A simple strategy was explored to systematically control the phase transition of an amphiphilic bottlebrush block copolymer (AmBBCP), ...poly(norbornene-graft-styrene)-block-(norbornene-graft-hydroxystyrene), with polymeric additives, such as poly(ethylene glycol) methyl ether (mPEG), poly(2-vinylpyridine) (P2VP), and poly(methyl methacrylate) (PMMA). The precursor polymers, poly(norbornene-graft-styrene)-block-(norbornene-graft-4-tert-butoxystyrene), were synthesized by sequential ring-opening metathesis polymerization of ω-end-norbornyl polystyrene and poly(4-tert-butoxystyrene). Acid hydrolysis of the tert-butyl groups in the precursor resulted in the AmBBCP with an ultrahigh molecular weight (∼2880 kDa) and relatively low dispersity (∼1.21). The disordered structures of neat AmBBCP were transformed to ordered lamellae by solvothermal annealing. AmBBCP and mPEG blended well because of H-bonding, maintaining well-ordered lamellae up to 40 wt % mPEG. The phase transition from ordered to disordered state occurred when increasing more than 50 wt %. The AmBBCP blended with P2VP and PMMA was compared. The effect of mPEG on phase transition, domain size, and refractive index and the photonic properties were determined.
Cube-like polyhedral oligomeric silsesquioxane (POSS) is a promising candidate for isotropically bulky pendants to expand the dimensional limit of polymer main chains. This paper presents molecular ...and kinetic insights into the controlled synthesis of rod-like POSS-containing polynorbornenes. Ring-opening metathesis polymerization (ROMP) was performed on three norbornene-substituted POSS monomers with different spacers. For monomers possessing non- and amide functionalities at the spacers, ROMP at the maximum concentration (M 0 = 0.4 M) led to 100% conversion, predictable molecular weights ( M n ≤ 1236 kDa) and low dispersities ( Đ ≤ 1.20) in homopolymers. Scaling analysis for POSS-containing polynorbornenes revealed an unusual finding, namely, that the periodic clustering of POSS pendants favored by long flexible spacers (16-atom chains) enhanced the rigidity of polynorbornene main chains, leading to their rod-like conformation. Kinetically optimized ROMP allowed the subsequent addition of a macromonomer to create POSS-bottlebrush copolymers (POSSBBCPs). These POSSBBCPs self-assembled into thin films to form ordered nanostructures with diverse morphologies and periodicities greater than 100 nm.
We present the facile synthetic platform for the production of amphiphilic bottlebrush block copolymers bearing pyridine pendants through combination of living anionic polymerization (LAP), ...ring-opening metathesis polymerization (ROMP), and copper-catalyzed azide–alkyne cycloaddition (CuAAC). ω-Norbornenyl poly(4-((trimethylsilyl)ethynyl)styrene) (NBPTMSESt) with controlled molecular weights (M n = 3–4 kDa) and low dispersity (Đ = 1.03–1.08) was synthesized by LAP and the subsequent end-capping reaction with exo-N-(n-decyl-10-phenylacrylate)-5-norbornene-2,3-dicarboximide. Well-defined bottlebrush block copolymers (M n = 134–548 kDa, Đ = 1.04–1.14) were achieved through sequential ROMP of ω-norbornenyl polystyrene with NBPTMSESt and subsequently deprotected with the clickable alkyne group. Amphiphilic bottlebrush block copolymers were obtained by the click reaction of alkyne and azide functional pyridines in the presence of the organic-soluble catalyst/ligand system of CuBr(PPh3)3 and N,N,N′,N″,N″-pentamethyldiethylenetriamine. These polymers exhibited the three-dimensional ordered porous films through breath-figure self-assembly.
Well-controlled polystyrene-polymethacrylate bottlebrush block copolymers (BBCPs) of ultrahigh molecular weight using ω-end-norbornyl polystyrene as the macromonomer for the first block were ...synthesized by combining living anionic polymerization (LAP) and ring-opening metathesis polymerization (ROMP). The ω-end-norbornyl polystyrene (NB-PSt), poly(tert-butyl methacrylate) (NB-PtBMA), poly(methyl methacrylate) (NB-PMMA), and poly(benzyl methacrylate) (NB-PBzMA) macromonomers (MMs) were synthesized by the LAP. The ROMP of the MMs led to poly(NB-g-St) (molecular weight, Mn = 1515 kDa, and dispersity, Ð = 1.12), poly(NB-g-tBMA) (Mn = 1470 kDa, Ð = 1.49), poly(NB-g-MMA) (Mn = 1128 kDa, Ð = 1.42), and poly(NB-g-BzMA) (Mn = 941 kDa, Ð = 1.16) bottlebrush homopolymers at degree of polymerization (DP) of 500. Synthesis of the BBCP, P(NB-g-St)-b-P(NB-g-tBMA) was well-controlled with high molecular weight and a low dispersity (Mn = 3002 kDa, Ð = 1.17) with a total DP of 976. The self-assembly of the resulting BBCP films revealed periodic lamellar morphologies with characteristic photonic crystal properties.
