OH Unit Research Articles

Synthesis, characterization and reactivity of a Mn(III)–hydroxido complex as a biomimetic model for lipoxygenase

Manganese hydroxido (Mn–OH) complexes supported by a tripodal N,N′,N″-[nitrilotris(ethane-2,1-diyl)]tris(P,P-diphenylphosphinic amido) ([poat]3−) ligand have been synthesized and characterized by spectroscopic techniques including UV–vis and electron paramagnetic resonance (EPR) spectroscopies. X-ray diffraction (XRD) methods were used to confirm the solid-state molecular structures of {Na2[MnIIpoat(OH)]}2 and {Na[MnIIIpoat(OH)]}2 as clusters that are linked by the electrostatic interactions between the sodium counterions and the oxygen atom of the ligated hydroxido unit and the phosphinic (P=O) amide groups of [poat]3−. Both clusters feature two independent monoanionic fragments in which each contains a trigonal bipyramidal Mn center that is comprised of three equatorial deprotonated amide nitrogen atoms, an apical tertiary amine, and an axial hydroxido ligand. XRD analyses of {Na[MnIIIpoat(OH)]}2 also showed an intramolecular hydrogen bonding interaction between the MnIII–OH unit and P=O group of [poat]3−. Crystalline {Na[MnIIIpoat(OH)]}2 remains as clusters with Na+---O interactions in solution and is unreactive toward external substrates. However, conductivity studies indicated that [MnIIIpoat(OH)]− generated in situ is monomeric and reactivity studies found that it is capable of cleaving C-H bonds, illustrating the importance of solution-phase speciation and its direct effect on chemical reactivity.Synopsis: Manganese–hydroxido complexes were synthesized to study the influence of H-bonds in the secondary coordination sphere and their effects on the oxidative cleavage of substrates containing C-H bonds.

An Air and Moisture Stable Boat Shaped Hydroxo‐Bridged Ruthenium(II) Binuclear Complex for the Catalytic Hydrogenation of CO2

AbstractA new hydroxo‐bridged ruthenium (II) complex [{Ru(η6‐p‐cymene)(iPr2P−O)}2(μ‐OH)]Cl (2) has fortuitously been isolated from the reaction between the known ruthenium(II) complex [RuCl2(η6‐p‐cymene)(iPr2P‐OH)] (1) in either CDCl3 or CHCl3 solutions in the presence of excess DBU (1,8‐diazabicyclo(5.4.0)undec‐7‐ene) at room temperature. Complex 2 is only formed under specific conditions as an orange‐colored air and moisture stable binuclear complex. It is formed via the deprotonation of the P−OH unit in [RuCl2(η6‐p‐cymene)(iPr2P‐OH)]. Complex 2 has been fully characterized by spectroscopic and analytical methods. Its structure was determined by single crystal X‐ray diffraction which reveals a boat‐shaped motif containing a bridging hydroxide unit which undergoes hydrogen bonding with a chloride counterion. Complex 2 was utilized as a catalyst for the hydrogenation of CO2 to formic acid salt using molecular hydrogen. The catalytic reactions were performed at 100 °C in THF in the presence of DBU as a base to isolate [DBU+H][OC(O)H] salt as the final product. Using catalyst loadings down to 0.01 mol%, it was possible to hydrogenate gaseous CO2 with TONs up to 9900.

Valence Tautomerism Induced Proton Coupled Electron Transfer:X−H Bond Oxidation with a Dinuclear Au(II) Hydroxide Complex

AbstractWe report the preparation and characterization of the dinuclear AuII hydroxide complex AuII2(L)2(OH)2 (L=N,N′‐bis (2,6‐dimethyl) phenylformamidinate) and study its reactivity towards weak X−H bonds. Through the interplay of kinetic analysis and computational studies, we demonstrate that the oxidation of cyclohexadiene follows a concerted proton‐coupled electron transfer (cPCET) mechanism, a rare type of reactivity for Au complexes. We find that the Au−Au σ‐bond undergoes polarization in the PCET event leading to an adjustment of oxidation levels for both Au centers prior to C(sp3)−H bond cleavage. We thus describe the oxidation event as a valence tautomerism‐induced PCET where the basicity of one reduced Au−OH unit provides a proton acceptor and the second more oxidized Au center serves as an electron acceptor. The coordination of these events allows for unprecedented radical‐type reactivity by a closed shell AuII complex.

