Benzimidazole Units Research Articles

Synthesis, Crystallography, and Magnetic Properties of 2-tert-Butylaminoxylbenzimidazole

The title nitroxide is stable at room temperature for months. ESR spectroscopy shows moderate spin delocalization from the nitroxide unit onto the benzimidazole unit. The radical crystallizes in th...

Fabrication of fibres from sulfuric acid solutions of copolyamides containing polyamide—Benzimidazole units and their heat treatment

Fibres based on the aromatic rigid-chain polyamides PABI/PPTA, PABI/PPTA-Cl, and PABI/PPTA-Cl/PPTA with a strength of 130–150 cN/tex were fabricated by spinning from LC sulfuric acid solutions through an air gap, demonstrating the induced elastic character of deformation with tensile stress greater than 50 cN/tex. The fibres obtained can be strengthened significantly as a results of heat treatment, and the best variant is preliminary thermal drawing at 90–175°C with subsequent heat treatment without tension. This heat treatment increases the strength of the fibres to 240–266 cN/tex and the modulus of elasticity to 145 GPa.

New π-Conjugated Polymers Derived from a Benzimidazole Unit. Preparation, Solvatochromism, and Oxidation of Poly(aryleneethynlene)s Composed of 2-(3,5-Di-tert-butyl-4-hydroxyphenyl)benzimidazole Bearing a Hindered Phenolic Substituent

New π-conjugated polymers constituted of a benzimidazole unit have been prepared. Palladium-catalyzed polycondensation between 4,7-dibromobenzimidazole bearing a hindered phenolic substituent (3,5-di-tert-butyl-4-hydroxyphenyl) and four kinds of diethynylaromatic compounds HC⋮CArC⋮CH (e.g., Ar = p-phenylene (p-Ph), m-phenylene (m-Ph), and pyridine-2,5-diyl (2,5-Py)) gives the corresponding poly(aryleneethynylene) (PAE) type polymers in high yields. The polymers with the p-Ph, m-Ph, and 2,5-Py groups have molecular weights of (0.4−3.3) × 104, as determined by GPC. The position of the π−π* absorption band as well as photoluminescence intensity of the polymers strongly depends on the kind of solvent. In general, the π−π* absorption peak of the PAE-type polymers with the p-Ph groups shifts to a shorter wavelength in acidic organic solvents, whereas that of the PAE-type polymers with the 2,5-Py unit shifts to a longer wavelength in the acidic solvent. Intensity of the photoluminescence increases in the acidic media. The polymers as well as a model compound are oxidized with PbO2. The oxidized products give rise to an IR peak at about 1680 cm-1, which is assigned to ν(CO) originated from resonance structures of the oxidized species, and their ESR signals appear at about g = 2.0 with a peak-to-peak line width of 8−11 G.

Self-Assembled Dinuclear Lanthanide Helicates: Substantial Luminescence Enhancement upon Replacing Terminal Benzimidazole Groups by Carboxamide Binding Units.

The segmental ligands bis{1-alkyl-2-[6'-(N,N-diethylcarbamoyl)pyridin-2'-yl]benzimidazol-5-yl}methane (alkyl = methyl (L(5)), ethyl (L(6))) react with lanthanide perchlorates (Ln = La, Eu, Gd, Tb) in acetonitrile to yield the f-f dinuclear homotopic triple-stranded helicates [Ln(2)(L(i)())(3)](6+) (i = 5, 6) under thermodynamic control. The crystal structure of [Tb(2)(L(6))(3)](ClO(4))(3)(MeCN)(2)(THF)(0.5)(EtOH)(0.5) (11a, C(124)H(145)N(26)O(31)Cl(6)Tb(2), triclinic, P&onemacr;, Z = 2) shows the wrapping of the ligands about a pseudo-C(3) axis passing through the metal ions. The Tb ions are 9-coordinate in facial pseudo-tricapped trigonal prismatic sites and are separated by 9.06 Å. (1)H-NMR and ES-MS data establish that the triple helical structure is maintained in solution. Spectrophotometric titrations (Ln = La, Eu) indicate log beta(23) = 24-25 and the formation of a 2:2 complex [Ln(2)(L(5))(2)](6+) (log beta(22) = 19-20). Quantum yield determination in acetonitrile shows that the terminal N,N-diethylcarboxamide groups in L(5) favor efficient intramolecular L(5) --> Eu(III) energy transfers leading to strong Eu-centered red luminescence, 50 times as intense as the luminescence observed when the carboxamide groups are replaced by substituted benzimidazole units in [Eu(2)(L(4))(3)](6+). Resistance toward hydrolysis also results from the use of carboxamide groups, and no quenching of luminescence is observed for [Eu(2)(L(5))(3)](6+) in moist acetonitrile up to 2.5 M water. The crucial role played by carboxamide groups for the control of structural, electronic, and photophysical properties is discussed. Replacing perchlorates by triflates allows the isolation of the dinuclear double-stranded helicate [Eu(2)(L(6))(2)(CF(3)SO(3))(4)(H(2)O(2))(2)](CF(3)SO(3))(2)(MeOH)(2)(H(2)O)(5)(.5), whose crystal structure (13a, C(85)H(106)Eu(2)F(18)N(16)O(30)S(6), monoclinic, C2/m, Z = 2) reveals a side-by-side arrangement of the two strands and 9-coordinate Eu ions linked through hydrogen-bonded water molecules.

