Electric field gradient at the Hf site and the phase transition in HfV2

The electric quadrupole interaction at the Hf site in the cubic HfV₂ compound, which shows lattice instability when cooled below 120 K, has been studied using the 482 keV (5/2⁺) state in¹⁸¹Ta. The time differential perturbed angular correlation (TDPAC) studies involving (133+136)-482 keV - cascade at room temperature show that only a fraction of¹⁸¹Ta nuclei see a cubic symmetry while the remaining experience a weak, randomly oriented, electric quadrupole interaction described by a Gaussian frequency distribution with _Q=6.1±1.0 Mrad/sec and the relative width =0.5. There is a dramatic change in TDPAC pattern indicating a phase transition when the compound is cooled down to 77 K. At this temperature the quadrupole interaction frequency is found to be _Q=40.6±3.0 Mrad/sec with =0.35. The experimentally observed EFG both at the Hf and the V sites are compared to the theoretical estimates based on point charge model.     

Binding and condensation of plasmid DNA onto functionalized carbon nanotubes: toward the construction of nanotube-based gene delivery vectors

Carbon nanotubes (CNTs) constitute a class of nanomaterials that possess characteristics suitable for a variety of possible applications. Their compatibility with aqueous environments has been made possible by the chemical functionalization of their surface, allowing for exploration of their interactions with biological components including mammalian cells. Functionalized CNTs (f-CNTs) are being intensively explored in advanced biotechnological applications ranging from molecular biosensors to cellular growth substrates. We have been exploring the potential of f-CNTs as delivery vehicles of biologically active molecules in view of possible biomedical applications, including vaccination and gene delivery. Recently we reported the capability of ammonium-functionalized single-walled CNTs to penetrate human and murine cells and facilitate the delivery of plasmid DNA leading to expression of marker genes. To optimize f-CNTs as gene delivery vehicles, it is essential to characterize their interactions with DNA. In the present report, we study the interactions of three types of f-CNTs, ammonium-functionalized single-walled and multiwalled carbon nanotubes (SWNT-NH3+; MWNT-NH3+), and lysine-functionalized single-walled carbon nanotubes (SWNT-Lys-NH3+), with plasmid DNA. Nanotube-DNA complexes were analyzed by scanning electron microscopy, surface plasmon resonance, PicoGreen dye exclusion, and agarose gel shift assay. The results indicate that all three types of cationic carbon nanotubes are able to condense DNA to varying degrees, indicating that both nanotube surface area and charge density are critical parameters that determine the interaction and electrostatic complex formation between f-CNTs with DNA. All three different f-CNT types in this study exhibited upregulation of marker gene expression over naked DNA using a mammalian (human) cell line. Differences in the levels of gene expression were correlated with the structural and biophysical data obtained for the f-CNT:DNA complexes to suggest that large surface area leading to very efficient DNA condensation is not necessary for effective gene transfer. However, it will require further investigation to determine whether the degree of binding and tight association between DNA and nanotubes is a desirable trait to increase gene expression efficiency in vitro or in vivo. This study constitutes the first thorough investigation into the physicochemical interactions between cationic functionalized carbon nanotubes and DNA toward construction of carbon nanotube-based gene transfer vector systems.     

New pyridine carboxamide ligands and their complexation to copper(II). X-Ray crystal structures of mono-, di, tri- and tetranuclear copper complexes

