Search results for "Molecular chemistry"

Concerted Halogen-Bonded Networks with N-Alkyl Ammonium Resorcinarene Bromides: From Dimeric Dumbbell to Capsular Architectures

2015

N-Alkyl ammonium resorcinarene bromides and 1,4-diiodooctafluorobutane via multiple intermolecular halogen bonds (XB) form different exotic supramolecular architectures through subtle changes of the upper rim substituents. Dimeric dumbbell-like assembly with encapsulated guest molecules is generated with N-benzyl substituents. The N-hexyl groups engender an XB-induced polymeric pseudocapsule and an XB-induced dimeric capsule with entrapped 1,4-dioxane guest molecules. The N-propyl and N-cyclohexyl groups generate deep cavity cavitands. The deep cavity cavitands possess cavities for self-inclusion leading to polymeric herringbone arrangement in one direction and that pack into 3D polymeric a…

Four new triterpene saponins from Bupleurum rigidum L.

2018

Abstract Four previously undescribed triterpene saponins (1-4) were isolated from the EtOH/H2O extract of the aerial parts of Bupleurum rigidum, together with a known structural analogue. Their structures were elucidated by analysis of 1D-(1H, 13C) and 2D-NMR (1H-1H COSY, TOCSY, ROESY, HSQC, HMBC) spectroscopic data and mass spectrometry (ESI- and HR-ESI-MS) and by comparison with those of related metabolites. An unusual structure was characterized as 3-O-β-D-glucopyranosyl-(1 → 2)-[ β-D-glucopyranosyl-(1 → 3)]- β-D-fucopyranosyl-21-O-β-D-glucoyranosyl-3β,16β,21β,23-tetrahydroxy-13,28-epoxyolean-11-ene (1). The three other compounds shared the same sugar sequence as 1 and differed by the st…

N ‐Annulated Perylene Bisimides to Bias the Differentiation of Metastable Supramolecular Assemblies into J‐ and H‐Aggregates

2020

The unique self-assembling features of N-annulated perylene bisimides (PBIs) 1 and 2 are reported. The stability of the aggregates of diester 1, in which no H-bonding interactions are operative, corroborates the significance of long-range van der Waals and dipole-dipole electrostatic interactions in the construction of stable supramolecular assemblies. The incorporation of amide functional groups within the N-annulated PBI in 2 stimulates pathway differentiation to achieve up to three J-type aggregates and a fourth H-type aggregate depending on the experimental conditions. The results presented demonstrate unprecedented levels of control over synthetic supramolecular self-assembly and the r…

Free-Standing Mono layer Two-Dimensional Supramolecular Organic Framework with Good Internal Order

2015

Utilizing dynamic self-assembly and self-sorting to obtain large-area, molecularly precise monolayered structures represents a promising approach toward two-dimensional supramolecular organic frameworks (2D SOF) or 2D supramolecular polymers. So far, related approaches suffer from small domain sizes, fragility and weak long-range internal order. Here we report on the self-assembly of a host-guest enhanced donor-acceptor interaction, consisting of a tris(methoxynaphthyl)-substituted truxene spacer, and a naphthalene diimide substituted with N-methyl viologenyl moieties as donor and acceptor monomers, respectively, in combination with cucurbit[8]uril as host monomer toward monolayers of an un…

Strategies for Exploring Functions from Dynamic Combinatorial Libraries

2020

Intermolecular interactions in dictating the self-assembly of halogen derivatives of bis-(N-substituted oxamato)palladate(ii) complexes

2016

Three palladium(II) complexes of formula (n-Bu4N)2[Pd(4-Fpma)2] (1), (n-Bu4N)2[Pd(4-Clpma)2]·4H2O (2) and (n-Bu4N)2[Pd(4-Brpma)2]·4H2O (3) [n-Bu4N+ = tetra-n-butylammonium cation, 4-Fpma = N-4-fluorophenyloxamate, 4-Clpma = N-4-chlorophenyloxamate and 4-Brpma = N-4-bromophenyloxamate] have been prepared and their structures determined by single crystal X-ray diffraction. Each palladium(II) ion in 1–3 is four-coordinate with two oxygen and two nitrogen atoms from two fully deprotonated oxamate ligands building PdO2N2 square planar surroundings, the oxamate ligands exhibiting trans (1 and 2) and cis (3) dispositions. The fluoro substituent and the organic counterion in 1 are involved in C–H⋯F…

Unveiling the nature of supramolecular crown ether–C60 interactions

2015

A series of exTTF-(crown ether)2 receptors, designed to host C60, has been prepared. The size of the crown ether and the nature of the heteroatoms have been systematically changed to fine tune the association constants, which were determined by a number of complementary spectroscopic techniques. Electrochemical measurements and transient absorption spectroscopy assisted in corroborating charge transfer in the ground state and in the excited state, leading to the formation of radical ion pairs featuring lifetimes in the range from 12 to 21 ps. To rationalize the nature of the exTTF-(crown ether)2$C60 stabilizing interactions, theoretical calculations have been carried out, suggesting a syner…

How To Design Selective Ligands for Highly Conserved Binding Sites: A Case Study Using N-Myristoyltransferases as a Model System

2019

A model system of two related enzymes with conserved binding sites, namely N-myristoyltransferase from two different organisms, was studied to decipher the driving forces that lead to selective inhibition in such cases. Using a combination of computational and experimental tools, two different selectivity-determining features were identified. For some ligands, a change in side-chain flexibility appears to be responsible for selective inhibition. Remarkably, this was observed for residues orienting their side chains away from the ligands. For other ligands, selectivity is caused by interfering with a water molecule that binds more strongly to the off-target than to the target. On the basis o…

Spatially ordered surfactant assemblies in the gas phase: negatively charged bis(2-ethylhexyl)sulfosuccinate-alkaline metal ion aggregates

2009

The formation and structural features of negatively charged aggregates of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) surfactant molecules in the gas phase have been investigated by electrospray ionization mass spectrometry (ESI-MS) and density functional theory calculations. Mainly driven by the interactions of alkali metal ions both with the oxygen atoms of the sulfonate group and with the succinate moiety of the AOT− anion, spatially ordered supramolecular assemblies, characterized by an internal core composed of surfactant counterions and hydrophilic head groups surrounded by the surfactant alkyl chains pointing outwards, are formed. Calculations have shown that surfactant self-organ…

Crystal structure analysis of supramolecular arrangements in bis(1-isoquinolinecarboxamide)alkanes and their Ag(i) complexes

2017

A homologous series of bis(1-isoquinolinecarboxamide)alkane derivatives (3a–f) with two to seven carbon atoms in the alkyl bridge and their Ag(I) complexes (4a–f) have been synthesized. Four ligand and five Ag(I) complex crystal structures were obtained by single crystal X-ray diffraction and analyzed in terms of: a) their structural patterns based on intra- and intermolecular hydrogen bonds which were compared to those of bis(2-quinolinecarboxamide)alkanes (1n) and bis(6-quinolinecarboxamide)alkanes (2n) attending to specific geometrical parameters and b) the Ag(I) coordinate bond effect on these patterns and the amide-to-amide hydrogen bonds. The crystal structures of the ligands 3a, 3c, …