The negative logarithm of the acid dissociation constant values (pKa1 and pKa2) of 4,4′-trimethylenedipiperidine (TMDP) was determined by a pH metric titration at 298 K. The experimentally determined pKa values were compared with the predicted pKa values by chem-bioinformatics software like ACD/Labs and ChemAxon. This experiment gave an excellent opportunity to deepen engagement with the Henderson–Hasselbalch equation, acid/base dissociation constant (Ka/Kb), and half equivalence point.
Knowing about the dissolution kinetics and solubility is necessary for controlling crystallization separation process of lysozyme. In this study, the impact of four ionic liquids (ILs), namely, 1-butyl-3-methylimidazolium tetrafluoroborate [C4mim]BF4, 1-butyl-3-methylimidazole chloride [C4mim]Cl, 1-butyl-3-methylimidazole bromide [C4mim]Br, and 1,3-dimethylimidazolium iodide [dmim]I, on the dissolution rate of lysozyme was determined in an aqueous solution at 20 ℃, pH 5.01, under 101.3 kPa. The results revealed that the dissolution rate of lysozyme increased with increasing concentrations of [C4mim]BF4 and [C4mim]Cl, while it remained stable with increasing concentrations of [C4mim]Br. In contrast, the dissolution rate gradually decreased with increasing concentrations of [dmim]I. This suggests that the interaction between lysozyme molecules is influenced by the ILs, leading to variations in the dissolution rates. Additionally, the effect of anions and cations on the equilibrium solubility was analyzed. The results indicated that the order of anionic and cationic effects on equilibrium solubility is as follows: BF4− < Cl− < Br− = [C4mim]+ < [dmim]+ < I−. Furthermore, dissolution kinetic models were established, which could be used to predict the dissolution behavior of large molecules like lysozyme in ILs aqueous solution. These findings have significant implications for the design of crystallization process and optimization of parameters during lysozyme recovery.
The hygrometric method is used to determine new thermodynamic data on water activity and saturated aqueous solution of the water/d-sucrose/ammonium dihydrogen phosphate (ADP) system in a wide range of NH4H2PO4 molality, ranging from 0.1 to 3 mol⋅kg−1, and for various d-sucrose contents from 0 to 4 mol⋅kg−1. Powder X-ray diffraction (XRD) and attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy were used to characterize the solid state. The Pitzer–Simonson–Clegg model (PSC) is used to fit the experimental data of osmotic coefficient obtained from water activities data. The predicted saturated aqueous solutions, with the PSC model, are in good agreement with experimental data. For the concentration inferior to 1 mol⋅kg−1, the negative deviation from ideality was shown with increasing the ADP concentrations. The estimated values of the activity coefficient of d-sucrose, activity coefficient of ADP, and the Gibbs energy of transfer of ADP from water to mixture (water/d-sucrose) show that both ADP and d-sucrose exert significant salting-out effects on the aqueous solution.
The intermolecular interactions and solution properties of the antihistamine drug chlorpheniramine (CP) in aqueous, aqueous solutions of electrolyte and non-electrolyte have been examined in the current work using volumetric and spectroscopic approaches to investigate how the drug is affected by co-solutes. Also, a drug’s behavior in water and other aqueous systems can be studied to learn more about the chemistry of biological systems. Using an Anton Paar density and sound velocity meter, densities and sound velocities for CP (0–0.10 mol⋅kg−1) at various temperatures (298.15, 308.15, and 318.15 K) in water and in aqueous 0.05 mol⋅kg−1 urea, glucose, and sodium chloride have been measured to determine apparent molar properties: apparent molar volume ((V_{phi} )) and apparent molar compressibility ((K_{phi, {mathrm{S}}})). A number of derived parameters, including limiting apparent molar volume (left( {V_{phi }^{0} } right)), limiting apparent molar compressibility ((K_{phi, {mathrm{S}}}^{0})), limiting apparent molar expansibility ((phi_{mathrm{E}}^{0} )), and isobaric thermal expansion coefficient (ɑ) were obtained using the data on apparent molar properties. While analyzing the data, solute–solvent interactions are taken into account, as well as their considerable effects on CP hydration when co-solutes, are introduced to the combination. The negative transfer properties suggest the predominance of ion-hydrophobic and hydrophobic-hydrophobic interactions in all the studied systems. Positive and small negative values of Hepler’s constant revealed the structure-making capability of CP in aqueous urea, glucose, and sodium chloride. Also, an IR study has been done to verify the results obtained from volumetric and compressibility data. Understanding how drugs behave in various solvent systems during drug development is made easier by understanding drug interactions.
The main purpose of this research was to evaluate the mass/volume percentage (%m/v) solubility of acetaminophen (ACP) in {ethanol (EtOH) (1) + propylene glycol (PG) (2) + water (3)} mixtures from 20.0 to 40.0 °C to expand the solubility database of this drug in mixed pharmaceutical solvents useful for designing high concentrated liquid products including injectable solutions. This is because ACP is an analgesic drug widely used available for oral administration as tablets or solutions. Besides, as injectable products, it is only available for perfusion in as 1 g in 100 mL (1.0%m/v). However, it is not available as 5 mL ampules for supplying doses of 500 mg. As demonstrated in this research some cosolvent mixtures allow ACP concentrations higher than 10.0%m/v, for instance the aqueous ternary mixture with 20% w/w of ethanol and 30% w/w of PG, among other possible mixtures. Flask shake method and UV–vis spectrophotometry were used for ACP solubility determinations at different temperatures. ACP solubility results are presented as Cartesian and triangular solubility profiles. ACP solubility increases with temperature arising and the cosolvent proportion in the mixtures. Maximum %m/v ACP solubility value is observed in the aqueous ethanol binary mixture of w1 = 0.80 at all temperatures being 21.18% at 25.0 °C. All the solubility values were well correlated using the Jouyban-Acree model obtaining mean percentage deviations of 3.8% (N = 330). In this way, %m/v equilibrium solubility of ACP in {EtOH + PG + water} mixtures has been studied and correlated at several temperatures as contribution to preformulation studies of injectable homogeneous liquid pharmaceutical dosage forms.
