Synthesis, crystal structure, hydrogen bonding and spectroscopy of transition-metal complexes with the ligand (N,N′-bis(2-pyridylmethyl)-1,3-propanediamine)

Six mononuclear complexes are reported with the tetradentate ligand N,N′-bis(2-pyridylmethyl)-1,3-propanediamine, (abbreviated as pypn) i.e. [Cu(pypn)(ClO₄)₂](H₂O)_1/2 (1), [Fe(pypn)Cl₂](NO₃) (2), [Zn(pypn)Cl](ClO₄) (3), [Co(pypn)(NCS)₂](ClO₄) (4), [Co(pypn)(N₃)₂](ClO₄) (5), [Zn(pypn)(NCS)₂] (6). The synthesis and X-ray crystal structures of all six compounds and their spectroscopic properties are presented.The geometry of the Cu²⁺, Co³⁺, Zn²⁺, Fe³⁺ ions is essentially octahedrally based, with the mm conformation (for Cu) and m_sf conformations for the other 3 metal ions; in compound 3 the geometry around the Zn²⁺ is distorted trigonal bipyramidal. The stabilisation of the crystal lattices is maintained by interesting, relative strong hydrogen bonds.     

A Kinetic and Structural Investigation of DNA‐Based Asymmetric Catalysis Using First‐Generation Ligands

The recently developed concept of DNA‐based asymmetric catalysis involves the transfer of chirality from the DNA double helix in reactions using a noncovalently bound catalyst. To date, two generations of DNA‐based catalysts have been reported that differ in the design of the ligand for the metal. Herein we present a study of the first generation of DNA‐based catalysts, which contain ligands comprising a metal‐binding domain linked through a spacer to a 9‐aminoacridine moiety. Particular emphasis has been placed on determining the effect of DNA on the structure of the Cu^II complex and the catalyzed Diels–Alder reaction. The most important findings are that the role of DNA is limited to being a chiral scaffold; no rate acceleration was observed in the presence of DNA. Furthermore, the optimal DNA sequence for obtaining high enantioselectivities proved to contain alternating GC nucleotides. Finally, DNA has been shown to interact with the Cu^II complex to give a chiral structure. Comparison with the second generation of DNA‐based catalysts, which bear bipyridine‐type ligands, revealed marked differences, which are believed to be related to the DNA microenvironment in which the catalyst resides and where the reaction takes place.     

Solid‐State Structural Characterization of Cutinase–ECE‐Pincer–Metal Hybrids

Crystal‐clear structures : The first crystal structures of organometallic pincer–cutinase hybrids (see figure) provide insight into the 3D structural arrangement of both the protein and the organometallic pincer moiety, and reveal different binding modes for different pincers.

     

Distance-two labellings of Hamming graphs

Let j≥k≥0 be integers. An ?-L(j,k)-labelling of a graph G=(V,E) is a mapping ?:V→{0,1,2,…,?} such that |?(u)−?(v)|≥j if u,v are adjacent and |?(u)−?(v)|≥k if they are distance two apart. Let λ_j,k(G) be the smallest integer ? such that G admits an ?-L(j,k)-labelling. Define to be the smallest ? if G admits an ?-L(j,k)-labelling with ?(V)={0,1,2,…,?} and ∞ otherwise. An ?-cyclic L(j,k)-labelling is a mapping ?:V→Z_? such that |?(u)−?(v)|_?≥j if u,v are adjacent and |?(u)−?(v)|_?≥k if they are distance two apart, where |x|_?=min{x,?−x} for x between 0 and ?. Let σ_j,k(G) be the smallest ?−1 of such a labelling, and define similarly to . We determine λ_2,0, , σ_2,0 and for all Hamming graphs K_q1□K_q2□?□K_qd (d≥2, q₁≥q₂≥?≥q_d≥2) and give optimal labellings, with the only exception being for q≥4. We also prove the following “sandwich theorem”: If q₁ is sufficiently large then for any graph G between K_q1□K_q2 and K_q1□K_q2□?□K_qd, and moreover we give a labelling which is optimal for these eight invariants simultaneously.     

Multiple packets of neutral molecules revolving for over a mile

The level of control that one has over neutral molecules in beams dictates their possible applications. Here we experimentally demonstrate that state-selected, neutral molecules can be kept together in a few mm long packet for a distance of over one mile. This is accomplished in a circular arrangement of 40 straight electrostatic hexapoles through which the molecules propagate over 1000 times. Up to 19 packets of molecules have simultaneously been stored in this ring structure. This brings the realization of a molecular low-energy collider within reach.     

Coherent reflection of he atom beams from rough surfaces at grazing incidence

We report coherent reflection of thermal He atom beams from various microscopically rough surfaces at grazing incidence. For a sufficiently small normal component k(z) of the incident wave vector of the atom the reflection probability is found to be a function of k(z) only. This behavior is explained by quantum reflection at the attractive branch of the Casimir-van der Waals interaction potential. For larger values of k(z) the overall reflection probability decreases rapidly and is found to also depend on the parallel component k(x) of the wave vector. The material specific k(x) dependence for this classic reflection at the repulsive branch of the potential is discussed in terms of an averaging out of the surface roughness under grazing incidence conditions.     

