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Structure, three-dimensional hydrogen bonds

The highly structured, three-dimensional hydrogen bonding state of ice and water is reflected in many of their unusual properties. [Pg.3]

Noncovalent interactions in metal complexes of biomolecules may play an important role in the creation of supramolecular structures around the metal center. For instance, extensive three-dimensional hydrogen-bonded stmcmres grow around metal complexes of barbiturates, recognized as the most widely used drugs for the treatment of epilepsy.Electrostatic interactions between a cation and the Trring of an aromatic molecule (cation-tt interactions) are common motifs in protein structures. Little is known about alkali and alkali-earth cation-tt inter-... [Pg.154]

The basic crystal structure consists of P04 (or As04 ) tetrahedra alternating with the K" " (or NH4 ) ions along the c-axis. The P04 units are connected by 0-H...0 hydrogen bonds in the ab plane, forming a three-dimensional hydrogen-bonded lattice [2]. In the ferroelectric phases, the H atoms are localized such that the two close protons are both on the top of the oxygen ions of the XO4 units, as depicted in Fig. 4b. In the antiferroelectric... [Pg.28]

The complexity of the physical properties of liquid water is largely determined by the presence of a three-dimensional hydrogen bond (HB) network [1]. The HB s undergo continuous transformations that occur on ultrafast timescales. The molecular vibrations are especially sensitive to the presence of the HB network. For example, the spectrum of the OH-stretch vibrational mode is substantially broadened and shifted towards lower frequencies if the OH-group is involved in the HB. Therefore, the microscopic structure and the dynamics of water are expected to manifest themselves in the IR vibrational spectrum, and, therefore, can be studied by methods of ultrafast infrared spectroscopy. It has been shown in a number of ultrafast spectroscopic experiments and computer simulations that dephasing dynamics of the OH-stretch vibrations of water molecules in the liquid phase occurs on sub-picosecond timescales [2-14],... [Pg.165]

The icosahedral cluster model1,2 offers a structure on which large molecules can be mapped in order to investigate their interaction with water within a three-dimensional hydrogen-bonded network, and here offers new insights into the ways fullerene and polyoxomolybdate molecules interact with water in aqueous solution. [Pg.3]

In water, there are two hydrogen atoms and two lone pairs in each molecule, allowing for a three-dimensional hydrogen bonded structure. [Pg.657]

V=9.267(1) nm, Z=4, Ri=0.0S3 and Rw=0,058. The complex is composed of copper cations, nitrate anions, 1,10-phenanthroline, protocatechuic acid and lattice water molecules. The structure of H3PCA, N03 and waters comprises packing of three-dimensional network by hydrogen bonds with cavities. The complex can be considered as a model of host/guest supermolecule. The three-dimensional hydrogen-bonding network is the host species. The Cu(phen)3 cations, guest species, occupy the cavities of the host. [Pg.355]

A generally similar pattern of changes was found [78] for the decompositions of lithium and caesium orthophosphates. This comparability of reactivity is ascribed to the similarities of the three-dimensional hydrogen bonding in the anion structure with those of the sodium salts. Reaction transforms these condensed hydrogen-bonded systems to the alternative oxygen-bonded structures. A trend towards lower reaction temperatures in the solids containing the smaller cations (which vary in radius from 0.068 to 0.134 nm) was attributed to the minor effect of increased polarization with reduction in ionic size. [Pg.397]

It appears that the methyl radical is more stable in crystals with the more open structure characteristic of two- or three-dimensional hydrogen-bonded networks. The structure of zinc acetate dihydrate, for example, is known (37), and the acetate ions are tied together by hydrogen bonds in two-dimensional sheets with only weak Van der Waals forces between layers. Since the formation of CH3 in hydrated acetates presumably is the result of dissociation of a precursor of the type CH3C002", which... [Pg.332]

The combination of a small size and a three-dimensional hydrogen-bonded network system is responsible for the complexity of the structure of water, which results in a large cohesive energy density (550 cal mL or 2200 MPa), a high surface tension and a high heat capacity. These three attributes give water its unique structure as a liquid, and give rise to the special properties known as hydrophobic effects, which... [Pg.40]

The first dipeptide nanotube system was L-Val-L-Ala (VA), which forms crystals with narrow hydrophobic channels (diameter about 5 A) lined by peptide side chains.This structure is conceptually different from those of the cyclic peptides in that the pores are generated from self-assembly of small molecules, which are hydrogen bonded, head-to-tail, into helices (Fig. 3a). The extremely robust three-dimensional hydrogen-bonding scaffold was since observed for a series of other hydro-phobic dipeptides.Pore size can be regulated from 3.3 A (L-Ile-L-Val) to 5.2 A (L-Ala-L-Val) by adjusting the bulk of the hydrophobic side chains. Furthermore, L-Ala-L-Val has pores that can adapt their shapes and sizes to absorb large solvent molecules like 2-butanol. [Pg.1037]


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See also in sourсe #XX -- [ Pg.10 ]




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Hydrogen bonding structures

Hydrogen structures

Hydrogenation structure

Three structures

Three-dimensional structure

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