Ionophore constructed from non-covalent assembly of a G-quadruplex and liponucleoside transports K+-ion across biological membranes.

The selective transport of ions across cell membranes, controlled by membrane proteins, is critical for a living organism. DNA-based systems have emerged as promising artificial ion transporters. However, the development of stable and selective artificial ion transporters remains a formidable task. We herein delineate the construction of an artificial ionophore using a telomeric DNA G-quadruplex (h-TELO) and a lipophilic guanosine (MG). MG stabilizes h-TELO by non-covalent interactions and, along with the lipophilic side chain, promotes the insertion of h-TELO within the hydrophobic lipid membrane. Fluorescence assays, electrophysiology measurements and molecular dynamics simulations reveal that MG/h-TELO preferentially transports K+-ions in a stimuli-responsive manner. The preferential K+-ion transport is presumably due to conformational changes of the ionophore in response to different ions. Moreover, the ionophore transports K+-ions across CHO and K-562 cell membranes. This study may serve as a design principle to generate selective DNA-based artificial transporters for therapeutic applications.

G-Quadruplex-Specific Cell-Permeable Guanosine-Anthracene Conjugate Inhibits Telomere Elongation and Induces Apoptosis by Repressing the c-MYC Gene.

We herein report a cell-membrane-permeable molecular probe ADG, prepared by conjugating guanosine with anthracene, selectively interacts with c-MYC G-quadruplex over other promoter and telomeric quadruplexes as well as duplex DNA. NMR spectroscopy suggests that ADG interacts with terminal G-quartets as well as with the nearby G-rich tract (G13-G14-G15 and G8-G9-G10) of c-MYC quadruplex. In vitro cellular studies indicate that ADG represses c-MYC expression by stabilizing its promoter G-quadruplex and alters c-MYC-related cellular events. ADG suppresses hTERT and BCL2 gene expressions in a promoter-independent manner, inhibits elongation of telomere length, and activates apoptotic cascades in cancer cells.

In vitro screening of known drugs identified by scaffold hopping techniques shows promising leishmanicidal activity for suramin and netilmicin.

OBJECTIVE: The rapid emergence of drug resistant Leishmanial strains makes it imperative to continue the development of cheap and effective drugs against the parasite. Due to the absence of effective vaccines against leishmaniasis, current therapeutic measures exclusively rely on chemotherapy. Here we attempt, to identify novel antileishmanial from a list of known drugs determined from a previous bioinformatics study. Synergism between various drug combinations (involving netilmicin, suramin, paromomycin and curcumin) have been estimated to identify potent multidrug therapies to combat the disease. RESULTS: The drugs were screened against Leishmania promastigotes by utilizing the MTT assay and against intracellular amastigotes using murine Macrophage like tumor cell, RAW 264.7 as a host. In vitro drug interactions were tested for several drug combinations with a modified fixed ratio isobologram method against both Leishmania major and Leishmania donovani. This work reports the in vitro antileishmanial activity for the aminoglycoside netilmicin (for some Leishmania parasites) and the anti-trypanosomatid suramin. Synergism was also observed between paromomycin-suramin and netilmicin-curcumin.

Self-Assembly of a Guanosine Derivative To Form Nanostructures and Transmembrane Channels.

We herein report the self-assembly of a lipophilic bromoguanosine derivative (G1) in homogeneous solution, in the solid state and in planar bilayer membranes. The self-assembly of G1, driven by H-bonding and π-π stacking interactions can form different nano-structures depending on incubation time. The G1 nanostructure is able to bind a bioactive dye like Rose Bengal. In crystal state, it shows ribbon type H-bonding pattern and exhibits birefringence in polarized light. And further, the self-assembled nanostructure of G1 can form discrete transmembrane ion channels in lipid bilayer membranes, enabling passage of potassium ions.

Interferometric focal length measurement of positive and negative lenses using a lateral-shearing cyclic path optical configuration setup and polarization phase-shifting interferometry.

We present a simple interferometric focal length measurement technique for measuring the focal length of positive and negative lenses using a lateral-shearing cyclic path optical configuration (CPOC) setup and polarization phase-shifting interferometry (PPSI). The technique requires an auxiliary lens, whose focal length need not be known accurately, for generating a focused point source at its focal plane. The focal point of the test lens is adjusted to be in the vicinity of the focus of the auxiliary lens. The radii of the resulting spherical wave fronts emerging from the test lens, due to the defocus, for two different longitudinal shifted positions of the test lens are measured using the lateral-shearing CPOC setup and PPSI. Focal length of the test lens is determined from the known longitudinal shift and from the measured radii of the spherical wave fronts. Results obtained for 200.0 mm convex and 100.0 mm concave test lenses are presented.

