Evaluation of Polycation-Stabilized Lactate Oxidase in a Silica Sol–Gel as a Biosensor Platform

 Whereas glucose oxidase and related proteins are encapsulated readily in silica sol–gels, α-hydroxy enzymes such as lactate oxidase (LOx), are reported to be damaged by electrostatic interaction with these matrices. Based on a previous report, poly(ethyleneimine), PEI, was evaluated as a protecting compound under conditions suited to analytical measurements. With LOx and PEI co-encapsulated in a silica sol–gel, the enzyme retained 62% of its initial activity after 20 days. In the absence of PEI, activity was lost during the processing. Batch analytical measurements with enzyme-doped sol–gel yielded a linear response over the range 0.5–2.0 mM lactate and a detection limit of 0.03 mM lactate. Both simple incorporation of LOx in a silica sol–gel and an alternative protection method, blocking the ion-exchange sites on silica with La(III), failed. These negative results supported the hypothesis that the efficacy of PEI was related to its formation of a protective sheath around the enzyme. Author for correspondence. E-mail: coxja@muohio.edu Received July 29, 2002; accepted December 15, 2002 Published online May 19, 2003     

Learning to Make Sense of Division of Fractions: One K–8 Preservice Teacher's Perspective

Current reform documents in mathematics education recommend that teachers help students develop both conceptual and procedural understandings. However, teachers often do not possess the in-depth mathematical reasoning necessary to accomplish this goal. The purpose of this article is to provide one way in which preservice teachers can come to better understand the mathematics they will teach.     

Innately transitive subgroups of wreath products in product action

A permutation group is innately transitive if it has a transitive minimal normal subgroup, which is referred to as a plinth. We study the class of finite, innately transitive permutation groups that can be embedded into wreath products in product action. This investigation is carried out by observing that such a wreath product preserves a natural Cartesian decomposition of the underlying set. Previously we classified the possible embeddings in the case where the plinth is simple. Here we extend that classification and identify several different types of Cartesian decompositions that can be preserved by an innately transitive group with a non-abelian plinth. These different types of decompositions lead to different types of embeddings of the acting group into wreath products in product action. We also obtain a full characterisation of embeddings of innately transitive groups with diagonal type into such wreath products.

     

NMR and X-ray crystallography, complementary tools in structural proteomics of small proteins

NMR spectroscopy and X-ray crystallography, the two primary experimental methods for protein structure determination at high resolution, have different advantages and disadvantages in terms of sample preparation and data collection and analysis. It is therefore of interest to assess their complementarity when applied to small proteins. Structural genomics/proteomics projects provide an ideal opportunity to make such comparisons as they generate data in a systematic manner for large enough numbers of proteins to allow firm conclusions to be drawn. Here we report a comparison for 263 unique proteins screened by both NMR spectroscopy and X-ray crystallography in our structural proteomics pipeline. Only 21 targets (8%) were deemed amenable to both methods based on an initial 2D 15N-HSQC NMR spectrum and optimized crystallization trials. However, the use of both methods in the pipeline increased the total number of targets amenable to structure determination to 107, with 43 amenable to NMR only and 43 amenable to X-ray crystallographic methods only. We did not observe a correlation between 15N-HSQC spectral quality and the success of the same protein in crystallization screens. Similar results were found for an independent set of 159 proteins as reported in the accompanying paper by Snyder et al. Thus, we conclude that both methods are highly complementary, and in order to increase the number of proteins suited for structure determination, we suggest that both methods be used in parallel in screening of all small proteins for structure determination.     

A new method for the preparation of 2-thio substituted furans by methylsulfanylation of gamma-dithiane carbonyl compounds

Several related methods for the preparation of differentially substituted 2-thiofurans are described. The general procedure involves the formation of a thionium ion from a gamma-dithianyl substituted carbonyl compound followed by cyclization of this reactive intermediate onto the tethered carbonyl group. Two methods for thionium ion generation were explored. One of these involved an acid-catalyzed reaction of beta-ketenedithioacetals, prepared from the condensation of 2,2-bis(methylsulfanyl)acetaldehyde with a variety of ketones. Cyclization followed by loss of methane thiol gave 2-thiofurans 17, 18 and 23, 24 in 70-90% yield. Attempts to prepare 5-heteroatom substituted 2-thiofurans from the corresponding beta-ketenedithioacetal amides or esters were unsuccessful, leading to 1,2-thio rearranged products. A more successful route involved the reaction of beta-acetoxy-gamma-thianyl carbonyl compounds with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF). Treatment of the dithiane with this reagent resulted in the smooth generation of a thionium ion. Cyclization followed by loss of acetic acid afforded thiofurans 17, 18, 23, 47-49, 51, and 61-64 in 40-100% yield. The N-butenyl substituted thioamido furan furnished a rearranged hexahydropyrroloquinolin-2-one in high yield when heated at 110 degrees C.     

