Trimeric Compounds Research Articles

Rubber pyrolysis: Kinetic modeling and vulcanization effects

Kinetic studies and the effect of the vulcanization process on the pyrolysis of natural rubber (NR), butadiene rubber (BR) and styrene-butadiene rubber (SBR) were investigated in this work. A comprehensive kinetic study using a model-based method, a model-free method and the distribution activation energy model (DAEM) was applied and a comparison between the different models was drawn. The DAEM showed a better fitting of the experimental results than the model-based method. The activation energy distribution of the DAEM verified by the model-free method indicated that the main decomposition of rubbers followed a chain reaction mechanism. Pyrolysis of raw rubbers and their corresponding vulcanized rubbers were conducted in a fixed-bed reactor. The sulfur content and product yields were quantified. Pyrolysis oils were characterized and compared. The oil yields reached a maximum at 430 °C for NR (90.82%), 470 °C for both BR (90.61%) and SBR (92.80%). Pyrolytic oils of raw rubbers were mainly composed of their corresponding monomer or dimer, trimer compounds. However, the results of vulcanized rubbers pyrolysis were significantly different. Sulfur in the vulcanized rubbers was released at low temperatures due to the lower bond energy. Higher temperatures led to the conversion of sulfur-containing oils to gaseous compounds. Vulcanization promoted the decomposition of rubbers at low temperatures but had an insignificant influence on pyrolysis products distribution at high temperature. Pyrolysis oils of vulcanized rubbers were more complex, constituting various aromatic hydrocarbons and thiophenes.

Synthesis and Study at a Solid/Liquid Interface of Porphyrin Dimers Linked by Metal Ions.

Several porphyrin dimers linked by metal ions were prepared. One trimeric compound was also isolated and one porphyrin dimer linked by palladium(II) could be structurally characterized. In solution, the size of the new compounds was estimated by DOSY NMR techniques. These compounds all contained long aliphatic chains (O-C12H25), which were used to assemble them at a highly oriented pyrolytic graphite (HOPG)/liquid interface. The highly ordered arrays were visualized by scanning tunneling microscopy (STM).

Dimeric and Trimeric Supramolecular Systems Formed by Donor‒Acceptor Interactions of ZnII, MnIII, and SnIV Porphyrin Complexes

The paper presents the methods of synthesis of dimeric and trimeric compounds formed by donor–acceptor interactions of ZnII, MnIII, and SnIV porphyrin complexes. The structure of the porphyrin ensembles was determined by 1H NMR spectroscopy. The extra coordination properties of the synthesized dimeric and trimeric supramolecular systems in relation to nitrogen-containing compounds were studied and the stability constants of the resulting porphyrin extra complexes were determined.

Anticancer activity and DNA binding property of the trimers of triphenylethylene–coumarin hybrids

Novel trimers of triphenylethylene–coumarin hybrid containing two amino side chains (5a–d and 6a–d) were designed and synthesized by the condensation of 1,3,5-benzenetricarboxylic acid with the varied amino monomeric hybrids catalyzed by HATU and DIPEA at room temperature. The extended trimeric compound 6a (R=piperidinyl) exhibited significant anti-proliferative activity against three cancer cells at IC50 of near 10μmol/L. UV–vis, fluorescence (lifetime) and thermal denaturation exhibited that 6a had significant interaction with Ct-DNA by the intercalative mode of binding. The order of their anti-proliferative activities was 6(a, d)>5(a, d) and (5–6)a>(5–6)d, respectively, in accordance with that of their DNA binding properties, which suggested that the prolonged linker (six carbons) and piperidinyl group on the side chains are beneficial to DNA binding and the anti-tumor activity.

Maize Tricin-Oligolignol Metabolites and Their Implications for Monocot Lignification.

Lignin is an abundant aromatic plant cell wall polymer consisting of phenylpropanoid units in which the aromatic rings display various degrees of methoxylation. Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], a flavone, was recently established as a true monomer in grass lignins. To elucidate the incorporation pathways of tricin into grass lignin, the metabolites of maize (Zea mays) were extracted from lignifying tissues and profiled using the recently developed 'candidate substrate product pair' algorithm applied to ultra-high-performance liquid chromatography and Fourier transform-ion cyclotron resonance-mass spectrometry. Twelve tricin-containing products (each with up to eight isomers), including those derived from the various monolignol acetate and p-coumarate conjugates, were observed and authenticated by comparisons with a set of synthetic tricin-oligolignol dimeric and trimeric compounds. The identification of such compounds helps establish that tricin is an important monomer in the lignification of monocots, acting as a nucleation site for starting lignin chains. The array of tricin-containing products provides further evidence for the combinatorial coupling model of general lignification and supports evolving paradigms for the unique nature of lignification in monocots.

