Cyclic Dimer Research Articles

Mathematical Modeling of Nylon 6/6,6 Copolymerization: Beneficial Influence of Comonomers on Degree of Polymerization in Batch Reactor

AbstractA model is developed for hydrolytic copolymerization of caprolactam with hexamethylene diamine (HMD) and adipic acid (ADA) in a batch reactor to produce nylon 6/6,6 copolymer. The reaction mechanism includes hydrolysis of caprolactam and cyclic dimer, polycondensation, polyaddition, transamidation, and ring formation via end biting and back biting. The catalyzing effect of carboxyl groups is accounted for using kinetic parameters from the literature. Model predictions are compared with low‐temperature literature data before simulating reactor conditions of industrial interest. The model predicts a higher degree of polymerization (DP) for nylon 6/6,6 copolymer compared to nylon 6 and 6,6 homopolymers produced using the same reactor conditions. Dynamic changes in concentrations of water, caprolactam, HMD, ADA, and end groups are tracked and used to explain the positive influence of comonomers on reaction rates and DP. Insights gained from this model will form a useful basis to build future models of continuous industrial reactors. image

Cis-Platinum Complex Encapsulated in Self-Assembling Cyclic Peptide Dimers.

A new cyclic peptide dimer that encapsulates cisplatin complexes in its internal cavity is described. The resulting complex showed cytotoxic activity at A2780 ovarian cancer cell lines independent of acquired platinum resistance.

Correlations between Structure and Near-Infrared Spectra of Saturated and Unsaturated Carboxylic Acids. Insight from Anharmonic Density Functional Theory Calculations.

By near-infrared (NIR) spectroscopy and anharmonic density functional theory (DFT) calculations, we investigate five kinds of saturated and unsaturated carboxylic acids belonging to the group of short-chain fatty acids: propionic acid, butyric acid, acrylic acid, crotonic acid, and vinylacetic acid. The experimental NIR spectra of these five kinds of carboxylic acids are reproduced by quantum chemical calculations in a broad spectral region of 7500-4000 cm-1 and for a wide range of concentrations. By employing anharmonic GVPT2 calculations on DFT level, a detailed interpretation of experimental spectra is achieved, elucidating structure-spectra correlations of these molecules in the NIR region. We emphasize the spectral features due to saturated and unsaturated alkyl chains, the location of a C═C bond within the alkyl chain, and the dimerization of carboxylic acids. In particular, the existence of a terminal C═C bond leads to the appearance of highly specific NIR bands. These pronounced bands are located at wavenumbers where no overlapping with other structure-specific bands occurs, thus making them good structural markers. Most of the spectral differences between these two groups of molecules remain subtle, and would be difficult to reliably ascribe without quantum chemically calculated NIR spectra. Moreover, anharmonic DFT calculations provide insights on the manifestation of hydrogen bonding through distinctive spectral features corresponding to cyclic dimers. The resulting spectral baseline elevation is common for all five investigated carboxylic acids, and remains consistent with previous results on acetic acid.

A novel nitronyl nitroxide radical containing thiophene and pyridine rings and its manganese(II) complex: synthesis, structure, and magnetic properties

A novel nitronyl nitroxide NIT-thien-3-Py (2-(3-(m-pyridyl)-2-thienyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and its Mn(II) complex [Mn(hfac)2(NIT-thien-3-Py)]2 (hfac = hexafluoroacetylacetonate) have been obtained. X-ray analysis indicates that the Mn(II) complex possesses a cyclic dimer structure in which two radical ligands link two Mn(II) ions through their NO groups and pyridine rings. The study of the magnetic data indicates that the manganese(II) ion strongly and antiferromagnetically interacts with the directly bonding NO group and there is weak ferromagnetic coupling between two Mn–NO pairs through the thiophene and pyridine rings of the radical ligand in agreement with a spin polarization mechanism.

