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The arene dioxides of five 1-substituted pyrenes have been synthesized using dimethyldioxirane. The diasteroisomeric distribution of the dioxides has been determined. X-ray crystallographic structures of the dioxides have also been obtained. These structures show that for the cis dioxides the molecular structures show a departure from planarity, the extent of which is dependent on the substituent. [ABSTRACT FROM PUBLISHER]

Herein we describe our investigation into the electronic structure of the first isolated monometallic iron azametallacyclobutene complex. Computational analysis through density functional theory calculations reveals electron delocalization throughout the four atoms of the ring system, in line with experimental observations and supporting the classification of this complex as a conjugated metallacycle. The results of this study also point to significant contribution from an imine-substituted iron carbene resonance structure to the overall bonding picture for the azametallacyclobutene. Accordingly, this complex participates in carbene-like reactivity in the presence of an isocyanide substrate to generate a ketenimine product. The related reaction with carbon monoxide leads to the isolation of a five-membered metallacycle that is analogous to the proposed intermediate in ketenimine formation, and confirms the α-carbon as the site of reactivity.

The preparation of bis(pyrazolyl)cyclopentadienyl iron complexes is described. Isopropyl substitution promotes solubility of the iron chloride complex that serves as a precursor to several derivatives through ligand exchange. Modification of the cyclopentadienyl substituent to replace a pyrazolyl unit with a phenyl group favors formation of a substituted ferrocene complex.

A highly efficient homogeneous catalyst system for production of CH3OH from CO2 using single molecular defined ruthenium and rhodium RAPTA-type catalysts [Ru(η6-p-cymene)X2(PTA)] (X = I(1), Cl(2); PTA = 1,3,5-triaza-7-phosphaadamantane) and rhodium catalysts [Rh(η5-C5Me5)X2(PTA/PTA-BH3)] (X = Cl(3), H(4) and PTA-BH3, H(5)) developed in acidic media under mild conditions. A TON of 4752 is achieved using a [Ru(η6-p-cymene)I2(PTA)] catalyst which represents the first example of CO2 hydrogenation to CH3OH using single molecular defined Ru and Rh RAPTA-type catalysts.

Herein we report the isolation, characterization, and photoreactivity of a stable Ni III dichloride complex supported by a tetradentate pyridinophane N-donor ligand. Upon irradiation, this complex undergoes an efficient photoreductive chlorine elimination reaction, both in solution and the solid-state. Subsequently, the Ni III Cl 2 species can be regenerated via a reaction with PhICl 2 .

The syntheses of four new cadmium and zinc complexes with 1,1'-bis(phosphanyl)ferrocene ligands and their phosphine chalcogenide derivatives are reported. The complexes were characterized by elemental analyses and IR, 1 H NMR, 31 P NMR and electronic absorption spectroscopy. The crystal structures of dichlorido[1-diphenylphosphinoyl-1'-(di-tert-butylphosphanyl)ferrocene-κ 2 O,P]cadmium(II), [CdCl 2 {(C 17 H 14 OP)(C 13 H 22 P)Fe}] or CdCl 2 (κ 2 P,O-dppOdtbpf) (1), bis[μ-(tert-butyl)(1'-diphenylphosphinoylferrocen-1-yl)phosphinato-κ 3 O,O':O'']bis[chloridozinc(II)], [Zn 2 {(C 9 H 13 O 2 P)(C 17 H 14 OP)Fe} 2 Cl 2 ] or [ZnOCl{κ 2 O,O'-Ph 2 POFcPO 2 (t-Bu)}] 2 (2), 1,1'-bis(di-tert-butylthiophosphinoyl)ferrocene, [Fe(C 13 H 22 PS) 2 ] or dtbpfS 2 (3), and [1,1'-bis(dicyclohexylphosphanyl)ferrocene-κ 2 P,P'][chlorido/cyanido(0.25/1.75)]zinc(II), [Zn(CN) 1.75 Cl 0.25 {(C 17 H 26 P) 2 Fe}] or Zn(CN) 2 (κ 2 -dcpf) (4), were determined crystallographically. Compound 1 has tetrahedral geometry in which the Cd II centre is coordinated by one dppOdtbpf ligand in a κ 2 -manner and by two Cl atoms, while compound 2 displays a centrosymmetric dimeric unit in which two oxide atoms bridge the two Zn atoms to generate an eight-membered ring. Compound 3 revealed a sandwich structure with both phosphane groups sulfurized. In compound 4, the Zn II atom adopts a tetrahedral geometry by coordinating to the 1,1'-bis(dicyclohexylphosphanyl)ferrocene ligand in a κ 2 -manner and to two cyanide ligands.

The five new copper(I) complexes [Cu 2 (μ-Cl) 2 (κ 1 -PCP t -Bu )] ( 1 ), [Cu 2 (μ-Br) 2 (κ 1 -PCP t -Bu )] ( 2 ), [Cu 2 (μ-I) 2 (κ 1 -PCP t -Bu )] ( 3 ), [Cu 2 (μ-CN) 2 (κ 1 -PCP t -Bu )] ( 4 ), and [Cu 4 (μ 3 -SCN) 4 (κ 1 -PCP t -Bu ) 2 ]·CH 2 Cl 2 ( 5 ) bearing a 1,3-bis[(di- tert -butylphosphino)methyl]benzene ligand were synthesized and characterized spectroscopically, and the molecular structures of 1 , 3 , and 5 were determined by single-crystal X-ray diffraction techniques. Structural studies for 1 and 3 revealed their binuclear structures with Cu···Cu separations of 2.609(3) and 2.6359(19) Å, respectively. However, 5 has a tetranuclear cubane structure with an 18-electron configuration at each copper without any metal-metal bonds. The two copper centers in 1 and 3 are bonded to one bridging PCP t -Bu ligand in a κ 1 -manner and two bridging (pseudo)halido ligands in a μ 2 -bonding mode to generate a nonplanar Cu 2 (μ-X) 2 framework. The four copper centers in 5 are at the vertices of a tetrahedron. Each copper center has pseudo-tetrahedral coordination provided by two bridging PCP t -Bu ligands in a κ 1 -manner and the four bridging thiocyanate groups in a μ 3 -manner. These complexes were used as catalysts for the hydrogenation of CO 2 to formate in the presence of DBU as a base to produce valuable energy-rich chemicals, and therefore it is a promising, safe, and simple strategy to conduct reactions under ambient pressure at room temperature. Among all of the five copper(I) complex based catalysts, 3 displayed the best catalytic performance with turnover number (TON) values of 38-8700 in 12-48 h of reaction at 25-80 °C. The outstanding catalytic performance of [Cu 2 (μ-I) 2 (κ 1 -PCP t -Bu )] ( 3 ) makes it a potential candidate for realizing the large-scale production of formate by CO 2 hydrogenation.

