Controlling spontaneous chirality in achiral materials: liquid crystal oligomers and the heliconical twist-bend nematic phase.

Liquid crystal oligomers, namely dimers, trimers and tetramers, consisting of cyanobiphenyl and benzylideneaniline-based mesogenic units connected by either linear or bent alkoxy or alkyl spacers are reported. These materials, although built from achiral molecules, show the spontaneously chiral heliconical twist-bend nematic (NTB) phase. We report the relationships between the shape of the oligomer, and the NTB phase stability, the temperature dependence of the helical pitch length and tilt angle, birefringence, and elastic constants.

Phase transitions in a high magnetic field of an odd, symmetric liquid crystal dimer having two nematic phases, N_{U} and N_{TB}, studied by NMR spectroscopy.

Both ^{1}H and ^{13}C NMR spectra have been obtained in a static magnetic field of 23.5 T on a bent-shaped dimer molecule, 1^{''},7^{''}-bis(4-cyanobiphenyl-4'-yl) nonane (CB9CB), which shows the sequence of liquid crystal phases twist-bend nematic, N_{TB}, and uniaxial nematic, N_{U}, before entering the isotropic phase. The ^{1}H spectra are used to locate the temperature at which the sample melts to form a twist-bend nematic, T_{CrN_{TB}}, and then T_{N_{U}I} when the isotropic phase is entered, both in a magnetic field of 23.5 T, and to compare these with those measured at the Earth's field. The differences between these transition temperatures are found to be zero within the error in their measurement, in stark contrast to previous measurements by Salili et al. [Phys. Rev. Lett. 116, 217801 (2016)10.1103/PhysRevLett.116.217801]. In the isotropic phase in the presence of the field the sample exists in a paranematic phase in which the molecules of CB9CB are partially ordered. The ^{1}H and ^{13}C NMR spectra in the paranematic phase are used to measure the critical temperature T* below which this phase is unstable. The spectra are also used to study the structure, molecular orientational order, and distribution of molecular conformations in the paranematic phase.

Spontaneous chirality through mixing achiral components: a twist-bend nematic phase driven by hydrogen-bonding between unlike components.

The spontaneous formation of a chiral phase via molecular recognition in a system consisting of achiral components is reported. Specifically, the liquid crystalline behaviour of two molecular complexes assembled by hydrogen bonding between a stilbazole-based template and alkoxybenzoic acids has been characterised. The complexes exhibit the heliconical twist-bend nematic phase (NTB) over a broad temperature range despite the hydrogen-bond acceptor not being liquid crystalline and the donor exhibiting the conventional achiral nematic phase.

Magnetically tunable selective reflection of light by heliconical cholesterics.

We present studies of chiral nematic liquid crystals composed of flexible dimer molecules subject to large dc magnetic fields between 0 and 31 T. We observe that these fields lead to selective reflection of light depending on temperature and magnetic field. The band of reflected wavelengths can be tuned from ultraviolet to beyond the IR-C band. A similar effect induced by electric fields has been presented previously, and was explained by a field-induced oblique-heliconical director deformation in accordance with early theoretical predictions. The use of magnetic field here instead of electric field allows precise measurements of some material constants and holds promise for wireless tuning of selective reflection.

Freezing survival, body ice content and blood composition of the freeze-tolerant European common lizard, Lacerta vivipara.

