Search

In this paper, thermal properties, atomic-scale structure, and molecular dynamics (at ambient and high pressure) of native melatonin (MLT) and its partially-deuterated derivative (MLT-d2) have been investigated. Based on infrared spectroscopy, it was shown that treating MLT with D2O causes the replacement of hydrogen atoms attached to the nitrogen by deuterium. The degree of such substitution was very high (> 99%) and the deuterated sample remained stable after exposure to the air as well as during the melting and vitrification processes. Further calorimetric studies revealed the appearance of a peculiar thermal event before the melting of crystalline MLT-d2, which was assigned by the X-ray diffraction to a local negative thermal expansion of the unit cell. Finally, the high-pressure dielectric experiments indicated a few interesting findings, including the variation in the shape of the structural relaxation peak during compression, the difference in the pressure evolution of the glass transition temperature, and the temperature dependence of activation volume for both MLT species. The variations in these parameters manifest a different impact of the compression/densification on the dynamics of hydrogen and deuterium bonds in the native and partially-deuterated MLT, respectively. [ABSTRACT FROM AUTHOR]

In this study, several experimental techniques were applied to probe thermal properties, molecular dynamics, crystallization kinetics and intermolecular interactions in binary mixtures (BMs) composed of flutamide (FL) and various poly(N-vinylpyrrolidone) (PVP) polymers, including a commercial product and, importantly, samples obtained from high-pressure syntheses, which differ in microstructure (defined by the tacticity of the macromolecule) from the commercial PVP. Differential Scanning Calorimetry (DSC) studies revealed a particularly large difference between the glass transition temperature (Tg) of FL+PVPsynth. mixtures with 10 and 30 wt% of the excipient. In the case of the FL+PVPcomm. system, this effect was significantly lower. Such unexpected findings for the former mixtures were strictly connected to the variation of the microstructure of the polymer. Moreover, combined DSC and dielectric measurements showed that the onset of FL crystallization is significantly suppressed in the BM composed of the synthesized polymers. Further non-isothermal DSC investigations carried out on various FL+10 wt% PVP mixtures revealed a slowing down of FL crystallization in all FL-based systems (the best inhibitor of this process was PVP Mn = 190 kg/mol). Our research indicated a significant contribution of the microstructure of the polymer on the physical stability of the pharmaceutical—an issue completely overlooked in the literature. [ABSTRACT FROM AUTHOR]

Star-shaped glycopolymers due to the attractive combination of the physicochemical, morphological, self-assembly properties along with biological activity have gained increased attention as innovative agents in novel cancer therapies. Unfortunately, the production of these highly desirable biomaterials remains a challenge in modern macromolecular chemistry. The main reason for that is the low polymerizability of ionic glycomonomers originated from their steric congestion and the occurrence of ionic interactions that generally negatively influence the polymerization progress and hinder controllable reaction pathway. In this work, the new ionic sugar monomer was (co)polymerized for the first time via Activator Generated by Electron Transfer Atom Transfer Radical Polymerization (AGET ATRP) using a three-arm resveratrol-based core to obtain star-like (co)polymers. The obtained products were examined in terms of their physicochemical properties and morphology. Aside from the synthesis of these new glycopolymers, also a thorough description of their thermal properties, ability to self-assembly, the formation of stable superstructures was studied in detail. It was found that examined (co)polymers did not show any heterogeneities and phase separation, while their variation of glass transition temperature (Tg) was strictly related to the change in the number of glycomonomer. Also, the stability and shapes of formed superstructures strictly depend on their composition and topology. Finally, we have shown that synthesized carbohydrate-based polymers revealed high antiproliferative activity against several cancer cell lines (i.e., breast, colon, glioma, and lung cancer). The cytotoxic activity was particularly observed for star-shaped polymers that were systematically enhanced with the growing concentration of amine moieties and molecular weight. The results presented herein suggest that synthesized star-shaped glyco(co)polymers are promising as drug or gene carriers in anticancer therapies or anti-tumor agents, depending on their cytotoxicity. [ABSTRACT FROM AUTHOR]