Bromine atom introduction improves the F- sensing ability of an indolo[3,2-b]carbazole-salicylaldehyde-based fluorescence turn-on sensor.

The heavy-atom effect usually quenches fluorescence, but scarcely enhances it. Herein, fluorescence turn-on sensors without or with a bromine atom for F- detection are presented, achieving fast response time within 1 min, and the LODs of 1.9 × 10-7 and 8.5 × 10-8 M, reflecting that halogen atom introduction is beneficial for F- detection ability improvement. The sensing mechanism of -OH unit deprotonation is confirmed based on the results of a 1 : 2 stoichiometric ratio, 1H NMR titration and TD-DFT calculation. The water environment F- detection and spiked recovery experiments demonstrate their potential for real sample detection.

Light-up, colorimetric anion sensing and fingerprint visualization using the salicylaldehyde-based aggregation-induced emission-active phosphorescent Pt(II) complexes formed by restricting the molecular configuration transformations

Developments of the AIE phosphorescent metal complexes are behind to these of pure organic AIEgens. Herein, Two AIE-active phosphorescent Pt(II) complexes applicating in anion detection and fingerprint visualization are reported. The distinct emission differences between dilute solutions and aggregated states manifest their AIE natures, supporting by the THF-H2O and film emission measurements. Importantly, it demonstrates that molecular configuration transformation (MCT) from the square planarity to the tetrahedron and the intramolecular rotation induce non-radiations of S1 and T1 states, thus almost no emissions of their dilute solutions. Upon aggregation or in rigid environment, the MCT and intramolecular rotation are restricted by themself or the matrix, radiative decays of excited states are aroused in aggregated or film states. Considering the acidity of the –OH unit in salicylaldehyde group, these complexes towards to fluoride ion detections including the naked-eye UV–Vis and light-up emission responses, anti-interference abilities, stoichiometry of 2 : 1, 10−7 M detection limits, deprotonation sensing mechanism and real sample test are fully covered and deeply investigated. Taking advantages of AIE natures, they are applicated in fingerprint detections featuring the fast speed, high resolution and multi-level characters. Eventually, the obtained results should expectedly offer valuable clues for phosphorescent AIE-active metal complexes and related application developing.

Afterglows from the indolocarbazole families

Indolocarbazoles (ICZs) and their derivates were immensely studied in the fields of organic opto-electronics, sensors and anti-cancer agents. However, the afterglow researches, the comprehensive syntheses and crystal structures of the isomeric ICZs remained shortages. Currently, the organic afterglows were mainly focused on the crystalline states, showing restrictions and inconveniences in practical applications, the organic amorphous afterglows were more favorable but were limitedly documented. Herein, the syntheses, single crystal structures, afterglow studies and data protection applications of the ICZ families with five isomers were together presented for the first time. For these ICZ crystals, the planar configurations and high void rates made them prone to stack and vulnerable to the O2 and humidity, affected by these factors, they were hard to radiate phosphorescence at room temperature, which can be more easily aroused at 77 K. By doping the ICZ into PVA, a rigid and confined environment was built by the hydrogen bond interaction between the –NH and –OH unit in the ICZ and PVA chain, greatly hindering the molecular motion, O2 and humidity quenchers. Consequently, the triplet states were efficiently stabilized, the nonradiative transitions were highly suppressed, blooming the phosphorescence of these ICZs at room temperature, the brilliant afterglow can be straight witnessed by the naked eyes. Impressively, the highest photoluminescence efficiency of 31.06% was obtained by the ICZ–o, the longest afterglow lasting time and phosphorescent lifetime of 35 s and 2.32 s were achieved by the ICZ–p2, rivaling to the reported organic amorphous afterglows. It’s believed that the synthetic, crystal structural and afterglow studies of the ICZ families should find a promising avenue for developing new organic amorphous afterglow materials and their applications.

