Electrochemical behavior of ferrocene in ionic liquid media

Chemistry and applicability of ionic liquids (IL), - organic salts with low melting point - are in the focus of interest today. The ILs with melting point below room temperature are expected to be good solvents. Their applicability in organic synthetic work, in separation processes as well as in electrochemistry is very promising. In the work reported here the voltammetric behavior of ferrocene in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM+ PF6-) ionic liquid has been investigated. Conventional size and micro platinum and carbon electrodes were employed in CV and in chronoamperometric measurements. Karl Fischer method was used for the determination of water content of the solvent. Voltammetric measurements without addition of background electrolyte could be carried out in (BMIM+ PF6-) ionic liquid. A broad potential window could be used. Concentration dependence of the electrochemically determined diffusion coefficient of the ferrocene was observed.     

Calorimetric and Microstructural Investigation of Frozen Hydrated Gluten

The thermal and microstructural properties of frozen hydrated gluten were studied by using differential scanning calorimetry (DSC), modulated DSC, and low-temperature scanning electron microscopy (cryo-SEM). This work was undertaken to investigate the thermal transitions observed in frozen hydrated gluten and relate them to its microstructure. The minor peak that is observed just before the major endotherm (melting of bulk ice) was assigned to the melting of ice that is confined to capillaries formed by gluten. The Defay–Prigogine theory for the depression of melting point of fluids confined in capillaries was put forward in order to explain the calorimetric results. The pore radius size of the capillaries was calculated by using four different empirical models. Kinetic analysis of the growth of the pore radius size revealed that it follows first-order kinetics. Cryo-SEM observations revealed that gluten forms a continuous homogeneous and not fibrous network. Results of the present investigation showed that is impossible to assign a T _g value for hydrated frozen gluten because of the wide temperature range over which the gluten matrix vitrifies, and therefore the construction of state diagrams is not feasible at subzero temperatures for this material. Furthermore, the gluten matrix is deteriorated with two different mechanisms from ice recrystallization, one that results from the growth of ice that is confined in capillaries and the other from the growth of bulk ice.     

Manifestation of the size effect during crystallization and melting of dispersed water in native and amorphous starches with various degrees of hydration

Differential scanning calorimetry (DSC) was used to study the melting and crystallization of frozen water dispersed in humid potato starch. Melting and crystallization temperatures and heats as functions of the degree of hydration of the starch were obtained for native and amorphous starch states. Manifestations of the size effect were observed in the dependences of heat for the processes in both starch states. Crystallization and melting heats of frozen water were found to change nonlinearly with the increasing degree of hydration in all cases. In contrast, a size effect in the dependences of melting and crystallization temperatures of frozen water was detected only for native starch. Reasons responsible for the absence of a size effect in the amorphous state were considered. Hysteresis, which is characteristic of small particles, was observed upon melting and crystallization of frozen water and its manifestation strongly differed in the native and amorphous states of potato starch.     

Effects of a type I antifreeze protein (AFP) on the melting of frozen AFP and AFP+solute aqueous solutions studied by NMR microimaging experiment

The effects of a type I AFP on the bulk melting of frozen AFP solutions and frozen AFP+solute solutions were studied through an NMR microimaging experiment. The solutes studied include sodium chloride and glucose and the amino acids alanine, threonine, arginine, and aspartic acid. We found that the AFP is able to induce the bulk melting of the frozen AFP solutions at temperatures lower than 0 °C and can also keep the ice melted at higher temperatures in the AFP+solute solutions than those in the corresponding solute solutions. The latter shows that the ice phases were in super-heated states in the frozen AFP+solute solutions. We have tried to understand the first experimental phenomenon via the recent theoretical prediction that type I AFP can induce the local melting of ice upon adsorption to ice surfaces. The latter experimental phenomenon was explained with the hypothesis that the adsorption of AFP to ice surfaces introduces a less hydrophilic water-AFP-ice interfacial region, which repels the ionic/hydrophilic solutes. Thus, this interfacial region formed an intermediate chemical potential layer between the water phase and the ice phase, which prevented the transfer of water from the ice phase to the water phase. We have also attempted to understand the significance of the observed melting phenomena to the survival of organisms that express AFPs over cold winters.     

