Aggregate, Polymer and Cluster Formation from Metal-Imino Carboxylate Complexes

Reaction of tris-(2-aminoethyl)amine (tren) andthe sodium salt of an -ketocarboxylic acid, typically sodium pyruvate, affordsin the presence of a lanthanide ion aseries of complexes and aggregates includingmononuclear, cyclic tetranuclear and polymerspecies of [L¹]^3- ([L¹]^3-=N[CH₂CH₂N=C(CH₃)COO^-]³).The aggregation of these and related d-block elementcomplexes with Na⁺ ions leadsto the formation of polymeric materials, and thefactors influencing the formation and controlof these various aggregation states are discussed.Metal cations also template the aggregationof the fragment [Ni(L²)] ([L²]^2- =CH₂[CH₂N = C(CH₃)COO^-]₂)to give, in high yield, the polynuclearaggregates {[Ni(L²)]₆M}^x+(M = Nd, Pr, Ce, La, x = 3; M = Sr, Ba, x = 2). The structures of{[Ni(L²)]₆M}^x+ show aninterstitial twelve co-ordinate, icosahedralcation M^x+ encapsulated by six [Ni(L²)]fragments. In the presence ofNa⁺, aggregation of [Ni(L²)] fragments affords {[Ni(L²)]₉Na₄(H₂O)(MeOH)(ClO₄)}³⁺ thestructure of whichshows four Na⁺ ions templating the formation ofa distorted tricapped trigonal prismatic[Ni(L²)]₉ cage. Thus, control overconstruction of various polynuclear cages viaself-assembly at octahedral junctions can beachieved using main group, transition metaland lanthanide ion templates.     

Synthesis and properties of water-soluble gold colloids covalently derivatized with neutral polymer monolayers

Citrate-capped gold nanoparticles as well as planar gold surfaces can be efficiently grafted with a covalently attached polymer monolayer a few nanometers thick, by simple contact of the metal surface with dilute aqueous solutions of hydrophilic polymers that are end-capped with disulfide moieties, as shown by UV/vis absorption, dynamic light scattering, and surface plasmon resonance studies. The hydrophilic polymer-coated gold colloids can be freeze-dried and stored as powders that can be subsequently dissolved to yield stable aqueous dispersions, even at very large concentrations. They allow for applying filtrations, gel permeation chromatography, or centrifugation. They do not suffer from undesirable nonspecific adsorption of proteins while allowing the diffusion of small species within the hydrogel surface coating. In addition, specific properties of the original hydrophilic polymers are retained such as a lower critical solution temperature. The latter feature could be useful to enhance optical responses of functionalized gold surfaces toward interaction with various substrates.     

Synthesis of titanium(IV) guanidinate complexes and the formation of titanium carbonitride via low-pressure chemical vapor deposition

The mono(guanidinato) complex [Ti(NMe2)2Cl{i-PrNC[N(SiMe3)2]N-i-Pr}] (1) was prepared by reaction of [Ti(NMe2)2Cl2] with 1 or 2 equiv of the lithium guanidinate salt [Li{i-PrNC[N(SiMe3)2]N-i-Pr}]. Compound 1 has been characterized by X-ray crystallography. Treatment of TiCl4 with 2 equiv of [Li{i-PrNC[N(SiMe3)2]N-i-Pr}] resulted in the formation of dark red crystals. X-ray crystallography showed that these crystals consist of a 70:30 mixture of two bis(guanidinato) complexes, namely, [TiCl2{i-PrNC[N(SiMe3)2]N-i-Pr}{i-PrNC(N=CMe2)N-i-Pr}] (2) and [TiCl2{i-PrNC[N(SiMe3)2]N-i-Pr}{i-PrNC[N(H)-i-Pr]N-i-Pr}] (3). Both compounds 2 and 3 possess a transformed guanidinate ligand. Low-pressure chemical vapor deposition of either compound 1 or [TiCl2{i-PrNC(NMe2)N-i-Pr}] (4) at 600 degrees C results in thin films of titanium carbonitride.     

Möbius aromaticity in [12]annulene: cis-trans isomerization via twist-coupled bond shifting

Density functional and coupled cluster calculations show that facile thermal configuration change in [12]annulene occurs via a twist-coupled bond-shifting mechanism. The transition state for this process is highly aromatic with M?bius topology. At the CCSD(T)/cc-pVDZ//BH&HLYP/6-311+G** level, the isomerization of tri-trans-[12]annulene 1a (CTCTCT) to its di-trans isomer 2 (CCCTCT) via such a mechanism has a barrier of 18.0 kcal/mol, in good agreement with earlier experiments. Two other aromatic M?bius bond-shifting transition states were located that result in configuration change for other [12]annulene conformers. This mechanism contrasts sharply with diradical configuration change for acyclic polyenes and with planar bond-shifting mechanisms generally assumed for annulenes. This constitutes evidence that neutral M?bius aromatic annulenes play a role in the dynamic processes of neutral [4n]annulenes.     

