Dehydropeptide Supramolecular Hydrogels and Nanostructures as Potential Peptidomimetic Biomedical Materials

Supramolecular peptide hydrogels are gaining increased attention, owing to their potential in a variety of biomedical applications. Their physical properties are similar to those of the extracellular matrix (ECM), which is key to their applications in the cell culture of specialized cells, tissue engineering, skin regeneration, and wound healing. The structure of these hydrogels usually consists of a di- or tripeptide capped on the N-terminus with a hydrophobic aromatic group, such as Fmoc or naphthalene. Although these peptide conjugates can offer advantages over other types of gelators such as cross-linked polymers, they usually possess the limitation of being particularly sensitive to proteolysis by endogenous proteases. One of the strategies reported that can overcome this barrier is to use a peptidomimetic strategy, in which natural amino acids are switched for non-proteinogenic analogues, such as D-amino acids, β-amino acids, or dehydroamino acids. Such peptides usually possess much greater resistance to enzymatic hydrolysis. Peptides containing dehydroamino acids, i.e., dehydropeptides, are particularly interesting, as the presence of the double bond also introduces a conformational restraint to the peptide backbone, resulting in (often predictable) changes to the secondary structure of the peptide. This review focuses on peptide hydrogels and related nanostructures, where α,β-didehydro-α-amino acids have been successfully incorporated into the structure of peptide hydrogelators, and the resulting properties are discussed in terms of their potential biomedical applications. Where appropriate, their properties are compared with those of the corresponding peptide hydrogelator composed of canonical amino acids. In a wider context, we consider the presence of dehydroamino acids in natural compounds and medicinally important compounds as well as their limitations, and we consider some of the synthetic strategies for obtaining dehydropeptides. Finally, we consider the future direction for this research area.     

Activation analysis of environmental pollutants

Activation analysis is a highly sensitive and specific technique for the detection of trace heavy metal pollutants in environmental materials. Comparison of natural “baseline” levels with elevated levels provides direct evidence of contamination. Neutron activation analysis (NAA) is used in this study to determine arsenic, zinc, cadmium, and mercury. Photo-nuclear activation analysis (PNAA) is used to determine lead in soils. Holland Marsh, a market-gardening area north of Toronto, has been studied as various herbicides and fungicides have been used there. The analyses of soil and vegetation samples, and of human head hair collected from residents are reported.     

TSTL: the template scripting testing language

International Journal on Software Tools for Technology Transfer - A test harness, in automated test generation, defines the set of valid tests for a system, as well as their correctness properties....     

Using artificial neural networks or Lagrange interpolation tocharacterize the faults in an analog circuit: an experimental study

A technique for diagnosing multiple faults in analog circuits from their impulse response function using a fault dictionary was developed. Dirac impulse input to the circuit was simulated and time domain features of the output response were used to build the dictionary. The test of a real circuit by means of a fault dictionary gives realistic results provided the simulated and measured values are similar. Consequently, the choice of the model used in the simulation is important. The precautions to realize the measurement are described     

The Application of Pattern Recognition Techniques to the Contingent Negative Variation for the Differentiation of Subject Categories

Pattern recognition techniques and the statistics of directional data have been applied to a repetitive waveform to differentiate between subject categories. Normal subjects and Huntington's Chorea patients were distinguished by comparing the patterns in the summarized results of statistical tests applied to the Fourier harmonics of their contingent negative variation (CNV) responses, by the consecutive phase angle variations of the first harmonic of their CNV's, and by their different averaged CNV's. A logic algorithm which may provide the basis of computerized diagnosis, or even prediction of the condition, is described.     

