Bounds on the inverses of nonnegative triangular matrices with monotonicity properties

Some bounds on the entries and on the norm of the inverse of triangular matrices with nonnegative and monotone entries are found. All the results are obtained by exploiting the properties of the fundamental matrix of the recurrence relation which generates the sequence of the entries of the inverse matrix. One of the results generalizes a theorem contained in a recent article of one of the authors about Toeplitz matrices.     

Coordination properties of 6-deoxy-6-[1-(2-amino) ethylamino]-β-cyclodextrin and the ability of its copper(II) complex to recognize and separate amino acid enantiomeric pairs

The functionalized cyclodextrin 6-deoxy-6-[1-(2-amino)ethylamino]--cyclodextrin was synthesized, and an NMR, EPR, pH-metric, and calorimetric investigation was carried out in aqueous solution in order to ascertain its behaviour towards protonation and copper(II) complex formation. The thermodynamic parameters of the ternary complex formation with alanine, phenylalanine and tryptophan enantiomeric pairs were also determined (25° C andI=0.1 mol dm^–3). No thermodynamic enantioselectivity was observed in these systems, while a chiral, though poor, discrimination was observed in LEC: c.d. spectra also show enantiomeric stereoselectivity. The results of the present investigation, compared with previously reported results, suggest the occurence of acis-complex trans-complex equilibrium in such systems.     

Thermodynamics of Dipeptides in Water. Influence of the hydrophobic forces of the side-chains on the dissociation processes for some series of dipeptides

A calorimetric study has been carried out on the dissociation processes in water of both the free α-amino group belonging to the amino terminal residue and the free α-carboxyl groups belonging to the carboxyl terminal residue for a series having phenylalanine as the first common term. These thermodynamic quantities have been compared with those of the proton dissociation processes related to the same groups of the corresponding singleα-amino acids. The dissociation process values of this series have also been considered in connection with those obtained from others series of dipeptides previously studied, in an effort to compare the alkyl groups and benzene ring hydrophobic effects on the salvation processes of the zwitterions, undissociated molecules and ionic forms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal denaturation of bovine serum albumin and its oligomers and derivativespH dependence

In a previous paper, we report a preliminary DSC study on bovine (BSA) and human (HSA) serum albumins. However, at accurate HPLC analysis the commercial proteins show three peaks: Fraction V-I, probably globulins (as declared by the producers), Fraction V-II (about 15–18% of the product) and Fraction V-III that represents pure BSA or HSA. A hypothesis is that the Fraction II is a covalent dimer, or trimer or a mixture of both, generated during the scalf-life of the commercial product. Denaturation enthalpies of the purified Fraction V-III and Fraction V-II of BSA, have been determined calorimetrically, at changing thepH, and the results of both compared with those obtained on the untreated protein. Few calorimetric experiments have been also carried on a BSA monomer derivative with sulphidril group protected. Computer program have been developed for the deconvolution of exo- and endothermic effects and for the analysis of thermal denaturation profiles.     

Significance of Non-isothermal Kinetic Data. A statistical study

Arrhenius parameters values, in non-isothermal kinetic vaporisation processes for a series of compounds with related structures, have been calculated. This was made using a method of calculation that allows to find the most probable vaporisation mechanisms. According to this method DTG curves were compared with some theoretical ones reported in literature, whose shape results to be only a function of the mechanisms. In this way the choice of the mathematical functions which can be inserted in the kinetic equations, was influenced by the shape of the DTG plots and other thermal analysis signals thus allowing to choose the most probable mechanisms. The kinetic parameters derived from these mechanisms were compared, using statistical analysis, with those obtained from another method of calculation based on ‘a priori’ vaporisation mechanism chosen for the investigated liquid–gas transition. The standard deviations of the slope and of the intercept, together with the standard deviation and the square correlation coefficient (r ²) of the linear regression equations related to the mechanisms of the two methods were calculated. Student t-test, Fisher F-test, confidence intervals (c.i.) and residuals valueswere also given. Statistical analysis shows that the mechanisms obtained with the former method (diffusive and geometrical models) and the related Arrhenius parameters result to be more significant (in terms of probability) than the corresponding quantities of the latter for which a first-order model was chosen. This revised version was published online in August 2006 with corrections to the Cover Date.     

