Im Molecules Research Articles

Synergistic effect of inhibitor mixture based on enhanced electron transfer

The inhibition performance of a mixture of an imidazoline quaternary ammonium salt (IM) and octylphenol polyoxyethene ether (OP) (IMO) toward carbon dioxide (CO2) corrosion of L245 steel in 3 wt% sodium chloride (NaCl) solution at 25°C was studied using electrochemical measurements. Notably, the inhibition efficiency of the IMO inhibitor stayed steadily in the long-term immersion test, and the inhibition efficiency increased with time. This was attributed to the improved electron-transfer performance between the inhibitor molecules and the metal surface. OP molecules promoted electrons to the metal, while IM molecules accepted electrons from the metal. The interactions between the inhibitor molecules and metal surface were enhanced, and the relative bonding intensities were improved. Moreover, the adsorption configurations of the mixture of IM and OP facilitated the improvement of the thickness and the compactness of the inhibitor layer. OP and IM showed a good synergistic inhibition effect.

Local Structures and Dynamics of Imidazole Molecules in Poly(vinylphosphonic acid)–Imidazole Composite Investigated by Molecular Dynamics

The composite materials of acidic polymers and imidazole (Im) exhibit good high-proton conduction, making them potentially useful in proton-exchange membrane fuel cells. The proton conduction mechanism must be clearly elucidated for the design of future high proton-conduction materials. This study examines the local hydrogen-bonding structures and dynamics of Im for proton-conducting poly(vinylphosphonic acid)-Im (PVPA-xIm) composites by using molecular dynamics simulations. Radial distribution functions (RDFs) characterize the hydrogen bonds between Im or imidazolium cation (ImH+) and phosphonic acid (PA) group and among Im molecules. RDFs and diffusion coefficients suggest that the intercalation of Im to PVPA reduces Im mobility because of the interaction between Im and PA groups. However, similar to pure Im, the amount of Im with fast rotational motions increases as the amount of Im increases. Our study leads us to conclude that long-range proton transport occurs through the hydrogen-bonding network of...

Proton conductivity of imidazole entrapped in H-forms of MFI zeolites

Imidazole (Im) introduced into the channels of H-MFI zeolites (with diverse framework Si/Al) shows remarkably enhanced proton conductivity in a broad temperature range (303–393 K), which increased with Im loading. Some conductivity raise is already noticed after its introduction into slilicalite-1 (i.e. SiO2) due to escalated Im dispersion and subsequently enhanced mobility inside the channels. The increase, however, becomes much more spectacular for the Im composites based on H-forms of aluminosilicate MFI zeolite matrices. It results from additional beneficial interaction of the guest Im with the zeolite acid sites, particularly OH groups, acting as additional proton carriers. Nevertheless, there is no straight correlation between the number of acid sites and the proton conductivity. It seems that the strong Lewis acid sites, contrary to Broensted centers, hinder the conduction, because of firm bonding the Im molecules and reducing their motion. Thus, both kind of sites compete with each other. The highest conduction noticed for the composites based on the H-zeolite with Si/Al = 50 results not so much from pronounced contribution of Broensted centers, but rather from the small number of Lewis sites which are relatively weak. Both Grotthuss and vehicle conductivity modes could be considered.

Local structure and hydrogen bond characteristics of imidazole molecules for proton conduction in acid and base proton-conducting composite materials.

Composite materials of acidic polymers and basic molecules have high proton-conductivity. Understanding the proton conduction mechanism of the composite materials, which depends on hydrogen bond characteristics, is an important task for developing materials with high proton-conductivity. This work is focused on poly(vinylphosphonic acid)-imidazole and alginic acid-imidazole as examples of composite materials of acidic polymers and basic molecules and examines the local structure and hydrogen bond characteristics of imidazole (Im) molecules in composite materials using density functional theory. The results show that Im molecules interact strongly with polymeric acids in these composite materials and that the interaction energy increases with the increase in the number of Im molecules. The rotational motion of Im molecules occurs in the segment where only Im molecules without excess protons are hydrogen-bonded to each other. The calculation results for the various segments, which depend on the hydrogen bonding environment, show that the proton conduction process in composite materials consists of the following steps: proton transfer in the segment where Im molecules interact with polymeric acids, proton transfer in the segment where Im molecules are affected by excess protons, and Grotthuss diffusion with reorientation of Im molecules in the segment where only Im molecules without excess protons are bonded to each other.

