Oligomer Dynamics of LL-37 Truncated Fragments Probed by α-Hemolysin Pore and Molecular Simulations

Oligomerization of antimicrobial peptides (AMPs) is critical in their effects on pathogens. LL-37 and its truncated fragments are widely investigated regarding their structures, antimicrobial activities, and application, such as developing new antibiotics. Due to the small size and weak intermolecular interactions of LL-37 fragments, it is still elusive to establish the relationship between oligomeric states and antimicrobial activities. Here, an α-hemolysin nanopore, mass spectrometry (MS), and molecular dynamic (MD) simulations are used to characterize the oligomeric states of two LL-37 fragments. Nanopore studies provide evidence of trapping events related to the oligomer formation and provide further details on their stabilities, which are confirmed by MS and MD simulations. Furthermore, simulation results reveal the molecular basis of oligomer dynamics and states of LL-37 fragments. This work provides unique insights into the relationship between the oligomer dynamics of AMPs and their antimicrobial activities at the single-molecule level. The study demonstrates how integrating methods allows deciphering single molecule level understanding from nanopore sensing approaches.     

Antibiofouling thin-film composite membranes (TFC) by in situ formation of Cu-(<Emphasis Type="Italic">m</Emphasis>-phenylenediamine) oligomer complex

In situ formation of a Cu-(m-phenylenediamine) (Cu-mPD) oligomer complex from copper chloride during the interfacial polymerization process was successfully employed to produce modified thin-film composite reverse osmosis membranes (TFC-RO) with antibiofouling properties. Membranes were characterized by field emission scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy, and contact angle measurements. Antibiofouling properties were studied using a colony-forming unit test with Escherichia coli. Moreover, an antiadhesion test was developed using fluorescence microscopy. Membrane performance using a cross-flow cell was evaluated, and copper concentration in permeate water was measured. FTIR, XPS and XRD results confirmed the formation of a Cu-mPD oligomer complex and its incorporation into the polyamide layer. A mechanism for formation of the oligomer within the membrane was proposed based on the interaction between the oxygen of the carbonyl group of the polyamide layer and copper ion of the Cu-mPD oligomer complex. The modified membrane showed a slight decrease in hydrophilicity and higher surface roughness. However, excellent antibacterial and antiadhesion effects were observed, attributed to copper toxicity as a result of Cu²⁺ ions release from the membrane surface. Release of copper ions in the permeate water was determined, and the maximum value observed was considered negligible according to the World Health Organization. The desalination performance of modified membrane showed an important salt rejection with stable water flux. In conclusion, a novel chemical method for the incorporation of Cu-mPD oligomer complex into the polyamide layer of TFC-RO membranes to improve their antibiofouling properties and desalination performance was achieved.     

UV curable lens production using molecular weight controlled PEEK based acrylic oligomer (Ac-PEEK)

We produced UV curable lenses with properties blocking short wave UV light. In the UV-curable formulations, we used an oligomer (Ac-PEEK) with another urethan oligomer (Mw = 2000). Radically active, molecular weight controlled Ac-PEEK was obtained by reacting 2-hydroxyl ethyl methacrylate with molecular- weight- controlled and isocyanate terminated PEEK (Mn = 4500). We characterized all synthesized monomer, oligomer and optical materials with UV/Vis spectrophotometer with interferogram, elemental analyser, mass spectrophotometer, proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermal gravimetric analyzer, differential scanning calorimeter, scanning electron microscopy and gas chromatography. Results suggested that newly synthesized oligomer with the structure of PEEK absorbs short wave UV-light. Ageing tests [ISO 11979-5, Ophthalmic implants—intraocular lenses (IOL)—Part 5: Biocompatibility] performed on the IOL materials were successful. High contact angle of the obtained lenses suggests that all lenses were hydrophobic and SEM results revealed that lenses are morphologically homogeneous. Based on all positive properties just mentioned, we safely conclude that the lenses produced in this study are very promising for IOL production.     

聚合物/齐聚物增韧环氧树脂的研究与发展

聚合物 /齐聚物增韧环氧树脂是近年研究的热点 ,而两相结构的存在是环氧树脂增韧的必要条件。文章从两相界面的相互作用角度出发 ,对比分析了不同聚合物 /齐聚物改性剂对环氧树脂改性增韧时相界面作用力的不同而引起的增韧效果的差异 ,并对近年来出现的新型改性增韧剂作了简要概括。     

