How weak an acid can be? Variations of H-bond and/or <Emphasis Type="Italic">van der Waals</Emphasis> Interaction of Weak Acids

Complex formation ability and stability of both weak and super-weak acids was studied by mean of in silico determined thermodynamic data of the complexes. While weak acids act like Brønsted acids forming hydrogen bond type Brønsted complexes, super-weak acids form Lewis complexes via van der Waals interaction. Unlike in the former type, upon complexation, C-H distances changes insignificantly, yet the complex formation is energy driven in the terms of zero-point corrected Energies, ΔE _zp  < 0 kcal mol^?1, which supports the Lewis complex formation, with the exception of CH₄, an extremely “weak acid”.

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Graphical abstract Selected NBOs of the complexes formed between NC-CH₂-H (Lewis acid) with dioxolane as well as NC-O-H (Brønsted acid) and dioxolane.

     

Effect of Oxide Coverage on the Growth of Amorphous Al2Pt Phase on an Al Surface

 In the present experiments the high temperature successive deposition (HTSD) of Al and Pt and the half shadowing technique producing wedge shaped area with increasing quantity of deposited Pt are applied for studying the initial stages of solid phase reaction producing amorphous Al₂Pt phase. The nucleation of Al₂Pt phase results in a decoration pattern which could be related to the characteristic local oxide coverage of the Al crystal surface developing by kinetic segregation of oxygen species during the Al film deposition. In the area of larger amount of deposited Pt, where the Al₂Pt phase is continuous Kirkendall voids are present. The samples were investigated in plane by transmission electron microscopy (TEM) and selected area electron diffraction (SAED) and analysed by energy dispersive X-ray spectroscopy (EDX).     

How does internal motion influence the relaxation of the water protons in Ln(III)DOTA-like complexes?

Taking advantage of the Curie contribution to the relaxation of the protons in the Tb(III) complex, and the quadrupolar relaxation of the 17O and 2H nuclei on the Eu(III) complex, the effect of the internal motion of the water molecule bound to [Ln(DOTAM)(H2O)]3+ complexes was quantified. The determination of the quadrupolar coupling constant of the bound water oxygen chi(Omicron)(1 + eta(Omicron)2/3)1/2 = 5.2 +/- 0.5 MHz allows a new analysis of the 17O and 1H NMR data of the [Gd(DOTA)(H2O)]- complex with different rotational correlation times for the Gd(III)-O(water) and Gd(III)-H(water) vectors. The ratio of the rotational correlation times for the Ln(III)-H(water) vector and the overall rotational correlation time is calculated tau(RH)/tau(RO) = 0.65 +/- 0.2. This could have negative consequences on the water proton relaxivity, which we discuss in particular for macromolecular systems. It appears that the final effect is actually attenuated and should be around 10% for such large systems undergoing local motion of the chelating groups.