255,340 research outputs found
Solvatochromic probes for detecting hydrogen-bond-donating solvents
Hydrogen bonding heavily influences conformations, rate of reactions, and chemical equilibria. The development of a method to monitor hydrogen bonding interactions independent of polarity is challenging as both are linked. We have developed two solvatochromic dyes that detect hydrogen-bond-donating solvents. The unique solvatochromism of the triazine architecture has allowed the development of probes that monitor hydrogen-bond-donating species including water
Compact phases of polymers with hydrogen bonding
We propose an off-lattice model for a self-avoiding homopolymer chain with
two different competing attractive interactions, mimicking the hydrophobic
effect and the hydrogen bond formation respectively. By means of Monte Carlo
simulations, we are able to trace out the complete phase diagram for different
values of the relative strength of the two competing interactions. For strong
enough hydrogen bonding, the ground state is a helical conformation, whereas
with decreasing hydrogen bonding strength, helices get eventually destabilized
at low temperature in favor of more compact conformations resembling
-sheets appearing in native structures of proteins. For weaker hydrogen
bonding helices are not thermodynamically relevant anymore.Comment: 5 pages, 3 figures; revised version published in PR
Three-body Hydrogen Bond Defects Contribute Significantly to the Dielectric Properties of the Liquid Water-Vapor Interface
In this Letter, we present a simple model of aqueous interfacial molecular
structure and we use this model to isolate the effects of hydrogen bonding on
the dielectric properties of the liquid water-vapor interface. By comparing
this model to the results of atomistic simulation we show that the anisotropic
distribution of molecular orientations at the interface can be understood by
considering the behavior of a single water molecule interacting with the
average interfacial density field via an empirical hydrogen bonding potential.
We illustrate that the depth dependence of this orientational anisotropy is
determined by the geometric constraints of hydrogen bonding and we show that
the primary features of simulated orientational distributions can be reproduced
by assuming an idealized, perfectly tetrahedral hydrogen bonding geometry. We
also demonstrate that non-ideal hydrogen bond geometries are required to
produce interfacial variations in the average orientational polarization and
polarizability. We find that these interfacial properties contain significant
contributions from a specific type of geometrically distorted three-body
hydrogen bond defect that is preferentially stabilized at the interface. Our
findings thus reveal that the dielectric properties of the liquid water-vapor
interface are determined by collective molecular interactions that are unique
to the interfacial environment.Comment: 5 pages, 4 figure, S
Intermolecular N-H...O=C hydrogen bonding in the crystal structure of 6-amino-1,3-dimethyluracil
The 6-amino- 1,3-dimethyluracil molecule [6-amino- 1,3-
dimethyl-2,4(1H,3H)-pyrimidinedione], C6H9N302 (I),
lies on a crystallographic mirror plane and participates
in an extensive two-dimensional hydrogen-bonding network
in the solid state. Each molecule is involved in N--
H...O=C hydrogen bonding involving the amino and
carbonyl gr. oups, with O...N separations of 2.894 (3) and
2.904 (3) A
Adhesion theory review
Bonding theories reviewed include physical adsorption, hydrogen bonding, chemisorption and surface energy; bond failure mechanisms include phase discontinuity, swelling and corrosion. Concept of bond failure by water desorption is introduced and discussed
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