Linear Oligomers Research Articles

Beyond Chaperoning: UCS Proteins Emerge as Regulators of Myosin-Mediated Cellular Processes.

The UCS (UNC-45/CRO1/She4p) family of proteins has emerged as chaperones specific for the folding, assembly, and function of myosin. UCS proteins participate in various myosin-dependent cellular processes including myofibril organization and muscle functions, cell differentiation, striated muscle development, cytokinesis, and endocytosis. Mutations in the genes that code for UCS proteins cause serious defects in myosin-dependent cellular processes. UCS proteins that contain an N-terminal tetratricopeptide repeat (TPR) domain are called UNC-45. Vertebrates usually possess two variants of UNC-45, the ubiquitous general-cell UNC-45 (UNC-45A) and the striated muscle UNC-45 (UNC-45B), which is exclusively expressed in skeletal and cardiac muscles. Except for the TPR domain in UNC-45, UCS proteins comprise of several irregular armadillo (ARM) repeats that are organized into a central domain, a neck region, and the canonical C-terminal UCS domain that functions as the chaperoning module. With or without TPR, UCS proteins form linear oligomers that serve as scaffolds that mediate myosin folding, organization into myofibrils, repair, and motility. This chapter reviews emerging functions of these proteins with a focus on UNC-45 as a dedicated chaperone for folding, assembly, and function of myosin at protein and potentially gene levels. Recent experimental evidences strongly support UNC-45 as an absolute regulator of myosin, with each domain of the chaperone playing different but complementary roles during the folding, assembly, and function of myosin, as well as recruiting Hsp90 as a co-chaperone to optimize key steps. It is becoming increasingly clear that UNC-45 also regulates the transcription of several genes involved in myosin-dependent cellular processes.

Theoretical insight on model linear oligomers and their ring-fused analogs used in organic electronics

Theoretical systematic study compares chemical and electronic structure of six series of linear aromatic oligomers and their ring-fused analogues with various chain length of 5- and 6-membered rings. Chemical structure was described by structural HOMED and one-electron density topology EL aromaticity descriptors. The calculations demonstrated that the diradical electronic ground-state system is energetically preferred for larger six-membered acenes where the electronic structure can be separated into two linear polyene chains. The influence of intermolecular interaction on the aromaticity perturbation in crystals was also analyzed for 20 available X-ray structures. The aromaticity of central ring is lowered for longer molecules in solids. Next, the primary effect of aromatic chain elongation on frontier orbital energies and vertical excitation energies was predicted. The calculated data were correlated with experimental ones and polymer limits on investigated properties were estimated. Quantitative criteria of aromaticity were explored for various linear organic molecules with increasing chain lengths to extrapolate electronic properties at the polymer limit. • Systematic DFT study of linear oligomers and ring-fused analogues. • The aromaticity indices are evaluated. • The structural conditions for diradical system are determined. • Electrochemical band gaps and optical transitions are calculated. • Polymer limits on investigated properties are estimated.

Many-body analysis and spectroscopic characterization of diazene oligomers: A theoretical study

The present study reports the many-body analysis and spectroscopic characterization of linear and cyclic diazene oligomers in gas and water solvent states. The oligomers of diazene from monomer to pentamer have been considered for the study. The spectroscopic studies such as geometrical parameters, infrared spectra, electronic absorption spectra, and natural transition orbitals (NTOs) were reported. Many-body analysis techniques have been implemented to study the interactions among the diazene oligomers. These calculations have been performed using exchange and correlation functional (B3LYP) and 6–311++G (d,p) basis set. The geometrical parameters and infrared modes of monomer diazene in the gas state are well-matched with the available experimental determinations at this level of theory. A significant change in vibrational modes of linear and cyclic diazene oligomers has been observed in the gas phase-to-water solvent state. The time-dependent density functional theory (TD-DFT) has been used to calculate the electronic absorption spectra of diazene oligomers. The Wavelength of electronic transitions, oscillator strength, and HOMO to LUMO gap has been reported. Many-body analysis shows that two-, three-, four-, and five-body energies have a remarkable contribution to the binding energy in addition to relaxation energies. All these calculations have been performed using Gaussian 16 program package.