Breast cancer is a leading cause of mortality affecting women across the world. Early detection and diagnosis can decrease the mortality rate due to this cancer. Machine learning-based models are gaining popularity for biomedical applications due to the ability of nonlinear mapping between input and output patterns using supervised training phase. The research work in the paper is focused on the optimal adaptive threshold for mammogram mass segmentation, and detection in order to assist radiologist in accurate diagnosis Legendre neural network with single layer is used to develop the model, and the training is performed through Block Based Normalized Sign-Sign Least Mean Square (BBNSSLMS) algorithm. Legendre neural network expands the input vector using standard Legendre polynomial, and the recursive update principle is followed for the weight vector in higher dimension. The optimal threshold is indirectly used for proper segmentation of mammogram mass. The proposed segmentation method involves training phase with 30 images and testing phase by 151 images obtained from standard Mammogram Image Analysis Society (MIAS) database. The proposed model achieved a sensitivity of 95% and accuracy of 96% with false positives per image calculated as 1.19. • Threshold selection is carried out using single-layer Legendre NN with reduced computational complexity. BNSSLMS algorithm process the data samples block wise instead of sample by sample basis. Optimal threshold is generated according to the varying image properties which helps in correct segmentation and detection. • Due to sparse nature of the adaptive model, more numbers of weight coefficients are tending to zero which also helps in faster convergence. Mammogram Mass Detection Steps.

The S -indolyl (SIn) anomeric moiety was investigated as a new leaving group that can be activated for chemical glycosylation under a variety of conditions including thiophilic and metal-assisted pathways. Understanding of the reaction pathways for the SIn moiety activation was achieved via the extended mechanistic study. Also reported is how the new SIn donors fit into selective activation strategies for oligosaccharide synthesis.

Pentacoordinate Al catalysts comprising bipyridine (bpy) and phenanthroline (phen) backbones were synthesized and their catalytic activity in epoxide/anhydride copolymerization was investigated and compared to (t-Busalph)AlCl. Stoichiometric reactions of tricyclic anhydrides with Al alkoxide complexes produced ring-opened products that were characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography, revealing key regio- and stereochemical aspects.

Palladium is a versatile transition metal used to catalyze a large number of chemical transformations, largely due to its ability to access various oxidation states (0, I, II, III, and IV). Among these oxidation states, Pd(I) is arguably the least studied, and while dinuclear Pd(I) complexes are more common, mononuclear Pd(I) species are very rare. Reported herein are spectroscopic studies of a series of Pd(I) intermediates generated by the chemical reduction at low temperatures of Pd(II) precursors supported by the tetradentate ligands 2,11-dithia[3.3](2,6)pyridinophane (N2S2) and N , N '-di- tert -butyl-2,11-diaza[3.3](2,6)pyridinophane ( tBu N4): [(N2S2)Pd II (MeCN)] 2 (OTf) 4 ( 1 ), [(N2S2)Pd II Me] 2 (OTf) 2 ( 2 ), [(N2S2)Pd II Cl](OTf) ( 3 ), [(N2S2)Pd II X](OTf) 2 (X = tBuNC 4 , PPh 3 5 ), [(N2S2)Pd II Me(PPh 3 )](OTf) ( 6 ), and [( tBu N4)Pd II X 2 ](OTf) 2 (X = MeCN 8 , tBuNC 9 ). In addition, a stable Pd(I) dinuclear species, [(N2S2)Pd I (μ-tBuNC)] 2 (ClO 4 ) 2 ( 7 ), was isolated upon the electrochemical reduction of 4 and structurally characterized. Moreover, the ( tBu N4)Pd I intermediates, formed from the chemical reduction of [( tBu N4)Pd II X 2 ](OTf) 2 (X = MeCN 8 , tBuNC 9 ) complexes, were investigated by EPR spectroscopy, X-ray absorption spectroscopy (XAS), and DFT calculations and compared with the analogous (N2S2)Pd I systems. Upon probing the stability of Pd(I) species under different ligand environments, it is apparent that the presence of soft ligands such as tBuNC and PPh 3 significantly improves the stability of Pd(I) species, which should make the isolation of mononuclear Pd(I) species possible.

There is a large interest in developing oxidative transformations catalyzed by palladium complexes that employ environmentally friendly and economical oxidizing reagents such as dioxygen. Recently, we have reported the isolation and characterization of various mononuclear Pd III and Pd IV complexes supported by the tetradentate ligands N , N '-dialkyl-2,11-diaza[3.3](2,6)pyridinophane ( R N4, R = t Bu, i Pr, Me), and the aerobically induced C-C and C-heteroatom bond formation reactivity was investigated in detail. Given that the steric and electronic properties of the multidentate ligands were shown to tune the stability and reactivity of the corresponding high-valent Pd complexes, herein we report the use of an asymmetric N4 ligand, N- mehtyl- N '-tosyl-2,11-diaza[3.3](2,6)pyridinophane ( TsMe N4), in which one amine N atom contains a tosyl group. The N-Ts donor atom exhibits a markedly reduced donating ability, which led to the formation of transiently stable Pd III and Pd IV complexes, and consequently the corresponding O 2 oxidation reactivity and the subsequent C-C bond formation were improved significantly.

Nickel-catalyzed reductive addition of phosphonodienes to aldehydes (the Mori-Tamaru reaction) gives hydroxy vinyl phosphonates in good yields with excellent control of the relative stereochemistry. Base-induced cyclization of the vinyl phosphonates yields phosphonomethyl-substituted tetrahydrofurans. Inversion of the hydroxyl stereochemistry by Mitsunobu reaction and then cyclization yields a different set of phosphonomethyl-substituted tetrahydrofuran diastereoisomers.

