Nonlinear elasticity and friction of liquid-crystalline polymer monolayers

In the present paper we consider nonlinear elasticity and friction of grafted persistent chains, which are highly stretched in the normal to the surface direction due to orientational interactions. We examine the normal and the lateral forces both in equilibrium and under shear sliding when the monolayer is confined by a bare surface. We show that in the confined monolayer in equilibrium the tilted orientation of the director becomes stable. In the sliding regime the friction force passes through a maximum value. The additional normal force in the sliding regime, when the distance between the surfaces is fixed, is also considered. We show that this force is attractive for small velocities and becomes repulsive for high velocities after the friction force passes through the maximum value

Regulation of intracellular pH during anoxia in rice coleoptiles in acidic and near neutral conditions

Rice coleoptiles, renowned for anoxia tolerance, were hypoxically pretreated, excised, ‘healed’, and then exposed to a combination of anoxia and pH 3.5. The putative acid load was confirmed by net effluxes of K+ to the medium, with concurrent net decreases of H+ in the medium, presumably mainly due to H+ influx. Yet the coleoptiles survived the combination of anoxia and pH 3.5 for at least 90 h, and even for at least 40 h when the energy crisis, inherent to anoxia, had been aggravated by supplying the coleoptiles with 2.5 mM rather than 50 mM glucose. Even in the case of coleoptiles with 2.5 mM glucose, an accumulation ratio of 6 for Cl– was attained at 4 h after the start of re-aeration, implying plasma membrane integrity was either maintained during anoxia, or rapidly restored after a return to aerated conditions. Cytoplasmic pH and vacuolar pH were measured using in vivo 31P nuclear magnetic resonance spectroscopy with 50 mM glucose in the basal perfusion medium. After 60 h in anoxia, external pH was suddenly decreased from 6.5 to 3.5, but cytoplasmic pH only decreased from 7.35 to 7.2 during the first 2 h and then remained steady for the next 16 h. During the first 3 h at pH 3.5, vacuolar pH decreased from 5.7 to 5.25 and then stabilized. After 18 h at pH 3.5, the initial values of cytoplasmic pH and vacuolar pH were rapidly restored, both upon a return to pH 6.5 while maintaining anoxia and after subsequent return to aerated solution. Summing up, rice coleoptiles exposed to a combination of anoxia and pH 3.5 retained pH regulation and cellular compartmentation, demonstrating tolerance to anoxia even during the acid load imposed by exposure to pH 3.5

Magneto-sensitive elastomers in a homogeneous magnetic field: a regular rectangular lattice model

A theory of mechanical behaviour of the magneto-sensitive elastomers is developed in the framework of a linear elasticity approach. Using a regular rectangular lattice model, different spatial distributions of magnetic particles within a polymer matrix are considered: isotropic, chain-like and plane-like. It is shown that interaction between the magnetic particles results in the contraction of an elastomer along the homogeneous magnetic field. With increasing magnetic field the shear modulus for the shear deformation perpendicular to the magnetic field increases for all spatial distributions of magnetic particles. At the same time, with increasing magnetic field the Young's modulus for tensile deformation along the magnetic field decreases for both chain-like and isotropic distributions of magnetic particles and increases for the plane-like distribution of magnetic particles.Comment: 38 pages, 15 figure

pH regulation in anoxic rice coleoptiles at pH 3.5: biochemical pHstats and net H+ influx in the absence and presence of NO3−

During anoxia, cytoplasmic pH regulation is crucial. Mechanisms of pH regulation were studied in the coleoptile of rice exposed to anoxia and pH 3.5, resulting in H+ influx. Germinating rice seedlings survived a combination of anoxia and exposure to pH 3.5 for at least 4 d, although development was retarded and net K+ efflux was continuous. Further experiments used excised coleoptile tips (7–10 mm) in anoxia at pH 6.5 or 3.5, either without or with 0.2 mM NO3−, which distinguished two processes involved in pH regulation. Net H+ influx (μmol g−1 fresh weight h−1) for coleoptiles with NO3− was ∼1.55 over the first 24 h, being about twice that in the absence of NO3−, but then decreased to 0.5–0.9 as net NO3− uptake declined from ∼1.3 to 0.5, indicating reduced uptake via H+–NO3− symports. NO3− reduction presumably functioned as a biochemical pHstat. A second biochemical pHstat consisted of malate and succinate, and their concentrations decreased substantially with time after exposure to pH 3.5. In anoxic coleoptiles, K+ balancing the organic anions was effluxed to the medium as organic anions declined, and this efflux rate was independent of NO3− supply. Thus, biochemical pHstats and reduced net H+ influx across the plasma membrane are important features contributing to pH regulation in anoxia-tolerant rice coleoptiles at pH 3.5

Chemorheology of photopolymerizable acrylates using a modified Boltzmann sigmoidal model

