The design of molecular sensing interfaces with lipid-bilayer assemblies

We describe the current status of techniques for preparing planar lipid bilayers, the fusion of sensory elements and the design of bilayer interfaces for analytical applications. Advances in bilayer fabrication have allowed preparation of lipid bilayers with membrane resistance of >1 GΩ (“gigaseal”) in flow, microfluidic and array formats, which have enabled single-channel and multi-channel recording. Not only biological but also engineered channels have been adopted as sensory elements for lipid-bilayer-based biosensors. Synthetic and inorganic channels are also emerging for designing membranes for lipid-bilayer sensors. We discuss the potential of lipid bilayers containing biological, engineered or synthetic channels for the design of biosensors, including drug-screening biosensors.     

Solid-stabilized emulsions

The comprehension of bulk properties of solid-stabilized emulsions (stability, compressibility, elasticity) in relation with interfacial properties has progressed. The association of oil, water and particles allows a large set of materials to be obtained, where emulsions are used either as intermediate or end products. The efficiency of some stimulus-responsive particles to stabilize or destabilize emulsions “on demand” has been experimentally evidenced.     

Reminiscences and lessons on the occasion of a silver jubilee

This paper, written to commemorate the publication of Walsh's classical paper on the potentialities of atomic absorption spectroscopy (AAS) 25 years ago, contains nothing new. It is a personal recollection of the work done independently at our laboratory prior to 1955 which resulted in the construction of a “negative filter” (for use in atomic emission spectroscopy) and an “absorption flame photometer.” Some lessons are drawn from the historical development of AAS about the inventing of new analytical methods in general.     

Probably counterfeit in Roman Imperial Age: Pattern recognition helps diagnostic performed with inductive coupled plasma spectrometry and thermogravimetry analysis of a torso and a head of Roman Age marble statue

This work deals with the attempt to classify marbles, coupling chemometry and two different instrumental techniques, such as inductive coupled plasma atomic emission spectroscopy (ICP-AES) and thermogravimetry analysis (TGA). Chemometrics have been hyphenated, firstly to obtain variables selection on weight loss vs temperature in TGA and after for unsupervised classification of 22 samples (5 ancient marble and 17 single samples from quarries) obtaining a well recognisable classification. The objects in “test set” are the body and the head of one statue and a Torso Virile statue; the “evaluation set” are two well-known ancient finds; the “training set” is constituted by 17 samples coming from marble assigned to Italian, Greek and Turkish quarries.22 elements (Ca, Si, Na, K, Mg Ti, Al, Fe, Pb, Zn, Sr, Zr, Cu, Mn, Rb, Y) are taken into consideration; with TGA 951 values of mass-residual vs temperature are considered. After selection 8 variables from ICP-AES and 4 from TG compose the matrix.We obtain a separation of Italian marbles cluster from marbles of other countries and recognise the different provenience of the body and head and classify the unknown one. This methodology can be applied to classification study of similar ancient artefacts as pottery, ceramics, glass and stones.Counterfeit, or substitution of parts such as head, legs, and hands was a current practice in the late Roman Age, and also in the Renaissance a lot of statues were “rebuilt” with spare parts, so this word describes an historical restoration practice and not just depreciative.     

“In situ” ESR and UV-visible spectroscopic studies of iron phthalocyanine films deposited on gold electrodes

The electrochemical behaviour of iron phthalocyanine (Fe^IIPc) films, supported on gold substrates, was studied in 3.5 M NaOH solution, using cyclic voltammetry and coupled “in situ” ESR and UV-visible spectroscopic techniques. Two types of electron transfer were observed in the potential range from −0.45 to −1.0 V vs. Hg/HgO. According to the “in situ” spectroscopy investigations, these two processes were assigned respectively to electron transfers involving first the ligand ring, and then the centre iron ion.     

