Effect Of Substituent Groups Research Articles

Effects of nitrogenous substituent groups on the benzene dication

ABSTRACTThe benzene dication possesses a pentagonal-pyramidal structure with a hexacoordinated carbon. In contrast, halogenated benzene dications retain a similar structure to their parent molecules. In this work, we report on theoretical studies of the structures of the dications of benzene with nitrogenous substituents. We find that the nitrobenzene dication favours a near ideal pentagonal-pyramidal structure, while the aniline dication favours a flat, hexagonal structure. Reduced-density-matrices methods give predictions in agreement with available ab initio calculations and experiment. These results are also compared with those from the Hartree–Fock method and density functional theory.

Direct amidation of non-activated phenylacetic acid and benzylamine derivatives catalysed by NiCl2.

This paper describes an eco-friendly and efficient direct amidation of benzylamine and phenylacetic acid derivatives in the presence of 10 mol% NiCl2 as catalyst without any drying agent. For the different phenylacetic acid and benzylamine derivatives, the direct catalysed amidation gave moderate-to-excellent yields in toluene. The steric and electronic effects of substituent groups on the phenyl ring of acid were crucial to the yields of the direct amidation. The catalyst NiCl2 can be recycled three times without loss of activity.

A possible target: triple-bonded indiumantimony molecules with high stability

Only bulkier substituents can thermodynamically stabilize the triple-bonded RInSbR molecules.

Unraveling substituent effects on frontier orbitals of conjugated molecules using an absolutely localized molecular orbital based analysis.

It is common to introduce electron-donating or electron-withdrawing substituent groups into functional conjugated molecules (such as dyes) to tune their electronic structure properties (such as frontier orbital energy levels) and photophysical properties (such as absorption and emission wavelengths). However, there lacks a generally applicable tool that can unravel the underlying interactions between orbitals from a substrate molecule and those from its substituents in modern electronic structure calculations, despite the long history of qualitative molecular orbital theory. In this work, the absolutely localized molecular orbitals (ALMO) based analysis is extended to analyze the effects of substituent groups on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of a given system. This provides a bottom-up avenue towards quantification of effects from distinct physical origins (e.g. permanent electrostatics/Pauli repulsion, mutual polarization, inter-fragment orbital mixing). For the example case of prodan (a typical dye molecule), it is found that inter-fragment orbital mixing plays a key role in narrowing the HOMO-LUMO gap of the naphthalene core. Specifically, an out-of-phase mixing of high-lying occupied orbitals on the naphthalene core and the dimethylamino group leads to an elevated HOMO, whereas an in-phase combination of LUMOs on the naphthalene core and the propionyl group lowers the LUMO energy of the entire molecule. We expect this ALMO-based analysis to bridge the gap between concepts from qualitative orbital interaction analysis and quantitative electronic structure calculations.

Theoretical insight into the mechanism, regioselectivity, and substituent group effect of Rh-catalyzed synthesis of 1,2-benzothiazines from NH-sulfoximines and diazo compounds.

This work presents a computational study of RhIII-catalyzed synthesis of 1,2-benzothiazines from NH-sulfoximines and diazo compounds reported by Bolm et al. (Angew. Chem., Int. Ed., 2015, 54, 12349). The reaction involves five sequent processes: elimination of dinitrogen, C-H activation, carbene insertion, protonation, and dehydration, and the C-H activation is identified as the rate-determining step with a barrier of 33.1 kcal mol-1. Phenyl sulfoximine is found to be the most favorable substrate with the lowest barrier in comparison with methoxybenzene sulfoximine and nitrobenzene sulfoximine. The noncovalent interaction is indicated to be mainly responsible for the experimentally observed regioselectivity. The theoretical results are expected to provide valuable guidance and assistance for the synthesis of 1,2-benzothiazines.

Design and Synthesis of L‐Proline Derivatives as Enantioselective Organocatalysts for Synthesis of the (S)‐Wieland‐Miescher Ketone

AbstractSome simple L‐proline derivatives were designed as the organocatalysts for asymmetric synthesis of (S)‐Wieland‐Miescher Ketone. Their catalytic efficiencies were predicted based on DFT (Density Functional Theory) calculations. The results of DFT calculations were in good agreement with that of experiment. In order to further investigate the effects of substituent groups attached to CONH on catalytic efficiencies, 12 other L‐proline derivatives were designed, synthesized and tested the catalytic efficiencies. Some of title organcatalysts (C04 and D01) exhibited excellent catalytic efficiencies (up to 93% ee and 88% yield) with a very low loading (0.5‐1 mol%) under solvent‐free conditions. Meanwhile, microwave irradiation was used for accelerating the reaction, and the reaction time had been decreased to 3 hours. Organocatalysts D01 derived from cheap isopropylamine would make the preparation of (S)‐Wieland‐Miescher Ketone a lot easier and cheaper.