Three-phase transport studies of benzimidazole ligands bearing hydrophobic N-alkyl substituents: transport of metal(II) ions (Ni, Cu, Zn, Cd) in single- and multiple-ion experiments †

New ligands having two benzimidazole units, or one benzimidazole and one carboxylic acid unit, the two functions linked by a chain, and bearing hydrophobic N-alkyl substituents have been tested as transfer agents for metal(II) ions (Ni, Cu, Zn, Cd) using three-phase transport techniques. The transport was pH-dependent, so all comparisons were made with buffered feed and receiving phases at fixed pH. Variations in the nature and number [single and double N-alkyl-substituted bis(benzimidazole) ligands] of N-alkyl substituents, linker chain and its donor atoms were explored and resultant transport trends are discussed. While single-ion transport results were ambivalent (singly alkylated 2-oxapropane derivatives being the best extractants for copper, and the analogous 2-thiapropane ligands for zinc), in multiple-ion experiments copper was always transported in preference to zinc. Even for ligands with a longer linking chain (based on 2,5-dioxaoctane) the order for extraction of metal(II) ions was always Cu > Zn > Cd and the transport of Ni was negligible. From the benzimidazole ligands screened, those having a carboxylic acid moiety reveal the highest metal-ion selectivity.

Synthesis and dynamic NMR studies of Rhenium(I) tricarbonyl bromide complexes of benzimidazolylpyridine ligands. Crystal structure of [ReBr(CO) 3{2,6-bis(1′,5′,6′-trimethylbenzimidazol-2′-yl)pyridine}

Pentacarbonylbromorhenium(I) reacted with 2,6-bis(benzimidazol-2′-yl)pyridine (bbip), 2,6-bis(1′-methylbenzimidazol-2′-yl)pyridine (bmbip), 2,6-bis(5′,6′-dimethylbenzimidazol-2′-yl)pyridine (bdmbip), and 2,6-bis(1′,5′,6′-trimethylbenzimidazol-2′-yl)pyridine (btmbip) to form stable octahedral complexes of type fac-[ [ReBr(CO) 3L] (L = bbip, bmbip, bdmbip or btmbip in which L is acting as a bidentate chelate ligand. At above-ambient temperatures in solution the complexes are fluxional with the nitrogen ligand oscillating between equivalent bidentate bonding modes. Rates and activation energies for these fluxions have been investigated by NMR methods. At low temperatures rotation of the uncoordinated nenzimidazolyl unit is restricted and for fac-[ReBr(CO) 3(btmbip)] in CD 2Cl 2 solution, two preferred rotamers exist in 89:11% relative abundances. A rotational energy barrier has been estimated. The X-ray crystal structure of fac-[ReBr(CO) 3)(btmbip)] confirms the bidentate chelate bonding of btmbip with a NReN angle of 74.2°. The pendant benzimidazole unit is inclined at an angle of 60.7° to the pyridine ring.

Novel poly(ether benzimidazole)s from bis(nitrobenzimidazole) derivatives

Summary In this paper, we present experimental findings on the synthesis and characterization of novel poly(ether benzimidazole)s (PEBIs). A group of new polybenzimidazoles has been prepared by condensation of activated aromatic dinitro compounds containing preformed benzimidazole units and 1,6-hexandiol in N-methylpyrrolidone (NMP). These polymers were obtained in high to quantitative yields and with varying molecular weights (inherent viscosities from 0.43 to 0.77 dL/g), which in some cases were in the fiber forming range. They show high thermal stability, decompose above 400 °C and have glass transition temperatures in the 240–300 °C range.

