Column-friendly reversed-phase high-performance liquid chromatography of peptides and proteins using formic acid with sodium chloride and dynamic column coating with crown ethers.

Reversed-phase high-performance liquid chromatography of proteins, traditionally carried out with strong acids like trifluoroacetic acid or phosphoric acid, which can damage reversed-phase columns, can be performed with excellent results using the far milder formic acid in the presence of salt. For certain separations, dynamic coating of the column with crown ethers can bring added resolution. Examples given are for peptides from a digest of methionine growth hormone, protein separations from whey proteins containing alpha-lactalbumin and the beta-lactoglobulins A and B, and bovine and porcine insulins. The separation of methionine-growth hormone from growth hormone is also described.     

Structures and anion-binding properties of M4L6 tetrahedral cage complexes with large central cavities

Reaction of the bis-bidentate bridging ligand L(3), in which two bidentate chelating 3(2-pyridyl)pyrazole units are separated by a 3,3'-biphenyl spacer, with Co(II) salts affords tetranuclear cage complexes of composition [Co(4)(L(3))(6)]X(8)(X =[BF(4)](-), [ClO(4)](-), [PF(6)](-) or I(-)) in which four 6-coordinate Co(II) ions in an approximately tetrahedral array are connected by six bis-bidentate bridging ligands, one spanning each of the six edges of the Co(4) tetrahedron. In every case, X-ray crystallography reveals that the 'apical' Co(II) ion has a fac tris-chelate geometry, whereas the other three Co(II) ions have mer tris-chelate geometries, resulting in (non-crystallographic)C(3) symmetry for the cages; that this structure is retained in solution is confirmed by (1)H NMR spectroscopy of the paramagnetic cages. In every case one of the anions is located inside the central cavity of the cage, with the remaining seven outside. We found no clear evidence for an anion-based templating effect. The cage superstructure is sufficiently large to leave gaps in the centres of the faces through which the internal and external anions can exchange. Variable-temperature (19)F NMR spectroscopy was used to investigate the dynamic behaviour of the cages with X =[BF(4)](-) and [PF(6)](-) in MeCN solution: in both cases two separate signals, corresponding to external and internal anions, are clear at 233 K which have coalesced to a single signal at room temperature. Analysis of the linewidth of the minor signal (for the internal anion) at various temperatures below coalescence gave an activation energy for anion exchange of ca. 50 kJ mol(-1) in each case, a figure which suggests that anion exchange can occur via a conformational rearrangement of the cage superstructure in solution rather than opening of the cavity by cleavage of metal-ligand bonds.     

Ion Association in Lanthanide Chloride Solutions

A better understanding of the solution chemistry of the lanthanide (Ln) salts in water would have wide ranging implications in materials processing, waste management, element tracing, medicine and many more fields. This is particularly true for minerals processing, given governmental concerns about lanthanide security of supply and the drive to identify environmentally sustainable processing routes. Despite much effort, even in simple systems, the mechanisms and thermodynamics of Ln^III association with small anions remain unclear. In the present study, molecular dynamics (MD), using a newly developed force field, provide new insights into LnCl₃(aq) solutions. The force field accurately reproduces the structure and dynamics of Nd³⁺, Gd³⁺ and Er³⁺ in water when compared to calculations using density functional theory (DFT). Adaptive-bias MD simulations show that the mechanisms for ion pairing change from dissociative to associative exchange depending upon cation size. Thermodynamics of association reveal that whereas ion pairing is favourable, the equilibrium distribution of species at low concentration is dominated by weakly bound solvent-shared and solvent-separated ion pairs, rather than contact ion pairs, reconciling a number of contrasting observations of Ln^III–Cl association in the literature. In addition, we show that the thermodynamic stabilities of a range of inner sphere and outer sphere coordination complexes are comparable and that the kinetics of anion binding to cations may control solution speciation distributions beyond ion pairs. The techniques adopted in this work provide a framework with which to investigate more complex solution chemistries of cations in water.     

