Development of an Intermittent-Flow Enantioselective Aza-Henry Reaction Using an Arylnitromethane and Homogeneous Brønsted Acid-Base Catalyst with Recycle

A stereoselective aza-Henry reaction between an arylnitromethane and Boc-protected aryl aldimine using a homogeneous Brønsted acid-base catalyst was translated from batch format to an automated intermittent-flow process. This work demonstrates the advantages of a novel intermittent-flow setup with product crystallization and slow reagent addition which is not amenable to the standard continuous equipment: plug flow tube reactor (PFR) or continuous stirred tank reactor (CSTR). A significant benefit of this strategy was the integration of an organocatalytic enantioselective reaction with straightforward product separation, including recycle of the catalyst, resulting in increased intensity of the process by maintaining high catalyst concentration in the reactor. A continuous campaign confirmed that these conditions could effectively provide high throughput of material using an automated system while maintaining high selectivity, thereby addressing nitroalkane safety and minimizing catalyst usage.

Functional group selective ion/molecule reactions: mass spectrometric identification of the amido functionality in protonated monofunctional compounds

A mass spectrometric method was developed for the screening of the amido functionality in monofunctional protonated analytes. This method is based on selective gas-phase derivatization of protonated analytes by (N,N-diethylamino)dimethylborane in a Fourier transform ion cyclotron resonance (FT-ICR) and triple quadrupole mass spectrometer. Examination of a series of protonated analytes demonstrated that only the compounds containing the amido functionality react with the aminoborane by the derivatization reaction. The mechanism involves proton transfer from the protonated analyte to the borane, followed by addition of the amide to the boron center, which leads to the elimination of neutral diethylamine. The derivatized analytes are readily identified on the basis of a shift of 40 m/z units relative to the m/z value of the protonated analyte and characteristic boron isotope patterns. Collision-activated dissociation was used to provide support for the structures assigned to the derivatized analytes. The structural information gained from this gas-phase derivatization method will aid in the functional group identification of unknown compounds and their mixtures.

Compound Screening for the Presence of the Primary N-Oxide Functionality via Ion−Molecule Reactions in a Mass Spectrometer

A mass spectrometry method is presented for the identification of compounds that contain the primary N-oxide functional group. This method utilizes a gas-phase ion-molecule reaction with dimethyl disulfide that rapidly and selectively derivatizes the protonated primary N-oxide functional group in a mass spectrometer to yield an ionic reaction product (with 31 Da higher mass than that of the protonated molecule) that is diagnostic for the presence of a primary N-oxide functionality. A variety of protonated analytes containing different functional groups were tested in Fourier transform ion-cyclotron resonance and triple quadrupole mass spectrometers to probe the selectivity of the reaction. Only molecules containing the protonated primary N-oxide functional group yielded the diagnostic reaction product; all other protonated molecules gave protonated dimethyl disulfide or no reaction products. The feasibility of this method for compound screening was tested by examining six analytes with the same molecular formula but different atom connectivity. The one analyte that contained the primary N-oxide functional group was readily differentiated from the other analytes.

Ion−Molecule Reactions for the Characterization of Polyols and Polyol Mixtures by ESI/FT-ICR Mass Spectrometry

A mass spectrometric method is described for the identification and counting of hydroxyl groups in an analyte. Analytes introduced into a FT-ICR mass spectrometer and ionized by positive mode ESI were allowed to react with the neutral reagent diethylmethoxyborane. This results in derivatization of the hydroxyl groups of the analytes by replacement of a proton with a diethylborenium ion. Protonated polyols react by consecutive derivatization reactions, wherein all, or nearly all, of the hydroxyls are derivatized. The polyol derivatization products are separated by 68 mass units in the mass spectrum. This 68 Da mass shift, along with 30 Da mass shifts arising from intramolecular derivatization of the primary derivatization products, makes it easy to count the number of functional groups present in the analyte. The utility of this method for the analysis of polyols as single-component solutions, as mixtures, or in HPLC effluent (LC-MS analysis) is demonstrated.