Supramolecular Hydrogel Inspired from DNA Structures Mimics Peroxidase Activity.

We herein report that hydrogels can be prepared from guanosine and boronic acids in the presence of K+ and Pb2+ ions. These supramolecular hydrogels are formed via G-quartet like self-assembly of guanosine and its boronate esters. The potential of this hydrogel construct in mimicking enzyme-like activity has been demonstrated for the first time. We have observed that the self-assembled structure present in K+ stabilized hydrogel binds to iron(III)-hemin and shows peroxidase activity, catalyzing oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. Furthermore, the conformation of the G-quartet assemblies in the hydrogel can be altered by varying the stabilizing cations K+ and Pb2+. This conformational switching has been used to devise a molecular logic gate for sensing of toxic Pb2+ ions.

Bis-triazolyl diguanosine derivatives as synthetic transmembrane ion channels.

In nature, ion channels facilitate the transport of ions across biological membranes. The development of artificial ion channels that can mimic the fundamental functions of the natural ones would be of great importance to biological research. Artificial ion channels based on nucleoside derivatives are expected to be biocompatible with functions that can be controlled by the presence or absence of biologically relevant molecules. This protocol describes the detailed procedures for the synthesis and ion-channel activity of four diguanosine derivatives, each made up of two guanosine moieties separated by a covalent linker (e.g., PEG). The procedure describes the preparation of guanosine azide and guanosine alkine building blocks, as well as the preparation of four distinct synthetic linkers each containing either two alkynes or two azides. The diguanosine derivatives are synthesized using a 'one-pot' modular synthetic approach based on Cu(I)-catalyzed azide and alkyne cycloaddition. The ion-channel activity of these diguanosine derivatives for the transportation of ions across a phospholipid bilayer is investigated using voltage-clamp experiment. By using the PEG-containing diguanosine as an example, we describe how to determine the ion-channel activity in the presence of different metal ions (e.g., Na(+), K(+) and Cs(+)) and the inhibition of the ion-channel activity using the nucleobase cytosine. The approximate time frame for the synthesis of the PEG dinucleoside is 3 d, and that for the experiments to evaluate its ability to transport K(+) ion across a phospholipid bilayer is ∼8-10 h.

Measurement of the surface form error of large aperture plane optical surfaces with a polarization phase-shifting liquid reference reflection Fizeau interferometer.

A polarization phase-shifting liquid reference reflection Fizeau interferometer has been proposed. A polarization cyclic path optical configuration along with a concave telescope mirror is used to produce a pair of expanded, collimated p and s polarized beams with a small angular separation between them. The collimated beams are deflected along a vertical direction toward a Fizeau interferometer cavity formed between a liquid surface that acts as a reference surface and a plane test surface. Either the p or s polarized beam is allowed to strike the liquid surface normally and the orientation of the test surface is adjusted to reflect the other beam, having orthogonal linear polarization, in the direction of the normally reflected reference beam from the liquid surface. A combination of a quarter-wave plate and linear polarizer is used to apply polarization phase shift between the test and reference beams, and quantitative surface form error is measured by applying phase-shifting interferometry. A method for elimination of the residual system aberration is discussed. Results obtained for an optically polished BK-7 disk of clear aperture diameter ≈160 mm are presented.

Langerhans cell histiocytosis revisited: Case report with review.

Langerhans cell histiocytosis (LCH) is a group of idiopathic disorders characterized by proliferation of bone marrow derived Langerhans cells and mature eosinophils. Their clinical features simulate common oral findings such as gingival enlargement, oral ulcers, and mobility of teeth, along with nonspecific radiographic features; hence, diagnosing such lesions becomes difficult for the oral physicians. These lesions are commonly seen in childhood; however, we are reporting a case of LCH in 29-year-old adult male. A provisional diagnosis of giant cell granuloma was considered based on history and examination, although the lesion was histologically proven to be LCH and was confirmed with immunohistochemical staining of S100 protein and CD1a antigen. The purpose of this paper is to enhance the understanding of diverse, nonpathognomical oral presentation of LCH that is easily misdiagnosed and overlooked by dentist.

Measurement of displacement and distance with a polarization phase shifting folded Twyman Green interferometer.

