Zur Chemie des Bis(methylsulfonyl)-amins (Dimesylamins). III. Onium-Salze des Dimesylamins

Investigations on Bis(methylsulfonyl)-amine (Dimesylamine). III. Onium Salts of Dimesylamine Thirty-five salts of the strong acid HN(SO₂Me)₂ containing onium cations are reported. These include higher quaternary ammonium salts which show excellent solubility in solvents of low polarity, thus being particularly useful for preparing solutions of “naked” (MeSO₂)₂N^? or corresponding ion-pairs. Pyrolysis of the quaternary ammonium salts at temperatures of 200—250°C produces tertiary amines and N-alkyl-dimesylamines by (N → N′)-alkyl transfer. Alkene formation is not observed.     

Etude par Spectrométrie de Masse de la Fragmentation d'une Série de Diols Aliphatiques

The mass spectrometric fragmentation of a series of diols having the general formula HO? (CH₂)_n? OH with n = 2-11 has been studied. Extensive labelling of n-butane-1,4 diol and n-hexane-1,6 diol with deuterium allows fragmentation modes to be proposed. The labelling reveals that intramolecular exchange of H atoms often precedes the fragmentation and becomes more important when the length of the chain increases.     

Neue Koordinationsverbindungen aus Triorganylzinn(IV)-dimesylamiden und Neutralliganden: Einkern- und Mehrkernkomplexe mit molekularer oder ionischer Kristallstruktur

Polysulfonylamines. CII. New Coordination Compounds Derived from Triorganyltin(IV) Dimesylamides and Uncharged Ligands: Mononuclear and Polynuclear Complexes with Molecular or Ionic Crystal Structures The purpose of this report is to draw attention to the remarkable versatility of the dimesylamides R₃SnA [A^– = (MeSO₂)₂N^–; R = Me ( 1 a ) or Ph ( 1 b )] as precursors for pentacoordinate triorganyltin(IV) complexes belonging to four distinct structural types. Representative complexes were prepared by treating 1 a or 1 b in the appropriate molar ratios with unidentate thiourea or urea-type ligands or with the bidentate ligand [Ph₂P(O)CH₂]₂ (DPPOE). The following compounds were characterized by X-ray analysis: [Me₃Sn(A)(thiourea)] ( 2 a ; monoclinic, space group P2₁/n), [Ph₃Sn(A)(tetramethylthiourea)] ( 2 b ; monoclinic, P2₁, two independent formula units), [Me₃Sn(1-methylurea)₂]⁺ · A^– ( 3 a ; monoclinic, P2₁/c), [Ph₃Sn(1,1-dimethylurea)₂]⁺ · A^– ( 3 c ; triclinic, P1), [{Ph₃Sn(A)}₂(μ-dppoe)] ( 4 ; triclinic, P1), [Ph₃Sn(μ-dppoe)]_nⁿ⁺ · n A^– · n MeCN ( 5 ; monoclinic, P2₁/c). The lattices of 2 a , 2 b and 4 contain discrete uncharged formula units which are mononuclear for 2 a and 2 b or dinuclear for 4 , whereas 3 a , 3 c and 5 have ionic structures featuring mononuclear cations for 3 a and 3 c or an infinite linear-polymeric cation for 5 . In all the structures, the tin atoms adopt trigonal-bipyramidal geometries, the apical positions being occupied in 2 a and 2 b by the S atom of the thiourea and one O atom of A^–, in 3 a and 3 c by the O atoms of two urea-type ligands, in 4 by an O atom of the bridging DPPOE molecule and one O atom of A^–, and in 5 by two phosphoryl O atoms from different bridging DPPOE ligands. In the structures of 2 a , 3 a and 3 c , the (thio)urea NH functions are connected to A^– via intermolecular or interionic N–H … O and N–H … N hydrogen bonds. Crystals of [{Me₃Sn(bipyH⁺ … A^–)}₂(μ-bipy)]²⁺ · 2 A^– ( 6 ; monoclinic, C2/c) formed adventitiously in a reaction mixture containing 1 a and 4,4′-bipyridine. The rod-like supramolecular cation of 6 (length ca. 4 nm) is built up from two Me₃Sn⁺ units bridged through bipy and unidentally coordinated by a monoprotonated bipy (= bipyH⁺), resulting in a trigonal-bipyramidal geometry around tin (N atoms apical); each of the terminal bipyH⁺ ligands forms an ⁺N–H … N^– hydrogen bond with one A^–.     

Polysulfonylamines. CXXXII.

