PubMed Health⌕ Search

Biomedical subjects

Martin Jansen

Publications and source records attributed to Martin Jansen.

At least 37 records · Page 2Linked to original sources
PubMed2005

Crystal structures and topological aspects of the high-temperature phases and decomposition products of the alkali-metal oxalates M2[C2O4] (M=K, Rb, Cs).

The high-temperature phases of the alkali-metal oxalates M2[C2O4] (M = K, Rb, Cs), and their decomposition products M2[CO3] (M = K, Rb, Cs), were investigated by fast, angle-dispersive X-ray powder diffraction with an image-plate detector, and also by simultaneous differential thermal analysis (DTA)/thermogravimetric analysis (TGA)/mass spectrometry (MS) and differential scanning calorimetry (DSC) techniques. The following phases, in order of decreasing temperature, were observed and crystallographically characterized (an asterisk denotes a previously unknown modification): *alpha-K2[C2O4], *alpha-Rb2[C2O4], *alpha-Cs2[C2O4], alpha-K2[CO3], *alpha-Rb2[CO3], and *alpha-Cs2[CO3] in space group P6(3)/mmc; *beta-Rb2[C2O4], *beta-Cs2[C2O4], *beta-Rb2[CO3], and *beta-Cs2[CO3] in Pnma; gamma-Rb2[C2O4], gamma-Cs[C2O4], gamma-Rb2[CO3], and gamma-Cs2[CO3] in P2(1)/c; and delta-K2[C2O4] and delta-Rb2[C2O4] in Pbam. With respect to the centers of gravity of the oxalate and carbonate anions, respectively, the crystal structures of all known alkali-metal oxalates and carbonates belong to the AlB2 family, and adopt either the AlB2 or the Ni2In arrangement depending on the size of the cation and the temperature. Despite the different sizes and constitutions of the carbonate and oxalate anions, the high-temperature phases of the alkali-metal carbonates M2[CO3] (M = K, Rb, Cs), exhibit the same sequence of basic structures as the corresponding alkali-metal oxalates. The topological aspects and order-disorder phenomena at elevated temperature are discussed.

Carbonates↗
PubMed2005

The role of carbon in the nitridic high performance ceramics in the system Si-B-N-C.

Using a multitude of modern solid-state NMR techniques including 11B-MQMAS-NMR, 11B-13C-REDOR NMR, 13C-11B-REAPDOR NMR, 15N-11B-REAPDOR NMR and 13C-2D-RFDR NMR experiments, the network organization in the quaternary high performance ceramic SiBN3C has been studied. Carbon is found to agglomerate into domains with predominant carbon-carbon bonding. The NMR results are compatible with carbon atoms involved in a graphite-like bonding scheme. The network adopted is quite similar to the corresponding one in the related ternary ceramic Si3B3N7, consisting of domains characterized by predominant Si-N bonding and domains of predominant B-N bonding with the carbon agglomerates located within the B-N domains of the network. The homogeneity with respect to the elemental distribution down to the nm regime, observed using electron spectroscopic imaging techniques puts an upper limit of ca. 1 nm to these agglomerates.

Journal Article↗
PubMed2004

Trisilver oxoruthenate(V), Ag3RuO4.

Ag3RuO4 is constituted of anionic helical chains of edge-sharing RuO6 octahedra, extending along the c axis. The metal atoms all lie at sites with imposed twofold symmetry. The oxide anions are arranged in an approximate cubic close packing. The Ag atoms occupy the remaining octahedral voids, so that Ag3RuO4 may be regarded as a derivative of the NaCl structure type.

Journal Article↗
PubMed2004

Immunoadsorption (IAS) as a rescue therapy in SLE: considerations on safety and efficacy.

