A benzene-core trinuclear GdIII complex: towards the optimization of relaxivity for MRI contrast agent applications at high magnetic field

A novel ligand, H(12)L, based on a trimethylbenzene core bearing three methylenediethylenetriamine-N,N,N',N'-tetraacetate moieties (-CH(2)DTTA(4-)) for Gd(3+) chelation has been synthesized, and its trinuclear Gd(3+) complex [Gd(3)L(H(2)O)(6)](3-) investigated with respect to MRI contrast agent applications. A multiple-field, variable-temperature (17)O NMR and proton relaxivity study on [Gd(3)L(H(2)O)(6)](3-) yielded the parameters characterizing water exchange and rotational dynamics. On the basis of the (17)O chemical shifts, bishydration of Gd(3+) could be evidenced. The water exchange rate, k(ex)(298)=9.0+/-3.0 s(-1) is around twice as high as k(ex)(298) of the commercial [Gd(DTPA)(H(2)O)](2-) and comparable to those on analogous Gd(3+)-DTTA chelates. Despite the relatively small size of the complex, the rotational dynamics had to be described with the Lipari-Szabo approach, by separating global and local motions. The difference between the local and global rotational correlation times, tau(lO)(298)=170+/-10 ps and tau(gO)(298)=540+/-100 ps respectively, shows that [Gd(3)L(H(2)O)(6)](3-) is not fully rigid; its flexibility originates from the CH(2) linker between the benzene core and the poly(amino carboxylate) moiety. As a consequence of the two inner-sphere water molecules per Gd(3+), their close to optimal exchange rate and the appropriate size and limited flexibility of the molecule, [Gd(3)L(H(2)O)(6)](3-) has remarkable proton relaxivities when compared with commercial contrast agents, particularly at high magnetic fields (r(1)=21.6, 17.0 and 10.7 mM(-1)s(-1) at 60, 200 and 400 MHz respectively, at 25 degrees C; r(1) is the paramagnetic enhancement of the longitudinal water proton relaxation rate, referred to 1 mM concentration of Gd(3+)).     

The tensor Golub–Kahan–Tikhonov method applied to the solution of ill-posed problems with a t-product structure

This paper discusses an application of partial tensor Golub–Kahan bidiagonalization to the solution of large-scale linear discrete ill-posed problems based on the t-product formalism for third-order tensors proposed by Kilmer and Martin (M. E. Kilmer and C. D. Martin, Factorization strategies for third order tensors, Linear Algebra Appl., 435 (2011), pp. 641-658). The solution methods presented first reduce a given (large-scale) problem to a problem of small size by application of a few steps of tensor Golub–Kahan bidiagonalization and then regularize the reduced problem by Tikhonov's method. The regularization operator is a third-order tensor, and the data may be represented by a matrix, that is, a tensor slice, or by a general third-order tensor. A regularization parameter is determined by the discrepancy principle. This results in fully automatic solution methods that neither require a user to choose the number of bidiagonalization steps nor the regularization parameter. The methods presented extend available methods for the solution for linear discrete ill-posed problems defined by a matrix operator to linear discrete ill-posed problems defined by a third-order tensor operator. An interlacing property of singular tubes for third-order tensors is shown and applied. Several algorithms are presented. Computed examples illustrate the advantage of the tensor t-product approach, in comparison with solution methods that are based on matricization of the tensor equation.     

GCV for Tikhonov regularization via global Golub–Kahan decomposition

Generalized cross validation is a popular approach to determining the regularization parameter in Tikhonov regularization. The regularization parameter is chosen by minimizing an expression, which is easy to evaluate for small‐scale problems, but prohibitively expensive to compute for large‐scale ones. This paper describes a novel method, based on Gauss‐type quadrature, for determining upper and lower bounds for the desired expression. These bounds are used to determine the regularization parameter for large‐scale problems. Computed examples illustrate the performance of the proposed method and demonstrate its competitiveness. Copyright © 2016 John Wiley & Sons, Ltd.     

On the strong Brillinger-mixing property of α-determinantal point processes and some applications

First, we derive a representation formula for all cumulant density functions in terms of the non-negative definite kernel function C(x, y) defining an α-determinantal point process (DPP). Assuming absolute integrability of the function C₀(x) = C(o, x), we show that a stationary α-DPP with kernel function C₀(x) is “strongly” Brillinger-mixing, implying, among others, that its tail-σ-field is trivial. Second, we use this mixing property to prove rates of normal convergence for shot-noise processes and sketch some applications to statistical second-order analysis of α-DPPs.     

Coupling techniques in speciation analysis

Summary Direct coupling techniques in speciation analysis lead to reproducible results with lower risks of trace contamination or losses of analytes in a shorter period of time. The direct coupling mode seems to be most promising for liquid chromatographic separation methods — especially gel permeation chromatography — and for some electrophoretic methods — as flow-through and capillary techniques. Promising detection methods are Flame-AAS and ICP-OES but also hydride-generation AAS and chemical reaction detectors in continuous-flow technique.     

