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Ceutics Final > Porter - Buffers / Complexation / Diffusion > Flashcards

Porter - Buffers / Complexation / Diffusion Flashcards

1
Q

Buffer Definition

A
  • Compounds or mixtures of compounds that
    • Resist changes in pH of the solution that they are dissolved
      • upon additions of small amounts of acid or base
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2
Q

Buffer Action

A

The resistance to change in pH of a buffer

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3
Q

Blood Buffer

pH range

A

7.4 pH

maintained by primary buffers in plasma

& secondary buffers in RBC’s

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4
Q

Purposes of Buffers in Pharmacy

A

Improve Stability

AVOID irritation

Achieve optimum physiological effect

Mimic bio systems

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5
Q

Buffer Composition

A

Weak Acid + Conj Base/salt

or vice versa

  • When dissolved in water it resists large changes in pH
    • that would other wise occur w/ addition of small amounts of acid or base
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6
Q

Debey-Huckel Expression

A

Used to approximate activity coefficient of a solution

used for solution where IONIC STRENGTH = U is modest

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7
Q

Factors Influencing pH

of a buffer solution

A
  • Increase Ionic Strength = U
    • ​adding neutral salts to buffer
  • Decrease Ionic Strength = U
    • ​adding WATER
  • ​Temperature
    • can increase or decrease
    • EXPERIMENTALLY DETERMINED
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8
Q

Buffer Capacity

weird B

A

The MAGNITUDE

of the resistance of a buffer to pH changes

aka buffer efficiency / buffer value / buffer index

Increase buffer capacity by

Increasing concentration of buffer components

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9
Q

Maximum Buffer Capacity

A

Occurs when

pH = pKa

or

[H3O+] = Ka

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10
Q

Buffer Capacity Range

A

Buffer solution is useful at a range of

pKa +1 or -1 ph units

generally do not exceed 0.2

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11
Q

Universal Buffer

A

A mixture of weak acids whose

pkA value DO NOT DIFFER by more than ~2pH units

–> buffer region overlap

WIDE pH range

ex. citric acid / boric acid / DE acid

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12
Q

Pharmaceutical Buffers

A
  • Isotonic buffers:
    • ​Phosphate Buffered Saline
    • Sorensen
    • Palitzsch/Hind & Goyan
    • Clark-Lubs Mixtures
      • ​KHphthalate
  • ​Gifford = not isotonic
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13
Q

Considerations for PREPARING buffers

A
  • Select a weak acid w/ pkA approx EQUAL to desired pH
  • 0.01 < Buffer capacity <0.1
    • ​LOWER THE BETTER
      • ​less irritation
      • more safe for parenteral solutions
  • Availability & cost of chemicals
  • Stability of drugs and buffers
  • No Adverse Toxic Effects
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14
Q

Interactions in Solutes

Cation-Anion Interactions

A
  • Drugs can interact with other ions
    • –> inc/decrease solubility
    • change colligative propertios (osmotic)
    • change chemical degradation rate
  • pH effects
  • LARGE anions/cations -
    • -> tend to form ion-pairs
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15
Q

Interactions in Solutes

Complexation

A
  • Originally restricted to lewis acid-base reactions
    • ​between 2+ chemical constituents
    • Substrate + Ligand = complex
  • ​Expanded to cover complexes held together by weaker forces
    • Van Der Waals Disperson
    • Dipole / Dipole Interactions
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16
Q

Interactions in Solutes

Chelation

A
  • Special type of coordination complex
    • Ligand = MULTIDENTATE
      • contains 2+ functional groups
      • each can interact with substrate
  • EDTA
    • Completely surrounds a metal ion in a cage stucture
17
Q

Interactions in Solutes

EDTA

A
  • Used widely in pharmacy to Sequester Metal Ions
    • ​copper and iron
  • Can complex calcium ions
    • –> prevent deposition of calcium salts
      • that may precipitate out of solution
    • used as a Antigoagulant with Gla
18
Q

Interactions in Solutes

y=Carboxyglutamatic Acid

(Gla)

A
  • Structurally modified amino acid
    • important component of enzymes involved in blood coagulation
    • chelate calcium ions
      • = cofacors for coagulation enzymes
  • Vitamin K
    • ​essential for biosynthesis of Gla
19
Q

Interactions in Solutes

Polyions

A
  • Can interact w/ other drugs to form Poorly soluble complexes
  • _​​_Ex. Heparin
    • form insoluble complexes w/ many large weakly basic drugs
    • –> incompatabilities (precipitation)
      • ​w/ other drugs that are IV administered
20
Q

Interactions in Solutes

Ion Exchange Polymers

A
  • Used in Delivery systems for drugs to:
    • ​Reduce volatility
    • Impart stability
    • Mask Taste
    • Improve Bioavailability
      • ​by altering physicochemmical properties of drugs
  • Ex. Carbopol / polystyrene beads
21
Q

Hydrophobic Complexation

4 categories

A
  • Pi-Pi Stacking
  • Channel Lattice Complexes
    • ​Bile salts / urea / bentonite
  • Clathrates
    • ​Hydroquinone cage –> traps molecules <4Angs
  • Host-Guest Inclusion Complexes
    • ​Cyclodextrins
22
Q

Interactions in Solutes

Cyclodextrins

A

Cyclic polymers of glucose w/ 6-8 glucose monomers

  • Exterior = -OH groups
    • water soluble
  • Interior = HydroPHOBIC
    • ​water is easily displaced by hydrophobic molecules
      • = DRUGS
23
Q

Surface Sorption

A
  • Sorption of drugs to surfaces
    • facilitated by ionic / polar interactions
      • ​glass / ressin
    • or hydrophobic interactions
      • teflon
  • Ex. Activated Charcoal
    • ​adsorbs many substances
      • specifically w/ low water solubility
        • like toxic alkaloids
24
Q

Complexation Model

A
  • Identical to models that describe ionization of acids or bases
    • ​BUT –> in terms of ASSOCIATION CONSTANTS
      • ​not dissociation constants
25
Q

Diffusion

A
  • Process by which concentration of sulute is
    • ​Reduced by spontaneous flow
    • High conc –> low concentration in solution
  • ENTROPY OF SYSTEM INCREASES
26
Q

Fick’s First Law

A

Flow of Material

vs

Concentration Gradient

  • Flux & Diffusivity
  • Displacement (inverse)
27
Q

Diffusivity

(D)

Stokes Einstein Equation

A
  • INVERSELY PROPORTIONAL TO
    • ​Molecular Size
      • & depends on molecular shape
    • Radius
    • Viscosity
  • ​Directely proportional to temperature
28
Q

Factors Affecting Diffusivity

A

We use these properties to prolong drug action

  • Slow Diffusion by:
    • ​Increasing viscosity
    • Increasing Radius of particle (or both)
  • ​Increase Diffusion by:
    • ​Reducing particle size
      • coarse particles diffuse slowly
    • Increase Temperature
29
Q
A

Ceutics Final (5 decks)

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