Spontaneous Deprotonation Research Articles

Red‐Shifting ESIPT Fluorescence by Site‐Specific Functionalization in 2‐(2’‐hydroxyphenyl)benzazole Derivatives

AbstractWe describe the synthesis, full photophysical study, and ab initio calculations of 2‐(2’‐hydroxyphenyl)benzazole (HBX) fluorophores substituted, at the meta position of the phenol group, by pyridine derivatives. HBX are commonly used as model dyes to study the stimuli‐induced modulation of the Excited State Intramolecular Proton Transfer (ESIPT) process. The meta‐substituted fluorophores reported herein, display a photophysical profile different from the previously reported ortho‐ and para‐substituted HBO pyridine isomers. Indeed, while all dyes undergo spontaneous deprotonation in neutral conditions, leading to highly emissive anionic species; upon protonation, ortho‐ and para‐pyridine substitution leads to resonance‐stabilized keto isomers, formed after ESIPT. Protonated meta derivatives, unable to stabilize their excited structure by such electronic delocalization process, display sizable intramolecular charge transfer (ICT) processes, translating into significantly redshifted emission. In addition, all dyes present a strong emission intensity, not only in neutral and acidic solutions, but also in the solid‐state. The nature of the emissive transitions was confirmed in each case by theoretical calculations combining Time‐Dependent Density Functional Theory (TD‐DFT) and second‐order Coupled Cluster (CC2) methods.

Supramolecular channels via crown ether functionalized polyaniline for proton-self-doped cathode in aqueous zinc-ion battery

Polyaniline (PANI) has been widely used as a cathode in aqueous zinc-ion batteries (AZIBs) because of its attractive conductivity and energy storage capability. However, the extensive application of PANI is limited by spontaneous deprotonation and slow diffusion kinetics. Herein, an 18-crown-6-functionalised PANI pseudorotaxane (18C6@PANI) cathode is successfully developed through a facile template-directed polymerisation reaction. The 18C6@PANI cathode exhibits a high specific capacity of 256 mAh g−1 at 0.2 A/g, excellent rate performance of 134 mAh g−1 at 6 A/g and outstanding cycle stability at a high current density of 3 A/g over 10,000 cycles. Experimental and theoretical analyses demonstrate the formation of the –N–Zn–O– structure. The abundant supramolecular channels in pseudorotaxane, induced by crown ether functional groups, are beneficial for achieving superior cyclability and rate capability. These encouraging results highlight the potential for designing more efficient PANI-based cathodes for high-performance AZIBs.

Substrate binding and catalytic mechanism of the Se-glycosyltransferase SenB in the biosynthesis of selenoneine

Selenium is an essential multifunctional trace element in diverse organisms. The only Se-glycosyltransferase identified that catalyzes the incorporation of selenium in selenoneine biosynthesis is SenB from Variovorax paradoxus. Although the biochemical function of SenB has been investigated, its substrate specificity, structure, and catalytic mechanism have not been elucidated. Here, we reveal that SenB exhibits sugar donor promiscuity and can utilize six UDP-sugars to generate selenosugars. We report crystal structures of SenB complexed with different UDP-sugars. The key elements N20/T23/E231 contribute to the sugar donor selectivity of SenB. A proposed catalytic mechanism is tested by structure-guided mutagenesis, revealing that SenB yields selenosugars by forming C-Se glycosidic bonds via spontaneous deprotonation and disrupting Se-P bonds by nucleophilic water attack, which is initiated by the critical residue K158. Furthermore, we functionally and structurally characterize two other Se-glycosyltransferases, CbSenB from Comamonadaceae bacterium and RsSenB from Ramlibacter sp., which also exhibit sugar donor promiscuity.

Syntheses and Structures of Arenethiolato Cobalt(II) Complexes Containing Acylamino Groups: Steric Effects of Bulky Ligands on Coordination and Geometry.

