ICT practice questions

Question 1

A buffering agent in oral liquid pharmaceutical solutions is also known as which ONE of the following?

a. Sweetening agent
b. Thickening agent
c. pH modifier
d. Wetting agent
e. Chelating agent

Answer 1

C. pH modifier

Question 2

Which ONE of the following is NOT a mechanism for the separation of a physically unstable suspension of magnesium hydroxide in water?
a. Flocculation
b. Aggregation
c. Ostwald ripening
d. Hydrolysis
e. Sedimentation

Answer 2

= D

Question 3

Only ONE of the following statements is CORRECT. Please select the CORRECT statement.
The pH of a solution containing 4 g of HCl (molar mass: 36.458 g/mol) in 100 mL of water is equal to which of the following (pH value rounded up):
a. pH= 0.041
b. pH= -0.041
c. pH= 3
d. pH= -3
e. None of the above.

Answer 3

=B

Question 4

Only ONE of the following statements regarding an isothermal process is CORRECT. Please select the CORRECT statement.
a. Any heat transferred to the system is used to increase the system temperature.
b. Internal energy changes only for work done or received by the system.
c. No work is done on or by the system.
d. Any heat transferred to the system is used to do work.
e. q is equal to zero.

Answer 4

=D

Question 5

Which ONE of the following statements is INCORRECT?
a. In a first-order reaction the plot of the natural log (ln) of the reactant concentration against time is a straight line.
b. In a pseudo-first order reaction, the concentration of one of the reactants is considered constant.
c. The rate of a second-order reaction is independent of the reactant concentration.
d. The half-life of the reactant in a zero-order reaction is proportional to the initial concentration.
e. In a complex reaction the overall rate equation cannot be directly written from the stoichiometric equation.

Answer 5

=C

Question 6

Which ONE of the following Phase I and Phase II transformations CANNOT happen to ibuprofen?
a. Conjugation with amino acids.
b. Conjugation with glucuronic acid.
c. Oxidation of exposed alkyl group.
d. Oxidation of activated carbon centres next to sp and sp2 carbons.
e. Oxidative deamination

Answer 6

=E

Question 7

Dextran is a branched polymer of α-d-glucose. Which ONE of the following is not a recognised use for this polymer?
a. Blood plasma expander
b. Anticoagulant
c. Ingredient in the enteric coating of tablets
d. Protectant in freeze drying
e. Bulking agent in freeze drying

Answer 7

=C

Question 8

The Noyes-Whitney equation is used to describe which ONE of the following processes?

a. Settling of solid particles in a suspension.
b. Dissolution of drugs present as solid particles.
c. Flow of a viscous liquid with shear stress.
d. Ionisation of a weak acid with respect to pH and pKa.
e. Change in the reaction rate constant against temperature.

Answer 8

=B

Question 9

A weakly acidic drug is known to have a pKa of 5.3. The aqueous solubility of the free acid is found to be 2.9 x 10-4 mol L-1. What is the minimum pH at which an aqueous solution containing 9.8 x 10-3 mol L-1 of the drug can be prepared?
a. 5.30
b. 2.90
c. 3.78
d. 6.82
e. 9.89

Answer 9

=D

Question 10

Only ONE of the following statements regarding the impact of temperature on a process is CORRECT. Please select the CORRECT statement.
a. Viscosity increases with increasing temperature.
b. Solubility of a gas generally decreases with increasing temperature.
c. Saturation solubility of a solid decreases as temperature increase (assuming dissolution is an endothermic process).
d. Reaction rate constant increases with decreasing temperature (assuming an endothermic reaction).
e. Reaction rate constant decreases with increasing temperature (assuming an endothermic reaction).

Answer 10

=B

Question 11

Which ONE of the options below would be the most appropriate way of expressing the concentration of a solid active ingredient in a solution to be applied externally?
a) mg per mL
b) mg per 5 mL
c) Parts
d) % v/v
e) % w/v

Answer 11

=E

Question 12

Provide one characteristic which would enable you to distinguish a colloidal drug formulation from a solution. (1 mark)

Answer 12

Tyndall effect – light beam path through colloid is visible due to light scatter (1 mark) - also accept dialysis or electrophoresis as answers.

