BODIPY-Based Fluorescent Probes for Selective Visualization of Endogenous Hypochlorous Acid in Living Cells via Triazolopyridine Formation.

In this work, the two pyridylhydrazone-tethered BODIPY compounds (2 and 3) were synthesized. These compounds aimed to detect hypochlorous acid (HOCl) species via cyclic triazolopyridine formation. The open forms and the resulting cyclic forms of BODIPYs (2, 3, 4, and 5) were fully characterized by nuclear magnetic resonance, mass spectrometry, infrared spectroscopy, and single-crystal X-ray diffraction. These two probes can selectively detect HOCl through a fluorescence turn-on mechanism with the limit of detections of 0.21 µM and 0.77 µM for compounds 2 and 3, respectively. This fluorescence enhancement phenomenon could be the effect from C = N isomerization inhibition due to HOCl-triggered triazolopyridine formation. In cell imaging experiments, these compounds showed excellent biocompatibility toward RAW 264.7 murine live macrophage cells and greatly visualized endogenous HOCl in living cells stimulated with lipopolysaccharide.

Nitric Oxide Decomposition via Selective Catalytic Reduction by Ammonia on a Transition-Metal Cluster of W2TcO6.

Decomposition of nitric oxide (NO) gas on a reactive transition-metal cluster of W2TcO6 has been examined and investigated via selective catalytic reduction by ammonia (NH3-SCR) using the M06-L density functional method. The transition-metal cluster of W2TcO6 can be employed to transform NO to N2 gas efficiently over an active site of tungsten (W). A reaction mechanism of NO conversion based on the NH3-SCR process has been elucidated by a potential energy surface along the reaction pathways. The reaction pathways of this NH3-SCR process begin with adsorption of NH3, adsorption of NO to the cluster, formation of nitrosamine (NH2NO) and NHNO/NHNOH intermediates, and rearrangement of NHNO/NHNOH to obtain N2 and H2O, respectively. Notably, a significant NH2NO as a key intermediate, namely, "nitrosamine", must be formed before further steps can take place in the generation of N2 from NO, followed by the involvement of the NHNO or NHNOH intermediate. From our calculated results, the NHNO intermediate via TS3a is found in pathway a, while NHNOH is found in pathway b via TS3b. Pathway b has a lower energy barrier of 35.1 kcal/mol than pathway a with an energy barrier of 41.8 kcal/mol, indicating that pathway b should be more energetically favorable. The step for NHNO intermediate rearrangement is a rate-determining step for the reaction occurring through pathway a, which is found to be more difficult in accordance with a difficult N-H bond cleavage to form the NNOH intermediate before N2 formation. The overall reaction is an exothermic process with thermodynamic and kinetic favors. Thus, this bimetallic W2TcO6 cluster could be used as a promising and active catalyst for NO decomposition via the NH3-SCR process to an eco-friendly gas, that is, N2.

Molecular design of benzo[c][1,2,5]thiadiazole or thieno[3,4-d]pyridazine-based auxiliary acceptors through different anchoring groups in D-π-A-A framework: A DFT/TD-DFT study.

Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, a novel series of D-π-A-A porphyrin sensitizers adsorbed on the TiO2 cluster has been investigated. The D-π-A-A configurations contained a donor of iminodibenzyl, π-linker of Zn-porphyrin, and two kinds of auxiliary acceptors (labeled as BT and TP), as well as five types of anchoring groups. The ground-state geometries, electronics, optics, and charge transfer properties of all free dyes including injection driving force (ΔGinj), regeneration energy (ΔGreg), and light-harvesting efficiency (LHE) were calculated. Additionally, reorganization energy (λtotal), electron affinity (EA), and ionization potential (IP) were also reported to confirm the transport properties of the designed dye. Furthermore, the interfacial system of dye@(TiO2)48 was further discussed to reveal the complexation energy of the system by considering the adsorption energy (Eads) between dyes and (TiO2)48. The results showed that the insertion of different auxiliary acceptors in the D-π-A-A motif and variations in the anchoring groups resulted in red-shift absorption along with the increase in photovoltaic properties. These results suggested that BT with the rhodanine-3-acetic acid group (BT4) and BT with 2-(1,1-dicyanomethylene)rhodanine group (BT5) and TP with the same rhodanine-3-acetic acid and 2-(1,1-dicyanomethylene)rhodanine groups (TP4 and TP5) had shown better properties among other candidates for DSSCs. BT4-BT5 and TP4-TP5 had pronounce effect on optical and charge transfer properties by showing small HOMO-LUMO gaps, red-shifted spectra (λmax), greater LHE and ICT characters, and maximum-negative Eads. Thus, our theoretical investigation using these auxiliary moieties can be helpful for the precise structural modifications and design for developing efficient dyes in dye-sensitized solar cells (DSSCs).

