Colloidal Stability & Conformational Changes in β-Lactoglobulin: Unfolding to Self-Assembly

A detailed understanding of the mechanism of unfolding, aggregation, and associated rheological changes is developed in this study for β-Lactoglobulin at different pH values through concomitant measurements utilizing dynamic light scattering (DLS), optical microrheology, Raman spectroscopy, and differential scanning calorimetry (DSC). The diffusion interaction parameter k_D emerges as an accurate predictor of colloidal stability for this protein consistent with observed aggregation trends and rheology. Drastic aggregation and gelation were observed at pH 5.5. Under this condition, the protein’s secondary and tertiary structures changed simultaneously. At higher pH (7.0 and 8.5), oligomerizaton with no gel formation occurred. For these solutions, tertiary structure and secondary structure transitions were sequential. The low frequency Raman data, which is a good indicator of hydrogen bonding and structuring in water, has been shown to exhibit a strong correlation with the rheological evolution with temperature. This study has, for the first time, demonstrated that this low frequency Raman data, in conjunction with the DSC endotherm, can be been utilized to deconvolve protein unfolding and aggregation/gelation. These findings can have important implications for the development of protein-based biotherapeutics, where the formulation viscosity, aggregation, and stability strongly affects efficacy or in foods where protein structuring is critical for functional and sensory performance.     

Polymer lifetime studies in hostile environments

Photo-oxidative degradation reactions are mainly responsible for reduced lifetime in polymers. These reactions are responsible for the decay in useful physical and chemical properties of polymers. In addition to high ultraviolet radiation doses, hostile environments have increased temperature, high humidity, and air-borne sand. In this work white pigmented polyvinyl chloride (PVC) pipe sections were exposed to natural weather at seven different locations. Characterization studies were made on exposed samples using Fourier transform infrared (FTIR) spectroscopic, gel permeation chromatographic (GPC), and scanning electron microscopic (SEM) studies. Performance characteristics were determined by testing changes in the mechanical properties. Functional groups introduced during the processing of PVC and irregularities in the polymer chain can be held responsible for the initiation and propagation of photo-oxidative degradation reactions catalyzed by high surface temperature and increased humidity.     

Impact of Site-Specific Benzo[a]Pyrene Diol Epoxide-dG Lesions at or near Single/Double-Strand DNA Junctions on DNA Bending

Adducts derived from the binding of the (+)-7R,8S,9S,10R and (?)-7S,8R,9R,10S enantiomers of r7,t8-dihydrodiol-t9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) to 2′-deoxyguanosine residues in DNA are known to induce mutations due to error-prone DNA replication. Because the conformational properties of these lesions may be important in these phenomena, we have examined the effects of the stereoisomeric (+)- and (?)-trans-anti-[BP]-N ²-dG lesions positioned site-specifically at or near primer/template oligonucleotide junctions on DNA bending using high resolution gel electrophoresis. Remarkable differences in electrophoretic mobilities μ are observed in the two adducts derived from the tumorigenic (+)-anti-BPDE, and the non-tumorigenic (?)-anti-BPDE enantiomer. With the (+)-trans lesion positioned on the template strand adjacent to the 3′-end of the primer strand, a remarkable decrease in μ is observed. This suggests the existence of a bend at the single strand-double strand junction. Only modest decreases in μ are observed in the case of the (?)-trans lesion, or when the 3′-end is opposite to, or more distant from the lesion site. These observations are discussed in terms of the known NMR solution structures of these lesions in the same sequence context, and the properties of primer/template DNA in polymerases.     

Comparison of the Morphological Transforming Activities of Fjord-Region PAHs with Dibenzo[a,e]Pyrene and Benzo[a]Pyrene

The morphological transforming activities in mouse embryo C3H10T1/2CL8 (C3H10T1/2) cells were examined for six PAHs: benzo[c]chrysene (B[c]C); benzo[g]chrysene (B[g]C); benzo[c]phenanthrene (B[c]P); dibenzo[a, l]pyrene (DB[a, l]P); dibenzo[a,e]pyrene (DB[a,e]P) and benzo[a]pyrene (B[a]P). C3H10T1/2 cells treated with B[c]P or B[g]C at concentrations of 0–3 μg/ml did not produce any transformed Type II or III foci after 24 hr of exposure. Concurrent cytotoxicity was observed. Under the same conditions, B[a]P and B[c]C were active, with B[c]C approximately one-half the activity of B[a]P. However, after a 48-hr treatment, B[c]P and B[g]C gave significant activity measured as both foci/dish or the number of dishes exhibiting foci. After a 24-hr treatment, comparison of B[a]P with two dibenzopyrenes, DB[a, l]P and DB[a,e]P, gave activities in the order: DB[a, l]P > B[a]P > DB[a,e]P. After 48 hr of treatment, both B[a]P and DB[a,e]P had similar activities.     