Design and Synthesis of Porphyrin Oligomers and Porphyrinoids Via Suzuki-Miyaura Reaction

In view of multi-porphyrin arrays and new porphyrinoids, whih has potential applications in optoelectronic devices, sensors, photovoltaic devices, non-linear optical(NLO) materials, photodynamic therapy (PDT) pigments, light-harvesting models, and host-guest chemistry. Both the manipulation of interporphyrinic interaction and design of new structural porphyrinods are often essential to achieve desirable electronic and photophysical properties. Recently, the Osuka group developed a transition metal-catalyzed coupling reaction that has been proven to be very useful to construct multiporphyrinic systems. Till now we have adopted this strategy and prepared many heterocycles bridged β-to-β porphyrin arrays, including direct-bridged β-to-β porphyrin nanorings[ 1 ], earring porphyrins[ 3 ]. The experiment results indicated that the building blocks will remarkably affect the target molecules. As the bridge is thienylene, the main products is cyclic dimer, trimer, when the bridge is pyridylene, there are trace cyclic products are obtained. when the bridge is free base or Zn(II) porphyrin, bigger loop are formed, while Ni(II)porphyrin is used, the products is much simple. As to synthesis of porphyrin nanobarrel, if the porphyrin monomer is free base or Zn(II) porphyrin, no porphyrin barrel is obtained, which means that only ruffled Ni(II)porphyrin monomers can be used to synthesis porphyrin barrels. Synthesis of direct linked porphyrin nanorings is affected by the meso-substituent on porphyrin, when the substituent is aryl, only trimer and twinned pentamer can be prepared, when the substituent is alkyl, tetramer and twinned heptamer can be obtained.The photophysical study revealed that these porphyrin arrays and porphyrinoids exhibit either longer fluorescent lifetime, larger two photon absorption values or Near-infrared absorptions. Some new porphyrin arrays or porphyrinnoids recently have been constructed through Pd-catalyzed cross-coupling reactions (Figure 1), further study on their properties is underway in our lab. Figure 1. Crystals of earring porphyrins and multi-porphyrin arrays

Facile Synthesis of Cofacial Porphyrin Oligomers Via the Catalyst-Free Aromatic Nucleophilic Substitution Reactions

Cofacial porphyrin dimers have attracted a considerable attention due to their potential as artificial reaction centers in the photosystem, bimetallic catalysts and function as host molecule. However, their syntheses have required troublesome multi-step reactions. Recently, we have reported a facile and efficient synthetic method for meso-heteroatom-substituted porphyrins from the corresponding meso-bromoporphyrins via the catalyst-free aromatic nucleophilic substitution (SNAr) reactions.1,2,3 In this work, we applied this efficient method to the synthesis of cofacial porphyrin dimers bridged by the dihydroxyarene derivatives. Reaction of resorcinol with an excess of meso-bromoporphyrin in the presence of base afforded the acyclic dimers 1 in good yield. The steric hindrance between porphyrin and substituents on resorcinol determined their formations. For example, 4,6-diethylresorcinol gave cofacial conformation whereas 2-methylresorcinol gave open conformation. Reaction of resorcinol or 2,7-dihydroxynaththalene with meso-dibromoporphyrin afforded cyclic porphyrin dimers 2 and 3 with rigid cofacial conformation in good yield. We will also report the synthesis, structural characterization, and physical properties of the obtained dimer and their metal complexes. References (1) K. Yamashita, K. Kataoka, M. S. Asano, K. Sugiura, Org. Lett. 2012, 14, 190–193. (2) K. Yamashita, S. Sakamoto, A. Suzuki, K. Sugiura, Chem. Asian J. 2016, 11, 1004–1007. (3) K. Yamashita, K. Kataoka, S. Takeuchi, M. S. Asano, K. Sugiura, J. Org. Chem. 2016, 81, 11176–11184. Figure 1

