OPTICAL INVESTIGATIONS OF PHASE TRANSITIONS IN (NH4) 2 SbF5 CRYSTAL

Results of optical thickness and refractive indices measurements for (NH4)2SbF5 crystal in the temperature range 100-310 K are presented. The measurements were done with interference method using He-Ne laser (λ = 632.8 nm). At To = 292 K and Ta = 168 K two continuous phase transitions with critical indices /3 1 = 0.38 and β2 ≤ 0.57 were observed. Additional anomaly of temperature changes of interference order with maximum at Ta 132 K were found. This anomaly resembles a diffused transition. Temperature-averaged values of derivatives of refractive indices dn g /dT = -3.3 x 10 -5 K and dn m /dT = -2.9 x 10 -5 K -1 evidenced a decrease in optical anisotropy (birefringence) along the b-axis on heating run

Optical and electric manifestations of incommensurate phase in NH₄HSeO₄ crystals

Temperature dependences of the optical path difference by the variable part of refractive index D = (n − 1)l and the components ε′ and ε′′ of complex dielectric permittivity for NH₄HSeO₄ single crystal are studied in the temperature range of 220–300 K. Anomalous behaviour of these dependences in the range of incommensurate phase 250–262 K was observed. Analysis of the results of dielectric investigation predicts a considerable decrease of the coefficient of elastic stiffness C in the narrow temperature range of 256–260 K at the transition from the paraelectric to incommensurate phase.Досліджено температурні залежності різниці оптичних шляхів за змінною частиною показника заломлення D = (n − 1)l та компонент ε′ і ε′′ комплексної діелектричної проникливості для монокристала NH₄HSeO₄ в області температур 220–300 K. Виявлено аномальну поведінку цих залежностей в області несумірної фази 250–262 K. Аналіз результатів діелектричних досліджень свідчить про значне зменшення коефіцієнта пружної жорсткості C у вузькій температурній області 256–260 K при переході з параелектричної у несумірну фазу

Thermodynamics and dielectric anomalies of DMAAS and DMAGaS crystals in the region of phase transitions (Landau theory approach)

A simple description of thermodynamics of DMAAS and DMAGaS ferroelectric crystals by means of Landau expansion is proposed. Conditions of occurrence of phase transitions are established and their temperatures are obtained. The influence of external hydrostatic pressure on phase transitions is described. The temperature behaviour of dielectric susceptibility components and their anomalies in the vicinity of phase transition points are investigated. The results obtained are compared with the experimental data.Запропоновано простий опис термодинаміки сегнетоелектричних кристалів типу DMAAS і DMAGaS за допомогою розкладу Ландау. Встановлено умови реалізації фазових переходів і отримано їх температури. Описано зміни температур фазових переходів під впливом зовнішнього всестороннього тиску. Досліджено температурну поведінку компонент діелектричної сприйнятливості та їх аномалії в околі точок фазових переходів. Отримані результати порівнюються з експериментальними даними

Tuning a sign of magnetoelectric coupling in paramagnetic NH2(CH3)2Al1-xCrx(SO4)*6H2O crystals by metal ion substitution

Hybrid organometallic systems offer a wide range of functionalities, including magnetoelectric interactions. However, the ability to design on-demand ME coupling remains challenging despite a variety of host-guest configurations and ME phases coexistence possibilities. Here, we report the effect of metal-ion substitution on the magnetic and electric properties in the paramagnetic ferroelectric DMAAS crystals. Doing so we are able to induce and even tune a sign of the ME interactions in the paramagnetic ferroelectric state. Both studied samples with 6.5% and 20% of Cr become paramagnetic, contrary to the initial diamagnetic compound. Due to the isomorphous substitution with Cr the ferroelectric phase transition temperature increases nonlinearly, with the shift being larger for the sample with Cr content of 6.5%. A magnetic field applied along the polar c axis increases ferroelectricity for this sample and shifts Tc to higher values, while inverse effects are observed for sample containing 20% of Cr. The ME coupling coefficient of 1.7ns/m found for a crystal with 20% of Cr is among the highest reported up to now. The observed sign change of ME coupling coefficient with a small change in Cr content paves the way for ME coupling engineering.Comment: 7 pages, 6 figures. New Organometallic Magnetoelectric and Ferroelectric compoun