Metal-Metal Interactions in Trinuclear Copper(II) Complexes [Cu3(RCOO)4(H2TEA)2] and Binuclear [Cu2(RCOO)2(H2TEA)2]. Syntheses and Combined Structural, Magnetic, High-Field Electron Paramagnetic Resonance, and Theoretical Studies.

The trinuclear [Cu3(RCOO)4(H2TEA)2] copper(II) complexes, where RCOO(-) = 2-furoate (1), 2-methoxybenzoate (2), and 3-methoxybenzoate (3, 4), as well as dimeric species [Cu2(H2TEA)2(RCOO)2]·2H2O, have been prepared by adding triethanolamine (H3TEA) at ambient conditions to hydrated Cu(RCOO)2 salts. The newly synthesized complexes have been characterized by elemental analyses, spectroscopic techniques (IR and UV-visible), magnetic susceptibility, single crystal X-ray structure determination and theoretical calculations, using a Difference Dedicated Configuration Interaction approach for the evaluation of magnetic coupling constants. In 1 and 2, the central copper atom lies on an inversion center, while in the polymorphs 3 and 4, the three metal centers are crystallographically independent. The zero-field splitting parameters of the trimeric compounds, D and E, were derived from high-field, high-frequency electron paramagnetic resonance spectra at temperatures ranging from 3 to 290 K and were used for the interpretation of the magnetic data. It was found that the dominant interaction between the terminal and central Cu sites J12 is ferromagnetic in nature in all complexes, even though differences have been found between the symmetrical or quasi-symmetrical complexes 1-3 and non-symmetrical complex 4, while the interaction between the terminal centers, J23, is negligible.

Synthesis of New Hexakis-Heterocyclic Compounds and their Use in the Formation and Stabilization of Au and Ag Nanoparticles

The stabilization of nanoparticles in solution is a challenge of major proportions, and avoiding the formation of aggregates and eventual coalescence of particles is directly linked to the conservation of its unique properties. In this work, we reported the synthesis of two hexakis-heterocyclic compounds, containing the tetrazole or 2-amino-1,3,4-thiadiazole group, respectively. The hexa-heterocyclic compounds were used in the synthesis and stabilization of Au and Ag nanoparticles. To obtain these molecules was used phosphonitrilic chloride trimer compound as core, which reacted with phenols properly substituted in theparaposition with either cyano or aldehyde group. The cyano group was successfully converted to the corresponding tetrazole using a 1,3-dipolar cycloaddition reaction with ammonium azide generatedin situ. In the case of aldehyde derivative, it was converted to the corresponding thiosemicarbazone, which was further cyclized using FeCl3. Compounds were characterized by RMN and IR spectroscopy. The UV-Vis spectroscopy was used for nanoparticles analysis.

Linear trimers of diruthenium linked by polyyndiyl or phenylenediethynyl bridges: A family of unique electronic wires

A new family of wire-like molecules with butadiyndiyl (1a/b), hexadiyndiyl (2) and phenylenediethynyl (3) bridges linking three diruthenium units have been prepared. The single crystal X-ray diffraction study of 1a revealed structural details of the trimeric compounds, including a distance of 18Å between two Ru2 termini. Both the voltammetric and spectroscopic data point to an extensive electronic delocalization in trimers 1 and 2, and the lack of delocalization in 3, demonstrating the advantage of linear polyyndiyl in mediating intermetallic electronic couplings. Magnetic studies of compound 1a reveal that a spin transition may occur as the temperature increases from 1.8 to 300K.

Design, Synthesis, and Conformational Analysis of Trispyrimidonamides as α-Helix Mimetics

The straightforward synthesis of trispyrimidonamides as a new class of α-helix mimetics is reported. Because of the versatility of our synthetic protocol, a variety of side chains including aliphatic, basic, aromatic, and heteroaromatic residues were included. A comprehensive conformational analysis revealed that in polar solvents a trimeric compound adopts conformations that can lead to i, i + 4, i + 8, or i, i + 8 patterns of side chain orientation. This suggests that trispyrimidonamides could be promising α-helix mimetics to target hot spots that are distributed over a wider angular range of an α-helix interface than in the classical i, i + 4, i + 7 case.

