Complex associations between membrane proteins analyzed by analytical ultracentrifugation: Studies on the erythrocyte membrane proteins band 3 and ankyrin

Associations between different water-soluble proteins can be studied by sedimentation equilibrium experiments in the analytical ultracentrifuge and subsequent mathematical analysis of thec(r)-distributions obtained. The analysis can be simplified by labelling one of the proteins with a dye absorbing at wavelengths >300 nm. The method can also be applied to intrinsic membrane proteins in solutions of a nonionic detergent. The present paper both reviews the method and reports application to the associations between two proteins of the human erythrocyte membrane: 1) band 3, the membrane's main intrinsic protein which, in detergent solutions and presumably also in the erythrocyte membrane, is in a monomer/dimer/tetramer association equilibrium, and 2) the cytoskeletal protein ankyrin which links the membrane skeleton to the lipid bilayer by binding to band 3. Ankyrin was labelled with fluorescein isothiocyanate and the detergent used was C₁₂E₉. It was found that the only aggregate of ankyrin and band 3 occurring in significant amounts was a complex of one ankyrin molecule and four band 3 molecules. This strongly suggests that, in the erythrocyte membrane, the band 3 tetramer represents the high affinity ankyrin binding site.This paper was presented at the VI. Symposium on Analytical Ultracentrifugation, Marburg, F.R.G., February 16–17, 1989.     

Experimental constraints on the phase in the Cabibbo-Kobayashi-Maskawa matrix

Using experimental results on |V _ub /V _cb |, (K⁰), (B⁰) and two experimental limits onm _t , and assuming that these five observations are fully described by standard physics, we determine values and errors for the two CKM matrix parameters and with a maximum-likelihood fit. The results depend strongly onf _B ; (, ) lies in the first quadrant forf _B >180 MeV and in the second forf _B <180 mev.=" as=" functions=">f _B , we present also values and errors onm _t , ₁₃, |V _td |, arg(V _td ), and M(B _s )/(B _s ).     

The fast and the curious: High‐throughput experimentation in synthetic polymer chemistry

The application of automated synthetic parallel methods in polymer chemistry is described. A brief overview of all different polymerization techniques that have been used is provided. Furthermore, the equipment and methodologies that were used in our approach for automated parallel polymerization reactions are discussed followed by detailed insight into recent developments on automated cationic ring‐opening polymerization, atom transfer radical polymerization, and emulsion polymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2425–2434, 2003     

Kristallstruktur von Cu10Sn3(m)

Zusammenfassung Cu₁₀Sn₃(m) hat eine hexagonale Struktur, die in enger Verwandtschaft zur Struktur des CuZn steht. Einer der Hauptunterschiede beider Strukturen ist eine Stapelvariation der Schichten parallel (111)_CuZn. Aus dieser folgen weitere Verschiebungen der Atome, so daß die Struktur auch als Variante der NiAs-Struktur beschrieben werden kann. Gründe für die Stapelvariation lassen sich aus Annahmen über die Ortskorrelation der Elektronen herleiten.

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Crystal structure of Cu₁₀Sn₃(m)

Cu₁₀Sn₃(m) has a hexagonal structure, which is closely related to the structure of Cuzn. One of the main differences of these structures is a stacking variation of the layers parallel (111)_CuZn, which implies further shifts of atoms so that the structure may also be described as a variant of the NiAs structure. Causes for the stacking variation may be derived from assumptions on the spatial correlation of the electrons.

     

Organofunctional Metal Oxide Clusters as Building Blocks for Inorganic-Organic Hybrid Materials

The controlled hydrolysis of metal alkoxides in the presence of methacrylic acid results in metal oxide clusters capped by polymerizable methacrylate ligands. Radical polymerization of small portions of such clusters with organic co-monomers allows the preparation of an interesting new type of inorganic-organic hybrid polymers in which the metal oxo clusters efficiently crosslink the organic polymers chains. SAXS investigations revealed that the clusters may aggregate to form clusters of clusters. The properties of the hybrid materials, such as thermal stability, swelling, dielectric and mechanical properties, depend not only on the portion of incorporated cluster, i.e. the crosslinking density, but also on the kind of employed cluster.     

