Synthesis, chiroptical properties and photoinduced birefringence of optically active methacrylic copolymers bearing side-chain bisazoaromatic moieties

Three series of optically active photochromic copolymers, deriving from methyl methacrylate (MMA) and the chiral bisazoaromatic monomers (S)-3-methacryloyloxy-1-[4′-phenylazo-(4-azobenzene)]-pyrrolidine [(S)-MPAAP], (S)-3-methacryloyloxy-1-[4′-cyanophenylazo-(4-azobenzene)]-pyrrolidine [(S)-MPAAP-C] and (S)-3-methacryloyloxy-1-[4′-nitrophenylazo-(4-azobenzene)]-pyrrolidine [(S)-MPAAP-N], have been prepared and characterized in solution and in the solid state with the aim to evaluate the effect on their chiroptical and thermal properties originated by the insertion of inactive MMA groups along the main chain. The optical activity displayed by the bisazo polymers is discussed in terms of extent of chiral conformation assumed by the macromolecules as a consequence of dipole-dipole interactions between the bisazoaromatic chromophores.The photoinduction of birefringence has been assessed on thin films of the investigated copolymers in order to evaluate their behaviour as materials for optical data storage. The results are interpreted in terms of copolymer composition and conformational stiffness of the bisazoaromatic chromophoric co-units, which are responsible for the optical response rates, and are compared to those of the similar derivatives containing only one azo bond. The observed enhanced thermal properties and the temporal stability appear of interest for a potential use of these materials in nano technologies for all-optical data manipulation and in optoelectronics.     

Influence of Excitation Wavelength (UV or Visible Light) on the Photocatalytic Activity of Titania Containing Gold Nanoparticles for the Generation of Hydrogen or Oxygen from Water

Gold nanoparticles supported on P25 titania (Au/TiO(2)) exhibit photocatalytic activity for UV and visible light (532 nm laser or polychromatic light λ > 400 nm) water splitting. The efficiency and operating mechanism are different depending on whether excitation occurs on the titania semiconductor (gold acting as electron buffer and site for gas generation) or on the surface plasmon band of gold (photoinjection of electrons from gold onto the titania conduction band and less oxidizing electron hole potential of about -1.14 V). For the novel visible light photoactivity of Au/TiO(2), it has been determined that gold loading, particle size and calcination temperature play a role in the photocatalytic activity, the most active material (Φ(H2) = 7.5% and Φ(O2) = 5.0% at 560 nm) being the catalyst containing 0.2 wt % gold with 1.87 nm average particle size and calcined at 200 °C.     

Dynamic processes in hydrido-carbonyl trirhenium clusters containing bridging nitrogen heterocyclic ligands: An NMR investigation

The dynamic processes occurring in the triangular clusters [Re₃(μ-H)₃(μ-pz-κN¹:κN²)(CO)₁₀]⁻ (pz = pyrazolate, 4), [Re₃(μ-H)₂(μ-pydz-κN¹:κN²)(CO)₁₀] ⁻ (pydz = pyridazine, 5) and [Re₃(μ-H)₃(μ-pydz-κN¹:κN²)(CO)₁₀] (6), have been investigated by ¹H and ¹³C NMR. In the pyrazolate derivative 4 the exchange (k ≈ 1 s⁻¹ at 320 K) between the two carbonyls in the trans-diaxial apical positions has been recognized, and its activation parameters, in C₂D₂Cl₄, have been determined (E_a = 68(3) kJ mol⁻¹). The exchange has been attributed to the rotation of the apical H₂Re(CO)₄ fragment with respect to the Re₂(μ-pz) basal fragment, a process analogous to that previously observed in the unsaturated dianion [Re₃(μ-H)₃(CO)₁₀] ²⁻ (2) and in the monoanion [Re₃(μ-H)₃(μ-NC₅H₄-κN¹:κC⁶)(CO)₁₀]⁻ (1), containing a bridging orthometallated pyridine ligand. The vertex rotation was not observed in the pyridazine derivatives 5 and 6. An explanation for this different behaviour is presented, based on the view of the fluxional clusters 1, 2 and 4 as adducts between the apical and basal moieties (π- or σ-complexes). The ΔG^#_312K value here measured in acetone for the σ-complex 4 (77 kJ mol⁻¹) is very similar to that previously determined for the other σ-complex 1 (ΔG^#_305K = 76 kJ mol^-1) and significantly higher than the values measured for the π-complex 2 (ΔG^#_260K = 60 kJ mol⁻¹). The di-hydrido derivative 5 shows a different much faster dynamic process, namely the hopping of one hydride between the two lateral edges, affording a pseudo C_s symmetry in the molecule. The process has been monitored by both ¹H and ¹³C analysis, affording quite similar activation parameters (E_a = 44(1) and 45(1) kJ mol⁻¹, respectively, in THF-d₈), that did not significantly change in CD₂Cl₂ solution, in agreement with an intramolecular process.     

