A diminished role for hydrogen bonds in antifreeze protein binding to ice

The most abundant isoform (HPLC-6) of type I antifreeze protein (AFP1) in winter flounder is a 37-amino-acid-long, alanine-rich, alpha-helical peptide, containing four Thr spaced 11 amino acids apart. It is generally assumed that HPLC-6 binds ice through a hydrogen-bonding match between the Thr and neighboring Asx residues to oxygens atoms on the {2021} plane of the ice lattice. The result is a lowering of the nonequilibrium freezing point below the melting point (thermal hysteresis). HPLC-6, and two variants in which the central two Thr were replaced with either Ser or Val, were synthesized. The Ser variant was virtually inactive, while only a minor loss of activity was observed in the Val variant. CD, ultracentrifugation, and NMR studies indicated no significant structural changes or aggregation of the variants compared to HPLC-6. These results call into question the role of hydrogen bonds and suggest a much more significant role for entropic effects and van der Waals interactions in binding AFP to ice.     

Real time observation of crystallization in polyethylene oxide with video rate atomic force microscopy

Video rate atomic force microscopy (VideoAFM), with a frame rate of 14 frames/s and a tip velocity of up to 15 cms⁻¹, is used to image polyethylene oxide films during crystal growth. The capabilities of VideoAFM when applied to semicrystalline polymer surfaces are explored. Image quality comparable to that found with conventional contact AFM is achieved but with a nearly 1000 times improvement in time resolution. By applying the technique to the real-time observation of crystal growth, different modes of rapid crystallization are followed in real time. Observation of the spherulite growth front allows measurement of growth rates at the lamellar scale, from which a factor of two difference in the rate of radial growth to the rate of tangential growth is observed, confirming that the elongated nature of spherulite lamellae is due to geometric constraints rather than an inherent fibrillar character. Measurements on screw dislocation growth, when large amounts of crystallizable material is trapped at the surface show that the terrace height does not influence the rate of crystal growth, confirming that under these conditions processes at the lamellar growth front control the rate of growth. When only a thin film of molten material is left on the surface of the already crystallized film dendritic growth is observed, implying a diffusion controlled process under these far from equilibrium conditions.     

Determination of the Impact of Glycolate on Cs,Sr, and Actinide Separations in High-Level Waste

The Defense Waste Processing Facility (DWPF), responsible for vitrifying high-level waste (HLW) at the Savannah River Site (SRS), is planning to introduce glycolic acid as a reductant during chemical conditioning of the waste prior to vitrification. A portion of this glycolic acid may be recycled back to the tank farm as sodium glycolate. Since glycolate can serve as a complexing agent for a variety of metallic ions, recent studies were performed to examine the effect of glycolate on the removal of Sr and actinides by monosodium titanate (MST) and modified MST (mMST) and the separation of Cs by the caustic-side solvent extraction (CSSX) process.     

Agglomeration of struvite crystals

Struvite crystallisation is widely studied as a way to remove phosphorus from wastewater effluents and simultaneously generates a valuable product for the fertiliser industry. However, to date, some crystallisation processes experimented at either pilot/or full scale face problems linked to the formation of fines. This paper presents results on the investigation of struvite agglomerative properties and the possible application of coagulants and/or flocculants to remove fines. Coagulants investigated were hydrolysing metals salts (Al(3+) and Fe(3+)), calcium compounds and a cationic polymer, polydiallyldimethylammoniumchloride (polyDADMAC). The effects of a natural flocculant (alginate) have also been tested. Results demonstrated that destabilisation of struvite particles by chemical addition was feasible and identified polyDADMAC as a good option for the agglomeration of struvite particles. However, optimisation of its dosage under typical pH conditions for struvite formation showed floc formation to be very pH sensitive.     

