Communication: Optically induced decoupling of the smectic-A and nematic order parameters at the AN phase transition in phototropic liquid crystals.

In the present work, by means of the photopyroelectric calorimetric investigations in liquid crystal/naphtopyran (NP) molecule mixtures, the effect of the photoisomerization of NP by UV light on the critical behavior of specific heat could be studied over the smectic-nematic phase transition. It is shown that the UV light irradiation of the sample can shift the critical exponent from a non-universal value typical of the non-irradiated mixture to one close to that of the 3D-XY universality class, predicted for such a transition. This witnesses the optically triggered reduction of the coupling between the smectic and nematic order parameters responsible for the deviation from the XY-like behavior. A tentative explanation is provided based on the weakening of the order parameter coupling caused by the NP molecules entering the smectic layers following the UV light illumination.

Simultaneous specific heat, thermal conductivity and imaging evaluations in thin samples of 8CB liquid crystal dispersed with microemulsion of DDAB/water micelles.

In this work we use a photopyroelectric calorimetric set up to analyze the transformations occurring in thin samples of liquid crystal-microemulsion system by combining the results of the simultaneously performed high temperature resolution polarization microscopy observations and the temperature dependence of the specific heat, and of the thermal conductivity. This enabled an accurate direct correlation of the observations concerning the different measured quantities for a most comprehensive interpretation of the obtained results. It is found that the I-N conversion progresses in the entire nematic range because of the micelles expelled from the nucleating nematic volumes remaining confined in the residual isotropic material. A hysteretic behavior is observed in the nematic range between cooling and heating run because of the different micelle content in the material during the cooling and heating runs. A moderate hysteresys also over the N-A transition indicated an additional material refinement from micelles during the transition. Finally in samples with different micelle concentration the same maximum micelle content is retained in the nematic and smectic phases.

Simultaneous calorimetric and polarization microscopy investigations of light induced changes over phase transitions in a liquid crystal-napthopyran mixture.

We have studied the specific heat and the thermal conductivity in a 4-(n-octyl)-4'-cyanobiphenyl liquid crystal (LC)-photochromic molecules mixture, before, during, and after the photo-activation of the dispersed photochromic molecules, over both the smectic A-nematic and the nematic-isotropic phase transitions. The evaluation of the specific heat has enabled the determination of the changes of the phase transition characteristics induced by the photochromic molecules photoisomerization, while that of the thermal conductivity could be used to monitor the modifications induced in the average LC molecular orientation. The polarization microscopy imaging of the sample texture constituted a valuable support for the interpretation of the obtained thermal conductivity results.

Study of the smecticA-hexaticB phase transition in homeotropic single domain samples of 65OBC liquid crystal by photopyroelectric calorimetry.

The smecticA-hexaticB phase transition was studied in a homeotropic single domain sample and in a non-aligned sample of n-hexyl-4'-n-pentyloxybiphenyl-4-carboxylate liquid crystal compound to probe the effect of different amount of defects on the phase transition. The specific heat, the thermal diffusivity and the enthalpy exchange were monitored over the transition and, at the same time, polarization microscopy observations could be carried out. The transition during the first cooling run was found to be accompanied by a considerably larger defect annealing in the non-aligned sample than in the homeotropic one, but the critical behaviour of the specific heat remained substantially the same.

Parchment processing and analysis: Ionizing radiation treatment by the REX source and multidisciplinary approach characterization.

Library material, and thus parchment, is frequently subjected to bio-deterioration processes caused by microorganisms. Fungi and bacteria cause alterations in the parchment inducing, in some cases, even the partial detachments of the surface layer and the loss of any text present on it. An important contribution to disinfection of the cultural heritage artefacts is given by the use of ionizing radiation. In this work, a preliminary study on the applicability of X-ray radiation as treatment for bio-deterioration removal is proposed. The results on the microbial growth after different irradiation treatments are shown in order to detect the dose protocol for the bio-degradation removal. Furthermore, the evaluation of the irradiation effects on the parchment microstructure is presented in order to define the applicability of the method on parchment artefacts.

Simultaneous characterization of optical and thermal parameters of liquid-crystal nanocolloids with high-temperature resolution.