Decreased plasma nociceptin/orphanin FQ levels after acute coronary syndromes

Foregoing researches made on the N/OFQ system brought up a possible role for this system in cardiovascular regulation. In this study we examined how N/OFQ levels of the blood plasma changed in acute cardiovascular diseases. Three cardiac patient groups were created: enzyme positive acute coronary syndrome (EPACS, n = 10), enzyme negative ACS (ENACS, n = 7) and ischemic heart disease (IHD, n = 11). We compared the patients to healthy control subjects (n = 31). We found significantly lower N/OFQ levels in the EPACS [6.86 (6.21–7.38) pg/ml], ENACS [6.97 (6.87–7.01) pg/ml and IHD groups [7.58 (7.23–8.20) pg/ml] compared to the control group [8.86 (7.27–9.83) pg/ml]. A significant correlation was detected between N/OFQ and white blood cell count (WBC), platelet count (PLT), creatine kinase (CK), glutamate oxaloacetate transaminase (GOT) and cholesterol levels in the EPACS group.Decreased plasma N/OFQ is closely associated with the presence of acute cardiovascular disease, and the severity of symptoms has a significant negative correlation with the N/OFQ levels. We believe that the rate of N/OFQ depression is in association with the level of ischemic stress and the following inflammatory response. Further investigations are needed to clarify the relevance and elucidate the exact effects of the ischemic stress on the N/OFQ system

Interplay of Protein and DNA Structure Revealed in Simulations of the lac Operon

The E. coli Lac repressor is the classic textbook example of a protein that attaches to widely spaced sites along a genome and forces the intervening DNA into a loop. The short loops implicated in the regulation of the lac operon suggest the involvement of factors other than DNA and repressor in gene control. The molecular simulations presented here examine two likely structural contributions to the in-vivo looping of bacterial DNA: the distortions of the double helix introduced upon association of the highly abundant, nonspecific nucleoid protein HU and the large-scale deformations of the repressor detected in low-resolution experiments. The computations take account of the three-dimensional arrangements of nucleotides and amino acids found in crystal structures of DNA with the two proteins, the natural rest state and deformational properties of protein-free DNA, and the constraints on looping imposed by the conformation of the repressor and the orientation of bound DNA. The predicted looping propensities capture the complex, chain-length-dependent variation in repression efficacy extracted from gene expression studies and in vitro experiments and reveal unexpected chain-length-dependent variations in the uptake of HU, the deformation of repressor, and the folding of DNA. Both the opening of repressor and the presence of HU, at levels approximating those found in vivo, enhance the probability of loop formation. HU affects the global organization of the repressor and the opening of repressor influences the levels of HU binding to DNA. The length of the loop determines whether the DNA adopts antiparallel or parallel orientations on the repressor, whether the repressor is opened or closed, and how many HU molecules bind to the loop. The collective behavior of proteins and DNA is greater than the sum of the parts and hints of ways in which multiple proteins may coordinate the packaging and processing of genetic information. © 2013 Czapla et al

Tuning a sign of magnetoelectric coupling in paramagnetic NH2(CH3)(2)Al1-xCrx(SO4)(2) x 6H(2)O crystals by metal ion substitution

