Effects Of Ring Substituents Research Articles

Substituent-Controlled Structural, Supramolecular, and Cytotoxic Properties of a Series of 2-Styryl-8-nitro and 2-Styryl-8-hydroxy Quinolines.

Styryl quinolines are biologically active compounds with properties largely depending on the substituents on the styryl and quinoline rings. The supramolecular aspects of this class of compounds are rarely explored. In this study, two new series of styryl quinoline derivatives, bearing −OH and −NO2 groups at the eighthposition of the quinoline ring and −SCH3, −OCH3, and −Br groups on the styryl ring, have been developed, and their structural, supramolecular, and cytotoxic properties have been analyzed. Crystallographic analyses revealed the exciting substituent-dependent structural and supramolecular features of these compounds. In general, the 8 −OH substituted derivatives (SA series) exhibited a non-planar molecular geometry having larger dihedral angles (5.75–59.3°) between the planes of the aromatic rings. At the same time, the 8 −NO2 substituted derivatives (SB series) exhibited a more or less planar molecular geometry, as revealed by the smaller dihedral angles (1.32–3.45°) between the aromatic rings. Multiple O–H···O, C–H···O, O–H···N, and π–π stacking interactions among the molecules lead to fascinating supramolecular architectures such as hydrogen-bonded triple helices, zig-zag 1D chains, π–π stacked infinite chains, and so forth in their crystal lattice. Hirshfeld surface analyses confirmed the existence of strong π–π stacking and other weak bonding interactions in these compounds. The preliminary cytotoxic properties of SA and SB series compounds were evaluated against the human cervical cancer cell lines (HeLa cells), which further highlighted the roles of functional substituents on the aromatic rings. The SA series compounds with the −OH substituent on the quinoline ring exhibited better cytotoxicity than the SB series compounds with a −NO2 substituent. Similarly, the electron-withdrawing group −Br on the styryl ring enhanced the cytotoxicity in both series. The IC50 values were 2.52–4.69 and 2.897–10.37 μM, respectively, for the SA and SB series compounds. Compound S3A having −OH and −Br groups on the quinoline and styryl ring, respectively, exhibited the best IC50 value of 2.52 μM among all the compounds tested. These findings confirm the relevance of the hydroxyl group in the eighth position of quinoline. In short, the present study attempts to provide a systematic analysis of the effects of aromatic ring substituents on the structural, supramolecular, and cytotoxic properties of styryl quinolines for the first time.

Reaction kinetics and degradation efficiency of halogenated methylparabens during ozonation and UV/H2O2 treatment of drinking water and wastewater effluent

This study investigated the reaction kinetics and degradation efficiency of methylparaben and its halogenated products (Cl-, Br-, Cl,Cl-, Br,Cl-, and Br,Br-methylparabens) during ozonation and UV254/H2O2 treatment. Second-order rate constants for reactions of the parabens with ozone and •OH were kO3 = 107 – 108 M−1 s−1 and k•OH = (2.3 – 4.3)× 109 M−1 s−1 at pH 7. Species-specific kO3 values of the protonated and deprotonated parabens were closely related to phenol ring substituent effects via quantitative structure-activity relationships with other substituted phenols. The UV photolysis rate of the parabens [kUV = (2.4 − 7.2)× 10−4 cm2 mJ−1] depended on the halogenation state of the paraben and solution pH, from which species-specific quantum yields were also determined. In simulated treatments of drinking water and wastewater effluent, the parabens were efficiently eliminated during ozonation, requiring a specific ozone dose of > 0.26 gO3/gDOC for > 97% degradation. During UV/H2O2 treatment with 10 mg L−1 H2O2, the degradation levels were > 90% at a UV fluence of 2000 mJ cm−2, except for Cl,Cl-methylparaben. Kinetic models based on the obtained reaction kinetic parameters could successfully predict the degradation levels of the parabens. Overall, ozonation and UV/H2O2 were effective in controlling parabens and their halogenated products during advanced water treatment.