Question 13

Give an example of one pharmaceutical suspension and one colloidal formulation. Choose two properties and briefly describe the differences between them. (4 marks)

Answer 13

Pharmaceutical suspension: paracetamol suspension, ibuprofen suspension, amoxicillin suspension, ciprofloxacin suspension, chloramphenicol palmitate suspension, phenytoin suspension, cholera vaccine etc. (1 mark)
Colloidal formulation: any creams or gels, Covid-19 vaccine etc. (1 mark)
Any two properties from below (2 marks)

Property:
Particle Size
1 nm to 1 µm (10-9 m to 10-6 m)
1 µm to 1 mm (10-6 m to 10-3 m)

Appearance
Cloudy, but uniform and homogeneous
Cloudy, heterogeneous, at least two substances visible

Separation
None Particles will eventually settle out
Filtration
Passes through filter Particles filtered out

Effect of light
Scatters light
Variable – generally cannot pass through

Visibility
Particles visible under microscope
Particles visible to naked eye

Question 14

Briefly describe the major types of non-bonding intermolecular interactions. (5 marks)

Answer 14

There are three types of non-bonding intermolecular interactions: dipole-dipole interactions, van der Waals forces and hydrogen bonding (1 mark if all the three are mentioned).

Dipole-dipole interactions are interactions between the positive end of one dipole and the negative end of another dipole (1 mark). Dipole–dipole interactions arise when electrons are not equally shared in the covalent bonds because of the difference in electronegativity. (0.5 marks)
van der Waals forces are relatively weak forces of attraction that exist between non-polar molecules (1 mark). These forces are distance-dependent interactions between atoms or molecules (0.5 marks).
Hydrogen bonding is the attractive force between the hydrogen attached to an electronegative atom of one molecule (0.5 marks) and an electronegative atom of the same or a different molecule (0.5 marks).

Question 15

Briefly explain why ethanol is often employed as a cosolvent in pharmaceutical solutions. (5 marks)

Answer 15

Cosolvents are added to aqueous formulations with the aim of improving the solubility of the active ingredient (1 mark).
Ethanol is a semi-polar solvent (1 mark) which means that it is typically able to dissolve polar and non-polar substances (1 mark).
The addition of ethanol as a cosolvent may mean that a pharmaceutical solution can be prepared when previously only an aqueous suspension was possible (1 mark). An example would be the use of ethanol in the production of paracetamol elixir – a solution (1 mark).

Question 16

A prescription calls for the extemporaneous dispensing of 100 mL of “Primidone oral solution”. Based upon your knowledge of the bench-scale manufacture of medicines, suggest an appropriate method that could be followed to prepare primidone suspension according to the formula below. (5marks)
Formula:
* Primidone 250 mg tablets x 20
* Xanthan gum 0.4% to 100 mL

Answer 16

1. Crush/grind around 10 bendroflumethiazide tablets in a pestle and mortar into a fine powder. (1 mark)
2. Add a small amount of Xanthan gum 0.4% to the mortar and mix well with the pestle. (1 mark)
3. • Transfer the suspension to a tared (100 mL) bottle and then rinse the mortar with further portions of Xanthan gum solution (and add to the bottle). (2 marks)
4. Make up to the final volume (shown by the tare mark) with Xanthan gum solution. (1 mark)
5. Shake well. (1 mark)

Question 17

Briefly describe the design and operation of a rotating viscometer and state the type of liquids with which it can be used. (5 marks)

Answer 17

A cylinder with a cone-shaped end (1 mark)
is rotated at a constant speed (1 mark)
in a second cylinder containing the liquid under investigation (1 mark).
The drag on the cone-shaped cylinder is measured and equated to the viscosity (1 mark).
Can be used for determining the viscosity of Newtonian and Non-Newtonian liquids (2 marks).

Question 18

A patient has accidentally overdosed on a weakly basic drug. As part of their treatment, it is decided to give the patient ammonium chloride (a urine acidifier). Explain how this course of action may help the patient. (5 marks)

Answer 18

Renal excretion of drugs can be controlled by altering the pH of the urine with salt solutions (1 mark)
By acidifying the urine a weakly basic drug is more likely to be ionised in the urine (2 marks). This will lead to a decrease in re-absorption (1 mark) and an increase in excretion of the drug (1 mark). Increased excretion of the drug will therefore lower the plasma levels of the drug (1 mark).

Question 19

Briefly explain the DLVO theory of colloidal stability. (5 marks)
0.5 marks for mentioning each point below and 0.5 marks for describing each term.

