Measurement of nitric oxide by 4,5-diaminofluorescein without interferences

The fluorescent reagent 4,5-diaminofluorescein (DAF-2) has been widely used for specific and quantitative measurements of nitric oxide (NO) in biological tissues. Recently it was reported that dehydroascorbic acid (DHA) and ascorbic acid (AA) interfere with the measurement of NO using DAF-2. A new method of assaying NO using DAF-2 eliminates these interferences; when frozen on dry ice, the NO in the original solution still diffuses and can react with an adjacent frozen block of DAF-2, but the confounding compounds such as DHA do not. Thus, placing the microliter-volume frozen blocks of solutions containing NO and the solutions of DAF-2 adjacent to each other for 30 min results in the concentration dependent formation of fluorescent product (DAF-2T) from the reaction of NO with DAF-2. The product has been characterized and the method validated using both fluorescence spectroscopy and capillary electrophoresis with laser induced fluorescence detection. With this approach, the presence of DHA and AA does not interfere with NO measurements, and product formation is inhibited in the presence of NO scavengers added to either of the solutions before freezing. The contactless DAF-2 method successfully assays NO in nitric oxide synthase-positive vertebrate and invertebrate tissues. This method allows nondestructive NO detection in biological samples that can subsequently be used for morphological and/or biochemical studies.     

Time-dependent density functional theory study of the spectroscopic properties related to aggregation in the platinum(II) biphenyl dicarbonyl complex

Singlet ground-state geometry optimization of the monomer, four dimers, and the trimer of [Pt(bph)(CO)(2)], where bph = biphenyl dianion, was performed at the B3LYP level of density functional theory (DFT) with a mixed basis set (6-311G** on C, O, and H atoms; the Stuttgart/Dresden (SDD) effective core potential (ECP) on the Pt core; [6s5p3d] on the Pt valence shell). The aggregation was based on Pt[bond]Pt binding as well as on pi[bond]pi and electrostatic interactions. The lowest-lying triplet-state geometries of the monomer, one dimer, and the trimer of the complex were also optimized using the above theory. Significant shortening of the Pt[bond]Pt bond was recorded in the triplet state compared to the singlet one. A number of low-energy singlet and triplet allowed excited states were calculated using time-dependent density functional theory (TDDFT) and analyzed with respect to absorption, excitation, and emission spectra collected under various conditions. Simulated spectra of the monomer and dimer based on the singlet excited states were correlated with the absorption spectrum. The emission in concentrated solution was due to the triplet dimer, and the emitting states were (3)MLCT and Pt-centered states.     

Interferences in the determination of aluminium by means of atomic absorption spectrophotometry

Summary The following substances have been investigated with regard to their interfering effect in the determination of aluminium by atomic absorption spectrophotometry: HCl, H₂SO₄, HNO₃, H₃PO₄, alkali and alkaline earth metals, Cu, Fe, Zn, Ni, Mn, Co, Mo, Ti, Cr, V, Si. Ternary systems with La have been examined also. Si exerts a strong depressive effect, whereas other elements in certain concentration ranges exhibit positive effects.

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Störungen bei der atomabsorptionsspektralphotometrischen Bestimmung von Aluminium

Zusammenfassung Folgende Substanzen wurden hinsichtlich einer möglichen Beeinflussung der Aluminiumbestimmung untersucht: HCl, H₂SO₄, HNO₃, H₃PO₄, Alkalimetalle, Erdalkalimetalle, Cu, Fe, Zn, Ni, Mn, Co, Mo, Ti, Cr, V, Si. Ternäre Systeme mit La wurden ebenfalls geprüft. Si übt eine stark depressive Wirkung aus, während andere Elemente in bestimmten Konzentrationsbereichen positiv wirken.

Lecture given on the 2nd Czechoslovak Conference on Flame Speotroscopy, Zvíkov, June 5–8, 1973.     