OBJECTIVE: In SLE, extracorporeal procedures aiming at reduction of immunoglobulin (Ig) and immune complexes (IC) are used as a rescue therapy. Plasma exchange (PE) has not been proven overall effective in SLE, and long-term treatment in particular has been associated with severe bacterial and viral infections. Immunoadsorption (IAS), in contrast, selectively removes Ig and IC and may thus be safer. We therefore investigated the rate of infections in SLE patients who were undergoing long-term IAS. METHODS: 16 SLE patients were treated with > or = 10 courses of IAS, and nine patients with highly active disease received pulse cyclophosphamide (IVCP) therapy in parallel. We retrospectively analysed the records of all these patients for the occurrence of infections. Patients receiving IAS therapy plus IVCP were compared with 25 patients with similarly active disease treated with standard IVCP therapy within the same observation period. Patients receiving IAS without additional IVCP were compared with patients with similarly moderate disease activity receiving neither IAS nor IVCP. RESULTS: No potentially life-threatening viral infection occurred in IAS-treated patients and episodes of herpes zoster were equally distributed. No severe infection was observed during IAS without concomittant cyclophosphamide. As expected, more patients with highly active disease receiving IVCP experienced infections than those with less active disease (16 of 34 [47%] vs. 2 of 22 [9%], p < 0.04). On comparing the two groups with highly active disease, infections were similar (IAS+IVCP: 3 of 9 patients [33%], IVCP only: 5 of 25 [20%]), but one patient receiving IAS+IVCP died of septicaemia. Disease activity significantly decreased in both groups treated with IAS. CONCLUSION: IAS has an acceptable safety profile with regard to severe infections and appears safe with regard to severe viral disease. Highly active disease and IVCP therapy increase the risk of severe infections in SLE.

Adolescent↗
PubMed2004

The structure of Ba@C74.

The title compound has been produced by using the radio frequency (RF) method. Barium and carbon were evaporated simultaneously under dynamic flow of helium at different temperatures. About 0.5 mg of pure Ba@C(74) was isolated via a three-step high-pressure liquid chromatography separation. For the first time, the structure of a monometallofullerene has been analyzed by means of single-crystal synchrotron diffraction on microcrystals of Ba@C(74).Co(OEP).2C(6)H(6) (Co(II)(OEP): cobalt(II) octaethylporphyrin) at 100 K. The monometallofullerene exhibits a high degree of localization of the endohedral metal ion, with just two split positions for Ba and two orientations of the C(74)-cage. The barium atom is localized inside the C(74)-cage and displaced off-center, toward the Co(OEP) molecule (d approximately 127 pm). The shortest Ba-C distance is 265 pm. The Co(OEP) molecules form dimers in which the coordination of the cobalt is (4 + 1). Due to the all-syn conformation of the ethyl groups, each Co(OEP) molecule of the dimer coordinates one C(74)-fullerene. The units (Ba@C(74))[Co(OEP)](2)(Ba@C(74)) are arranged in a distorted primitive hexagonal packing. The free space between these complex units is filled by benzene molecules of crystallization. The Ba L(III) XANES spectrum of a thin film sample of Ba@C(74) exhibits a pronounced double maximum structure at about E = 5275 eV. The comparison of the shape resonances of the experimental data with simulated XANES spectra, based on different exo- and endohedral structure models, confirm that the Ba atom is located inside the C(74)-cage (D(3)(h)()) in an off-center position. The Ba atom is shifted by about 130-150 pm from the geometric center of the C(74)-cage. This is in good agreement with quantum chemical results. Thus, despite the disorder still present, a consistent and conclusive structure model for the title compound has been derived by employing a combination of X-ray diffraction, XANES spectroscopy, and quantum chemical calculations.

Journal Article↗
PubMed2004

Covalently bonded 1(infinity)[Pt]- chains in BaPt: extension of the Zintl-Klemm concept to anionic transition metals?

BaPt has been synthesized by reaction of a 1:1 mixture of Ba and Pt at 1223 K in argon and characterized by single-crystal X-ray structure determination and electrical resistivity and magnetic susceptibility measurements. The compound crystallizes in the NiAs structure type with an extremely low value for the c/a ratio (hexagonal space group P6(3)/mmc with a = 5.057(2) A, c = 5.420(3) A, c/a = 1.072, R1 = 0.0297, N(hkl)() = 93). This c/a ratio reflects structural features that are unusual for the NiAs type: Pt is coordinated linearly by two other Pt atoms at a distance as short as 2.71 A, thus forming a chain along [001] of homonuclearly bonded platinum. Band structure calculations and electron localization function analyses reveal a covalent character of Pt-Pt interactions along the c axis and two-dimensional metallic conductivity parallel to the ab plane. In terms of the Zintl-Klemm concept, in its most general sense, BaPt can be formulated as (Ba(2+)(1(infinity)[Pt]-) x e-), and it can be considered a new example of platinide anions in the solid state.