Synthesis and characterization of poly(amide imides) containing benzimidazole-rings

New poly(amide imides) were prepared from benzimidazole-ring containing diamine via one-pot synthetic method. The diamine monomer, 6,4′-diamino-2-phenylbenzimidazole, was prepared from 4-nitrobenzoyl chloride and 4-nitro-1,2-phenylenediamine with 3 steps. It was found that the degree of imidization of the poly(amide imides) containing benzimidazole-ring can be controlled by monomer composition and solution imidization conditions. All partially imidized poly(amide imides) were soluble in polar aprotic solvent, but became insoluble in any organic solvents after thermal curing. The thermal stability of the poly(amide imides) increased as the polymers contain more benzimidazole units.

A tetracyclic benzimidazole derivative of Kemp's triacid

Fusion of Kemp's triacid with o-phenylenediamine produced a unique tetracyclic compound, identified structurally by X-ray crystallography and solution NMR spectroscopy, having one of the original carboxylic groups free, one forming a benzimidazole unit, which itself forms an amide with the remaining carboxylic group.

2-Hydroxymethyl-1-pentylbenzimidazole Hemi(1,4-dioxane) Solvate

2-Hydroxymethyl-1-pentylbenzimidazole serves as a simple model for the active site of hydrolytic metalloenzymes. The crystal structure shows that this compound crystallizes with 1,4-dioxane molecules: two benzimidazole units for one solvent molecule, C 13 H 18 N 2 O.0.5C 4 H 8 O 2 . The benzimidazole rings are hydrogen bonded (O-H...N) into dimers.

Self-assembly and photophysical properties of lanthanide dinuclear triple-helical complexes

The dinucleating ligand bis[ 1- methyl-2-(6'- [ 1”-(3,5 imethoxybenzyl)benzimidazol-2~'-ylp]y rid-2'-y1)benzimidazol- 5-yllmethane (L) reacts with lanthanide perchlorates to give dinuclear 2:3 complexes [Lnz(L)#+ (Ln = La, Eu, Gd, Tb, and Lu). Detailed ES-MS, lH-NMR, luminescence, and spectrophotometric measurements in acetonitrile show that the cations [Ln2(L)#+ are produced by strict self-assembly and adopt a triple-helical structure in solution (pseudo-D3s ymmetry). The crystal structure of [EU~(L)~] C~O~)~((1C1H, E~UC2NC1)9s~H 177N39036_Cl6,a = 17.634- (3) A, b = 21.408(4) A, c = 29.437(7) A, a = 82.13(1)', /3 = 85.76(1)', y = 89.79(1)', triclinic, P1, Z = 2) shows a dinuclear pseudo-D3 triple- elical cation, [Eu2(L)#+, where the three bis(terdentate) ligands L are wrapped around the helical axis defined by the europium atoms. The Eu(II1) of each site is 9-coordinated by six nitrogen atoms of the benzimidazole units occupying the vertices and three nitrogen atoms of the pyridine units occupying the capping positions of a slightly distorted, tricapped trigonal prism. Luminescence studies of the crystalline complex [Eu~(L)~]- (ClO.n n = 2, solv = H20,6; n = 9, solv = H20,7) confirm the pseudo-D3 symmetry of the Eu(II1) sites in 11 and show that secondary interactions with water molecules in 6 and 7 destroy the trigonal symmetry. An efficient intramolecular energy transfer between the %A* excited state centered on L and the excited levels of Eu(II1) and Tb(II1) is observed (antenna effect) together with a dipole4ipolar Tb - Eu intramolecular energy transfer in the heterodinuclear-doped Eu-Tb compound. Stability constants and 1H NMR in acetonitrile show that the homodinuclear complexes [LI I ~ (L) ~ ]a~re+ l ess stable for the heavier lanthanides Tb and Lu. The origin of this effect is discussed together with the nonstatistical distribution of the different species observed when stoichiometric quantities of L (3 equiv) are mixed with Ln1(C104)3 (1 equiv) and L I I ~ ( C ~ O(1~ e)q~ui v) in solution (Ln1 # Ln2; Ln1 = La, Eu, Tb, and Lu; Ln2 = Tb and Lu).

