Publications by authors named "Surajit Dhara"

50 Publications

Microrheology to probe smectic clusters in bent-core nematic liquid crystals.

Soft Matter 2020 Aug;16(32):7556-7561

School of Physics, University of Hyderabad, Hyderabad, India.

Many bent-core nematic liquid crystals exhibit unusual physical properties due to the presence of smectic clusters, known as "cybotactic" clusters, in the nematic phase. Here, we investigate the effect of these clusters on the complex shear modulus (G*(ω)) of two asymmetric bent-core liquid crystals using a microrheological technique. The compound with a shorter hydrocarbon chain (8OCH3) exhibits only a nematic (N) phase whereas the compound with a longer chain (16OCH3) exhibits both nematic (N) and smectic-A (SmA) phases. The rheological results are correlated with the measurements of curvature elastic constants. Our results show that the directional shear modulus of 16OCH3, just above the SmA to N phase transition temperature, is strikingly different than that of 8OCH3, owing to the smectic clusters. An approximate size of the clusters is estimated using a simple model. Therefore, microrheological studies on bent-core nematic liquid crystals are very useful in extracting information about underlying smectic clusters.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0sm00796jDOI Listing
August 2020

Chiral Bent-Shaped Molecules Exhibiting Unusually Wide Range of Blue Liquid-Crystalline Phases and Multistimuli-Responsive Behavior.

Chemistry 2020 May 21;26(26):5859-5871. Epub 2020 Apr 21.

Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Sector 81, Knowledge City, Manauli, 140306, India.

Recently, an unprecedented observation of polar order, thermochromic behavior, and exotic mesophases in new chiral, bent-shaped systems with a -CH moiety placed at the transverse position of the central core was reported. Herein, a homologous series of compounds with even-numbered carbon chains from n=4 to 18 were synthesized, in which -Cl was substituted for -CH at the kink position and a drastic modification in the phase structure of the bent-shaped molecule was observed. An unusual stabilization of the cubic blue phase (BP) over a wide range of 16.4 °C has been witnessed. Two homologues in this series (1-12 and 1-14) exhibit an interesting phase sequence consisting of BPI/II, chiral nematic, twist grain boundary, smectic A, and smectic X (SmX) phases. The higher homologues (1-16 and 1-18) stabilize the SmX phase enantiotropically over the entire temperature range. Crystal structure analysis confirmed the bent molecular architecture, with a bent angle of 148°, and revealed the presence of two different molecular conformations in an asymmetric unit of compound 1-4. A DFT study corroborated that the -Cl moiety at the central core of the molecule led to an increase in the dipole moment along the transverse direction, which, in turn, facilitated the unusual stabilization of frustrated structures. Crystal polymorphism has been evidenced in three homologues (1-10, 1-12, and 1-14) of the series. On the application of mechanical pressure through grinding, compound 1-10 transformed from a bright yellow crystalline solid to a dark orange-green amorphous solid, which reversed upon dropwise addition of dichloromethane, indicating reversible mechanochromism in this class of compounds. In addition, excellent thermochromic behavior has been observed for compound 1-10 with a controlled temperature-color combination.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/chem.201905707DOI Listing
May 2020

Whispering gallery mode lasing in mesomorphic liquid crystal microdroplets.

Soft Matter 2019 Oct;15(39):7832-7837

School of Physics, University of Hyderabad, Hyderabad-500046, India.

In recent years, investigation on the non-display applications of liquid crystals has increased considerably. One of the emerging applications is whispering gallery mode (WGM) lasing. Here, we report experimental studies on the morphology and WGM lasing in nematic (N), smectic-A (SmA) and smectic-C (SmC) microdroplets dispersed in a highly transparent and low refractive index perfluopolymer. The mesomorphic microdroplets, obtained by varying the temperature, exhibit radial director configuration. The SmA microdroplets are found to be highly stable and robust against mechanical stress compared to the N and SmC microdroplets. We study lasing properties such as intensity, threshold pump energy and linewidth, and show that overall the SmA microdroplets are superior to the N and SmC microdroplets. The experimental results are discussed based on the orientation of the dye molecules, director fluctuations and tilting at the interface.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c9sm01132cDOI Listing
October 2019

Colloidal analogues of polymer chains, ribbons and 2D crystals employing orientations and interactions of nano-rods dispersed in a nematic liquid crystal.

Sci Rep 2019 Mar 15;9(1):4652. Epub 2019 Mar 15.

