Comment on "structure of smectic defect cores: X-ray study of 8CB liquid crystal ultrathin films".
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Comment↗
Biomedical subjects
M Kleman
Publications and source records attributed to M Kleman.
Liquid crystal helical ribbons as isometric textures.
Deformations that conserve the parallelism and the distances--between layers, in smectic phases; between columns, in columnar phases--are commonplace in liquid crystals. The resulting isometric deformed textures display specific geometric features. The corresponding order parameter singularities extend over rather large, macroscopic, distances, e.g., cofocal conics in smectics. This well-known picture is modified when, superimposed to the 1D or 2D periodicities, the structure is helical. However isometry can be preserved. This paper discusses the case of a medium whose structure is made of 1D modulated layers (a lamello-columnar phase), assuming that the modulations rotate helically from one layer to the next. The price to pay is that any isometric texture is necessarily frustrated; it consists of layers folded into a set of parallel helicoids, in the manner of a screw dislocation (of macroscopic Burgers vector), the modulations being along the helices, i.e. double-twisted. The singularity set is made of two helical disclination lines. We complete this geometric analysis by a crude calculation of the energy of a helical ribbon. It is suggested that the helical ribbons observed in the B7 phase of banana-like molecules are such isometric textures. As a side result, let us mention that the description of double-twist, traditionally made in terms of a partition of the director field into nested cylinders, could more than often be profitably tested against a partition into nested helicoids.
Biopolymers↗
Textural analysis of a mesophase with banana shaped molecules.
Observed under the polarizing microscope, the B7bis phase in the banana compound D14F3 [J.P. Bedel et al., Liq. Cryst. 27, 1411 (2000)] displays two types of textures of defects, namely (a): helical ribbons, that nucleate in large quantities when the samples are quenched from a sufficiently high temperature in the isotropic phase (b)- shapes with no helicity having the structure of developable domains much akin to those observed in columnar phases, either resulting from the annealing of the helical ribbons or nucleating under slow cooling processes. The existence of these two kinds of defects points toward the complex nature of the structure of the B7 phase, which is at the same time a columnar and a smectic phase. Our observations fit the model [M. Kleman, J. Phys. France 46, 1193 (1985)] according to which the geometry of a helical ribbon is that one of the central region of a screw dislocation with a giant Burgers vector, split into two helical disclination lines of strength k = 1/2 which bound the ribbon. Textures and defects, already partly documented, and growth features and annealing processes, not yet reported in the literature, are analyzed. We conclude that the helical ribbons and the developable domains with no helicity are textures of two different B7 states, namely a metastable state and the ground state respectively. Comparative textural analysis is performed for two other banana compounds exhibiting B2 phases.
Journal Article↗
Defects in a TGBA phase: a theoretical approach.
Following our experimental observations of disclination lines in freely suspended droplets and free-standing films (Yu.A. Nastishin et al., Eur. Phys. J. E 5 353 (2001)), topological defects of the twist grain boundary (TGBA) phase are considered according to two aspects: topological and energetical. There are two classes of line defects, disclinations (as in the cholesteric (N*) phase and the liquid vortices phase (NL*), relating to the directors tripod symmetries) and dispirations (relating to the translation-rotation symmetries); there are no topological point defects. Differences between N*, NL* and TGBA disclinations are physical, not topological. The absence of focal conic domains in the TGBA phase is an immediate consequence of the materialization of the helical axis (along the chi-director); the same feature, coupled to the trend to parallelism of the smectic layers, accounts for the predominance of lambda-lines. Finally, the presence of defects akin to developable domains is explained in the frame of the least curvature model, that requires the introduction of a third type of defects: the densities of edge dislocations of the smectic layers.
