Continuous chemiluminescence determination of formaldehyde in air based on Trautz-Schorigin reaction

A new continuous method for the determination of formaldehyde in air is described. A cylindrical wet effluent diffusion denuder is used for the collection of formaldehyde from air into a thin film of absorption liquid (distilled-deionized water). Formaldehyde in the denuder concentrate is on-line detected employing a chemiluminescence flow method based on a reaction of formaldehyde and gallic acid with hydrogen peroxide in an alkaline solution. The collection efficiency of formaldehyde is quantitative at the air flow rate of 0.5 L min⁻¹ (absorption liquid flow rate of 336 μL min⁻¹). The limit of detection (S/N = 3) is 0.60 μg m⁻³ HCHO (0.49 ppb). The calibration graph is linear up to 300 μg m⁻³ HCHO (244 ppb). The relative standard deviations of chemiluminescence method for 1 × 10⁻⁶ and 5 × 10⁻⁶ M HCHO are 2.87% and 1.49%, respectively. Acetaldehyde interferes negligible, other compounds do not interfere. The method was employed for formaldehyde measurement in ambient air. The comparison measurement illustrates the good agreement of results obtained by proposed method with those obtained by reference fluorimetric method.     

Interaction of porphyrins with a dendrimer template: self-aggregation controlled by pH

The interaction between self-aggregated porphyrins such as 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and 5,10,15,20-tetrakis(4-phosphonatophenyl)porphyrin (TPPP), and a generation 5 (G5) PAMAM dendrimer template is governed by minute differences of porphyrin acido-basic properties. While at neutral pH both monomeric TPPS and TPPP form complexes with G5, decreasing pH did not lead to porphyrin ring protonation (pK(a) approximately 5) but rather to the preferential formation of H-aggregates (probably H-dimers), most likely due to protonation of the G5. Upon further acidification of the solution, this face-to-face orientation of the porphyrin units is being converted to edge-to-edge aligned J-aggregates with a tightly defined structure. This process starts by protonation of the porphyrin ring at pH below 2.3 and 2.8 for TPPS and TPPP, respectively. The AFM imaging of porphyrin/G5 nanostructures obtained at pH 0.7 shows the formation of long nanorods of TPPS with partially aggregated G5 and small aggregates of TPPP connected to individual G5 molecules.     

The role of quantum interference in determining transport properties of molecular bridges

An analytical approach to the electron transport phenomena in molecular devices is presented. The analyzed devices are composed of various molecular bridges attached to two semi-infinite electrodes. Molecular system is described within the tight-binding model, while the coupling to the electrodes is analyzed through the use of Newns-Anderson chemisorption theory. The current-voltage (I-V) characteristics are calculated through the integration of transmission function in the standard Landauer formulation. The essential question of quantum interference effect of electron waves is diseussed in three aspects: (i) the geometry of a molecular bridge, (ii) the presence of an external magnetic field and (iii) the location of chemical substituent.     

Vibrational features in inelastic electron tunneling spectra

A theoretical analysis of inelastic electron tunneling spectroscopy (IETS) experiments conducted on molecular junctions is presented, where the second derivative of the current with respect to voltage is usually plotted as a function of applied bias. Within the nonperturbative computational scheme, adequate for arbitrary parameters of the model, we consider the virtual conduction process in the off-resonance region. Here we study the influence of few crucial factors on the IETS spectra: the strength of the vibronic coupling, the phonon energy, and the device working temperature. It was also shown that weak asymmetry in the IETS signal with respect to bias polarity is obtained as a result of strongly asymmetric connection with the electrodes.     

Biparametric multicommutated flow analysis system for determination of human serum phosphoesterase activity

A multicommutated flow analysis (MCFA) system constructed of microsolenoid valves and pumps offering simultaneous determination of activity of acid phosphatase (ACP) and alkaline phosphatase (ALP) in human serum samples has been developed. The MCFA system is based on optoelectronic flow-through detector made of two light emitting diodes and operating according to paired emitter detector diode (PEDD) principle. This photometric PEDD device has been dedicated for detection of p-nitrophenol (NP) generated in the course of enzymatic hydrolysis of p-nitrophenyl phosphate and optimized for the determination of NP in human serum samples. The developed PEDD-based MCFA system allows independent optimization of conditions for reaction and detection steps of photometric ACP and ALP bioassays. Moreover, it allows elimination of photometric interferences from serum matrix components according to two-points kinetic mode of measurement. The single measurement cycle takes 12 min, consists of four measurements (two for each phosphoesterase) and enables determination of serum ACP and ALP activities at physiological and pathological levels. The real analytical utility of the developed MCFA system has been confirmed by analysis of control sera as well as real human serum samples from healthy persons and oncological patients.     

Interaction of Quillaja bark saponins with food-relevant proteins

The surface activity and aggregation behaviour of two Quillaja bark saponins (QBS) are compared using surface tension, conductometry and light scattering. Despite formally of the same origin (bark of the Quillaja saponaria Molina tree), the two QBS show markedly different ionic characters and critical micelle concentrations (7.7 · 10^− 6 mol·dm^− 3 and 1.2 · 10^− 4 mol·dm^− 3). The new interpretation of the surface tension isotherms for both QBS allowed us to propose an explanation for the previous discrepancy concerning the orientation of the saponin molecules in the adsorbed layer.     

The preparation and properties of “porous silicon–nickel ferrite” nanoheterocomposites for gas detectors

This paper discusses the preparation and properties of gas detectors based on “porous silicon–nickel ferrite” nanocomposites. Impedance spectroscopy was used to measure sensitivity to ethanol and isopropanol vapours in the presence of an alternating electric field. The results were interpreted with the help of an equivalent electrical circuit. In the analysis of the resistive–capacitive properties in the equivalent circuit a constant phase element was used.     

New heterocyclic metallomesogens: synthesis,mesomorphic and thermal behaviours of Cu(II) complexes with 1,2,3-triazole-based Schiff bases ligands

Two series of new Cu(II) complexes derived from the reaction of copper acetate with the non-linear 1,2,3-triazole-based Schiff bases have successfully been synthesised. The structures of the ligands and its complexes were elucidated by elemental analysis, FT-IR, ¹H-NMR and UV–visible spectroscopic techniques. The differential scanning calorimetry and polarizing optical microscopy supported the anisotropic properties of uncoordinated ligands in which the focal conic fan-shaped texture and/or broken fan-shaped texture characteristics of respective SmA and SmC phases were recorded. However, not all of their corresponding Cu(II) complexes are mesogenic. Although the iodo-substituted ligands with even parity C₁₀H₂₉ to C₁₄H₃₃ are non-stable and exhibit SmA phase which is not reproducible, the ultimate Cu(II) complexes show exclusively stable SmA phase. This observation can be ascribed to the enhanced colinearity and molecular anisotropic by the presence of Cu-N and Cu-O coordination modes. On the other hand, the comparison studies show that different positions of ortho-hydroxyl group affect the mesomorphic and thermal behaviour of ligands and Cu(II) complexes.