Synthesis and DNA cross-linking of a phototriggered FR900482 mitosene progenitor

[reaction: see text] The synthesis and biochemical reactivity of the first photoactivated mitosene-based DNA interstrand cross-linking agent is described.     

Pentakis(methoxycarbonyl)cyclopentadiene,a strong organic acid: Crystal and molecular structures of HC5(CO)2Me)5 and Li[C5(CO2Me)5](H2O)

Contrary to some previously depicted structures, the proton in HC₅(CO₂Me)₅ is bonded to two oxygens rather than to carbon; the lithium ion in Li[C₅(CO₂Me)₅] (H₂O) is tetrahedrally coordinated by two carbonyl oxygens from one C₅ anion, one from a second anion, and a water molecule.     

Theoretical aspects of a preparative continuous chromatograph

Summary Equipment which has been used or suggested for preparative scale chromatography is reviewed. Particular attention is paid to one form of equipment for continuous counter-current chromatography which employs a moving mechanical seal. The theoretical effects of practical operating conditions and the mode of operation of this equipment are discussed. The influence of these effects on polymer fractionation is also considered. A theoretical model, based on the equilibrium stage concept, is proposed for the simulation of continuous gel permeation chromatography of a binary feed on such an apparatus. Examples of the results obtained from the computer simulation are given.     

Effect of amine ligand bulk on the interaction of methionine with platinum(II) diamine complexes

Molecular mechanics and dynamics calculations have been used in conjunction with experimental data to study the effects of amine ligand bulk on the formation of both guanine and methionine complexes with platinum diamine compounds. The AMBER force field has been supplemented with previous modifications [Yao; et al. Inorg. Chem. 1994, 33, 6061-6077. Cerasino; et al. Inorg. Chem. 1997, 36, 6070-6079] and has been further modified to include parameters for platinum bound to the sulfur atom of methionine. Molecular mechanics calculations with this modified AMBER force field have suggested that a platinum complex with two sulfur-bound methionine ligands and a bulky diamine ligand (N,N,N',N'-tetramethylethylenediamine, Me(4)en) would have severe interligand clashes; such interligand clashes are less pronounced in bis(9-ethylguanine) complexes. Consistent with these observations, NMR studies with [Pt(Me(4)en)(D(2)O)(2)](2+) have indicated that guanine 5'-monophosphate reacts in a 2:1 guanine:platinum ratio while both methionine and N-acetylmethionine react with only a 1:1 stoichiometry. Methionine forms a chelate via the sulfur and nitrogen atoms whereas N-acetylmethionine forms a chelate via the sulfur and oxygen atoms. The oxygen of the latter chelate can be displaced by the addition of guanosine 5'-monophosphate, although complete displacement of the N-acetylmethionine was not observed.     

Thermogravimetric Evidence of Cobalt or Manganese Isomorphously Substituted into a Zeolite

Pure silica zeolite ZSM-5 has been synthesised in a slightly acidic aqueous fluoride medium which produces the protonated form of the zeolite ZSM-5 [1]. Tetrahalometallate [2] species of cobalt and manganese have been synthesised and increasing mole fractions incorporated into the zeolite synthesis gel. The products have been analysed and characterised using simultaneous thermogravimetric-derivative thermogravimetric analysis (TG-DTG). The thermal decomposition, under nitrogen of the associated tetraethylammonium (TEA⁺) and tetrapropylammonium (TPA⁺) cations occluded within the zeolite channels is indicative and characteristic of the incorporation of the heteroatoms into the zeolitic framework. Analysis by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), and Fourier transform infrared spectroscopy (FTIR) has confirmed the reliability of thermogravimetric (TG) and derived thermogravimetric analysis (DTG) as a diagnostic tool. This revised version was published online in July 2006 with corrections to the Cover Date.     

Field and flow programming in frit-inlet asymmetrical flow field-flow fractionation

The separation of wide molecular mass (Mr) ranges of macromolecules using frit inlet asymmetrical flow field-flow fractionation (FI-AFlFFF) has been improved by implementing a combination of field and flow programming. In this first implementation, field strength (governed by the cross flow-rate through the membrane-covered accumulation wall) is decreased with time to obtain faster elution and improved detection of the more strongly retained (high Mr) materials. The channel outlet flow-rate is optionally held constant, increased, or decreased with time. With circulation of the flow exiting the accumulation wall to the inlet frit, the dual programming of cross flow and channel outlet flow could be implemented using just two pumps. With this flow configuration, the channel outlet flow-rate is always equal to the channel inlet flow-rate, and these may be programmed independently of the cross flow-rate through the membrane. FI-AFlFFF retains its operational advantage over conventional asymmetrical flow FFF (AFlFFF). Unlike conventional AFlFFF, FI-AFlFFF does not require time consuming, and experimentally inconvenient, sample focusing and relaxation steps involving valve switching and interruption of sample migration. The advantages of employing dual programming with FI-AFlFFF are demonstrated for sets of polystyrene sulfonate standards in the molecular mass range of 4 to 1000 kDa. It is shown that programmed FI-AFlFFF successfully expands the dynamic separation range of molecular mass.