Facile synthesis of pH‐responsive glycopolypeptides with adjustable sugar density

Well‐defined pH‐responsive glycopolypeptides were prepared by polymer‐analogous aqueous amide coupling of d ‐glucosamine to poly(α,l ‐glutamic acid) (PGA) using the coupling agent 4‐(4,6‐dimethoxy‐1,3,5‐triazin‐2‐yl)‐4‐methylmorpholinium chloride (DMT‐MM) without any organic solvents, additives, or buffers. Degrees of substitution (DS) up to 80% can be achieved, and the DS is adjustable by the molar ratio of DMT‐MM to PGA repeating units. Successful glycosylation of both low MW and high MW PGA was confirmed by ¹H NMR and FTIR spectroscopy as well as by an enhanced solubility at low pH. CD spectroscopy revealed that glycosylated PGAs with a DS up to 0.63 are able to undergo a pH‐responsive and reversible helix‐coil transition. However, for polymers with higher DS no transition occurs. A comparison with PGAs functionalized with monoethanolamine showed that the low helicity at high DS is not a steric effect due to the bulky sugar moieties, but a solvation effect. Preliminary turbidimetric tests with the lectin Concanavalin A indicate a biological activity of these glycosylated polypeptides. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3925–3931     

Di- and Tetracyano-Substituted Pyrene-Fused Pyrazaacenes: Aggregation in the Solid State

Five di- and tetracyano-substituted pyrene-fused pyrazaacenes were synthesized and studied as potential electron acceptors in the solid state. Single crystals of all compounds were grown and the crystal packing studied by DFT calculations (transfer integrals and reorganization energies) to get insight into possible use for semiconducting charge transport.     

Mixing of phases in non-crystalline materials: Application to carbon

The atomic structure of non-crystalline solids is described by the correlation function. When more than one phase is present, the simple addition of the correlation functions for the various phases in proportion to their concentrations within the system is not valid, except in the case of the completely phase-separated system. The overall correlation function must reflect the boundaries between the various phases within the system. The cross correlation functions between the phases have a dependence both on the degree of mixing of the phases and also on the sizes of the domains of the phases. The correlation function for a non-crystalline solid with more than one phase has been derived in a general way. Particular application has been made to non-crystalline carbon for which the correlation function given previously did not have the correct limits because of absence of the cross correlation terms.     

Self-assembly in complex mixed surfactant solutions: the impact of dodecyl triethylene glycol on dihexadecyl dimethyl ammonium bromide

The impact of the nonionic surfactant, dodecyl triethyleneglycol ether (C(12)E(3)) on the solution microstructure of the dialkyl chain cationic surfactant, dihexadecyl dimethyl ammonium bromide, (DHDAB) has been investigated. The variation in solution microstructure has been studied using a combination of small angle neutron scattering, ultra small angle neutron scattering, optical texture and photon correlation spectroscopy. At low surfactant concentrations (1.5 mM) the microstructure takes the form of bilamellar vesicles (BLV) for compositions containing less than 20 mol % of added C(12)E(3). Multilamellar vesicles (MLV) are the predominant microstructure for solutions richer in composition than 20 mol % C(12)E(3). At more than 80 mol % C(12)E(3), the solution microstructure reverts to that of a lamellar phase dispersion consistent with studies on the pure nonionic surfactant. At higher concentrations (60 mM) a wide continuous L beta phase region is observed for compositions in the range 20 to 80 mol % C(12)E(3). The fine details of the phase diagram were obtained from quantitative analysis of the SANS data using a well-established lamellar membrane model. Irrespective of the nonionic content, the bilayers are in general highly rigid, consistent with those stabilized by charge interactions. Furthermore estimates of the product of membrane moduli (compressibility and bending modulus) indicate that the different phase regions have very different membrane properties, however the magnitude of the variations observed are not predicted using existing theoretical treatments.     

Synthesis and Absorption Properties of Long Acenoacenes

Acenes, polyaromatic hydrocarbons composed of linearly fused benzene rings have received immense attention due to their performance as semiconductors in organic optoelectronic applications. Their appealing physicochemical properties, such as extended delocalization, high charge carrier mobilities, narrow HOMO-LOMO gaps and partially radical character in the ground state make them very attractive targets for many potential applications. However, the intrinsic synthetic challenges of unsubstituted members such as high reactivity and poor solubility are still limiting factors for their wider exploitation. Herein, we report a simple general synthesis of a new family of angularly fused acenoacenes with improved stability compared to their isoelectronic linear counterparts. The synthesis and comprehensive characterization of pentacenopentacene, pentacenohexacene and hexacenohexacene, with lengths between decacene and dodecacene, are disclosed.     

Preparation of the stabilized glycoenzymes by cross-linking their carbohydrate chains

Each of the three high-mannose type glycoproteins studied, acid phosphatase, invertase, and glucose oxidase, could be specifically cross-linked through its carbohydrate chains. The procedure involves periodate oxidation of carbohydrate residues followed by reaction of the generated aldehyde groups with adipic acid dihydrazide as a cross-linker. The amount and size as well as solubility of the formed polymers could be efficiently controlled by varying the reaction conditions, i.e., the oxidation degree and the concentrations of glycoproteins, cross-linker, and hydrogen ions during the cross-linking reaction. It was found that the quantity and size of polymers increased with oxidation degree and protein concentration and by lowering the pH. When the protein concentration was above and pH below certain values, depending on the glycoenzyme, insoluble polymers formed. The soluble cross-linked polymers retained a high level of original activity, and the minor decrease in specific activity noticed was shown to occur during the periodate oxidation step. The cross-linked glycoenzymes are much more resistant to denaturation by high temperature and by changes in pH, demonstrating the usefulness of this method in preparation of the stabilized glycoprotein derivatives.     

Capillary neutron optics for prompt-gamma activation analysis

A neutron lens has been constructed to focus cold neutrons from the exit of a⁵⁸Ni neutron guide, which delivers a beam to the Prompt-Gamma Activation Analysis (PGAA) station at the NIST Cold Neutron Research Facility. The lens compresses a neutron beam of cross section 50 mm× 45 mm onto a focal spot of diameter 0.53 mm (fwhm) wich an average gain of 80 in neutron current density. PGAA measurements have been performed to demonstrate the enhanced sensitivity and detection limits for various elements and the spatial resolution in one transverse dimension. For the two test particles (a gadolinium glass bead and cadmium metal of sizes less than 0.5 mm), the gain in the -count rate with the lens is a factor of 60, and the detection limit is improved by a factor of 20. The system can be used for two-dimensional mapping of samples on a sub-millimeter scale to complement other analytical techniques such as neutron depth profiling (NDP).     

Perturbations of symmetric elliptic Hamiltonians of degree four

In this paper four-parameter unfoldings Xλ of symmetric elliptic Hamiltonians of degree four are studied. We prove that in a compact region of the period annulus of X₀ the displacement function of Xλ is sign equivalent to its principal part, which is given by a family induced by a Chebychev system; and we describe the bifurcation diagram of Xλ in a full neighborhood of the origin in the parameter space, where at most two limit cycles can exist for the corresponding systems.