerization (ROMP) mechanism, which endows it with a range of excellent properties, including recyclability and structural controllability. In order to facilitate the production of polycyclopentene, a tungsten olefin metathesis catalytic system was developed. The influence of ligand steric hindrance and electronic effects on the reaction was investigated through kinetic experiments and density functional theory (DFT) calculations. The results show that increased ligand steric hindrance enhances reaction stability, while the electro-withdrawing group on the ligand accelerates catalyst activation. Additionally, a ligand “release-return” mechanism for polymerization initiation was proposed. The polycyclopentene's thermal properties and stereoregularity were explored.

Theoretical study on effect of substituent on aromaticity of tetrazole ring

Tetrazole compounds are a category of energetic materials with great potential. Their stability is inherently related to their aromatics. On the basis of research in DFT at b3lyp/6–311** level on three compounds interested, viz. 5-amino-1 H-tetrazole, 5-carboxyl-1 H-tetrazole, and 2-methyl-5-carboxyl-tetrazole, their aromatic characters are extensively analyzed by virtue of different estimation method. Analyses show that these methods, Nucleus-independent Chemical Shift, iso-chemical shielding surface, adaptive natural density partitioning, π-electrons density, and localized orbital locator of π-electron density are efficient for substituted-tetrazole ring aromaticity estimation. Conclusion denotes that both substituent and substituted position can significantly affect the aromaticity of tetrazole ring of tetrazole compound. Among these given substituents, electro-withdrawing group -COOH significantly increases the aromaticity of the tetrazole rings due to the withdrawing to π-electrons thereof but electro-donating group -NH2 weakens the one of the tetrazole rings due to the donating to π-electrons thereof. But for 2-methyl-5-carboxyl-tetrazole, the aromaticity increasing of -COOH imposed on π-electrons of tetrazole ring thereof is partially balanced by the existence of the electron-donating group -CH3 at asymmetric meta-position of tetrazole ring. Consequently, the aromaticity order is 5-Carboxyl-1 H-tetrazole > 2-methyl-5-Carboxyl-tetrazole > 5-amino-1 H-tetrazole.

Regulating the activity of intrinsic sites in covalent organic frameworks by introducing electro-withdrawing groups towards highly selective H2O2 electrosynthesis

Oxidized carbon catalysts have shown the potential of producing H2O2 electrochemically, and the seeking of a champion active site is usually the primary concern. However, preparing an optimal catalyst requires more activation factors rather than identifying the only oxygen-containing group that activates the adjacent carbon atoms. In this work, we treat the commonly studied oxygenated groups as the main activation factor and introduce groups with varied electron-withdrawing abilities into the system additionally, attempting to break the catalytic limit imposed by a single factor. In detail, we designed dioxin-linked covalent organic frameworks (COFs) in which each structural unit contains four C-O-C groups as the main activation factor and two more functional groups (-CN, -COOH, or -CH2OH) as the additional regulation factors. The active carbon atoms are located between these chemical groups and thus their catalytic activities are impacted by them simultaneously. Results show that the catalytic activity is positively associated with the electron-withdrawing ability of the additional groups. The well-tailored COF-CN achieved an ultrahigh H2O2 selectivity of 97.2% and an outstanding H2O2 yield of 901 mmol g−1 h−1, allowing it to be directly used for wood pulping and waste paper recycling without extra separation processes. Further calculations and extended modeling of a nitrogen-dopant system suggest the universal potential of such an additional chemical influence design to go beyond the current electrocatalytic limit.

Quinoxaline-specific enantioselective sulfa-michael reaction catalyzed by chiral phosphoric acid

Highly enantioselective sulfa-Michael additions (SMA) between 2-alkenyl quinoxalines and aromatic thiols are accomplished using a low loading of chiral phosphoric acid catalyst (1 mol%). It was confirmed by an investigation of a lot of azaarenes that the two C=N units of quinoxalines are indispensable for controlling the reaction enantioselectivities. A series of non-terminal 2-alkenes substituted with aryls or alkyls, even other electro-withdrawing groups such as ketones, esters, or amides, selectively reacted and afforded the desired SMA products (48 examples) in good regioselectivities with high yields (up to 99%) and good ee values (up to 97%).

