Roughness and ordering at the interface of oxidized polystyrene and water

For the first time, atomistically detailed molecular dynamics calculations revealed molecular ordering of the water-oxidized atactic polystyrene (aPS) interface. Both ordering of the water molecules and the phenyl rings occur. In addition, the natural roughness of the surface has been simulated and compared to experimental values. The composition of the simulated aPS films is based on spin-coated aPS films that have been oxidized and characterized experimentally. The aPS surfaces are oxidized with ultraviolet-ozone radiation and have been characterized by XPS, AFM, and water contact angle measurements. XPS measurements show that the oxygen content in the sample increases rapidly with exposure and reaches saturation near 24 at. % of oxygen. The molecular dynamics simulations show smoothening of an hydrophobic aPS surface upon transition from vacuum to water. The smoothening decreases with increasing hydrophilicity. The calculations reveal ordering of oxidized phenyl rings for aPS surfaces in water. The order increases with increasing hydrophilicity. Additionally, we investigated the water structure near the aPS-water interface as a function of the surface hydrophilicity. With increasing hydrophilicity, the density of water at the aPS-water interface increases. The water density profile is steeper in the presence of hydrophobic aPS. The water shows an ordered layer near both the hydrophobic and hydrophilic surfaces; the position of this layer shifts toward the interface with increasing hydrophilicity.     

Representation of Hydrogen Atoms in Molecular Dynamics Simulations: The Influence on the Computed Properties of Thin Polystyrene Films

The united atoms (UA) and dummy hydrogen atom (DHA) approaches for molecular dynamics simulations of the interface between oxidized atactic polystyrene (aPS) thin films and water are compared. For both oxidized and non‐oxidized aPS films the polymer density profile decays steepest when using the UA model. The surface roughness of the aPS film and the ordering of the phenyl rings near the surface decrease upon changing from vacuum to water for the UA, but not for the DHA model. This also supports the fact that the non‐oxidized aPS films modeled in DHA representation become less hydrophobic. The water structure close to the interface also suggests that the aPS films modeled using UA are more hydrophobic compared to the aPS films modeled with DHA in the phenyl rings.

     

Surface‐enhanced Raman spectroscopy of DNA from leaves of in vitro grown apple plants

Ultrasensitive Raman measurements of nucleic acids are possible by exploiting the effect of surface‐enhanced Raman scattering (SERS). In this work, the vibrational spectra of eight genomic DNAs from in vitro grown apple leaf tissues (Malus domestica Borkh., Fam Rosaceae, cvs. Florina, Idared, Rebra, Goldrush, Romus 3, Romus 4 and the rootstocks M9 and M26) were analyzed using surface‐enhanced Raman spectroscopy, in the wavenumber range 200–1800 cm⁻¹. SERS signatures, spectroscopic band assignments and structural interpretations of these plant genomic DNAs are reported. Strong dependences of the SERS spectra on genomic DNA amount in the measured sample volume and on time were observed. Similarities of the SERS signals of DNAs from Rebra and Romus 3 leaves were detected. To our knowledge, this is the first SERS study on genomic DNA from leaf tissues. The present work provides a basis for future use of surface‐enhanced Raman spectroscopy to analyze specific plant DNA–ligand interactions or DNA structural changes induced by plants' stress conditions associated with their natural environment. Besides, this study will generate information that is valuable in the development of low‐level plant DNA‐based analytical sensors. Copyright © 2010 John Wiley & Sons, Ltd.     

Introducing axial chirality into mesoionic 4,4'-bis(1,2,3-triazole) dicarbenes

Mesoionic 4,4'-bis(1,2,3-triazole-5,5'-diylidene) Rh(I) complexes having a C2 chiral 4,4'-axis were accessed from 3-alkyltriazolium salts in virtually complete de. Their structure and configurational integrity were assessed by NMR spectroscopy, X-ray crystallography, and chiral HPLC. Computational analysis of the MICs involved in the reaction suggested the formation of a highly stable and unprecedented cation-carbene intermediate species, which could be evidenced experimentally by cyclic voltammetry analysis.     