丙烯酸酯共聚物无皂水性涂料室温固化研究（Ⅰ）固化剂的合成与性能

合成了以ＨＤＩ改性的烯类单体齐聚物。ＩＲ分析了齐聚物的组成，并对丙烯酸酯共聚物水溶胶／ＨＤＩ齐聚物交联体系的固化过程进行了跟踪分析。结果表明，齐聚物能够减缓ＮＣＯ基团的反应活性，基本消除其与水的反应，提供施涂操作的充分时间；通过测定ＨＤＩ齐聚物粘度随贮存时间的变化，对其稳定性进行了研究，作为涂料固化剂，符合涂料施涂工艺的要求。     

羟基封端的有机硅低聚物的合成

采用甲基三乙氧基硅烷,二甲基二乙氧基硅烷,苯基三乙氧基硅烷为原料,通过水解-缩合反应合成一种羟基封端的有机硅低聚物,并初步研究了有机硅低聚物的合成条件。实验表明:反应温度为70℃,时间为4h,pH为3,可合成羟基封端的有机硅低聚物。红外光谱表明,合成的有机硅低聚物在Si-OC2H5及Si-O-Si处都出现吸收峰,其结构与理论基本相符。     

耐高温乙炔基封端聚酰亚胺的制备与性能

基于单体4-苯基醚-1,3-二胺制备了一种新型乙炔基封端热固性聚酰亚胺.利用傅里叶变换红外光谱仪、核磁共振氢谱仪和X射线衍射仪对其结构进行表征,其结果表明制备得到了相应结构的预聚体.利用差示扫描量热仪测得预聚体的玻璃化转变温度(Tg)仅为155℃.预聚体在有机溶剂中具有高的溶解性,常温下在N-甲基吡咯烷酮中的溶解度高于...     

TiO2 hollow spheres as effective additives in oligomer electrolytes for dye-sensitized solar cells

TiO₂ hollow spheres are employed as an additive of oligomer electrolytes for dye-sensitized solar cells (DSSCs). The measurement of steady-state currents confirms that introducing TiO₂ hollow spheres can facilitate ionic diffusion in oligomer electrolytes. Even compared with conventional nanoparticle additives, the hollow spheres are more favorable to increase the diffusion coefficients of I^? and I₃^? in oligomer electrolytes. Furthermore, the hollow structure with a submicron size is effective to scatter incident light and thereby enhance the light-harvesting efficiency of DSSCs. The energy-conversion efficiency of the DSSCs with TiO₂ hollow sphere additives significantly improves up to 7.22% due to the facilitated ionic diffusion and the enhanced light-harvesting efficiency.     

Synergistic effects of oxidized CNTs and reactive oligomer on the fracture toughness and mechanical properties of epoxy

The soft modifiers added to improve the fracture toughness of epoxies generally deteriorate their mechanical properties. Hence, oxidized multi-walled carbon nanotubes (O-CNTs) were added to the epoxy modified with reactive oligomer. The NCO terminated reactive oligomer acts as a cross-linker between the O-CNTs and the OH groups of the epoxies. The impact strengths of the 15 wt.% oligomer modified epoxy containing 0.5 wt.% of O-CNTs at room temperature (RT) and cryogenic temperature (CT) are enhanced by 23.6% and 69.5% compared to that of the unmodified epoxy. In addition to increasing fracture toughness, the tensile strength (TS) of the modified epoxy/O-CNTs at CT is found to be 91.7 MPa, which is comparable to that of the unmodified epoxy (92.1 MPa). Hence, the attachment of O-CNTs to the reactive oligomer modified epoxy can be an efficient approach to toughen epoxy resins without compromising their tensile properties.     

Influence of Chain Architecture on Nanopore Accessibility in Polyelectrolyte Block‐Co‐Oligomer Functionalized Mesopores

Functionalized ordered mesoporous silica materials are commonly investigated for applications such as drug release, sensing, and separation processes. Although, various homopolymer functionalized responsive mesopores are reported, little focus has been put on copolymers in mesopores. Mesoporous silica films are functionalized with responsive and orthogonally charged block‐co‐oligomers. Responsive 2‐dimethylamino)ethyl methacrylate)‐block‐2‐(methacryloyloxy)ethyl phosphate (DMAEMA‐b‐MEP) block‐co‐oligomers are introduced into mesoporous films using controlled photoiniferter initiated polymerization. This approach allows a very flexible charge composition design. The obtained block‐co‐oligomer functionalized mesopores show a complex gating behavior indicating a strong interplay between the different blocks emphasizing the strong influence of charge distribution inside mesopores on ionic pore accessibility. For example, in contrast to mesopores functionalized with zwitterionic polymers, DMAEMA‐b‐MEP block‐co‐oligomer functionalized mesopores, containing two oppositely charged blocks, do not show bipolar ion exclusion, demonstrating the influence of the chain architecture on mesopore accessibility. Furthermore, ligand binding–based selective gating is strongly influenced by this chain architecture as demonstrated by an expansion of pore accessibility states for block‐co‐oligomer functionalized mesopores as compared to the individual polyelectrolyte functionalization for calcium induced gating.     