Carbon dioxide (CO2) is an important reactant and can be used for the syntheses of various types of industrially important chemicals. Hence, investigation concerning the conversion of CO2 into valuable energy-rich chemicals is an important and current topic in molecular catalysis. Recent research on molecular catalysts has led to improved rates for conversion of CO2 to energy-rich products such as formate, but the catalysts based on first-row transition metals are underdeveloped. Copper(i) complexes containing the 1,1'-bis(di-tert-butylphosphino) ferrocene ligand were found to promote the catalytic hydrogenation of CO2 to formate in the presence of DBU as the base, where the catalytic conversion of CO2via hydrogenation is achieved using in situ gaseous H2 (granulated tin metal and concentrated HCl) to produce valuable energy-rich chemicals, and therefore it is a promising, safe and simple strategy to conduct reactions under ambient pressure at room temperature. Towards this goal, we report an efficient copper(i) complex based catalyst [CuI(dtbpf)] to achieve ambient-pressure CO2 hydrogenation catalysis for generating the formate salt (HCO2-) with turnover number (TON) values of 326 to 1.065 × 105 in 12 to 48 h of reaction at 25 °C to 80 °C. The outstanding catalytic performance of [CuI(dtbpf)] makes it a potential candidate for realizing the large-scale production of formate by CO2 hydrogenation.

Nickel complexes have been widely employed as catalysts in C-C and C-heteroatom bond formation reactions. While Ni(0), Ni(i), and Ni(ii) intermediates are most relevant in these transformations, recently Ni(iii) and Ni(iv) species have also been proposed to play a role in catalysis. Reported herein is the synthesis, detailed characterization, and reactivity of a series of Ni(ii) and Ni(iii) metallacycle complexes stabilized by tetradentate pyridinophane ligands with various N-substituents. Interestingly, while the oxidation of the Ni(ii) complexes with various other oxidants led to exclusive C-C bond formation in very good yields, the use of O 2 or H 2 O 2 as oxidants led to formation of appreciable amounts of C-O bond formation products, especially for the Ni(ii) complex supported by an asymmetric pyridinophane ligand containing one tosyl N-substituent. Moreover, cryo-ESI-MS studies support the formation of several high-valent Ni species as key intermediates in this uncommon Ni-mediated oxygenase-type chemistry., (This journal is © The Royal Society of Chemistry 2019.)

Two copper(ii) coordination polymers, viz. [Cu2(OAc)4(μ4-hmt)0.5]n (1) and [Cu{C6H4(COO-)2}2]n·2C9H14N3 (2), have been synthesized solvothermally and characterized. The solid-state structure reveals that 1 is an infinite three-dimensional (3D) motif with fused hexagonal rings consisting of Cu(ii) and hmt in a μ4-bridging mode, while 2 is an infinite two dimensional (2D) motif containing Pht-2 in a μ1-bridging mode. CP 1 has a two-fold interpenetrated diamondoid network composed of 4-connected sqc6 topology with the point symbol of {66}, while 2 has a Shubnikov tetragonal plane network possessing a 4-connected node with an sql topology with a point symbol of {44·.62}-VS [4·4·4·4·*·*]. Both CPs 1 and 2 serve as efficient catalysts for CO2-based chemical fixation. Moreover, 1 demonstrates one of the highest reported catalytic activity values (%yield) among Cu-based MOFs for the chemical fixation of CO2 with epoxides. 1 shows high efficiency for CO2 cycloaddition with small epoxides but its catalytic activity decreases sharply with the increase in the size of epoxide substrates. The catalytic results suggested that the copper(ii) motif-catalyzed CO2 cycloaddition of small substrates had been carried out within the framework, while large substrates could not enter into the framework for catalytic reactions. The high efficiency and size-dependent selectivity toward small epoxides on catalytic CO2 cycloaddition make 1 a promising heterogeneous catalyst for carbon fixation and it can be used as a recoverable stable heterogeneous catalyst without any loss of performance. The solvent-free synthesis of the cyclic carbonate from CO2 and an epoxide was monitored by in situ FT-IR spectroscopy and an exposed Lewis-acid metal site catalysis mechanism was proposed.

The reaction of epoxy aldehydes with tetraethyl methylenediphosphonate gave γ,δ-epoxy vinyl phosphonates. The palladium-catalyzed addition of primary alcohols gave the monoprotected diols as single diastereoisomers. The trans- and cis-epoxides lead to opposite ( syn and anti) diastereoisomers of the addition products. The alkene of the vinyl phosphonates was subjected to hydrogenation, and the resulting saturated phosphonates underwent base-catalyzed cyclization to give phostones with a very high diastereoselectivity in the formation of the new chiral center at the phosphorus atom.

The formation and photoreactivity of a series of mixed co-crystals containing 4-stilbazole along with both 4,6-dichlororesorcinol and 4,6-dibromoresorcinol at various ratios is reported. In all cases, the quantitative [2 + 2] cycloaddition reaction yields an identical head-to-tail photoproduct, namely rctt-1,3-bis(4-pyridyl)-2,4-bis(phenyl)cyclobutane. The selectivity in the cycloaddition reaction occurred due to a shorter distance observed between two carbon-carbon double bonds that were found between and not within the hydrogen-bonded assemblies.

The spectroscopically observed magic-size nanoclusters (ZnSe) 34 and (CdTe) 34 are isolated as amine derivatives. The nanoclusters [(ZnSe) 34 ( n-octylamine) 29±6 (di- n-octylamine) 5±4 ] and [(CdTe) 34 ( n-octylamine) 4±3 (di- n-pentylamine) 13±3 ] are fully characterized by combustion-based elemental analysis, UV-visible spectroscopy, IR spectroscopy, and mass spectrometry. Amine derivatives of both (ZnSe) 34 and (CdTe) 34 are observed to convert to the corresponding (ZnSe) 13 and (CdTe) 13 derivatives, indicating that the former are kinetic products and the latter thermodynamic products, under the conditions employed. This conversion process is significantly inhibited in the presence of secondary amines. The isolation of the two new nanocluster derivatives adds to a total of nine of 12 possible isolated derivatives in the (II-VI) 13 and (II-VI) 34 families (II = Zn, Cd; VI = S, Se, Te), allowing comparisons of their properties. The members of these two families exhibit extensive spectroscopic homologies. In both the (II-VI) 13 and (II-VI) 34 families, linear relationships are established between the lowest-energy nanocluster electronic transition and the band gap of the corresponding bulk semiconductor phase.