Effect of Water Microsolvation on the Excited-State Proton Transfer of 3-Hydroxyflavone Enclosed in γ-Cyclodextrin.

The effect of microsolvation on excited-state proton transfer (ESPT) reaction of 3-hydroxyflavone (3HF) and its inclusion complex with γ-cyclodextrin (γ-CD) was studied using computational approaches. From molecular dynamics simulations, two possible inclusion complexes formed by the chromone ring (C-ring, Form I) and the phenyl ring (P-ring, Form II) of 3HF insertion to γ-CD were observed. Form II is likely more stable because of lower fluctuation of 3HF inside the hydrophobic cavity and lower water accessibility to the encapsulated 3HF. Next, the conformation analysis of these models in the ground (S0) and the first excited (S1) states was carried out by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, respectively, to reveal the photophysical properties of 3HF influenced by the γ-CD. The results show that the intermolecular hydrogen bonding (interHB) between 3HF and γ-CD, and intramolecular hydrogen bonding (intraHB) within 3HF are strengthened in the S1 state confirmed by the shorter interHB and intraHB distances and the red-shift of O-H vibrational modes involving in the ESPT process. The simulated absorption and emission spectra are in good agreement with the experimental data. Significantly, in the S1 state, the keto form of 3HF is stabilized by γ-CD, explaining the increased quantum yield of keto emission of 3HF when complexing with γ-CD in the experiment. In the other word, ESPT of 3HF is more favorable in the γ-CD hydrophobic cavity than in aqueous solution.

Theoretical Prediction and Analysis of the UV/Visible Absorption and Emission Spectra of Chiral Carbon Nanorings.

UV/vis absorption and emission spectra of recently synthesized chiral carbon nanorings were simulated using first-principles-based molecular dynamics and time-dependent density functional theory (TD-DFT). The chiral carbon nanorings are derivatives of the [ n]cycloparaphenylene ([ n]CPP) macrocycles, containing an acene unit such as naphthalene, ([ n]CPPN), anthracene ([ n]CPPA), and tetracene ([ n]CPPT), in addition to n paraphenylene units. In order to study the effect of increasing molecular size on absorption and emission spectra, we investigated the cases where n = 6 and 8. Frontier molecular orbital analysis was carried out to give insight into the degree of excitation delocalization and its relationship to the predicted absorption spectra. The lowest excited singlet state S1 corresponds to a HOMO-LUMO π-π* transition, which is allowed in all chiral carbon nanorings due to lack of molecular symmetry, in contrast to the forbidden HOMO-LUMO transition in the symmetric [ n]CPP molecules. The S1 absorption peak exhibits a blue-shift with increasing number of paraphenylene units in particular for [ n]CPPN and [ n]CPPA and less so in the case of [ n]CPPT. In the case of CPPN and CPPA, the transition density is mainly localized over a semicircle of the macrocycle with the acene unit in its center but is strongly localized on the tetracene unit in the case of CPPT. Molecular dynamics simulations performed on the excited state potential energy surfaces reveal red-shifted emission of these chiral carbon nanorings when the size of the π-conjugated acene units is increased, although the characteristic [ n]CPP blue-shift with increasing paraphenylene unit number n remains apparent. The anomalous emission blue-shift is caused by the excited state bending and torsional motions that stabilize the π HOMO and destabilize the π* LUMO, resulting in an increasing HOMO-LUMO gap.

Theoretical Insights on Solvent Control of Intramolecular and Intermolecular Proton Transfer of 2-(2'-Hydroxyphenyl)benzimidazole.

Excited-state proton transfer (ESPT) processes of 2-(2'-hydroxyphenyl)benzimidazole (HBI) and its complexation with protic solvents (H2O, CH3OH, and NH3) have been investigated by both static calculations and dynamics simulations using density functional theory (DFT) at B3LYP/TZVP theoretical level for ground state (S0) and time-dependent (TD)-DFT at TD-B3LYP/TZVP for excited state (S1). For static calculations, absorption and emission spectra, infrared (IR) vibrational spectra of O-H mode, frontier molecular orbitals (MOs), and potential energy curves (PECs) of proton transfer coordinate were analyzed. Simulated absorption and emission spectra show an agreement with available experimental data. The hydrogen bond strengthening in the S1 state has been proved by the changes of IR vibrational spectra and bond parameters of the hydrogen moiety with those of the S0 state. The MOs provide the visual electron density redistribution confirming the hydrogen bond strengthening mechanism. The PECs show that the proton transfer (PT) process is easier to occur in the S1 state than the S0 state. Moreover, on-the-fly dynamics simulations of all systems were carried out to provide the detailed information on time revolution. The results revealed that the excited-state intermolecular proton transfer for HBI is fast, whereas the excited-state intermolecular proton transfer for HBI with protic solvents are slower than that of HBI because the competition between intra- and intermolecular hydrogen-bonds between HBI and protic solvent. These intermolecular hydrogen-bonds hinder the formation of tautomer, hence explaining the low quantum yield found in the protic solvent experiment. Especially for HBI complexing with methanol, only ESIntraPT occurs with small probability compared to HBI with water and ammonia.

