Annie Castonguay

Organometallic Pincer Chemistry

Gerard van Koten: The Mono-anionic ECE-Pincer Ligand - a Versatile Privileged Ligand Platform: General Considerations.- Elena Poverenov, David Milstein: Non-Innocent Behavior of PCP and PCN Pincer Ligands of Late Metal Complexes.- Dean M. Roddick: Tuning of PCP Pincer Ligand Electronic and Steric Properties.- Gemma R. Freeman, J. A. Gareth Williams: Metal Complexes of Pincer Ligands: Excited States, Photochemistry, and Luminescence.- Davit Zargarian, Annie Castonguay, Denis M. Spasyuk: ECE-Type Pincer Complexes of Nickel.- Roman Jambor and Libor Dostal: The Chemistry of Pincer Complexes of 13 - 15 Main Group Elements.- Kalman J. Szabo: Pincer Complexes as Catalysts in Organic Chemistry.- Jun-ichi Ito and Hisao Nishiyama: Optically Active Bis(oxazolinyl)phenyl Metal Complexes as Multi-potent Catalysts.- Anthony St. John, Karen I. Goldberg, and D. Michael Heinekey: Pincer Complexes as Catalysts for Amine Borane Dehydrogenation.- Dmitri Gelman and Ronit Romm: PC(sp3)P Transition Metal Pincer Complexes: Properties and Catalytic Applications.- Jennifer Hawk and Steve Craig: Physical Applications of Pincer Complexes.

Differential Regulation of Transmitter Release by Presynaptic and Glial Ca2+ Internal Stores at the Neuromuscular Synapse

The differential regulation of synaptic transmission by internal Ca2+ stores of presynaptic terminals and perisynaptic Schwann cells (PSCs) was studied at the frog neuromuscular junction. Thapsigargin (tg), an inhibitor of Ca2+-ATPase pumps of internal stores, caused a transient Ca2+ elevation in PSCs, whereas it had no effect on Ca2+ stores of presynaptic terminals at rest. Tg prolonged presynaptic Ca2+ responses evoked by single action potentials with no detectable increase in the resting Ca2+ level in nerve terminals. However, Ca2+ accumulation was observed during high frequency stimulation. Tg induced a rapid rise in endplate potential (EPP) amplitude, accompanied by a delayed and transient increase. The effects appeared presynaptic, as suggested by the lack of effects of tg on the amplitude and time course of miniature EPPs (MEPPs). However, MEPP frequency was increased when preparations were stimulated tonically (0.2 Hz). The delayed and transient increase in EPP amplitude was occluded by injections of the Ca2+chelator BAPTA into PSCs before tg application, whereas a rise in intracellular Ca2+ in PSCs induced by inositol 1,4,5-triphosphate (IP3) injections potentiated transmitter release. Furthermore, increased Ca2+buffering capacity after BAPTA injection in PSCs resulted in a more pronounced synaptic depression induced by high frequency stimulation of the motor nerve (10 Hz/80 sec). It is concluded that presynaptic Ca2+ stores act as a Ca2+clearance mechanism to limit the duration of transmitter release, whereas Ca2+ release from glial stores initiates Ca2+-dependent potentiation of synaptic transmission.

New ruthenium(II)-letrozole complexes as anticancer therapeutics.

Novel ruthenium-letrozole complexes have been prepared, and cell viability of two human cancer cell types (breast and glioblastoma) was determined. Some ruthenium compounds are known for their cytotoxicity to cancer cells, whereas letrozole is an aromatase inhibitor administered after surgery to post-menopausal women with hormonally responsive breast cancer. A significant in vitro activity was established for complex 5·Let against breast cancer MCF-7 cells and significantly lower activity against glioblastoma U251N cells. The activity of 5·Let was even higher than that of 4, a compound analogous to the well-known drug RAPTA-C. Results from the combination of 5·Let (or 4) with 3-methyladenine (3-MA) or with curcumin, respectively, revealed that the resultant cancer cell death likely involves 5·Let-induced autophagy.

New derivatives of PCP-type pincer complexes of nickel.

