Metal Complexes as Self-Indicating Titrants for Acid–Base Reactions in Chloroform

The paper reports an unprecedented spectrophotometric determination of amines in chloroform, in which amines are not transformed into colored derivatives. This result has been achieved by exploiting the acid–base properties of the tight-ion-paired metal complexes [(HR₂DTO)­Pt­(H₂R₂DTO)]­[Cl], which are able to donate a HCl molecule to an amine, giving rise to an ammonium salt and to the neutral complexes [(HR₂DTO)₂Pt]. The circumstance that [(HR₂DTO)­Pt­(H₂R₂DTO)]­[Cl] and [(HR₂DTO)₂Pt] species show different absorptions in the visible region of the electromagnetic spectrum enables the aforementioned platinum complexes to behave as self-indicating titrants in the spectrophotometric determination of aliphatic amines, which are known to be UV–vis transparent. The new method has been tested by determining a series of fatty amines in the bulk and gave excellent results. The limits of applicability of this method (p<i>K</i>_a > 4) were found by testing a series of benzodiazepines

Self-Catalyzed Mannich-Type Reaction of Enolizable Cyclic 1,3-Dicarbonyls to Acyclic Nitrones: An Entry to Functionalized β‑Enamino Diones

A new method for the preparation of highly functionalized β-enamino diones has been developed. The protocol involves an initial self-catalyzed Mannich-type reaction of enolizable cyclic 1,3-dicarbonyls to nitrones, followed by a spontaneous intramolecular reorganization of the resulting nonisolated hydroxylamine to enamino derivatives. These compounds retain the features of unnatural α-amino acids. The ease of preparation makes them attractive intermediates for the synthesis of peptidomimetics, polyheterocycles, and other multifunctional compounds. All experimental results have been efficiently rationalized by in silico studies at the M06-2X level of theory, and a valid mechanistic pathway has been proposed

Acid–Base Properties and Alkali and Alkaline Earth Metal Complex Formation in Aqueous Solution of Diethylenetriamine‑<i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>″,<i>N</i>″‑pentakis(methylenephosphonic acid) Obtained by an Efficient Synthetic Procedure

Diethylenetriamine-<i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>″,<i>N</i>″-pentakis­(methylenephosphonic acid) (DTPMPA) is used in a wide range of industrial applications, mainly because of its binding ability toward several metal cations. Because of difficulties in its synthesis and purification, very little reliable data have been reported in the literature about the coordination chemistry of this ligand in aqueous solution. For these reasons, in this article, we report an efficient procedure for the synthesis and purification of DTPMPA. The pure product obtained was used to determine its acid–base properties in different aqueous ionic media, namely, (C₂H₅)₄NI­(aq), NaCl­(aq), and KCl­(aq), at 288.15 ≤ <i>T</i>/K ≤ 318.15 [only <i>T</i> = 298.15 K for KCl­(aq)] by potentiometry (H⁺ ion-selective electrode, glass electrode) and at different ionic strengths (0 < <i>I</i>/mol L^–1 ≤ 1.0). Measurements performed in alkali metal chlorides were also interpreted in terms of weak complex formation between DTPMPA and Na⁺ and K⁺, and further measurements were also performed in NaCl­(aq) at <i>T</i> = 298.15 K and different ionic strengths (0 < <i>I</i>/mol L^–1 ≤ 1.0) in the presence of Mg²⁺ or Ca²⁺, to determine the stability constants of species formed by DTPMPA and these cations. The protonation and complex-formation constants obtained at different ionic strengths and temperatures were modeled by different equations, providing all of the thermodynamic data necessary to define the solution behavior and the chemical speciation of DTPMPA under a wide number of variable conditions, such as those encountered in the very different industrial applications in which this chelating agent is used and those involving many natural fluids

Two-Dimensional Electronic Spectroscopy Reveals Dynamics and Mechanisms of Solvent-Driven Inertial Relaxation in Polar BODIPY Dyes

In this work, we demonstrate the use of two-dimensional electronic spectroscopy (2DES) to study the mechanism and time scale of the femtosecond Stokes shift dynamics in molecules characterized by intramolecular charge transfer, such as distyryl-functionalized boron dipyrromethene (BODIPY) molecules. The obtained results demonstrate that 2DES allows clear and direct visualization of the phenomenon. The analysis of the 2D data in terms of 2D frequency–frequency decay associated maps provides indeed not only the time scale of the relaxation process but also the starting and the final point of the energy flow and the associated reorganization energy, identified by looking at the coordinates of a negative signature below the diagonal. The sensitivity of the 2DES technique to vibrational coherence dynamics also allowed the identification of a possible relaxation mechanism involving specific interaction between a vibrational mode of the dye and the solvent