Dilation theorems for positive definite operator kernels having majorants

Dilation theorems for Banach space valued stochastic processes and operator valued positive definite kernels are considered. It is shown, e.g., that a Banach space valued stochastic process X can be dilated to another process Y, if and only if the covariance kernel of Y is a majorant of the covariance kernel of X. Positive definite operator kernels having majorants of certain special type are characterized.     

UV/VIS Spectrophotometric Studies on the Antileukemic Agent Glyoxal bis(Amidinohydrazone) [‘Glyoxal bis(Guanylhydrazone)’]

Glyoxal bis(amidinohydrazone) (GBG) and several analogs thereof are compounds of considerable pharmacological interest, and a variety of HPLC and MECC methods have been developed for their analysis. In these methods, detection is invariably based on the strong UV absorption of the compound. Yet, almost nothing has been known of their UV and VIS spectral properties. In the present paper the UV and VIS Spectroscopy of GBG has been studied in several solvent systems (water, 0. 03 M aqueous sodium acetate buffer, 0. 1 inM aqueous NaOH and dimethylsulfoxide). In the case of solutions in bare water, the shape of the UV spectrum depends drastically on concentration, probably because of changes in the species distribution of GBG as a function of concentration. The spectrum comprises one maximum at ca. 200 nm, and between ca. 250 nin and 400 nm an absorption region with distinctly higher absorbance. In the case of aqueous sodium acetate as well as NaOH solutions, one strong maximum can be detected (at ca. 285–288 nm and 332–337 nm, respectively). In both cases, the maximum occurs at constant wavelength, being independent of concentration. In dimethylsulfoxide, the spectrum of GBG contains an absorption band at distinctly higher wavelengths (λ_max 354 nm) than in any one of the aqueous solvents studied, indicating that solvent effects are considerable in the UV spectrum of GBG. In no case, distinct absorption could be detected at wavelengths higher than 400 nm. The results indicate that if aqueous media are used as elements in HPLC analyses of bis(amidinohydrazones) or as solvents in direct UV analysis, they must be buffered.     

The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

Background  

In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment.     

Bonding in Cu,Ag, and Au clusters: relativistic effects,trends, and surprises

Electronic structure and bonding in anionic coinage metal clusters are investigated via density-functional calculations, focusing on an extensive set of isomers of Cu(-)(7), Ag(-)(7), and Au(-)(7). While the ground states of Cu(-)(7) and Ag(-)(7) are three dimensional (3D), that of Au(-)(7) is planar, separated from the optimal 3D isomer by 0.5 eV. The simulated thermally weighted photoabsorption spectrum of Au(-)(7) is dominated by planar structures, and it agrees well with the measured one. The propensity of Au(-)(N) clusters to favor planar structures (with N as large as 13) is correlated with strong hybridization of the atomic 5d and 6s orbitals due to relativistic effects.     

Multiple Li positions inside oxygen octahedra in lithiated TiO2 anatase

Intercalation of Li in TiO2 anatase results in a phase separation in a Li-poor and a Li-rich phase. The local lithium configuration in the coexisting crystallographic phases is resolved by detailed analysis of neutron diffraction data. In each of the phases, two distinct positions within the octahedral interstices are found, with a temperature-dependent occupancy. A combination of quasi-elastic neutron scattering and force field molecular dynamics simulations shows that Li is hopping on a picosecond time scale between the two sites in the octahedral interstices. The results also suggest a specific Li arrangement along the crystallographic a direction, albeit without long range order. It is likely that multiple discrete Li sites within a distorted oxygen octahedron occur not only in intercalated TiO2 anatase but also in other (transition metal) oxides.     

The electronic structure of Ge9[Si(SiMe3)3]3-: a superantiatom complex

We report on the electronic structure of Ge(9)[Si(SiMe(3))(3)](3)(-). Systematic density functional theory analysis of the electronic shell structure of the cluster and its derivatives reveals that the Ge(9)[Si(SiMe(3))(3)](3)(-) and its neutral counterpart have electronic shells that can be explained using the superatom model. The ligand-core interaction of these complexes is distinctly different from previously identified gold, gallium, and aluminium superatom complexes, indicating an electron-donating rather than electron-withdrawing ligand. We modify the electron-counting rule for this case and introduce a simple picture for superatom and superantiatom complexes. Discussions comparing shell models, Zintl clusters, the superhalogen Al(13) and superatom complexes to Ge(9)[Si(SiMe(3))(3)](3)(-) are presented.     