The dynamic behaviour of a chemical system made of two coupled reactions is compared with that of a mechanical system consisting of two oscillating bodies connected by springs. First, the principle of energy departure from equilibrium is employed to derive the motion equations of both systems. Subsequently, the relevant characteristic frequencies and the amplitude parameters are obtained and analysed in terms of “Normal Modes”. The results show that systems belonging to different branches of science can be analysed using the same methodologies. To elucidate the application of Normal Modes to chemistry, the dynamic analysis of a system consisting of a proton transfer reaction coupled to a complex formation reaction is described in the Supporting Information: the procedure enables the evaluation of rate constants, equilibrium constants and reaction enthalpies of a reacting chemical system made of two coupled reactions. The method is then extended to a cycle of three reactions.
Thermal degradation of piperazine (PZ) in aqueous and mixed sulfolane (SFL) (30% by weight) + H2O solution as a hybrid context was investigated as a function of temperature and two levels of piperazine concentrations and two levels of carbon dioxide loadings. Degradation of PZ in aqueous solution has been found to be first order. The pseudo rate constants for 5%wt solution of piperazine at 145, 160 and 175 °C in aqueous solution are 2.24 × 10–9, 1.09 × 10–8 and 2.27 × 10–7 and in the hybrid media are 3.56 × 10–8, 7.67 × 10–8 and 1.19 × 10–7 per second, respectively, and the activation energies for the aqueous and hybrid media were estimated 238.71 and 62.77 kJ/mole, respectively. Considering the most abundant degradation products identified; 3-(hydroxyethyl)-2-oxazolidone (HEOD), N,N-bis-(2-hydroxyethyl)-piperazine (BHEP), N,N’,N-tris-(hydroxyethyl) ethylenediamine (THEED), 1-[2-[(2-Aminoethyl) amino] ethyl] piperazine (AEAEPZ) and 1-Methylpiperazine (1-MPZ), the degradation pathway of PZ in both media is expected to proceed through ring opening of protonated PZ with the attack of other piperazine molecules on its alpha carbon. The presence of SFL only accelerates the reactions without changing the degradation mechanism.
The local structure and molecular interactions of Li+ salt in aqueous solutions is important in many fields. However, whether solvent shared ion pairs and the direct contact ion pairs exist in aqueous LiCl solutions or not, and the details about these ion pairs are still under debate. Here, we proposed a novel IR ratio method. Using this method, the hydration spectra of Cl− in LiCl, NaCl, and KCl aqueous solutions were measured from the diluted concentration to the highly concentrated solution. Hydration number of Cl− from the hydration spectra was determined to be ~ 2 in the aqueous LiCl. These data demonstrated that about 3–4 Li+ replaced some water molecules in the first hydration shell of Cl−. As the concentration of LiCl increased, an abnormal increase in the hydration number was observed. This is because the water molecule that bridges Li+ and Cl− in the solvent-shared ion pair are particularly stable, which was directly proven by the red shift of the hydration spectra of Cl− in the O–H stretching region. All the hydration spectra and hydration numbers not only applied to uncover the solvent shared ion pairs and direct contacted ion pairs in LiCl aqueous solution, but also can be employed to the benchmark of force fields in the classical molecular dynamics simulations.
Study of some physicochemical properties of l-aspartic aid in water and aqueous ammonium acetate has been undertaken for this investigation. Density, viscosity and conductivity of the solutions were measured at different temperatures. Volumetric parameters such as apparent molar volume (({V}_{Phi })), partial molar volume (({V}_{Phi }^{0})), partial molar expansibility (({E}_{Phi }^{0})) and Hepler’s constant (({{partial }^{2}{V}_{Phi }^{0}/{partial T}^{2})}_{{p}})) and viscometric parameters such as relative viscosity({(eta }_{r })), viscosity coefficients ({(B}_{J }mathrm,{text{and} },{ A}_{F})), Gibbs free energy of activation of viscous flow of solvent and solute ({(Delta mu }_{1}^{#,0}mathrm,text{ and },{Delta mu }_{2}^{#,0})) respectively) and corresponding change in enthalpy ({Delta H}_{2}^{#,0}) and entropy ({Delta S}_{2}^{#,0}) have been derived from the experimentally measured density and viscosity values. Variation of these parameters with concentration and temperature was analysed in the light of ion–ion and ion–hydrophilic interactions. The possibility of ion pair formation and its effect on migration of charged particles in solution have been determined by analysing the molar conductance (Λm), association constant ({(K}_text{A})), Walden product and thermodynamic functions. These parameters were qualitatively correlated with changes in structure of water that occurs when l-Aspartic acid interacts with ammonium acetate in aqueous media.
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