Diketoenamine-Based Vitrimers via Thiol-ene Photopolymerization.

Likened to both thermosets and thermoplastics, vitrimers are a unique class of materials that combine remarkable stability, healability, and reprocessability. Herein, this work describes a photopolymerized thiol-ene-based vitrimer that undergoes dynamic covalent exchanges through uncatalyzed transamination of enamines derived from cyclic ß-triketones, whereby the low energy barrier for exchange facilitates reprocessing and enables rapid depolymerization. Accordingly, an alkene-functionalized ß-triketone, 5,5-dimethyl-2-(pent-4-enoyl)cyclohexane-1,3-dione, is devised which is then reacted with 1,6-diaminohexane in a stoichiometrically imbalanced fashion (≈1:0.85 primary amine:triketone). The resulting networks exhibit subambient glass transition temperature (Tg = 5.66 °C) by differential scanning calorimetry. Using a Maxwell stress-relaxation fit, the topology-freezing temperature (Tv ) is calculated to be -32 °C. Small-amplitude oscillatory shear rheological analysis enables to identify a practical critical temperature above which the vitrimer can be successfully reprocessed (Tv,eff ). Via the introduction of excess primary amines, this work can readily degrade the networks into monomeric precursors, which are in turn reacted with diamines to regenerate reprocessable networks. Photopolymerization provides unique spatiotemporal control over the network topology, thereby opening the path for further investigation of vitrimer properties. As such, this work expands the toolbox of chemical upcycling of networks and enables their wider implementation.

Antimicrobial Activity of, and Cellular Pathways Targeted by, p-Anisaldehyde and Epigallocatechin Gallate in the Opportunistic Human Pathogen Pseudomonas aeruginosa.

Plant-derived aldehydes are constituents of essential oils that possess broad-spectrum antimicrobial activity and kill microorganisms without promoting resistance. In our previous study, we incorporated p-anisaldehyde from star anise into a polymer network called proantimicrobial networks via degradable acetals (PANDAs) and used it as a novel drug delivery platform. PANDAs released p-anisaldehyde upon a change in pH and humidity and controlled the growth of the multidrug-resistant pathogen Pseudomonas aeruginosa PAO1. In this study, we identified the cellular pathways targeted by p-anisaldehyde by generating 10,000 transposon mutants of PAO1 and screened them for hypersensitivity to p-anisaldehyde. To improve the antimicrobial efficacy of p-anisaldehyde, we combined it with epigallocatechin gallate (EGCG), a polyphenol from green tea, and demonstrated that it acts synergistically with p-anisaldehyde in killing P. aeruginosa We then used transcriptome sequencing to profile the responses of P. aeruginosa to p-anisaldehyde, EGCG, and their combination. The exposure to p-anisaldehyde altered the expression of genes involved in modification of the cell envelope, membrane transport, drug efflux, energy metabolism, molybdenum cofactor biosynthesis, and the stress response. We also demonstrate that the addition of EGCG reversed many p-anisaldehyde-coping effects and induced oxidative stress. Our results provide insight into the antimicrobial activity of p-anisaldehyde and its interactions with EGCG and may aid in the rational identification of new synergistically acting combinations of plant metabolites. Our study also confirms the utility of the thiol-ene polymer platform for the sustained and effective delivery of hydrophobic and volatile antimicrobial compounds.IMPORTANCE Essential oils (EOs) are plant-derived products that have long been exploited for their antimicrobial activities in medicine, agriculture, and food preservation. EOs represent a promising alternative to conventional antibiotics due to their broad-range antimicrobial activity, low toxicity to human commensal bacteria, and capacity to kill microorganisms without promoting resistance. Despite the progress in the understanding of the biological activity of EOs, our understanding of many aspects of their mode of action remains inconclusive. The overarching aim of this work was to address these gaps by studying the molecular interactions between an antimicrobial plant aldehyde and the opportunistic human pathogen Pseudomonas aeruginosa The results of this study identify the microbial genes and associated pathways involved in the response to antimicrobial phytoaldehydes and provide insights into the molecular mechanisms governing the synergistic effects of individual constituents within essential oils.

Racial and Ethnic Differences in Pregnancy Rates Following Intrauterine Insemination with a Focus on American Indians.

