Selection of internal standards for quantitative analysis by matrix-assisted laser desorption-ionization (MALDI) time-of-flight mass spectrometry

The selection of an appropriate internal standard (IS) for quantification by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is critical for the successful application of quantitative MALDI. Selection of the IS depends on the chemical similarity of the analyte and IS and the mass separation of the analyte and IS as a function of instrumental peak resolution. For the quantification of bovine insulin, a series of internal standards including horse heart cytochrome C, bovine insulin chain B, des-pentapeptide human insulin, and des-octapeptide porcine insulin was investigated. Des-pentapeptide human insulin was found to be the most appropriate internal standard (relative standard deviation of the standard curve slope = 2.99%, correlation coefficient = 0.988 in the range of 0.5-0.4 μmol/L). Two methods for measuring of the MALDI signal intensity were evaluated, direct peak integration following subtraction of a linear background and non-linear least squares curve fitting. The results obtained with these methods were equivalent.     

Theoretical analysis of bonding properties in 1,1-dicyanocyclopentane and 1,1-dichlorocyclopentane by applying the AIM and NBO approaches

Using Bader’s quantum-topological theory of atoms in molecules (AIM) and Weinhold’s Natural Bond Orbital (NBO) analysis we could rationalize the impact of the geminal substitution by C≡N and Cl on the geometry and electronic structure of the cyclopentane ring in 1,1-dicyanocyclopentane (DCCP) and 1,1-dichlorocyclopentane (DClCP). Among the crucial results we obtained are: 1. The topological quantities, particularly the bond ellipticity of 0.035 for the C–CN bond, indicate that this bond possesses higher bond order than a single bond. This conclusion is clearly supported by the NBO results. 2. The AIM theory as well as the NBO analysis confirm uniformly the non-linearity of the C–C≡N moiety. 3. Regardless the quantum mechanical method that has been employed for a variety of nitriles the sign of the Laplacian of the charge density, ∇²ρ(r), of the C≡N group changes its sign from negative to positive upon moving from the triple zeta to the double zeta basis set. A possible explanation for this striking behavior has been provided. By invoking the AIM and NBO approaches the different endocyclic C–C bond lengths in DCCP and DClCP as a consequence of the geminal substitution could be explained. Also the variations of these bond lengths upon moving from the more stable C _s to the energetically less favorable C ₂ conformer of both compounds could be rationalized. For the purpose of comparison and verification of some findings of this work, we also carried out AIM and NBO calculations on various related cyclic and non-cyclic compounds.     

Complex network approach for recurrence analysis of time series

We propose a novel approach for analysing time series using complex network theory. We identify the recurrence matrix (calculated from time series) with the adjacency matrix of a complex network and apply measures for the characterisation of complex networks to this recurrence matrix. By using the logistic map, we illustrate the potential of these complex network measures for the detection of dynamical transitions. Finally, we apply the proposed approach to a marine palaeo-climate record and identify the subtle changes to the climate regime.     

How do global temperature drivers influence each other?

We investigate a network of influences connected to global mean temperature. Considering various climatic factors known to influence global mean temperature, we evaluate not only the impacts of these factors on temperature but also the directed dependencies among the factors themselves. Based on an existing recurrence-based connectivity measure, we propose a new and more general measure that quantifies the level of dependence between two time series based on joint recurrences at a chosen time delay. The measures estimated in the analysis are tested for statistical significance using twin surrogates. We find, in accordance with earlier studies, the major drivers for global mean temperature to be greenhouse gases, ENSO, volcanic activity, and solar irradiance. We further uncover a feedback between temperature and ENSO. Our results demonstrate the need to involve multiple, delayed interactions within the drivers of temperature in order to develop a more thorough picture of global temperature variations.     

Phenylalkylamine alkaloids from Stapelia hirsuta L

Four alkaloids of the phenethylamine derivatives have been isolated from the n-butanol fraction of the aerial parts of Stapelia hirsuta L. The structures of the isolated alkaloids were determined as N-acetyl hordenine (a new natural compound), hordenine, candicine and hordenine-1-O-beta-D-glucoside, in addition to luteolin-7-O-beta-D-glucopyranoside.     

