Synthesis and properties of synthetic analogs of natural humic acids

A new procedure was suggested for preparing analogs of natural humic acids using as precursor a nitrogen-containing amphoteric polyelectrolyte prepared by condensation of pyrocatechol with hexamethylenetetramine. The physicochemical and spectral properties of the product were examined.     

Synthesis and self-assembling properties of diacetylene-containing glycolipids

Diacetylene-containing glycolipids are interesting molecules that have many potential applications. The polydiacetylenes formed by the cross-linking of the diacetylene lipids are new stimuli-responsive materials. In particular, diacetylene lipids that can form gels in aqueous solution are of great interest in designing functional biocompatible materials. We have synthesized a series of diacetylene-containing sugar lipids with different chain lengths, substituents, and positions of diyne and studied their self-assembling properties in several solvents including hexane, ethanol, and ethanol/water mixture. Among the 24 diacetylene-containing glycolipids synthesized, many of them exhibited excellent gelation properties in ethanol or ethanol/water mixture. Typically very long chain diacetylene lipids formed gels in ethanol and hexane. Shorter chain diacetylene lipids and compounds with one free hydroxyl group can form gels in aqueous solution. The position of the diyne and chain length affect the self-assembling properties significantly. The systematic study of the gelation properties for diacetylene lipids with different lipid chains can help us to understand the structure requirement for the desired physical properties. Optical microscopy studies showed that the molecules form interesting architectures such as tubules, rods, sheets, and belts. The resulting organogels can also be cross-linked and give different colored polymerized gels depending on their structures.     

A synthetic alternative to natural lecithins with antimicrobial properties

Two soft biocompatible cationic surfactants from the amino acid arginine, 1,2-dilauroyl-3-acetylarginyl-rac-glycerol (1212RAc) and 1,2-dimirystoyl-3-acetylarginyl-rac-glycerol (1414RAc), were prepared. Their physicochemical properties show that they can be classified as multifunctional surfactants with self-aggregation behaviour comparable to that of short-chain lecithins. The two surfactants can simultaneously stabilise water-in-oil (W/O) droplets and oil-in-water (O/W) droplets, forming multiple emulsions. They have antimicrobial activity similar to that of conventional cationic surfactants and are as harmless as amphoteric betaines. These surfactants constitute an interesting alternative to the diglycerides and lecithins in formulations that require antimicrobial properties.     

Effect of polymerization of synthetic glycolipids on their supramolecular assemblies

Sugar-derived surfactants bearing a polymerizable acryloyl moiety on one of the branches of the double-chain hydrophobic tail were prepared. The non–ionic hydrophilic head and the biantennary hydrophobic tail were built on, respectively, an aspartic acid and a tris(hydroxymethyl)aminomethane core. Ultraviolet irradiation of aqueous dispersions of these surfactants above their transition phase temperature (T_c) was achieved. The morphology of self-assemblies produced in such a way were investigated by transmission electron microscopy. TEM photographs revealed that irradiation leads to the formation of unilamellar vesicles. Neither fibers nor tubules were detected in contrast to what was observed before polymerization.     

Polarographic properties and potential carcinogenicity of some natural nucleosides and their synthetic analogues

The polarographic reduction and the index of potential carcinogenicity tg alpha determined polarographically in aprotic conditions and in the presence of alpha-lipoic acid of nine naturally occurring and synthetic pyrimidine and six synthetic 1,3,5-triazine (5-aza) nucleosides was compared to the reduction of eight synthetic 1,3,6-triazine (6-aza) nucleosides. Nucleosides are of interest because of their key role in the nucleic acid structure and because of the antimetabolite and cytotoxic/antileukemia properties of their synthetic analogues. It was shown that polarographic reduction of the studied compounds is achieved at gradually increased potentials in the order of 6-aza < 5-aza < pyrimidine nucleosides. On other hand, the potential carcinogenicity of studied compounds increases usually in the order of pyrimidine < 6-aza < 5-aza nucleoside. The only compounds with remarkable potential carcinogenicity identified at this study were those ones from the 5-aza (1,3,5-triazine) antimetabolite series-arabinosyl-5-azacytosine (0.275), 5-aza-cytidine (0.295) and 5-aza-uracil (0.400)-and 2,2'-anhydrouridine (0.260). The relation of the data obtained to biological activity of nucleosides included in the study is discussed.     

Total synthesis of the tricyclic skeleton of the natural Celastraceae sesquiterpenoids and related synthetic analogs

A concise and efficient synthesis of the C₁₃ tricyclic core of the dihydro-β-agarofuran skeleton common to the natural Celastraceae sesquiterpenoids is described. The strategy entails a Mukaiyama aldol reaction of a tetrahydronaphthalene enol silane with acetone, epoxidation, ketone reduction, and acid-catalyzed cyclization. This key scaffold was converted into diverse polyhydroxylated derivatives, which were tested for insecticidal activity.     