Dispersion of single-walled carbon nanotubes in water by the use of novel fluorinated dendrimer-type copolymers

New fluorinated dendrimer-type block copolymers were applied to the dispersion of single-walled carbon nanotubes (SW-CNTs) and single-walled carbon nanotubes containing carboxy groups [(SW-CNT)-COOH] in water. Fluorinated block copolymer could disperse SW-CNTs more effectively in water, compared to that of the corresponding ABA triblock-type fluoroalkyl end-capped dimethylacrylamide oligomer [R_F-(DMAA)_n-R_F]. Dynamic light-scattering (DLS) measurements and transmission electron microscopy (TEM) images show that SW-CNTs could be smoothly encapsulated into fluorinated copolymeric aggregates cores. Interestingly, it was demonstrated that SW-CNTs could be in part released from the fluorinated copolymeric aggregates/SW-CNTs composites or encapsulated into these composites with increasing the dispersion times. On the other hand, fluorinated block copolymer and R_F-(DMAA)_n-R_F oligomer were not able to disperse well (SW-CNT)-COOH in water; however, ABA triblock-type fluoroalkyl end-capped acrylic acid oligomer was able to disperse quite effectively (SW-CNT)-COOH in water.     

聚合物中小分子扩散的分子动力学模拟

采用分子动力学(MD)方法,以研究低聚体在聚甲基丙烯酸甲酯中的扩散为例,通过分析高分子链长、低聚体含量、聚合度和温度对扩散系数的影响,揭示小分子在聚合物中扩散过程.通过比较扩散系数的模拟值与实验值,发现两者比值在4左右.为获得小分子在聚合物中的扩散系数提供了一种较好的方法.     

Enhanced emission from single component organic core-shell nanoparticles

By one-step mixed-solvent mediated approach, we have prepared fluorescent organic core-shell nanoparticles with an oligomer (1) derived from the Schiff base condensation reaction of 2,6-diformyl-4-methylphenol and o-phenylenediamine at room temperature. The core and shell structures are generated by the same oligomer (1) featuring the aggregation structure in core different from that in shell. The radial packing factor distribution of oligomer cluster depending on the solvent interaction in the time of nucleation is mainly responsible for the single component core-shell formation. Different morphologies of the core-shell nanospheres (CSNS) and core-shell nanohemispheres (CSNHS) were generated simply by changing the concentration of 1 in chloroform-methanol mixed solvent (1:2). We observed that fluorescent emission from those core-shell nanoparticles is intense whereas as-synthesized oligomer (1) itself is non-fluorescent in dilute solution. The enhanced emission in the core-shell form with more than 50 times increase in fluorescent quantum yield vis-à-vis 1 is a remarkable feature of the study. As UV absorption spectra of nanoparticles are blue-shifted relative to their properties in solution, the observed strong emission in the solid state makes the oligomer an outstanding exception to a well-established rule based on the molecular exciton model. The core-shell nanoparticles have been characterized by FE-SEM, TEM, XRD, nanosecond (ns) time-resolved fluorescence dynamics, UV-Vis and fluorescence spectroscopy. The longer fluorescence lifetimes (tau) of core-shell nanoparticles (3.50 ns and 3.52 ns for CSNS and CSNHS respectively) than 1 as-synthesized (1.28 ns) implies that the formation of the nanoparticles restricts the rotation and vibration of the groups in the molecules. The factor that induces fluorescent enhancement of nanoparticles is mainly ascribed to the increase of radiative rate constant (k(r)) and simultaneous decrease of nonradiative rate constant (k(nr)).     

Influence of Kinetic Factors on the Distinctive Features of the Rheological Behavior of Oligomer Systems

The distinctive features of the rheological behavior of oligomer liquids have been considered within the framework of the concept of the aggregative nature of their supermolecular structure. It has been shown that the dependence of the rheological properties of oligomers on the temperature–time and deformation prehistory is a consequence of the system's nonequilibrium at the instant of measurement. Theoretical models quantitatively describing the evolution of the system to thermodynamic equilibrium have been proposed. Account for the kinetics of formation of the supermolecular structure of oligomer liquids enables one to correctly explain certain experimental anomalies, thus transferring them to the class of fundamental physicochemical regularities.     

