Supramolecular networks stabilise and functionalise black phosphorus

The limited stability of the surface of black phosphorus (BP) under atmospheric conditions is a significant constraint on the exploitation of this layered material and its few layer analogue, phosphorene, as an optoelectronic material. Here we show that supramolecular networks stabilised by hydrogen bonding can be formed on BP, and that these monolayer-thick films can passivate the BP surface and inhibit oxidation under ambient conditions. The supramolecular layers are formed by solution deposition and we use atomic force microscopy to obtain images of the BP surface and hexagonal supramolecular networks of trimesic acid and melamine cyanurate (CA.M) under ambient conditions. The CA.M network is aligned with rows of phosphorus atoms and forms large domains which passivate the BP surface for more than a month, and also provides a stable supramolecular platform for the sequential deposition of 1,2,4,5-tetrakis(4-carboxyphenyl)benzene to form supramolecular heterostructures

Carbon nanotubes as excitonic insulators

Fifty years ago Walter Kohn speculated that a zero-gap semiconductor might be unstable against the spontaneous generation of excitons-electron-hole pairs bound together by Coulomb attraction. The reconstructed ground state would then open a gap breaking the symmetry of the underlying lattice, a genuine consequence of electronic correlations. Here we show that this excitonic insulator is realized in zero-gap carbon nanotubes by performing first-principles calculations through many-body perturbation theory as well as quantum Monte Carlo. The excitonic order modulates the charge between the two carbon sublattices opening an experimentally observable gap, which scales as the inverse of the tube radius and weakly depends on the axial magnetic field. Our findings call into question the Luttinger liquid paradigm for nanotubes and provide tests to experimentally discriminate between excitonic and Mott insulators

[NMR-relaxation in hydrated collagen from the spotted dogfish]].

Collagen samples from dog-fish egg case at different water content were studied by the 1H NMR relaxation method. The dependences of the proton spin-lattice and spin-spin relaxation rates on the concentration of water in hydrated native collagen were measured. The fractions of water protons of different mobility and their corresponding spin-spin and spin-lattice relaxation rates were determined in a multi-phase model of water protons in natural biopolymer-water systems. The correlation times were calculated as the characteristics of molecular motion in hydrated collagens with different content of absorbed water. The results obtained were compared with literature data of pulse NMR studies of molecular mobility in other collagen fibers

Structure and properties of interpolymer complexes as polymer carriers of biologically active substances

Structure and properties of interpolymer complexes (IPC) composed of poly(methacrylic acid) (PMAA) and poly(ethylene glycol) (PEG) as polymer carriers for biologically active substances were studied using high-resolution solution 1H and 13C NMR and 13C solid-state CP/MAS NMR methods. Release of drugs from polymer matrix of IPC into the environment was studied using the IPC-theophilline composition as an example. It was demonstrated that information on specific features of the association of complementary chains of PMAA and PEG both for the solid state of polymer matrix and for its aqueous solution may be basically obtained by NMR methods. It was revealed that various synthesis procedures result in the formation of IPCs differing by their structures. A scheme of quantitative estimation of the fraction of the hydrogen bonds that are formed between IPC components was proposed. The results obtained allow us to assume that the synthesis procedure and composition of the forming complex are interrelated due to the mechanism of the formation of interpolymer complexes. © 1996 MAHK Hayka/Interperiodica Publishing

Aqueous dispersions of xenon clathrates

The state of water during the formation of xenon clathrates in water and aqueous tert-butanol solutions is studied by the method of NMR relaxation. Xenon crystal hydrates in liquid water are shown to present structured systems where the dispersed phase is represented by clathrate crystals dispersed in liquid water. Clathrate nonuniformities (with characteristic sizes on the order of several microns) are completely responsible for the relaxation of liquid water protons. The modifying effect of tert-butanol on the dispersions of xenon clathrates and the relaxation characteristics of water is discussed. The factors responsible for the disperse structure of the samples (inhomogeneous contribution to the relaxation rate) are analyzed and approaches to their estimation are singled out

[NMR-relaxation in hydrated collagen from the spotted dogfish]].

Collagen samples from dog-fish egg case at different water content were studied by the 1H NMR relaxation method. The dependences of the proton spin-lattice and spin-spin relaxation rates on the concentration of water in hydrated native collagen were measured. The fractions of water protons of different mobility and their corresponding spin-spin and spin-lattice relaxation rates were determined in a multi-phase model of water protons in natural biopolymer-water systems. The correlation times were calculated as the characteristics of molecular motion in hydrated collagens with different content of absorbed water. The results obtained were compared with literature data of pulse NMR studies of molecular mobility in other collagen fibers