Hydrogen bonding in dicyclohexylmethane – or diphenylmethane based urea compounds and their polymer counterparts investigated by NMR spectroscopy: Interplay of electronic and geometrical factors

2020 ◽  
Vol 739 ◽  
pp. 137047
Author(s):  
Maxim V. Mokeev ◽  
Stepan A. Ostanin ◽  
Vjacheslav V. Zuev
Chemistry ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 149-163
Author(s):  
Duncan Micallef ◽  
Liana Vella-Zarb ◽  
Ulrich Baisch

N,N′,N″,N‴-Tetraisopropylpyrophosphoramide 1 is a pyrophosphoramide with documented butyrylcholinesterase inhibition, a property shared with the more widely studied octamethylphosphoramide (Schradan). Unlike Schradan, 1 is a solid at room temperature making it one of a few known pyrophosphoramide solids. The crystal structure of 1 was determined by single-crystal X-ray diffraction and compared with that of other previously described solid pyrophosphoramides. The pyrophosphoramide discussed in this study was synthesised by reacting iso-propyl amine with pyrophosphoryl tetrachloride under anhydrous conditions. A unique supramolecular motif was observed when compared with previously published pyrophosphoramide structures having two different intermolecular hydrogen bonding synthons. Furthermore, the potential of a wider variety of supramolecular structures in which similar pyrophosphoramides can crystallise was recognised. Proton (1H) and Phosphorus 31 (31P) Nuclear Magnetic Resonance (NMR) spectroscopy, infrared (IR) spectroscopy, mass spectrometry (MS) were carried out to complete the analysis of the compound.


2013 ◽  
Vol 8 (1) ◽  
pp. 1934578X1300800 ◽  
Author(s):  
William L. Whaley ◽  
Ekua M. Okoso-amaa ◽  
Cody L. Womack ◽  
Anna Vladimirova ◽  
Laura B. Rogers ◽  
...  

The flavonoids are a structurally diverse class of natural products that exhibit a broad spectrum of biochemical activities. The flavones are one of the most studied flavonoid subclasses due to their presence in dietary plants and their potential to protect human cells from reactive oxygen species (ROS). Several flavone compounds also mediate beneficial actions by direct binding to protein receptors and regulatory enzymes. There is current interest in using Quantitative Structure Activity Relationships (QSARs) to guide drug development based on flavone lead structures. This approach is most informative when it involves the use of accurate physical descriptors. The Abraham summation solute hydrogen bonding acidity ( A) is a descriptor in the general solvation equation. It defines the tendency of a molecule to act as a hydrogen bond donor, or acid, when surrounded by solvent molecules that are hydrogen bonding acceptors, or bases. As a linear free energy relationship, it is useful for predicting the absorption and uptake of drug molecules. A previously published method, involving nuclear magnetic resonance (NMR) spectroscopy, was used to evaluate A for the monohydroxyflavones (MHFs). Values of A ranged from 0.02, for 5-hydroxyflavone, to 0.69 for 4′-hydroxyflavone. The ability to examine separate NMR signals for individual hydroxyl groups allowed the investigation of intramolecular interactions between functional groups. The value of A for the position 7 hydroxyl group of 7-hydroxyflavone was 0.67. The addition of a position 5 hydroxyl group (in 5,7-dihydroxyflavone) increased the value of A for the position 7 hydroxyl group to 0.76. Values of A for MHFs were also calculated by the program ACD-Absolve and these agreed well with values measured by NMR. These results should facilitate more accurate estimation of the values of A for structurally complex flavones with pharmacological activities.


2020 ◽  
Vol 117 (22) ◽  
pp. 11908-11915 ◽  
Author(s):  
Joana Paulino ◽  
Myunggi Yi ◽  
Ivan Hung ◽  
Zhehong Gan ◽  
Xiaoling Wang ◽  
...  