Stabilizing Halogen-Bonded Complex between Metallic Anion and Iodide.

Halogen bonds (XBs) between metal anions and halides have seldom been reported because metal anions are reactive for XB donors. The pyramidal-shaped Mn(CO)5- anion is a candidate metallic XB acceptor with a ligand-protected metal core that maintains the negative charge and an open site to accept XB donors. Herein, Mn(CO)5- is prepared by electrospray ionization, and its reaction with CH3I in gas phase is studied using mass spectrometry and density functional theory (DFT) calculation. The product observed experimentally at m/z = 337 is assigned as [IMn(CO)4(OCCH3)]-, which is formed by successive nucleophilic substitution and reductive elimination, instead of the halogen-bonded complex (XC) CH3-I···Mn(CO)5-, because the I···Mn interaction is weak within XC and it could be a transient species. Inspiringly, DFT calculations predict that replacing CH3I with CF3I can strengthen the halogen bonding within the XC due to the electro-withdrawing ability of F. More importantly, in so doing, the nucleophilic substitution barrier can be raised significantly, ~30 kcal/mol, thus leaving the system trapping within the XC region. In brief, the combination of a passivating metal core and the introduction of an electro-withdrawing group to the halide can enable strong halogen bonding between metallic anion and iodide.

Evaluation of the anticancer activity and chemiluminescence of a halogenated coelenterazine analog

Chemiluminescence is a remarkable process in which light is emitted due to a chemical reaction, without the need for photoexcitation. Among some of the most well-known chemiluminescent systems is that of marine Coelenterazine. Herein, we report the synthesis of a novel halogenated Coelenterazine analog, as well as the characterization of its potential anticancer activity and chemiluminescence. We have found that this analog is capable of significantly enhanced emission in aqueous solution when triggered by superoxide anion while being compatible with human cell lines. So, this compound presents great potential for the sensitive and dynamic sensing of a molecule of interest in biological media. Furthermore, the analysis of its cytotoxicity provided structural insight into the properties of brominated Coelenterazines, which were previously found to possess selective anticancer activity. Namely, the introduction of bromine heteroatoms is not enough to provide cytotoxicity, while the introduction of electro-withdrawing groups eliminates all previously reported anticancer activity. Finally, while this compound is not active, its use in a combination approach allowed to improve the profile of a known chemotherapeutic agent. These results should be useful to guide future optimizations of halogenated Coelenterazine analogs.

Size and stability modulation of Pd nanoparticles on porous hypercrosslinked ionic polymer for heterogeneous aerobic oxidative coupling of diaryl ether

Oxidative coupling of two aromatic CH bonds is normally catalyzed by Pd(II) species involving an electrophilic attacking step. Herein, we demonstrated surprisingly the high activity of heterogeneous Pd(0) nanoparticles (NPs) in catalyzing the intramolecular oxidative coupling of diaryl ether with O2. The Pd(0) NPs with different average particle sizes were constructed by using the supports of ionic hypercrosslinked porous polymers that were straightforwardly synthesized through the copolymerization of 2,3-pyridinedicarboxylic anhydride and biphenyl in a chlorosulfonic acid-catalyzed route. In the case of moderate ionic moiety content, the constructed Pd(0) NPs were highly active in the coupling of diphenylether to dibenzofuran, affording a high yield of 72 % associated with a large turnover number of 91 that exceeded 18-folds of homogeneous palladium acetate. Kinetic analysis and radical quenching results demonstrate a carbon radical related catalytic pathway. Following the same methodology, various other diaryl ether with electro-donating and electro-withdrawing groups were converted into the corresponding dibenzofuran derivatives.

Synthesis and properties of novel N,C,N terdentate skeleton based on 1,3-di(pyridin-2-yl)benzene moiety—new tricks for old dogs

Utilization of intermolecular Friedel–Crafts and intramolecular condensation reaction, novel 1,3-di(pyridine-2-yl)benzene(N,C,N terdentate) skeleton with electro-withdrawing group in 6' position of pyridyl and a cyclization between 6' position of pyridyl and 6 position of benzyl ring were firstly designed and synthesized. The structures of these novel N,C,N terdentate were confirmed by NMR, MS and X-ray single crystalanalyses. The photophysical properties of these compounds were briefly explored.

