association constants
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Chemistry ◽  
2021 ◽  
Vol 4 (1) ◽  
pp. 18-30
Author(s):  
Atena B. Solea ◽  
Liangru Yang ◽  
Aurelien Crochet ◽  
Katharina M. Fromm ◽  
Christophe Allemann ◽  
...  

The complexation behavior of two novel, chiral pinene–bipyridine-type ligands ((–)-HL1 and (–)-HL2) containing a carboxylic arm towards lanthanide Ln(III) (Ln = La, Eu, Lu) ions was investigated through spectroscopic methods. The association constants of the mononuclear complexes determined from the UV-Vis titrations indicated that the ligand (–)-HL1 possessing a shorter carboxylic arm formed more stable complexes compared with (–)-HL2, whose carboxylic arm had one more methylene unit. This is due to the formation of more stable seven-member metal chelate rings in the first case as compared with the eight-member metal chelate rings in the second. IR and fluorescence spectroscopy provided additional information about the structure of these complexes.


2021 ◽  
Author(s):  
Daniel A. Rothschild ◽  
Aaron Tran ◽  
William P. Kopcha ◽  
Jianyuan Zhang ◽  
Mark C. Lipke

Discrete nanocages provide a way to solubilize, separate, and tune the properties of molecular guests, including fullerenes and other aromatics. However, few such nanocages can be synthesized efficiently from inexpensive starting materials, limiting their practical utility. To address this limitation, we developed a new pyridinium-linked cofacial porphyrin nanocage (Cage4+) that can be prepared efficiently on a gram scale. NMR studies in CD3CN reveal that Cage4+ binds C60 and C70 with association constants >108 M-1 and complete selectivity for extracting C70 from mixtures of both fullerenes. The solubility of Cage4+ in polar solvents enabled electrochemical characterization of the host-guest complexes C60@Cage4+ and C70@Cage4+, finding that the redox properties of the encapsulated fullerenes are minimally affected despite the positive charge of the host. Complexes of the −1 and −2 charge states of the fullerenes bound in Cage4+ were subsequently characterized by UV-vis-NIR and NMR spectroscopies. The relatively easy preparation of Cage4+ and its ability to bind fullerenes without substantially affecting their redox properties suggests that C60@Cage4+ and C70@Cage4+ may be directly useful as solubilized fullerene derivatives.


2021 ◽  
Vol 3 (2) ◽  
pp. 1-8
Author(s):  
Shapovalov S.A ◽  

The ability of rhodamine cations to form cation-anionic associates with tetraphenylborate-anion in an aqueous solution has been studied. The thermodynamic values of the equilibrium association constants Kasт were determined spectrophotometrically. The values of a number of properties of dye molecules (surface area, effective volume, hydrophobicity index log P, standard enthalpy of hydration ΔНohydr) were calculated using the QSAR model. The possibility of dependence of the value of Kasт on these factors has been reviewed. It was shown that changes in lg Kasт in the series of rhodamine associates are consistent with changes in the parameters log P and ΔНohydr.


Molecules ◽  
2021 ◽  
Vol 26 (23) ◽  
pp. 7205
Author(s):  
Agata Krzak ◽  
Olga Swiech ◽  
Maciej Majdecki ◽  
Piotr Garbacz ◽  
Paulina Gwardys ◽  
...  

β-Cyclodextrin (CD) derivatives containing an aromatic triazole ring were studied as potential carriers of the following drugs containing an anthraquinone moiety: anthraquinone-2-sulfonic acid (AQ2S); anthraquinone-2-carboxylic acid (AQ2CA); and a common anthracycline, daunorubicin (DNR). UV-Vis and voltammetry measurements were carried out to determine the solubilities and association constants of the complexes formed, and the results revealed the unique properties of the chosen CDs as effective pH-dependent drug complexing agents. The association constants of the drug complexes with the CDs containing a triazole and lipoic acid (βCDLip) or galactosamine (βCDGAL), were significantly larger than that of the native βCD. The AQ2CA and AQ2S drugs were poorly soluble, and their solubilities increased as a result of complex formation with βCDLip and βCDGAL ligands. AQ2CA and AQ2S are negatively charged at pH 7.4. Therefore, they were less prone to form an inclusion complex with the hydrophobic CD cavity than at pH 3 (characteristic of gastric juices) when protonated. The βCDTriazole and βCDGAL ligands were found to form weaker inclusion complexes with the positively charged drug DNR at an acidic pH (pH 5.5) than in a neutral medium (pH 7.4) in which the drug dissociates to its neutral, uncharged form. This pH dependence is favorable for antitumor applications.


2021 ◽  
Vol 22 (23) ◽  
pp. 12679
Author(s):  
Chenming Li ◽  
Philipp Hilgeroth ◽  
Nazmul Hasan ◽  
Dieter Ströhl ◽  
Jörg Kressler ◽  
...  