School of Physics, University of Hyderabad, Hyderabad, 500046, India.

Robust control over the position, orientation and self-assembly of nonspherical colloids facilitate the creation of new materials with complex architecture that are important from technological and fundamental perspectives. We study orientation, elastic interaction and co-assembly of surface functionalized silica nano-rods in thin films of nematic liquid crystal. With homeotropic boundary condition, the nano-rods are predominantly oriented perpendicular to the nematic director which is different than the mostly parallel orientation of the micro-rods. The percentage of perpendicular nano-rods are significantly larger than the parallel nano-rods. The perpendicular nano-rods create very weak elastic deformation and exhibit unusual, out-of-plane, attractive interaction. On the other hand, the nano-rods oriented parallel to the director create strong elastic deformation and shows anisotropic, in-plane, dipolar interaction. In both orientations, the induced defects reside in the nano-rods. With the help of a dynamic laser tweezers and using nano-rods as building blocks we demonstrate colloidal analogues of linear polymer chains, ribbons and two-dimensional binary crystals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-019-40198-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6420569PMC
March 2019

Orientation, elastic interaction and magnetic response of asymmetric colloids in a nematic liquid crystal.

Sci Rep 2019 Jan 14;9(1):81. Epub 2019 Jan 14.

School of Physics, University of Hyderabad, Hyderabad, 500046, India.

Colloidal particles in nematic liquid crystals create elastic distortion and experience long-range forces. The symmetry of elastic distortion and consequently the complexity of interaction strongly depends largely on the liquid crystal anchoring, topology and shape of the particles. Here, we introduce a new nematic colloidal system made of peanut-shaped hematite particles. We report experimental studies on spontaneous orientation, mutual interaction, laser assisted self-assembly and the effect of external magnetic fields on the colloids. Majority of the colloids spontaneously orient either parallel or perpendicular to the nematic director. The colloids that are oriented perpendicularly exhibit two types of textures due to the out of plane tilting, which is corroborated by the Landau-de Gennes Q-tensor modelling. The transverse magnetic moment of the peanut-shaped colloids is estimated by using a simple analysis based on the competing effects of magnetic and elastic torques.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-018-36467-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6331558PMC
January 2019

N-SmA-SmC phase transitions probed by a pair of elastically bound colloids.

Phys Rev E 2018 Mar;97(3-1):032702

School of Physics, University of Hyderabad, Hyderabad 500046, India.

The competing effect of surface anchoring of dispersed microparticles and elasticity of nematic and cholesteric liquid crystals has been shown to stabilize a variety of topological defects. Here we study a pair of colloidal microparticles with homeotropic and planar surface anchoring across N-SmA-SmC phase transitions. We show that below the SmA-SmC phase transition the temperature dependence of interparticle separation (D) of colloids with homeotropic anchoring shows a power-law behavior; D∼(1-T/T_{AC})^{α}, with an exponent α≈0.5. For colloids with planar surface anchoring the angle between the joining line of the centers of the two colloids and the far field director shows characteristic variation elucidating the phase transitions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.97.032702DOI Listing
March 2018

Electrical and thermal tuning of quality factor and free spectral range of optical resonance of nematic liquid crystal microdroplets.

Phys Rev E 2017 Aug 4;96(2-1):022702. Epub 2017 Aug 4.

School of Physics, University of Hyderabad, Hyderabad 500046, India.

We experimentally study the effect of temperature and electric field on the quality (Q) factor and free spectral range (FSR) of whispering-gallery-mode optical resonance of dye-doped nematic liquid crystal microdroplets. Both the Q factor and the FSR are highly sensitive to the temperature and electric field and are tunable. The Q factor decreases, whereas the FSR increases substantially, with increasing temperature and electric field. The variation of the Q factor and FSR is understood based on the change in the effective refractive index and the dynamic size of the microdroplets.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.96.022702DOI Listing
August 2017

Room-Temperature Oligomeric Discotic Nematic Liquid Crystals over a Wide Temperature Range: Structure-Property Relationships.

Chemistry 2017 Aug 19;23(44):10626-10631. Epub 2017 Jul 19.

Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Sector-81, Knowledge City, Manauli, 140306, India.