Electronic transmission across a metal /conjugated-oligomer/metal structure: role of intrinsic disorder

We have studied electronic transmission across metal/conjugated-oligomer/metal structures: (a) one oligomer chain, and (b) two oligomer chains sandwiched between metal contacts, in the presence of lattice fluctuations. The lattice fluctuations are approximated by static white noise disorder. Resonant transmission occurs when the energy of an incoming electron coincides with a discrete electronic level of the oligomer. Because of disorder there is an enhancement of electronic transmission for energies that lie within the electronic gap of the oligomer. If fluctuations are sufficiently strong, a transmission peak within the gap is found at the midgap energy E = 0 for degenerate conjugated oligomers. For the two-chain case the spatial mirror symmetry is broken and coherence between the wavefunctions of two chains is partly lost when fluctuations are introduced.     

Temperature tuning effect in coordination reaction with the oligomer ligand sodium [N-(4-O-phenyldithiocarboxylate) maleimide]n: Variations in crystallinity, morphology and fluorescence emission

The temperature tuning effect in coordination reaction with the oligomer ligand, sodium [N-(4-O-phenyldithiocarboxylate) maleimide]_n (n = 10-15), has been studied. It is found that more Ti-S coordination bonds have been formed with reaction temperature increasing, which results in the variations in crystallinity, morphology and solid fluorescence of the prepared complex materials. The nature of temperature tuning is to improve the activity of oligomer ligands and increase the contacting probability between Ti(IV) and -CS₂ groups. Based on the experiment results, a Ti-S tetrahedral coordination model is also proposed for this case.     

影响酚醛型苯并口恶嗪软化点的结构因素

合成了分子量不同的酚醛树脂预聚体,以此为多元酚基体采用悬浮法通过控制苯酚与苯胺的摩尔配比合成了一系列苯并口恶嗪环状结构含量不同的酚醛型苯并口恶嗪中间体树脂(P-BOZ),并用FT-IR和1H-NMR对其结构进行了表征,用环球法对其软化点进行了测量。研究表明,P-BOZ的软化点随酚醛树脂预聚体分子量的增加而提高,随苯并口恶嗪环状结构含量的增加而降低,这一现象与分子间酚羟基的氢键作用有关。因此,通过分子设计可以提高其软化点。     

A cellular automaton simulation of the degradation of porous polylactide scaffold: I. Effect of porosity

A cellular automaton method that includes a fabricating model for solvent casting/porogen leaching and a multiple-particle random walk model for oligomer molecular diffusion was used to simulate degradation behaviors and their dependence on the initial porosities (80%, 90% and 95%) of porous polylactide (PLA) scaffolds. Changes in the mass loss, molecular weight, numbers of PLA chains and ester groups, oligomer molecules release and average degradation rate with degradation time were investigated. The results show that during degradation, higher initial porosity resulted in greater molecular weight and a higher average number of ester groups and less mass loss, a lower number of oligomer molecules being released and a lower ratio of oligomer molecules remaining in the scaffold to those in the whole model. The average degradation rate and average number of PLA chains initially changed in direct proportion to the initial porosity, but there was an inverse change later in the degradation. In addition, no hollow structures were found in any of the scaffolds during the degradation, which indicates there was no dramatic autocatalytic phenomenon such as that seen for massive solid structures such as a plate in the porous PLA scaffold. The above simulated results are consistent with recent experimental reports, suggesting our simulating method has potential application in studying the degradation behaviors of porous scaffolds for tissue engineering.     

MOLECULAR WEIGHT EFFECTS OF OLIGOMERIC DISPERSANTS ON AQUEOUS ALUMINA SUSPENSIONS

The objectives of this study are to synthesize an oligomer (75% acrylic acid, 15% acrylamide, and 10% methyl acrylate) with different molecular weights and determine the effects of molecular weight on the dispersing ability of the oligomers. Molecular weights were calculated using Proton NMR spectroscopy for end-group analysis. Rheology and adsorption measurements of aqueous alumina slurries at various polymer dosages were acquired at pH 9.5. Based on the results of these studies, it was concluded that the molecular weight of an oligomer does have a significant effect on alumina suspensions. Moreover, there is an optimum molecular weight at which suspension viscosity is the lowest due to the amount of oligomer adsorbed onto alumina particles. In this study, oligomer C (1970 g/mol) with 2 mg/g of alumina dosage in 0.50 volume fraction alumina suspensions yielded the lowest viscosity and highest adsorption. Viscosity and adsorption values increased above and below 1970 g/mol molecular weight. In summary, efficiency of a dispersant is essentially related to the conditions under which it is used. Therefore, it is important to optimize all conditions, molecular weight and charge interactions being most fundamental.     

环氧树脂预聚物分子量对其固化物性能的影响

本文着重研究了环氧树脂预聚物分子量对叔胺促进剂催化的酸酐固化剂固化的环氧树脂体系固化物电气、力学和耐热性能的影响。结果表明,环氧树脂预聚物分子量对性能有显着影响,且具有规律性。