Computational examination on monomeric,dimeric, trimeric structural and vibrational interactions,AIM, Hirshfeld,IGM and oxygenated solvent effect on optical properties for pyridine N-oxide

This work reports DFT (Density functional theory) and topological examination by means of AIM (Atom in molecule) theory, Laplacian electron density (ED), Electron –Localization function (ELF) and Hirshfeld surface were executed monomer, dimer and trimer structure of PNO molecule. These structures were optimized and Structural parameters like bond – length and Angles are compared by using B3LYP/6-311G++(d,p) basis set. Computed vibrational – frequencies and corresponding PED (Potential energy – Distribution) were also compared. Polarizability, Dipole moment and the electronic properties were calculated for all three cases of PNO molecule. Hirshfeld surface investigation has been executed to achieve the C–H?O/N–O?H type of hydrogen -bond intermolecular interactions. Moreover, Reactive site, inter/intra interactions are calculated, the optical behaviors for monomer structure of PNO were investigate by using UV–Vis spectroscopy in oxygenated solvents.     

Unusual fluorescent monomeric and dimeric dialkynyl dipyrromethene-borane complexes

Novel monomeric and dimeric dialkynyl borondipyrromethene dyes (E-Bodipy) have been prepared in two different ways, providing systems in which the boron center is attached to either two similar or two dissimilar acetylenic units incorporating chromophores such as pyrene or anthracene. Both families exhibit interesting fluorescence and redox properties in which almost quantitative intramolecular energy transfer occurs.     

One-pot efficient synthesis of dimeric, trimeric, and tetrameric BODIPY dyes for panchromatic absorption

One-pot Knoevenagel self-condensation reaction of β-formyl BODIPY dye bearing a formyl group at 2-position offered dimeric, trimeric and tetrameric BODIPY dyes containing a formyl capping end group, exhibiting panchromatic absorption.     

The reaction of anthranilonitrile and triethylorthoformate revisited: formation of dimeric and trimeric species

The reaction of anthranilonitrile and triethylorthoformate was performed under different experimental conditions, leading to substituted quinazolines, triazachrysenes or quinazolinyl-aminophenyl quinazolines. A mechanistic proposal is presented to rationalize the formation of these compounds. The fluorescence properties of the highly conjugated triazachrysene structures were studied and the fluorescence quantum yield for compounds 5 and 13 was comparable to that of pyrene.     

Transformations of the natural dimeric phthalide diligustilide

A series of intramolecular condensation products were obtained by base-catalyzed treatment of the natural bioactive dimeric phthalide diligustilide (1) using different reaction conditions and the yields remarkably depend on these. The reaction conditions to obtain selectively the intramolecular condensation derivatives or the hydrolysis products of diligustilide (1) are described.     

Variation in crystallization conditions allows the isolation of trimeric as well as dimeric and monomeric forms of [(alkyl isocyanide)4RhI]+

Trimeric green [(i-PrNC)12Rh(I)3]Cl3.4.5H2O, monomeric [(C6H11NC)4Rh(I)](BPh4) and [(i-PrNC)4Rh(I)](BPh4) (both yellow), and red, dimeric [(C6H11NC)8Rh(I)2]Cl2.0.5C6H6.2H2O have been crystallized.     

Tannins of cornaceous plants. I. Cornusiins A, B and C, dimeric monomeric and trimeric hydrolyzable tannins from Cornus officinalis, and orientation of valoneoyl group in related tannins

Cornusiin A (1), cornusiin B (2) and cornusiin C (3), new dimeric, monomeric and trimeric hydrolyzable tannins, were isolated from the fruits of Cornus officinalis (Cornaceae). Their structures, including the orientation of the valoneoyl group in 1 and 3, were established on the basis of chemical and spectroscopic data. 2,3-Di-O-galloyl-D-glucose (7), 1,2,3-tri-O-galloyl-beta-D-glucose, 1,2,6-tri-O-galloyl-beta-D-glucose, 1,2,3,6-tetra-O-galloyl-beta-D-glucose, gemin D (5), isoterchebin, tellimagrandin I (6) and tellimagrandin II were also isolated from the fruits. The orientation of the valoneoyl group in camptothin A (14) and that in camptothin B (15), which had been isolated from Camptotheca acuminata (Nyssaceae), were also determined based on that in 1.     

