Characterization of a poly(ethersulphone) by on-line coupling of size exclusion chromatography with NMR and FTIR spectroscopy

An on-line detection „on the flow”︁ during the size exclusion chromatography run using FTIR and NMR spectrometers was applied to investigate the liquid chromatographic separation process of oligomers and to identify the separated chromatographic compounds. The FTIR and NMR detectors give real-time information about the chemical structure and functional groups of the eluated species. The preferences and limits of the on-line coupling were discussed using an oligomeric hydroxyl terminated poly(ethersulphone) as an example. Molecular weights could be calculated from the ¹H-NMR spectra of the separated species using the intensities of end-group and main-chain signals. Residues of N-methylpyrrolidone which was used as solvent in the oligomer synthesis were identified by the FTIR detector.     

Dynamic contact angle and spreading rate measurements for the characterization of the effect of dentin surface treatments

A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other.     

Hydridoorganostannylene Coordination: Group 4 Metallocene Dichloride Reduction in Reaction with Organodihydridostannate Anions

Organodihydridoelement anions of germanium and tin were reacted with metallocene dichlorides of Group 4 metals Ti, Zr and Hf. The germate anion [Ar*GeH₂]⁻ reacts with hafnocene dichloride under formation of the substitution product [Cp₂Hf(GeH₂Ar*)₂]. Reaction of the organodihydridostannate with metallocene dichlorides affords the reduction products [Cp₂M(SnHAr*)₂] (M=Ti, Zr, Hf). Abstraction of a hydride substituent from the titanium bis(hydridoorganostannylene) complex results in formation of cation [Cp₂M(SnAr*)(SnHAr*)]⁺ exhibiting a short Ti–Sn interaction. (Ar*=2,6-Trip₂C₆H₃, Trip=2,4,6-triisopropylphenyl).     

Reduced molybenum-oxide-based core-shell hybrids: "blue" electrons are delocalized on the shell

The present study refers to a variety of reduced metal-oxide core-shell hybrids, which are unique with regard to their electronic structure, their geometry, and their formation. They contain spherical {Mo72Fe30} Keplerate-type shells encapsulating Keggin-type polyoxomolybdates based on very weak interactions. Studies on the encapsulation of molybdosilicate as well as on the earlier reported molybdophosphate, coupled with the use of several physical methods for the characterization led to unprecedented results (see title). Upon standing in air at room temperature, acidified aqueous solutions obtained by dissolving sodium molybdate, iron(II) chloride, acetic acid, and molybdosilicic acid led to the precipitation of monoclinic greenish crystals (1). A rhombohedral variant (2) has also been observed. Upon drying at room temperature, compound 3 with a layer structure was obtained from 1 in a solid-state reaction based on cross-linking of the shells. The compounds 1, 2, and 3 have been characterized by a combination of methods including single-crystal X-ray crystallography, magnetic studies, as well as IR, M?ssbauer, (resonance) Raman, and electronic absorption spectroscopy. In connection with detailed studies of the guest-free two-electron-reduced {Mo72Fe30}-type Keplerate (4) and of the previously reported molybdophosphate-based hybrids (including 31P NMR spectroscopy results), it is unambiguously proved that 1, 2, and 3 contain non-reduced Keggin ion cores and reduced {Mo72Fe30}-type shells. The results are discussed in terms of redox considerations (the shell as well as the core can be reduced) including those related to the reduction of "molybdates" by FeII being of interdisciplinary including catalytic interest (the MoVI/MoV and FeIII/FeII couples have very close redox potentials!), while also referring to the special formation of the hybrids based on chemical Darwinism.     

En route to coordination chemistry under confined conditions in a porous capsule: Pr3+ with different coordination shells

The highly charged nanocontainer capsule of the type [pentagon]12[linker]30 identical with [(Mo)Mo5O21(H2O)6]12[Mo2O4(SO4)]30 with 20 nanosized pores and channels allows the entrance of cations like Pr3+: the latter are positioned at two different sites and have two different coordination shells, corresponding to a coordination chemistry under confined conditions; a fascinating aspect is that capsule encapsulated water shells fixed by hydrogen bonds act formally as polydentate ligands.     

Thermodynamic and kinetic data for adduct formation, cis-trans isomerization and redox reactions of ML4 complexes: a case study with rhodium- and iridium-tropp complexes in d8, d9 and d10 valence electron configurations (tropp=dibenzotropylidene phosphanes)

The formation of adducts of the square-planar 16-electron complexes trans-[M(tropp(ph))(2)](+) and cis-[M(tropp(ph))(2)](+) (M=Rh, Ir; tropp(Ph)=5-diphenylphosphanyldibenzo[a,d]cycloheptene) with acetonitrile (acn) and Cl(-), and the redox chemistry of these complexes was investigated by various physical methods (NMR and UV-visible spectroscopy, square-wave voltammetry), in order to obtain some fundamental thermodynamic and kinetic data for these systems. A trans/cis isomerization cannot be detected for [M(tropp(ph))(2)](+) in non-coordinating solvents. However, both isomers are connected through equilibria of the type trans-[M(tropp(ph))(2)](+)+L<==>[ML(tropp(ph))(2)](n)<==>cis-[M(tropp(ph))(2)](+)+L, involving five-coordinate intermediates [ML(tropp(ph))(2)](n) (L=acn, n=+1; L=Cl(-), n=0). Values for K(d) (K(f)), that is, the dissociation (formation) equilibrium constant, and k(d) (k(f)), that is, the dissociation (formation) rate constant, were obtained. The formation reactions are fast, especially with the trans isomers (k(f)>1x10(5) m(-1) s(-1)). The reaction with the sterically more hindered cis isomers is at least one order of magnitude slower. The stability of the five-coordinate complexes [ML(tropp(ph))(2)](n) increases with Ir>Rh and Cl(-)>acn. The dissociation reaction has a pronounced influence on the square-wave (SW) voltammograms of trans/cis-[Ir(tropp(ph))(2)](+). With the help of the thermodynamic and kinetic data independently determined by other physical means, these reactions could be simulated and allowed the setting up of a reaction sequence. Examination of the data obtained showed that the trans/cis isomerization is a process with a low activation barrier for the four-coordinate 17-electron complexes [M(tropp(ph))(2)](0) and especially that a disproportionation reaction 2 trans/cis-[M(tropp(ph))(2)](0)-->[M(tropp(ph))(2)](+)+[M(tropp(ph))(2)](-) may be sufficiently fast to mask the true reactivity of the paramagnetic species, which are probably less reactive than their diamagnetic equilibrium partners.     

Reactive scattering of sodium clusters with molecular oxygen

The first reactive differential scattering study for atomic clusters is reported. Oxidation of Na _x (x8) with O₂ is investigated in a crossed beam apparatus. Sodium oxide (Na _n O,n4) and sodium dioxide (Na _n O₂,n6) are produced with a total reactive cross section from 50 to 80 Ų, depending on the cluster size. The excess energies for these reactions are estimated by an SCF type ab initio calculation and range from 0.5 to 5 eV. The large cross section may then be understood quantitatively in terms of a harpooning mechanism as a first step in the reaction path. Angular distributions have been determined for the most abundant products, showing strong forward scattering. Two different schemes are discussed for the reaction: while the dioxides Na _n O₂ may be formed by an evaporative cooling process from a highly excited collision complex, formation of Na _n O appears to originate from a direct process. In both cases the experimental data suggest that most of the exothermicity remains in the reaction products.