Surface Grafted Antimicrobial Polymer Networks with High Abrasion Resistance.

In this work, we have investigated a quaternary ammonium compound that exhibits excellent antimicrobial activity and can be permanently grafted to substrates containing C-H bonds to form a durable polymeric film within 1 min. The compound consists of a biocidal component, dodecyl-alkylated quaternary ammonium, and a benzophenone moiety that, under mild UV irradiation, generates a densely cross-linked network and covalently attaches to a variety of substrates, including plastics, fabrics, and alkyl-modified glass surfaces. The surface attachment is 1 order of magnitude faster than that of previously reported benzophenone-associated cross-linkers, due to the electron-withdrawing effect of quaternary ammonium on the benzophenone chromophore. The modified surfaces are nonleaching and exhibit contact-killing and highly effective antimicrobial activity against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) using cell count and live/dead staining methods. The charged ammonium group also promotes photoreaction efficiency with respect to network robustness, leading to a thin film that can sustain high shear forces and abrasion when compared to commercially available silane-based quaternary ammonium compounds. The biocidal activity is also retained after exposure to mechanical stress and abrasion.

Rapid electrochemical reduction of Ni(II) generates reactive monolayers for conjugated polymer brushes in one step.

This article reports the development of a robust, one-step electrochemical technique to generate surface-bound conjugated polymers. The electrochemical reduction of arene diazonium salts at the surface of a gold electrode is used to generate tethered bromobenzene monolayers quickly. The oxidative addition of reactive Ni(0) across the aryl halide bond is achieved in situ through a concerted electrochemical reduction of Ni(dppp)Cl2. This technique limits the diffusion of Ni(0) species away from the surface and overcomes the need for solution deposition techniques which often require multiple steps that result in a loss of surface coverage. With this electrochemical technique, the formation of the reactive monolayer resulted in a surface coverage of 1.29 × 10(14) molecules/cm(2), which is a 6-fold increase over previously reported results using solution deposition techniques.

π-Complexation in nickel-catalyzed cross-coupling reactions.

The kinetic isotope effect (KIE) is used to experimentally elucidate the first irreversible step in oxidative addition reactions of a zerovalent nickel catalyst to a set of haloarene substrates. Halogenated o-methylbenzene, dimethoxybenzene, and thiophene derivatives undergo intramolecular oxidative addition through irreversible π-complexation. Density functional theory computations at the B3LYP-D3/TZ2P-LANL2TZ(f)-LANL08d level predict η(2)-bound π-complexes are generally stable relative to a solvated catalyst plus free substrate and that ring-walking of the Ni(0) catalyst and intramolecular oxidative addition are facile in these intermediates.

Palladium-Mediated Surface-Initiated Kumada Catalyst Polycondensation: A Facile Route Towards Oriented Conjugated Polymers.

Palladium-mediated surface-initiated Kumada catalyst transfer polycondensation is used to generate poly(3-methyl thiophene) films with controlled thickness up to 100 nm. The palladium initiator density is measured using cyclic voltammetry and a ferrocene-capping agent, where the surface density is found to be 55% (1.1 × 10(14) molecules per cm(2)). UV-Vis spectroscopy and AFM show increased aggregation in palladium-initiated films due to the higher grafting density of palladium initiators on the surface. The anisotropy of the P3MT films is determined using polarized UV-Vis spectroscopy, which indicates a degree of orientation perpendicular to the substrate. Evidence that palladium can maintain π-complexation even at elevated temperatures, is also shown through the exclusive intramolecular coupling of both a phenyl and thiophene-based magnesium bromide with different dihaloarenes.

Surface-initiated poly(3-methylthiophene) as a hole-transport layer for polymer solar cells with high performance.

In this work, uniform poly(3-methylthiophene) (P3MT) films are fabricated on indium-tin oxide (ITO) surfaces using surface-initiated Kumada catalyst-transfer polycondensation (SI-KCTP) from surface-bound arylnickel(II) bromide initiators. The P3MT interfacial layer is covalently bound to the ITO surface, thereby preventing possible delamination during the processing of additional layers. These surface-bound P3MT layers successfully serve as the hole-transport layer for solution-processed bulk heterojunction polymer solar cells. Efficiencies greater than 5% have been achieved on devices based on doped thin P3MT interfacial layers. Moreover, because of the excellent stability of the covalently immobilized P3MT on ITO substrates, devices based on reused P3MT/ITO substrates extracted from old devices exhibit efficiencies similar to those of the original devices.

