SiO2 surfaces—silica gel particles and silica wafers—were modified by covalently immobilizing three poly(ethylene-co-acrylic acid) copolymers, (−CH2CH2−) x [CH2CH/(CO2H)−] y , with different chain lengths and mass fractions of acrylic acid. 13C solid-state NMR spectroscopy on the modified silica gel particles revealed both mobile gauche and rigid trans aligned alkyl chains in the copolymers. For copolymers attached to silica wafers via a 3-aminopropyltriethoxysilane spacer molecule, ellipsometric measurements revealed a mean value of the layer thickness distribution of 6.5 and 4.3 nm, respectively, for the more acidic and the shorter copolymers with mobile alkyl chains mostly in the gauche conformation. For the longest and least acidic copolymer with more rigid trans ordered alkyl chains, however, a mean phase thickness of 10.6 nm was found. When this copolymer was immobilized via a 3-glycidoxypropyltrimethoxysilane spacer molecule we measured a mean layer thickness of 9.9 nm. A model of the surface morphology of this immobilization strategy was derived using spin-diffusion 13C NMR measurements on the corresponding modified silica. It was thereby proven that the trans and gauche-aligned alkyl chains occur in distinct domains of certain sizes on the silica surface. The surface polarity of all modified silica wafers was also investigated by measurement of contact-angle.

Silica gels, chemically modified with n-alkyl chains of various lengths (CnH2n+1, n = 8, 9, 10, 12, 16, 18, 22, and 30), in the dry state were examined over a broad temperature range (123-353 K) via infrared spectroscopy. Here, for the first time a comprehensive variable temperature FT-IR study is available dealing with the conformational order of alkyl modified silica gels. The conformational state of the alkyl chains in their bound state was monitored via various conformation-sensitive vibrational bands. A qualitative statement about the conformational order was possible based on the analysis of the symmetric and antisymmetric CH2 stretching bands. Likewise, CH2 wagging bands were used to identify and determine the relative amounts-i.e., integral values over the whole chains-of gauche-trans-gauche, double gauche, and end gauche conformers. The amount of gauche conformers at a specific site in the alkyl chains was accessible via the analysis of CD2 rocking bands of samples beating selectively deuterated alkyl chains. These latter data are consistent with those obtained from a complementary analysis of the CD2 stretching vibrational bands. The present study lucidly demonstrates that the conformational. state of the chemically attached alkyl chains strongly depends on temperature, actual chain length, and chain position. The total number of gauche conformers per chain of the systems examined here varies between 2.4 and 5.1, depending on the actual sample temperature and alkyl chain length. The total number of gauche conformers is found to vary linearly with temperature. Shorter alkyl chains, such as octyl and decyl chains, are found to possess a high degree of conformational disorder. The observed increase in alkyl chain length is accompanied by a decrease in conformational disorder, most probably due to a better chain packing. For the C18 modified system, selectively deuterated samples were available. Here, at room temperature the percentage of gauche conformers for positions C-4, C-6 and C-12 are 40%, 20%, and 25%, respectively, reflecting a pronounced position dependence for the degree of conformational order. The present data on the conformational alkyl chain order are discussed in conjunction with studies on other n-alkyl modified silica gels as well as related systems involving n-alkyl segments in various environments, such as pure hydrocarbons, biological membranes, and self-assembled monolayers (SAMs). On the bases of the results from the present variable temperature FT IR study, overall structures of the alkyl chains, chemically attached to the silica surface, are proposed.

The core-shell structure of lycopene micronizates can be verified by employing a combination of solid-state and suspended-state NMR spectroscopy. The type of molecular aggregation of carotenoid nanoparticles can be clearly determined from their characteristic fingerprint pattern in the solid-state NMR spectra.

A new approach for the synthesis of long alkyl chain length stationary phases for use in reversed-phase liquid chromatography is described. Poly(ethylene-co-acrylic acid) copolymers (i.e., (-CH2CH2-)x[CH2CH(CO2H)-]y) with different levels of acrylic acid were covalently bonded to silica via glycidoxypropyl or aminopropyl linkages. 13C cross polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy was used to characterize the new reversed-phase materials. Aspects of shape selectivity were evaluated for six different columns with Standard Reference Material (SRM) 869a, Column Selectivity Test Mixture for Liquid Chromatography. Selectivity for isomer separations was enhanced for stationary phases prepared with poly(ethylene-co-acrylic acid) containing a mass fraction of 5% acrylic acid. The relationship between alkyl conformation and chromatographic properties was studied by 13C magic angle spinning (MAS) NMR measurements, and correlations were made with the composition of the polymer. Finally, the effectiveness of this phase is demonstrated by the separation of several beta-carotene isomers.

