introduction : the aim of this in vitro study was to evaluate the effect of smear layer on the push-out bond strength of white mineral trioxide aggregate (wmta) with and without disodium hydrogen phosphate (na 2 hpo 4 ). materials and methods: dentin discs with standard cavities were obtained from extracted human single-rooted teeth and divided to 4 groups ( n =15) according to the irrigation r...

Widespread arguments of the hydrogen bond are criticized with respect to theories of protein folding and interactions of proteins with their specific ligands. Contrary to popular belief, by no means does the hydrogen bond play an important role in determining the conformation of proteins and the interactions of proteins with specific substrates. Stereotypical thinking on the hydrogen bond const...

Two mol-ecules of the title compound, C(15)H(13)N(3)O(3)S, are linked by an inter-molecular N-H⋯S hydrogen bond. There is also an intra-molecular N-H⋯O hydrogen bond, forming a six-membered ring. The steric restriction of the m-methyl and p-nitro groups, as well as the intra-molecular hydrogen bond, are the main factors influencing the mol-ecular conformation.

The title compound, C11H13NO6, exhibits an intra-molecular O-H⋯O=C hydrogen bond between the N-hydroxyl H atom and carbonyl O atom of the neighboring acetyl group. This finding contradicts a previously published model in which the hydrogen bond was postulated to occur with the neighboring carbomethoxy group. This relatively strong hydrogen bond [O-H⋯O: D = 2.5583 (11) Å and θ = 152°] may underl...

The title compound, C10H13NO4, is essentially planar, with an r.m.s. deviation of 0.049 Å. An intra-molecular C-H⋯O hydrogen bond occurs and the amino group forms an intra-molecular N-H⋯Oester hydrogen bond; the other H atom forms an inter-molecular N-H⋯Ocarbon-yl hydrogen bond, leading to the formation of a helical chain that runs along the b-axis direction.

In the title compound, C(11)H(12)N(2)O(3)·H(2)O, the water mol-ecule is a hydrogen-bond donor to the double-bond amide and the carbonyl O atoms of two acid mol-ecules; it is also a hydrogen-bond acceptor to the acid -OH and amide -NH- groups. These hydrogen-bonding inter-actions give rise to a layer structure, with the layers parallel to the ab plane.

Protein backbone helical structures have the same values of dihedral angles φ and ψ from unit to unit and thus, can be uniquely determined by a pair (φ,ψ). We focus our attention on two types of protein secondary structure αand 310-helices stabilized by 1-5 and 1-4 hydrogen bonding pattern respectively. Even though both αand 310-helices each represent a group of helices, various studies show th...

The PM3 semiempirical quantum-mechanical method was found to systematically describe intermolecular hydrogen bonding in small polar molecules. PM3 shows charge transfer from the donor to acceptor molecules on the order of 0.02-0.06 units of charge when strong hydrogen bonds are formed. The PM3 method is predictive; calculated hydrogen bond energies with an absolute magnitude greater than 2 kcal...