Determination of unfrozen water in winter cereals at subfreezing temperatures

The freezing of water in acclimated and nonacclimated cereals was studied using pulsed nuclear magnetic resonance spectroscopy. The quantity of unfreezable water per unit dry matter was not strongly dependent on the degree of cold acclimation. In contrast, the fraction of water frozen which was tolerated by nonacclimated winter cereals and by an acclimated spring wheat (Triticum aestivum L.) was less than in acclimated hardy cereals. The freezing curves had the following form:L_T = L₀ΔTm/T + KL_T and L₀ are liquid water per unit dry matter at T and 0 C, respectively. ΔTm is the melting point depression and K is the liquid water which does not freeze.     

Evidence for Ideal and Non-Ideal Equilibrium Freezing of Leaf Water in Frosthardy Ivy (Hedera helix) and Winter Barley (Hordeum vulgare)

Temperature dependences of leaf water potentials (ψ_leaf) of frozen leaves of frosthardy ivy and winter barley were determined psychrometrically and found to coincide with the respective water potentials of ice which were obtained using the same technique. The water potentials of ice showed good agreement with theoretically established data. Analysis of the components of ψ of frozen leaves of Hedera helix revealed ideal equilibrium freezing, i.e. the governing of the relative content of liquid (or frozen) water solely by the osmotic potential. In winter barley, by contrast, a negative pressure potential was demonstrated to contribute to ψ_leaf. even under conditions of moderate frost. This reduced the degree of protoplast dehydration and the extent to which the concentrations of the cellular solutes rose. Such a freezing behavior is termed non-ideal equilibrium freezing. Depending on the original content of leaf water, the volume increments of liquid water due to the negative pressure potential amounted up to 10% at ?6 °C and even more at a lower temperature. In addition to the experimental data, a theoretical treatment of psychrometry at subzero temperatures is presented.     

Effect of temperature on cold-hardiness and tissue ice formation in the adult chrysomelid beetle Melasoma collaris L

The freeze-tolerant chrysomelid beetle Melasoma collaris overwinters in plant litter on windswept ridges or covered with snow for 8-9 months in the Norwegian alpine region. Lower lethal temperature, supercooling and melting point depression were correlated to accumulation of glycerol. The lower limit of freeze tolerance was associated with the freezing of 73-75% body water. About 23-15.5% of the body water was osmotically inactive, and the highest percentage was revealed in individuals depleted of glycerol at 21 degrees C. A shift in cooling rate from 1 degrees Cmin(-1) to 1 degrees C every 13.5min lowered nucleating temperature markedly. The alteration in nucleating activity probably arises from the structure of the haemolymph nucleating agent that functions to slow embryo growth at the slow cooling rate. An enhanced supercooling is particularly beneficial in autumn before M. collaris has accumulated glycerol, since supercooled individuals accumulate glycerol in higher concentrations than frozen ones. Freezing at higher temperatures is probably a better survival strategy during brief intervals with pronounced decrease in air temperature.     

Effect of melatonin and caffeine interaction on caffeine induced oxidative stress and sleep disorders

Effect of interaction of melatonin and caffeine on caffeine induced oxidative stress and sleep disorders was studied. Fifteen wistar rats were randomly assigned into three study groups. The animals in group 1 (the control) received a placebo of 10.0 ml distilled water via gastric intubation. The hosts in groups 2 and 3 were treated with 100 mg caffeine/ kg, or melatonin/ kg, respectively, in a total volume of 10.0 ml vehicle. The experiment lasted for 30 days. One day after the final exposure, the animals were euthanized by inhalation of overdose of chloroform. Blood was collected by cardiac puncture. Serum was obtained by centrifugation (6000 Xg, 30 mins), and used for serum total protein and serum blood urea nitrogen levels. The brain of each rat was also harvested and processed into whole homogenate, frozen in liquid nitrogen (N2), and maintained at -80oC until used for total brain cholesterol and tryptophan levels. The results showed that interaction of melatonin and caffeine enhanced protein synthesis; stimulated gonadotrophin release, and could be used as oral contraceptive for women, and may be beneficial in the treatment of impotence (androgen depression), leading to improved reproductive and sex life; stimulated tryptophan metabolism, which prevents vitamin B6 deficiency, anemia, negative nitrogen balance, tissue wasting and accumulation of xanthurenic acid, which promotes sleep; and could be beneficial in the treatment of hyper cholesterolemia, thereby preventing coronary heart disease, and post menopausal osteoporosis.     

