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An investigation into the role of the pyridyl arm in the reduction of nitrite via OAT in unsymmetrical β-diketiminato copper(ii) nitrite complexes.

Although the application of cationic aluminum complexes in catalysis has been extensively investigated, the incorporation of an aluminum cation into a chiral environment is less explored. In this s...

A dynamic covalent system of the picolyl heterocyclic amino aminals has been studied. The aminals are characterized as a metastable species and easily switch to other forms via external stimuli. The solvent, temperature, acid–base and substituent effects have been examined to evaluate the dynamic covalent system. The results reveal that a more polar solvent, a lower temperature, basic conditions and an electron-withdrawing moiety contribute to the stabilities of aminals. The existence of the n → π* interaction between acetonitrile and the CN moiety makes the N-pyrimidyl imine (4c and 4d) yield higher in CD3CN. In a similar fashion, all aminals tend to convert to the corresponding hemiaminal ethers in a methanol environment. According to these findings, we successfully synthesized the following species: (a) N-2-picolylpyrimidin-2-amine 6c obtained by reduction using acetonitrile as the specific solvent; (b) a picolyl aromatic amino aminal 3e prepared from 2-pyridinecarboxaldehyde and the electron withdrawing 2-methoxy-5-nitroaniline.

The chemistry of the boron cation has been revitalized in the past decade due to its newfound application in stoichiometric and catalytic organic reactions. To extend the frontier of boron cation c...

A series of Al complexes bearing diethyl 2-((arylamino)methylene)malonate and diethyl 2-((alkylamino)methylene)malonate ligands (AMM ligands) were synthesized and their application in the ring-opening polymerization of e-caprolactone was studied. All the Al complexes bearing AMM ligands exhibited higher catalytic activity (approximately 2.8–16.5 fold) than those Al complexes bearing ketiminate ligands did, except OiPrAlMe2 (2 fold lower catalytic activity). In addition, Al complexes with steric hindrance or electron-withdrawing groups in the ligands revealed the greater catalytic activity, and the chelating effect reduced the reactivity of ring-opening polymerization.

Neferine, a bisbenzylisoquinoline alkaloid present in Nelumbo nucifera, has been reported to exhibit neuroprotective effects. Because reduced glutamatergic transmission through inhibition of glutamate release has been proposed as a mechanism of neuroprotection, we investigated whether and how neferine inhibits glutamate release in the nerve terminals of the cerebral cortex of rats. The results demonstrated that neferine inhibits the glutamate release that is evoked by the potassium channel blocker 4-aminopyridine, doing so in a dose-dependent manner. This effect was prevented by removing extracellular calcium and blocking vesicular transporters or N- and P/Q-type calcium channels but not by blocking glutamate transporters. Neferine decreased the 4-aminopyridine-stimulated elevation in intrasynaptosomal calcium concentration; however, it had no effect on the synaptosomal membrane potential. The inhibition of glutamate release by neferine was also eliminated by the selective 5-hydroxytryptamine 1A (5HT

A series of titanium (Ti) complexes bearing ONO-tridentate Schiff bases were synthesized and their application to the ring-opening polymerization of L-lactide and e-caprolactone was studied. Ti complexes bearing ONO-tridentate Schiff bases revealed a greater catalytic activity compared to other previously synthesized Ti complexes bearing multi-dentate phenolate ligands. We hypothesize that using ONO-tridentate Schiff bases as ligands reduces the occupied space and increases the monomer coordination around the Ti center, thereby increasing catalytic activity. The electronic effect of the phenolate group on the polymerization rate was also studied, showing that electron-donating substituents on the ligands could drastically increase polymerization activity.

In an attempt to prepare the heavier analogue of NHC-stabilized borenium cation, we have prepared a silylene-coordinated borenium equivalent (1a), which can be viewed as a contact ion pair of borenium and triflate. The triflate anion coordinates to the oxophilic silicon center, leaving the boron center existing in a trigonal-planar geometry in the solid state and in solution. Nucleophilic substitution reactions of 1a all result in the release of free silylene ligand, demonstrating the borenium-ion-like reactivity of 1a. Chemical reduction of 1a leads to a neutral radical possessing a partial Si–B double bond.