A Sagnac interferometer (SI), consisting of a polarization beam splitter (PBS), along with two equally spaced plane mirrors that are inclined at 45° to each other, is transformed into a folded Twyman Green interferometer (TGI) by placing a mirrored parallel plate (MPP) into the hypotenuse arm of the SI. The converging input beam produced by a telescope objective (TO) is split into reflected (s-polarized) and transmitted (p-polarized) components by the PBS. The p- and s-polarized focal spots are made to fall on the mirrored end surfaces of the parallel plate (PP). The retroreflected p- and s-polarized beams become collimated after passing through the TO. A linear shift of the PP in either (longitudinal) direction alters the positions of the p- and s-polarized focal spots and results in a set of converging and diverging spherical wavefronts that interfere to form concentric circular fringes. We applied polarization phase-shifting interferometry to obtain the optical path difference (OPD) variation of the interference field. The displacement is calculated from the OPD variation. A validation experiment has been carried out by introducing known shifts to the PP. The setup can be used for displacement as well as distance measurement.

A DNA-inspired synthetic ion channel based on G-C base pairing.

A dinucleoside containing guanosine and cytidine at the end groups has been prepared using a modular one-pot azide-alkyne cycloaddition. Single channel analysis showed that this dinucleoside predominantly forms large channels with 2.9 nS conductance for the transport of potassium ions across a phospholipid bilayer. Transmission electron microscopy, atomic force microscopy, and circular dichroism spectroscopy studies reveal that this dinucleoside can spontaneously associate through Watson-Crick canonical H-bonding and π-π stacking to form stable supramolecular nanostructures. Most importantly, the ion channel activity of this G-C dinucleoside can be inhibited using the nucleobase cytosine.

Clear cell carcinoma of minor salivary gland: A case of clinical dilemma.

Clear cell tumor in oral cavity constitutes an assorted group of lesions, which may be odontogenic, metastatic or of salivary gland origin. Those associated with salivary glands accounts for less than 1% of total cases mainly seen in the major salivary gland. Occurrence of clear cell carcinoma in minor salivary gland is rare and uncommon. Hence, this case of intraoral clear cell carcinoma associated with minor salivary gland of palate in a 57-year-old male patient is being reported.

Determination of the surface form error of a spherical mirror with phase shifting Sagnac interferometer.

A polarization Sagnac interferometer (SI) is used to produce two laterally separated, identical, convergent emergent beams with linear orthogonal polarizations. The emergent p-polarized and s-polarized beams converge toward their respective focal points. The test and reference spherical mirrors are placed at confocal positions with respect to the s and p focal points so as to normally reflect back the test and reference beams through the SI that recombines the test and reference waves. Polarization phase shifting interferometry is applied to obtain the surface form error of the test surface with respect to the reference surface. A two-step measurement procedure eliminates the system aberrations. Results obtained for a concave spherical test surface with respect to a convex spherical reference surface are presented. The optical configuration is relatively less susceptible to external mechanical vibration.

Triazole-tailored guanosine dinucleosides as biomimetic ion channels to modulate transmembrane potential.

A "click" ion channel platform has been established by employing a clickable guanosine azide or alkyne with covalent spacers. The resulting guanosine derivatives modulated the traffic of ions across the phospholipid bilayer, exhibiting a variation in conductance spanning three orders of magnitude (pS to nS). Förster resonance energy transfer studies of the dansyl fluorophore with the membrane binding fluorophore Nile red revealed that the dansyl fluorophore is deeply embedded in the phospholipid bilayer. Complementary cytosine can inhibit the conductance of the supramolecular guanosine channels in the phospholipid bilayers.

Determination of the index inhomogeneity of transparent isotropic optical material with a dual Sagnac interferometer.

A technique for the measurement of inhomogeneity of optical glass, fused silica, etc., using a Sagnac interferometer (SI) has been presented. An SI produces a pair of laterally separated, mutually parallel, collimated beams with orthogonal planes of polarization, i.e., p and s polarizations from an expanded, linearly polarized (45°) collimated He-Ne (632.8 nm) input laser beam. The p and s beams pass through a liquid-filled cell with plane parallel glass windows. The test glass with plane parallel end surfaces is kept in the path of the p beam in the index matching liquid, while the s beam traverses a parallel path through the liquid. Another SI recombines the emergent p and s beams by removing the lateral shear. A quarter-wave plate transforms the state of polarization of the beams to opposite circular polarizations of which the components selected by a linear polarizer interfere to form Fizeau fringes. Polarization phase shifting interferometery has been applied to determine the optical path difference (OPD) variations. The OPD variation without the test glass is subtracted from that with test glass to eliminate the effect of system aberration. The results for a phosphate laser glass sample have been presented.

