The solid−liquid equilibrium data of vinpocetine in nine pure solvents and ethanol−water binary system at temperatures ranging from 283.15 to 323.15 K was experimentally measured by gravimetric method under atmospheric pressure. For the different types of investigated solvent, the solid−liquid equilibrium solubility of vinpocetine increased with augmented temperature. Experimental solubility was fitted with several thermodynamic models including the modified Apelblat model, λh model, and nonrandom two-liquid (NRTL) model, as well as the combined nearly ideal binary solvent/Redlich− Kister model. All the fitted values were in satisfactory agreement with the experimental results. The thermodynamic parameters were calculated by the activity coefficients of vinpocetine in different solvents, which were obtained by NRTL model. The results demonstrated that the mixing process of vinpocetine with experimental solvents was spontaneous and entropy-driven.
Combined
with rigorous and accurate experimental protocols, the
key influencing factors of the formation of macroscopic defects in
vinpocetine (VIP) solution were studied with the aim to propose a
universal strategy toward the inquiry of the formation mechanism of
crystal defects in organic crystals. By screening solvents and polymorphism,
it was determined that vinpocetine has two crystal habits (habits
I & II); the content and formation mechanism of the defects in
two crystal habits was confirmed to be disparate. The impacts of temperature,
supersaturation, agitation, and ultrasound on the defects of the habit
I were investigated in a targeted manner. The crystal surface indexation
method was used to visually analyze the growth behavior of VIP single
crystals. It was revealed that the stepwise lowered layers of {(100)}
crystal planes in crystal habit I were primary factors inducing negative
defects formation. In addition, the molecular dynamics simulation
was employed to investigate the interactions between the surface of
vinpocetine crystal and the pure solvent. The growth rate and surface
roughness of the crystal faces were simulated using the modified attachment
energy model. Through the discussion of surface structure and adsorption
mechanism, it was expounded that the crystal growth kinetics induced
the formation of depressions and further contributes to the formation
of defects in cavities and fine inclusions.
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