Distinguishing and quantification of the human visual pathways using high-spatial-resolution diffusion tensor tractography

Quantification of the living human visual system using MRI methods has been challenging, but several applications demand a reliable and time-efficient data acquisition protocol. In this study, we demonstrate the utility of high-spatial-resolution diffusion tensor fiber tractography (DTT) in reconstructing and quantifying the human visual pathways. Five healthy males, age range 24–37 years, were studied after approval of the institutional review board (IRB) at The University of Texas Health Science Center at Houston. We acquired diffusion tensor imaging (DTI) data with 1-mm slice thickness on a 3.0-Tesla clinical MRI scanner and analyzed the data using DTT with the fiber assignment by continuous tractography (FACT) algorithm. By utilizing the high-spatial-resolution DTI protocol with FACT algorithm, we were able to reconstruct and quantify bilateral optic pathways including the optic chiasm, optic tract, optic radiations free of contamination from neighboring white matter tracts.     

Microwave-Assisted Synthesis and Antimicrobial Activity of 3-(Arylsulfanyl)-4-hydroxy-2<Emphasis Type="Italic">H</Emphasis>-chromen-2-ones

An efficient microwave-assisted synthesis of 3-(arylsulfanyl)-4-hydroxy-2H-chromen-2-ones by condensation of arenesulfonohydrazides with 4-hydroxy-2H-chromen-2-one in the presence of iodine is described. The synthesized compounds were characterized by spectral data (IR, ¹H and ¹³C NMR, and mass spectra and elemental analyses) and were tested for their in vitro antimicrobial activity against bacterial and fungal organisms.     

A three‐dimensional net of Δ‐tris(1,10‐phenanthroline)ruthenium(II) in the dual‐metal self‐assembly of bis[tris(1,10‐phenanthroline)ruthenium(II)] tetraisothiocyanatoiron(II) bis(perchlorate)

The title compound, [Ru(C₁₂H₈N₂)₃]₂[Fe(NCS)₄](ClO₄)₂, crystallizes in a tetragonal chiral space group (P4₁2₁2) and the assigned absolute configuration of the optically active molecules was unequivocally confirmed. The Δ‐[Ru^II(phen)₃]²⁺ complex cations (phen is 1,10‐phenanthroline) interact along the 4₁ screw axis parallel to the c axis, with an Ru...Ru distance of 10.4170 (6) Å, and in the ab plane, with Ru...Ru distances of 10.0920 (6) and 10.0938 (6) Å, defining a primitive cubic lattice. The Fe atom is situated on the twofold axis diagonal in the ab plane. The supramolecular architecture is supported by C—H...O interactions between the [Ru^II(phen)₃]²⁺ cation and the disordered perchlorate anion. This study adds to the relatively scarce knowledge about intermolecular interactions between [Ru(phen)₃]²⁺ ions in the solid state, knowledge that eventually may also lead to a better understanding of the solution state interactions of this species; these are of immense interest because of the photochemical properties of these ions and their interactions with DNA.     

Complexation behavior of alpha-, beta-, and gamma-cyclodextrin in modulating and constructing polymer networks

A systematic study of the host-guest complexation by alpha-, beta-, and gamma-cyclodextrin (CD) in either the free state or as substituents of poly(acrylic acid) (PAA) with the hydrophobic n-octadecyl groups, C18, substituted onto PAA (HMPAA) and its effect on polymer aggregation and network formation is reported. Free alpha-CD, beta-CD, and gamma-CD mask hydrophobic associations between the C18 substituent of HMPAA in aqueous solution and form host-guest complexes with a 1:1 or CD:C18 substituent stoichiometry at 0.5 wt % polymer concentration. For alpha-CD this host-guest stoichiometry changes to 2:1 or 2alpha-CD:C18 at > or =1 wt % polymer concentrations but not for beta-CD and gamma-CD. Shear-thickening occurs when gamma-CD complexes C18 HMPAA substituents. Upon addition of sodium dodecyl sulfate, SDS (SDS:CD = 1:1), the hydrophobic associations between C18 diminished by alpha-CD masking were fully restored, were only partly restored in the case of beta-CD, and not restored for gamma-CD. When alpha- and beta-CD substituted PAA (alpha-CDPAA and beta-CDPAA) were mixed with HMPAA polymer, networks formed. As for free beta-CD, the beta-CD substituents of beta-CDPAA also formed 1:1 or beta-CD:C18 stoichiometry host-guest complexes with the C18 substituents of HMPAA. The alpha-CD substituents of alpha-CDPAA also formed 1:1 or alpha-CD:C18 stoichiometry host-guest complexes with some indication of the formation of 2:1 or 2alpha-CD:C18 stoichiometry host-guest complexes at polymer concentrations > or =1 wt %. The polymer networks formed by beta-CDPAA with HMPAA are less viscous than those formed by alpha-CDPAA, for which shear-thickening occurs at polymer concentrations > or =2 wt %. It is evident that the difference in CD annular size and its match with the C18 of HMPAA control the diversity of the interactions of alpha-CD, beta-CD, gamma-CD, alpha-CDPAA, and beta-CDPAA with HMPAA.     

Photoswitched DNA-binding of a photochromic spiropyran

The dramatically different DNA-binding properties of the two isomeric forms of a photochromic spiropyran have been demonstrated, enabling photoswitched DNA binding. The closed, UV-absorbing form shows no signs of interaction with DNA. Upon UV exposure the spiropyran is isomerized to the open form that binds to DNA by intercalation. The process is fully reversible as the corresponding dissociation process is induced by visible light.     

