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Achim Müller

Publications and source records attributed to Achim Müller.

17 recordsLinked to original sources
PubMed2003

Synergetic activation of "silent receptor" sites leading to a new type of inclusion complex: integration of a 64-membered ring comprising K+ and SO4(2-) ions into a molybdenum oxide-based nanoobject.

The new type of inclusion species [Mo(VI)114Mo(V)32O429(H2O)50(KSO4)16]30- comprising 16 encapsulated K+ and SO4(2-) ions shows an unusual 64-membered [K(SO4)]16 ring integrated into a wheel-shaped type nanocluster host; it is formed by a synergetically induced functional complementarity and represents a text-book example of a very complex non-biological material.

Chemical Phenomena↗
PubMed2003

Characterization of a tungsten-substituted nitrogenase isolated from Rhodobacter capsulatus.

In the phototrophic non-sulfur bacterium Rhodobacter capsulatus, the biosynthesis of the conventional Mo-nitrogenase is strictly Mo-regulated. Significant amounts of both dinitrogenase and dinitrogenase reductase were only formed when the growth medium was supplemented with molybdate (1 microM). During cell growth under Mo-deficient conditions, tungstate, at high concentrations (1 mM), was capable of partially (approximately 25%) substituting for molybdate in the induction of nitrogenase synthesis. On the basis of such conditions, a tungsten-substituted nitrogenase was isolated from R. capsulatus with the aid of anfA (Fe-only nitrogenase defective) mutant cells and partially purified by Q-sepharose chromatography. Metal analyses revealed the protein to contain an average of 1 W-, 16 Fe-, and less than 0.01 Mo atoms per alpha(2)beta(2)-tetramer. The tungsten-substituted (WFe) protein was inactive in reducing N(2) and marginally active in acetylene reduction, but it was found to show considerable activity with respect to the generation of H(2) from protons. The EPR spectrum of the WFe protein, recorded at 4 K, exhibited three distinct signals: (i) an S = 3/2 signal, which dominates the low-field region of the spectrum (g = 4.19, 3.93) and is indicative of a tungsten-substituted cofactor (termed FeWco), (ii) a marginal S = 3/2 signal (g = 4.29, 3.67) that can be attributed to residual amounts of FeMoco present in the protein, and (iii) a broad S = 1/2 signal (g = 2.09, 1.95, 1.86) arising from at least two paramagnetic species. Redox titrational analysis of the WFe protein revealed the midpoint potential of the FeWco (E(m) < -200 mV) to be shifted to distinctly lower potentials as compared to that of the FeMoco (E(m) approximately -50 mV) present in the native enzyme. The P clusters of both the WFe and the MoFe protein appear indistinguishable with respect to their midpoint potentials. EPR spectra recorded with the WFe protein under turnover conditions exhibited a 20% decrease in the intensity of the FeWco signal, indicating that the cofactor can be enzymatically reduced only to a small extent. The data presented in the current study demonstrate the pivotal role of molybdenum in optimal N(2) fixation and provides direct evidence that the inability of a tungsten-substituted nitrogenase to reduce N(2) is due to the difficulty to effectively reduce the FeW cofactor beyond its semi-reduced state.

Blotting, Western↗
PubMed2002

A potassium selective 'nanosponge' with well defined pores.

The novel spherical cluster-compound K2Na6[K20 [symbol: see text] Mo80-V22O282(SO4)12(H2O)66]. approximately 140H2O 1 has been obtained in a 'one-pot' reaction and exhibits several remarkable structural features: 30 open shell centers, i.e. 8 Mov and 22 VIV spanning an icosidodecahedron, the incorporation of 20 K+ cations capping 20 appropriate [M6O6] pores/rings present at the surface of the spherical cluster-anion, and an encapsulated aggregate of water molecules.

Journal Article↗
PubMed2002

Inelastic neutron scattering on three mixed-valence dodecanuclear polyoxovanadate clusters.