Crystal structure of Co(III) α-dimethylglyoximates with imidazole

Two new dimethylglyoximate complexes [Co(DmgH)2(Im)Cl] (I) and (ImH)[Co(DmgH2)2Cl2] (II), where DmgH− is the dimethylglyoxime residue and Im is the imidazole molecule, are synthesized. The composition and structure of the crystals are determined from the elemental analysis, IR spectra, and single crystal X-ray diffraction. Complex I is molecular, containing the Im molecule as a coordinated ligand; complex II is of the ionic type with (ImH)+ involved as an outer-sphere organic cation. The mode of component packing in the crystals mainly depends on the imidazole position in the compounds.

Effects of Imidazole-Type Ligands in CuI/TEMPO-Mediated Aerobic Alcohol Oxidation

Selective aerobic oxidation of benzyl alcohol to benzaldehyde by a (bpy)CuI(IM)/TEMPO catalyst (IM represents differently substituted imidazoles) has been studied by simultaneous operando electron paramagnetic resonance/UV-vis/attentuated total reflectance infrared spectroscopy in combination with cyclic voltammetry to explore the particular role of imidazole in terms of ligand and/or base as well as of its substitution pattern on the catalytic performance. For molar ratios of IM/Cu ≥ 2, a (bpy)CuI/II(IM)a(IM)b complex is formed, in which the Cu-N distances and/or angles for the two IM ligands a and b are different. The coordination of a second IM molecule boosts the oxidation of CuI to CuII and, thus, helps to activate O2 by electron transfer from CuI to O2. The rates of CuI oxidation and CuII reduction and, thus, the rates of benzaldehyde formation depend on R of the R-N moiety in the IM ligand. Oxidation is fastest for R = H and alkyl, while reduction is slowest for R = H. The CuI/CuII interplay leads to decreasing total benzaldehyde formation rates in the order R (I+ effect) > R (conjugated system) > R = H.

Study on Synergistic Mechanism of Inhibitor Mixture Based on Electron Transfer Behavior.

Mixing is an important method to improve the performance of surfactants due to their synergistic effect. The changes in bonding interaction and adsorption structure of IM and OP molecules before and after co-adsorbed on Fe(001) surface is calculated by DFTB+ method. It is found that mixture enable the inhibitor molecules with higher EHOMO donate more electrons while the inhibitor molecules with lower ELUMO accept more electrons, which strengthens the bonding interaction of both inhibitor agent and inhibitor additive with metal surface. Meanwhile, water molecules in the compact layer of double electric layer are repulsed and the charge transfer resistance during the corrosion process increases. Accordingly, the correlation between the frontier orbital (EHOMO and ELUMO of inhibitor molecules and the Fermi level of metal) and inhibition efficiency is determined. Finally, we propose a frontier orbital matching principle for the synergistic effect of inhibitors, which is verified by electrochemical experiments. This frontier orbital matching principle provides an effective quantum chemistry calculation method for the optimal selection of inhibitor mixture.

Effect of surface coating of microcrystalline cellulose by imidazole molecules on proton conductivity

The proton conductivity properties of a newly synthetized proton-conducting composite (Cell-Im) composed of the microcrystalline cellulose grains (Cell) coated with different amount of imidazole molecules (Im) have been investigated. For the composite with the highest concentration of Im (on average 1 Im molecules is bonded to approximately 5.44 glucose rings; 5Cell-Im), the increase in the maximum conductivity by nearly 3 orders of magnitude with respect to that of neat cellulose, and the extension of the temperature range application up to 160°C was evidenced in anhydrous conditions. Under these conditions two contributions to the overall conductivity of 5Cell-Im were recognized in the temperature range of 60–150°C. They are related to the imidazole layers at grain surfaces and intergrain contacts, respectively. The interior of the cellulose grains is treated as a nearly “perfect” dielectric with a negligible contribution to conductivity. The lowering of the Im concentration at the cellulose grain surface leads to decreasing of the surface conductivity. A characteristic phase transition from proton conductivity state to non-conductivity one with typical percolation threshold is well documented.

Local Structure and Dynamics of Imidazole Molecules in Proton-Conducting Poly(vinylphosphonic acid)–Imidazole Composite Material

Many proton-conducting polymers, including imidazole and its derivatives, have been developed for their applications in solid electrolyte fuel cells. It is thought that proton conduction is caused by the Grotthuss mechanism associated with the reorientational motion of imidazole molecules in these materials. However, there are still very few analyses of the relation between proton conduction and the reorientational motion of imidazole molecules following the detailed investigation of the molecular motion of imidazole. In the present work, molecular motions and their influence on proton conductivity were investigated for poly(vinylphosphonic acid) (PVPA)–imidazole (Im) composite material (PVPA/xIm, where x is the molar ratio of Im to polymer repeat unit) by solid-state NMR. Between 20 and 50 °C, the Im molecule undergoing pseudoisotropic rotation with small anisotropy accounted for more than 90% and that undergoing rotational vibration for less than 10% for PVPA/2Im. The tight segment, where Im molecules undergo rotational vibration, prevents long-range proton conduction. Above 60 °C, efficient proton conduction accompanied by pseudoisotropic rotation of the Im molecules was confirmed in PVPA/2Im.

