Immobilized tris(hydroxymethyl)aminomethane as a scaffold for ion-selective ligands: the auxiliary group effect on metal ion binding at the phosphate ligand

The metal ion affinities of a ligand in a polymer-supported reagent can be enhanced by the presence of a proximate group capable of hydrogen bonding. A new polymer-supported reagent has been synthesized by immobilizing tris(hydroxymethyl)aminomethane (Tris) onto cross-linked poly(vinylbenzyl chloride) and then phosphorylating the -OH moieties. The -NH- acts as the auxiliary group to increase the extent of complexation by the phosphate ligand. Additionally, Tris acts as a scaffold, wherein the phosphate ligands are in a known stereochemical arrangement. The Tris resin is mono-, di-, and triphosphorylated, depending on the concentration of the phosphorylating agent. The highest metal ion affinities are found with the resin having a phosphorus-to-nitrogen ratio of 2.36, consistent with one-third of the ligands being triphosphorylated and the remainder being diphosphorylated. The unphosphorylated Tris and phosphonate diester resins have no ionic affinities under the same conditions. Trivalent ions (Fe(III), Al(III), La(III), Eu(III), Lu(III)) are preferred over divalent ions (Pb(II), Cd(II), Cu(II), Zn(II)) from solutions at pH 2. The distribution coefficients of the divalent ions correlate with the Misono softness parameters, indicating that the polarizability of the phosphoryl oxygen is important to binding of the metal ions. The mechanism of complexation is probed with Fe(III) in 0.01-5 M HNO3 and HCl. The high affinities are ascribed to activation of the P=O ligand toward metal ion binding by the N-H moieties acting as auxiliary groups, coupled with intraligand cooperation among the phosphate moieties at a given site. FTIR spectra show that the P=O band at 1261 cm-1 shifts as a function of the extent of hydrogen bonding. Binding at the P=O requires a balance between activation by hydrogen bonding and availability of the lone pair electrons to the metal ions.     

A weight-function approach for determining watershed initial conditions for combustion waves

In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed.     

Polyols as scaffolds in the development of ion-selective polymer-supported reagents: the effect of auxiliary groups on the mechanism of metal ion complexation

In developing ion-selective polymer-supported reagents, the inherent affinity of a given ligand for a targeted metal ion is found to be affected by auxiliary groups on a scaffold. A series of polyols (ethylene glycol, glycerol, tris(hydroxymethyl)ethane, pentaerythritol, and pentaerythritol triethoxylate) are immobilized onto cross-linked poly(vinylbenzyl chloride), then monophosphorylated. The pentaerythritol, glycerol, and pentaerythritol triethoxylate polymers have the highest affinities for both trivalent and divalent ions. The distribution coefficients of divalent ions (Pb(II), Cd(II), Cu(II), Ni(II), and Zn(II)) correlate with the Misono softness parameter, reflecting a single-site interaction between the metal ion and the phosphoryl oxygen. The distribution coefficients for trivalent ions are in the order Fe(III) < Al(III) < Y(III) less, approximately < La(III) approximately Eu(III) approximately Lu(III). For example, the phosphorylated pentaerythritol polymer has distribution coefficients (also reported as percent complexed) for Fe of 68.4 (75.3%); for Al of 182 (88.5%); and for the rare earth ions Y, Lu, Eu, and La of 374 (94.4%), 1390 (98.4%), 1690 (98.4%), and 708 (96.9%), respectively, from solutions at pH 2.0. The opposite trend (i.e., Fe(III) > Al(III) > (rare earths)) correlates with their hardness, acidity, electron affinity, electronegativity, and formation constants with soluble complexants, including tributyl phosphate. A binding mechanism is proposed wherein the polymer initially has the auxiliary -OH groups hydrogen-bonded to the phosphate ligand; then, binding to the polarizable phosphoryl oxygen with the divalent ions dominates, while the trivalent ions are drawn closer to the phosphoryl oxygen because of their greater charge and, once closer, bind in a multisite interaction with both the phosphate and -OH groups.     

Synthesis of cytotoxic cyanobactin,Wewakazole B

We report herein the synthesis of cytotoxic cyanobactin, Wewakazole B through an efficient solution-phase approach. The key steps of the synthesis are the macrocyclic lactamization of linear dodecapeptide and construction of two hexapeptides with three different substituted oxazole rings.     

Synthesis,characterization, crystal structures, in vitro and in vivo antitumor activity of palladium(II) and zinc(II) complexes with 2-formyl and 2-acetyl pyridine N(4)-1-(2-pyridyl)-piperazinyl thiosemicarbazone

The present paper includes synthesis and spectral characterization of the novel prepared palladium(II) and zinc(II) complexes with 2-formyl pyridine N(4)-1-(2-pyridyl)-piperazinyl thiosemicarbazone, HFo4Npypipe, 1 and the 2-acetyl pyridine N(4)-1-(2-pyridyl)-piperazinyl thiosemicarbazone, HAc4Npypipe, 2. The Pd(II) complexes [PdCl(Fo4Npypipe)], 3, [PdCl(Ac4Npypipe)], 4 and the Zn(II) complexes [ZnCl₂(Fo4Npypipe)], 5 and [ZnCl₂(Ac4Npypipe)], 6 have been characterized by elemental analyses and spectroscopic studies. The crystal structure of the complexes [PdCl(Fo4Npippy)], 3 and [PdCl(Ac4Npippy)], 4, have been solved by single-crystal X-ray diffraction. The electronic, IR, UV/Vis, and NMR spectroscopic data of the complexes are reported. The results of the cytotoxic activity of 1–6 have been evaluated in vitro against the cells of three human cancer cell lines: MCF-7, T24, A-549 and a mouse L-929 (a fibroblast-like cell line cloned from strain L). For selected compounds 2 and 6 the acute toxicity and antitumor activity were evaluated on leukemia P388-bearing mice. The Zn(II) compounds 5 and 6 are considered as agents with potential antitumor activity, and can therefore be candidates for further stages of screening in vitro and/or in vivo.     

Effects of molecular entanglements during electrospray of high molecular weight polymers

Concentration-dependent bimodal size distributions (comprised of single-molecule particles and multimolecule clusters) observed by microscopic examination of particles collected during electrospray (ES) of dilute solutions of high molecular weight polymers suggest that chain entanglement can interfere with the droplet subdivisions believed to be intrinsic to the electrospray process. The feasibility of such interference is discussed in the context of the spray model of Kebarle, along with its potential impact on the ES mass spectrometry of macromolecules.     

A cation affinity series for a phosphinic acid ion-exchange resin

A cation affinity series was determined by the batch method for an ion-exchange resin with a phenylphosphinic acid group attached to a polystyrene/10% divinylbenzene matrix. The series in order of decreasing affinity is Pb(II), Mn(II), Cd(II), Ca(II), Zn(II), Mg(II), Ni(II), Ba(II), Sr(II), Co(II), Fe(III), Cs(I), Li(I), Na(I), Rb(I). These affinities are expressed quantitatively in terms of selectivity coefficients, and all ion-exchange reactions can be described in terms of simple displacement equations.