Improved protein identification efficiency by mass spectrometry using N-terminal chemical derivatization of peptides from Angiostrongylus costaricensis, a nematode with unknown genome

Matrix-assisted laser desorption ionization (MALDI), Peptide Mass Fingerprinting (PMF) and MALDI-MS/MS ion search (using MASCOT) have become the preferred methods for high-throughput identification of proteins. Unfortunately, PMF can be ambiguous, mainly when the genome of the organism under investigation is unknown and the quality of spectra generated is poor and does not allow confident identification. The post-source decay (PSD) fragmentation of singly charged tryptic peptide ions generated by MALDI-TOF/TOF typically results in low fragmentation efficiency and/or complex spectra, including backbone fragmentation ions (series b and y), internal fragmentation etc. Interpreting these data either manually and/or using de novo sequencing software can frequently be a challenge. To overcome this limitation when studying the proteome of adult Angiostrongylus costaricensis, a nematode with unknown genome, we have used chemical N-terminal derivatization of the tryptic peptides with 4-sulfophenyl isothiocyanate (SPITC) prior to MALDI-TOF/TOF MS. This methodology has recently been reported to enhance the quality of MALDI-TOF/TOF-PSD data, allowing the obtainment of complete sequence of most of the peptides and thus facilitating de novo peptide sequencing. Our approach, consisting of SPITC derivatization along with manual spectra interpretation and Blast analysis, was able to positively identify 76% of analyzed samples, whereas MASCOT analysis of derivatized samples, MASCOT analysis of nonderivatized samples and PMF of nonderivatized samples yielded only 35, 41 and 12% positive identifications, respectively. Moreover, de novo sequencing of SPITC modified peptides resulted in protein sequences not available in NCBInr database paving the way to the discovery of new protein molecules.     

Immunochemical method for sulfasalazine determination in human plasma

Sulfasalazine is an antibiotic used in the treatment of inflammatory bowel diseases. For the assessment of sulfasalazine in several biological matrices, an Enzyme-Linked Immunosorbent Assay (ELISA) method based on polyclonal antibodies was developed and characterized.The immunoassay showed a high sensitivity (IC₅₀ = 0.51 ng mL⁻¹) and specificity, a detection limit of 0.02 ng mL⁻¹ and a dynamic range of 0.06-3.75 ng mL⁻¹ (80-20% inhibition). The immunoassay performed well when it was applied to spiked plasma samples (from 0.5 to 2.0 ng mL⁻¹) previously cleaned up by protein precipitation with methanol. Recoveries ranged from 83 to 119%, with a mean value of 99% (CV = 13%).Since sulfasalazine remaining of a treatment reaches the systemic circulation in unchanged form, the immunoassay can be applied to the determination of this pharmaceutical in human plasma in order to facilitate the control of the patients through the application of personal doses.     

Propagation of Smoothness and the Rate of Exponential Convergence to Equilibrium for a Spatially Homogeneous Maxwellian Gas

We prove an inequality for the gain term in the Boltzmann equation for Maxwellian molecules that implies a uniform bound on Sobolev norms of the solution, provided the initial data has a finite norm in the corresponding Sobolev space. We then prove a sharp bound on the rate of exponential convergence to equilibrium in a weak norm. These results are then combined, using interpolation inequalities, to obtain the optimal rate of exponential convergence in the strong L¹ norm, as well as various Sobolev norms. These results are the first showing that the spectral gap in the linearized collision operator actually does govern the rate of approach to equilibrium for the full non-linear Boltzmann equation, even for initial data that is far from equilibrium.     

Differences between ab initio and density functional electron densities

We analyzed the energy contributions and the spatial distribution differences of several electron densities of atoms and small molecules. The results show the insensitivity of local spin density correlation functionals in respect to differences in the electron densities. On the other hand, significant changes in one-electron and two-electron energy contributions are observed, although both compensate each other. The projection of the differences between these electron densities, referred to as the Hartree-Fock density, shows a qualitative resemblance between multideterminantal and Kohn-Sham wavefunctions. Finally, a comparative analysis of the optimized conformational parameters obtained using several methods shows that the inclusion of the correlation energy in SCF or in post-SCF procedures gives similar results and that the exchange potential is more important than is the correlation potential to improve these conformational parameters. © 1997 John Wiley & Sons, Inc.     

A Polycationic Metallodendrimer with 24 [Fe(η5-C5Me5)(η6-N-Alkylaniline)]+ Termini That Recognizes Chloride and Bromide Anions

Pronounced dendritic effects are shown by the title compound 1 in the recognition of Cl⁻ and Br⁻—this is shown by the comparison with a mononuclear compound with one dendrimer arm and a trinuclear compound with a tripodal dendrimer branch. Thus, 1 differs distinctly from 24-ferrocene dendrimers of comparable topology.     

Can the disproportion of oxidation state III be favored in RuII-OH2/RuIV=O systems?

