Тhe economic value of volunteering

Voluntary work is a non-remunerated activity, which is usually performed to satisfy a moral need of the individual as well as to contribute to the collective goal of the society. It usually leads to the creation of goods or services that would in a normal situation require the use of workforce that needs to be paid, meaning it would mean an expense. The goods and services produced through the voluntary work are usually not part of the official measures of production, but volunteers make significant contributions to the economy and society

Site-Specific Description of the Enhanced Recognition Between Electrogenerated Nitrobenzene Anions and Dihomooxacalix[4]arene Bidentate Ureas

Electron transfer controlled hydrogen bonding was studied for a series of nitrobenzene derivative radical anions, working as large guest anions, and substituted ureas, including dihomooxacalix[4]­arene bidentate urea derivatives, in order to estimate binding constants (<i>K</i>_b) for the hydrogen-bonding process. Results showed enhanced <i>K</i>_<i>b</i> values for the interaction with phenyl-substituted bidentate urea, which is significantly larger than for the remaining compounds, e.g., in the case of 4-methoxynitrobenzene a 28-fold larger <i>K</i>_b value was obtained for the urea bearing a phenyl (<i>K</i>_b ∼ 6888) vs <i>tert</i>-butyl (<i>K</i>_b ∼ 247) moieties. The respective nucleophilic and electrophilic characters of the participant anion radical and urea hosts were parametrized with global and local electrodonating (ω^–) and electroaccepting (ω⁺) powers, derived from DFT calculations. ω^– data were useful for describing trends in structure–activity relationships when comparing nitrobenzene radical anions. However, ω⁺ for the host urea structures lead to unreliable explanations of the experimental data. For the latter case, local descriptors ω_<i>k</i>⁺(<i><b>r</b></i>) were estimated for the atoms within the urea region in the hosts [∑_<i>k</i>ω_<i>k</i>⁺(<i><b>r</b></i>)]. By compiling all the theoretical and experimental data, a <i>K</i>_b-predictive contour plot was built considering ω^– for the studied anion radicals and ∑_<i>k</i>ω_<i>k</i>⁺(<i><b>r</b></i>) which affords good estimations

Competition between Hydrogen Bonding and Proton Transfer during Specific Anion Recognition by Dihomooxacalix[4]arene Bidentate Ureas

Competition between hydrogen bonding and proton transfer reactions was studied for systems composed of electrogenerated dianionic species from dinitrobenzene isomers and substituted dihomooxacalix[4]­arene bidentate urea derivatives. To analyze this competition, a second-order E_rC_rC_i mechanism was considered where the binding process is succeeded by proton transfer and the voltammetric responses depend on two dimensionless parameters: the first related to hydrogen bonding reactions, and the second one to proton transfer processes. Experimental results indicated that, upon an increase in the concentration of phenyl-substituted dihomooxacalix[4]­arene bidentate urea, voltammetric responses evolve from diffusion-controlled waves (where the binding process is at chemical equilibrium) into irreversible kinetic responses associated with proton transfer. In particular, the 1,3-dinitrobenzene isomer showed a higher proton transfer rate constant (∼25 M^–1 s^–1) compared to that of the 1,2-dinitrobenzene (∼5 M^–1 s^–1), whereas the 1,4-dinitrobenzene did not show any proton transfer effect in the experimental conditions employed

Electrophilic Reactivity of Tetrabromorhodamine 123 is Bromine Induced: Convergent Interpretation through Complementary Molecular Descriptors

Nucleophilic addition of water and of methanol to 3,6-diamino-2,4,5,7-tetrabromo-9-[2-(methoxycarbonyl) phenyl]-9<i>H</i>-xanthen-9-ylium, 4BrR123, yields respectively 2-(3,6-diamino-2,4,5,7-tetrabromo-9-hydroxy-9<i>H</i>-xanthen-9-yl)­xanthyl benzoate, HO4BrR123 and 2-(3,6-diamino-2,4,5,7-tetrabromo-9-methoxy-9<i>H</i>-xanthen-9-yl)­xanthyl benzoate, MeO4BrR123. The novel experimental results are addressed theoretically. The linear free energy relationship, LFER, second-order perturbation theory analysis of the natural bond orbital, NBO, and quantum theory of atoms in molecules, QTAIM, lead to the same conclusion: the electron-withdrawing effect of bonded Br atoms in 4BrR123 extremely enhances the molecular electrophilicity, as compared to 3,6-diamino-9-[2-(methoxycarbonyl) phenyl]-9<i>H</i>-xanthen-9-ylium, R123. The reactivity of these diaminoxanthylium cations is discussed in the context of local and global softness in extended conjugated systems

