Structure of “dimethylenetricyclohexanone”

The structure of the product of condensation in basic medium of two molecules of formaldehyde with three molecules of cyclohexanone has been proved using X-ray structural analysis.Far Eastern State University, Vladivostok 690600, Russia; e-mail: vlad@chem.dvgu.ru. A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow 117813, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1491–1496, November, 1999.     

“Wet” Versus “Dry” Folding of Polyproline

When the all-cis polyproline-I helix (PPI, favored in 1-propanol) of polyproline-13 is introduced into water, it folds into the all-trans polyproline-II (PPII) helix through at least six intermediates [Shi, L., Holliday, A.E., Shi, H., Zhu, F., Ewing, M.A., Russell, D.H., Clemmer, D.E.: Characterizing intermediates along the transition from PPI to PPII using ion mobility-mass spectrometry. J. Am. Chem. Soc. 136, 12702–12711 (2014)]. Here, we show that the solvent-free intermediates refold into the all-cis PPI helix with high (>90%) efficiency. Moreover, in the absence of solvent, each intermediate appears to utilize the same small set of pathways observed for the solution-phase PPII → PPI transition upon immersion of PPII_aq in 1-propanol. That folding in solution (under conditions where water is displaced by propanol) and folding in vacuo (where energy required for folding is provided by collisional activation) occur along the same pathway is remarkable. Implicit in this statement is that 1-propanol mimics a “dry” environment, similar to the gas phase. We note that intermediates with structures that are similar to PPII_aq can form PPII under the most gentle activation conditions—indicating that some transitions observed in water (i.e., “wet” folding, are accessible (albeit inefficient) in vacuo. Lastly, these “dry” folding experiments show that PPI (all cis) is favored under “dry” conditions, which underscores the role of water as the major factor promoting preference for trans proline.

Open image in new window

Graphical Abstract ?

     

Question of “bound” and “free” water

Summary The physical meaning of the correction for the binding of water by ions is clarified, and an equation is proposed for its accurate calculation.     

Hydrodynamic Properties of “Pseudo-Dendrimer”

Summary: Hyperbranched polycarbosilane with terminal butyl groups is obtained by chemical modification of hyperbranched polyallylcarbosilane using the reaction of hydrosilylation with methyldichlorosilane, followed by treatment of the polychlorosilyl derivative with butyllithium. Its hydrodynamic and conformational properties are studied by the methods of light scattering, sedimentation-diffusion analysis, and viscosimetry in dilute solutions of methyl-tert-butyl ether, hexane, THF, chloroform, and toluene. The results obtained are compared with the data for the initial polyallylcarbosilane and carbosilane dendrimer with butyl terminal groups. It is demonstrated that branching regularity is the decisive factor determining the solution properties at fixed degree of the branching.     

“Relay” Stabilization of Polyimides

With triphenyl phosphate as example, thermal stabilization of polyimides was studied in a widetemperature range, and the step mechanism of the process, termed relay stabilization, was suggested.     

Catalytic Mechanism of the “Noncatalytic” Autooxidation of Sulfite

Iron ions are shown to play a special role among transition metal ions in the oxidation of sulfite by oxygen. The thermodynamically favorable formation of chain carriers S : FeOH²⁺+ HSO₃ ^– Fe²⁺+ H₂O + , H _{r 298} ⁰ –250 kJ/mol accompanied by the regeneration of the active Fe(III) form in the reactions of Fe(II) with and HSO₅ ^–provides the efficient catalytic mechanism for sulfite consumption even at [Fe]₀ 10^–8mol/l. Any aqueous solution contains iron ions in this amounts. Thus, the noncatalytic oxidation of sulfite is in fact the catalytic reaction involving unavoidable microadmixtures of iron ions. Other transition metal ions (Mn²⁺, Co²⁺, etc.) can only enhance the catalytic effect of iron admixture.     

“Binding” of water by ions

Summary We confirmed the inadequacy of the correction for, binding of water by ions for explaining the discrepancy between the electrostatic theory in [2] and experiment.     