Synthesis of cycloparaphenylene under spatial nanoconfinement

Suzuki coupling reactions between symmetrical monomers were conducted in various mesoporous silica nanoreactors grafted with palladium catalysts, enabling the selective formation of [12]cycloparaphenylene precursor with separate yield up to 25% in one-pot reactions, much higher than that in homogeneous reaction. The spatial nanoconfinement of the nanoreactors promotes the macrocyclization while limits the concomitant linear oligomer formation, offering more possibilities for the synthesis of macrocycles from symmetrical monomers in one-pot reaction.

Oligomers in polybutylene terephthalate for food contact—strategies on identification, quantification, and risk assessment

Oligomers are a significant group of migrating substances from food contact materials made of polyesters like polybutylene terephthalate (PBT). Twenty-three cyclic and linear oligomers with different end groups including olefin-terminated oligomers, which are associated with thermal stress of the material, were tentatively identified in PBT extracts by high-performance liquid chromatography with mass spectrometry and diode array detection. Quantification approaches based on chromophore concentration, relative response factors, and overall oligomer determination after hydrolysis to the monomer terephthalic acid were employed. An exhaustive extraction of thirteen PBT samples yielded an overall oligomer content of 1.87–6.10 mg/g material (sum of individual oligomers < 1,000 Da) with a predominant content of cyclic over linear oligomers. Migration experiments were performed according to Regulation (EU) No. 10/2011 using the official food simulants as well as cows’ milk. A total of 218 µg cyclic oligomers/L milk were detected in the third migrate relevant for risk assessment of repeated-use articles under hot-fill conditions (70 °C, 2 h). The official food simulant for milk, 50% ethanol, was found to overestimate the actual migration into milk by a factor of four. Frying conditions using sunflower oil as the food simulant (200 °C, 10 min) resulted in a migration of 7.5 mg cyclic oligomers/kg oil. The exposure to migrating oligomers is critical in some scenarios when evaluated by the threshold of toxicological concern concept; however, the toxicological evaluation poses a challenge due to the possible hydrolysis of cyclic oligomers in the human gastrointestinal tract. Our experiments display the need for a toxicological evaluation of PBT oligomers because the migration of cyclic oligomers is expected to exceed the current in silico–based thresholds under foreseeable conditions of use.

Synthesis of Linear and Cyclic Discrete Oligomers with Defined Sequences via Efficient Anionic Coupling Reaction

We hereby report a new strategy to prepare sequence-defined discrete oligomers with uniform molecular weight through carbanionic addition and coupling reactions using specific monomers possessing 1,1-diphenylethylene (DPE) and tert-butyldimethylsilyloxy (TBS) moieties. The strategy allows the molecular weight growth by iterative attaching of the sec-butyllithium (s-BuLi) activated monomer or dimer unit to the halomethyl end-group, released from deprotection of TBS, of the proceeding oligomer starting from a dichloromethyl core. A series of linear discrete oligomers with alternating and ABCD/ACBD sequences are synthesized. These linear sequence-defined oligomers are subsequently modified with double vinyl groups and cyclized through ring-closing metathesis (RCM) reaction into corresponding sequence-defined macrocycles. The molecular structures of the linear and cyclic oligomers are analyzed by using size exclusion chromatography (SEC), nuclear magnetic resonance (NMR), and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). The features of the present approach are the presynthesized monomers or dimers with specific functionalities, the efficient carbanionic reactions, as well as the easy separation of the products due to the increasing difference between the molecular weights of the monomer/dimer and the products. More interestingly, sequence and topology effects were observed on Förster resonance energy transfer (FRET) measurements using naphthalene (donor) and pyrene (acceptor) functionalized linear and cyclic ABCD/ACBD oligomers having identical molecular weights and compositions for the two sequences.

