Solubility and Solution Structure of Cellulose Derivatives

Strongly interacting solvents are needed to dissolve cellulose; therefore, in the past the interpretation of the uncommon solution behavior of cellulose and its derivatives was based mainly on energetic (enthalpic) considerations, for example, hydrogen bonding. These attempts have not been very successful. The present paper demonstrates that entropic effects influence the solution behavior much stronger than hitherto supposed. In the well-known Flory–Huggins theory the driving force for dissolution of flexible chains is the configurational entropy of mixing. This large entropy is strongly reduced by the chain stiffness of the cellulose backbone and by the strictly regular primary structure of this polysaccharide. It strongly reduces the driving force for dissolution. The entropy of mixing becomes largely increased again by the attachment of long side chains and causes solubility with surprising efficiency (hairy rod principle). This effect is demonstrated with several examples. Among others, the surprising insolubility of short, regular-selectively substituted cellulose chains is explained, although long chains of the same substitution pattern are soluble. The striking behavior of cellulose ethers in water is based on the hydrophobic effect, which causes an increased order of the polymer surrounding water molecules. The induced order results in a very pronounced decrease of entropy of mixing that overcompensates the positive configurational entropy of mixing. Common rules of basic thermodynamics now predict phase separation on heating, contrary to the Flory–Huggins theory, which can only predict phase separation on cooling.     

Investigations of a series of nonionic surfactants of sugar-lipid hybrids by light scattering and electron microscopy

Sugar-lipid hybrids of the type C_nC_m were prepared by coupling an alkane chain (C_n) with a maltooligosaccharide (G_m) over an amide linkage. Coupling was performed with maltobionolactone (G₂) and n-alkylamine chains C_n withn=8,10,12,14,16, i.e. variation of the hydrophobic part of the molecule, and with hexadecylamine (C₁₆) and different maltooligosaccharides (G_m, m=2,3,4,6). The solution properties of the various products were studied by means of static and dynamic light scattering (LS) and by electron-microscopy (EM).The results may be summarized as follows: If the alkane chain is shorter thann=14, small spherical micelles with a radius of about 3 nm are observed. In time these micelles aggregate further to form increasingly larger spherical clusters which eventually precipitate. Long rod-like micelles form whenn 14. Contour length and chain stiffness were determined by applying theories of semiflexible chains. A qualitative confirmation of the light scattering results, i.e., micelle size and shape, was obtained from electron microscopy.     

Structure of casein micelles II. α s1-casein

Following the earlier study of the- and-casein micelle structure, we will now report results from the _s1-casein. Static and dynamic light scattering measurements were performed in a concentration range from 0.5 to 6.0 mg/ml atT=35 °C. A constant apparent molecular weight of 3.4×10⁶ daltons was found over the whole range. The apparent radii of gyration and the diffusion coefficients also show no detectable concentration dependence. The ratio of the two radiiR _g /R _H =2.78+0.21 is characteristic of extended rigid structures.R _g is the radius of gyration andR _H the hydrodynamic radius defined via the Stokes-Einstein relationship from the translational diffusion coefficient. This is in agreement with the analysis of the pronounced angular dependence of the scattered light, which leads to the conclusion that _s1-casein forms very long worm-like micelles. The contour length of one cylinder was found to beL1600 nm and the chains appear to be composed of about 12 Kuhn segments. At higher concentrations, lateral aggregation proportional to the concentration is observed. Beyond the overlap concentrationc ^* the asymptotic scattering curve changes its shape, which is interpreted as the beginning of a reversible gelation.     