Self-intersection points in classical area-minimizing surfaces

In this paper we study the structure at a point of tangential self-intersection in an area-minimizing classical minimal surface inR ⁿ. The result is that the lowest order homogeneous term in the splitting function, i.e. the difference of the height functions from the tangent plane, has the form

Photochemical reactivity of α,β-unsaturated δ-lactams: Synthesis of seco-steroids. Photochemical reactions. XIII [1]

The UV. irradiation of 17 β-hydroxy-2-aza-4-androsten-3-one (1) , N-methyl-17 β-hydroxy-2-aza-4-androsten-3-one (3) , 17 β-hydroxy-4-aza-5 β-androst-1-en-3-one (2) and N-methyl-17 β-hydroxy-4-aza-5 β-androst-1-en-3-one (4) , gives rise to 1,10-seco (from 1 and 3 ) and 5, 10-seco (from 2 and 4 ) steroids.     

Characterization of low-molecular weight peptides in champagne wine by liquid chromatography/tandem mass spectrometry

This paper reports the use of an on-line LC–ESI–MS/MS method for the identification and quantification of di- and tripeptides in champagne wine without laborious sample pretreatment. The identification of these compounds, in their underivatised form, is based on identical retention times and ESI–MS spectra to those of reference standards. The presence of nine dipeptides (Arg–Ile, Ile–Arg, Ile–Val, Lys–Phe, Lys–Tyr, Phe–Lys, Tyr–Gln, Tyr–Lys, Val–Ile) and the absence of two tripeptides (Phe–Arg–Arg and Lys–Met–Asn) have been evidenced in the matrix. Calibration curves for each analyte were established using Phe–Arg as internal standard. The calibration curves were linear in the concentration range 0.1–10 mg L⁻¹ with a determination coefficient, r², better than 0.992. The accuracy for the calibration standard was estimated at between 92 and 102%. This method allows high recovery and satisfies the necessary requirements with respect to accuracy, repeatability and sensitivity. The first application of this analytical method to the measurement of di- and tri-peptides in different vintages of champagne wine is reported. Compositional changes in the peptides occurred depending on the vintage.     

Synthesis and small molecule reactivity of uranium(IV) alkoxide complexes with both bound and pendant N-heterocyclic carbene ligands

The syntheses of two tetravalent uranium alkoxide-carbene complexes are reported, [UIL3], and [UL4] where L = OCMe2CH2[1-C(NCHCHNiPr)]. The latter shows dynamic behaviour of the alkoxycarbene ligands in solution at room temperature, and the crystal structure of [UL4] shows that one carbene group remains uncoordinated. The unbound N-heterocyclic carbene group is trapped by a range of reagents such as 16-valence-electron metal carbonyl fragments and BH3 moieties, forming, for example, [UL3(mu-L)W(CO)5], [UL2(mu-L)2Mo(CO)4], and [UL(n)(L-BH3)(4-n)] (n = 1-4), demonstrating the potential for these hemilabile electropositive metal-carbene complexes to participate in the bifunctional activation of small molecules.     

New organolithium addition methodology to diversely functionalized indoles

A novel synthetic approach to diversely functionalized indoles is described. Boc-protected ortho-aminostyrenes undergo an alkyllithium addition reaction, thereby generating a lithiated intermediate, which upon reaction with specific electrophiles sets up a cascade reaction process between the reacted electrophile and ortho-amino substituent, facilitating an in situ ring closure, followed by dehydration, to generate an indole ring system. This methodology is demonstrated by the synthesis of a range of 3,5-, 1,3,5-, and 2,3,5-substituted indoles.     

Lanthanide complexes of new nonadentate imino-phosphonate ligands derived from 1,4,7-triazacyclononane: synthesis, structural characterisation and NMR studies

The polyamino ligand 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane (1) has been used to synthesise two new ligands by Schiff-base condensation with methyl sodium acetyl phosphonate to give ligand L and methyl sodium 4-methoxybenzoyl phosphonate to give ligand L1 in the presence of lanthanide ion as templating agent to form the complexes [Ln(L)] and [Ln(L1)](Ln = Y, La, Gd, Yb). Both ligands L and L1 have nine donor atoms comprising three amine and three imine N-donors and three phosphonate O-donors and form Ln(III) complexes in which the three pendant arms of the ligands wrap around the nine-coordinate Ln(III) centres. Complexes with Y(III), La(III), Gd(III) and Yb(III) have been synthesised and the complexes [Y(L)], [Gd(L)] and [Gd(L1)] have been structurally characterised. In all the complexes the coordination polyhedron about the lanthanide centre is slightly distorted tricapped trigonal prismatic with the two triangular faces of the prism formed by the macrocyclic N-donors and the phosphonate O-donors. Interestingly, given the three chiral phosphorus centres present in [Ln(L)] and [Ln(L1)] complexes, the three crystal structures reported show the presence of only one diastereomer of the four possible. 1H, 13C and 31P NMR spectroscopic studies on diamagnetic [Y(L)] and [La(L)] and on paramagnetic [Yb(L)] complexes indicate the presence in solution of all the four different diastereomers in varying proportions. The stability of complexes [Y(L)] and [Y(L1)] in D2O in both neutral and acidic media, and the relaxivity of the Gd(III) complexes, have also been investigated.