Friction measurement in precision glass molding: An experimental study

Understanding the frictional behavior between glass and metals at elevated temperatures is necessary for accurate modeling and simulation of the state of the art applications such as the PGM process, pressing of micro lens arrays, hot embossing, and extrusion or drawing of glass fiber. In this research, the frictional behavior of N-BK7, an oxide glass, at elevated temperatures in contact with polished and coated tungsten carbide (WC) material and under conditions similar to the PGM process has been studied.The experimental results show that the friction coefficient between a polished and coated WC mold and N-BK7, which is a typical material for glass molding, and in conditions similar to those used in the PGM process ramps up to 0.7 and then levels off around 0.6 with a smooth transition, meaning that there is not a specific point to differentiate between static and dynamic friction. The friction coefficient of 0.6 is reported in literature for best fitting in micro lens molding simulation. Moreover, increasing the temperature in the transition regime in the mold/glass interface causes the friction force to increase which is in good agreement with the data published for the friction between soft polymeric material and metal in the transition regime.     

Supramolecular structure of calcium(II) based on chelidamic acid: An agreement between theoretical and experimental studies

A novel supramolecular structure of an s-Block metal ion, Ca(II) atom, formulated as (pnH₂)₂au][Ca₂(H₂O)₂(Hhypydc)₄]·4H2O (1), was synthesized and characterized by elemental analysis, IR, 1H and 13C NMR spectroscopies and single crystal X-ray diffraction. Compound 1 is a member of a large family of supramolecular metallic compounds recently derived from a proton transfer ion pair, (pnH2)(Hhypydc), where pn is propane-1,3-diamine and (Hhypydc)^2-is 4-hydroxypyridine-2,6-dicarboxylate ion. Based upon the molecular structure analysis of the binuclear anionic complex, the coordination environment around each Ca(II) atom is pentagonal bipyramidal with seven-coordination number. The strong hydrogen bonding between hydroxyl groups of two neighboring anionic complexes produce the nice tape as X-like supramolecular structure. Optimization was carried out using two standard basis sets of 6-31G (d,p) for the single anionic complex (S) and LanL2MB basis set for the double anionic complexes (D) which describe the electrons of all atoms. As an interesting finding from our theoretical calculations, when we reoptimized the double complexes in the presence of strong hydrogen bond interaction between two hydroxyl groups, O3-H3A??O8ⁱⁱ (ii = x-1, y, z-1), it was revealed that the parallel position of ligands to each other was exactly like that of the solid state. The complexation reaction of H3hypydc with Ca²⁺ in aqueous solution was investigated by potentiometric pH titrations, the equilibrium constants and species distribution in various pHs. The for major complexes formed are described.     

Hydrothermal synthesis, X-Ray crystallography, TGA and SEM analyses and solution studies of a novel Nano-sized 1D zinc(II) coordination Polymer

A novel coordination polymer of zinc(II) atom, [(pipzH₂)[Zn(pyzdc)₂].6H₂O]_n (1) (H₂pyzdc and pipz are pyrazine-2,3- dicarboxylic acid and piperazine, respectively), was successfully synthesized under hydrothermal conditions and structurally characterized by means of elemental analysis, FTIR, TGA and SEM. Polymer 1 was further structurally characterized by single crystal X-ray diffraction consisting of 1D-polymeric units. The crystal structure of the title polymer consisted of polymeric Zn complex anions and discrete piperazindiium cations. The Zn cation, located on the inversion center, was N,O-chelated by two (pyzdc)^2? anions in the basal plane, and was further coordinated by two carboxyl O atoms from the adjacent pyzdc anions in the axial directions with a longer Zn-O bond distance of 2.1746(15) ?, forming a distorted ZnN₂O₄ coordination geometry. The pyzdc anions bridged the Zn cations to the one-dimensional polymeric chains running along the crystalographic b axis. The (pipzH₂)²⁺ linked with the complex chains via kinds of hydrogen bonds. The polymer 1 crystallized in the monoclinic space group P2₁/n with Z = 2. The cell parameters of the title polymer were a = 6.5318(16) ?, b = 17.492(4) ?, c = 10.688(3) ? and ?? = 100.841(4)°. The polymer 1 bears ion-pairing interactions, O-H?O, N-H?O, and C-H?O hydrogen bonds as main factors in the formation of its 1D supramolecular architecture. Obtained results from TGA showed that the title polymer was thermally quite stable, and so its framework possessed remarkable thermal stability up to 700 °C. The SEM analysis verified that layers present in 1 were formed in Nano-sized particle. The protonation constants of acridine (Acr), H₂pyzdc, and pipz as the building blocks of the proton transfer systems including pyzdc-Acr in mixed 20% dioxane-80% water (V/V) solvent and pyzdc-pipz in aqueous solvent, and the corresponding stability constants of these systems were determined by potentiometric study. The stoichiometry and stability of complexation of these systems with Zn²⁺ ion were investigated by potentiometric pH titration method. The stoichiometry of the most complex species in the solution was compared with the corresponding crystalline metal ion complexes.     

A brief review of structural concepts of novel supramolecular proton transfer compounds and their metal complexes (part II)

In continuation of our previous brief review of structural concepts of novel supramolecular proton transfer compounds and their metal complexes by Aghabozorg et al. [1], we briefly surveyed the current research in the field of proton transfer compounds supramolecular synthons and their self-assembled metallic complexes from the points of view of Crystal Engineering and Density Functional Theory (DFT) since 2008. Our research groups have recently focused on the proton delivery from acids, which are considered to be suitable proton donors, to amines as proton acceptors. The results were the production of several proton transfer ion pairs possessing some remaining donor sites applied for coordination to metal centers in the preparation of metal-organic compounds. Some of the complexes showed contributions of both cationic and anionic fragments of the starting ion pair, while some others contained only one of these species as ligand. Our review and investigation of compounds revealed that they mainly focused on the concept of supramolecular systems, co-crystallization, stereochemically active lone pairs, coordination polyhedron, mainly on the various interactions involved, including van der Waals, ion pairing, hydrogen bondings, face to face ??-?? stackings and edge to face C-H???, C-O???, N-H3?? and S?S. These interactions were the most commonly used strategies in the extension of supramolecular structures.     