A Novel Organosulfonate Cadmium(II) Complex with Graphite‐like 2D Layer Linked by Hydrogen Bonds

AbstractA novel mixed‐ligand complex, [Cd(im)6][Cd(im)3(H2O)3]2(ans)6·8H2O (1), was obtained from the reaction ofCd(OAc)2·2H2O, imidazole (im) and sodium 4‐aminonaphthalene‐1‐sulfonate tetrahydrate (Na‐ans) in a mixed solvent at 25 °C. The complex was characterized by elemental analysis, IR spectroscopy, and X‐ray single crystal diffraction. There are two kinds of cations constructed by CdII atoms with a octahedral coordination arrangement in 1. The CdII atom is bonded by six nitrogen atoms from six im ligands in the first cation, and the second central CdII atom is bonded by three nitrogen atoms of im molecules and three oxygen atoms belonging to water molecules. The ans anion acts as a counterion to balance the charge, and the adjacent anions are reversed but non‐parallel interlinked by N–H···O(S) hydrogen bonds into graphite‐like 2D sheet viewed from the c axis. The anionic channels along the [110] direction are filled with the cations, and the two kinds of cations are alternatingly arranged in the channels. The hydrogen‐bonding interactions together with the ionic bonds stabilize the crystal structure. The thermostability of the complex was investigated by TG and DSC.

Proton conduction of DNA–imidazole composite material under anhydrous condition

Materials with high anhydrous proton conduction at intermediate temperatures (100–200 °C) have attracted remarkable interest for applications in a polymer electrolyte membrane fuel cell (PEMFC). Especially, for the development of PEMFC technology, an anhydrous proton-conductive material, which is low cost and benign for the environment, has been desired. In this study, an anhydrous proton conductor was prepared by mixing double-stranded DNA (dsDNA), the most important genetic material of living organisms, and the imidazole (Im) molecule, a heterocyclic molecule. This DNA–Im composite material showed a thermal stability owing to electrostatic interaction between the phosphate group of DNA and −N= group of the Im molecule. In addition, DNA–Im showed an anhydrous proton conduction of 5.2 × 10−3 S cm−1 at intermediate temperature. On the other hand, the single-stranded DNA–Im composite material did not show high anhydrous proton conduction. Therefore, the high anhydrous proton conduction in dsDNA–Im composite material was due to the arrangement of phosphate groups along the one-dimensional molecular chain. These results suggested that the DNA–Im composite material possesses two proton-conducting pathways in the composite material. An anhydrous proton conductor was prepared by mixing with double-stranded DNA (dsDNA), the most important genetic material of living organisms, and the imidazole (Im) molecule, one of the heterocyclic molecules. This DNA–Im showed an anhydrous proton conduction of 5.2×10−3 S cm−1 at the intermediate temperature. On the other hand, the single-stranded DNA–Im composite material did not show the high anhydrous proton conduction. Therefore, the high anhydrous proton conduction in dsDNA–Im composite material was due to the arrangement of phosphate groups along the one-dimensional molecular chain.

Vibrational predissociation spectroscopy and theory of Ar-tagged, protonated Imidazole (Im) Im1–3H+·Ar clusters

We report vibrational predissociation spectra and theoretical analysis of the Ar-tagged cluster ions of imidazole, Im1–3H+·Ar. The frequencies of the external N–H stretches are observed to incrementally blue-shift toward that of neutral imidazole upon addition of the second and third Im molecules, consistent with the calculated behavior of the Im3H+ complex in which the excess charge is symmetrically shared by two internal N–H–N hydrogen bonds. A very strong, symmetrical doublet near 1000cm−1 is observed for the Im2H+ complex and attributed to the parallel bridging proton displacement based on anharmonic frequency calculations.

