We have designed new chiral smectic mesogens with the -CH2O group near the chiral center. We synthesized two unique rod-like compounds. We determined the mesomorphic properties of these mesogens and confirmed the phase identification using dielectric spectroscopy. Depending on the length of the oligomethylene spacer (i.e., the number of methylene groups) in the achiral part of the molecules, the studied materials show different phase sequences. Moreover, the temperature ranges of the observed smectic phases are different. It can be seen that as the length of the alkyl chain increases, the liquid crystalline material shows more mesophases. Additionally, its clearing (isotropization) temperature increases. The studied compounds are compared with the structurally similar smectogens previously synthesized. The helical pitch measurements were performed using the selective reflection method. These materials can be useful and effective as chiral components and dopants in smectic mixtures targeted for optoelectronics and photonics.
Chiral liquid crystalline compounds belonging to the homologous series of (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[m-(2,2,3,3,4,4,4-heptafluorobutoxy)alk-1-oxy]-2-fluorobenzoates show various behaviors on cooling depending on the length of the CmH2m chain. The homologue with m = 2 crystallizes, while for m = 5, 6, 7, and presumably also for m = 3, the glass of the anticlinic smectic CA* phase is formed. The previous results for m = 4 suggest that this homologue may also be a glassformer. This paper presents the study of the crystallization kinetics for the compound with m = 4 in isothermal conditions (by polarizing optical microscopy) and for the 5-40 K min-1 cooling rates (by differential scanning calorimetry). Microscopic observations enable estimation of the energy barrier for nucleation, which equals 409 kJ mol-1. The threshold cooling rate necessary for complete vitrification of the smectic CA* phase, obtained by extrapolating the enthalpy change during crystallization to zero, is equal to 81 K min-1 or 64 K min-1 for the linear and parabolic fits, respectively. The structural studies by X-ray diffraction show that crystal phases have lamellar structures both in the pristine sample and after crystallization from the melt but with different layer spacing. A weak relaxation process is detected in the sample after melt crystallization, revealing the presence of the conformational disorder. The dynamic glass transition temperature of the SmCA* phase, estimated from the relaxation time of the PH process (as the α-relaxation time could not be registered in a wide enough temperature range), is 244 K.
A Siamese neural network, which is a deep learning technique, was applied to investigate phase transitions based on polarising microscopic textures of liquid crystals like: antiferroelectric smectic CA* phase and its glass, smectic I phase and its glass, and smectic G and its glass. It is an example of a subtle transition without significant structural changes, where textures above and below the glass transition temperature are similar. The Siamese neural network could distinguish textures of the chosen liquid crystal phases from a glass of that phase. This publication provides details of the Siamese neural network and its implementation based on three different convolutional neural networks has been tested.
We investigated the impact of carbon quantum dots (CQDs) of sizes â¼2-5 nm in a room temperature tri-component fluorinated antiferroelectric liquid crystal (AFLC) mixture. The synthesised CQDs have been characterised by high-resolution transmission electron microscopy and X-ray diffraction spectroscopy. An increase in the transition temperature and enthalpy to the isotropic liquid phase indicates stabilization of the AFLC mixture in the presence of CQDs. The dielectric studies have been carried out in the frequency range of 1 Hz-40 MHz under the planar anchoring conditions of the molecules. An appreciable increase in the permittivity, dielectric strength, and conductivity has been observed owing to the existence of sp2/sp3 hybridization in the CQDs which form a strong coupling and develop a dipolar ordering in the systems. Various relaxation frequencies were increased with the incarceration of CQDs in the AFLC mixture. Overall, the different studies suggest that the doped CQDs are very well settled in between the host molecules without disturbing the molecular ordering of the hosts. Such results are encouraging and reveal the potential applicability of the CQD doped systems to produce highly efficient tuneable optical devices and other multifaceted applications.
The formation of glass of the anticlinic high-tilted smectic CA* phase even at low cooling rates (≥2 K min-1) is reported for (S)-4'-(1-ethylhexyloxycarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy)pentyl-1-oxy]benzoate. The kinetics of crystallization is investigated via differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy. The temperature region of the largest crystallization rate, the activation energy of cold crystallization and the energy barrier of nucleation are determined. The coupling of the characteristic crystallization time with the α-relaxation time is studied. A high fragility index equal to 139 is obtained for this glassformer. Comparison with a very similar glassforming compound, with the chiral centre based on (S)-(+)-2-octanol instead of (S)-(+)-3-octanol, is presented.