Switching the O–O bond-formation mechanism by controlling water activity

Switching the O–O bond-formation mechanism by controlling water activity

QM/MM Studies into the H2O2-Dependent Activity of Lytic Polysaccharide Monooxygenases: Evidence for the Formation of a Caged Hydroxyl Radical Intermediate

Lytic polysaccharide monooxygenases (LPMOs) are promising enzymes for the conversion of lignocellulosic biomass into biofuels and biomaterials. Classically considered oxygenases, recent work suggests that H2O2 can, under certain circumstances, also be a potential substrate. Here we present a detailed mechanism of the activation of H2O2 by a C4-acting LPMO using small-model DFT and QM/MM calculations. We show that there is an efficient mechanism to break the O–O bond of H2O2, with a low barrier of 5.8 kcal/mol, via a one-electron transfer from the LPMO-Cu(I) site to form an HO• radical, stabilized by hydrogen bonding interactions. Our QM/MM calculations further show that the H-bonding machinery of the enzyme directs the HO• radical to abstract a hydrogen atom from the Cu(II)–OH unit rather than from the substrate in what is essentially a caged-radical reaction, thereby forming a Cu(II)-oxyl species. The Cu(II)-oxyl species then exclusively oxidizes the C4–H bond due to the suitable position of the substrat...

Formation of hydroxyl radicals and kinetic study of 2-chlorophenol photocatalytic oxidation using C-doped TiO2, N-doped TiO2, and C,N Co-doped TiO2 under visible light.

This work reports on synthesis, characterization, adsorption ability, formation rate of hydroxyl radicals (OH(•)), photocatalytic oxidation kinetics, and mineralization ability of C-doped titanium dioxide (TiO2), N-doped TiO2, and C,N co-doped TiO2 prepared by the sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy were used to analyze the titania. The rate of formation of OH(•) for each type of titania was determined, and the OH-index was calculated. The kinetics of as-synthesized TiO2 catalysts in photocatalytic oxidation of 2-chlorophenol (2-CP) under visible light irradiation were evaluated. Results revealed that nitrogen was incorporated into the lattice of titania with the structure of O-Ti-N linkages in N-doped TiO2 and C,N co-doped TiO2. Carbon was joined to the Ti-O-C bond in the C-doped TiO2 and C,N co-doped TiO2. The 2-CP adsorption ability of C,N co-doped TiO2 and C-doped TiO2 originated from a layer composed of a complex carbonaceous mixture at the surface of TiO2. C,N co-doped TiO2 had highest formation rate of OH(•) and photocatalytic activity due to a synergistic effect of carbon and nitrogen co-doping. The order of photocatalytic activity per unit surface area was the same as that of the formation rate of OH(•) unit surface area in the following order: C,N co-doped TiO2 > C-doped TiO2 > N-doped TiO2 > undoped TiO2.

Binuclear CuLn complexes (LnIII = Gd, Tb, Dy) of alcohol-functionalized bicompartmental Schiff-base ligand. Hydrogen bonding and magnetic behaviors

Preparation, crystal structures and magnetic properties of a series of four binuclear Cu–Ln complexes are reported (Ln=GdIII, TbIII, and DyIII). These are based on a bicompartmental Schiff-base ligand formed by condensation of 1,3-diaminopropan-2-ol with ortho-vanillin. This Schiff-base is known to usually involve its deprotonated alcohol group in metal coordination, which is not the case here. Instead the OH unit is engaged in H-bonding interactions. Intra- and inter-molecular H-bonds are formed when the alcohol group is located in axial position of the six-member ring formed by the diamino moiety and the Cu atom. In equatorial position, this group is only involved in intermolecular bonding. The corresponding Cu–Tb derivative is shown to behave as a Single Molecule Magnet with ΔkB=24.6K and τ0=2.1×10−8s (HDC=1.5kOe).

