Solvent gradient operation of simulated moving beds. 2. Langmuir isotherms

Simulated Moving Bed separations of enantiomers or fine chemicals are usually carried out in the isocratic mode, i.e. by applying the same operating conditions (temperature, pressure, mobile phase composition, pH) in the whole SMB unit. However, it has been recently recognized that by properly modulating operating conditions in the SMB sections. i.e. Sections 1-4 normally, separation performance in terms of productivity and solvent consumption can be significantly improved. In this work, we study solvent gradient SMB (SG-SMB) operation, where the concentration of a modifier in the main solvent constituting the mobile phase is adjusted along the SMB unit, so as to have weaker retention of the species to be separated in the first two sections, and stronger retention in Sections 3 and 4. Overload chromatographic conditions are considered, where the adsorption behavior is characterized by a nonlinear competitive adsorption isotherm, e.g. a binary Langmuir isotherm. Design criteria to achieve complete separation are developed in the frame of the equilibrium theory of chromatography. The theoretical findings are discussed in view of typical effects of the modifier concentration on retention times and solubility of the species to be separated, and an overall assessment of the SG-SMB technology is attempted.     

Pyrimidoquinazolinophenanthroline Opens Next Chapter in Design of Bridging Ligands for Artificial Photosynthesis**

The synthesis and detailed characterization of a new Ru polypyridine complex containing a heteroditopic bridging ligand with previously unexplored metal-metal distances is presented. Due to the twisted geometry of the novel ligand, the resultant division of the ligand in two distinct subunits leads to steady state as well as excited state properties of the corresponding mononuclear Ru(II) polypyridine complex resembling those of prototype [Ru(bpy)₃]²⁺ (bpy=2,2'-bipyridine). The localization of the initially optically excited and the nature of the long-lived excited states on the Ru-facing ligand spheres is evaluated by resonance Raman and fs-TA spectroscopy, respectively, and supported by DFT and TDDFT calculations. Coordination of a second metal (Zn or Rh) to the available bis-pyrimidyl-like coordination sphere strongly influences the frontier orbitals, apparent by, for example, luminescence quenching. Thus, the new bridging ligand motif offers electronic properties, which can be adjusted by the nature of the second metal center. Using the heterodinuclear Ru−Rh complex, visible light-driven reduction of NAD⁺ to NADH was achieved, highlighting the potential of this system for photocatalytic applications.     

Two-step synthesis of hexaammonium triptycene: an air-stable building block for condensation reactions to extended triptycene derivatives

A simple two-step synthesis of an air-stable hexaammoniumtriptycene is introduced, which can be used for a variety of transformations by condensation reactions, e.g., to benzimidazole, benzotriazole, and quinoxaline derivatives in high yields.     

Morphology of adsorbed polymers and solid surface wettability

The adsorption of a polyacrylamide (MW 14600) and two polysaccharides (MW 9260 and 706 x 10(3)) onto model silica surfaces of different hydrophobicities was investigated. In all cases, adsorption adhered to the Freundlich isotherm, reflecting the heterogeneous character of the solid substrates. The latter strongly influenced the character of the adsorbed polymer, with morphologies from chainlike structures to thin films and patches being observed. Surface roughness, polymer type, and molecular weight also play roles in controlling adsorbed polymer morphology. Surface wettability is strongly influenced by the thickness of the adsorbed layer.     

{[CuSn5Sb3]2−}2: A Dimer of Inhomogeneous Superatoms

Reaction of the binary Zintl anion (Sn₂Sb₂)^2? with the β‐diketiminato complex [LCu(NCMe)] (L=nacnac=[(N(C₆H₃ⁱPr₂‐2,6)C(Me))₂CH]^?) in ethylenediamine or DMF affords the ternary cluster dimer {[CuSn₅Sb₃]^2?}₂ ( 1 ) as its [K(crypt‐222)]⁺ salt. The chemical formulation of 1 is supported by energy‐dispersive X‐ray spectroscopy (EDX) and quantum chemical calculations. Each monomeric part of the dimer represents a trimetallic “[CuSn₅Sb₃]^2?” cluster, with an architecture in between a tricapped trigonal prism and a capped square antiprism. As shown by quantum chemical investigations, the presence of Sb atoms and, in particular, of Cu atoms in the cluster skeleton makes the monomeric unit behave like an inhomogeneous superatom, which clearly prefers to dimerize, thereby producing a relatively short, yet virtually non‐bonding Cu???Cu distance.     

