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Hydrogen bond
About: Hydrogen bond is a research topic. Over the lifetime, 57701 publications have been published within this topic receiving 1306326 citations.
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TL;DR: A RhIII-catalysed tandem C–H/C–F activation for the synthesis of (hetero)arylated monofluoroalkenes and the employment of alcoholic solvent and the in-situ generated hydrogen fluoride are found to be beneficial in this transformation, indicating the possibility of the involvement of hydrogen bond activation mode with regards to the C–F bond cleavage step.
Abstract: Fluoroalkenes represent a class of privileged structural motifs, which found widespread use in medicinal chemistry. However, the synthetic access to fluoroalkenes was much underdeveloped with previous reported methods suffering from either low step economy or harsh reaction conditions. Here we present a Rh(III)-catalysed tandem C-H/C-F activation for the synthesis of (hetero)arylated monofluoroalkenes. The use of readily available gem-difluoroalkenes as electrophiles provides a highly efficient and operationally simple method for the introduction of α-fluoroalkenyl motifs onto (hetero)arenes under oxidant-free conditions. Furthermore, the employment of alcoholic solvent and the in-situ generated hydrogen fluoride are found to be beneficial in this transformation, indicating the possibility of the involvement of hydrogen bond activation mode with regards to the C-F bond cleavage step.
185 citations
TL;DR: The crystal structure of the liganded form of the sulfate-binding protein, an initial receptor for active transport of sulfate in Salmonella typhimurium, has been solved and refined at 2.0 A resolution and bears strong similarity to the structures of four other periplasmic binding proteins solved in the laboratory.
185 citations
TL;DR: In this paper, the ability of one H-bond in a chain to affect others is assessed by comparing the CH···O bonds in (H2CO)n and (HFCO)n to the OH··· O bonds in H2On.
Abstract: The ability of one H-bond in a chain to affect others is assessed by comparing the CH···O bonds in (H2CO)n and (HFCO)n to the OH···O bonds in (H2O)n. Both sorts of interactions grow stronger, and t...
185 citations
TL;DR: Extension of the approach will allow, in those cases where there is good complementarity between ligand and receptor, the prediction of approximate peptide-peptide binding constants in aqueous solution.
Abstract: An expression is presented for the estimation of approximate binding constants for bimolecular associations in solution. The consequences of the approach have been examined for the bimolecular association of two peptide components in aqueous solution: specifically for the binding of two vancomycin group antibiotics, vancomycin itself and ristocetin A, to the peptide cell wall analogue ^V-Ac-D-AIa-D-AIa and related ligands. Uncertainties in the treatment are relatively large, but the physical insights gained into the binding process (in part with the aid of calorimetric data obtained by others) are enlightening. We conclude that for amide-amide hydrogen bond formation in aqueous solution at room temperature, the intrinsic binding energy is ca. 24 kJ mol"1 (an intrinsic binding constant of ca. 104); this process is almost completely driven by a favorable entropy change associated with the release of water molecules from the amide NH and CO groups involved in hydrogen bond formation. The bimolecular association of N-Ac-D-AIa-D-Ala with ristocetin A has a remarkably small entropy change at 298 K (TAS = 3 ± 1.5 kJ mol"1)- We conclude that the release of water from polar and hydrocarbon groups involved in the binding almost exactly compensates for (i) the unfavorable entropy change due to the freezing out of four rotors of /V-Ac-D-AIa-D-AIa upon binding and (ii) the unfavorable entropy change of a bimolecular association. A crude quantitation of these effects is presented. We also present an estimate of the increase in translational plus rotational free energy, as a function of the ligand mass, occurring when a ligand binds to a larger receptor. This quantity, fundamental to all binding processes, is relatively insensitive to the shape of the ligand. Extension of the approach will allow, in those cases where there is good complementarity between ligand and receptor, the prediction of approximate peptide-peptide binding constants in aqueous solution.
185 citations
TL;DR: In this article, a mixed DFT/AM1 procedure was used for the entire helical structures, while AM1 was initially used to optimize the side chains, followed by reoptimization at the DFT level.
Abstract: Five peptides, each containing 17 amino acids, have been completely geometrically optimized in their α-helical and β-strand forms using a mixed DFT/AM1 procedure. B3LYP/D95** was used for the entire helical structures, while AM1 was initially used to optimize the side chains, followed by reoptimization at the DFT level. The energetic and structural results show (1) that the helices are favored over the strands by 29.5 to 37.4 kcal/mol; (2) that alkyl groups on the amino acid side chains favor helix formation even in the absence of solvent; (3) that C−H···O hydrogen bonds contribute to the relative stability of the helices that contain amino acids (val, leu and ile) with β-hydrogens in their alkyl side chains; (4) that formation of these helices entails approximately 6.6 kcal/mol of strain within the backbone per hydrogen bond; and (5) that H-bond cooperativity is essential for the α-helix to become more stable than a corresponding β-strand. This last observation strongly suggests that pairwise potentials ...
185 citations