Mikrochemische Nachweise und Bestimmungen organischer Bestandteile des menschlichen oder tierischen Organismus

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Electrodeposition of diamond-like carbon (DLC) films on Ti

Diamond-like carbon films (DLC) were deposited on titanium substrates in acetonitrile and N,N-dimethyl formamide (DMF) liquids by the liquid-phase electrodeposition technique at ambient pressure and temperature. The applied voltage between the electrodes was high (1200 V) due to the use of resistive organic liquids. The surface morphology was examined by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Corrosion performance of the coatings was investigated by potentiodynamic polararization tests in phosphate buffer saline solution. Raman spectroscopy analysis of the films revealed two broad bands at approximately 1360 cm⁻¹ and 1580 cm⁻¹, related to D and G-band of DLC, respectively. The coated Ti was tested in a ball-on-plate type wear test machine with Al₂O₃ balls. The films presented a low friction coefficient (about 0.1), and the films deposited from DMF presented the best wear resistance.     

In situ ATR-FTIR and SFM Studies on the Influence of Adsorption time on Deposition and Nanostructure of Poly(ethyleneimine)/Poly(acrylic acid) Multilayers

Summary: The deposition and the nanostructure of polyelectrolyte multilayers (PEM) of branched poly(ethyleneimine)/poly(acrylic acid) (PEI/PAC) was studied in dependence of the adsorption time (t_ADS) of the individual steps. PEM were reproducibly deposited applying up to z = 20 adsorption steps at the fixed pH combination of 10/4 and polyelectrolyte concentration c_PEL = 0.005 M in a flow cell using an automated valve system. in situ ATR-FTIR spectroscopy and SFM were used for quantitative determination of deposited amount and thickness, respectively. A linear relation between PEL band integrals and thickness of thin PEM films was found. Varying t_ADS from 0.5 to 5 min in each of the adsorption steps resulted in a steep rise of the deposited PEM amount. For t_ADS > 5 min the deposition did only marginally increase. Evidence for the release of outermost located PEI upon PAC immersion (even step) and of outermost PAC upon PEI immersion (odd step) was obtained. SFM images on consecutively deposited PEM-6 showed a slight increase in structure size and roughness for increasing t_ADS. These studies help to prepare polyelectrolyte based films with controlled thickness for the interaction with biofluids in the biomedical and food field.     

Formation of guided Cherenkov radiation in silicon-based nanocomposites

We use a monochromated 200 keV electron beam as a nanometer-resolution probe of the photonic density of states in bulk and nanoparticle Si/SiO(2) systems, observing infrared to ultraviolet waveguided Cherenkov modes in Si slabs, but none in SiO2. While isolated Si nanoparticles are too small to support Cherenkov radiation, we find high densities of Si nanoparticles in SiO2 support a damped form of the radiation, with the modes determined by the effective medium of the Si/SiO(2) mixture. The guided nature of the radiation is confirmed by the presence of a thickness-dependent cutoff.     

Laser applications and system considerations in ocular imaging

We review laser applications for primarily in‐vivo ocular imaging techniques, describing their constraints based on biological tissue properties, safety, and the performance of the imaging system. We discuss the need for cost‐effective sources with practical wavelength‐tuning capabilities for spectral studies. Techniques to probe the pathological changes of layers beneath the highly scattering retina and diagnose the onset of various eye diseases are described. The recent development of several optical‐coherence‐tomography‐based systems for functional ocular imaging is reviewed, as well as linear and nonlinear ocular‐imaging techniques performed with ultrafast lasers, emphasizing recent source developments and methods to enhance imaging contrast.     

Steric and electronic evaluations of P(o‐tol)R2, where R is phenyl or cyclohexyl: crystal structures of SeP(o‐tol)R2