Release of electrolytes from W/O/W double emulsions stabilized by a soluble complex of modified pectin and whey protein isolate

W/O/W double emulsions (DEs) stabilized by charged soluble complexes of whey protein isolate (WPI) and modified pectins were investigated in relation to their stability and the release of two types of electrolytes, NaCl and sodium ascorbate.WPI alone cannot properly stabilize the DEs. The droplet size is relatively large (100 μm) and increases with time. However, addition of modified pectin to form a soluble complex with WPI significantly improved the stability.DEs prepared with two types of oils (medium chain triglycerides (MCT) and R(+)-limonene) were studied by measuring droplet size, creaming, viscosity, and electrolyte release. Irrespective of their very different oil phase nature, both emulsions were stable against coalescence, but R(+)-limonene formed smaller droplets (25 μm) than MCT (35 μm). The electrolyte release rate was significantly higher from the R(+)-limonene that formed DEs with much lower viscosity. R(+)-limonene-DE released 75% of the NaCl after 28 days, while MCT-DE released only 50%. NaCl was released more slowly than sodium ascorbate.Apparently, the release mechanism from R(+)-limonene-DE was found to be “thinning the outer interface and release of the entire inner droplets” while it seems that the release from MCT-DE was slower and “diffusion controlled”.DEs stabilized by WPI/C63 released 12% of the sodium ascorbate after 1 day in milk and remained stable for at least 8 days. However, DEs stabilized with only WPI released about 50% of the sodium ascorbate after 1 day, and phase separated after 8 days.     

A thermodynamic interpretation of the behavior of higher fatty alcohols and acids upon the chromatographic paper

An idea was presented of treating the chromatographed substance as a “solute,” and the chromatographic system, composed of the stationary and the mobile phase as a “solvent.” Moreover the concept of “local equilibrium” was introduced, allowing to regard a given chromatographic spot as a “binary solution.” Thus a possibility arose to apply the classical thermodynamic approach, normally used for binary solutions, and namely: μ_i = μ_i + RT ln x_iƒ_i, where μ_i—chemical potential of the “i”-th compound in the solution, μ_i—chemical potential of the pure “i”-th compound, x_i-molar fraction of the “i”-th compound, ƒ_i—its activity coefficient, in a modified form, suitable for the chromatographic purpose.     

Amine groups functionalized gel-type resin supported Pd catalysts: Physicochemical and catalytic properties in hydrogenation of alkynes

Palladium catalysts (0.125–0.5 wt.% Pd) supported by amine groups—functionalized gel-type resin (FCN) were studied in the hydrogenation of alkynes reagents, 2-butyne-1,4-diol and phenylacetylene. The catalysts were prepared by two routes. The first, “OAc” is based on the immobilization of Pd-precursor in the pre-swollen resin from THF solution of Pd(OAc)₂, followed by chemical reduction of the Pd-centers. This method produces Pd particles of size in nano-scale. The second procedure, “aq” implies the deposition of Pd-species on dry resin beads using aqueous solution of PdCl₂. Reduction of these Pd-species gives relatively large Pd particles, dominating are 30–50 nm in size. The SEM studies performed over the cross-section of catalysts grains showed location of Pd in outer shell of polymer beads in both “OAc” and “aq” catalysts; however, thinner layer of Pd appears in “aq” series catalysts. In the presence of all catalysts, prepared by “OAc” and “aq” methods the selectivity towards alkenes is high, above 90%. The catalysts of “aq’ series are much more active and more selective than “OAc” analogues giving selectivity to alkene ca. 94% at almost complete conversion of alkynes. Moreover, catalytic performance of “aq’ series catalyst is unchanged under recycling use. The catalyst was recovered and reused 4 times, maintaining its catalytic efficiency.     

Preparation of alpha-elastin nanoparticles by gamma irradiation

Nanoparticles were prepared by utilizing the thermosensitive aggregation of alpha-elastin and gamma ray crosslinking. Three different heating process, “Slow heating”, “Fast heating”, and “Heat shock”, were applied for the aggregation of the alpha-elastin and examined to yield nanoparticles by gamma rays crosslinking. As a result, only “Slow heating” process yielded nanoparticles with diameters of about ca. 300 nm above cloud point (CP) and about ca. 100 nm below CP, and a narrow size distribution above 1.0 mg/ml concentration (exclude 1.0 mg/ml).     

On the ionic conductivity and phase transitions in the Li2SO4---Li2WO4 system and their relation to ion transport mechanism

Secco et al. have performed several measurements of ionic conductivity, which they have considered as “convincing evidence” that the “paddle-wheel” mechanism does not contribute significantly to ion conductivity in Li₂SO₄-based compositions. However, a comparison of their results in the high-conductivity range with those of other investigators suggests that their data are artifacts. The cause of this is that the resistance of their sulfate-rich samples is about 0.1 ohm at high temperatures. Thus, their results are reliable only for “normal,” i.e., low, conductivities. It is briefly summarized why the “paddle-wheel” mechanism for ion transport is superior to a percolation-type mechanism for a few high-conducting phases.     