Experiments were conducted to evaluate the influence of ambient photoconversion on rheology for a range of photopolymerizable urethane dimethacrylate (UDMA) resins containing varying amounts of three comonomers including 1,6 hexane diol-dimethacrylate (HDDMA), an alkoxylated cyclohexane dimethanol diacrylate monomer (CD-582), and hydroxyethyl methacrylate (HEMA). Experiments were performed both as a function of composition and time-dependent dose varying the intensity using a photorheometer. A semilog-based sigmoidal model allowed the determination of four physical model parameters to define the relationship between reaction kinetics and its dynamic influence on viscosity. We have observed induction times and viscosity changes associated with the model that shows a trend in reaction kinetics in the following order from most to least reactive: UDMA > CD582 > HDDMA > HEMA. With increasing amounts of reactive diluent included in the formulation, the kinetics of reaction was more sluggish. The value of this sigmoidal model is that it could help define formulation and process conditions most likely to control crosslinking to maximize dimensional stability or other thermophysical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2319–2325, 2008Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/61230/1/21563_ftp.pd

Эффективность дорназы альфа (пульмозим) у детей с хроническими заболеваниями легких

Effect of Pulmozyme is studied in 28 children aged 8 to 16 with chronic lung diseases (14 children with congenital bronchi defects, 6 ones with the Kartagener's syndrome, 2 ones with hypogammaglobulinemia, 6 ones with chronic pneumonia). The drug was given in the dose of 2.5 mg once a day by inhalation. The treatment course was 10 days. Eight children received endobronchial Pulmozyme during bronchoscopic procedure. The sputum viscosity was tested with a rotary viscometer Reotest 2.1 (Germany) using a cone — flat working joint under the standard temperature of 20°C.The Pulmozyme therapy caused a positive clinical dynamics in all the children such as easier sputum expectoration due to reduction of its viscosity resulted in more effective bronchial drainage and improvement in the patients' general status. The study in vitro showed Pulmozyme to diminish the sputum viscosity and structuring from 104 to 103—102 mPa/s; the mucolytic effect of Pulmozyme kept for a day. The sputum viscosity in vitro was investigated before the drug inhalation, just after and in 4 and 8 hrs. The maximal viscosity decrease from 104 to 103—102 mPa/s was found 4 hrs after the inhalation followed by the viscosity growth up to the initial level 8 hrs after the inhalation. The adverse effect of Pulmozyme was noted in 1 patient (sore throat). The endobronchial delivery provided fast mucolytic effect and an improved expectoration after the bronchoscopic procedure.Действие пульмозима исследовано у 28 детей в возрасте от 8 до 16 лет с хроническими заболеваниями легких (14 детей с врожденными пороками развития бронхов, 6 с синдромом Картагенера, 2 с гипогаммаглобулинемией, 6 с хронической пневмонией). Препарат назначался в дозе 2,5 мг в ингаляции 1 раз в сутки. Курс лечения составлял 10 дней. 8 детям пульмозим вводился эндобронхиально при бронхоскопии. Вязкость мокроты исследована на ротационном вискозиметре Реотест 2.1 (Германия) с использованием рабочего узла конус-плоскость при стандартной температуре 20°С.На фоне лечения пульмозимом у всех больных была отмечена положительная клиническая динамика, выражавшаяся в легком откашливании мокроты за счет уменьшения ее вязкости, что приводило к эффективному дренажу трахеобронхиального дерева и улучшало общее состояние пациентов. При исследованиях in vitro показано, что добавление пульмозима приводит к снижению вязкости и степени структурирования мокроты с 104 до 103— 102 мПа/с; муколитический эффект пульмозима сохраняется в течение суток. In vivo вязкость мокроты исследована до ингаляции, сразу после и через 4 и 8 ч. Максимальное снижение вязкости с 104 до 103—102 мПа/с отмечено через 4 ч после ингаляции с последующим нарастанием вязкости практически до исходного уровня через 8 ч после ингаляции. Побочный эффект отмечены у 1 больного (першение в горле). При эндобронхиальном введении отмечен быстрый муколитический эффект и улучшение экспекторации после бронхоскопии

Evidence for the adaptation of protein pH-dependence to subcellular pH

<p>Abstract</p> <p>Background</p> <p>The availability of genome sequences, and inferred protein coding genes, has led to several proteome-wide studies of isoelectric points. Generally, isoelectric points are distributed following variations on a biomodal theme that originates from the predominant acid and base amino acid sidechain pKas. The relative populations of the peaks in such distributions may correlate with environment, either for a whole organism or for subcellular compartments. There is also a tendency for isoelectric points averaged over a subcellular location to not coincide with the local pH, which could be related to solubility. We now calculate the correlation of other pH-dependent properties, calculated from 3D structure, with subcellular pH.</p> <p>Results</p> <p>For proteins with known structure and subcellular annotation, the predicted pH at which a protein is most stable, averaged over a location, gives a significantly better correlation with subcellular pH than does isoelectric point. This observation relates to the cumulative properties of proteins, since maximal stability for individual proteins follows the bimodal isoelectric point distribution. Histidine residue location underlies the correlation, a conclusion that is tested against a background of proteins randomised with respect to this feature, and for which the observed correlation drops substantially.</p> <p>Conclusion</p> <p>There exists a constraint on protein pH-dependence, in relation to the local pH, that is manifested in the pKa distribution of histidine sub-proteomes. This is discussed in terms of protein stability, pH homeostasis, and fluctuations in proton concentration.</p