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•Ultrahigh molecular weight BBCPs based on polystyrene and polymethylacrylates are synthesized for the first time.•The ROMP for NB-PSt as the first block led to facile and well-controlled ROMP of norbornyl-functionalized polymethacrylates.•The resulting BBCPs showed the characteristic photonic crystal properties except those of PSt and PBzMA.
•An in vitro model for melanocyte senescence using UVB exposure is proposed.•The protocol relies on UVB exposure twice and subsequent 2-week cultivation.•Melanocyte senescence accompanies ...hyperpigmentation via prolonged p53 expression.
Ultraviolet radiation (UVR) is a well-known factor in skin aging and pigmentation, and daily exposure to subcytotoxic doses of UVR might accelerate senescence and senescence-associated phenomena in human melanocytes.
To establish an in vitro melanocyte model to mimic the conditions of repeated exposure to subcytotoxic doses of UVB irradiation and to investigate key factor(s) for melanocyte senescence and senescence-associated phenomena.
Human epidermal melanocytes were exposed twice with 20 mJ/cm2 UVB over a 24-h interval and subsequently cultivated for 2 weeks. Senescent phenotypes were addressed morphologically, and by measuring the senescence-associated β-galactosidase (SA-β-Gal) activity, cell proliferation capacity with cell cycle analysis, and melanin content.
The established protocol successfully induced melanocyte senescence, and senescent melanocytes accompanied hyperpigmentation. Prolonged expression of p53 was responsible for melanocyte senescence and hyperpigmentation, and treatment with the p53-inhibitor pifithrin-α at 2-weeks post-UVB irradiation, but not at 48 h, significantly reduced melanin content along with decreases in tyrosinase levels.
Melanocyte senescence model will be useful for studying the long-term effects of UVB irradiation and pigmentation relevant to physiological photoaging, and screening compounds effective for senescence-associated p53-mediated pigmentation.
After the introduction of a ban on the use of antibiotic growth promoters (AGPs) for livestock, the feeding environment, including the composition of animal intestinal microbiota, has changed ...rapidly. We hypothesized that the microbial genomes have also been affected by this legal prohibition, and investigated an important member of the swine gut microbiota, Lactobacillus salivarius, with a pan-genomic approach. Here, we isolated 21 L. salivarius strains composed of 6 strains isolated before the AGP prohibition (SBPs) and 15 strains isolated after the AGP prohibition (SAPs) at an interval of a decade, and the draft genomes were generated de novo. Several genomic differences between SBPs and SAPs were identified, although the number and function of antibiotic resistance genes were not different. SBPs showed larger genome size and a higher number of orthologs, as well as lower genetic diversity, than SAPs. SBPs had genes associated with the utilization of L-rhamnose and D-tagatose for energy production. Because these sugars are also used in exopolysaccharide (EPS) synthesis, we tried to identify differences in biofilm formation-associated genes. The genes for the production of EPSs and extracellular proteins were different in terms of amino acid sequences. Indeed, SAPs formed dense biofilm and survived better than SBPs in the swine intestinal environment. These results suggest that SAPs have evolved and adapted to protect themselves from new selection pressure of the swine intestinal microenvironment by forming dense biofilms, adopting a distinct antibiotic resistance strategy. This finding is particularly important to understand the evolutionary changes in host-microbe interaction and provide detailed insight for the development of effective probiotics for livestock.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Summary
MicroRNAs are known to be the important regulators of skin physiology and considered as new therapeutic targets to treat skin diseases. In this study, miR‐125b was identified as a potent ...regulator of steady‐state melanogenesis. We found that the expression of miR‐125b was inversely related to pigment levels. A miR‐125b mimic decreased the expression of pigmentation‐related gene and melanin content, implying that miR‐125b functions to decrease pigmentation. Moreover, we observed that the reduction in miR‐125b expression in pigmented cells was at least partially due to the hypermethylation of the MIR125B‐1 promoter, and miR‐125b expression was regulated by intracellular cAMP levels.