Bulky thiolato ligands have been developed for creating biomimetic model complexes of active sites in metalloenzymes. Herein, we report a series of di-ortho-substituted arenethiolato ligands containing bulky acylamino groups (RCONH; R = t-Bu-, (4-t-BuC6H4)3C-,{3,5-(Me2CH)2C6H3}3C-, and {3,5-(Me3Si)2C6H3}3C-) that were developed for biomimetics. Bulky hydrophobic substituents generate a hydrophobic space around the coordinating sulfur atom through the NHCO bond. This steric environment induces the formation of low-coordinate mononuclear thiolato Co(II) complexes. The well-positioned NHCO moieties in the hydrophobic space coordinate to the vacant sites of the cobalt center with different coordination modes, viz., the S,O-chelate of the carbonyl C═O or the S,N-chelate of the acylamido CON-. The solid (crystalline) and solution structures of the complexes were investigated in detail using single-crystal X-ray crystallography, 1H NMR, and absorption spectroscopic analyses. The spontaneous deprotonation of NHCO, which is commonly observed in metalloenzymes but requires a strong base in artificial systems, was simulated by forming a hydrophobic space in the ligand. This new ligand design strategy is advantageous for creating model complexes that have never been constructed artificially.

Pithecellobium dulce Leaf-Derived Carbon Dots for 4-Nitrophenol and Cr(VI) Detection

Luminescent carbon dots (CDs) synthesized from Pithecellobium dulce (P. Dulce) leaves, in a simple, single-step carbonization procedure, were used as optical nanosensors. TEM revealed the crystalline nature of the CDs with the average dimension of 20 nm with a quantum yield of 24%. In addition to carbon, the X-ray photoelectron spectroscopy shows the presence of oxygen and nitrogen. The FTIR spectra and Zeta potential were used for additional characterization of the nanoprobes. Among the contaminants and heavy metals, the proposed nanoprobes were found to be selective towards 4-nitrophenol (4-NP) and Cr(VI), respectively. The emission response of CDs towards 4-NP solution not only reveals the high sensitivity of the CDs (Limit of detection (LOD) of 14 nM) but also demonstrates a color change (light to dark yellow) that is attributed to spontaneous deprotonation detectable with the naked eye. The selectivity of CDs towards Cr(VI) (LOD 0.9 nM) was also tested in the presence of other metals. The quenching mechanism has been attributed to the inner filter effect for both analytes. The observed low detection limits in river and tap water opens up the possible applicability of the proposed nanoprobes as optical sensors in environmental pollution monitoring.

Adsorption structures of catechol on the ZnO(10-10) surface

The details of catechol interacting with the ZnO surfaces are critical for understanding how the organic chromophores anchor on and hence functionalize the ZnO materials. In this work, we apply low-temperature scanning tunneling microscopy (LT-STM) in combination with density functional theory (DFT) calculations to investigate the adsorption state and interface charge transfer of catechol on a ZnO(10-10) surface. For the molecules deposited at liquid nitrogen temperature, the fully-protonated (FP) status prevails in the isolated molecules despite the synergistic formation of half-protonated (HP) and fully-deprotonated (FD) ones. However, annealing to elevated temperature drives all the molecules to assemble into either linear or a c(2 × 2) superstructure composed of only FD catechols. Such spontaneous deprotonation of catechol is different from the predicted water-assisted process and plays critical roles in switching the catechol from electron acceptors to electron donors relative to the ZnO surface. These results may bring new insights into the design of optoelectronic and biomedical applications of the ZnO-organic compositional system.

Computational Insights into the Catalytic Mechanism of Is-PETase: An Enzyme Capable of Degrading Poly(ethylene) Terephthalate.

Is-PETase has become an enzyme of significant interest due to its ability to catalyse the degradation of polyethylene terephthalate (PET) at mesophilic temperatures. We performed hybrid quantum mechanics and molecular mechanics (QM/MM) at the DSD-PBEP86-D3/ma-def2-TZVP/CHARMM27//rev-PBE-D3/dev2-SVP/CHARMM level to calculate the energy profile for the degradation of a suitable PET model by this enzyme. Very low overall barriers are computed for serine protease-type hydrolysis steps (as low as 34.1 kJ mol-1 ). Spontaneous deprotonation of the final product, terephthalic acid, with a high computed driving force indicates that product release could be rate limiting.

