Imidazole Conjugates Research Articles

Modeling Interfacial Proton-Coupled Electron Transfer Reactions Involving Imidazolium Proton Donors

Proton-coupled electron transfer (PCET) is an elementary reaction that plays a pivotal role in various electrochemical energy conversion and storage processes. PCET reactions involving nonaqueous proton donors are of interest for applications in energy storage such as redox flow batteries, as well as in CO2 and O2 reduction catalysis. Yet, there remains much to be understood about the molecular reactivity of these systems. In this talk, I will describe periodic density functional theory (DFT) studies of interfacial PCET reactions involving different imidazolium proton donors on Pt(111) electrode surfaces.The imidazole conjugate bases adsorb strongly to the electrode surface; however, this adsorption behavior varies with isomers that feature distinct proton positions and with different functional substituent groups. Because the adsorption of imidazole conjugate bases could affect reactivity, these models are used as a foundation to understand the intrinsic PCET kinetics of these systems. The Volmer and Heyrovsky steps of hydrogen evolution reaction are two of the most basic heterogeneous electrochemical PCET reactions and are therefore chosen as model interfacial PCET reactions in this study. Potential-dependent reaction energies and activation barriers are calculated using the charge extrapolation method, where the electrode potential is tuned by modifying proton coverage for different-sized unit cells. This approach is used to develop relationships between PCET reaction thermodynamics and kinetics through Brønsted–Evans–Polanyi (BEP) relationships for different imidazoles, where BEP slopes are analogs to charge transfer coefficients in the Butler–Volmer equation. Investigating reaction parameters influencing charge transfer kinetics at the electrode-electrolyte interface is crucial for designing efficient energy storage systems, impacting overall device performance. These studies show trends in the kinetic behavior of different functionalized imidazoles, which can aid in the design of catalytic and energy storage systems.

Synthesis of naphthalimide-phenanthro[9,10-d]imidazole derivatives: In vitro evaluation, binding interaction with DNA and topoisomerase inhibition.

The synthesis and characterization of a series of naphthalimide and phenanthro[9,10-d]imidazole conjugate is described. These compounds are evaluated in vitro for their cytotoxicity towards 60 human cancer cell lines. Derivative 16 shows excellent cytotoxic activity against these cancer cell lines with the range of growth inhibition from -55.78 to 94.53. The most potent derivative (ethylpiperazine, 16) is further studied to evaluate the interaction with ct-DNA using absorption and emission spectroscopy as well as DNA viscosity measurement. The DNA binding studies indicate that compound 16 is significantly interacted with DNA through groove binding having binding constant value of 7.81×104 M-1 alongwith partial intercalation between the base pairs of DNA strands. Further, topoisomerase inhibition study suggests that compound 16 is induced apoptosis and inhibits human topoisomerase (Topo-IIα) as a possible intracellular target. Molecular docking study of compound 16 with ct-DNA shows good docking score.

Pyrene-imidazole conjugate as a fluorescent sensor for the sequential detection of iron(III) and histidine in aqueous solution.

We developed PIM, a pyrene-based fluorescence sensor bearing an imidazole moiety and a carbonyl group as the binding sites for Fe3+ ions. The pyrene-based control compounds 1 and 2 were synthesized to demonstrate the structure-activity relationships. Compound 1, which contained a thiazoline moiety and a carbonyl group, displayed high selectivity for Cu2+ ions. This property indicated that heterocycles play an important role in the metal ion selectivity modulation. Compound 2, which lacked a carbonyl group, did not display metal ion selectivity. This characteristic demonstrated that introducing an additional recognition unit (cooperative recognition strategy) should be an effective way to improve metal ion selectivity. Furthermore, the PIM-Fe3+ ensemble can serve as a fluorescent sensor for histidine (His) detection via the removal of Fe3+ from the ensemble by His and the release of PIM. The sequential detection of Fe3+ and His exhibited on-off-on phenomenon, and the Fe3+ and His detection limits were 0.11 and 3.06 μM, respectively. These results will help in the further enhancement or modulation of metal ion selectivity in the development of fluorescent sensor systems. Moreover, the organic-metal ensemble provides an effective platform for detecting amino acids through the displacement strategy.