Highly Robust but Surface‐Active: An N‐Heterocyclic Carbene‐Stabilized Au25 Nanocluster

Surface organic ligands play a critical role in stabilizing atomically precise metal nanoclusters in solutions. However, it is still challenging to prepare highly robust ligated metal nanoclusters that are surface‐active for liquid‐phase catalysis without any pre‐treatment. Now, an N‐heterocyclic carbene‐stabilized Au₂₅ nanocluster with high thermal and air stabilities is presented as a homogenous catalyst for cycloisomerization of alkynyl amines to indoles. The nanocluster, characterized as [Au₂₅(ⁱPr₂‐bimy)₁₀Br₇]²⁺ (ⁱPr₂‐bimy=1,3‐diisopropylbenzimidazolin‐2‐ylidene) ( 1 ), was synthesized by direct reduction of AuSMe₂Cl and ⁱPr₂‐bimyAuBr with NaBH₄ in one pot. X‐ray crystallization analysis revealed that the cluster comprises two centered Au₁₃ icosahedra sharing a vertex. Cluster 1 is highly stable and can survive in solution at 80 °C for 12 h, which is superior to Au₂₅ nanoclusters passivated with phosphines or thiols. DFT computations reveal the origins of both electronic and thermal stability of 1 and point to the probable catalytic sites. This work provides new insights into the bonding capability of N‐heterocyclic carbene to Au in a cluster, and offers an opportunity to probe the catalytic mechanism at the atomic level.     

Quantitation of perfluoroalkyl acids,parabens and cotinine from single low volume serum sample by validated analytical method

ABSTRACT

In this paper, we present the results of an analytical method that has been recently developed, validated and successfully applied in a biomonitoring approach. In the environmental pollutant studies it is desirable that the analytical method can determine multiple classes of compounds from a single, small volume sample. The presented analytical method with a simple sample pre-treatment allows the quantitation of 13 perfluoroalkyl acids (PFAAs), 6 parabens and cotinine (used as nicotine biomarker) from a single, small volume of 100 µL serum sample by liquid chromatography-triple quadrupole mass spectrometer (LC-MS/MS). The limits of quantitation (LOQ) for PFAAs, parabens and cotinine were 0.10–0.50, 0.20–0.80 and 0.10 ng/mL, respectively. Besides sensitivity the method has excellent trueness/accuracy and repeatability. The trueness of the method for the determination of PFAAs ranged from 95% to 106% and the repeatability (as RSD %) from 0.6% to 5.6%. The accuracy and RSD for parabens were 73–120% and 1.3–9.7%, respectively, and 100–106% and 1.3–3.5 % for cotinine. Biomonitoring data reveals the presence of several PFAAs and parabens in serum samples of Finnish population. The total concentrations for PFAAs and parabens were from 2.0 to 33 ng/mL and from <LOQ to 1100 ng/mL, respectively. Nearly all non-smokers had the serum cotinine concentration below 1.0 ng/mL, which can be suggested as the cut point for cotinine concentration to identify smoking.     

Atomically Precise Nanocluster Assemblies Encapsulating Plasmonic Gold Nanorods

The self‐assembled structures of atomically precise, ligand‐protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding‐directed self‐assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p‐mercaptobenzoic acid (pMBA)‐protected atomically precise silver nanocluster, Na₄[Ag₄₄(pMBA)₃₀], and pMBA‐functionalized GNRs were used. High‐resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H‐bonding, leading to octahedral symmetry. The use of water‐dispersible gold nanoclusters, Au_≈250(pMBA)_n and Au₁₀₂(pMBA)₄₄, also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles are a new category of precision hybrids with diverse possibilities.     

A procedure for one-parametric linear programming

A procedure is proposed for the parametric linear programming problem where all the coefficients are linear or polynomial functions of a scalar parameter. The solution vector and the optimum value are determined explicitly as rational functions of the parameter. In addition to standard linear programming technique, only the determination of eigenvalues is required. The procedure is compared to those by Dinkelbach and Zsigmond, and a numerical example is given.