Investigation of the chemistry of phenoxazines

Depending on the position of the annelated benzene ring, benzophenoxazinones add thiophenols in the benzenoid, quinonoid, or both parts of the molecule to give mono- or diarylmercapto derivatives. A substituent in the benzenoid portion of the molecule hinders polarographic reduction and shifts the visible absorption band bathochromically, while a substituent in the quinonoid portion has practically no effect on the E_1/2 value.See [1] for communication IV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1345–1350, October, 1972     

Investigation of the chemistry of heterocycles

The reaction of ethoxalylanthranil with aryl(heteryl)amines was studied, a method for obtaining 2-carbethoxy-3-R-substituted 4-quinazolones was developed, and the transformations of the latter were investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1575–1578, November, 1970.     

Smectic C phenylpyridines with an alkenyloxy chain

Abstract

The known 5-n-alkoxy-2-[4-(n-alkoxy)phenyl]pyridines exhibit high smectic C transition temperatures as well as various highly ordered smectic mesophases. An unsaturated carbon-carbon double bond has now been introduced into the terminal alkoxy chain of these heterocyclic materials to produce the corresponding alkenyloxy substituted derivatives. The postion and nature (E/Z) of the double bond has been varied systematically and the effect on the liquid crystal transition temperatures determined. A number of homologous series of the most promising alkenyloxy substituted materials has been prepared and evaluated. The position and nature (E/Z) of the double bond changes the conformation of the alkenyloxy chain to a significant degree. This can lead to slightly higher smectic C transition temperatures for compounds with a trans-double bond (E) at an even number of carbon atoms from the molecular core. However, the highly ordered mesophase transition temperatures are increased to a greater degree leading to a reduction in the smectic C temperature range. Significantly lower transition temperatures (including the melting point) are observed for materials with a cis-double bond (Z) at an odd number of carbon atoms from the molecular core. Comparisons with the corresponding alkoxy substituted materials (i.e. without a double bond) are made. These new alkenyloxy materials can be used to increase the smectic C and nematic transition temperatures of chiral mixtures for electrooptical display devices based on ferroelectric effects.     

Investigation of gravity lanthanide separation chemistry

Lanthanides are common fission products and the ability to separate and quantify these elements is critical to rapid radiochemistry applications. Published lanthanide separations using Eichrom Ln Spec resin utilize an HCl gradient. Here it is shown that the efficacy and resolution of the separation is improved when a nitric acid gradient is used instead. The described method allows parallel processing of many samples in 1.5 h followed by 60 min counting for quantification of 9 radioisotopes of 7 lanthanide elements.     

Investigation of the sol-gel chemistry of ethylacetoacetate modified aluminum sec-butoxide

Hydrolysis of aluminum sec-butoxide leads usually to precipitation; however, modification of the Al center with one ethylacetoacetate gives a new precursor, Al(OBu ^s )₂(etac). Hydrolysis of Al(OBu ^s )₂(etac) leads to transparent, homogeneous gels rather than precipitates and thus appears as an interesting precursor for the sol-gel synthesis of alumina-containing ceramics. The investigation of the sol-gel chemistry of Al(OBu ^s )₂(etac) by Nuclear Magnetic Resonance and infrared techniques provides a detailed understanding of the effects of the ethylacetoacetate group on the chemistry at the Al center. ²⁷Al NMR shows that in solution Al(OBu ^s )₂(etac) exists as oligomeric species that contain hexa-, penta- and tetra-coordinated Al. When dissolved in ethanol, Al(OBu ^s )₂(etac) undergoes exchange reactions with solvent as shown by ¹³C NMR, which strongly influence the nature of the species in equilibrium, favoring the formation of pentacoordinated Al sites. The effects of changes in reaction conditions on the species formed on hydrolysis were followed by ²⁷Al, ¹³C NMR and infrared spectroscopies. These techniques indicate that the etac groups are much less susceptible to hydrolysis than the butoxy groups. Some of the etac groups survive to hydrolysis procedure, thus preventing complete condensation of the oxide network.     