The synthesis and crystal structures of two tris-(tri-alkyl-sil-yl)silyl bromide compounds, C 9 H 27 BrSi 4 ( I , HypSiBr) and C 27 H 63 BrSi 4 ( II , TipSiBr), are described. Compound I was prepared in 85% yield by free-radical bromination of 1,1,1,3,3,3-hexa-methyl-2-(tri-methyl-sil-yl)tris-ilane using bromo-butane and 2,2'-azobis(2-methyl-propio-nitrile) as a radical initiator at 333 K. The mol-ecule possesses threefold rotational symmetry, with the central Si atom and the Br atom being located on the threefold rotation axis. The Si-Br bond distance is 2.2990 (12) Å and the Si-Si bond lengths are 2.3477 (8) Å. The Br-Si-Si bond angles are 104.83 (3)° and the Si-Si-Si bond angles are 113.69 (2)°, reflecting the steric hindrance inherent in the three tri-methyl-silyl groups attached to the central Si atom. Compound II was prepared in 55% yield by free-radical bromination of 1,1,1,3,3,3-hexa-isopropyl-2-(triiso-propyl-sil-yl)tris-ilane using N -bromo-succinimide and 2,2'-azobis(2-methyl-propio-nitrile) as a radical initiator at 353 K. Here the Si-Br bond length is 2.3185 (7) Å and the Si-Si bond lengths range from 2.443 (1) to 2.4628 (9) Å. The Br-Si-Si bond angles range from 98.44 (3) to 103.77 (3)°, indicating steric hindrance between the three triiso-propyl-silyl groups.

In an attempt to refine a CAN-mediated synthesis of 1,3,4,6-tetra-O-acetyl-α-d-glucopyranose (2-OH glucose) we unexpectedly discovered that this reaction proceeds via the intermediacy of glycosyl nitrates. Improved mechanistic understanding of this reaction led to the development of a more versatile synthesis of 2-OH glucose from a variety of precursors. Also demonstrated is the conversion of 2-OH glucose into a variety of building blocks differentially protected at C-2, a position that is generally hard to protect regioselectively in the glucopyranose series.

Advanced biomedical research has established that cancer is a multifactorial disorder which is highly heterogeneous in nature and responds differently to different treatment modalities, due to which constant monitoring of therapy response is becoming extremely important. To accomplish this, different theranostic formulations have been evaluated. However, most of them are found to suffer from several limitations extending from poor resolution, radiation damage, to high costs. In order to develop a better theranostic modality, we have designed and synthesized a novel platinum(ii)-based 'aggregation induced emission' (AIE) molecule (named BMPP-Pt) which showed strong intra-cellular fluorescence and also simultaneously exhibited potent cytotoxic activity. Due to this dual functionality, we wanted to explore the possibility of using this compound as a single molecule based theranostic modality. This compound was characterized using elemental analysis, NMR and IR spectroscopy, mass spectrometry and single crystal X-ray structure determination. BMPP-Pt was found to exhibit a high AIE property with emission maxima at 497 nm. For more efficient cancer cell targeting, BMPP-Pt was encapsulated into mesoporous silica nanoparticles (Pt-MSNPs) and the MSNPs were further surface modified with an anti-EpCAM aptamer (Pt-MSNP-E). Pt-MSNPs exhibited higher intracellular fluorescence compared to free BMPP-Pt, though both of them induced a similar degree of cell death via the apoptosis pathway, possibly via cell cycle arrest in the G1 phase. Anti-EpCAM aptamer modification was found to increase both cytotoxicity and intracellular fluorescence compared to unmodified MSNPs. Our study showed that EpCAM functionalized BMPP-Pt loaded MSNPs can efficiently internalize and induce apoptosis of cancer cells as well as show strong intracellular fluorescence. This study provides clues towards the development of a potential single compound based theranostic modality in future.

New Schiff base ligands are prepared by the condensation of 7-hydroxy-3-formylchromone with semicarbazone and phenyl semicarbazone. The complexation of these ligands with Cu(II) ion is proposed in the light of spectral studies (IR, UV-Vis, 1 H NMR, 13 C NMR, Mass and ESR). In the complexes 1 and 2, the ligands coordinate to the Cu(II) ion in a neutral fashion via ONO donor atoms. The single crystal XRD studies reveal a slightly distorted square-pyramidal geometry for cationic complex (1) and an octahedral geometry for neutral complex (2). Preliminary biological studies such as DNA and Protein binding are carried out by using absorption and emission titration methods. Observation of intercalative mode of binding with Calf Thymus DNA (CT-DNA) is confirmed by means of viscosity measurements. The micro-environmental changes occurring in Bovine Serum Albumin (BSA) and Human Serum Albumin (HSA) are monitored via three dimensional (3D) fluorescence studies. The compounds ability in inhibiting microbial growth is tested against different pathogens. MCF-7 (human breast cancer) and A549 (human lung carcinoma) cell lines are utilized to check the anticancer potential of the synthesized compounds by using MTT, LDH and NO assays. The results show that complexes 1 and 2 exhibited potent cytotoxic activity over standard drug cisplatin., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Several new Pd II and Pd III complexes supported by electronically and sterically tuned tetradentate pyridinophane ligands Me N4 OMe , Me N4, and tBu N4 were isolated and fully characterized ( Me N4 OMe : N,N'-dimethyl-2,11-diaza[3,3](2,6)-para-methoxypyridinophane; Me N4: N,N'-dimethyl-2,11-diaza[3,3](2,6)pyridinophane; tBu N4: N,N'-di-tert-butyl-2,11-diaza[3,3](2,6)pyridinophane). Cyclic voltammetry studies, UV-vis and EPR spectroscopy, and X-ray crystallography were employed to reveal that the steric properties of the N-substituents of the R N4 ligands have a pronounced effect on the electronic properties of the corresponding Pd III complexes, while the electronic tuning of the ligand pyridyl groups has a surprisingly minimal effect. An explanation for these observations was provided by DFT and TD-DFT calculations which suggest that the electronic properties of the Pd III complexes are mainly dictated by their frontier molecular orbitals that have major atomic contributions from the Pd center (mainly the Pd d z 2 atomic orbital) and the axial N atom donors.

