Pentamethylene Spacer Research Articles

Three Distinct Polar Phases, Isotropic, Nematic, and Smectic-A Phases, Formed from a Fluoro-Substituted Dimeric Molecule with Large Dipole Moment.

A dimeric molecule, di-5(3FM-C4T), with fluoro-substituted mesogenic cores composed of three-aromatic rings and linked by a pentamethylene spacer is prepared. Di-5(3FM-C4T) forms the ferroelectric nematic (NF), ferroelectric smectic-A (SmAPF), and polar isotropic (IsoP) phases. The NF phase is composed of molecules in U-shaped conformation that behave like polar rod-like molecules. The reversal spontaneous polarization (Ps) is approximately 8 μC cm-2, which is extremely large and reflects the huge dipole moment (11.2 D) of the one-side mesogenic core. On the other hand, the SmAPF phase is formed by bent-shaped molecules. The NF-SmAPF phase transition thus follows the conformational change of molecules. The reversal Ps of the SmAPF phase is around 4 μC cm-2, which is half of that in the NF phase, and this is an expected value from the bent shape of the molecules. It is interesting that the highest temperature IsoP phase still exhibits the polar structure and possibly retains some polar aggregation of molecules in small domains. The three polar phases exhibit the dielectric mode due to the collective polarization fluctuation at around 100 Hz, giving the high dielectric constant over 8000.

Dimeric Cholic Acid Peptide Conjugates Act as Effective Antibiotic Adjuvants against Multidrug Resistance (MDR) Gram‐Negative Bacterial Infections

AbstractMacrolides, glycopeptides, lipopeptides, and oxazolidinones class of antibiotics are used only for Gram‐positive bacteria, and are ineffective against Gram‐negative bacteria due to inability of these antibiotics to cross the Gram‐negative bacterial membranes. Here, dimeric cholic acid peptide conjugates as effective adjuvants that allow penetration of erythromycin across Gram‐negative bacteria are presented, making it effective antimicrobial. Here, it is shown that synthesized dimers2and3,having tetramethylene and pentamethylene spacers respectively between cholic acid‐triglycine conjugates, in combination with erythromycin cause synergistic antimicrobial effect against Gram‐negative bacteria. Biochemical studies reveal that dimer3causes outer and inner membrane permeabilization by interacting with lipopolysaccharide and displacing Mg2+ions, thereby allowing the erythromycin to cross bacterial membranes. Dimer3in combination with erythromycin can clear the preformed biofilms ofE. coliandP. aeruginosaeffectively. It is further demonstrated that combination of dimer3and erythromycin can clear wound infections ofE. coliandP. aeruginosa. Additionally, activities against multidrug resistant clinical strains ofE. coliandP. aeruginosawitness that combination of dimer3and erythromycin is an ideal combination to mitigate drug‐resistant infections.

Effect of the linking unit on the twist-bend nematic phase in liquid crystal dimers: a comparative study of two homologous series of methylene- and ether-linked dimers

ABSTRACTTwo series of bimesogens with phenyl benzoate mesogenic units were prepared: one series having a heptamethylene spacer and the other a pentamethylene spacer with two ether-linking groups. These materials were prepared to provide experimental backing to the widely held hypothesis that methylene-linked bimesogens are more likely to exhibit the twist-bend nematic mesophase than their ether-linked counterparts. Several of the methylene-linked materials exhibited nematic and NTB mesophases, whereas the analogous ether-linked materials gave only nematic phases albeit with significantly higher clearing points. Virtual N–NTB transition temperatures for both methylene- and ether-linked bimesogens were extrapolated by constructing binary phase diagrams with the well-studied twist-bend material CB9CB. Contrary to our expectations these virtual transition temperatures were in most cases higher for the ether-linked bimesogens than in the analogous methylene compounds, this runs counter to reported theories and hypotheses that the incorporation of ether-linking groups should serve to destabilise the NTB phase.

