Weak Secondary Bonds Research Articles

Investigating molecular conformation and packing of oxidized asphaltene molecules in presence of paraffin wax

This study investigates the effect of paraffinic wax (as a base component in many commercial rejuvenators) on the rheological and intermolecular properties of aged asphalt binder. Samples of oxidized asphalt binder doped with (1%, 3%, 5%, and 10%) paraffin wax were characterized using the rotational viscometer (RV), dynamic shear rheometer (DSR), bending beam rheometer (BBR) and direct tension test (DTT). The RV results showed an improvement trend in workability of aged binder as wax content increased. The DSR results (for a temperature range of 10–76 °C) showed lower complex modules for wax-doped specimen than control specimen. The BBR test results performed at sub-zero temperature showed that an increase of wax dosage led to higher creep stiffness modulus indicating that the asphalt binder became generally stiffer in presence of wax at low temperature. However, fracture energy measured through DTT test showed a significant reduction in presence of wax. The latter can be attributed to plausible weak secondary bonds between wax and asphaltene molecules as well as crystallization of wax molecules at low temperature within the asphalt matrix. This in turn can lead to wax crystals playing as stress localization point giving rise to crack nucleation at the wax-asphalt interface reducing overall fracture energy; it was further observed that as the wax content increased, the asphalt binder became more brittle.To further investigate the effect of wax on the molecular conformation and packing in aged asphalt binder, a molecular simulation was performed on a system of wax and oxidized asphaltene. The results of molecular simulations showed a reduction in formation of oxidized asphaltene nano-aggregates as the amount of wax increased in the wax-doped oxidized asphaltene matrix at room temperature, which was also confirmed by size exclusion chromatography. Furthermore, the radial distribution function results showed a less packed structure of oxidized asphaltene molecules in presence of wax molecules. Increasing the wax content also increased the diffusion coefficient of wax into the oxidized asphaltene matrix within a solvent medium. It was also showed that interaction energy of a dimer of oxidized asphaltene is at a lower energy state in presence of wax molecules, which suggests that wax molecules can promote dimerization of oxidized asphaltene molecules while suppressing nano-aggregates formation.

Synthesis, characterization and crystal structure of four new asymmetric triazene ligands: An example of linear HgII complex with Hg... π secondary bonding interactions

In this work, the asymmetric ligands [1-(phenyl)-3-(2-nitro-4-methylphenyl)]triazene (1), [1-(4- methylphenyl)-3-(2-nitro-4-methylphenyl)]triazene (2), [1-(4-ethylphenyl)-3-(2-nitro-4-methylphenyl)]triazene (3) and [1-(4-ethoxyphenyl)-3-(2-nitro-4-methylphenyl)]triazene (4), were synthesized. The reaction of the ligand (3) with HgCl 2 in methanol resulted in the formation of the [HgL 2] complex, (5). All compounds were characterized by means of CHN analysis, FT-IR, 1H NMR, 13C NMR spectroscopy. In addition, the crystal structures of the ligands (2) to (4) were investigated by single crystal X-ray analysis. In the solid state, all ligands exhibited trans conformation about the –N =N– double bond. The Hg II complex (5) crystallized in monoclinic system with C2/c space group. The triazene ligand was found to be deprotonated prior to coordination and acts as monodentate ligand. The Hg II which lies on inversion center (site symmetry ı̄), is surrounded by two N atoms from L ligands forming a linear geometry. The other two Hg–N bonds are relatively longer and can only be regarded as weak secondary bonds. Also, Hg- η 3-arene π-interactions are present in this compound. Hydrogen bonds, π⋯π and C–H ⋯π stacking interactions help in the stabilization of the resulted frameworks. These C–H ⋯π edge-to-face interactions are present with H ⋯π distance of 3.00 Å. Synthesis, characterization and X-Ray crystal structures of a few asymmetric triazenes with (–NH–N=N–) moieties and a linear HgII complex (HgL 2) with Hg...π secondary bonding interactions are described.