Histamine is released from mast cells when tissues are inflamed or stimulated by allergens. Activation of histamine receptors and calcium influx via TRPV1 could be related to histamine-induced itch and skin inflammation. Quercetin is known to have anti-inflammatory and anti-itching effects. This study aims to understand whether quercetin can directly affect histamine-induced calcium influx in human keratinocyte. In it, we investigated quercetin, which acts on histamine-induced intracellular free calcium ([Ca2+]i) elevation in human keratinocyte. Changes in [Ca2+]i were measured using spectrofluorometry and confocal Imaging. We detected the expression of IL-8 after treatment of quercetin using qRT-PCR and evaluated its anti-itching effect in BALB/c mice. We also performed a docking study to estimate the binding affinity of quercetin to H4 receptors. We found that quercetin pretreatment decreased histamine-induced [Ca2+]i elevation in a concentration-dependent manner. The inhibitory effect of quercetin on histamine-induced [Ca2+]i elevation was blocked by JNJ7777120, a selective H4 antagonist, as well as by U73122, a PLC inhibitor, and by GF109203X, a PKC inhibitor. We also found that H4 agonist (4-methylhistamine)-induced [Ca2+]i elevation could be inhibited by quercetin. Moreover, the selective TRPV1 blocker capsazepine significantly suppressed the quercetin-mediated inhibition of histamine-induced [Ca2+]i elevation, whereas the TRPV4 blocker GSK2193874 had no effect. Last, quercetin decreased histamine and H4 agonist-induced IL-8 expression in keratinocyte and inhibited the scratching behavior-induced compound 48/80 in BALB/c mice. The molecular docking study also showed that quercetin exhibited high binding affinities with H4 receptors (autodock scores for H4 = −8.7 kcal/mol). These data suggest that quercetin could decrease histamine 4 receptor-induced calcium influx through the TRPV1 channel and could provide a molecular mechanism of quercetin in anti-itching, anti-inflammatory, and unpleasant sensations.

As the synthetic applications of boron monocations as stoichiometric reagents or catalysts have expanded significantly in the past decade, investigation on the molecular electronics and reactivity of the related boron dications remains in its infancy. This mini-review highlights the recent advancements in boron polycations consisting of one or multiple boron centers. The structure–reactivity relationship of these dicationic species will also be discussed.

A series of five- and six-membered-ring Al complexes bearing Schiff bases was synthesized and their application to the ring-opening polymerization of e-caprolactone (CL) was studied. The five-membered-ring Al complexes have been shown to have a significantly higher polymerization rate than six-membered-ring Al complexes (2–3 fold for CL polymerization). The X-ray data revealed that the Al center of a five-membered-ring Al complex is farther from the Schiff base ligand than is that of a six-membered-ring Al complex. The results of density functional theory calculations also suggest that more space around the Al center of five-membered-ring Al complexes may reduce the steric repulsion in CL polymerization and increase the catalytic activity of five-membered-ring Al complexes.