The composites of asymmetric Co phthalocyanines-graphitic carbon nitride quantum dots-aptamer as specific electrochemical sensors for the detection of prostate specific antigen: Effects of ring substituents

• .Aptamer - phthalocyanine - quantum dots are used as sensors for prostate antigen. • Electrochemical impedance spectroscopy is employed to determine detection limits. • Low detection limit of 0.27 ng/mL in real sample. Asymmetrical phthalocaynine molecules have been employed in combination with graphitic carbon nitride quantum dots covalently linked to an amine-functionalized aptamer for the electrochemical detection of prostate cancer biomarker. The combination of the phthalocyanine complexes with the quantum dots-aptamer conjugate resulted in an overall improved electrocatalytic ability as well as enhanced signal response. Moreover, results proved one of the complexes being superior over the other functionality wise, indicating the significance of substituent type of the phthalocyanines. The best performing aptasensor showed detection limits as low as 0.23 ng/mL in buffer solutions as well as 0.27 ng/mL in serum samples. Moreover, the sensor showed good stability, reproducibility and repeatability.

Effect of Polyvinyl Alcohol Ligands on Supported Gold Nano-Catalysts: Morphological and Kinetics Studies.

The effect of polyvinyl alcohol (PVA) stabilizers and gold nanoparticles supported on active carbon (AuNPs/AC) was investigated in this article. Polymers with different molecular weights and hydrolysis degrees have been synthesized and used, like the stabilizing agent of Au nano-catalysts obtained by the sol-immobilization method. The reduction of 4-nitrophenol with NaBH4 has been used as a model reaction to investigate the catalytic activity of synthesized Au/AC catalysts. In addition, we report several characterization techniques such as ultraviolet-visible spectroscopy (UV-Vis), dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) in order to correlate the properties of the polymer with the metal nanoparticle size and the catalytic activity. A volcano plot was observed linking the catalytic performance with hydrolysis degree and the maximum of the curve was identified at a value of 60%. The Au:PVA-60 weight ratio was changed in order to explain how the amount of the polymer can influence catalytic properties. The effect of nitroaromatic ring substituents on the catalytic mechanism was examined by the Hammett theory. Moreover, the reusability of the catalyst was investigated, with little to no decrease in activity observed over five catalytic cycles. Morphological and kinetic studies reported in this paper reveal the effect of the PVA polymeric stabilizer properties on the size and catalytic activity of supported gold nanoparticles.

The effect of benzene ring substituent at different position of main ligand on electronic structure and photophysical properties of a series of iridium(III) complexes

The electronic structure and photophysical properties of a series of iridium(III) complexes have been theoretically explored by DFT/TDDFT calculations. Ionization potential, electron affinities, and reorganization energy have been calculated to evaluate the charge transfer and balance properties between hole and electron for the three complexes. The lowest lying absorption of 3 is obviously blue-shifted in contrast to those of 1 and 2, which is consistent with the variation of the energy gap between of LUMO and HOMO values. The calculated lowest energy emissions of complexes 1, 2 and 3 are located at 607, 634 and 698 nm, respectively.

Effect of aromatic ring substituents on the ability of catechol to produce brown carbon in iron(iii)-catalyzed reactions

Our previous work demonstrated formation of highly insoluble and strongly light-absorbing organic particles in reactions between catechol or guaiacol with Fe(iii) under pH = 3 conditions characteristic of aerosol liquid water.

Development of Rhodamine 6G-Based Fluorescent Chemosensors for Al3+-Ion Detection: Effect of Ring Strain and Substituent in Enhancing Its Sensing Performance.

Four rhodamine 6G-based chemosensors (H3L1–H3L4) are designed for selective detection of Al3+ ion. They are characterized using various spectroscopic techniques and X-ray crystallography. All absorption and emission spectral studies have been performed in 10 mM N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (HEPES) buffer solution at pH 7.4 in H2O/MeOH (9:1, v/v) at 25 °C. In absorption spectra, chemosensors exhibit an intense band around 530 nm in the presence of Al3+ ion. Chemosensors (H3L1–H3L4) are nonfluorescent when excited around 490 nm. The presence of Al3+ ion enhances the emission intensity (555 nm) many times. The formation of complexes 1–4 is established with the aid of different spectroscopic techniques. The limit of detection value obtained in the nanomolar range confirms the high sensitivity of the probes toward Al3+ ion. It has been observed that the presence of aliphatic spacers in the diamine part and different halogen substituents in the salicylaldehyde part strongly influences the selectivity of the chemosensors toward Al3+ ion. The propensity of the chemosensors to identify intracellular Al3+ ions in triple-negative human breast cancer cell line MDA-MB-468 by fluorescence imaging is also examined in this study.