BACKGROUND: No research exists on American Indian pregnancy rates following infertility treatment. Most racial/ethnic fertility research has focused on pregnancy following in vitro fertilization, with only rare studies looking at intrauterine insemination (IUI). The objective of our study was to compare fecundability following IUI by race/ethnicity, with a special focus on American Indians. METHODS: This was a retrospective analysis of subjects undergoing IUI July 2007-May 2012 at a university-based infertility clinic. The primary outcome was positive pregnancy test, with a secondary outcome of ongoing pregnancy/delivery (OP/D). We calculated risk ratios (RR) and 95% confidence intervals (CI) using cluster-weighted generalized estimating equations method to estimate modified Poisson regression models with robust standard errors to account for multiple IUI cycles in the same patient. RESULTS: A total of 663 females (median age 32) undergoing 2007 IUI cycles were included in the analysis. Pregnancy rates overall were 15% per IUI cycle. OP/D rates overall were 10% per IUI cycle. The American Indian patients had significantly lower pregnancy (RR 0.34, 95% CI 0.16-0.72) and OP/D rates (RR 0.33, 95% CI 0.12-0.87) compared to non-Hispanic whites when patient and cycle characteristics were controlled. Pregnancy and OP/D rates for blacks, Asians, and Hispanics did not differ from those of non-Hispanic whites. CONCLUSIONS: Our finding of lower IUI treatment success among American Indian patients is novel, as no published studies of assisted reproductive technology or other fertility treatments have examined this subgroup separately. Further investigation of patient and clinical factors that may mediate racial/ethnic disparities in fertility treatment outcomes is warranted.

Rational Design of Superhydrophilic/Superoleophobic Surfaces for Oil-Water Separation via Thiol-Acrylate Photopolymerization.

We report a simple, rapid, and scalable strategy to fabricate surfaces exhibiting in-air superoleophobic/superhydrophilic wetting via sequential spray deposition and photopolymerization of nanoparticle-laden thiol-acrylate resins comprising both hydrophilic and oleophobic chemical constituents. The combination of spray deposition with nanoparticles provides hierarchical surface morphologies with both micro- and nanoscale roughness. Mapping the wetting behavior as a function of resin composition using high- and low-surface-tension liquid probes enabled facile identification of coatings that exhibit a range of wetting behavior, including superhydrophilic/superoleophilic, superhydrophobic/superoleophobic, and in-air superhydrophilic/superoleophobic wetting. In-air superhydrophilic/superoleophobic wetting was realized by a dynamic rearrangement of the interface to expose a greater fraction of hydrophilic moieties in response to contact with water. We show that these in-air superoleophobic/superhydrophilic coatings deposited onto porous supports enable separation of model oil-water emulsions with separation efficiencies up to 99.9% with 699 L·m-2 h-1 permeate flux when the superhydrophilic/superoleophobic coatings are paired with 0.45 µm nylon membrane supports.

Using Aldehyde Synergism To Direct the Design of Degradable Pro-Antimicrobial Networks.

We describe the design and synthesis of degradable, dual-release, pro-antimicrobial poly(thioether acetal) networks derived from synergistic pairs of aromatic terpene aldehydes. Initially, we identified pairs of aromatic terpene aldehyde derivatives exhibiting a synergistic antimicrobial activity against Pseudomonas aeruginosa by determining fractional inhibitory concentrations. Synergistic aldehydes were converted into dialkene acetal monomers and copolymerized at various ratios with a multifunctional thiol via thiol-ene photopolymerization. The step-growth nature of the thiol-ene polymerization ensures every cross-link junction contains a degradable acetal linkage enabling a fully cross-linked polymer network to revert into its small molecule constituents upon hydrolysis, releasing the synergistic aldehydes as active antimicrobial compounds. A three-pronged approach was used to characterize the poly(thioether acetal) materials: (i) determination of the degradation/aldehyde release behavior, (ii) evaluation of the antimicrobial activity, and (iii) identification of the cellular pathways impacted by the aldehydes on a library of mutated bacteria. From this approach, a polymer network derived from a 40:60 p-bromobenzaldehyde/p-anisaldehyde monomer ratio exhibited potent antimicrobial action against Pseudomonas aeruginosa, a common opportunistic human pathogen. From a transposon mutagenesis assay, we showed that these aldehydes target porins and multidrug efflux pumps. The aldehydes released from the poly(thioether acetal) networks exhibited negligible toxicity to mammalian tissue culture cells, supporting the potential development of these materials as dual-release antimicrobial biomaterial platforms.