Towards the Development of a Selective Ruthenium‐Catalyzed Hydroformylation of Olefins

The ruthenium‐catalyzed hydroformylation of 1‐ and 2‐octene to give preferentially the corresponding linear aldehyde is reported. The catalyst system comprising of Ru₃(CO)₁₂ and an imidazole‐substituted monophosphine ligand allows for high chemo‐ and regioselectivity. The hydroformylation proceeds with unprecedented rates for a ruthenium‐based catalyst.     

Biosensor Based on Electrocodeposition of Carbon Nanotubes/Polypyrrole/Laccase for Neurotransmitter Detection

A new biosensor has been developed by a simple electrocodeposition of multiwalled carbon nanotubes (MWCNT), polypyrrole (PPy) and laccase (Lac) on the platinum (Pt) electrode surface. The neurotransmitter biosensor was applied to the detection of dopamine in urine samples using differential pulse voltammetry (DPV). The Pt/MWCNT/PPy/Lac biosensor exhibited a detection limit of 0.14 µM, which is an adequate level for monitoring dopamine in urine. Reproducibility and repeatability values of 2.9 % and 1.7 %, respectively, were obtained compared to the conventional procedure. The proposed biosensor was successfully applied in the determination of dopamine in urine, and the obtained results were in full agreement with those from the HPLC procedure.     

Inhibition of Candida albicans CC biofilms formation in polystyrene plate surfaces by biosurfactant produced by Trichosporon montevideense CLOA72

This study evaluated the effects of glycolipid-type biosurfactant produced by Trichosporon montevideense CLOA72 in the formation of biofilms in polystyrene plate surfaces by Candida albicans CC isolated from the apical tooth canal. Biofilm formation was reduced up to 87.4% with use of biosurfactant at 16 mg/ml concentration. It has been suggested that the interaction with the cell or polystyrene plate surface could ultimately be responsible for these actions. Therefore, the interaction of C. albicans CC cells with the biosurfactant, as well as the corresponding thermodynamic parameters, have been determined by isothermal titration calorimetry and zeta potential measurements. This process is endothermic (((int)H°=+1284±5 cal/mg OD(600)) occurring with a high increase of entropy (T((int)S°=+10635 cal/mg OD(600)). The caloric energy rate data released during the titulation indicates saturation of the cell-biosurfactant at 1.28 mg/ml OD(600). Also, the zeta potential of the cell surface was monitored as a function of the biosurfactant concentration added to cell suspension showing partial neutralization of net surface charge, since the value of zeta potential ranged from -16 mV to -6 mV during the titration. The changes of cell surface characteristics can contribute to the inhibition of initial adherence of cells of C. albicans in surface. The CMC of the purified biosurfactant produced from T. montevideense CLOA72 is 2.2 mg/ml, as determined both by ITC dilution experiments and by surface tension measurements. This biomolecule did not presented any cytotoxic effect in HEK 293A cell line at concentrations of 0.25-1 mg/ml. This study suggests a possible application of the referred biosurfactant in inhibiting the formation of biofilms on plastic surfaces by C. albicans.     

Native red electrophoresis--a new method suitable for separation of native proteins

A new type of native electrophoresis was developed to separate and characterize proteins. In this modification of the native blue electrophoresis, the dye Ponceau Red S is used instead of Coomassie Brilliant Blue to impose uniform negative charge on proteins to enable their electrophoretic separation according to their relative molecular masses. As Ponceau Red S binds less tightly to proteins, in comparison with Coomassie Blue, it can be easily removed after the electrophoretic separation and a further investigation of protein properties is made possible (e.g. an enzyme detection or electroblotting). The tested proteins also kept their native properties (enzyme activity or aggregation state).     

Structural diversification of the coordination mode of divalent metals with 1,3-propanediaminetetraacetate (1,3-pdta): The missing crystal structure of the s-block metal complex [Sr2(1,3-pdta)(H2O)6]·H2O

This paper reports the synthesis and X-ray characteristics of the missing homonuclear s-block metal complex {[Sr₂(1,3-pdta)(H₂O)₆]·H₂O}_n. In the title compound, the hexadentate 1,3-propanediaminetetraacetate (1,3-pdta) ligand joins to two Sr(II) centers via the diamine chain. Moreover, each Sr(II) is bridged through two carboxylate O atoms and a water molecule to two neighboring Sr(II) ions. The coordination sphere around each Sr(II) ion consists of one diamine nitrogen, four carboxylate oxygens and four water molecules. Comparison with the previously reported M(II)-1,3-pdta complexes reveals that increasing of the ion size results in the incorporation of water molecules into its first coordination sphere and consequent increase of the coordination number (C.N.) from six to seven or eight, while keeping the hexadentate coordination mode of the ligand. Further increase of the metal ion size leads to the loss of the chelating properties of the diamine and formation of a bis-tridentate complex. Associated with it is the change in the binding mode of the carboxylate groups. This forms the basis for classification of divalent metal 1,3-pdta complexes into five distinct structural classes. Additionally, in the present study X-ray powder diffraction and IR spectroscopy were used to distinguish the different structural types of M(II)-1,3-pdta complexes, including Ba[Ba(1,3-pdta)]·2H₂O which has been used for their preparation.     