To investigate the freeze tolerance of the European common lizard, Lacerta vivipara, we froze 17 individuals to body temperatures as low as -4 degrees C under controlled laboratory conditions. The data show that this species tolerates the freezing of 50% of total body water and can survive freezing exposures of at least 24-h duration. Currently, this represents the best known development of freeze tolerance among squamate reptiles. Freezing stimulated a significant increase in blood glucose levels (16.15+/- 1.73 micromol x ml(-1) for controls versus 25.06 +/- 2.92 micromol x ml(-1) after thawing) but this increase had no significant effect on serum osmolality which was unchanged between control and freeze-exposed lizards (506.0 +/- 23.8 mosmol x l(-1) versus 501.0 +/- 25.3 mosmol x l(-1), respectively). Tests that assessed the possible presence of antifreeze proteins in lizard blood were negative. Recovery at 5 degrees C after freezing was assessed by measurements of the mean time for the return of breathing (5.9 +/- 0.5 h) and of the righting reflex (44.8 +/- 4.5 h). Because this species hibernates in wet substrates inoculative freezing may frequently occur in nature and the substantial freeze tolerance of this lizard should play a key role in its winter survival.

Influence of exercise on the activity and the distribution between free and bound forms of glycolytic and associated enzymes in tissues of horse mackerel

The effects of short-term burst (5 min at 1.8 m/s) swimming and long-term cruiser (60 min at 1.2 m/s) swimming on maximal enzyme activities and enzyme distribution between free and bound states were assessed for nine glycolytic and associated enzymes in tissues of horse mackerel, Trachurus mediterraneus ponticus. The effects of exercise were greatest in white muscle. The activities of phosphofructokinase (PFK), pyruvate kinase (PK), fructose-1,6-bisphosphatase (FBPase), and phosphoglucomutase (PGM) all decreased to 47, 37, 37 and 67 percent, respectively, during 60-min exercise and all enzymes except phosphoglucoisomerase (PGI) and PGM showed a change in the extent of binding to subcellular particulate fractions during exercise. In red muscle, exercise affected the activities of PGI, FBPase, PFK, and lactate dehydrogenase (LDH) and altered percent binding of only PK and LDH. In liver, exercise increased the PK activity 2.3-fold and reduced PGI 1.7-fold only after 5 min of exercise but altered the percent binding of seven enzymes. Fewer effects were seen in brain, with changes in the activities of aldolase and PGM and in percent binding of hexokinase, PFK and PK. Changes in enzyme activities and in binding interactions with subcellular particulate matter appear to support the altered demands of tissue energy metabolism during exercise

Influence of exercise on the activity and the distribution between free and bound forms of glycolytic and associated enzymes in tissues of horse mackerel.

The effects of short-term burst (5 min at 1.8 m/s) swimming and long-term cruiser (60 min at 1.2 m/s) swimming on maximal enzyme activities and enzyme distribution between free and bound states were assessed for nine glycolytic and associated enzymes in tissues of horse mackerel, Trachurus mediterraneus ponticus. The effects of exercise were greatest in white muscle. The activities of phosphofructokinase (PFK), pyruvate kinase (PK), fructose-1,6-bisphosphatase (FBPase), and phosphoglucomutase (PGM) all decreased to 47, 37, 37 and 67%, respectively, during 60-min exercise and all enzymes except phosphoglucoisomerase (PGI) and PGM showed a change in the extent of binding to subcellular particulate fractions during exercise. In red muscle, exercise affected the activities of PGI, FBPase, PFK, and lactate dehydrogenase (LDH) and altered percent binding of only PK and LDH. In liver, exercise increased the PK activity 2.3-fold and reduced PGI 1.7-fold only after 5 min of exercise but altered the percent binding of seven enzymes. Fewer effects were seen in brain, with changes in the activities of aldolase and PGM and in percent binding of hexokinase, PFK and PK. Changes in enzyme activities and in binding interactions with subcellular particulate matter appear to support the altered demands of tissue energy metabolism during exercise.

Gene up-regulation in heart during mammalian hibernation.