An SEM–EDX and Raman spectroscopic study of the fibrous arsenate mineral liskeardite and in comparison with other arsenates kaňkite, scorodite and yvonite

The mineral liskeardite, an arsenate mineral with major cations of iron and aluminium, has been studied by a combination of scanning electron microscopy with energy dispersive spectroscopy and Raman spectroscopy. The mineral shows a fibrous nature. Semi-quantitative chemical analysis shows an Al and Fe arsenate phase with minor amounts of K, Cu, S and Si. Scanning electron microscopy shows a fibrous material. Intense Raman bands at 893, 867 and 843cm−1 are assigned to the ν1 and ν3 AsO43− and HOAsO32− symmetric and antisymmetric stretching vibrations. Raman bands are observed at 514, 499, 485 and 477cm−1 and are assigned to the ν4 out of plane bending modes of the AsO43− and HOAsO32− units. The series of bands at 373, 356 and 343cm−1 are assigned to the ν2 symmetric bending modes. Two groups of OH stretching bands are observed and assigned to OH unit and water stretching vibrations. A comparison of the Raman spectrum of liskeardite with scorodite, kaňkite and yvonite is made.

“Quinone–phenol” transduction activated excited-state intramolecular proton transfer: A new strategy toward ratiometric fluorescent probe for sulfite in living cells

2-(2′-Hydroxyphenyl) benzothiazoles (HBT) are well-known excited-state intramolecular proton transfer (ESIPT) molecules and have been ingeniously elaborated for fluorescent probes construction. However, most of HBT-based ratiometric fluorescent probes are based on the phenolic hydroxyl (-OH) protection/deprotection strategy. In this work, we integrate the π-conjugation interruption reaction and the “quinone–phenol” transduction-activated ESIPT within a benzothiazole-containing rhodol derivative (1), and develop a ratiometric fluorescent probe for sulfite. Upon treating with sulfite, the π-conjugation system of 1 was interrupted and the “quinone–phenol” transduction occurred simultaneously, which leads to the ESIPT process between the phenolic OH and benzothiazole unit upon photoexcitation. The above conversions result in the decrease of the emission band at 578 nm along with a concomitant increase of a new fluorescence peak at 453 nm. The fluorescent intensity (I453/I578) increases linearly with sulfite concentration up to 8 μM with a detection of 0.22 μM (3δ). The proposed probe shows excellent selectivity toward sulfite over other common anions and nucleophiles. Moreover, the cellular imaging experiment indicated probe 1 possesses low cytotoxicity and desirable cell permeability for biological applications.

A Raman and infrared spectroscopic study of the sulphate mineral aluminite Al2(SO4)(OH)4·7H2O

The mineral aluminite has been studied using a number of techniques, including scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDX) and Raman and infrared spectroscopy. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a low intensity band at 1069cm−1 which may be attributed to a carbonate symmetric stretching mode, indicating the presence of thaumasite. The observation of multiple bands in this ν4 spectral region offers evidence for the reduction in symmetry of the sulphate anion from Td to C2v or even lower symmetry. The Raman band at 3588cm−1 is assigned to the OH unit stretching vibration and the broad feature at around 3439cm−1 to water stretching bands. Water stretching vibrations are observed at 3157, 3294, 3378 and 3439cm−1. Vibrational spectroscopy enables an assessment of the molecular structure of aluminite to be made.

O-H bond oxidation by a monomeric Mn(III)-OMe complex.