Formation of supramolecular complex between imidazole and dichloro(5,10,15,20-tetraphenylporphinato)zirconium(IV)

By the reaction of 5,10,15,20-tetraphenyl-21H,23H-porphin (H2TPP) with zirconium tetrachloride in boiling benzonitrile a complex was obtained, dichloro(5,10,15,20-tetraphenylporphinato)zirconium(IV), (Cl)2ZrTPP. The equilibrium and reaction rate of stepwise reactions of (Cl)2ZrTPP with imidazole (Im) in toluene were investigated by spectrophotometry. It was established that the three steps of the complex formation include reversible processes of coordination of Im molecule and substitution of 2Cl− by the second and third Im molecules. The products of the first and second stages of the reaction, (Cl)2(Im)ZrTPP and [(Cl)(Im)2ZrTPP]+Cl−, respectively, are unstable and dissociate slowly at one Zr-Cl bond. By the analysis of the numerical values of the reactions parameters with accounting for the existence of definite spectral response to the presence of an organic base was shown a better prospect of application of (Cl)2ZrTPP in sensor systems than those of metallophtalocyianines and doubly charged cation complexes with porphyrins.

Hydrogen-bonded assembly of [Ni(Im)6]2+ ion and phosphorus anions: Different sandwiched-type/tessellate-type supramolecular architectures and 1D water chains

Four new [Ni(Im)6]2+-phosphorus compounds, namely, [Ni(Im)6](PO4)·ImH·4 H2O (1), [Ni(Im)6][Ni(AEDPH)(Im)3]2 (2) [Ni(Im)6][Ni(AEDP)(Im)3]·Im·3 H2O (3), [Ni(Im)6][Ni(Im)3(APTPH)]·Im·ImH·8 H2O (4), (AEDPH4 = 1-aminoethylidenediphosphonic acid, APTPH6 = 1-aminopropane-1,1,3-triphosphonic acid), are synthesized and characterized. These compounds illustrate various three-dimensional (3D) supramolecular structures. Compounds 1 and 2 both contain a two-dimensional (2D) packing arrangement of [Ni(Im)6]2+ ions however they feature different sandwich-type structures: in 1, PO43− ions and ImH+ ions are self-assembled to form a one-dimensional (1D) zigzag supramolecular chain; while a 2D pillared layer structure is generated by the interconnection of [Ni(AEDPH)(Im)3]− ions in 2. Compounds 3 and 4 both comprise a 1D packing arrangement of [Ni(Im)6]2+ ions however they form dissimilar tessellate-type architectures: in 3, 1D double chain structure is constructed by [Ni(AEDPH)(Im)3]2− ions and Im molecules, whereas in 4, [Ni(Im)3(APTPH)]3− ions, Im molecules and ImH+ ions are integrated to generate a 3D supramolecular network with extended 1D channels. Moreover, compounds 1, 3 and 4 all contain diverse 1D water chain structures: C8 helix water chain in 1, C4 zigzag water chain in 3, and 1(1)8(1)C14 wavelike water chain in 4. The effects of phosphorus counterions on the structural types of the final products, as well as the hydrogen bond motifs, are also discussed in detail.

Ligand substitution equilibrium in the macrocyclic molybdenum(V) complex

The thermodynamics of the reaction of tetraphenylporphyrin(oxo)(hydroxo)molybdenum with imidazole (Im) in toluene was studied spectrophotometrically in a polythermal mode. It was established that the reaction of Im with O=Mo(OH)TPP includes several stages, two of which can be studied by spectrophotometrical titration. The first equilibrium stage is Im coordination to the eighth coordination site (K 1 = 1.85 × 103 l/mol), the second stage is the coordination of the second Im molecule with the displacement of OH− into the outer sphere (K 2 = 4.80 × 102 l/mol). The enthalpy and entropy contributions to the stability constant of tetrapheny lporphyrin molybdenum(V) complexes with Im were determined.

Structure characterization of several oxalate-bridged transition-metal coordination polymers

Four oxalate-bridged transition-metal supramolecular compounds [Co 2(im) 4(ox) 2] 1, [Co(im) 2(ox)] 2, [Mn(2,2′-bpy)(ox)] 3 and [Fe(H 2O) 2(ox)] 4 (im, imidazole; ox, oxalate; bpy, bipyridine) were obtained from the simple hydrothermal reactions of M n+ ox L (M, transition metal; L, aromatic N-donor ligand) system. They all exhibit the 1-D chain structures, consisting of the ML 2 2 + (or ML 2+) units linked by oxalate bridges. Interestingly, the 1-D oxalate chains in the title compounds are further self-assembled into the 3-D supramolecular networks through the interchain various secondary bonding interactions. Because the ML 2 2 + units adopt the different configuration, the oxalate chains show either zigzag type as in compounds 1– 3 or linear type as in compound 4. Compounds 1 and 2 are isomeric, and only in packing modes of interchain im molecules there exists the difference.