Answer 19

1. Electrostatic repulsive forces (VR)
2. Van der Waals forces of attraction (VA)
3. Primary minimum
4. Primary maximum
5. Secondary minimum
6. Arises from the interaction of ELECTRICAL DOUBLE LAYERS surrounding pairs of particles
10. At large distances of separation, particles experience a minimal attraction. Forces of attraction are weak (flocculation) not coalescence i.e can redisperse upon shaking.

Question 20

If a reaction is said to be a Zero order reaction, what will the rate of the reaction be?
. 0
b. 1
c. The value of k
d. Depends on the concentration of the reactants
e. None of the above

Answer 20

c

Question 21

A mother read about the news of a bad batch of cough syrup containing dextromethorphan that had
led to the hospitalisation and death of at least 16 children in India. She is about to buy a common
cough syrup OTC for her child, and she would like to find out from you a bit more about what
common excipients are in cough syrups? List at least FIVE excipients and state their function. (5
marks)

Answer 21

Solvent: Purified water
Co-solvent: Ethanol, Glycerol
Viscosity-increasing agent: Carboxymethylcellulose sodium, hydroxymethcylcellulose
 Antimicrobial preservative: Sodium benzoate, benzalkonium chloride Chelating/complexing agent: Disodium edetate/ EDTA
Sweetening agent: Maltitol, Sorbitol, Sodium cyclamate, Acesulfame, sucrose, fructose potassium
 Antioxidant: Citric acid, ascorbic acid
 Colourant: Amaranth, Caramel
 Flavouring agent: Levomenthol, Cherry/Grenadine flavour

Question 22

The HPV vaccine and the Johnson & Johnson/Janssen COVID-19 vaccine contain polysorbate 80 as a
stabiliser.
a. Explain why Polysorbate 80 is used in this injectable formulation. (3 marks)
b. Explain why this formulation needs to be stored in the fridge and in the original carton. (2
marks)

Answer 22

a. Non-ionic surfactant (1 mark)
Contributes to steric stabilisation/entropic effects (1 mark)
The hydrophilic polymeric groups (polyoxyethylene groups) overlap which is thermodynamically unfavourable (a loss of entropy), causing them to separate (1 mark)

b. Store in the fridge to reduce rate of antibody degradation and microbial growth (1 mark)
Store in the original carton to protect from light (1 mark)

Question 23

Describe the approaches you can take, according to the DLVO theory, to stabilise the emulsion as
shown below to prevent the drug particles from aggregation. (5 mark)

Answer 23

Van der Waals attraction causes drug particles to aggregate (1 mark)
At primary minimum, the particles coagulate irreversibly (1 mark)
The height of this repulsive force (Vmax) at primary maximum determines the stability of the system
(1 mark)
The height can be increased by electrostatic stabilisation using different surfactants and electrolyte
concentration (1 mark)

Question 24

Give a brief explanation as to how pH-partition theory suggests that the weak base chlordiazepoxide
(pKa 4.8) will be better absorbed from the small intestines than the stomach. (5 marks)

Answer 24

• Explanation of pH-partition theory (1 mark)
• pH changes along the GI tract: in the stomach, the pH can be as low as 1.5, but it rises to pH 6 or higher in the small intestines (1 mark)
• Chlordiazepoxide is a weak base so it is more likely to be ionised at low pH values (at pH 2.8 it will be
  99% ionised). (2 marks)
  In the small intestines, the pH of >6 will mean that chlordiazepoxide is mostly (>90%) unionised and
  therefore uncharged (1 mark) it is therefore more likely to cross the lipophilic gastro-intestinal
  epithelium (1 mark)

Note: marks NOT awarded for information about small intestine surface area, long residence times
etc. The question asked for “how pH-partition theory suggests…

Question 25

Explain why the polysaccharide cellulose is insoluble in water. How might we be able to alter its molecular structure to develop polymers which have improved aqueous solubility and more pharmaceutical uses? (5 marks)

