SAXS and DSC studies of the crystallization and melting phenomena of poly(ϵ‐caprolactone)

The relationships between the crystallization temperature, T_c, the crystal thickness, d_c and the melting peak temperature, T_m of poly(ϵ‐caprolactone) have been determined by carrying out time‐ and temperature‐dependent small angle x‐ray scattering experiments. A two‐step melting has been suggested, resulting in the occurrence of two well defined independent boundary lines, indicating the transformation from melt into the partially crystalline state. For crystallization temperatures lower than 40°C, during heating, more pronounced peak shifts are observed with the final melting of the crystallites having the same thickness of d_c ≈︁ 7 nm. In this region, it is evident that crystals have relatively good stabilities, since they have fairly uniform thickness. At higher temperatures, above 40°C, T_m increases with T_c, together with the thickness. The transformation of the melt into the partially crystalline state depicts a two‐step process, beginning with the formation of a well defined initial structure with lower order, which is subsequently stabilized.     

Molecular Gold Wire from Mixed‐Valent AuI/III Complexes

Crystals of mixed‐valent Au complexes have been grown from solutions of cyclohexanecarbonitrile and a stoichiometric amount of gold(I) and gold(III) chloride. The purely obtained compound was characterized as bis(cyclohexanecarbonitrile)gold(I) tetrachloridoaurate(III). The crystal packing of the mixed valent Au(I/III) compound demonstrates a columnar arrangement of the gold(I) and gold(III) atoms. The new structure displays the shortest unsupported gold(I)–gold(III) interactions with the sub‐van der Waals distance of 324–325 pm, which is assumed as an aurophilic bonding interaction.     

Tracing glycoprotein structures: electrospray ionization tandem mass spectrometric analysis of sugar-peptide adducts

Owing to the diversity of carbohydrate structures and their significance for the function of many biopolymers, structural analysis of various carbohydrate-related compounds is of great importance. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was used to establish the fragmentation behaviour of a range of sugar-peptide adducts as model compounds of widespread glycoprotein structures. The compounds used in this study were chosen to provide correlation of distinct fragment ions with specific structural differences, namely position and type of carbohydrate-peptide bond and structure of the sugar moiety. All compounds show N- and C-terminal sequence ions along with losses of up to three water molecules. Fructose-related Amadori compounds exhibit M + 78 modified N-terminal peptide fragment ions. Fragmentation of glucose-peptide esters is characterized by the sugar ring fragmentation. Additionally, under the ESI-MS conditions applied, the esters studied undergo intramolecular reaction giving cyclic sugar-peptide structures that can be traced by the presence of N-terminal peptide M + 42 adducts. Detailed analysis of cyclic fructose-related compound comprising structural features of both studied groups revealed a rich fragmentation pattern derived from amino acid residues and water molecules losses from [M - 2H(2)O + H](+) ion. Also, some interesting differences were found with respect to the nature of carbohydrate moieties.     

Interplay between domain microstructure and nematic order in liquid crystalline/isotropic block copolymers

The domain microstructure and the nematic LC mesophase in a series of side-chain liquid crystalline/isotropic (LC/I) diblock copolymers with systematically varied block volume fractions were studied in a broad temperature range (25–170 °C) by DSC, polarized microscopy, and wide and small angle X-ray scattering. At all temperatures the block copolymers are microphase separated. The PSLC block copolymers exhibit order at two length-scales: on one hand, a nematic LC mesophase with characteristic length-scale of 0.43 nm (intermesogen distance); on the other hand, lamellar, hexagonal or cubic domain microstructures with characteristic length-scales of 27–44 nm (lattice parameter). The LC block was either located in the matrix or confined inside the microdomains. The thermotropic behavior is characterized by the sequence g/~35 °C/n/~115 °C/i and is not affected by the domain microstructure and/or dimensions. Analysis of the lamellar dimensions showed that the LC chain is stretched. With increasing temperature, a thermal expansion of both blocks takes place followed by a retraction of the LC chain above T_NI. The phase diagram is asymmetric and does not alter above T_NI. No order-to-order transitions triggered by the nematic-isotropic transition are observed. It was shown that domain microstructures of low interfacial curvature (lamellar and hexagonal) are energetically favored over the geometrically expected ones of high interfacial curvature (micellar cubic) due to the presence of nematic LC mesophase in the matrix or in the microdomains. By comparison to theory a Kuhn segment length of the LC block b_LC=0.86 nm was derived from the location of the lamellar/hexagonal phase boundaries.This paper is dedicated to Prof. Fischer on the occasion of his 75th birthday.     