A cDNA library prepared from heart of hibernating golden-mantled ground squirrels, Spermophilus lateralis, was differentially screened to clone genes that were up-regulated during hibernation. Two differentially expressed clones were found after three rounds of screening and were confirmed as up-regulated by Northern blotting. Clone Ang6 encoded a polypeptide with 116 amino acids that was identified as the ventricular isoform of myosin light chain 1 (MLC1(v)). Clone Ang19 coded for 274 amino acid residues of the mitochondrially encoded protein subunit 2 of NADH-ubiquinone oxidoreductase (ND2). Both proteins showed high amino acid sequence identity with their human counterparts, 97.5% for MLC1(v) and 66% for ND2. Northern blot hybridization revealed differential expression of these genes in multiple organs during hibernation. Transcript levels of both were approximately twofold higher in heart and three- to fourfold higher in skeletal muscle of hibernating, versus euthermic, animals. ND2 was also up-regulated in hibernator liver. Hibernation-induced up-regulation of MLC1(v) suggests that a restructuring of myosin subunit composition could contribute to changes in muscle contractility needed for hypothermic function, whereas changes in ND subunit composition may affect the function of the electron transport chain during hibernation.

Gene expression during estivation in spadefoot toads, Scaphiopus couchii: upregulation of riboflavin binding protein in liver.

A cDNA library constructed from liver of 2-month estivating female spadefoot toads, Scaphiopus couchii, was differentially screened to reveal genes that were induced or upregulated during estivation. After two rounds of screening a clone was isolated that showed 60% higher expression in liver of estivating, versus control, toads. The clone possessed a 1.0 kb insert which annealed to a single 0.7 kb band on Northern blots. Sequencing revealed a 1053 nucleotide full-length cDNA; the largest potential open reading frame was 708 nucleotides which encoded a protein of 235 amino acids. A homology search in Genbank indicated that the protein was a riboflavin binding protein (RfBP), a monomeric phosphoglycoprotein produced by the liver of female birds, reptiles, and mammals that functions to bind plasma riboflavin and load the vitamin into eggs or fetus. To our knowledge, this is the first demonstration that RfBP is also present in amphibians. Toad RfBP showed 50% of residues identical with the chicken or turtle liver proteins and many essential structural features were conserved in the toad protein including 18 cysteine residues, two asparagine glycosylation sites, and 6 tryptophan residues. However, a region with eight phosphoserines in the chicken or turtle proteins that functions in RfBP binding to the oocyte membrane contained only three serine residues in toad RfBP, suggesting that recognition and binding to oocyte receptors must be different in toads. Northern hybridization showed that toad RfBP was largely liver-specific; no mRNA transcripts were detected in brain, gut, heart, or kidney but low message levels occurred in hind leg skeletal muscle of estivating, but not control, toads. Upregulation of RfBP in liver of estivating toads may be linked with maturation of eggs in preparation for the explosive breeding that occurs immediately upon emergence from estivation but might also have a role for the adult in "caching" riboflavin to maintain an endogenous vitamin pool over the 9-10 months of each year that toads are dormant.

Solid-phase extraction cleanup and liquid chromatography with ultraviolet detection of ephedrine alkaloids in herbal products.

A solid-phase extraction (SPE) cleanup and a liquid chromatographic (LC) method with UV detection is presented for analysis of up to 7 ephedrine alkaloids in herbal products. Alkaloids from herbal products are extracted with acidified buffer, isolated on a propylsulfonic acid SPE column, eluted with a high-ionic-strength buffer, and separated by LC with detection at 255 nm. LC separation is performed by isocratic elution on a YMC phenyl column with 0.1 M sodium acetate-acetic acid (pH = 4.8) containing triethyl-amine and 2% acetonitrile. Ephedrine alkaloids are completely separated in 15 min. Average recovery of 5 common alkaloids from 3 spiked matrixes is 90%, with an average relative standard deviation (RSD) of 4.4% for alkaloid spikes between 0.5 and 16 mg/g. Average quantitation of ephedrine and pseudoephedrine from 6 herbal products is 97% of declared label claims, and average quantitation of synephrine from an herbal dietary product is 85% of label claim (RSD, 3.2%). Recoveries of synephrine, norephedrine, ephedrine, pseudoephedrine, N-methylephedrine, and N-methylpseudoephedrine spiked in 4 herbal products averaged 95%. Results of ruggedness testing and of a second laboratory validation of the procedure are also presented.