Design, Synthesis, and Biological Evaluation of (S)‐Valine Thiazole‐Derived Cyclic and Noncyclic Peptidomimetic Oligomers as Modulators of Human P‐Glycoprotein (ABCB1)

Multidrug resistance caused by ATP binding cassette transporter P-glycoprotein (P-gp) through extrusion of anticancer drugs from the cells is a major cause of failure in cancer chemotherapy. Previously, selenazole-containing cyclic peptides were reported as P-gp inhibitors and were also used for co-crystallization with mouse P-gp, which has 87 % homology to human P-gp. It has been reported that human P-gp can simultaneously accommodate two to three moderately sized molecules at the drug binding pocket. Our in silico analysis, based on the homology model of human P-gp, spurred our efforts to investigate the optimal size of (S)-valine-derived thiazole units that can be accommodated at the drug binding pocket. Towards this goal, we synthesized varying lengths of linear and cyclic derivatives of (S)-valine-derived thiazole units to investigate the optimal size, lipophilicity, and structural form (linear or cyclic) of valine-derived thiazole peptides that can be accommodated in the P-gp binding pocket and affects its activity, previously an unexplored concept. Among these oligomers, lipophilic linear (13) and cyclic trimer (17) derivatives of QZ59S-SSS were found to be the most and equally potent inhibitors of human P-gp (IC50 =1.5 μM). As the cyclic trimer and linear trimer compounds are equipotent, future studies should focus on noncyclic counterparts of cyclic peptides maintaining linear trimer length. A binding model of the linear trimer 13 within the drug binding site on the homology model of human P-gp represents an opportunity for future optimization, specifically replacing valine and thiazole groups in the noncyclic form.

Synthesis of a trimeric lignin model compound composed of α-O-4 and β-O-4 linkages under microwave irradiation

Abstract A trimeric lignin model compound composed of α-O-4 and β-O-4 linkages was prepared by the microwave-assisted synthesis, which consisted of three steps: (a) the synthesis of 3-methoxy-4-benzyloxyacetophenone (2) from acetovanillone (1), (b) the bromination of compound 2 to produce 3-methoxy-4-benzyloxy-α-bromoacetophenone (3), and (c) followed by a nucleophilic substitution of compound (3) to obtain 3-methoxy-4-benzyloxy-α-(3-methoxy-4-(1-propenyl)phenol)-acetophenone (4). The target product was characterized by MS, 1H NMR and 13C NMR spectroscopy. It was found that the trimeric compound synthesized can be used as a preferable lignin model compound because it contains guaiacyl structural unit (3-methoxy-4-hydroxy phenyl propane) linked by α-O-4 and β-O-4 linkages. In addition, under the conditions of microwave irradiation, the reaction time of each step is significantly reduced, and the selectivity of target product is greatly improved. The yields of each step and the overall sequence are 95.31%, 87.3%, 90.6% and 75.4% (95.31% × 87.3% × 90.6%), respectively.

Doping-induced spin-manipulation in complex trimer system Ca3Cu3(PO4)4: A density functional investigation

Doping induced spin-manipulation with magnetic (Ni) and non-magnetic (Mg) dopants constitutes the experimental attempts to obtain a singlet ground state system from the linear chain Heisenberg antiferromagnetic Cu-based d9 spin-1/2 trimer compound Ca3Cu3(PO4)4 with doublet ground state. The present study is a density-functional investigation of the effects of such doping on the spin-exchange mechanism and electronic structure of the parent compound. Site-selective doping with zero-spin dopants like Mg is proved to be more efficient than an integral spin dopant Ni in obtaining a spin-gap system with singlet ground state, as also observed in the experimental studies. Doping induced dimerized state is found to be the lowest in ground-state energy. Calculated spin exchange couplings along various possible pathways are observed to attain good agreement with earlier experimental results with suitable optimization of Coulomb repulsion (U) and exchange (J) parameters.