Symmetric bent-shaped liquid crystal dimers showing transitions between optically uniaxial and biaxial smectic phases

We report the synthesis of a new homologous series of symmetric bent-shaped liquid crystal dimers bearing oxybiphenylcarboxylate mesogens linked by a pentamethylene spacer. The dimers were characterised by optical, thermal, X-ray diffraction and computational techniques. Shorter dimers showed an I-N-SmA-SmC phase sequence with strong first-order phase transitions. For the longer dimers, the unconventional uniaxial SmA phase present in shorter members collapsed. A 9:1 binary mixture of a bent dimer with a non-mesogenic dimer exhibited upon the SmA-SmC phase transition a maximum layer contraction of 1%.

Double cyclizative polymerization of trienes catalyzed by Pd complexes. Combined ring-forming and chain-walking reactions of the growing end

Diimine Pd complexes catalyze polymerization of 1,6,13-heptadecatrienes to produce the polymers with two functionalized trans-1,2-cyclopentylene groups and ethylene or pentamethylene spacers between them.

Binuclear trans‐Bis(β‐iminoaryloxy)palladium(II) Complexes Doubly Linked with Pentamethylene Spacers: Structure‐Dependent Flapping Motion and Heterochiral Association Behavior of the Clothespin‐Shaped Molecules

The synthesis, structure, and solution-state behavior of clothespin-shaped binuclear trans-bis(β-iminoaryloxy)palladium(II) complexes doubly linked with pentamethylene spacers are described. Achiral syn and racemic anti isomers of complexes 1-3 were prepared by treating Pd(OAc)2 with the corresponding N,N'-bis(β-hydroxyarylmethylene)-1,5-pentanediamine and then subjecting the mixture to chromatographic separation. Optically pure (100 % ee) complexes, (+)-anti-1, (+)-anti-2, and (+)-anti-3, were obtained from the racemic mixture by employing a preparative HPLC system with a chiral column. The trans coordination and clothespin-shaped structures with syn and anti conformations of these complexes have been unequivocally established by X-ray diffraction studies. (1)H NMR analysis showed that (±)-anti-1, (±)-anti-2, syn-2, and (±)-anti-3 display a flapping motion by consecutive stacking association/dissociation between cofacial coordination planes in [D8]toluene, whereas syn-1 and syn-3 are static under the same conditions. The activation parameters for the flapping motion (ΔH(≠) and ΔS(≠)) were determined from variable-temperature NMR analyses as 50.4 kJ mol(-1) and 60.1 J mol(-1) K(-1) for (±)-anti-1, 31.0 kJ mol(-1) and -22.7 J mol(-1) K(-1) for (±)-anti-2, 29.6 kJ mol(-1) and -57.7 J mol(-1) K(-1) for syn-2, and 35.0 kJ mol(-1) and 0.5 J mol(-1) K(-1) for (±)-anti-3, respectively. The molecular structure and kinetic parameters demonstrate that all of the anti complexes flap with a twisting motion in [D8]toluene, although (±)-anti-1 bearing dilated Z-shaped blades moves more dynamically than I-shaped (±)-anti-2 or the smaller (±)-anti-3. Highly symmetrical syn-2 displays a much more static flapping motion, that is, in a see-saw-like manner. In CDCl3, (±)-anti-1 exhibits an extraordinary upfield shift of the (1)H NMR signals with increasing concentration, whereas solutions of (+)-anti-1 and the other syn/anti analogues 2 and 3 exhibit negligible or slight changes in the chemical shifts under the same conditions, which indicates that anti-1 undergoes a specific heterochiral association in the solution state. Equilibrium constants for the dimerizations of (±)- and (+)-anti-1 in CDCl3 at 293 K were estimated by curve-fitting analysis of the (1)H NMR chemical shift dependences on concentration as 26 M(-1) [KD(racemic)] and 3.2 M(-1) [KD(homo)], respectively. The heterochiral association constant [KD(hetero)] was estimated as 98 M(-1), based on the relationship KD(racemic) = 1/2 KD(homo) +1/4 KD(hetero). An inward stacking motif of interpenetrative dimer association is postulated as the mechanistic rationale for this rare case of heterochiral association.

