Surfactants modify the torsion properties of proteins: a single molecule study.

Surfactants are widely used in diagnostic assays to prevent protein aggregation and non-specific adsorption at surfaces. Here, a single molecule magnetic torque tweezers study is reported, aiming to quantify surfactant-induced changes in the torsional flexibility of a protein model system: protein-G-immunoglobulin G (IgG) attached to a glass surface. The influences of Sodium Dodecyl Sulphate (SDS) and Polysorbate 20 (Tween 20) on the protein pair have been investigated. The proteins were exposed to the surfactants at concentrations relative to the Critical Micelle Concentration (CMC), namely 0.1× CMC, 1× CMC and 10× CMC. Both surfactants increase the torsional flexibility of the protein-G-IgG complex. Tween 20 is most effective at increasing the torsional flexibility of the complex at the surface while SDS is more effective at dissociating the protein bonds. Tweezer data on the IgG-IgG protein pair show no influence of Tween 20 on the torsional flexibility. Furthermore, temperature dependent near-UV and far-UV Circular Dichroism (CD) data at 10× CMC show that Tween 20 does not significantly alter the secondary and tertiary structure of both protein-G and IgG while SDS does. These results provide evidence that both the mechanical properties of the protein structure and the interaction between proteins can alter the torsional rigidity measured with magnetic torque tweezers. This study shows for the first time the ability to use magnetic torque tweezers as a probe for surfactant-induced changes in proteins at a single molecule level.

Reconstruction of the nose damaged by cocaine.

Nasal snorting of cocaine crystals causes destruction of the septal and nasal mucosa, which eventually provides exposure of the septal cartilage and nasal bones. This exposure eventually leads to septal chrondritis and nasal bone osteomyelitis. As this process continues, the severe loss of cartilage and bone allows gradual to total collapse of the nose. Correction of this deformity is best achieved by supplying new lining; this is possible by turning nasolabial flaps into the nasal vestibule to replace the lost and released lining. Once this has been accomplished, costal cartilage grafts can be inserted along the bridge and alae to maintain the structural integrity of the reconstruction.

Dentin bond strength of packable composites using one-bottle adhesives.

PURPOSE: To evaluate the shear bond strength to dentin of packable composites using their respective one-bottle adhesives. MATERIALS AND METHODS: Human, noncarious extracted permanent molars stored in distilled water were used. Flat buccal and lingual dentin surfaces were ground wet on 600-grit silicon carbide paper. The teeth were then distributed at random into four groups of 8 teeth (16 surfaces) each: Group 1: Gluma Comfort Bond/Solitaire II; Group 2: Bond 1/Alert; Group 3: Prime & Bond NT/Surefil; Group 4: OptiBond Solo/Prodigy Condensable. Group 5: Single Bond/Z250 (control) Cylindrical samples of the materials were prepared in plastic molds and bonded to the dentin surface according to the manufacturers' instructions. All samples were placed in distilled water for 24 hrs, thermocycled for 500 cycles in distilled water at 6 degrees C and 60 degrees C and sheared with a universal testing machine at a crosshead speed of 0.5 mm/min. RESULTS: In MPa: Group 1: 24.39 +/- 3.54; Group 2: 28.96 +/- 4.62; Group 3: 30.77 +/- 4.71; Group 4: 30.82 +/- 3.29; Group 5: 24.93 +/- 5.14. ANOVA revealed that Groups 1 and 2 were statistically significantly different from the other groups; there was no statistically significant difference between Groups 2, 3 and 4.