Enantioselective Protonation of Radical Anion Intermediates in Photoallylation and Photoreduction Reactions of 3,3-Diaryl-1,1-dicyano-2-methylprop-1-ene with Allyltrimethylsilane.

Photoreactions of acetonitrile solutions of 3,3-diaryl-1,1-dicyano-2-methylprop-1-enes (1a–c) with allyltrimethylsilane (2) in the presence of phenanthrene as a photoredox catalyst and acetic acid as a proton source formed photoallylation (3) and photoreduction (4) products via photoinduced electron transfer pathways. When (S)-mandelic acid was used as the proton source, the reactions proceeded with 3.4 and 4.8 %ee for formation of 3 and 4, respectively. The results of studies of the effect of aryl ring substituents and several chiral carboxylic acids suggested that the enantioselectivities of the reactions are governed by steric controlled proton transfer in intermediate complexes formed by π-π and OH-π interactions of anion radicals derived from 1a–c and chiral carboxylic acids.

Metal-Free Nitrogen-Containing Polyheterocyclic Near-Infrared (NIR) Absorption Dyes: Synthesis, Absorption Properties, and Theoretical Calculation of Substituted 5-Methylisoindolo[2,1-a]quinolines.

We have synthesized and theoretically calculated 5-methylisoindolo[2,1-a]quinoline derivatives as novel near-infrared absorption dyes via a ruthenium-catalyzed one-pot metathesis/oxidation/1,3-dipolar cycloaddition protocol. The reactivity in 1,3-dipolar cycloaddition was governed by the electronic effect of aromatic ring substituents. Substrates with an electron-withdrawing group on the aromatic ring afforded higher yields. The maximal absorption wavelength of 3,5-dimethyl-11-phenylisoindolo[2,1-a]quinoline-7,10-dione and 11-(4-methoxyphenyl)-5-methylisoindolo[2,1-a]quinoline-7,10-dione in MeOH increased to 736 and 737 nm, although that of 3a was 727 nm.

Recurrent supramolecular motifs in discrete complexes and coordination polymers based on mercury halides: prevalence of chelate ring stacking and substituent effects

We report the synthesis, X-ray characterization and DFT study of five Hg(ii) complexes with Schiff bases containing a nicotinohydrazide core to explore the formation of chelate-ring π-stacking interactions.

The structural analysis and modelling of ring substituent effect for the ortho-derivatives of 1-hydroxynaphthalene-2-carboxanilides and 2-hydroxynaphthalene-1-carboxanilides

The quantum chemical DFT study of 1-hydroxynaphthalene-2-carboxanilide (A–H) and 2-hydroxynaphthalene-1-carboxanilide (B–H) and their selected ortho-derivatives (A–R, B–R) is presented. The structural analysis showed that the energetically preferred conformation is stabilized via the intramolecular hydrogen bonds occurring between the CO⋯H–O1 of A–H molecule and CO⋯H–O2 groups of B–H molecule. The A–R derivatives are practically planar, while the B–R derivatives are slightly distorted due to the spatial repulsion of hydrogen atoms. The conformation analysis of molecules with deprotonated hydroxyl group supports the concept of existence of two conformer types with respect to the NHCO bridge orientation. Stabilization of the naphtholate moiety by a hydrogen bond to the amide NH group may allow the compound to cross the membrane to the extracellular space. The ortho substitution effect on the selected calculated properties was analyzed and the theoretical data were correlated with the substituent constants. For the B–R derivatives, the antitubercular activity concentrations were correlated and predicted by the calculated quantities.