The magnetic exchange interactions in the mixed-valence dodecanuclear polyoxovanadate compounds Na(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(H(2)O)].23H(2)O, Na(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(D(2)O)].16.5D(2)O, and (NHEt(3))(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(H(2)O)].H(2)O were investigated by an inelastic neutron scattering (INS) study using cold neutrons. In addition, the synthesis procedures and the single-crystal X-ray structures of these compounds have been investigated together with the temperature dependence of their magnetic susceptibilities. The magnetic properties below 100 K can be described by simply taking into account an antiferromagnetically exchange coupled tetramer, consisting of four vanadium(IV) ions. Up to four magnetic transitions between the cluster S = 0 ground state and excited states could be observed by INS. The transition energies and the relative INS intensities could be modeled on the basis of the following exchange Hamiltonian: H(ex) = -2J(12)(xy)[S(1x)S(2x)+ S(3x)S(4x)+ S(1y)S(2y)+ S(3y)S(4y)] - 2J(12)(z)[(S(1z)S(2z)+ S(3z)S(4z)] - 2J(23)(xy)[(S(2x)S(3x)+ S(1x)S(4x)+ S(2y)S(3y)+ S(1y)S(4y)] - 2J(23)(z)[(S(2z)S(3z)+ S(1z)S(4z)]. The following sets of parameters were derived: for Na(4)[V(12)As(8)O(40)(H(2)O)].23H(2)O, J(12)(xy)() = J(12)(z)= -0.80 meV, J(23)(xy) = J(23)(z) = -0.72 meV; for Na(4)[V(12)As(8)O(40)(D(2)O)].16.5D(2)O, J(12)(xy) = J(12)(z) = J(23)(xy) = J(23)(z = -0.78 meV; for (NHEt(3))(4)[V(12)As(8)O(40)(H(2)O)].H(2)O, J(12)(xy) = -0.80 meV, J(12)(z) = -0.82 meV, J(23)(xy)() = -0.67 meV, J(23)(z) = -0.69 meV. This study of the same [V(12)As(8)]-type cluster in three different crystal environments allows us to draw some conclusions concerning the applicability on INS in the area of nondeuterated molecular spin clusters. In addition, the effects of using nondeuterated samples and different sample container shapes for INS were evaluated.

Journal Article↗
PubMed2002

Heterobinuclear complexes as building blocks in designing extended structures.

The heterobinuclear complex [CuPrL(NO(3))(3)] has been used as a building block for the construction of a two-dimensional coordination polymer with the formula [CuPrL(NO(3)(2)(IN)], 1 (L(2-) = the dianion of the compartmental Schiff-base ligand obtained from the 2:1 condensation of 3-methoxysalicylaldehyde with 1,3-propanediamine; IN(-) = the isonicotinate ion). The heterobinuclear units, [CuPrL(NO(3))(2)](+), are connected through the unsymmetrical exo-bidentate ligands, IN(-), leading to a unique extended structure. Crystal data for compound 1: FW, 790.94; monoclinic, space group P2(1)/n, a = 11.2837(3) A, b = 14.7785(4) A, c = 16.9745(4) A, beta = 100.427(1) degrees; V = 2783.86(12) A(3); Z = 4; R1 = 0.0210, wR2 = 0.0562 [I > 2sigma(I)].

Journal Article↗
PubMed2002

Urea as 'deus ex machina' in giant molybdenum blue type cluster synthesis: an unusual hybrid compound with perspectives for related nano, supramolecular and extended structures.

The reaction of an aqueous solution of ammonium heptamolybdate with sodium dithionite and urea--a glue and cluster hydration shell destructing agent corresponding to its role in inclusion compound chemistry--at low pH value results in the formation of nanosized ring shaped molybdenum-oxide based clusters which in a short time get linked to chains.

Journal Article↗
PubMed2002

Soccer-playing metal oxide giant spheres: a first step towards patterning structurally well defined nano-object collectives.

In context with the challenge to assemble giant molecules into patterns with limited size, molybdenum oxide giant spheres (with a molecular mass of about 16 kDa) could be 'kicked out' like soccer balls into the gas phase using matrix assisted laser desorption and ionization (MALDI) and detected by TOF mass spectrometry while cluster collectives ranging from dimers to pentamers were observed.

Journal Article↗
PubMed2002

The Fe-only nitrogenase and the Mo nitrogenase from Rhodobacter capsulatus: a comparative study on the redox properties of the metal clusters present in the dinitrogenase components.

