Durable,acid-resistant copolymers from industrial by-product sulfur and microbially-produced tyrosine

The search for alternative feedstocks to replace petrochemical polymers has centered on plant-derived monomer feedstocks. Alternatives to agricultural feedstock production should also be pursued, especially considering the ecological damage caused by modern agricultural practices. Herein, l-tyrosine produced on an industrial scale by E. coli was derivatized with olefins to give tetraallyltyrosine. Tetraallyltyrosine was subsequently copolymerized via its inverse vulcanization with industrial by-product elemental sulfur in two different comonomer ratios to afford highly-crosslinked network copolymers TTS_x (x = wt% sulfur in monomer feed). TTS_x copolymers were characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis (DMA). DMA was employed to assess the viscoelastic properties of TTS_x through the temperature dependence of the storage modulus, loss modulus and energy damping ability. Stress–strain analysis revealed that the flexural strength of TTS_x copolymers (>6.8 MPa) is more than 3 MPa higher than flexural strengths for previously-tested inverse vulcanized biopolymer derivatives, and more than twice the flexural strength of some Portland cement compositions (which range from 3–5 MPa). Despite the high tyrosine content (50–70 wt%) in TTS_x, the materials show no water-induced swelling or water uptake after being submerged for 24 h. More impressively, TTS_x copolymers are highly resistant to oxidizing acid, with no deterioration of mechanical properties even after soaking in 0.5 M sulfuric acid for 24 h. The demonstration that these durable, chemically-resistant TTS_x copolymers can be prepared from industrial by-product and microbially-produced monomers via a 100% atom-economical inverse vulcanization process portends their potential utility as sustainable surrogates for less ecofriendly materials.

Copolymers of waste sulfur and bacterially-produced tyrosine are reported.     

Expression of a neurally related laminin binding protein by neural crest-derived cells that colonize the gut: relationship to the formation of enteric ganglia.

In order to give rise to the enteric nervous system (ENS), cells migrating from the neural crest must find the bowel and cease migrating at appropriate locations within the gut. Previous studies of the development of the ENS in a mutant mouse have led to the hypothesis that laminin in the enteric mesenchyme may act as a signal to crest-derived cells to cease migrating and extend neurites (or glial processes). Implied in this hypothesis is the idea that crest-derived cells, as a prelude to their participation in ganglion formation, acquire a neurally related laminin receptor, which they do not express at pre-enteric stages of migration. As a partial test of this hypothesis, single and double label immunocytochemistry at light and electron microscopic (EM) levels were used to study the expression of cell surface laminin binding proteins by crest-derived cells in the process of migrating to or within the developing chick gut. Two antibodies (called 3070 and alpha-110) raised against neuronal cell surface laminin binding proteins were employed for this purpose. Laminin binding protein immunoreactivity was found to be expressed within the bowel and ganglion of Remak by a subset of crest-derived cells (identified immunocytochemically with NC-1/HNK-1 antibodies) and by all of those developing as neurons (identified immunocytochemically with antibodies to neurofilament-associated proteins). Laminin binding protein immunoreactivity was also found to be expressed in fixed neural structures elsewhere in the embryos, including cranial and spinal roots, nerves, and ganglia. In contrast, laminin binding protein immunoreactivity was not expressed by migrating crest-derived cells in the vicinity of the vagal or sacral regions of the neuraxis (from which the precursors of the ENS take origin); nor was it expressed by juxta-pharyngeal vagal crest-derived cells migrating to the foregut through the caudal branchial arches or by the caudal stream of sacral crest-derived cells approaching the hindgut. EM immunocytochemistry confirmed that laminin binding protein immunoreactivity in the bowel was located on the surfaces of crest-derived cells, and was exhibited both by those cells that could only be distinguished from their neighbors by their NC-1/HNK-1 immunoreactivity and by cells developing as neurons or glia. EM immunocytochemistry also revealed that the surfaces of crest-derived cells migrating through the enteric mesenchyme were contacted by many small osmiophilic "puffs" of laminin-immunoreactive extracellular material. These puffs coincided in location with membrane sites that expressed the immunoreactivity of the laminin binding protein. These observations are consistent with the hypothesis that laminin plays a role in the formation of enteric ganglia.     

