Thermodynamic studies of the complexation of 18-crown-6 and dibenzo-24- crown-8 with potassium ion in mixed non-aqueous solvents

568-574<span style="font-size:14.0pt;font-family: " times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">The formation constant of 1:1 complexes of 18-crown-6 (18C6) with potassium ion in dimethylformamide (DMF)-methanol (MeOH), DMF-nitrobenzene (NB), DMF- benzonitrile (BN) binary solvents and dibenzo-24-crown-8 (DB24C8) with potassium ion in DMF-MeOH binary mixtures have been determined conductometrically at different temperatures. The values of thermodynamic parameters <span style="font-size:14.0pt;font-family:HiddenHorzOCR; mso-hansi-font-family:" times="" new="" roman";mso-bidi-font-family:hiddenhorzocr;="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">(∆ <span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">H°<span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa;="" mso-bidi-font-style:italic"="" lang="EN-US">C <span style="font-size:14.0pt; font-family:" times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">and <span style="font-size:14.0pt;font-family:HiddenHorzOCR; mso-hansi-font-family:" times="" new="" roman";mso-bidi-font-family:hiddenhorzocr;="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">(∆ S<span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">°<span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa;="" mso-bidi-font-style:italic"="" lang="EN-US">C) for complexion reactions have been determined from temperature dependence of formation constants. In all cases, the complexes are enthalpy stabilized but with very few exceptions entropy destabilized and the results show that both parameters are very sensitive to solvent composition. The origins of the enthalpies and entropies of the complexation are discussed in terms of the solvent composition and the structural features of the ligand. The stability of complexes is strongly affected by the nature of solvent and solvent composition. The stability constants of complexes increase with increase in the concentration of solvent with lower donocity (smaller Gutman Donor Number) in binary mixtures. In addition, it has been found that the variation of stability constant<span style="font-size:14.0pt; font-family:HiddenHorzOCR;mso-hansi-font-family:" times="" new="" roman";mso-bidi-font-family:="" hiddenhorzocr;mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:="" ar-sa"="" lang="EN-US"> (log <span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">K°f) of 18C6- K+ complex versus the solvent composition is linear in DMF-BN and DMF-NB binary mixtures, but a nonlinear behaviour is observed for 18C6-K+  and of DB24C6-K+  complexes in DMF-MeOH binary systems.</span

Gut Microbiota and Microbiota-Related Metabolites as Possible Biomarkers of Cognitive Aging

Gut microbiota composition and functionality can influence the pathophysiology of age-related cognitive impairment and dementia, according to a large number of animal studies. The translation of this concept to humans is still uncertain, due to the relatively low number of clinical studies focused on fecal microbiota and large number of environmental factors that influence the microbiota composition. However, the fecal microbiota composition of older patients with dementia is deeply different from that of healthy active controls, conditioning a different metabolic profile. The possible use of fecal microbiota-related parameters and microbiota-derived metabolites as biomarkers of cognitive performance and dementia is critically reviewed in this paper, focusing on the most promising areas of research for the future