Antioxidant defenses and metabolic depression. The hypothesis of preparation for oxidative stress in land snails.

The roles of enzymatic antioxidant defenses in the natural tolerance of environmental stresses that impose changes in oxygen availability and oxygen consumption on animals is discussed with a particular focus on the biochemistry of estivation and metabolic depression in pulmonate land snails. Despite reduced oxygen consumption and PO2 during estivation, which should also mean reduced production of oxyradicals, the activities of antioxidant enzymes, such as superoxide dismutase and catalase, increased in 30 day-estivating snails. This appears to be an adaptation that allows the snails to deal with oxidative stress that takes place during arousal when PO2 and oxygen consumption rise rapidly. Indeed, oxidative stress was indicated by increased levels of lipid peroxidation damage products accumulating in hepatopancreas within minutes after arousal was initiated. The various metabolic sites responsible for free radical generation during arousal are still unknown but it seems unlikely that the enzyme xanthine oxidase plays any substantial role in this despite being implicated in oxidative stress in mammalian models of ischemia/reperfusion. We propose that the activation of antioxidant defenses in the organs of Otala lactea during estivation is a preparative mechanism against oxidative stress during arousal. Increased activities of antioxidant enzymes have also observed under other stress situations in which the actual production of oxyradicals should decrease. For example, antioxidant defenses are enhanced during anoxia exposure in garter snakes Thamnophis sirtalis parietalis (10 h at 5 degrees C) and leopard frogs Rana pipiens (30 h at 5 degrees C) and during freezing exposure (an ischemic condition due to plasma freezing) in T. sirtalis parietalis and wood frogs Rana sylvatica. It seems that enhancement of antioxidant enzymes during either anoxia or freezing is used as a preparatory mechanism to deal with a physiological oxidative stress that occurs rapidly within the early minutes of recovery during reoxygenation or thawing. Thus, a wide range of stress tolerant animals display coordinated changes in antioxidant defenses that allow them to deal with oxidative stress that occurs as part of natural cycles of stress/recovery that alter oxygen levels in tissues. The molecular mechanisms that trigger and regulate changes in antioxidant enzyme activities in these species are still unknown but could prove to have key relevance for the development of new intervention strategies in the treatment of cardiovascular ischemia/reperfusion injuries in humans.

Synthesis and confirmation of structure for a new gibberellin, 2 beta-hydroxy-GA12 (GA110), from spinach and oil palm.

The identity of a new gibberellin (GA) in spinach and oil palm sap has been confirmed as 2 beta-hydroxy-GA12 (GA110) by comparisons of GC-mass spectral data obtained for the trimethylsilyl ether methyl ester derivatives with those of a synthetic sample prepared by means of a 24 step sequence from gibberellic acid; 2 beta-hydroxy-GA24 was also prepared. Experimental details for the latter part of the syntheses are described.

De novo protein biosynthesis responses to water stresses in wood frogs: freeze-thaw and dehydration-rehydration.

