Simulation of organic monolayers as templates for the nucleation of calcite crystals

Living organisms can control the size, shape, and structure of minerals. Attempts to reproduce this biological control in the laboratory often use Langmuir monolayers of long-chain carboxylic acids. We use large-scale molecular dynamics simulations to calculate the interfacial energies of calcite crystals grown on stearic (octadecanoic) acid monolayers. In light of these simulations we discuss the argument that the orientation of the growing mineral is controlled by the organic substrate acting as a template which the mineral must fit in order to grow.     

Modular syntheses of isoxazoloazepinones and pyrazoloazepinones

Herein we described an optimised synthesis of isoxazoloazepinone and novel heterocycle pyrazoloazepinone. These syntheses are modular in nature and fast to execute. The title compounds were obtained pure without the intervention of chromatography.     

Improving nature's enzyme active site with genetically encoded unnatural amino acids

The ability to site-specifically incorporate a diverse set of unnatural amino acids (>30) into proteins and quickly add new structures of interest has recently changed our approach to protein use and study. One important question yet unaddressed with unnatural amino acids (UAAs) is whether they can improve the activity of an enzyme beyond that available from the natural 20 amino acids. Herein, we report the >30-fold improvement of prodrug activator nitroreductase activity with an UAA over that of the native active site and a >2.3-fold improvement over the best possible natural amino acid. Because immense structural and electrostatic diversity at a single location can be sampled very quickly, UAAs can be implemented to improve enzyme active sites and tune a site to multiple substrates.     

Synthesis and metal-binding properties of chelating fluorescein derivatives

[reaction: see text] Two routes to highly functionalized metal-chelating fluorescein derivatives have been pursued. Compound 3 is partially quenched by a variety of first-row transition metal ions in aqueous solution, with EC(50) values ranging from 0.4 to 60 microM. Compounds of this type may find application in biological sensing.     

Analysis of ppb levels of organics in water by means of purge-and-trap, capillary gas chromatography and selective detectors

The Environmental Protection Agency (EPA) has issued a series of methods (500 and 600 series) for the analysis of organics in drinking water and industrial discharges. Methods 601 and 602 employ packed-column gas chromatography (GC) with electrolytic conductivity (E1CD) and photoionization detection (PID), respectively. A purge-and-trap system is used for concentration of volatiles. The EPA is in the process of converting methods 601 and 602 and certain 500-series methods to capillary column analysis. We have also initiated the conversion of a number of these methods, using E1CD and PID and have described them in detail in this paper. We have evaluated both 0.32- and 0.53-mm diameter capillary columns, using helium and nitrogen as carrier gases with each detector. We found that with nitrogen optimum results are obtained at a flow-rate of 15 ml/min, and with helium at 6-8 ml/min. As a result of system optimization, including operation of the two detectors in series, and converting from packed to capillary columns, we found that analysis time could be reduced from 80 min (for two methods separately) to ca. 30 min. In addition, the elution of more than five components in one peak, observed when the packed column specified in method 601 are used, was eliminated.     

Total synthesis of (+/-)-cameroonan-7alpha-ol and biomimetic rearrangements to related nopsane sesquiterpenes

A total synthesis of the novel silphinane sesquiterpene alcohol (+/-)-cameroonanol (6-OH) from bicyclic enone 10 was accomplished by conjugate addition of crotylsilane, photochemical hydrobromination, intramolecular alkylation, and hydride reduction. The stereoisomers cameroonan-7beta-ol (18-OH) and 9-epicamerooonanols (19 and 20) were separated from isomer mixtures and the 9-desmethylcameroonanols (21-OH and 22-OH) were obtained by similar means. Solvolysis of 6-OMs and 18-OMs effected skeletal rearrangements to (+/-)-silphiperfol-6-ene (5), (+/-)-prenopsanol (7) and (+/-)-nopsanol (8), and (+/-)-silphiperfolan-7beta-ol (9) in parallel with biogenetic schemes proposed for these naturally occurring sesquiterpenes. The nor analogues 21-OMs and 22-OMs underwent solvolytic rearrangments to a similar set of nor products. The increase in solvolytic rates for the 7beta-mesylates 18-OMs and 22-OMs in comparison to the 7alpha epimers is attributed to concerted antiperiplanar Wagner-Meerwein rearrangements to the prenopsyl and norprenopsyl carbocations. Further analysis of the kinetic data and comparisons with solvolysis rates for the structurally related silphin-1beta-yl and silphin-1alpha-yl mesylates (28 and 29) are presented. The rearrangements observed afford chemical precedent for the biogenetic pathways in the literature for these silphinane sesquiterpenes.     

Total synthesis of (+/-)-cameroonanol

[reaction: see text]The structure and relative stereochemistry of the novel silphiperfolane-type sesquiterpene cameroonan-7alpha-ol (1) were confirmed by a total synthesis of (+/-)-1 from 3,3,5-trimethylbicyclo[3.3.0]oct-1(8)-en-2-one (6) by means of a Sakurai reaction with (Z)-crotylsilane, free radical hydrobromination, base-induced cyclization, and LiAlH4 reduction.     

Determination of the cardiolipin content of individual mitochondria by capillary electrophoresis with laser-induced fluorescence detection

We report the application of capillary electrophoresis (CE) with postcolumn laser-induced fluorescence (LIF) detection to measure the cardiolipin content of individual mitochondria from cultured NS1 cells. Mitochondria were isolated by differential centrifugation and stained with the fluorescent dye 10-N-nonyl acridine orange which stoichiometrically binds to cardiolipin in a 1:1 or 2:1 ratio depending on the dye concentration. The green fluorescence resulting from the 1:1 complex was chosen for analysis because it is substantially more intense than the red fluorescence resulting from the 2:1 complex. Two dye concentrations that resulted in maximal and submaximal formation of the 1:1 10-N-nonyl acridine orange-cardiolipin complex were identified by spectrofluorometry. Individual mitochondria stained with both dye concentrations were separated and detected by CE with LIF detection. The data from mitochondria dosed with the lower dye concentration, where it is assumed that all the dye added to the mitochondrial sample was bound to cardiolipin, were used to derive a sensitivity factor relating fluorescence intensity of a mitochondrial event to its cardiolipin content. Using this factor, the cardiolipin contents of individual mitochondria stained with the higher dye concentration were determined, and ranged from 1.2 to 920 amol, with a median value of 4 amol. These results suggest a new strategy for estimating the organellar content of compounds that can be fluorescently tagged.