Neferine, a bisbenzylisoquinoline alkaloid present in Nelumbo nucifera, has been reported to exhibit neuroprotective effects. Because reduced glutamatergic transmission through inhibition of glutamate release has been proposed as a mechanism of neuroprotection, we investigated whether and how neferine inhibits glutamate release in the nerve terminals of the cerebral cortex of rats. The results demonstrated that neferine inhibits the glutamate release that is evoked by the potassium channel blocker 4-aminopyridine, doing so in a dose-dependent manner. This effect was prevented by removing extracellular calcium and blocking vesicular transporters or N- and P/Q-type calcium channels but not by blocking glutamate transporters. Neferine decreased the 4-aminopyridine-stimulated elevation in intrasynaptosomal calcium concentration; however, it had no effect on the synaptosomal membrane potential. The inhibition of glutamate release by neferine was also eliminated by the selective 5-hydroxytryptamine 1A (5HT1A) receptor antagonist WAY100635, Gi/o protein inhibitor pertussis toxin, adenylyl cyclase inhibitor MDL12330A, and protein kinase A inhibitor H89. Moreover, immunocytochemical analysis revealed the presence of 5-HT1A receptor proteins in the vesicular transporter of glutamate type 1 positive synaptosomes. The molecular docking study also demonstrated that neferine exhibited the highest binding affinity with 5-HT1A receptors (Autodock scores for 5-HA1A = −11.4 kcal/mol). Collectively, these results suggested that neferine activates 5-HT1A receptors in cortical synaptosomes, which decreases calcium influx and glutamate release through the activation of Gi/o protein and the inhibition of adenylyl cyclase/cAMP/protein kinase A cascade.

Bridging-type polydentate N-heterocyclic carbene (NHC) ligands are valuable building blocks for organometallic supramolecules. In order to quickly expand the ligand library of poly-NHC, we have ass...

The reaction mechanism of the [Et3BH]−-induced conversion of a dicationic boron compound ([Cp*B-IMes]2+, [1]2+) to a planar neutral carbene-coordinated borabenzene (2) is investigated experimentally and theoretically. Owing to the steric congestion around the boron center, bulky [Et3BH]− attacks the less encumbered carbon atom of Cp*, leading to a metastable 5-borabicyclo[2.1.1]hex-2-ene borenium cation ([3-CH]+) at low temperature. Upon raising the temperature, the bicyclic-borenium ion undergoes sequential pericyclic reactions, including suprafacial [1,3]-sigmatropic shift, two-electron electrocyclic ring opening, and then [1,2]-hydrogen shift to a planar cyclic borenium ion, [4-CH]+, which can then be deprotonated to yield the neutral aromatic borabenzene. The attack of hydride at the boron center of [1]2+ was excluded through the preparation and isolation of 6-borabicyclo[3.1.0]hexenylium, [3-BH]+, which could not be transformed into [3-CH]+ or [4-CH]+. The borenium ion rearrangement follows first-ord...

Boron mono- and di-cations featuring a nucleophilic N-heterocyclic olefin and the pentamethylcyclopentadienyl substituent have been prepared and structurally characterized. Experimental and theoretical investigations show that [η5-Cp*B-NHO]2+is considerably more Lewis acidic than [η5-Cp*B-IMes]2+due to the steric congestion imposed by the bent geometry of NHO around the central boron atom.

A series of magnesium complexes bearing 2-(arylideneamino)phenolate (forming 5-membered ring Mg complexes) and 2-((arylimino)methyl)phenolate (forming 6-membered ring Mg complexes) ligands were synthesized, and their application in the ring-opening polymerization of L-lactide (LA) was investigated. The Mg complexes with 5-membered rings exhibit a higher polymerization rate and controllability for polylactide production than those with 6-membered rings do (one-fold to three-fold for LA polymerization). The density function theory calculation results revealed that benzyl alcohol approaches LA through the hydrogen bond with phenolate oxygen, and then initiates LA, with the proton transferring to phenolate oxygen to form the LA-OBn adduct. The LA-OBn adduct was activated using the proton present on phenolate oxygen to open the ring of the LA-OBn adduct. Moreover, the LA polymerization using L5ThioMg as a catalyst needs to overcome a 17.7 kcal/mol activation free energy that is lower than that of L6ThioMg (21.0 kcal/mol)

Two copper(I)–nitro complexes [Tpm3-tBuCu(NO2)] (1) and [(Ph3P)2N][Tp3-tBuCu(NO2)] (2), containing steric bulky neutral tris(3-tert-butylpyrazolyl)methane and anionic hydrotris(3-tert-butylpyrazolyl)borate ligands, have been synthesized and characterized. Complex 2 adopts a unique κ2-binding mode of Tp3-tBu around the copper(I)–nitro environment in the solid state and shows a four-coordinated tetrahedral geometry surrounded by a nitro and three pz3-tBu groups in solution. Both complexes 1 and 2 allow for the stoichiometric reduction of NO2− to NO with H+ addition. The results of this effort show that increasing steric bulk and electron donation properties on the nitrogen ancillary ligand will improve the nitrite reduction ability of the copper(I)–nitro model complexes.

