Ion‐Pair Complexation with a Cavitand Receptor

The capability of resorcinarenes to bind anions within the alkyl feet at the lower rim has been exploited as the starting point for developing a new cavitand able to engulf contact ion pairs of primary ammonium salts in chlorinated solvents with association constants (K_ass) in the range of 10³–10⁴ M ^?1. Methylene bridges were introduced into the upper rim to freeze the resorcinarene in the cone conformation with the four H_down protons converging in the lower pocket, thereby maximizing the CH–anion interactions responsible for the anion binding. Four additional phosphate moieties were introduced into the lower rim in close proximity to the anionic site to provide hydrogen‐bonding‐acceptor P?O groups and promote cation complexation at the bottom of the cavitand. The binding ability of the synthesized ligands was analyzed by ¹H NMR spectroscopy and, when possible, by isothermal titration calorimetry (ITC); the data were in agreement when complementary techniques were used.     

Interplay of Magnetic Exchange Interactions and Ni?S?Ni Bond Angles in Polynuclear Nickel(II) Complexes

The ability of bridging thiophenolate groups (RS^?) to transmit magnetic exchange interactions between paramagnetic Ni^II ions is examined. Specific attention is paid to complexes with large Ni? SR? Ni angles. For this purpose, dinuclear [Ni₂L¹(μ‐OAc)?I₂][I₅] ( 2 ) and trinuclear [Ni₃L²(OAc)₂][BPh₄]₂ ( 3 ), where H₂L¹ and H₂L² represent 24‐membered macrocyclic amino‐thiophenol ligands, are prepared and fully characterized by IR‐ and UV/Vis spectroscopy, X‐ray crystallography, static magnetization M measurements and high‐field electron spin resonance (HF‐ESR). The dinuclear complex 2 has a central N₃Ni₂(μ‐S)₂(μ‐OAc)Ni₂N₃ core with a mean Ni? S? Ni angle of 92°. The macrocycle L² supports a trinuclear complex 3 , with distorted octahedral N₂O₂S₂ and N₂O₃S coordination environments for one central and two terminal Ni^II ions, respectively. The Ni? S? Ni angles are at 132.8° and 133.5°. We find that the variation of the bond angles has a very strong impact on the magnetic properties of the Ni complexes. In the case of the Ni₂‐complex, temperature T and magnetic field B dependencies of M reveal a ferromagnetic coupling J=?29 cm^?1 between two Ni^II ions (H=JS₁S₂). HF‐ESR measurements yield a negative axial magnetic anisotropy (D<0) which implies a bistable (easy axis) magnetic ground state. In contrast, for the Ni₃‐complex we find an appreciable antiferromagnetic coupling J′=97 cm^?1 between the Ni^II ions and a positive axial magnetic anisotropy (D>0) which implies an easy plane situation.     

Retention of functional polymers in liquid adsorption chromatography: Effect of the end groups in PEGs and their methyl ethers in different mobile phases

It is shown that the end group parameter, which describes the influence of the end group on retention, can be determined in RP chromatography from two chromatograms of a nonfunctional and a monofunctional sample, if a sufficient number of peaks with the same number of repeat units in each sample can be reasonably resolved and identified. The same procedure can also be applied for pairs of di‐ and monofunctional polymers. End group parameters have been determined in three different mobile phases: acetonitrile–water, acetone–water and methanol–water of different compositions. The temperature dependence of the interaction parameter of the repeat unit and the end group parameter has been found to be different, which allows a fine‐tuning of retention.     

SERS Labels for Red Laser Excitation: Silica‐Encapsulated SAMs on Tunable Gold/Silver Nanoshells

In a glass house : Silica‐encapsulated self‐assembled monolayers (SAMs) on tunable gold/silver nanoshells were used as labels for surface‐enhanced Raman scattering (SERS). This concept combines the spectroscopic advantages arising from maximum surface coverage and uniform molecular orientation of the Raman reporter molecules within the complete monolayer together with the high chemical and mechanical stability of the glass shell.

     

On the Stability Analysis of Decoupled Solution Schemes

Many problems in engineering, physics or other disciplines require an integrated treatment of coupled fields. These problems are characterised by a dynamic interaction among two or more physically or computationally distinct components, where the undergoing mathematical model commonly consists of a system of coupled PDE. Considerable progress has been made in the development of appropriate computational schemes to solve such coupled PDE systems. These attempts have resulted in various monolithic and decoupled numerical solution approaches. Despite the unconditional stability offered by implicit monolithic solution strategies, their use is not always recommended. The reason mainly lies in the complexity of the resulting system of equations and the limited flexibility in choosing appropriate time integrators for individual components. This has motivated the elaboration of tailored decoupled solution schemes, which follow the idea of splitting the problem into several sub-problems. But selection of the way of splitting can have a direct influence on the stability of the resulting solution algorithm. This necessitates the stability analysis of such an algorithm. Here, we introduce a general framework for the stability analysis of decoupled solution schemes. The approach is then used to study the stability behaviour of established decoupling strategies applied to typical volume- and surface-coupled problems, namely, coupled problems of thermoelasticity, porous media dynamics and structure-structure interaction. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