Framework robustness in early d-block metal complexes with tripodal polyalcohol ligands

While performing our research on the tetranuclear “star-shaped” complexes formulated as [M3M'(LR)2(dpm)6], where M, M' are first-row d-block metals; H3LR is a tripodal alcohol, RC(CH2OH)3, with R = Et, Me or Ph; and Hdpm = dipivaloylmethane, we isolated a series of binuclear, alkoxide-bridged chelate complexes of titanium and chromium upon spontaneous deprotonation of the polyalcohol. In the titanium system, both [TiIII2Cl4(H2LEt)2]·4thf and [TiIV2Cl4(HLEt)2]·2thf were identified; they present analogous binuclear frameworks but distinct metal oxidation states and polyalcohol deprotonation degrees. Four similar CrIII2 compounds were also isolated, differing in the tripodal R groups and cocrystallized solvent or proligand molecules. The products were characterized by single-crystal X-ray diffraction analysis and spectroscopic, thermogravimetric and magnetic measurements. Cocrystallization influences the nature, strength and pattern of intermolecular interactions. Among the binuclear MIII products, all those containing solvating tetrahydrofuran, [M2Cl4(H2LR)2]·x thf (R = Et, Ph; x = 4 or 5 respectively), lose solvent upon gradual polyalcohol deprotonation, mild heating or vacuum drying. The versatile tripodal skeleton assembles the alkoxide-bridged M2 units (M = TiIII/IV or CrIII) in various experimental conditions, including air or inert atmosphere and non-protic or protic media, and confers remarkable robustness to the final binuclear aggregates.

Transformation of Supramolecular Membranes to Vesicles Driven by Spontaneous Gradual Deprotonation on Membrane Surfaces

The various proteins and asymmetric lipid bilayers present in cell membranes form curvatures, resulting in structural transformations to generate vesicles. Fission and fusion processes between vesicles and cell membranes are reversible in living organisms. Although the transformation of a two-dimensional membrane to a three-dimensional vesicle structure is a common natural phenomenon, the lack of a detailed understanding at the molecular level limits the development of synthetic systems for functional materials. Herein, we report a supramolecular membrane system through donor-acceptor interactions using a π-deficient acceptor and π-rich donor as building blocks. The reduced electrostatic repulsion between ammonium cations and the spontaneously deprotonated neutral amino group induced anisotropic membrane curvature, resulting in membrane fission to form vesicles with a detailed understanding at the molecular level. Furthermore, the reversible transformation of vesicles to membranes upon changing the pH provides a novel synthetic system exhibiting both fission and fusion processes.

Polyaniline-functionalized graphene composite cathode with enhanced Zn2+ storage performance for aqueous zinc-ion battery

Polyaniline (PANI) as a typical conductive polymer has been widely applied in cathode materials of aqueous zinc ion battery (AZIB), owing to the features of high electronic conductivity and simple synthesized methods. However, the cycling instability caused of spontaneous deprotonation still limited the extensive application of PANI cathode materials. In this work, a functionalized commercial graphene (MEG) and PANI composite (MGP-1) was successfully assembled by a facile two-step method. When the MGP-1 acted as cathode material in AZIB, it demonstrated a high capacity of 184.5 mAh/g (0.2 A/g) and excellent rate performance of 137.6 mAh/g (3 A/g) compared to the PANI cathode. The corresponding analysis revealed that the boosted electrochemical behavior of MGP-1 was attributed to the large conductive network fabricated by the MEG and PANI, and the formations of -N-Zn-O- structures during discharging process. Moreover, based on the conventional H+ insertion mechanism, this work furtherly provided a H+ and Zn2+ insertion mechanism. In addition, the utilization of cheap and abundant commercial graphene would allow the graphene/polyaniline composite to be a promising cathode material applied in AZIB.

Sulfur and Phosphorus Oxyacid Radicals.