The design and synthesis of three room-temperature discotic nematic (N ) liquid crystals (LCs) is presented. The LC consists of an azobenzene core attached to which are four pentaalkynylbenzene (PA) units through flexible alkyl spacers. The presence of a short azo linking group provides more disorder in the system, thereby reducing the packing efficiency among the PA units and resulting into the formation of a room-temperature N phase over a wide temperature range. Dielectric constant and birefringence studies were performed to gain further insights into the physical properties of the mesophase.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/chem.201701578DOI Listing
August 2017

Propelling and spinning of microsheets in nematic liquid crystals driven by ac electric field.

Phys Rev E 2017 Jan 30;95(1-1):012710. Epub 2017 Jan 30.

School of Physics, University of Hyderabad, Hyderabad-500046, India.

Dynamics of microparticles in isotropic liquids by transducing the energy of an applied electric field have been studied for decades. Recently, such studies in anisotropic media like liquid crystals have opened up new perspectives in colloid science. Here, we report studies on ac-electric-field-driven dynamics of microsheets in nematic liquid crystals. In planar aligned liquid crystals, with negative dielectric anisotropy, the microsheets are propelled parallel to the director. A steady spinning of the microsheets is observed in homeotropic cells with positive dielectric anisotropy liquid crystals. The velocity of propelling and the angular frequency of spinning depends on the amplitude and the frequency of the applied electric field. The electrokinetic studies of anisotropic microparticles are important as they are potential for applications in microfluidics and in areas where the controlled transport or rotation is required.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.95.012710DOI Listing
January 2017

A new strategy towards the synthesis of a room-temperature discotic nematic liquid crystal employing triphenylene and pentaalkynylbenzene units.

Chem Commun (Camb) 2017 Mar;53(21):3014-3017

Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Sector-81, Knowledge City, Manauli-140306, India.

A new approach is reported for the design of a room-temperature discotic nematic (N) liquid crystal (LC) dimer consisting of a triphenylene and a pentaalkynylbenzene unit linked via flexible alkyl spacers. The formation of the N phase is realized most likely through folding of the dimeric molecule that prevent stacking between the triphenylene units, as suggested by modelling in the mesophase derived from X-ray scattering results and high-level DFT calculations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c6cc09509gDOI Listing
March 2017

Magnetic-field tuning of whispering gallery mode lasing from ferromagnetic nematic liquid crystal microdroplets.

Opt Express 2017 Jan;25(2):1073-1083

We report magnetic field tuning of the structure and Whispering Gallery Mode lasing from ferromagnetic nematic liquid crystal micro-droplets. Microlasers were prepared by dispersing a nematic liquid crystal, containing magnetic nanoparticles and fluorescent dye, in a glycerol-lecithin matrix. The droplets exhibit radial director structure, which shows elastic distortion at a very low external magnetic field. The fluorescent dye doped ferromagnetic nematic droplets show Whispering Gallery Mode lasing, which is tunable by the external magnetic field. The tuning of the WGM lasing modes is linear in magnetic field with a wavelength-shift of the order of 1 nm/100 mT. Depending on the lasing geometry, the WGMs are red- or blue-shifted.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OE.25.001073DOI Listing
January 2017

Macrophage Ontogeny Underlies Differences in Tumor-Specific Education in Brain Malignancies.

Cell Rep 2016 11 10;17(9):2445-2459. Epub 2016 Nov 10.

Cancer Biology and Genetics Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA; Department of Oncology, University of Lausanne, 1066 Lausanne, Switzerland; Ludwig Institute for Cancer Research, University of Lausanne, 1066 Lausanne, Switzerland. Electronic address:

Extensive transcriptional and ontogenetic diversity exists among normal tissue-resident macrophages, with unique transcriptional profiles endowing the cells with tissue-specific functions. However, it is unknown whether the origins of different macrophage populations affect their roles in malignancy. Given potential artifacts associated with irradiation-based lineage tracing, it remains unclear if bone-marrow-derived macrophages (BMDMs) are present in tumors of the brain, a tissue with no homeostatic involvement of BMDMs. Here, we employed multiple models of murine brain malignancy and genetic lineage tracing to demonstrate that BMDMs are abundant in primary and metastatic brain tumors. Our data indicate that distinct transcriptional networks in brain-resident microglia and recruited BMDMs are associated with tumor-mediated education yet are also influenced by chromatin landscapes established before tumor initiation. Furthermore, we demonstrate that microglia specifically repress Itga4 (CD49D), enabling its utility as a discriminatory marker between microglia and BMDMs in primary and metastatic disease in mouse and human.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2016.10.052DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5450644PMC
November 2016

Dynamics of electro-orientation of birefringent microsheets in isotropic and nematic liquid crystals.