Ion−Molecule Reactions for Mass Spectrometric Identification of Functional Groups in Protonated Oxygen-Containing Monofunctional Compounds

Protonated oxygen-containing monofunctional compounds react with selected methoxyborane reagents by proton transfer followed by nucleophilic substitution of methanol at the boron atom in a Fourier transform ion cyclotron resonance mass spectrometer. The derivatized oxygen functionality can be identified by H/D exchange, collision-activated dissociation, or both. This information on the identity of the functionalities in the analyte, in conjunction with molecular formula information obtained from exact mass measurements on either the protonated or derivatized analyte, facilitates structure elucidation of unknown organic compounds in a mass spectrometer.

Laser desorption in transmission geometry inside a Fourier-transform ion cyclotron resonance mass spectrometer

We report here the first application of laser desorption (LD) in transmission geometry (backside irradiation of the sample through a transparent support) inside a Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR). A probe-mounted fiber optic assembly was used to simplify the implementation of this LD technique. This setup requires little or no instrument modifications, has minimum maintenance requirements, and is relatively inexpensive to build. The performance of the probe was tested by determining the molecular weight of a commercial polystyrene standard from its matrix-assisted laser desorption/ionization (MALDI) spectrum. The measured average molecular weight is comparable to that obtained for the same sample by MALDI in the conventional top-illumination arrangement (reflection geometry) and by the manufacturer of the sample by gel permeation chromatography. The average velocities measured for ions evaporated by transmission mode LD of several neat samples are about half the velocity of those obtained by using the reflection geometry. Therefore, transmission mode irradiation of the sample holds promise to desorb ions that are easier to trap in an ICR cell. An oscillating capillary nebulizer was adapted for the deposition of analytes to improve sampling reproducibility.

Reliability of goniometric measurements and visual estimates of knee range of motion obtained in a clinical setting

The purpose of this study was to examine the intratester and intertester reliability for goniometric measurements of knee flexion and extension passive range of motion (PROM). In addition, parallel-forms reliability for PROM measurements of the knee obtained by use of a goniometer and by visual estimation was examined. The intertester reliability for visual estimates of the PROM of the knee was also examined. Repeated measurements were obtained on 43 patients in a clinical setting. The intraclass correlation coefficients (ICCs) for intratester reliability of measurements obtained with a goniometer were .99 for flexion and .98 for extension. Intertester reliability for measurements obtained with a goniometer was .90 for flexion and .86 for extension. The ICCs for parallel-forms reliability for measurements obtained with a goniometer and by visual estimation ranged from .82 to .94. The intertester reliability for measurements obtained by visual estimation was .83 for flexion and .82 for extension. Results suggest clinicians should use a goniometer to take repeated PROM measurements of a patient's knee to minimize the error associated with these measurements.

Facial hair and respirator fit: a review of the literature

The effect of facial hair on the quality of fit obtained while wearing a tight-fitting respirator has been and continues to be a controversial subject. Many people hold strong opinions on both sides of the issue, but it is not opinion that is needed. Rather what is needed is quantitative study of the situation to determine precisely what effect facial hair has on respirator fit. The results of fourteen studies of the facial hair leakage question have been summarized. All but two of the fourteen studies found that in the presence of facial hair, face seal leakage increases from 20 times to 1000 times. In addition both intersubject and interrespirator face seal leakage variability increased when facial hair was present. In the other two studies, one completed with positive pressure SCBAs and the other completed in the workplace, no statistically significant leakage differences were found.

Intracellular and intraluminal aspects of renal calculosis in the marine mollusc Macrocallista nimbosa

The intracellular and intraluminal development of renal calculi in the bivalved mollusc Macrocallista nimbosa was investigated by histologic techniques. The origin of calculi is within the renal tubule cell. Early events involve the formation of a stone precursor into which are incorporated calcium salts, heavy metals, and mucopolysaccharides. The stone is eventually extruded into the tubule lumen where it continues to grow by epitaxy and aggregation. Various forms of calcium phosphate calculi were identified, including hydroxylapatite, whitlockite, brushite, and chlorapatite.