Positron emission tomography (PET) is emerging as one of the most important diagnostic tools for brain imaging, yet the most commonly used radioisotopes in PET imaging, 11 C and 18 F, have short half-lives, and their usage is thus somewhat limited. By comparison, the 64 Cu radionuclide has a half-life of 12.7 h, which is ideal for administering and imaging purposes. In spite of appreciable research efforts, high-affinity copper chelators suitable for brain imaging applications are still lacking. Herein, we present the synthesis and characterization of a series of bifunctional compounds (BFCs) based on macrocyclic 1,4,7-triazacyclononane and 2,11-diaza[3.3](2,6)pyridinophane ligand frameworks that exhibit a high affinity for Cu 2+ ions. In addition, these BFCs contain a 2-phenylbenzothiazole fragment that is known to interact tightly with amyloid β fibrillar aggregates. Determination of the protonation constants (pK a values) and stability constants (log β values) of these BFCs, as well as characterization of the isolated copper complexes using X-ray crystallography, electron paramagnetic resonance spectroscopy, and electrochemical studies, suggests that these BFCs exhibit desirable properties for the development of novel 64 Cu PET imaging agents for Alzheimer's disease.

Cadmium bis(phenyldithiocarbamate) [Cd(PTC) 2 ] is prepared and structurally characterized. The compound crystallizes in the monoclinic space group P2 1 /n. A one-dimensional polymeric structure is adopted in the solid state, having bridging PTC ligands and 6-coordinate pseudo-octahedral Cd atoms. The compound is soluble in DMSO, THF, and DMF and insoluble in EtOH, MeOH, CHCl 3 , CH 2 Cl 2 , and toluene. {CdSe[n-octylamine] 0.53 } quantum belts and Cd(PTC) 2 react to deposit epitaxial CdS shells on the nanocrystals. With an excess of Cd(PTC) 2 , the resulting thick shells contain spiny CdS nodules grown in the Stranski-Krastanov mode. Stoichiometric control affords smooth, monolayer CdS shells. A base-catalyzed reaction pathway is elucidated for the conversion of Cd(PTC) 2 to CdS, which includes phenylisothiocyanate and aniline as intermediates, and 1,3-diphenylthiourea as a final product.

This article describes the development of alkylated S -benzimidazolyl (SBiz) imidates as versatile building blocks for chemical glycosylation. The SBiz imidates have been originally developed as a new platform for active-latent glycosylations and its utility was further extended to other common strategies for oligosaccharide synthesis. This article expands upon the utility of these compounds. We developed a general protocol for the synthesis of a series of N -alkylated SBiz glycosides from N -protected SBiz aglycones by Lewis acid-mediated coupling with glucose pentaacetate. The N -alkylated SBiz moiety was found to be stable under strong basic conditions which allowed us to obtain both armed and disarmed N -alkylated SBiz donors. These donors showed good reactivity at a variety of activation conditions, and generally provided high yields in glycosylations.

The tetradentate ligands N,N'-dialkyl-2,11-diaza[3,3](2,6)pyridinophane ( R N4, where R = Me or tBu) were employed to synthesize and fully characterize [( R N4)M I (COD)] + complexes (M = Rh or Ir; COD = cyclooctadiene). Interestingly, these complexes exhibit accessible oxidation potentials and can generate detectable [( R N4)M II (COD)] 2+ complexes, which were characterized by electron paramagnetic resonance and high-resolution electrospray ionization mass spectrometry. Moreover, a rare mononuclear [( Me N4)Rh II (COD)] 2+ complex was isolated and crystallographically characterized, allowing for a direct comparison with its rhodium(I) analogue. The detailed characterization of such paramagnetic rhodium(II) and iridium(II) complexes enables further investigation of their redox reactivity.

This article describes the development of S-benzimidazolyl (SBiz) imidates as versatile building blocks for oligosaccharide synthesis. The SBiz imidates have been originally developed as a new platform for active-latent glycosylations. This article expands upon the utility of these compounds. The application to practically all common concepts for the expeditious oligosaccharide synthesis including selective, chemoselective, and orthogonal strategies is demonstrated. The strategy development was made possible thanks to our enhanced understanding of the reaction mechanism and the modes by which SBiz imidates interact with various promoters of glycosylation.

A new series of superarmed glycosyl donors has been investigated. It was demonstrated that the S-ethyl leaving group allows for high reactivity, which is much higher than that of equally equipped S-phenyl glycosyl donors that were previously investigated by our groups. The superarmed S-ethyl glycosyl donors equipped with a 2-O-benzoyl group gave complete β-stereoselectivity. Utility of the new glycosyl donors has been demonstrated in a one-pot one-addition oligosaccharide synthesis with all of the reaction components present from the beginning.

The use of the tridentate ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me 3 tacn) and the cyclic alkyl/aryl C-donor ligand -CH 2 CMe 2 -o-C 6 H 4 - (cycloneophyl) allows for the synthesis of isolable organometallic Ni II , Ni III , and Ni IV complexes. Surprisingly, the five-coordinate Ni III complex is stable both in solution and the solid state, and exhibits limited C-C bond formation reactivity. Oxidation by one electron of this Ni III species generates a six-coordinate Ni IV complex, with an acetonitrile molecule bound to Ni. Interestingly, illumination of the Ni IV complex with blue LEDs results in rapid formation of the cyclic C-C product at room temperature. This reactivity has important implications for the recently developed dual Ni/photoredox catalytic systems proposed to involve high-valent organometallic Ni intermediates. Additional reactivity studies show the corresponding Ni II species undergoes oxidative addition with alkyl halides, as well as rapid oxidation by O 2 , to generate detectable Ni III and/or Ni IV intermediates and followed by C-C bond formation.