• The structural (α)-process in loratadine (LOR) is sensitive to compression. • The pressure dependence of τ JG β is weaker with respect to that of τ α. • There is a breakdown of exact isochronal α and JG β superpositioning in LOR. • Reason for that is probably the increase of order in the system due to densification. In this paper, high-pressure (HP) dielectric studies on the van der Waals active pharmaceutical ingredient (API) - loratadine (LOR) were carried out. It was found that, surprisingly, the secondary (β) relaxation, which, according to the Coupling Model (CM) predictions, was classified as a Johari-Goldstein (JG) process, separates from the structural (α)-mode with compression (although the shape of the α -peak is invariant to the thermodynamic conditions at constant τ α). Consequently, there is a breakdown of the isochronal superpositioning of α - and β - relaxation times (τ α and τ β) in this system, which is a typical behavior for the secondary process with intermolecular character. Based on these findings, two possibilities concerning the origin of the β -relaxation in LOR have been proposed: 1) it is a non-JG process (probably originating from fluctuations within cyclic rings of the API molecule), which, however, satisfies the CM predictions; or 2) it is a JG-process, which similarly to a few earlier examined H-bonded compounds (e.g., probucol and sorbitol) is characterized by a different sensitivity to compression when compared to the α -process. Moreover, it was found that the activation entropy for the β -process takes negative values, irrespective of the pressure conditions. That may be interpreted as a result of conformational variation or the loss of translational and rotational degrees of freedom, leading to increased order in API due to densification. The results presented herein give a new insight into the relationship between the structural and secondary relaxations in the close vicinity of the glass transition temperature. Furthermore, they show that HP studies are crucial in elucidating the correlation between these processes. [ABSTRACT FROM AUTHOR]

In this paper, we studied for the first time the impact of the molecular weight, M n , and the topology on the molecular dynamics of a series of grafted poly(poly(dimethylsiloxane methacrylate)) (polyPDMSMA). The behavior of grafted (molecular brushes) polyPDMSMA and their three-armed counterparts of tailor-made properties prepared by Atom Transfer Radical Polymerization (ATRP) was monitored by means of broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC) and comprehensive rheology analysis. Surprisingly, the dielectric loss spectra of all studied polyPDMSMA exhibit the presence of two dielectric relaxation processes above their glass transition temperature, T g. A comparison of dielectric, calorimetric and mechanical data indicated that the faster and slower relaxation processes identified in loss spectra can be related to the segmental and chain dynamics, respectively. Interestingly, we observed that the "local" segmental dynamics of studied polyPDMSMA, involving the mobility of few repeatable units creating a segment, is almost unaffected by neither the length of polymer chain, number of grafts nor its topology. This is also reflected in a weak molecular weight-dependences of T g of studied polyPDMSMA independently to their topology. On the other hand, the time-scale separation between segmental and the chain modes as well as the amplitude of the latter process increase with growing M n of all examined polyPDMSMA. Additionally, it should be mentioned that the mechanical data collected for samples characterized by high molecular weight (of M n > 280 kg/mol) reveal the emergence of additional process (most likely related to the grafts and/or the star arm relaxation) at the intermediate regime, independently to their topology. Interestingly, this mode was observed to be much slower for the star-shaped macromolecules when compared to the grafted polymers, despite their lower M n. This implies that the observed differences are not a result of different molecular weights, but rather originate from a various molecular mechanism due to the different topology of the studied samples. In this context, one can assume that in the case of high-molecular-weight macromolecules, the backbone architecture has a significant influence on the behavior of polymers, including their molecular dynamics. [Display omitted] • Increase of the glass transition of studied polyPDMSMA with their molecular weight. • Loss spectra of polyPDMSMA exhibit multiple dielectric relaxation processes. • Observed dielectric processes were assigned as the chain and segmental modes. • Presence of grafts/arms relaxation (or entanglement segments) in mechanical data. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated dielectric response at ambient and elevated pressure of poly(mercaptopropyl)methylsiloxane (PMMS) based oligomeric brushes, where the thiol moiety was substituted by various butyl acrylate isomers (n -butyl acrylate (nBA), iso -butyl acrylate (isoBA), tert -butyl acrylate (tertBA)). It was found that the glass transition temperature, T g , of PMMS is much lower with respect to the other systems despite its ability to form weak hydrogen (H) bonds. What is more, the length scale of cooperativity was the highest in homopolymer and scaled with the steric hindrance of the graft. We also demonstrated that in the examined grafted copolymers, there is one broad relaxation process in dielectric spectra which is wider than that recorded in mechanical response. That probably means that similarly to PMMS, there are two relaxation processes above T g in grafted copolymers. However, due to similar timescale, they cannot be separated. Further, high-pressure experiments revealed that pressure coefficient of the glass transition temperature, d T g / d p , as well as the activation volume, Δ V , calculated for the segmental process surprisingly does not scale with either the size of monomer nor steric hindrance. This unexpected result must be related to the specific structure adopted by the studied grafted oligomers. Presented herein data expand our understanding on the impact of topology on the dynamics of polymers at ambient and high pressure. [Display omitted] • The glass transition temperature is strongly affected by a graft structure. • All grafted materials revealed the broad segmental relaxation process. • The shape of the α -process remains constant with pressure for all materials. • The pressure coefficient of the glass transition changes with graft structures. [ABSTRACT FROM AUTHOR]

