A New Approach for Synthesis of Low‐moisture Glycidyl Azide Polymer

In this work, low‐moisture glycidyl azide polymer (GAP) was successfully prepared using a modified two‐step method. The modified method resembles the structure of the classical two‐step method, which is widely used to prepare the GAP. Firstly, epichlorohydrin (ECH) is polymerized into polyepicholorohydrin (PECH), which is subjected afterward to azidation step using sodium azide (NaN₃). Interestingly, minimizing the water content in the final GAP product, which is a challenging when dealing with GAP as a rocket propellant binder, was effectively achieved by utilizing low boiling point solvents instead of the relatively high boiling point Dimethyl formamide (DMF), monitoring the volatility of ECH and controlling the exothermicity of the reaction. Prepared GAP samples were investigated using Fourier transformer infra‐red (FT‐IR), gel‐permeation chromatography (GPC) and elemental analysis apparatus (CHNS) were used to characterize the product. The moisture % in the final product was examined using the Karl‐Fisher Technique. Results showed the successful preparation of GAP with low water content (<0.01 %), high average molecular weight (> 2000 g · mol^–1), 42.82 % nitrogen, a viscosity of 3484 cP at 20 °C, yield ranges between 95–98 % and a polydispersity index of 1.2. The prepared GAP is promising for replacement of the classical GAPs in the energetic materials applications.     

Ultrasound-assisted immersion freezing reduces the structure and gel property deterioration of myofibrillar protein from chicken breast

The effects of air freezing (AF), immersion freezing (IF) and ultrasound-assisted immersion freezing (UF) at different power levels (125, 165, 205 and 245 W) on the structure and gel properties of the myofibrillar protein (MP) of chicken breast were investigated. UF at 165 W (UF-165) had no obvious negative impact on the primary structure of the MP and effectively reduced the change in the secondary and tertiary structure. In addition, UF-165 significantly reduced the losses in the elastic modulus (G′), gel strength, and gel water holding capacity (P < 0.05). According to low field nuclear magnetic resonance analysis, the T₂₁ and T₂₂ of the UF-165 MP gels were shorter than those of the AF and IF samples, which meant that the UF-165 reduced the mobility of the immobilized water and free water in MP gel. A scanning electron microscopy analysis showed that the appropriate ultrasonic power promoted the formation of a compact and homogeneous protein gel network. These results suggested that the appropriate ultrasonic power maintained the MP structure and reduced the loss of gel quality.     

A Gel Polymer Electrolyte with 2D Filler-reinforced for Dendrite Suppression Li-Ion Batteries

Gel polymer electrolytes (GPEs) incorporate both the high ionic conductivity of organic liquid electrolyte and the high safety performance of all-solid-state electrolytes (ASSEs), greatly improving the electrochemical performance of solid polymer electrolytes (SPEs). However, the practical application of GPEs is still limited by inferior interface compatibility, lithium dendrites, etc. Herein, we prepared GPEs based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) further co-blended the two-dimensional sheet inorganic filler hectorite and poly(methyl methacrylate) (PMMA) to improve the mechanical and electrochemical properties of the GPEs. When the content of PMMA and hectorite is optimal, this GPEs have an ionic conductivity of 1.06×10⁻³ S cm⁻¹ and outstanding lithium symmetric cells cycle time of more than 3000 h, indicating that the introduction of filler effectively inhibits the growth of lithium dendrites at room temperature. Moreover, the GPEs adopt a relatively simple solution casting method to provide a fresh idea for the synthesis of high-performance GPEs.     