Are nanometric films of liquid undercooled interfacial water bio-relevant?

It is known that life processes below the melting point temperature can actively evolve and establish in micrometer-sized (and larger) veins and structures in ice and permafrost soil, filled with unfrozen water. Thermodynamic arguments and experimental results indicate the existence of much smaller nanometer-sized thin films of undercooled liquid interfacial (ULI) water on surfaces of micrometer sized and larger mineral particles and microbes in icy environments far below the melting point temperature. This liquid interfacial water can be described in terms of a freezing point depression, which is due to the interfacial pressure of van der Waals forces. The physics behind the possibly also life supporting capability of nanometric films of undercooled liquid interfacial water, which also can “mantle” the surfaces of the much larger and micrometer-sized microbes, is discussed. As described, biological processes do not necessarily have to proceed in the “bulk” of the thin interfacial water, as in “vinical” water and in the micrometer-sized veins e.g., but they can be supported or are even made possible already by covering thin mantles of liquid interfacial water. These can provide liquid water for metabolic processes and act as carrier for the necessary transport of nutrients and waste. ULI water supports two different and possibly biologically relevant transport processes: 2D molecular diffusion in the interfacial film, and flow-like due to regelation. ULI-water, which is “lost” by transport into microbes, e.g., will be refilled from the neighbouring ice. In this way, the nanometric liquid environment of microbes in ULI-water is comparable to that of microbes in bulk water. Another probably also biologically relevant property of ULI is, depending on the hydrophobic or hydrophilic character of the surfaces, that it is of lower density (LDL) or higher density (HDL) than bulk water.Furthermore, capillary effects and ions in ULI-water solutions can support, enhance, and stabilize the formation of layers of interfacial water. A more detailed future investigation of the possible support of life processes by nanometric ULI water in ice is a challenge to current cryomicrobiology. Related results of Rivkina et al. [22] indeed indicate that life processes can remain active at water contents corresponding to about or less than two monolayers of ULI water.     

Sequential chromosome analysis of Walker Carcinosarcoma-256 implanted into rats after frozen storage

The Walker Carcinosarcoma-256 was preserved for 404 days at liquid nitrogen temperature. The cytological analysis of frozen cells was performed sequentially. The modal chromosome number was constantly 57 in each frozen generation. The karyotype constitutions were also stable throughout the experiments. The 6 marker chromosomes, i.e., largest submetacentric, large metacentric, large submetacentric, medium-sized metacentric, medium-sized submetacentric, and small satellited telocentric were always confirmed in each of the frozen cells analyzed. No differences existed in the results of the chromosomal observations of the frozen cells and the stock cells of the continuous animal-passaged line. The frozen-thawed specimens of cell suspension resulted in as high a percentage of successful transplants into rats as small pieces of tumor tissue. It was clearly demonstrated that tumor cells of solid Walker rat tumor, when placed in suspension, can be stored at liquid nitrogen temperatures for a year or more without chromosomal abnormality.     

冰冻切片技术在海滨锦葵细胞学研究中的应用

为解决普通石蜡切片观察植物样品繁琐与耗时长的问题,利用改进的蔗糖保护—液氮速冻切片法,进行海滨锦葵不同器官细胞学研究。结果表明:(1)适合于海滨锦葵不同器官的最适蔗糖浓度不同,适于含水量较大的营养器官(根、茎和叶)的最适蔗糖浓度比含水量较小的花器官(柱头裂片、花柱、子房和花药)高。(2)利用最适蔗糖浓度的蔗糖保护-液氮速冻切片方法,获得了完整而清晰的海滨锦葵各器官组织细胞结构的切片;海滨锦葵具有典型的双子叶草本植物营养器官的组织细胞结构特征,花柱为闭合型花柱,子房为多室复子房。表明基于蔗糖保护-液氮速冻的冰冻切片技术在植物细胞学研究中具有广阔的应用前景。     

Dehydration of earthworm cocoons exposed to cold: a novel cold hardiness mechanism

