Electrolytic Nature of Aqueous Sulfuric Acid. 2. Acidity

Long-term sciatic nerve block led by a supramolecular arrangement of self-delivery local anesthetic nano systems

Classical local anesthetics are unsuitable to treat regional pain lasting several days due to their limited duration and systemic toxicity. Self-delivery nano systems without excipients were designed for long-term sensory blocks. 1a self-assembled into different vehicles with different fractions of intermolecular π-π stacking, transported itself into nerve cells, and released single molecules slowly to achieve long-term duration for rats' sciatic nerve block for 11.6 h in water, 12.1 h in water with CO₂ and 3.4 h in NS (normal saline). After the counter ions were changed to SO₄^2-, 1e can self-assemble into vesicles and prolong the duration to 43.2 h, which was much longer than the 3.8 h led by (s)-bupivacaine hydrocloride (0.75%). This was mainly caused by the enhancement of self-release and counter ion exchange inside nerve cells, which were affected by the gemini surfactant structure, pK_a of the counter ions and π-π stacking interactions.

Vanadium Electrolyte for All-Vanadium Redox-Flow Batteries: The Effect of the Counter Ion

In this study, 1.6 M vanadium electrolytes in the oxidation forms V(III) and V(V) were prepared from V(IV) in sulfuric (4.7 M total sulphate), V(IV) in hydrochloric (6.1 M total chloride) acids, as well as from 1:1 mol mixture of V(III) and V(IV) (denoted as V3.5+) in hydrochloric (7.6 M total chloride) acid. These electrolyte solutions were investigated in terms of performance in vanadium redox flow battery (VRFB). The half-wave potentials of the V(III)/V(II) and V(V)/V(IV) couples, determined by cyclic voltammetry, and the electronic spectra of V(III) and V(IV) electrolyte samples, are discussed to reveal the effect of electrolyte matrix on charge-discharge behavior of a 40 cm2 cell operated with 1.6 M V3.5+ electrolytes in sulfuric and hydrochloric acids. Provided that the total vanadium concentration and the conductivity of electrolytes are comparable for both acids, respective energy efficiencies of 77% and 72–75% were attained at a current density of 50 mA∙cm−2. All electrolytes in the oxidation state V(V) were examined for chemical stability at room temperature and +45 °C by titrimetric determination of the molar ratio V(V):V(IV) and total vanadium concentration.

Does H4SO5 exist?

The possible existence of H₄SO₅ in aqueous sulfuric acid is analyzed in detail. For bare H₄SO₅, the computed free energy barrier for the exergonic transformation of H₄SO₅ into the H₂SO₄H₂O complex is only 3.8 kcal mol^-1. The presence of water or sulfuric acid catalyzes the dehydration to such an extent that it becomes almost a barrierless process. In the gas phase, dehydration of H₄SO₅ is an autocatalytic reaction as the water molecule produced by the decomposition of one H₄SO₅ molecule induces further dissociation. Thus, in solution, the surrounding water molecules make the para-sulfuric acid a very vulnerable species to exist. The simulated Raman spectra also corroborate the absence of H₄SO₅ in solution.

Structure and ionization of sulfuric acid in water

High-sensitivity Raman spectra of aqueous H₂SO₄ indicate that the acid in water is H₄SO₅ dissociating to 3H₃O⁺ and 1HSO₅³⁻.

Electrolytic nature of aqueous sulfuric acid. 1. Activity

According to the literature, when H(2)SO(4) dissolves in water, (1) it retains its molecular formula and tetrahedral structure of two O atoms and two OH groups bonded to a central S atom, and (2) it ionizes partially, as a 1-1 electrolyte, to H(+) (H(3)O(+)) and HSO(4)(-); the latter ion further dissociates at low concentrations (<0.1 M) to H(+) and SO(4)(2-). Using the Debye-Hückel (DH) limiting law at very low concentration, and the smaller-ion shell (SiS) model of strong electrolyte solutions-an extension of the DH model for ion size dissimilarity-up to moderate concentration, I examine the theory-experiment fit of the mean ionic activity coefficient (γ(±)) of the acid as a function of concentration (at 0 to ∼6 m) and of temperature (at 0-60 °C). The fit is impossible if H(2)SO(4) in water is assumed to be a 1-1 or 1-2 electrolyte, but is excellent when the acid is treated instead as a strong 1-3 electrolyte; that is, aqueous sulfuric acid behaves as a fully dissociated H(3)A acid. At 25 °C, the SiS best fit is achieved with the H(+) diameter being 1.16 Å (as obtained for strong mineral 1-1 protonic acids) and with the A(3-) ionic diameter being 5.77 Å. On the basis of the present study, H(2)SO(4) in water may be H(4)SO(5) (dubbed "sulfoxuric", or parasulfuric acid) completely ionized to 3H(+) and the ("bisulfoxate", or parabisulfate) anion HSO(5)(3-). The calculated standard potential of a newly proposed half-cell reaction, H(2) + HSO(5)(3-) ↔ H(+) + SO(4)(2-) + H(2)O + 2e(-), at 25 °C, is -1.0933 V.