Theoretical study on the cross-linking reaction mechanism of cellulose nanofibrils initiated by fluorine.

Theoretical investigation on the cross-linking reaction process and mechanism of cellulose nanofibrils (CNFs) initiated by fluorine is accomplished by density functional theory. Three reaction pathways generated aldehyde and ester are identified. The reaction potential energy information of the ten reaction channels at B3LYP/6-311+G(d,p) level are obtained. The calculation results show that the reaction pathway of forming ester thereafter acyl fluoride has realized the cross-linking of cellulose. The reaction pathway of forming ester is more kinetically and thermodynamically favorable than the others of forming aldehyde with the lower energy barriers. The oxidation site mainly occurred at the methylene hydrogen of the hydroxymethyl group in the cellulose. The cross-linking of two cellulose molecules initiated by fluorine forming a covalent ester bond would be beneficial to improve cellulose mechanical properties of the insulating paper, which is better to add cellulose nanofibrils served as a "bridge" for strengthening the connection between celluloses.

The influence of mouth opening on pharyngeal pressure loss and its underlying mechanism: A computational fluid dynamic analysis.

Objective: During inspiration, mechanical energy generated from respiratory muscle produces a negative pressure gradient to fulfill enough pulmonary ventilation. The pressure loss, a surrogate for energy loss, is considered as the portion of negative pressure without converting into the kinetic energy of airflow. Mouth opening (MO) during sleep is a common symptom in patients with obstructive sleep apnoea-hypopnea syndrome (OSAHS). This study aimed to evaluate the effects of mouth opening on pharyngeal pressure loss using computational fluid dynamics (CFD) simulation. Methods: A total of four subjects who were morphologically distinct in the pharyngeal characteristics based on Friedman tongue position (FTP) grades were selected. Upper airway computed tomography (CT) scan was performed under two conditions: Mouth closing (MC) and mouth opening, in order to reconstruct the upper airway models. computational fluid dynamics was used to simulate the flow on the two different occasions: Mouth closing and mouth opening. Results: The pharyngeal jet was the typical aerodynamic feature and its formation and development were different from mouth closing to mouth opening in subjects with different Friedman tongue position grades. For FTP I with mouth closing, a pharyngeal jet gradually formed with proximity to the velopharyngeal minimum area plane (planeAmin). Downstream the planeAmin, the jet impingement on the pharyngeal wall resulted in the frictional loss associated with wall shear stress (WSS). A rapid luminal expansion led to flow separation and large recirculation region, corresponding to the interior flow loss. They all contributed to the pharyngeal total pressure loss. While for FTP I with mouth opening, the improved velopharyngeal constriction led to smoother flow and a lower total pressure loss. For FTP IV, the narrower the planeAmin after mouth opening, the stronger the jet formation and its impingement on the pharyngeal wall, predicting a higher frictional loss resulted from higher WSS. Besides, a longer length of the mouth opening-associated constant constrictive segment was another important morphological factor promoting frictional loss. Conclusion: For certain OSAHS patients with higher Friedman tongue position grade, mouth opening-related stronger jet formation, more jet breakdown and stronger jet flow separation might contribute to the increased pharyngeal pressure loss. It might require compensation from more inspiratory negative static pressure that would potentially increase the severity of OSAHS.

Nanomaterials-based photosensitizers and delivery systems for photodynamic cancer therapy.

The increasing cancer morbidity and mortality requires the development of high-efficiency and low-toxicity anticancer approaches. In recent years, photodynamic therapy (PDT) has attracted much attention in cancer therapy due to its non-invasive features and low side effects. Photosensitizer (PS) is one of the key factors of PDT, and its successful delivery largely determines the outcome of PDT. Although a few PS molecules have been approved for clinical use, PDT is still limited by the low stability and poor tumor targeting capacity of PSs. Various nanomaterial systems have shown great potentials in improving PDT, such as metal nanoparticles, graphene-based nanomaterials, liposomes, ROS-sensitive nanocarriers and supramolecular nanomaterials. The small molecular PSs can be loaded in functional nanomaterials to enhance the PS stability and tumor targeted delivery, and some functionalized nanomaterials themselves can be directly used as PSs. Herein, we aim to provide a comprehensive understanding of PDT, and summarize the recent progress of nanomaterials-based PSs and delivery systems in anticancer PDT. In addition, the concerns of nanomaterials-based PDT including low tumor targeting capacity, limited light penetration, hypoxia and nonspecific protein corona formation are discussed. The possible solutions to these concerns are also discussed.