Phys Rev E 2016 Sep 29;94(3-1):032701. Epub 2016 Sep 29.

School of Physics, University of Hyderabad, Hyderabad 500046, India.

We study the dynamics of electric field driven multiaxis electro-orientation of birefringent microsheets in both the isotropic and nematic phases of a liquid crystal. For a fixed direction of applied field in the isotropic phase, there are two critical fields above which the microsheets show two orientations. In the nematic phase, it shows three rotations in both planar and homeotropic cells. These orientations are observed at varying voltages and wide time scales and are explained based on the competing effect of the electric, elastic, and viscous torques. The control of the orientation of anisotropic microparticles (both optically and geometrically) by transducing external energy may be useful in electro-optics and photonics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.94.032701DOI Listing
September 2016

Effect of temperature and electric field on 2D nematic colloidal crystals stabilised by vortex-like topological defects.

Soft Matter 2016 Aug;12(32):6812-6

School of Physics, University of Hyderabad, Hyderabad, India.

We report experimental studies on 2D colloidal crystals of dimers stabilized by vortex-like defects in planar nematic and π/2 twisted nematic cells. The dimers are prepared and self-assembled using a laser tweezer. We study the effect of temperature and electric field on the lattice parameters of the colloidal crystals. The lattice parameters vary with the temperature in the nematic phase and a discontinuous structural change is observed at the nematic to smectic-A phase transition. In the nematic phase, we observed a large change in the lattice parameters (≃30%) by applying an external electric field perpendicular to the plane of the 2D crystals. The idea and the active control of the lattice parameters could be useful for designing tunable colloidal crystals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c6sm01244bDOI Listing
August 2016

Unusual temperature dependence of elastic constants of an ambient-temperature discotic nematic liquid crystal.

Soft Matter 2016 Mar;12(11):2960-4

School of Physics, University of Hyderabad, Hyderabad-500046, India.

We report the first experimental studies on the temperature dependence of viscoelastic properties of a room temperature discotic nematic liquid crystal. The splay elastic constant is greater than the bend elastic constant and both show unusual temperature and order parameter dependence. The rotational viscosity is remarkably larger than conventional calamitic liquid crystals. We provide a simple physical explanation based on the columnar short-range order to account for the the unusual temperature dependence of the elastic constants.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c6sm00065gDOI Listing
March 2016

Correction: Experimental studies on the rheology of cubic blue phases.

Soft Matter 2016 Jan;12(4):1330

School of Physics, University of Hyderabad, Hyderabad-500046, India.

Correction for 'Experimental studies on the rheology of cubic blue phases' by Rasmita Sahoo et al., Soft Matter, 2016, DOI: .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c5sm90212fDOI Listing
January 2016

Spherical microparticles with Saturn ring defects and their self-assembly across the nematic to smectic-A phase transition.

Phys Rev E Stat Nonlin Soft Matter Phys 2015 Nov 2;92(5):052501. Epub 2015 Nov 2.

School of Physics, University of Hyderabad, Hyderabad-500046, India.

We report experimental studies on the Saturn ring defect associated with a spherical microparticle across the nematic (N) to smectic-A (SmA) phase transition. We observe that the director distortion around the microparticle changes rapidly with temperature. The equilibrium interparticle separation and the angle between two quadrupolar particles in the N phase are larger than those of the SmA phase. They are almost independent of the temperature in both phases, except for a discontinuous jump at the transition. We assembled a few particles using a laser tweezer to form a two-dimensional colloidal crystal in the N phase. The lattice structure of the crystal dissolves irreversibly across the N-SmA phase transition. The results on the pretransitional behavior of the defect are supported by the Landau-de Gennes Q-tensor modeling.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.92.052501DOI Listing
November 2015

Experimental studies on the rheology of cubic blue phases.

Soft Matter 2016 Jan;12(4):1324-9

School of Physics, University of Hyderabad, Hyderabad-500046, India.

We report detailed experimental studies on the rheology of cubic blue phases. We observe several flow regimes within each blue phase from rheomicroscopy and small angle light scattering experiments. Both the cubic blue phases exhibit solid-like response while the cholesteric phase shows gel-like behavior. The elastic modulus of BP-I is larger than that of BP-II. The shear induced yield transition occurs at a higher strain in BP-II than BP-I. Both the blue phases show stress relaxation through periodic modulation in step-strain experiments. Our results show that the rheological responses of these two phases are significantly different owing to the distinct networks of defect-disclinations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c5sm02299aDOI Listing
January 2016

Orientation, interaction and laser assisted self-assembly of organic single-crystal micro-sheets in a nematic liquid crystal.