Investigation of the unusual behavior of projectile fragments using nuclear chemistry techniques

In recent years the question of the unusual behavior of projectile fragments formed in the interaction of relativistic heavy ions with copper nuclei was studied using nuclear chemistry techniques. As targets we used various copper disk arrangements. It is not the intention of this conference contribution to give a complete account of the entire procedure and its results. However, we want to present a few more recent experimental findings, some of them even in a preliminary form. We want to stimulate the discussion about the entire problem which might be part of the so-called anomalon phenomenon, as observed in the field of relativistic heavy ion interactions with a few other techniques such as nuclear emulsions or bubble chambers.     

Contributions to the chemistry of carbenemetal chemistry

This paper provides a brief review of our researches on carbenemetal complexes. The main emphasis is on saturated heterocyclic bis(amino)carbene ligands, referred to here as electron-rich olefin- or ERO-derived ligands, as outlined in Sections 2 and 3. The following Section deals with Fischer-type carbene complexes, based on reactions of a transition metal substrate with an imidoyl chloride, Vilsmeyer reagent or Eschenmoser salt. The researches of Sections 2, 3, 4 have resulted in the synthesis, characterisation and selected reactions (including as catalysts) of carbene complexes of V, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt and Au in various oxidation states. A final Section describes some more recent work on C[(NCH₂Bu^t)₂C₆H₄–1,2], its adducts with M[(NCH₂Bu^t)₂C₆H₄–1,2] (M = Si, Ge, Sn, or Pb) and the biphenyl- bis(carbene), [C{NCH₂Bu^t}₂C₆H₃–3,4]₂.     

Investigation of corannulene for molecular hydrogen storage via computational chemistry and experimentation

Molecular simulations for hydrogen physisorption with corannulene molecules arranged according to their crystal structure result in good agreement with the weight-percent hydrogen stored as determined experimentally employing a 3-g sample of highly crystalline corannulene at ambient temperatures and 72 bar of pressure. Calculated enthalpies of adsorption for corannulene/hydrogen molecular systems obtained from ab initio calculations which take into account electron correlation via second-order M?ller-Plesset perturbation theory are in good agreement with literature experimental enthalpies of adsorption for activated carbons interacting with molecular hydrogen. Ab initio results also show that corannulene molecules arranged in a sandwich structure are important for approximately doubling the binding energy of corannulene interacting with molecular hydrogen through a cooperative interaction. To test the effects of finite temperatures and pressures, stack arrays were used as input for molecular dynamics simulations and indicate that physisorption mechanisms including van der Waals forces and dipole-induced dipole interactions may yield enhanced adsorption capacity in relation to other carbon-based materials. These results will be instrumental in identifying interlayer separations of an array of corannulene or related molecules that may provide a high weight percent of physisorbed hydrogen.     

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.     

Investigation of addition mechanism of diazoles to vinylorganosilanes by methods of quantum chemistry

The behavior of pyrazole and imidazole in the reactions with vinyltrimethoxysilane and vinylsilatrane in the presence of the catalytic amount of lithium was studied by the B3LYP/6-311G(d,p) method. It is established that these processes are accompanied by the formation of lithium salts of diazoles. These substances exist in the planar and pyramidal forms in which lithium atom is bound with all atoms of the aromatic ring. Thermodynamic parameters of the process are considered, and the transition states and potential barriers are found in the approximation of isolated molecules.     

Putting the chemistry back into analytical chemistry

Aspects of the current status of and research in analytical chemistry are briefly discussed and the need for cost effective analytical procedures is emphasized. The present and future of a number of aspects of flow-injection analysis are considered. These include the basic theory, the kinetic features, the control features, time-based methodology, and the coupling of sample pretreatment with instrumentation. Several aspects of this latter topic are considered with particular reference to the flow-injection atomic spectrometry combination. Problems of kinetic mismatch between chemistry, manifold residence, and instrument operation are discussed and some possible solutions proposed including the use of closed loop manifolds.     

Investigation on the chemistry of berbans—VIII : Synthesis of “inside” depyrrolo-yohimbine analogues

Previously known ketonitrile 1 with phosponic acid ester 2 produced the two geometrical isomers 3 and 4 which upon reduction afforded 5b and 6b. By hydrolysis and subsequent esterification the two methyl esters 5a and 6a were obtained. Dieckmann condensation of 5a led to 7a and 7b. Reduction of the latter compounds yielded the corresponding “inside” yohimbine analogues 8a and 8b. Methyl ester 6a was converted into the ketoester 9. The stereochemistry of the isomers was proved by physical (H¹ NMR, IR, MS) and by chemical methods.     