Theoretical investigation on the water-assisted excited-state proton transfer of 7-azaindole derivatives: substituent effect.

A systematic study on the first excited-state proton transfer (ESPT) in 2RAI-H2O (R=OH, OCH3, CN, NO2, CHO) complexes in solution were investigated at the TD-M06-2X/6-31+G(d, p) level. The double proton transfer occurred in an asynchronous but concerted protolysis fashion no matter which substituent R was used at C2 position in pyrrole ring in the 7AI-H2O complex. The specific vibrational-mode of ESPT in the model systems was confirmed and contributed to promote the reaction rate by shortening the reaction path. The substituent effects of different groups on the ESPT thermodynamics and kinetics were discussed. It was obvious that the geometries, barrier height, asynchrony, and specific vibration-mode of excited-state proton transfer changed with the different substituent groups. Graphical Abstract The distance between two neighboring heavy atoms such as N1-O11 (R1) and O11-N8 (R2) distances played an important role in the proton transfer reaction. The sum of the N1-O11 and O11-N8 distances in the reactant of 2RAI-H2O (R=H, OH, OCH3; CN, CHO, NO2) complexes is in the range of 5.542Å~5.692Å and changes along with the substituent group at C2 position in the pyrrole ring. The ESDPT barrier height and the sum of the N1-O11 and O11-N8 distances have a good correlation.

Effect of substituent groups on the structures of two semi-flexible bis(imidazole) directed Zn(II)-5-sulfoisophthalate coordination polymers: Syntheses, structures and photoluminescent properties

Two new metal organic architectures, formulated as {(pbetixH2)0.5[Zn(µ-sip)(µ-pbetix)0.5]}n (1) and {[Zn2(µ-sip)2(pbisopix)(pbisopixH)2]·4H2O}n (2), were synthesized based on the rarely employed 1,4-bis((2-ethylimidazol-1-yl)methyl)benzene (pbetix) and 1,4-bis((2-isopropylimidazol-1-yl)methyl)benzene (pbisopix) ligands, along with the 5-sulfoisophthalate (sip) ligand. Complexes 1 and 2 were synthesized in basic medium and under mild hydrothermal conditions. Both complexes were characterized by elemental analysis, FT-IR spectroscopy and single crystal X-ray diffraction studies. Crystallographic studies of complexes 1 and 2 reveal that the Zn(II) ions are µ-bridged by trianionic sip3− ligands in the bis(monodentate) coordination mode to generate 1D polymer chains. In the complexes, adjacent chains are linked by the bis(imidazole) ligands to form a 2D structure. Complex 1 is the first example containing a protonated bis(imidazole) ligand, namely the pbetixH2 cation, while complex 2 is the first example with a monoprotonated bis(imidazole) ligand, namely pbisopixH. Topological analyses of the 2D coordination polymers reveal that complex 1 is a 3-fold polycatenated 4-connected uninodal net with the point symbol of {44.62}, whereas complex 2 is a 3-connected uninodal net with the point symbol of 63. The thermal behavior, photoluminescent properties and topological analysis of the complexes are also discussed herein.

Effect of substituent groups (R= [sbnd]CH3, [sbnd]Br and [sbnd]CF3) on the structure, stability and redox property of [Cr(R-pic)2(H2O)2]NO3·H2O complexes