Soft Matter 2015 Oct;11(38):7674-9

School of Physics, University of Hyderabad, Hyderabad-500046, India.

Colloidal self-assembly has been one of the major driving themes in material science to obtain functional and advanced optical materials with complex architecture. Most of the nematic colloids reported so far are based on the optically isotropic spherical microparticles. We study organic single crystal micro-sheets and investigate their orientation, interaction and directed assembly in a nematic liquid crystal. The micro-sheets induce planar surface anchoring of the liquid crystal. The elasticity mediated pair interaction of micro-sheets shows quadrupolar characteristics. The average orientation angle of the micro-sheets in a planar cell and the angle between two micro-sheets in a homeotropic cell are supported by the Landau-de Gennes Q-tensor modeling. The self-assembly of the micro-sheets is assisted by a laser tweezer to form larger two-dimensional structures which have the potential for application of colloids in photonics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c5sm01991eDOI Listing
October 2015

Hedgehog signaling pathway is active in GBM with GLI1 mRNA expression showing a single continuous distribution rather than discrete high/low clusters.

PLoS One 2015 16;10(3):e0116390. Epub 2015 Mar 16.

National Institute of Biomedical Genomics, P.O. N.S.S. Kalyani, West Bengal 741251, India.

Hedgehog (Hh) signaling pathway is a valid therapeutic target in a wide range of malignancies. We focus here on glioblastoma multiforme (GBM), a lethal malignancy of the central nervous system (CNS). By analyzing RNA-sequencing based transcriptomics data on 149 clinical cases of TCGA-GBM database we show here a strong correlation (r = 0.7) between GLI1 and PTCH1 mRNA expression--as a hallmark of the canonical Hh-pathway activity in this malignancy. GLI1 mRNA expression varied in 3 orders of magnitude among the GBM patients of the same cohort showing a single continuous distribution-unlike the discrete high/low-GLI1 mRNA expressing clusters of medulloblastoma (MB). When compared with MB as a reference, the median GLI1 mRNA expression in GBM appeared 14.8 fold lower than that of the "high-Hh" cluster of MB but 5.6 fold higher than that of the "low-Hh" cluster of MB. Next, we demonstrated statistically significant up- and down-regulation of GLI1 mRNA expressions in GBM patient-derived low-passage neurospheres in vitro by sonic hedgehog ligand-enriched conditioned media (shh-CM) and by Hh-inhibitor drug vismodegib respectively. We also showed clinically achievable dose (50 μM) of vismodegib alone to be sufficient to induce apoptosis and cell cycle arrest in these low-passage GBM neurospheres in vitro. Vismodegib showed an effect on the neurospheres, both by down-regulating GLI1 mRNA expression and by inducing apoptosis/cell cycle arrest, irrespective of their relative endogenous levels of GLI1 mRNA expression. We conclude from our study that this single continuous distribution pattern of GLI1 mRNA expression technically puts almost all GBM patients in a single group rather than discrete high- or low-clusters in terms of Hh-pathway activity. That is suggestive of therapies with Hh-pathway inhibitor drugs in this malignancy without a need for further stratification of patients on the basis of relative levels of Hh-pathway activity among them.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0116390PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4361547PMC
January 2016

Variant allele frequency enrichment analysis in vitro reveals sonic hedgehog pathway to impede sustained temozolomide response in GBM.

Sci Rep 2015 Jan 21;5:7915. Epub 2015 Jan 21.

National Institute of Biomedical Genomics, Kalyani, West Bengal 741251, India.