Structural organization and thermal behavior of the heteropolynuclear complex [Au2{S2CN(CH3)2}4][ZnCl4] and the heterovalent complex ([Au{S2CN(CH3)2}2][AuCl2]) n obtained in the chemisorption system [Zn2{S2CN(CH3)2}4]-Au3+/2 M HCl

Reactions of freshly precipitated binuclear zinc dimethyldithiocarbamate with [AuCl4]− anions in 2 M HCl were studied. The heteropolynuclear complex [Au2{S2CN(CH3)2}4][ZnCl4] (I) and the polymeric heterovalent complex ([Au{S2CN(CH3)2}2][AuCl2])n (II) were preparatively isolated from the chemisorption system [Zn2{S2CN(CH3)2}4]-Au3+/2 M HCl. The products were characterized by 13C MAS NMR data and by X-ray diffraction determination of crystal and molecular structures. The principal structural units of compounds I and II are the tetragonal planar complex cations [Au{S2CN(CH3)2}2]+ (in which the complex-forming ion coordinates two MDtc ligands in the S,S′-bidentate mode) and the anions, namely, the distorted tetrahedral anion [ZnCl4]2− in I and the linear [AuCl2]− anion in II. The further structural self-organization of complexes at the supramoleular level occurs through relatively weak secondary bonds Au⋯S and Au⋯Cl. The chemisorption capacities of zinc dimethyldithiocarbamate calculated from gold(III)-binding reactions are 644.1 and 1288.2 mg of gold per gram of the sorbent. Simultaneous thermal analysis studies of the thermal behavior of I and II were used to elucidate the conditions of gold recovery.

Mercury(II) complexes containing new ortho-functionalized asymmetric triazene ligands: synthesis, crystal structures, and solution studies

Synthesis of two new asymmetric ligands: 1-(2-ethoxyphenyl)-3-(2-methoxycarbonylphenyl)triazene (HL) (1) and 1-(2-methoxyphenyl)-3-(2-methoxycarbonylphenyl)triazene (HL′) (2) are reported. The prepared triazenes are functionalized by ethoxy and methoxy groups in the ortho positions, respectively. The related monomeric complexes, [HgL2] (3) and [HgL′2] (4), were prepared by the reacting of the corresponding ligands with Hg(NO3)2 salt in methanol as solvent. All compounds were characterized by CHN analysis, FT-IR, 1H NMR, and 13C NMR spectroscopy. According to the crystal structures of 1 and 2, the N–N bond distances indicate the presence of alternating single and double bonds, and hence the –N=N–NH– moiety. On coordination, each triazene was deprotonated and as a result, a resonance structure is formed between nitrogens which let them to be a tridentate ligand. In the crystal structure of 3, [HgL2], the central Hg(II) is surrounded by two N atoms from interlocked L forming linear geometry, in which the other four Hg–N and Hg–O bonds are longer and can only be regarded as weak secondary bonds. An interesting feature of 3 is also the presence of π⋯π [centroid–centroid distance of 3.744(3) Å] and C–H⋯π interactions. The results of solution studies for the formation of 3 in methanol support its solid-state stoichiometry.

Computational conformational antimicrobial analysis developing mechanomolecular theory for polymer biomaterials in materials science and engineering.

