Improved CE(SDS)-CZE-MS method utilizing an 8-port nanoliter valve

Capillary sieving electrophoresis utilizing SDS (CE(SDS)) is one of the most applied methods for the analysis of antibody (mAb) size heterogeneity in the biopharmaceutical industry. Inadequate peak identification of observed protein fragments is still a major issue. In a recent publication, we introduced an electrophoretic 2D system, enabling online mass spectrometric detection of generic CE(SDS) separated peaks and identification of several mAb fragments. However, an improvement regarding system stability and handling of the approach was desired. Here, we introduce a novel 8-port valve in conjunction with an optimized decomplexation strategy. The valve contains four sample loops with increased distances between the separation dimensions. Thus, successively coinjection of solvent and cationic surfactant without any additional detector in the second dimension is enabled, simplifying the decomplexation strategy. Removal efficiency was optimized by testing different volumes of solvents as presample and cationic surfactant as postsample zone. 2D measurements of the light and heavy chain of the reduced NIST mAb with the 8-port valve and the optimized decomplexation strategy demonstrates the increased robustness of the system. The presented novel set-up is a step toward routine application of CE(SDS)-CZE-MS for impurity characterization of proteins in the biopharmaceutical field.     

Access to Optically Active 3‐Substituted Piperidines by Ring Expansion of Prolinols and Derivatives

The ring expansion of prolinols via an aziridinium intermediate gives C3‐substituted piperidines in good yields and enantiomeric excess, the substituent at the C3 position being derived from the most reactive nucleophile in the reaction mixture. Depending on the nucleophile, the reaction proceeds under thermodynamic or kinetic control. The regioselectivity of attack of nucleophiles on the aziridinium intermediate depends on the nature of the substituents on the nitrogen atom and the C4 position of the starting prolinols.     

A Silver Bite: Crystalline Heterometallic Architectures Based on Ag–π Interactions with a Bis‐Dipyrrin Zinc Helicate

An unprecedented mode of assembly of helical motives and Ag^I ions in the crystalline state is described. The combination of a Zn^II helicate based on a 2,2′‐bisdpm bearing peripheral benzonitrile moieties with AgX salts, leads to the formation of a tetranuclear core containing Ag–π interactions. Depending on the coordinating ability of the X^? anion and the solvents used, the tetranuclear complex self‐assembles into coordination polymers of varying dimensionality. From the sequence of coordination events (Ag–π or Ag–peripheral site), one may envisage two possible construction scenarios. However, the Ag–π as primary event seems reasonable owing to the rather weak binding propensity of the nitrile group and the chelating nature of the π‐clefts.     

Multiscale Approach to the Study of the Electronic Properties of Two Thiophene Curcuminoid Molecules

We studied the electronic and conductance properties of two thiophene–curcuminoid molecules, 2‐thphCCM ( 1 ) and 3‐thphCCM ( 2 ), in which the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV/Vis absorption studies to obtain the values of the HOMO–LUMO band gap energies, showing that molecule 1 has lower values than 2 . Theoretical calculations show the same trend. Self‐assembled monolayers (SAMs) of these molecules were studied by using electrochemistry, showing that the interaction with gold reduces drastically the HOMO–LUMO gap in both molecules to almost the same value. Single‐molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations, we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der Waals interaction between the thiophene ring and the electrodes. The one order of magnitude higher conductance value for molecule 2 corresponds to a coordinate (dative covalent) interaction between the sulfur atoms and the gold electrodes.     

Novel bis-betaines and betaines within [1(4)]meta-heterophane frameworks

After prior selection of betaine building blocks for the construction of quadrupolar heterophane frameworks, a convergent "3+1" synthetic strategy is reported for the synthesis of the title macrocycles composed of heterocyclic betaine subunit(s). These typify the first example of simple cyclophanes constructed out of both highly pi-excessive and highly pi-deficient heteroaromatic moieties linked in a 1,3-alternating fashion. The chemical reactivity of the quadrupolar heterophanes 1a and 1c toward electrophiles under neutral conditions corroborated their bis-betaine structure. The structural features of the bis-betaines 1, betaines 2 x PF6 and 5 x X, and the corresponding dicationic [1(4)]heterophanes 3 x 2X and 4 x 2Cl were studied by 1H and 13C NMR spectroscopy and electrospray ionization mass spectrometry, and confirmed by single-crystal X-ray diffraction analysis of macrocycles 1a and 2a x PF6.     

Quasi-K-Cosymplectic submersions

In this paper we study the Riemannian submersions between manifolds belonging to those classes of almost contact metric manifolds which can be assembled under the common denomination of quasi-K-cosymplectic manifolds.     

On equilibrium solutions of diffusion equations with nonlinear boundary conditions

The existence or the nonexistence of nonconstant stable equilibrium solutions for a diffusion equation with nonlinear Neumann boundary conditions is studied. We prove the nonexistence of nonconstant stable equilibria when the nonlinearity has a small Lipschitz constant or a second derivative of constant sign or either when the domain is a ball. We construct an example of existence for a connected domain with several disconnected boundary components.This work is partially supported by the project PB91-0497-C02-02 of the DGICYT (Spain).