Polyelectrolyte complex membranes – surface and permeability properties

In order to study, how the membrane hydrophilicity influences the pervaporation (PV) separation properties in dehydration of alcohols, two polyelectrolyte complex (PELC) membranes, based on interfacial reaction of polyanionic sodium salt of sulfoethyl cellulose (SEC) with polycationic poly[dimethyl(diallyl)ammonium chloride] (pDMDAAC), or cationic surfactant benzyl(dodecyl)dimethylammonium chloride (BDDDMAC), were prepared and tested. Contact angle measurements on membrane surfaces made in various media showed that the membrane hydrophilicity, in the sense of water wettability, had not influence neither to flux nor selectivity in the PV dehydration process. On the contrary, the membrane wettability determined by contact angle measurements in the real water/alcohol separation mixture, correlated very well with the PV experiments. These findings are confronted with the solution-diffusion PV model.     

Metrology in chemistry – a public task

 The importance of analytical chemistry is increasing in many public fields, and the demand for reliable measurement results is growing accordingly. A measurement result will be reliable only if its uncertainty has been quantified. This can be achieved only by tracing the result back to a standard realizing the unit in which the measurement result is expressed. The National Metrology Institutes (NMIs) can contribute to the reliability of the measurement results by developing measuring methods, and by providing reference materials and standard measuring devices. In fields in which the comparability of measurement results is of particular importance, they establish traceability structures. Responding to the globalization of trade and industry the International Committee for Weights and Measures (CIPM) agreed on an arrangement on the mutual recognition of calibration certificates (CIPM MRA) issued by the NMIs. Received: 19 April 2000 / Accepted: 28 July 2000     

Bioanalytical chemistry of cytokines – A review

Cytokines are bioactive proteins produced by many different cells of the immune system. Due to their role in different inflammatory disease states and maintaining homeostasis, there is enormous clinical interest in the quantitation of cytokines. The typical standard methods for quantitation of cytokines are immunoassay-based techniques including enzyme-linked immusorbent assays (ELISA) and bead-based immunoassays read by either standard or modified flow cytometers. A review of recent developments in analytical methods for measurements of cytokine proteins is provided. This review briefly covers cytokine biology and the analysis challenges associated with measurement of these biomarker proteins for understanding both health and disease. New techniques applied to immunoassay-based assays are presented along with the uses of aptamers, electrochemistry, mass spectrometry, optical resonator-based methods. Methods used for elucidating the release of cytokines from single cells as well as in vivo collection methods are described.     

Coordination properties of dehydroacetic acid – binary and ternary complexes

Complex formation equilibria of dehydroacetic acid with Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺ and Mn²⁺ and the ternary complexes involving Cu²⁺, dehydroacetic acid and some amino acids containing different functional groups are investigated. Stoichiometry and stability constants for the complexes are estimated at 25°C and 0.1 M ionic strength in 25% dioxane-water mixtures. The concentration distribution diagrams of the complexes were evaluated. The effect of temperature and organic solvent on the acid dissociation constant of dehydroacetic acid and the formation constant of Cu²⁺ complex was studied and thermodynamic parameters calculated.     

Solution and surface properties of amphiphilic drug – nonelectrolyte systems

The surface tension values of amphiphilic drugs amitriptyline hydrochloride (AMT, an antidepressant) and promethazine hydrochloride (PMT, a phenothiazine) solutions in the presence of different fixed concentrations of alcohols (ethanol to octanol) and sugars were measured by the ring detachment method. The results indicated that long-chain alcohols form mixed micelles with both the drugs (as critical micelle concentration, cmc, decreases in their presence). Short-chain alcohols remain in aqueous phase and almost constant cmc values were obtained. Sugars, by increasing the hydrophobic interactions, decrease the drug cmcs. Maximum surface excess concentration at the air/solution interface (Γ_max) decreases for long-chain alcohols and sugars, but remains constant for short-chain alcohols. The minimum area per drug molecule (A _min) follows the opposite trend.     