We report on the high-temperature resolution measurements of the optical and thermal parameters of a liquid-crystal-silica nanoparticle colloid, as well as its video inspection, simultaneously performed in an upgraded photopyroelectric calorimeter. Over the nematic-isotropic coexistence region, the determined nematic correlation length, obtained from turbidity measurements, showed the characteristic two-step nematic nucleation process previously reported only for the specific heat.

Finite-length models of carbon nanotubes based on Clar sextet theory.

Finite-length models of metallic and semiconducting carbon nanotubes (CNTs) based on Clar sextet theory of aromatic systems are proposed. For metallic CNTs, the electronic properties of finite-length models converge monotonically to the values expected for quasi-monodimensional metallic systems. For semiconducting CNTs, the use of finite-length models as proposed in this work leads to a fast convergence of the electronic properties to the values expected for the corresponding infinite-length nanotube.

Strain effects at the hexatic-B-smectic-A transition in the 65OBC liquid crystal.

We have studied the hexatic-B-smectic-A (HexB-SmA) transition in n -hexyl- 4'-n -pentyloxybiphenyl-4-carboxylate (65OBC) by means of a high-resolution ac photopyroelectric (PPE) calorimetric technique. A procedure for the interpretation of the PPE data, which allows the detection of an internal heating source due to strain annealing and/or latent heat, has been applied. We have found that the strain present in the sample depends on the kinetics of formation of the smectic phase once the sample is cooled from the isotropic one. The strain field keeps memory of this kinetics and can be only partially annealed on decreasing the temperature or cycling it around the Hex-SmA transition. A reversible ordering-disordering process has been found at T(c) and has been explained in terms of the competition between the order parameter variation with temperature and the constraints imposed by the disorder. The results confirm that the transition has a weakly first-order character with a specific heat critical exponent that disagrees with the available theoretical predictions. Our data show the importance of the disorder in 65OBC and we tried to clarify what would be the consequence of this result in theoretical modeling devoted to solving the puzzle of the HexB-SmA transition in this compound.

Defective intracellular antioxidant enzyme production in type 1 diabetic patients with nephropathy.

There is an individual susceptibility to diabetic nephropathy, and oxidative stress is believed to play an important role in the pathogenesis of diabetic complications. Active oxygen species induce antioxidant enzyme expression in tissues, an effect considered to be a defensive mechanism. To test whether altered intracellular antioxidant enzyme production might explain the predisposition to diabetic nephropathy, we studied the effect of long-term (12 weeks) exposure to normal (5 mmol/l) or high (22 mmol/l) glucose concentrations on fibroblast antioxidant enzyme gene expression and protein activity in type 1 diabetic patients with and without nephropathy, nondiabetic nephropathic patients, and nondiabetic control subjects. Under conditions of normal glucose concentration in the culture media, CuZnSuperoxide-dismutase, MnSuperoxide-dismutase, catalase, and glutathione-peroxidase activity and mRNA expression were not different among the four groups. Under high-glucose conditions, CuZnSuperoxide-dismutase mRNA and activity increased similarly in all groups (P < 0.001 vs. basal), whereas MnSuperoxide-dismutase did not change. In contrast, catalase mRNA and activity as well as glutathione-peroxidase mRNA and activity increased in fibroblasts from type 1 diabetic patients without nephropathy (P < 0.001), in fibroblasts from nondiabetic nephropathic patients (P < 0.001), and in fibroblasts from nondiabetic control subjects (P < 0.001), but not in fibroblasts from type 1 diabetic patients with nephropathy. Exposure to high glucose concentrations significantly increased lipid peroxidation in cells, higher levels being found in cells from diabetic patients with nephropathy (P < 0.001). These data, while confirming that exposure to high glucose concentrations induces an antioxidant defense in skin fibroblasts from normal subjects, demonstrate a failure of this defensive mechanism in cells from type 1 diabetic patients with nephropathy, whereas skin fibroblasts from diabetic patients without complications or from nondiabetic nephropathic patients have an intact antioxidant response to glucose-induced oxidative stress.

The microscopic switching mechanism of a [2]catenane.

We apply numerical simulations at an all-atom level to investigate the switching mechanism of a [2]catenane, a prototype of a molecular machine. This system is able to switch reversibly between two different stable states, upon external stimuli, with a time scale ranging from microseconds up to milliseconds, well over the typical domain of molecular dynamics (MD) computer simulations. However, combining a strategy recently developed for investigating rare events with ordinary MD, we are able to unravel the microscopic mechanism of the conformational rearrangements involved in the switching process, including dynamical effects. Along the path that connects the product and reactant state, we find several intermediate states characterized by pi-pi stacking interactions and hydrogen bonds. Moreover, counterions interact strongly with the system in a correlated way, in agreement with recent static calculations performed on [2]rotaxanes.

