Idempotent bounded C-semigroups

A semigroup with zero isidempotent bounded (IB) if it is the 0-direct union of idempotent generated principal left ideals and the 0-direct union of idempotent generated principal right ideals. Notable examples are completely 0-simple semigroups and the wider class of primitive abundant semigroups. Significant to the structure of these semigroups is that they are all categorical at zero. In this paper we describe IB semigroups that are categorical at zero in terms ofdouble blocked Rees matrix semigroups. This generalises Fountain's characterisation of primitive abundant semigroups via blocked Rees matrix semigroups [1], which in turn yields the Rees theorem for completely 0-simple semigroups.     

ChemInform Abstract: X-Ray Structural Studies of the Polymorphic Elpasolites K2LiAlF6 and Rb2LiGaF6.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Ion-pair reversed-phase high-performance liquid chromatography analysis of oligonucleotides: retention prediction

An ion-pair reversed-phase HPLC method was evaluated for the separation of synthetic oligonucleotides. Mass transfer in the stationary phase was found to be a major factor contributing to peak broadening on porous C18 stationary phases. A small sorbent particle size (2.5 microm), elevated temperature and a relatively slow flow-rate were utilized to enhance mass transfer. A short 50 mm column allows for an efficient separation up to 30mer oligonucleotides. The separation strategy consists of a shallow linear gradient of organic modifier, optimal initial gradient strength, and the use of an ion-pairing buffer. The triethylammonium acetate ion-pairing mobile phases have been traditionally used for oligonucleotide separations with good result. However, the oligonucleotide retention is affected by its nucleotide composition. We developed a mathematical model for the prediction of oligonucleotide retention from sequence and length. We used the model successfully to select the optimal initial gradient strength for fast HPLC purification of synthetic oligonucleotides. We also utilized ion-pairing mobile phases comprised of triethylamine (TEA) buffered by hexafluoroisopropanol (HFIP). The TEA-HFIP aqueous buffers are useful for a highly efficient and less sequence-dependent separation of heterooligonucleotides.     

Crystal and molecular structure of [(C6H5)3Sb]3CuCl·CHC13

The X-ray crystallographic structure determination of [(C₆H₅)₃Sb]₃ Cu(I)Cl·CHC1₃ reveals that the compound crystallizes in the triclinic space groupP¯1 witha=18.827(3),b=14.279(3),c=14.399(3) Å,=84.43,=87.39(2), and=75.18(1)°,V=2734.7(9) ų,Z=2. Least-squares refinement based on 4689 independent observed data [(F _obs)²3(F _obs)²], resulted in a finalR value of 0.064. The cocrystallized solvent molecules were highly disordered. The coordination about Cu(I) of three Sb(C₆H₅)₃ molecules and one Cl ligand is approximately tetrahedral. The Cu-Cl distance, 2.235(5) Å, is extremely short in comparison to previously reported Cu-Cl distances in four-coordinate Cu(I) complexes. In keeping with the short Cu-Cl distance are very long Cu-Sb distances, av. 2.554(5) Å.