Seven new pyridine dicarboxamide ligands H2L(1-7) have been synthesised from condensation reactions involving pyridine-2,6-dicarboxylic acid (H2dipic), pyridine-2,6-dicarbonyl dichloride or 2,6-diaminopyridine with heterocyclic amine or carboxylic acid precursors. Crystallographic analyses of N,N'-bis(2-pyridyl)pyridine-2,6-dicarboxamide monohydrate (H2L8 x H2O), N,N'-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide and N,N'-bis[2-(2-pyridyl)ethyl]pyridine-2,6-dicarboxamide monohydrate revealed extensive intramolecular hydrogen bonding interactions. 2,6-Bis(pyrazine-2-carboxamido)pyridine (H2L6) and 2,6-bis(pyridine-2-carboxamido)pyridine (H2L7) reacted with copper(II) acetate monohydrate to give tricopper(II) complexes [Cu3(L)2(mu2-OAc)2]. X-Ray crystallography confirmed deprotonation of the amidic nitrogen atoms and that the (L6,7)2- ligands and acetate anions hold three copper(II) ions in approximately linear fashion. H2L8. Reacted with copper(II) tetrakis(pyridine) perchlorate to give [Cu(L8)(OH2)]2 x 2H2O, in which (L8)2- was tridentate through the nitrogen atoms of the central pyridine ring and the deprotonated carboxamide groups at one copper centre, with one of the terminal pyridyl rings coordinating to the other copper atom in the dimer. The corresponding reaction using H2L7 gave [Cu3(L7)2(py)2][ClO4]2, which transformed during an attempted recrystallisation from ethanol under aerobic conditions to a tetracopper(II) complex [Cu4(L7)2(L7-O)2].     

Polymers with advanced structural and supramolecular features synthesized through topochemical polymerization

Polymers are an integral part of our daily life. Hence, there are constant efforts towards synthesizing novel polymers with unique properties. As the composition and packing of polymer chains influence polymer''s properties, sophisticated control over the molecular and supramolecular structure of the polymer helps tailor its properties as desired. However, such precise control via conventional solution-state synthesis is challenging. Topochemical polymerization (TP), a solvent- and catalyst-free reaction that occurs under the confinement of a crystal lattice, offers profound control over the molecular structure and supramolecular architecture of a polymer and usually results in ordered polymers. In particular, single-crystal-to-single-crystal (SCSC) TP is advantageous as we can correlate the structure and packing of polymer chains with their properties. By designing molecules appended with suitable reactive moieties and utilizing the principles of supramolecular chemistry to align them in a reactive orientation, the synthesis of higher-dimensional polymers and divergent topologies has been achieved via TP. Though there are a few reviews on TP in the literature, an exclusive review showcasing the topochemical synthesis of polymers with advanced structural features is not available. In this perspective, we present selected examples of the topochemical synthesis of organic polymers with sophisticated structures like ladders, tubular polymers, alternating copolymers, polymer blends, and other interesting topologies. We also detail some strategies adopted for obtaining distinct polymers from the same monomer. Finally, we highlight the main challenges and prospects for developing advanced polymers via TP and inspire future directions in this area.

This perspective showcases the potential of topochemical polymerization as an effective tool for synthesizing polymers with advanced molecular and supramolecular structures.     

Diphenic acid as a selective reagent for the amperometric determination of thorium(IV)

Th(IV) has been titrated amperometrically at an applied e.m.f of −1.0 V (dropping mercury electrode vs. SCE) with diphenic acid (neutralized with sodium hydroxide). Th(IV) in the range 8.0–60.0 mg/100ml can be determined with an error of ±0.5%. A number of foreign ions including Ce(IV), Zr(IV), La(III), U(IV), U(VI) do not interfere even if present in excess but traces of Ti(IV) do. The method is rapid and selective and has been used for the determination of Th(IV) in monazite sand.     

ENERGETICS OF DNA REPAIR IN UV-IRRADIATED PERIPHERAL BLOOD LEUKOCYTES FROM CHRONIC MYELOID LEUKAEMIA PATIENTS

Abstract— The relationship between energy metabolism and UV-induced (251 nm) DNA repair has been investigated in leukocytes obtained from peripheral blood of chronic myeloid leukaemia patients. Energy supply was modulated by using inhibitors of respiratory (antimvcin-A) and glycolytic (2-deoxy-o-glucose and other glucose analogues) pathways for adenosine-triphosphatc (ATP) production. DNA repair was measured by the unscheduled DNA synthesis technique. Parameters of energy metabolism like glucose utilization. lactate production and ATP content of cells. were measured under similar experimental conditions. The observations made indicate the following results: (1) ATP for DNA repair can be supplied by the respiratory and/or by the glycolytic pathway. (2) In the absence of respiration, the rate of glycolysis bears a linear correlation with DNA repair. (3) A minimum threshold rate of ATP-production is necessary for DNA repair.     