A Polarized Gel Electrolyte for Wide-Temperature Flexible Zinc-Air Batteries

The development of flexible zinc-air batteries (FZABs) has attracted broad attention in the field of wearable electronic devices. Gel electrolyte is one of the most important components in FZABs, which is urgent to be optimized to match with Zn anode and adapt to severe climates. In this work, a polarized gel electrolyte of polyacrylamide-sodium citric (PAM-SC) is designed for FZABs, in which the SC molecules contain large amount of polarized −COO⁻ functional groups. The polarized −COO⁻ groups can form an electrical field between gel electrolyte and Zn anode to suppress Zn dendrite growth. Besides, the −COO⁻ groups in PAM-SC can fix H₂O molecules, which prevents water from freezing and evaporating. The polarized PAM-SC hydrogel delivers a high ionic conductivity of 324.68 mS cm⁻¹ and water retention of 96.85 % after being exposed for 96 h. FZABs with the PAM-SC gel electrolyte exhibit long cycling life of 700 cycles at −40 °C, showing the application prospect under extreme conditions.     

Comparison of benzothiazole-based dyes for sensitive DNA detection

For efficient and quantitative DNA detection, fluorescence staining is the most often explored approach, which relies on non-covalent binding of dyes with double stranded DNA (dsDNA). Ethidium bromide (EB) is the most classic DNA stain, but suffers from its high carcinogenicity. A series of less toxic alternatives were developed, many of which contain the core structure of the benzothiazole ring. However, the relationship between the structure and the DNA detection performance was not illustrated. Herein, five benzothiazole dyes, namely thiazole orange, SYBR Green I, PicoGreen, SYBR Safe, and thioflavine-T, were compared for DNA detection through direct fluorescence and gel electrophoresis, with particular focus on the structure-performance relationship. It turned out that SYBR Green I is currently the best choice for DNA detection. The results in this work may be useful for future DNA-staining dye developments.     

Comparison of antimicrobial peptide purification via free‐flow electrophoresis and gel filtration chromatography

Antimicrobial peptides (AMPs) are usually small and cationic biomolecules with broad‐spectrum antimicrobial activities against pathogens. Purifying them from complex samples is essential to study their physiochemical properties. In this work, free‐flow zone electrophoresis (FFZE) was utilized to purify AMPs from yeast fermentation broth. Meanwhile, gel filtration chromatography (GFC) was conducted for comparison. The separation efficiency was evaluated by SDS‐PAGE analysis of the fractions from both methods. Our results demonstrated as follows: (i) FFZE had more than 30‐fold higher processing capacity as compared with GFC; (ii) FFZE could achieve 87% purity and 89% recovery rate while in GFC these parameters were about 93 and 82%, respectively; (iii) the former had ∼2‐fold dilution but the latter had ∼13‐fold dilution. Furthermore, Tricine‐SDS‐PAGE, Native‐PAGE, and gel IEF were carried out to characterize the purified AMPs. We found that two peptides existed as a pair with the molecular mass of ∼5.5 and 7.0 kDa, while the same pI 7.8. These two peptides were proved to have the antimicrobial activity through the standardized agar diffusion method. Therefore, FFZE could be used to continuously purify AMPs with high bioactivity, which will lead to its wide application in the clinical and pharmaceutical fields.     

Electrokinetic actuation of an uncharged polarizable dielectric droplet in charged hydrogel medium

Electrokinetic transport of an uncharged nonconducting microsized liquid droplet in a charged hydrogel medium is studied. Dielectric polarization of the liquid drop under the action of an externally imposed electric field induces a non-homogeneous charge density at the droplet surface. The interactions of the induced surface charge of the droplet with the immobile charges of the hydrogel medium generates an electric force to the droplet, which actuates the drop through the charged hydrogel medium. A numerical study based on the first principle of electrokinetics is adopted. Dependence of the droplet velocity on its dielectric permittivity, bulk ionic concentration, and immobile charge density of the gel is analyzed. The surface conduction is significant in presence of charged gel, which creates a concentration polarization. The impact of the counterion saturation in the Debye layer due to the dielectric decrement of the medium is addressed. The modified Nernst–Planck equation for ion transport and the Poisson equation for the electric field is considered to take into account the dielectric polarization. A quadrupolar vortex around the uncharged droplet is observed when the gel medium is considered to be uncharged, which is similar to the induced charge electroosmosis around an uncharged dielectric colloid in free-solution. We find that the induced charge electrokinetic mechanism creates a strong recirculation of liquid within the droplet and the translational velocity of the droplet strongly depends on its size for the dielectric droplet embedded in a charged gel medium.     