A quantitative measure of halogen bond activation in cocrystallization.

A theoretical investigation of bond lengths and bond energies for several kinds of halogen bonding interactions is carried out using the PIXEL method. The effect of different kinds of activating agents, fluoro-, nitro-, ethynyl substitution and combinations thereof, is assessed quantitatively, and is found to be fully consistent with the results of literature screenings of the corresponding strengths, as judged by the ease of formation of cocrystals. In the best combination of activators the halogen bond is comparable or superior to a strong O-HO hydrogen bond in what concerns stabilization energies and stretching force constants. At least with iodine acceptors, in our picture the halogen-bonding effect is a localized interaction arising from the detail of the electron distribution at the halogen atom, mainly of a Coulombic-polarization nature but with dispersion energies contributing significantly. Binding energies correlate with the electrostatic potential at the tip of the halogen and even with Mulliken population analysis atomic charges, providing easily accessible guidelines for crystal engineers. For one typical cocrystal structure the analysis of separate molecule-molecule energies reveals the nature of the packing forces and rank halogen bonding as the main influence, closely followed by coplanar stacking of coformers.

Substituent effects on the TiO2 photosensitized oxidation reaction of benzyl thioethers and thiols in deaerated acetonitrile

Abstract The TiO 2 photosensitized oxidation of benzyl methyl sulfides (X-C 6 H 4 CH 2 SCH 3 ) and benzyl thiols (X-C 6 H 4 CH 2 SH) has been investigated in Ar-saturated CH 3 CN. Steady-state irradiation produced benzaldehydes or dibenzylsulfides as oxidation products with sulfides and thiols, respectively. The results obtained through kinetic competitive experiments, aimed to evaluate the ring substituent effect on the reactivity, suggested the involvement of radical cation intermediates, formed by the favorable electron transfer from the substrate to the TiO 2 photogenerated hole, which reasonably deprotonate to give the final products. This process was poorly affected by the adsorption of the substrate at the TiO 2 surface, as demonstrated by similar results, both in terms of products and reactivity, collected for the homogeneous photooxidation of the same substrates sensitized by N -methoxyphenanthridinium hexafluorophosphate (MeOP + PF 6 − ). This behavior is likely due to the low hydrogen-bond acceptor ability of divalent sulfur systems. Density functional theory calculations pointed out that the most stable conformations of X-C 6 H 4 CH 2 SH + are characterized by having the C S bond almost collinear with the π system of the aromatic ring and by a significant charge and spin delocalization involving both the phenyl ring and the sulfur atom.

Spectroscopic and Computational Investigation of Low-Spin Mn(III) Bis(scorpionate) Complexes.

Six-coordinate MnIII complexes are typically high-spin (S = 2), however, the scorpionate ligand, both in its traditional, hydridotris(pyrazolyl)borate form, Tp- and Tp*- (the latter with 3,5-dimethylpyrazole substituents) and in an aryltris(carbene)borate (i.e., N-heterocyclic carbene, NHC) form, [Ph(MeIm)3B]-, (MeIm = 3-methylimidazole) lead to formation of bis(scorpionate) complexes of MnIII with spin triplet ground states; three of which were investigated herein: [Tp2Mn]SbF6 (1SBF6), [Tp*2Mn]SbF6 (2SBF6), and [{Ph(MeIm)3B}2Mn]CF3SO3 (3CF3SO3). These trigonally symmetric complexes were studied experimentally by magnetic circular dichroism (MCD) spectroscopy (the propensity of 3 to oxidize to MnIV precluded collection of useful MCD data) including variable temperatures and fields (VTVH-MCD) and computationally by ab initio CASSCF/NEVPT2 methods. These combined experimental and theoretical techniques establish the 3A2g electronic ground state for the three complexes, and provide information on the energy of the "conventional" high-spin excited state (5Eg) and other, triplet excited states. These results show the electronic effect of pyrazole ring substituents in comparing 1 and 2. The tunability of the scorpionate ligand, even by perhaps the simplest change (from pyrazole in 1 to 3,5-dimethylpyrazole in 2) is quantitatively manifested through perturbations in ligand-field excited-state energies that impact ground-state zero-field splittings. The comparison with the NHC donor is much more dramatic. In 3, the stronger σ-donor properties of the NHC lead to a quantitatively different electronic structure, so that the lowest lying spin triplet excited state, 3Eg, is much closer in energy to the ground state than in 1 or 2. The zero-field splitting (zfs) parameters of the three complexes were calculated and in the case of 1 and 2 compare closely to experiment (lower by < 10%, < 2 cm-1 in absolute terms); for 3 the large magnitude zfs is reproduced, although there is ambiguity about its sign. The comprehensive picture obtained for these bis(scorpionate) MnIII complexes provides quantitative insight into the role played by the scorpionate ligand in stabilizing unusual electronic structures.

