scholarly journals The Photoinitiator Lithium Phenyl (2,4,6-Trimethylbenzoyl) Phosphinate with Exposure to 405 nm Light Is Cytotoxic to Mammalian Cells but Not Mutagenic in Bacterial Reverse Mutation Assays

Polymers ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1489
Author(s):  
Alexander K. Nguyen ◽  
Peter L. Goering ◽  
Rosalie K. Elespuru ◽  
Srilekha Sarkar Das ◽  
Roger J. Narayan
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Mammalian Cells ◽  
Light Exposure ◽  
Collecting Duct ◽  
Radical Chain ◽  
Reverse Mutation ◽  
E Coli ◽  
A Cell ◽  
Chain Polymerization

Lithium phenyl (2,4,6-trimethylbenzoyl) phosphinate (LAP) is a free radical photo-initiator used to initiate free radical chain polymerization upon light exposure, and is combined with gelatin methacryloyl (GelMA) to produce a photopolymer used in bioprinting. The free radicals produced under bioprinting conditions are potentially cytotoxic and mutagenic. Since these photo-generated free radicals are highly-reactive but short-lived, toxicity assessments should be conducted with light exposure. In this study, photorheology determined that 10 min exposure to 9.6 mW/cm2 405 nm light from an LED light source fully crosslinked 10 wt % GelMA with >3.4 mmol/L LAP, conditions that were used for subsequent cytotoxicity and mutagenicity assessments. These conditions were cytotoxic to M-1 mouse kidney collecting duct cells, a cell type susceptible to lithium toxicity. Exposure to ≤17 mmol/L (0.5 wt %) LAP without light was not cytotoxic; however, concurrent exposure to ≥3.4 mmol/L LAP and light was cytotoxic. No condition of LAP and/or light exposure evaluated was mutagenic in bacterial reverse mutation assays using S. typhimurium strains TA98, TA100 and E. coli WP2 uvrA. These data indicate that the combination of LAP and free radicals generated from photo-excited LAP is cytotoxic, but mutagenicity was not observed in bacteria under typical bioprinting conditions.

scholarly journals The Acidaminococcus sp. Cas12a nuclease recognizes GTTV and GCTV as non-canonical PAMs

2019 ◽  
Vol 366 (8) ◽  
Author(s):  
Thomas Jacobsen ◽  
Chunyu Liao ◽  
Chase L Beisel
Keyword(s):  
Dna Cleavage ◽  
Mammalian Cells ◽  
Consensus Sequence ◽  
Wild Type ◽  
E Coli ◽  
Cleavage Efficiency ◽  
Protospacer Adjacent Motif ◽  
Short Palindromic Repeat ◽  
A Cell ◽  
Validation Experiments

ABSTRACT The clustered regularly interspaced short palindromic repeat (CRISPR)-associated (Cas) nuclease Acidaminococcus sp. Cas12a (AsCas12a, also known as AsCpf1) has become a popular alternative to Cas9 for genome editing and other applications. AsCas12a has been associated with a TTTV protospacer-adjacent motif (PAM) as part of target recognition. Using a cell-free transcription-translation (TXTL)-based PAM screen, we discovered that AsCas12a can also recognize GTTV and, to a lesser degree, GCTV motifs. Validation experiments involving DNA cleavage in TXTL, plasmid clearance in Escherichia coli, and indel formation in mammalian cells showed that AsCas12a was able to recognize these motifs, with the GTTV motif resulting in higher cleavage efficiency compared to the GCTV motif. We also observed that the -5 position influenced the activity of DNA cleavage in TXTL and in E. coli, with a C at this position resulting in the lowest activity. Together, these results show that wild-type AsCas12a can recognize non-canonical GTTV and GCTV motifs and exemplify why the range of PAMs recognized by Cas nucleases are poorly captured with a consensus sequence.

Kinetics of the thermal reactions of ethylene. Part II. Ethylene–ethane mixtures

1968 ◽  
Vol 46 (14) ◽  
pp. 2427-2433 ◽  
Author(s):  
M. L. Boyd ◽  
M. H. Back
Keyword(s):  
Free Radical ◽  
Product Formation ◽  
Radical Chain ◽  
Thermal Reactions ◽  
Temperature Range ◽  
Initiation Step ◽  
Chain Polymerization ◽  
Main Effects ◽  
Kinetics Of ◽  
Simplified Mechanism

Mixtures of ethane and ethylene have been pyrolyzed in the temperature range 563–600 °C and at pressures from 30–60 cm. The products were similar to those obtained from the pyrolysis of ethylene by itself, described m Part I, with a marked increase in the yields of the saturated products. The initial rates of product formation and the dependence of these rates on the concentration of ethane suggest that the initiation step is the same as that proposed in the pyrolysis of ethylene alone, viz.[Formula: see text]and that the reaction[Formula: see text]is not an important source of radicals. A simplified mechanism is outlined to account for the main effects of ethane on the free radical chain polymerization.

Effects of oxygen upon freeze-dried and freeze-thawed bacteria: viability and free radical studies

1973 ◽  
Vol 19 (2) ◽  
pp. 189-194 ◽  
Author(s):  
C. S. Cox ◽  
R. J. Heckly
Keyword(s):  
Escherichia Coli ◽  
Free Radicals ◽  
Free Radical ◽  
Serratia Marcescens ◽  
Oxygen Concentration ◽  
Simple Relationship ◽  
E Coli ◽  
Freeze Dried ◽  
Escherichia Coli B ◽  
Oxygen Concentrations

Viability of freeze-dried Serratia marcescens 8UK was studied at 24.5 °C as a function of oxygen concentration and time. Results depended upon the source of the inoculum. Oxygen proved to be toxic and the kinetics (with respect to oxygen concentration) were first order at low oxygen concentrations and zero order at high oxygen concentrations. This indicates that the site for the action of oxygen can become saturated with oxygen. No simple relationship between viability and time was observed. Free radical studies were also made and showed that the detected free radicals were not involved in causing oxygen-induced loss of viability.The survival of Escherichia coli B frozen quickly and stored at −80 °C was found to be little, if at all, influenced by oxygen. Similar results were obtained with Serratia marcescens 8UK. Free radical studies were performed on E. coli B at −80 °C, but no free radicals were detected even after storing E. coli B for 30 days at −80 °C, −20 °C, and −10 °C. Under the last two conditions appreciable loss of viability occurred when E. coli B was frozen slowly.The results indicate that oxygen-induced loss of viability in freeze-dried and frozen and thawed Serratia marcescens 8UK and Escherichia coli B does not involve the formation of free radicals as has been suggested by other workers.

scholarly journals THE STRUCTURE OF BUTADIENE DIMERS PRODUCED BY A FREE-RADICAL CHAIN-TRANSFER MECHANISM

1957 ◽  
Vol 35 (12) ◽  
pp. 1467-1474 ◽  
Author(s):  
L. J. Gendron ◽  
R. V. V. Nicholls
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Chain Transfer ◽  
Transfer Mechanism ◽  
The Other ◽  
Chain Transfer Agent ◽  
Radical Chain

Butadiene was dimerized by using acetyl peroxide as source of free radicals and chloroform as solvent and chain-transfer agent. The dimers were identified and their structures were determined by means of ozonolysis and oxidative hydrolysis. It was established that two dimers were produced in nearly equal amount. One dimer was formed only by 1,4-additions, the other only by 1,2-additions. This result implies that polybutadienes may be mixtures of two varieties: one variety resulting from 1,4-additions, the other from 1,2-additions.

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