Size-selective template-assisted electrophoretic assembly of nanoparticles for biosensing applications

The precise, size-selective assembly of nanoparticles gives rise to many applications where the assembly of nano building blocks with different biological or chemical functionalizations is necessary. We introduce a simple, fast, reproducible-directed assembly technique that enables a complete sorting of nanoparticles with single-particle resolution. Nanoparticles are size-selectively assembled into prefabricated via arrays using a sequential template-directed electrophoretic assembly method. Polystyrene latex (PSL) nanoparticles with diameters ranging from 200 to 50 nm are selectively assembled into vias comparable to nanoparticle diameter. We investigate the effects of particle size and via size on the sorting efficiency. We show that complete sorting can be achieved when the size of the vias is close to the diameter of the nanoparticles and the size distribution of the chosen nanoparticles does not overlap. The results also show that it is necessary to keep the electric field on during the insertion and removal of the template. To elucidate the versatility and nil effects that the electrophoresis assembly technique has on the assembled nanoparticle characteristics, we have assembled cancer-specific monoclonal antibody-2C5-coated nanoparticles and have also shown that they can successfully measure low concentrations of the nucleosome (NS) antigen.     

Effects of low-dose dexamethasone and prednisolone long term administration in beef calf: chemical and morphological investigation

An analytical, pharmacokinetic and histopathologic investigation was conducted by two experimental trials on beef cattle in order to determine fate and effects of dexamethasone and prednisolone, administered to distinct cattle groups at low dosage for long periods of time. In trial 1, eighteen Charolaise beef cattle, male, 17-22-months-old, were divided in three groups: to group A (n=6) dexamethasone-21-sodium-phosphate 0.7 mg day(-1) per os for 40 days was administered; group B (n=6) was orally treated with prednisolone 15 mg day(-1) for 30 days, while group C (n=6) served as negative control. Urine was collected at days 0, 7, 15, 25 and 47 from groups A and C, and at days 0, 8, 18 and 42 from group B. In trial 2, sixteen Friesian cattle, male, 10-17-months-old, were randomly divided into two groups: group D (n=8) was administered prednisolone 30 mg day(-1) per os for 35 days, while group K (n=8) served as control. In both trials, the animals were slaughtered after a 6-days drug withdrawal and thymus and livers were collected and properly stored until the analysis was performed. Quantitative determinations of dexamethasone, prednisolone and its main metabolite, prednisone, in urine and liver samples were conducted by HPLC-MS/MS, after the analytical procedure was optimized and fully validated. The method validation included the assessment of specificity, linearity, precision, trueness, robustness, CC(α) and CC(β) values. By a morphological point of view, severe atrophy of thymus parenchyma was observed in group A, together with a significant (P<0.005) reduction of the mean thymus weight (217±94 g), while group B (646±215 g) presented normal thymus features and weights (group C, 415±116 g). Accordingly, no differences were found in trial 2 for groups D (727±275g) and K (642±173 g). Average dexamethasone concentrations in group A urine samples ranged from 1.4 to 3.0 μg L(-1) during the treatment, while no residue was detected in the urine samples collected 6-7 days after the end of the treatment. Low amounts of dexamethasone (<1 μg L(-1)) were detected in liver samples of group A. All average prednisolone concentrations in group B urine samples (sum of conjugate and free form) turned out to be below 1.0 μg L(-1) during the treatment, despite the much higher concentration administered (15-30 mg day(-1)) with respect to dexamethasone in group A (0.7 mg day(-1)). No prednisolone residues were found in the urine and liver samples taken at the slaughterhouse. The absence of any prednisolone residue in the urine samples of control group animals supports the theory that the origin of this molecule is fundamentally exogenous, at least for this cattle category maintained under unstressing conditions. Remarkable findings are represented by the absence of thymus atrophy in the prednisolone treated animals and the extremely low residue concentrations found in urine during the treatment. Both findings reveal that the detection of illegal growth-promoting treatments with this drug is difficult.     

Antiviral properties of lactoferrin--a natural immunity molecule

Lactoferrin, a multifunctional iron binding glycoprotein, plays an important role in immune regulation and defence mechanisms against bacteria, fungi and viruses. Lactoferrin's iron withholding ability is related to inhibition of microbial growth as well as to modulation of motility, aggregation and biofilm formation of pathogenic bacteria. Independently of iron binding capability, lactoferrin interacts with microbial, viral and cell surfaces thus inhibiting microbial and viral adhesion and entry into host cells. Lactoferrin can be considered not only a primary defense factor against mucosal infections, but also a polyvalent regulator which interacts in viral infectious processes. Its antiviral activity, demonstrated against both enveloped and naked viruses, lies in the early phase of infection, thus preventing entry of virus in the host cell. This activity is exerted by binding to heparan sulphate glycosaminoglycan cell receptors, or viral particles or both. Despite the antiviral effect of lactoferrin, widely demonstrated in vitro studies, few clinical trials have been carried out and the related mechanism of action is still under debate. The nuclear localization of lactoferrin in different epithelial human cells suggests that lactoferrin exerts its antiviral effect not only in the early phase of surface interaction virus-cell, but also intracellularly. The capability of lactoferrin to exert a potent antiviral activity, through its binding to host cells and/or viral particles, and its nuclear localization strengthens the idea that lactoferrin is an important brick in the mucosal wall, effective against viral attacks and it could be usefully applied as novel strategy for treatment of viral infections.     