Structure‐interaction relationship study of N‐(4‐phenylsubstituted) cyanoacetamides by multivariate methods

AbstractDerivatives of amides belong to a very attractive group of compounds due to a broad spectrum of different biological activities. The type of molecule activity significantly depends on its interactions with the environment, which on the other hand largely depends on the nature of the substituent attached to the basic molecule as well as of solvents properties. In this work, the influence of the mentioned parameters on the interaction ability of the group of N‐(4‐phenylsubstituted) cyanoacetamides is investigated by using multivariate methods, based on the results obtained by reverse‐phase thin‐layer chromatography and ultraviolet absorption spectroscopy. Results obtained by the used chemometrics methods are very similar, within which the principal component analysis has provided the most detailed information. The obtained results suggest that the interactions of the investigated compounds are dominantly regulated by the polarity of the used solvents and their proton donor ability inside the chromatographic measurements, while in the case of the spectrophotometric data, the solvent's hydrogen bond ability has the greatest impact on the future interaction capability of the investigated cyanoacetamides. In the case of the substituent effect which is attached to the benzene ring, the greatest impact on the future interaction ability of the investigated cyanoacetamides is the orientation effect of ring substituent. Based on all the obtained results, it can be noticed that the used multivariate methods are able to detect effects of the substituent and solvent properties on the future interaction ability of the investigated derivatives. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Ring Substituent Effects on the Thiol Addition and Hydrolysis Reactions of N-Arylmaleimides.

Maleimide groups are used extensively in bioconjugation reactions, but limited kinetic information is available regarding their thiol addition and hydrolysis reactions. We prepared a series of fluorogenic coumarin maleimide derivatives that differ by the substituent on their maleimide C═C bond. Fluorescence-based kinetic studies of the reaction with β-mercaptoethanol (BME) yielded the second-order rate constants (k2), while pH-rate studies from pH 7 to 9 gave base-catalyzed hydrolysis rate constants (kOH). Linear free-energy relationships were studied through the correlation of log k2 and log kOH to both electronic (σ(+)) and steric (Es(norm)) parameters of the C═C substituent. These correlations revealed the thiol addition reaction is primarily sensitive to the electronic effects, while steric effects dominate the hydrolysis reaction. These mechanistic studies provide the basis for the design of novel bioconjugation reactants or fluorogenic labeling agents.

The effects of ring substituents in aniline on the reactivity of PANI with hydrogen tetrachloroaurate and the dispersion of gold nanoparticles

As expected from theoretical predictions, the polymerization of aniline was affected by the substituent group on the benzene ring. The rate of the polymerization varied as poly(2-chloroaniline) (PANICl) < < poly(2-methylaniline) (PANIMe) < polyaniline (PANI). While the rate of polymerization was determined largely by electronic effects of the substituent groups, the reactivity of the polymers was determined by the steric effects. The order of the rate of reaction of the polymers with AuCl4− was PANIMe < PANICl < < PANI. The amount of Au incorporated into the polymer matrix followed a similar trend. However, the size of the gold nanoparticles did not differ greatly. Gold nanoparticles dispersed on PANICl and PANIMe were more stable in acidic media than those on PANI. Copyright © 2015 John Wiley & Sons, Ltd.

