Substituent

About: Substituent is a research topic. Over the lifetime, 42877 publications have been published within this topic receiving 516716 citations. The topic is also known as: side chain & side group.

A unique NH-spacer for N-benzamidothiourea based anion sensors. Substituent effect on anion sensing of the ICT dual fluorescent N-(p-dimethylaminobenzamido)-N′-arylthioureas

Abstract: A series of N-(p-dimethylaminobenzamido)-N′-(substituted-phenyl)thioureas (substituent = p-CH3, H, p-Cl, p-Br, m-Br, m-NO2, and p-NO2) were designed as anion sensors in order to better understand the –NH-spacer via a substituent effect investigation. In these molecules the dual fluorescent intramolecular charge transfer (ICT) fluorophore p-dimethylaminobenzamide as the signal reporter was linked to the anion-binding site, the thiourea moiety, via an N–N single bond. Correlation of the NMR signals of the aromatic and –NH protons with substituents in these molecules indicated that the N–N single bond stopped the ground-state electronic communication between the signal reporter and the anion-binding site. Dual fluorescence was observed in highly polar solvents such as acetonitrile with the former five derivatives. The fact that the CT emission wavelength and the CT to LE emission intensity ratio of the sensors were independent of the substituent existing in the anion-binding moiety suggested that the substituent electronic effect could not be communicated to the CT fluorophore in the excited-state either. Yet in acetonitrile both the CT dual fluorescence and the absorption of the sensors were found to be highly sensitive toward anions. A conformation change around the N–N bond in the sensor molecules was suggested to occur upon anion binding that established the electronic communication between the signal reporter and the anion-binding site. The anion binding constants of the N-(p-dimethylaminobenzamido)thiourea sensors were found higher than those of the corresponding traditional N-phenylthiourea counterparts and the substituent effect on the anion binding constant was much higher than that in the latter. “–NH–“ was shown to be a unique spacer that affords N-benzamidothiourea allosteric anion sensors.

Mechanistic studies on the nickel-catalyzed polymerization of isocyanides

Abstract: All mechanistic aspects of nickel-mediated isocyanide polymerizations have been examined experimentally. Chain initiation has been studied by [sup 13]C [sup 1]H NMR at low temperature using a living polymerization system. Chain propagation has been examined by cyclic voltammetry, ESR spectroscopy, magnetic susceptibility measurements, temperature dependent kinetic studies, and substituent effect analysis. The chain-propagation studies were performed on both living and classical heterogeneous systems and were found to be invariant with respect to the type of nickel initiator used. Finally, chain-transfer reactions were studied by NMR, kinetic studies, substituent effect analyses, and chemical studies. Comprehensive mechanistic schemes have been derived from the experimental data and are presented as the most probable reaction pathways. 39 refs., 7 figs., 1 tab.

Assessing the Impact of Electronic and Steric Tuning of the Ligand in the Spin State and Catalytic Oxidation Ability of the FeII(Pytacn) Family of Complexes

Abstract: A family of iron complexes with the general formula [FeII(R,R′Pytacn)(X)2]n+ is described, where R,R′Pytacn is the tetradentate ligand 1-[(4-R′-6-R-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, R refers to the group at the α-position of the pyridine, R′ corresponds to the group at the γ-position, and X denotes CH3CN or CF3SO3. Herein, we study the influence of the pyridine substituents R and R′ on the electronic properties of the coordinated iron center by a combination of structural and spectroscopic characterization using X-ray diffraction, 1H NMR and UV–vis spectroscopies, and magnetic susceptibility measurements. The electronic properties of the substituent in the γ-position of the pyridine ring (R′) modulate the strength of the ligand field, as shown by magnetic susceptibility measurements in CD3CN solution, which provide a direct indication of the population of the magnetically active high-spin S = 2 ferrous state. Indeed, a series of complexes [FeII(H,R′Pytacn)(CD3CN)2]2+ exist as mixture...

7-Substituted 5-amino-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidines as A2A adenosine receptor antagonists: a study on the importance of modifications at the side chain on the activity and solubility.

Abstract: It was demonstrated in the early 1990s that adenosine exerts many physiological functions through the interaction with four different receptors, named A1, A2A, A2B, and A3. In the past few years, our group has been involved in the development of A2A antagonists, which led to the synthesis of SCH 58261 (1), the first potent and selective adenosine A2A antagonist, which has been widely used as a reference compound. In this paper, we present an extended series of pyrazolotriazolopyrimidines synthesized with the aim to investigate the influence of the substitutions on the pyrazole ring. The choice of the substituents was based on their capability to improve water solubility while retaining high affinity and selectivity at the human A2A adenosine receptor subtype. In this series, some structural characteristics that are important for activity, i.e., tricyclic structure, free amino group at 5-position, furan ring, and substituent at 7-position on the pyrazole moiety, have been maintained. We focused our attenti...