Pure organic polyalkvlvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C4VE) and n-octadecylvinyl ether (C18VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and 1H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of 1H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the 1H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin-lattice relaxation times (T1) as well as accumulation of a 2D wide line separation NMR spectrum.

A new bicyclic phase for liquid chromatography was prepared by solution polymerization approaches. To introduce a C4 spacer the starting molecule 3-formylpinane was reduced to the alcohol followed by a substitution of the hydroxy group through a bromide. The obtained halide reacted with magnesium and allyl bromide to the 3-(but-3'-enyl)pinane which was hydrosilylated with trichlorosilane and finally immobilized to silica gels with different pore sizes using the technique of solution polymerization. To elucidate the structure of 3-(but-3'-enyl)pinane high-resolution two-dimensional nuclear magnetic resonance (NMR) spectra were carried out. The new phases were characterized, on the one hand by employing 13C and 29Si solid-state NMR spectroscopy and on the other hand, by separating a standard test mixture consisting of mainly monosubstituted aromatic compounds. The results achieved in chromatography were correlated with the information gained from 29Si CP/MAS NMR measurements.

Spindiffusions-Festkörper-NMR-Messungen beweisen die Existenz von Alkylkettendomänen unterschiedlicher Mobilität bei C30-Umkehrphasen und geben einen Einblick in deren räumliche Strukturaufteilung (siehe Bild: Bereich a: starr, 32 Å; Bereich b: mobil, 112 Å). Die computergestützte Auswertung des Signalverlaufs im Spindiffusions-Experiment ermöglicht die Bestimmung von Größenverhältnissen der Alkylketten-Cluster.

Spin-diffusion solid-state NMR measurements prove the existence of alkyl-chain domains with different mobilities at C30 reversed phases and give insight into the spatial distribution (see picture: region a: rigid, 32 Å; region b: mobile, 112 Å). A computerized simulation of the change in the signal during the spin-diffusion experiment allows the determination of the areas of the alkyl-chain cluster.

Technetium(V) and rhenium(V) nitrido complexes of the compositions [MNL(2)] and [MN(Cl)(PPhMe(2))L] have been synthesized by reaction of Na[N(SPPh(2))(2)] and [MNCl(2)(PPh(3))(2)] or [MNCl(2)(PPhMe(2))(3)] complexes, respectively [M = Re or Tc; L = N(SPPh(2))(2)(-)]. The amide anion acts in all isolated complexes as a chelating ligand co-ordinated via the sulfur atoms. The complexes [TcN{N(SPPh(2))(2)}(2)], [ReN{N(SPPh(2))(2)}(2)] and [TcN(Cl)(PPhMe(3))(2){N(SPPh(2))(2)}] have been studied by X-ray crystallography. The bis-chelates are five-co-ordinate with the nitrogen atoms at the apexes of square pyramids. The Tc atom in [TcN(Cl)(PPhMe(2))(2){N(SPPh(2))(2)}] has a distorted-octahedral co-ordination sphere with Cl bonded trans to the nitrido function. The complex [ReN{N(SPPh(2))(2)}(2)] is the first five-co-cordinate nitride which reacts with BCl3 to form a nitrido bridge between rhenium and boron; [Re(NBCl3){N(SPPh(2))(2)}(2)] is characterized by a covalent N-B bond of 1.539(5) Angstrom. The Re-N multiple bond. distance is only slightly influenced by addition of the Lewis acid. The complex [ReN(Cl)(PPhMe(2))(2){N(SPPh(2))(2)}] reacts with BCl3 with substitution of N(SPRh2)(2)(-) and formation of the well known [Re(NBCl3)Cl-2(PPhMe(2))(3)]. The corresponding technetium complexes do not form Tc-N-B bridges upon reactions with BCl3. The [MN(Cl)(PPhMe(2))(2){N(SPPh(2))(2)}] (M = Tc or Re) complexes reacted with S2Cl2 to give thionitrosyl compounds with the metals in lower oxidation states; [Re(NS)Cl-2(PPhMe(2))(3)] and [Re(NS)Cl-3(PPhMe(2))(2)] have been characterized spectroscopically, [Tc(NS)Cl-3(PPhMe(2))(2)] was studied by X-ray diffraction and EPR spectroscopy. The phosphine ligands are trans to each other.