Theoretical study on the hydrogen addition reactions to bismaleimide in the ultra-violet radiation cross-linking process of polyethylene.

Theoretical investigation on the multiple-channel addition reactions of hydrogen in polyethylene to bismaleimide in the Ultra-violet (UV) radiation cross-linking process is accomplished by density functional theory. Their energetic information of the nineteen reaction channels at B3LYP/6-311 + G(d,p) level is obtained. Two types of electrophilic addition reaction, one is the 4-position hydrogen in 4-methylheptane to C of C=C groups in bismaleimide and the other one is the 4-position hydrogen in 4-methylheptane to O of C=O groups in bismaleimide, are identified. The effects of introducing the heteroatom O and/or the benzene ring among both ends of the two maleimide rings have been evaluated. The results show that the addition reaction potential barrier height to O in C=O groups is lower than that of the C in C=C groups in the conjugative bismaleimide system.The founding of the addition reaction channel to O in C=O groups could clear further the mechanism of grafting bismaleimide to polyethylene.

Reaction Mechanism of Etherification of Rice Straw with Epichlorohydrin in Alkaline Medium.

Wood plastic composites (WPCs) made from plant fibres and plastics have gained more and more attention. Studies have been focused on preparation and mechanical performance of WPCs. While mechanism of chemical modification of cereal straw has rarely been reported. In the present work, rice straw was etherified with epichlorohydrin (EPI) and the mechanism of etherification was investigated. Natural rice straw (NRS) was pretreated with NaOH to move most of hemicellulose and lignin. The alkali treated rice straw (ARS), whose dominant component being cellulose, was etherified with EPI at 120 °C for 1-8 h in toluene with NaOH as catalyst. NRS, ARS and etherified rice straw (ERS) were characterized and analyzed by FT-IR, solid CP/MAS 13C-NMR, elemental analysis and neutral sugar analysis. The etherification reaction was finished within 5 h, and C3H6O units were introduced into the structure of cellulose, leading to the increase of contents of C and H in ERS. The etherification process of ARS in alkaline medium was divided into three stages, during which two hydroxyl groups were replaced by two ether bonds successively, and a new hydroxyl group was formed in the last step. The number of hydroxyl groups in ERS was reduced, and reduction of hydrophilicity of ERS could be expected.

Theoretical study on the mechanisms of polyethylene electrical breakdown strength increment by the addition of voltage stabilizers.

A theoretical investigation on the mechanisms of electrical breakdown strength increment of polyethylene at the atomic and molecular levels is accomplished. The addition of aromatic carbonyl and carboxyl compounds as voltage stabilizers may increase the electrical breakdown strength of polyethylene. The HOMO-LUMO energy gaps, the ionization potentials, the electron affinities, and the reorganization energies at the ground states of a series of aromatic carbonyl and carboxyl compounds are obtained at the B3LYP/6-311+G(d,p) level. The 24 isomerization reactions at the S0 and T1 states, including the harmonic vibration frequencies of the equilibrium geometries and the minimum energy path (MEP) by the intrinsic reaction coordinate (IRC) theory, are obtained at the same level. The results show that 4,4'-didodecyloxybenzil (Bd) molecule, which has much smaller HOMO-LUMO energy gap, much larger reorganization energy than others, and excellent compatibility with polymers matrix, can increase the electrical breakdown strength effectively. This result is in good agreement with the available experimental findings.