Design and computational evaluation of structural, electronic and optical properties of the oligomers of nC20 fullerene (n = 1–6)

In this research, linear and non-linear oligomers of fullerene C20 oligomers with different number of units were designed and their structural, electrical and optical properties were investigated. Cohesive energy which may be a reason for the stability of oligomers was calculated that the increase in cohesive energy was seen with increasing the number of fullerene units. Linear oligomers also have more cohesive energy than their nonlinear homologous. The tendency to form a ring was observed in nonlinear oligomers, which a complete ring with perfectly symmetrical structure was obtained in a 6-membered ring. HOMO-LUMO gap (Eg) values representing electrical conductivity were calculated and in the case of linear oligomers it increased with increasing number of C20 fullerene units. Analysis of partial electrical charges and MEP diagrams showed that the two ends of the oligomers have a negative charge and the junction of fullerene units has a positive partial charge. The polarizability, α, and the first hyperpolarizability, β, were calculated and an improvement in the non-linear optical (NLO) response was observed in the C20 oligomer, so that the α values for the linear pentamer oligomer and the β value for the Config-b-A tetramer were approximately 1300 and 18,000, respectively.

High-performance and low-dielectric cyanate ester resin optimized by regulating the structure of linear polyhydroxy ether modifier

Cyanate ester resin (CE) is an ideal candidate for low dielectric constant (low-k) materials in the microelectronic industry, however the incoordination among mechanical, thermal and low-k properties greatly restricts their practical applications. Herein, two kinds of fluorinated polyhydroxy ether (PHE) with or without polyhedral oligomeric silsesquioxane (FPHE, FPHE-POSS) were designed and synthesized by regulating the structure of the linear PHE chains, to modify CE resin for elevating its comprehensive performances. Results reveal that FPHE can improve the mechanical properties and reduce the k of CE resin to some extent owing to its weakly polarizable flexible chains. Whereas FPHE-POSS can not only enlarge the optimization effects from FPHE, but also significantly improve thermostability simultaneously due to the extra-contribution of the heat-resistant rigid skeleton (POSS). Especially, FPHE-POSS6/CE possesses lower k values (2.48, 1 MHz), superior impact strength (24.59 kJ/m2, increased by 65.0 %) and higher glass transition temperature (307.6°C, increased by 18.8°C) as compared with pure CE resin. This work proposed a facile strategy to break through the incoordination among dielectric, thermal, and mechanical properties of CE resin via using weak-polarizable and flexible-rigid linear oligomer, which could be a guidance for advanced researches.

Synthesis of Glycoluril Dimers with the Ability to Form Polymeric Self-Associates in Water

Supramolecular self-assembly in water resulting in polymeric structures is emerging because of its potential in the preparation of adaptive materials with applications in biology and medicine. Here, we report the first example of host molecules based on glycoluril dimers, which self-associate into linear oligomers in water. The degree of polymerization for the resulting supramolecular aggregates was calculated using the isodesmic model and the Carothers equation. The model compound was prepared to enable a deeper understanding of the forces responsible for the self-association of the glycoluril dimer-based monomers in water.

Investigation of Curing Mechanism and Mechanical Properties of Polypropylene/Aliphatic Epoxy Composites

Temperature-sensitive cure kinetics based on bisphenol A oligomeric diglycidyl ether and branching diphenylmethane di-isocyanate, polymer aliphatic or lower molecular weight aromatic amines, and polypropylene and epoxy composites were examined. Polypropylene networks are formed initially, followed by amine hardeners interfering with epoxy oxirane rings to frame linear oligomers. Finally, the system is formed by a reaction between amines obtained in the second phase and epoxy oxirane rings during the curing step. This three-stage treatment was illustrated. The activation energy was calculated using the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose isoconversational approaches to cure degree. The Ea-to-αcorrelation was determined using these approaches, revealing that the research curing systems exhibited autocatalytic effects. Among the materials studied, compounds with low molecular weight aromatic amines had the strongest and longest-lasting tensile characteristics. There are numerous advantages to slow curing and discrete stages of composite creation, including better mechanical properties.