DIESEL-MP2: a new program to perform large-scale multireference-MP2 computations

This article presents a new MR‐MP2 code (Multi‐Reference Møller–Plesset 2nd order) suitable for the computation MR‐MP2 energies of extended systems with strong near degeneracy effects (e.g., open shell systems). It is based on the DIESEL program package developed by Hanrath and Engels. Due to improved algorithms the new code is able to handle systems with 400–500 basis functions and more than 100 electrons. The code is made for parallel computers with distributed memory, but can also be run on local machines. It possesses two integral interfaces (MOLCAS, TURBOMOLE). The algorithms are briefly introduced and timings for the Neocarzinostatin chromophore are presented. The efficiencies of the codes obtained with Intel or GNU compilers are compared. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1055–1062, 2006     

Ion mobility spectrometric investigation of aromatic cations in the gas phase

In this work, ion mobility (IM) spectra of more than 50 aromatic compounds were recorded with a laser-based IM spectrometer at atmospheric pressure. IM spectra of PAH in the laser desorption experiment show a high complexity resulting from the occurrence of monomeric, dimeric, and oligomeric cluster ions. The mobilities of all compounds were determined in helium as drift gas. This allows the calculation of the diffusion cross sections (Omega(calc)) on the basis of the exact hard sphere scattering model and their comparison with the experimentally determined diffusion cross sections (Omega(exp)). Extended Omega(exp)/Omega(calc) and Omega(exp)/mass correlations were performed in order to gain insight into conformational properties of cationic alkyl benzenes and internal rotation of phenyl rings in aromatic ions. This is demonstrated with some examples, such as the evaluation of the dihedral angle of the ions of 9,10-diphenylanthracene, o- and m-terphenyl, and 1,2,3- and 1,3,5-triphenylbenzene. Furthermore, sandwich and T-structures of dimeric PAH cations are discussed. The analysis was extended to oligomeric ions with up to nine monomer units. Experimental evidence is presented suggesting the formation of pi-stacks with a transition toward modified pi-stacks with increasing cluster size. The distance between monomeric units in dimeric and oligomeric ions was obtained.     

Influence of phosphonation and phosphation on surface acid-base and morphological properties of CaO as investigated by in situ FTIR spectroscopy and electron microscopy

Pure, phosphated, and phosphonated CaO samples were prepared and characterized by X-ray powder diffractometry, FTIR spectroscopy, scanning electron microscopy, and energy-dispersive X-ray microprobing. Surface acid-base properties were probed by in situ FTIR spectroscopy of adsorbed CO (at 85 K), CDCl3 (at RT), CO2 (at RT), and methyl butynol decomposition reactions (at 473 K). Results obtained have shown phosphate and, to a larger extent, phosphonate additives to enhance the strength of Lewis acid sites exposed on CaO surfaces, at the expense of the Lewis base site strength. The phosphonation has been found, moreover, to make CaO particles grow in a preferential direction and be less susceptible to rehydration. These findings may establish surface chemical attributes for the application of the methylene bisphosphonate (MBP) class of drugs to hamper acid-induced resorption of bone materials (osteoporosis).     

Asymmetric synthesis of highly substituted azapolycyclic compounds via 2-alkenyl sulfoximines: potential scaffolds for peptide mimetics

The application of metalated, enantiomerically pure acyclic and cyclic 2-alkenyl sulfoximines for the synthesis of highly substituted aza(poly)cyclic ring systems is described. The method relies on a one-pot combination of a reagent-controlled allyl transfer reaction to alpha- or beta-amino aldehydes, followed by a Michael-type cyclization of the intermediate vinyl sulfoximines generated in the first step. The sulfur-free target compounds are preferentially obtained by samarium iodide treatment of the sulfonimidoyl substituted heterocycles. In addition to this methodological work, initial results on the biological activity of selected examples are reported. Furthermore, a concept for the transformation of peptidic lead structures into non-peptide mimetics is described, and the relevance of the new approach to highly substituted azaheterocycles in this context is discussed.     

The conformation of cyclo(-D-Pro-Ala4-) as a model for cyclic pentapeptides of the DL4 type

The conformation of the cyclic pentapeptide cyclo(-D-Pro-Ala(4)-) in solution and in the solid state was reinvestigated using modern NMR techniques. To allow unequivocal characterization of hydrogen bonds, relaxation behavior, and intramolecular distances, differently labeled isotopomers were synthesized. The NMR results, supported by extensive MD simulations, demonstrate unambiguously that the preferred conformation previously described by us, but recently questioned, is indeed correct. The validation of the conformational preferences of this cyclic peptide is important given that this system is a template for several bioactive compounds and for controlled "spatial screening" for the search of bioactive conformations.