Oxalate-bridged transition-metal supramolecular polymers: syntheses, structures and properties of [Co(im) 2(C 2O 4)] and [Fe 2(im) 4(C 2O 4) 2

The hydrothermal reactions of K 3[M(C 2O 4) 3] (M=Co, Fe) and imidazole (im) molecule result in the syntheses of two oxalate-bridged transition-metal supramolecular polymers: [Co(im) 2(C 2O 4)] 1 and [Fe 2(im) 4(C 2O 4) 2] 2. Both exhibit the one-dimensional (1D) zigzag chain structures with the tetradentate oxalato bridges and ancillary im molecules, and are further propagated into a 3D supramolecular network via the interchain weak N–H⋯O hydrogen bonds. The TG behaviors of both are studied and thermally stable up to ca. 180 and 270°, respectively. The third-order non-linear optical properties of both were also studied, and both exhibit the reverse saturable absorption and self-defocusing performance with the γ values of 1.55×10 −31 esu for 1 and 1.02×10 −31 esu for 2, respectively.

Crystal Structures and Properties of New Mixed-Ligand Complexes of Nickel(II) Diisobutyldithiophosphinate with Imidazole and 3,5-Dimethylpyrazole

The reaction of Ni{(i-C4H9)2PS2}2 with imidazole and 3,5-dimethylpyrazole in ethanol gave paramagnetic (μef = 3.02 and 3.11 BM) mixed-ligand complex compounds [Ni(Im)2{(i-C4H9)2PS2}2] (I) and [Ni(Pyr){(i-C4H9)2PS2}2] (II). Single crystals were grown and the crystal structures of I and II were determined from X-ray diffraction data (CAD-4 diffractometer, Mo\(K_\alpha \) radiation, 1483 \(F_{hkl} \), R = 0.0344 for I and 2630 \(F_{hkl} \), R = 0.0486 for II). The crystals are monoclinic with cell dimensions a = 12.845(2), b = 10.250(1), c = 13.431(1) A, β = 115.89(1)°, V = 1591(1) A3, Z = 2, dcalc = 1.281 g/cm3, space group \(P2_{1/c} \) (for I); a = 11.152(3), b = 12.483(2), c = 23.389(4) A, β = 100.78(1)°, V = 3199(2) A3, Z = 4, dcalc = 1.191 g/cm3, space group \(P2_{1/n} \) (for II). The structures consist of discrete monomer molecules. The coordination polyhedron of the Ni atom is a compressed octahedron NiN2S4 (in I) and a tetragonal pyramid NiNS4 (in II) formed by four S atoms of the two cyclic bidentate ligands i-Bu2\(PS_{2^\_ } \) and the N atoms of two monodentate ligands (Im molecules in trans-positions) or the N atom of the monodentate Pyr ligand in complexes I and II, respectively. The character of interaction between molecules I and II and molecular packing modes are considered. The electronic spectra of the complexes are consistent with the symmetry of chromophores found from X-ray data.

Wladimir Markownikoff (1838–1904)

ON December 22 occurs the centenary of the birth of the Russian chemist Wladimir Markownikoff, whose investigations in the latter part of last century were of great importance to the petroleum industry. He was born in the neighbourhood of Nijni-Novgorod and was a student at the University of Kasan, where he came into contact with Alexander Mikhailovitch Butlerow (1828-1886), whom he succeeded in 1869 when the latter had been transferred to the chair of chemistry in the University of St. Petersburg. Meanwhile, Markownikoff had been sent to Germany, where he worked under Kopp, Baeyer and Kolbe. After his return to Kasan he published his memoir “Ueber die reciproke Beeinflussung der Atomie im Molecule”. In 1871, with five colleagues, he resigned his post for political reasons, but received an invitation to the chair of chemistry at Odessa, whence he was transferred to Moscow in 1873. Here he began his long and arduous investigations of Caucasian petroleum. In 1893, without · any reason being assigned, he was deprived of his chair, his emoluments, and his official residence, but nevertheless he continued to carry on his researches in his own house, assisted by his faithful servant Mikhailo. He died suddenly on February 11, 1904. He wrote some sixty memoirs relating to petroleum, army disinfection practice, the plague and the chemical industry in Russia. In 1898 he was elected a foreign member of the Chemical Society, in the Proceedings of which E. J. Mills wrote of him as a conscientious man of science of unremitting industry, and in political affairs an outspoken patriot.