Journal Article↗
Curvature energy of a focal conic domain with arbitrary eccentricity
The most frequently observed focal conic domains (FCD's) in lamellar phases are those based on confocal paris of ellipse and hyperbola. Experimentally, the eccentricity of the ellipse takes a broad range of values 0</=e<1. We present an analytical expression for the curvature energy of a FCD that is valid in the entire range 0</=e<1. Generally, the curvature energy of an isolated FCD reaches a minimum only at e-->1 (under the constraint of a fixed major semiaxis of the ellipse); exceptions include situations with large saddle-splay elastic constant and small domains where the applicability of the elastic theory is limited. In realistic cases, a value of eccentricity smaller than 1 is stabilized by factors other than the curvature energy: by dislocations emerging from the FCD's with e not equal0, compression of layers and surface anchoring.
Journal Article↗
Tiling the plane with noncongruent toric focal conic domains
This paper deals with regular arrays of macroscopic defects (focal conic domains) observed when a slab of lamellar phase is sandwiched between two substrates imposing different orientational anchorings. We report, in particular, detailed observations of the texture of a lyotropic lamellar phase in contact with a glass substrate and a lyotropic sponge phase. We consider several models for the defects depending on the material and the substrate parameters. Their energy has a common form, and the main features of the textures are explained in the framework of a simple model where disks of different sizes tile a plane in order to minimize a particular interface energy.
Journal Article↗
Evidence of a Phenomenon of Epitaxy at the Interface between a Lamellar L alpha Phase and a L3 Sponge.
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Journal Article↗
Interactions of procarcinogenic heterocyclic amines and indolocarbazoles with the dioxin receptor.
Cooking of protein-rich food generates procarcinogenic heterocyclic aromatic amines (HCA) in amounts that range in the part per billion levels. HCA have been reported to induce xenobiotic metabolizing enzymes of the cytochrome P450 1A (CYP1A) subfamily, most notably the CYP1A2 isoform. The regulator mechanism of the CYP1A induction by HCA is, however, unclear. Studies in vivo in rats and in primary hepatocyte cultures revealed "that MelQx induced both CYP1A1/1A2 proteins and the corresponding catalytic activities. In contrast to previous studies, no preferential induction of CYP1A2 was observed in the present study. CYP1A1 and CYP1A2 are target genes of the intracellular dioxin receptor. This receptor interacts with xenobiotic response elements (XREs) of target promoters upon binding the environmental pollutant dioxin or related compounds. HCA exhibited capacity to activate the dioxin receptor to a form which interacts with XRE in vitro. Taken together, these results suggest that MelQx regulates both CYP1A isozymes by the same mechanism involving the dioxin receptor. Another group of putative dioxin receptor ligands of dietary orgin are the indolocarbazoles, which are produced in vivo from precursor molecules in cruciferous plants. Indolocarbazoles potently regulated gene expression of a reporter gene driven by a minimal XRE in both mouse and human hepatoma cells. The indolocarbazole-induced human receptor appeared to form more stable complexes with XRE in vitro relative to those generated by the dioxin-activated receptor. This study indicates that the HCA and the indolocarbazoles both represent distinct classes of dietary dioxin receptor agonists.
Amines↗
Physiologic responses of coronary care patients to visiting.
The authors examined physiologic changes in myocardial infarction patients during a family visit in the cardiac intensive care unit (CICU) and the relationship of these changes to illness variables, patient preference for visits, and patients' perceptions of the supportiveness of the visit. Forty-eight patients were studied for changes in heart rate, blood pressure, ST segment, and oxygen saturation. Patients who had the greatest physiologic changes were among those who had had more severe infarcts. However, many patients in the severe category did not show such changes. Examination of the reactive group revealed that, in addition to having more severe infarcts, it included a greater percentage of smokers than did the nonreactive group. Visit preferences were relatively low, but as visit preferences increased, so did cardiovascular changes. Supportiveness scores were quite high, and these were positively correlated with cardiovascular changes. Clinical and research implications are discussed.
Adult↗
Mutagenic and cytotoxic action of heated pork meat extracts in human diploid fibroblasts.
