Supramolecular and Hybrid Bonding Polymers

Staudinger established a century ago the existence of covalent macromolecules, work that led to the development of transformative materials of great benefit to society and a “quantum leap” in our understanding of biological systems. Over the past few decades the concept of supramolecular polymers has emerged–chemical systems in which structural units bond strongly to each other non-covalently. These dynamic systems actually exist in the natural world and can create soft materials with structures, properties, and functions beyond the ones we know in Staudinger polymers. We reflect here on the potential of novel systems in which covalent and supramolecular polymers are chemically integrated and describe them as hybrid bonding polymers. This paper describes the concept with recent examples from the Stupp laboratory, and discusses their potential functions as robotic materials that mimic living matter and structures that offer new ideas on how to recycle and reuse soft materials.     

Adhesion and degradation of hard coatings on poly (methyl methacrylate) substrates

The adhesion and time dependent crack growth behavior of polysiloxane based hard coatings on poly (methyl methacrylate) substrates were investigated. The adhesive fracture energies for different coatings were quantitatively characterized and varied between 1.4 J/m² and 22 J/m². Significant time dependent crack growth in various moist environments was observed and was consistent with a viscoelastic crack growth model. The effect of selected weathering treatments was also examined and resulted in a significant drop in coating adhesion. The coatings were analyzed using surface sensitive techniques; structural changes in the coatings resulting from various exposure doses were studied and mechanisms responsible for the observed degradation in adhesion were discussed.     

Depressive manifestations and differential patterns of treatment outcome in an intensive partial hospitalization treatment program.

Patients with personality disorder demonstrate heterogeneity in symptom presentation and treatment needs. Methods of subtyping patient presentations may illuminate important patient-treatment matches. Previous studies of an intensive partial hospitalization approach for patients with affective and personality disorders had demonstrated significant treatment effects. The current study aimed at identifying differential patterns of treatment engagement and outcome within this context of substantial aggregate benefit. Our sample was comprised of 107 outpatients, all of whom presented with Diagnostic and Statistical Manual of Mental Disorders (4th ed., American Psychiatric Association, 1994) Axis II traits or full disorders. In a prior cluster analysis, measures of depressive symptom manifestation were employed to identify four distinct patient subgroups. The cluster designation was tested as an independent factor influencing in-treatment ratings (well-being, anxiety, depression) and pre- to posttreatment ratings of outcome. The patient clusters showed significantly different patterns of change in anxiety (slopes) over the course of treatment. Significant differences between clusters were also evident in the proportion of patients achieving clinically significant change on 3 central outcome indexes. Results are considered in terms of the match between the patient’s clinical presentation (e.g., anaclitic depression) and the treatment approach, with attention to implications for patient selection and preparation for the partial hospital program. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structure‐Specific Recognition of Friedreich's Ataxia (GAA)n Repeats by Benzoquinoquinoxaline Derivatives

Expansion of GAA triplet repeats in intron 1 of the FXN gene reduces frataxin expression and causes Friedreich's ataxia. (GAA)_n repeats form non‐B‐DNA structures, including triple helix H‐DNA and higher‐order structures (sticky DNA). In the proposed mechanisms of frataxin gene silencing, central unanswered questions involve the characterization of non‐B‐DNA structure(s) that are strongly suggested to play a role in frataxin expression. Here we examined (GAA)_n binding by triplex‐stabilizing benzoquinoquinoxaline (BQQ) and the corresponding triplex‐DNA‐cleaving BQQ‐1,10‐phenanthroline (BQQ‐OP) compounds. We also examined the ability of these compounds to act as structural probes for H‐DNA formation within higher‐order structures at pathological frataxin sequences in plasmids. DNA‐complex‐formation analyses with a gel‐mobility‐shift assay and sequence‐specific probing of H‐DNA‐forming (GAA)_n sequences by single‐strand oligonucleotides and triplex‐directed cleavage demonstrated that a parallel pyrimidine (rather than purine) triplex is the more stable motif formed at (GAA)_n repeats under physiologically relevant conditions.     