Hydrido-Silyl-Komplexe. V. Strukturelle Änderungen in Hydrido-Silyl-Komplexen infolge Si?H-Wechselwirkung; Strukturvergleich zwischen (π-CH3C5H4)(CO)2Mn(H)SiR3- und analogen (π-C5H5)(CO)2FeSiR3-Komplexen

Hydrido Silyl Complexes. V. Structural Changes in Hydrido Silyl Complexes Due to Si? H Interaction; Comparison between the Structures of (π-CH₃C₅H₄)(CO)₂Mn(H)SiR₃ and Analogous (π-C₅H₅)(CO)₂FeSiR₃ Complexes The structures of the complexes Cp(CO)₂FeSiFPh₂ ( 2a ) and Cp(CO)₂FeSiCl₃ ( 2b ), containing ?normal”? metal-silicon bonds, are compared with the known structures of the complexes MeCp(CO)₂Mn(H)SiFPh₂ ( 1a ) and MeCp(CO)₂Mn(H)SiCl₃ ( 1b ), containing Mn? H? Si three-center bonds. 2a crystallizes in space group P2₁/c, a = 805.8(3), b = 1417.5(6), c = 1498.2(4) pm, β = 90.99(3)°, 2b in space group P2₁/n, a = 817(1), b = 1244(1), c = 1142(1)pm, β = 99.9(1)°. In 2a gauche conformation in respect to the Fe? Si bond is found; in 2b the silylligand is rotated 12° around the Fe? Si axis out of a staggered conformation. Possible reasons for the unsymmetrical conformations are discussed. Lengthening of the Fe? Si distance from 221.6(1)pm in 2b to 227.8(1) pm in 2a corresponds to the expected increase in the bond radius of silicon due to exchange of the substituents at silicon. Additional lengthening of the Mn? Si distance by about 3.5 pm in 1a compared with 1b is attributed to the increased delocalization of the Mn? H? Si bond in 1a .     

Über Chalkogenolate. 142. Untersuchungen über Trimethylsilylxanthogensäure. 2. S-Methyl- und S-Ethyltrimethylsilylxanthat

On Chalcogenolates. 142. Studies on Trimethylsilyl Xanthic Acid. 2. S-Methyl and S-Ethyl Trimethylsilyl Xanthates The hitherto unknown S-alkyl trimethylsilyl xanthates (CH₃)₃SiO? CS? SR, where R = CH₃ and C₂H₅, have been characterized with electron absorption, infrared, nuclear magnetic resonance (¹H, ¹³C, and ²⁹Si), and mass spectra.     

14C-labeled and large-scale synthesis of the angiotensin-(1-7)-receptor agonist AVE 0991 by cross-coupling reactions

The synthesis of (14)C-labeled AVE 0991 ((14)()C-1a) and large-scale synthesis of AVE 0991 (1a) are described. In the key step of the synthesis, the C-C coupling reaction of the imidazole (2) and thiophene (3) building blocks was studied under Suzuki and Stille reaction conditions, respectively. Suzuki reaction gave only moderate yields, whereas the best results were obtained under Stille reaction conditions with up to 64% yield.     

Electronic state of push-pull alkenes: an experimental dynamic NMR and theoretical ab initio MO study

The (1)H and (13)C NMR spectra of a number of push-pull alkenes were recorded and the (13)C chemical shifts calculated employing the GIAO perturbation method. Of the various levels of theory tried, MP2 calculations with a triple-zeta-valence basis set were found to be the most effective for providing reliable results. The effect of the solvent was also considered but only by single-point calculations. Generally, the agreement between the experimental and theoretically calculated (13)C chemical shifts was good with only the carbons of the carbonyl, thiocarbonyl, and cyano groups deviating significantly. The substituents on the different sides of the central C=C partial double bond were classified qualitatively with respect to their donor (S,S < S,N < N,N) and acceptor properties (C identical with N < C=O < C=S) and according to the ring size on the donor side (6 < 7 < 5). The geometries of both the ground (GS) and transition states (TS) of the restricted rotation about the central C=C partial double bond were also calculated at the HF and MP2 levels of theory and the free energy differences compared with the barriers to rotation determined experimentally by dynamic NMR spectroscopy. Structural differences between the various push-pull alkenes were reproduced well, but the barriers to rotation were generally overestimated theoretically. Nevertheless, by correlating the barriers to rotation and the length of the central C=C partial double bonds, the push-pull alkenes could be classified with respect to the amount of hydrogen bonding present, the extent of donor-acceptor interactions (the push-pull effect), and the level of steric hindrance within the molecules. Finally, by means of NBO analysis of a set of model push-pull alkenes (acceptors: -C identical with N, -CH=O, and -CH=S; donors: S, O, and NH), the occupation numbers of the bonding pi orbitals of the central C=C partial double bond were shown to quantitatively describe the acceptor powers of the substituents and the corresponding occupation numbers of the antibonding pi orbital the donor powers of the substituents. Thus, for the first time an estimation of both the acceptor and the donor properties of the substituents attached to the push-pull double bond have been separately quantified. Furthermore, both the balance between strong donor/weak acceptor substituents (and vice versa) and the additional influences on the barriers to rotation (hydrogen bonding and steric hindrance in the GSs and TSs) could be differentiated.