Extracts from lean pork heated at 200 degrees C have a strong mutagenic activity in the Ames Salmonella assay (strain TA98 +S9). The formation of mutagenicity is highly temperature dependent, thus an extract heated at 100 degrees C is not mutagenic in this system. This paper shows that the 200 degrees C extract also causes mutations at the hprt locus in normal human fibroblasts, as demonstrated by a dose-dependent increase of 6-thioguanine resistant mutants. The mutation frequencies were increased 6 and 13 times, respectively, for extract concentrations corresponding to 100 and 200 mg meat/ml medium. Heterocyclic amines, previously shown to be present in the 200 degrees C extract are conceivably responsible for at least part of the observed mutagenicity. The extracts prepared at 100 degrees C had no significant effect on the mutant frequency in human fibroblasts. A pronounced, dose-dependent, decrease in cell survival was observed with both the 100 and the 200 degrees C extracts. The nature of the cytotoxic components is not clear and might be different in the two extracts.
Animals↗
Effects of the food mutagens MeIQx and PhIP on the expression of cytochrome P450IA proteins in various tissues of male and female rats.
The promutagenic 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) found in cooked food are converted to their active forms mainly by cytochrome P450 forms IA1 and IA2. By induction of these isoenzymes the food mutagens could thus influence their own rate of activation. Male and female Wistar rats were given MeIQx, PhIP, beta-naphthoflavone (BNF) or saline i.p. at 50 mg/kg body wt on three consecutive days. On the fourth day the rats were killed and lungs, kidneys, liver and intestines taken. The microsomal fraction from each organ was prepared as well as 9000 g supernatant from the liver. The induction of cytochrome P450IA was measured at the protein level by enzymatic assays (ethoxyresorufin-O-deethylation, Ames' mutagenicity test) and immunoassays (Western blot) and at the pretranslational level by RNA hybridization (Northern blot). The binding affinities of MeIQx, PhIP and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) for the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-receptor were studied by evaluation of the competition with 3H-labelled TCDD for specific binding. Ethoxyresorufin-O-deethylase (EROD) activity was significantly increased in the liver (males 2.1-fold, females 3.3-fold), kidneys (males 2.1-fold, females 1.8-fold) and lungs (males 4.3-fold, females 3-fold) of the MeIQx-treated rats. Furthermore, the levels of cytochrome P450IA proteins were increased in these animals. It was not possible, however, to detect the corresponding mRNA. In the case of the PhIP-treated animals a significantly increased EROD activity (2.7-fold) and an increased cytochrome P450IA protein level were seen only in the male lungs. Only a very weak TCDD-receptor affinity was observed for PhIP, whereas MeIQx or IQ did not appear to compete significantly with [3H]TCDD for binding to the TCDD-receptor. It is concluded that MeIQx is a weak inducer of cytochrome P450IA in several organs of the rat, while PhIP induced these isoenzymes only in the male lungs. More work is needed to clarify the mechanism(s) whereby this induction occurs.
Animals↗
Chemistry and biological activity of volatile and nonvolatile mutagenic compounds from cooked food.
Cooking fumes constitute a major part of the mutagenic activity detected in indoor air samples. The chemical nature of the smoke mutagens has not been determined, but existing data indicate the presence of carcinogenic heterocyclic amines, previously identified in crust and pan residue from fried meat. Reports on the chemical nature and biological activity of these compounds are reviewed.
Animals↗
Influence of creatine, amino acids and water on the formation of the mutagenic heterocyclic amines found in cooked meat.
