Rxn Rates, Partitioning, Assays (Classes 13-15) Flashcards
What is temperatures effect on reaction rate?
increased temp = increased rxn rate
What are 4 ways to affect reaction rate besides temperature?
Light, moisture, pH, catalysts
For every 10 degree increase in temperature, how much do you expect the reaction rate will increase?
2-3 fold increase for every 10 degree increase
For the arrhenius equation, what value gives you the slope?
“-Ea/R”
What is the purpose of using the arrhenius equation?
To calculate reaction rate and activation energy
What is k in the arrhenius equation and what are its units?
rate constant; 1/conc*time
What is A in the arrhenius equation and what does it represent?
A = Arrhenius Factor; Represents collision frequency
What are the units for A in the arrhenius equation?
1/sec or s^-1
What is the arrhenius equation?
ln(k) = lnA - Ea/RT
In an arrhenius plot, what is used in the y and x axes?
ln(k) vs. 1/T
What R value do you use in the Arrhenius equation and what are its units?
8.314 J/mol*K
If you are given k values and temperature values, how do you calculate Ea (Activation energy)?
Calculate ln of k and 1/T values; Calculate slope then calculate Ea from Slope = -Ea/R
How do you calculate the arrhenius factor once you have activation energy?
Plug in slope & 1/T values into Arrhenius equation [ln(k) = lnA - Ea/R * 1/T] and solve for A
What are the advantages of accelerated stability testing?
quick detection of drug degradation, prediction of shelf-life/half-life, rapid quality control
What are 2 reasons to do accelerated stability testing rather than testing in real time?
More efficient, More economical
What is the effect of increased temperature on the rate of drug degradation?
More temp, More degradation
Which analytical detection method utilizes adsorption in the assessment process?
HPLC
What do detection methods not tell you?
Structure of the drug; They tell you quantity present & degradation products present
For what reasons would you use UV-Vis spectroscopy?
determination of pKa/partition coefficient, determine rxn kinetics, determine drug release
What detection methods prefer a chromophore to be present on the molecule for detection?
UV-Vis & HPLC
What is the wavelength range for using UV-Vis?
200-700nm
What are some advantages to using UV-Vis?
Easy to use, inexpensive, good precision, automated, determines some properties
What are some disadvantages to using UV-Vis?
Not useful for mixtures, Must have chromophore, moderately selective
How does HPLC work?
A pump passes a pressurized liquid solvent containing the sample through a column with adsorbent material. Each component interacts differently with the adsorbent material causing variable flow rates/variable separation of the components as they pass out of the column
What is the active component of a column in HPLC called?
Sorbent
What is the significance of “HP” in the HPLC detection method?
HP stands for High Performance (or Pressure). The pressure is 50-250 bar in HPLC, whereas normal liquid chromatography uses gravity
What’s the main reason to use HPLC?
To separate and analyze the components of a mixture
Besides separating and analyzing mixtures, what are some other uses of HPLC?
Monitor drug stability, measure partition coefficient, and drug-protein binding
In straight-phase HPLC, is a polar or nonpolar substance used for the mobile phase?
Non-polar mobile phase, Polar stationary phase
In straight-phase HPLC, will hydrophilic or hydrophobic compounds be eluted first?
Hyrophobic compounds
In straight-phase HPLC, would you add a hydrophilic or lipophilic solvent to slow down elution?
Lipophilic solvent
In reverse-phase HPLC, is a polar or nonpolar substance used for the mobile phase?
Polar (Hydrophilic) Mobile Phase, Non-polar (Hydrophobic) stationary phase
Why is reverse-phase used over straight-phase?
Because adjustments can be made most easily and inexpensively in reverse-phase HPLC
In reverse-phase HPLC, will a polar solvent elute more quickly or more slowly than a non-polar compound?
More Quickly. Since RP-HPLC uses a polar sorbent, polar solvents elute more quickly
What are the strengths of HPLC?
Easily controlled, precise, selectivity can be adjusted, automated
What are some weaknesses of using HPLC?
Expensive, Drugs must be extracted prior to use, large amounts of waste
How does mass spectrometry work?
Uses electron bombardment to ionize fragments and then measure molecular weight of the fragments
On a mass spectrometry report, what will the x and y axis represent?
y-axis: percent abundance; x-axis: mass/charge ratio
What do the small spikes in a mass spec report represent?
molecule fragments or impurities
What are the main advantages of using mass spec?