Molecular recognition between ligands and nucleic acids: novel pyridine- and benzoxazole-containing agents related to Hoechst 33258 that exhibit altered DNA sequence specificity deduced from footprinting analysis and spectroscopic studies

The syntheses of certain analogues of the DNA minor groove binding agent Hoechst 33258 designed to exhibit altered sequence recognition are described. The structural modifications include the following: substitution of pyridine for the benzene ring of the benzimidazole moiety, replacement of one benzimidazole unit by a benzoxazole in the two possible orientations with respect to the DNA receptor, and a synthesis of 2,2'-m-phenylene-bis[6-(4-methyl-1-piperazinyl)benzimidazole]. Sequence recognition of these agents on a HindIII/EcoRI fragment of pBR322 DNA was determined by MPE footprinting procedures. Some of the analogues exhibited altered DNA sequence preference compared with Hoechst 33258. In particular, a structure bearing a benzoxazole moiety with the oxygen oriented inward to the minor groove together with an inward-directed pyridine nitrogen appears to confer the property of recognition of a GC base pair within the binding sequence. The possible factors, structural, stereochemical, and electrostatic, contributing to the altered DNA sequence recognition properties are discussed.

Isohelical analysis of DNA groove-binding drugs

Many antitumor drugs, and many carcinogens, act by binding within the minor groove of double-helical DNA, interfering with both replication and transcription. Several of these, including netropsin and distamycin, are quite base specific, recognizing and binding only to certain base sequences. The repeating pyrrole-amide unit of netropsin, and the repeated benzimidazole unit of the DNA stain and carcinogen Hoechst 33258, both are approximately 20% too long for synchronous meshing with base pairs along the floor of the minor groove in B DNA. We have carried out a systematic computer search for possible repeating drug backbones that are isohelical with DNA and that also provide chemical groups capable of reading and differentiating between A X T and G X C base pairs. These isohelical sequence-reading drug polymers or "isolexins" should offer the possibility of targeting synthetic drug analogues specifically against one region of a genome rather than another, or against neoplastic cells in preference to normal cells.

Preparation and complexation of polydentate and macrocyclic ligands incorporating benzimidazole. X-Ray crystal structure of 6,7,9,10,12,13,15,16-octahydro-23H,25H-bis(benzimidazo[1,2-j:2′,1′-o])[1,4,7,13,10,16]tetraoxadiazacyclo-octadecine

A number of ligands, including some macrocycles, all with benzimidazole units incorporated, have been synthesised. These co-ordinate CuII and other transition metals with the imidazole nitrogen and other donor atoms included in the ligand design. The crystal structure data for a representative macrocycle, 6,7,9,10,12,13,15,16-octahydr-23H,25H-bis(benzimidazo[1,2-j:2′,1′-o])[1,4,7,13,10,16]tetraoxadiazacyclo-octadecine, are presented, together with spectroscopic and other details of representative complexes.

Topological analysis of non-linearity in auditory evoked potentials : A. Shikata, T. Kawashima, Y. Sekimoto, T. Masuzaki, S. Watanabe and Y. Shikata

A series of benzimidazole derivatives with varied benzimidazole groups, i.e., mono- (B-1), di- (B-2 and B-3), and trifunctional (B-4), are focused as model compounds for a systematic study to understand the relationship between the hydrogen bond network including its consequent packing structure and the proton conductivity in an anhydrous system. The different number of benzimidazole units in a molecule initiates a different packing structure under the hydrogen bond network of which B-1 provides a perpendicular hydrogen bond network, B-2 and B-3 provide a parallel hydrogen bond network under a lamellar structure, and B-4 forms a helical hydrogen bond network under a columnar structure. The study reveals that the proton conductivity of heterocycles in anhydrous system and doped with polyphosphoric acid is significant when (i) more benzimidazole groups is exist in a single molecule to form hydrogen bond networks, (ii) each benzimidazole is closely packed to allow an effective proton transfer from an NH in one benzimidazole unit to another, and (iii) the packing structure forms a specific channel to favour efficient proton transfer such as columnar packing structure. The present work is a guideline to develop high efficient benzimidazole-based membrane for a high temperature polymer electrolyte membrane fuel cell (PEMFC).

Oligomeric benzimidazoles with reactive end groups

AbstractThe condensation of aromatic diamines with aromatic dinitriles and the subsequent conversion of the amidines formed to benzimidazole units has been adapted to the preparation of oligomeric benzimidazoles with nitrile and carboxyl end groups. These are promising new dibasic acids for the preparation of heat‐stable condensation polymers.

Polysiloxanes having aromatic heterocyclic units. I. Polydimethylsiloxane benzimidazole polymer

AbstractA polymer containing dimethylsiloxane units (35) and benzimidazole units (1) has been prepared by the condensation of 3,3′‐diaminobenzidine and an α,ω‐bis‐(γ‐carboxy‐n‐propyl) polydimethylsiloxane. The new polymer has some rubbery properties, but it decomposes catastrophically at 400°C.