Water wires are critical for the functioning of many membrane proteins, as in channels that conduct water, protons, and other ions. Here, in liquid crystalline lipid bilayers under symmetric environmental conditions, the selective hydrogen bonding interactions between eight waters comprising a water wire and a subset of 26 carbonyl oxygens lining the antiparallel dimeric gramicidin A channel are characterized by17O NMR spectroscopy at 35.2 T (or 1,500 MHz for1H) and computational studies. While backbone15N spectra clearly indicate structural symmetry between the two subunits, single site17O labels of the pore-lining carbonyls report two resonances, implying a break in dimer symmetry caused by the selective interactions with the water wire. The17O shifts document selective water hydrogen bonding with carbonyl oxygens that are stable on the millisecond timescale. Such interactions are supported by density functional theory calculations on snapshots taken from molecular dynamics simulations. Water hydrogen bonding in the pore is restricted to just three simultaneous interactions, unlike bulk water environs. The stability of the water wire orientation and its electric dipole leads to opposite charge-dipole interactions for K+ions bound at the two ends of the pore, thereby providing a simple explanation for an ∼20-fold difference in K+affinity between two binding sites that are ∼24 Å apart. The17O NMR spectroscopy reported here represents a breakthrough in high field NMR technology that will have applications throughout molecular biophysics, because of the acute sensitivity of the17O nucleus to its chemical environment.


2009 ◽  
Vol 64 (11-12) ◽  
pp. 1542-s1554 ◽  
Author(s):  
Maria Georgiou ◽  
Simone Wöckel ◽  
Vera Konstanzer ◽  
Sebastian Dechert ◽  
Michael John ◽  
...  

A set of pyrazole-bridged bis(imidazolium) compounds [H3L1]X2 - [H3 L4]X2 (L1 = 3,5-bis[1-(tert-butyl)imidazolium-1-ylmethyl]-1H-pyrazole; L2 = 3,5-bis[1-(tert-butyl)imidazolium- 1-ylmethyl]-4-phenyl-1H-pyrazole; L3 = 3,5-bis[1-(1-adamantyl)imidazolium-1-ylmethyl]-1Hpyrazole; L4 = 3,5-bis[1-(1-adamantyl)imidazolium-1-ylmethyl]-4-phenyl-1H-pyrazole; X = Cl−, BF4 − or PF6 −) has been prepared, and three compounds have been characterized by X-ray crystallography. The unique [H3L4][H2L4](PF6)3 features a dimeric face-to-face arrangement of two molecules due to the involvement of both the pyrazole-NH and the imidazolium C2H in hydrogen bonding. [H3L1]X2 - [H3L4]X2 serve as precursors for silver(I) complexes with compartmental pyrazolate-bridged bis(NHC) ligands. The complexes have been readily prepared by the Ag2O route and feature either the known [(L1−4)2Ag4]2+ or the new [(H2L1)4Ag4]8+ motif, depending on the solvent for the reaction (MeCN or acetone). [(H2L1)4Ag4](PF6)8 contains a central (pzAg)4 ring with pendant imidazolium side arms. Upon further reaction with Ag2O in MeCN it was found to undergo transformation to the corresponding [(L1)2Ag4](PF6)2. All complexes have been thoroughly studied by NMR spectroscopy in solution, and preliminary luminescence data of [(H2L1)4Ag4](PF6)8 have been recorded


2000 ◽  
Vol 55 (9) ◽  
pp. 863-870 ◽  
Author(s):  
Alfonso Castiñeiras ◽  
Maria Gil ◽  
Elena Bermejo ◽  
Douglas X. West

Pyridil bis{N(4)-substituted thiosemicarbazones}, in which the substituents replacing the NH2 group on the thiosemicarbazone moieties are piperidyl, H2Plpip; hexamethyleneiminyl, H2Plhexim; diethylamino, H2Pl4DE; and dipropylamino, H2PI4 DP, have been synthesized. Representative palladium(II) complexes of these bis (thiosemicarbazones) have been characterized by IR, electronic, mass, and 1H and 13C NMR spectroscopy. Crystal structures have been determined for H2Plhexim and two of its palladium(II) complexes. H2Plhexim is in the Z isomeric form with intramolecular hydrogen bonding from both thiosemicarbazone moieties to pyridine nitrogens. [Pd(Plhexim)] has square-planar N2S2 coordination (i.e., imine nitrogen and thiolato sulfur atoms). [Pd2 (Plhexim)Cl2 · DMSO has two PdNNSCl centers with the pyridine nitrogen, imine nitrogen or hydrazinic nitrogen and thiolato sulfur atoms coordinated


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