Answer 25

Cellulose is a long straight-chain polymer made up of many beta-glucose monomers. Cellulose is insoluble as it is made up of many H bonds and this holds the microfibrils together strongly, this means that the bonds cannot be broken down when added to water. To inc solubility, cellulose can be converted to HPMC or HEC which bother have a higher aqueous solubility than that of cellulose. (2) * mention methylcellulose, structure of cellulose (OH groups), MS: Cellulose has three hydroxyl groups on each monomer (1 mark) and this leads to extensive intermolecular attractions – similar to the covalent crosslinks (1 mark) Because the cellulose polymer molecules are held together strongly, they cannot be separated (or “pulled apart”) which would allow them to enter solution (1 mark) In methylcellulose about a third of the hydroxyl groups have been etherified – methyl cellulose is slowly soluble in cold water (1 mark) HPMC is another cellulose ether derivative with an even better aqueous solubility (1 mark) Some uses for methylcellulose /HPMC listed (1 mark)

Question 26

Explain why the bioavailability of a drug administered orally is usually lower than the same drug administered via the intravenous route. (5 marks)

Answer 26

IV route= 100% bioavailability. This is because drug is administered through the skeletal muscle and directly into bloodstream. Whereas oral has several barriers before being absorbed through the phospholipid bilayer and then into the bloodstream. It also does not need to surpass digestion in the stomach and the first-pass metabolism in the liver, where some of the drug is metabolised and so does not enter the blood. (3 marks)- need to mention solubility, molecular weight or log P (2 more marks) MS: When a drug is administered via the oral route there are several factors which can reduce the bioavailability, these could include: 1. Drug broken down by stomach acid or enzymes (1 mark) 2. Non-ideal physicochemical properties, e.g. low aqueous solubility (1 mark), log P too high/low (1 mark), molecular weight too high (1 mark) 3. First pass metabolism – this is when the drug is successfully absorbed but then a proportion of it is metabolised on its “first pass” through the liver (2 marks

Question 27

What type of surfactant is polyoxyethylene (10) oleyl ether? Non ionic Cationic Anionic Zwitterionic Co-surfactant

Answer 27

Non-ionic (zwitterionic has 2 charges, cationic= positive charge, anionic= neg charge)

Question 28

One-third of all drugs used in cancer therapy are hydrophobic. Which of the following is NOT a reason for using drugs in a micellar form? a. Micelles can be used to deliver water-insoluble drugs in their hydrophobic core b. Micelles provide favourable changes in drug biodistribution for hydrophobic drugs c. Micelles improve the permeability of drugs across the physiological barriers d. Drug in a micellar form is protected from possible inactivation under the effect of biological surrounding e. Drug in a micellar form provokes undesirable side effects on non-target organs and tissues

Answer 28

=E (opposite is correct)

Question 29

Flocculation of a suspension dosage form can be controlled by.. a. Electrolytes to reduce electrical forces of repulsion b. Surfactants to form liquid bridges c. Polymers to adjust interparticulate interactions d. All the above e. None of the above

Answer 29

=D

Question 30

According to the Stokes-Einstein equation, an/a __________ in viscosity of the solvent and an/a __________ in radius of the solute molecule lead to greater diffusion coefficient. a. Increase; increase b. Decrease; decrease c. Increase; decrease d. Decrease; increase e. Increase; fixed value

Answer 30

=B

Question 31

The process of disappearance of small particles or droplets by dissolution and deposition on the larger particles or droplets is known as a. Flocculation b. Sedimentation c. Creaming d. Caking e. Ostwald ripening

Answer 31

= E

Question 32

Which of the following is NOT an approach to enhance the solubility of a non-ionic drug in oral solution? a. Addition of glycerol b. Addition of ethanol c. Addition of propylene glycol d. Addition of polyethylene glycol e. Addition of benzoic acid

Answer 32

=E (all are co-solvents except benzoic acid which is a preservative)

Question 33

A drug has the initial concentration of 5.0 x 10-3 g cm-3 in aqueous solution. After 24 months, the concentration drops to 3.48 x 10-3 g cm-3. This degradation process is known to follow first-order kinetics. Which one of the following is the rate constant for this reaction? a. -1.5 x 10-2 month-1 b. 1.5 x 10-2 month-1 c. -3.0 x 10-2 month-1 d. 3.0 x 10-2 month-1 e. 3.2 x 10-2 month-1

Answer 33

ln (A)t= ln[A]0-kt

Question 34

Arrhenius equation represents graphically the variation between the __________ and temperature. a. Rate of reaction b. Frequency factor c. Rate constant d. Activation energy e. Molar gas constant

Answer 34

C= Rate constant

Question 35

Creams and ointments containing the same active pharmaceutical ingredient are available. Discuss their differences in terms of their constituents, viscosity, spreadability, greasiness and duration of action. (5 marks)