Spectroscopical study of bacteriopurpurinimide–naphthalimide conjugates for fluorescent diagnostics and photodynamic therapy

Two novel bis(chromophoric) dyads ABPI–NI1 and ABPI–NI2 containing 1,8-naphthalimide and bacteriopurpurinimide units linked by p-phenylene-methylene (ABPI–NI1) and pentamethylene (ABPI–NI2) spacers were prepared to test their ability to be used in the design of effective agents for both photodynamic therapy (PDT) and fluorescent tumor imaging. Photophysical studies revealed that the emission from the naphthalimide chromophore in both conjugates was partially quenched due to resonance energy transfer between the photoactive components. Compound ABPI–NI2 with more sterically flexible oligomethylene group demonstrated higher fluorescence intensity as compared with that for ABPI–NI1.

Synthesis and Mesomorphic Behavior of Novel Calamitic Liquid Crystalline Dimesogens Possessing a Cholesteryl Moiety Connected to a Pyrimidine Core

Novel non-symmetric dimesogens consisting of a cholesteryl moiety and a pyrimidine unit interconnected through a pentamethylene or decamethylene spacer have been prepared through palladium-mediated Sonogashira cross-coupling. The novel mesogens show only a chiral nematic phase. The liquid crystalline phase was investigated through polarizing optical microscopy and differential scanning calorimetry. All the compounds were characterized through elemental analyses and spectral data.

Two dimensional self-assembly of bis-acylureas having various functional end groups

We present the synthesis and morphology study of thirteen bis-acylurea molecules with various functional end groups. The bis-acylureas have two acylurea groups, NH CO NH CO , divided by a pentamethylene spacer, (CH 2) 5 , and two symmetric functional end groups, such as, aliphatic, benzyl, mono- and bi-thiophenyl, sulfur-containing, and propargyl (HC CCH 2 ) moieties. The bis-acylureas were synthesized by the coupling reactions of ureas with pimeloyl chloride or pimelic acid. Upon cooling from hot isotropic solutions, the bis-acylureas spontaneously form supermolecules. In the cases of aliphatic, benzyl, mono- and bi-thiophenyl functional groups, two dimensional supramolecular structures with molecularly flat surfaces were formed. Single crystal X-ray diffraction results demonstrate that each bis-acylurea molecule forms biaxial hydrogen bonds with four adjacent molecules forming a grid-like crystalline structure. Among the bis-acylureas with sulfur-containing end groups, those with sulfide ( S ) and disulfide ( SS ) moieties self-organize into two dimensional superstructures, while those with thiol ( SH) and bulky protecting group ( S trityl) precipitate with irregular shapes. The bis-acylurea with propargyl end groups form superstructures of low order possibly due to the steric effect between the rigid moieties. However, the derivatives prepared by click reactions have lamellar molecular packing similar to those of bis-acylureas forming multilayered nanosheet structures.

Synthesis and characterization of novel cholesterol based mesogenic compounds using ‘click’ chemistry

An efficient route for the synthesis of hitherto unreported non-symmetric dimesogens consisting of a cholesteryl moiety and an aromatic mesogenic unit interconnected through a pentamethylene or decamethylene spacer by Cu(I)-catalyzed azide–alkyne cycloaddition ‘click’ chemistry has been developed. The aromatic units consist of two phenyl rings linked to a triazole moiety. A new trimesogen consisting two cholesteryl esters and an aromatic segment joined by pentamethylene spacer has also been synthesized. The newly synthesized mesogens show N*, TGB and partially bilayered SmC* (SmCd*) phases. The liquid crystalline phases were investigated with the help of polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction studies. DFT study was also used to locate the orientation of the dipole at the centre position i.e. at ester linkage. All the compounds were characterized from their elemental analyses and spectral data.

Synthesis and mesomorphic behaviour of new mesogenic compounds possessing a cholesteryl ester moiety connected to a pyrimidine core

New mesogenic compounds containing a cholesteryl ester and a pyrimidine moiety connected through a polymethylene spacer have been prepared. The mode of linkage has been made via –C C– and –C N– to understand the structure-property relationship. Only two compounds with a pentamethylene spacer show mesomorphic behaviour. The mesomorphic behaviour has been investigated by polarizing optical microscopy, differential scanning calorimetry and HRXRD studies. Enantiotropic smectic A, twist grain boundary (TGB) and chiral nematic mesophases are exhibited by the newly synthesized compounds.