The Photochemistry of Thymine in Frozen Aqueous Solution: Trimeric and Minor Dimeric Products

Early work identified three compounds, namely the c,s cyclobutane dimer, the so-called (6-4) photoproduct (5-hydroxy-6-4'-(5-methylpyrimidin-2'-one)-5,6-dihydrothymine) and a trimer hydrate, as products formed upon UV irradiation of thymine in frozen aqueous solution. More recent work has shown that an (α-4) product, namely α-4'-(5'-methylpyrimidine-2'-one)-thymine, is a likely product formed under these reaction conditions. During a thorough reinvestigation of the photochemistry of Thy in ice at -78.5°C, we found that a variety of other products could be detected. In addition to the c,s dimer, the other three known cyclobutane dimers, namely the c,a, t,s and t,a forms, are produced, although in considerably smaller amounts. The so-called "spore product" of thymine (5,6-dihydro-5-(α-thyminyl)thymine) is likewise formed. Two other dimers have been identified as minor products; one of these has been determined to be 5-(thymin-3-yl)-5,6-dihydrothymine and the other has been tentatively assigned to be a (5-4) adduct (6-hydroxy-5-4'-(5-methylpyrimidin-2'-one)-5,6-dihydrothymine). Compounds with the behavior expected of true trimeric compounds have been isolated via HPLC and characterized by mass spectrometry and photochemical behavior. One of these materials, putatively containing an oxetane ring, decomposes thermally to a secondary trimeric product that is then converted into the known trimer hydrate.

Chemical Analysis of Complex Organic Mixtures Using Reactive Nanospray Desorption Electrospray Ionization Mass Spectrometry

Reactive nanospray desorption electrospray ionization (nano-DESI) combined with high-resolution mass spectrometry was utilized for the analysis of secondary organic aerosol produced through ozonolysis of limonene (LSOA). Previous studies have shown that LSOA constituents are multifunctional compounds containing at least one aldehyde or ketone groups. In this study, we used the selectivity of the Girard's reagent T (GT) toward carbonyl compounds to examine the utility of reactive nano-DESI for the analysis of complex organic mixtures. In these experiments, 1-100 μM GT solutions were used as the working solvents for reactive nano-DESI analysis. Abundant products from the single addition of GT to LSOA constituents were observed at GT concentrations in excess of 10 μM. We found that LSOA dimeric and trimeric compounds react with GT through a simple addition reaction resulting in formation of the carbinolamine derivative. In contrast, reactions of GT with monomeric species result in the formation of both the carbinolamine and the hydrazone derivatives. In addition, several monomers did not react with GT on the time scale of our experiment. These molecules were characterized by relatively high values of the double bond equivalent and low oxygen content. Furthermore, because addition of a charged GT tag to a neutral molecule eliminates the discrimination against the low proton affinity compounds in the ionization process, reactive nano-DESI analysis enables quantification of individual compounds in the complex mixture. For example, we were able to estimate for the first time the amounts of dimers and trimers in the LSOA mixture. Specifically, we found that the most abundant LSOA dimer was detected at the ~0.5 pg level and the total amount of dimers and trimers in the analyzed sample was ~11 pg. Our results indicate that reactive nano-DESI is a valuable approach for examining the presence of specific functional groups and for the quantification of compounds possessing these groups in complex mixtures.

Spin trimers in Ca3Cu2Ni(PO4)4

The nature of spin trimer and 3d spin dynamics in Ca3Cu2Ni(PO4)4 is studied using 31P NMR measurements. The data are obtained by replacing one of the Cu ions by a Ni ion in the one dimensional spin trimer compound Ca3Cu3(PO4)4. The NMR spectrum suggests the presence of two types of magnetically inequivalent phosphorous atoms, as in the parent compound. This reveals the presence of only one type of trimer, Cu2-Ni-Cu2, rather than of three types, Cu2-Cu1-Cu2, Cu2-Cu1-Ni and Ni-Cu1-Ni, as indicated by neutron scattering. Hence, the ground state of Ca3Cu2Ni(PO4)4 appears to be a quintet. These results also explain the magnetic susceptibility behavior, which indicates no reduction in the net spin of the trimer in Ca3Cu2Ni(PO4)4, as expected for JNi-Cu = −0.85 meV compared to the value JCu-Cu = −4.74 meV derived from neutron scattering. The spin lattice relaxation rate suggests that the three magnon mediated scattering process dominant in Ca3Cu3(PO4)4 is reduced in Ca3Cu2Ni(PO4)4.