Manganese-containing, mid-valent oxidants (Mn(III)-OR) that mediate proton-coupled electron-transfer (PCET) reactions are central to a variety of crucial enzymatic processes. The Mn-dependent enzyme lipoxygenase is such an example, where a Mn(III)-OH unit activates fatty acid substrates for peroxidation by an initial PCET. This present work describes the quantitative generation of the Mn(III)-OMe complex, [Mn(III)(OMe)(dpaq)](+) (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate) via dioxygen activation by [Mn(II)(dpaq)](+) in methanol at 25 °C. The X-ray diffraction structure of [Mn(III)(OMe)(dpaq)](+) exhibits a Mn-OMe group, with a Mn-O distance of 1.825(4) Å, that is trans to the amide functionality of the dpaq ligand. The [Mn(III)(OMe)(dpaq)](+) complex is quite stable in solution, with a half-life of 26 days in MeCN at 25 °C. [Mn(III)(OMe)(dpaq)](+) can activate phenolic O-H bonds with bond dissociation free energies (BDFEs) of less than 79 kcal mol(-1) and reacts with the weak O-H bond of TEMPOH (TEMPOH = 2,2'-6,6'-tetramethylpiperidine-1-ol) with a hydrogen/deuterium kinetic isotope effect (H/D KIE) of 1.8 in MeCN at 25 °C. This isotope effect, together with other experimental evidence, is suggestive of a concerted proton-electron transfer (CPET) mechanism for O-H bond oxidation by [Mn(III)(OMe)(dpaq)](+). A kinetic and thermodynamic comparison of the O-H bond oxidation reactivity of [Mn(III)(OMe)(dpaq)](+) to other M(III)-OR oxidants is presented as an aid to gain more insight into the PCET reactivity of mid-valent oxidants. In contrast to high-valent counterparts, the limited examples of M(III)-OR oxidants exhibit smaller H/D KIEs and show weaker dependence of their oxidation rates on the driving force of the PCET reaction with O-H bonds.

Vibrational spectroscopy of the sulphate mineral sturmanite from Kuruman manganese deposits, South Africa

The mineral sturmanite is a hydrated calcium iron aluminium manganese sulphate tetrahydroxoborate hydroxide of formula Ca6(Fe, Al, Mn)2(SO4)2(B(OH)4)(OH)12·26H2O. We have studied the mineral sturmanite using a number of techniques, including SEM with EPMA and vibrational spectroscopy. Chemical analysis shows a homogeneous phase, composed by Ca, Fe, Mn, S, Al and Si. B is not determined in this EPMA technique. An intense Raman band at 990cm−1 is assigned to the SO42− symmetric stretching mode. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a band at 1069cm−1 which may be attributed to a carbonate symmetric stretching mode, indicating the presence of thaumasite. Infrared spectra display two bands at 1080 and 1107cm−1 assigned to the SO42− antisymmetric stretching modes. The observation of multiple bands in this ν4 spectral region offers evidence for the reduction in symmetry of the sulphate anion from Td to C2v or even lower symmetry. The Raman band at 3622cm−1 is assigned to the OH unit stretching vibration and the broad feature at around 3479cm−1 to water stretching bands. Infrared spectroscopy shows a set of broad overlapping bands in the OH stretching region. Vibrational spectroscopy enables an assessment of the molecular structure of sturmanite to be made.

Preparation, molecular modeling and biodistribution of 99mTc-phytochlorin complex

Phytochlorin [21H, 23H-Porphine-7-propanoicacid, 3-carboxy-5-(carboxymethyl)13-ethenyl-18-ethyl-7,8-dihydro-2,8,12,17-tetramethyl-,(7S,8S)] was labeled with 99mTc and the factors affecting the labeling yield of 99mTc-phytochlorin complex were studied in details. At pH 10, 99mTc-phytochlorin complex was obtained with a high radiochemical yield of 98.4 ± 0.6 % by adding 99mTc to 100 mg phytochlorin in the presence of 75 μg SnCl2·2H2O after 30 min reaction time. The molecular modeling study showed that the structure of 99mTc-phytochlorin complex presents nearly linear HO–Tc–OH unit with an angle of 179.27° and a coplanar Tc(N1N2N3N4) unit. Biodistribution of 99mTc-phytochlorin complex in tumor bearing mice showed high T/NT ratio (T/NT = 3.65 at 90 min post injection). This preclinical study showed that 99mTc-phytochlorin complex is a potential selective radiotracer for solid tumor imaging and afford it as a new radiopharmaceutical suitable to proceed through the clinical trials for tumor imaging.

