Pretreatment of corn fiber by pressure cooking in water

The pretreatment of corn fiber using liquid water at temperatures between 220 and 260°C enhances enzymatic hydrolysis. This paper describes the laboratory reactor system currently in use for cooking of corn fiber at temperatures ranging from 200 to 260°C. The corn fiber at approx 4.4% solid/liquid slurry was treated in a 2-L, 304 SS, Parr reactor with three turbine propeller agitators and a Proportional-Integral-Derivative (PID), controller that controlled temperature within ±1°C. Heat-up times to the final temperatures of 220, 240, or 260°C were achieved in 50 to 60 min. Hold time at the final temperature was less than 10 s. A serpentine cooling coil, through which tap water was circulated at the completion of the run, cooled the reactor’s contents to 180°C within 2 min after the maximum temperature was attained. Ports in the reactor’s head plate facilitated sampling of the slurry and monitoring the pH. A continuous pH monitoring system was developed to help observe trends in pH during pretreatment and to assist in the development of a base (2.0M KOH) addition profile to help keep the pH within the range of 5.0 to 7.0. Enzymatic hydrolysis gave 33 to 84% conversion of cellulose in the pretreated fiber to glucose compared to 17% for untreated fiber.     

Disposable pipette extraction for the analysis of pesticides in fruit and vegetables using gas chromatography/mass spectrometry

Organochlorine, organophosphate pesticides and fungicides in fruits and vegetables were analyzed using disposable pipette extraction (DPX) followed by gas chromatography–mass spectrometry-selective ion monitoring (GC/MS-SIM). The intrinsic rapid mixing capabilities of DPX result in fast and efficient extractions, and eluates are concentrated by using minimal elution solvent volumes rather than solvent evaporation methods. Matrix-matched calibrations were performed with reversed phase mechanisms (DPX-RP), and the limits of detection (LOD) were determined to be lower than 0.1 μg/mL for all targeted pesticides in carrot and orange sample matrices. Coefficients of determination (r²) were greater than 0.995 for most studied pesticides. DPX-RP exhibited recoveries between 72 and 116% for nonpolar and slightly polar pesticides (log P > 2) with most of the recoveries over 88%. Only very polar pesticides (e.g., acephate, mathamidophos) were not extracted well using DPX-RP.     

The conformational bias of aryl, arylsulfonyl geminally substituted tertiary carbon centers: applications in substrate-based stereocontrol

Intramolecular nitrile oxide-olefin cycloaddition to form hexahydrobenzisoxazole 14, which engenders a phenylsulfonyl, 2,5-difluorophenyl geminally substituted carbon substructure, proceeds with up to 99% ds. A rationalization of the high level of substrate-based stereo-induction observed in this and related ketone and acrylonitrile metallohydride reductions, supported by single crystal X-ray crystallography, is presented.     

Infrared detection of a phenylboronic acid terminated alkane thiol monolayer on gold surfaces

Polarization modulation infrared reflectance absorption spectroscopy (PM-IRRAS) and infrared reflectance absorption spectroscopy (IRRAS) have been used to characterize the formation of a self-assembled monolayer of N-(3-dihydroxyborylphenyl)-11-mercaptoundecanamide) (abbreviated PBA) on a gold surface and the subsequent binding of various sugars to the PBA adlayer through the phenylboronic acid moiety to form a phenylboronate ester. Vibrationally resonant sum frequency generation (VR-SFG) spectroscopy confirmed the ordering of the substituted phenyl groups of the PBA adlayer on the gold surface. Solution FTIR spectra and density functional theory were used to confirm the identity of the observed vibrational modes on the gold surface of PBA with and without bound sugar. The detection of the binding of glucose on the gold surface was confirmed in part by the presence of a C-O stretching mode of glucose and the observed O-H stretching mode of glucose that is shifted in position relative to the O-H stretching mode of boronic acid. An IR marker mode was also observed at 1734 cm(-1) upon the binding of glucose. Additionally, changes in the peak profile of the B-O stretching band were observed upon binding, confirming formation of a phenylboronate ester on the gold surface. The binding of mannose and lactose were also detected primarily through the IR marker mode at approximately 1736 to 1742 cm(-1) depending on the identity of the bound sugar.