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Donor Interactions (donor + interaction)
Selected AbstractsComparison of the effects of pressure on three layered hydrates: a partially successful attempt to predict a high-pressure phase transitionACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009Russell D. L. Johnstone We report the effect of pressure on the crystal structures of betaine monohydrate (BTM), l -cysteic acid monohydrate (CAM) and S -4-sulfo- l -phenylalanine monohydrate (SPM). All three structures are composed of layers of zwitterionic molecules separated by layers of water molecules. In BTM the water molecules make donor interactions with the same layer of betaine molecules, and the structure remains in a compressed form of its ambient-pressure phase up to 7.8,GPa. CAM contains bi-layers of l -cysteic acid molecules separated by water molecules which form donor interactions to the bi-layers above and below. This phase is stable up to 6.8,GPa. SPM also contains layers of zwitterionic molecules with the waters acting as hydrogen-bond donors to the layers above and below. SPM undergoes a single-crystal to single-crystal phase transition above 1,GPa in which half the water molecules reorient so as to form one donor interaction with another water molecule within the same layer. In addition, half of the S -4-sulfo- l -phenylalanine molecules change their conformation. The high-pressure phase is stable up to 6.9,GPa, although modest rearrangements in hydrogen bonding and molecular conformation occur at 6.4,GPa. The three hydrates had been selected on the basis of their topological similarity (CAM and SPM) or dissimilarity (BTM) with serine hydrate, which undergoes a phase transition at 5,GPa in which the water molecules change orientation. The phase transition in SPM shows some common features with that in serine hydrate. The principal directions of compression in all three structures were found to correlate with directions of hydrogen bonds and distributions of interstitial voids. [source] Long-range and short-range mechanisms of hydrophobic attraction and hydrophilic repulsion in specific and aspecific interactionsJOURNAL OF MOLECULAR RECOGNITION, Issue 4 2003Carel Jan van Oss Abstract Among the three different non-covalent forces acting in aqueous media, i.e. Lifshitz,van der Waals (LW), Lewis acid,base (AB) and electrical double layer (EL) forces, the AB forces or electron,acceptor/electron,donor interactions are quantitatively by far the predominant ones. A subset of the AB forces acting in water causes the hydrophobic effect, which is the attraction caused by the hydrogen-bonding (AB) free energy of cohesion between the water molecules which surround all apolar as well as polar molecules and particles when they are immersed in water. As the polar energy of cohesion among water molecules is an innate property of water, the hydrophobic attraction (due to the hydrophobic effect) is unavoidably always present in aqueous media and has a value of ,Ghydrophobic,=,,102,mJ/m2, at 20,°C, being equal to the AB free energy of cohesion between the water molecules at that temperature. The strong underlying hydrophobic attraction due to this effect can, however, be surmounted by very hydrophilic molecules and particles that attract water molecules more strongly than the free energy of attraction of these molecules or particles for one another, plus the hydrogen-bonding free energy of cohesion between the water molecules, thus resulting in a net non-electrical double layer repulsion. Each of the three non-covalent forces, LW, AB or EL, any of which can be independently attractive or repulsive, decays, dependent on the circumstances, as a function of distance according to different rules. These rules, following an extended DLVO (XDLVO) approach, are given, as well as the measurement methods for the LW, AB and EL surface thermodynamic properties, determined at ,contact'. The implications of the resulting hydrophobic attractive and hydrophilic repulsive free energies, as a function of distance, are discussed with respect to specific and aspecific interactions in biological systems. The discussion furnishes a description of the manner by which shorter-range specific attractions can surmount the usually much stronger long-range aspecific repulsion, and ends with examples of in vitro and in vivo effects of hydrophilization of biopolymers, particles or surfaces by linkage with polyethylene oxide (PEO; also called polyethylene glycol, PEG). Copyright © 2003 John Wiley & Sons, Ltd. [source] An examination of binding motifs associated with inter-particle interactions between facetted nano-crystals of acetylsalicylic acid and ascorbic acid through the application of molecular grid-based search methods,JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2009R.B. Hammond Abstract Grid-based intermolecular search methods using atom,atom force fields are used to assess the structural nature of potential crystal,crystal interfacial binding associated with the examination of representative pharmaceutical formulation components, viz acetylsalicylic acid (aspirin) and ascorbic acid (vitamin C). Molecular models of nano-sized molecular clusters for these two compounds, shaped in accordance with an attachment energy model of the respective particle morphologies, are constructed and used together with a grid-based search method to model the likely inter-particle interactions. The most-stable, mutual alignments of the respective nano-clusters based on their interaction energies are identified in the expectation that these are indicative of the most likely inter-particle binding configurations. The stable inter-particle binding configurations identified reveal that the number of interfacial hydrogen bonds formed between the binding particles is, potentially, an important factor in terms of the stability of inter-particle cohesion. All preferred inter-particle alignments are found to involve either the (1,0,0) or the (1,1,0) face of aspirin crystals interacting with a number of the growth forms of ascorbic acid. Four main types of interfacial hydrogen bonds are found to be associated with inter-particle binding and involve acceptor,donor interactions between hydroxyl, carbonyl, ester and lactone acceptor groups and hydroxyl donor groups. This hydrogen bonding network is found to be consistent with the surface chemistry of the interacting habit faces with, in general, the number of hydrogen bonds increasing for the more stable alignments. The likely usefulness of this approach for predicting solid-state formulation properties is reviewed. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4589,4602, 2009 [source] Comparison of the effects of pressure on three layered hydrates: a partially successful attempt to predict a high-pressure phase transitionACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009Russell D. L. Johnstone We report the effect of pressure on the crystal structures of betaine monohydrate (BTM), l -cysteic acid monohydrate (CAM) and S -4-sulfo- l -phenylalanine monohydrate (SPM). All three structures are composed of layers of zwitterionic molecules separated by layers of water molecules. In BTM the water molecules make donor interactions with the same layer of betaine molecules, and the structure remains in a compressed form of its ambient-pressure phase up to 7.8,GPa. CAM contains bi-layers of l -cysteic acid molecules separated by water molecules which form donor interactions to the bi-layers above and below. This phase is stable up to 6.8,GPa. SPM also contains layers of zwitterionic molecules with the waters acting as hydrogen-bond donors to the layers above and below. SPM undergoes a single-crystal to single-crystal phase transition above 1,GPa in which half the water molecules reorient so as to form one donor interaction with another water molecule within the same layer. In addition, half of the S -4-sulfo- l -phenylalanine molecules change their conformation. The high-pressure phase is stable up to 6.9,GPa, although modest rearrangements in hydrogen bonding and molecular conformation occur at 6.4,GPa. The three hydrates had been selected on the basis of their topological similarity (CAM and SPM) or dissimilarity (BTM) with serine hydrate, which undergoes a phase transition at 5,GPa in which the water molecules change orientation. The phase transition in SPM shows some common features with that in serine hydrate. The principal directions of compression in all three structures were found to correlate with directions of hydrogen bonds and distributions of interstitial voids. [source] | ||||||||||