Improving chemistry teacher education with the philosophy of chemistry

Foundations of Chemistry -     

Investigation of pyrite oxidation by hexavalent chromium: solution species and surface chemistry

Pyrite oxidation processes by aqueous Cr(VI) were investigated at 25 degrees C under an argon atmosphere. Synthetic pyrite suspensions (6 g L(-1)) were reacted for 20 h with a range of Cr(VI) solutions from 0 to 700 microM and at pH 2-12. The main objective of this work was to investigate the reaction mechanisms by emphasizing the role of sulfur species. Aqueous chemical processes were well illustrated in acidic media where significant amounts of sulfate and iron species were determined. Sulfate anions are the final stable sulfur species involved in the reaction pathway. Experiments showing complete Cr(VI) removal from solution displayed ratios [S(VI)]/[Fe](tot)<2, probably due to a deficit in aqueous sulfur species. Experiments showing incomplete Cr(VI) removal displayed ratios [Cr(VI)](removed)/[S(VI)] close to 1.5. This ratio was found to be consistent with the formation of thiosulfate (S(2)O(2-)(3)). Thiosulfate ions disproportionated into elemental sulfur S(0) and tetrathionate ions (S(4)O(2-)(6)) that were finally oxidized to sulfate anions under acidic conditions. The distribution of the oxidation state of sulfur atoms at the pyrite surface determined by XPS was additional evidence for the multistep sulfur oxidation process. The presence of elemental sulfur in the S(2p) spectra correlated well with the disproportion of thiosulfate under acidic conditions.     

Investigation of the role of surface chemistry and accessibility of cadmium adsorption sites on open-surface carbonaceous materials

Carbon nanotubes fabricated by the dc arc discharge method (ADCNTs) and chemical vapor deposition method (CVDCNTs) were oxidized with concentrated HNO 3 to modify their surface chemistry. The materials were characterized using SEM, TEM, FTIR, XPS, potentiometric titration, and nitrogen adsorption. The initial and oxidized materials were used as adsorbents of cadmium from aqueous solutions with different pH. Langmuir and Freundlich adsorption models were applied to fit the isotherm data, and both models fit the experimental data very well. The acid oxidation resulted in an increase in the number of oxygen-containing groups without drastic changes in the texture of the adsorbents. Although the small volume of micropores is present, the nanotube structure can be considered as nonporous. The lack of developed microporosity in carbonaceous materials eliminates the inner surface diffusion problems and makes the vast majority of surface groups available for adsorption of cadmium. The availability of these centers depends on the pH of the solution, which controls the protonation level. In spite of the fact that the pH of the solution affects the speciation of cadmium to some degree, the surface chemistry is the predominant force for adsorption at the pH range adopted in the present study, while the texture of materials also affects the nanotube's cadmium-adsorbing performance.     

Investigation on the chemistry of berbans—VII: Synthesis of 10,11-dimethoxy(depyrrolo)raunescine stereoisomers

Acyloxy-ketone rearrangement, proceeding by the action of base, has been observed in the case of ketone 2. By the reduction of ketones 2 and 3 with sodium boron hydride, new 10, 11-dimethoxy(depyrrolo)raunescine stereoisomers (5a–7a) have been prepared. Previously known alcohols with alloberban skeleton (12,13) have been similarly converted into tetracyclic raunescine stereoisomers (8a,9) by the oxido-reductive method. The stereochemistry of these compounds has been investigated by physical (¹H NMR, IR) and by chemical methods.     

On chemistry and teaching chemistry at school. Report at the I All-Russian congress of chemistry teachers

A brief historical background of the formation of chemistry and the development of modern science is given. A role of chemical knowledge in the student’s personal development is emphasized. Particular attention is paid to the interaction of Lomonosov Moscow State University with schools (school subject competitions, schools for training teachers etc.). A brief analysis of current reforms in the sphere of science and education is given.