Geometrically similar monocationic gallium(iii) complexes and their radiolabeled SPECT counterparts were obtained from Schiff base precursor ligands using ligand exchange reactions to evaluate the impact of cis and trans -isomers on their cellular accumulation profiles in rat cardiomyoblasts (H9c2(2-1)) and human breast carcinoma (MCF-7neo) cells. 67 Ga-metalloprobes comprising trans -phenolates showing an overall octahedral geometry and exhibiting uniform spatial distribution of positive charges on their molecular surface show steady-state accumulation in H9c2(2-1) and MCF-7neo cells, and localize in the mitochondria of the cells. Importantly, the surrogate geometrically similar and monocationic metalloprobe counterparts possessing the cis arrangement of phenolates do not show cellular uptake in H9c2(2-1) and MCF-7neo cells. Exploiting their modest fluorescent traits, live cell imaging indicates that trans -isomers of metalloprobes localize within the mitochondria of cells following their penetration, thereby indicating the excellent correlation of radiotracer data and live-cell microscopy results. Overall, these results indicate that the cell uptake profiles of metalloprobes within this class are mediated by the spatial distribution of charges over their molecular surface and hydrophobicity.

Fluselenamyl (5), a novel planar benzoselenazole shows traits desirable of enabling noninvasive imaging of Aβ pathophysiology in vivo; labeling of both diffuse (an earlier manifestation of neuritic plaques) and fibrillar plaques in Alzheimer's disease (AD) brain sections, and remarkable specificity for mapping Aβ compared with biomarker proteins of other neurodegenerative diseases. Employing AD homogenates, [ 18 F]-9, a PET tracer demonstrates superior (2-10 fold higher) binding affinity than approved FDA tracers, while also indicating binding to high affinity site on Aβ plaques. Pharmacokinetic studies indicate high initial influx of [ 18 F]-9 in normal mice brains accompanied by rapid clearance in the absence of targeted plaques. Following incubation in human serum, [ 18 F]-9 indicates presence of parental compound up to 3h thus indicating its stability. Furthermore, in vitro autoradiography studies of [ 18 F]-9 with AD brain tissue sections and ex vivo autoradiography studies in transgenic mouse brain sections show cortical Aβ binding, and a fair correlation with Aβ immunostaining. Finally, multiphoton- and microPET/CT imaging indicate its ability to penetrate brain and label parenchymal plaques in transgenic mice. Following further validation of its performance in other AD rodent models and nonhuman primates, Fluselenamyl could offer a platform technology for monitoring earliest stages of Aβ pathophysiology in vivo.

Gram-negative uropathogenic Escherichia coli (UPEC) bacteria are a causative pathogen of urinary tract infections (UTIs). Previously developed antivirulence inhibitors of the type 1 pilus adhesin, FimH, demonstrated oral activity in animal models of UTI but were found to have limited compound exposure due to the metabolic instability of the O-glycosidic bond (O-mannosides). Herein, we disclose that compounds having the O-glycosidic bond replaced with carbon linkages had improved stability and inhibitory activity against FimH. We report on the design, synthesis, and in vivo evaluation of this promising new class of carbon-linked C-mannosides that show improved pharmacokinetic (PK) properties relative to O-mannosides. Interestingly, we found that FimH binding is stereospecifically modulated by hydroxyl substitution on the methylene linker, where the R-hydroxy isomer has a 60-fold increase in potency. This new class of C-mannoside antagonists have significantly increased compound exposure and, as a result, enhanced efficacy in mouse models of acute and chronic UTI.

Estrone and 17β-estradiol are phenolic steroids that are known to be neuroprotective in multiple models of neuronal injury. Previous studies have identified the importance of their phenolic steroid A-ring for neuroprotection and have identified ortho substituents at the C-2 and C-4 positions on the phenol ring that enhance this activity. To investigate the importance of the steroid ring system for neuroprotective activity, phenolic compounds having the cyclopent[b]anthracene, cyclopenta[b]phenanthrene, benz[f]indene, benz[e]indene, indenes linked to a phenol, and a phenolic spiro ring system were prepared. New synthetic methods were developed to make some of the cyclopent[b]anthracene analogues as well as the spiro ring system. Compounds were evaluated for their ability to protect HT-22 hippocampal neurons from glutamate neurotoxicity and their activity relative to a potent neuroprotective analogue of 17β-estradiol was determined. An adamantyl substituent placed ortho to the phenolic hydroxyl group gave neuroprotective analogues in all ring systems studied.

A series of organometallic Ni II and Ni III complexes supported by tertadendate R N3C - ligands were synthesized and fully characterized using X-ray crystallography, CV, and EPR. Based on the solid state structures, the substituents on the two amine N-donors significantly affect the coordination of the Ni III centers, while the para substituents of the phenyl C-donor have a reduced effect. This is further supported by electrochemical and spectroscopic measurements that suggest the presence of a less bulky N-substituent of the R N3C - ligand leads to a more accessible Ni III center. These results also suggest that the ( Np N3C)Ni system should be more reactive toward oxidation than the corresponding ( tBu N3C)Ni and ( pOMe N3C)Ni systems. Indeed, aerobic oxidative aromatic cyanation was achieved with the ( Np N3C)Ni system at room temperature.

The peroxisome proliferator, WY 14,643 exhibits a pure non-competitive inhibition pattern in the aldehyde reduction and in alcohol oxidation activities of human Aldose reductase (hAR). Fluorescence emission measurements of the equilibrium dissociation constants, K d , of oxidized (hAR•NADP + ) and reduced (hAR•NADPH) holoenzyme complexes display a 2-fold difference between them. K d values for the dissociation of WY 14,643 from the oxidized (hAR•NADP + •WY 14,643) and reduced (hAR•NADPH•WY 14,643) ternary complexes are comparable to each other. The ternary complex structure of hAR•NADP + •WY 14,643 reveals the first structural evidence of a fibrate class drug binding to hAR. These observations demonstrate how fibrate molecules such as WY 14,643, besides being valued as agonists for PPAR, also inhibit hAR.