Journal Article↗
PubMed2004

Strategies for the structure determination of endohedral fullerenes applied to the example of Ba@C(74)xCo(octaethylporphyrin)x2C(6)H(6).

The structure determination of endohedral fullerenes is complicated because of the high degree of disorder which may affect the different structural components, e.g. the endohedral atom/molecule, the fullerene cage and solvent molecules. Even worse, the data-to-parameter ratio and, in particular, the scattering power is low. Different strategies are employed to deal with these problems. The observed fraction of the reciprocal lattice may be increased by means of synchrotron diffraction studies. The number of parameters may be reduced by applying rigid-body refinement strategies and by restricting the displacement parameters in the framework of the TLS approach. In the first section, we will give a short overview of the structure determinations of endohedral fullerenes from single-crystal data and discuss the severe problems one may encounter. Then we will give an example of a successful structure analysis of a metal-containing endohedral fullerene, i.e. Ba@C(74)xCo(OEP)x2C(6)H(6) (OEP = octaethylporphyrin). Several strategies of refinement, beyond the black box level, have been checked and compared, e.g. TLS, split-atom models, twin and single crystal models, anharmonic displacement parameters, and rigid-body models.

Journal Article↗
PubMed2004

Tetraorganylammonium superoxide compounds: close to unperturbed superoxide ions in the solid state.

Trimethylphenylammonium superoxide (1) and tetrabutylammonium superoxide (2) were prepared by ion-exchange reaction in liquid ammonia. Both compounds were structurally characterized by single-crystal X-ray diffraction. The crystal structure of 2 contains solvent ammonia molecules that are hydrogen bonded to the superoxide ion and therefore may influence the bonding properties of the superoxide ion. The crystal structure of 1 does not contain any solvent molecules. Therefore, it represents the best known approximation to the virtually isolated superoxide ion in the solid state to date. The O-O bond length is 1.332(2) A in 1 and 1.312(2) A in 2. Magnetization measurements show that the susceptibilities of both compounds follow an ideal Curie law down to 2 K reflecting an absence of intermolecular exchange effects between the superoxide ions. The effective magnetic moments of both compounds are larger than the spin-only value due to contributions of the orbital momentum in the superoxide ion. The values of the magnetic moment comply well with the g factors obtained from electron paramagnetic resonance spectra. The g tensors themselves reflect the anisotropic environment of the superoxide ions. The Pi(g) energy levels which are degenerate in the free superoxide ion split up in crystal fields of lower than tetragonal symmetry. The energy splitting is estimated from the diagonal elements of the g tensor of 1.

Crystallography, X-Ray↗
PubMed2004

New insights into the structural and dynamical features of lithium hexaoxometalates Li7MO6 (M = Nb, Ta, Sb, Bi).

We present a (re)investigation of the hexaoxometalates Li(8)MO(6) (M = Sn, Pb, Zr, Hf) and Li(7)MO(6) (M = Nb, Ta, Sb, Bi). Lithium motion and ionic conductivity in the hexaoxometalates were studied using impedance spectroscopy (for Li(7)MO(6), M = Sb, Bi, Ta) and (6)Li and (7)Li solid-state nuclear magnetic resonance (for Li(7)TaO(6)). The NMR data indicate a considerable exchange of Li among the tetrahedral and octahedral voids even at ambient temperature. In an investigation of the crystal structures using laboratory and synchrotron X-ray powder diffraction techniques, the structures of Li(7)TaO(6), Li(7)NbO(6), and Li(7)SbO(6) could be solved and refined. All three reveal a triclinic metric (Li(7)SbO(6), triclinic, P1, a = 5.38503(6) A, b = 5.89164(7) A, c = 5.43074(6) A, alpha = 117.2210(6) degrees, beta = 119.6311(6) degrees, gamma = 63.2520(7) degrees, V = 127.454(3) A(3), Z = 1; Li(7)NbO(6), triclinic, P1, a = 5.37932(9) A, b = 5.91942(11) A, c = 5.37922(9) A, alpha = 117.0033(9) degrees, beta = 119.6023(7) degrees, gamma = 63.2570(9) degrees, V = 126.938(4) A(3), Z = 1; Li(7)TaO(6), triclinic, P1, a = 5.38486(2) A, b = 5.92014(3) A, c = 5.38551(2) A, alpha = 117.0108(2) degrees, beta = 119.6132(2) degrees, gamma = 63.2492(2) degrees, V = 127.208(1) A(3), Z = 1.