Complexes [Cr(3-CH3-pic)2(H2O)2]NO3·H2O (1), [Cr(5-Br-pic)2(H2O)2]NO3·H2O (2) and [Cr(5-CF3-pic)2(H2O)2]NO3·H2O (3) were synthesized (pic = pyridine-2-carboxylic acid) and characterized by X-ray crystal diffraction. Crystal structure indicates that two bidentate ligands occupy equatorial position and two H2O occupy axial positions in trans-configuration. (i) Decomposition of complexes 1, 2 and 3 in different medium (phosphate buffered saline (PBS), apo-ovotransferrin (apootf) and EDTA) indicates that decomposition rate constants of these complexes follow the sequence of 1 < 2 < 3. (ii) The redox potential of Cr(III)/Cr(II) by cyclic voltammetry follows the sequence of 1 (−1.20 V) > 3 (−1.29 V) > 2 (−1.31 V). (iii) In addition, ·OH-generation of the new synthesized complexes was determined by Fenton-like reaction in comparison with Cr(pic)3, and it may be related to the reduction potential of the complexes. (iv) Moreover, Hammett substituent constants σp (inductive) and σm (resonance) (R = 3-CH3, 5-Br, 5-CF3) were introduced to evaluate the impact of substituent groups on the bond length and decomposition kinetics. The substituent group on the ligand has great effect on the properties of the complexes.

Density Function Theory Study on Effects of Different Energetic Substituent Groups and Bridge Groups on Performance of Carbon-Linked Ditetrazole 2N-Oxides

Based on the parent tetrazole 2N-oxide, six series of novel carbon-linked ditetrazole 2N-oxides with different energetic substituent groups (-NH2, -N3, -NO2, NF2, -NHNO2) and energetic bridge groups (-CH2-, -CH2−CH2-, -NH-, -N=N-, -NH−NH-) were designed. The overall performance and the effects of different energetic substituent groups and energetic bridge groups on the performance were investigated by density functional theory and electrostatic potential methods. The results showed that most of designed compounds have oxygen balance around zero, high heats of formation, high density, high energy, and acceptable sensitivity, indicating that tetrazole N-oxide is a useful parent energetic compound employed for obtaining high energy compounds, even only combined with some very common energetic substituent groups and bridge groups. Comprehensively considering the effects on energy and sensitivity, the -NO2, -NF2, -NH- and -NH−NH- are appropriate substituent groups for combining tetrozale N-oxide to design new energetic compounds, while -NH2, -N3, -CH2−CH2-, and -N=N- are inappropriate.

In vitro phase I metabolism of gamabufotalin and arenobufagin: Reveal the effect of substituent group on metabolic stability

Bufadienolides are a major class of bioactive compounds derived from amphibian skin secretion. Gamabufotalin (GB) and arenobufagin (AB) are among the top of the intensively investigated natural bufadienolides for their outstanding biological activities. This study aimed to characterize the phase I metabolism of GB and AB with respect to the metabolic profiles, enzymes involved, and catalytic efficacy, thereafter tried to reveal substituent effects on metabolism. Two mono-hydroxylated products of GB and AB were detected in the incubation mixtures, and they were accurately identified as 1- and 5-hydroxylated bufadienolides by NMR and HPLC-MS techniques. Reaction phenotyping studies demonstrated that CYP3A mediated the metabolism of the two bufadienolides with a high specific selectivity. Further kinetic evaluation demonstrated that the metabolism stability of GB and AB were better than other reported bufadienolides. Additionally, the CYP3A5 preference for hydroxylation of AB was observed, which was different to the selectivity of CYP3As for bufadienolides suggested by our previous report. This study can provide important data for elucidating the phase I metabolism of GB and AB and can lead to a better understanding of the bufadienolide–CYP3A interaction which is helpful for preclinical development and rational use of bufadienolides.

Low-Energy and Long-Lived Emission from Polypyridyl Ruthenium(II) Complexes Having A Stable-Radical Substituent.

Novel polypyridyl ruthenium(II) complexes having a 2,2'-bipyridine (bpy) derivative which possesses a 1,5-dimethyl-6-oxoverdazyl radical (OV) group as a stable-radical substituent were designed and synthesized. The radical-ruthenium(II) complexes showed low-energy/intense MLCT absorption and low-energy/long-lived MLCT emission, and these characteristics of the complexes were explained by the electron-withdrawing nature of the OV group. Furthermore, the radical-substituent effects were enhanced by the presence of the electron-donating methyl groups at the 4- and 4'-positions of bpy in the ancillary ligands. The detailed electrochemical, spectroscopic, and photophysical properties of the complexes were discussed in terms of the systematic modification of the second coordination sphere in the main and ancillary ligands.