Computational studies of effects of tubular lengths on the NMR properties of pristine and carbon decorated boron phosphide nanotubes

Density functional theory (DFT) calculations were performed to investigate the effects of tubular lengths on the nuclear magnetic resonance (NMR) properties of boron phosphide (BP) nanotubes. To this aim, the properties of pristine and carbon decorated (C-decorated) models of representative zigzag and armchair BP nanotubes were investigated. The results indicated that the atoms at the edges of nanotubes do not detect any significant changes. The NMR properties of boron atoms only detect slight changes but those of phosphorous atoms are more notable.     

QTIPS: A novel method of unsupervised determination of isotopic amino acid distribution in SILAC experiments

Stable incorporation of labeled amino acids in cell culture is a simple approach to label proteins in vivo for mass spectrometric quantification. Full incorporation of isotopically heavy amino acids facilitates accurate quantification of proteins from different cultures, yet analysis methods for determination of incorporation are cumbersome and time-consuming. We present QTIPS, Quantification by Total Identified Peptides for SILAC, a straightforward, accurate method to determine the level of heavy amino acid incorporation throughout a population of peptides detected by mass spectrometry. Using QTIPS, we show that the incorporation of heavy amino acids in baker’s yeast is unaffected by the use of prototrophic strains, indicating that auxotrophy is not a requirement for SILAC experiments in this organism. This method has general utility for multiple applications where isotopic labeling is used for quantification in mass spectrometry.     

Synthesis, X-Ray characterization and molecular structure of a novel supramolecular compound of antimony(III); Theoretical investigation on molecular and electronic properties based on the ab initio HF and various DFT methods

A new compound of Sb(III), formulated as (pipzH₂)[Sb₂(pydc)₄].2H₂O (1), was synthesized and characterized by IR, ¹H and ¹³C NMR spectroscopy, elemental analysis and single crystal X-ray diffractometry. The compound (1) is a member of a great family of supramolecular metallic compounds recently derived from a proton transfer ion pair i.e. (pipzH₂)(pydc), where pipz is piperazine and pydcH₂ is pyridine-2,6-dicarboxylic acid. In the title compound with a binuclear structure, Sb(III) atoms are pentacoordinated and the coordination polyhedra show distortion from a regular trigonal bipyramid due to stereochemically active lone pair on metallic centers. The four (pydc)^2? ligands of the formula unit behave differently against metallic centers, i.e. two act as tridentate, and the other two as bidentate ligands. A variety of intermolecular O-H…O, N-H…O and C-H?O hydrogen bonds involving water molecules, cationic and anionic fragments are responsible for the extension of the supramolecular network of the compound. Optimized geometries were calculated for the title compound with the HF, B3LYP, B3PW91, B3P86 and B1LYP methods of theory by using the combination of LanL2DZ basis set with standard basis set 6-31G (d,p). The agreement between the optimized and experimental geometries was in the decreasing order: B3P86, B3PW91, B1LYP, B3LYP and HF. Electronic properties of the title compound were also investigated based on the natural bond orbital (NBO) analysis.     

Hydrogen Bonds of Peptide Group in Four Acetamide Derivatives: DFT Study of Oxygen and Nitrogen NQR and NMR Parameters

A computational study was conducted to examine hydrogen bond (HB) properties of peptide group in four derivatives of acetamide by density functional theory (DFT) calculations of nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) parameters at the sites of oxygen and nitrogen nuclei of peptide groups. The available crystalline structures of four derivatives; 2,2,2-trifluoro-N-(2-hydroxy-5-nitrophenyl)acetamide, N-(2-acetylphenyl)acetamide, 2-chloro-N-(4-nitrophenyl) acetamide, and N-(4-fluorophenyl)acetamide were obtained from literature. Following the influence of HB interactions, calculations were done on non-hydrogen bonded (single) and hydrogen bonded (cluster) models of derivatives. The results revealed different behaviors of peptide group in contributing to HB interactions in different derivative structures. HB interactions are the strongest in 2-chloro-N-(4-nitrophenyl)acetamide. However, the strengths of HB interactions in all of the four derivatives are still less than that of acetamide. The calculations are done at the level of B3LYP method and 6-311++G** standard basis set using GAUSSIAN 98 package of program.     

Synthesis and characterization of 2-alkyl -5-{4-[(3-nitrophenyl-5-isoxazolyl)methoxy]phenyl}-2H-tetrazoles

Heteroaryl substituted analogs of antirhnoviral (A), was prepared by a convergent approach. 3-Nitrophenyl-5- bromooromethylisoxazoles 5a–b were synthesized by [3+2] cycloaddition of 3-(benzoyloxy)-propyne 2 to in situ generated arylnitrile oxides followed by deprotection of cycloadducts 3a–b and bromination of the resulting alcohols 4a–b. Coupling of 3- nitrophenyl-5-bromooromethylisoxazoles (5a–b) with 4-[5-(2-alkyl-2H-tetrazolyl)]phenols (6a–d) in N-methylpyrrolidinone under mild conditions afforded a new series of 2-alkyl-5-{4-[1-(3-nitrophenyl-5-isoxazolyl)methyloxy]phenylr}-2H-tetrazoles (7a–h) in high yields. The structures of the synthesized compounds were confirmed by their ¹H NMR, Mass spectral, and Elemental Analysis data.