Die Ammonolyse von Halogenokomplexen des vierwertigen Platins

Ammonolysis of Halogeno Complexes of Tetravalent Platinum Reactions of liquid ammonia and ammonium hexahalogenoplatinates(IV) at ?40°C yield mixtures of halogenoammine complexes [Pt(NH₃)_6?nX_n]X_4?n (X = Cl, Br, I; n = 3, 2, 1, 0). Hexaammine platinum(IV) salts, [Pt(NH₃)₆]X₄, may be isolated as main product only after several weeks of reaction. Interactions at room temperature of liquid ammonia and hexachloro or hexabromo complexes produce quantitatively the novel dinuclear di-m?-amido-bis[tetraammineplatinum(IV)] complex, [(H₃N)₄Pt(NH₂)₂Pt(NH₃)₄]X₆. By interaction of gaseous or liquid ammonia and subsequent addition of potassium amide solution in excess potassium hexaamido platinate(IV), K₂[Pt(NH₂)₆], is formed in good yield.     

Decharging of globular proteins and protein complexes in electrospray

Electrospray ionization mass spectrometry (ESI-MS) is a valuable tool in structural biology for investigating globular proteins and their biomolecular interactions. During the electrospray ionization process, proteins become desolvated and multiply charged, which may influence their structure. Reducing the net charge obtained during the electrospray process may be relevant for studying globular proteins. In this report we demonstrate the effect of a series of inorganic and organic gas-phase bases on the number of charges that proteins and protein complexes attain. Solution additives with very strong gas-phase basicities (GB) were identified among the so-called "proton sponges". The gas-phase proton affinities (PA) of the compounds that were added to the aqueous protein solutions ranged from 700 to 1050 kJ mol(-1). Circular dichroism studies showed that in these solutions the proteins retain their globular structures. The size of the proteins investigated ranged from the 14.3 kDa lysozyme up to the 800 kDa tetradecameric chaperone complex GroEL. Decharging of the proteins in the electrospray process by up to 60 % could be achieved by adding the most basic compounds rather than the more commonly used ammonium acetate additive. This decharging process probably results from proton competition events between the multiply protonated protein ions and the basic additives just prior to the final desolvation. We hypothesize that such globular protein species, which attain relatively few charges during the ionization event, obtain a gas-phase structure that more closely resembles their solution-phase structure. Thus, these basic additives can be useful in the study of the biologically relevant properties of globular proteins by using mass spectrometry.     

Isotopic fractionation in thin-layer chromatography.

The thin-layer chromatography of imipramine on silica gel plates was studied in fifteen solvent systems. The mobility of imipramine labeled with deuterium in the methyl groups of the dimethylaminopropyl side chain differs markedly from that of unlabeled imipramine. Partial or complete separations between unlabeled and deuterated imipramine were observed in all basic and neutral solvent systems investigated, but not in weakly acidic solvents. Isotopic fractionations of imipramine were also found on alumina thin-layer plates, but were not detected in cellulose chromatography. In all thin-layer isotopic separations, the unlabeled compound migrates more rapidly than the deuterated molecule. These results can be explained by a stronger basicity of deuterated imipramine relative to its unlabeled counterpart.