Agonistic and Antagonistic Bivalent Ligands for Serotonin and Dopamine Receptors Including their Transporters

This review deals with the literature (1982-2006) concerning bivalent ligands for dopamine (D) and serotonin (5-HT) receptors, as well as for their respective transporters. The design, synthesis, and pharmacological evaluation of bivalent agonists and antagonists for dopamine and serotonin receptors have been successfully pursued. Increased potencies for 5-HT(1B/1D) receptor agonists were achieved as well as improved selectivities. At these receptors, selectivity seems to depend strongly on spacer length, whereas the improved affinities seem to be based on the presence of two pharmacophores within one molecule. Intrinsic activities and pharmacokinetic properties may differ from those of the respective monovalent ligands. Additionally, improved central nervous system penetration was achieved. Bivalent dopamine receptor agonists and antagonists can exhibit selectivity profiles different from their monomeric analogues with no loss in potency. For dopamine antagonists, affinities depend strongly on spacer length. For agonistic dimers different pharmacokinetic properties were observed. Bivalency was also applied to inhibitors of monoamine re-uptake transporters. Selectivity profiles and affinities depend strongly on the length of the alkylene-spacer: For some dimeric inhibitors the norepinephrine transporter (NET) and the dopamine transporter (DAT) affinities changed gradually, but for the serotonin transporter (SERT) a pentamethylene spacer showed the highest potency. Because the bivalent ligand approach has just begun to be applied to these versatile, therapeutically important targets, many advances in affinity enhancement, as well as the achievement of novel selectivity profiles and improved pharmacokinetics can be expected.

Synthesis and aldose reductase inhibitory activities of novel thienocinnolinone derivatives.

A novel series of tetrahydrothieno[2,3-h]cinnolinone derivatives were synthesized and evaluated in vitro for their ability to inhibit aldose reductase (ALR2), an enzyme involved in the appearance of diabetic complications. Compounds 2e and 2j exert a remarkable inhibitory effect, with IC(50) of 7.6 and 18 microM, respectively. These compounds incorporate a valid pharmacophore for aldose reductase inhibitory activity represented by a thienocinnolinone template linked through a pentamethylene spacer to a carboxylic function.

Novel Phosphine‐Catalyzed Zipper Cyclization of Aliphatic Diyne—Dione and Yne—Dione Systems.

An unexpected tri-n-butylphosphine-catalyzed zipper cyclization of diyne−diones (1a−d) or yne−diones (1e and 1f) is described. Bicyclic ketones (2a, 2b, 2c, 2e, and 2f) with five- or six-membered rings fused to the five-membered ring were obtained from both aliphatic diyne−diones (1a−c) and yne−diones (1e and 1f) having tetra- or pentamethylene spacers. The bicyclic products (2) were produced with high diastereoselectivity.

Comparison of the liquid crystalline properties of dimesogenic compounds bearing alkoxy and perfluoroalkoxy tails

The liquid crystalline properties of two series of nonsymmetric dimesogenic compounds consisting of cholesterol and Schiff base, azobenzene or stilbene mesogens interlinked by a pentamethylene spacer are compared. Compounds in the first series bear the fluorinated OCH2(CF2)6CF3 tail, whereas those in the second series bear the corresponding alkoxy tail. In general, compounds with the fluorinated alkoxy tail exhibited mesophases over a much wider temperature range than those with the alkoxy tail. Moreover, the former favored the formation of smectic phases (either chiral smectic C (Sc*) and SA phases, or SA phase) and suppressed the formation of the cholesteric phase. All of the three compounds of the second series were able to form the cholesteric phase. It was also observed that the layer spacing in compounds with the fluorinated tail was greater by 3 Å than those with the alkoxy tail. The compounds that form the Sc* phases exhibited very high spontaneous polarization, 400–500 nC cm−2. The compound with the fluorinated tail has a much shorter response time, 80 µs, than those with the alkoxy tail, 400–500 µs.

Novel phosphine-catalyzed zipper cyclization of aliphatic diyne-dione and yne-dione systems.