The pincer-type complexes (PC(sp3)P(i-Pr))NiR (PC(sp3)P(i-Pr) = (i-Pr(2)PCH(2)CH(2))(2)CH) react with HBF(4) (R = C[triple bond]CMe, Ph, Me) or AgBF(4) (R = Br) to give (PC(sp3)P(i-Pr))Ni(BF(4)), 1, which was found to involve fluxional Ni-F-BF(3) interactions. Competition experiments revealed that the relative ease of protonation of the Ni-hydrocarbyl moiety follows the order Ni-Me > Ni-C[triple bond]CMe > Ni-Ph. Complex 1 reacts with water to give [(PC(sp3)P(i-Pr))Ni(H(2)O)][BF(4)], 2, that in turn undergoes H(2)O exchange with CH(3)CN, i-PrNH(2), and CO to give the corresponding cationic adducts 3, 4, and 5; alternatively, 3-5 can also be obtained directly from the reaction of 1 with CH(3)CN, i-PrNH(2), and CO, respectively. Deprotonation of complex 2 gives the neutral hydroxo complex (PC(sp3)P(i-Pr))Ni(OH), 6. All complexes have been characterized by NMR spectroscopy and, in the case of 2-6, by X-ray crystallography.

ECE-Type Pincer Complexes of Nickel

Pincer complexes of transition metals have demonstrated valuable catalytic reactivities and desirable properties as functional materials. Much more is known about pincer complexes of noble metals, but the pincer chemistry of nonprecious, 3d metals is poised for rapid growth over the next decade. This chapter presents a literature survey of nickel complexes based on tridentate ECE-type pincer ligands featuring a meridional coordination of the central metal atom through two dative E → Ni interactions and a covalent C–Ni linkage. The discussion is focused on the synthesis, characterization, and reactivities of complexes featuring both symmetrical and unsymmetrical ligands, ECE and ECE′. The material is organized into various sections according to the type of donor moiety E and E′ (phosphine, amine, phosphinite, phosphinimine, thioether, and N-heterocyclic carbene) and the hydrocarbyl linker (aromatic or aliphatic). Where possible, the presentation reflects the chronological order of the developments in this field of study. The review concludes with an overview of the current state of the chemistry of (ECE)Ni complexes and offers some predictions on the future prospects of this field.

Dendrimer templated construction of silver nanoparticles

Silver nanoparticles continue to evoke great current interest due to their tremendous potential in designing smart materials for a wide variety of applications. Much emphasis has been placed lately in developing methodologies that could modulate the size and shape of these metal particles. Dendrimers that are monodisperse in nature with a regular and highly branched three-dimensional architecture, provide a useful platform to accomplish this goal. These hyperbranched macromolecules have been widely explored as templates in the construction of silver metal nanoparticles, and this review aims to provide a detailed overview of dendrimer-assisted synthesis of silver nanoparticles.

Dendrimers as bactericides

Hyperbranched and monodisperse macromolecules of nanodimensions, commonly referred to as dendrimers, have offered significant potential in addressing key issues in biology. In addition, their monodisperse nature and a generally described globular architecture with high surface group density, make them very coveted candidates as antimicrobial agents. Here, we provide an overview of what has been accomplished in exploring the potential of dendrimers as bactericides, as well as an analysis of the factors influencing their biocidal activity.

Caspase-1 Activity in Microglia Stimulated by Pro-Inflammagen Nanocrystals

Although caspase-1 is a key participant in inflammation, there is no sensitive assay to measure its enzymatic activity in real time in cells or animals. Here we describe a nanosensor for caspase-1 ratiometric measurements, consisting of a rhodamine-labeled, caspase-1 cleavable peptide linked to quantum dots (QDs). Microglia cells were stimulated by lipopolysaccharide (LPS) and by hybrid nanoparticles LPS-QDs. These stimuli activated caspase-1 in microglia monolayers and in the mouse brain, while a selected caspase inhibitor markedly reduced it. LPS-QDs entered into the lysosomal compartment and led to an enlargement of these cellular organelles in the exposed microglia. Both lysosomal swelling and mitochondrial impairment contributed to caspase-1 activation and to the consequent interleukin-1β release. The results from these studies highlight how the unique properties of QDs can be used to create versatile biotools in the study of inflammation in real time in vivo.

