Controlling Rheology of Fluid Interfaces through Microblock Length of Sequence-Controlled Amphiphilic Copolymers

Previous studies have demonstrated that films of sequence-controlled amphiphilic copolymers display contact angles that depend on microblock size. This suggests that microblock length may provide a means of tuning surface and interfacial properties. In this work, the interfacial rheology of a series of sequence-controlled copolymers, prepared through the addition of bicyclo[4.2.0]oct-1(8)-ene-8-carboxamide (monomer A) and cyclohexene (monomer B) to generate sequences up to 24 monomeric units composed of (A m B n ) i microblocks, where m, n, and i range from 1 to 6. Interfacial rheometry is used to measure the mechanical properties of an air-water interface with these copolymers. As the microblock size increases, the interfacial storage modulus, G', increases, which may be due to an increase in the size of interfacial hydrophobic domains. Small-angle X-ray scattering shows that the copolymers have a similar conformation in solution, suggesting that any variations in the mechanics of the interface are due to assembly at the interface, and not on solution association or bulk rheological properties. This is the first study demonstrating that microblock size can be used to control interfacial rheology of amphiphilic copolymers. Thus, the results provide a new strategy for controlling the dynamics of fluid interfaces through precision sequence-controlled polymers.

Substituent Effects Provide Access to Tetrasubstituted Ring-Opening Olefin Metathesis of Bicyclo[4.2.0]oct-6-enes

Herein, we report the origin of unexpected reactivity of bicyclo[4.2.0]oct-6-ene substrates containing an α,β-unsaturated amide moiety in ruthenium-catalyzed alternating ring-opening metathesis polymerization reactions. Specifically, compared with control substrates bearing an ester, alkyl ketone, nitrile, or tertiary amide substituent, α,β-unsaturated substrates with a weakly acidic proton showed increased rates of ring-opening metathesis mediated by Grubbs-type ruthenium catalysts. ¹H NMR and IR spectral analyses indicated that deprotonation of the α,β-unsaturated amide substrates resulted in stronger coordination of the carbonyl group to the ruthenium metal center. Principal component analysis identified ring strain and the electron density on the carbonyl oxygen (based on structures optimized by means of ωB97X-D/6311+G(2df,2p) calculations) as the two key contributors to fast ring-opening metathesis of the bicyclo[4.2.0]oct-6-enes; whereas the dipole moment, conjugation, and energy of the highest occupied molecular orbital had little to no effect on the reaction rate. We conclude that alternating ring-opening metathesis polymerization reactions of bicyclo[4.2.0]oct-6-enes with unstrained cycloalkenes require an ionizable proton for efficient generation of alternating polymers.

Targeting Multiple Binding Sites on Cholera Toxin B with Glycomimetic Polymers Promotes the Formation of Protein-Polymer Aggregates

The canonical binding site on the B subunit of cholera toxin (CTB) binds to GM1 gangliosides on host cells. However, the recently discovered noncanonical binding site on CTB with affinity for fucosylated molecules has raised the possibility that both sites can be involved in initiating intoxication. Previously, we showed that blocking CTB binding to human and murine small intestine epithelial cells can be increased by simultaneously targeting both binding sites with multivalent norbornene-based glycopolymers [ACS Infect. Dis. 2020, 6, 5, 1192-1203]. However, the mechanistic origin of the increased blocking efficacy was unclear. Herein, we observed that mixing CTB pentamers and glycopolymers that display fucose and galactose sugars results in the formation of large aggregates, which further inhibits binding of CTB to human granulocytes. Dynamic light scattering analysis, small-angle X-ray scattering analysis, transmission electron microscopy, and turbidimetric assays revealed that the facial directionality of CTB promotes interchain cross-linking, which in turn leads to self-assembly of protein-polymer networks. This cross-linking-induced self-assembly occurs only when the glycopolymer system contains both galactose and fucose. In an assay of the glycopolymer's ability to block CTB binding to human granulocytes, we observed a direct correlation between IC₅₀ and self-assembly size. The aggregation mechanism of inhibition proposed herein has potential utility for the development of low-cost macromolecular clinical therapeutics for cholera that do not have exotic architectures and do not require complex synthetic sequences.

