Determination of the surface characteristics of particulate fillers by inverse gas chromatography at infinite dilution: a critical approach

CaCO3 fillers were investigated by inverse gas chromatography (IGC) to determine the dispersion component of their surface tension as well as their acid-base character. Because of the high energy of the filler surface, it readily adsorbs water, thus the parameters measured by IGC depend on the conditioning temperature, as well as on the measurement conditions. As a consequence, the determined surface characteristics are not material constants; different fillers or the effect of coating can be compared only under standard conditions. The use of the same conditioning and measurement temperature eliminates the effect of measurement time. Under appropriate standard conditions the acid-base characteristics of the filler can be determined reliably. However, the accuracy of the determination and the value of the derived parameters depend very much on the selected approach and on the acid-base constants used for the probe molecules. A critical analysis of the approaches used in the current literature pointed out those that yield the most reasonable and accurate values. The results prove that the surface of CaCO3 is strongly basic in character. Coating significantly reduces basicity. Surprisingly, the filler coated with an amount of stearic acid resulting in minimum surface tension showed relatively strong acidity, which indicates a coating exceeding monolayer coverage and/or the uneven distribution of the surfactant on the surface.     

Conversions of Nitroalkyl to Carbonyl Groups in Carbohydrates

Summary.  Since the development of the Sowden methodology in the middle of the twentieth century, several other efficient and complementary methods for the transformation of sugar nitromethyl groups to aldehyde functionalities in their free, hemiacetal, or otherwise derivatized forms have been developed. Hydrogen peroxide oxidation as well as ozonolysis of 1-deoxyalditol-1-nitronates in aqueous solution provide free aldoses, thus presenting alternatives to the well-known Nef reaction. When applied to 2,5- or 2,6-anhydro-1-deoxy-1-nitroalditols, also known also as glycosylnitromethanes, the Nef reaction fails, and the hydrogen peroxide oxidation overoxidizes the expected products to 2,5- or 2,6-anhydroaldonic acids. On the other hand, the ozonolysis of such compounds under pH-controlled conditions results in up to 85% of the interesting glycosylformaldehydes. The Nef reaction carried out in anhydrous low alcohols, however, has revealed a new conversion of glycosylnitromethanes to glycosylmethanal dialkyl acetals, even more interesting C-glycoside synthons. A similar acid-catalyzed methanolysis of 1-deoxyalditol-1-nitronates leads to methyl furanosides. Finally, a treatment of per-O-substituted glycosylnitromethanes with tributyltin hydride in boiling benzene causes their radical reduction under a nearly quantitative formation of glycosylmethanal oximes. Received November 12, 2001. Accepted November 20, 2001     

The physicochemical and biological properties of zinc(II) complexes

Spectroscopic (IR), thermoanalytical (TG/DTG, DTA) and biological methods were applied to investigate physicochemical and biological properties of seven zinc(II) complex compounds of the following formula Zn(HCOO)₂·2H₂O (I), Zn(HCOO)₂·tph (II), Zn(CH₃COO)₂·2H₂O (III), Zn(CH₃COO)₂·tph (IV), Zn(CH₃COO)₂·2phen (V), Zn(CH₃CH₂COO)₂·2H₂O (VI), Zn(CH₃CH₂CH₂COO)₂·2H₂O (VII), where tph=theophylline, phen=phenazone. The formation of various intermediates during thermal decomposition suggests the dependence on the length of aliphatic carboxylic chain and type of N-donor ligand (tph, phen). The final product of the thermal decomposition was ZnO. The antimicrobial activity of these complexes were tested against G⁺ and G^– bacteria. Strong inhibitive effect was observed towards E. coli, salmonellae and Staph. aureus.     

Novel strategies for isolation and characterization of cyclotides: the discovery of bioactive macrocyclic plant polypeptides in the Violaceae

This review focuses on the discovery of cyclotides in the Violaceae, their isolation and their anti-cancer effects. These macrocyclic plant peptides consist of about 30 amino acids, including three conserved disulfide bonds in a cystine knotted arrangement, which renders them a remarkable stability. Their unique structure, combined with a wide array of biological activities, makes them of great interest as possible leads in drug development or as carriers of grafted peptide sequences. Here we describe the work conducted in our laboratory, which started with the overall aim of identifying peptides and small proteins of the size 10-50 amino acid residues in plants with novel chemical structures and biological profiles with a potential for drug development or for use as pharmacological tools. Thus we developed a fractionation protocol to directly address major challenges encountered when dealing with plant material, such as removal of chlorophyll, polyphenols, and low molecular compounds omnipresent in plants. Using this protocol, we then discovered a suite of cyclotides, the varv peptides, from the plant Viola arvensis (Violaceae). Following this, separation methods directly targeting cyclotides were developed, e.g. by adsorption, ion exchange chromatography and solvent-solvent partitioning, which then were used in the isolation of additional cyclotides. To structurally examine cyclotides we have also developed methods based on mass spectrometry for cyclotide sequencing and mapping of disulfide bonds. Finally, to assess structure-activity relationships, regarding their anti-cancer and cytotoxic effects that we focus upon, we have also characterized the three dimensional structure of cyclotides by homology modeling techniques.     

