A PRELIMINARY INVESTIGATION OF THE USE OF LIMONENE FOR DETECTING SINGLET OXYGEN AS A COMPONENT OF POLLUTED AIR

Abstract— Exploratory experiments using simulated conditions indicate that the terpene, (+)-limonene can serve to detect O₂(¹Δ_g) in polluted atmospheres. ¹O₂ attack on limonene results in the formation of specific oxidation products in a specific distribution; quantitative identification of these products is a highly specific test for ¹O₂.     

The role of proficiency testing in the detection and resolution of calibration bias in the LeadCare® blood lead analyzer; limitations of peer-group assessment

Following implementation of the CLIA ‘88 laboratory regulations, the primary role of proficiency testing (external quality assessment, PT) in the U.S. has been widely viewed as one of assuring regulatory compliance. PT can also be an effective tool for detecting widespread analytical problems, subject to limitations based on the method of PT assigned value determination. A recent case study describes the role of two PT programs in detecting and resolving a calibration bias in the LeadCare blood lead analyzer, and illustrates the limitations of peer-group target determination in fulfilling that PT role.     

Reaction of 3-Diazocamphor with Silver Ion - Formation of Tricyclanone

The usual method of formation of tricyclanone (1) involves thermolysis of an intimate mixture of 3-diazocamphor (3) and copper powder and is thought to involve ketocarbene (5).¹ Recently this method has been supplemented² by one which involves reaction of 3,3-dibromocamphor with diethylzinc in benzene where α-elimination to give ketocarbene (5) is mediated by 3-bromocamphor carbanion whose role is indicated by trapping as 3-bromocamphor; this material accounts for ca. 10% of product even after prolonged reaction times.     

Selective Enzymatic Oxidation of Silanes to Silanols

Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wild‐type cytochrome P450 monooxygenase (P450_BM3 from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this non‐native activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves C?H bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native C?H hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire.     

The estimation of leucine aminopeptidase produced by molting nematodes with labeled leucinamide as substrate

Leucine aminopeptidase activity was measured using l-[U-¹⁴C]leucinamide as substrate. The leucine freed by hydrolysis was separated by high voltage electrophoresis and estimated in a scintillation counter. The method was especially useful for studying the production of LAP during the molting of infective juveniles of the nematodes, H. contortus, because activity could be measured without purifying or concentrating the enzyme.     

Finding the convex hull of a simple polygon

It is well known that the convex hull of a set of n points in the plane can be found by an algorithm having worst-case complexity O(n log n). A short linear-time algorithm for finding the convex hull when the points form the (ordered) vertices of a simple (i.e., non-self-intersecting) polygon is given.     

Transverse Frames for Petrov Type I Spacetimes: A General Algebraic Procedure

We develop an algebraic procedure to rotate a general Newman-Penrose tetrad in a Petrov type I spacetime into a frame with Weyl scalars ₁ and ₃ equal to zero, assuming that initially all the Weyl scalars are non vanishing. The new frame highlights the physical properties of the spacetime. In particular, in a Petrov type I spacetime, setting ₁ and ₃ to zero makes apparent the superposition of a Coulomb-type effect ₂ with transverse degrees of freedom ₀ and ₄.