Standard molar enthalpies and entropies of vaporization for twolow-melting trichlorophenoxy herbicides

The standard sublimation enthalpies of (2,4,5-trichlorophenoxy)acetonitrile and (2,4,5-trichlorophenoxy)aniline were determined by isothermal thermogravimetry using the Langmuir equation and by non-isothermal differential scanning calorimetry for comparison. The used procedure was previously tested using three reference compounds: benzoic acid, succinic acid and salicylic acid. The results compared to those reported in literature show an excellent agreement for two of the three compounds while the third agrees quite well. For (2,4,5-trichlorophenoxy)acetonitrile and (2,4,5-trichlorophenoxy)aniline, the extrapolation of data at 298.15 K were obtained, respectively: Δ_subH°(298 K)={(106±4) and (101±4)} kJ mol^–1. From Clausius Clapeyron equation obtained after the determination of the vaporization constant α′, the following standard sublimation entropies for (2,4,5-trichlorophenoxy)acetonitrile and (2,4,5-trichlorophenoxy)aniline equal to Δ_subS°(298 K)=(251 and 237) J K^–1 mol^–1, respectively, were derived, with an error of ±4 J K^–1 mol^–1 equal for the studied herbicides.     

Effect of Mo–Fe substitution on glass forming ability and thermal stability of Fe–C–B–Mo–Cr–W bulk amorphous alloys

Amorphous Fe_67?xC₁₀B₉Mo_7+xCr₄W₃ (x = 1–7 at.%) plates with 0.64 mm thickness were prepared by copper mold casting. The thermal properties and microstructural development during heat treatments were investigated by a combination of differential scanning calorimetry, differential thermal analysis, and X-ray diffraction. The glass forming ability (GFA) and activation energy for crystallization have a distinct dependence on Mo content. Fe₆₂C₁₀B₉Mo₁₂Cr₄W₃ was the best glass former in this study, demonstrating a supercooled liquid region, ΔT_x = 51 K, and an activation energy for crystallization, Q = 453 kJ/mol. The GFA of alloys in this system was governed by elastic strain optimization resulting directly from the variation in Mo content. Heat treatments were performed to demonstrate resistance to crystallization under typical processing conditions. Alloys in this system exhibited a three phased evolution during crystallization. A second set of heat treatments was performed to identify each phase. An analysis of phase evolution revealed a distinct dependence of phase evolution with stepwise substitution of Mo for Fe in this system.     

Spectroscopic studies of trimetoxypropylsilane and bis(trimethoxysilyl)ethane sol-gel coatings on aluminum and copper

Trimethoxypropylsilane (TMPS) and bis(trimethoxysilyl)ethane (BTMSE) were used as surface modifiers of metal vie the sol-gel process and dip coating. In addition to the single coating of Al, Cu and Sn, double treatments of Al were also conducted by combining coatings with these sol-gels in different sequences. Reflection and absorption infrared spectroscopy (RAIR) was employed to characterize and to trace the proceeding of the sol-gel process of the films. It was found that the silanol condensation occurs in the coating films on Al and the covalent linkage exists between the TMPS film and copper surface. From the assigned vibration modes, two conformers were identified in pure TMPS, TMPS sol-gel and coated film. A series of dip coating experiments with different concentrations of TMPS sol-gel was conducted, and the results from the collected RAIR spectra of the coated samples suggested that the coated Cu consistently has a better RAIR spectrum than that of the coated Al. The TMPS sol-gel appeared to have a better affinity to Cu than to Al. The temperature effect and the aging effect in the coating films were studied. X-ray photoelectronic spectroscopy (XPS) was employed to characterize the coated film, and the XPS data confirm the formation of the siloxane film from the silane coupling agents (SCA). Electrochemical impedance spectra (EIS) have been collected for bare Al and Cu, BTMSE sol-gel coated Al, and TMPS sol-gel coated Cu in 0.15M NaCl solution. The corresponding electronic circuit parameters have been determined to match the experimental EIS data.     

Synergistic Strategies in Aminocatalysis

Synergistic catalysis offers the unique possibility of simultaneous activation of both the nucleophile and the electrophile in a reaction. A requirement for this strategy is the stability of the active species towards the reaction conditions and the two concerted catalytic cycles. Since the beginning of the century, aminocatalysis has been established as a platform for the stereoselective activation of carbonyl compounds through HOMO-raising or LUMO-lowering. The burgeoning era of aminocatalysis has been driven by a deep understanding of these activation and stereoinduction modes, thanks to the introduction of versatile and privileged chiral amines. The aim of this review is to cover recent developments in synergistic strategies involving aminocatalysis in combination with organo-, metal-, photo-, and electro-catalysis, focusing on the evolution of privileged aminocatalysts architectures.