Hydrogen bonded arrays: the power of multiple hydrogen bonds

Hydrogen bond interactions in small covalent model compounds (i.e., deprotonated polyhydroxy alcohols) were measured by negative ion photoelectron spectroscopy. The experimentally determined vertical and adiabatic electron detachment energies for (HOCH(2)CH(2))(2)CHO(-)(2a), (HOCH(2)CH(2))(3)CO(-) (3a), and (HOCH(2)CH(2)CH(OH)CH(2))(3)CO(-) (4a)reveal that hydrogen-bonded networks can provide enormous stabilizations and that a single charge center not only can be stabilized by up to three hydrogen bonds but also can increase the interaction energy between noncharged OH groups by 5.8 kcal mol(-1) or more per hydrogen bond. This can lead to pK(a) values that are very different from those in water and can provide some of the impetus for catalytic processes.     

Influence of Ca2+ on tetracycline adsorption on montmorillonite

The adsorption of tetracycline (TC) on montmorillonite was studied as a function of pH and Ca(2+) concentration using a batch technique complemented with X-ray diffraction and transmission electron microscopy. In the absence of Ca(2+), TC adsorption was high at low pH and decreased as the pH increased. In the presence of Ca(2+), at least two different adsorption processes took place in the studied systems, i.e., cation exchange and Ca-bridging. Cation exchange was the prevailing process at pH<5, and thus, TC adsorption decreased by increasing total Ca(2+) concentration. On the contrary, Ca-bridging was the prevailing process at pH>5, and thus, TC adsorption increased by increasing Ca(2+) concentration. The pH 5 represents an isoadsorption pH where both adsorption processes compensate each other. TC adsorption became independent of Ca(2+) concentration at this pH. For TC adsorption on Ca(2+)-montmorillonite in 0.01 M NaCl experiments, the ratio adsorbed TC/retained Ca(2+) was close to 1 in the pH range of 5-9, indicating an important participation of Ca(2+) in the binding of TC to montmorillonite. X-ray diffraction and transmission electron microscopy showed that TC adsorption induced intercalation between montmorillonite layers forming a multiphase system with stacking of layers with and without intercalated TC.     

Conformational rigidity and dielectric properties of polyimides

On the basis of two series of polyimides it was shown that the conformational rigidity and the presence of side voluminous substituents determine the packing of macromolecular chains in glassy state. The presence of hexafluoroisopropylidene groups leads to the increase of free volume of polymers due to the repulsion of such groups belonging to different macromolecular chains. The physical properties studied here, such as dielectric permittivity and electrets properties depend on the size of free volume. The normalized surface potential is determined by the mass fraction of fluorine content and by the conformational rigidity of those polymers.     

d,h-m̈-Alkoxoalkylphosphonato-e-m̈-alkoxo-f-m̈-oxo-bis[trichloroantimon(V)]-Verbindungen

d,h-m?-Alkoxoalkylphosphonato-e-m?-alkoxo-f-m?-oxo-bis[trichloroantimony(V)] Compounds The binuclear antimony(V) complexes Cl₃Sb(O)[R³(R¹O)PO₂](OR²)SbCl₃ 1 to 7 with R¹, R² and R³ = Me or Et in solution slowly exchanges the R² groups between the equatorial oxygen atoms of the Sb₂O₂ ring. The SbO(3)PO(3)Sb ringsystem makes rapid pseudorotation. The resulting isomeres are detected by nmr spectroscopy.     

Copolymerization of 2,2-dimethyltrimethylene carbonate and cyclic esters

The anionic and/or insertion copolymerization of 2,2-dimethyltrimethylene carbonate (DTC) with ϵ-caprolactone (ECL), pivalolactone (PVL) and L-lactide (LLA) is presented with special emphasis on the copolymerization mechanism. Statistical copolymers are obtained by copolymerization of DTC with ECL and with LLA, while with PVL a block copolymer is obtained. The role of transesterification on the microstructure is discussed.     

Easy dual-mode ambient mass spectrometry with Venturi self-pumping, canned air, disposable parts and voltage-free sonic-spray ionization

An exceptionally easy to assemble source for ambient mass spectrometry is described. Based on Venturi easy ambient sonic-spray ionization (V-EASI), the source was further simplified by the use of a can of compressed air which simultaneously provides solution or solvent Venturi self-pumping and continuous, stable and abundant low-noise ion signal via voltage-free sonic-spraying. Further simplification was also attained by the use of inexpensive and readily commercially available parts: a surgical 2-way catheter, an aerosol can of compressed air, a 30 cm long fused-silica capillary and a hypodermic needle. This "Spartan" V-EASI source seems to offer one of the easiest and cheapest ways to make ions for ambient desorption/ionization mass spectrometry analysis of both liquid and solid samples.     

Poly(acrylic acid)-poly(ethylene glycol) layers on positively charged surface coatings: molecular structure, protein resistance, and application to single protein deposition

A new copolymer (PAA-PEG2000) has been designed, consisting of a negatively charged poly(acrylic acid) (PAA) backbone to which poly(ethylene glycol) (PEG) side chains with a molecular weight of about 2 kDa were grafted in a molecular ratio of 3:10. It readily adsorbs to positively charged surfaces and may be considered to be the anionic counterpart of PEG-grafted poly(l-lysine) (PLL-PEG), which was first described by Kenausis et al. and is widely used to render negatively charged surfaces protein-resistant. The synthesis of PAA-PEG2000 can be carried out in aqueous solution at room temperature and does not require any sophisticated techniques such as handling in an inert gas atmosphere. Using ellipsometry and infrared reflection absorption spectroscopy (IRRAS), the film structure has been carefully analyzed for copolymer adsorption onto three different positively charged surfaces, namely, thin layers of poly(allylamine) (PAH), poly(ethyleneimine) (PEI) and (3-aminopropyl)triethoxysilane (APTES). Besides the film thickness, the conformation of the PEG chains and their orientation with respect to the surface normal appear to be important parameters for the protein resistance of the films. Although PAA-PEG2000 adsorbed to PAH and PEI renders the surfaces inert, only partial protein resistance has been observed if the copolymer is deposited on APTES. In a model application, we have generated heterogeneous surfaces composed of isolated small Au nanoparticles (AuNP's) embedded in a protein-resistant layer of PAA-PEG2000 and demonstrated that the AuNP's can serve as adsorption sites for single protein species. In the future, these nanopatterned surfaces may be used for the investigation of isolated proteins.     

Catalytic C-H amination with aromatic amines

Aniline joins the club: A β-diketiminato copper(I) catalyst enables C-H amination of anilines employing low catalyst loadings to preclude oxidation to the diazene ArN=NAr. Electron-poor anilines are particularly resistant towards diazene formation and participate in the amination of strong and unactivated C-H bonds. N-alkyl anilines also take part in C-H amination.