Linear and nonlinear shear rheology of nearly unentangled H-polymer melts and solutions

We investigate the linear and nonlinear shear rheology of a marginally entangled H-polymer melt and two solutions made by diluting high molecular weight H-polymers in linear oligomer. In order to approach a nearly unentangled state, dilution is conducted at volume fractions such that the two solutions attain a similar number of entanglements of the melt. Start-up shear experiments demonstrate that the nonlinear behavior of the H-polymer melt is analogous to that of a linear melt with comparable span chain length. Concerning solutions, the increase of chain elasticity in fast flows, coupled with a lesser role of monomeric friction reduction, allows to attain strong stretch in start-up shear tests. As a result, transient strain hardening occurs. Furthermore, a failure of the Cox-Merz rule is observed for the solutions, which indicates that they better conform to a FENE-Rouse chain behavior compared to melts.

Dry gaseous remote plasma deposition of perfluorinated material with tuneable crystallinity and hydrophobic properties

Hydrophobic surfaces are needed in countless applications. Anti freezes surfaces, anti-bacterial surfaces or antithermal among others. A gaseous approach allows to quickly hydrophobize and conformally coat complex surfaces without altering the bulk material. In the present paper, we suggest a facile route to quickly deposit thin hydrophobic material from methane and tetrafluoromethane via remote plasma deposition while being able to tune the degree of hydrophobicity (from hydrophobic to ultrahydrophobic) by studying the effect of ratio between the two reactants and the temperature of the substrate. We found out that linear oligomer chains can be synthesized in the gas phase and we postulate that with the appropriate substrate T°, a nucleation process takes place, which produce microscopic rose petals-like structures which gives rise to a Cassie-Baxter like ultrahydrophobicity.

Unexpected core-shell char from polycarbonate/polyborosiloxane composites and its application in improving flame retardancy

A rare charring behaviour was found during the combustion of polycarbonate (PC) composites containing polyborosiloxane (PBS), in which a highly intumescent char layer with core–shell structure was formed. Particularly the core–shell structure is composed of an outer porous structure and an inner lamellar structure, which can effectively isolate external heat radiation and limit the diffusion of degradation products and oxygen. PC/PBS-X composites with 2 wt% PBS-X showed excellent flame retardancy without compromising mechanical properties, including passing the UL-94 V-0 rating and increasing the limiting oxygen index (LOI) to 31.2%. Compared to PC, the peak heat release rate (pHRR) and peak smoke production rate (pSPR) in the case of PC/PBS-1 composites were reduced by 63.2% and 45.5%, respectively. The mechanism for promoting the flame retardancy of PC by PBS-X was studied. The results showed that the PBS decomposed to form linear polysiloxane oligomer with terminal Si-H bond (L-PDMS-H), which reacted with the degraded products of PC to quickly form intumescent char layer with core–shell structure during the combustion. This is the reason why to PBS presented the striking effect on improving flame retardancy of PC.

Pyrolysis and thermal degradation studies of silane-carbosilane transformation using hyphenated thermal analysis

Pyrolysis process accompanying polydimethylsilane to polycarbosilane transformation and the decomposition behaviors of polydimethylsilane (PDMS), polycarbosilanes (PCS Mk-I/II and III) were investigated applying evolved gas analysis and pyrolysis–gas chromatography-mass spectrometry. Volatile fractions evolved during the reactions were recorded as specific pyrograms. The degradation of the polymer skeleton under argon leads to the evolution of methyl silane and higher linear oligomers in the molar mass range 42 ̶ 348 Da; the escape of hydrogen starts simultaneously. Based on the results, specific pyrolysis patterns and decomposition behavior of PDMS, PCS Mk-III were established. Mass spectral data revealed the structural and compositional identification of molecular moieties evolved during the pyrolysis reactions. Thermal data confirmed and complemented the pyrolysis data.

Sequencing Biodegradable and Potentially Biobased Polyesteramide of Sebacic Acid and 3-Amino-1-propanol by MALDI TOF-TOF Tandem Mass Spectrometry.

