Sublimation kinetics of scandium β-diketonates

The volatile scandium-β-diketonates are synthesised using acetylacetone (acac) and tetramethylheptanedione (tmhd) as coordinative ligands for CVD application. The X-ray powder patterns are indexed and analysed and found to be orthorhombic and monoclinic phases for Sc(acac)₃(1) and Sc(tmhd)₃(2) respectively. The sublimation and evaporation kinetics have been analyzed using three calculating techniques. The non-isothermal based activation energy values are found to be 38 ± 2 and 73 ± 2 kJ mol⁻¹ by Flynn–Wall technique for (1) and (2) respectively. The measured E_a values are close to the value obtained using Kissinger method.     

Solid-phase synthesis of backbone-cyclized β-helical peptides

This paper describes the synthesis and purification of two 22-residue cyclic peptides, cyclo{[(l-Val-d-Val)₄-(l-Val-d-Pro-Gly)]₂-} 3 and cyclo{[(d-Leu-l-Leu)₄-(d-Leu-l-Pro-Gly)]₂-} 4, that were designed to fold into double-stranded antiparallel β-helical structures. Due to intramolecular hydrogen bonding and the conformational constraints imposed by the two reverse-turn segments (d-Pro-Gly and l-Pro-Gly, respectively), the linear precursors to 3 and 4 (lin-3 and lin-4) were expected to adopt preorganized conformations that would bring the N and C termini close together and thereby favor ring closure. Precursors lin-3 and lin-4 were constructed by stepwise Boc solid-phase peptide synthesis using the commercially available alkanesulfonamide ‘safety-catch’ linker and cyclized head-to-tail via the method of cleavage-by-cyclization. The crude cyclic peptides were highly hydrophobic and contained minor impurities that could not be removed solely by reversed-phase HPLC (RP-HPLC); however, two-step purification—first by RP-HPLC with i-PrOH/water gradients, followed by gel-permeation chromatography (GPC) on Sephadex LH-20 with CHCl₃/MeOH—afforded both peptides in pure form (≥95% by ¹H NMR) and in acceptable yield (23%). Subsequent ¹H NMR experiments supported the expected structures of 3 and 4. The successful formation of the 66-membered rings of 3 and 4 is consistent with the notion of conformational preorganization in the linear precursors; furthermore, the protocols for synthesis and purification described should prove useful for preparing additional cyclic β-helical peptides, including longer peptides and peptides having polar residues.     

Copper(II) and lanthanoid(III) complexes of a new β-diketonate ligand with an appended non-coordinating phenol group

New mononuclear compounds of the ligand 1-(2-hydroxyphenyl)-3-phenylpropane-1,3-dione (H₂L) with Cu(II) and several lanthanoid(III) ions, where Ln(III) = Pr, Nd, Eu, Gd, have been synthesized and characterized by spectroscopic methods and X-ray crystal structure determinations. In all compounds, the ligand coordinates in a bidentate chelating manner, using the diketone function. In the [Cu(HL)₂], the coordination geometry of Cu(II) ion is slightly distorted square-planar; two strong intramolecular (OH?O) hydrogen-bonding interactions are established between the phenolate group and the neighboring ketone function. The lanthanoid(III) compounds have the general formula [Ln(HL)₃(CH₃OH)₂] · CH₃OH · 2H₂O; the lanthanoid(III) ion (Ln) is eight-coordinated and the coordination geometry is based on a distorted square-antiprism. In addition to the intramolecular hydrogen bonding (OH?O), intermolecular hydrogen-bonding interactions are also present between the coordinated methanol molecule and the non-coordinated methanol molecule giving rise to a three-dimensional network.     

Creation of an artificial metalloprotein with a Hoveyda-Grubbs catalyst moiety through the intrinsic inhibition mechanism of α-chymotrypsin

An L-phenylalanyl chloromethylketone-based inhibitor equipped with a Hoveyda-Grubbs catalyst moiety was regioselectively incorporated into the cleft of α-chymotrypsin through the intrinsic inhibition mechanism of the protein to construct an artificial organometallic protein.     

Characteristics of a High-Resolution Mass Spectrum of an Adduct of 2-(Diethylamino)Ethylthiol with a Dipeptide (Cys–Pro)

Journal of Analytical Chemistry -     

A synthon for a 14-electron Ir(iii) species: catalyst for highly selective β-(Z) hydrosilylation of terminal alkynes

A synthon for a 14-electron Ir(iii) species is described. The geometrical control exerted by the ligand system over the Ir-alkenyl intermediate in hydrosilylation of terminal alkynes precludes formation of the more thermodynamically stable β-(E)-vinylsilane, thus affording the β-(Z) isomer in excellent yields.     

