OPTICALLY ACTIVE AMINO ACIDS WITH HIGHLY BRANCHED SIDE CHAIN (I) SYNTHESIS OF D- AND L- 2-AMINO-5,5-DIMETHYLHEXANOIC ACID AND 2-AMINO-6,6-DIMETHYLHEPTANOIC ACID

The title compounds were prepared by the enzymatic resolution of the corresponding N-acetylated DL-amino acids methyl esters, which were obtained from t-butyl chloride via an 8-step synthesis.

Improving gene transfection efficiency of highly branched poly(β-amino ester)s through the in-situ conversion of inactive terminal groups

Highly branched poly(β-amino ester)s(HPAEs)have emerged as a safe and efficient type of non-viral gene delivery vectors.However,the presence of inactive terminal secondary amine groups compromises their gene transfection capability.In this study,HPAEs with similar topological structures and chemical compositions but varying numbers of terminal secondary 4-amino-1-butanol(S4)and secondary/tertiary 3-morpholinopropylamine(MPA)groups were synthesized.The results demonstrate that an increased number of secondary/tertiary MPA groups in-situ significantly enhances the DNA binding capability of HPAEs,leading to the formation of smaller HPAE/DNA polyplexes with higher zeta potential,ultimately resulting in superior gene transfection efficiency in bladder epithelial cells.This study establishes a sim-ple yet effective strategy to maximize the gene transfection potency of HPAEs by converting the inactive terminal groups in-situ without the need for complex modifications to their topological structure and chemical composition.

Effects of Branching Strategy on the Gene Transfection of Highly Branched Poly(β-amino ester)s

Highly branched poiy(β-amino ester)s(HPAEs)have emerged as one type of the most viable non-viral gene delivery vectors,both in vitro and in viva.However,the effects of different branching strategies on the gene transfection performance have not yet been explored.Here,using triacrylate(B3)and diamine(B4)as the branching monomers,a series of HPAEs were synthesized via the"A2+B3+C2"and"A2+B4+C2"strategies,respectively.Results show that the branching strategy plays a pivotal role in dictating the physiological properties of the HPAE/DNA polyplexes and thus leads to obviously different cell viability and transfection efficiency.Comparatively,HPAEs synthesized via the"A2+B3+C2"branching strategy are more favorable for DNA transfection than that synthesized via the"A2+B4+C2"strategy.This study may provide new insights into the development of HPAEs based non-viral DNA delivery system.

Characterisation and functional roles of a highly branched dextran produced by a bee pollen isolate Leuconostoc mesenteroides BI-20

Lactic Acid Bacteria(LAB)from different niches can be responsible for the production of distinct exopolysaccharides(EPS)that might possess important structural and technological features.In this respect,the aim of this study was to isolate an EPS producer LAB strain from bee pollen environment.Leuconostoc mesenteroides BI-20 with a slimy-mucoid colony morphology was identified from bee pollen and the structural,technological and functional characteristics of EPS produced by this strain were determined.EPS BI-20 was a highly branched dextran containing 20%(1→3)-linked α-D-glucose branches determined by ^(1)H and ^(13)C NMR analysis.The presence of(1→6)/(1→3)-linkedα-D-glucose linkages in dextran BI-20 was also confirmed by FTIR analysis.Dextran BI-20,with a molecular weight of 1×10^(8) Da,possessed strong thermal properties,amorphous nature and highly branched and fibrous microstructural characteristics determined by DSC,TGA,XRD and SEM analysis,respectively.In terms of functional roles,dextran BI-20 demonstrated strong antioxidant capacity detected by ABTS and CUPRAC tests.Finally,no digestion was observed in dextran BI-20 under simulated gastric conditions.Results of this study unveiled techno-functional characteristics of dextran BI-20 produced by a bee pollen isolate LAB strain.

Efficient gene transfection of suspension cells by highly branched poly(β-amino ester)

Suspension cells play a crucial role in many biological processes. However, compared to adherent cells, it is particularly challenging to introduce exogenous genes into suspension cells to regulate their biological functions with non-viral gene vectors, mainly due to the low cellular uptake and endosomal escape of polyplexes. Herein, to improve the interactions of polyplexes with cellular membranes, we design and synthesize highly branched poly(β-amino ester)(HPAE) via an “A2 + B4 + C2” Michael addition strategy.Results show that branching significantly increases DNA condensation of HPAE, cellular uptake and endosomal escape of HPAE/DNA polyplexes. In mast cells(MCs), HPAE exhibits up to 80-fold higher gene transfection efficiency compared to the corresponding linear poly(β-amino ester)(LPAE) and the leading commercial gene transfection reagents PEI25k, jetPEI, and Lipofectamine 3000, without causing obvious cytotoxicity. Our study establishes a reliable non-viral platform for efficient gene transfection of suspension cells.