Impact of cryoprotectants and cryopreservation on metabolic activity and cytoskeleton proteins of zebrafish (Danio rerio) ovarian fragments

Cryopreservation of reproductive cells and tissues of aquatic species offers many benefits to the field of conservation, aquaculture and biomedicine. Although cryopreservation of fish sperm has been successfully achieved, cryopreservation of embryos and oocytes remains unsuccessful. Several studies have been undertaken on cryopreservation of isolated fish ovarian follicles at different stages, although the protocols used lead to a compromised viability. The present study investigates the effect of cryoprotectants and cryopreservation on the viability of ovarian tissues of zebrafish (Danio rerio). The effect of permeating cryoprotectants (CPAs) methanol, dimethyl sulfoxide (DMSO), and ethylene glycol (EG) on ovarian tissues were investigated in a series of toxicity tests. Controlled slow cooling of ovarian tissues using 1M and 4M methanol was also carried out. Ovarian tissue viability was assessed by trypan blue (TB) and fluorescence diacetate (FDA)-propidium iodide (PI) tests. In addition, the effect of methanol exposure and cryopreservation on ovarian follicle ATP level, mitochondria, actin and tubulin distribution were also investigated. Results showed that cryoprotectant toxicity to ovarian fragments increased in the order of methanol, DMSO and EG. The results from controlled slow cooling showed that 1M methanol was more effective than 4M methanol although subsequent cryopreservation induced decreases in ATP levels. Immunocytochemistry and actin staining results showed impacts of cryopreservation on mitochondria and cytoskeleton proteins distribution.     

Steric and Electronic Effects on the Configurational Stability of Residual Chiral Phosphorus‐Centered Three‐Bladed Propellers: Tris‐aryl Phosphanes

A series of tris‐aryl phosphanes, structurally designed to exist as residual enantiomers or diastereoisomers, bearing substituents differing in size and electronic properties on the aryl rings, were synthesized and characterized. Their electronic properties were evaluated on the basis of their electrochemical oxidation potential determined by voltammetry. The configurational stability of residual phosphanes, evaluated by dynamic HPLC on a chiral stationary phase or/and by dynamic ¹H and ³¹P NMR spectroscopy, was found to be rather modest (barriers of about 18–20 kcal mol^?1), much lower than that shown by the corresponding phosphane oxides (barriers of about 25–29 kcal mol^?1). For the first time, the residual antipodes of a tris‐aryl phosphane were isolated in enantiopure state and the absolute configuration assigned to them by single‐crystal anomalous X‐ray diffraction analysis. In this case, the racemization barrier could be calculated also by CD signal decay kinetics. A detailed computational investigation was carried out to clarify the helix reversal mechanism. Calculations indicated that the low configurational stability of tris‐aryl phosphanes can be attributed to an unexpectedly easy phosphorus pyramidal inversion which, depending upon the substituents present on the blades, can occur even on the most stable of the four conformers constituting a single residual stereoisomer.     

Internal quality control as a tool for planning a robustness study regarding a multiresidue method for pesticides found in olive oil

The implementation of the internal quality assurance program allows for demonstration of the performance characteristics of a method, as well as the avoidance of erroneous results. There is increasing concern in testing laboratories to ensure that the analytical process remains stable, giving reliable results under statistical control. Robustness is tested by introducing variations in experimental conditions and examining the effects on the results. The European document SANCO/12495/2011, “Method validation and quality control procedures for pesticide residue analysis in food and feed”, defines robustness as a parameter that can be derived from ongoing method verification. Internal quality control tools, such as the recovery control chart, were employed in this study to enhance the stability of the recovery rates and to investigate the experimental conditions that have a major influence on the quantification of recovery rates. The method investigated in this study permitted us to investigate eighteen pesticides in olive oil by using a gas chromatography–mass spectrometry technique. This method has been accredited to ISO/IEC 17025:2005 standards and was applied for 1 year in routine conditions for pesticide residues at the Italian National Reference Laboratory. The recovery control chart has showed that all recovery rates for 1 year were close to the maximum limit (120 %) of recovery performance criteria. Consequently, a “positive” bias has affected all data over longer periods of time. A robustness test was planned in order to investigate the grounds that most influenced the variability of the results. The robustness test involved the following three parameters: solvent used to dissolve the final extract, internal standards, and type of olive oil.