Redox behavior of Fe(I) complexes bearing a PNP-pincer-type phosphaalkene ligand, 2,6-bis[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine (BPEP-Ph), is reported. The four-coordinate Fe(I) complex [FeBr(BPEP-Ph)] (1) readily reacts with 1 equiv of tBuNC in toluene at −35 °C to give [FeBr(tBuNC)(BPEP-Ph)] (2) with a 17e configuration. Complex 2 is fairly stable in neat benzene at room temperature, but smoothly undergoes disproportionation in the presence of added tBuNC to afford the Fe(0) complex [Fe(tBuNC)2(BPEP-Ph)] (3) and the Fe(II) complex [FeBr2(tBuNC)4] (4) along with free BPEP-Ph. The single-crystal X-ray diffraction studies of 3 and 4 reveal distorted trigonal bipyramidal and square pyramidal arrangements around Fe, respectively. The yield of 3 increases up to 50%/2 when 2 equiv of tBuNC is added to the system. A disproportionation process involving a 19e intermediate is proposed.

The effect of a ligand on the electron deficiency and Lewis acidity of the Cp*-substituted boron dication has been investigated experimentally and theoretically. In addition to the reported IMes- and N-heterocyclic olefin (NHO)-stabilized boron dications, the related cyclic alkylamino carbene (CAAC)-coordinated boron mono- and dications have also been synthesized and structurally characterized. An electrochemical study of dications [3a–3c]2+ confirms the higher electron deficiency of the dicationic system than the related boron monocations. Moreover, the presence of a π-acidic CAAC ligand is critical for realizing stable radical species generated from the chemical reduction of boron cations. The nature of the axial ligand also significantly affects the selectivity of the hydride addition reaction of boron dications. While bulky superhydride reacts with [3a–3c]2+ in the same manner to give the cyclic boreniums, [BH4]− attacks three different electrophilic sites of boron dications: the sp2 carbon of Cp* of ...

The reactivity and the reaction conditions of the ring-opening polymerization of ɛ-caprolactone (ɛ-CL) and L-lactide (LA) initiated by aluminum ketiminate complexes have been shown differently. Herein, we account for the observation by studying the mechanisms on the basis of density functional theory (DFT) calculations. The calculations show that the ring-opening polymerization of ɛ-CL and LA are rate-determined by the benzoxide insertion and the C&ndash, O bond cleavage step, respectively. Theoretical computations suggest that the reaction temperature of L&ndash, LA polymerization should be higher than that of ɛ-CL one, in agreement with the experimental data. To provide a reasonable interpretation of the experimental results and to give an insight into the catalyst design, the influence of the electronic, steric, and thermal effects on the polymerization behaviors will be also discussed in this study.

Coagulation or dense membrane processes, i.e. nanofiltration (NF) and reverse osmosis (RO), are intensively used in surface water treatment. Conventional coagulation process is used to remove colloids and particles, while the dense membrane processes are used to remove trace dissolved contaminants. This paper applied an in-situ surface modification technique by directly depositing the laboratory synthesized coagulant, aluminium tridecamer ([AlO4Al12(OH)24(H2O)12]Cl7, Al13), as a coating solution for two NF and one RO membranes. The dense membranes can completely reject the Al13 compounds; while the coated membranes were effectively removing humic acid and 17β-estradiol (E2) from waters. The coated Al13 layer revealed structural stability subjected to salt (NaCl), acid (pH 5) and base (pH 9) challenges.

