Characterization of the quantitative relationship between signal-to-noise (S/N) ratio and sample amount on-target by MALDI-TOF MS: Determination of chondroitin sulfate subsequent to enzymatic digestion

Chondroitin sulfate (CS) is an important glycosaminoglycan of the extracellular matrix and its quantitative detection is of interest in different pathologies. Although there are already methods of quantitative CS determination, many of them are laborious, require time-consuming sample workup and/or suffer from low sensitivity. It will be shown here that the CS content of biological samples can be easily assessed in the picomole range subsequent to enzymatic digestion. MALDI-TOF MS (matrix-assisted laser desorption and ionization time-of-flight mass spectrometry) was used to determine the concentrations of the unsaturated disaccharide of CS obtained by enzymatic digestion of native CS with chondroitin ABC lyase. The signal-to-noise (S/N) ratio can be used as a quantitative measure: amounts of CS (measured as the disaccharide) down to at least 500 fmol could be detected and there is a direct correlation between the S/N ratio and the amount of CS between about 2 and 200 pmol although the curve per se is sigmoidal. The influence of different parameters such as the used matrix, the applied laser intensity and different methods of data analysis were also tested. Advantages and drawbacks of this approach are critically discussed. Finally, the method was validated by the determination of the CS content in samples of known concentration as well as in enzymatically digested bovine nasal cartilage and compared with two further established methods of CS determination (Carbazole and Alcian Blue method).     

Domino reactions of 5-deoxy-5-iodo-d-xylo- and -l-arabinofuranose derivatives with organometallic reagents. A way towards polyfunctionalized building-blocks

Domino reactions involving metal-halogen exchange, furanose ring-opening and nucleophilic addition from 3-O-benzyl-5-deoxy-5-iodo-1,2-O-isopropylidene-α-d-xylofuranose and the epimeric l-arabino derivative with various organometallic reagents are reported. In anhydrous conditions, with a large excess of organolithium or Grignard reagents, vicinal diols are obtained with good yields and a fair diastereoselectivity. Interestingly, with α-trimethylsilyl organolithium reagents, the fragmentation of the furanose ring to the substituted pent-4-enal is followed by a Peterson olefination giving dienic compounds in a four-step one-pot process.     

Synthesis and Crystal Structures of Novel Copper(I) Complexes of a Phosphanylborane

The novel copper iodide clusters [Cu₃(μ‐I)(μ₃‐I)₂(PH₂BH₂·NMe₃)₃] ( 2 ) and [Cu₄(μ‐I)₂(μ₃‐I)₂(PH₂BH₂·NMe₃)₃] ( 3 ) were synthesized by treating CuI with the primary phosphine (H₂PBH₂·NMe₃). The novel features of both compounds, which have been characterized by X‐ray crystallography, are the unsymmetrical constitution of the copper iodide core due to the influence of the monodentate phosphorus ligand. This results in copper atoms with different coordination numbers within the compound. Complex 2 , the major product of the reaction, contains a distorted octahedral Cu₃I₃‐core, in which one vertex is missing. Complex 3 was isolated as a by‐product and is composed of a Cu₄I₄‐core in a distorted octahedral coordination.     

An entropy satisfying MUSCL scheme for systems of conservation laws

Summary. For the high-order numerical approximation of hyperbolic systems of conservation laws, we propose to use as a building principle an entropy diminishing criterion instead of the familiar total variation diminishing criterion introduced by Harten for scalar equations. Based on this new criterion, we derive entropy diminishing projections that ensure, both, the second order of accuracy and all of the classical discrete entropy inequalities. The resulting scheme is a nonlinear version of the classical Van Leer's MUSCL scheme. Strong convergence of this second order, entropy satisfying scheme is proved for systems of two equations. Numerical tests demonstrate the interest of our theory. Received March 28, 1995 / Revised version received June 17, 1995     

Development and validation of a fast RP-HPLC method for determination of methotrexate entrapment efficiency in polymeric nanocapsules

A rapid and effective isocratic chromatographic procedure is successfully developed to determinate methotrexate (MTX) entrapment efficiency (EE) in polymeric nanocapsules using reversed-phase high-performance liquid chromatography. The method employed a RP-C(18) Shimadzu Shim-pack CLC-ODS (150 mm x 4.6 mm, 5 microm) column with mobile phase constituted by a mixture of water-acetonitrile-tetrahydrofuran (65:30:5 v/v/v; pH 3.0) at a flow rate of 0.8 mL/min. The eluate is monitored with a UV detector set at 313 nm. The parameters used in the validation process are: linearity, specificity, precision, accuracy, and limit of quantitation (LOQ). The linearity is evaluated by a calibration curve in the concentration range of 10-50 microg/mL and presented a correlation coefficient of 0.9998. The polymers (PLA or PLA-PEG), oil, and surfactants used in the nanocapsule formulation did not interfere with analysis and the recovery was quantitative. The intra and inter-day assay relative standard deviation were less than 0.72%. Results are satisfactory, and the method proved to be adequate for the determination of methotrexate in nanocapsules formulations.     

A method to find generators of a semi-simple Lie group via the topology of its flag manifolds

In this paper we continue to develop the topological method to get semigroup generators of semi-simple Lie groups. Consider a subset \(\Gamma \subset G\) that contains a semi-simple subgroup \(G_{1}\) of G. If one can show that \( \Gamma \) does not leave invariant a contractible subset on any flag manifold of G, then \(\Gamma \) generates G if \(\mathrm {Ad}\left( \Gamma \right) \) generates a Zariski dense subgroup of the algebraic group \(\mathrm {Ad}\left( G\right) \). The proof is reduced to check that some specific closed orbits of \(G_{1}\) in the flag manifolds of G are not trivial in the sense of algebraic topology. Here, we consider three different cases of semi-simple Lie groups G and subgroups \(G_{1}\subset G\).     

Modified locus equations categorize stop place in a perceptually realistic time frame

Slope and y-intercepts of locus equations have previously been shown to successfully classify place of articulation for English voiced stop consonants when derived from measurements at vowel onset and vowel midpoint. However, listeners are capable of identifying English voiced stops when less than 30 ms of vowel is presented. The present results show that modified locus equation measurements made within the first several pitch periods of a vowel following an English voiced stop were also successful at classifying place of articulation, consistent with the amount of vocalic information necessary for perceptual identification of English voiced stops /b d g/.