Asymmetric sulfenylation of 3-CF 3 -Oxindoles through organocatalysis with a quinidine derivative

An asymmetric sulfenylation of 3-CF3-oxindoles catalyzed by a quinidine derivative was described. 3-CF3-oxindoles with electro-donating groups led to corresponding products in good yield and with good enantioselectivity while 3-CF3-oxindoles bearing electro-withdrawing groups were not competent substrates due to its significant decomposition at the optimal reaction conditions. As for the sulfenylation reagents based on thiophenol, both electro-donating groups and electro-withdrawing groups were well tolerated.

Ultrasensitive near-infrared fluorescence-enhanced probe for in vivo nitroreductase imaging.

Nitroreductase (NTR) can be overexpressed in hypoxic tumors, thus the selective and efficient detection of NTR is of great importance. To date, although a few optical methods have been reported for the detection of NTR in solution, an effective optical probe for NTR monitoring in vivo is still lacking. Therefore, it is necessary to develop a near-infrared (NIR) fluorescent detection probe for NTR. In this study, five NIR cyanine dyes with fluorescence reporting structure decorated with different nitro aromatic groups, Cy7-1-5, have been designed and explored for possible rapid detection of NTR. Our experimental results presented that only a para-nitro benzoate group modified cyanine probe (Cy7-1) could serve as a rapid NIR fluorescence-enhanced probe for monitoring and bioimaging of NTR. The structure-function relationship has been revealed by theoretical study. The linker connecting the detecting and fluorescence reporting groups and the nitro group position is a key factor for the formation of hydrogen bonds and spatial structure match, inducing the NTR catalytic ability enhancement. The in vitro response and mechanism of the enzyme-catalyzed reduction of Cy7-1 have been investigated through kinetic optical studies and other methods. The results have indicated that an electro-withdrawing group induced electron-transfer process becomes blocked when Cy7-1 is catalytically reduced to Cy7-NH2 by NTR, which is manifested in enhanced fluorescence intensity during the detection process. Confocal fluorescence imaging of hypoxic A549 cells has confirmed the NTR detection ability of Cy7-1 at the cellular level. Importantly, Cy7-1 can detect tumor hypoxia in a murine hypoxic tumor model, showing a rapid and significant enhancement of its NIR fluorescence characteristics suitable for fluorescence bioimaging. This method may potentially be used for tumor hypoxia diagnosis.

Molecular modelling studies for the discovery of new substituted pyridines derivatives with angiotensin II AT1 receptor antagonists.

A QSAR study has been performed on a series of pyridines derivatives with potent angiotensin II AT1 receptor antagonists. Structural features responsible for the activity of the compounds were characterized by using topological, electrotopological, group based and 3D descriptors, calculated from the Molecular Design Suite software (V-life MDS 3.5). To elucidate the structural properties required for antihypertensive activity, four different molecular modeling techniques; two-dimensional, Group-based (G-QSAR), k-nearest neighbour and pharmacophore approach. A suitable set of molecular descriptors was calculated and stepwise - partial component regression (SW-PCR) was employed to select the descriptors that resulted in the models with the best fit to the data. This study was performed with twenty two compounds using sphere exclusion algorithm method for the division of the data set into training and test set. The statistically significant 2D QSAR model having r(2) = 0.8407 and q(2) = 0.7395 with pred_r(2) = 0.7971 was developed by stepwise-partial component regression (SW-PCR) and best Group based QSAR model having R(2) = 0.8132 and Q(2) = 0.6804 with pred_r(2) = 0.7661 was developed by SW-PCR. The analyzed k-nearest neighbour MFA model revealed a good fit, having q(2) value of 0.7635. The predictive power of the model generated was validated using a test set molecules with pred _r(2) value of 0.7314. The generated k-nearest neighbour models suggest that steric and electrostatic interactions play an important role in describing the variation in binding affinity. Additionally the pharmacophore model well corraborated with k-nearest neighbour studies as the contours of later were in good agreement with the 3D orientation of the pharmacophoric features. The present analysis has shown that the antihypertensive activity can be improved with the presence of specific steric substituent and electro-donating and electro-withdrawing groups nearby the pyridine moiety. The Pharmacophore information shows that the four features used were two AroC feature, one HAc, one AlaC features. The structural variations in the molecular fields at particular regions in the space provide underlying structural requirements and 3D-QSAR models generated give good predictive ability and aid in the design of potent antihypertensive activity.