Thermodynamic properties of piperidine and cyclic alkanone mixtures

The excess molar enthalpies, $$H^{\text{E}}$$ , of piperidine (1) + cyclopentanone or cyclohexanone or cycloheptanone (2) at 308.15 K and densities, ρ, speeds of sound, u, and molar heat capacities, $$C_{\text{P}}^{{}}$$ , of the same set of the mixtures have been measured as a function of composition at temperatures from 293.15 to 308.15 K. The measured ρ, u, and $$C_{\text{P}}^{{}}$$ data have been employed to determine excess molar volumes, $$V^{\text{E}}$$ , excess isentropic compressibilities, $$\kappa_{\text{S}}^{\text{E}}$$ , and excess heat capacities, $$C_{\text{P}}^{\text{E}}$$ . The thermodynamic properties have been fitted to Redlich–Kister equation to compute binary adjustable parameters and their standard deviations. The results have been analyzed in terms of Graph theory (which deals with the topology of the molecule) to correctly predict (1) state of the components in pure and mixed states, (2) to understand the nature and extent of molecular interactions existing in their mixtures, (3) $$V^{\text{E}}$$ , $$\kappa_{\text{S}}^{\text{E}}$$ , $$H^{\text{E}}$$ , and $$C_{\text{P}}^{\text{E}}$$ values. The analysis of $$V^{\text{E}}$$ data in terms of Graph theory suggests that while piperidine is characterized by hydrogen bonding and exists as associated molecular entity, cyclopentanone, cyclohexanone, and cycloheptanone exist as mixture of open and cyclic dimers. The estimated inter-nuclear distances among the interacting atoms using quantum mechanical calculations also support the existence of proposed molecular entities in pure and mixed states. It has been found that $$V^{\text{E}}$$ , $$\kappa_{\text{S}}^{\text{E}}$$ , $$H^{\text{E}}$$ and $$C_{\text{P}}^{\text{E}}$$ data predicted by Graph theory compare well with the their experimental data. The IR studies also support this view point.

Planar Anthracene-Acetylene Frameworks as a Stereogenic Motif.

Planar and rigid frameworks that consist of two 1,8-substituted anthracene units and two acetylene linkers were utilized as key structures for the generation of stereoisomers through the introduction of extra substituents. These compounds were synthesized from 1,8-substituted anthracene building units by a combination of coupling reactions. We designed diastereomers, enantiomers, and topomers by modifying the combination of the two linkers and the number of substituents at sterically crowded intraannular positions. The molecular structures, stereochemistry, and properties of these compounds were investigated by means of spectroscopic techniques and theoretical calculations. A prochiral cyclic dimer with one extraannular substituent was designed to generate a stereochemical phenomenon in two dimensions. Scanning tunneling microscopy measurements revealed that the molecules formed a self-assembled monolayer at the liquid-solid interface in a conglomerate-type manner. The scope and potential of the macrocyclic frameworks in studies of π-conjugated compounds are presented.

Synthesis, Crystal Structure, Spectroscopic Properties, and DFT Studies of 7,9-Dibromobenzo[h]quinolin-10-ol

7,9-Dibromobenzo[h]quinolin-10-ol (1), a benzo[h]quinolin-10-ol derivative, was synthesized and characterized by single-crystal X-ray diffraction. The crystal belongs to monoclinic space group P21/n, with a = 3.9573(4), b = 18.0416(18), c = 15.8210(16) Å, α = 90°, β = 96.139(3)°, and γ = 90°. Compound 1 exhibits an intramolecular six-membered-ring hydrogen bond, from which excited-state intramolecular proton transfer takes place, resulting in a proton-transfer tautomer emission of 625 nm in cyclohexane. The crystal structure is stabilized by intermolecular π–π interactions, which links a pair of molecules into a cyclic centrosymmetric dimer. Furthermore, the geometric structures, frontier molecular orbitals, and potential energy curves (PECs) for 1 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations.