Supramolecular edifices and switches based on metals

Our studies allowed to unravel at least partially, the “so-called” spontaneous self-assembly processes of supramolecular edifices based on metals. The formation of a tricuprous double-stranded helix in solution was found to be driven by thermodynamics via highly distorted intermediates. Dinuclear europium(III) triple-stranded helices were built in solution via alternative “braiding” and “keystone” mechanism. The overall process was also dominated by thermodynamics. Moreover, multipodal ligand with the appropriate binding sites can operate as Cu(II)/Cu(I) molecular switches. Recently, we examined ligands with neighboring binding functionalities (N,N) and (N,O) which confer to the corresponding divalent metal complexes new properties. They could operate as proton-driven multistage molecular switching devices based on region-selective metal binding.     

Investigation of the interactions between ginsenosides and amino acids by mass spectrometry and theoretical chemistry

In order to evaluate the essence of the interactions of ginsenosides and proteins which are composed by α-amino acids, electrospray ionization mass spectrometry was employed to study the noncovalent interactions between ginsenosides (Rb₂, Rb₃, Re, Rg₁ and Rh₁) and 18 kinds of α-amino acids (Asp, Glu, Asn, Phe, Gln, Thr, Ser, Met, Trp, Val, Gly, Ile, Ala, Leu, Pro, His, Lys and Arg). The 1:1 and 2:1 noncovalent complexes of ginsenosides and amino acids were observed in the mass spectra. The dissociation constants for the noncovalent complexes were directly calculated based on peak intensities of ginsenosides and the noncovalent complexes in the mass spectra. Based on the dissociation constants, it can be concluded that the acidic and the basic amino acids, Asp, Glu, Lys and Arg, bound to ginsenosides more strongly than other amino acids. The experimental results were verified by theoretical calculations of parameters of noncovalent interaction between ginsenoside Re and Arg which served as a representative example. Two kinds of binding forms, “head–tail” (“H–T”) and “head–head” (“H–H”), were proposed to explain the interaction between ginsenosides and amino acids. And the interaction in “H–T” form was stronger than that in “H–H” form.     

Conventional and unconventional infrared spectrometry and their quantitative interpretation

In condensed matter, optical properties can be described by a dielectric function (DF), and the structures observed in spectra are then related to the poles and zeros of the DF. As an example, model functions are calculated by a fit to measured spectroscopic data for polystyrene and silica. The first material shows weak, narrow bands and the latter strong, broad bands and a negative real part of the DF.Based on these model DFs, spectra are simulated which are expected to be obtained by “conventional” methods such as transmittance or reflectance measurements, or by “unconventional” methods such as reflectance at oblique incidence, diffuse reflectance, photoacoustic spectroscopy and attenuated total reflectance. A variety of simulated, typical spectra are plotted as a small “atlas”. Conditions are discussed that allow a straightforward procedure for interpreting the spectra quantitatively, i.e., the evaluation of the resonance frequency and the concentration of the oscillators under consideration.It is shown that for systems characterized by weak, narrow oscillator lines, mostly an intuitive interpretation is possible, looking only at the position and strength of “lines” in the spectra. Materials showing strong polar vibrations, however, require more sophisticated procedures for interpreting the spectra.     

Prebiotic chemistry: A fuzzy field

If prebiotic chemistry is defined as the study of the chemical steps, which lead to the first organisms, a clear-cut definition of “living organism” is needed. Unfortunately, no unambiguous and universally accepted definition exists for the concept “living”. Under these conditions, fuzzy logic is probably the methodological tool that can best be used to handle questions pertaining to “the origin of life”. A conventional scale must, however, be defined which interestingly enough, depends necessarily on our present-day scientific knowledge.     

Reply to “Comments on the paper entitled ‘The formulation and modelling of the anodic dissolution of zinc through adsorbed intermediates’ ” by C. Cachet et al.

The points raised in the paper entitled “Comments on the paper entitled ‘The formulation and modelling of the anodic dissolution of zinc through adsorbed intermediates”’ have been discussed. It has been shown that, in contrast to the statements in the “Comments”, most of the papers concerning the reaction schemes suggested for the interpretation of the dissolution or deposition of metals, which were considered as a support for the opinion of the Authors of the “Comments”, support the views expressed in our original paper [J. Electroanal. Chem. 583 (2005) 148]. On the other hand, it has been stressed again that the criticism expressed in the original paper refers to dubious conclusions drawn on the basis of transient measurements.     