Quantum-mimic Optical Coherence Tomography (Qm-OCT) images are cluttered with artefacts - parasitic peaks which emerge as a by-product of the algorithm used in this method. However, the shape and behaviour of an artefact are uniquely related to Group Velocity Dispersion (GVD) of the layer this artefact corresponds to and consequently, the GVD values can be inferred by carefully analysing them. Since for multi-layered objects the number of artefacts is too high to enable layer-specific analysis, we employ a solution based on Machine Learning. We train a neural network with Qm-OCT data as an input and dispersion profiles, i.e. depth distribution of GVD within an A-scan, as an output. By accounting for noise during training, we process experimental data and estimate the GVD values of BK7 and sapphire as well as provide a qualitative GVD value distribution in a grape and cucumber. Compared to other GVD-retrieving methods, our solution does not require user input, automatically provides dispersion values for all the visualised layers and is scalable. We analyse the factors affecting the accuracy of determining GVD: noise in the experimental data as well as general physical limitations of the detection of GVD-induced changes, and suggest possible solutions.
Complementary methods are applied to investigate the phase transitions and crystallization kinetics of the liquid crystalline compound denoted as 3F5FPhH6. Two crystal phases are confirmed, and one of them is the conformationally disordered (CONDIS) phase. Complexity of the melt crystallization process is revealed by the analysis with Friedman's isoconversional method. The melt crystallization of 3F5FPhH6 shows different mechanisms depending on temperature, which is explained by the relation between the thermodynamic driving force and the thermal energy of translational degrees of freedom. The studied compound crystallizes even during fast cooling (30 K/min), unlike similar compounds with different fluorosubstitutions of the benzene ring, which form the smectic glass for moderate cooling rates. The tendency to vitrification of the smectic phase decreases apparently with the decreasing stability width of the SmCA* phase and the increasing relaxation time of the collective relaxation process in this phase, at least for homologues differing from 3F5FPhH6 only by the type of fluorosubstitution.
The behavior of two newly formulated bi-component orthoconic antiferroelectric liquid crystalline (OAFLC) systems, i.e., the Compound A + Compound B mixture system and Compound C + Compound B mixture system has been discussed in light of temperature and concentration dependencies of helical pitch length, spontaneous polarization, relaxation time, bulk viscosity, and the anchoring energy strength coefficient, together with static dielectric permittivity (ε) and dielectric anisotropy. Compound A + Compound B mixtures possess spontaneous polarization between 190-340 nC.cm-2 and fast relaxation times between 190-320 µs in the smectic antiferroelectric SmCA* phase at room temperature. Compound C + Compound B mixtures also have a spontaneous polarization in the range of 190-280 nC.cm-2 and relaxation times in the range of 190-230 µs at room temperature. Most of the mixtures have a helical pitch below one micrometer in the SmCA* phase. These advanced mixtures show a broad temperature range of the antiferroelectric SmCA* phase, fast switching of molecules under an applied electric field, negative dielectric anisotropy and a short helical pitch, confirming the advantage of designing new polymer-stabilized OAFLC that is targeted for novel application in sensing devices, utilizing the fast responsive electro-optical modulation elements.
Vitrification of the antiferroelectric smectic-C_{A}^{*} phase is reported for the orthoconic mixture W-1000 and its new derivative W-356. The crystallization is not observed even upon slow cooling and the cold crystallization on subsequent heating is also absent. Molecular dynamics in the smectic phases of both mixtures is investigated down to 173 K and the fragility parameters are determined from the temperature behavior of the α-process. X-ray diffraction is applied to compare the structural parameters of W-356 and W-1000 as well as to study the structural changes during the glass transition of the Sm-C_{A}^{*} phase. The evolution of the smectic layer order within the Sm-C_{A}^{*} glass is reported, while the correlation length of the short-range order in the smectic layers is shown to be almost constant below the glass transition temperature. Electrooptic properties of W-356: spontaneous polarization, tilt angle and switching time are determined and compared with these of W-1000. The observed differences between the properties of W-356 and W-1000 might be explained by the dimer formation of components with the -C≡N terminal group, present only in the W-356 mixture, and by the different structure of the aromatic molecular core in one of the W-356 components.
Standard rheometers assess mechanical properties of viscoelastic samples up to 100 Hz, which often hinders the assessment of the local-scale dynamics. We demonstrate that high-frequency analysis can be achieved by inducing broadband waves and monitoring their media-dependent propagation using optical coherence tomography. Here, we present a new broadband wave analysis based on two-dimensional Fourier transformation. We validated this method by comparing the mechanical parameters to monochromatic excitation and a standard oscillatory test data. Our method allows for high-frequency mechanical spectroscopy, which could be used to investigate the local-scale dynamics of different biological tissues and the influence of diseases on their microstructure.