The physicochemical properties and solubility of pharmaceuticals – Methyl xanthines

The aim of this study was to evaluate the physio-chemical properties and solubility of three pharmaceuticals (Phs): theophylline, 7-(β-hydroxyethyl) theophylline, and theobromine in binary systems in different solvents. The solvents used were water, ethanol, and 1-octanol. Score of the solubility of these substances is being important for their dissolution effect inside the cell, the transportation by body fluids and the penetration possibility of lipid membranes.The Phs were classified to the group of methyl xanthines, which contain purine in their structure. Although they are mainly obtained via chemical synthesis, they can be also found in natural ingredients such as cocoa beans and tea leaves. These drugs are mainly acting on the central nervous system but are also used in the treatment of asthma or blood vessels.Solubility of 7 (β-hydroxyethyl) theophylline and theophylline were tested using synthetic method. In case of theobromine, which solubility is very small in the solvents noted, the spectrophotometric method has been used to measure its solubility. After designating phase diagrams of each of the solubility in the bipolar system, the experimental points have been correlated with the equations: Wilson, NRTL, UNIQUAC. Results show that theophylline and its derivatives show the best solubility from all tested Phs.Another method also used during this study was the differential scanning calorimetry (DSC), which allowed designation of the thermal properties of Phs. The fusion temperature and the enthalpy of melting were measured. Unfortunately, it was not possible to determine the fusion temperature and enthalpy of melting of theobromine, because of the decomposition of Ph at high temperature.The important property tested was the constant acidity, to this end, the spectrophotometric method of Bates–Schwarzenbach was used. Unfortunately, with this method it was not possible to determine the value of pK_a 7-(β-hydroxyethyl) theophylline. For other Phs, these values do not differ significantly from those proposed in the literature.Both awareness and knowledge of values of the drug pK_a and solubility are important in Phs production. This allows the selection of a suitable solvent and allows estimation of the correct dose and its capacity to absorb in human body.     

Phosphorus-fluorine chemistry—XXXVI: Preparation and chemistry of thienyldifluorophosphine

2-Thienyldifluorophosphine has been prepared by chlorine-fluorine exchange in the corresponding dichlorophosphine; the difluorophosphine has been found to undergo redox disproportionation with formation of 2-thienyltetrafluorophosphorane and pentathienylcyclopentaphosphine. Upon reaction with nickel carbonyl, 2-thienyldifluorophosphine forms a tetrasubstituted derivative which may be oxidized by iodine to give tris(thienyldifluorophosphine)nickel(II)iodide. Di- and tri-substituted derivatives of molybdenum carbonyl have been obtained through displacement of the coordinated cycloolefin by the fluorophosphine in bicycloheptadienetetracarbonyl molybdenum and cycloheptatrient-tricarbonyl molybdenum. All compounds were characterized by i.r., n.m.r., and mass spectrometry. A comparison of δ_P values for thienyl-phosphorus compounds with data for the analogous phenyl-phosphorus compounds has shown a high-field shift for the thiophene derivatives in every case. A comparison of δ_F values has shown the opposite effect.     

Intermolecular interactions and electrostatic properties of the β-hydroquinone apohost: implications for supramolecular chemistry

The crystal structure of the β-polymorph of hydroquinone (β-HQ), the apohost of a large family of clathrates, is reported with a specific focus on intermolecular interactions and the electrostatic nature of its cavity. Hirshfeld surface analysis reveals subtle close contacts between two interconnecting HQ networks, and the local packing and related close contacts were examined by breakdown of the fingerprint plot. An experimental multipole model containing anisotropic thermal parameters for hydrogen atoms has been successfully refined against 15(2) K single microcrystal synchrotron X-ray diffraction data. The experimental electron density model has been compared with a theoretical electron density calculated with the molecule embedded in its own crystal field. Hirshfeld charges, interaction energies and the electrostatic potential calculated for both models are qualitatively in good agreement, but small differences in the electrostatic potential persist due to charge transfer from all hydrogen atoms to the oxygen atoms in the theoretical model. The electrostatic potential in the center of the cavity is positive, very shallow and highly symmetric, suggesting that the inclusion of polar molecules in the void will involve a balance between opposing effects. The electric field is by symmetry zero in the center of the cavity, increasing to a value of 0.0185 e/?(2) (0.27 V/?) 1 ? along the 3-fold axis and 0.0105 e/?(2) (0.15 V/?) 1 ? along the perpendicular direction. While these values are substantial in a macroscopic context, they are quite small for a molecular cavity and are not expected to strongly polarize a guest molecule.     