A novel fragmentation-cyclization reaction of steroidal α-hydroxy oximes

By a novel “one pot” fragmentation-cyclization reaction 17β-hydroxy-17α-substituted-16-oximino derivatives in the androstane and estrane series were converted to a new type of D-homo derivative.     

Evaluation of fresh and old eluate of <Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generators used for labeling of different pharmaceutical kits

Summary Sixty ⁹⁹Mo/^99mTc wet column generators, loaded with two different ⁹⁹Mo activities, were analyzed in order to assess the quality of their eluates. Each elution was used for labeling of different radiopharmaceuticals, in order to evaluate whether “risky” elutions, namely those performed just after generator delivery and at 72 hours or more from the last elution, could be conveniently employed when fresh available radioactivity is not enough for the planned labeling or when shipping problems arise, or delay in delivery of a new generator occurs. Radiochemical quality control of all radiopharmaceuticals labeled with these elutions was performed. The elutions differed mainly in ⁹⁹Tc ground state (^99gTc) and amounts of oxidizing impurities. Radiolabeling procedures, however, were not affected, suggesting that these “risky” elutions might be appropriately used, in “emergency” conditions, for labeling radiopharmaceuticals although their radiochemical purity control is recommended prior to patient administration.     

Iron-modified mesoporous SBA-15 silica: Preparation and characterization studies

Fe-SBA-15 materials with different Si/Fe ratios (Si/Fe = 100, 60, 15) have been synthesized by hydrothermal method and characterized by several spectroscopic techniques. Electron spin resonance and Mössbauer spectroscopy, along with electron microscopy and X-ray diffraction, allowed differentiation of several iron species. These species correspond to hematite particles, very small “isolated” or oligomeric Fe^III species possibly incorporated in the mesoporous silica wall, and Fe^III oxide clusters either isolated or agglomerated, forming “rafts” at the surface of the silica and exhibiting ferromagnetic ordering. Because of their agglomeration, these clusters appear with a two-peak size distribution, with one peak corresponding to the isolated clusters formed in the mesopores and still embedded in them and the other corresponding to the agglomerates spread on the surface of the mesoporous silica particles.     

An infrared spectroscopic study of hydrogen bonding in ethyl phenol: A model system for polymer phenolics

A detailed analysis of the bands appearing in the OH stretching region of the infrared spectrum of ethyl phenol solutions is presented. In cyclohexane solutions, the band due to “free” (non-hydrogen-bonded groups) contains overlapping contributions from both monomeric and end-group species. Other assignments are made on the basis of whether the proton and oxygen in a particular OH group are both involved in hydrogen bonds (as “donors” and “acceptors”, respectively), or if only the proton is acting as a donor. The strongest band in the spectra obtained at the highest concentration of ethyl phenol is due to OH groups present in linear chains of hydrogen-bonded OH groups (as recognized in numerous other studies), but a band due to cyclic trimers has also been identified. The assignment of other modes is more uncertain and various possibilities are discussed. In toluene solutions, assignments are more complicated, because bands due to OH–π hydrogen bonds are observed instead of free groups. Finally, the data from cyclohexane solutions was used to calculate equilibrium constants capable of describing the distribution of species present. A new methodology for determining the equilibrium constant describing association in the form of dimers is described.     

Adsorption of NOM onto Activated Carbon: Effect of Surface Charge, Ionic Strength, and Pore Volume Distribution

Adsorption of natural organic matter (NOM) onto seven activated carbons with a wide range of surface properties was studied at high and low ionic strength over a range of pH values. From adsorption isotherm studies it was found that, for six of seven carbons, at low surface concentrations, increased ionic strength decreased NOM adsorption. As the surface concentration increased, the adsorption isotherms converged and intersected, after which the addition of salt resulted in increased adsorption. This “crossover point” marked a change in the adsorption mechanism from the “screening reduced” to the “screening enhanced” adsorption regimes. The adsorption mechanisms are extremely complicated and appear attributable to various factors, including electrostatic forces, pore volume distribution, and chemical interactions between the NOM and the surface functionalities on the carbon surfaces.