Carbonyl-centered hydrogen bonds with various strength and geometries are often exploited in materials to embed dynamic and adaptive properties, with the use of thiocarbonyl groups as hydrogen-bonding acceptors remaining only scarcely investigated. We herein report a comparative study of C2=O and C2=S barbiturates in view of their differing hydrogen bonds, using the 5,5-disubstituted barbiturate B and the thiobarbiturate TB as model compounds. Owing to the different hydrogen-bonding strength and geometries of C2=O vs. C2=S, we postulate the formation of different hydrogen-bonding patterns in C2=S in comparison to the C2=O in conventional barbiturates. To study differences in their association in solution, we conducted concentration- and temperature-dependent NMR experiments to compare their association constants, Gibbs free energy of association ∆Gassn., and the coalescence behavior of the N-H‧‧‧S=C bonded assemblies. In Langmuir films, the introduction of C2=S suppressed 2D crystallization when comparing B and TB using Brewster angle microscopy, also revealing a significant deviation in morphology. When embedded into a hydrophobic polymer such as polyisobutylene, a largely different rheological behavior was observed for the barbiturate-bearing PB compared to the thiobarbiturate-bearing PTB polymers, indicative of a stronger hydrogen bonding in the thioanalogue PTB. We therefore prove that H-bonds, when affixed to a polymer, here the thiobarbiturate moieties in PTB, can reinforce the nonpolar PIB matrix even better, thus indicating the formation of stronger H-bonds among the thiobarbiturates in polymers in contrast to the effects observed in solution.


Synlett ◽  
2021 ◽  
Author(s):  
Oliver Dumele ◽  
Niklas Grabicki

AbstractStrained aromatic macrocycles based on cycloparaphenylenes (CPPs) are the shortest repeating units of armchair single-walled carbon nanotubes. Since the development of several new synthetic methodologies for accessing these structures, their properties have been extensively studied. Besides the fundamental interest in these novel molecular scaffolds, their application in the field of materials science is an ongoing topic of research. Most of the reported CPP-type macrocycles display strong binding toward fullerenes, due to the perfect match between the convex and concave π-surfaces of fullerenes and CPPs, respectively. Highly functionalized CPP derivatives capable of supramolecular binding with other molecules are rarely reported. The synthesis of highly functionalized [n]cyclo-2,7-pyrenylenes leads to CPP-type macrocycles with a defined cavity capable of binding non-fullerene guests with high association constants.


Author(s):  
Олег Евгеньевич Журавлев ◽  
Глеб Сергеевич Юлмасов ◽  
Екатерина Сергеевна Суратова ◽  
Людмила Ивановна Ворончихина

Авторами работы получены ионные жидкости с катионом 1-алкил-2-метилпиридиния и неорганическими анионами. Проведены исследования электропроводности их растворов в ацетонитриле. Методом Ли-Уитона рассчитаны константы ионной ассоциации K, предельная молярная электрическая проводимости (λ) и энергия Гиббса ассоциации (ΔG) в растворах. The authors of the work obtained ionic liquids with 1-alkyl-2-methylpiridinium cation and inorganic anions. Studies of the electrical conductivity of their solutions in acetonitrile have been carried out. The Li-Wheaton method was used to calculate the ion association constants K, the limiting molar electrical conductivity (λ), and the Gibbs association energy (ΔG) in solutions.


Molecules ◽  
2021 ◽  
Vol 26 (17) ◽  
pp. 5389
Author(s):  
Johan Mendoza ◽  
Luis Cruz ◽  
Victor de Freitas ◽  
Fernando Pina ◽  
Nuno Basílio

Flavylium-based compounds in their acidic and cationic form bring color to aqueous solutions, while under slightly acidic or neutral conditions they commonly bring discoloration. Selective host-guest complexation between water-soluble p-sulfonatocalix[n]arenes (SCn) macrocycles and the flavylium cationic species can increase the stability of the colored form, expanding its domain over the pH scale. The association constants between SCn and the cationic (acid) and neutral basic forms of flavylium-based compounds were determined through UV-Vis host-guest titrations at different pH values. The affinity of the hosts for synthetic chromophore was found to be higher than for a natural anthocyanin (Oenin). The higher affinity of SC4 for the synthetic flavylium was confirmed by 1H NMR showing a preferential interaction of the flavylium phenyl ring with the host cavity. In contrast with its synthetic counterpart, the flavylium substitution pattern in the anthocyanin seems to limit the inclusion of the guest in the host’s binding pocket. In this case, the higher affinity was observed for the octamer (SC8) likely due to its larger cavity and higher number of negatively charged sulfonate groups.


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