Vibrational spectroscopy of the multianion mineral gartrellite from the Anticline Deposit, Ashburton Downs, Western Australia

The multianion mineral gartrellite PbCu(Fe3+,Cu)(AsO4)2(OH,H2O)2 has been studied by a combination of Raman and infrared spectroscopy. The molecular structure of gartrellite is assessed. Gartrellite is one of the tsumcorite mineral group based upon arsenate and/or sulphate anions. Crystal symmetry is either triclinic in the case of an ordered occupation of two cationic sites, triclinic due to ordering of the H bonds in the case of species with two water molecules per formula unit, or monoclinic in the other cases. Characteristic Raman spectra of the mineral gartrellite enable the assignment of the bands to specific vibrational modes. These spectra are related to the structure of gartrellite. The position of the hydroxyl and water stretching vibrations are related to the strength of the hydrogen bond formed between the OH unit and the AsO43- anion.

The spectroscopic characterization of the sulphate mineral ettringite from Kuruman manganese deposits, South Africa

The mineral ettringite has been studied using a number of techniques, including XRD, SEM with EDX, thermogravimetry and vibrational spectroscopy. The mineral proved to be composed of 53% of ettringite and 47% of thaumasite in a solid solution. Thermogravimetry shows a mass loss of 46.2% up to 1000°C. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a band at 1072cm−1 attributed to a carbonate symmetric stretching mode, confirming the presence of thaumasite. The observation of multiple bands in the ν4 spectral region between 700 and 550cm−1 offers evidence for the reduction in symmetry of the sulphate anion from Td to C2v or even lower symmetry. The Raman band at 3629cm−1 is assigned to the OH unit stretching vibration and the broad feature at around 3487cm−1 to water stretching bands. Vibrational spectroscopy enables an assessment of the molecular structure of natural ettringite to be made.

Kinetics and Mechanism of Indene C–H Bond Activation by [(COD)Ir(μ2-OH)]2

The hydroxy-bridged dimer [(COD)Ir(μ2-OH)]2 (COD = 1,5-cyclooctadiene) cleanly cleaves C–H bonds in indene and cyclopentadiene to produce (COD)Ir(η3-indenyl) and (COD)Ir(η5-C5H5), respectively. The kinetics of the formation of (COD)Ir(η3-indenyl) are consistent with a mechanism that involves coordination of indene to [(COD)Ir(μ2-OH)]2 followed by rate-determining C–H activation from the iridium dimer–indene unit. Transition-state analysis of the Ir and Rh hydroxy dimers indicates that the C–H activation proceeds through a direct deprotonation of indene by the M–OH unit rather than a stepwise oxidative addition/reductive elimination mechanism. The crystal structure of [(COD)Ir]5(μ4-O)(μ3-O)(μ2-OH), a dehydration product of [(COD)Ir(μ2-OH)]2, is presented.

MCTDH calculations on the rigid OH radical moving along a (10,0) carbon nanotube

The dynamics of a rigid OH radical inside a (10,0) single-walled carbon nanotube is examined through a multi-configuration time-dependent Hartree (MCTDH) scheme. The interaction potential used is based on an atom–atom potential previously used in calculations of the adsorption of H2O on graphite. Various parameters of the OH unit are monitored as a function of time, such as coordinates (radial and angular) and orientation and alignment parameters of the OH angular momentum.