In this work, we examined the effect of length of alkyl chain attached to the benzene ring on the self-assembling phenomena for the series of phenol alcohol (PhA) derivatives, from...
A series of five alcohols (3-methyl-2-butanol, 1-cyclopropylethanol,
1-cyclopentylethanol, 1-cyclohexylethanol, and 1-phenylethanol) was
used to study the impact of the size of steric hindrance and its aromaticity
on self-assembling phenomena in the liquid phase. In this Letter,
we have explicitly shown that the phenyl ring exerts a much stronger
effect on the self-organization of molecules via the O–H···O scheme than any other
type of steric hindrance, leading to a significant decline in the
size and concentration of the H-bonded clusters. Given the combination
of calorimetric, dielectric, infrared, and diffraction studies, this
phenomenon was ascribed to its additional proton-acceptor function
for the competitive intermolecular O–H···π
interactions. The consequence of this is a different packing of molecules
on the short- and medium-range scale.
Herein, we examined the effect of finite size and wettability on the structural dynamics and the molecular arrangement of the propylene carbonate derivative, (S)-(−)-4-methoxymethyl-1,3-dioxolan-2-one (assigned as s-methoxy-PC), incorporated into alumina and silica porous templates of pore diameters d = 4 nm–10 nm using Raman and broadband dielectric spectroscopy, differential scanning calorimetry, and x-ray diffraction. It was demonstrated that only subtle changes in the molecular organization and short-range order of confined s-methoxy-PC molecules were detected. Yet, a significant deviation of the structural dynamics and depression of the glass transition temperatures, Tg, was found for all confined samples with respect to the bulk material. Interestingly, these changes correlate with neither the finite size effects nor the interfacial energy but seem to vary with wettability, generally. Nevertheless, for s-methoxy-PC infiltrated into native (more hydrophilic) and modified (more hydrophobic) silica templates of the same nanochannel size (d = 4 nm), a change in the dynamics and Tg was negligible despite a significant variation in wettability. These results indicated that although wettability might be a suitable variable to predict alteration of the structural dynamics and depression of the glass transition temperature, other factors, i.e., surface roughness and the density packing, might also have a strong contribution to the observed confinement effects.
Herein, broadband dielectric (BDS) and Fourier transform infrared spectroscopy (FTIR), together with differential scanning calorimetry (DSC) and X-ray diffraction (XRD), were applied to study the molecular dynamics, molecular interactions as well as physical stability of an amorphous Active Pharmaceutical Ingredient (API) probucol (PRO)infiltrated into anodic aluminum oxide (AAO) membranes of pore size, d ∼ 10−160 nm. Interestingly, the behavior of examined substance strongly depends on the applied thermal protocol. Remarkably, for the first time, we observed that the structural dynamics of the slowly cooled PRO under confinement is significantly enhanced when compared to that of the quenched material. This unusual behavior was interpreted as a result of surface-induced effects (including the formation of well-resolved interfacial H-bonded layer and adsorption− desorption processes near the interface) that are magnified by the extremely high sensitivity to density fluctuation of studied PRO, reflected in the enormous pressure coefficient of the glass transition temperature dT g /dp = 427 K/GPa. In fact, FTIR investigations revealed that PRO tends to self-associate under confinement and forms a strongly bonded interfacial layer, which controls the variation in the structural dynamics of core molecules. Finally, we observed that the tendency to crystallize of confined API is reduced with respect to the bulk, even though the critical size of PRO nuclei (r c ∼ 3 nm) is significantly lower than the smallest examined pore size. Nevertheless, after few weeks of storage, the investigated substance crystallized in larger pores, while it remained stable in the nanochannels of d = 10 nm. A combination of XRD and DSC measurements indicated that the infiltrated PRO forms two polymorphs, the stable form I (dominating in bulk) and unstable form II (prevailing under confinement). That means that porous matrices might be used to obtain and maintain prolonged stability of unstable polymorphic forms of API.
In this paper, we have analyzed structural, thermal, and dynamical properties of four azole antifungals: itraconazole (ITZ), posaconazole (POS), terconazole (TER) and ketoconazole (KET), differing mainly in the length of...
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