Kinetic characterization of an extremely slow DNA binding equilibrium

We here exploit the recently reported thermodynamic preference for poly(dAdT)(2) over mixed-sequence calf thymus (ct) DNA of two binuclear ruthenium complexes, DeltaDelta-[mu-bidppz(bipy)4Ru2](4+) (B) and DeltaDelta-[mu-bidppz(phen)(4)Ru(2)](4+) (P), that bind to DNA by threading intercalation, to determine their intrinsic dissociation rates. After adding poly(dAdT)(2) as a sequestering agent to B or P bound to ct-DNA, the observed rate of change in luminescence upon binding to the polynucleotide reflects the rate of dissociation from the mixed sequence. The activation parameters for the threading and dissociation rate constants allow us for the first time to characterize the thermodynamics of the exceedingly slow threading intercalation equilibrium of B and P with ct-DNA. The equilibrium is found to be endothermic by 33 and 76 kJ/mol, respectively, and the largest part of the enthalpy difference between the complexes originates from the forward threading step. At physiological temperature (37 degrees C) B and P have dissociation half-lives of 18 and 38 h, respectively. This is to our knowledge the slowest dissociating noncovalently bound DNA-drug reported. SDS sequestration is the traditional method for determination of rate constants for cationic drugs dissociating from DNA. However, the rates may be severely overestimated for slowly dissociating molecules due to unwanted catalysis by the SDS monomers and micelles. Having determined the intrinsic dissociation rates with poly(dAdT)(2) as sequestering agent, we find that the catalytic effect of SDS on the dissociation rate may be up to a factor of 60, and that the catalysis is entropy driven. A simple kinetic model for the SDS concentration dependence of the apparent dissociation rate suggests an intermediate that involves both micelles and DNA-threaded complex.     

Direct determination of glyphosate using hydrophilic interaction chromatography with coulometric detection at copper microelectrode

A simple, rapid, and low-cost coulometric method for direct detection of glyphosate using hydrophilic interaction chromatography is presented. The principle of detection is based on the enhancement of the anodic current of copper microelectrode in the presence of complexing agents, such as glyphosate, with the formation of a soluble Cu(II) complex. Under optimized conditions, the limit of detection (S/R = 3) for glyphosate was 0.1 mg L⁻¹ (0.59 μM) without any preconcentration method. The calibration curve has been found linear in all concentration range tested (from limit of detection to 34 mg L⁻¹) with an excellent correlation coefficient (0.9999). The present method was successfully applied for the determination of glyphosate in fruit juices without any kind of extraction, clean-up, or preconcentration step, with recoveries of 92 and 90% for apple and grape juice, respectively.     

Λ‐{1,4,7,10‐Tetrakis­[(S)‐2‐hydroxy­propyl‐κO]‐1,4,7,10‐tetra­aza­cyclo­do­decane‐κ4N}cadmium(II) bis(2,4,6‐tri­nitro­phenolate) aceto­nitrile solvate

Crystallization of [Cd(S‐thpc12)](ClO₄)₂·H₂O {S‐thpc12 is 1,4,7,10‐tetrakis­[(S)‐2‐hydroxy­propyl]‐1,4,7,10‐tetra­aza­cyclo­do­decane} in the presence of two equivalents of sodium picrate monohydrate (sodium 2,4,6‐tri­nitro­phenolate monohydrate) diastereoselectively produces a neutral receptor complex, viz. the title compound, Λ‐[Cd(C₂₀H₄₄N₄O₄)](C₆H₂N₃O₇)₂·CH₃CN. In this complex, two picrate anions hydrogen bond, via their phenolate moieties, to the pendant hydroxyl groups of the receptor which, together with the four N atoms, themselves bond to Cd^II in an approximately cubic arrangement. One picrate anion hydrogen bonds to all four hydroxyl groups, one of which also acts as the sole hydrogen‐bond donor to the second picrate anion.     

Characterization of PDMS-modified glass from cast-and-peel fabrication

In glass/poly(dimethylsiloxane) (PDMS) hybrid microfluidic chips, two different fabrication approaches are used: photolithographic or solid ink molds, or cast-and-peel methods. In the latter, a thin slab of PDMS is laid down and fluid channels are cut manually or by machine. The cast-and-peel approach has been used successfully for low-shear culture devices, among other applications. The main drawback, not reported to date, of cast-and-peel methods is that removal of PDMS (exposing the glass substrate) results in nanoscopic domains of PDMS still attached to the surface. This residual PDMS is not observable by eye, but affects the hydrophobicity of the device. Using contact angle measurement, atomic force and fluorescence microscopy, the changes in glass surfaces from the cast-and-peel technique were elucidated. This study demonstrates the enhanced protein (NeutrAvidin) adsorption on PDMS treated glass surfaces, and the potential influence of altered glass properties on microfluidic applications has been discussed as well.     

New RNA labeling methods offer dramatic sensitivity enhancements in 2H NMR relaxation spectra

A new labeling strategy is presented that greatly facilitates the measurement of 2H spin relaxation rates in RNA molecules as a probe of pico- to nanosecond time scale dynamics. In this labeling scheme the sugar positions are uniformly 13C-labeled, with position 2' protonated and all other sites on the sugar deuterated. Pulse sequences are presented for measurement of 2H R1 and R2 relaxation rates at positions 1', 3', and 4' with sensitivity gains that are on the order of 5-fold relative to previous methods that employed random fractional deuteration. The improved sensitivity is transformative and facilitates the study of motion in moderately sized RNA molecules with good sensitivity. The utility of the approach is demonstrated with an application to HIV-2 TAR, where the site-specific measures of molecular dynamics at sugar positions obtained here complement previous studies of dynamics at aromatic sites in the molecule.