Cyclopalladation of 1,1′-Azonaphthalene (= Di(naphthalen-1-yl)diazene): Isolation and characterization of two isomeric complexes

The cyclopalladation of 1,1′-azonaphthalene (= di(naphthalen-1-yl)diazene; 2 ) with bis(hexafluoroacetyl-acetonato)palladium(II) (3; [Pd(hfa)₂]) yields the ortho-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ²O,O′)[1-(naphthalen-1-ylazo-κN²)naphthalen-2-yl-κC²]palladium(II) ( 4 ) as well as the peri-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ²O,O′)[8-(naphthalen-1-ylazo-κN²)naphthalen-1-yl-κC¹]-palladium(II) ( 5 ); their structures were corroborated by X-ray analyses. The formation of the novel peri-metallated product 5 containing a six-membered palladacycle strongly depends upon the reaction conditions.     

Automated determination of carboxylic acids in biological and geochemical samples by means of a chemical reaction detector

Rapid evaluation of carboxylic acids by means of an automated spectrophotometric determination in a continuous-flow system is described. The system was applied to food and soil extracts either as a stand-alone device or as a chemical reaction detector coupled to a chromatographic separation column. Calibration in the automated system was performed with citric acid as a reference standard in the concentration range 4.76 × 10^?5?4.76 × 10^?3 mol l^?1. The molar calibration equation was A=64x ? 6.7 × 10^?5 (x=concentration ) with a correlation coefficient of 0.9997 ( six points). The sample volume was 0.5 ml. In addition to the semi-quantitative evaluation of carboxylic groups, it is shown that the system is also applicable to species analyses.     

A Demonstrated Example of Competing D and Id Mechanisms for Dimethylformamide Exchange on the Octakis (dimethylformamide)-erbium (III) Ion

Dimethylformamide exchange on [Er(DMF)₈]³⁺ is shown to take place via two competing dissociative-type mechanisms: D and I_d. It is concluded that a mechanistic crossover occurs along the series Tb-Yb and this behaviour is contrasted with the changeover observed for the solvent exchange on the first-row transition metal ions.     

Ab initio studies of structural features not easily amenable to experiment. 42. Molecular geometries and conformational analysis of methylbutanoate

Conformational energy profiles were calculated for τ₁, the C? C? C?O torsion, and τ₂, the C? C? C? C torsion, of methyl butanoate, using Pulay's ab initio gradient procedure at the 4-21G level with geometry optimization at each point. In addition, the structures of seven conformations were fully relaxed, including the energy minima (τ₁, τ₂) = (0, ?60), (0, 180), (120, 180), (120, ?60), and the maxima (0, 0), (180, 180), and (60, ?60). The calculated geometries confirm the previously formulated rule that, in saturated hydrocarbons, a C? H bond trans to a C? C bond (C? H_s) is consistently shorter than a C? H bond (C? H_a) trans to another C? H bond. Specifically, for X? C(α) (? O)? C(β)? C(γ)? C(δ) systems, the following rules can be formulated, incorporating results from previous studies of butanal, butanoic acid, and 2-pentanone: (1) C(δ)? H_s < C(δ)? H_a in all the conformers in which the δ-methyl group is remote from the ester group; whereas, in all the conformers in which nonbonded interactions are possible between the C(δ)-methyl and the ester groups, the bonding pattern is affected by a C? H ?O?C interaction. (2) In the most stable conformers, (0, 60), C(β)? H_a < C(β)? H_s, and C(γ)? H_a < C(γ)? H_s, regardless of X. (3) The average C? C bonds in the τ₂ = 180° conformers are consistently shorter than those with τ₂ = 60° (compared at τ₁ constant). In the most stable conformations (τ₁ = 0°, τ₂ = 60° or 180°), the bonding sequence is consistently C(α)? C(β) < C(β)? C(γ) < C(γ)? C(δ); whereas, when τ₁ = 120°, C(α)? C(β) < C(β)? C(γ) > C(γ)? C(δ).     

Low-dimensional Compounds Containing Cyano Groups. XI. Preparation,Crystal Structure and Properties of Two Copper(II) Dicyanamide Complexes with PF<Stack><Subscript>6</Subscript><Superscript>−</Superscript></Stack> Anions

From the reaction mixtures containing Cu(NO₃)₂, Na[N(CN)₂], KPF₆ and 2,2′-bipyridine (bpy) or 1,10- phenanthroline (phen) in 1:1:1:2 molar ratios, [Cu(bpy)₂N(CN)₂][Cu(bpy)₂(H₂O)](PF₆)₃ (1b) and [Cu (phen)₂N(CN)₂]PF₆ (1p) complexes were isolated. Measured i.r. spectra confirm the presence of all functional groups in both complexes and, moreover, they indicate monodentate coordination of dicyanamide through the cyano nitrogen atom in (1p). The structure of (1b) contains two crystallographically independent complex cations. In both, Cu is coordinated by two chelating bpy molecules, and either dicyanamide anion or water molecule fills the fifth position, completing the basal plane. The Cu^II atoms in (1p) are coordinated by two chelating phen ligands and by one dicyanamide anion in the equatorial plane. Hexafluorophosphate anions in (1b) and (1p) remain uncoordinated. Besides the ionic forces in both structures, the structure of (1b) is stabilized by strong O—H···F and O—H···N hydrogen bonds and, moreover, both structures are stabilized by weak C—H···F hydrogen bonds and possible π-π interactions between pyridine rings of bpy or phen molecules.