Journal Article↗
PubMed2004

Surface step structure of Ag13OsO6, experimental evidence for Ag13 cluster building blocks.

The surface of single crystal Ag(13)OsO(6) has been investigated using atomic force microscopy. Growth spirals with very large flat terraces, separated by steps of equal height, have been observed. The measured step height of approximately 6.7 Angstrom corresponds to the diameter of one Ag13-icosahedron and identifies the cluster as the key structural building block.

Journal Article↗
PubMed2004

Effects of LDL-immunoapheresis on plasma concentrations of vitamin E and carotenoids in patients with familial hypercholesterolemia.

Recently very potent extracorporeal cholesterol-lowering treatment options have become available for patients with hypercholesterolemia. LDL immunoapheresis treatment selectively removes LDL and lipoprotein(a) from the circulation. Since LDL is the major carrier of lipophilic antioxidants in plasma, the purpose of the present study was to assess the effects of a single LDL apheresis treatment on plasma concentrations of tocopherols (alpha- and gamma-tocopherol) and carotenoids (alpha- and beta-carotene, zeaxanthin, cryptoxanthin, canthaxanthin, lycopene, and retinol). Plasma antioxidant concentrations were determined by HPLC in 7 patients with familial hypercholesterolemia before and after LDL immunoapheresis treatment. Plasma concentrations of both alpha- and gamma-tocopherol and the different carotenoids were significantly reduced by LDL apheresis. However, when standardized for cholesterol to adjust for cholesterol removal, alpha- and gamma-tocopherol, retinol, and the more polar carotenoids lutein and zeaxanthin increased in response to apheresis treatment, while the more unpolar carotenoids such as beta-carotene and lycopene did not change. These data demonstrate that a single LDL immunoapheresis treatment affects tocopherols and individual carotenoids differently. This may be explained by differences in chemical structure and preferential association with different lipoproteins. These results further imply that tocopherols, lutein, zeaxanthin, and retinol, are associated in part with lipoproteins and other carriers such as retinol-binding protein that are not removed during apheresis treatment.

Adult↗
PubMed2004

MAS-NMR at very high temperatures.

We report MAS-NMR experiments at temperatures of approx. 1200 K using a CO(2) laser as the heating device. An internal NMR thermometer based on the (7)Li T1 data of Li(0.24)La(0.54)TiO(3) is used for temperature calibration. Using this setup, temperatures as high as 1191 K could be reached under MAS conditions as confirmed by the melting of Li(2)B(4)O(7) at 1191 K which could be followed by (7)Li-MAS-NMR.

Hot Temperature↗
PubMed2004

Mercury exposure in protein A immunoadsorption.