Photochemical approach to naphthoxazoles and fused heterobenzoxazoles from 5-(phenyl/heteroarylethenyl)oxazoles

A new synthetic approach is presented for the synthesis of naphthoxazoles and fused heterobenzoxazoles. The starting 5-(aryl/furyl/thienyl/pyridyl ethenyl)oxazoles are prepared from the corresponding α,β-unsaturated aldehydes using Van Leusen reagent in very good yields and are transformed into naphthoxazoles and fused heterobenzoxazoles on irradiation under aerobic conditions and in the presence of iodine.     

A Spectrophotometric Study of Streptomycin Effect on the Clinical Urea Determination

The results of studying inhibitory effect of streptomycin on the modified Berthelot reaction were presented in this paper and a new kinetic method for determining streptomycin in pharmaceutical preparations and human urine was developed on the basis of the obtained results. The rates of catalytic and catalytic‐inhibitory reaction were monitored at 700 nm (t=25±0.1°C) using UV/vis spectrophotometer. By analyzing the spectra and experimental dependences of the catalytic and catalytic‐inhibitory reaction rates on the reactant concentrations, it was noticed that streptomycin attacked nitroprusside and hypochlorite causing the inhibition of the production of 2,2′‐dicarboxylindophenol. According to this effect, an analytical decrease for determination of urea by modified Berthelot reaction appeared in the presence of small amounts of streptomycin. Beer's law was obeyed in the interval of streptomycin sulfate concentration from 18.2 to 182 µg·mL^?1. The detection limit calculated by two methods was obtained at 11.75 µg·mL^?1 and 8.54 µg·mL^?1. The relative standard deviation of 0.55%–8.83% and the recovery of 109.10% were determined. The obtained results were validated using the referent HPLC method.     

A new approach to study cadmium complexes with oxalic acid in soil solution

This study presents a new analytical approach for the determination of heavy metals complexed to low-molecular-weight-organic acids in soil solutions, which combines the sensitivity of differential pulse anodic stripping voltammetry (DPASV) with the molecular insight gained by electrospray ionization mass spectrometry (ESI-MS). The combination of these analytical methods allows the investigation of such complexes in complex matrixes. On the voltammograms of the soil solutions, in addition to the expected complexes of oxalic acid with cadmium and lead, respectively, also peaks belonging to mixed complexes of cadmium, lead, and oxalic acid (OAH(2)) were observed. In order to verify the possible formation of complexes with OAH(2), aqueous solutions of OAH(2) with traces of Cd(II) were investigated as model systems. Signals corresponding to several distinct molecular complexes between cadmium and oxalic acid were detected in the model solutions using negative-ion ESI-MS, which follow the general formula [Cd(n)(X,Y)((2n+1))](-), where n is the number of cadmium atoms, X=Cl(-), and Y=OAH(-). Some of these complexes were also identified in the ESI mass spectra taken from the soil solutions.     

A New Indirect Electrochemical Method for Determination of Ozone in Water Using Multiwalled Carbon Nanotubes

A new electrochemical methodology has been developed for the detection of ozone using multiwalled carbon nanotubes (MWCNT). The method presented here is based on the reaction of ozone with indigo blue dye producing anthranilic acid (ATN). The electrochemical profile of ATN on an electrode of glassy carbon (GC) modified with MWCNT showed an oxidation peak potential at 750 mV vs. Ag/AgCl. An analytical method was developed using differential pulse voltammetry (DPV) to determine ATN in a range of 50–400 nmol L^?1, with a detection limit of 9.7 nmol L^?1. Ozonated water samples were successfully analyzed by GC/MWCNT electrode and the recovery procedure yielded values between of 96.5 and 102.3 %.     

Use of Lagrangian statistics for the analysis of the scale separation hypothesis in turbulent channel flow

Turbulence models often involve Reynolds averaging, with a closure providing the Reynolds stress tensor as function of mean velocity gradients, through a turbulence constitutive equation. The main limitation of this linear closure is that it rests on an analogy with kinetic theory. For this analogy to be valid there has to be a scale separation between the mean velocity variations and the turbulent Lagrangian free path whose mean value is the turbulent mixing length. The aim of this work is to better understand this hypothesis from a microscopic point of view. Therefore, fluid elements are tracked in a turbulent channel flow. The flow is resolved by direct numerical simulation (DNS). Statistics on particle trajectories ending on a certain distance y₀ from the wall are computed, leading to estimations of the turbulent mixing length scale and the Knudsen number. Comparing the computed values to the Knudsen number in the case of scale separation, we may know in which region of the flow and to what extent the turbulence constitutive equation is not verified. Finally, a new non-local formulation for predicting the Reynolds stress is proposed.