Single-bond rotations or pyramidal inversions tend to either hide or expose relative energies that exist for atoms with nonbonding lone-pair electrons. Availability of lone-pair electrons depends on overall molecular electron distributions and differences in the immediate polarity of the surrounding pico/nanoenvironment. Stereochemistry three-dimensional aspects of molecules provide insight into conformations through single-bond rotations with associated lone-pair electrons on oxygen atoms in addition to pyramidal inversions with nitrogen atoms. When electrons are protected, potential energy is sheltered toward an energy minimum value to compatibilize molecularly with nonpolar environments. When electrons are exposed, maximum energy is available toward polar environment interactions. Computational conformational analysis software calculated energy profiles that exist during specific oxygen ether single-bond rotations with easy-to-visualize three-dimensional models for the trichlorinated bisaromatic ether triclosan antimicrobial polymer additive. As shown, fluctuating alternating bond rotations can produce complex interactions between molecules to provide entanglement strength for polymer toughness or alternatively disrupt weak secondary bonds of attraction to lower resin viscosity for new additive properties with nonpolar triclosan as a hydrophobic toughening/wetting agent. Further, bond rotations involving lone-pair electrons by a molecule at a nonpolar-hydrocarbon-membrane/polar-biologic-fluid interface might become sufficiently unstable to provide free mechanomolecular energies to disrupt weaker microbial membranes, for membrane transport of molecules into cells, provide cell signaling/recognition/defense and also generate enzyme mixing to speed reactions.

Phenyltellurenyl halide complexes of ruthenium and rhenium (CO)2RuBr2(PhTeBr)2 and (CO)3Re(PhTeI)3(μ3-I): Synthesis and crystal and molecular structures

Reactions of Ru3(CO)12 with PhTeBr3 and of Re(CO)5Cl with PhTeI in benzene give the stable complexes (CO)2RuBr2(PhTeBr)2 (I) and (CO)3Re(PhTeI)3(μ3-I) (II) containing two and three ligands PhTeX (X = Br or I), respectively. The bonds between these ligands and the central metal atom are fairly shortened (on average, Ru-Te, 2.608 A; Re-Te, 2.7554(12)-2.7634(13) A). The Te-X bonds in the ligands PhTeBr (2.5163(5) A) and PhTeI (2.7893(15) A) are not lengthened appreciably. In complex II, the iodide anion is not coordinated by rhenium, yet being attached through weak secondary bonds to three Te atoms of the three ligands PhTeI.

Thermal Mechanical Testing of Low Density Thermoplastic Foam

Foams made from engineered thermoplastic resin systems possess high glass transition temperatures. When compared to most thermoset resins, it was anticipated that lightly cross-linked foam candidates might survive high temperature/ pressure cures. This is especially true if the viscosity decline (i.e., loosening of weak secondary bonds) during sandwich bond cycles were found to be gradual enough to be controllable. To test this supposition, a low-cost five-step screening down-select methodology was utilized: (a) survey and evaluate vendor data, (b) pre-screen candidate foams using a vertical flame test, (c) characterize basic material properties using room temperature quasi-static compression testing, (d) evaluate failure mechanisms via elevated temperature compression testing, and (e) validate material functionality by conducting flat and contoured autoclave sandwich panel bond trials. None of the three candidate materials evaluated individually met all research requirements. Still, the population taken as a whole exhibited the potential for fulfilling the study's objectives. It is hypothesized that foam chemistry modifications, cell structure manipulation, and/or additional cure cycle process parameter management could lead to extended usage of foam in structurally demanding applications.

Enhanced paint adhesion to metals using in situ phosphatizing coatings

Adhesion of an organic coating is related to the density of weak secondary bonds, in general, and strong primary chemical bonds, in particular, produced between the coating and the substrate as well as their distributions, and also on the morphology and quality of coating. A 'green technology' for metal finishing, based on in situ phosphatizing coatings (ISPCs), is described to enhance the presence of primary bonds and applied to cold-rolled steel, 2024 T3 aluminum alloy, and Ti-6Al-4V titanium alloy. When an ISPC is applied to an untreated metal substrate, the in situ phosphatizing reagent (ISPR) reacts chemically and/or physically with the metal surface to produce a metal phosphate layer and simultaneously forms covalent phosphorus–oxygen–carbon linkages with the polymer coating. In an ISPC, the ISPR is designed both to phosphate the metal surface in situ and, at the same time, to catalyze the curing of the polymer coating or paint. Paint systems cured by ISPR give a dense and corrosion-resistant and a thermally stable and defect-free coating. The primary bonds and the less permeable paint coatings produced in ISPCs are shown to have enhanced adhesion and inhibit substrate corrosion. Moreover, an ISPC is a chromate-free single-step process in which the phosphate formation and polymer curing can occur independently, but simultaneously.

