Inclusion of menadione with cyclodextrins studied by calorimetry and spectroscopic methods

Complex formation of menadione with α‐, hydroxypropyl α‐, β‐, hydroxypropyl‐β‐, methyl‐β‐ and hydroxypropyl‐γ cyclodextrins in aqueous solution at 298.15 K was studied by using isothermal titration calorimetry, ¹H NMR, and UV–vis spectrophotometry. The experimental data indicated the partial insertion of menadione into macrocyclic cavity upon formation of two alternative types of 1:1 inclusion complexes, whose thermodynamic parameters (K, Δ_cG⁰, Δ_cH⁰, and Δ_cS⁰) were calculated. The influence of host size on the complex formation process was analyzed. β‐Cyclodextrin and its hydroxypropylated and methylated derivatives were found more effective binders towards menadione than α‐ and γ‐cyclodextrins. Copyright © 2007 John Wiley & Sons, Ltd.     

Su un procedimento per il calcolo degli autovalori di problemi al contorno per equazioni differenziali di ordine 2n

Sunto Si espone un metodo per la determinazione degli autovalori per difetto e se ne dà un'applicazione al calcolo delle frequenze di una piastra. A Mauro Picone nel suo 70^mo compleanno. Lavoro eseguito nell'Istituto Nazionale per le Appliczaioni del Calcolo.     

Self-organizing neural networks for modeling robust 3D and 4D QSAR: application to dihydrofolate reductase inhibitors

We have used SOM and grid 3D and 4D QSAR schemes for modeling the activity of a series of dihydrofolate reductase inhibitors. Careful analysis of the performance and external predictivities proves that this method can provide an efficient inhibition model.     

A Generalization of the Bargmann’s Theory of Ray Representations

The paper contains a complete theory of factors for ray representations acting in a Hilbert bundle, which is a generalization of the known Bargmanns theory. With its help, we have reformulated the standard quantum theory so that the gauge freedom emerges naturally from the very nature of quantum laws. The theory is of primary importance in the investigations of covariance (in contradistinction to symmetry) of a quantum theory which possesses a nontrivial gauge freedom. In that case the group in question is not any symmetry group but a covariance group only – the case not yet investigated in depth. It is shown that the factor of a covariance group representation depends on space and time when the system in question possesses gauge freedom. In nonrelativistic theories, the factor depends on time only. In relativistic theory, the Hilbert bundle is built over spacetime while in the nonrelativistic case-over time. We explain two applications of this generalization: in the theory of a quantum particle in gravitational field in the nonrelativistic limit, and in quantum electrodynamics.     

Liquid crystalline dendrimers containing photoactive cinnamate units

Cinnamate‐containing dendrimers have been prepared by peripheral functionalization of the amine groups of a poly(propyleneimine) dendrimer with 4‐methoxycinnamate‐ or 4‐(N,N‐dimethylamino)cinnamate‐derived units and/or 4‐cyanobiphenyl units in different proportions. The synthesis, full characterization in solution, thermal properties and optical properties of the novel monomers, homodendrimers and codendrimers are reported. The composition of the molecular structure of the codendrimers has been elucidated by matrix assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). These liquid crystalline dendrimers display lamellar SmA mesophases. The codendrimers have been tailored in such a way that the photoactive units and the liquid crystal units absorb in different regions in order to allow better control over the processes induced by light. Linearly polarized UV light irradiation studies performed on thin films of the cinnamate codendrimers show that they are photoresponsive. A photoinduced anisotropy is generated with increasing exposure time, but in‐plane amplification of anisotropy by thermal annealing in the mesophase was not observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

The MM2QM tool for combining docking,molecular dynamics,molecular mechanics,and quantum mechanics†

The use of the MM2QM tool in a combined docking + molecular dynamics (MD) + molecular mechanics (MM) + quantum mechanical (QM) binding affinity prediction study is presented, and the tool itself is discussed. The system of interest is Mycobacterium tuberculosis (MTB) pantothenate synthetase in complexes with three highly similar sulfonamide inhibitors, for which crystal structures are available. Starting from the structure of MTB pantothenate synthetase in the “open” conformation and following the combined docking + MD + MM + QM procedure, we were able to capture the closing of the enzyme binding pocket and to reproduce the position of the ligands with an average root mean square deviation of 1.6 Å. Protein–ligand interaction energies were reproduced with an average error lower than 10%. The discussion on the MD part and a protein flexibility importance is carried out. The presented approach may be useful especially for finding analog inhibitors or improving drug candidates. © 2012 Wiley Periodicals, Inc.     

Solving chromatographic challenges in comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry using multivariate curve resolution–alternating least squares

Multivariate curve resolution–alternating least squares (MCR–ALS) analysis is proposed to solve chromatographic challenges during two-dimensional gas chromatography–time-of-flight mass spectrometry (GC?×?GC–TOFMS) analysis of complex samples, such as crude oil extract. In view of the fact that the MCR–ALS method is based on the fulfillment of the bilinear model assumption, three-way and four-way GC?×?GC–TOFMS data are preferably arranged in a column-wise superaugmented data matrix in which mass-to-charge ratios (m/z) are in its columns and the elution times in the second and first chromatographic columns are in its rows. Since m/z values are common for all measured spectra in all second-column modulations, unavoidable chromatographic challenges such as retention time shifts within and between GC?×?GC–TOFMS experiments are properly handled. In addition, baseline/background contributions can be modeled by adding extra components to the MCR–ALS model. Another outstanding aspect of MCR–ALS analysis is its extreme flexibility to consider all samples (standards, unknowns, and replicates) in a single superaugmented data matrix, allowing joint analysis. In this way, resolution, identification, and quantification results can be simultaneously obtained in a very fast and reliable way. The potential of MCR–ALS analysis is demonstrated in GC?×?GC–TOFMS analysis of a North Sea crude oil extract sample with relative errors in estimated concentrations of target compounds below 6.0 % and relative standard deviations lower than 7.0 %. The results obtained, along with reasonable values for the lack of fit of the MCR–ALS model and high values of the reversed match factor in mass spectra similarity searches, confirm the reliability of the proposed strategy for GC?×?GC–TOFMS data analysis.      

Profiles analysis of proanthocyanidins in the argun nut (Medemia argun—an ancient Egyptian palm) by LC–ESI–MS/MS

Medemia argun is an ancient palm rich in proanthocyanidins (PACs). These polyphenolic compounds are widely distributed in plants and are an integral part of the human diet. A sensitive high‐performance liquid chromatography and electrospray ionization mass spectrometry (HPLC–ESI–MS) method in the negative ion mode for sequencing these ubiquitous and highly beneficial antioxidants is described in order to profile different PACs in M. argun nuts. The analytical protocol based on tandem mass spectrometry was used to sequence dimers, trimers, tetramers and pentamers with different A‐type, B‐type and A/B‐type linkages. Diagnostic ions resulting from heterocyclic ring fission and retro‐Diels–Alder reaction of flavan‐3‐ol provided information on the hydroxylation pattern and the type of interflavan bond. The sequences were discovered through ions derived from quinone methide cleavage of the interflavan bond. The identification of PACs linkages through LC–MSⁿ eliminates a number of tedious separation steps. The method was successfully applied to give a view of PAC profile in M. argun nuts. M. argun nuts contained 636.88 mg/g PACs (as equivalent of (þ)‐catechin). The data obtained in our research show that M. argun is a rich source of hydrolyzable PACs. Copyright © 2014 John Wiley & Sons, Ltd.