The crystal structures of SeP(o‐tol)R₂, where o‐tol is ortho‐tolyl (2‐methylphenyl) and R is Ph (phenyl), namely (2‐methylphenyl)diphenylphosphane selenide, C₁₉H₁₇PSe, or Cy (cyclohexyl), namely dicyclohexyl(2‐methylphenyl)phosphane selenide, C₁₉H₂₉PSe, were determined to aid in the evaluation of the steric and electronic behaviour of these analogous phosphane compounds. The compounds crystallized in similar monoclinic crystal systems, but are differentiated in their unit cells by a doubling of the number of independent molecules for R = Cy (Z′ = 2) and the choice of glide plane by convention. The preferred orientation for the o‐tolyl substituent obtained from the X‐ray structural analysis is gauche for R = Ph and anti for R = Cy (using the Se—P—C_ipso—C_ortho torsion angles as reference). Density functional theory (DFT) calculations showed both conformations to be equally probable and indicate that the preferred solid‐state conformer is probably due to the minimization of repulsion energies, resulting in a packing arrangement primarily featuring weak C—H…Se interactions and additional C—H…π interactions in the R = Ph structure. A detailed electronic and steric analysis was conducted on both phosphanes using Se—P bond lengths, multinuclear NMR ¹J_Se–P coupling constants, theoretical topological evaluation and crystallographic and solid‐angle calculations, and compared to selected literature examples. The results indicate that the use of the o‐tolyl substituent increases both the electron‐donating capability and the steric size, but is also dependent on whether the o‐tolyl group adopts a gauche or anti conformation. The single‐crystal geometrical data are unable to detect electronic differences between these two structures due to the somewhat large displacement parameters observed for the Se atom in the R = Cy structure.     

MALDI-TOF mass spectrometric analysis for the characterization of the 5,10,15,20-tetrakis- (m-hydroxyphenyl)bacteriochlorin (m-THPBC) photoproducts in biological environment

Photoproducts formation upon irradiation (739 nm) of 5,10,15,20-tetrakis(m-hydroxyphenyl)bacteriochlorin (m-THPBC) in phosphate buffer saline (PBS) supplemented with human serum albumin (HSA) were studied by means of absorption spectroscopy and MALDI-TOF mass spectrometry. The experiments were performed with a freshly prepared PBS-HSA solution of m-THPBC and with a PBS-HSA m-THPBC solution incubated for 6 h at 37 degrees C. The incubation of m-THPBC solution leads to the dye monomerisation, whereas in the freshly prepared solution, m-THPBC is under an aggregated form. Regardless of the incubation condition, photobleaching experiments carried out by absorption spectroscopy demonstrate the degradation of the photosensitizer and its phototransformation in m-THPC. Moreover, m-THPC was the sole photoproduct detected using absorption spectroscopy. Together with a degradation of m-THPBC and formation of m-THPC, MALDI-TOF mass spectrometry evidenced several other photoinduced modifications. Photoproducts such as dihydroxy m-THPBC and dihydroxy m-THPC were detected in both conditions; however, the formation of hydroxylated photoproducts was significantly greater in incubated solution. In addition, small molecules arising from the degradation of the photosensitizer and identified as dipyrin derivatives and dipyrrolic synthon were observed.     

Copolymerization studies of vinyl chloride and vinyl acetate with ethylene using a transition-metal catalyst

Since the advent of Ziegler-Natta polymerization of ethylene, attempts have been made to extend coordination polymerization to commercially important monomers with polar functionality. In this study we examined the copolymerization of perdeuterated vinyl chloride (VC) and perdeuterated vinyl acetate (VA) with ethylene using a tridentate Fe(II) dichloride pyridine diimine metal catalyst. The resulting ethylene oligomers were examined by GC/MS and 2H NMR spectroscopy. It was shown that VC was inserted once for every approximately 180 ethylene monomers and VA was inserted once for every approximately 350 ethylene monomers. VC and VA behave as comonomers for coordination/insertion polymerizations with ethylene. However, we find that insertion with either monomer leads to termination of the growing chain via beta-elimination processes. The deuterium atoms are exclusively located at the olefin terminus for each of the monomers.     

An evaluation of the contributions of diffusion and exchange in relaxation enhancement by MRI contrast agents

Magnetic compounds are known to enhance water proton relaxation, either by diffusion or by proton exchange. An experimental procedure to distinguish both mechanisms is proposed and validated by relaxation measurements made in water-methanol solutions of Dy(3+), Ni(2+), Gd(3+), Tempo, and AMI-25. The test discriminates according to the character of the transverse relaxation in water-methanol solutions: a mono-exponential decay corresponds to diffusion, while a bi-exponential decay indicates the contribution of a proton exchange. The study of ferritin and akaganeite particle solutions confirms the occurrence of a proton exchange between protons belonging to hydroxyl groups of the particle surface and free water protons.