Design of new super-high birefringent isothiocyanato bistolanes – synthesis and properties

We report the synthesis of new laterally ethyl-substituted high birefringent phenylethynyltolane liquid crystals with alkylsulphanyl chain and isothiocyanate terminal group. The thermal and optical properties such as birefringence are measured and discussed based on their molecular structures. The compounds exhibit birefringence (Δn) in the range of 0.63–0.75 and are expected to be excellent components of high birefringent nematic mixtures for various applications.     

Strecker reaction and α-amino nitriles: Recent advances in their chemistry,synthesis, and biological properties

α-Amino nitrile compounds have a profound impact on bio-chemical sciences, as they have been prepared from inexpensive starting materials and have become valuable intermediates in the chemical synthesis of vitally important heterocyclic and carbocyclic molecules, which serve as suitable models in pharmacological and biological research. The α-amino nitrile moiety has been found in the structure of different alkaloids, while the α-amidoacetonitrile group is an essential fragment of new anti-hyperglycemic drugs and promising pharmacological and agrochemical agents. Due to their synthetic, biological and practical importance, this review highlights the recent information about the preparation of α-amino nitriles through the Strecker-type and α-cyanation reactions, their chemical and biological properties, as well as their synthetic application, paying attention on the wonderful capacity for generating novel molecular diversity for pharmacological, biological and agrochemical researches, which ends with the total synthesis of complex alkaloids, preparation of new N-heterocycles and α-aminonitrile-containing drugs. Analyzing modern synthetic protocols for the Strecker-type reactions and cyanation reactions based on cross-dehydrogenative coupling (CDD) process, the advantages and disadvantages of new catalysts and green reaction conditions are also discussed. In addition, remarkable biological properties of α-amidoacetonitrile derivatives as potent and selective protease inhibitors as well as promising pesticidal agents were briefly reviewed. The bibliography includes 461 references.     

Dihydro-1,2-diazetes – the preparative chemistry since 1980

Chemistry of Heterocyclic Compounds - This article reviews the preparative studies regarding syntheses and reactions of the three possible types of dihydro-1,2-diazetes (formerly 1,2-diazetines)...     

Electrical field-induced extraction and separation techniques: Promising trends in analytical chemistry – A review

Sample preparation is an important issue in analytical chemistry, and is often a bottleneck in chemical analysis. So, the major incentive for the recent research has been to attain faster, simpler, less expensive, and more environmentally friendly sample preparation methods. The use of auxiliary energies, such as heat, ultrasound, and microwave, is one of the strategies that have been employed in sample preparation to reach the above purposes. Application of electrical driving force is the current state-of-the-art, which presents new possibilities for simplifying and shortening the sample preparation process as well as enhancing its selectivity. The electrical driving force has scarcely been utilized in comparison with other auxiliary energies. In this review, the different roles of electrical driving force (as a powerful auxiliary energy) in various extraction techniques, including liquid-, solid-, and membrane-based methods, have been taken into consideration. Also, the references have been made available, relevant to the developments in separation techniques and Lab-on-a-Chip (LOC) systems. All aspects of electrical driving force in extraction and separation methods are too specific to be treated in this contribution. However, the main aim of this review is to provide a brief knowledge about the different fields of analytical chemistry, with an emphasis on the latest efforts put into the electrically assisted membrane-based sample preparation systems. The advantages and disadvantages of these approaches as well as the new achievements in these areas have been discussed, which might be helpful for further progress in the future.     