Fluorescence immunoassay of α-fetoprotein with iron(III) tetrasulfonatophthalocyanine as a mimetic enzyme labeling reagent

A new fluorimetric immunoassay for α-fetoprotein (AFP) has been developed using a novel promising mimetic peroxidase, iron(III) tetrasulfonatophthalocyanine (FeTSPc), as a labeling reagent to catalyze the fluorescence reaction of P- hydroxyphenylacetic acid (P-HPA) and hydrogen peroxide (H₂O₂). In the competitive immunoassay, anti-AFP antibody was coated on a 96-well plate (polystyrene) and a constant amount of FeTSPc-labeled AFP and a known amount of test solution were added. Non-labeled and FeTSPc-labeled AFP compete for binding to the plate-bound antibody. After the immunoreaction, the immunochemically adsorbed FeTSPc–AFP conjugate moiety was determined by measuring the fluorescence produced in a solution containing P-HPA and H₂O₂. AFP can be determined in the concentration range of 1–300 ng mL^–1 with a detection limit of 0.5 ng mL^–1. Received: 14 November 2000 / Revised: 29 December 2000 / Accepted: 15 January 2001     

Extraction of copper(II) ions from ammonia solutions with a β-diketone extractant

The extraction of copper(II) ions from ammonia solutions with a new β-diketone extractant, DX-510A, has been studied. Kinetic features of the copper(II) extraction and back extraction have been established: the reaction orders have been determined, and extraction and stripping rate constants have been calculated to be k_e1 = 4.14 × 10^–2 s^–1 and k_be1 = 3.20 × 10^–2 s^–1, respectively. It has been demonstrated that the extraction of copper(II) ions is not accompanied by the coextraction of ammonia. The type of extracted complex has been determined and its formula has been suggested.     

Encapsulation of Cyano(cyclopentadienyl) Complexes of Iron with β-cyclodextrin

Inclusion compounds have been prepared comprising g -cyclodextrin (CD) molecules as the host and half-sandwich cyano complexes of iron as the guests. High yields of crystalline one-to-one adducts were obtained by treatment of CpFe(CO) 2 CN and K[CpFe(CO)(CN) 2 ] with g -CD. In the case of CpFe(dppe)CN [dppe=bis(diphenylphosphine)ethane], a non-stoichiometric product is obtained and it is evident that the organometallic guests are easily liberated from the host cavities. The products were characterized in the solid-state by elemental analysis, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), FTIR and CP MAS NMR ( 13 C, 31 P) spectroscopy. Additional information concerning the possible structure of the inclusion compounds was obtained from ab initio calculations using a two-layer approximation. The best organometallic- g -CD interaction is obtained with deep inclusion of the cyclopentadienyl ring, a geometry that is not possible in the case of the CpFe(dppe)CN system due to the size and orientation of the dppe ligand.     

High Trans-1,4(Co)Polymerization of β-Myrcene and Isoprene with an Iminophosphonamide Lanthanum Catalyst

β-Iminophosphonamide ligated lanthanum bis(benzyl) complex(NPNDipp)La(CH2Ph-4-Me)2(THF)(NPNDipp = Ph2P(NC6H3iPr2-2,6)2), upon activation of Al Et3 and [Ph3C][B(C6F5)4], exhibited high catalytic activity and high trans-1,4 stereoselectivity for the polymerization of bio-sourced b-myrcene(MY). Based on which, a series of novel trans-1,4 regulated elastomers could be generated by random/block copolymerization of MY and isoprene(IP).     

Reaction of nickel(II) β-diketonates with hydroxylamine. Synthesis of nickel(II) complexes of mono-oximes of β-diketones (β-ketooximes)

Nickel(II) acetylacetonate or benzoylacetonate on treatment with hydroxylamine at O°C give adducts of the type Ni(β-diket)₂(NH₂OH) ₂ which on heating in refluxing ethanol afford β-ketooximato complexes of the type Ni(β-ketox)₂(H₂O)₂.     

Complexes of copper(II) with the β-blocker atenolol

Mono- and binuclear copper(II) complexes with atenolol (HAt) can be obtained, depending on the reaction conditions. The mononuclear violet complex cation has the general formula Cu(HAt)₄ ²⁺ with an elongated octahedral geometry. The two ligands in the equatorial plane are bound in a bidentate fashion through the hydroxyl oxygen and amino nitrogen, while the other two atenolol molecules in axial position are coordinated in a monodentate way. The binuclear green complex Cu₂At₂Cl₂, is neutral, where atenolol acts as a bidentate (O^–, NH) bridging ligand. The bridge between the two Cu atoms is realized by the deprotonated oxygen of the alcohol group.     

ESR spectra of γ-irradiated samples of iron(iii) binuclear complexes

-Irradiation of -oxo-bridged binuclear iron complexes Fe^III ₂OL _n in a glycerol or dimethylformamide matrix at 77 K affords unstable mixed-valence Fe^IIF^III forms resulting from the transfer of a mobile electron generated by the ionizing radiation. These nonequilibrium forms retain the ligand environment of the original complexes, and their ESR spectra at 77–200 K are characterized by an asymmetric signal with an axially anisotropicg-factor, which is in agreement with the spectra of the Fe^IIFe syu forms obtained by chemical reduction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 869–871, April, 1996.     

