Synthesis and properties of Hg-based high-T c superconductors

Il Nuovo Cimento D - The formation of Hg-based HTSC materials was investigated through the development of non-conventional techniques. The former was based on a singlestep synthesis at temperatures...     

Determination of ionizable groups of proteins by potentiometric titration in concentrated solutions of guanidine hydrochloride

A linearization method based on modified Gran functions, and a general nonlinear regression program were used to study potentiometric titration curves of denatured ovalbumin and lysozyme in 6 mol L^–1 guanidine hydrochloride medium with the aim of determining the ionizable species. With both numerical techniques it was possible to determine the sum of the carboxylic groups, the imidazol, the α-amine, and the sum of ɛ-amine, phenolic and sulfhydryl groups, if the protein is completely denatured, and assumes a randomly coiled conformation. A total of 87.8 ± 2.5 and 20.7 ± 0.6 groups per mol were determined in the ovalbumin and lysozyme, respectively. These values are very close to the 88 and 21 groups expected by aminoacid composition of both proteins, indicating that all ionizable groups were exposed to the solvent. For ovalbumin the distribution of groups was very similar to that expected by the aminoacid composition, but for lysozyme some anomalies were observed, suggesting the existence of interactions between ionizable groups, altering the dissociation constants. Received: 9 December 1996 / Revised: 27 February 1997 / Accepted: 4 March 1997     

Phase stability study of the pseudobinary system Gd2O2CO3–Nd2O2CO3 (420 °C ≤ T ≤ 850 °C, P = 1 atm. CO2)

Hexagonal as well as tetragonal rare earth oxycarbonates can act as hosts for optically active ions; hence, the knowledge of the structural modifications occurring when foreign hosts are inserted into the parent compound is of fundamental importance for the design of new phosphors. In this article, a phase stability study of the pseudobinary system Gd₂O₂CO₃–Nd₂O₂CO₃ at P = 1 atm. CO₂ between 420 and 850 °C is presented, to study the amplitude of the existence fields of the different structures typical of rare earth oxycarbonates. The samples were prepared by thermal decomposition of the corresponding oxalates in CO₂ atmosphere. According to composition and temperature, all the three structural forms reported for oxycarbonates (hexagonal, tetragonal, and monoclinic) have been observed. Above a certain temperature, that depends on composition and increases with Nd amount, all the samples decompose into the corresponding Gd–Nd-mixed oxides and crystallize into one of the three possible structural forms typical of rare earth sesquioxides. Structural refinements performed on the hexagonal oxycarbonates demonstrate that the insertion of Nd³⁺ in Gd₂O₂CO₃ results in a linear increase of the lattice parameters (Vegard’s law) and in a reorganization of the distances between and in the CO ₃ ^2? groups and the (Nd/Gd₂O₂)²⁺ layers.     

Spectrophotometric determination of phenylephrine hydrochloride in pharmaceuticals by flow injection analysis exploiting the reaction with potassium ferricyanide and 4-aminoantipyrine

This paper presents a method for the determination of phenylephrine hydrochloride in pharmaceuticals by spectrophotometric flow injection analysis exploiting the reaction with potassium ferricyanide and 4-aminoantipyrine, which leads to the formation of a condensation product with strong absorptivity at 500 nm. The linear dynamic range was between 0.95 and 9 mg/L, with a limit of detection of 0.2 mg/L and a sampling throughput of 120 samples per hour. The method was applied to eyewashes and nasal decongestant liquid medicines.     

Preparation of oriented thick HTSC films by cryoelectrophoretic technique

Il Nuovo Cimento D - A new technique, specifically designed for the preparation of preferentially oriented HTSC (YBCO and BSCCO) films on metallic substrates has been developed. The method, named...     