Biodegradable and potentially biobased polyesteramide oligomers (PEA-Pro), obtained from melt condensation of sebacic acid and 3-amino-1-propanol, were characterized by nuclear magnetic resonance (NMR), matrix assisted laser desorption/ionization-time of flight/time of flight-mass spectrometry/mass spectrometry (MALDI-TOF/TOF-MS/MS), thermogravimetric analysis (TGA), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). NMR analysis showed the presence of hydroxyl and amino terminal groups as well as carboxylic groups of the sebacate moiety. Hydroxyl and carboxyl termination had the same abundance, while the amine termination was 2.7-times less frequent. Information regarding the fragmentation pathways and ester/amide bond sequences was obtained by MALDI-TOF/TOF-MS/MS analysis performed on sodiated adducts of cyclic species and linear oligomers. Different end groups did not influence the observed fragmentation. Three fragmentation pathways were recognized. The β-hydrogen-transfer rearrangement, which leads to the selective scission of the –O–CH2– bonds, was the main mechanism. Abundant product ions originating from –CH2–CH2– (β–γ) bond cleavage in the sebacate moiety and less abundant ions formed by –O–CO– cleavages were also detected. TGA showed a major weight loss (74%) at 381 °C and a second degradation step (22% weight loss) at 447 °C. Py-GC/MS performed in the temperature range of 350–400 °C displayed partial similarity between the degradation products and the main fragments detected in the MALDI-TOF/TOF-MS/MS experiments. Degradation products derived from amide bonds were related to the formation of CN groups, in agreement with the literature.

Simplified Synthetic Approach to Tetrabrominated Spiro-Cyclopentadithiophene and the Following Derivation to A-D-A Type Acceptor Molecules for Use in Polymer Solar Cells.

4,4'-Spiro-bis[cyclopenta[2,1-b;3,4-b']dithiophene] (SCT) is a versatile building block for constructing three-dimensional (3D) π-conjugated molecules for use in organic electronics. In this paper, we report a more convenient synthetic route to SCT and its derivatives, where a structurally symmetric 3,3'-dibromo-5,5'-bis(trimethylsilyl)-2,2'-bithiophene (2) serves as the precursor for both the synthesis of 4H-cyclopenta[2,1-b:3,4-b']dithiophen-4-one (4) and 4-(5,5'-bis(trimethylsilyl)-2,2'-bithiophen-3-yl)-2,6-bis(trimethylsilyl)-4-hydroxy-cyclopenta[2,1-b;3,4-b']dithiophene (5). The later one is the key intermediate for the final brominated SCT building block. Such a "two birds with one stone" strategy simplifies the synthetic approach to the SCT core. Functionalization on the SCT core with different terminal electron-deficient groups, including 1H-indene-1,3(2H)-dione (ID), 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC), and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (FIC), was carried out, yielding three spiro-conjugated A-D-A type molecules, SCT-(TID)4, SCT-(TIC)4, SCT-(TFIC)4, respectively. The optical spectroscopy and electrochemical properties of these three compounds were investigated and compared to the corresponding linear oligomers. Results revealed that the IC and TFIC terminated compounds showed low-lying HOMO/LUMO energy levels with reduced optical bandgap, making them more suitable for use in polymer solar cells. A power conversion efficiency of 3.73% was achieved for the SCT-(TFIC)4 based cell, demonstrating the application perspective of 3D molecules.