BACKGROUND: Immunoadsorption is increasingly used to treat antibody-mediated autoimmune diseases. To prevent microbial growth during storage, reusable protein A-Sepharose gel columns are primed with ethyl mercury thiosalicylate (thiomersal, 0.1% solution) and rinsed with phosphate buffer before use. In this study, we tested the hypothesis of systemic mercury exposure in protein A immunoadsorption. METHODS: Whole blood mercury levels were measured by atomic absorption spectroscopy before and after protein A immunoadsorption (11 patients, 26 treatments), anti-IgG immunoadsorption (eight patients, 13 treatments) and LDL apheresis (DALI and Therasorb systems; nine patients, 14 treatments). RESULTS: Patients treated with protein A immunoadsorption had significantly elevated baseline mercury levels compared with the other groups, which were not different from healthy controls. Following protein A immunoadsorption, mercury levels increased from 5.9+/-1.4 microg/l (mean+/-SEM, normal, <5 microg/l) to 32.3+/-5.7 microg/l, P<0.001). In one intensively treated patient, acute neurological toxicity developed at a mercury level of 107 microg/l. Symptoms abated slowly and did not recur after switching to a thiomersal-free system and chelation therapy. No mercury release to patients occurred in anti-IgG immunoadsorption or LDL apheresis treatments. CONCLUSION: This preliminary report suggests that protein A immunoadsorption columns primed with thiomersal during storage may cause a sustained increase of systemic mercury concentrations, which exceed current safety recommendations in a proportion of patients. Considering the potential for mercury-induced toxicity, every effort should be undertaken to reduce systemic mercury exposure, either by adding chelators to the rinsing solution or ideally by replacement of thiomersal.

Adult↗
PubMed2004

Dose-dependent effect of parenteral iron therapy on bleomycin-detectable iron in immune apheresis patients.

BACKGROUND: Iron deficiency and anemia are commonly encountered in patients with autoimmune diseases undergoing immune apheresis. This makes erythropoietin and iron substitution necessary in most patients. However, intravenous iron therapy may result in an increase of potentially toxic nontransferrin-bound iron. METHODS: We examined the effect of 50 mg or 100 mg of iron (III) sucrose on bleomycin-detectable iron (BDI) in immune apheresis patients. Six patients with autoimmune disorders and normal kidney function were enrolled. Before and after the injection of 50 mg or 100 mg of iron (III) sucrose, BDI was measured in serum samples at five different time points. RESULTS: There was no BDI traceable before injection of iron (III) sucrose. BDI was present in serum of all patients after the administration of 100 mg of iron (III) sucrose in concentrations up to 0.49 micromol/L. In contrast, only one patient showed BDI at a concentration of 0.16 micromol/L after the administration of 50 mg of iron (III) sucrose. CONCLUSION: We conclude that if parenteral iron is administered after apheresis treatment, despite the equal tolerability, use of 50 mg of iron (III) sucrose is superior to 100 mg of iron (III) sucrose in avoiding the formation of potentially toxic nontransferrin-bound iron.

Adult↗
PubMed2003

Synthesis of a single four-ring (S4R) molecular zinc phosphate and its assembly to an extended polymeric structure: a single-crystal and in-situ MAS NMR investigation.

A reaction of ZnO, HCl, H(3)PO(4), and 2-pyridylpiperazine in THF/H(2)O mixture at 75 degrees C for 72 h produces a new zinc phosphate, [(C(5)NH(5))(C(4)N(2)H(10))][Zn(H(2)PO(4))(2)(HPO(4))], I. Zinc phosphate I consists of single four-ring (S4R) units with terminal phosphoryl groups hanging from the Zn center. On reaction with zinc acetate dihydrate in the presence of water at 100 degrees C, I gave another new zinc phosphate, [(C(5)NH(5))(C(4)N(2)H(10))][Zn(2)(H(2)PO(4))(HPO(4))(PO(4))] x 2H(2)O, II. II has a layer structure with apertures formed by 4- and 8-T atoms (T = Zn, P). An examination of the two structures reveals that I and II are related, II being formed by the direct addition of Zn(2+) ions to I. Room-temperature (31)P MAS NMR studies show the presence of different phosphorus species in both compounds. An in-situ (31)P MAS NMR investigation on the formation of II from I in the presence of Zn(2+) ions and water reveals the transformation to be facile. What is noteworthy in this study is that the structural integrity of the S4Rs has been maintained during the formation of II. Donor-acceptor hydrogen bond interactions and pi-pi interactions involving the pyridyl groups also appear to play subtle roles in both phosphates. This study, the first attempt of its kind, combines the principles of supramolecular organic chemistry with inorganic building units and contributes to our understanding of the formation of framework solids.

Journal Article↗