Synthesis of 1,8‐Anthracene–Ethenylene Cyclic Dimers and Related Compounds: Effects of Linkers on their Structures, Electronic Properties, and Dynamic Behavior

AbstractCyclic compounds consisting of two 10‐mesityl‐1,8‐anthracene units with trans‐ or cis‐ethenylene linkers and their ethynylene and ethylene analogs were synthesized by cross‐coupling reactions and catalytic hydrogenation reactions. The structures of the four compounds were investigated by X‐ray analysis and DFT calculations. The trans‐ethenylene and ethylene compounds had nonplanar stair‐like frameworks, whereas the cis‐ethenylene compound had a rigid folded framework. In the UV/Vis spectra, the absorption bands red‐shifted in the order of ethylene, cis‐ethenylene, trans‐ethenylene, and ethynylene compounds according to an increase in π‐conjugation. The fluorescence spectra showed that these compounds were emissive in solution as well as in the solid state. Dynamic processes involving the exchange between the two syn forms were observed for the trans‐ethenylene and ethylene compounds by variable temperature 1H NMR measurements. The effects of linkers on electronic properties and dynamic behavior are discussed on the basis of their molecular structures and molecular orbitals.

Thermodynamic properties of mixtures containing 1-butyl-2,3-dimethylimidazolium tetrafluoroborate and cyclopentanone or cyclohexanone

The densities, ρ, speeds of sound, u, and molar heat capacities, CP, of 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (1) + cyclopentanone or cyclohexanone (2) mixtures at 293.15, 298.15,303.15 and 308.15 K and excess molar enthalpies, HE of same mixtures at 298.15 K have been measured as a function of composition. The observed ρ, u, and CP values are used to determine excess molar volumes, VE, excess isentropic compressibilities, κSE and excess heat capacities, CPE. The analysis of VE data in terms of Graph theory has suggested that while 1-butyl-2,3-dimethylimidazolium tetrafluoroborate exists as monomer; cyclopentanone and cyclohexanone exist as mixture of open and cyclic dimer. The analysis of inter-nuclear distances among interacting atoms (predicted by quantum mechanical calculations) also supports the presence of proposed molecular entities in pure and mixed states. It has been observed that VE, κSE, CPE and HE estimated by Graph theory compare well with their experimental values.

Thermodynamic Studies of Molecular Interactions in Mixtures Containing Tetrahydropyran, 1,4-Dioxane, and Cyclic Ketones

The densities ρ, speeds of sound u, and molar heat capacities CP of tetrahydropyran or 1,4-dioxane (1) + cyclohexanone or cycloheptanone (2) mixtures at 293.15, 298.15, 303.15, and 308.15 K, and excess molar enthalpies, HE at 308.15 K and atmospheric pressure 0.1 MPa have been measured over the entire composition range. The excess molar volumes VE, excess isentropic compressibilities κSE, and excess heat capacities, CPE of the studied mixtures have been determined using the measured experimental data. The observed VE, κSE, HE, and CPE data have been tested in terms of graph theory. The analyses of VE data by graph theory suggest that while tetrahydropyran or 1,4-dioxane exists as a mixture of monomer and dimer; cyclohexanone or cycloheptanone exists as a mixture of open and cyclic dimer. Further, (1 + 2) mixtures are characterized by interactions between oxygen atom/s and hydrogen atom of tetrahydropyran or 1,4-dioxane with hydrogen atom/s and oxygen atom of cyclohexanone or cycloheptanone. The quantum mechanical calculations and analysis of IR spectral data of (1 + 2) mixtures also support this viewpoint. It has been observed that graph theory correctly predicts the VE, κSE, HE, and CpE data of the present mixtures.

Cost-Effective Sustainable Synthesis of High-Performance High-Molecular-Weight Poly(trimethylene terephthalate) by Eco-Friendly and Highly Active Ti/Mg Catalysts

Efficient sustainable synthesis of high-performance poly(trimethylene terephthalate) (PTT) with simultaneously high molecular weight, narrow molecular weight distribution, and tiny cyclic dimer suitable for high end applications at low cost still faces challenges. Novel nontoxic and 1,3-propanediol-soluble Ti/Mg bimetal catalyst mainly based on biobased 1,3-propanodiol and food grade materials has been productively synthesized and also carefully characterized. The Ti/Mg catalyst was found to be exceptionally active catalysts for the polycondensation of terephthalic acid and 1,3-propanediol from a renewable resource capable of producing high-molecular-weight PTT as an environmentally friendly and recyclable material in both laboratory reactor and continuous pilot plant. The high-quality PTT samples with the highest number-average molecular weight up to 68 870 g/mol ever reported so far, the narrowest molecular weight distribution index down to 1.92, and the second lowest cyclic dimer content down to 2.21% ...

