The Ups and Downs of Percent (and Some Interesting Connections)

Percent is a standardized ratio comparison that is often used to describe relative amounts of increase and decrease. In this paper, the nonsymmetric relationship between percent of increase and percent of decrease is explored in several ways. Beginning with a simple graphical representation of the relationship, the functional relationship is developed, with relative decrease expressed as a function of relative increase. Once expressed in the form f(x) = 100x/(100 + x), an immediate connection is made to two other topics commonly found within the study of rates—the work problem and the harmonic mean. Finally, successive percents of increase or decrease are shown to be everyday applications of the geometric mean. This deeper look at a common mathematical concept has uncovered rich structural relationships between topics that are often isolated in the curriculum.     

Ion-exchange selectivity of anion exchange resin modified with polystyrenesulfonic acid.

In order to change the ion-exchange selectivity of anion-exchange resin, the surface of a gel-type anion exchange resin was modified with anionic polyelectrolyte, polystyrenesulfonic acid. Using this modified resin, the ion-exchange rate of nitrate was little decreased, but that of sulfate was evidently decreased. It is considered that the ion-exchange reaction of the multivalent anion is suppressed by the greater electrostatic repulsive force against the modification layer than that against the monovalent anion. Thus, this modified resin may be suitable for the selective separation of monovalent anions. The influence of the modified condition on the ion-exchange rate was examined. Furthermore, this modified resin was used to separate nitrate ions from sulfate ions in the aqueous solution.     

Hypervalent Iodine(III) Sulfonate Mediated Synthesis of Imidazo[1,2‐a]pyridines

A direct and efficient method for the conversion of alkyl aryl ketones to imidazo[1,2‐α]pyridines has been developed based on initial formation of α‐organosulfonyloxy ketones and their subsequent cyclocondensation by 2‐aminopyridines in one‐pot conditions.     

Synthesis of Imidazo[2,1‐a]isoquinolines from α‐Tosyloxyketones and 1‐Aminoisoquinoline in Ionic Liquid Solvent

The room temperature ionic liquid n‐butylpyridinium tetrafluoroborate (BPyBF₄) is used as a ‘green’ recyclable alternative to classical molecular solvents for the cyclocondensation of α‐tosyloxyketones with 1‐aminoisoquinoline to prepare imidazo[2,1‐a]isoquinolines in good yields.     

On the choice of active space orbitals in MCSCF calculations

We describe a procedure which may be used to aid selection of the active space in multiconfigurational self-consistent field (MCSCF) calculations for general chemical systems. Starting from a restricted Hartree-Fock calculation, we define a hierarchy of interacting virtual orbitals for every occupied orbital. The most strongly interacting orbitals are then taken to constitute the active space in a configuration interaction (CI) calculation. The natural orbital occupation numbers obtained from the CI calculation are then used to choose the active space to be used in a subsequent MCSCF calculation. We illustrate our method on a number of systems (Li₂, B₂, C₂, carbonyl oxide and the transition state for oxidation of H₂S by dioxirane). In all these cases, ‘intuitive’ active spaces are inadequate, as are active spaces derived from the natural orbitals of unrestricted Hartree-Fock calculations.     

Germacrene A is a product of the aristolochene synthase-mediated conversion of farnesylpyrophosphate to aristolochene

