Thermoresponsive nanostructures by self-assembly of a poly(N-isopropylacrylamide)-lipid conjugate

The synthesis and purification of a poly(N-isopropylacrylamide)-lipid conjugate and its use in the preparation of a thermoresponsive lipid mesophase is described. Specifically, poly(N-isopropylacrylamide) with a single carboxyl group at one end was activated with dicyclohexylcarbodiimide/N-hydroxysuccinimide to form an active ester. This N-hydroxysuccinimide ester was then used to form a dimyristoyl-sn-glycero-3-phosphoethanolamine conjugate with poly(N-isopropylacrylamide) via an amide bond, rendering the conjugate amphiphilic. Quaternary phases comprising the conjugate, a phosopholipid, dimyristoylphosphatidylcholine, and a cosurfactant, N,N-dimethyldodecylamine-N-oxide, dispersed in water were found to self-assemble at room temperature to form liquid crystalline gels, adopting an expanded lamellar structure. A modest increase in temperature triggered the reversible conversion of the aggregate to a collapsed lamellar structure, while a modest reduction in temperature resulted in its conversion to a nonlamellar phase. The phases were characterized by polarized optical microscopy and small-angle X-ray scattering (SAXS).     

Über die Systeme AJ/CoJ2 und die kristallchemischen Beziehungen in der Gruppe der Doppelhalogenide AnCoX(n+2) mit X = Cl,Br, J [1]

The Systems AI/CoI₂ (A = Alkali Metal, Tl, Ag) and the Crystal Chemistry of the Double Halides A_nCoX_(n+2) with X = Cl, Br, I The systems AI/CoI₂ (A = Cs, Rb, K, Tl, Na, Ag) were investigated by differencethermal analysis. The systems of NaI and AgI are found to be eutectical. A compound A₂CoI₄ always exists in the other systems. Cs₂CoI₄ crystallizes in the β-K₂SO₄ type with a coordination number (C.N.) for Cs equal to 9/10. Results obtained with single crystal technique reveal for the first time that among the double halides Rb₂CoI₄ is of the monoclinic Sr₂GeS₄ type (C. N. for Rb = 6(+2)). The compounds K₂CoJ₄, Tl₂CoJ₄, T-K₂CoBr₄, and T-Tl₂CoBr₄ are isotypic. Both structure groups are characterized by isolated CoX₄^2? tetrahedra. Reflectance spectra and magnetic susceptibilities can be explained on the basis of crystal field theory. – Our results close presently existing gaps in the knowledge on systems of CoBr₂ and CoCl₂ too.     

Carbocyclic analogs of nucleosides. Part 2.. Synthesis of 2′,3′-dideoxy-5′-homonucleoside analogs

A set of derivatives of cyclopentaneacetic acid cis-substituted at position 3 by nucleoside bases (both purines and pyrimidines) were prepared and characterized (see 11, 14 , and 23a, b; Schemes 2–4). These molecules are carbocyclic analogs of 2′,3′-dideoxy-5′-homonucleosides. In this synthesis, the skeleton was constructed from norbornanone and a novel method based on Mitsunobu chemistry used for the introduction of nucleoside-base substituents. The scope of this method was further explored via the preparation of a cyclobutyl analog of dideoxyguanosine (see 17 , Scheme 3).     

Anomalous grazing incidence small-angle x-ray scattering studies of platinum nanoparticles formed by cluster deposition

The size evolution of platinum nanoparticles formed on a SiO2/Si(111) substrate as a function of the level of surface coverage with deposited clusters has been investigated. The anisotropic shapes of sub-nanometer-size nanoparticles are changed to isotropic on the amorphous substrate as their sizes increased. Using anomalous grazing incidence small-angle x-ray scattering (AGISAXS), the scattering from nanoparticles on the surface of a substrate is well separated from that of surface roughness and fluorescence. We show that AGISAXS is a very effective method to subtract the background and can provide unbiased information about particle sizes of less than 1 nm.     

Ein isoperiboles lösungskalorimeter zur messung von lösungsenthalpien der doppelchloride des magnesiums

For measuring solution enthalpies of the strong hygroscopic double chlorides, an isoperibol solution calorimeter was built. Samples of 2–5 g could be solved to a molar dilution 1 : 3000. The temperature difference between reaction vessel and thermostat was measured by a thermopile; the temperature of the thermostat was constant to 2 · 10^?4°C. From the molar enthalpies of solution (ΔH^L), enthalpies for the reactions nACl + MCl₂ = A_sMCl(_{s + 2}) were calculated: ΔHP^R = ? ΔH^L (double chloride) + ΔH^L(n Cl) + ΔH^L(MCL₂) These values are relatively small: about ? 50 kJ for the Cs-compounds, nearly zero for the K- and Na-compounds.     

Synthesis and Spectroscopic Characterization of N2-(N-Acetyl-6-O-stearoyl-α-D-muramoyl)-L-alanyl-D-isoglutamine

Title compound 1 was synthesized by a published route which had to be modified (seven steps from readily obtainable starting materials). Characterization of 1 was achieved by spectroscopic means (FAB-MS, ¹H-NMR, including 2D-COSY). Furthermore, commercially available reference material purchased for comparison, was unequivocally established to be 10 , i.e. incompletely deprotected 1 .     

Geometric and electronic structure of clusters

The interplay between electronic and geometric structure is investigated for covalently bonded phosphorus clusters. We use a modification of the molecular dynamics/ density functional (MD/DF) method of Car and Parrinello, describing the electronic structure by a simplified linear combination of atomic orbitals (LCAO) approach. The results show clearly the tendency of phosphorus to threefold coordination, and substantial variations in bond angles lead to a large variety of isomers.     

Discovery of a new phosphotyrosine mimetic for PTP1B using breakaway tethering

Protein tyrosine phosphatases play important roles in many signaling cascades involved in human disease. The identification of druglike inhibitors for these targets is a major challenge, and the discovery of suitable phosphotyrosine (pY) mimetics remains one of the key difficulties. Here we describe an extension of tethering technology, "breakaway tethering", which is ideally suited for discovering such new chemical entities. The approach involves first irreversibly modifying a protein with an extender that contains both a masked thiol and a known pY mimetic. The extender is then cleaved to release the pY mimetic, unmasking the thiol. The resulting protein is screened against a library of disulfide-containing small molecule fragments; any molecules with inherent affinity for the pY binding site will preferentially form disulfides with the extender, allowing for their identification by mass spectrometry. The ability to start from a known substrate mimimizes perturbation of protein structure and increases the opportunity to probe the active site using tethering. We applied this approach to the anti-diabetic protein PTP1B to discover a pY mimetic which belongs to a new molecular class and which binds in a novel fashion.     

Electronic structure of niobium-doped molybdenum disulfide nanotubes

The effect of doping transition metal disulfide nanotubes on their structural and electronic properties was studied for the first time using self-consistent band-structure calculations by the density functional tight-binding method (DFTB). The influence of partial Nb → Mo substitution in the walls of MoS₂ nanotubes of various diameters and atomic configurations (armchair and zigzag) on their electronic structure, structural parameters, and relative stability is exemplified by a series of “mixed” Mo_0.9Nb_0.1S₂ nanotubes. The electronic properties of Mo_0.9Nb_0.1S₂ nanotubes are discussed as a function of the possible types of distribution of doping Nb atoms in the tubes.