[reaction: see text] An unexpected tri-n-butylphosphine-catalyzed zipper cyclization of diyne[bond]diones (1a-d) or yne-diones (1e and 1f) is described. Bicyclic ketones (2a, 2b, 2c, 2e, and 2f) with five- or six-membered rings fused to the five-membered ring were obtained from both aliphatic diyne-diones (1a-c) and yne-diones (1e and 1f) having tetra- or pentamethylene spacers. The bicyclic products (2) were produced with high diastereoselectivity.

Synthesis of poly(alkyl aryl ether) dendrimers.

Poly(alkyl aryl ether) dendrimers of up to four generations composed of a phloroglucinol core, branching components, and pentamethylene spacers are synthesized by a divergent growth methodology. A repetitive synthetic sequence of phenolic O-alkylation and O-benzyl deprotection reactions are adopted for the synthesis of these dendrimers. The peripheries of the dendrimers contain 6, 12, 24, and 48 phenolic hydroxyl groups, either in the protected or unprotected form, for the first, second, third, and fourth generations, respectively. Because of the presence of hydrophilic exterior and relatively hydrophobic interior regions, alkaline aqueous solutions of these dendrimers are able to solubilize an otherwise insoluble pyrene molecule and these supramolecular complexes precipitate upon neutralization of the aqueous solutions.

A novel cyclophane–anthracene complex

A cyclophane host formed by connecting the oxygen atoms of two α,α′-di-(4-hydroxyphenyl)-1,4-diisopropylbenzene units with two pentamethylene spacers forms a unique solid-state complex with anthracene.

Pharmacological and behavioral analysis of the effects of some bivalent ligand-based monoamine reuptake inhibitors.

Novel piperidine-based bivalent ligands were prepared in enantiomerically pure form and evaluated for their ability to inhibit reuptake of dopamine (DA), serotonin (5-HT), and norepinephrine (NE) into rat brain nerve endings (synaptosomes). In this study, we have succeeded in using (1) the length of the linking chain connecting the two piperidine-based monomer units and (2) the absolute configuration of the piperidine monomer as a means to tailor activity and selectivity at the three monoamine transporters tested. In this series, the bivalent ligand 16, comprised of two (+)-trans-piperidine units linked by a pentamethylene spacer, exhibits a combination of high DA transporter (DAT) and 5-HT transporter (SERT) activity (K(i) = 39 nM and 7 nM, respectively). Piperidine 16 is capable of reducing cocaine's locomotor effects in mice while not having any effect on locomotion when tested alone. Additionally, compound 16 (1-10 mg/kg) does not substitute for cocaine in drug discrimination studies in rats. However, the analogous bivalent ligand 15 comprised of two (-)-trans-piperidine units, which is SERT selective, was less effective in antagonizing cocaine's locomotor stimulant activity. The piperidine-based bivalent inhibitors described herein constitute a new class of monoamine reuptake inhibitors that exhibit varying levels of monoamine transporter activity and selectivity, and these ligands may serve as lead candidates in the discovery of new therapeutics to treat a range of neurological disorders including cocaine addiction.

Dimesogenic compounds with an electron-attracting terminal group

Non-symmetric dimesogens composed of a classical aromatic mesogenic unit linked to a cholesteryl moiety by a flexible spacer form several types of smectic periodicities: one is connected to the cholesteryl length and the other to the length of the associated dimesogens. In some peculiar cases, anomalies of periodicity resulting from the competition between these incommensurate lengths are observed through the occurrence of two-dimensional modulated phases or incommensurate low ordered smectic phases (Sic). As part of our continuing effort to understand the influence on the smectic arrangement of the molecular parameters of such non-symmetric dimesogens, new homologues with a cholesteryl unit linked by a pentamethylene spacer to an aromatic mesogenic moiety bearing different electron attracting terminal groups have been prepared. For these compounds, only the periodicity resulting from the associated dimesogens is observed. Nevertheless, an incommensurate smectic phase can be induced by mixing one of these compounds with another appropriate dimesogen. Molecular mechanics calculations suggest that the origin of the different smectic structures is strongly connected to the repartition of electrostatic potential along the dimesogen.