Elasticity Imaging Techniques , Elasticity Imaging Techniques/methods , Phantoms, Imaging , Spectrum Analysis , Tomography, Optical Coherence/methods , Viscosity
The phase transitions, crystallization kinetics and molecular dynamics of (S)-4'-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy)pent-1-oxy] benzoate (3F5HPhH6) are investigated by differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy. The vitrification of the antiferroelectric hexatic phase is observed for cooling rates ≥5 K min-1 and the fragility index determined from dielectric data is mf ≈ 90. Two regimes of non-isothermal cold crystallization are distinguished using the Kissinger and Augis-Bennett methods in the heating rate ranges of 1-5 K min-1 (larger activation energy) and 8-20 K min-1 (lower activation energy). The correlation between the time of non-isothermal cold crystallization (using isothermal approximation) and relaxation time of the α-process is determined. The obtained coupling coefficient ξ ≈ 0.7 and temperature dependence of the crystallization rate Z from the Ozawa model imply a mainly diffusion-controlled cold crystallization below 275 K. The Avrami exponents n and Ozawa exponents nO determined for isothermal melt crystallization and non-isothermal cold crystallization, respectively, weigh in favour of two- rather than three-dimensional crystal growth. The transition between crystal phases is observed on heating, with a lower activation energy for 1-3 K min-1 than for 5-20 K min-1 rates.
In this paper, for the first time, the influence of the BaTiO3 particles on the antiferroelectric liquid crystalline phase was shown. Low concentrations and two different sizes of BaTiO3 particles (nano- and submicroparticles) were used. It was found that admixture of the ferroelectric particles causes a decrease in the concentration of free ions in the liquid crystal matrix. Despite the small amount of admixture, a decrease in spontaneous polarization, switching time and rotational viscosity, was observed, while the tilt angle of molecules and the smectic layer thickness did not change. It turns out that BaTiO3 particles have a very large impact on the dielectric spectra not only in the antiferroelectric phase but also in the ferroelectric and paraelectric phases of the polymorphic mixture studied. The dopants affect also the complex conductivity. In this paper, we explain why some properties are modified by BaTiO3 particles and others are not.
BACKGROUND: Multiple studies of probiotics used to prevent nosocomial diarrhea have provided conflicting results. The effects likely depend on the probiotic strain and/or dosage. The aim of this study was to assess the effectiveness of Lactobacillus reuteri DSM 17938 (L. reuteri; daily dose of 1 × 10 colony forming units) for preventing nosocomial diarrhea in children. METHODS: We conducted a multicenter, randomized, double-blind, placebo-controlled trial in 184 children, 1-48 months of age, admitted to the hospital for reasons other than diarrhea. A computer-generated randomization scheme was used to allocate participants to receive either L. reuteri (n = 91) at a daily dose of 1 × 10 colony forming units, for the duration of hospitalization, or an identical appearing placebo (n = 93). Patients, study personnel and data analysts were blinded to assignment. The primary outcome was the occurrence of nosocomial diarrhea (≥3 loose or watery stools in 24 hours that occurred >72 hours after admission). Analysis was by intention-to-treat. RESULTS: Baseline characteristics were similar in the 2 groups. Nosocomial diarrhea occurred in 13 (7.1%) children. No difference was found between the L. reuteri and the placebo groups (7/91 vs 6/93, respectively; relative risk: 1.19; 95% confidence interval: 0.43-3.27). There was also no difference between the L. reuteri and placebo groups for any of the secondary outcomes, including adverse effects. Rotavirus vaccination status had no effect on the results. CONCLUSION: L. reuteri in the dosage regimen used was not effective in preventing nosocomial diarrhea in children.
Cross Infection/prevention & control , Diarrhea/prevention & control , Limosilactobacillus reuteri/growth & development , Probiotics/administration & dosage , Child, Preschool , Double-Blind Method , Female , Humans , Infant , Male , Placebos/administration & dosage , Treatment Outcome
UNLABELLED: We aimed to systematically evaluate evidence on the effectiveness of Lactobacillus reuteri DSM 17938 (L. reuteri) for treating and preventing diseases in infants and children. MEDLINE and the Cochrane Library were searched in December 2013, with no language restrictions, for relevant randomized controlled trials (RCTs) and meta-analyses. The search was updated in April 2014. One systematic review and 14 RCTs met the inclusion criteria. The use of L. reuteri may be considered in the management of acute gastroenteritis as an adjunct to rehydration. There is some evidence that L. reuteri is effective in reducing the incidence of diarrhea in children attending day care centers. There is no evidence of effectiveness of L. reuteri in preventing nosocomial diarrhea in children. The administration of L. reuteri is likely to reduce crying time in infants with infantile colic in exclusively or predominantly exclusively breast-fed infants, but not in formula-fed infants. More studies are needed. Preliminary data suggest that L. reuteri may be effective in the prevention of some functional gastrointestinal disorders, such as colic and regurgitation. This innovative approach needs further evaluation by an independent research team. Preliminary evidence provides a rationale for further assessing the efficacy of L. reuteri for treating functional constipation or functional abdominal pain. However, it is too soon to recommend the routine use of L. reuteri for these conditions. There are no safety concerns with regard to the use of L. reuteri in nonimmunocompromised subjects. There are also data to support the safety of using L. reuteri in preterm infants. CONCLUSION: Our results precisely define current evidence on the effects of the administration of L. reuteri DSM 17938 to the pediatric population.