Generic serial and parallel on-line direct-injection using turbulent flow liquid chromatography/tandem mass spectrometry

The development of turbulent flow chromatography (TFC) has enabled considerable growth in the utility of on-line direct-injection technologies. TFC has now become established in a large number of varied analytical environments, particularly drug discovery/pharmacokinetics, metabolite profiling, combinatorial library purification, pre-clinical and clinical GLP applications. The utility of turbulent flow technology for in-house pre-clinical and clinical quantitative applications has necessitated extensive valve-cleaning procedures, and consequently lengthy cycle-times, to effectively remove the system carry-over. In-house requirements for assay validation require carry-over less than 20% of the lowest level of quantification (LLOQ), corresponding to 0.02% carry-over for a linear calibration range incorporating 3 orders. A generic turbulent flow chromatography protocol has been developed for drug discovery that incorporates polymeric turbulent flow extraction (cyclone) with C18-based reverse-phase chromatography. Further, multiple wash steps are incorporated within the methodology to meet in-house requirements for carry-over. Selection of novel switching-valve materials based on polyarylethyl ketone (PAEK) and Hastelloy/Valcon E autosampler injection hardware has enabled us to significantly impact the cycle-time required to reduce carry-over. Consequently, optimal usage of switching valves has enabled parallel operation for a generic on-line direct-injection methodology to successfully reduce the total cycle-time. Overall reductions from 4 min per sample to 90 s per sample are shown with comparable data quality using a proprietary target molecule from 0.1-100 ng/mL. This paper describes the hardware configuration and methodologies utilized to perform generic serial and parallel on-line direct-injection using a Turboflow HTLC 2300 system.     

Synthesis and electronic characterization of bipyridine dithiolate rhodium(III) complexes

Five new mixed diimine 1,1'-dithiolate or dithiocarbamate ligand complexes of the form [Rh(bpy)2(SS)][PF6]n, where bpy = 2,2'-bipyridine and SS = various substituted dialkyldithiocarbamates or 1,1'-dithiolates, were synthesized from cis-[Rh(bpy)2(OTf)2][OTf]. The triflate ligands are easily displaced by other ligands and allow these syntheses to proceed in high yields (80-90% overall) under relatively mild reaction conditions and to give high purity products. Electrochemistry shows irreversible two-electron reduction of Rh(III) to Rh(I) and a concomitant loss of one bipyridine ligand; this is followed by reversible one-electron reduction of the remaining 2,2'-bipyridine ligand. The electronic characterizations of these complexes are consistent with significant delocalization of the sulfur electron density onto the empty metal d orbitals. The 1,1'-dithiolate ligands induce larger red shifts in the absorption and emission spectra than the dithiocarbamates as the 1,1'-dithiolates have a more extensive conjugation system.     

Interannular communication in the radical anions of bis-cyclooctatetraene systems

[reaction: see text] The room-temperature potassium reduction of 1,2-bis-cyclooctatetraeneoxypropane yields two different regio-spin isomer anion radicals in equilibrium (COT-O-C(Me)HCH(2)CH(2)-O-COT(*)(-) = (*)(-)COT-O-C(Me)HCH(2)CH(2)-O-COT) that is shifted far to the right. The presence of the unreduced ring perturbs the spin density on the reduced ring. Addition of more electrons generates the diradical dianion ((*)(-)COT-O-C(Me)HCH(2)CH(2)-O-COT(*)(-)), and the anion radical on the secondary side splits the degeneracy of the psuedo-ortho protons of the anion radical on the primary side.     

Orientational ordering of 4-substituted phenylcyclohexanes studied by carbon-13 two-dimensional N.M.R.

Abstract

An N.M.R. method combining the techniques of separated local field spectroscopy (SLF) and variable angle spinning (VAS) is valuable in the investigtion of nematic liquid crystals. Rapid sample spinning causes the nematic director to align along the spinning axis, resulting in narrow peaks in the C-13 N.M.R. spectrum. SLF is a two-dimensional N.M.R. method which produces a first order splitting pattern for each carbon signal from which C–H dipolar coupling constants can be determined. The order parameters for all segments of the liquid crystal molecule can then be calculated. Results for three 4′-cyanophenylcyclohexanes are considered here. These compounds are trans-substituted at the 4 position of cyclohexane ring with n-pentane (PCH5), 1-pentene (3d ₁CP) and 3-pentene (1d ₃CP), respectively.     

Locally s-distance transitive graphs and pairwise transitive designs

The study of locally s-distance transitive graphs initiated by the authors in previous work, identified that graphs with a star quotient are of particular interest. This paper shows that the study of locally s-distance transitive graphs with a star quotient is equivalent to the study of a particular family of designs with strong symmetry properties that we call nicely affine and pairwise transitive. We show that a group acting regularly on the points of such a design must be abelian and give general construction for this case.