Highly branched poly(β-amino ester)s with narrow molecular weight distribution: Fractionation and gene transfection activity

Highly branched poly(β-amino ester)s(HPAEs) have shown their great promise in gene delivery. However, their broad molecular weight distribution(MWD) poses an additional challenge to the mechanistic understanding of the influence of molecular weight(MW) on their gene transfection activity. Using a stepwise precipitation strategy, HPAEs were fractionated. It is shown that MW has a significant effect on the transfection activity and cytotoxicity of HPAEs. The intermediate MW mediates higher transfection efficiency while maintaining high cell viability. Mechanistic studies show that the intermediate MW confers stronger DNA binding affinity to HPAEs, leading to the formulation of polyplexes with a relatively smaller size and more positive zeta potential. This study not only suggests a simple strategy to fractionate HPAEs with narrow MWD but also provides new insights into understanding the structure-property relationship, which would facilitate the clinical translation of HPAEs in gene therapy.

Crystallization Behavior of Polymer Derived Silicon Carbide Sintered Through Microwave Heating Technique

A self-crosslinkable liquid highly branched polycarbosilane（LHBPCS） with 5.07% vinyl group and a C/Si ratio of 1.33 was used as the precursor to prepare Si C ceramic material. Microwave heating technique and conventional heating method were applied for the heating treatment process. It was found that, compared with conventional heating method, microwave heating technique could enhance the crystallinity of Si C ceramic material with small grain size at much lower curing temperature and within shorter time. In addition, the SiO_2 additive could lead to less α-Si C and excess carbon, but worsen the crystallinity of β-Si C in the final samples.

A SYNTHETIC APPROACH FOR WATER SOLUBLE HYPERBRANCHED POLY(N,N-ETHYLIDENEBIS(N-2-CHLOROACETYL ACRYLAMIDE)) WITH HIGH DEGREE OF BRANCHING VIA ATOM TRANSFER RADICAL POLYMERIZATION/SELF-CONDENSING VINYL POLYMERIZATION

A novel acrylamide A2B2＊ （A = alkene, B＊ = alkyl chlorine） type inimer was obtained from commercially available 1,2-ethylenediamine, chloroacetyl chloride and acryloyl chloride. The as-prepared monomer can form water-soluble hyperbranched poly（N,N-ethylidene bis（N-2-chloroacetyl acrylamide））s （HPECA） through atom transfer radical polymerization/self-condensing vinyl polymerization method in the presence alkyl chlorine/CuCl/2,2-bipyridine activation system which can effectively suppress the gelation formation.1H-NMR spectra and dual detector size exclusion chromatography proved the hyperbranched structure indisputably, and the degree of branching was determined by the detailed analyses of 1H-NMR spectra. The trend of the degree of branching was in consistent with the result of Mark- Houwink exponent a. The experiment results suggested that the conversion was 67%, Mw = 13.2 x 104, Mark-Houwink a = 0.282 and the degree of branching = 64% when the reaction temperature was 120 ℃, reaction time = 168 h and N,N- ethylidene bis（N-2-chloroacetyl acrylamide）：Cu（I） = 50：0.62.

High-Performanceα-Diimine Nickel Complexes for Facile Access of PE Elastomers with Exceptional Material Properties

For practicable elastomeric polyethylene,achieving high catalyst thermal stability and activity,along with precise control of polymer properties such as branching density,molecular weights,and distribution,is crucial but challenging.In this study,two sets of symmetricalα-diimine nickel complexes,each comprising four nickel bromide or chloride complexes,were synthesized and investigated their performance for ethylene polymerization under various reaction conditions.Upon activation with either Et2AlCl or MMAO cocatalysts,these complexes displayed not only high activity but also generated high molecular weight polyethylenes with controlled polydispersity and a substantial number of branches.The catalyst with the least steric hindrance displayed the remarkable high activity(up to 1.2×10^(7) g·mol^(-1)·h^(-1)).Notably,nickel bromides demonstrated higher activity compared to their chloride counterparts.The investigation into the effect of reaction temperature on catalytic performance revealed that NiBrMe-MMAO system displayed high thermal stability(activity up to 2.51×10^(6) g·mol^(-1)·h^(-1) at 100℃)and consistently yielded high polymer molecular weights with narrow polydispersity over a broad temperature range of 30-100℃.Of significant note,mechanical analysis of the resulting polyethylene demonstrated excellent ultimate tensile strength and high strain at break.Particularly,the polyethylene sample prepared at 100℃exhibited ultimate tensile strength up to 10 MPa with 1863%maximum strain at break and a strain recovery of up to 54.9%after ten cycles at a fixed strain of 300%,indicating excellent material properties of prepared thermoplastic polyethylene elastomers(TPE).