Theoretical study of thieno-thiophene based low band gap copolymers and substituent effect on the optoelectronic properties of them

This paper studies donor-acceptor systems which incorporate benzodithiophene (BDT), benzodifuran (BDF) and benzodipyrrole (BDP) units as the electron-rich monomer with TT unit representing the electron-deficient monomer. This research is based on employing density functional theory (DFT) and time-dependent DFT (TD-DFT). The highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO), HOMO-LUMO gaps and dihedral-angles of these copolymers were calculated using oligomer extrapolation technique and periodic boundary condition (PBC) method. The optical band gaps and UV–vis absorption spectra of aforementioned copolymers were obtained by TD-DFT at the same level of theory. Based on the fair agreement between PBC-DFT calculated results and experimental data, the substituent effects of Cl, Br, CCH, COH, NO2, OH, SH and NH2 groups were investigated by PBC-DFT method. The difference between the ground and excited-states dipole moment (Δμge) of all derivatives were also calculated. Taking these results into account, a better understanding of the substituent effects on the photo-physical properties of the copolymers under study was achieved. Due to the shift of HOMO and LUMO energy levels, smaller band gaps and higher Δμge are observed in some derivatives. The calculation results demonstrate that the substitution of COH and NO2 by fluorine in BDF-TT and BDP-TT leads to higher maximum theoretical efficiencies (η).

Silver(I) Complexes of Diphenylpyridines: Crystal Structures, Luminescence Studies, Theoretical Insights, and Biological Activities.

A series of simple two-coordinated cationic silver(I) complexes, namely, [Ag{4-(4-R1 -phenyl)-2,6-diphenylpyridine}2 ]X (X=ClO4 - , BF4 - , or SO3 CF3 - ), with different electron-donating or -withdrawing groups (e.g., R1 =N(Me)2 , Me, H, Cl, and Br) on the phenyl ring, were successfully prepared. Extensive characterization of these complexes by various NMR spectroscopy techniques and mass spectrometry was further corroborated by single-crystal XRD analyses. Detailed photophysical investigations of [Ag{4-(4-N,N-dimethylaminophenyl)-2,6-diphenylpyridine}2 ]ClO4 (C1) displayed a strong room-temperature fluorescence in solution with an anomalously high luminescence quantum yield of 0.83. The effects of distinct substituent groups (C2-C5), π-conjugated aromatic rings (C6 and C7), and anions (C8 and C9) on the photoluminescence properties were evaluated. Furthermore, DFT and time-dependent DFT calculations were performed to discern the composition of the excited state, as well as to confirm the obtained relative emission energies upon substitution with electronically different ligands. These results indicated that the strong electron-donating substituent of N,N-dimethylamine played an important role in the unprecedented high luminescence quantum yield of C1. In addition, preliminary antimicrobial studies and confocal microscopy fluorescent imaging of HeLa cells labeled with these complexes reveal their potential applications in biological activities.

Approaching an experimental electron density model of the biologically active trans‐epoxysuccinyl amide group—Substituent effects vs. crystal packing

AbstractThe trans‐epoxysuccinyl amide group as a biologically active moiety in cysteine protease inhibitors such as loxistatin acid E64c has been used as a benchmark system for theoretical studies of environmental effects on the electron density of small active ingredients in relation to their biological activity. Here, the synthesis and the electronic properties of the smallest possible active site model compound are reported to close the gap between the unknown experimental electron density of trans‐epoxysuccinyl amides and the well‐known function of related drugs. Intramolecular substituent effects are separated from intermolecular crystal packing effects on the electron density, which allows us to predict the conditions under which an experimental electron density investigation on trans‐epoxysuccinyl amides will be possible. In this context, the special importance of the carboxylic acid function in the model compound for both crystal packing and biological activity is revealed through the novel tool of model energy analysis.

Effect of flavin compounds on uranium(VI) reduction- kinetic study using electrochemical methods with UV-vis spectroscopy

The reduction of uranium hexavalent (U(VI)) to tetravalent (U(IV)) is an important reaction because of the change in its mobility in the natural environment. Although the flavin mononucleotide (FMN) has acted as an electron shuttle for the U(VI) reduction in vivo system, which is called an electron mediator, only the rate constant for the electron transfer from FMN to U(VI) has been determined. This study examined the rate constant for the U(VI) reduction process by three flavin analogues (riboflavin, flavin mononucleotide, flavin adenine dinucleotide) to elucidate their substituent group effect on the U(VI) reduction rate by electrochemical methods. The formation of the U(IV) was monitored by UV-vis spectrometry at 660 nm during the constant potential electrolysis of the U(VI) solution in the presence of the mediator. The cyclic voltammograms indicated that the three flavin analogues behaved as electron mediator to reduce U(VI). The logarithmic rate constant for the U(VI) reduction was related to the standard redox potential of the mediators. This linear relationship indicated that the redox-active group of the mediator and the substituent group of the mediator dominate capability of the U(VI) reduction and its rate, respectively. The apparent reduction potential of U(VI) increased about 0.2 V in the presence of the mediators, which strongly suggests that the biological electron mediator makes the U(VI) reduction possible even under more oxidative conditions.