Neoplastic cells of Glioblastoma multiforme (GBM) may or may not show sustained response to temozolomide (TMZ) chemotherapy. We hypothesize that TMZ chemotherapy response in GBM is predetermined in its neoplastic clones via a specific set of mutations that alter relevant pathways. We describe exome-wide enrichment of variant allele frequencies (VAFs) in neurospheres displaying contrasting phenotypes of sustained versus reversible TMZ-responses in vitro. Enrichment of VAFs was found on genes ST5, RP6KA1 and PRKDC in cells showing sustained TMZ-effect whereas on genes FREM2, AASDH and STK36, in cells showing reversible TMZ-effect. Ingenuity pathway analysis (IPA) revealed that these genes alter cell-cycle, G2/M-checkpoint-regulation and NHEJ pathways in sustained TMZ-effect cells whereas the lysine-II&V/phenylalanine degradation and sonic hedgehog (Hh) pathways in reversible TMZ-effect cells. Next, we validated the likely involvement of the Hh-pathway in TMZ-response on additional GBM neurospheres as well as on GBM patients, by extracting RNA-sequencing-based gene expression data from the TCGA-GBM database. Finally, we demonstrated TMZ-sensitization of a TMZ non-responder neurosphere in vitro by treating them with the FDA-approved pharmacological Hh-pathway inhibitor vismodegib. Altogether, our results indicate that the Hh-pathway impedes sustained TMZ-response in GBM and could be a potential therapeutic target to enhance TMZ-response in this malignancy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/srep07915DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4300501PMC
January 2015

Discontinuous anchoring transition and photothermal switching in composites of liquid crystals and conducting polymer nanofibers.

Phys Rev E Stat Nonlin Soft Matter Phys 2014 May 8;89(5):052503. Epub 2014 May 8.

School of Physics, University of Hyderabad, Hyderabad 500046, India.

We prepared nanocomposites of a nematic liquid crystal and nanofibers of a conducting polymer (polyaniline). All the nanocomposites exhibit a discontinuous surface anchoring transition from planar to homeotropic in the nematic phase on a perfluoropolymer coated surface with a thermal hysteresis (≈ 5.3 °C). We observe a relatively large bistable conductivity and demonstrate a light driven switching of conductivity and dielectric constant in dye doped nanocomposites in the thermal hysteresis (bistable) region. The experimental results have been explained based on the reorientation of the nanofibers driven by the anchoring transition of the nematic liquid crystal. We show a significant enhancement of the bistable temperature range (≈ 13 °C) by an appropriate choice of compound in the binary system.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.89.052503DOI Listing
May 2014

Rheology of nematic liquid crystals with highly polar molecules.

Phys Rev E Stat Nonlin Soft Matter Phys 2014 Feb 24;89(2):022510. Epub 2014 Feb 24.

School of Physics, University of Hyderabad, Hyderabad 500046, India.

We report experimental studies on the rheology of a few nematic liquid crystals with highly polar molecules (CCH-7, PCH-7, CB-7). The selected molecules have the same alkyl chain (-C(7)H(15)) and cyano (-CN) end group. In the core part of the molecule, CCH-7 has two cyclohexane rings, PCH-7 has one cyclohexane and one aromatic ring, and CB-7 has two aromatic rings. Two viscosities were measured as a function of temperature, namely, η(2) (director parallel to the shear direction) and η(1) (director perpendicular to the shear direction). The orientation of the director was studied using small angle light scattering techniques. η(2) was measured in presheared sample, whereas the electrorheological technique was used to measure η(1). We show that both viscosities of the liquid crystals depend on the number of aromatic rings and Kirkwood correlation factor. The temperature dependent viscosities can be understood based on the intramolecular π-electron conjugation and intermolecular association of highly polar molecules.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.89.022510DOI Listing
February 2014

Rheology of twist-grain-boundary-A liquid crystals.

Phys Rev E Stat Nonlin Soft Matter Phys 2014 Jul 11;90(1):012506. Epub 2014 Jul 11.

School of Physics, University of Hyderabad, Hyderabad 500046, India.

We report studies on the rheological properties of a liquid crystalline analog of Abrikosov phase in type-II superconductors known as twist-grain-boundary-A (TGB(A)) phase. The TGB(A) phase shows a large apparent yield stress compared to the cholesteric (N*) phase. The storage modulus (G') of the TGB(A) phase is significantly larger than the loss modulus (G''). The dynamic relaxation measurements indicate a solid-like behavior of N*, TGB(A), and smectic-C* phases. The complex shear modulus of the TGB(A) phase exhibits a power-law behavior G*(ω) ∼ ω(α) with α ≃ 0.5. The relative amplitude of G' and G'' at various temperatures indicate that the enhanced elasticity of TGB(A) phase is due to the structural defects.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.90.012506DOI Listing
July 2014

Effect of smectic short-range order on the discontinuous anchoring transition in nematic liquid crystals.

J Chem Phys 2014 Jul;141(4):044706

School of Physics, University of Hyderabad, Hyderabad-500046, India.