The crystal structure of the title compound, C₅H₇N₂⁺·C₁₂H₁₀NO₄S₂⁻, consists of two independent cation–anion pairs, A and B. Within each pair, the H—N—C—N*—H grouping (N*—H is the pyridinium function) and one N—S—O moiety of the anion are linked by N*—H⃛N and N—H⃛O hydrogen bonds to form an antidromic ring motif of type R²₂(8). The remaining amino donors give rise to N—H⃛O hydrogen bonds, connecting the ion pairs into A–B–A–B– chains. The structure testifies to the persistence of the R²₂(8) motif in question, which was previously detected as a highly robust supramolecular synthon in a series of onium di(methane­sulfonyl)­amidates. The structure is pseudosymmetric; the anion positions correspond to space group P2₁/n, but those of the cations do not.     

Ichthyosan in fish eye

Ichthyosan A and V are two highly elastoviscous glycan complexes present in the aqueus and vitreus [here aqueus and vitreus are used as nouns as was suggested by Balazs and Denlinger in The eye, vol 1A. Vegetative physiology and biochemistry, 3rd edn. Academic Press, New York, pp 533–589, 1984] of the fish eye. Ichthyosan A, with its high elastic properties, surrounds and stabilizes the lens of the eye. Ichthyosan V, within the collagen fibers, serves as a structure stabilizer of the gel vitreus. These two molecular complexes are non-covalent aggregates composed of hyaluronan, a chondroitin-proteoglycan (sulfate free), and a keratan-like molecule. The ratio of hyaluronan to chondroitin–proteoglycan varies in the two ichthyosans. Electrophoretic separation methods (both free and gel electrophoresis) demonstrate that the hyaluronan–proteoglycan aggregates move as one molecular entity. The average molecular weight of the ichthyosan varies from 5.2 to 13.0 million in various species. Aquatic mammals do not have ichthyosan in their eyes.     

Dynamic updates of the barrier parameter in primal-dual methods for nonlinear programming

We introduce a framework in which updating rules for the barrier parameter in primal-dual interior-point methods become dynamic. The original primal-dual system is augmented to incorporate explicitly an updating function. A Newton step for the augmented system gives a primal-dual Newton step and also a step in the barrier parameter. Based on local information and a line search, the decrease of the barrier parameter is automatically adjusted. We analyze local convergence properties, report numerical experiments on a standard collection of nonlinear problems and compare our results to a state-of-the-art interior-point implementation. In many instances, the adaptive algorithm reduces the number of iterations and of function evaluations. Its design guarantees a better fit between the magnitudes of the primal-dual residual and of the barrier parameter along the iterations.     

Pyridinium salt liquid crystals Effect of mesogen extension and alkyl chain length

The thermotropism of 1-n-alkyl-(4-methyl and 4-tolyl)pyridinium bromides were compared for alkyl chain lengths ranging from n = 12 to 22 carbons. A smectic A mesophase is present in both series for the longer chain compounds, n ≥ 16, with the clearing temperature being similar for both series but increasing rapidly with chain length. The series with the elongated mesogen also possesses an ordered mesophase identified as smectic G. The transition between this mesophase and the S_A or isotropic phase in the 4-tolyl series, and the transition to and from the crystalline phase in both series, are affected relatively little by the alkyl chain length. It seems that the S_A mesophase is governed primarily by the amphiphilic character of the substances, whereas elongation of the ionic head group is responsible for the appearance of a more ordered mesophase at intermediate temperatures.     

What are the structural features of the active site that define binuclear copper proteins function?

The structural basis that define the physiological functions of binuclear copper enzymes is discussed in the frame of the data generated by a broad spectroscopic approach, spanning from paramagnetic NMR and pulsed EPR to x-ray absorption spectroscopies. The structural features discussed for the different oxidation and ligation states accessible to a binuclear copper sites are the coordination geometry for the first and second shell, the metal-metal distance and the role of the bridging exogenous ligand(s). A structural model will be presented to rationalize both the differentiation in function within the protein families and the reaction mechanism of those proteins that are enzymatically active.     

Evidence of the key role of metal-molecule bonding in metal-molecule-metal transport experiments

The transport properties of two oligothiophene derivatives, that differ only by the chemical group coupling to gold, are compared. It is shown that the role of the coupling group in the transport properties can be decoupled from that of the conjugated body of the molecules and that Se is a better electronic coupling group than S. These results are accounted for semiquantitatively within the frame of the scattering theory of transport, using results from ultraviolet photoemission spectroscopy experiments as inputs for the position in energy of the molecular orbitals with respect to the Fermi level of the electrodes.     

Droplet traffic at a simple junction at low capillary numbers

We report that, when a train of confined droplets flowing through a channel reaches a junction, the droplets either are alternately distributed between the different outlets or all collect into the shortest one. We argue that this behavior is due to the hydrodynamic feedback of droplets in the different outlets on the selection process occurring at the junction. A "mean field" model, yielding semiquantitative results, offers a first guide to predict droplet traffic in branched networks.