Identification and localization of insulin-like growth factor-binding protein (IGFBP) messenger RNAs in human hair follicle dermal papilla.

The role of the insulin-like growth factors (IGFs) in hair follicle biology has recently been recognized, although their actions, sites of production, and modulation by the insulin-like growth factor-binding proteins (IGFBPs) have not to date been defined. IGF-I is essential for normal hair growth and development, and may be important in regulation of the hair growth cycle. In many culture systems, IGF-I actions are modulated by the IGFBPs. Thus, if IGFBPs are produced in the human hair follicle, they may play a role in targeting IGF-I to its receptor or may modulate IGF-I action by interaction with matrix proteins. We have used in situ hybridization to localize messenger RNA for the six IGFBPs in anagen hair follicles. Anti-sense and sense RNA probes for the IGFBPs (IGFBP-1 to -6) were produced, and 5-micrometer sections of adult facial skin were probed. Messenger RNA for IGFBP-3, -4, and -5 were identified, with predominantly IGFBP-3 and -5 mRNA found in the dermal papilla, and to a lesser extent IGFBP-4 mRNA. IGFBP-4 mRNA was also found at the dermal papilla/epithelial matrix border. Messenger RNAs for both IGFBP-4 and -5 were also demonstrated in the dermal sheath surrounding the hair follicle. Messenger RNAs for IGFBP-1, -2, and -6 were not identified. These studies demonstrate specific localization of IGFBP mRNAs in hair follicles, suggesting that they each play specific roles in the local modulation of IGF action during the hair growth cycle.

Identification, localization, and regulation of insulin-like growth factor binding proteins and their messenger ribonucleic acids in the newborn rat olfactory bulb.

Insulin-like growth factor binding proteins (IGFBPs) have been identified in most tissues, including the central nervous system, where the major IGFBPs have been localized. The regulation and roles of IGFBPs in IGF action in the developing brain remain unclear. In this study we examined the expression and anatomical distribution of IGFBP messenger RNAs (mRNAs) in the newborn rat olfactory bulb (OB) during the first postnatal week. We used our recently developed newborn rat OB organ culture system, which emulates the first week of in vivo development, to identify and characterize expressed and secreted IGFBPs and to determine the role of the local growth factors IGF-I and basic fibroblast growth factor (bFGF) in their regulation. Postnatal day 1 rat OBs were cultured serum free for 6 days in the absence or presence of IGF-I (150 ng/ml) and bFGF (25 ng/ml), alone or in combination, as previously shown by us to maintain morphology and differentiation of neuronal and glial cells. Conditioned medium was subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western ligand blotting using [125I]IGF-I, and IGFBPs were characterized by immunoprecipitation. Western ligand blotting of conditioned medium revealed two bands at 24 kilodaltons (kDa) and 30 kDa and a doublet at 38-42 kDa. All bands were enhanced by IGF-I treatment, whereas bFGF enhanced the 24-kDa and 30-kDa bands only. In combination, IGF-I and bFGF enhanced all four bands above that seen with either growth factor alone. Total RNA was extracted from fresh day 1, day 6, and cultured OBs for Northern blotting using complementary DNA probes for IGFBP-2, -3, -4, and -5. In fresh day 1 OBs, mRNA was detected for IGFBP-2, -4, and -5, but not for IGFBP-3. In fresh day 6 OBs IGFBP-2 mRNA was more abundant, whereas IGFBP-4 mRNA showed lower expression than at day 1, and IGFBP-5 mRNA was similarly expressed. When day 1 OBs were cultured for 6 days, mRNA was also readily detected for IGFBP-2, -4, and -5, but not for IGFBP-3. All detected mRNA species were enhanced by IGF-I. Basic FGF enhanced IGFBP-2 mRNA whether alone or in combination with IGF-I and enhanced only IGFBP-4 mRNA when given alone. IGFBP-5 mRNA was not affected by bFGF alone, but its enhancement by IGF-I was attenuated by bFGF. Sites of transcription of IGFBP and IGF-I mRNAs were located by in situ hybridization in both fresh and cultured bulbs.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of messenger ribonucleic acid for insulin-like growth factor-binding proteins in human skin by in situ hybridization.