TD-DFT Study of Absorption and Emission Spectra of 2-(2'-Aminophenyl)benzothiazole Derivatives in Water.

Reduction of aromatic azides to amines is an important property of hydrogen sulphide (H2S) which is useful in fluorescence microscopy and H2S probing in cells. The aim of this work is to study the substituent effect on the absorption and emission spectra of 2-(2'-aminophenyl)benzothiazole (APBT) in order to design APBT derivatives for the use of H2S detection. Absorption and emission spectra of APBT derivatives in aqueous environment were calculated using density functional theory (DFT) and time-dependent DFT (TD-DFT) at B3LYP/6-311+G(d,p) level. The computed results favoured the substitution of strong electron-donating group on the phenyl ring opposite to the amino group for their large Stokes' shifts and emission wavelengths of over 600 nm. Also, three designed compounds were suggested as potential candidates for the fluorescent probes. Such generalised guideline learnt from this work can also be useful in further designs of other fluorescent probes of H2S in water.

Excited-state intermolecular proton transfer reactions of 7-azaindole(MeOH)(n) (n = 1-3) clusters in the gas phase: on-the-fly dynamics simulation.

Ultrafast excited-state intermolecular proton transfer (PT) reactions in 7-azaindole(methanol)(n) (n = 1-3) [7AI(MeOH)(n=1-3)] complexes were performed using dynamics simulations. These complexes were first optimized at the RI-ADC(2)/SVP-SV(P) level in the gas phase. The ground-state structures with the lowest energy were also investigated and presented. On-the-fly dynamics simulations for the first-excited state were employed to investigate reaction mechanisms and time evolution of PT processes. The PT characteristics of the reactions were confirmed by the nonexistence of crossings between S(ππ*) and S(πσ*) states. Excited-state dynamics results for all complexes exhibit excited-state multiple-proton transfer (ESmultiPT) reactions via methanol molecules along an intermolecular hydrogen-bonded network. In particular, the two methanol molecules of a 7AI(MeOH)(2) cluster assist the excited-state triple-proton transfer (ESTPT) reaction effectively with highest probability of PT.

Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes.

The reaction of CoX2 (X = Cl, Br, NO3) with KTp(Ph2) in tetrahydrofuran (THF) yields the half-sandwich compounds [Tp(Ph2)CoX] (X = Cl 1, Br 2, NO3 3). The reaction of [Tp(Ph2)CoBr] with NaX (X = N3, NO2) or potassium thiocyanate (KNCS) permits isolation of [Tp(Ph2)CoX] (X = N3 4, NCS 5, NO2 6). In contrast, the reaction of cobalt(II) acetate with KTp(Ph2) yields [Tp(Ph2)CO(OAc)(Hpz(Ph2))] 7 as a result of B-N bond cleavage. Subsequent reaction of 7 with a range of beta-diketones in the presence of NaOMe produces the beta-diketonate complexes, [Tp(Ph2)Co(beta-diketonate)] (beta-diketonate = acac 8, hfac 9, dbm 10, tmhd 11). IR spectroscopy suggests that the Tp(Ph2) ligands are kappa3-coordinated and that the beta3-diketonate ligands adopt a bidentate coordination mode. Electronic spectra are consistent with four- or five-coordinate species in solution. X-Ray crystallographic studies of 7 reveal an intermediate five-coordinate cobalt centre with a hydrogen bonding interaction between the pyrazole hydrogen and the acetate carbonyl oxygen. The molecular structures of 9 and 10 show cobalt centres with square pyramidal coordination geometries and kappa2-coordinated beta-diketonate ligands. Cyclic voltammetric studies of 6 reveal irreversible one-electron reduction to Co(I). However, the beta-diketonate complexes, 8, 10 and 11 undergo irreversible one-electron oxidation. The redox potential and reversibility increases as the steric bulk of the substituent on the beta-diketonate ligand increases.