Photochromic azobenzene functionalised banana–calamitic dimers and trimers: mesophase behaviour and photo-orientational phenomena

Azobenzene functionalised banana–calamitic dimers and a novel type of banana–calamitic–banana trimers have been synthesised. Their thermotropic behaviour and the structure of the mesophases have been characterised by differential scanning calorimetry, polarising optical microscopy and X-ray diffractions measurements. Electro-optical studies evidence the polar properties of the smectic phases. A rare anticlinic–synclinic smectic CP (SmCP) phase transition could be proven for two of the twins upon cooling without an electric field although the molecules are not optically active. Remarkably, the phase sequence SmCa–SmCs has been observed upon cooling, the inverse sequence to that reported for non-chiral compounds up to now. A comparative study of the photochemical properties of dilute solutions and of thin films of two compounds has been performed. Irradiation with polarised ultra-violet (365 nm) and visible light (473 nm) induces a photo-orientation process of the chromophores in a direction perpendicular to the polarisation plane of the exciting light. For a trimeric compound bearing an azobenzene bridge between both bent-core mesogenic units this process is associated with cycles of the E–Z–E isomerisation of the azobenzene groups followed by rotational diffusion of molecules in the films. For a bis(azobenzene) containing dimer the E–Z isomerisation in films is strongly suppressed and the photo-induced orientation has a rotational diffusion mechanism.

From rods to knots using cyclohexane in smectic liquid crystals

The effects of using cyclohexane as a bulky terminal group or as a linkage between multiple mesogens using 1,4-cyclohexane dicarboxylic acid and 1,3,5-cyclohexane tricarboxylic acid has been investigated. We demonstrate that the diversity of mesomorphism is reduced as the complexity of the molecule increases such that twist grain boundary phases, chiral nematic, ferroelectric and antiferroelectric behaviour are observed in the mono compounds but only ferroelectric behaviour is observed for the trimeric compounds. The electro-optical behaviour is discussed with a focus on the ferroelectric behaviour and the nature of the twist grain boundary phase.

Synthesis and molecular modeling study of new trimeric quinoline derivatives

Di- and trimeric quinoline derivatives have been recently described as potential modulators of Bcl-2 family protein interactions. However, only a few trimeric compounds have been described so far and an enlargement of the number of analogs of this class is needed to expand the structure–activity relationship study. Therefore, the synthesis of six new trimeric quinoline derivatives is reported. Moreover molecular modeling experiments were performed to study the conformational arrangement of compound 36 in Bak binding site of Bcl-x L, showing that these compounds could be potential ligands for Bcl-x L.

ChemInform Abstract: Nucleophilic Substitution Reactions Between Diphosphonate and Orthophosphate Characterized by High-Performance Liquid Chromatography and 31P NMR Spectroscopy.

Inorganic diphosphonate with phosphorus of an oxidation number +3 was found to react with orthophosphate (oxidation number +5) at 50 °C to give phosphonylated compounds; dimeric isohypophosphate (oxidation numbers +3 and +5) and a novel trimeric compound (oxidation numbers +3 and +5). Orthophosphate ion is considered to act as a ligand with two or three nucleophilic sites that were phosphonylated stepwise by diphosphonate. Kinetic processes of the nucleophilic reactions were monitored by HPLC and 31P NMR. Two products, the dimer having one P–H bond and the trimer with two P–H bonds, were well-resolved by HPLC and their yields, based on orthophosphate applied, were 85% (dimer) and 3% (trimer) when a mixed solution of 0.5 M diphosphonate and 0.1 M orthophosphate was incubated at 50 °C for 21 h. A complicated 31P NMR spectrum that indicated a large coupling constant(JPH=650 Hz) and grew with incubation time is reasonably assigned to the unsymmetrical isohypophosphate composed of both a phosphate group and a ...

Unexpected reactivity of 2-fluoro-4-(trifluoromethyl)-phenylacetonitrile: isolation and characterization of a trimeric impurity

An uncommon reactivity of 2-fluoro-4-(trifluoromethyl)-phenylacetonitrile, with the loss of three fluorine atoms, is herein reported, the resulting trimeric compound was isolated and characterized by NMR and MS/MS studies. An unprecedented mechanism has been proposed.