Fucose-Galactose Polymers Inhibit Cholera Toxin Binding to Fucosylated Structures and Galactose-Dependent Intoxication of Human Enteroids

A promising strategy to limit cholera severity involves blockers mimicking the canonical cholera toxin ligand (CT) ganglioside GM1. However, to date the efficacies of most of these blockers have been evaluated in noncellular systems that lack ligands other than GM1. Importantly, the CT B subunit (CTB) has a noncanonical site that binds fucosylated structures, which in contrast to GM1 are highly expressed in the human intestine. Here we evaluate the capacity of norbornene polymers displaying galactose and/or fucose to block CTB binding to immobilized protein-linked glycan structures and also to primary human and murine small intestine epithelial cells (SI ECs). We show that the binding of CTB to human SI ECs is largely dependent on the noncanonical binding site, and interference with the canonical site has a limited effect while the opposite is observed with murine SI ECs. The galactose–fucose polymer blocks binding to fucosylated glycans but not to GM1. However, the preincubation of CT with the galactose–fucose polymer only partially blocks toxic effects on cultured human enteroid cells, while preincubation with GM1 completely blocks CT-mediated secretion. Our results support a model whereby the binding of fucose to the noncanonical site places CT in close proximity to scarcely expressed galactose receptors such as GM1 to enable binding via the canonical site leading to CT internalization and intoxication. Our finding also highlights the importance of complementing CTB binding studies with functional intoxication studies when assessing the efficacy inhibitors of CT.

Fucosylated Molecules Competitively Interfere with Cholera Toxin Binding to Host Cells

Cholera toxin (CT) enters host intestinal epithelia cells, and its retrograde transport to the cytosol results in the massive loss of fluids and electrolytes associated with severe dehydration. To initiate this intoxication process, the B subunit of CT (CTB) first binds to a cell surface receptor displayed on the apical surface of the intestinal epithelia. While the monosialoganglioside GM1 is widely accepted to be the sole receptor for CT, intestinal epithelial cell lines also utilize fucosylated glycan epitopes on glycoproteins to facilitate cell surface binding and endocytic uptake of the toxin. Further, l-fucose can competively inhibit CTB binding to intestinal epithelia cells. Here, we use competition binding assays with l-fucose analogs to decipher the molecular determinants for l-fucose inhibition of cholera toxin subunit B (CTB) binding. Additionally, we find that mono- and difucosylated oligosaccharides are more potent inhibitors than l-fucose alone, with the LeY tetrasaccharide emerging as the most potent inhibitor of CTB binding to two colonic epithelial cell lines (T84 and Colo205). Finally, a non-natural fucose-containing polymer inhibits CTB binding two orders of magnitude more potently than the LeY glycan when tested against Colo205 cells. This same polymer also inhibits CTB binding to T84 cells and primary human jejunal epithelial cells in a dose-dependent manner. These findings suggest the possibility that polymeric display of fucose might be exploited as a prophylactic or therapeutic approach to block the action of CT toward the human intestinal epithelium.

Azide-based heterobifunctional poly(ethylene oxide)s: NaN3-initiated “living” polymerization of ethylene oxide and chain end functionalizations

Sodium azide (NaN₃)-initiated “living” ring-opening polymerization of ethylene oxide and chain end functionalizations.

Differences in stress and coping models of emotional distress among Korean, Korean-American and White-American caregivers

This study compares path models of emotional distress among three groups of caregivers for elderly patients with dementia: 64 Koreans residing in Korea, and 53 Korean-Americans and 54 White-Americans living in the USA. The results support a common core model throughout the three groups: patient's disruptive behavior leads to caregiver burden, which then affects caregivers' depression and anxiety. Instrumental support was found to be an important factor for Korean caregivers and emotional support was important for Korean-Americans. Only Korean-American caregivers appraised all three patient's problems--patient's disruptive behaviors, memory problems, and depression as burdensome. These findings suggest that stress and coping processes in caregivers from different cultures involve a common core with important differences in the effects of the patient's problems and of social support.