The dinitrogenase component proteins of the conventional Mo nitrogenase (MoFe protein) and of the alternative Fe-only nitrogenase (FeFe protein) were both isolated and purified from Rhodobacter capsulatus, redox-titrated according to the same procedures and subjected to an EPR spectroscopic comparison. In the course of an oxidative titration of the MoFe protein (Rc1Mo) three significant S = 1/2 EPR signals deriving from oxidized states of the P-cluster were detected: (1) a rhombic signal (g = 2.07, 1.96 and 1.83), which showed a bell-shaped redox curve with midpoint potentials (Em) of -195 mV (appearance) and -30 mV (disappearance), (2) an axial signal (g(parallel) = 2.00, g perpendicular = 1.90) with almost identical redox properties and (3) a second rhombic signal (g = 2.03, 2.00, 1.90) at higher redox potentials (> 100 mV). While the 'low-potential' rhombic signal and the axial signal have been both attributed to the one-electron-oxidized P-cluster (P1+) present in two conformationally different proteins, the 'high-potential' rhombic signal has been suggested rather to derive from the P3+ state. Upon oxidation, the FeFe protein (Rc1Fe) exhibited three significant S = 1/2 EPR signals as well. However, the Rc1Fe signals strongly deviated from the MoFe protein signals, suggesting that they cannot simply be assigned to different P-cluster states. (a) The most prominent feature is an unusually broad signal at g = 2.27 and 2.06, which proved to be fully reversible and to correlate with catalytic activity. The cluster giving rise to this signal appears to be involved in the transfer of two electrons. The midpoint potentials determined were: -80 mV (appearance) and 70 mV (disappearance). (b) Under weakly acidic conditions (pH 6.4) a slightly altered EPR signal occurred. It was characterized by a shift of the g values to 2.22 and 2.05 and by the appearance of an additional negative absorption-shaped peak at g = 1.86. (c) A very narrow rhombic EPR signal at g = 2.00, 1.98 and 1.96 appeared at positive redox potentials (Em = 80 mV, intensity maximum at 160 mV). Another novel S = 1/2 signal at g = 1.96, 1.92 and 1.77 was observed on further, enzymatic reduction of the dithionite-reduced state of Rc1Fe with the dinitrogenase reductase component (Rc2Fe) of the same enzyme system (turnover conditions in the presence of N2 and ATP). When the Rc1Mo protein was treated analogously, neither this 'turnover signal' nor any other S = 1/2 signal were detectable. All Rc1Fe-specific EPR signals detected are discussed and tentatively assigned with special consideration of the reference spectra obtained from Rc1Mo preparations.

Electron Spin Resonance Spectroscopy↗
PubMed2002

Local anaesthetic properties of ambroxol hydrochloride lozenges in view of sore throat. Clinical proof of concept.

UNLABELLED: Acute oro-pharyngeal catarrh is characterised by mild to severe sore throat, such as pain on swallowing, feeling of scratchiness, burning and urge to cough. The present study was conducted to explore whether the test compound is going to show clinical relevance and is a suitable medication for the relief of these symptoms. OBJECTIVE: Description and comparison of the efficacy and tolerability of lozenges containing 20 mg ambroxol hydrochloride (trans-4-[(2-amino-3,5-dibrombenzyl)amino]cyclohexano hydrochloride, CAS 18683-91-5) in relieving acute sore throat, in comparison to placebo. DESIGN: Multi-centre, prospective, placebo-controlled, randomised, double-blind trial involving two days of treatment with up to 6 lozenges containing 20 mg ambroxol hydrochloride per day. SUBJECTS: Two-hundred-eighteen (218) patients were enrolled (97 males, 121 females, average age: 39.4 +/- 15 years, range: 17-81 years); 215 were treated: 107 with 20 mg ambroxol and 108 with placebo; 26 discontinued prematurely (13 in each treatment group). 208 patients constituted the intent-to-treat (ITT) dataset (105 and 103 for treatment with ambroxol and placebo, respectively); 196 patients constituted the perprotocol (PP) dataset (97 and 99, respectively); all treated patients were part of the dataset for safety analysis. TREATMENTS: Double-blind treatment with up to 6 lozenges per day containing 20 mg ambroxol hydrochloride or placebo (a lozenge with a distinct minty flavour). MAIN OUTCOME MEASURES: The time-weighted average pain relief over the first 3 h after the first lozenge as a ratio of the baseline pain intensity of sore throat (SPIDnorm) and the patients' evaluation of efficacy and tolerability at the end of each day of treatment. RESULTS: Both treatments led to a reduction of pain intensity; the mean (+/- SD) SPIDnorm after the 1st lozenge were 0.39 +/- 0.27 and 0.28 +/- 0.25 for 20 mg ambroxol hydrochloride and placebo, respectively; the treatment effect of ambroxol was statistically significantly superior compared to placebo (p: 0.0029; 95% confidence interval estimate of the mean treatment difference for ambroxol minus placebo: 0.04 to 0.18). At the end of each subsequent ambulatory treatment day with up to 6 lozenges per day, a statistically significantly higher proportion of patients scored a higher level of efficacy for the active treatments with ambroxol hydrochloride compared to placebo. The investigational treatments were equally well tolerated. CONCLUSIONS: Sucking lozenges containing 20 mg ambroxol hydrochloride has a beneficial pain relieving effect in patients with acute sore throat, superior to that which otherwise can be achieved by sucking a placebo lozenge. This finding confirms that the preclinical local anaesthetic properties of ambroxol hydrochloride may have beneficial clinical implications.