Conformational–Induced Doping Effect of Sodium Dodecyl Benzene Sulfonate on Single Walled Carbon Nanotubes

The doping behavior of single-walled carbon nanotubes (SWCNTs) was investigated with an emphasis on the control of the conformation of sodium dodecylbenzene sulfonate (NaDDBS) with sulfonate groups acting as an electro-withdrawing group. The conformation of adsorbed NaDDBS on SWCNTs was controlled as a function of the amount of NaDDBS. The doping behavior of SWCNTs was significantly affected by the dosing amount of NaDDBS due to the conformational change of NaDDBS adsorbed on the SWCNT surface, which affected the spatial distance between the SWCNT surface and the sulfonate groups in NaDDBS. At a higher concentration, the spatial distance between the sulfonate group in NaDDBS and SWCNT was not sufficiently close enough to dope SWCNT due to the repulsive forces between the sulfonate groups in NaDDBS. Alternatively, at a lower concentration, NaDDBS acted as a p-type dopant for SWCNTs. To this end, this paper demonstrates a new tendency of doping that is related to the adsorbed behavior of a dispersant.

A Synthetic Chalcone as a Potent Inducer of Glutathione Biosynthesis

Chalcones continue to attract considerable interest due to their anti-inflammatory and antiangiogenic properties. We recently reported the ability of 2',5'-dihydroxychalcone (2',5'-DHC) to induce both breast cancer resistance protein-mediated export of glutathione (GSH) and c-Jun N-terminal kinase-mediated increased intracellular GSH levels. Herein, we report a structure-activity relationship study of a series of 30 synthetic chalcone derivatives with hydroxyl, methoxyl, and halogen (F and Cl) substituents and their ability to increase intracellular GSH levels. This effect was drastically improved with one or two electrowithdrawing groups on phenyl ring B and up to three methoxyl and/or hydroxyl groups on phenyl ring A. The optimal structure, 2-chloro-4',6'-dimethoxy-2'-hydroxychalcone, induced both a potent NF-E2-related factor 2-mediated transcriptional response and an increased formation of glutamate cysteine ligase holoenzyme, as shown using a human breast cancer cell line stably expressing a luciferase reporter gene driven by antioxidant response elements.

PH-Triggered Release from Nonphospholipid LUVs Modulated by the pKa of the Included Fatty Acid

It has been shown that mixtures of palmitic acid (PA) and cholesterol (Chol) or cholesterol sulfate (Schol) can form fluid bilayers. These bilayers could be extruded using standard extrusion techniques to obtain nonphospholipid large unilamellar vesicles (LUVs). These LUVs displayed a very limited passive permeability, associated with their high sterol content (typically 70 mol %). In addition, they showed a pH-dependent behavior dictated by the electrostatic interfacial interactions, which are drastically modulated by the protonation state of PA. Interestingly, the LUVs prepared with cholesterol were stable at high pH and the release of the content could be triggered by a pH decrease (i.e., the protonation of PA). In contrast, the LUVs including Schol were stable at low pH and a pH increase (leading to the deprotonation of PA) would induce the release. In the present study, we demonstrate that the pH triggering the release in these two systems can be dictated in a predictable manner by selecting a fatty acid with an appropriate pK(a). The pK(a) of the fatty acids was modulated by the presence of an electro-withdrawing group (hydroxyl or fluoro) in the alpha position of the carboxylic function. The fatty acid protonation state is shown to be a critical factor for the modulation of the liposome permeability. The described systems display a remarkable versatility regarding the pH-sensitivity because the nature of the sterol controls the overall pH stability of the LUVs while the fatty acid pK(a) fine-tunes the pH-induced release. Therefore, it is possible to rationally design LUVs with controlled release at a specific pH; this original aspect is beneficial to the use of LUVs for encapsulation, vectorization, and controlled release of active agents.