Tuning the AIE Activities and Emission Wavelengths of Tetraphenylethene-Containing Luminogens

Aggregation-induced emission (AIE) has attracted rapidly growing interest, owing to the high fundamental importance and diverse applications. The study of structure-property correlation of AIE luminogens is of high importance for the design and application of new AIE luminogens. In this contribution, we synthesized two pairs of tetraphenylethene-phenanthro[9,10-d]imidazole conjugates, and investigated the structure-property correlation of the luminogens. The optical properties, fluorescence lifetimes, electronic structures, electrochemical properties, and electroluminescence properties of the luminogens were comparatively studied. It was found that embedding benzo-2,1,3-thiadiazole moieties into the molecular backbones not only tuned the fluorescence feature of aggregation-enhanced emission to moderate aggregation-caused quenching, but also strongly red-shifted the fluorescence of luminogens from sky-blue to red. The underlying mechanism of this phenomenon was studied and discussed combined with theoretical calculation results. Undoped organic light-emitting diodes with varied electroluminescence colors and good performances are fabricated using these luminogens as light-emitting layers.

D-metal folates and the folic acid–imidazole conjugate

Metal folates MFol • nH2O (M2+ = Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+; n = 4–6), silver folate Ag2Fol • 3H2O, and the folic acid–imidazole conjugate H2Fol • 3Im • 2H2O were synthesized in aqueous solutions at a 1 : 1 M2+ : H2Fol molar ratio and pH 5.5–6.6. The compositions of the resulting compounds were determined by chemical, thermal, and gravimetric analysis. The composition of copper(II) folate was confirmed by elemental analysis; the solubility product of nickel folate (9.65 × 10–9) was estimated using solubility data. IR and electron absorption spectroscopy was used to show that oxygen atoms of carboxyl groups in folic acid and the pyridine nitrogen atom in imidazole are involved in bond formation in folates and the conjugate.

Imine/amide–imidazole conjugates derived from 5-amino-4-cyano-N1-substituted benzyl imidazole: Microwave-assisted synthesis and anticancer activity via selective topoisomerase-II-α inhibition

Microwave-accelerated synthesis and anticancer activity of novel imine/amide–imidazole conjugates derived from 5-amino-4-cyano-N1-substituted benzyl imidazole against a panel of seven cancer cell lines are reported for the first time. Compounds ARK-4, 10 and 12 in the series show promising in vitro anti proliferative activity with low micromolar IC50 values against A-459 (lung), Hep-G2 (liver) and H-460 (liver) cancer cell lines. Compounds caused the increase in ROS levels as well as mitochondrial membrane depolarization, which might induce apoptosis. Further, mechanistic interventions on biological and molecular modeling data supported that compounds inhibited topoisomerase-II selectively.

Synthesis and radical scavenging activity of phenol–imidazole conjugates

Novel hydroxylated benzylideneamino imidazole derivatives were synthesized and their radical scavenging activity was assessed against DPPH and hydroxyl radicals. In the DPPH assay, most of the synthesized compounds showed an IC50 in the range 3.2μM⩽IC50⩽8.4μM, lower than the reference compound trolox (IC50=9.5μM) or the parent aldehydes (5.4μM⩽IC50⩽11.6μM). The activity depends mainly on the phenolic subunit (number and position of the hydroxyl groups) and the extent of conjugation with the imidazole ring. In the deoxyribose assay, all the compounds, including parent imidazoles and aldehydes, showed high activity against the hydroxyl radical and the ability to chelate iron ions. At 5μM concentration, the compounds protected the deoxyribose from degradation by hydroxyl radical between 62% and 38%.

Synthesis and fluorescent characteristics of imidazole–indocyanine green conjugates

We have successfully synthesized imidazole-dye conjugates by linking imidazole and nitroimidazoleacetic acids to an indocyanine green (ICG) carboxylic acid derivative, using an ethanolamine linker. These dye-conjugates show absorbance peaks at 754–756 nm and fluorescence peaks at 780 nm. The dye-conjugates show a blue shift of 25 nm and 30 nm in the absorption and fluorescence spectra respectively when compared to that of standard cardiogreen. There is no change in absorption and fluorescence spectral profiles between the ICG derivative and imidazole conjugates. The extinction coefficients of new ICG derivative and imidazole conjugates are 1.8 times higher than that of standard ICG. The relative quantum yields of the new compounds are 4.5–5.5 times higher than that of the Sigma–Aldrich’s ICG. The dyes are tested for hypoxia in-vitro with 4T1 luc cell lines and it is found that the cells treated with 2-nitroimidazole ICG show a contrast of fluorescence signal of 2.5–3.0 for the cells under hypoxic to that of cells under normoxic. However pure ICG shows no significant difference between hypoxic and normoxic cells.