This work demonstrates the effect of a high dc bias field (up to 160 kV/cm) on the polyaddition reaction of the modeled epoxy resin system. Polymerization of bisphenol A diglycidyl ether (DGEBA) supported by high electric field results in obtaining epoxides with significantly increased molecular weight, which is seven-fold higher than the zero-field reference (M n = 4.7 kg/mol). We also found a markedly reduced dispersity (Ð = 1.52 at 0 kV/cm, Đ = 1.21 at 160 kV/cm). The molecular weight and dispersity of obtained polymers change almost linearly with the reaction time. By following polymerization kinetics in the real-time of the experiment, via dielectric spectroscopy, we observe slowing down the reaction progress at dc fields of E = 160 kV/cm, compared to the zero-field case, E = 0 kV/cm. The polymer materials obtained in the presence/absence of static electric fields exhibit distinctly different glass transition temperatures. Our study highlights a better control over the reaction and product properties attained by using only the magnitude of the applied field as the control variable. Thus, a high electric field could provide an alternative pathway in synthesizing and developing advanced polymer materials using simpler, "green", less-expensive, and technologically demanding approaches. [Display omitted] [ABSTRACT FROM AUTHOR]

• There is a narrowing of the α -dispersion with pressure (p) in ritonavir (RTV). • The reason for that is most likely variation in the local molecular ordering with p. • Changes in H-bonding pattern are also responsible for the observed finding. • An additional secondary process emerges in the high- p spectra measured at T < T g. In this paper, high-pressure (HP) dielectric studies on H-bonded active pharmaceutical ingredient – ritonavir indicated the narrowing of α- dispersion with compression, and consequently, a breakdown of the temperature-pressure superpositioning rule. To understand such peculiar behavior, reported so far only for a few van der Waals compounds, we performed calorimetric, structural, and infrared measurements on the pressure densified glass (as well as on ordinary glass) of the examined substance. These investigations demonstrated that variations in the structural organization of molecules and H-bonding pattern are responsible for the observed changes in the shape of the structural relaxation peak. Moreover, further isobaric HP studies at pressure 400 MPa revealed the presence of an additional secondary relaxation process (not detected at p = 0.1 MPa) in the loss spectra collected below the glass transition temperature for this compound. [ABSTRACT FROM AUTHOR]