Weather-Induced Degradation of Plastic Pipes

A number of plastic materials, such as unplasticized poly(viny1 chloride) (uPVC), acrylonitrile-butadiene-styrene (ABS), high-density polyethylene (HDPE), poly-(vinylidene fluoride) (PVDF), and chlorinated poly(viny1 chloride) (cPVC), are available for numerous applications. uPVC and HDPE pipes are used in pressurized piping systems in Saudi Arabia for industrial, agricultural, domestic, and general-purpose applications. Some studies have been carried out to investigate the causes of failure in plastic pipes, which is very high in the area. In this chapter an overview of the failure of plastic pipes is presented, with emphasis given to failure of pipes due to severe weather conditions in Saudi Arabia.     

Photocrosslinking of styrene–isoprene–styrene; effect of benzoin and ethylene glycol dimethacrylate on physical properties

Crosslinking reaction of polymer by ultraviolet (UV) irradiation has been important in industries. In this work, photocrosslinking of styrene–isoprene–styrene (SIS) triblock copolymer in the presence of benzoin photoinitiator and a dimethacrylate monomer as crosslinking agent was investigated. Curing of samples was initiated under UV irradiation. Benzoin was used as photoinitiator because it contains chromophore group that could absorb UV irradiation. Ethylene glycol dimethacrylate (EGDMA) was used as crosslinking agent, since it has alkene functional groups that could react with the alkene group of SIS. ATR-FTIR spectra of samples show that absorption band of double bond at 1500–1600?cm^?1 decreases after UV exposure. Increasing the concentration of benzoin (0.1–1?phr) and EGDMA (1–10?phr) leads to an increase in gel content and hardness, while swelling ratio decreases. After 5?min heating at 150?°C, about 20%wt of the unirradiated compound became insoluble, because heating of compound at 150?°C causes crosslinking reaction without any irradiation.     

One-pot synthesis of glucose functionalized multi-walled carbon nanotubes: Dispersion in hydroxylated poly(amide-imide) composites and their thermo-mechanical properties

Multi-wall carbon nanotubes (MWCNTs) were functionalized with glucose using a covalent, non-specific functionalization approach. Fourier-transformed infrared spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) confirmed that glucose structures were covalently attached to CNTs. Hydroxylated poly(amide-imide) (PAI)-based composites were developed by dispersing of glucose-functionalized MWCNTs (MWCNTs-Gl) as reinforcement in different concentrations varying from 5 to 15 wt.%. Nanocomposites have slightly higher degree of crystallinity than neat PAI and their thermo-oxidative stability was significantly affected by the addition of MWCNTs-Gl. According to mechanical tensile tests, the tensile strength and the Young's modulus of the MWCNT-Gl/PAI composites were increased with increasing MWCNTs-Gl content. The tensile strength remarkably increased from 81 to 129 MPa, which was about 59% higher than that of the neat PAI, with the addition of MWCNT-Gl contents within 15 wt.% and the elongation at break decreased about 0.2% at a 5 wt.% loading of MWCNT-Gl in comparison with the pure PAI film.     

Passivity and passivity breakdown of a zinc electrode in aerated neutral sodium nitrate solutions

The passivation and pitting corrosion behaviour of a zinc electrode in aerated neutral sodium nitrate solutions was investigated by cyclic voltammetry and chronopotentiometry techniques, complemented by ex situ scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) examinations of the electrode surface. Measurements were conducted under different experimental conditions. The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of ZnO on the anode surface. The passive region is followed by pitting corrosion as a result of breakdown of the passive film. SEM images confirmed the existence of pits on the electrode surface. The breakdown potential decreases with an increase in NO₃⁻ concentration and temperature, but increases with increasing potential scan rate. Addition of SO₄²⁻ ions to the nitrate solution accelerates pitting corrosion, while addition of WO₄²⁻ and MoO₄²⁻ ions inhibits pitting corrosion. The chronopotentiometry measurements show that the incubation time for pitting initiation decreases with increasing NO₃⁻ concentration, temperature and applied anodic current density. Addition of SO₄²⁻ ions decreases the rate of passive film growth and the incubation time, while the reverse changes produced by addition of either WO₄²⁻ or MoO₄²⁻ ions.