Effects of some phosphorus substituents on the carbon-13 chemical shifts of alkyl chains

The carbon-13 NMR spectra of 16 aliphatic phosphorus compounds with -PCl₂, -P(OCH₃)₂, -P(CH₃)₂ or -PS(CH₃)₂ groups were determined and interpreted on the basis of the usual α, β-deshielding and γ-shielding effects. The α-effects of all the groups were quite large (15 to 30 ppm), though the β-effects were small (0 to 3 ppm). The γ-effects were also small (0·2 to 1·6 ppm), but of significance in suggesting reduced steric compression relative to that found for methyl and most of the common organic functional groups. This may be attributed to the greater length of the C? P bond. The phosphorus-31 NMR spectra of these compounds also show the existence of interaction with γ-carbons by exhibiting small additive upfield shifts.     

Three-bond 31P?31P coupling and 31P chemical shift effects in dimers of phospholium salts and phosphole oxides

The chemically nonequivalent ³¹P nuclei of the Diels-Alder dimers of phospholium ions and phosphole oxides are coupled through three bonds by as much as 35–45 Hz. The chemical shift for a phosphorus atom in the 2-phospholene moiety falls in the expected range; the shift for the constricted atom bridging the 6-membered ring is far downfield, making Δδ as much as 43.5 ppm for one phospholium ion dimer.     

A Case for August Wilhelm Hofmann as the Originator of the Field of Organophosphorus Chemistry

August Wilhelm Hofmann, 1818–1892, discovered many of the functional groups of organophosphorus chemistry, including primary, secondary, and tertiary phosphines, oxides and sulfides of the latter, phosphonic and phosphinic acids and their chloro derivatives, dithiophosphinic acids, tetraalkyl phosphonium hydroxides, and Lewis salts from both tertiary phosphines and their oxides. Some of his procedures are still in use today. Some fundamental properties of these groups were also discovered. In spite of these contributions, much current literature fails to recognize him as the founder of the field, generally giving credit to Carl Arnold August Michaelis and sometimes to Alexander E. Arbuzov, both of whom followed Hofmann chronologically. The contributions of Michaelis and Arbusov were indeed most impressive and extensive. However, the case made in this paper, established by studying the original German literature, will be that August W. Hofmann deserves recognition as the originator of the field of organophosphorus chemistry, indeed as the founding father of the field.     

A dual sensor spin trap for use with EPR spectroscopy

Redox active metal ions, carbon-centered radicals, and oxygen-centered radicals are important to oxidative stress. A radical detector combining a nitrone spin trap, a phenol, and a cyclopropane radical clocklike unit was prepared and used with EPR spectroscopy to detect and distinguish between hydroxyl radicals, methyl radicals, and iron(III) ions. Iron(III) reacts with the phenol unit inducing opening of the cyclopropane ring and cyclization to generate a stable nitroxyl radical.     

A critical evaluation of the graphite furnace conditions for the direct determination of chromium in urine

A critical study of the conditions for the direct determination of Cr in urine using GFAAS was carried out. A chemometric approach showed that the most important parameters that influence the efficiency of atomic Cr cloud formation were the atomization from the tube wall and the proper implementation of a pyrolysis step. The established procedure does not require any sample pre-treatment thus minimizing the risk of contamination. The Cr content in urine was determined using a calibration curve prepared with Cr spiked urine, easily correcting all potential matrix interferences. The heating program proposed took 68 s for a 30 μL urine sample. The procedure was applied for the determination of Cr in urine to investigate the absorption rate of Cr picolinate. The limit of detection and the characteristic mass for a 30 μL urine sample were 0.18 μg/L and 5.4 pg, respectively. Received: 22 June 1998 / Revised: 13 January 1999 / Accepted: 18 January 1999     

Monophosphorylation of ethylenediamine with systems generating low-coordination phosphoryl species

Phenyldioxophosphorane was generated by thermal fragmentation of N-(1-adamantyl)phenylphosphonamidic acid in ethylenediamine to give a 61% yield of N-(2-aminoethyl)phenylphosphonamidic acid. The zwitterionic structure repressed reaction of the other amino group. Neopentyl metaphosphate and ethyl metaphosphate were generated in the presence of ethylenediamine by heating appropriate derivatives of the 2,3-oxaphosphabicyclo[2.2.2]octene system in toluene. Again, the metaphosphate phosphorylated only one amino group to give O-alkyl N-(2-amino-ethyl)phosphoramidic acids, in zwitterionic form. © 1996 John Wiley & Sons, Inc.     

Selective uncoupling of individual mitochondria within a cell using a mitochondria-targeted photoactivated protonophore

Depolarization of an individual mitochondrion or small clusters of mitochondria within cells has been achieved using a photoactivatable probe. The probe is targeted to the matrix of the mitochondrion by an alkyltriphenylphosphonium lipophilic cation and releases the protonophore 2,4-dinitrophenol locally in predetermined regions in response to directed irradiation with UV light via a local photolysis system. This also provides a proof of principle for the general temporally and spatially controlled release of bioactive molecules, pharmacophores, or toxins to mitochondria with tissue, cell, or mitochondrion specificity.     

In situ molecular spectroscopic evidence for CO2 intercalation into montmorillonite in supercritical carbon dioxide

The interaction of anhydrous supercritical CO(2) (scCO(2)) with both kaolinite and ~1W (i.e., close to but less than one layer of hydration) calcium-saturated montmorillonite was investigated under conditions relevant to geologic carbon sequestration (50 °C and 90 bar). The CO(2) molecular environment was probed in situ using a combination of three novel high-pressure techniques: X-ray diffraction, magic angle spinning nuclear magnetic resonance spectroscopy, and attenuated total reflection infrared spectroscopy. We report the first direct evidence that the expansion of montmorillonite under scCO(2) conditions is due to CO(2) migration into the interlayer. Intercalated CO(2) molecules are rotationally constrained and do not appear to react with waters to form bicarbonate or carbonic acid. In contrast, CO(2) does not intercalate into kaolinite. The findings show that predicting the seal integrity of caprock will have complex dependence on clay mineralogy and hydration state.     

The behaviour of the negative-branch unstable resonator with an aperture inside

The negative-branch unstable resonator with an aperture inside the cavity at one conjugate image point is studied. The analysis shows that there is only one unique wave existing. The behaviour of the cavity depends only on the magnification and Fresnel numberN ₁.