Structure and stability of natural organic matter/soil complexes and related synthetic and mixed analogues

This review aimed at the presentation of recent, new approaches which have been developed to improve our knowledge of soil structure and some related characteristics. The investigations reviewed addressed a large number of solid/polymer systems, from strictly synthetic to fully natural systems. Only studies correlating adsorption and solid structuring were considered, so that a great number of adsorption studies were not taken into account.Despite the very complex chemical nature, composition and structure of natural organic matter and soils, some analogues appeared to be useful for determining the role of the natural substances in the stability of soils. Stability means that the soil was able to resist fragmentation and dispersion induced by successive drying and wetting processes. Actually, in the domain of low polymer content, the cohesion of soils was found to be correlated to the concentration of natural organic matter and established by a mechanism which is similar to that inducing the flocculation of suspended colloidal particles. The paper reviews some characteristics of synthetic, natural and mixed systems which display the correlation existing between the structuring of solid agglomerates and the adsorption of polymers.     

Thermodynamic properties of synthetic natural gases: Part 4. Dew point curves of synthetic natural gases and their mixtures with water: measurement and correlation

Experimental measurements of dew points for five synthetic natural gases (SNG)+water mixtures were carried out between 2.1×10⁵ and 73.2×10⁵ Pa in the temperature range from 224.3 to 270.2 K. The experimental results were analysed in terms of both an equation of state (EOS) model and an excess function–EOS method, which reproduced the experimental data with an AAD from 2.1 to 3.4 K and from 1.9 to 3.0 K, respectively.     

Polysaccharide-based natural and synthetic nanocomposites

Modern concepts on the supramolecular organization of natural nanocomposite materials based on structural polysaccharides are discussed, beginning from the stage of biosynthesis. The methods for obtaining nanocrystals and nanofibrils of cellulose and chitin, as well as their structure and properties, are discussed. Various methods for the synthesis of nanocomposites with the use of water-soluble, water-dispersed, and hydrophobic polymer matrixes are described. Special attention is given to surmounting the incompatibility of polymer and polysaccharide particles.     

Dehydration of synthetic and natural vivianite

Thermal analyses of synthetic and natural vivianite (Fe²⁺)₃(PO₄)₂·8H₂O) were determined using a high-resolution thermal analyser coupled to a mass spectrometer.Five dehydration weight loss steps were observed for the natural vivianite at 105, 138, 203, 272 and 437 °C. The first weight loss step involves the reaction (Fe²⁺)₃(PO₄)₂·8H₂O→(Fe²⁺)₃(PO₄)₂·3H₂O+5H₂O. The TGA/MS for the synthetic vivianite gave similar results to that of the natural sample. Mass spectrometry shows that water is lost up to 450 °C and after this temperature oxygen is lost. Changes in the structure of vivianite were followed using infrared emission spectroscopy. A model is proposed for the dehydration of vivianite.     

DTA of natural and synthetic uranium compounds

A brief outline of structural considerations is given, concerning compounds one can meet as secondary uranium minerals. The authors report the thermal analysis of minerals deposited at the National Museum Collection in Prague. Three different types of instruments were used: a MOM derivatograph, a Netzsch DTA equipment, and an instrument constructed according to Rosický for microspecimens. The thermal analysis results were correlated with X-ray structure analysis and infrared spectra analysis data. The examples applied were: synthetic rutherfordine and related compounds, synthetic andersonite and the minerals liebigite and schoeckingerite, and synthetic schoepite.

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Zusammenfassung Ein kurzer Bericht über strukturelle Erwägungen bezüglich sekundärer Uraniumerz-Verbindungen wird gegeben. Es werden an die durch thermoanalytische Überprüfung der in der Sammlung des Nationalmuseums zu Prag befindlichen Erze gewonnenen Erfahrungen mitgeteilt. Drei verschiedene Typen von Geräten wurden eingesetzt: der Derivatograph MOM, die DTA-Vorrichtung Netzsch und ein nach Rosický gebautes Gerät für Mikroproben. Die Ergebnisse der Thermoanalyse wurden mit den Daten der Röntgen-Strukturanalyse und denen der Analyse des Infrarotspektrums in Zusammenhang gebracht. Als Beispiele wurden synthetisches Rutherfordin und verwandte Verbindungen, synthetisches Andersonit, sowie die Erze Liebigit und Schoekingerit und synthetisches Schopit verwendet.

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Résumé Un bref rappel sur les considérations structurales concernant les composés que l'on peut rencontrer comme minéraux secondaires d'uranium est donné. Les auteurs ont eu l'intention de faire partager leur expérience acquise lors de la révision des minéraux déposés dans la Collection du Musée National de Prague, à l'aide de l'analyse thermique. Trois types d'instruments ont été utilisés le Derivatograph MOM, l'appareil ATD Netsch et un instrument construit d'après Rosický, pour l'étude de microéchantillons. On a établi une corrélation entre les résultats de l'analyse thermique et ceux obtenus lors des analyses de structures par rayons X et par spectroscopie infrarouge. Les exemples cités concernent la rutherfordine synthétique et les composés analogues, l'andersonite synthétique, ainsi que les minéraux liebigite et schoeckingérite et la schopite synthétique.