Polymer cements by copolymerization of waste sulfur,oleic acid,and pozzolan cements

A host of emerging cementitious products derived from waste materials or sustainable precursors have drawn increasing interest in response to economic, social and regulatory pressures. Among the more well-studied and abundant of such cement products are sulfur cements and pozzolans like fly ash, silica fume, ground granulated blast furnace slag, and metakaolin. For the current study, oleic acid was combined with these compounds to make a series of pastes. Oleic acid is an attractive additive because it is a primary constituent of low value, high-volume by-products of biodiesel production and animal product rendering. The current work is thus a comparative study of pastes prepared by heating sulfur and oleic acid with either ordinary Portland cement or one of the pozzolan-extended cements. The mechanical properties of the cured sulfur-oleic acid pastes were assessed by dynamic mechanical analysis to provide stress-strain curves both before and after acid challenge. All of the blocks prepared from the pastes retain significantly more mechanical strength (up to 100%) after exposure to strong oxidizing acid solutions than does ordinary Portland cement. Surface damage to these sulfur cement blocks can be healed to varying extents by thermal annealing, as assessed by optical microscopy.     

Florida Cognitive Activities Scale: initial development and validation.

We used a rational-empirical approach in the construction and validation of a cognitive activity scale for use with elderly populations. The scale development effort produced a 25-item scale with a reasonably high level of internal consistency in a sample of 200 elderly individuals. Scale scores were positively correlated with years of education and measures of various domains of cognitive ability. In a separate cross-validation sample, a similar pattern of reliability and validity coefficients was obtained. The full scale score was found to contribute significantly to the prediction of cognitive ability after controlling for the effects of age, education, and gender. Two subscales (Higher Cognitive Abilities and Frequent Cognitive Abilities) and a measure of self-reported maintenance of cognitive activity were also developed. In a separate study, the maintenance score was found to differ significantly between the validation sample and a sample of individuals with a history of neurological disorder, with a moderate effect size (d approximately = .7). Further cross-validation studies in minority groups and groups of varying socioeconomic status will be critical in establishing the research and clinical value of the scale and subscales.     

Bed/population ratios in South African public sector mental health services

Background In post-apartheid South Africa, mental health service planners face critical decisions regarding appropriate and affordable inpatient care. Before a fashion of deinstitutionalisation is followed blindly in South Africa, effective community services should be in place and sufficient psychiatric beds should remain in hospitals for those who cannot be catered for in the community. In order to maintain the delicate balance between hospital and community-based services, it is essential that useful indicators of inpatient care are established. This study documents current bed/population ratios per 100 000 population in public sector mental health services in South Africa. Method A questionnaire was distributed to provincial mental health coordinators requesting psychiatric bed numbers in acute and medium-long stay facilities across all service levels. The information was supplemented by consultations with mental health coordinators in each of the nine provinces. Population data were obtained from preliminary findings of the 1996 census. Results For acute facilities, the mean bed/population ratio was 13 (provincial range: 6–18) per 100 000 population. For medium-long stay facilities, it was 16 (provincial range: 0–29) excluding contracted facilities, and 35 (provincial range: 0–83) including contracted facilities per 100 000 population. Conclusions There were low levels of inpatient service provision in South Africa, and there was considerable variability between provinces. This study gives further support to the need to develop acute inpatient psychiatric services, reduce levels of chronic care where appropriate, and redirect resources towards the development of community-level residential and day-care services. It is crucial to develop accurate indicators to monitor this process. Accepted: 1 March 2002     

Conjugated Polymers Featuring Oxacyclophane‐Scaffolded π‐Stacking Interactions

An oxacyclophane framework is modified to include π‐conjugated segments positioned so as to allow an optimized face‐to‐face π‐stacking interaction between them. This unique architecture is first employed for the preparation of model compounds with defined interaction between two small molecular organic chromophores. The interaction allows facile through‐space energy transfer between the chromophores when they are held in the appropriate geometry. The oxacyclophane is thus employed in a polymer with consecutive short stretches of phenylene ethynylene such that polymer chain conjugation requires through‐space interaction between segments rather than the through‐bond π‐conjugation that typifies traditional conjugated polymers. The extent of the through‐space interactions along the polymer backbone is explored through photophysical measurements, calculations, X‐ray diffraction, and comparison with a variety of model and control materials.