Topic
Hydrogen bond
About: Hydrogen bond is a research topic. Over the lifetime, 57701 publications have been published within this topic receiving 1306326 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: The upper temperature limit for the existence of hydrogen bonding in supercritical water is discussed with respect to the recent statement by Postorino et al. as mentioned in this paper that hydrogen bonds can be observed experimentally up to 800 K using both spectroscopic and diffraction techniques, yet it may be predicted that hydrogen bonding persists to even higher temperatures.
Abstract: The upper temperature limit for the existence of hydrogen bonding in supercritical water is discussed with respect to the recent statement by Postorino et aL8 about hydrogen bonds disappearing at 673 K. This paper demonstrates, on the contrary, that hydrogen bonds in supercritical water can be observed experimentally at least up to 800 K using both spectroscopic and diffraction techniques, yet it may be predicted that hydrogen bonding persists to even higher temperatures. An attempt has been made to estimate quantitatively the temperature dependence of the degree of hydrogen bonding.
184 citations
TL;DR: Crystal structures of 2a and rac-5a show the presence of organisational motifs and intermolecular interactions in agreement with those in gel fibres elucidated by spectroscopic methods.
Abstract: Bis(LeuOH) (1a), bis-(ValOH) (2a) and bis(PhgOH) (5a) (Phg denotes (R)-phenylglycine) oxalyl amides are efficient low molecular weight organic gelators of various organic solvents and their mixtures as well as water, water/DMSO, and water/DMF mixtures. The organisational motifs in aqueous gels are dominated primarily by lipophilic interactions while those in organic solvents are formed by intermolecular hydrogen bonding. Most of the gels are thermoreversible and stable for many months. However, 2a forms unstable gels with organic solvents which upon ageing transform into variety of crystalline shapes. For some 1a/alcohol gels, a linear correlation between alcohol dielectric constants (epsilon) and gel melting temperatures (Tg) was found. The 1H NMR and FTIR spectroscopic investigations of selected gels reveal the existence of temperature dependent network assembly/dissolution equilibrium. In the 1H NMR spectra of gels only the molecules dissolved in entrapped solvent could be observed. By using an internal standard, the concentration of dissolved gelator molecules could be determined. In FTIR spectra, the bands corresponding to network assembled and dissolved gelator molecules are simultaneously present. This enabled determination of the Kgel values by using both methods. From the plots of InKgel versus 1/T, the deltaHgel values of selected gels have been determined (-deltaHgel in 10-36 kJ mol(-1) range) and found to be strongly solvent dependent. The deltaHgel values determined by 1H NMR and FTIR spectroscopy are in excellent agreement. Crystal structures of 2a and rac-5a show the presence of organisational motifs and intermolecular interactions in agreement with those in gel fibres elucidated by spectroscopic methods.
183 citations
TL;DR: The open-structured trihydrate forms a series of isostructural compounds with other divalent transition metal ions as well as with mixed-metal compositions, indicative that the hydrogen bonding controls the type of structure formed irrespective of the cation.
Abstract: Nitrilotris(methylenephosphonic acid) (NTP, [N(CH2PO3H2)3]) recently has been found to form three-dimensional porous structures with encapulation of templates as well as layered and linear structures with template intercalation. It was, therefore, of interest to examine the type of organic−inorganic hybrids that would form with metal cations. Mn(II) was found to replace two of the six acid protons, while a third proton bonds to the nitrilo nitrogen, forming a zwitter ion. Two types of compounds were obtained. When the ratio of acid to Mn(II) was less than 10, a trihydrate, Mn[HN(CH2PO3H)3(H2O)3] (2) formed. Compound 2 is monoclinic P21/c, with a = 9.283(2) A, b = 16.027(3) A, c = 9.7742(2) A, β = 115.209(3)°, V = 1315.0(5) A3, and Z = 4. The Mn atoms form zigzag chains bridged by two of the three phosphonate groups. The third phosphonate group is only involved in hydrogen bonding. The metal atoms are octahedrally coordinated with three of the sites occupied by water molecules. Adjacent chains are hydrogen...
183 citations
TL;DR: This Perspective describes how chemists can control intermolecular [2 + 2] photodimerizations in the solid state using small molecules as linear templates using hydrogen bond donor and acceptor groups of the templates.
Abstract: This Perspective describes how chemists can control intermolecular [2 + 2] photodimerizations in the solid state using small molecules as linear templates. The templates assemble olefins into positions for the reaction via hydrogen-bond-driven self-assembly. We attach functional groups to the olefins that complement hydrogen bond donor and acceptor groups of the templates. The resulting cyclobutane-based products form stereospecifically, quantitatively, and in gram amounts. The templates are used to direct the formation of a [2.2]paracyclophane and ladderanes. The organic solid state is an exciting medium within which to control chemical reactivity since it is possible to synthesize, or construct, molecules that may be, otherwise, unobtainable from solution. The products form with a high degree of stereocontrol provided by a crystal lattice. The critical covalent-bond-forming process also occurs in a solvent-free environment. That molecules are virtually frozen in position in a solid also means that this ...
183 citations
TL;DR: Empirical guidelines for steering molecular assembly into prescribed crystal architectures via hydrogen bonding continue to emerge, with recent developments demonstrating that charge-assisted hydrogen bonds introduce both strength and compliance that can facilitate solid state design.
183 citations