Protein biosynthesis responses occurring during the postthaw (after 12 h freezing at -1.4 degrees C), dehydration (to 27 or 40% of total body water lost), or rehydration (after the loss of 40% of body water) were monitored in tissues of spring-collected wood frogs (Rana sylvatica) after intraperitoneal injection of 35S-labeled methionine + cysteine. All six organs tested accumulated radiolabeled amino acids and organs of both thawing and rehydrating frogs held at 3-5 degrees C showed a linear increase in amino acid incorporation into the acid-precipitable protein fraction over time. By contrast, dehydrating animals showed little or no increment in protein bound radioactivity over the course of the stress, a result that may be indicative of metabolic suppression in organs when dehydration became severe. Isoelectrofocusing (IEF) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were used to characterize the proteins synthesized by liver under each experimental state. IEF revealed both new peaks of 35S-labeled proteins and enhanced labeling of others in extracts from experimental animals, compared with controls. In particular, new synthesis of proteins with isoelectric points of about 6.0 was prominent and labeled proteins in this IEF peak persisted at 5, 10, or 24 h postinjection, becoming proportionally more important over time. SDS-PAGE analysis of the p(I) 6.0 peaks from thawed, dehydrated, and rehydrated frogs revealed the presence of one major low molecular weight protein in each case with molecular masses of 15, 13, and 21 kDa, respectively. These data indicate that the biochemical adaptations supporting freeze tolerance and dehydration tolerance in anurans include the stress-induced biosynthesis of a suite of proteins including the novel synthesis of selected specific proteins. These proteins may represent stress-related (or shock) proteins or may have specific roles in metabolic adaptation in each state such as in water and ionic balance or cell volume regulation.

Biochemistry below 0 degrees C: nature's frozen vertebrates.

Although alien to man, the ability to endure the freezing of extracellular body fluids during the winter has developed in several species of terrestrially hibernating frogs and turtles as well as in many species of insects and other invertebrates. Wood frogs, for example, can endure freezing for at least 2 weeks with no breathing, no heart beat or blood circulation, and with up to 65% of their total body water as ice. Our studies are providing a comprehensive view of the requirements for natural freezing survival and of the physical and metabolic protection that must be offered for effective cryopreservation of vertebrate organs. Molecular mechanisms of natural freeze tolerance in lower vertebrates include: 1) control over ice crystal growth in plasma by ice nucleating proteins, 2) the accumulation of low molecular weight cryoprotectants to minimize intracellular dehydration and stabilize macromolecular components, and 3) good ischemia tolerance by all organs that may include metabolic arrest mechanisms to reduce organ energy requirements while frozen. Cryomicroscopy of tissue slices and magnetic resonance imaging (MRI) of whole animals is revealing the natural mode of ice propagation through an organism. MRI has also revealed that thawing is non-uniform; core organs (with high cryoprotectant levels) melt first, facilitating the early resumption of heart beat and blood circulation. Studies of the production and actions of the natural cryoprotectant, glucose, in frogs have shown its importance in maintaining a critical minimum cell volume in frozen organs and new work on the metabolic effects of whole body dehydration in 3 species of frogs has indicated that adaptations supporting freeze tolerance grew out of mechanisms that deal with desiccation resistance in amphibians. Studies of the regulation of cryoprotectant glucose synthesis by wood frog liver have shown the role of protein kinases and of alpha and beta adrenergic receptors in regulating the glycemic response, and of changes in membrane glucose transporter proteins to facilitate cryoprotectant distribution.

Biochemistry below 0§C: nature's frozen vertebrates

Although alien to man, the ability to endure the freezing of extracellular body fluids during the winter has developed in several species of terrestrially hibernating frogs and turtles as well as in many species of insects and other invertebrates. Wood frogs, for example, can endure freezing for at least 2 weeks with no breathing, no heart beat or blood circulation, and with up to 65 per cent of their total body water as ice. Our studies are providing a comprehensive view of the requirements for natural freezing survival and of the physical and metabolic protection that must be offered for effective cryopreservation of vertebrate organs. Molecular mechanisms of natural freeze tolerance in lower vertebrates include: 1) control over ice crystal growth in plasma by ice nucleating proteins, 2) the accumulation of low molecular weight cryoprotectants to minimize intracellular dehydration and stabilize macromolecular components, and 3) good ischemia tolerance by all organs that may include metabolic arrest mechanisms to reduce organ energy requirements while frozen. Cryomicroscopy of tissue slices and magnetic resonance imaging (MRI) of whole animals is revealing the natural mode of ice propagation through an organism. MRI has also revealed that thawing is non-uniform; core organs (with high cryoprotectant levels) melt first, facilitating the early resumption of heart beat and blood circulation. Studies of the production and actions of the natural cryoprotectant, glucose, in frogs have shown its importance in maintaining a critical minimum cell volume in frozen organs and new work on the metabolic effects of whole body dehydration in 3 species of frogs has indicated that adaptations supporting freeze tolerance grew out of mechanisms that deal with desiccation resistance in amphibians. Studies of the regulation of cryoprotectant glucose synthesis by wood frog liver have shown the role of protein kinases and of (alpha and beta adrenergic receptors in regulating the glycemic response, and of changes in membrane glucose transporter proteins to facilitate cryoprotectant distribution.

