Cooperative diastereoselectivity of palladium- and platinum-promoted intramolecular [4 + 2] Diels-Alder cycloaddition reactions of 3,4-dimethyl-1-phenylphosphole

The complexes [(DMPP)2M(CH3CN2)]X2 (DMPP = 3,4-dimethyl-1-phenylphosphole; M = Pd, Pt; X = BF4-, NO3-, ClO4-) react with 2 equiv of the dienophiles N,N-dimethylacrylamide (DMAA), 2-vinylpyridine (VyPy), and diphenylvinylphosphine (DPVP) to form bis-[4 + 2] Diels-Alder cycloaddition products. The [M(DMPP)2(DMAA)2]2+ and [M(DMPP)2(VyPy)2]2+ complexes form exclusively as the cis-geometric isomers, whereas for [M(DMPP)2(DPVP)2]2+, both cis- and trans-geometric isomers are formed. The two Diels-Alder cycloadditions occur sequentially, and the absolute configuration of the first reaction influences the absolute configuration of the second. In all cases, recemic mixtures of the (R,R) and (S,S) diastereomers are formed; none of the meso (R,S) diastereomer is observed. New complexes were characterized by elemental analyses, physical properties, infrared spectroscopy, 1H, 1H(31P), 13C(1H), and 31P(1H) NMR spectroscopy, and, in most cases, X-ray crystallography.     

Extending the language of DNA molecular recognition by polyamides: unexpected influence of imidazole and pyrrole arrangement on binding affinity and specificity

Pyrrole (Py) and imidazole (Im) polyamides can be designed to target specific DNA sequences. The effect that the pyrrole and imidazole arrangement, plus DNA sequence, have on sequence specificity and binding affinity has been investigated using DNA melting (DeltaT(M)), circular dichroism (CD), and surface plasmon resonance (SPR) studies. SPR results obtained from a complete set of triheterocyclic polyamides show a dramatic difference in the affinity of f-ImPyIm for its cognate DNA (K(eq) = 1.9 x 10(8) M(-1)) and f-PyPyIm for its cognate DNA (K(eq) = 5.9 x 10(5) M(-1)), which could not have been anticipated prior to characterization of these compounds. Moreover, f-ImPyIm has a 10-fold greater affinity for CGCG than distamycin A has for its cognate, AATT. To understand this difference, the triamide dimers are divided into two structural groupings: central and terminal pairings. The four possible central pairings show decreasing selectivity and affinity for their respective cognate sequences: -ImPy > -PyPy- > -PyIm- approximately -ImIm-. These results extend the language of current design motifs for polyamide sequence recognition to include the use of "words" for recognizing two adjacent base pairs, rather than "letters" for binding to single base pairs. Thus, polyamides designed to target Watson-Crick base pairs should utilize the strength of -ImPy- and -PyPy- central pairings. The f/Im and f/Py terminal groups yielded no advantage for their respective C/G or T/A base pairs. The exception is with the -ImPy- central pairing, for which f/Im has a 10-fold greater affinity for C/G than f/Py has for T/A.     

Rapid determination of five probe drugs and their metabolites in human plasma and urine by liquid chromatography/tandem mass spectrometry: application to cytochrome P450 phenotyping studies

A liquid chromatography/mass spectrometry method, for rapid determination of five cytochrome P450 (CYP) probe drugs and their relevant metabolites in human plasma and urine, is described. The five specific probe substrates/metabolites, caffeine/paraxanthine (CYP1A2), tolbutamide/4-hydroxytolbutamide/carboxytolbutamide (CYP2C9), omeprazole/5-hydroxyomeprazole (CYP2C19), debrisoquine/5-hydroxydebrisoquine (CYP2D6) and midazolam/1'-hydroxymidazolam (CYP3A), together with the internal standards (phenacetin and paracetamol), in plasma and urine, were extracted using solid-phase extraction. The chromatography was performed using a C18 column with an isocratic mobile phase consisting of acetonitrile and 0.1% formic acid in water (70:30). The triple-quadrupole mass spectrometer was operated in both positive and negative modes, and multiple reaction monitoring was used for quantification. The method was validated over the concentration ranges 0.05-5 microg/mL for caffeine and paraxanthine, 0.02-2 microg/mL for tolbutamide, 0.1-20 microg/mL for 4-hydroxytolbutamide, carboxytolbutamide, debrisoquine and 5-hydroxydebrisoquine, 5-2500 ng/mL for omeprazole and 5-hydroxyomeprazole, and 1-100 ng/mL for midazolam and 1'-hydroxymidazolam. The intra- and inter-day precision were 0.3-13.7% and 1.9-14.3%, respectively, and the accuracy ranged from 93.5-107.2%. The lower limit of quantification varied between 1 and 100 ng/mL. The present method provides a robust, fast and sensitive analytical tool for the five-probe drug cocktail, and has been successfully applied to a clinical phenotyping study in 16 subjects.     

Critical Casimir effect in dilute He–He mixture films

Recently, we have found that ⁴He films thin near the lambda point. Based on our measurements, the thinning appears to be caused by the confinement of superfluid order parameter fluctuations in the films. The phenomenon of the thinning is believed to be analogous to the Casimir effect in electromagnetism where the confinement of electromagnetic fluctuations causes the vacuum layer that separates two metal plates to thin. In this paper, we report the result of an experiment extending our previous study to ³He–⁴He mixture films. Thinning is found near the new lambda points and the characteristics of the thinning are similar to that found in pure ⁴He films.     

Eine Zusammenstellung von L?throhrreactionen

Ohne Zusammenfassung     

Surface properties of LiCoO2, LiNiO2 and LiNi1−xCoxO2

The surface composition and chemical environment of LiCoO₂, hexagonal LiNiO_2, cubic LiNiO₂, and the mixed transition metal oxide LiNi_0.5Co_0.5O₂ have been determined by Auger electron and X-ray photoelectron spectroscopies. While the LiCoO₂ surface properties can easily be extrapolated from bulk composition, the nickel-containing materials are less straightforward. Their surface concentration tends to be depleted in lithium relative to that of the bulk and shows an atypical chemical environment for the constituent elements. The Ni 2p XPS photoemission suggests a near “ NiO-like” selvedge through the XPS binding energies and satellite structure which are essentially identical to that of NiO; the spectrum appears fairly insensitive to lithium concentration. Although there is little evidence for higher binding energy Ni³⁺ species or for an electron poor Ni^2.δ+-derived band structure in the XPS, the lattice oxygen is very electron-rich and yields among the lowest binding energies reported for a transition metal oxide. The nickel-containing lithium oxide selvedge is thus not simply “NiO” and the surface lithium cations have a measurable effect on the electronic structure even in their more highly depleted levels. This is explained in the context of the charge-transfer model of the oxide band structure.     

Pressure dependence of the second virial coefficient of dilute polystyrene solutions

The pressure derivatives of the second virial coefficients [dA₂/dP; 0.1 ≤ P (MPa) ≤ 35.0] for dilute polystyrene (PS) solutions in good, θ, and poor solvents were measured with static light scattering. The solvent quality improved (dA₂/dP > 0) in the good and poor solvents that we investigated (toluene, chloroform; and methylcyclohexane) but deteriorated (dA₂/dP < 0) in θ solvents (cyclohexane and 50‐50 cis,trans‐decalin). The effects of temperature [22 < T (°C) < 45] and molecular weight [25 × 10³ < weight‐average molecular weight (amu mol^?1) < 900 × 10³] on dA₂/dP for PS/cyclohexane solutions were examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3070–3076, 2003