The involvement of metal-to-CO charge transfer and ligand-field excited states in the spectroscopy and photochemistry of mixed-ligand metal carbonyls. A theoretical and spectroscopic study of [W(CO)(4)(1,2-ethylenediamine)] and [W(CO)(4)(N,N'-bis-alkyl-1,4-diazabutadiene)

A new interpretation of the electronic spectroscopy, photochemistry, and photophysics of group 6 metal cis-tetracarbonyls [M(CO)(4)L(2)] is proposed, that is based on an interplay between M --> L and M --> CO MLCT excited states. TD-DFT and resonance Raman spectroscopy show that the lowest allowed electronic transition of [W(CO)(4)(en)] (en = 1,2-ethylenediamine) has a W(CO(eq))(2) --> CO(ax) charge-transfer character, whereby the electron density is transferred from the equatorial W(CO(eq))(2) moiety to pi orbitals of the axial CO ligands, with a net decrease of electron density on the W atom. The lowest, emissive excited state of [W(CO)(4)(en)] was identified as a spin-triplet W(CO(eq))(2) --> CO(ax) CT excited state both computationally and by picosecond time-resolved IR spectroscopy. This state undergoes 1.5 ps vibrational relaxation/solvation and decays to the ground state with a approximately 160 ps lifetime. The nu(CO) wavenumbers and IR intensity pattern calculated by DFT for the triplet W(CO(eq))(2) --> CO(ax) CT excited state match well the experimental time-resolved spectrum. For [W(CO)(4)(R-DAB)] (R-DAB = N,N'-bis-alkyl-1,4-diazabutadiene), the W(CO(eq))(2) --> CO(ax) CT transition follows in energy the W --> DAB MLCT transition, and the emissive W(CO(eq))(2) --> CO(ax) CT triplet state occurs just above the manifold of triplet W --> DAB MLCT states. No LF electronic transitions were calculated to occur in a relevant energetic range for either complex. Molecular orbitals of both complexes are highly delocalized. The 5d(W) character is distributed over many molecular orbitals, while neither of them contains a predominant metal-ligand sigma 5d(W) component, contrary to predictions of the traditional ligand-field approach. The important spectroscopic, photochemical, and photophysical roles of M(CO(eq))(2) --> CO(ax) CT excited states and the limited validity of ligand field arguments can be generalized to other mixed-ligand carbonyl complexes.     

Non-destructive measurement of the mobility in semiconductors by means of the microwave Faraday effect

The paper describes the measurement of the electron mobility in semiconducting plates placed between two cylindrical antennas with diameterd–0·75 ₀ by means of the microwave Faraday effect. This system enables (i) to measure the Faraday rotation in semiconducting plates of arbitrary transverse dimensions, greater or at least equal to the diameter of dielectric antennas, (ii) to evaluate the unknown value of the charge carrier mobility from the measured rotation in an unbounded solid state plasma slab approximation. The measurement of the Faraday rotation in n-type Ge plates are reported. The comparison of the experimental data with the theory shows good agreement.     

Ultrathin functional films of titanium(IV) oxide

Chemistry and physics of thin semiconducting layers of various types are subjects of intense research. Especially when nanotechnology methods such as self-assembly are involved, amazing structural and/or functional properties may appear. Also modern physical methods using variously organized plasma arrangements are able to produce uniform structures with distinctive functionality. In this review, based virtually on our own work, discussions on the preparation, structure, morphology, and function of titanium(IV) oxide nanoscopic thin films are presented. It was shown that structurally and functionally similar titanium(IV) oxide films can be prepared via completely different preparation techniques. Function tests were arranged as “primary”, covering the assessment of the light induced charge separation efficiency, and “secondary”, based on photocatalytic surface oxidations.     

Molecular dynamics simulation of poly(3‐hexylthiophene) helical structure In Vacuo and in amorphous polymer surrounding

The stability of poly(3‐hexylthiophene) (P3HT) helical structure has been investigated in vacuo and in amorphous polymer surrounding via molecular dynamics‐based simulations at temperatures below and above the P3HT melting point. The results show that the helical chain remains stable at room temperature both in vacuo and in amorphous surrounding, and promptly loses its structure at elevated temperatures. However, the amorphous surrounding inhibits the destruction of the helix at higher temperatures. In addition, it is shown that the electrostatic interactions do not significantly affect the stability of the helical structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2448–2456