A fluorescent guanosine dinucleoside as a selective switch-on sensor for c-myc G-quadruplex DNA with potent anticancer activities.

Like likes like! A novel fluorescent C2 -symmetric guanosine-based dinucleoside has been engineered by chemical ligation of two guanosine units with a biocompatible dansyl tag. The nucleoside exhibits high selectivity for c-myc G-quadruplex DNA through fluorescence enhancement over duplex DNA and other promoter G-quadruplexes (see scheme). It stains the nucleus preferentially, arrests the cell cycle at the G2/M phase, inhibits cell growth, and induces apoptosis in A375 cancer cells.

Self-referenced technique for the determination of meridional figure errors of a toroidal mirror with a Sagnac interferometer.

A simple, self-referenced technique for the determination of meridional surface slope errors of toroidal mirrors (TMs) used in synchrotron radiation is presented. An expanded, collimated, linearly polarized laser beam is allowed to fall on a TM, and the reflected toric wavefront from the TM is allowed to enter a Sagnac interferometer based lateral shearing interferometer setup, which duplicates the beam into identical wavefront components having orthogonal linear polarizations, i.e., p and s polarizations, and introduces appropriate lateral shear between the identical pair of wavefronts along the meridional direction. The laterally sheared identical wavefronts interfere when brought to the same state of polarization. The optical path difference (OPD) variation along the direction of the lateral shear in the interference field is a map of the slope variation. Polarization phase shifting interferometery has been applied to find the OPD variation and thus the slope distribution and errors. Results obtained for a TM of moderately long average radius of curvature along the central meridional section and a relatively shorter radius of curvature along the sagittal section are presented and compared with that obtained with a long trace profiler.

Simultaneous determination of refractive index and thickness of moderately thick plane-parallel transparent glass plates using cyclic path optical configuration setup and a lateral shearing interferometer.

We present a simple technique for simultaneous determination of refractive index and thickness of moderately thick plane-parallel transparent glass plates (GPs) using a cyclic path optical configuration (CPOC) setup and a wedge shear plate as lateral shearing interferometer. The CPOC setup is used to simultaneously focus the counterpropagating converging beams at a common point at its hypotenuse arm. The apparent thickness and real thickness of the test GP are determined by observing three retrocollimation positions of the GP surfaces with respect to the common focus point. The RI is obtained by dividing the real thickness with apparent thickness of the GP. Presented in this paper are the results obtained for a test GP with a thickness of 14.983 mm and a RI of 1.515.

Opaque optics thickness measurement using a cyclic path optical configuration setup and polarization phase shifting interferometry.

Thickness measurement of an opaque optics using a cyclic path optical configuration (CPOC) setup and polarization phase shifting interferometry (PPSI) is presented. The CPOC setup is used to simultaneously focus two orthogonally polarized counterpropagating converging beams at its hypotenuse arm. The opaque optics is placed at the hypotenuse arm of the CPOC setup such that one of its surfaces reflects back one of the counterpropagating focusing beams. Because of the thickness of the opaque optics, the other focusing beam suffers a longitudinal shift in the beam focus. Applying PPSI, the longitudinal shift in the beam focus which is twice the thickness of the opaque optics is determined. The results obtained for a silicon plate of thickness 0.660 mm with a measurement uncertainty of 0.013 mm are presented.

Diffusion and birefringence of bioactive dyes in a supramolecular guanosine hydrogel.

Transparent self-standing supramolecular hydrogels were readily prepared by the potassium-ion-mediated self-organization of guanosine and 8-bromoguanosine whilst the individual components precipitated within a few hours. VT-NMR spectroscopy showed that bromoguanosine was a superior gelator compared to guanosine. XRD analysis showed that gel formation was caused by stacked G-quartets. AFM analysis revealed dendritic architectures of the nanofibers in the two-component hydrogel network. DSC profiles showed that the hybrid hydrogels underwent sol-gel transition at lower temperature than the pure guanosine and bromoguanosine hydrogels. Interestingly, bioactive dyes, such as rose bengal, rhodamine-6-G, and fluorescein, could be diffused and released in a controlled manner. UV/Vis absorption and fluorescence spectroscopy and CLSM were used to investigate the diffusion behavior of dyes in the hydrogel network. These dyes exhibited strong birefringence in the gel network (0.07-0.1) as a result of the anisotropic organization.