Hybrid organometallic systems offer a wide range of functionalities, including magnetoelectric (ME) interactions. However, the ability to design on-demand ME coupling remains challenging despite a variety of host-guest configurations and ME phases coexistence possibilities. Here, we report the effect of metal-ion substitution on the magnetic and electric properties in the paramagnetic ferroelectric NH2(CH3)(2)Al1-xCrx(SO4)(2) x 6H(2)O. Doing so we are able to induce and even tune a sign of the ME interactions, in the paramagnetic ferroelectric (FE) state. Both studied samples with x = 0.065 and x = 0.2 become paramagnetic, contrary to the initial diamagnetic compound. Due to the isomorphous substitution with Cr the ferroelectric phase transition temperature (T-c) increases nonlinearly, with the shift being larger for the 6.5% of Cr. A magnetic field applied along the polar c axis increases ferroelectricity for the x = 0.065 sample and shifts Tc to higher values, while inverse effects are observed for x = 0.2. The ME coupling coefficient alpha(ME) = 1.7 ns/m found for a crystal with Cr content of x = 0.2 is among the highest reported up to now. The observed sign change of aME with a small change in Cr content paves the way for ME coupling engineering

A Map of Dielectric Heterogeneity in a Membrane Protein: the Hetero-Oligomeric Cytochrome b 6 f Complex

The cytochrome b6f complex, a member of the cytochrome bc family that mediates energy transduction in photosynthetic and respiratory membranes, is a hetero-oligomeric complex that utilizes two pairs of b-hemes in a symmetric dimer to accomplish trans-membrane electron transfer, quinone oxidation–reduction, and generation of a proton electrochemical potential. Analysis of electron storage in this pathway, utilizing simultaneous measurement of heme reduction, and of circular dichroism (CD) spectra, to assay heme–heme interactions, implies a heterogeneous distribution of the dielectric constants that mediate electrostatic interactions between the four hemes in the complex. Crystallographic information was used to determine the identity of the interacting hemes. The Soret band CD signal is dominated by excitonic interaction between the intramonomer b-hemes, bn and bp, on the electrochemically negative and positive sides of the complex. Kinetic data imply that the most probable pathway for transfer of the two electrons needed for quinone oxidation–reduction utilizes this intramonomer heme pair, contradicting the expectation based on heme redox potentials and thermodynamics, that the two higher potential hemes bn on different monomers would be preferentially reduced. Energetically preferred intramonomer electron storage of electrons on the intramonomer b-hemes is found to require heterogeneity of interheme dielectric constants. Relative to the medium separating the two higher potential hemes bn, a relatively large dielectric constant must exist between the intramonomer b-hemes, allowing a smaller electrostatic repulsion between the reduced hemes. Heterogeneity of dielectric constants is an additional structure–function parameter of membrane protein complexes

Combined Tumor Cell-Based Vaccination and Interleukin-12 Gene Therapy Polarizes the Tumor Microenvironment in Mice

Tumor progression depends on tumor milieu, which influences neovasculature formation and immunosuppression. Combining immunotherapy with antiangiogenic/antivascular therapy might be an effective therapeutic approach. The aim of our study was to elaborate an anticancer therapeutic strategy based on the induction of immune response which leads to polarization of tumor milieu. To achieve this, we developed a tumor cell-based vaccine. CAMEL peptide was used as a B16-F10 cell death-inducing agent. The lysates were used as a vaccine to immunize mice bearing B16-F10 melanoma tumors. To further improve the therapeutic effect of the vaccine, we combined it with interleukin (IL)-12 gene therapy. IL-12, a cytokine with antiangiogenic properties, activates nonspecific and specific immune responses. We observed that combined therapy is significantly more effective (as compared with monotherapies) in inhibiting tumor growth. Furthermore, the tested combination polarizes the tumor microenvironment, which results in a switch from a proangiogenic/immunosuppressive to an antiangiogenic/immunostimulatory one. The switch manifests itself as a decreased number of tumor blood vessels, increased levels of tumor-infiltrating CD4+, CD8+ and NK cells, as well as lower level of suppressor lymphocytes (Treg). Our results suggest that polarizing tumor milieu by such combined therapy does inhibit tumor growth and seems to be a promising therapeutic strategy