The excess enthalpies of (carbon dioxide + cyclohexane) at 308.15, 358.15, and 413.15 K from 7.50 to 12.50 MPa

The excess molar enthalpies H_m^E for (carbon dioxide + cyclohexane) were measured in the vicinity of their critical locus and in the supercritical region. Mixtures at 308.15 K and at 7.50 MPa show very exothermic mixing and a region where H_m^E varies linearly with mole fraction x while at 10.50 and 12.50 MPa they show only moderately endothermic mixing. Mixtures at 358.15 and 413.15 K and at all pressures studied except for 358.15 K and 12.50 MPa have an exothermic section in the cyclohexane-rich region, a linear section which starts at a mole fraction x corresponding very closely to that of the minimum value of H_m^E, and an endothermic section in the carbon-dioxide-rich region. The H_m^E results exhibiting a linear section allow the determination of values for the vapor and liquid equilibrium-phase compositions. The changes observed in the excess enthalpy with both pressure and temperature are discussed in terms of liquid-vapor equilibrium and critical constants for (carbon dioxide + cyclohexane).     

Orthmodular lattices whose MacNeille completions are not orthomodular

The only known example of an orthomodular lattice (abbreviated: OML) whose MacNeille completion is not an OML has been noted independently by several authors, see Adams [1], and is based on a theorem of Ameniya and Araki [2]. This theorem states that for an inner product space V, if we consider the ortholattice ?(V,⊥) = {A \( \subseteq \) V: A = A ^⊥⊥} where A ^⊥ is the set of elements orthogonal to A, then ?(V,⊥) is an OML if and only if V is complete. Taking the orthomodular lattice L of finite or confinite dimensional subspaces of an incomplete inner product space V, the ortholattice ?(V,⊥) is a MacNeille completion of L which is not orthomodular. This does not answer the longstanding question Can every OML be embedded into a complete OML? as L can be embedded into the complete OML ?(V,⊥), where V is the completion of the inner product space V. Although the power of the Ameniya-Araki theorem makes the preceding example elegant to present, the ability to picture the situation is lost. In this paper, I present a simpler method to construct OMLs whose Macneille completions are not orthomodular. No use is made of the Ameniya-Araki theorem. Instead, this method is based on a construction introduced by Kalmbach [7] in which the Boolean algebras generated by the chains of a lattice are glued together to form an OML. A simple method to complete these OMLs is also given. The final section of this paper briefly covers some elementary properties of the Kalmbach construction. I have included this section because I feel that this construction may be quite useful for many purposes and virtually no literature has been written on it.     

Amphoteric polystyrene latex colloids: polymerization pathway and the control of particle size and potential

Amphoteric polystyrene latex colloids were prepared by the emulsifier-free emulsion polymerization of styrene. Two co-monomers, methacrylic acid (MA) (anionic) and dimethyl aminoethyl methacrylate (DMAM) (cationic) were used to promote the amphoteric nature of the resultant surfaces. Parameters such as particle size and the isoelectric point (IEP) were measured as a function of polymerization recipe. Particle size decreased with increasing initiator concentration according to the equation: log [d _w]=–0.67 log [I] + 0.316 whered _w is the weight average particle diameter andI is the concentration of initiator (potassium persulphate).The particle size also decreased with increasing temperature, increasing pH and addition of surfactant. Particle size was unaffected by the methacrylic acid content. The isoelectric point pH was decreased on decreasing initiator concentration and on increasing methacrylic acid content.The polymerization pathway was deduced to involve the cationic DMAM during the initiation phase and to involve the anionic MA as well as styrene, during the growth stage. A full polymerization pathway involving the formation of oligomeric DMAM micelles was postulated.     

Synthèse du mèthyl-1 diformyl-2,3 pyrrole,de la méthyl-1 pyrrolo[2,3-d] pyridazine et de la méthyl-1 oxo-6 (6h)cycloheptatrieno[b] pyrrole

This communication describes the synthesis of l-methyl-2,3-diformylpyrrole. This new compound is used to prepare a new heterocycle, l-methylcyclohepta[b]pyrrol-6-one and thus allows a new synthesis of l-methylpyrrolo[2,3-d]pyridazine.