Requirement of β-alanine components in sequence-specific DNA alkylation by pyrrole–imidazole conjugates with seven-base pair recognition

To investigate the effect of incorporation of β-alanine in alkylating N-methylpyrrole (Py)– N-methylimidazole (Im) polyamide, seco-CBI conjugates 2– 8 were synthesized by an Fmoc solid-phase method and subsequent coupling with an alkylating moiety. DNA-alkylating activities of conjugates 2– 8 were evaluated by high-resolution denaturing gel electrophoresis with 202-base pair (bp) DNA fragments. Alkylation by conjugates 2 and 3, which have antiparallel pairings of β-alanine (β) opposite β (β/β) and Py/β, occurred mainly at the adenine (A) of the matching sequences, 5′-AGCTCC A-3′ (site 1) and 5′-AGCACC A-3′ (site 3). However, conjugate 4, with β/Py, did not show any DNA-alkylating activities. Similarly, conjugate 5, which possessed a Py/Py pair, weakly alkylated the matching sites at micromolar concentrations. Conjugates 6 and 7, which possessed β/β and Py/β pairs, respectively, alkylated at the A of the matching sequences, 5′-ACTACC A-3′ (site 2) and 5′-ACAACC A-3′ (site 4). In contrast, conjugated 8, with a Py/Py pair, showed lower activity and less alkylated DNA at sites 2 and 4 with mismatched alkylation at site 1 at a higher concentration than that of 6 and 7. These results demonstrate that incorporation of β-alanine is required for the sequence-specific alkylation by seco-CBI Py–Im conjugates with a seven-base pair sequence.

Targeted inhibition of the hepatitis C internal ribosomal entry site genomic RNA with oligonucleotide conjugates

Hepatitis C is a major public health concern, with an estimated 170 million people infected worldwide and an urgent need for new drug development. An attractive therapeutic approach is to prevent the ‘cap-independent’ translation initiation of the viral proteins by interfering with both the structure and function of the hepatitis C viral internal ribosomal entry site (HCV IRES). Towards this goal, we report the design, synthesis and purification of novel bi-functional molecules containing DNA or RNA antisenses attached to functional groups performing RNA hydrolysis. These 5′ or 3′-coupled conjugates bind the HCV IRES with affinity and specificity and elicit targeted hydrolysis of the viral genomic RNA after short (1 h) incubation at low (500 nM) concentration at 37°C in vitro. Additional secondary cleavage sites are induced and their mapping within the RNA structure indicates that functional domains IIIb-e are excised from the IRES that, based on cryo-EM studies, becomes incapable of binding the small ribosomal subunit and initiation factor 3 (eIF3). All these molecules inhibit, in a dose-dependent manner, the ‘IRES-dependent’ translation in vitro. The 5′-coupled imidazole conjugate reduces viral protein synthesis by half at a 300 nM concentration (IC50), corresponding to a 4-fold increase of activity when compared to the naked oligonucleotide. These new conjugates are now being tested for activity on infected hepatic cell lines.

Tunable DNA Photocleavage by an Acridine−Imidazole Conjugate

We report the synthesis and characterization of photonucleases N,N'-bis[2-[bis(1H-imidazol-4-ylmethyl)amino]ethyl]-3,6-acridinediamine (7) and N-[2-[bis(1H-imidazol-4-ylmethyl)amino]ethyl]-3,6-acridinediamine (10), consisting of a central 3,6-acridinediamine chromophore attached to 4 and 2 metal-coordinating imidazole rings, respectively. In DNA reactions employing 16 metal salts, photocleavage of pUC19 plasmid is markedly enhanced when compound 7 is irradiated in the presence of either Hg(II), Fe(III), Cd(II), Zn(II), V(V), or Pb(II) (low-intensity visible light, pH 7.0, 22 degrees C, 8-50 microM 7). We also show that DNA photocleavage by 7 can be modulated by modifying buffer type and pH. Evidence of metal complex formation is provided by EDTA experiments and by NMR and electrospray ionization mass spectral data. Sodium azide, sodium benzoate, superoxide dismutase, and catalase indicate the involvement of type I and II photochemical processes in the metal-assisted DNA photocleavage reactions. Thermal melting studies show that compound 7 increases the Tm of calf thymus DNA by 10 +/- 1 degrees C at pH 7.0 and that the Tm is further increased upon the addition of either Hg(II), Cd(II), Zn(II), or Pb(II). In the case of Fe(III) and V(V), a colorimetric assay demonstrates that compound 7 sensitizes one electron photoreduction of these metals to Fe(II) and V(IV), likely accelerating the production of type I reactive oxygen species. Our data collectively indicate that buffer, pH, Hg(II), Fe(III), Cd(II), Zn(II), V(V), Pb(II), and light can be used to "tune" DNA cleavage by compound 7 under physiologically relevant conditions. The 3,6-acridinediamine acridine orange has demonstrated great promise for use as a photosensitizer in photodynamic therapy. In view of the distribution of iron in living cells, compound 7 and other metal-binding acridine-based photonucleases should be expected to demonstrate excellent photodynamic action in vivo.