Crystal structures, spectroscopic and theoretical study of novel Schiff bases of 2-(methylthiomethyl)anilines

New Schiff bases derived from p-methoxysalicylaldehyde and 2-(methylthiomethyl)anilines (substituted with methyl, methoxy, nitro) were synthesized and characterized by elemental analyses, FT-IR, NMR, electronic spectra and quantum chemical calculations. X-ray crystallography of two compounds showed the solid structures are stabilized by intramolecular and intermolecular H-bonds. The effect of OH⋯N interaction between the phenolic hydrogen and imine nitrogen on the proton and carbon NMR shifts, and the role of CH⋯O and CH⋯S contacts are discussed. The bond lengths and angles, 1H and 13C NMR data, ELUMO–HOMO, dipole moments and polarizability of the compounds were predicted by density functional theory, DFT (B3LYP/6-31G∗∗) method. The experimental geometric parameters and the NMR shifts were compared with the calculated values, which gave good correlations. The electronic effects of aryl ring substituents (methyl, methoxy and nitro) on the properties of the resulting compounds, such as the color, NMR shifts, electronic spectra and the calculated energy band gaps, dipole moments and polarizability are discussed. Increase in electron density shifted the phenolic proton resonance to lower fields. The methoxy-substituted compound has a small dipole moment and subsequent large polarizability value. Highest polarity was indicated by the nitro compound which also showed high polarizability due to its larger size. The energy gaps obtained from ELUMO–HOMO calculations suggest these compounds may have applications as organic semiconducting materials.

Diverse topologies in copper aromatic dicarboxylate coordination polymers containing 3-pyridylmethylnicotinamide: Effect of geometric isomerism and ring substituent

Hydrothermal reaction of copper nitrate and 3-pyridylmethylnicotinamide (3-pmna) with aromatic dicarboxylates has afforded a series of coordination polymers that were structurally characterized via single-crystal X-ray crystallography. [Cu(tere)(3-pmna)]n (1, tere=terephthalate) displays a 3,5-connected 3-D binodal net with uncommon (63)(698) gra topology. {[Cu(iph)(3-pmna)(H2O)]·3H2O}n (2, iph=isophthalate) possesses an extremely rare 4-connected 3-D self-penetrated net with 86tcb topology. [Cu2(nip)2(3-pmna)2]n (3, nip=5-nitroisophthalate) manifests a doubled chain 1-D structure, while increased steric bulk in [Cu(tbip)(3-pmna)]n (4, tbip=5-tert-butylisophthalate) results in a 1-D single chain motif. A significant dependence of the dimensionality and topology of these materials on the part of the carboxylate donor disposition and ring substituent was thus revealed. Thermal properties of these new materials were also investigated.

Reaction Pathways of Alkoxyl Radicals. The Role of Solvent Effects on C–C Bond Fragmentation and Hydrogen Atom Transfer Reactions

This account describes the results of our recent mechanistic studies on unimolecular C–C bond fragmentation (β-scission and <i>O</i>-neophyl rearrangement) and bimolecular hydrogen atom transfer (HAT) reactions of alkoxyl radicals. Particular attention is devoted to the study of solvent effects on these reactions by means of time-resolved techniques such as laser flash photolysis. Information is provided on the effect of ring substituents and of the solvent on the spectral properties of arylcarbinyloxyl radicals and on their reactivity in β-scission and <i>O</i>-neophyl rearrangement reactions, showing that a change in solvent can influence the fragmentation reactivity and selectivity. Detailed information has also been obtained on the role of the substrate structure and of the solvent on HAT reactions involving the cumyloxyl radical, showing the importance of solvent hydrogen bond interactions with the substrate and/or the radical on these processes, and providing a general mechanistic description of the kinetic solvent effects observed in HAT reactions from C–H bonds, as well as expanding on the previously available description for HAT from phenolic O–H bonds. The possible application of these findings to synthetically useful C–H functionalization procedures is discussed. 1 Introduction 2 C–C β-Scission Reactions 3 <i>O</i>-Neophyl Rearrangement 4 Hydrogen Atom Transfer (HAT) Reactions 5 Concluding Remarks