This study conducted electrospray ionization mass spectrometry (ESI-MS) tests on 90–95% pure aluminum tridecamer (Al13) salt dissolved in a 50:50 (v/v) water/methanol mixture. The mass spectra for water/methanol mixture revealed no major characteristic peaks for Al13, but showed a few series with incremental difference of 32u, 18u (or 9u), and 14u in the m/z = 200–500 regime. The methanol molecule typically replaces one by one the ligated aqua ligand and adducts to the aluminum center to destruct aluminum tridecamer into smaller, singly or doubly charged polymeric species. A species network with ligand substitution and addition reactions was for the first time revealed.

Aluminum tridecamer (Al 13 ) salt of 70% purity can be yielded by slowly adding base to a mixed aluminum chloride solution with sodium chloride as the primary byproduct. The purity of the so-produced Al 13 solution is typically increased to >90% using sulfate precipitation and nitrate metathesis reactions (the SO 4 2− /Ba 2+ separation method). However, the presence of excess sulfate and, as demonstrated in this study, excess chloride ions can destabilize Al 13 clusters. This study applied the organic solvent precipitation technique to purify crude Al 13 salt. The solution and solid-state 27 Al nuclear magnetic resonance (NMR) spectra indicate that Al 13 purity was >95%. The infrared adsorption spectra had clear Al 13 characteristic bands. The electrospray ionization mass spectrometry (ESI-MS) tests identified Al 13 7+ species. The organic solvent precipitation method purified Al 13 clusters with minimal free Cl − ions.

Cationic methylpalladium complexes bearing hemilabile bidentate α-amino–pyridines can serve as effective precursors for catalytic alternating copolymerization of norbornene (N) and ethylene (E), under mild conditions. The norbornyl palladium complexes in the formula of {[RHNCH2(o-C6H4N)]Pd(C7H10Me)(NCMe)}(BF4) (R = iPr (2a), tBu (2b), Ph (2c), 2,6-Me2C6H3 (2d), 2,6-iPr2C6H3 (2e)) were synthesized via single insertion of norbornene into the corresponding methylpalladium complexes 1a–1e, respectively. Both square planar methyl and norbornyl palladium complexes exhibit facile equilibria of geometrical isomerization, via sterically-controlled amino decoordination–recoordination of amino–pyridine. Kinetic studies of E-insertion, N-insertion of complexes 1 and 2, and the geometric isomerization reactions have been examined by means of VT-NMR, and found in excellent agreement with the results estimated by DFT calculations. The more facile N-insertion in the cis-isomers, and ready geometric isomerization, cooperatively lead to a new mechanism that accounts for the novel catalytic formation of alternating COC.

This study conducted electrospray ionization mass spectrometry (ESI-MS) tests on 90-95% pure [AlO(4)Al(12)(OH)(24)(H(2)O)(12)]Cl(7) (Al(13)) salt dissolved in a 50:50 v/v water/acetonitrile solution. Acetonitrile typically replaces the ligated aqua ligands and adducts to the aluminum center, leading to aluminum tridecamer breakdown. The chloride anions cannot coordinate with the aluminum center in the presence of acetonitrile molecules. The acetonitrile deconstructs the "cagelike" aluminum tridecamer structure into smaller polymeric species, which are further transformed into a brucite-like structure. The present work obtained the mass spectra of incremental difference of 18u for fresh solution and of 9u for aged solution in the m/z = 200-900 regime, providing support to the occurrence of water ligand exchange reaction during aluminum tridecamer decomposition.

Treatment of the Fe(I) mesityl complex [Fe(Mes)(BPEP-Ph)] (BPEP-Ph = 2,6-bis[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine) with π-acid ligands (L = CO, RNC) leads to one-electron reduction via Mes group migration from Fe to P, followed by homolytic elimination of the 2,4,6-tBu3C6H2 group, to afford Fe(0) complexes of the formula [Fe(L)2(BPEP-Ph*)] (BPEP-Ph* = 2-[1-phenyl-2-mesityl-2-phosphaethenyl]-6-[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine). This reduction process is supported by radical trapping experiments and theoretical studies. The 2,4,6-tBu3C6H2˙ radical is captured by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in high yield. DFT calculations reveal the mechanism of Mes group migration with a reasonable energy profile.