Substituent Effects on Boron–Bismuth Triple Bond: A New Target for Synthesis

The substituent effects on the potential energy surfaces of RB≡BiR (R = F, OH, H, CH3, SiH3, Tbt, Ar*, SiMe(SitBu3)2, and SiiPrDis2) are determined using density functional theories (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp). The theoretical results show that all of the triply bonded RB≡BiR molecules prefer to adopt a bent geometry (i.e., ∠RBBi ≈ 180° and ∠BBiR ≈ 90°), which agrees well with the valence-electron bonding model. It is also demonstrated that the smaller groups, such as R = H, F, OH, CH3, and SiH3, neither kinetically nor thermodynamically stabilize the triply bonded RB≡BiR compounds, except for H3SiB≡BiSiH3. However, triply bonded R′B≡BiR′ molecules that feature bulkier substituents (R′ = SiiPrDis2, SiMe(SitBu3)2, Tbt, and Ar*) are predicted to have a thermodynamic and kinetic global minimum. This theoretical study finds that both the steric and the electronic effects of bulkier substituent groups play a significant role in forming triply bonded RB≡BiR species that are experi...

The effect of different substituent groups of auxiliary ligands on the photochromic behaviors of bipyridinium-based coordination polymers

Two bipyridinium-based coordination polymers, {[Cd(BCbpy)2(o-BDC)]·13H2O} (1) and {[Cd(BCbpy)2(SA)]·6H2O} (2), have been synthesized and structurally characterized. Single-crystal X-ray diffraction analysis shows that the two compounds have similar one-dimensional coordination polymeric chain structures but different packing patterns. Compound 1 displays fast eye-detectable photochromic behavior while compound 2 is photoinert under 365nm irradiation. The influence of different substituent groups in same site of auxiliary ligands on the photochromic behaviors of the two compounds has been studied in detail.

Interaction of isoflavones with different structures and transferrin

ABSTRACTTransferrin, as a drug carrier, holds promise for targeted drug delivering into cancer cells where transferrin receptors (TfRs) are overexpressed. In the present study, the influence of structure characteristics of isoflavones have been explored, which are critical for binding to transferrin. Three isoflavones, daidzein, puerarin, and genistein, with characteristic daidzein core structures were selected for the study of the effects of substituent group on the A-ring on interaction with transferrin. The results demonstrated that daidzein-bound transferrin with an affinity almost 7 or more than 20 times higher than that of puerarin or genistein attributed to the addition of C(8)-glycosyl or C(5)-hydroxyl on the aromatic A-ring. Our docking study indicated that daidzein had strong hydrogen bond and hydrophobic interactions with transferrin, which believed to contribute to its higher binding affinity. Furthermore, daidzein binding induced fewer structures changes of transferrin than that by puerarin or genistein, suggesting that daidzein binding result in less disturbance of normal biological function of transferrin. Together these findings not only corroborated that daidzein was a superior ligand for transferrin, but also provided substantive information for possible modification and design methods of isoflavone.

Effect of substituent groups on quinoxaline-based random copolymers on the optoelectronic and photovoltaic properties

Abstract In this study, three low band gap donor-acceptor (D-A) type quinoxaline-based random copolymers were synthesized. The effect of varying substituent groups on quinoxaline groups on optoelectronic properties and the performance of bulk-heterojunction polymer solar cells was investigated. Electrochemical and optical studies indicate that these copolymers are promising materials for both electrochromic and polymer solar cells applications. Two random polymers were found as excellent candidates for NIR electrochromic devices owing to their 60% and 94% optical contrast values respectively in NIR region with less than 1 s switching times. Polymer solar cells were constructed using the copolymers as the donor components together with PC71BM as the acceptor in the active layer. Among all, the highest PCE was reported as 2.13%.