Clinical experience with patient-controlled and staff-administered intermittent bolus epidural analgesia in labour.

A prospective, randomized study was performed to detail clinical experience with both patient-controlled epidural analgesia (PCEA) and midwife-administered intermittent bolus (IB) epidural analgesia during labour, under the conditions pertaining in a busy obstetric delivery unit. Both methods used 0.125% bupivacaine plus fentanyl, and similar rescue supplementation, although management decisions related to epidural analgesia were made principally by attending midwives. One hundred and ninety-eight women were recruited and data analysed from 167 (PCEA n = 82, IB n = 85). The groups were demographically similar. Median hourly pain scores, ratings of analgesia and satisfaction did not differ. Maximum pain scores were significantly higher in those receiving IB epidural analgesia (P < 0.05). The PCEA group had a significantly higher rate of supplementation and bupivacaine use (P < 0.01), and a longer duration of the second stage of labour (P < 0.03). The relative risk of instrumental delivery with PCEA versus the IB method was 1.57 (CI 1.07-2.38). Experience within our unit with PCEA is contrasted with that of IB epidural analgesia, the method most commonly used; and with that of controlled trials comparing these two methods.

Vogt-Koyanagi-Harada syndrome in a 4-year-old child.

Vogt-Koyanagi-Harada syndrome is an acquired illness with ocular, cutaneous, and/or neurologic features. A 4-year-old child who acutely developed visual disturbances and headache and was found to have serous retinal detachments and aseptic meningitis is presented. Improvement was rapid with corticosteroid therapy. This is the youngest reported patient with Vogt-Koyanagi-Harada syndrome.

Gas chromatographic determination of chloramphenicol residues in shrimp: interlaboratory study.

An interlaboratory study of a gas chromatographic method for determining chloramphenicol (CAP) residues in shrimp was conducted. An internal standard (Istd), the meta isomer of CAP, was added to the shrimp, and the treated shrimp were homogenized with ethyl acetate. The ethyl acetate extract was defatted with hexane, and the CAP was partitioned into ethyl acetate from an aqueous salt solution. The ethyl acetate was evaporated, and the dried residue was treated with Sylon, a trimethylsilyl derivatizing agent, to yield the trimethylsilyl derivative of CAP. A portion of the solution containing the derivative was injected into a gas chromatograph equipped with an electron capture detector. Levels of fortified and incurred CAP were calculated from the peak area ratio of standard CAP to Istd. Recoveries of CAP from tissue directly fortified at 5 ppb were 102% (within-laboratory relative standard deviation [RSDr] = 5.6%), 104% (RSDr = 5.5%), and 108% (RSDr = 6.3%) from Laboratories 1, 2, and 3, respectively. Incurred-CAP residues at 5 and 10 ppb levels were also determined, with the following results: Laboratory 1: composite A, 4.56 ppb (RSDr = 14.0%); composite B, 8.38 ppb (RSDr = 11.6%); Laboratory 2: composite A, 4.17 ppb (RSDr = 12.5%); composite B, 8.90 ppb (RSDr = 5.60%); Laboratory 3: composite A, 4.66 ppb (RSDr = 14.9%); composite B, 11.0 ppb (RSDr = 11.8%).