Linear SPDEs Driven by Stationary Random Distributions

Using tools from the theory of stationary random distributions developed in It? (Mem. Coll. Sci., Univ. Kyoto, Ser. A: Math., 28:209?C223,?1954) and Yaglom (Theory Probab. Appl., 2:273?C320,?1957), we introduce a new class of processes which can be used as a model for the noise perturbing an SPDE. This type of noise is not necessarily Gaussian, but it includes the spatially homogeneous Gaussian noise introduced in Dalang (Electron. J. Probab. 4(6)?1999), and the fractional noise considered in Balan and Tudor (Stoch. Process. Appl., 120:2468?C2494,?2010). We derive some general conditions for the existence of a random field solution of a linear SPDE with this type of noise, under some mild conditions imposed on the Green function of the differential operator which appears in this equation. This methodology is applied to the study of the heat and wave equations (possibly replacing the Laplacian by one of its fractional powers), extending in this manner the results of Balan and Tudor (Stoch. Process. Appl., 120:2468?C2494,?2010) to the case H<1/2.     

Zero cancellation for general rational matrix functions

The problem of cancelling a specified part of the zeros of a completely general rational matrix function by multiplication with an appropriate invertible rational matrix function is investigated from different standpoints. Firstly, the class of all factors that dislocate the zeros and feature minimal McMillan degree are derived. Further, necessary and sufficient existence conditions together with the construction of solutions are given when the factor fulfills additional assumptions like being J-unitary, or J-inner, either with respect to the imaginary axis or to the unit circle. The main technical tool are centered realizations that deliver a sufficiently general conceptual support to cope with rational matrix functions which may be polynomial, proper or improper, rank deficient, with arbitrary poles and zeros including at infinity. A particular attention is paid to the numerically-sound construction of solutions by employing at each stage unitary transformations, reliable numerical algorithms for eigenvalue assignment and efficient Lyapunov equation solvers.     

High-Resolution Tandem Mass Spectrometry Identifies a Particular Ganglioside Pattern in Early Diabetic Kidney Disease of Type 2 Diabetes Mellitus Patients

Considering the valuable information provided by glycosphingolipids as molecular markers and the limited data available for their detection and characterization in patients suffering from Type 2 diabetic kidney disease (DKD), we developed and implemented a superior method based on high-resolution (HR) mass spectrometry (MS) and tandem MS (MS/MS) for the determination of gangliosides in the urine of DKD patients. This study was focused on: (i) testing of the HR MS and MS/MS feasibility and performances in mapping and sequencing of renal gangliosides in Type 2 DM patients; (ii) determination of the changes in the urine gangliosidome of DKD patients in different stages of the disease—normo-, micro-, and macroalbuminuria—in a comparative assay with healthy controls. Due to the high resolution and mass accuracy, the comparative MS screening revealed that the sialylation status of the ganglioside components; their modification by O-acetyl, CH₃COO⁻, O-fucosyl, and O-GalNAc; as well as the composition of the ceramide represent possible markers for early DKD detection, the assessment of disease progression, and follow-up treatment. Moreover, structural investigation by MS/MS demonstrated that GQ1d(d18:1/18:0), GT1α(d18:1/18:0) and GT1b(d18:1/18:0) isomers are associated with macroalbuminuria, meriting further investigation in relation to their role in DKD.     

Long-range response to transmission line disturbances in DC electricity grids

We consider a DC electricity grid composed of transmission lines connecting power generators and consumers at its nodes. The DC grid is described by nonlinear equations derived from Kirchhoff's law. For an initial distribution of consumed and generated power, and given transmission line conductances, we determine the geographical distribution of voltages at the nodes. Adjusting the generated power for the Joule heating losses, we then calculate the electrical power flow through the transmission lines. Next, we study the response of the grid to an additional transmission line between two sites of the grid and calculate the resulting change in the power flow distribution. This change is found to decay slowly in space, with a power of the distance from the additional line. We find the geographical distribution of the power transmission, when a link is added. With a finite probability the maximal load in the grid becomes larger when a transmission line is added, a phenomenon that is known as Braess’ paradox. We find that this phenomenon is more pronounced in a DC grid described by the nonlinear equations derived from Kirchhoff's law than in a linearised flow model studied previously in Ref. [1]. We observe furthermore that the increase in the load of the transmission lines due to an added line is of the same order of magnitude as Joule heating. Interestingly, for a fixed system size the load of the lines increases with the degree of disorder in the geographical distribution of consumers and producers.     

Theoretical treatment of volume localized NMR spectroscopy in weakly coupled spin systems

A pulse sequence is proposed for obtaining volume selective echoes with both chemical shift and homonuclear scalar coupling refocused. Theory, in terms of product operator formalism, is presented and the full response of the spin system is computed. The theoretical spatial dependence of the power signal given by spins localized in different planes (x=0,y=0, respectivez=0) is presented.