biotin binding (Kd is ~ 10‘ M ). Free monomeric avidin in solution can be obtained by treatment of native tetrameric avidin with acid or guanidine-HCl (Sharma, Bagshawe, and Begent, 2005). Modification for pre-targeting: In pre-targeting strategies to deliver cancer therapeutics, faster dissociation kinetics of avidin-biotin system may be required. Increased dissociation kinetics is a different goal from purification. It cannot be achieved either by iminobiotin since the pH in the body is not much different or by monomeric avidin since at least two binding sites on avidin are required for its bridging function. To apply the avidin-biotin system to tumor pre-targeting strategies, protein engineering approaches have been used to further tailor avidin/streptavidin. For example, site-directed mutagenesis techniques have been used to alter the avidin/streptavidin direct binding contacts to biotin. Stayton et al. reported that the off-rate constant of biotin was increased to ~10 '3 s '1 with a mutant streptavidin, compared to 10 '6 s’1with the wild streptavidin (Senter, and Springer, 2001). The effects of the biotinylated derivatives on the binding constant have also been investigated. The off-rate constant increases due to steric hindrance when a bulky substitute is coupled with biotin. However, high affinity and metastability of the avidin-biotin interaction could be restored if 7-27 atom spacers were introduced between biotin and peptide hormones or fluorophores. It was reported…
HCl has a high dissociation constant which means it releases all the hydrogen atoms when dissolved in water whereas, CH3COOH has a low dissociation constant which means it dissociates incompletely, releasing only some hydrogen when dissolved in water. Also, it was evident in the experiment where electricity was passes through the 0.1M of CH3COOH and 0.1M of HCl solutions. The light bulb only lit when electricity was passed through the HCl solution due to the high number of ions. A6. Explain…
DETERMINATION OF pKa AND pKb USING ACID-BASE TITRATIONS Introduction Acid-base titrations can be used to determine pKa of a weak acid and pKb of a base. A weak acid and a weak base incompletely dissociate in water. For this reason, the concentration of hydrogen ions (H+) and hydroxide ions (OH-) depend on equilibrium coefficients of acid (Ka) and base (Kb). Equation 1 shows the chemical dissociation equation of a weak acid. Furthermore, Equation 2 describes the equilibrium constant of a weak…
Ka, or the acid dissociation constant, gives a measure to which an acid dissociates in a solution. It also provides a measure of the strength of an acid. If the value of Ka is high, the said acid s largely dissociated, making the acid strong. However, when the value of Ka is small, the little amount of acid is dissociated, making the acid weak. In the experiment, acetic acid (HOAc), is shown to have a computed Ka of 1.1148 x 10-5. It has a very little value meaning it is considered as a weak…
The pKa was determined to be 7.21 while the average Ka was 6.17*10^-8. The Ka % error was -21.91 which means that the yield was lower than expected compared to the literature value which was given to be 7.9*10^-8. (See equation 4) Results and Discussion In this lab the experimental pKa value was determined to be 7.21 and the average Ka was determined to be 6.17x10^-8. This value shows that through he dissociation of the hydronium in the solution it made the solution more acidic than a basic…
From the absorbance of sample A3 and B3 and their diluted versions, the following graphs can be drawn: Figure 2- A graph showing the relation between concentration of bromophenol blue in M and their absorbance for the acidic form of the molecule, showing the molar absorptivity constant of the molecule at wavelengths 440 nm and 590 nm. The reading with concentration 6 x 10-4 M at wavelength 440 nm was discarded as it is too off from the trend line that it is not following the trend at all.…
Optimisation studies were carried out on the basis of varying initial concentration of Chitosan and Xanthan, and varying pH of Chitosan solution. The results obtained were interesting. Unstable capsules were formed with the following combination of Xanthan and Chitosan concentration. The Chitosan solution pH was kept constant at 5. The above table gives the inference that when Xanthan concentration is less than or equal to 0.5% or Chitosan concentration is less than or equal to 0.5%, the…
Ka value. When calculated, our Ka value comes out to be 4.27 × 〖10〗^(-5) not the actual with a value of 6.46 × 〖10〗^(-5) This seemed odd seeing as our pKa values are very close to each other. The pKa value of benzoic acid is 4.19, while our calculated value turns out to be 4.37 giving us a 4.30%error. This tells us that our approximation is very close to our goal, but when the Ka values are calculated, their difference is large that it gives us a 33.90% error. Discussion Questions Why can you…
The determination of the pH of a buffer solution and the pKa for of a weak acid Introduction A practical was carried out to show how the Henderson-Hasselbalch equation works and to apply and hone the skills of pipetting, buffer-making, pH-meter use and graphing. The primary goal of the practical was to determine the pKa value of a weak acid. The Ka is an acid dissociation constant, it is a quantitative measure of the strength of an acid in solution. The pKa is defined as the negative log of…
Because there are 5 things simultaneously present, 5 equations must be made. Two for the equilibrium constants, one mass balance equation for all A containing material and one for Na+, and 1 charge balancing equation as shown in the appendix. Since we are looking for the KA we need the equation in the form of KA = [H3O+][A-]/[HA]. Therefore the 5 equations must be rearranged to fit the equation. Once the equations are rearrange and put into the KA equation then the KA at different points can be…