Valine and phenylalanine as precursors in the biosynthesis of alkamides in Acmella radicans

Acmella radicans (Asteraceae) produces at least seven alkamides, most with either an isobutyl- or phenylethyl group as the amine moiety. These moieties suggest that the amino acids valine and phenylalanine are the biosynthetic precursors of these alkamides. On the basis of labeled feeding experiments using either L-[2H8]valine or L-[2H8]phenylalanine we present evidence for the involvement of these two amino acids in the biosynthesis of (2E,6Z,8E)-N-isobutyl-2,6,8-decatrienamide (affinin) (1), (2Z,4E)-N-(2-phenylethyl)-2,4-octadienamide (2), (2E)-N-(2-phenylethyl)-nona-2-en-6,8-diynamide (3), and 3-phenyl-N-(2-phenylethyl)-2-propenamide (4). Alkamides were isolated from young A. radicans plants and analyzed by gas chromatography-mass spectrometry (GC-MS). Additionally, in cell free in vitro experiments based on isobutyl and phenylethylamide biosynthesis, using a colorimetric assay and GC-MS, valine and phenylalanine decarboxylase activities were assayed in the soluble extract of A. radicans leaves.     

Counting lattice chains and Delannoy paths in higher dimensions

Lattice chains and Delannoy paths represent two different ways to progress through a lattice. We use elementary combinatorial arguments to derive new expressions for the number of chains and the number of Delannoy paths in a lattice of arbitrary finite dimension. Specifically, fix nonnegative integers n₁,…,n_d, and let L denote the lattice of points (a₁,…,a_d)∈Z^d that satisfy 0≤a_i≤n_i for 1≤i≤d. We prove that the number of chains in L is given by where . We also show that the number of Delannoy paths in L equals Setting n_i=n (for all i) in these expressions yields a new proof of a recent result of Duchi and Sulanke [9] relating the total number of chains to the central Delannoy numbers. We also give a novel derivation of the generating functions for these numbers in arbitrary dimension.     

Determination of NAD(P)H by A Bioluminescent Enzyme Fiber Optic Probe

Abstract

A fiber optic probe was interfaced to a photon counting system for the determination of nicotinamide adenine dinucleotide reduced [NAD(P)H] by a bioluminescence method. The reagents employed in a bacterial luciferase/flavin mononucleotide /decanal system were optimized. Attempts were made to increase the quantum yield of the system. Dodecanal, tridecanal, and tetradecanal were evaluated as alternative aldehyde reagents for decanal, and hydrogen peroxide was added to the system. Neither attempt increased the quantum yield of the system. However, a relatively low detection limit of 1.6 × 10^?9 M for NAD(P)H was obtained with a linear dynamic range of 3.8 orders of magnitude. These results demonstrate the sensitivity of this instrumentation and assay.     

Exploring college students’ mental representations of inferential statistics

We report a case study that explored how three college students mentally represented the knowledge they held of inferential statistics, how this knowledge was connected, and how it was applied in two problem solving situations. A concept map task and two problem categorization tasks were used along with interviews to gather the data. We found that the students’ representations were based on incomplete statistical understanding. Although they grasped various concepts and inferential tests, the students rarely linked key concepts together or to tests nor did they accurately apply that knowledge to categorize word problems. We suggest that one reason the students had difficulty applying their knowledge is that it was not sufficiently integrated. In addition, we found that varying the instruction for the categorization task elicited different mental representations. One instruction was particularly effective in revealing students’ partial understandings. This finding suggests that modifying the task format as we have done could be a useful diagnostic tool.     

Notable features in the molecular structure of W2(OCH2-t-Bu)6(NCNMe2)3: Three different modes of bonding for NCNMe2(2-) ligands

Hydrocarbon solutions of W₂(OCH₂-t-Bu)₆(HNMe₂)₂(MM) and Me₂NCN (?3 equiv) react at 0°C to give a compound of formula W₂(OCH₂-Bu-t)₆(NCNMe₂)₃. The crystal and molecular struture of the latter compound, deduced from an X-ray study, reveals the loss of the WW triple bond (WW = 3.85 Å) and the formal reduction of each Me₂NCN molecule to a 2- ligand for which three different modes of bonding are seen.     

Indole-2,3-quinodimethanes : Synthesis of selectively protected derivatives of the fused dimeric indole alkaloid staurosporinone

The imine 1 was converted via an indole-2,3-quinodimethane cyclization to the hexahydroindolocarbazole 7, which was further converted to the N-carbomethoxy derivative of staurosporinone 2.     

Supervisor and Teacher Educator Perceived Relevance of Recommendations in the NCTM Curriculum Standards

Based on judgments of mathematics supervisors and teacher educators, the findings of this empirical study confirm that the Curriculum and Evaluation Standards (National Council of Teachers of Mathematics [NCTM], 1989) reflect content that is relevant to mathematics instruction. However, some concern did exist about the relevancy of teaching statistics and probability at the elementary level. Despite the general consensus about the Standards, total agreement was not evident. Respondents with asecondary-school focus rated many of the standards and criteria across grade levels significantly lower in importance than did other respondents; elementary- and middle-school respondents judged several K-8 standards and criteria to be more important than did some higher-education and secondary respondents, while secondary-and middle-school respondents judged the 9–12 standards and critera to be more important than did elementary and some higher education respondents. Respondents with 30 or more years of experience or who were less familiar with the standards rated the K-8 standards and criteria to be lower in importance than did other respondents.