On “Coordinational Stabilization” of High Oxidation States of Metals

A hypothesis of the ligand matrix stabilization of metal ions in high oxidation states is considered using the structural thermodynamic model and stabilization of Zr⁴⁺ ion in ZrC₆₀ cluster as an example. The corresponding energy estimates are presented for fullerides of the M ^z @C _m M ^s type (m 60). The possibility of using fullerenes as matrices with a high electron affinity is shown.     

Investigation of technical characteristics of chemical adsorbent “mercerized wood”

Investigations on the influence of the velocity (flow) of gas on the surface integrity of the layer of adsorbent “mercerized wood” were carried out, the data on the aerodynamic resistance of the layer depending on the specific consumption of the air and value of the residual pressure of gases above dried adsorbent were obtained. At density of the adsorbent within 0.25 to 0.35 g cm⁻³ the consumption of gas can vary up to the value of 1.4 l cm⁻³ min⁻¹. It is shown that the aerodynamic resistance of the layer is insignificant at the density of the layer of the adsorbent no more than 0.35 g cm⁻³. Functional dependences of aerodynamic resistance on the specific consumption of gas for different densities of the layer of the adsorbent were obtained. The empirical equation of Shilov-Dubinin for calculation of the process of absorption of HF is illustrated.     

Formation of “monodispersed” SnO2 powders of various morphologies

Several procedures for the preparation of colloidal SnO₂ powders, consisting of particles of narrow size distribution and of various morphologies, are described. The hydrolysis of SnCl₄ aerosols in the presence of gaseous ammonia produces poorly crystalline SnO₂ spheres of modal diameters <2 m. Depending on the preparation conditions, the forced hydrolysis of acidic (HCl) SnCl₄ solutions yields either prismatic particles or spherulites composed of tiny, strongly aggregated, elongated subunits. In both cases the particles are in the nanometer size range (<100 nm) having crystalline rutile structure. Rod-like SnO₂ particles (0.3 m) of good crystallinity can be obtained by hydrolysis of SnCl₄ solutions in the presence of formamide. It is concluded that the hydrolysis of dissolved SnCl₄ tends to produce elongated SnO₂ particles which, depending on the experimental conditions, may be at different aggregation states.     

Parameters of cation “hardness” and “softness” and application thereof for calculation of extraction constants

Analysis of published data was performed on the basis of solvation energies of a number of “transition” and “soft” cations. A dependence of the solvation energy of cations on the donor and acceptor numbers of the solvent was derived. Donor and acceptor ability parameters of Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, and Tl⁺ were calculated. The resultant parameters were used to calculate the extraction constants of the specified cations with di-2-ethylhexyl-phosphoric acid (DEHPA) solution in neutral solvents; the model represented has a good predictive power.     

Solution properties of new “core-shell” structured polyorganosilsesquioxanes with two different types of “core-shell” surroundings

Two “core-shell” structured polyorganosilsesquioxanes, differing in the arrangement of vinyl groups over the macromolecule volume, were studied in dilute solutions in toluene and ethyl acetate. It is shown that solution behavior is determined by the transposition of the functional vinyl groups in the core or shell of the macromolecule. This correlation is manifested in increasing the intrinsic viscosity values.     

NMR Microscopy of an “Anisotropic” Polymer

Two different samples of high-density polyethylene (HDPE) have been studied. One (isotropic) is extracted from the material core whereas the other (anisotropic) involves two sides which have been in contact with the injection mold. It is observed by NMR microscopy (using radiofrequency field gradients) that these two sides favor toluene penetration into the material. The distribution of toluene nuclear spin relaxation times (extracted from proton T₁ and T₂ images) exhibits likewise important differences between the two samples. These differences can be accounted for by partial molecular ordering at the vicinity of the “mold sides”. Finally, in investigating the anisotropic sample (without solvent), three different phases (two amorphous and one crystalline) are revealed by ¹³C chemical shift imaging experiments (performed with radiofrequency field gradients under CP/MAS conditions). Each amorphous component is preferentially present at one of the two “mold sides”.     

Synthesis of bicyclohomofarnesane compounds by the ozonization of “sclareol oxide”

Ozonolytic pathways for the selective transformation of sclareol oxide (I) with good yield into the bicyclohomofarnesane derivatives (II), (III), (V), and (VII) have been developed.Institute of Chemistry, Academy of Sciences of the Moldavian SSR, Kishinev. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 209–214, March–April, 1991.