Evaluation of double-tuned single-sided planar microcoils for the analysis of small 13C enriched biological samples using 1H-13C 2D heteronuclear correlation NMR spectroscopy

Microcoils provide a cost-effective approach to improve detection limits for mass-limited samples. Single-sided planar microcoils are advantageous in comparison to volume coils, in that the sample can simply be placed on top. However, the considerable drawback is that the RF field that is produced by the coil decreases with distance from the coil surface, which potentially limits more complex multi-pulse NMR pulse sequences. Unfortunately, ¹H NMR alone is not very informative for intact biological samples due to line broadening caused by magnetic susceptibility distortions, and ¹H-¹³C 2D NMR correlations are required to provide the additional spectral dispersion for metabolic assignments in vivo or in situ. To our knowledge, double-tuned single-sided microcoils have not been applied for the 2D ¹H-¹³C analysis of intact ¹³C enriched biological samples. Questions include the following: Can ¹H-¹³C 2D NMR be performed on single-sided planar microcoils? If so, do they still hold sensitivity advantages over conventional 5 mm NMR technology for mass limited samples? Here, 2D ¹H-¹³C HSQC, HMQC, and HETCOR variants were compared and then applied to ¹³C enriched broccoli seeds and Daphnia magna (water fleas). Compared to 5 mm NMR probes, the microcoils showed a sixfold improvement in mass sensitivity (albeit only for a small localized region) and allowed for the identification of metabolites in a single intact D. magna for the first time. Single-sided planar microcoils show practical benefit for ¹H-¹³C NMR of intact biological samples, if localized information within ~0.7 mm of the 1 mm I.D. planar microcoil surface is of specific interest.     

Characterization of Ta and TaN diffusion barriers beneath Cu layers using picosecond ultrasonics

In computer chips, aluminum is being replaced with copper in order to produce smaller, faster and more efficient electronic devices. The usage of copper allows higher current densities and thus higher packaging densities than aluminum. However, copper leads to new challenges and problems. It has different mechanical properties and a tendency to migrate into the surrounding dielectric and/or semiconducting layers. These diffusion processes can be prevented by so called diffusion barriers. A diffusion barrier is a very thin layer consisting of tantalum and tantalum nitride or titanium and titanium nitride, deposited between the copper and the substrate. A pump-probe setup is used to determine the mechanical properties of the barrier layers and of the copper layer. This short-pulse-laser-acoustic method is contact-free and non-destructive. Mechanical waves are excited and detected thermoelastically using laser pulses of 70 fs duration. Thin film measurements of buried diffusion layers are provided and compared with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Rutherford Backscattering Spectroscopy measurements (RBS). Results of a thermo-elasto-mechanical simulation are presented and a short overview of the simulation procedure is given. Current limits of the presented method are discussed and future directions of the on-going research project are presented.     

Self-assembly of a hexagonal boron nitride nanomesh on Ru(0001)

Hexagonal boron nitride (h-BN) nanostructures were grown on Ru(0001), and are very similar to those previously reported on Rh(111). They show a highly regular 12 x 12 superstructure, comprising 2 nm wide apertures with a depth of about 0.1 nm. Valence band photoemission reveals two distinctly bonded h-BN species, and X-ray photoelectron spectroscopy indicates an h-BN monolayer film. The functionality of the h-BN/Ru(0001) nanomesh is demonstrated by using this structure for the assembly of gold nanoclusters.     

A note on the depth dependence and current density effects upon the radiation damage in graphite

This note is in two parts. The first describes the surprisingly large depth at which the radiation damage can be observed after irradiating graphite with²MeV⁴He⁺ ions. The second part deals with the dependence of the induced damage with the deposited power density at sample temperatures up to 1250°C.     

Combined solution-phase and solid-phase synthesis of 2-amino-7,8-dihydropteridin-6(5H)-ones

An efficient and general synthesis of substituted 2-amino-7,8-dihydropteridin-6(5H)-ones using a combination of solution-phase and solid-phase chemistry is described. Solution-phase chemistry was used to produce two pyrimidine regioisomers that were separated by flash column chromatography. Utilizing the desired regioisomer, solid-phase chemistry was used to effect the rapid construction of the substituted 2-amino-7,8-dihydropteridin-6(5H)-one system in high overall yield and purity.     

Structure-based design of potent CDK1 inhibitors derived from olomoucine

Cyclin-dependent kinase 1 (CDK1), an enzyme participating in the regulation of the cell cycle, constitutes a possible target in the search for new antitumor agents. Starting from the purine derivative olomoucine and following a structure-based approach, potent inhibitors of this enzyme were rapidly identified. The molecular modeling aspects of this work are described.     

A simple pretreatment of unrine for the direct differential-pulse anodic stripping voltammetric determination of lead

Lead can be determined directly in urine at the μg l^?1 level after a simple clean-up procedure consisting of an adsorptive removal of parts of the organic matrix on an apolar chromatographic medium followed by a filtration step.     

On the role of lattice dynamics on low-temperature oxygen mobility in solid oxides: a neutron diffraction and first-principles investigation of {\hbox{L}}{{\hbox{a}}_2}{\hbox{Cu}}{{\hbox{O}}_{{4 + \delta }}}

The structure of oxygen-intercalated La₂CuO_4.07 has been investigated at 20 and 300?K by neutron diffraction on an electrochemically oxidized single crystal. At 20?K, reconstruction of the nuclear density by maximum entropy method shows strong displacements of the apical oxygen atoms towards [100] with respect to the F-centred unit cell, whilst displacements towards [110] and [100] were both found to be present at ambient temperature. Combining structural studies with first-principles lattice dynamical calculations, we interpret the displacements of the apical oxygen atoms to be at least partially of dynamic origin already at ambient temperature. Strong displacements of the apical oxygen atoms of stoichiometric and oxygen-doped $ {\hbox{L}}{{\hbox{a}}_{{2}}}{\hbox{Cu}}{{\hbox{O}}_{{{4} + \delta }}} $ and corresponding associated lattice instabilities, i.e. low-energy phonon modes, are considered as a general prerequisite of low-temperature oxygen diffusion mechanisms. Lattice dynamical calculations on $ {\hbox{L}}{{\hbox{a}}_{{2}}}{\hbox{Cu}}{{\hbox{O}}_{{{4} + \delta }}} $ suggest that the oxygen species diffusing at low temperature are not the interstitial but, more prominently, the apical oxygen atoms. The presence of interstitial oxygen atoms is, however, important to amplify via specific, low-energy phonon modes, a dynamic exchange mechanism between apical and vacant interstitial oxygen sites, thus allowing a dynamically triggered, shallow potential oxygen diffusion pathway. The crucial role of lattice dynamics to enable low-temperature oxygen mobility in K₂NiF₄-type oxides is discussed on a microscopic scale and compared to similar low-temperature oxygen diffusion mechanisms, recently proposed for non-stoichiometric oxides with Brownmillerite-type structure.