Creatine or one of 15 amino acids were mixed with minced pork before broiling at 200 degrees C. Total mutagenic activity and reversed-phase HPLC-separated mutagenicity profiles were determined for the crust and pan residue of all samples and also in the aerosol fraction of the smoke formed during cooking of the creatine-fortified samples. Addition of 5% (w/w) creatine increased the total mutagenicity 4-fold without changing the mutagenicity profile of either crust, pan residue or aerosol. Amino acid addition (1% w/w) increased the total mutagenicity between 1.5 (lysine) and 43 times (threonine). In most cases the mutagenicity profiles of crust and pan residues were changed by amino acid addition. Dry-heated mixtures of amino acids and creatine were all mutagenic with a 250-fold range between the amino acids. The production of known food mutagens in these mixtures was analyzed by LC-MS of HPLC-fractionated mutagenic peaks. Serine, threonine, phenylalanine, alanine, leucine and tyrosine were all shown to give rise to one of the known food mutagens 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) or 2-amino-trimethylimidazopyridine (TMIP). Lyophilized and subsequently fried meat patties and a heated powder of lyophilized meat juice were both mutagenic, with mutagenicity profiles similar to the regular meat crust, showing that water is not a prerequisite for mutagen formation in meat. MeIQx, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-di-MeIQx) and PhIP were shown, by LC-MS, to be present in the dry-heated meat juice. It is concluded that creatine and free amino acids are the main reactants of the mutagen-forming reactions that occur during frying of meat. Creatine is probably a necessary part of all of these reactions; what specific compounds are formed in each case therefore depends upon the levels in the meat of certain free amino acids and their interactions with other, as yet unknown, compounds in the meat.
Amines↗
The food-mutagens 2-amino-1-methyl-6-phenylimidazo-[4,5-b]-pyridine (PhIP) and 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline (MeIQx) initiate enzyme-altered hepatic foci in the resistant hepatocyte model.
The initiating activity of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and a mutagenic meat extract obtained from cooked meat was examined, using the resistant hepatocyte model (RH-model). Male Wistar rats were given a single i.p. injection of PhIP (50 or 75 mg/kg body weight) or MeIQx (50 mg/kg body weight) after a 2/3 partial hepatectomy (PH). The meat extract (corresponding to 1050 g meat/animal) was given by gastric feeding at three time points after PH. Two weeks after initiation the rats received a diet containing 0.02% 2-acetylaminofluorene for a period of 2 weeks. In the middle of this period a single dose of carbon tetrachloride was given. Rats were killed 6 weeks after the experimental start. The number of enzyme-altered (gamma-glutamyl-transferase positive) hepatic foci was significantly increased in the animals given MeIQx (P less than 0.05) and the highest dose of PhIP (P less than 0.01) whereas no effect of the meat extract was observed. The mutagenic meat extract was also studied with regard to promotive capacity in vivo, the meat extract was given in the diet of diethylnitrosamine initiated rats for a period of 6 weeks. No significant changes were detected after administration of the meat extract in the diet. It is concluded that both MeIQx and PhIP are weak initiators in the RH-model, in the same order of magnitude as the previously investigated, structurally related pyrolysis products. The meat extract was not active in the RH-model under the conditions used in this study.
Animals↗
Attention versus avoidance: attributional search and denial after myocardial infarction.
OBJECTIVE: In this study the focus was on two strategies: denial (an avoidant strategy) and causal thinking (an attention strategy) and their relationships to affect after myocardial infarction. DESIGN: Descriptive, correlational. SETTING: Large rural medical center. SAMPLE: The sample comprised 152 recently hospitalized patients with first-time myocardial infarction. MEASURES: A denial scale, a question about causal thinking, and an affect adjective checklist measuring anxiety, hostility, and depression. RESULTS: Denial had a weak but significant negative correlation with anxiety (r = -0.18, p < 0.05). However, denial was not significantly related to either depression or hostility. Regression analysis indicated that both denial (F = 4.84, p = 0.02) and the interaction of denial with causal search (f = 4.77, p = 0.009) were predictors of affect. The interaction indicated that those with high denial who had not searched for a cause were least anxious. A large number of subjects used both attention and avoidant strategies. CONCLUSIONS: The main effect for denial suggests that avoidance is a more effective strategy for reducing anxiety after myocardial infarction than causal search, an attention strategy. However, the fact that many subjects used both strategies suggests that they are not mutually exclusive in the process of adaptation after a heart attack.
Affect↗