513 research outputs found
Activation volume of selected liquid crystals in the density scaling regime
In this paper, we demonstrate and thoroughly analyze the activation volumetric properties of selected liquid crystals in the nematic and crystalline E phases in comparison with those reported for glass-forming liquids. In the analysis, we have employed and evaluated two entropic models (based on either total or configurational entropies) to describe the longitudinal relaxation times of the liquid crystals in the density scaling regime. In this study, we have also exploited two equations of state: volumetric and activation volumetric ones. As a result, we have established that the activation volumetric properties of the selected liquid crystals are quite opposite to such typical properties of glass-forming materials, i.e., the activation volume decreases and the isothermal bulk modulus increases when a liquid crystal is isothermally compressed. Using the model based on the configurational entropy, we suggest that the increasing pressure dependences of the activation volume in isothermal conditions and the negative curvature of the pressure dependences of isothermal longitudinal relaxation times can be related to the formation of antiparallel doublets in the examined liquid crystals. A similar pressure effect on relaxation dynamics may be also observed for other material groups in case of systems, the molecules of which form some supramolecular structures
Dielectric relaxation behavior in antiferroelectric metal organic framework [(CH3)2NH2][FeIIIFeII(HCOO)6] single crystals
The fundamental aspects of the relaxation dynamics in niccolite-type, mixed valence metalâorganic framework, multiferroic [(CH3)2NH2][Fe3+Fe2+(HCOO)6] single crystals have been reported using dielectric relaxation spectroscopy covering eight decades in frequency (10â2 †f †106) in the temperature range 120 K †T †250 K. The compound shows antiferroelectric to paraelectric phase transition near T = 154 K with the relaxor nature of electric ordering. The temperature dependent dielectric response in modulus representation indicates three relaxation processes within the experimental window. The variable range hopping model of small polarons explains the bulk non-Debye type conductivity relaxation. The fastest relaxation with activation energy Ea = 0.17 eV is related to progressive freezing of the reorientation motions of DMA+ cations. X-ray diffraction data revealed that complete freezing of orientational and translational motions of DMA+ cations occurs well below phase transition temperature. These experimental observations are fundamentally important for the theoretical explanation of relaxation dynamics in niccolite-type metalâorganic frameworks
Molecular dynamics and physical stability of amorphous nimesulide drug and its binary drug-polymer systems
yesIn this paper we study the effectiveness of three well known polymers: inulin, Soluplus and PVP in stabilizing amorphous form of nimesulide (NMS) drug. The re-crystallization tendency of pure drug as well as measured drug-polymer systems were examined at isothermal conditions by using broadband dielectric spectroscopy (BDS), and at non-isothermal conditions by differential scanning calorimetry (DSC). Our investigation has shown that the crystallization half-life time of pure NMS at 328 K is equal to 33 minutes. We found that this time can be prolonged to 40 years after adding to NMS 20% of PVP polymer. This polymer proved to be the best NMSâs stabilizer, while the worst stabilization effect was found after adding the inulin to NMS. Additionally, our DSC, BDS and FTIR studies indicate that for suppression of NMSâs re-crystallization in NMS-PVP system, the two mechanisms are responsible: the polymeric steric hindrances as well as the antiplastization effect excerted by the excipient.The authors J.K., Z.W., K.G. and M.P., are grateful for the financial support received within the Project No. 2015/16/W/NZ7/00404 (SYMFONIA 3) from the National Science Centre, Poland. H.M. and L.T. are supported by Science Foundation Ireland under grant No. 12/RC/2275 (Synthesis and Solid State Pharmaceuticals Centre)
Impact of alternative solid state forms and specific surface area of high-dose, hydrophilic active pharmaceutical ingredients on tabletability
YesIn order to investigate the effect of using different
solid state forms and specific surface area (TBET) of active
pharmaceutical ingredients on tabletability and dissolution
performance, the mono- and dihydrated crystalline forms of
chlorothiazide sodium and chlorothiazide potassium (CTZK)
salts were compared to alternative anhydrous and amorphous
forms, as well as to amorphous microparticles of chlorothiazide
sodium and potassium which were produced by spray drying and
had a large specific surface area. The tablet hardness and tensile
strength, porosity, and specific surface area of single-component,
convex tablets prepared at different compression pressures were characterized. Results confirmed the complexity of the
compressibility mechanisms. In general it may be concluded that factors such as solid-state form (crystalline vs amorphous), type
of hydration (presence of interstitial molecules of water, dehydrates), or specific surface area of the material have a direct impact
on the tabletability of the powder. It was observed that, for powders of the same solid state form, those with a larger specific
surface area compacted well, and better than powders of a lower surface area, even at relatively low compression pressures.