Hypercalcaemia in patients with newly diagnosed tuberculosis in Malaysia

A giant hidradenocarcinoma presented by a 75-year-old female is reported. The patient had a malignant transformation within a nodular hidradenoma involving the right postauricular area, which was treated by mass removal and a right radical neck dissection with a free-flap covering. Malignant hidradenocarcinoma is the least common adnexal tumor of uncertain origin. They are usually malignant from their inception, but some develop from a benign counterpart. To the authors' knowledge, only three cases have been reported previously. Two histologically distinct components were seen in this tumor: (i) typical nodular hidradenoma, which constituted a small part of the tumor; and (ii) carcinoma with areas of transition. The secretory cells of hidradenocarcinoma showed decapitation secretion on light and electron microscopic observations, which is evidence of apocrine differentiation. Histologically, this case was concluded as a hidradenocarcinoma arising from a long-standing nodular hidradenoma. A literature review is presented and the histological, immunohistochemical and ultrastructural features are described.     

Cor pulmonale due to obstructive sleep apnoea

A 47 year old man with a long history of chronic loud snoring and daytime sleepiness presented with hypercapnic respiratory failure and right ventricular failure. The diagnosis of obstructive sleep apnoea (OSA) leading to the 'obesity-hypoventilation syndrome', was supported by the findings of an overnight cardio-respiratory monitoring during sleep. His symptoms and arterial blood gases improved following treatment with nocturnal nasal continuous positive airway pressure (CPAP).     

Molecular self-assembly into one-dimensional nanostructures

Self-assembly of small molecules into one-dimensional nanostructures offers many potential applications in electronically and biologically active materials. The recent advances discussed in this Account demonstrate how researchers can use the fundamental principles of supramolecular chemistry to craft the size, shape, and internal structure of nanoscale objects. In each system described here, we used atomic force microscopy (AFM) and transmission electron microscopy (TEM) to study the assembly morphology. Circular dichroism, nuclear magnetic resonance, infrared, and optical spectroscopy provided additional information about the self-assembly behavior in solution at the molecular level. Dendron rod-coil molecules self-assemble into flat or helical ribbons. They can incorporate electronically conductive groups and can be mineralized with inorganic semiconductors. To understand the relative importance of each segment in forming the supramolecular structure, we synthetically modified the dendron, rod, and coil portions. The self-assembly depended on the generation number of the dendron, the number of hydrogen-bonding functions, and the length of the rod and coil segments. We formed chiral helices using a dendron-rod-coil molecule prepared from an enantiomerically enriched coil. Because helical nanostructures are important targets for use in biomaterials, nonlinear optics, and stereoselective catalysis, researchers would like to precisely control their shape and size. Tripeptide-containing peptide lipid molecules assemble into straight or twisted nanofibers in organic solvents. As seen by AFM, the sterics of bulky end groups can tune the helical pitch of these peptide lipid nanofibers in organic solvents. Furthermore, we demonstrated the potential for pitch control using trans-to-cis photoisomerization of a terminal azobenzene group. Other molecules called peptide amphiphiles (PAs) are known to assemble in water into cylindrical nanostructures that appear as nanofiber bundles. Surprisingly, TEM of a PA substituted by a nitrobenzyl group revealed assembly into quadruple helical fibers with a braided morphology. Upon photocleavage of this the nitrobenzyl group, the helices transform into single cylindrical nanofibers. Finally, inspired by the tobacco mosaic virus, we used a dumbbell-shaped, oligo(phenylene ethynylene) template to control the length of a PA nanofiber self-assembly (<10 nm). AFM showed complete disappearance of long nanofibers in the presence of this rigid-rod template. Results from quick-freeze/deep-etch TEM and dynamic light scattering demonstrated the templating behavior in aqueous solution. This strategy could provide a general method to control size the length of nonspherical supramolecular nanostructures.