Principal component and linear discriminant analysis of T1 histograms of white and grey matter in multiple sclerosis

Twenty-three relapsing remitting multiple sclerosis (RRMS) patients and 14 controls were imaged to produce normal-appearing white and grey matter T1 histograms. These were used to assess whether histogram measures from principal component analysis (PCA) and linear discriminant analysis (LDA) out-perform traditional histogram metrics in classification of T1 histograms into control and RRMS subject groups and in correlation with the expanded disability status score (EDSS). The histograms were classified into one of two groups using a leave-one-out analysis. In addition, the patients were scanned serially, and the calculated parameters correlated with the EDSS. The classification results showed that the more complex techniques were at least as good at classifying the subjects as histogram mean, peak height and peak location, with PCA/LDA having success rates of 76% for white matter and 68%/65% for grey matter. No significant correlations were found with EDSS for any histogram parameter. These results indicate that there is much information contained within the grey matter as well as the white matter histograms. Although in these histograms PCA and LDA did not add greatly to the discriminatory power of traditional histogram parameters, they provide marginally better performance, while relying only on data-driven feature selection.     

Reversible phase transition of colloids in a binary liquid solvent

We report fluid-fluid and fluid-solid phase transitions of charge-stabilized polystyrene particles suspended in a binary liquid mixture of 3-methylpyridine and water. These thermally reversible phase transitions occur in the homogeneous phase of the binary liquid mixture below the coexistence temperature of the two liquids. Close density matching of the particles and the solvent allows us to follow the phase behavior until complete coexistence of macroscopic phases with temperature as the control parameter. We use small angle x-ray scattering to characterize these phases as colloidal gas, liquid, fcc crystal, and glass.     

Two Mononuclear Compounds with bis(Pyrimidin-2-yl)amine as a Ligand and as a Hydrogen-bonded Lattice Molecule. Synthesis, Structure and Spectroscopy of {[M(dipm)(H2O)(A)](dipm)(A)(H2O)} (M?=?Cd with A?=?ClO4; and Zn with A?=?BF4)

Abstract  Two isostructural mononuclear compounds with formula {[Cd(dipm)(H₂O)(ClO₄)](dipm)(ClO₄)(H₂O)} (1) {[Zn(dipm)(H₂O)(BF₄)](dipm)(BF₄)(H₂O)} (2) and (in which dipm = bis(pyrimidin-2-yl)amine) have been synthesised and characterised by X-ray crystallography and infrared spectroscopy. The structure of compound 1 has been solved in the space group P2₁/n with a = 18.860(4), b = 8.579(2), c = 20.917(4) ?, β = 101.33(3)°, V = 3318.4(12) ?³, Z = 4 with final R = 0.0454. The structure of compound 2 has also been solved in the space group P2₁/n with a = 19.026(4), b = 8.389(1), c = 20.720(4) ?, β = 101.37(3)°, V = 3242.2(10) ?³, Z = 4 with final R = 0.0689. The geometry around the metal ions is octahedral, and is constituted by four nitrogen atoms from two dipm molecules, an oxygen atom from a water molecule and a semi-coordinating anion atom ( for compound 1 and for compound 2). In the lattice are also present: a non-coordinating water molecule, an anion molecule and a dipm molecule. For compound 1, the Cd–N distances are between 2.296 and 2.328 ?. The distance is 2.310 ? and the is 2.477 ?. The Zn–N distances in compound 2 are between 2.121 and 2.164 ?. The distance is 2.147 ? and the distance is 2.373 ?. A hydrogen bond interaction of the Watson–Crick type is observed between the amine N atom of a dipm ligand to a pyrimidyl N atom and a non-coordinating dipm ligand with N···N distances, which vary from 3.066(5) to 3.109(5) ?. Furthermore medium to strong hydrogen bond interactions are present between oxygen atoms of the water molecules and the anions of the compounds. Index Abstract  Two isostructural mononuclear compounds with formula {[Cd(dipm)(H₂O)(ClO₄)](dipm)(ClO₄)(H₂O)} (1) {[Zn(dipm)(H₂O)(BF₄)](dipm)(BF₄)(H₂O)} (2) and (in which dipm = bis(pyrimidin-2-yl)amine) have been synthesised and characterised by X-ray crystallography and infrared spectroscopy. . Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Region of interest and pixel-by-pixel analysis of dynamic contrast enhanced magnetic resonance imaging parameters and time-intensity curve shapes: a comparison in chondroid tumors

Dynamic contrast enhanced (DCE) MRI is widely acknowledged to be a helpful tool in the diagnosis and differentiation of tumors. In common clinical settings, the dynamic changes described by the time-intensity curves (TICs) are evaluated to find patterns of atypical tissue behavior, i.e., areas characterized by rapid contrast wash-in and wash-out. Despite the ease of this approach, there is no consensus about the specificity of the TIC shapes in discriminating tumor grades. We explore a new way of looking at TICs, where these are not averaged over a selected region of interest (ROI), but rendered pixel-by-pixel. In this way, the characteristic of the tissue is not given as a single TIC classification but as a distribution of the different TIC patterns. We applied this method in a group of patients with chondroid tumors and compared its outcome with the outcome of the standard ROI-based averaged TIC analysis. Furthermore, we focused on the problem of ROI selection in these tumors and how this affects the outcome of the TIC analysis. Finally, we investigated what relationship exists between the "standard" DCE-MRI parameter maximum enhancement (ME) and the TIC shape. CONCLUSIONS: We demonstrate that, where the ROI approach fails to show the presence of areas of rapid contrast wash-in and wash-out, the pixel-by-pixel approach reveals the coexistence of a heterogeneous pattern of TIC shapes. Secondly, we point out the differences in the DCE MRI parameters and tumor volume that can result when selecting the tumor based on DCE parameter maps or post-contrast T1-weighted images. Finally, we show that ME maps and TIC shape maps highlight different tissue areas and, therefore, the use of the ME maps is not appropriate for the correct identification of areas of atypical TICs.