2'-Ribose-ferrocene oligonucleotides for electronic detection of nucleic acids

We have synthesized two novel phosphoramidites with a ferrocenyl moiety at the 2'-ribose position linked through a butoxy linker. Using automated DNA/RNA synthesis techniques, oligonucleotides containing ferrocene at various positions were prepared and characterized by HPLC, MALDI-TOF mass spectrometry, and electrochemistry. Thermal stability studies of the ferrocene-modified DNA duplexes revealed that introduction of one or two ferrocenyl complexes does not result in an observed change of the T(m) values of the corresponding DNA duplexes when compared to the nonmodified hybrids. These data indicate that the introduction of a ferrocenyl group at the 2'-position of the ribose ring containing either a purine or pyrimidine base has no effect on the stability of the modified DNA. The electrochemical behavior of the ferrocene-containing DNA was examined by cyclic voltammetry. The modified 2'-ferrocene-oligonucleotides are electrochemically active and can be used as signaling probes for the electronic detection of nucleic acids on bioelectronic sensors.     

Volumetric properties of some methyl substituted benzoic acids and their sodium salts in water as a function of temperature

Density data are presented for benzoic, the toluic and 2,6-dimethylbenzoic acids and their sodium salts at temperatures from 5 to 65°C. Apparent and partial molar volumes have been calculated from the experimental data. From the partial molar volume data the volume change on substitution of a methyl group has been calculated as has the volume change on ionization of the acids. It is found that the volume contribution of a methyl group is somewhat dependent on the substituent position and on the temperature. The relation between volume change on ionization and the corresponding entropy change is presented for a range of temperature. The data support the idea that electrostriction is an important feature of these systems and that its importance increases with rising temperature.     

The crystal structure and molecular conformation of threo 5-methylmetadone in relation to opioid receptor binding

Crystals of the hydrochloride salt of the biologically inactive threo isomer of 5-methylmethadone, C₂₂H₃₀ONCl, are monoclinic space group P2₁ with unit cell dimnsionsa = 11.019 Å, b = 8.6153Å, c = 10.680Å and β = 93.026°. The observed conformation is one in which the nitrogen bearing chain is extended with the substituents on C(5) and C(6) nearly eclipsed, a feature compatible with NMR studies and molecular mechanics calculations. The very potent agonist (5S, 6S)-erythro-5-methylmethadone has a solid state conformation in which the N atom is rotated back toward the phenyl rings [C(4)-C(5)-C(6)-N = 97°]in agreement with molecular mechanics calculations. The fact that the more potent enantiomers, (6R)-methadone and (5S)-isomethadone, and the inactive threo isomer are observed in the extended solid state conformation in contrast to (5S, 6S)-erythro-5-methylmethadone is consistent with three different models for their interaction with opioid receptors. It is proposed that the more likely of these involves a receptor bound conformation of (6R)-methadone and (5S)-isomethadone that resembles the conformation of (5S, 6S)-erythro-5-methylmethadone or that opioid receptors recognize both gauche-like and extended conformations.     

Aqueous iodic acid: Conductance and thermodynamics

Precision conductance measurements are reported on aqueous solutions of iodic acid for 16 concentrations between 17 and 0.7 mM and for 20 temperatures between 5° and 100°C. RlnK _a (m) and _o were calculated at each temperature and the data expressed by suitable temperature functions. From RlnK _a (m) as a function of temperature changes in standard enthalpy, entropy, and heat capacity were calculated. C _p proved to be independent of temperature so that H⁰ was a linear function of temperature. Comparisons have been made with other published data for iodic acid. The pattern of variation of Walden products with temperature was similar to that found earlier for substituted benzoic acids.     

Halogenation of vinyl ketoximes. Synthesis of isoxazoles and preparation and silver ion-promoted reactions of 4-halo-2-isoxazolines

Reaction of several α,β-unsaturated ketoximes with N-bromosuccinimide (NBS) gave isoxazoles, but yields were lower and the reaction less general than a similar transformation using iodine under basic conditions. With β,β-disubstituted oximes, 4-halo-5,5-disubstituted-2-isoxazolines were obtained using NBS, iodine, or N-chlorosuccinimide. Treatment of the 4-bromoisoxazo-lines with silver acetate or silver nitrate caused either elimination with rearrangement to give isoxazoles or substitution at C-4, depending upon the nature of the substituents at C-5.     