Nickel-catalyzed cross-coupling reactions are experiencing a dramatic resurgence in recent years given their ability to employ a wider range of electrophiles as well as promote stereospecific or stereoselective transformations. In contrast to the extensively studied Pd catalysts that generally employ diamagnetic intermediates, Ni systems can more easily access various oxidation states including odd-electron configurations. For example, organometallic Ni III intermediates with aryl and/or alkyl ligands are commonly proposed as the active intermediates in cross-coupling reactions. Herein, we report the first isolated Ni III -dialkyl complex and show that this species is involved in stoichiometric and catalytic C-C bond formation reactions. Interestingly, the rate of C-C bond formation from a Ni III center is enhanced in the presence of an oxidant, suggesting the involvement of transient Ni IV species. Indeed, such a Ni IV species was observed and characterized spectroscopically for a nickelacycle system. Overall, these studies suggest that both Ni III and Ni IV species could play an important role in a range of Ni-catalyzed cross-coupling reactions, especially those involving alkyl substrates.

A Ni(ii) complex with two t-butylisocyanide ligands supported by a N3C(-) type tetradentate ligand was synthesized and characterized. Quantitative generation of the aromatic cyanation product, (tBu)N3C-CN, is observed by reacting this Ni(ii) complex with 1 equiv. of an oxidant. Reactivity studies suggest that this oxidatively-induced cyanation involves a heterolytic cleavage of the N-(t)Bu bond and is mediated by Ni(iii).

Two chiral binuclear copper(II) complexes were synthesized and characterized for the first time as efficient chemoselective catalysts for the hydrolysis of aryl glycosides and disaccharides in aqueous solution at near neutral pH. Under these conditions, discrimination of epimeric aryl α -glycopyranosides was observed both by 29-fold different reaction rates and 3-fold different proficiency of the catalyst. Additionally, large differentiation of the nature of α - and β - glycosidic bond in aryl glycosides as model compounds is apparent, but also noted in selected disaccharides. The influence of the chirality of the complexes and the role of the configuration of the carbohydrate upon interaction with the catalyst is discussed in detail. Lastly, a putative mechanism for the metal complex-catalyzed hydrolysis is derived from the experimental evidence pointing at deprotonation of the hydroxyl group at C-2 as a pre-requisite for glycoside hydrolysis.

Herein we report an atom- and step-economic aromatic cyanoalkylation reaction that employs nitriles as building blocks and proceeds through Csp(2)-H and Csp(3)-H bond activation steps mediated by Ni(III). In addition to cyanomethylation with MeCN, regioselective α-cyanoalkylation was observed with various nitrile substrates to generate secondary and tertiary nitriles. Importantly, to the best of our knowledge these are the first examples of C-H bond activation reactions occurring at a Ni(III) center, which may exhibit different reactivity and selectivity profiles than those corresponding to analogous Ni(II) centers. These studies provide guiding principles to design catalytic C-H activation and functionalization reactions involving high-valent Ni species.

2-O-Picolinyl protected glycosyl donors lead to the formation of 1,2-trans glycosides with complete stereoselectivity. This is due to the participatory effect of the picolinyl nitrogen that is able to block the bottom face of the ring via a six-membered cyclic intermediate. Herein we demonstrate that if the nitrogen atom of the O-picolinyl moiety is temporarily blocked by coordination to the metal center (Pd), it becomes unavailable to participate in glycosylation and hence the stereoselectivity of 2-O-picolinyl-assisted glycosylations can be "switched".

Four copper(i) complexes, [CuBr(dtbpf)] (1), [CuI(dtbpf)] (2), [Cu4(μ2-I)2(μ3-I)2(μ-dtbpf)2] (3) and [Cu6(μ3-I)6(μ-dtbpf)2]·2CH3CN (4), were prepared using CuX (X = Br, I) and 1,1'-bis(di-tert-butylphosphino)ferrocene (dtbpf). These complexes have been characterized by elemental analyses, IR, (1)H and (31)P NMR, ESI-MS and electronic absorption spectroscopy. Molecular structures of the complexes 2 and 4 were determined crystallographically. Complex 2 is the first monomeric isolated Cu(i) complex of dtbpf with the largest P-Cu-P bite angle (120.070(19)°) to date. Complex 4 shows a centrosymmetrical dimeric unit with two [Cu3(μ3-I)3] motifs bridged by two bidentate dtbpf ligands in the κ(1)-manner. Each [Cu3(μ3-I)3] motif unites to form a pyramid with one copper atom at the apex and one of the triangular faces capped by an iodine atom. All the complexes were found to be efficient catalysts for the conversion of terminal alkynes into propiolic acids with CO2. Owing to the excellent catalytic activity, the reactions proceeded at atmospheric pressure and ambient temperature (25 °C). The catalytic products were obtained in moderate to good yields (80-96%) by using complex loading to 2 mol%. To the best of our knowledge, this is the first example of an active ferrocenyl diphosphine Cu(i) catalyst for the carboxylation of terminal alkynes with CO2.

Herein we report the synthesis and reactivity of several organometallic Ni(III) complexes stabilized by a modified tetradentate pyridinophane ligand containing one phenyl group. A room temperature stable dicationic Ni(III)-disolvento complex was also isolated, and the presence of two available cis coordination sites in this complex offers an opportunity to probe the C-heteroatom bond formation reactivity of high-valent Ni centers. Interestingly, the Ni(III)-dihydroxide and Ni(III)-dimethoxide species can be synthesized, and they undergo aryl methoxylation and hydroxylation that is favored by addition of oxidant, which also limits the β-hydride elimination side reaction. Overall, these results provide strong evidence for the involvement of high-valent organometallic Ni species, possibly both Ni(III) and Ni(IV) species, in oxidatively induced C-heteroatom bond formation reactions.

Organometallic Ni(III) intermediates have been proposed in several Nickel-catalyzed cross-coupling reactions, yet no isolated bis(hydrocarbyl)Ni(III) complexes have been reported to date. Herein we report the synthesis and detailed characterization of stable organometallic Ni(III) complexes that contain two trifluoromethyl ligands and are supported by tetradentate N-donor ligands (R)N4 (R = Me or tBu). Interestingly, the corresponding Ni(II) precursors undergo facile oxidation, including aerobic oxidation, to generate uncommonly stable organometallic Ni(III) complexes that exhibit limited reactivity.