Determination of PEGylation homogeneity of polyethylene glycol-modified canine uricase

Polyethylene glycol-modified canine uricase (PEG-UHC) was prepared by modifying the ε-amino group of lysine residues on the canine uricase (UHC) protein to near-saturation with 5 kDa monomethoxyl-polyethylene glycol succinimide (mPEG-SPA-5k). In order to accurately determine the PEGylation uniformity of PEG-UHC, CZE, 3–8% gradient gel SDS-PAGE, and imaging CIEF (iCIEF) analyses were compared. CZE could not effectively separate PEG-UHC proteins with different degrees of modification, 3–8% gradient gel SDS-PAGE could separate PEG-UHC into seven gel bands; however, most of the gel bands were smeared or blurred, and the separation of PEG-UHC samples by iCIEF was significantly better than that by 3–8% gradient gel SDS-PAGE. Under denatured conditions, iCIEF separated 12 pI peaks, and could also accurately quantify the relative monomer PEG-UHC content. More than 85% of the total monomeric PEG-UHC was conjugated with 7–12 PEG molecules; of this 85%, approximately 40% was conjugated with 9–10 PEG molecules. These results demonstrated that iCIEF exhibits good potential for determining the PEGylation homogeneity of PEGylated protein drugs.     

Crystal growth,spectral characterization and structural studies of a luminescent coordination polymer of calcium(II) complex of benzilic acid

Single crystals of a new calcium(II) complex of benzilic acid, [Ca(C₁₄H₁₁O₃)₂(C₁₄H₁₂O₃)₂] have been successfully grown by gel diffusion technique at room temperature. Single crystal X-ray diffraction study reveals that the compound belongs to orthorhombic system with space group Fddd. The adjacent CaO₈ units are linked via O–H–O interaction to form one dimensional polymeric chains. The extensive hydrogen bonding interactions lead to a supramolecular structure. The grown crystals were further characterized by elemental analysis, FT-IR, UV–Visible, thermogravimetric, powder X-ray diffraction and solid state photoluminescence studies.     

Rheological properties of poly(vinyl chloride)/plasticizer systems—relation between sol–gel transition and elongational viscosity

Poly(vinyl chloride) (PVC)/di-isononyl phthalate systems with PVC content of 45.5 (PVC8) and 70.4 wt% (PVC6) were prepared by a hot roller at 150 °C and press molded at 180 °C. The dynamic viscoelasticity and elongational viscosity of PVC8 and PVC6 were measured in the temperature range from 150 to 220 °C. We have found that the storage and loss shear moduli, G′ and G″, of PVC8 and PVC6 exhibited the power-law dependence on the angular frequency ω at 190 and 210 °C, respectively. Correspondingly, the tan δ values did not depend on ω. These temperatures indicate the critical gel temperature T _gel of each system. The critical relaxation exponent n obtained from these data was 0.75 irrespective of PVC content, which was in agreement with the n values reported previously for the low PVC concentration samples. These results suggest that the PVC gels of different plasticizer content have a similar fractal structure. Below T _gel, the gradual melting of the PVC crystallites takes place with elevating temperature, and above T _gel, a densely connected network throughout the whole system disappears. Correspondingly, the elongational viscosity behavior of PVC8 and PVC6 exhibited strong strain hardening below T _gel, although it did not show any strain hardening above T _gel. These changes in rheological behavior are attributed to the gradual melting of the PVC crystallites worked as the cross-linking domains in this physical gel, thereby inapplicability of the of time–temperature superposition for PVC/plasticizer systems.