Protein analysis, Coupling to chromatagraphic instruments, & rapid ID of molecule/impurities
What are some disadvantages of Mass spec?
Expensive, Not routinely used in QC, Requires trained personnel/maintenance
What are 2 types of mass spec that are used for protein analysis?
electrospray MS & time-of-flight MS
What would an anesthesiologist use mass spec for?
determine respiratory quotient (CO2 eliminated/O2 consumed)
How many diastereomers are there in penicillin, given that there are 3 chiral carbons?
8 diastereomers; Using 2^n with n being the number of diastereomers, 2^3 = 8
What 2 things can photodegradation do to a drug?
cause the drug to be inactive or cause it to be harmful
What 3 things can you do to prevent photodegradation in a drug?
Store away from light, add an antioxidant, Use an additive that will absorb light
What regions of drugs are responsible for light absorption?
double bonds; benzyl rings
What clinical advice would you give to a patient taking photo-sensitive drugs?
Use drugs at night, store drug away from light, Use sunscreen or avoid sun, Do not take with other drugs that also cause sun sensitivity
What is the definition of diffusion?
random movement of particles from high concentration to low concentration; often across a membrane
What are three types of membranes for diffusion?
monolithic, porous, fibrous
What is the difference between Fick’s first and second laws?
First law is used under steady state conditions; Second law is used under variable conditions
For what reason would you use Fick’s First law?
To determine flux (diffusion rate) under steady state conditions
What must be true in order for Fick’s first law to apply?
Steady state conditions & constant rate of diffusion
What is the formula for Fick’s first law?
J = -D(dC/dx)
How will the thickness of a membrane affect flux?
Thicker membrane = slower flux
Which is more thermodynamically favorable, positive or negative flux?
positive;
What value should be negative to generate a positive flux?
dC (Change in concentration); This means that flux is going from high concentration to low concentration
What are the units for flux, J?
mol/cm^2s or g/cm^2s
For what reason would you use Fick’s Second law?
To determine flux (diffusion rate) under non-steady state conditions
What is the stokes-einstein equation used for?
To determine the diffusion coefficient
Increasing particle radius has what effect on magnitude of flux?
decreases
Increasing viscosity has what effect on magnitude of flux?
decreases
What is the diffusion coefficient primarily dependent on?
Particle radius
What factors affect the diffusion coefficient?
Temperature, Viscosity, and particle radius
What are the units of the diffusion coefficient, D?
cm^2/sec
What is partitioning?
Deposition of a drug between 2 phases based on affinity of drug for 1 layer vs another
What is the partition coefficient?
Ratio of concentration of drug in oil layer vs water layer ([Co]/[Cw])
If drug is more lipophilic, will that make the PC go higher or lower?
higher
What is the difference between intrinsic and apparent partition coefficients?
Apparent coefficient looks at sum of all species (ionized & unionized) in aqueous phase (denominator); Intrinsic only looks at concentration of drug in aqueous phase
Does log P represent the log of PCo or PC’?
PCo
Which partition coefficient measurement would you use for in vivo assessments?
Apparent PC (need to assess drug at various pHs)
As pH increases, what happens to the apparent partition coefficient?
decreases for base, increases for acid
At a pH lower than pKa, would the PC’ of a weak base be higher or lower than its 1/2 Pco?
lower (in weak bases, increased H+ ionizes the base causing more drug particles to increase in aqueous phase -> increases denominator -> decreases total number)
To calculate pKA, how would you use the partition coefficient?
Pco/2 = point to determine pKa
Is partitioning an appropriate method with surfactants?
No. Surfactants will tend to reside at the oil/water interface & may form micelles
What does the pH-partition hypothesis state?
Absorption of drugs dependent upon fraction of non-dissociated drug at intestinal pH
How is drug absorption related to the partition coefficient?
Higher PC = higher absorption
How do antacids affect the partition coefficient in relation to an acidic drug?
Antacids raise pH -> increases drug ionization -> decreases PC -> decreases acidic drug absorption
What are the benefits of developing prodrugs?
change solubility, permeability, stability
What is one way you could create a prodrug?
Convert a carboxylic acid functional group to an ester
Differentiate between log P and log D values?
A log P value is the log of the intrinsic partition coefficient, whereas a log D is the log of the apparent partition coefficient