Antioxidant activity of eugenol and related monomeric and dimeric compounds

Since the inhibitory effect of eugenol (a), which was isolated as an antioxidative component from plant, Caryopylli flos, on lipid peroxidation was less than that of alpha-tocopherol, we synthesized the eugenol-related compounds dieugenol (b), tetrahydrodieugenol (c), and dihydroeugenol (d), to find new strong antioxidants and assessed them for their inhibitory effect on lipid peroxidation and scavenging ability for superoxide and hydroxyl radicals. The antioxidative activities were in the order: (b)>(c)>(d)>(a) for the thiobarbituric acid reactive substance (TBARS) formation. These results suggest that the dimerized compounds have higher antioxidant activities than that of the monomers. Electron spin resonance (ESR) spin trapping experiments revealed that eugenol and its dimer, having allyl groups in the structure, scavenged superoxide, and that only eugenol trapped hydroxyl radicals under the conditions used. These finding suggest that eugenol and dieugenol have a different mechanism of antioxidation, i.e. eugenol may inhibit lipid peroxidation at the level of initiation, however, the related dimeric compounds may inhibit lipid peroxidation at the level of propagation of free radical chain reaction like alpha-tocopherol.     

Antioxidant activity of propofol and related monomeric and dimeric compounds

This study was carried out to investigate the antioxidant activity of propofol (2,6-diisopropylphenol) and its related compounds, butylated hydroxyanisole (BHA), 2,6-dimethylphenol, 2,6-di-t-butylphenol, and their dimeric compounds. The degree of antioxidant activity was evaluated based on the degree of peroxidation induced with Fe-ascorbic acid in egg phosphatidylcholine through the determination of thiobarbituric acid-reactive substances (TBARS) formed during peroxidation. Their antioxidant activities were in the order of dipropofol>di(2,6-di-t-butylphenol)>diBHA>di(2,6-dimethylphenol). Dipropofol, a dimeric compound of propofol, showed the highest antioxidant activities. Dimeric compounds had higher activities than monomeric compounds, and the 1,1-diphenyl-p-picryhydrazyl-trapping ability of dimeric compounds was also greater than those of monomeric compounds (4-10-fold). These results suggest that dimeric phenols may increase their antioxidant activities along with increments in the conjugation system and play a inhibitory role in the propagation of free radical chain reactions.     

New dimeric, trimeric and supramolecular organotin(IV) dithiocarboxylates: Synthesis, structural characterization and biocidal activities

Some new tri-, chlorodi- and diorganotin(IV) dithiocarboxylates (1–10) of 4-benzylpiperidine-1-carbodithioate ligand (L), with general formulae R₃SnL {R = n-C₄H₉ (1), C₆H₁₁ (2), CH₃ (3) and C₆H₅ (4)}, R₂SnClL {R = n-C₄H₉ (5), C₂H₅ (7), CH₃ (9)} and R₂SnL₂ {R = n-C₄H₉ (6), C₂H₅ (8), CH₃ (10)}, have been synthesized by the reaction of organotin(IV) chlorides with the ligand-salt in the appropriate molar ratio. Elemental analysis, Raman, IR, multinuclear NMR (¹H, ¹³C and ¹¹⁹Sn) and X-ray crystallographic studies have been undertaken to elucidate the structures of the complexes, both in solution and in solid state. Single-crystal X-ray diffraction study indicate trimeric, dimeric, supramolecular cyclic and supramolecular zig–zag chain structures for complexes 2, 4, 6 and 9, respectively. Square-pyramidal geometry is attributed to complex 9 on the basis of the τ value (0.4). A subsequent antimicrobial study indicates that the compounds are biologically active.     