Кислотно-основні взаємодії в двокомпонентній системі «карбонова кислота – апротонний розчинник».

The behavior of carboxylic acids (benzoic, trichloroacetic, acetic) in aprotic solvents in the temperature range 5– 60 °C was studied by methods of UV spectroscopy, cryoscopy, and IR spectroscopy. Analyzing the values of the dimerization constants, one can see that with increase of temperature and the acid properties of carboxylic acids, the amount of dimeric form decreases, and the content of the monomeric form increases due to the equilibrium shift. Additionally, on the ground of the values of the equilibrium constants and the enthalpy of the dimerization, cyclization and addition of the monomer to the linear polymer obtained from the NMR spectroscopy data, it was shown that the equilibrium constant for the formation of a linear dimer from two monomers differs significantly from the monomer addition constant to the linear polymer. The state of the acetic acid–CCl 4 system is mostly affected by cyclic and linear dimerization processes. Comparison of the enthalpy of formation data represents that the strength of the hydrogen bond in the cyclic dimer is much less than in the linear dimer, while the stabilization energy is higher. Also, according to the equilibrium constants of the corresponding process, the amount and stability of the self-associates formed were analyzed: cyclic dimer, linear dimer, linear polymer. Comparison of the values of the equilibrium constant and the enthalpy of the association processes in different media shows that the content of various associated forms and the acid monomer depends on the nature of the solvent. Moreover, the molecules of the solvent can themselves act as bases – a participant of the acid-base processes. For dicarboxylic acids (aliphatic, phthalic) in DMSO and acetonitrile, the strength of the intramolecular hydrogen bond was estimated on the basis of the values of the homoconjugation constants.

Singlet oxygen generation properties of an inclusion complex of cyclic free-base porphyrin dimer and fullerene C60

We demonstrate that a cyclic free-base porphyrin dimer and its inclusion complex with fullerene C60 possess the ability to generate singlet oxygen (1O2) under visible light irradiation.

Three tetracyclic dibenzoazepine derivatives exhibiting different molecular conformations, different patterns of intermolecular hydrogen bonding and different modes of supramolecular aggregation.

The biological potential of compounds of the tricyclic dibenzo[b,e]azepine system has resulted in considerable synthetic efforts to develop efficient methods for the synthesis of new derivatives of this kind. (9RS,15RS)-9-Ethyl-11-methyl-9,13b-dihydrodibenzo[c,f]thiazolo[3,2-a]azepin-3(2H)-one, C19H19NOS, (I), crystallizes as a kryptoracemate with Z' = 2 in the space group P21, with one molecule each of the (9R,15R) and (9S,15S) configurations in the asymmetric unit, while (9RS,15RS)-9-ethyl-7,12-dimethyl-9,13b-dihydrodibenzo[c,f]thiazolo[3,2-a]azepin-3(2H)-one, C20H21NOS, (II), crystallizes with Z' = 1 in the space group C2/c. Ethyl (13RS)-2-chloro-13-ethyl-4-oxo-8,13-dihydro-4H-benzo[5,6]azepino[3,2,1-ij]quinoline-5-carboxylate, C22H20ClNO3, (III), exhibits enantiomeric disorder in the space group P-1 such that the reference site is occupied by the 13R and 13S enantiomers, with occupancies of 0.900 (6) and 0.100 (6). In each of the two independent molecules in (I), the five-membered ring adopts an envelope conformation, but the corresponding ring in (II) adopts a half-chair conformation, while the six-membered ring in the major form of (III) adopts a twist-boat conformation. The conformation of the seven-membered ring in each of (I), (II) and the major form of (III) approximates to the twist-boat form. The molecules of compound (I) are linked by two C-H...O hydrogen bonds to form two independent antiparallel C(5) chains, with each type containing only one enantiomer. These chains are linked into sheets by two C-H...π(arene) hydrogen bonds, in which the two donors are both provided by the (9R,15R) enantiomer and the two acceptor arene rings form part of a molecule of (9S,15S) configuration, precluding any additional crystallographic symmetry. The molecules of compound (II) are linked by inversion-related C-H...π(arene) hydrogen bonds to form isolated cyclic centrosymmetric dimers. The molecules of compound (III) are linked into cyclic centrosymmetric dimers by C-H...O hydrogen bonds and these dimers are linked into chains by a π-π stacking interaction. Comparisons are made with some related structures.