β-Donor Interactions as Secondary Bonds in Dichlorobis(dimethylaminoxy)silane and -germane

The compounds Cl2Si(ONMe2)2 and Cl2Ge(ONMe2)2 were prepared by the reaction of the appropriate tetrachlorides with N,N-dimethylhydroxylamine in the presence of 2,6-lutidine as an auxiliary base. The compounds were obtained as crystalline solids and characterised by elemental analysis, IR and NMR spectroscopy (nuclei 1H, 13C, 15N, 17O, and 29Si). Their molecular structures were determined by single-crystal X-ray diffraction. The compounds are isostructural and both show the presence of weak secondary bonds between the nitrogen and silicon centres (β-donor bonds), as is indicated by the small angles SiON [102.8(1) and 103.7(1)°] and GeON [102.0(1)°], and the distances Si···N (2.438 and 2.450 A) and Ge···N (2.519 and 2.520 A). The conformation is anti-gauche in both compounds (one O–Si–O–N torsion angle being about 180°, the other 60°), but the strength of the β-donor interaction is not significantly affected by the different anti-substituents at the nitrogen centres, although such behaviour was expected from earlier studies carried out on ClH2SiONMe2. The β-donor interactions are also weaker than those found in ClH2SiONMe2.

β-Donor Interactions as Secondary Bonds in Dichlorobis(dimethylaminoxy)silane and -germane

The compounds Cl2Si(ONMe2)2 and Cl2Ge(ONMe2)2 were prepared by the reaction of the appropriate tetrachlorides with N,N-dimethylhydroxylamine in the presence of 2,6-lutidine as an auxiliary base. The compounds were obtained as crystalline solids and characterised by elemental analysis, IR and NMR spectroscopy (nuclei 1H, 13C, 15N, 17O, and 29Si). Their molecular structures were determined by single-crystal X-ray diffraction. The compounds are isostructural and both show the presence of weak secondary bonds between the nitrogen and silicon centres (β-donor bonds), as is indicated by the small angles SiON [102.8(1) and 103.7(1)°] and GeON [102.0(1)°], and the distances Si···N (2.438 and 2.450 Å) and Ge···N (2.519 and 2.520 Å). The conformation is anti-gauche in both compounds (one O–Si–O–N torsion angle being about 180°, the other 60°), but the strength of the β-donor interaction is not significantly affected by the different anti-substituents at the nitrogen centres, although such behaviour was expected from earlier studies carried out on ClH2SiONMe2. The β-donor interactions are also weaker than those found in ClH2SiONMe2.

Elastic Attributes of Heated Egg Protein Gels

ABSTRACTThe equilibrium stress of egg white (EW) and ovalbumin (OV) gels using the statistical theory of rubber elasticity suggested that 3.9 covalent disulfide cross‐links per OV molecule were formed on gelling. DTNB and PCMB reacted with approximately 4 sulfhydryls of OV in 2% SDS and/or at 82°C. Moreover, the equivalent of 3 secondary bonds, calculated from the initial stress and presumably a composite of numerous weak secondary bonds, contributed significantly to the protein gel stress.