Molecular and quantum mechanical studies on the monomer recognition of a highly-regular β-helical antifreeze protein

The possible interaction models for an antifreeze protein from Tenebrio molitar (TmAFP) have been systematically studied using the methods of molecular mechanics, molecular dynamics and quantum chemistry. It is hoped that these approaches would provide insights into the nature of interaction between protein monomers through sampling a number of interaction possibilities and evaluating their interaction energies between two monomers in the course of recognition. The results derived from the molecular mechanics indicate that monomerś β-sheets would be involved in interaction area and the side chains on two p-faces can match each other at the two-dimensional level. The results from molecular mechanics and ONIOM methods show that the strongest interaction energy could be gained through the formation of H-bonds when the twoβ-sheets are involved in the interaction model. Furthermore, the calculation of DFT and analysis of van der Waals bond charge density confirm further that recognition between the two TCTs mainly depends on inter-molecular hydroxyls. Therefore, our results demonstrate that during the course of interaction the most favorable association of TmAFPs is via their β-sheets.     

Molecular and quantum mechanical studies on the monomer recognition of a highly-regular β-helical antifreeze protein

The possible interaction models for an antifreeze protein from Tenebrio molitar (TmAFP) have been systematically studied using the methods of molecular mechanics, molecular dynamics and quantum chemistry. It is hoped that these approaches would provide insights into the nature of interaction between protein monomers through sampling a number of interaction possibilities and evaluating their interaction energies between two monomers in the course of recognition. The results derived from the molecular mechanics indicate that monomer's β-sheets would be involved in interaction area and the side chains on two β-faces can match each other at the two-dimensional level. The results from molecular mechanics and ONIOM methods show that the strongest interaction energy could be gained through the formation of H-bonds when the two β-sheets are involved in the interaction model. Furthermore, the calculation of DFT and analysis of van der Waals bond charge density confirm further that recognition between the two     

Pistagremic acid,a novel β-secretase enzyme (BACE1) inhibitor from Pistacia integerrima Stewart

A new triterpenic compound named pistagremic acid (PA) was once again isolated from Pistaciaintegerrima. The β-secretase inhibition study was carried out. Compound PA was found significantly active against β-secretase enzyme (BACE1) with IC₅₀ value of 350 ± 2 nM in comparison to the standard inhibitors [Asn670, Sta671, Val672]-amyloid-β/A4 precursor protein 770 fragment 662–675 (IC₅₀ = 290.71 ± 1 nM). The selectivity of this compound was also evaluated against the acetylcholinesterase and butyrylcholinesterase enzymes. Interestingly compound PA was found to be inactive against them and showed selectivity towards β-secretase enzyme (BACE1).     

Synthesis and reactivity of an isolable cobalt(I) complex containing a β-diketiminate-based acyclic tetradentate ligand

A model for cobalamin was synthesized using a new monoanionic tetradentate nitrogen donor ligand; 2-(4-tolyl)-1,3-bis(2-isopropylpyridyl)propenediimine (Tol-BDI((2-pp)2)H) (1), which utilizes isopropylpyridines as pendant arms on a β-diketiminate (BDI) backbone. During the synthesis of 1, the rearrangement product, Tol-BDI((2-pp)(4-pp))H (2) was observed. Metalation of 1 with zinc iodide and cobalt chloride yielded the corresponding Tol-BDI((2-pp)2)ZnI (3) and Tol-BDI((2-pp)2)CoCl (4) complexes. The redox properties of 4 in comparison to cobalamin were examined through electrochemical studies. Electrochemical and bulk reduction of complex 4 gave a diamagnetic cobalt(I) complex, Tol-BDI((2-pp)2)Co (5). Reactivity of 5 toward C-X bonds was investigated using methyl iodide and 1-iodo-2-(trimethylsilyl)acetylene, yielding Tol-BDI((2-pp)2)Co(CH(3))I and Tol-BDI((2-pp)2)Co(C(2)Si(CH(3))(3))I respectively. Synthesis and characterization details for these complexes, including the crystal structure of 3, are reported.     

The reactions of phosphorus(III) halides with β-diketiminato ligands

Reactions of the lithium or sodium salt, [HC(CMeNDipp)₂]M (Dipp = 2,6-diisopropylbenzene, M = Li or Na), with PBr₃ or PCl₃ affords a series of phosphenium cations that were characterized in the solid state by X-ray crystallography. Solid-state analysis reveals that for compounds 1 and 2, C–H activation of the ligand occurs and the phosphorus is bound to a nitrogen and carbon atom of the ligand. Compound 3 exhibits the more traditional nitrogen chelation of the ligand to the phosphorus atom.     

Transesterification of copper(II) β-ketoesterates and acylpyruvates with borneol

Transesterification of copper(II) acetoacetates, copper(II) trifluoroacetoacetate, and copper(II) acylpyruvates with borneol gives the copper(II) chelates of the corresponding bornyl esters in 92–95 % yields. Bornyl acetyl- and perfluoroacylpyruvates were synthesized for the first time by decomposing the respective chelates with hydrogen chloride. Bornyl acylpyruvates react with hydrazine hydrate to give 5-alkyl-3-bornyloxycarbonylpyrazoles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 902–904, May, 1993.