Synthesis, structure, and properties of a dimeric chromium(II) pyrazolato complex with a long chromium-chromium distance. Maintenance of a dimeric structure in solution and interconversion between dimeric and monomeric structures

The synthesis, solid-state structure, and solution structure of Cr2(tBu2pz)4 are described. This complex is obtained by sublimation of the monomeric species Cr(tBu2pz)2(4-tBupy)2 and contains long chromium-chromium distances that are enforced by the divergent nature of the pyrazolato ligands.     

Binding of monomeric and dimeric Concanavalin A to mannose-functionalized dendrimers

Because of the central role of Concanavalin A (Con A) in the study of protein-carbohydrate interactions, a thorough understanding of the multivalent functions of Con A is imperative. Here, the association of monomeric and dimeric derivatives of Con A with mannose-functionalized generation two through six PAMAM dendrimers is reported. Hemagglutination assay results indicate relatively low activity of the dendrimers for monomeric Con A, with small increases as the dendrimer generation increases. Isothermal titration microcalorimetry experiments indicate monovalent binding by the dendrimers with monomeric Con A and divalent binding by the dendrimers with dimeric Con A. Continuous (and comparable) but narrowing increases in enthalpy and entropy and the slight increase in association constants with monomeric Con A as the dendrimer generation increases suggest favorable proximity effects on binding. Both the hemagglutination assay and the calorimetry experiments suggest that statistical binding enhancements can be observed with monomeric Con A. The results described here should allow for a more quantitative evaluation of the enhancements that are often observed in protein-carbohydrate interactions for glycosylated frameworks binding to Con A.     

Comparative study of planar motion in monomeric and dimeric discotics

Deuterium NMR spectra are reported in powder samples of discotic monomer and dimer as a function of temperature in their column Col(ho) phases. To simulate the observed powder patterns, a threefold jump model is used in the monomer, while in the related dimer the libration motion of the monomeric core is described using the infinitesimal jump method under a restricting potential due to the spacer. By comparing the diffusive rates for the two samples, it is concluded that the planar motion in the dimer is at least 30 times smaller than that of the monomer. This could lead to an enhancement of charge and energy transport in discotic dimer systems.     

pH and molar ratio dependent formation of monomeric,dimeric and tetrameric cobalt malate complexes

The reactions of cobalt(II) chloride with racemic malic acid (H₃mal = C₄H₆O₅) result in the isolation of monomeric, dimeric and tetrameric cobalt malato complexes: (NH₄)₂[Co(R-Hmal)(S-Hmal)] · 2H₂O (1), [Co₂(R-Hmal)(S-Hmal)(H₂O)₄]_n · 2nH₂O (2), K₄[Co₄(OH)₂(R-mal)₂(S-mal)₂(H₂O)₄] · 10H₂O (3) and trans-[Co(R-H₂mal)(S-H₂mal)(H₂O)₂] · 2H₂O (4). The formations of the malato complexes are dependent on the pH value, the molar ratio of the solutions, the reaction temperature and the counterions. In the water-soluble compound 1, the Co^II ion is octahedrally coordinated by two tridentate malates via their α-hydroxy, α-carboxy and β-carboxy groups. The malate ligands in 2 coordinate with the cobalt ion via their α-hydroxy and α-carboxy groups, while the β-carboxy group acts as a bridging ligand for the other two cobalt ions, forming a novel dimeric unit [Co₂(R-Hmal)(S-Hmal)(H₂O)₄], which further connects into a layered structure through links from the oxygen atoms of the β-carboxy groups. Complex 3 is a tetranuclear mixed-valence species. Both of the Co^II ions exist in trans-[Co(R-mal)(S-mal)(H₂O)₂] units, which are linked by a Co^III₂(OH)₂ unit with bridging α-alkoxy and β-carboxy groups. Compound 4 is the main product of reaction between cobalt chloride and excess malate under weakly acidic conditions.     

Selective amination of secoiridoid glycosides to give monomeric pyridine, dimeric pyridine, and naphthyridine alkaloids

Treatment of the secoiridoids oleuropein (4), ligstroside (5) and methyloleoside (6) by beta-D-glucosidase in the presence of ammonium chloride led exclusively to monomeric pyridine alkaloids 7, 1, and 8. Dimeric 3,4,5-trisubstituted pyridines were obtained from methyloleoside (6) when ammonium chloride was generated in the reaction mixture by successive additions of ammonia and hydrochloric acid. The use of ammonium acetate permitted conversion of secoiridoids 4 and 5 into the naphthyridine alkaloid jasminine (3).     

Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.     

Lithium aminoborohydrides 16. Synthesis and reactions of monomeric and dimeric aminoboranes

Aminoboranes are synthesized in situ from the reaction of the corresponding lithium aminoborohydrides (LABs) with methyl iodide, trimethylsilylchloride (TMS-Cl), or benzyl chloride under ambient conditions. In hexanes, the reaction using methyl iodide produces aminoborane and methane, whereas in tetrahydro-furan (THF) this reaction produces amine-boranes (R1R2HN:BH3) as the major product. The reaction of iPr-LAB with TMS-Cl or benzyl chloride yields exclusively diisopropylaminoborane [BH2-N(iPr)2] in THF as well as in hexanes at 25 degrees C. Diisopropylaminoborane and dicyclohexylaminoborane exist as monomers due to the steric requirement of the alkyl group. All other aminoboranes studied are not sterically hindered enough to be monomers in solution, but instead exist as a mixture of monomers and dimers. The dimers are four-membered rings formed through boron-nitrogen coordination. In general aminoboranes are not hydroborating reagents. However, monomeric aminoboranes, such as BH2-N(iPr)2, can reduce nitriles in the presence of catalytic amounts of LiBH4. This BH2-N(iPr)2/LiBH4 reducing system also re-duces ketones, aldehydes, and esters. Diisopropylaminoborane, synthesized from iPr-LAB, can be converted into boronic acids by a palladium-catalyzed reaction with aryl bromides. Aminoboranes derived from heterocyclic amines, such as pyrrole, pyrazole, and imidazole, can be prepared by the direct reaction of borane/tetrahydrofuran (BH3:THF) with these heterocyclic amines. It has been reported that pyrazole-derived aminoborane forms a six-membered dimer through boron-nitrogen coordination, where as, pyrrolylborane forms a dimer through boron-hydrogen coordination. Pyrrolylborane monohydroborates both alkenes and alkynes at ambient temperatures. Hydroboration of styrene with pyrrolylborane followed by hydrolysis gives the corresponding boronic acid, 2-phenylethylboronic acid, in 40% yield. Similarly phenylacetylene is mono-hydroborated by pyrrolylborane, to give E-2-phenylethenylboronic acid in 50% yield.     

Hydrothermal synthesis of dimeric lanthanide compounds: X-ray structure,magnetic study and heterogeneous catalytic epoxidation of olefins

A series of dimeric lanthanide carboxylato complexes [La(5-Br-NIC)₃(H₂O)₂]₂·H₂O (1); [Gd(5-Br-NIC)₃(H₂O)₂]₂ (2), [5-Br-NIC = 5-bromonicotinate] and [Sm(NIC)₃(H₂O)₂]₂ (3) [NIC = nicotinate], have been hydrothermally synthesized and structurally characterized by single crystal X-ray analysis. Complexes 1, 2 and 3 are of similar structure and consist of a basic unit [La(carboxylato)₃(H₂O)₂]₂. In compound 1 lanthanide cation is surrounded by one chelating 5-bromo-nicotinato ligand, two bridging oxygen atoms from 5-bromo-nicotinato and two water molecules, in which each La(III) ion is nine coordinated in a tricapped prismatic geometry. However, in compounds 2 and 3 four carboxylate groups link a pair of lanthanide atoms in the O,O′-bridging mode to generate a paddle-wheel-like centrosymmetric dimer. All the compounds exhibit excellent catalytic performance in olefin epoxidation reaction. The variable temperature magnetic susceptibility measurements showed that the magnetic interaction in [Gd(5-Br-NIC)₃(H₂O)₂]₂ (2), is antiferromagnetic (J = −0.048 cm⁻¹), while compound [Sm(NIC)₃(H₂O)₂]₂ (3), showed a complicated low-temperature magnetic property.