Secondary bonding. Part 9. Crystal and molecular structures of µ-oxo-bis[nitratodiphenyltellurium(IV)]–diphenyltellurium(IV) hydroxide nitrate (1/1), oxophenyltellurium(IV) nitrate, and diphenyltellurium(IV) dinitrate

The crystal and molecular structures of the title compounds have been determined from diffractometer data by the heavy-atom method. Crystals of [{Ph2Te(No3)}2O]–Ph2Te(NO3)(OH)(1) are triclinic, space group P, with unit-cell dimensions (290 K)a= 11.839(3), b= 11.220(1), c= 14.793(3)A, α= 90.85(1), β= 100.98(2), γ= 99.28(2)°, Z= 2, and for 5 577 observed reflections [I/σ(l) 3.0], R= 0.022. Crystals of [PhTeO(NO3)]n(2) are triclinic, space group P, with unit-cell dimensions (290 K)a= 11.555(5), b= 5.350(2), c= 14.987(3)A, α= 94.89(3), β= 110.68(3), γ= 106.07(3)°, Z= 4, and for 2 465 observed reflections, R= 0.026. Crystals of Ph2Te(NO3)2(3) are monoclinic, space group C2/c, with unit-cell dimensions (233 K)a= 17.929(6), b= 7.100(2), c= 11.193(2)A, β= 94.38(2)°, Z= 4, and for 1 100 observed reflections, R= 0.031. All three compounds contain four-co-ordinate pseudo-trigonal-bipyramidal tellurium atoms each with the lone pair in the vacant equatorial position. Compound (3) is essentially monomeric, while in (1) the component molecules are linked by bridging nitrate groups and (2) is polymeric. All contain weak secondary bonds Te ⋯ O (2.862–3.514 A), Te–C 2.094–2.120, Te–OH in (1) 1.953(3), Te–O(bridge) 1.887–2.015, and Te–O(NO3) 2.171–2.533 A.

ChemInform Abstract: SECONDARY BONDING. PART 5. THE CRYSTAL AND MOLECULAR STRUCTURES OF PHENYLIODINE(III) DIACETATE AND BIS(DICHLOROACETATE)

The crystal structures of the title compounds (1) and (2) respectively have been determined at –60 °C from diffractometer data by the heavy-atom method. Crystals of (1) are orthorhombic, space group Pnn2, with unit-cell dimensions a= 15.693(3), b= 8.477(2), c= 8.762(2)A, Z= 4, and R= 0.021 for 1 063 observed reflections. Crystals of (2) are triclinic, space group P with a= 10.462(3), b= 4.870(2), c= 15.445(5)A, α= 101.03(3), β= 99.89(3), γ= 94.40(3)°, Z= 2, and R= 0.058 for 1 580 observed reflections. For (1) the results are in good agreement with a recent independent determination. In both (1) and (2) the iodine(III) atoms form three covalent bonds with distorted T-shaped geometry. The I–C distances in both compounds are the same (2.08–2.09 A). The two I–O distances are the same (av. 2.156 A) for (1) but differ significantly for (2)[2.136(6) and 2.163(7)A]. The overall geometry of each iodine, however, can be described as a pentagonal-planar arrangement of three strong and two weak secondary bonds. In (1) both of these secondary I–O bonds are intramolecular. In (2), however, one of the ligands is unidentate, the other unsymmetrically bidentate, forming inter- and intra-molecular I ⋯ O contacts to give a dimeric arrangement. The formation and nature of the secondary bonds in (1) and (2) is discussed and compared with other pentagonal-planar systems. A possible orbital-overlap scheme is proposed to explain this geometry.

Secondary bonding. Part 5. The crystal and molecular structures of phenyliodine(III) diacetate and bis(dichloroacetate)