Compacts prepared at lower compression pressures from high surface area porous microparticles presented the shortest times to
dissolve, when compared with compacts made of equivalent materials, which had to be compressed at higher compression
pressures in order to obtain satisfactory compacts. Therefore, materials composed of nanoparticulate microparticles (NPMPs)
may be considered as suitable for direct compaction and possibly for inclusion in tablet formulations as bulking agents, APIs,
carriers, or binders due to their good compactibility performanceSolid State Pharmaceutical Cluster (SSPC), supported by Science Foundation Ireland under Grant No. 07/SRC/B1158
Intracellular microrheology of motile Amoeba proteus
The motility of motile Amoeba proteus was examined using the technique of
passive particle tracking microrheology, with the aid of newly-developed
particle tracking software, a fast digital camera and an optical microscope. We
tracked large numbers of endogeneous particles in the amoebae, which displayed
subdiffusive motion at short time scales, corresponding to thermal motion in a
viscoelastic medium, and superdiffusive motion at long time scales due to the
convection of the cytoplasm. Subdiffusive motion was characterised by a
rheological scaling exponent of 3/4 in the cortex, indicative of the
semiflexible dynamics of the actin fibres. We observed shear-thinning in the
flowing endoplasm, where exponents increased with increasing flow rate; i.e.
the endoplasm became more fluid-like. The rheology of the cortex is found to be
isotropic, reflecting an isotropic actin gel. A clear difference was seen
between cortical and endoplasmic layers in terms of both viscoelasticity and
flow velocity, where the profile of the latter is close to a Poiseuille flow
for a Newtonian fluid
Formation and physicochemical properties of crystalline and amorphous salts with different stoichiometries formed between ciprofloxacin and succinic acid
YesMulti-ionizable compounds, such as dicarboxylic
acids, offer the possibility of forming salts of drugs with
multiple stoichiometries. Attempts to crystallize ciprofloxacin,
a poorly water-soluble, amphoteric molecule with succinic acid
(S) resulted in isolation of ciprofloxacin hemisuccinate (1:1)
trihydrate (CHS-I) and ciprofloxacin succinate (2:1) tetrahydrate
(CS-I). Anhydrous ciprofloxacin hemisuccinate (CHS-II)
and anhydrous ciprofloxacin succinate (CS-II) were also
obtained. It was also possible to obtain stoichiometrically
equivalent amorphous salt forms, CHS-III and CS-III, by spray
drying and milling, respectively, of the drug and acid. Anhydrous CHS and CS had melting points at âŒ215 and âŒ228 °C, while
the glass transition temperatures of CHS-III and CS-III were âŒ101 and âŒ79 °C, respectively. Dynamic solubility studies revealed
the metastable nature of CS-I in aqueous media, resulting in a transformation of CS-I to a mix of CHS-I and ciprofloxacin 1:3.7
hydrate, consistent with the phase diagram. CS-III was observed to dissolve noncongruently leading to high and sustainable drug
solution concentrations in water at 25 and 37 °C, with the ciprofloxacin concentration of 58.8 ± 1.18 mg/mL after 1 h of the
experiment at 37 °C. This work shows that crystalline salts with multiple stoichiometries and amorphous salts have diverse
pharmaceutically relevant properties, including molecular, solid state, and solubility characteristics.Solid State Pharmaceutical Cluster (SSPC), supported by Science Foundation Ireland under grant number 07/SRC/ B1158
Granular aluminium nanojunction fluxonium qubit
Mesoscopic Josephson junctions, consisting of overlapping superconducting electrodes separated by a nanometre-thin oxide layer, provide a precious source of nonlinearity for superconducting quantum circuits. Here we show that in a fluxonium qubit, the role of the Josephson junction can also be played by a lithographically defined, self-structured granular aluminium nanojunction: a superconductorâinsulatorâsuperconductor Josephson junction obtained in a single-layer, zero-angle evaporation. The measured spectrum of the resulting qubit, which we nickname gralmonium, is indistinguishable from that of a standard fluxonium. Remarkably, the lack of a mesoscopic parallel plate capacitor gives rise to an intrinsically large granular aluminium nanojunction charging energy in the range of tens of gigahertz, comparable to its Josephson energy. We measure coherence times in the microsecond range and we observe spontaneous jumps of the value of the Josephson energy on timescales from milliseconds to days, which offers a powerful diagnostics tool for microscopic defects in superconducting materials
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