Parallel Supported Synthesis of Polyamine−Imidazole Conjugates

[reaction: see text] A small collection of nine polyamine-imidazole conjugates, potentially acting as RNases A mimics, has been synthesized on SynPhase lanterns using amino alcohols and diamines as building blocks. Couplings were performed via S(N)2 alkylation of methanesulfonates with amines. The final introduction of N-4-nitrobenzyloxycarbonyldiamines allowed easy purification of the cleaved compounds.

Ferrocene-histidine conjugates: N-ferrocenoyl-histidyl(im N-ferrocenoyl)methylester: synthesis and structure

The preparation of the new ferrocenoyl histidyl conjugates N-Fc-His-OMe ( 2) and N-Fc-His( ε- N-Fc)-OMe ( 3) and of a simple ferrocenoyl imidazole conjugate Fc-Im ( 4) is reported together with their spectroscopic and electrochemical characterization. The electrochemistry of 3 exhibits two fully reversible one-electron oxidations, which are due to the stepwise oxidation of the two ferrocenoyl groups. The crystal structure of 3 shows the difference in the chemical environment of the two Fc groups, one being attached to the α-N and one being attached to the ε-N of the imidazole of histidine. There is no discernible intermolecular interaction present in the crystal structure.

RNase Activity of a DNA Minor Groove Binder with a Minimalist Catalytic Motif from RNase A

Imidazole and compounds containing imidazole residues have been shown to cleave RNA in an RNase A-mimicking manner. Di-imidazole lexitropsin is a compound which is derived from the polyamide drugs distamycin and netropsin essentially by the replacement of two pyrrole heterocycles with N-methyl-imidazole residues. This enables it to bind to the minor groove of B-DNA in a sequence-specific manner. We demonstrate here that this lexitropsin derivative has RNA cleavage activity, as tested on model RNAs. Optimal cleavage conditions and cleavage specificity resemble those known from other imidazole conjugates and are thus consistent with an RNase A type cleavage mechanism. The optimum concentration of the compound for cleavage is similar to previously investigated imidazole-based RNase mimics. As a whole new class of chemical compounds capable of interacting with nucleic acids through extensive hydrogen bonding, these imidazole containing compounds constitute promising scaffolds and ligands, for the construction of novel RNase mimics with high affinity.

Preparation of an IMI dye (imidazole functional group) containing a 4-( N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole fluorophore for labeling of phosphomonoesters

We are studying dye–imidazole conjugates (“IMI dyes”) as reagents for labeling phosphomonoesters such as nucleotides. Previously we have employed a BODIPY dye in our IMI reagents, and analyzed the labeled products by capillary electrophoresis with laser-induced fluorescence detection (CE–LIF) involving an argon ion laser. (The BODIPY fluorophore is a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene). Here we broaden the technology by preparing a DBD–IMI dye [DBD=4-( N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole], and using a helium–cadmium laser. While DBD–IMI (IMI3) is about 50× more stable photolytically than a BODIPY–IMI dye (IMI2, a conjugate of a BODIPY dye with histamine, was tested), the detection limit for IMI2 (5·10 −11 M; S/ N=5, CE–LIF with an argon ion laser) is tenfold better than that for IMI3 (5·10 −10 M, S/ N=5, helium–cadmium laser). IMI3 conjugates of the four major DNA nucleotides were prepared and detected by CE–LIF.