We report studies on the temperature dependent alignment behavior of a homologous series of trans, trans- 4, 4'-dialkyl-(1α,1' α-bicyclohexyl)-4β-carbonitrile (CCNs) on a perfluoropolymer coated cells. Among six compounds in the series, one (CCN-35) has only nematic phase and the remaining five have either smectic-A or smectic-B in addition to the nematic phase. We simultaneously performed temperature dependent dielectric measurements and optical polarising microscope observation. It is found that except for CCN-35 and CCN-73, the remaining four compounds exhibit discontinuous anchoring transition from planar to homeotropic and vice versa with increasing thermal hysteresis. We developed a simple theory taking into account the effect of smectic short-range order at the substrates to explain the experimental observations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4890532DOI Listing
July 2014

Antagonistic flexoelectric response in liquid crystal mixtures of bent-core and rodlike molecules.

Phys Rev E Stat Nonlin Soft Matter Phys 2013 Jan 24;87(1):012506. Epub 2013 Jan 24.

School of Physics, University of Hyderabad, Hyderabad-500046, India.

We report the measurements of the temperature variations of the flexoelastic coefficient (e(*)/K) of a host calamitic liquid crystal (RO) and its mixture with two guest bent-core (BC-120 and BC-60) liquid crystals. The bent-core (BC) molecules have different core structures and bend angles; namely, θ=/~120° and =/~60°, respectively. We find that e(*)/K is independent of temperature and decreases rapidly with increasing concentration of BC-120 molecules and changes sign from positive to negative. In mixtures with BC-60, e(*)/K is always positive and its concentration-dependent variation is not unique. At 7M% it is significantly large (three times) near the nematic-isotropic transition and decreases strongly with reducing temperature. Dielectric measurement suggests antagonistic orientation of the dipole axes (arrow axes) of the two BC molecules in the host liquid crystal, and based on this, the opposite sign of e(*)/K is explained.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.87.012506DOI Listing
January 2013

Inactivation of the Cdkn2a locus cooperates with HMGA1 to drive T-cell leukemogenesis.

Leuk Lymphoma 2013 Aug 1;54(8):1762-8. Epub 2013 Feb 1.

Hematology Division, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA,

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive leukemia with high relapse rates compared to B-lineage ALL. We previously showed that HMGA1a transgenic mice develop aggressive T-ALL, indicating that HMGA1 causes leukemic transformation in vivo. HMGA1 is also highly expressed in embryonic stem cells, hematopoietic stem cells and diverse, refractory human cancers. Disruption of the CDKN2A tumor suppressor locus occurs in most cases of T-ALL and is thought to contribute to leukemic transformation. To determine whether loss of function of CDKN2A cooperates with HMGA1 in T-ALL, we crossed HMGA1a transgenics onto a Cdkn2a null background. We discovered that T-ALL is markedly accelerated in HMGA1a transgenic Cdkn2a null mice. In addition, these mice recapitulate salient clinical and pathologic features of human T-ALL. HMGA1 is also highly overexpressed in human T-ALL. These findings suggest that HMGA1 plays a causative role in T-ALL and could represent a rational therapeutic target.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3109/10428194.2013.764422DOI Listing
August 2013

Rheological properties of a reentrant nematic liquid crystal.

Phys Rev E Stat Nonlin Soft Matter Phys 2012 Jul 25;86(1 Pt 1):011710. Epub 2012 Jul 25.

School of Physics, University of Hyderabad, Hyderabad 500046, India.

We report experimental studies on small angle light scattering (SALS), and rheodielectric and electrorheological properties of a binary mixture of octyloxy cyanobiphenyl and hexyloxy cyanobiphenyl liquid crystals. The mixture exhibits nematic (N) to smectic-A (SmA) phase transitions, and then again to a reentrant nematic (N(R)) phase transition. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases observed from SALS experiments is attributed to the realignment of the director within the domains. The domains are elongated along the shear direction at higher shear rates. The temperature variation of the effective viscosity and static dielectric constant reveals the changes in the director orientation across N-SmA-N(R) phase transitions. At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at much higher fields. It also exhibits two anomalous peaks across N-SmA-N(R) phase transitions beyond a particular field. The shear modulus of the SmA phase in an intermediate field is significantly larger than that measured at both low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased dislocation density.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.86.011710DOI Listing
July 2012

Slow dynamics in a liquid crystal: 1H and 19F NMR relaxometry.