We report a computational study of the little-studied neutral bisulfite, bisulfate, dihydro-phosphite, and dihydro-phosphate radicals (HSOx•, H2POx•, x = 3,4), calling special attention to their various tautomeric structures together with pKa values estimated from the Gibbs free energies of their dissociations (at the G4 and CAM-B3LYP levels of density functional theory). The energetics of microhydration clusters with up to four water molecules for the S-based species and up to eight water molecules for the P-based species were investigated. The number of microhydrating water molecules needed to induce spontaneous de-protonation is found to correlate the acid strength of each radical. According to the computed Gibbs free reaction and activation energies, S- and P-centered radicals preferentially add to the double bond of propene (a lipid model), whereas the O-centered radical tautomers prefer H-abstraction. The likely downstream reactions of these radicals in biological media are discussed.

D-[formula omitted]-A dye attached on TiO2(101) and TiO2(001) surfaces: Electron transfer properties from ab initio calculations

The stability, electronic, and transfer properties of a photo-sensitizer donor-(π-bridge)-acceptor (D-π-A) zinc-porphyrin dye adsorbed on anatase TiO2(101) and TiO2(001) surfaces are studied by periodic density functional theory calculations, including the screened hybrid functional. We also study the dye adsorption on the TiO2(101) surface with an oxygen vacancy. Our results show that the deprotonated dye attaches strongly on surface Ti5c atoms forming both bidentate bridging and chelating linkage modes. The protonated dye is found stable on pristine TiO2(101), forming the monodentate linkage mode. However, on TiO2(001) and defective TiO2(101), the monodentate mode stabilizes after a spontaneous dye deprotonation. The electronic band structure of the TiO2-dye assemblies shows the dye lowest-unoccupied molecular-orbital resonant with TiO2 conduction bands, exhibiting a strong hybridization, where the electron injection potentials are calculated around 1 eV for all systems under study. This high value, together with the favorable electronic coupling, suggest a fast electron injection from the dye into the semiconductor as experimentally reported. Moreover, the electronic properties of TiO2-dye assemblies show similarities independent of the adsorption modes or the surface characteristic, suggesting that the high efficiency of anatase TiO2-based dye sensitized solar cell resides largely in its favorable electron injection properties.

Reaction mechanism and dynamics for C8-hydroxylation of 9-methylguanine radical cation by water molecules.

In contrast to their spontaneous deprotonation in aqueous solution, reactions of guanine and guanosine radical cations with water in the gas phase are exclusively initiated by hydration of the radical cations as reported in recent work (Y. Sun et al., Phys. Chem. Chem. Phys., 2018, 20, 27510). As gas-phase hydration reactions closely mimic the actual scenario for guanine radical cations in double-stranded DNA, exploration of subsequent reactions within their water complexes can provide an insight into the resulting oxidative damage to nucleosides. Herein guided-ion beam mass spectrometry experiment and direct dynamics trajectory simulations were carried out to examine prototype complexes of the 9-methylguanine radical cation with one and two water ligands (i.e., 9MG˙+·(H2O)1-2) in the gas phase, wherein the complexes were activated by collisional activation in the experiment and by thermal excitation at high temperatures in the simulations. Guided by mass spectroscopic measurements, trajectory results and reaction potential energy surface, three reaction pathways were identified. The first two reaction pathways start with H-atom abstraction from water by the O6 and N7 atoms in 9MG˙+ and are referred to as HAO6 and HAN7, respectively. The primary products of HAO6 and HAN7 reactions, including [9MG + HO6]+/[9MG + HN7]+ and ˙OH, react further to either form [8OH-9MG + HO6]˙+ and [8OH-9MG + HN7]˙+via C8-hydroxylation or form radical cations of 6-enol-guanine (6-enol-G˙+) and 7H-guanine (7HG˙+) via SN2-type methanol elimination. The third reaction pathway corresponds to the formation of 8OH-9MG+ by H elimination from the complex, referred to as HE. Among these product channels, [8OH-9MG + HN7]˙+ has the most favorable formation probability, especially in the presence of additional water molecules. This product may serve as a preceding structure to the 8-oxo-7,8-dihydroguanine lesion in DNA and has implications for health effects of radiation exposure and radiation therapy.