Molecular simulations of the structure-property relationships of N-A-S-H gels

A good understanding of the relationship between the micro- and macroscopic properties of N-A-S-H gel is crucial for designing and developing geopolymer binders. This paper develops molecular models for N-A-S-H gels based on aluminosilicate oligomers with different Si/Al ratios and configurations. Our models mimic the geopolymerization process through a poly-condensation reaction between hydroxyls, generating water and forming the aluminosilicate network. The simulation results indicate that more than 50% of the hydroxyls in oligomers are reacted, reflecting the geopolymerization degree. The oligomers with a higher Si/Al ratio and linear configuration exhibit a higher reaction degree, while those with cyclic configurations exhibit a higher complexity for network structure. Decreasing the Si/Al ratio narrows the bond angle distribution and reduces the skeleton stability of N-A-S-H gel structure. This also decreases the dynamic water mobility due to the higher restriction of hydrogen atoms. Chains’ breakage and the associated hydrolysis reaction at their ends are observed with the consumption of almost 2.5% of the generated water molecules. Furthermore, the enhancement in tensile strength is mainly attributed to increased bridge oxygen numbers, especially for those in Si-O-Si bonds. The elastic modulus is mainly influenced by the amount of hydroxyl and network complexity. In addition, increasing the Si/Al ratio increases the number of Si-O-Si bonds and decreases the hydroxyls, enhancing the tensile strength and elastic modulus of N-A-S-H gels. N-A-S-H gels constructed with cyclic oligomers show around 20% higher tensile strength than those with linear oligomers. Thus, this study will provide valuable insights on the molecular structure understanding and design optimization of geopolymer materials.

A New Platform of B/N-Doped Cyclophanes: Access to a π-Conjugated Block-Type B3 N3 Macrocycle with Strong Dipole Moment and Unique Optoelectronic Properties.

We herein describe a new design principle to achieve B/N-doped cyclophane where an electron-donor block of three triarylamines (Ar3 N) and an acceptor block of three triarylboranes (Ar3 B) are spatially separated on opposite sides of the π-extended ring system. DFT computations revealed the distinct electronic structure of the block-type macrocycle MC-b-B3N3 with a greatly enhanced dipole moment and reduced HOMO-LUMO energy gap in comparison to its analogue with alternating B and N sites, MC-alt-B3N3. The unique arrangement of borane acceptor Ar3 B and amine donor Ar3 N components in MC-b-B3N3 induces exceptionally strong intramolecular charge transfer in the excited state, which is reflected in a largely red-shifted luminescence at 612 nm in solution. The respective linear open-chain oligomer L-b-B3N3 was also synthesized for comparison. Our new approach to donor-acceptor macrocycles offers important fundamental insights and opens up a new avenue to unique optoelectronic materials.

Directing Multivalent Aptamer-Receptor Binding on the Cell Surface with Programmable Atom-Like Nanoparticles.

Multivalent interactions of biomolecules play pivotal roles in physiological and pathological settings. Whereas the directionality of the interactions is crucial, the state-of-the-art synthetic multivalent ligand-receptor systems generally lack programmable approaches for orthogonal directionality. Here, we report the design of programmable atom-like nanoparticles (aptPANs) to direct multivalent aptamer-receptor binding on the cell interface. The positions of the aptamer motifs can be prescribed on tetrahedral DNA frameworks to realize atom-like orthogonal valence and direction, enabling the construction of multivalent molecules with fixed aptamer copy numbers but different directionality. These directional-yet-flexible aptPAN molecules exhibit the adaptability to the receptor distribution on cell surfaces. We demonstrate the high-affinity tumor cell binding with a linear aptPAN oligomer (≈13-fold improved compared to free aptamers), which leads to ≈50 % suppression of cell growth.

Directing Multivalent Aptamer‐Receptor Binding on the Cell Surface with Programmable Atom‐Like Nanoparticles

AbstractMultivalent interactions of biomolecules play pivotal roles in physiological and pathological settings. Whereas the directionality of the interactions is crucial, the state‐of‐the‐art synthetic multivalent ligand–receptor systems generally lack programmable approaches for orthogonal directionality. Here, we report the design of programmable atom‐like nanoparticles (aptPANs) to direct multivalent aptamer–receptor binding on the cell interface. The positions of the aptamer motifs can be prescribed on tetrahedral DNA frameworks to realize atom‐like orthogonal valence and direction, enabling the construction of multivalent molecules with fixed aptamer copy numbers but different directionality. These directional‐yet‐flexible aptPAN molecules exhibit the adaptability to the receptor distribution on cell surfaces. We demonstrate the high‐affinity tumor cell binding with a linear aptPAN oligomer (≈13‐fold improved compared to free aptamers), which leads to ≈50 % suppression of cell growth.