The role of the insulin-like growth factors (IGFs) in human skin physiology has been increasingly recognized, although relatively little is known about the cell types involved or the cellular mechanisms that mediate these responses. Epidermal keratinocytes and dermal fibroblasts both possess IGF-I receptors and are responsive to IGF-I. IGF-binding proteins (IGFBPs), known modulators of IGF action, may also be responsible for targeting IGF-I to its receptors and are produced by both cultured keratinocytes and fibroblasts. To demonstrate sites of production of IGFBPs in human skin, we have used in situ hybridization to localize messenger ribonucleic acid (mRNA) for the six IGFBPs. Antisense and sense RNA probes for the IGFBPs (IGFBP-1 to -6) were produced, and 5-microns sections of normal adult human male chest skin were probed. The control probe used was keratin-5, which is known to hybridize to the basal keratinocytes of the epidermis. mRNAs for human IGFBP-2, -3, -4, and -5 were identified, with mRNAs for IGFBP-2 and IGFBP-4 localized in sebaceous glands and eccrine sweat glands (epidermal origin), IGFBP-3 mRNA in the basal layer of the epidermis and mRNAs for IGFBP-4, and IGFBP-5 found throughout the dermis. mRNAs for IGFBP-1 and -6 were not identified in human skin. These studies demonstrate specific localization of IGFBP mRNAs in adult human skin, suggesting that each IGFBP may play a specific role in targeting IGF-I to its receptor on responsive cells and, ultimately, in modulation of IGF-I action in skin.

Matrix metalloproteinases 19 and 20 cleave aggrecan and cartilage oligomeric matrix protein (COMP).

Matrix metalloproteinase (MMP)-19 and MMP-20 (enamelysin) are two recently discovered members of the MMP family. These enzymes are involved in the degradation of the various components of the extracellular matrix (ECM) during development, haemostasis and pathological conditions. Whereas MMP-19 mRNA is found widely expressed in body tissues, including the synovium of normal and rheumatoid arthritic patients, MMP-20 expression is restricted to the enamel organ. In this study we investigated the ability of MMP-19 and MMP-20 to cleave two of the macromolecules characterising the cartilage ECM, namely aggrecan and the cartilage oligomeric matrix protein (COMP). Both MMPs hydrolysed aggrecan efficiently at the well-described MMP cleavage site between residues Asn(341) and Phe(342), as shown by Western blotting using neo-epitope antibodies. Furthermore, the two enzymes cleaved COMP in a distinctive manner, generating a major proteolytic product of 60 kDa. Our results suggest that MMP-19 may participate in the degradation of aggrecan and COMP in arthritic disease, whereas MMP-20, due to its unique expression pattern, may primarily be involved in the turnover of these molecules during tooth development.

Pax-8 protein levels regulate thyroglobulin gene expression.

Pax proteins are transcription factors that control differentiation of several cell types. In adult organisms Pax-8 is expressed in the follicular thyroid cell where it interacts with sequences of thyroglobulin and thyroperoxidase promoters. In this study, we provide evidence indicating that Pax-8 protein levels regulate thyroglobulin gene transcription. The most critical approach consisted in increasing Pax-8 protein levels by transfecting thyroid cells with a Pax-8 expression vector. In this situation the thyroglobulin promoter transcriptional activity was significantly increased with respect to untransfected cells. In contrast, the transfection of thyroid transcription factor-1 (TTF-1) expression vector causes a modest decrease of thyroglobulin promoter activity, rather than an increase. Northern blots of human papillary cancers reveal a significant correlation between Pax-8 and thyroglobulin mRNAs. Gel-retardation assays suggest that the mechanism by which the Pax-8 protein levels modulate thyroglobulin promoter activity may occur through competition with TTF-1 for a common binding site. Since we also demonstrate that Pax-8 expression is subjected to TSH control, our data strongly suggest that Pax-8 protein levels could represent an important determinant for the regulation of thyroid cells.

Coordinate induction of interferon alpha and gamma by recombinant HIV-1 glycoprotein 120.

