Using (1)H and (13)C NMR and DFT calculations, the structure and interactions of the symmetric ethereally fenced hexaarylbenzene receptor 1 with hydronium ions were studied. Both 1 and its ...equimolecular complex 1.H(3)O(+) exhibit C(3v) symmetry. According to DFT, two similar optimal structures of the complex exist, the more stable one being 15.4 kJ/mol lower in energy. The equilibrium between 1 and 1.H(3)O(+) complexes is characterized by the stabilization constant K = 1.97 x 10(6) (i.e., the binding constant eta = 6.3) according to both proton and carbon NMR spectra. The exchange dynamics between 1 and the complex measured by the delay-varied CPMG sequence had to be corrected for the internal exchange processes in both 1 (conformation change) and the complex (vacillation between the two minima). After this correction, the correlation time of exchange was found to be 4.76 x 10(-5) s. Such relatively fast exchange can be explained only by it being mediated by the excess water molecules present in the system.
Interaction of dibenzo-18-crown-6 (DBC) with H 3O (+) (HP) in nitrobenzene- d 5 and dichloromethane- d 2 was studied by using (1)H and (13)C NMR spectra and relaxations, FTIR spectra, and quantum ...chemical DFT calculations. NMR shows that the DBC*HP complex is in a dynamic equilibrium with the reactants, the equilibrium constant K being 0.66 x 10 (3), 1.16 x 10 (4), and 1.03 x 10 (4) L x mol (-1) in CD 2Cl 2, nitrobenzene, and acetonitrile, respectively. The complex appears to have a C 2 v symmetry in NMR, but FTIR combined with DFT normal mode calculations suggest that such high symmetry is only apparent and due to exchange averaging of the structure. FTIR spectra as well as energy-optimized DFT calculations show that the most stable state of the complex in solution is that with three linear hydrogen bonds of HP with one CH 2-O-CH 2 and two Ar-O-Ar oxygen atoms. The structure is similar to that found in solid state but adopts a somewhat different conformation in solution. The dynamics of exchange between bound and free DBC was studied by NMR transverse relaxation. It was found to be too fast to give reproducible results when measured with the ordinary CPMG sequence or its variant DIFTRE removing residual static dipolar interaction, but it could be established by rotating-frame measurements with high intensity of the spin-lock field. The correlation time of exchange was found to be 5.6 x 10 (-6) and 3.8 x 10 (-6) s in dichloromethane and nitrobenzene, respectively. Such fast exchange can be explained by cooperative assistance of present water molecules.
The teaching method of virtual co-teaching helps the mutual sharing of new experiences and methods of pedagogues in teaching in formal education, through digital technologies. It also facilitates the ...involvement of practitioners in teaching, which can be a key mechanism for ensuring quality education. This article focused on comparing the effectiveness of co-teaching in two environments, face-to-face and virtual. In terms of methodology, an experiment was used, which was implemented in three independently selected schools, from which eight groups of thirty students were formed. The phenomenon measured was the level of understanding of the material taught during these lessons of history, mathematics and a foreign language. The test results of the individual groups were subsequently analyzed. From the results, we can confirm the null hypothesis based on the independent samples t-test and the Mann-Whitney U test, which indicates that there is no statistically significant difference between the test results of the two groups. However, it is essential to emphasize the added value in virtual co-teaching, which is primarily in the economic aspect and flexibility. Specifically, it is a reduction in the cost of commuting, reduced time and easy availability of experts. These results form the basis for follow-up research that can focus on improving the quality of teaching using this method.
According to (1)H and (13)C NMR spectra, relaxations, and PFG NMR self-diffusion measurements, partially hydrophobic additives methyl-ethyl ketone (MEK), methyl-isopropyl ketone (MIPK), and ...methyl-t-butyl ketone (MTBK) facilitate the conformation change and subsequent self-association of the copolymer Pluronic L64. The correlation time (4-9 ms) and activation energy (43-52 kJ/mol) of transition between its conformation states decrease with the increasing hydrophobicity and bulkiness of the additive. The temperature of the first PPO self-association decreases in the same order (by 4 K for MTBK). The interaction of the additives was indirectly proved by the decrease of their rotational and translational mobility in the presence of L64. The rotational correlation time τ(c) is between 3 and 6 × 10(-11) s, whereas that of the same molecules in the absence of L64 is lower than 6 × 10(-12) s. The normalized self-diffusion coefficient decreases to about 0.7 of its original value in the presence of L64. The interaction of the additive with the PPO block is transient but effective enough to facilitate its conformational change and self-association. Its mediation by a water molecule bound to PPO as a possible mechanism is suggested.
Controlled radical reversible addition-fragmentation chain transfer (RAFT) polymerisation was used to prepare water-soluble polymer–drug carriers based on copolymers of
...N-(2-hydroxypropyl)methacrylamide (HPMA) with a hydrazide group-containing monomer, showing well-defined structure with narrow molecular weight distribution (approx. 1.1–1.2). The anticancer therapeutic doxorubicin was bound to the polymeric carrier by a hydrazone bond, enabling pH-controlled release under mildly acid conditions that mimics the environment in endosomes/lysosomes of tumour cells. RAFT polymerisation facilitated the synthesis of semitelechelic copolymers, which were used in the synthesis of monoclonal anti-CD20 antibody–polymer–drug conjugate designed for cell-specific tumour targeting. They were also used for producing a biodegradable high-molecular-weight graft polymer–drug conjugate that degrade in the presence of glutathione, which is designed for passive targeting to solid tumours. The conjugates exhibited well-defined structures with narrow molecular weight distributions of approx. 1.3 and pH-controlled drug release.
Using NMR spectroscopy, PFG measurements, relaxations and NOESY, as well as FTIR spectroscopy and DFT calculations, 1,2-dimethoxyethane is shown to form a hydrate with five water molecules bound by ...cooperative hydrogen bonds.
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► Binding of water to DME leads to
tgt conformation at all water/DME ratios. ► Water is bound to DME in a tight envelope containing at least five water molecules. ► The hydration envelope is built up by cooperative O–H⋯O and O⋯H–C hydrogen bonds.
Using
1H and
13C NMR spectra, PFG NMR self-diffusion measurements,
1H and
13C NMR relaxations and
1H NOESY NMR spectra, FTIR spectra and quantum-chemical DFT and MP2 calculations, the interaction of 1,2-dimethoxyethane (DME) with water (W) was re-examined. It was confirmed that, primarily, one W molecule forms two O···H hydrogen bonds with DME in
tgt conformation. At medium and higher W contents, however, larger hydrates of DME are formed, predominantly with five W molecules. The compact structure of the hydrate is warranted by O⋯H hydrogen bonds, some of them perceptibly tighter than those in the primary hydrate, and by non-classical CH
3⋯O hydrogen bonds.
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