Answer 35

Constituents: Cream- more watery, less hydrocarbons, waxes, polyols Ointment- less water, more hydrocarbons, waxes, polyols Viscosity Cream- thin, less viscous Ointment- thick, more viscous Spreadability: Cream- More spreadable Ointment- Less spreadable Greasiness Cream- Less greasy Ointment- Greasier Duration of action Cream- Lasts for a shorter duration on skin Ointment- Lasts longer on skin

Question 36

Briefly explain the DLVO theory of colloidal stability. (5 marks)

Answer 36

Graph: Repulsion on Top and Attraction at bottom, Distance on Y axis Drawn from R to L: distance is closes, then they have repulsion then goes down to fully attracted (were coagulation happens) Electrostatic repulsive forces Van der waals forces cause attraction. Primary minimum Primary maximum Secondary minimum

Question 37

A patient has accidentally overdosed on a weakly basic drug. As part of their treatment, it is decided to give the patient ammonium chloride (a urine acidifier). Explain how this course of action may help the patient. (5 marks)

Answer 37

Basic drugs ionise at a lower pH. So decreasing pH will mean drug is more likely to ionise in urine, so will be excreted and not reabsorbed.

Question 38

The rate constant k for the decomposition of a compound in solution is k=2.5 x 10-5 mol·dm-3 s-1. If the initial concertation of the compound is 0.15 mol·dm-3. What will the half-life of the compound be? a. 300 seconds b. 500 minutes c. 50 minutes d. 30000 seconds e. 0.5 hours

Answer 38

= C t1/2 = initial conc/ rate (k) 0.15/2.5 x10-5 = 3000s= 50 minutes

Question 39

A compound is known to contain only one oxygen atom and an unknown number of carbon and hydrogen atoms. If the molecular ion has a m/z value of 100, what is the molecular formula of the compound? a. C6H12O b. C7H16 c. C5H8O2 d. C5H12O e. C4H36O

Answer 39

= A

Question 40

What are the aromatic peaks in the IR spectrum?

Answer 40

3000= C-H stretch indicating aromatic ring 1620= C=C stretching of an aromatic

Question 41

UV/Vis spectroscopy can be used to determine the pKa of a compound if either the acidic form or basic form of the compound absorbs UV or visible light. a) According to the Henderson-Hasselbalch equation, for a weak acid, when will the pH of a solution be equal to the pKa of the compound? (1 mark) b) The absorbance of a solution of weak acid was measured under the same conditions at a series of pH values, as shown in the table below. The conjugate base of the acid is the only species in the solution that absorbs UV light at the wavelength used. Estimate the pKa of the acid from the data obtained. (4 marks)

Answer 41

a) When the concentration of the compound in the acidic form is the same as the concentration of the compound in the basic form. (1 mark) b) Overall answer is: pKa = 4.0 (4 marks if correct answer given) - Partial credit for each of the following (up to a maximum of 4 marks): - Noting absorbance does not increase with pH beyond 1.80 (1 mark) - This means the compound in the basic form when absorbance is 1.80 (1 mark) - Therefore when absorbance is half of 1.80 (0.90), half the compound is in acidic form and half in basic form therefore [acidic] = [basic] (1 mark) - Absorbance is 0.90 at pH 4.0, therefore pKa = 4.0 (1 mark)

Question 42

The presence, or absence, of an absorption band in IR spectroscopy is a good method for determining which functional groups are present in a molecule. a) Assuming the force constants are the same, which occurs at a higher wavenumber: a C – O stretch or a C – Cl stretch? Why? (2 marks) b) How can IR spectroscopy be used to distinguish between an aldehyde and a ketone? (1 mark) c) An oxygen containing compound shows an absorption band at ≈ 1700 cm-1 and no absorption bands at ≈ 3300 cm-1, ≈ 2700 cm-1, or ≈ 1100 cm-1. What class of compound is it? (2 marks)

Answer 42

a. C-O, the vibration of lighter atoms occur at larger wavelengths b. An aldehyde would show absorption bands at 2820cm-1 and 2720cm-1 whereas a ketone would not have these absorption bands c. Ketone Carbonyl group at 1700cm-1 Not at 3300cm-1 so not COOH No band at 2700cm-1 so not an aldehyde No band at 1100cm-1 so not an ester or an amide

Question 43

Briefly describe the design and operation of a rotating viscometer and state the type of liquids with which it can be used. (5 marks)

Answer 43

Marking scheme: A cylinder with a cone-shaped end (1 mark) is rotated at a constant speed (1 mark) in a second cylinder containing the liquid under investigation (1 mark). The drag on the cone-shaped cylinder is measured and equated to the viscosity (1 mark). Can be used for determining the viscosity of Newtonian and Non-Newtonian liquids (2 marks). Marks awarded up to 5 marks. Marks may be awarded for other relevant information in lieu the points above.