Differences in familism values and caregiving outcomes among Korean, Korean American, and White American dementia caregivers

Recent theories have suggested that burden and distress among dementia caregivers may be higher in American culture, which emphasizes individualism, and lower in cultures with higher levels of familism. However, immigrants may experience higher levels of burden because of acculturation with attendant values, conflicts and stresses. Forty-four Korean caregivers and 32 Korean American caregivers were compared with 54 White American caregivers on sociodemographic variables, familism, burden, anxiety, and depression. Familism was highest in Korean caregivers and lowest in Whites, with Korean Americans in the middle. Koreans and Korean Americans reported higher levels of burden. Koreans showed higher levels of depression and of anxiety than White American caregivers, with Koreans and Korean Americans higher than Whites on anxiety. These results suggest a need for greater specificity in theories about familism values, with attention to the specific meaning of familism in different cultures.

Sexual activities and attitudes of adolescent Koreans

Data regarding the sexual behaviors of 849 Korean adolescents (mean = 18.8 years) were collected. Behaviors reported for males vs. females were 36.5 vs. 27.0% for kissing, 27.2 vs. 14.8% for petting, and 22.9 vs. 9.8% for coitus. In addition to reporting a greater number of experiences, males reported a greater number of partners for all three behavior categories. Among those who participated in coitus, nearly one third of the males and two thirds of the females reported only one partner. Two thirds of the males considered their recent experiences with coitus to be satisfactory, whereas over half of the females gave a neutral response. About 37% of males and 55% of females reported that their most recent coital experience was less than a month ago. On average, the coitally active adolescents began sexual activity at about 18 years of age. Interpretations of these data must take into consideration the respondents' hesitancy in the Korean setting to admit to having sexual experiences. Because premarital sex for adolescents is considered very undesirable in the Korean social setting, the respondents' reporting bias might be in the direction of underreporting. Findings are discussed in the context of unplanned pregnancy and abortion.

Evaluating questions used to assess cognitive orientation for very old adults

A number of standardized tools have been developed to assist in the diagnosis of suspected dementia in aged people. In this study, 9 orientation questions were administered to 186 elderly Koreans, aged 60 to 108 years. Analysis showed a significantly inverse relation (r = -.70) between their ages and their performance on the questionnaire. The finding raises questions about the suitability of using standard measures of orientation with very old or with uneducated persons.

Aging Koreans' perceived conflicts in relationships with their offspring as a function of age, gender, cohabitation status, and marital status

The Youn Scale was used to assess aging Koreans' perceived conflicts in relationships with their adult offspring. The sample consisted of 623 elderly Koreans between the ages of 55 and 84 years. Results indicated that aging Koreans experienced significantly more conflicts in their relationships as they grew older. There were also differences in the perceptions of problems in relationships with their offspring between those who lived together with their adult children and the those who did not, and also between those who were married and those who were single. The findings imply that aging Koreans want to have qualitatively better (i.e., warmer and closer) relationships with their offspring, regardless of their bereavement status and cohabitation status.

Influence of training and performance IQ on the psychomotor skill of Down syndrome persons

Training effects on the psychomotor performance of Down syndrome individuals were assessed. 32 boys and 25 girls (6 to 16 years old) were divided randomly into trained or untrained groups and into either severely or moderately mentally retarded using their WISC-R Performance IQs. Analysis showed that the group who had pretest training opportunities to manipulate experimental materials performed significantly better than those without that training while the moderately retarded children did significantly better than the severely retarded ones. It appears that the performance of persons with Down syndrome could be developed through training.

On using public media for prevention of rape

There has been an increasing interest in rape. Rape by a nonstranger, especially, is the most psychologically damaging type of sexual assault. It is argued that use of the mass media should be considered for prevention of rape by nonstrangers.

The life-span trend in the magnitude of the Mueller-Lyer illusion as a function of hue and age

Mueller-Lyer illustrations produced by hue contrast were used to investigate age differences with participants ranging in age from 20 to 79 years. As expected, there was no age difference in the magnitude of the illusion when the Mueller-Lyer figure was produced by hue contrast. A significant main effect of hue was found, with no interaction between hue and age. These findings support Pollack's nondevelopmental explanation for age effects on Type I illusions.