The biosynthesis of several sesquiterpenes has been proposed to proceed via germacrene A. However, to date, the production of germacrene A has not been proven directly for any of the sesquiterpene synthases for which it was postulated as an intermediate. We demonstrate here for the first time that significant amounts of germacrene A (7.5% of the total amount of products) are indeed released from wild-type aristolochene synthase (AS) from Penicillium roqueforti. Germacrene A was identified through direct GC-MS comparison to an authentic sample and through production of beta-elemene in a thermal Cope rearrangement. AS also produced a small amount of valencene through deprotonation of C6 rather than C8 in the final step of the reaction. On the basis of the X-ray structure of AS, Tyr 92 was postulated to be the active-site acid responsible for protonation of germacrene A (Caruthers, J. M.; Kang, I.; Rynkiewicz, M. J.; Cane, D. E.; Christianson, D. W. J. Biol. Chem. 2000, 275, 25533-25539). The CD spectra of a mutant protein, ASY92F, in which Tyr 92 was replaced by Phe, and of AS were very similar. ASY92F was approximately 0.1% as active as nonmutated recombinant AS. The steady-state kinetic parameters were measured as 0.138 min(-1) and 0.189 mM for k(cat) and K(M), respectively. Similar to a mutant protein of 5-epi-aristolochene (Rising, K. A.; Starks, C. M.; Noel, J. P.; Chappell, J. J. Am. Chem. Soc. 2000, 122, 1861-1866), the mutant released significant amounts of germacrene A (approximately 29%). ASY92F also produced various amounts of a further five hydrocarbons of molecular weight 204, valencene, beta-(E)-farnesene, alpha- and beta-selinene, and selina-4,11-diene.     

Comment: 2004's fastest organic and biomolecular chemistry!

In January 2003, the Royal Society of Chemistry launched Organic & Biomolecular Chemistry (OBC)--a journal promising to provide high quality research from all aspects of synthetic, physical and biomolecular organic chemistry. The journal was set to build upon the foundations laid down by its predecessor publications (J. Chem. Soc., Perkin Trans. 1 and J. Chem. Soc., Perkin Trans. 2) as well as complement the subject coverage already published in prestigious general chemistry journals such as Chemical Communications and Chemical Society Reviews. Nearly two years on, just how is the programme developing and what can the community expect to see from the Royal Society of Chemistry (RSC)?     

Facile synthesis of novel functionalized bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives

An improved and efficient synthetic route to four functionalized bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) derivatives 2-5 is reported. Tetrathiolate 1 was readily prepared from 2,2'-bis(1,3,4,6-tetrathiapentalen-5-one) under carefully controlled conditions. Subsequent reaction of 1 with selected primary alkyl halides affords new functionalized BEDT-TTF derivatives in good yields.     

Comment: 2004's fastest organic and biomolecular chemistry!

In January 2004, the Royal Society of Chemistry launched Organic & Biomolecular Chemistry (OBC) - a journal promising to provide high quality research from all aspects of synthetic, physical and biomolecular organic chemistry. The journal was set to build upon the foundations laid down by its predecessor publications (J. Chem. Soc., Perkin Trans. 1 and J. Chem. Soc., Perkin Trans. 2) as well as complement the subject coverage already published in prestigious general chemistry journals such as Chemical Communications and Chemical Society Reviews. Nearly two years on, just how is the programme developing and what can the community expect to see from the Royal Society of Chemistry (RSC)?     

Synthetic alpha-mannosyl ceramide as a potent stimulant for an NKT cell repertoire bearing the invariant Valpha19-Jalpha26 TCR alpha chain

A NKT cell repertoire is characterized by the expression of the Valpha19-Jalpha26 invariant TCR alpha chain (Valpha19 NKT cell). This repertoire, as well as a well-established Valpha14-Jalpha281 invariant TCR alpha(+) NKT cell subset (Valpha14 NKT cell), has been suggested to have important roles in the regulation of the immune system and, thus, is a major therapeutic target. Here, we attempted to find specific antigens for Valpha19 NKT cells. Valpha19 as well as Valpha14 NKT cells exhibited reactivity to alpha-galactosyl ceramide (alpha-GalCer). Thus, a series of monoglycosyl ceramides with an axially oriented glycosidic linkage between the sugar and ceramide moiety were synthesized and their antigenicity to Valpha19 NKT cells was determined by measuring their immune responses in culture with glycolipids. Comprehensive examinations revealed substantial antigenic activity for Valpha19 NKT cells by alpha-mannosyl ceramide.