J Chem Phys 2011 Dec;135(24):244507

School of Physics, University of Hyderabad, Hyderabad, India.

Spin-lattice relaxation rates (R(1H) and R(1F)) of two nuclear species ((1)H and (19)F) are measured at different temperatures in the isotropic phase of a liquid crystal (4(')-butoxy-3(')-fluoro-4-isothiocyanatotolane-4OFTOL), over a wide range of Larmor frequency (10 kHz-50 MHz). Their dispersion profiles are found to be qualitatively very different, and the R(1F) in particular shows significant dispersion (varying over two orders of magnitude) in the entire isotropic range, unlike R(1H). The proton spin-lattice relaxation, as has been established, is mediated by time modulation of magnetic dipolar interactions with other protons (case of like spins), and the discernable dispersion in the mid-frequency range, observed as the isotropic to nematic transition is approached on cooling, is indicative of the critical slowing of the time fluctuations of the nematic order. Significant dispersion seen in the R(1F) extending to very low frequencies suggests a distinctly different relaxation path which is exclusively sensitive to the ultra slow modes apparently present in the system. We find that under the conditions of our experiment at low Zeeman fields, spin-rotation coupling of the fluorine with the molecular angular momentum is the dominant mechanism, and the observed dispersion is thus attributed to the presence of slow torques experienced by the molecules, arising clearly from collective modes. Following the arguments advanced to explain similar slow processes inferred from earlier detailed ESR measurements in liquid crystals, we propose that slowly relaxing local structures representing such dynamic processes could be the likely underlying mechanism providing the necessary slow molecular angular momentum correlations to manifest as the observed low frequency dispersion. We also find that the effects of the onset of cross-relaxation between the two nuclear species when their resonance lines start overlapping at very low Larmor frequencies (below ~400 kHz), provide an additional relaxation contribution.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.3672180DOI Listing
December 2011

Effect of nitroxoline on angiogenesis and growth of human bladder cancer.

J Natl Cancer Inst 2010 Dec 18;102(24):1855-73. Epub 2010 Nov 18.

Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA.

Background: Angiogenesis plays an important role in tumor growth and metastasis; therefore, inhibition of angiogenesis is a promising strategy for developing new anticancer drugs. Type 2 methionine aminopeptidase (MetAP2) protein is likely a molecular target of angiogenesis inhibitors.

Methods: Nitroxoline, an antibiotic used to treat urinary tract infections, was identified from a high-throughput screen of a library of 175,000 compounds for MetAP2 inhibitors and from a parallel screen using the Johns Hopkins Drug Library to identify currently used clinical drugs that can also inhibit human umbilical vein endothelial cells (HUVEC) proliferation. To investigate the mechanism of action of nitroxoline, inhibition of MetAP2 activity and induction of senescence were assessed in HUVEC. To test the antiangiogenic activity of nitroxoline, endothelial tube formation in Matrigel and microvessel formation in Matrigel plugs in vivo were assessed. Antitumor efficacy of nitroxoline was evaluated in mouse models of human breast cancer xenograft (n = 10) and bladder cancer orthotopic xenograft (n = 11). Furthermore, the mechanism of action of nitroxoline was investigated in vivo.

Results: Nitroxoline inhibited MetAP2 activity in vitro (half maximal inhibitory concentration [IC(50)] = 54.8 nM, 95% confidence interval [CI] = 22.6 to 132.8 nM) and HUVEC proliferation (IC(50) = 1.9 μM, 95% CI = 1.54 to 2.39 μM). Nitroxoline inhibited MetAP2 activity in HUVEC in a dose-dependent manner and induced premature senescence in a biphasic manner. Nitroxoline inhibited endothelial tube formation in Matrigel and reduced microvessel density in vivo. Mice (five per group) treated with nitroxoline showed a 60% reduction in tumor volume in breast cancer xenografts (tumor volume on day 30, vehicle vs nitroxoline, mean = 215.4 vs 86.5 mm(3), difference = 128.9 mm(3), 95% CI = 32.9 to 225.0 mm(3), P = .012) and statistically significantly inhibited growth of bladder cancer in an orthotopic mouse model (tumor bioluminescence intensities of vehicle [n = 5] vs nitroxoline [n = 6], P = .045).

Conclusion: Nitroxoline shows promise as a potential therapeutic antiangiogenic agent.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/jnci/djq457DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3001967PMC
December 2010