Three new Ru-aqua complexes containing a mixed carbene and pyridylic ligands with general formulas [Ru(CNC)(bpy)(H2O)](PF6)2 (1) (CNC is 2,6-bis(butylimidazol-2-ylidene)pyridine; bpy is 2,2'-bipyridine) and cis-/trans-[Ru(CNC)(nBu-CN)(H2O)](PF6)2 (cis-2 and trans-2) (nBu-CN is 2-(butylimidazol-2-ylidene)pyridine) have been prepared and structurally characterized both in the solid state (monocrystal X-ray diffraction analysis for 1 and for the related complex trans-[Ru(Br)(CNC)(nBu-CN)](PF6)) and in solution (for all of them) through NMR. The electrochemical properties of these three Ru-aqua complexes have been investigated by cyclic voltammetry, differential pulse voltammetry and Coulombimetric techniques. It is found that, for complex 1 at pH 7, the difference between the IV/III and the III/II redox couples (DeltaE1/2) is 50 mV, which is the smallest ever reported for this type of complex. On the other hand, for complexes cis-2 and trans-2, the oxidation state III is unstable with respect to disproportionation to II and IV. The reactivity of their Ru=O species has been tested toward cis-beta-methylstyrene oxidation, and it has been compared to [Ru(O)(trpy)(bpy)]2+. An inverse correlation between the degree of cis/trans-epoxide isomerization and DeltaE1/2 is found. In particular, for complexes cis-2 and trans-2, which have a DeltaE1/2 < 0, the epoxidation is highly stereoselective, yielding only cis-epoxide.     

Liquid-crystalline bisadducts of [60]fullerene

A second-generation cyanobiphenyl-based dendrimer was used as a liquid-crystalline promoter to synthesize mesomorphic bisadducts of [60]fullerene. Liquid-crystalline trans-2, trans-3, and equatorial bisadducts were obtained by condensation of the liquid-crystalline promoter, which carries a carboxylic acid function, with the corresponding bisaminofullerene derivatives. A monoadduct of fullerene was also prepared for comparative purposes. All the compounds gave rise to smectic A phases. An additional mesophase, which could not be identified, was observed for the trans-2 derivative. The supramolecular organization of the monoadduct derivative is governed by steric constraints. Indeed, for efficient space filling, adequacy between the cross-sectional areas of fullerene (approximately 100 A(2)) and of the mesogenic groups (approximately 22-25 A(2) per mesogenic group) is required. As a consequence, the monoadduct forms a bilayered smectic A phase. The supramolecular organization of the bisadducts is essentially governed by the nature and structure of the mesogenic groups and dendritic core. Therefore, the bisadducts form monolayered smectic A phases. The title compounds are promising supramolecular materials as they combine the self-organizing behavior of liquid crystals with the properties of fullerene.     

Laser Control of Zeolite Nucleation

Precursor solutions for the synthesis of zeolites are irradiated by means of a Nd‐YAG laser. These solutions are subsequently submitted to a hydrothermal treatment and the results analyzed by X‐ray diffraction and electron microscopy. Laser irradiation promotes the formation of silica nanoparticles that nucleate into zeolite (silicalite‐1), following a hydrothermal treatment. The average crystal size (in the 0.6–3.6 μm range) of the zeolite exponentially decreases as a function of laser irradiation time. In addition, a longer irradiation time results in a narrower crystal size distribution.     

The Use of the Electron-Reservoir Complexes [Fe(I)Cp(arene)] for the Electrocatalytic Synthesis of Redox-Reversible Metal-Carbonyl Clusters Containing Ferrocenyldiphenylphosphine

Starting from [M₃(CO)₁₂] (M = Fe or Ru) and [CH₃CCo₃(CO)₉], the electron-tranfer-chain catalyzed synthesis of new Fe, Ru, and Co carbonyl clusters in which one or several carbonyl ligands have been selectively substituted by one or several ferrocenyldiphenylphosphine (FDPP) ligands has been achieved using the electron-reservoir complexes [Fe(I)Cp(arene)] as electrocatalysts. The number of FDPP ligands selectively introduced can be chosen from one per cluster for the three clusters up to one per metal for the Ru and Co clusters. The advantage of this family of electrocatalysts is that the driving force for the initiation step can be varied by changing the number of methyl groups on the rings. The FDPP substituted clusters show one reversible wave by cyclic voltammetry.     

Asymptotic Expansions for Two Singularly Perturbed Convection–Diffusion Problems with Discontinuous Data: The Quarter Plane and the Infinite Strip

We consider a singularly perturbed convection–diffusion equation,     , defined on two domains: a quarter plane,  ( x , y ) ∈ (0, ∞) × (0, ∞)  , and an infinite strip,  ( x , y ) ∈ (−∞, ∞) × (0, 1)  . We consider for both problems discontinuous Dirichlet boundary conditions:   u ( x , 0) = 0  and   u (0, y ) = 1  for the first one and   u ( x , 0) =χ_{[ a , b ]}( x )  and   u ( x , 1) = 0  for the second. For each problem, asymptotic expansions of the solution are obtained from an integral representation in two limits: (a) when the singular parameter  ε→ 0⁺  (with fixed distance r to the discontinuity points of the boundary condition) and (b) when that distance   r → 0⁺  (with fixed ε). It is shown that in both problems, the first term of the expansion at  ε= 0  is an error function or a combination of error functions. This term characterizes the effect of the discontinuities on the ε-behavior of the solution and its derivatives in the boundary or internal layers. On the other hand, near the discontinuities of the boundary condition, the solution u ( x , y ) of both problems is approximated by a linear function of the polar angle at the discontinuity points.