Oligomerization of vinyl monomers 20. Carbon-13 NMR of oligomers of 2-vinylpyridine. Studies of labelled end groups

Oligomers of 2-vinylpyridine initiated with Li, Na, K, and Rb salts of ¹³C-labeled or-unlabeled 2-ethylpyridine and terminated with ¹³C-labeled or -unlabeled methyl iodide were separated by liquid chromatography and analyzed by ¹³C-NMR of the initial or terminal CH₃ group. The stereochemistry of the three dyads which flank the initial or terminal methyl group could be determined and this allowed us to evaluate the stereochemistry of both methylation and vinyl addition. The methylation of the Li and Na salts of the oligomer anions is highly (> 95%) stereoselective and independent of chain length, whereas the stereoselectivity of the K and Rb salts is substantially less. These data indicate that the Li and Na oligomer and polymer anions exist in a chelated form in which the metal ion is complexed with the penultimate 2-pyridine group, the other counterions being chelated to a lesser extent. The stereochemistry of monomer addition was found to be less stereoselective than that of methylation for the Li and Na salts. In addition, the apparent meso-stereoselectivity of monomer addition of the Na, K, and Rb systems was greater than that of the Li ion. For the latter system, in particular, the mechanism appeared to be Markoff-like and consistent with different reactivities of anions flanked by a distinct dyad or triad stereochemistry. These data appear to be consistent with the intramolecular coordination that tends to hold the third asymmetric center close to the propagating carbanion.     

The siderocalin/enterobactin interaction: a link between mammalian immunity and bacterial iron transport

The siderophore enterobactin (Ent) is produced by enteric bacteria to mediate iron uptake. Ent scavenges iron and is taken up by the bacteria as the highly stable ferric complex [Fe (III)(Ent)] (3-). This complex is also a specific target of the mammalian innate immune system protein, Siderocalin (Scn), which acts as an antibacterial agent by specifically sequestering siderophores and their ferric complexes during infection. Recent literature suggesting that Scn may also be involved in cellular iron transport has increased the importance of understanding the mechanism of siderophore interception and clearance by Scn; Scn is observed to release iron in acidic endosomes and [Fe (III)(Ent)] (3-) is known to undergo a change from catecholate to salicylate coordination in acidic conditions, which is predicted to be sterically incompatible with the Scn binding pocket (also referred to as the calyx). To investigate the interactions between the ferric Ent complex and Scn at different pH values, two recombinant forms of Scn with mutations in three residues lining the calyx were prepared: Scn-W79A/R81A and Scn-Y106F. Binding studies and crystal structures of the Scn-W79A/R81A:[Fe (III)(Ent)] (3-) and Scn-Y106F:[Fe (III)(Ent)] (3-) complexes confirm that such mutations do not affect the overall conformation of the protein but do weaken significantly its affinity for [Fe (III)(Ent)] (3-). Fluorescence, UV-vis, and EXAFS spectroscopies were used to determine Scn/siderophore dissociation constants and to characterize the coordination mode of iron over a wide pH range, in the presence of both mutant proteins and synthetic salicylate analogues of Ent. While Scn binding hinders salicylate coordination transformation, strong acidification results in the release of iron and degraded siderophore. Iron release may therefore result from a combination of Ent degradation and coordination change.     

Internal Friction Study of Diluent Effect on Polymers at Cryogenic Temperatures

Abstract

The dynamic mechanical properties of polystyrene/ethyl benzene, polymethyl methacrylate/water, polyethyl methacrylate/ethyl hexyl adipate, and poly-2-hydroxyethyl methacrylate/water were studied between 10 and 100°K. A free-decay resonance acoustic spectrometer was designed for this purpose. It was found that the presence of diluents causes the low-temperature loss peaks of the polyrners in question to shift to higher temperatures. This observation is compatible with the hypothesis that at very low temperatures, the diluent molecules are immobilized to occupy free space between adjacent polymer chains. The hindering action of these molecules on the kinetic motions of the side groups of the polymer thus renders greater thermal energy necessary to initiate the relaxation processes.