Negative ion electrospray ionization mass spectral study of dicarboxylic acids in the presence of halide ions

The negative ion electrospray ionization (ESI) mass spectra of a series of dicarboxylic acids, a pair of isomeric (cis/trans) dicarboxylic acids and two pairs of isomeric (positional) substituted benzoic acids, including a pair of hydroxybenzoic acids, were recorded in the presence of halide ions (F(-), Cl(-), Br(-) and I(-)). The ESI mass spectra contained [M--H](-) and [M+X](-) ions, and formation of these ions is found to be characteristic of both the analyte and the halide ion used. The analytes showed a greater tendency to form adduct ions with Cl(-) under ESI conditions compared with the other halide ions used. The isomeric compounds yielded distinct spectra by which the isomers could be easily distinguished. The collision-induced dissociation mass spectra of [M+X](-) ions reflected the gas-phase basicities of both the halide ion and [M--H](-) ion of the analyte. However, the relative ordering of gas-phase basicities of all analyte [M--H](-) and halide ions could not account for the dominance of chloride ion adducts in ESI mass spectra of the analytes mixed with equimolar quantities of the four halides.     

Total synthesis of rutamycin B and oligomycin C

The asymmetric synthesis of the macrolide antibiotics (+)-rutamycin B (1) and (+)-oligomycin C (2) is described. The approach relied on the synthesis and coupling of the individual spiroketal fragments 3a and 3b with the C1-C17 polyproprionate fragment 4. The preparation of the spiroketal fragments was achieved using chiral (E)-crotylsilane bond construction methodology, which allowed the introduction of the stereogenic centers prior to spiroketalization. The present work details the synthesis of the C19-C28 and C29-C34 subunits as well as their convergent assembly through an alkylation reaction of the lithiated N,N-dimethylhydrazones 6 and 8 to afford the individual linear spiroketal intermediates 5a and 5b, respectively. After functional group adjustment, these advanced intermediates were cyclized to their respective spiroketal-coupling partners 40 and 41. The requisite polypropionate fragment was assembled in a convergent manner using asymmetric crotylation methodology for the introduction of six of the nine-stereogenic centers. The use of three consecutive crotylation reactions was used for the construction of the C3-C12 subunit 32. A Mukaiyama-type aldol reaction of 35 with the chiral alpha-methyl aldehyde 39 was used for the introduction of the C12-C13 stereocenters. This anti aldol finished the construction of the C3-C17 advanced intermediate 36. A two-carbon homologation completed the construction of the polypropionate fragment 38. The completion of the synthesis of the two macrolide antibiotics was accomplished by the union of two principal fragments that was achieved with an intermolecular palladium-(0) catalyzed cross-coupling reaction between the terminal vinylstannanes of the individual spiroketals 3a and 3b and the polypropionate fragment 4. The individual carboxylic acids 46 and 47 were cyclized to their respective macrocyclic lactones 48 and 49 under Yamaguchi reaction conditions. Deprotection of these macrolides completed the synthesis of the rutamycin B and oligomycin C.     

Pinacol Formation and Reduction of Aromatic Carbonyls with Magnesium–Methanol at Ambient Temperature

A simple and inexpensive procedure for the pinacol formation of aromatic aldehydes and reduction of aromatic ketones to the corresponding alcohols with magnesium in dry methanol at ambient temperature is reported. The pinacol formation and reduction are proposed to be proceeding by SET from magnesium.