Total synthesis of alternariol

Total synthesis of alternariol, a toxic secondary metabolite of various Alternaria fungi, was achieved in seven steps starting with orcinol and 3,5-dimethoxybromobenzene. The longest linear sequence consists of six steps. Key reaction is a palladium-catalyzed Suzuki-type coupling of an orcinol-derived boronic acid with a brominated resorcylic aldehyde. The final demethylation furnished alternariol in 73% yield containing a smaller fraction of alternariol 9-methyl ether (approximately 20%).     

Mössbauer spectroscopy of iron /II/ formates

Fe/OOCH/₂.2HCOOH obtained by solvolytic reaction of FeCl₂.4H₂O in formic acid was studied by Mössbauer spectroscopy. It displays two quadrupole doublets. Upon air contact it easily transforms to a high-spin octahedral iron/III/ complex, whereas Fe/OOCH/₂.2H₂O undergoes a very slow oxidation. The formate complex coordinated with pyridine could not be prepared, instead we obtained the anhydrous phase Fe/OOCH/₂.     

Electrodeposition of a nickel-based hydrotalcite on Pt nanoparticles for ethanol and glucose sensing

Two different substrates, GC and graphite electrodes, have been coated with electrodeposited Pt nanoparticles (PtNPs) of different morphologies and sizes (from 2 μm to 20 nm). The electrochemical behavior of the platinised GC electrodes has been mainly evaluated in terms of the increase of the real surface area. A nickel-based hydrotalcite-like compound (HT) has been electrosynthesised on the GC platinised electrodes, by the cathodic reduction of a 0.03 M Ni and Al nitrates solution, and the cyclic voltammetric responses to these electrodes have been measured in a 0.1 M NaOH solution. Finally, the electrocatalytic performances of the GC–PtNPs–HT electrodes to ethanol and glucose have been investigated and compared with the performances of HT electrodeposited onto bare Pt, in the same conditions.     

The photoenol tautomer of 5-methyl-1, 4-naphthoquinone

Irradiation of pale yellow 5-methyl-1, 4-naphthoquinone ( 1 , Scheme 1) yields the blue photoenol 4-hydroxy-5-methylidene-1(5H)-naphthalenone (2) which is stable at 77 K. At room temperature the enol retautomerizes to starting material, the reaction rate being strongly dependent on the hydrogen-bond-acceptor basicity of the solvent. The enol is trapped in the presence of acid by protonation at the remaining carbonyl oxygen atom and subsequent electrophilic reaction of the exocylclic methylene group.     

Decomposition of alkyl-substituted urea molecules at a hydroxide-bridged dinickel center

The interactions between N-methylurea, N,N'-dimethylurea, N,N-dimethylurea, tetramethylurea, and thiourea and the hydroxide-bridged dinickel complex [Ni(2)(mu-OH)(mu-H2O)(bdptz)(H2O2](OTs)(3) were investigated. Structural characterization of [Ni(2)(mu-OH)(mu-H2O)(bdptz)(Me-urea)(CH3CN)](ClO4)(3) (1) and [Ni(2)(mu-OH)(mu-H2O)(bdptz)(thiourea)(CH3CN)](ClO4)(3) (2) provided insight into the interactions of the substrates with the dinickel center. In 1, the methylurea molecule coordinates to the dinickel complex through its carbonyl oxygen atom. Complex 2 has a similar geometry, with the thiourea molecule bound to a nickel ion through its sulfur atom. When the urea substrates are heated in the presence of the hydroxide-bridged dinickel complex, N-methylurea and N,N-dimethylurea react to form methylammonium cyanate and dimethylammonium cyanate, respectively. After long reaction times, thiourea reacts similarly, producing ammonium thiocyanate. The other substrates are unreactive. These results indicate that the dinickel complex promotes the elimination of alkylamines from urea substrates to form cyanate but cannot effect the direct hydrolysis of such substrates.     

Sn-containing liquid crystalline side group homopolymers with two glass transitions

Three homologous tin-containing homopolymers with a terminal CN-dipole in the side group have been synthesized and characterized by dynamical calorimetry, polarization microscopy, X-ray and dielectric methods. AFM was used to evaluate the texture at room temperature. Four different phase transitions were detected by DSC. The high temperature phases were identified by polarization microscopy as SmA and SmC. AFM-measurements show focal-conic domains at room temperature and confirm so the smectic nature of all phases. X-ray measurements on nonoriented samples give hints to a phase segregation on nanometer scale. Dielectric investigation and temperature-modulated DSC (TMDSC) confirm clearly phase separation by appearance of two glass transitions related to the liquid order of the main chains and the liquid crystalline of the side groups.