Halide-bridged polymers of divalent metals with donor ligands – structures and properties

Coordination polymers and organic–inorganic hybrid materials represent an area of very active research. Halide-bridged polymers of divalent transition or post-transition metals coordinated to donor ligands are reviewed. The article is organized according to structural features of the compounds: the main sections of chain polymers, crosslinked systems and networks of high metal-halide content are subdivided according to connectivity aspects. Structural trends are highlighted and the correlation between chemical composition and topology on the one hand and derived properties and dynamics on the other hand is discussed.     

Asymmetric azomethine amines with azobenzene moieties – liquid crystalline and optical properties

ABSTRACT

Three asymmetric azomethine-azobenzene intermediates (M1-M3), having internal reactive amine functional group, and both n-butoxy and p-chloro, p-methyl, o-methyl terminal moieties, have been synthesised by reacting asymmetric substituted azobenzene diamines with 4-butoxybenzaldehyde. Their proposed chemical structures were confirmed by FTIR and 2D-NMR spectroscopy. The mesomorphic behaviour was investigated by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and room temperature powder X-ray diffraction techniques. Characteristic textures of smectic A and nematic phases have been observed for samples M1 and M2, while only unsolved texture was revealed for sample M3 at room temperature, showing sharp reflections in the medium-wide angle region. From X-ray diffraction measurements, a layered ordered structure of all compounds was established by analyzing successive scattering vectors ratios (q_i/q₁). The dependence of thermal behaviour on molecular parameters like: interdigitation parameter γ, dipole moment, molecular polarisability, halogen radius, was commented. The UV-Vis spectral investigations of the intermediates, performed in six solvents, revealed that the absorption bands were influenced by the substituent nature.     

Nano-scaled titanium dioxide – properties and use in coatings with special functionality

Nano-scaled titanium dioxides are used as UV-absorbers and to obtain certain color effects in pigmented coatings. For this they are generally required to have good phototresistivity. This is accomplished by doping of the crystal lattice with other elements than titania and by surface treatment with layers of inorganic substances. Currently the use of photoreactive nano-scaled titanias is being studied to formulate self cleaning and antimicrobial coatings.     

Supramolecular synthons and pattern recognition in adenine amides – synthesis,structures and thermal properties

An effective method for the synthesis of novel adenine amides was developed and successfully implemented, leading to 4-propyloxy-N-(9H-purin-6-yl)benzamide (1) and 4-dodecyloxy-N-(9H-purin-6-yl)benzamide (2). The compounds were fully characterised by means of spectroscopic (¹H NMR, ¹³C NMR, FT-IR) and thermal (TG, DSC) analysis. The crystallographic analysis revealed that the formation of supramolecular chains relies on hydrogen bonding between amide functionalities. All supramolecular synthons found in the crystal structure of 1 were confirmed with the temperature-dependent IR method. The temperature-dependent IR method is useful in determining supramolecular interactions for compound 2, for which the crystal structure could not be obtained. A detailed analysis of temperature-dependent FT-IR spectra was used for the first time to identify the hydrogen bonds that exist in the solid state of our compounds; it can therefore be considered a promising method for the pattern recognition of hydrogen bonding in supramolecular chemistry.     

Application of multi-capillary column – ion mobility spectrometry (MCC-IMS) in rubber chemistry and technology

In this paper the possibility for authentication and differentiation of various styrene butadiene rubbers (SBRs) was investigated. Seven types of SBR were analyzed by multi-capillary column (MCC) ion mobility spectrometer (IMS) and their spectra compared. The analysis of volatile organic compounds (VOCs) releasing from the rubbers revealed the presence of characteristics signals, which can be assigned only to a specific material. Such “markers”, when defined for other polymer materials, can be used for their authentication. In the second part of the paper, the blend of epoxidized natural rubber and poly-3-hydroxybutyrate-co-4-hydroxybutyrate (ENR/P(3,4)HB) was subjected to different types of aging. MCC-IMS spectra of not aged, thermal, climatic and UV aged samples were collected and differences between the signals discussed. The study showed possibility of authentication of polymeric materials and processes. The paper is a some kind of introduction to the use of analytical properties and advantages of MCC-IMS technique in chemistry, technology and exploitation of polymer materials.     

Photocatalysis applied to organic synthesis – A green chemistry approach

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