Forced modulation of biological processes: A review

Cell culture or biochemical processes utilizing free or immobilized cells or enzymes are candidates for periodic operation. Even though these processes are isothermal, inhibition frequently arises giving their kinetics a push-pull character of the Turing type so that excited states or multiplicity are observed. Modulation of an input such as a substrate or a nutrient concentration or the cell environment such as the pH can enhance the rates of biochemical reactions that are occurring. This possibility was realized by explorers of reactor periodic operation in the 1980s. However, the use of rotating disc biological filters for aerobic waste treatment precedes these activities by at least a decade. The biologically active slime on the disc surface is exposed alternately to air and to an aqueous media containing dissolved and/or suspended waste matter. Indeed, periodic variation of reactor volume in a CSTR, which is equivalent to periodic variation of space velocity, was explored in the early 1970s. The application of this was to activated sludge waste treatment. Periodic operation has been used to address the problem of plasmid loss in continuous fermenters to produce genetically altered microorganisms. A twofold increase in the concentration of plasmid bearing cells using square wave modulation of the dilution rate has been found in a simulation using a model validated by experimental data. These results are in agreement with other studies attempting to control species populations in chemostats. Improvement in the rate of fermentation of a substrate to form a metabolite has been addressed by modulation. It has been shown that the rate of xylose utilization by a yeast is affected by a periodic variation of pH. These were lowered, but the metabolite yield, ethanol, remained the same. With secondary metabolites associated with the non-growth period in fermentation, modulation of the growth-limiting substrate concentration fed to immobilized live cells resulted in significantly higher yields. Differences in the effect of cycling on primary and secondary metabolites has been observed in several biochemical systems, such as those used for penicillin and monoclonal antibody production or in citric acid fermentation.     

Examining Extrinsic Factors that Influence Product Acceptance: A Review

Drivers of liking (DOL) studies are useful for product development to formulate acceptable products; however, DOL alone are insufficient for understanding why a product is purchased and repurchased, which is ultimately the indication of a successful product. Ultimately sensory attributes drive product success (that is, repeat and continued purchase). However, ignoring the importance of extrinsic factors may neglect the vital product attributes responsible for the initial purchase, which may in turn, affect repeat purchase. The perception of sensory attributes assessed by DOL is mitigated by external perceptions of quality. If the sensory attributes do not deliver based upon the quality cues, the product will not be acceptable. Four key extrinsic factors that affect DOL are the perceived satiety, brand and labeling, price, and the emotional impact to decision making. In order to more thoroughly understand what the DOL for a product is, these 4 product cues should be considered in conjunction with sensory attribute perception to gain a holistic understanding of product acceptance.     

Heat resistance of Salmonella weltevreden in low-moisture environments

The heat resistance of Salmonella weltevreden inoculated into flour and heated in hot air was determined for (a) an initial water activity (aw) range of 0.20 to 0.60 prior to heating, (b) a range of storage relative humidities of 6.0 to 35.5% prior to heating, and (c) temperatures of 57 to 77 degrees C. The death curves obtained were biphasic, demonstrating an initial rapid decline in the numbers of survivors (1.0- to 1.5-log reductions) during the first 5 to 10 min of heating for all the temperature-water activity combinations tested. Following this initial rapid decline in the number of cells, a linear survivor curve was obtained where inactivation occurred at a slower rate. The initial decline in survivors coincided with a rapid decrease in the water activity of all the samples tested. Irrespective of the initial water activity level in the samples prior to heating, the aw decreased to < 0.2 during the first 5 to 10 min of heating. The D values obtained for these experimental parameters ranged from a D60-62 of 875 min at an initial aw of 0.4 to a D63-65 of 29 min at an initial aw of 0.5. The results demonstrated that, for any temperature, as the initial water activity of the sample prior to heating decreased, the heat resistance of the cells increased. The z values obtained from these data ranged from 15.2 to 53.9 degrees C. The relative humidity during storage prior to heating did not appear to have a significant effect on the heat resistance of S. weltevreden in flour. These results demonstrate that the amount of available water in foods that are considered to be "dry" (i.e., with a water activity less than 0.60) will significantly influence the effectiveness of the heat processing of foods and, in addition to the temperature, the aw prior to heating is a critical controlling factor during these processes.     

The volatilization of iodine species over dilute iodide solutions

The volatility of iodine above dilute CsI solutions has been investigated experimentally. The partitioning of iodine between air and solutions prepared with iodide was found to increase with decreasing _pH and iodide concentration. Aqueous to gaseous partition coefficients ranging from 3 X 10³ to 10⁷ were observed indicating that only a very small fraction of the iodide was oxidized to volatile forms. It was concluded that under these very dilute conditions, the rate of iodide oxidation was proportional to the square root of the iodide concentration; the rate also depended on _pH under acidic conditions but not under basic conditions.