Abdominal Pain/therapy , Colic/therapy , Diarrhea/therapy , Gastroenteritis/therapy , Gastrointestinal Diseases/therapy , Limosilactobacillus reuteri , Probiotics/therapeutic use , Acute Disease , Child , Cross Infection/therapy , Humans , Infant , Safety
Gelatin tannate (GT) is a complex of tannic acid, which possesses astringent, antibacterial, and anti-inflammatory properties, and a protective gelatin. It is increasingly being marketed as an antidiarrheal drug. Our aim was to review data on the effectiveness of GT in treating acute gastroenteritis (AGE) in children and adults. The MEDLINE, EMBASE, and the Cochrane Library databases were searched in July 2013, with no language restrictions, for controlled clinical trials. Additional references were obtained from reviewed articles. Two trials met the inclusion criteria. In adults, one randomized controlled trial involving 40 subjects (mean age: 43±13 years) found that, compared with placebo, GT may be more effective at reducing some symptoms of AGE in the first 48 h after initiation of treatment. In children, one poor quality study (no randomization and no blinding) involving 211 children (mean age: 2.5±2.4 years) reported some beneficial effect of GT at 12 h after initiation of treatment. None of the studies evaluated the effect of GT on the primary outcome measures for this review such as stool output, duration of diarrhea, admission to hospital, duration of hospital stay, and (in children) weight gain after rehydration. Currently, there is no evidence to support the use of GT for treating AGE in children and only sparse evidence to support the use of GT in adults. Further well-designed trials, with sufficient power, adequate follow-up periods, and clinically relevant outcome measures, are needed. These include stool volume, duration of diarrhea, admission to hospital, duration of hospital stay, weight gain after rehydration, and adverse effects.
UNLABELLED: Diarrhea treatment with either Lactobacillus GG (LGG) or smectite as an adjuvant to standard rehydration therapy has proven efficacy. In countries where both LGG and smectite are available, concomitant use is frequently practiced. We investigated whether LGG plus smectite is superior to LGG alone in the management of children with acute gastroenteritis (AGE). A double-blind, placebo-controlled, randomized trial was performed. Children aged 4 to 60 months with AGE received LGG 6 × 10(9) colony forming units/day plus randomly either smectite (3 g) or placebo as an adjuvant to the standard rehydration therapy. Of the 88 children randomized, 81 (92 %) were available for intention-to-treat analysis. The duration of diarrhea in the LGG/smectite group (n = 44) compared with the LGG/placebo group (n = 37) was similar (P = 0.43). There were no significant differences between the study groups for the secondary outcomes, with three exceptions. On day 4, in the LGG/placebo group compared to the LGG/smectite group, there was significantly reduced stool frequency (P = 0.03). While there was a significant (P = 0.05) difference in stool consistency on the Bristol Stool Form Scale on day 4, it was not of clinical relevance. Finally, in the LGG/smectite group compared to the LGG/placebo group, there was a significantly shorter duration of intravenous therapy after randomization (P = 0.02). No adverse events were observed in the study groups. CONCLUSION: LGG plus smectite and LGG alone are equally effective for treating young children with AGE. Combined use of the two interventions is not justified.
Diarrhea/therapy , Gastroenteritis/therapy , Lactobacillus , Probiotics/therapeutic use , Silicates/therapeutic use , Acute Disease , Child, Preschool , Diarrhea, Infantile/therapy , Double-Blind Method , Female , Humans , Infant , Intention to Treat Analysis , Male , Silicates/pharmacology , Treatment Outcome
Statins are well-established and effective drugs in the treatment of hyperlipidemias. However the effects of statins extend beyond lipid-lowering. The pleiotropic effects of statins have been shown to modify inflammatory cell signaling of the immune response to infection. Statins have emerged as potential immunomodulatory and antioxidant agents that might impact on sepsis outcomes. It was postulated that statins may be candidates for the treatment of sepsis. Recent animal and human data suggest that statin therapy might be beneficial in patients before the onset of sepsis or in its initial period, but should be used with care when patients are diagnosed with severe sepsis or septic shock. Some analyses also provide evidence for statins as an adjuvant therapy in sepsis. Because of the divergent results of studies, the potential benefit needs to be validated in randomized, controlled trials. In this review, we describe current evidence on the use of statins in the prevention and treatment of sepsis.
