Synthesis of the reported structure of crassiflorone, a naturally occurring quinone isolated from the African ebony Diospyros crassiflora, and regioisomeric pentacyclic furocoumarin naphthoquinones

A synthesis of the structure reported for the natural product crassiflorone, a furocoumarin naphthoquinone, is described. The key steps are a Diels-Alder reaction to form 2-bromo-8-hydroxy-6-methylnaphthoquinone, followed by O-protection and copper(II) mediated coupling to 4-hydroxy-5-methylcoumarin to establish the pentacyclic framework whose structure was unambiguously confirmed by X-ray crystallography. Since the spectroscopic data of the synthetic material did not match those reported for the natural product, three further regioisomeric furocoumarin naphthoquinones were prepared by copper(II) mediated coupling of 4-hydroxy-5- or 8-methyl coumarins with 5-benzyloxy-2-bromo-7-methyl- or 8-benzyloxy-2-bromo-6-methyl-1,4-naphthoquinone. Again the spectroscopic data did not match those of the natural material and therefore the true structure of crassiflorone remains unknown.     

An evaluation of solvent mediators for ion-selective electrode membranes based on calcium bis(dialkylphosphate) sensors trapped in poly(vinyl chloride) matrices

This study on several alkan-1-ols, di-n-octylphenyl phosphorate and di-n-nonyl phthalate as solvent materials in ion-selective electrode membranes based on calcium bis(dialkylphosphate) sensors trapped in a PVC matrix indicates that the best electrodes are made with di-n-octylphenyl phosphonate. These are selective for calcium. The liquid alcohols readily exude from the PVC matrix, and solid alcohols are completely unsuitable for membrane fabrication. However, despite a tendency to be exuded, decan-1-ol gives acceptable electrodes responsive to bivalent cations if calcium bis (di-2-ethylhexylphosphate) is used as sensor. Several selectivity coefficients, k(caj), greater than unity were found, but though such values for j = Na or K do not involve complete loss of selectivity towards calcium, a value of K(CaCu) = 13 for a membrane with di-n-nonyl phthalate as mediator and calcium bis(di-n-decylphosphate) as sensor indicates greater selectivity for copper than for calcium.     

Simple method for determining nucleobase pK(a) values by indirect labeling and demonstration of a pK(a) of neutrality in dsDNA

Phosphorothioates were substituted into double-stranded DNA to study protonated Class I A+.C basepairs by 31P NMR. The method was effective in reporting the A+.C pKa. pKa values near 7.0 were found with optimal nearest-neighbor partners. Such pKa values could expand the catalytic repertoire of nucleic acids.     

Radiotracer studies on ion-selective electrode membranes containing metal complexes of a nonylphenoxypoly(ethyleneoxy)ethanol in poly(vinyl chloride) matrices

Radiotracer studies with (133)Ba, (45)Ca and (36)Cl are reported for PVC matrix membranes containing 2-nitrophenyl phenyl ether and the tetraphenylborate of a barium (or calcium) complex with a nonylphenoxypoly(ethyleneoxy)ethanol (NP), Antarox CO880. The results show that there is very limited permeation of radioactive barium and calcium ions through the membrane systems. However, the continued uptake (with time) of radioactive barium ions by the membranes (the uptake of calcium ion is less) suggests that in relation to selective electrode response the stabilization of ions by the NP ligand within the membrane is important in addition to the simple availability of membrane pathways for primary-ion transport through the membrane. Permselectivity to counter-ions is indicated by the non-permeation of radioactive chloride ions.     

Structural and energetic consequences of expanding a highly cooperative stable DNA hairpin loop

Many hairpin loops are expanded versions of smaller, stable ones. Herein we investigate the extent to which the energetics and structure of d(cGNAg) hairpin loops will tolerate sequence variation. Changing the closing base pair from CG to GC was found to completely eliminate loop-loop interactions; in contrast, expanding the loop at the 3'-end resulted in similar energetics and nonadditivity parameters as the parent loop, suggesting that loop-loop interactions remain intact and highly coupled upon expansion. Together, these data suggest that the CG closing base pair forms an essential platform upon which a stable d(GNA) hairpin loop can fold and that this loop can undergo 3'-expansion with little effect to its structure or energetics.     

Monte Carlo simulation methodology of the ghost interface theory for the planar surface tension

A novel "ghost interface" expression for the surface tension of a planar liquid-vapor interface is derived in detail from consideration of the free energy of the system, and a methodology for utilization of this new technique is given. An augmented Monte Carlo computer simulation procedure is developed specifically for the ghost interface, including derivation of long-range corrections resulting from potential truncation and a modified Gibbs ensemble technique for the simulation of adjacent coexisting phases. Results generated from the ghost interface theory for the surface tension are presented and found to be in good quantitative agreement with those resulting from the Kirkwood-Buff equation. Applications of this new approach to curved and to supersaturated systems are also discussed.     

The ultra-clean chemical laboratory (UCCL) at the Institute for Reference Materials and Measurements (IRMM)

An Ultra-Clean Chemical Laboratory (UCCL) has been built at IRMM to allow reliable, contamination-free chemical treatment of samples prior to inorganic elemental or isotopic analysis. The concept is intended to guarantee a dust-free environment as well as resistance to corrosion even if hot concentrated mixtures of acids are continuously used, thus establishing not a clean or dust-free room but a clean laboratory. The excellent air quality is demonstrated both by particle measurements and the analysis of acids purified by subboiling distillation in the UCCL.