A comparative study of the surface structure, acidity, and catalytic performance of tungstated zirconia prepared from crystalline zirconia or amorphous zirconium oxyhydroxide

Tungstated zirconias prepared from W deposition on zirconium oxyhydroxide are reportedly active for alkane isomerization, whereas solids synthesized by impregnation of zirconia are inactive. The origin of the differences between the two preparations is not fully understood. The present paper examines the influence of W surface density and the nature of the support on the surface structure, development of the acidity, and catalytic performance of WO(x)()/ ZrO(2) catalysts. Two series of catalysts containing W surface densities up to 5.2 at. W/nm(2) were prepared by pore volume impregnation of two different supports: zirconium oxyhydroxide and predominantly tetragonal zirconia (65% tetragonal, 35% monoclinic). The texture and structure of the catalysts were investigated by BET measurements, X-ray diffraction, Raman and infrared spectroscopy. The catalytic activity was tested for 2-propanol dehydration and n-hexane isomerization. For catalysts obtained by impregnation of Zr oxyhydroxide, Raman results showed that W was present as a surface phase. Infrared spectra indicated an increase in the degree of polymerization of W species with increasing W surface density. The development of the acidity was monitored by lutidine adsorption and desorption at 523 K, followed by infrared spectroscopy. The results indicated the presence of a threshold of W surface density at 1.3 at. W/ nm(2) for the detection of these acid sites, followed by a progressive increase in their abundance with increasing W surface density. The development of Br?nsted acidity correlated with the evolution of the infrared bands attributed to "extensively" polymerized W species. A direct relationship was observed between the abundance of Br?nsted acid sites and the catalytic activity for 2-propanol dehydration. For n-hexane isomerization, compared to 2-propanol dehydration, a higher threshold of W surface densities (3.4 at. W/ nm(2)) for the development of activity was observed. The difference was attributed to stronger Br?nsted acid sites required for n-hexane isomerization. The catalysts prepared by impregnation of zirconia exhibited comparable behavior. For a given W surface density, the crystalline composition of the support (tetragonal/monoclinic zirconia), the W surface structure, abundance of Br?nsted acid sites, and catalytic performance were similar. Thus, in an apparent variance with some of the results reported in the literature with respect to the influence of preparation methods, no significant effect of the initial form of the support (Zr oxyhydroxide versus predominantly tetragonal zirconia) was evidenced.     

Electronic structure of iron chlorins: characterization of bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(III)triflate and bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(II)

The synthesis and characterization of the two iron chlorin complexes [Fe(III)(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) and Fe(II)(TPC)[(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2))](2) (2) are reported. The crystal structure of complex 1 has been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 2.034(4) A, and to the pyrrole trans to it N(2), 2.012(4) A, are longer than the distances to the two remaining nitrogens [N(1), 1.996(4) A, and N(3), 1.984(4) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. The (1)H NMR isotropic shifts at 20 degrees C of the different pyrrole protons of 1 varied from -0.8 to -48.3 ppm according to bis-ligated complexes of low-spin ferric chlorins. The EPR spectrum of [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) in solution is rhombic and gives the principal g values g(1) = 2.70, g(2) = 2.33, and g(3) = 1.61 (Sigmag(2) = 15.3). These spectroscopic observations are indicative of a metal-based electron in the d(pi) orbital for the [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) complex with a (d(xy))(2)(d(xz)d(yz))(3) ground state at any temperature. The X-ray structure of the ferrous complex 2 also shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 1.991(5) A, and to the pyrrole trans to it N(2), 2.005(6) A, are slightly different from the distances to the two remaining nitrogens [N(1), 1.988(5) A, and N(3), 2.015(5) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole.     

Analysis of the nonlinear dynamics of inter-cycle combustion variations in an ethanol fumigation-diesel dual-fuel engine

Nonlinear Dynamics - The nonlinear dynamics of a combustion system in a modern common-rail dual-fuel engine has been studied. Using nonlinear dynamic data analysis (phase space reconstruction,...     

A mathematical approach to solve the network reconstruction problem

The reconstruction of biochemical and genetic networks from experimental data is an important challenge in biology and medical basic research. We formalize this problem mathematically and present an exact algorithm for its solution. Our procedure yields either a complete list of all alternative network structures that explain the observed phenomena or proves that no solution exists using the given data set. This work was supported by the German Ministry of Education and Research (BMBF) through the FORSYS initiative.