Hydroxymethylglutaryl-CoA Reductase Inhibitors/pharmacology , Hydroxymethylglutaryl-CoA Reductase Inhibitors/therapeutic use , Sepsis/drug therapy , Animals , Humans , Sepsis/prevention & control , Shock, Septic/drug therapy
An attempt was made to produce and test, according to the guidelines of Polish Pharmacopeia VIII, new prescriptions of hydrogels which could be applied in the treatment of skin diseases associated with hyperpigmentation. Hydrogel formulations containing a substance of skin-whitening activity (arbutin) and glycol plant extract was produced on Carbopol Ultrez 10 base. Two glycol plant extracts of confirmed beneficial effect on skin were selected: an extract of ginkgo leaves and of rosemary. For comparative purposes also preparations with arbutin were produced in which propylene glycol was introduced instead of glycol plant extracts. The assumption of the carried out study was to investigate physicochemical properties of model formulations, estimation of arbutin pharmaceutical availability from the suggested formulations and the assessment of the effect of glycol plant extract components on the process of arbutin diffusion from the produced hydrogel formulations. The formulation viscosity parameters were determined using cone-plate digital rheometer. Gravimetric method was applied to estimate the kinetics of volatile components from the preparations. Potentiometric method was used to measure pH. The rate of arbutin release through a semipermeable membrane to the acceptor fluid was tested in vitro. Spectrophotometric method was used for the determination of the quantity of the released therapeutic substance at defined time intervals. All the proposed formulations are viscoelastic systems having yield stress. There is a strict dependence between rheological properties characterizing the tested hydrogels and the quantity of the arbutin released from them. The process of arbutin release to the acceptor fluid through a semipermeable membrane was most effective from the formulation containing glycol extract of ginkgo (F1A+M).
Arbutin/chemistry , Bleaching Agents/chemistry , Hydrogels/chemistry , Models, Chemical , Phytotherapy , Plant Extracts/chemistry , Skin Pigmentation/drug effects , Administration, Topical , Arbutin/administration & dosage , Bleaching Agents/administration & dosage , Chemistry, Pharmaceutical , Ginkgo biloba , Hydrogels/administration & dosage , Hydrogen-Ion Concentration , Oils, Volatile , Plant Extracts/administration & dosage , Rheology , Rosmarinus
An attempt was made to estimate pharmaceutical availability of the components of dry extract of bearberry from model dermatological preparations of skin-bleaching activity. Formulations containing in their composition dry extract of bearberry were produced for this purpose. The preparations were produced on the base of two kinds of Carbopol: Carbopol Ultrez 10, Carbopol 980. Physicochemical properties of the produced preparations were tested. Viscosity parameters were determined using digital cone-plate rheometer. Gravimetric method was used to estimate the kinetics of volatile components from the preparations. Potentiometric method was applied to measure pH of the produced hydrogels. The rate of release of the dry extract components through a semipermeable membrane to the acceptor fluid was tested in vitro. Spectrophotometric method was used to determine the amount of released therapeutic substance at defined time intervals. The obtained results indicate that the kind of the applied gelating substance has a significant influence on rheological parameters and on the process of release of therapeutic substances from model hydrogels. The formulation with dry extract of bearberry on Carbopol Ultrez 10 base demonstrates higher value of the area under the curve of therapeutic substances release to acceptor fluid than the formulation produced on Carbopol 980 base. Also more beneficial rheological parameters of application were obtained for formulation F1-M (lower value of structural viscosity and yield stress). The suggested model formulations with dry extract ofbearberry of confirmed skin-bleaching effect may be the base for offering a new line of dermatological preparations applied in the treatment of melanoderma.
Arctostaphylos/chemistry , Bleaching Agents/chemistry , Drug Carriers/chemistry , Hydrogels/chemistry , Plant Extracts/chemistry , Polyvinyls/chemistry , Acrylic Resins , Area Under Curve , Biological Availability , Chemistry, Pharmaceutical , Diffusion , Hydrogen-Ion Concentration , Rheology , Spectrophotometry , Viscosity