Coordination-mode control of bound nitrile radical complex reactivity: Intercepting end-on nitrile-mo(III) radicals at low temperature

Variable temperature equilibrium studies were used to derive thermodynamic data for formation of eta(1) nitrile complexes with Mo(N[(t)Bu]Ar)(3), 1. (1-AdamantylCN = AdCN: DeltaH(degrees) = -6 +/- 2 kcal mol(-1), DeltaS(degrees) = -20 +/- 7 cal mol(-1) K(-1). C(6)H(5)CN = PhCN: DeltaH(degrees) = -14.5 +/- 1.5 kcal mol(-1), DeltaS(degrees) = -40 +/- 5 cal mol(-1) K(-1). 2,4,6-(H(3)C)(3)C(6)H(2)CN = MesCN: DeltaH(degrees) = -15.4 +/- 1.5 kcal mol(-1), DeltaS(degrees) = -52 +/- 5 cal mol(-1) K(-1).) Solution calorimetric studies show that the enthalpy of formation of 1-[eta(2)-NCNMe(2)] is more exothermic (DeltaH(degrees) = -22.0 +/- 1.0 kcal mol(-1)). Rate and activation parameters for eta(1) binding of nitriles were measured by stopped flow kinetic studies (AdCN: DeltaH(on)(++) = 5 +/- 1 kcal mol(-1), DeltaS(on)(++) = -28 +/- 5 cal mol(-1) K(-1); PhCN: DeltaH(on)(++) = 5.2 +/- 0.2 kcal mol(-1), DeltaS(on)(++) = -24 +/- 1 cal mol(-1) K(-1); MesCN: DeltaH(on)(++) = 5.0 +/- 0.3 kcal mol(-1), DeltaS(on)(++) = -26 +/- 1 cal mol(-1) K(-1)). Binding of Me(2)NCN was observed to proceed by reversible formation of an intermediate complex 1-[eta(1)-NCNMe(2)] which subsequently forms 1-[eta(2)-NCNMe(2)]: DeltaH(++)(k1) = 6.4 +/- 0.4 kcal mol(-1), DeltaS(++)(k1) = -18 +/- 2 cal mol(-1) K(-1), and DeltaH(++)(k2) = 11.1 +/- 0.2 kcal mol(-1), DeltaS(++)(k2) = -7.5 +/- 0.8 cal mol(-1) K(-1). The oxidative addition of PhSSPh to 1-[eta(1)-NCPh] is a rapid second-order process with activation parameters: DeltaH(++) = 6.7 +/- 0.6 kcal mol(-1), DeltaS(++) = -27 +/- 4 cal mol(-1) K(-1). The oxidative addition of PhSSPh to 1-[eta(2)-NCNMe(2)] also followed a second-order rate law but was much slower: DeltaH(++) = 12.2 +/- 1.5 kcal mol(-1) and DeltaS(++) = -25.4 +/- 5.0 cal mol(-1) K(-1). The crystal structure of 1-[eta(1)-NC(SPh)NMe(2)] is reported. Trapping of in situ generated 1-[eta(1)-NCNMe(2)] by PhSSPh was successful at low temperatures (-80 to -40 degrees C) as studied by stopped flow methods. If 1-[eta(1)-NCNMe(2)] is not intercepted before isomerization to 1-[eta(2)-NCNMe(2)] no oxidative addition occurs at low temperatures. The structures of key intermediates have been studied by density functional theory, confirming partial radical character of the carbon atom in eta(1)-bound nitriles. A complete reaction profile for reversible ligand binding, eta(1) to eta(2) isomerization, and oxidative addition of PhSSPh has been assembled and gives a clear picture of ligand reactivity as a function of hapticity in this system.

{2,6‐Bis[(dimethyl­amino)meth­yl]phenyl‐κ2N,C1,N′}chloro­nickel(II)

The title complex, [Ni(C12H19N2)Cl], consists of a slightly distorted square-planar NiII center coordinated by an anionic terdentate NCN pincer-type ligand, where both N atoms are trans to each other, and by a chloride ion. It is isostructural with two platinum analogues.