“…The solid–liquid equilibria for the monosolvent and the solvent mixtures systems were measured by the isothermal saturation method in the temperature range of 283.15 to 323.15 K, − and the solubility of levetiracetam was tested by HPLC.…”
In
this work, the solid–liquid equilibrium for levetiracetam
in 10 neat solvents (methanol, ethanol, n-propanol,
isopropanol, acetone, acetonitrile, ethyl acetate, 1,4-dioxane, toluene,
and cyclohexane) and binary liquid mixtures (ethanol + ethyl acetate)
was measured by using a static gravimetric method at temperatures T = 283.15–323.15 K under pressure of 101.2 kPa.
In general, the equilibrium solubility was highest in methanol and
lowest in cyclohexane. The modified Apelblat equation, λh equation, Wilson model, and NRTL model were used to correlate the
solubility data in monosolvents; and the Jouyban–Acree model,
van’t Hoff–Jouyban–Acree model, and Apelblat–Jouyban–Acree
model were used to correlate the experiment data in the binary solvent
mixtures. Compared with the results of the above models, the calculated
solubility provided good results with the experimental data. Consequently,
for the monosolvents, the values of root-mean-square deviation and
relative average deviation were not exceeding 9.91 × 10–4 and 2.50%, respectively; and for the binary solvent mixtures, 2.75
× 10–4 and 0.80%. Furthermore, the thermodynamic
properties of levetiracetam in monosolvents were calculated. From
the analysis results, the dissolution process of levetiracetam was
an endothermic, spontaneous, and entropy driven process. It is crucially
important to understand the solubility and thermodynamic properties
of levetiracetam in drug development. In particular, purification,
recrystallization, and formulation development of levetiracetam in
industry were effected by its solubility values.
“…The solid–liquid equilibria for the monosolvent and the solvent mixtures systems were measured by the isothermal saturation method in the temperature range of 283.15 to 323.15 K, − and the solubility of levetiracetam was tested by HPLC.…”
In
this work, the solid–liquid equilibrium for levetiracetam
in 10 neat solvents (methanol, ethanol, n-propanol,
isopropanol, acetone, acetonitrile, ethyl acetate, 1,4-dioxane, toluene,
and cyclohexane) and binary liquid mixtures (ethanol + ethyl acetate)
was measured by using a static gravimetric method at temperatures T = 283.15–323.15 K under pressure of 101.2 kPa.
In general, the equilibrium solubility was highest in methanol and
lowest in cyclohexane. The modified Apelblat equation, λh equation, Wilson model, and NRTL model were used to correlate the
solubility data in monosolvents; and the Jouyban–Acree model,
van’t Hoff–Jouyban–Acree model, and Apelblat–Jouyban–Acree
model were used to correlate the experiment data in the binary solvent
mixtures. Compared with the results of the above models, the calculated
solubility provided good results with the experimental data. Consequently,
for the monosolvents, the values of root-mean-square deviation and
relative average deviation were not exceeding 9.91 × 10–4 and 2.50%, respectively; and for the binary solvent mixtures, 2.75
× 10–4 and 0.80%. Furthermore, the thermodynamic
properties of levetiracetam in monosolvents were calculated. From
the analysis results, the dissolution process of levetiracetam was
an endothermic, spontaneous, and entropy driven process. It is crucially
important to understand the solubility and thermodynamic properties
of levetiracetam in drug development. In particular, purification,
recrystallization, and formulation development of levetiracetam in
industry were effected by its solubility values.
Radical coupling was used to modify graphite with maleic anhydride (MAH). Azobisisobutyronitrile (AIBN) as radical generator activated MAH radically and it was reacted with defects at the surface of nanolayers. A set of batches with different reaction times (24, 48 and 72 h) were performed to obtain fully-modified nanolayers (GMA1, GMA2 and GMA3, respectively). Fourier transform infrared results approved the synthesis of MAHgrafted graphite. Thermogravimetric analysis showed that 5.9, 11.1 and 13.2 wt% of MAH was grafted onto the surface of GMA1, GMA2 and GMA3, respectively, and that was approved by X-ray photoelectron spectroscopy results. Also, X-ray diffraction patterns showed that d-spacing increased from 0.34 nm for graphite to 1.00 nm for all modified samples. However, GMA1 showed a weak peak related to graphite structure that disappeared when reaction time was increased. After modification with MAH, lamella flake structure of graphite was retained whereas the edges of sheets became distinguishable as depicted by scanning electron microscopy images. According to Raman spectra, modification progression resulted in more disorder structure of nanolayers due to grafting of MAH. Also, transmission electron microscopy images showed graphite as transparent layers while after modification, surface of nanolayers became folded due to the opposite effects of π-conjugated domains and electrostatic repulsion of oxygen-containing groups.
“…Aqueous solutions of alcohols and acids associated with hydrogen bonds take special place among binary liquids. A particular interest to the study of optical properties of acetic acid and its aqueous solutions in a wide range of concentrations is related to their wide application in modern chemical engineering, for example, in the production of drugs (aspirin, phenacetin), 1 acetates and maleic anhydride, 2 and others. Acetic acid and its aqueous solutions are involved in the tricarboxylic acid (TCA) cycle, 3 the metabolism of ethanol by two dehydrogenases.…”
Section: Introductionmentioning
confidence: 99%
“…1. Figure 1.Changes of excess refractive index n E of freshly prepared aqueous solutions of acetic acid at different initial concentrations of components (curve 1), calculated values of excess dielectric constant ɛ E (curve 2), and squared excess refractive index ( n E ) 2 .Figure 2.The number of hydrogen bonds forms between water and acetic acid molecules at different concentrations of component.…”
Section: Introductionmentioning
confidence: 99%
“…Changes of excess refractive index n E of freshly prepared aqueous solutions of acetic acid at different initial concentrations of components (curve 1), calculated values of excess dielectric constant ɛ E (curve 2), and squared excess refractive index ( n E ) 2 .…”
A refractometric method, coupled with molecular dynamics study, attenuated total reflection Fourier transform infrared (ATR FT-IR), and Raman spectroscopy, was used to determine optical characteristics of concentration features of aqueous solutions of acetic acid. Measurements of the refractive index of aqueous solutions of acetic acid in the wide range of acetic acid concentrations (∼ 0 ÷ 1 mole fraction) in a solution at a room temperature were conducted. Maximum value of refractive index was detected at a concentration of ∼0.3 mole fraction. The deviation from the parabolic form of the dependence of the refractive index on the concentration occurs at a concentration of ∼0.8 mole fraction. As far as we know, this deviation has been observed for the first time. The maximum is attributed to the largest number of molecular interactions between water and acetic acid molecules, while the deviation is associated with the parallel orientation of acetic acid molecules. To identify the reconstructing of molecules in the system, FT-IR and Raman spectra of these solutions at a concentration of ∼0.3 and ∼0.8 mole fraction were recorded and compared with pure solutions. The data obtained by using ATR FT-IR and Raman spectroscopy support the idea that the refractometric method is sensitive to determine the structural states of aqueous solutions of acetic acid.
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