The conformationally flexible tetradentate pyridinophane ligand (tBu)N4 effectively lowers the oxidation potential of ((tBu)N4)Pd(II) complexes and promotes their facile chemical and electrochemical oxidation, including unpredecented aerobic oxidation reactivity. While the low potential of a number of Pd(II) (and Pt(II)) complexes supported by various fac-chelating polydentate ligands is often attributed to the presence of a coordinating group in the axial position of the metal center, no detailed electrochemical studies have been reported for such systems. Described herein is the detailed electrochemical investigation of the effect of ligand conformation on the redox properties of the corresponding Pd(II) complexes. These Pd complexes adopt different conformations in solution, as supported by studies using variable scan rate, variable-temperature cyclic voltammetry (CV), differential pulse voltammety, and digital CV simulations at variable scan rates. The effect of the axial amine protonation on the spectroscopic and electrochemical properties of the complexes was also investigated. A number of new Pd(III) complexes were characterized by electron paramagnetic resonance, UV-vis spectroscopy, and X-ray diffraction including [((tBu)N4)Pd(III)Cl2]ClO4, a dicationic [((tBu)N4)Pd(III)Me(MeCN)](OTf)2, and an unstable tricationic [((tBu)N4)Pd(III)(EtCN)2](3+) species. Although the electron-rich neutral complexes ((tBu)N4)PdMeCl and ((tBu)N4)PdMe2 are present in solution as a single isomer with the axial amines not interacting with the metal center, their low oxidation potentials are due to the presence of a minor conformer in which the (tBu)N4 ligand adopts a tridentade (κ(3)) conformation. In addition, the redox properties of the ((tBu)N4)Pd complexes show a significant temperature dependence, as the low-temperature behavior is mainly due to the contribution from the major, most stable conformer, while the room-temperature redox properties are due to the formation of the minor, more easily oxidized conformer(s) with the (tBu)N4 ligand acting as a tridentate (κ(3)) or tetradentate (κ(4)) ligand. Overall, the coordination to the metal center of each axial amine donor of the (tBu)N4 ligand leads to a lowering of the Pd(II/III) oxidation potential by ∼0.6 V. These detailed electrochemical studies can thus provide important insights into the design of new ligands that can promote Pd-catalyzed oxidation reactions employing mild oxidants such as O2.

Two structurally related and photoresponsive cyanide-bridged Fe/Co square complexes, {Fe2Co2}, are reported: {[(Tp(Me))Fe(CN)3]2[Co(bpy)2]2[(Tp(Me))Fe(CN)3]2}·12H2O (2) and {[(Tp(Me))Fe(CN)3]2[Co(bpy)2]2[BPh4]2}·6MeCN (3), where Tp(Me) and bpy are hydridotris(3-methylpyrazol-1-yl)borate and 2,2'-bipyridine, respectively. Through electrochemical and spectroscopic studies, the Tp(Me) ligand appears to be a moderate σ donor in comparison to others in the [NEt4][(Tp(R))Fe(III)(CN)3] series [where Tp(R) = Tp, hydridotris(pyrazol-1-yl)borate; Tp(Me) = hydridotris(3-methylpyrazol-1-yl)borate; pzTp = tetrakis(pyrazol-1-yl)borate; Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate; Tp*(Me) = hydridotris(3,4,5-trimethylpyrazol-1-yl)borate]. The spectroscopic, structural, and magnetic data of the {Fe2Co2} squares indicate that thermally-induced intramolecular electron transfer reversibly converts {Fe(II)LS(μ-CN)Co(III)LS} pairs into {Fe(III)LS(μ-CN)Co(II)HS} units near ca. 230 and 244 K (T1/2) for 2 and 3, respectively (LS: low spin; HS: high spin). These experimental results show that 2 and 3 display light-induced {Fe(III)LS(μ-CN)Co(II)HS} metastable states that relax to thermodynamic {Fe(II)LS(μ-CN)Co(III)LS} ones at ca. 90 K. Ancillary Tp(R) ligand donor strength appears to be the dominant factor for tuning electron transfer properties in these {Fe2Co2} complexes.

Multifunctional metal chelators that can modulate the amyloid β (Aβ) peptide aggregation and its interaction with metal ions such as copper and zinc hold considerable promise as therapeutic agents for Alzheimer's disease (AD). However, specific rather than systemic metal chelation by these compounds is needed in order to limit any side effects. Reported herein are two novel small bifunctional chelators, 2-[2-hydroxy-4-(diethylamino)phenyl]benzothiazole (L1) and 2-(2-hydroxy-3-methoxyphenyl)benzothiazole (L2), in which the metal-binding donor atoms are integrated within a molecular framework derived from the amyloid-binding fluorescent dye thioflavin T (ThT). The metal-binding properties of L1 and L2 were probed by pH spectrophotometric titrations to determine their pKa values and the corresponding metal complex stability constants, and the isolated metal complexes were structurally characterized. The amyloid-fibril-binding properties of L1 and L2 were investigated by fluorescence titrations and ThT competition assays. Interestingly, L1 and L2 do not lead to the formation of neurotoxic Aβ42 oligomers in the presence or absence of metal ions, as observed by native gel electrophoresis, Western blotting, and transmission electron microscopy. In addition, L1 and L2 were able to reduce the cell toxicity of preformed Aβ42 oligomers and of the copper-stabilized Aβ42 oligomers. Given their ability to reduce the toxicity of soluble Aβ42 and Cu-Aβ42 species, L1 and L2 are promising lead compounds for the development of chemical agents that can control the neurotoxicity of soluble Aβ42 species in AD.

Lipophilic cationic technetium-99m-complexes are widely used for myocardial perfusion imaging (MPI). However, inherent uncertainties in the supply chain of molybdenum-99, the parent isotope required for manufacturing 99Mo/99mTc generators, intensifies the need for discovery of novel MPI agents incorporating alternative radionuclides. Recently, germanium/gallium (Ge/Ga) generators capable of producing high quality 68Ga, an isotope with excellent emission characteristics for clinical PET imaging, have emerged. Herein, we report a novel 68Ga-complex identified through mechanism-based cell screening that holds promise as a generator-produced radiopharmaceutical for PET MPI.