Mass spectrometry for the detection of differentially expressed proteins: a comparison of surface-enhanced laser desorption/ionization and capillary electrophoresis/mass spectrometry

The discovery of biomarkers is currently attracting much interest as it harbors great potential for the diagnosis and monitoring of human diseases. Here we have used two advanced mass spectroscopy based technologies, surface enhanced laser desorption ionization (SELDI-MS) and capillary electrophoresis/mass spectrometry (CE/MS), to obtain proteomic patterns of urine samples from patients suffering from membranous glomerulonephritis (MGN) and healthy volunteers. The results indicate that CE/MS analysis is able to display a rich and complex pattern of polypeptides with high resolution and high mass accuracy. In order to analyze these patterns, the MosaiqueVisu software was developed for peak identification, deconvolution and the display of refined maps in a three-dimensional format. The polypeptide profiles obtained with SELDI-MS from the same samples are much sparser and show lower resolution and mass accuracy. The SELDI-MS profiles are further heavily dependent on analyte concentration. SELDI-MS analysis identified three differentially expressed polypeptides, which are potential biomarkers that can distinguish healthy donors from patients with MGN. In contrast, approximately 200 potential biomarkers could be identified by CE/MS. Thus, while SELDI-MS is easy to use and requires very little sample, CE/MS generates much richer data sets that enable an in-depth analysis.     

On an isoperimetric inequality for a Schrödinger operator depending on the curvature of a loop

Let y be a smooth closed curve of length 2π in ?³, and let κ(s) be its curvature, regarded as a function of arc length. We associate with this curve the one-dimensional Schrödinger operator $H_\gamma = - \tfrac{{d^2 }}{{ds^2 }} + \kappa ^2 (s)$ acting on the space of square integrable 2π-periodic functions. A natural conjecture is that the lowest spectral value e₀ (y) of H_y is bounded below by 1 for any y (this value is assumed when y is a circle). We study a family of curves y that includes the circle and for which e₀(y) = 1 as well. We show that the curves in this family are local minimizers, i.e., e₀(y) can only increase under small perturbations leading away from the family. To our knowledge, the full conjecture remains open.     

Quantitative determination of large structures by small-angle light scattering

A new small-angle light scattering camera has been developed. In contrast to conventional detection the present system is based on a recently developed two-dimensional charge-coupled-device chip made by Thomson (France). The advantage of this chip is its excellent linear response and very low dark signal even at room temperature. The best linearity was obtained by leading each pixel signal through the same amplifying system. The optical system covered a diffraction angular region from about 1° to 15° (q = 0.2–2.6 μm⁻¹). The camera was calibrated with grids and pinholes and was tested with polymer latex particles in solution and with spherulites from polymer films. Received: 06 December 1999 Accepted: 04 February 2000     

Gd4B4O11F2: Synthesis and crystal structure of a rare-earth fluoride borate exhibiting a new “fundamental building block” in borate chemistry

A new gadolinium fluoride borate Gd₄B₄O₁₁F₂ was yielded in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C. Gd₄B₄O₁₁F₂ crystallizes monoclinically in the space group C2/c with the lattice parameters a=1361.3(3) pm, b=464.2(2) pm, c=1374.1(3) pm, and β=91.32(3)° (Z=4). The crystal structure exhibits a structural motif not yet reported from borate chemistry: two BO₄-tetrahedra (□) and two BO₃-groups (?) are connected via common corners, leading to the fundamental building block 2?2□:?□□?. In the two crystallographically identical BO₄-tetrahedra, a distortion resulting in a very long B-O-bond is found.     

Concept of deterministic single ion doping with sub-nm spatial resolution

We propose a method for deterministic implantation of single atoms into solids which relies on a linear ion trap as an ion source. Our approach allows a deterministic control of the number of implanted atoms and a spatial resolution of less than 1 nm. Furthermore, the method is expected to work for almost all chemical elements. The deterministic implantation of single phosphor or nitrogen atoms is interesting for the fabrication of scalable solid state quantum computers, in particular for silicon and diamond based schemes. A wide range of further applications is expected for the fabrication of nano and sub-nano electronic devices. PACS 03.67.-a; 29.25.Ni; 61.72.Ji; 81.16.Rf; 85.40.Ry