On the Role of Disproportionation Energy in Kumada Catalyst-Transfer Polycondensation.

Kumada catalyst-transfer polycondensation (KCTP) is an effective method for the controlled polymerization of conjugated polymers. Nevertheless, side reactions leading to early termination and unwanted chain coupling cause deviations from the target molecular weight, along with increasing polydispersity and end group variation. The departure from the KCTP cycle stems from a disproportionation reaction that leads to experimentally observed side products. The disproportionation energies for a series of nickel-based initiators containing bidentate phosphino attendant ligands were computed using density functional theory at the B3LYP/DZP level. The initiator was found to be less favorable toward disproportionation by 0.5 kcal mol-1 when ligated by 1,3-bis(diphenylphosphino)propane (dppp) rather than 1,2-bis(diphenylphosphino)ethane (dppe). Trends in disproportionation energy (Edisp) with a variety of bidentate phosphine ligands match experimental observations of decreased polymerization control. Theoretical Edisp values can thus be used to predict the likelihood of disproportionation in cross-coupling reactions and, therefore, aid in catalyst design.

Virtual reality in the assessment of selected cognitive function after brain injury.

OBJECTIVE: To assess selected cognitive functions of persons with traumatic brain injury using a computer-simulated virtual reality environment. STUDY DESIGN: A computer-simulated virtual kitchen was used to assess the ability of 30 patients with brain injury and 30 volunteers without brain injury to process and sequence information. The overall assessment score was based on the number of correct responses and the time needed to complete daily living tasks. Identical daily living tasks were tested and scored in participants with and without brain injury. Each subject was evaluated twice within 7 to 10 days. A total of 30 tasks were categorized as follows: information processing, problem solving, logical sequencing, and speed of responding. RESULTS: Persons with brain injuries consistently demonstrated a significant decrease in the ability to process information (P = 0.04-0.01), identify logical sequencing (P = 0.04-0.01), and complete the overall assessment (P < 0.01), compared with volunteers without brain injury. The time needed to process tasks, representing speed of cognitive responding, was also significantly different between the two groups (P < 0.01). CONCLUSION: A computer-generated virtual reality environment represents a reproducible tool to assess selected cognitive functions and can be used as a supplement to traditional rehabilitation assessment in persons with acquired brain injury.

Levels of self-awareness after acute brain injury: how patients' and rehabilitation specialists' perceptions compare.

OBJECTIVE: To examine self-awareness regarding performance on 4 daily living tasks and to test theoretical predictions for a model of self-awareness in persons with acquired brain injury. DESIGN: A comparative design examining the level of self-awareness recorded by patients and actual patient performance as judged by rehabilitation clinicians. SETTING: A community-based residential center providing comprehensive rehabilitation services to persons with acquired brain injury. PARTICIPANTS: Fifty-five persons with acquired brain injury and the identified potential to return to independent function in the community. Ten subjects without brain injury provided comparison data. INTERVENTION: Information was collected by using patient self-report, clinician rating of patient performance, patient rating of non-brain-injured subjects, and clinician rating of non-brain-injured subjects. MAIN OUTCOME MEASURES: Three self-awareness criteria were examined: intellectual, emergent, and anticipatory. Self-awareness was rated for 3 tasks: dressing, meal planning, and money management. RESULTS: Statistically significant differences (p <.05) were found for all levels of self-awareness across the 3 tasks. Persons with brain injury judged their abilities higher than clinician ratings of actual performance. No statistical support was found for a hierarchy among intellectual, emergent, and anticipatory self-awareness. CONCLUSIONS: No evidence was found supporting a hierarchy among levels of self-awareness as defined and measured in the present study. New methods for operationally defining intellectual, emergent, and anticipatory self-awareness are necessary to examine the relationship between self-awareness and performance.