The crystal structures of the title compounds (1) and (2) respectively have been determined at –60 °C from diffractometer data by the heavy-atom method. Crystals of (1) are orthorhombic, space group Pnn2, with unit-cell dimensions a= 15.693(3), b= 8.477(2), c= 8.762(2)Å, Z= 4, and R= 0.021 for 1 063 observed reflections. Crystals of (2) are triclinic, space group P with a= 10.462(3), b= 4.870(2), c= 15.445(5)Å, α= 101.03(3), β= 99.89(3), γ= 94.40(3)°, Z= 2, and R= 0.058 for 1 580 observed reflections. For (1) the results are in good agreement with a recent independent determination. In both (1) and (2) the iodine(III) atoms form three covalent bonds with distorted T-shaped geometry. The I–C distances in both compounds are the same (2.08–2.09 Å). The two I–O distances are the same (av. 2.156 Å) for (1) but differ significantly for (2)[2.136(6) and 2.163(7)Å]. The overall geometry of each iodine, however, can be described as a pentagonal-planar arrangement of three strong and two weak secondary bonds. In (1) both of these secondary I–O bonds are intramolecular. In (2), however, one of the ligands is unidentate, the other unsymmetrically bidentate, forming inter- and intra-molecular I ⋯ O contacts to give a dimeric arrangement. The formation and nature of the secondary bonds in (1) and (2) is discussed and compared with other pentagonal-planar systems. A possible orbital-overlap scheme is proposed to explain this geometry.

The crystal structure of nuffieldite, Pb2Cu(Pb,Bi)Bi2S7*

Abstract Nuffieldite, a rare bismuth sulfosalt from Alice Arm, British Columbia, is orthorhombic, space group Pbnm, with a = 14.387(7), b = 21.011(15), c = 4.046(6) Å, ϱ meas = 7.01(7) g cm−3 and ϱ cal = 7.21 g cm−3 for Z = 4. Intensity data were photographically recorded with an integrating equi-inclination Weissenberg camera employing the multiple-film technique, and were measured with the aid of an automated photoscanner. The structure was solved with the symbolic addition procedure and refined, by least-squares techniques, to a disagreement index of 14.1%. The asymmetric unit of the structure contains 13 atoms: 5 heavy-metal atoms, Cu, and seven S atoms. On the basis of interatomic distances and coordination geometry, Pb and Bi were each assigned to a pair of heavy-metal sites; a fifth site is believed to contain Pb and Bi in disorder. The Cu atom is in tetrahedral coordination. The dominant feature of the structure is a quadruple PbBiS3 chain which is flanked by a pair of chains with Cu in tetrahedral coordination. This structural unit is identical to that found in the simpler sulfosalt aikinite, PbCuBiS3. The aikinite-like ribbons share an edge with a pair of new three-membered chains to form ten-membered ribbons which are linked only by Cu tetrahedra and weak secondary bonds.

分散系のレオロジー

Various colloidal systems including paints, printing inks, flour dough, clay paste, butters, powder bed etc. behave as substances showing very complicated mechanical properties.Their flow is non-Newtonian. Their specific viscosity-concentration relationships do not obey the Einstein law. They show thixotropy or rheopexy. Some powder systems appear as bodies showing dilatancy. Concentrated suspensions and emulsions behave as visco-elastic.The above-mentioned peculiar flow properties of colloidal suspensions and emulsions are characterized by various nonlinear nature and, from the structural point of view, formation of a scaffolding structure by the suspended or emulsified particles; the structure, which is formed by weak secondary bonds, is easily broken and regenerated in the field of flow.Some schemes of studying the complicated mechanical properties of colloidal disperse systems are discussed.One of the most classical methods of analysis is to describe their flow properties by a plastic yield value and plastic viscosity first proposed by Bingham. The concept of Bingham plasticity is conveniently applicable to the study of concentrated suspensions.Measurement of dynamic visco-elasticity of colloidal dispersions reveals the nature and the structural aspects of many rheological peculiarities. For example, spinnability or thread-forming property of some lyophile colloidal solutions is described as the superposed phenomena of viscous flow and elastic elongation.Description of their stress-strain-time behavior by the power law which was proposed by Nutting and Scott Blair makes an other way of studying rheology of pasty matters.Other schemes are of experimental nature. For example, it is recommendable to study the rheological properties of suspension of particles whose surface physico-chemical nature can be controlled by chemical treatment. Various synthetic latexes and suspensions of powders of ion-exchange resins are conveniently used as the model substances for the study of complicated rheological properties of colloids. Their surfaces are well-defined and easily controlled by chemical techniques.