Inflammatory myofibroblastic tumor in children

The authors presented the cases of two children with inflammatory myofibroblastic (IMF) tumor and reviewed the literature to facilitate the preoperative recognition, delineate the clinical features, and describe the natural history of this entity. The first child had IMF tumor arising from the mesentery of the small intestine. He presented with an abdominal mass associated with severe inflammatory response manifested by fever, impaired growth, thrombocytosis, and microcytic, hypochromic anemia. After surgical resection, his fever resolved and his growth rate and the laboratory abnormalities normalized. Five months after initial diagnosis, the fever, anemia, and thrombocytosis recurred along with two tumors arising from the omentum and the abdominal soft tissue. After the second surgery, he remains free of recurrent disease for 30 months. The second child presented with a lung mass that was radiologically indistinguishable from pulmonary sequestration. After surgical resection, she remains free of recurrent disease for 18 months. IMF tumor should be considered in any solid tumor that occurs in association with a chronic inflammatory response. IMF tumor should also be considered in the differential diagnosis of pulmonary sequestration.     

The morphology and deformation behavior of poly(butylene terephthalate)/BPA polycarbonate blends

Summary In this communication the results of a series of recent studies of the morphology and deformation behavior of toughened poly(butylene terephthalate) (PBT)/BPA polycarbonate (PC) blends are briefly summarized. Several papers containing a more detailed account are currently in press (1–3). Among the unique morphological features of these blends are the consistent isolation of the core/shell impact modifier (IM) in the PC phase and the crystallization and phase separation of the PBT from the partially miscible PBT/PC melt on slow cooling. DSC studies provide corroborating evidence for melt miscibility of the two resins. The blends deform through a combination of cavitation and shear processes. In all cases cavitation occurs exclusively within the IM particles and is suppressed at higher PC concentrations and elevated temperatures.     

Extensive restriction site polymorphism at the human phenylalanine hydroxylase locus and application in prenatal diagnosis of phenylketonuria

A total of 10 restriction site polymorphisms have been identified at the human phenylalanine hydroxylase locus using a full-length human phenylalanine hydroxylase cDNA clone as a hybridization probe to analyze human genomic DNA. These polymorphic patterns segregate in a Mendelian fashion and concordantly with the disease state in various PKU kindreds. The frequencies of the restriction site polymorphisms at the human phenylalanine hydroxylase locus among Caucasians are such that the observed heterozygosity in the population is 87.5%. Thus, most families with a history of classical phenylketonuria can take advantage of the genetic analysis for prenatal diagnosis and carrier detection of the hereditary disorder.     

Effects of age, breast density, ethnicity, and estrogen replacement therapy on screening mammographic sensitivity and cancer stage at diagnosis: review of 183,134 screening mammograms in Albuquerque, New Mexico

PURPOSE: To examine how common patient factors affect screening mammographic sensitivity and cancer stage at diagnosis. MATERIALS AND METHODS: The authors used a population-based database of 183,134 screening mammograms and a statewide tumor registry to identify 807 breast cancers detected at screening mammography. RESULTS: Sensitivity varied significantly with ethnicity, use of estrogen replacement therapy, mammographic breast density, and age. Sensitivity was 54% (13 of 24) in women younger than 40 years, 77% (121 of 157) in women aged 40-49 years, 78% (224 of 286) in women aged 50-64 years, and 81% (277 of 340) in women older than 64 years. Sensitivity was 68% (162 of 237) for dense breasts and 85% (302 of 356) for nondense breasts and 74% (180 of 244) in estrogen replacement therapy users and 81% (417 of 513) in nonusers. Sensitivity was most markedly reduced with the combination of dense breasts and estrogen replacement therapy use; there was little difference when only one factor was present. Median cancer size and the percentage of early cancers showed little change with any factors. CONCLUSION: Age is a minor determinant of mammographic sensitivity in women aged 40 years or older. Sensitivity is substantially decreased with the combination of higher breast density and estrogen replacement therapy use. There was not a notable shift in cancer outcomes in the groups with lower mammographic sensitivity. These data do not support different screening recommendations in women aged 40-49 years or in estrogen replacement therapy users.     

Morphology and properties of toughened poly(phenylene oxide)-polyamide blends

High impact strength poly(phenylene oxide)-polyamide blends can be prepared by chemically coupling the two components and incorporating a rubbery impact modifier in the resin. The resulting materials exhibit a distinctive morphology in which the rubber is selectively incorporated in the dispersed poly(phenylene oxide) phase. In this paper both the structure and toughening mechanisms in these blends are examined. An analysis of their deformation behaviour is presented in a companion paper.