Controlling chiral organization of molecular rods on Au(111) by molecular design

Chiral self-assembled structures formed from organic molecules adsorbed on surfaces have been the subject of intense investigation in the recent decade, owing both to relevance in applications such as enantiospecific heterogeneous catalysis or chiral separation as well as to fundamental interest, for example, in relation to the origin of biomolecular homochirality. A central target is rational design of molecular building blocks allowing transfer of chirality from the molecular to the supramolecular level. We previously studied the surface self-assembly of a class of linear compounds based on an oligo(phenylene ethynylene) backbone, which were shown to form a characteristic windmill adsorption pattern on the Au(111) surface. However, since these prochiral compounds were intrinsically achiral, domains with oppositely oriented windmill motifs and related conformational surface enantiomers were always realized in equal proportion. Here we report on the enantioselective, high yield chemical synthesis of a structurally related but intrinsically chiral compound in which two peripheral tert-butyl substituents are replaced by sec-butyl groups, each containing an (S) chiral center. Using scanning tunneling microscopy under ultrahigh vacuum conditions, we characterize the adsorption structures formed from this compound on the Au(111) surface. The perturbation introduced by the modified molecular design is found to be sufficiently small so structures form that are closely analogous to those observed for the original tert-butyl substituted compound. However, as demonstrated from careful statistical analysis of high-resolution STM images, the introduction of the two chiral (S)-sec-butyl substituents leads to a strong preference for windmill motifs with one orientation, demonstrating control of the chiral organization of the molecular backbones through rational molecular design.     

Chiral induction by seeding surface assemblies of chiral switches

It is demonstrated by scanning tunneling microscopy that coadsorption of a molecular chiral switch with a complementary, intrinsically chiral induction seed on the Au(111) surface leads to the formation of globally homochiral molecular assemblies.     

Study of the formation temperature of mixed LaREO<Subscript>3</Subscript> (RE ≡ Dy,Ho, Er,Tm, Yb,Lu) and NdGdO<Subscript>3</Subscript> oxides

Mixed LaREO₃ (RE ≡ Dy, Ho, Er, Tm, Yb, Lu) and NdGdO₃ oxides were prepared by thermal decomposition of the corresponding co-precipitated mixed oxalates. The decomposition of La/RE and Nd/Gd oxalates was studied by means of differential thermal analysis and thermogravimetric (DTA-TG) measurements; in particular the last step, consisting of the loss of a CO₂ molecule from the corresponding oxycarbonate, has been thoroughly investigated, as it is particularly interesting for the study of the formation temperature of mixed rare earth oxides. After the release of CO₂, the oxides crystallize in a distorted perovskitic cell or one of the structures typical of rare earth sesquioxides, depending on the cationic size difference and on the average cationic radius. The mixed rare earth oxycarbonate decomposition has been studied in comparison to the decomposition of single rare earth oxycarbonates. A trend of the mixed oxides formation temperature as a function both of the average cationic size and of the cationic sizes difference has been observed and compared to the behaviour of single rare earth oxides.     

Biosystem response to soft-X-rays irradiation: non-monotonic effects in the relevant biological parameters of yeast cells

Summary Soft-X-rays irradiation of yeast cells allows selective interference with different cellular structures. The monitoring of different physical parameters leads to substantial variations in the response to X-rays showing that monotonicity should not be taken for granted. Also at INFM (Istituto Nazionale di Fisica della Materia).     

Development of a sequential injection anodic stripping voltammetry (SI-ASV) method for determination of Cd(II), Pb(II) and Cu(II) in wastewater samples from coatings industry

This paper describes the development and validation of a sequential injection (SI) anodic stripping voltammetry (ASV) method using the hanging mercury drop electrode for accumulation of the heavy metal cations Cu(II), Pb(II) and Cd(II). The method was applied to wastewater samples after proper acid digestion in open vessels to eliminate matrix effects. For a deposition time of 90 s at the flow rate of 10 μl s⁻¹, the detection limits of the method were 0.06, 0.09 and 0.16 μmol L⁻¹ for Cd, Pb and Cu, respectively. Under these conditions the linear dynamic range was between 0.20 and 9.0 μmol L⁻¹ and the sampling frequency was 30 analyses per hour. The relative standard deviation of the method was 3%(n=7) at the concentration level of 2.0 μmol L⁻¹. The accuracy of the method was evaluated by spiking the samples with known amounts of the metal cations, and by comparison with an independent analytical technique, the inductively coupled plasma atomic emission spectroscopy (ICP-AES). Average recoveries were around of 84%, and the results showed no evidence of systematic errors in comparison to the ICP-AES.