12-(cis-5-Norbornene-exo-2,3-dicarboximido)dodecanoate pentafluorophenyl ester ( exo-NBC12-PFP) was used as a norbornene-substituted end-capping terminator of living anionic polymers. Polystyrene ...with a terminal 1,1-diphenylethyllithium (PSt(DPE)−Li+), poly(2-vinylpyridine) with a terminal 2-pyridinylethyllithium (P2VP–Li+), and poly(benzyl methacrylate) with a terminal lithium ester enolate (PBzMA–Li+) reacted with exo-NBC12-PFP under appropriate reaction conditions to generate norbornenyl-ω-end macromonomers, NBC12-PSt, NBC12-P2VP, and NBC12-PBzMA, respectively, each with a 12-carbon spacer. To estimate the efficiency of end-capping, these macromonomers were polymerized by grafting-through ring-opening metathesis polymerization (ROMP). The end-capping reaction of PSt(DPE)−Li+ and P2VP–Li+ suffered from side reactions resulting in low end-capping efficiencies and the generation of by-products. On the other hand, the side reactions were minimal in the end-capping reaction of PBzMA–Li+, resulting in a high end-capping efficiency of 95%. The ROMP of NBC12-PBzMA allowed the synthesis of poly12-(5-norbornene-exo-2,3-dicarboximido)dodecanoylate-graft-poly(benzyl methacrylate)s (PNBC12-g-PBzMAs) with a wide range of controlled molecular weights (M n = 436–4048 kDa, Đ = 1.07–1.23).
We compared the interfacial activity of two classes of POSS-bottlebrush block copolymers (POSSBBCPs) in the breath-figure (BF) self-assembly. ...Poly3-(5-norbornene-exo-2,3-dicarboximido)propyl-heptaisobutyl POSS-block-poly(exo-5-norbornene-2-carbonylate-graft-benzyl methacrylate) (P1- b -P(NB- g -BzMA)) and poly3-(2-(5-norbornene-exo-2,3-dicarboximido)ethylamino)propyl-heptaisobutyl POSS-block-poly(exo-5-norbornene-2-carbonylate-graft-benzyl methacrylate) (P2- b -P(NB- g -BzMA)), which contain nonfunctionalized and secondary-amino-functionalized POSS-based blocks, respectively, were prepared by sequential ring-opening metathesis polymerization of norbornenyl monomers (P1- b -P(NB- g -BzMA) with f P1 = 50 wt % (1–50): M n = 213 kDa, Đ = 1.12; P2- b -P(NB- g -BzMA)s with f P2 = 5/11/20/50 wt % (2–5/11/20/50): M n = 2464/1043/581/268 kDa, Đ = 1.46/1.26/1.24/1.20). Of 1–50 and 2–50, only 2–50 afforded the three-dimensional porous films with unimodal pore size distributions. At high wet thickness, the efficient encapsulation of water droplets through the adsorption of water by the secondary amino groups allowed the 2–50 chains to stabilize the solvent–water interfaces, thus preventing the formation of giant pores. The interfacial activity of P2- b -P(NB- g -BzMA) was enhanced by increasing the weight fraction of the P2 block from 5 to 50 wt %.
Abstract
The etiological agents of streptococcosis were isolated from diseased olive flounder collected on the Jeju island of Korea. A total of 151 bacterial isolates were collected between 2003 and ...2006. The isolates were examined using various phenotypic and proteomic analyses, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting, and glycoprotein assays. In addition, isolates were grown on blood agar to assess hemolytic activity, and biochemical assays were performed using the API20 Strep kit. Our results revealed that all isolates were nonmotile, Gram-positive cocci that displayed negative catalase and oxidase activities. Multiplex PCR assays revealed that 43% and 57% of the isolates were Streptococcus iniae and Streptococcus parauberis, respectively. These results were consistent with those of the SDS-PAGE and immunoblot analyses using whole-cell lysates of bacterial isolates. Significant differences were observed with respect to the Voges–Proskauer, pyrrodonyl arylamidase, alkaline phosphatase, and hemolytic activities of the S. iniae and S. parauberis isolates. Isolates of S. iniae displayed uniform profiles in the immunoblot and glycoprotein assays; however, immunoblot assays of S. parauberis isolates (using a chicken IgY antibody raised against a homologous isolate) revealed three distinct antigenic profiles. Our findings suggest that S. parauberis and S. iniae are endemic pathogens responsible for the development of streptococcosis in olive flounder.
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