Mechanisms involved in cold hardiness of cocoons of the lumbricid earthworm Dendrobaena octaedra were elucidated by osmometric and calorimetric studies of water relations in cocoons exposed to subzero temperatures. Fully hydrated cocoons contained ca. 3 g water · g dry weight^-1; about 15% of this water (0.5 g·g dry weight^-1) was osmotically inactive or bound. The melting point of the cocoon fluids in fully hydrated cocoons was-0.20°C. Exposure to frozen surroundings initially resulted in supercooling of the cocoons dehydrated (as a result of the vapour pressure difference at a given temperature between supercooled water and ice) to an extent where the vapour pressure of water in the body fluids was in equilibrium with the surrounding ice. This resulted in a profound dehydration of the cocoons, even at mild freezing exposures, and a concomitant slight reduction in the amount of osmotically inactive water. At temperatures around-8°C, which cocoons readily survive, almost all (>97%) osmotically active water had been withdrawn from the cocoons. It is suggested that cold injuries in D. octaedra cocoons observed at still lower temperatures may be related to the degree of dehydration, and possibly to the loss of all osmotically active water. The study indicates that ice formation in the tissues is prevented by equilibrating the body fluid melting point with the exposure temperature. This winter survival mechanism does not conform with the freeze tolerance/freeze avoidance classification generally applied to cold-hardy poikilotherms. Implications of this cold hardiness mechanism for other semi-terrestrial invertebrates are discussed.Abbreviations DSC differential scanning calorimetry - dw dry weight - MP melting point(s) - II water potential - R universal gas constant - T absolute temperature - V specific volume of water     

Solid phase synthesis of oligodeoxyribonucleoside phosphorodithioates from thiophosphoramidites.

Oligonucleoside phosphorodithioates 1 are modified DNA sequences with potential use as antisense oligonucleotides. The preparation of up to 20-mers containing all four bases by solid phase synthesis is described, with details on the preparation of the four monomer units (protected nucleoside thiophosphoramidites 2), the conditions used for the assembly of the strands with up to 19 phosphorodithioate linkages, and the purification and characterisation of the products. Full-length homogeneity of HPLC-purified all-phosphorodithioate products is demonstrated by PAGE, but 31P NMR discloses the presence of phosphorothioate impurities (typically 8-9%), the origin of which is discussed. Oligonucleoside phosphorodithioates are freely soluble in water at neutral or basic pH, and are very stable towards oxidation, hydrolysis, and nuclease cleavage. Their ability to hybridize to complementary DNA has been studied by UV melting point (Tm) measurements. The observed depression of Tm, 0.5-2 degrees C per phosphorodithioate linkage, is higher that the 0.4-0.6 degrees C found for phosphorothioates.     

天山北坡积雪消融对不同冻融阶段土壤温湿度的影响

积雪作为一种特殊的覆被,直接影响着土壤温度、土壤水分分布及其冻结深度、冻结速率等,影响当地的生态水文过程。利用2017年11月1日至2018年3月31日天山北坡伊犁阿热都拜流域的土壤含水率资料,划分土壤不同冻融阶段,结合积雪不同阶段,进而分析积雪消融对季节性冻土温湿度的影响。结果表明:在整个土壤冻融期间,土壤温湿度的变化取决于积雪深度、大气温度和雪面温度的高低,且与其稳定性有关。土壤冻结阶段,土壤温湿度持续下降,表层土壤温湿度受气温影响较大,且波动明显,而深层土壤的温湿度变化平缓;土壤完全冻结时,有稳定积雪覆盖,由于积雪的高反射性、低导热性,影响着地气之间的热量传递,因此土壤的温湿度变化较为平稳,积雪有一定的保温作用;冻土消融阶段,气温回升,积雪消融,地表出露,各层土壤温度随气温变化而变化,且越靠近地表,土壤温度越高,变幅越大,与冻结期完全相反。由于融雪水的下渗,土壤湿度快速增加。进一步分析积雪与土壤温湿度的相关性得出,积雪对土壤温湿度的影响分不同时期,对土壤温度的影响主要在积雪覆盖时,对土壤湿度的影响主要是在积雪消融时期,这对于研究该地生态水文循环及后续融雪性洪水的模拟与预报具有一定的参考价值。     

Bioprospecting for microbial products that affect ice crystal formation and growth

At low temperatures, some organisms produce proteins that affect ice nucleation, ice crystal structure, and/or the process of recrystallization. Based on their ice-interacting properties, these proteins provide an advantage to species that commonly experience the phase change from water to ice or rarely experience temperatures above the melting point. Substances that bind, inhibit or enhance, and control the size, shape, and growth of ice crystals could offer new possibilities for a number of agricultural, biomedical, and industrial applications. Since their discovery more than 40 years ago, ice nucleating and structuring proteins have been used in cryopreservation, frozen food preparation, transgenic crops, and even weather modification. Ice-interacting proteins have demonstrated commercial value in industrial applications; however, the full biotechnological potential of these products has yet to be fully realized. The Earth’s cold biosphere contains an almost endless diversity of microorganisms to bioprospect for microbial compounds with novel ice-interacting properties. Microorganisms are the most appropriate biochemical factories to cost effectively produce ice nucleating and structuring proteins on large commercial scales.     