Syntheses, crystal structures, and magnetic properties of cyclic dimer Ln2L2 complexes constructed from (3-pyridinylmethoxy)phenyl-substituted nitronyl nitroxide ligands

Herein, five lanthanide-radical cyclic dimer complexes have been obtained and complex Tb shows the relaxation behavior in zero dc field with an anisotropy barrier Δ/kB = 21.6 K.

Recent advances in controlling the internal and external properties of self-assembling cyclic peptide nanotubes and dimers.

One of the most powerful strategies for the preparation of nanotubes is based on the stacking of flat-shaped cyclic peptide components. This strategy allows precise control of the nanotube internal diameter, the external properties and, more recently, the structural characterisitics of the internal cavity. The recent advances in these technologies and the applications of the resulting materials are described.

Enhancement of Mechanical and Thermal Properties of Poly(L-lactide) Nanocomposites Filled with Synthetic Layered Compounds

The effects of a layered double hydroxide (LDH) (Zn/Al palmitate) and two layered hydroxide salts (LHS), intercalated with the anion salicylate or palmitate, on the properties of poly(L-lactide) (PLLA) nanocomposites were investigated. PLLA and the nanocomposites were synthesized by ring opening polymerization of the cyclic dimer of lactic acid (lactide), using tin(II) 2-ethylhexanoate (stannous octanoate) as catalyst. PLLA nanocomposites containing two different fillers concentrations (1 wt% and 2 wt%) were produced. Compared to PLLA, almost all the nanocomposites exhibited an enhancement on thermal resistance. The sample containing 1 wt% of Zn/Al palmitate exhibited a decomposition temperature 51°C higher than neat polymer. Results of flexural properties demonstrated that the nanocomposites containing Zn/Al palmitate displayed the highest values of maximum flexural stress and elongation at break. The sample with 2 wt% of this filler revealed values of maximum flexural stress and strain at break, 15% and 157%, respectively, higher than PLLA. Contrary to PLLA, which only exhibited break point, this nanocomposite showed a less fragile behavior, as a yield point was observed. In this case, it was possible to promote a higher flexibility without reducing the flexural stress, revealing an advantage of the Zn/Al palmitate under the plasticizers that have been used so far for PLLA.

Synthesis of Poly (Lactic Acid) and Production of Scaffolds by Electrospinning

In this research, the synthesis of L-lactide (L-Lc), the cyclic dimer of poly (L-lactic acid) (PLLA) with a 55.20% yield and its polymerization to PLLA with different molecular weights is reported. The product was used to produce fibrous scaffolds by electrospinning using variations in concentration, distance, flow and voltage. A high-resolution stereoscope was employed to find fiber diameter (500 y 1000 μm); PLLA with 295,000 g/mol molecular weight (viscometry) was obtained after 96 hours of reaction and yielded the best results in the electrospinning process. These scaffolds were evaluated in vitrofor cell growth and cytotoxicity with human skin fibroblasts. None of the samples were cytotoxic above the permitted threshold of 50%. This study provides an important increase in performance for the synthesis of poly (L-lactic acid) (PLLA) and further development in the manufacturing of scaffolds which have multiple uses.