Development of Ru(bpy)32+-amisulpride electrogenerated chemiluminescence system for ultrasensitive and selective detection of amisulpride in pharmaceuticals and real plasma

In this study, a new electrogenerated chemiluminescence (ECL) reaction is presented through an oxidative-reductive pathway for amisulpride (AMS) as a new coreactant and Ru(bpy)32+ luminophore for the first time. The unique chemical structure of AMS through the presence of electroactive tertiary amino group in combination with the presence bulky electron donating group attached to α‑carbon of its amino group demonstrates the dramatic increase in ECL intensity of luminophore. Upon electrochemical oxidation of both the AMS and Ru(bpy)32+, the electrogenerated AMS+ undergoes spontaneous deprotonation to produce strong reductant that is reacted with electrogenerated Ru(bpy)33+ for excited state production. The developed method presented highly sensitive, selective, rapid, simple and cost-effective ECL approach for AMS detection. Under optimized parameters, the ECL-concentration plot showed a good linear relationship between ECL intensity and AMS concentrations in presence of 1.0 mM Ru(bpy)32+ over the concentration range of (5.0 × 10−10–2.0 × 10−7 M) with a lower detection limit of 7.6 × 10−9 M and a lower quantification limit of 2.51 × 10−8 M. The developed ECL method is successfully utilized for the determination of AMS in Amipride tablets and real human plasma.

Designing a highly stable coordination-driven metallacycle for imaging-guided photodynamic cancer theranostics.

Coordination-driven self-assembly features good predictability and directionality in the construction of discrete metallacycles and metallacages with well-defined sizes and shapes, but their medicinal application has been limited by their low stability and solubility. Herein, we have designed and synthesized a highly stable coordination-driven metallacycle with desired functionality derived from a perylene-diimide ligand via a spontaneous deprotonation self-assembly process. Brilliant chemical stability and singlet oxygen production ability of this emissive octanuclear organopalladium macrocycle make it a good candidate toward biological studies. After cellular uptake by endocytosis, the metallacycle exhibits potent fluorescence cell imaging properties and cancer photodynamic therapeutic ability through enhancing ROS production, with high biocompatibility and safety. This study not only provides a rational design strategy for highly stable luminescent organopalladium metallacycles, but also sheds light on their application in imaging-guided photodynamic cancer therapy.

Conjugated System of PEDOT:PSS-Induced Self-Doped PANI for Flexible Zinc-Ion Batteries with Enhanced Capacity and Cyclability.

Owing to its electronic conductivity and electrochemical reactivity, polyaniline (PANI) can serve as the cathode for rechargeable zinc-ion batteries (ZIBs). However, it suffers from fast deactivation and thus performance deterioration because of spontaneous deprotonation during charge/discharge. Here, we report an effective strategy to improve the electrochemical reactivity and stability of the PANI-based cathode by constructing a π-electron conjugated system between PANI and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on carbon nanotubes (CNTs). The impressive performance of the post-treated CNTs-PANI-PEDOT:PSS (t-CNTs-PA-PE) cathode is largely attributed to the -SO3-H+ groups in PSS, which acts as an internal proton reservoir and provides enough H+ for PANI's protonation, thus promoting its electrochemical activity and reversibility. Besides, the strong interactions between PANI and PEDOT:PSS assist the stretching of π-π conjugation chains, bringing about enhanced electronic conductivity. Consequently, the t-CNTs-PA-PE cathode achieves a high capacity of 238 mA h g-1, together with good rate capability and long-term stability (over 1500 cycles with 100% Coulombic efficiency). Through exerting the freestanding t-CNTs-PA-PE, a flexible ZIB was further constructed with both outstanding electrochemical properties and superior high safety. This work demonstrates the availability of conducting polymer cathodes for high-performance ZIBs, fulfilling the need of flexible electronics.

Molecular and Structural Characterization of a Promiscuous C‐Glycosyltransferase from Trollius chinensis

AbstractHerein, the catalytic promiscuity of TcCGT1, a new C‐glycosyltransferase (CGT) from the medicinal plant Trollius chinensis is explored. TcCGT1 could efficiently and regio‐specifically catalyze the 8‐C‐glycosylation of 36 flavones and other flavonoids and could also catalyze the O‐glycosylation of diverse phenolics. The crystal structure of TcCGT1 in complex with uridine diphosphate was determined at 1.85 Å resolution. Molecular docking revealed a new model for the catalytic mechanism of TcCGT1, which is initiated by the spontaneous deprotonation of the substrate. The spacious binding pocket explains the substrate promiscuity, and the binding pose of the substrate determines C‐ or O‐glycosylation activity. Site‐directed mutagenesis at two residues (I94E and G284K) switched C‐ to O‐glycosylation. TcCGT1 is the first plant CGT with a crystal structure and the first flavone 8‐C‐glycosyltransferase described. This provides a basis for designing efficient glycosylation biocatalysts.