From Molecules to Crystals: The Solvent Plays an Active Role Throughout the Nucleation Pathway of Molecular Organic Crystals

Crystallization is indisputably one of the oldest and most widely used purification methods. Despite this fact, our current understanding of the early stages of crystallization is still in its infancy. In this work dynamic light scattering and proton nuclear magnetic resonance were used to investigate the changes occurring in 4′-hydroxyacetophenone colloidal particles, as they form in a supersaturated aqueous solution and evolve toward anhydrous or hydrate materials during a cooling crystallization process. In the concentration range probed, the particles are initially composed by both solute and water. If the outcome of crystallization is an anhydrous phase, a complete loss of solvent from the particles is progressively observed up to the onset of crystal precipitation. These findings provide unique experimental evidence that the role of solvent in the formation of crystals can go well beyond influencing the self-assembly and clustering of solute molecules prior to nucleation

Selective Binding of Spherical and Linear Anions by Tetraphenyl(thio)urea-Based Dihomooxacalix[4]arene Receptors

Three novel tetra­(thio)­ureido dihomo­oxa­calix­[4]­arene anion receptors (phenylurea <b>4a</b>, phenylthiourea <b>4b</b>, and <i>tert</i>-butylurea <b>4c</b>) were synthesized and obtained in the cone conformation in solution, as shown by NMR studies. The X-ray crystal structure of <b>4c</b> is reported. The host–guest properties of these receptors toward several anions were investigated by ¹H NMR titrations. Phenylurea <b>4a</b> displayed a very efficient binding toward the spherical F^– and Cl^– anions, and the linear CN^– (log <i>K</i>_ass = 3.46, 3.50, and 4.02, respectively). In comparison to related bidentate phenylurea dihomooxacalix[4]­arenes, tetraphenylurea <b>4a</b> is more preorganized and the higher number of hydrogen bond donor sites provides a remarkable enhancement of its binding efficiency

Alkylammonium Cation Complexation into the Narrow Cavity of Dihomooxacalix[4]arene Macrocycle

How big should a calixarene macrocycle be for <i>endo</i>-cavity complexation to occur or to allow <i>through-the-annulus</i> threading? To answer these questions, a complete study on the complexation of primary and secondary (di)­alkylammonium cations by 18-membered <i>p</i>-<i>tert</i>-butyldihomooxacalix­[4]­arene macroring has been performed in the presence of the “superweak” TFPB counterion. Thus, it was found that this macrocycle is currently the smallest calixarene able to host linear and branched alkylammonium guests inside its aromatic cavity. Molecular mechanics calculations revealed that this recognition event is mainly driven by a H-bonding interaction between the guest ammonium group and the host CH₂OCH₂ bridge. The <i>endo</i>-cavity complexation of chiral <i>s</i>-BuNH₃⁺ guest results in an asymmetric complex in the NMR time scale. The chirality transfer from guest to host is likely due to a restricted guest motion inside the tight cavity. The complexation study with secondary di-<i>n</i>-alkylammonium·TFPB salts revealed that the 18-membered dihomooxacalix[4]­arene macroring cannot give the <i>through-the-annulus</i> threading with them because of its small dimension. However, the macrocycle is able to complex such ions, which can only be accommodated in an hook-like conformation characterized by two unfavorable gauche interactions around the CH₂–NH₂⁺ bonds. The strain generated by this unfavorable folding is very likely compensated by stronger H-bonds and more favorable CH/π interactions between guest and host

Diffusion Coefficients of Fluorinated Surfactants in Water: Experimental Results and Prediction by Computer Simulation

Intradiffusion coefficients of 2,2,2-trifluoroethanol in water have been measured by the pulsed field gradient (PFG)-NMR spin–echo technique as a function of temperature and composition on the dilute alcohol region. The measurements extend the range of compositions already studied in the literature and, for the first time, include the study of the temperature dependence. At the same time, intradiffusion coefficients of 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoropropan-1-ol, and 2,2,3,3,4,4,4-heptafluorobutan-1-ol in water were obtained by computer simulation (molecular dynamics) as a function of composition and temperature. The intradiffusion coefficients of 2,2,2-trifluoroethanol in water obtained by simulation agree with the experimental results, while those of 2,2,3,3,3-pentafluoropropan-1-ol and 2,2,3,3,4,4,4-heptafluorobutan-1-ol are the first estimation of this property for those systems. The molecular dynamics simulations were also used to calculate the intradiffusion coefficients of perfluoro­octanesulfonic acid and perfluoro­octanoic acid in water at infinite dilution as a function of temperature, which are very difficult to obtain experimentally because of the very low solubility of these substances. From the dependence of the intradiffusion coefficients on temperature, diffusion activation energies were estimated for all the solutes in water