Question 44

What is Flocculation? Sedimentation? Creaming? Caking? Ostwald ripening? Aggregation? Coagulation?

Answer 44

Flocculation= Aggregates have an open structure with particles a small distance apart, attracted by weak forces to form flocs/flakes vb Ostwald ripening= The process of disappearance of small particles or droplets by dissolution and deposition on the larger particles or droplet Aggregation= Particles in groups Coagulation= Closely aggregated and difficult to redisperse

Question 45

A patient receives a 50 mg intravenous bolus dose of Drug A and the plasma levels of the drug are monitored. After a washout period, the same patient is given the same drug as a 100 mg oral dose. What is the bioavailability (F) of Drug A if the AUCIV is 150 h μg L-1 and the AUCoral is 240 h μg L-1? a. 0.80 b. 0.90 c. 0.62 d. 3.20 e. 50%

Answer 45

Formula on DS = A

Question 46

Tamoxifen (pKa 8.9) is a weakly basic drug used to treat breast cancer in both women and men. What proportion of the drug is ionised at pH 5.5 a. 90.91% b. 99.96% c. 99.01% d. 50% e. 10%

Answer 46

= B pH= 7.9 would be 90% ionised pH=6.9= 99% ionised pH=5.9 = More than 99.01%

Question 47

Systemic delivery is NOT the intention when a drug is administered by which ONE of the following delivery routes? a. Oral route b. Sublingual route c. Topical route d. Intravenous route e. Buccal route

Answer 47

C= Topical is for local delivery

Question 48

The drug hydrocortisone has a molecular weight of 362.5. Which ONE of the following denotes the greatest concentration of hydrocortisone? a. 320 mg / L b. 0.5 mmol / L c. 0.1 % w/v d. 0.5 umol / mL e. 320 ng / mL

Answer 48

= C

Question 49

A new eye-drop formulation is to be sterilised by autoclaving in the final container at 121 °C. Which ONE of the following materials would NOT be suitable primary packaging? a. High-density polyethylene (HDPE) b. Polypropylene (PP) c. Type I glass d. Type II glass e. Polyethylene terephthalate

Answer 49

= E

Question 50

Cellulose acetate phthalate (CAP) is a pH-sensitive polymer with a pKa of 5.5. The structure of CAP is shown below. Which ONE of the following statements regarding this polymer is incorrect? a. It is a derivative of the naturally occurring polymer cellulose. b. CAP would potentially be suitable to use in the enteric coating of tablets. c. The letter “n” denotes the polymerisation number. d. CAP would be a suitable polymer material to be used in primary packaging. e. CAP is a homopolymer

Answer 50

= D

Question 51

Which ONE of the following formulations is most likely to exhibit “shear thinning”? a. Syrup BP b. A suspension stabilised with methylcellulose c. Purified Water BP d. Sodium Bicarbonate 8.4% w/v Solution for Injection e. Sodium Chloride Oral Solution

Answer 51

= B

Question 52

Which ONE of the following strategies is LEAST likely to increase the dissolution rate of a poorly soluble drug? (You can assume that the dissolution of the drug is an endothermic process). a. Reduce the particle size of the drug. b. Increase the temperature. c. Addition of a cosolvent. d. Use a more soluble salt of the drug. e. Use a crystalline form of the drug instead of an amorphous form

Answer 52

=E

Question 53

How do you calculate DBE?

Answer 53

- Counts rings, count double bonds (1) and triple bonds (2) - OR 2C + 2 + N - H- Hal / 2

Question 54

What is the ionisation of the acid HA in water?

Answer 54

K H20 + HA = H3O+ A-

Question 55

How to calculate pI from a polypeptide? What is pI?