Administration, Oral↗
PubMed2002

Efficacy and tolerability of ambroxol hydrochloride lozenges in sore throat. Randomised, double-blind, placebo-controlled trials regarding the local anaesthetic properties.

UNLABELLED: Two confirmatory clinical trials were performed to investigate the efficacy and tolerability of ambroxol lozenges at doses of 20 mg and 30 mg relative to placebo in relieving the symptoms of sore throat of at least moderately severe intensity in patients suffering from oro-pharyngeal catarrh accompanied by pain on swallowing, feeling of scratchiness, burning and urge to cough. OBJECTIVE: Description and comparison of the efficacy and tolerability of lozenges containing 20 mg or 30 mg ambroxol hydrochloride (trans-4-[(2-amino-3,5-dibrom-benzyl)amino]cyclohexano hydrochloride, CAS 18683-91-5) in relieving acute sore throat, in comparison to placebo. DESIGN: Two similar, multi-centre, prospective, placebo-controlled, randomised, double-blind trials involving three days of treatment with up to 6 lozenges containing 20 or 30 mg ambroxol hydrochloride per day. SUBJECTS: There were enrolled three-hundred-thirty-one (331, study I) and three-hundred-eighty-three (383, study II) outpatients with acute uncomplicated sore throat of at least moderately severe intensity which is not suspected to be due to bacterial pharyngitis. TREATMENTS: Double-blind treatment with up to six lozenges per day containing either 20 mg or 30 mg ambroxol hydrochloride or placebo (a lozenge with a distinct minty flavour). MAIN OUTCOME MEASURES: The time-weighted average pain relief over the first 3 h after the first lozenge as a ratio of the baseline pain intensity of sore throat (SPIDnorm) and the patients' evaluation of efficacy and tolerability at the end of each day of the three days treatment. RESULTS: All treatments led to a reduction of pain intensity; the means (+/- SD) SPIDnorm after the 1st lozenge were 0.53 +/- 0.28 or 0.50 +/- 0.30 or 0.38 +/- 0.28 with 20 mg or 30 mg ambroxol hydrochloride or placebo respectively in study I, and 0.53 +/- 0.30 or 0.60 +/- 0.28 or 0.39 +/- 0.31 in study II; the effect of treatment was statistically significant (p: 0.0002 or p: 0.0033 in study I and p: 0.0005 or p: 0.0001 in study II, respectively, for the comparison of 20 mg or 30 mg ambroxol hydrochloride vs. placebo). The improvement with the active treatments was greater than with placebo (95% confidence interval (CI) estimates of the mean treatment differences vs. placebo were 0.08 to 0.23 or 0.05 to 0.20 for lozenges with 20 mg or 30 mg ambroxol hydrochloride, respectively, in study I, and 0.06 to 0.21 or 0.13 to 0.28 in study II). At the end of each subsequent ambulatory treatment day with up to six lozenges per day, a statistically significantly higher proportion of patients scored a higher level of efficacy for the active treatments with ambroxol hydrochloride compared to placebo. The treatments investigated were equally well tolerated. CONCLUSIONS: Sucking lozenges containing 20 mg or 30 mg ambroxol hydrochloride has a beneficial pain-relieving effect in patients with acute sore throat, superior to that achieved by sucking a placebo lozenge. While both strengths were equally well tolerated, the higher strength of 30 mg ambroxol hydrochloride did not prove more effective. The findings confirm that the previously discovered local anaesthetic properties of ambroxol hydrochloride do have beneficial clinical implications.

Acute Disease↗
PubMed2001

"Nanoobjects" by Self-Assembly Concomitant with Modifications under Alterable Boundary Conditions: Incorporation of Paramagnetic Metal Centers (Cu(2+)) in Ring-Shaped Molybdenum-Oxide Based Clusters The authors thank Prof. D. Gatteschi, University of Florence (Italy), for helping with the interpretation of the ESR spectrum, and Dipl.-Chem. A. Berkle and Dr. J. Hockemeyer, University of Bielefeld (Germany), for their collaboration. C. R. thanks the Alexander von Humboldt Foundation for her fellowship. Financial support by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully acknowledged.

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Journal Article↗