A series of α-aminopyridines in the form of (2,6-C(6)H(3)N)(R(1))(CHR(2)NR(3)R(4)) (R(1) = R(2) = H R(3) = H R(4) = (i)Pr (L1a), R(4) = (t)Bu (L1b), R(4) = Ph (L1c), R(4) = 2,6-Me(2)C(6)H(3) (L1d), R(4) = 2,6-(i)Pr(2)C(6)H(3) (L1e), R(1) = R(2) = H R(3) = R(4) = Et (L1f), R(1) = H R(2) = Me R(3) = H R(4) = (i)Pr (L2a), R(4) = Ph (L2c), R(4) = 2,6-Me(2)C(6)H(3) (L2d), R(4) = 2,6-(i)Pr(2)C(6)H(3) (L2e), R(1) = Me R(2) = H R(3) = H R(4) = 2,6-(i)Pr(2)C(6)H(3) (L3e)) and β-aminopyridines in the form of (2-C(6)H(4)N)(CH(2)CH(2)NR(1)R(2)) (R(1) = H R(2) = (i)Pr (4a), R(2) = (t)Bu (L4b), R(1) = R(2) = Et (L4f)) have been prepared. Their corresponding halonickel complexes 1a-4f are synthesized by ligand substitution from (DME)NiBr(2) and the molecular structures are characterized. Four types of coordination modes include four-coordinate mononuclear species with one ligand, five-coordinate mononuclear species with two ligands, five-coordinate dinuclear species with two ligands, and a six-coordinate polymeric framework were determined by X-ray crystallography. Using methylaluminoxanes (MAO) as the activator, the nickel complexes can catalyze ethylene polymerization under moderate pressure and ambient temperature. The activity reaches 10(5) g PE mol(-1) Ni h. The PE products with high branching and high crystallinity have M(n) ~ 10(3) with PDI2.

Ethylene polymerization catalyzed by Ni(ii) complexes that bear new bidentate ligands with a functional hybrid of amine and imine has been studied. A class of new alpha-aminoaldimines and their nickel complexes [R(1)R(2)NCMe(2)CH[double bond, length as m-dash]N(2,6-R(3)(2)C(6)H(3))]NiBr(2) (R(1) = R(2) = Me, R(3) = Me (Ni-); R(3) = (i)Pr (Ni-); R(1) = R(2) = Et, R(3) = H (Ni-); Me (Ni-); (i)Pr (Ni-); R(1) = R(2) = (n)Pr, R(3) = (i)Pr (Ni-); (R(1)R(2)) = c-C(3)H(6) R(3) = (i)Pr (Ni-); (R(1)R(2)) = c-C(4)H(8), R(3) = (i)Pr (Ni-)) were synthesized. The molecular structures of six nickel complexes were determined by X-ray crystallography, showing distorted tetrahedral configurations. The SQUID data of Ni- confirms its ground state of triplet spin. Using methylaluminoxanes (MAO) as the activator, the nickel complexes are found to catalyze ethylene polymerization under moderate pressure and ambient temperature. The activity reaches to 10(6) g PE mol Ni(-1) h(-1), and increases with the ethylene pressure in the range of 14-28 bar. The highly branching PE products have M(n) approximately 10(5) with PDI2. The amine and imine functionalities demonstrate independent control to the polymerization reactions, wherein the activity appears to be facilitated by using the catalysts installed with bulky imino substituents as well as with less sterically hindered amino substituents. This is ascribed to the C(2) unsymmetric coordination in the square planar resting state in which the bulky polymer chain prefers cis to the imine and the small ethylene monomer is cis to the amine.