Answer 55

Isoelectric point pI : pH at which concentration of the zwitterion (double charged form of an amino acid) is maximum) zwitterion is neutral. If pH > pKa (FG does not have the H) COOH will be COO- NH2 will be NH2 If pH < pKa (FG has the H) COOH will be COOH NH2 will be NH3+ pK1 and pK2 are the values BEFORE and AFTER the species with net charge 0

Question 56

Briefly describe the Virtual Screening method (HTVS) adopted in the Hit discovery process. Make sure you mention/briefly describe HTVS advantages and all the different types of HTVS (5 marks)

Answer 56

- Advantages: faster, easier, cheaper, and safer [0.5 marks] - Only positive virtual hit are tested [0.5 marks]. - 3 types of virtual screening: structure-based virtual screening, ligand-based virtual screening and a mixed virtual screening. [1 mark]. - Structure-based virtual screening: based on the 3D structure of the target receptor or enzyme [0.5 mark]. The software takes each virtual compound and explore its possible conformation, so docking pose, within the binding site [0.5 marks] - If the crystal structure of a target is not available, the 3D structure of any know active molecule or natural substrate of that target can be used to perform a ligand based virtual screening [0.5 marks]. The software screens libraries of virtual compounds that can match the 3D shape and the functional groups disposition of the query molecule [0.5 marks]. - Virtual compound libraries can also be screened for their matching of a pharmacophoric query, in a mixed virtual screening [0.5 marks]. All the possible conformations of the screened molecules are explored and evaluatedfor their fitting to a given pharmacophoric model [0.5 marks]. Marks may be aw arded for other relevant information in lieu of these points.

Question 57

What is the Ka value for strong and weak acids?

Answer 57

STRONG = Large value for Ka and produce a high H3O+ concentration WEAK= Small value for Ka and produce a low H3O+ conc

Question 58

What does the smaller value of pKa mean?

Answer 58

The stronger the acid. Large Ka and small pKa

Question 59

What does the larger value of pKa mean?

Answer 59

The weaker the acid. Small Ka and large pKa

Question 60

ΔG = ΔH − TΔS How does the reaction proceed if: ΔG is negative ΔG zero ΔG is positive

Answer 60

Neg= Reaction proceeds spontaneously in the forward direction (irreversible) Zero= Reaction is at equilibrium, can proceed in either directions Pos=Reaction is non-spontaneous and will not proceed in the fwd direction unless coupled with an energetically favourable reaction.

Question 61

Reaction orders: What is the half-life equation for First, second, Third order?

Answer 61

zero= 0.5 [A]0/k' first= 0.693/k second= 1/[A]0k

Question 62

Examples of excipients:

Question 63

How to assign R and S:

Answer 63

1. Assign priority to highest atomic number (this is C1) and follow on 2. Double or triple bonds are assigned priorities as if both atoms were duplicated or tripled 3) H is last priority usually.. if facing away from you (dashed) keep it the same. If its towards you (wedge) then flip the sign

Question 64

What are the stretching frequencies for: OH? (alc and acid) C-O (alc and ethers) N-H (Amine)

Answer 64

O-H Alcohol O-H = 3300cm-1 Acid= 3000cm-1 C-O Alcohols and ethers 1000-1200cm-1 N-H Amine 3300, broad

Question 65

Ketones and Aldehydes: What are the stretching frequencies for: C=O C-H

Answer 65

C=O is 1700cm-1 Aldehyde= 1725cm-1 Ketone= 1710cm-1 C-H= 2700 and 2800cm-1 So aldehyde has 1 and ketone has 3

Question 66

Carbon and Hydrogen NMR Where would you find the aromatic peaks?

Answer 66

RHS and aliphatic compounds on LHS

Question 67

Calculation of a sample concentration using UV: What equation is used? [On DS]

Answer 67

Beer lambert equation- plot should be straight line A= ECL where A is absorbance, E is molar absorption coefficient, C is molar concentration, l is optical path length

Question 68

What is the N+1 rule?

Answer 68

If the signal is split by N neighbouring equivalent protons, it will be split into N+1 peaks

Question 69

What are the important 1H NMR stretching freq you need to know?

Answer 69

COOH= 10-12ppm COH= 9-10ppm Aromatic= 6-8ppm HC-R= 0.5-2ppm OH and NH can be anywhere and not split peaks

Question 70

What are the important 13C NMR stretching freq you need to know?

Answer 70

C-C = 0-50ppm C-O = 50-90ppm C=O - 160-220ppm Aromatic or C=C -110-160ppm