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Pyrolysis of natural and synthetic humic substances

Thermogravimetric and Rock-Eval techniques were used for the characterization of natural (humic) and synthetic (melanoidins) substances and their hydrocarbon generation potential. A similarity between the thermal behaviour of humic substances and of melanoidins (prepared from an excess of sugar) and the unique thermal properties of melanoidins (prepared from basic amino acids) was observed. Rock-Eval analysis indicated that most synthetic melanoidins (also clay-complexed) generated more hydrocarbons and related compounds than terrestrial humic substances.     

Raman spectra of synthetic and natural mullite

Mullite (Al_4+2xSi_2−2xO_10−x) is a very rare alumino-silicate mineral that requires high alumina containing rocks and high temperature for its synthesis. In the frame of planetary exploration, this mineral can be a useful probe of very specific past environmental conditions. In this study, we discuss the Raman characterisation (457, 514.5, 633 and 785 nm laser excitation wavelengths) of natural mullite from Mull Island and compare it with the artificial mullite. The natural mullite samples show partially altered {010} cleaved crystals with OH and more octahedral [AlO₆] than synthetic samples.     

Raman spectroscopy of synthetic and natural iowaite

The chemistry of a magnesium based hydrotalcite known as iowaite Mg6Fe2Cl2(OH)16.4H2O has been studied using Raman spectroscopy. Iowaite has chloride as the counter anion in the interlayer. The formula of synthetic iowaite was found to be Mg5.78Fe2.09(Cl,(CO3)0.5)(OH)16.4H2O. Oxidation of natural iowaite results in the formation of Mg4FeO(Cl,CO3) (OH)8.4H2O. X-ray diffraction (XRD) shows that the iowaite is a layered structure with a d(001) spacing of 8.0 angtsroms. For synthetic iowaite three Raman bands at 1376, 1194 and 1084 cm(-1) are attributed to CO3 stretching vibrations. These bands are not observed for the natural iowaite but are observed when the natural iowaite is exposed to air. The Raman spectrum of natural iowaite shows three bands at 708, 690 and 620 cm(-1) and upon exposure to air, two broad bands are found at 710 and 648 cm(-1). The Raman spectrum of synthetic iowaite has a very broad band at 712 cm(-1). The Raman spectrum of natural iowaite shows an intense band at 527 cm(-1). The air oxidized iowaite shows two bands at 547 and 484 cm(-1) attributed to the (CO3)(2-)nu2 bending mode. Raman spectroscopy has proven most useful for the study of the chemistry of iowaite and chemical changes induced in natural iowaite upon exposure to air.     

Nomenclature of synthetic steroids and related substances

Summary A system of nomenclature has been proposed for synthetic steriod compounds.In view of the nature of this article, the names of compounds have been transcribed as directly, as possible. American practice, however, has been foKowed for indicating positions of double bonds (^9:11 etc. is used in the original). The Russian ending—an has been transcribed as—ane for fully saturated compounds, and in .other cases as—an. (Publisher.)     

NMR studies on natural and synthetic Amavadin

The stereochemistry of isolated natural product Amavadin, which contains a 1:2 complex of V(IV) with N-hydroxyimino-2,2'-dipropionic acid (HIDPAH(3)), and some synthetic complexes have been investigated. Amavadin was isolated from Amanita muscaria and oxidized with [NH(4)](2)[Ce(NO(3))(6)]. H(2)[Delta-V(S,S-HIDPA)(2)].3H(2)O, H(2)[Delta,Lambda-V(S,S-HIDPA)(2)].3H(2)O and their equivalent oxidized species have been synthesized and characterized spectroscopically. A combination of COSY, NOE, (1)H, (13)C-NMR and CD spectroscopy have been used to prove that the isolated natural product Amavadin consists of an almost equal mixture of the Delta- and Lambda-isomers of [V(S,S-HIDPA)(2)](2-).     

Raman piezo-spectroscopic analysis of natural and synthetic biomaterials

Raman piezo-spectroscopy of bone, teeth, and artificial joints is reviewed with emphasis placed on confocal microprobe techniques. Characteristic spectra are presented and quantitative assessments of their phase structure and stress dependence are shown. Vibrational spectroscopy is used here to study the microscopic stress response of cortical bone to external stress (with or without internal damages), to define microscopic stresses across the dentine–enamel junction under increasing external compressive load, and to characterize interactions between prosthetic implants and biological environment. Confocal spectroscopy allows acquisition of spatially resolved spectra and stress imaging with high spatial resolution.