Flux synthesis of (3,4)-connected zinc phosphites with different framework topologies

Two three-dimensional open-framework zinc phosphites, H₂aem·Zn₃(HPO₃)₄·0.5H₂O (1) and H₂apm·Zn₃(HPO₃)₄ (2), have been synthesized by a phosphorous acid flux method, where aem=4-(2-aminoethyl)morpholine and apm=4-(3-aminopropyl)morpholine. Compound 1 crystallizes in the monoclinic system, P2₁/c, a=9.5852(7) Å, b=20.3941(8) Å, c=10.5339(8) Å, β=94.125(9)°, V=2053.8(2) Å³, Z=4, R₁=0.0319, wR₂=0.0628. Compound 2 crystallizes in the monoclinic system, P2₁/n, a=8.589(2) Å, b=14.020(3) Å, c=16.606(3) Å, β=97.190(8)°, V=1983.9(7) Å³, Z=4, R₁=0.0692, wR₂=0.1479. Both compounds are based on (3,4)-connected networks with 8- and 12-ring channels, which are constructed from Zn₃(HPO₃)₄ clusters as the same secondary building units. These inorganic clusters are spatially organized by different structure-directing agents into different three-dimensional frameworks.     

Characterization of complex assemblages of organic acids in geological samples by negative electrospray ionization mass spectrometry using a double‐focusing magnetic sector field mass spectrometer

Four different geological sample types (a crude oil, a crude oil asphaltene, a reservoir core extract and a reservoir core asphaltene) have been characterized by negative ionization electrospray mass spectrometry at low and high mass resolution using a double‐focusing magnetic sector field mass spectrometer. The mass range, shape of the spectra and the signal distribution of the acidic constituents as well as the average molecular weights, the total ion abundance and signal intensity in the spectra were compared for the different sample types. Nominal mass classes have been evaluated and Kendrick mass plots were generated in order to identify homologous series. For the crude oil sample, accurate mass assignments were made by high‐resolution double‐focusing magnetic sector field mass spectrometry (DFMSFMS) and were compared with those obtained by negative ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). With both instrument types, compounds with the molecular composition C_nH_2n+zO₂, among which carboxylic acids predominated, were the main acidic compound class detectable in negative ESI mass spectra. Good agreement was achieved for the double bond class distribution and the carbon number distribution of the O₂ class. In addition, minor compound classes could be identified using FTICRMS. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrophilic Carotenoids: Surface Properties and Aggregation Behavior of the Potassium Salt of the Highly Unsaturated Diacid Norbixin

The oft‐claimed ‘good’ water solubility of the food color norbixin ( 3 ) could not be confirmed. In contrast, the potassium salt 5 of norbixin formed suitable dispersions. The surface and aggregation properties of salt 5 were investigated and compared with other naturally occurring and synthetic hydrophilic carotenoids (Table).     

Preparation and Conformation of Organo‐Bridged Bis[tris(arylchalcogenolato)tin] Compounds – An Experimental and Quantum Chemical Study

Seven organo‐bridged bis[tris(arylchalcogenolato)tin] compounds with the general formulae (R′E)₃Sn–R–Sn(ER′)₃ (R = –(CH₂)₄–, 1,4‐bis(methyl)benzene, 4,4′‐bis(methyl)biphenyl; R′ = Ph, 1‐Np, 2‐Np; E = S, Se) were synthesized and characterized by means of X‐ray diffractometry as well as NMR spectroscopy. Three different conformations of the arylchalcogenolato groups ER′ with respect to the bridging group R were rationalized and explained by means of quantum chemical investigations.