Similarly to HIV-infected cells, recombinant HIV-1 glycoprotein 120 induces acid-labile interferon production in peripheral blood mononuclear cells from healthy donors. Acid lability of this interferon is due to the presence of both IFN-alpha and -gamma molecules. In fact, although not revealed by neutralization of antiviral activity with antibody to IFN-gamma, the presence of IFN-gamma was shown both immunoenzymatically and by detection of specific mRNA in gp120-stimulated cells. The source of IFN-gamma appears to be a T cell present in the CD4-enriched subpopulation. Cultures treated with monoclonal antibodies to the ICAM-1 and LFA-1 adhesion molecules showed an impaired release of both IFN types after gp120 stimulation, suggesting a crucial role of cell-to-cell interactions in the process leading to IFN production. Our data suggest that the HIV envelope glycoprotein could be responsible for the induction of endogenous IFN-alpha and -gamma observed in AIDS patients.

Oxidative stress evaluation in diabetes.

Over the recent years, researches have focused their attention on the pathologic role of free radicals in a variety of diseases, among which the most important are atherosclerosis, cancer, and diabetes. The set of intracellular and extracellular conditions that leads to chemical or metabolic generation of reactive species is termed "oxidative stress." The susceptibility to oxidative stress is a function of the overall balance between the factors that exert oxidative stress and those that exhibit antioxidant capability. There is currently great interest in the potential contribution of increased oxidative stress to the development of complications in diabetes mellitus. Direct measurement of oxidative stress in vivo is a very complex question, because free radicals are highly reactive, have a very short life, and are present in very low concentrations. Thus, indirect methods, used for measuring secondary products of oxidative stress, are rather unspecific and may give conflicting data. Nitrotyrosine detection in plasma and tissues may be a useful method to demonstrate peroxynitrite-mediated damage. The total radical-trapping potential (TRAP) in plasma represents a more reliable estimation of serum antioxidant capability than the measurement of each known antioxidant. The detection of increased levels of oxidation products in tissue and biological fluids is important to investigate the relation between free radical production and the development of pathology. This hypothesis suggests the possibility of a therapeutic intervention with antioxidant agents. The identification of a useful marker to assess the effect of antioxidants on oxidative stress seems to be mandatory.

Membrane interactions involved in the induction of acid labile interferon alpha.

Human normal peripheral blood mononuclear cells (PBMC) produce acid-labile interferon (IFN) alpha when stimulated in vitro with HIV-infected cells fixed with glutaraldehyde. The cells responsible for IFN production are mainly B lymphocytes. The present study was aimed to further elucidate the cellular source of this IFN and to analyze the membrane interactions involved in the induction process. To this purpose PBMC were stimulated with inducers of acid labile IFN alpha in the presence or absence of a panel of monoclonal antibodies (MoAbs) against antigens of the lymphocyte membrane, namely HLA Class I and II and CD4. The results indicate that both HLA Class II and CD4 antigens are involved in the induction process. Conversely B cell lines seem capable of producing conventional alpha IFN but they fail to produce acid labile IFN alpha even in the presence of cooperating CD4 positive T cell lines. Furthermore PBMC cultured for more than 20 hours prior to stimulation lose the ability to produce acid labile IFN alpha, while remaining fully capable of producing conventional IFN alpha and gamma. It remains to be established whether this phenomenon reflects the disappearance of some membrane structure necessary for acid labile IFN alpha induction, or whether it is due to some early appearing functional alteration of B cells.

Thermal and optical study of the kinetics of the nematic-isotropic transition in octylcyanobiphenyl.

It is shown in this paper that the kinetics of the nematic-isotropic (NI) transition in 30-microm-thick octylcyanobiphenyl liquid crystal films is strongly affected by the cell walls. We have found that this is due to the modification of the wetting properties of the liquid crystal depending on the surface treatment. The results have been obtained with an experimental setup which allows the simultaneous high resolution study of the sample thermal properties and texture evolution with temperature. An accurate determination of the width of the two phase coexistence region associated with the NI transition has been possible and it is shown that it is affected by the presence of a surfactant. The results have been interpreted with a simple model which is based on the possible presence of a well-defined interface between the nematic and the isotropic phases in the coexistence region, which depends not only on the thermal gradients in the sample but also on the surface treatments.

Small quartz silica spheres induced disorder in octylcyanobiphenyl (8CB) liquid crystals: a thermal study.

A photopyroelectric technique has been applied to the study of specific heat and thermal conductivity of homeotropically aligned mixtures of small quartz spheres (aerosil) and octylcyanobiphenyl (8CB) with concentration 0