Estimation of Water Diffusion Coefficients in Freeze-Concentrated Matrices of Sugar Solutions Using Molecular Dynamics: Correlation Between Estimated Diffusion Coefficients and Measured Ice-Crystal Recrystallization Rates

The diffusion coefficient of the water component in a freeze-concentrated matrix is a useful parameter for predicting and controlling the recrystallization rate of ice crystals in sugar solutions relevant to frozen desserts. Herein, application of molecular dynamics (MD) for estimating the water diffusion coefficient in a freeze-concentrated matrix of sugar solutions is described. Diffusion coefficients evaluated using MD with the optimized potentials for liquid simulations all atom force field and water models of three types (simple point charge, simple point charge extended, and transferable intermolecular potential-4 point) show a good positive linear relation with measured values, indicating that the MD methods used in this study are useful for predicting differences in water diffusion coefficients in a sugar freeze-concentrated matrix. Furthermore, similarly to measured values, the estimated diffusion coefficients show a good positive correlation with recrystallization rates of ice crystals, which suggests that MD is useful to predict differences in recrystallization rates of ice crystals in frozen sugar solutions.     

Explorative screening of complex microbial communities by real-time 16S rDNA restriction fragment melting curve analyses

We have developed restriction fragment melting curve analyses (RFMCA), which is a novel method for the real-time analysis of microbial communities. The major advantage of RFMCA compared to, for example, terminal restriction fragment length polymorphism (T-RFLP) or temperature/denaturing gradient gel electrophoresis (TGGE/DGGE) is that the physical separation of DNA fragments is avoided. The RFMCA detection is done by melting point analyses in closed tube systems, which enables high-throughput applications. The robustness of RFMCA was demonstrated by analyzing both mixtures of known samples and the microbial communities in the cecal content of poultry. Our conclusions are that RFMCA is robust, gives a relatively high resolution, and has the potential for high-throughput explorative screenings of microbial communities and large clone libraries.     

PITFALLS IN THE USE OF RAPID FREEZING FOR STOPPING BRAIN AND SPINAL CORD METABOLISM IN RAT AND MOUSE

The rate at which the metabolism is stopped by means of freezing in Freon-12 (–150°C) was studied in various areas of the rat and mouse CNS, using changes in temperature and levels of glucose and lactate as parameters for this rate. The rat cerebral cortex was frozen after 0.5 min while the hypothalamus reached 0°C after more than 1.5 min. The skin on the skull was found to be the most important temperature isolator for the cortex. Substrate levels can be studied in this area only if this piece of skin is removed previously. In the mouse, the cerebral cortex was frozen after 6 s, the hypothalamus after 0.5 min. The lumbar level of the mouse spinal cord was frozen after 15 s, the cervical level only after 47 s. Liquid nitrogen alone cooled the mouse cerebral cortex at least as fast as did Freon at its melting point. A gradual decrease from dorsal to ventral was observed in the glucose level of the molecular layer of the mouse cerebellum. The existence of a freezing front, moving slowly from dorsal to ventral, and its consequences for the measured levels of biologically labile substrates, are discussed.     

Effect of cryoprotectants on the activity of hemolymph nucleating agents in physical solutions

The ability of 11 different organic solutes in physical solution to mask the effect of nucleating agents from hemolymph of freezing tolerant insects was tested. The masking effect was tested by measuring the supercooling points of samples with various solute concentrations, with and without hemolymph. Hemolymph was obtained from freeze-tolerant Eleodes blanchardi tenebrionid beetles.The depressive effect of the solutes on the supercooling points was nearly equivalent to the corresponding melting point depression, indicating that the depression was due only to the colligative properties of the solutes. Thus, no ability for nucleator masking was demonstrated.