The modulation of electronic and optical properties of OXD-X through introduction of the electron-withdrawing groups: A DFT study

A comparative study using density functional theory (DFT) on the molecular structure, electronic structure and relative properties of 1,3,4-oxadiazole dimers 1,3-bis[2-(4-methylphenyl)-1,3,4-oxadiazol-5-yl]benzene (OXD-X) and its derivatives with alkoxy substituents –O(CH 2) n−1 CH 3 (OXD-An, n = 1, 2) and electron-withdrawing substituents –CN (OXD-C), –CF 3 (OXD-TFM), –NO 2 (OXD-N) added at meta-substitution in the phenyl ring are presented. The ground state structures of the title complexes are optimized at B3LYP/6-31G level of theory. In addition, the time dependent density functional theory (TDDFT) method is applied to calculate the absorption and emission spectra of the derivatives based on the ground state geometries. Comparing with the alkoxy substituents, the results show that the electron-withdrawing substituents have remarkable influences on the energy levels of the frontier molecular orbitals, the spectra and the transition compositions. Especially, –NO 2 group plays the prominent role and the fluorine improves the energy level of LUMO further. The experimental absorption wavelengths for OXD-X, OXD-A3 and OXD-A7 are well reproduced by the TDDFT technique. Moreover the absorption wavelengths and the transition compositions can be effectively adjusted through introducing electro-withdrawing groups in the phenyl ring. The reorganization energies for hole and electron are smaller than that of typical hole and electron transport materials.

The electrochemical signature of functionalized single-walled carbon nanotubes bearingelectroactive groups

We report the modification and characterization of single-walled carbon nanotubes(SWCNTs) in view of molecular sensing applications. We found that ultrasonicatedSWCNTs present sticking properties that make them adhere on electrode surfaces. Thisallows excellent characterization of SWCNTs by cyclic voltammetry (CV) before and afterchemical functionalization with diazonium salts bearing electroactive groups. BareSWCNTs presented distinct invariant shapes in CV, used as control curves, in comparisonwith functionalized SWCNTs for which specific signatures corresponding to the presence ofgrafted molecules were identified. According to the electronic substituents in the paraposition of the diazonium salts, divergent behaviours were observed for the graftingreactions. Diazonium salts having electrowithdrawing groups could be graftedwithout electrochemical induction whereas those bearing electron donating groupsrequired a cathodic potential to generate the formation of the radical species.

The relationship between redox potentials and substituent constants in biologically active arylazoxy compounds

Seven compounds containing the cyanoazoxy group were studied by cyclic voltammetry, in protic (aqueous/ethanolic phosphate buffer, pH 6.9) and aprotic (DMF + TBAP 0.1 mol L −1) media. In protic medium, all the arylazoxycyanides containing electrowithdrawing groups behaved similarly. A 4e −/4H + reduction wave generating the hydrazo derivative is evident, as well as its counterpart for oxidation, in the reverse scan, to the azo derivative, which undergoes further reduction, in a successive scan. For the compounds with electrodonating substituents, slightly different reduction behaviour is evident, due to the instability of the electrogenerated azo compound. In aprotic medium, all the arylazoxycyanides follow a similar and standard electrochemical reduction pathway, represented by two main waves, the first one reversible, corresponding to the uptake of one electron to form a stable anion-radical and a second one, much more intense and irreversible. In the case of the electrowithdrawing nitro and cyano derivatives, additional waves are observed, due to the reducibility of those groups. In both media, linear relationships between E pIc (potential of first cathodic wave), E redox (for aprotic) and Hammett substituent constants ( σ p, σ −) were observed. The reduction potentials correlate considerably better with ( σ p, σ −), showing the strong influence of resonance factors in the mechanism of reduction.