Molecular and Structural Characterization of a Promiscuous C-Glycosyltransferase from Trollius chinensis.

Herein, the catalytic promiscuity of TcCGT1, a new C-glycosyltransferase (CGT) from the medicinal plant Trollius chinensis is explored. TcCGT1 could efficiently and regio-specifically catalyze the 8-C-glycosylation of 36 flavones and other flavonoids and could also catalyze the O-glycosylation of diverse phenolics. The crystal structure of TcCGT1 in complex with uridine diphosphate was determined at 1.85 Å resolution. Molecular docking revealed a new model for the catalytic mechanism of TcCGT1, which is initiated by the spontaneous deprotonation of the substrate. The spacious binding pocket explains the substrate promiscuity, and the binding pose of the substrate determines C- or O-glycosylation activity. Site-directed mutagenesis at two residues (I94E and G284K) switched C- to O-glycosylation. TcCGT1 is the first plant CGT with a crystal structure and the first flavone 8-C-glycosyltransferase described. This provides a basis for designing efficient glycosylation biocatalysts.

New mechanistic insights into osmium-based tamoxifen derivatives

The electrochemical behavior of osmociphenol (3, Oc-OH), an organometallic osmium-based anticancer drug candidate, has been investigated by cyclic voltammetry in the absence and presence of lutidine used as a base model. Osmociphenol exhibited spontaneous deprotonation of the phenol function upon oxidation of the osmocene moiety due to its high acidity. In the presence of lutidine, a base-dependent and different electrochemical behavior was observed at low scan rates indicating a second oxidation step leading to the corresponding cationic quinone methide precursor (3b+). However, compared to ruthenocene derivatives, the stability of 3b+ prevented its conversion into quinone methide as the final and stable complex. Despite differences in their oxidative processes, osmociphenol and ruthenociphenol derivatives exhibit similar biological activities.

The symmetry breaking phenomenon in heteronine analogues due to the pseudo Jahn-Teller effect.

The pseudo Jahn-Teller effect (PJTE) is employed in C8AH8 (A = O, S, Se, Te), and C8EH8 + 1 (E = N, P, As, Sb) with planar configurations to show symmetry breaking phenomena (SBP) in heteronine analogues, and to explain why molecules with (C2v) high-symmetry configurations cannot maintain planarity and pucker to their (C2) and (Cs) lower-symmetry structures, respectively. To investigate this phenomenon, geometry optimization and frequency calculations through the density functional B3LYP method using the cc-pVTZ basis set (for Te, and Sb cc-pVTZ-PP) were carried out for all compounds in the series. The state average-complete active space self-consistent field wave-function method was employed to calculate the electronic ground and several low-lying excited states to specify the adiabatic potential energy surface along the a2 and b1 puckering nuclear displacements. The PJTE (A1 + A2 + A1') a2 and (A1 + B1 + A1') b1 problems were formulated as the effects originating via the PJTE theorem. Moreover, replacing hydrogen atoms in C8NH9, a stable planar structure, with fluorine ligands demonstrated that SBP occur from C2v to C2 symmetry. Furthermore, thermochemical calculations via B3LY/cc-pVTZ illustrated that the planarity of the C8E ring is restored in C8EH8- (E = P, As, Sb) anions ,with the change in free energy corresponding to spontaneous deprotonation reactions as 23.67kJmol-1, 21.88kJmol-1, and 16.57kJmol-1, respectively. In fact, despite C8EH8 + 1 having a donor electron-pair and potentially being Lewis base compounds, it acts as a Bronsted-Lowry acid releasing a H+ proton instead in this case.