Untitled Quiz

Pharmacognosy and Phytochemistry

• This presentation covers extraction and identification of medicinal plants.
• The presenter is Dr. Farah Al-Mamoori.

Phytochemical Study Points

• Selection of promising plant materials
• Proper collection of selected plants
• Authentication of plant material
• Drying of plant materials
• Grinding of dried plants
• Garbling of dried plants
• Packing, storage and preservation
• Extraction and fractionation of constituents
• Methods of separation and purification
• Methods of identification of isolated compounds (e.g. UV, IR, MS, 1H-NMR and 13C-NMR).

Plant Selection

• Plant selection for drug discovery uses various approaches:
  • Random selection
  • Ethnopharmacology
  • Chemotaxonomy
  • Geographical
  • Computer-based selection
  • Literature information selection

Plant Authentication

• Herb authentication ensures correct plant species and parts are used.
• Authentication can be confirmed by:
  • Establishing identity by taxonomic experts.
  • Comparing collected plant with a voucher specimen (herbarium sheet).
• This presentation has previously discussed points 4-7:
  • Drying of plant materials
  • Grinding of dried plants
  • Garbling of dried plants
  • Packing, storage and preservation

Extraction

• Extraction separates medicinal components of plants from inactive elements using selective solvents.
• Solvents used for extraction include water, ethanol, methanol, chloroform, petroleum ether, acetone, etc.
• Selecting a suitable solvent ensures extraction of active chemical constituents.
• Extraction methods include liquid-liquid and solid-liquid techniques.
• Mass transfer is critical, involving the movement of soluble material from the solid plant to a liquid.

Solvent Extraction Approach

• The extraction method's selection should mirror traditional procedures—e.g, if a culture uses a specific procedure like a water extract, adapt that method to the laboratory.
• Incorrect extraction (e.g., strongly heating biomass with a solvent) can degrade compounds and reduce biological activity.

Solid-Liquid Extraction Mechanism

• The solvent mixes with the plant material.
• The solvent diffuses onto the solid surface.
• The solvent penetrates into the plant particles.
• The solvent gradually dissolves the soluble ingredients.
• Internal diffusion is the movement from within the cell to the surface, while external diffusion involves the transfer from the surface to the bulk of the solvent.

Factors Affecting Extraction Rate

• Solvent: A solvent similar to the product's polarity is ideal. The ideal solvent is non-toxic, non-reactive, environmentally friendly, and affordable.
• Particle size: Grinding the plant material increases the contact area between solvent and material, enhancing extraction efficiency.
• Sample humidity: Water in the plant material can compete with the solvent for the extract, thus sample dryness before extraction is key.
• Temperature: Increased temp enhances the solubility and diffusion of plant components. However, avoid over-heating in order to avoid degradation.
• Solvent agitation: Agitation increases turbulent diffusion and material transfer rates

Extraction Solvents(Table)

• A table is provided with different solvents, their polarity, boiling point, and density at 25°C.

Extraction Solvents(Miscibility-Compatibility Chart)

• A chart displays solvent miscibility in a grid format.

Choice of Solvent

• Nonpolar solvents (e.g., petroleum ether, hexane) dissolve nonpolar compounds (e.g., fats, waxes).
• Polar solvents (e.g., methanol, ethanol, and water) dissolve polar compounds (e.g., alkaloids, salts, sugars).

After Extraction

• Filtration: Separates the solid components from the liquid extract.
• Rotary evaporator: Used to remove solvent under reduced pressure, boiling at lower temperatures.
• Freeze-drying: Removes water while maintaining bioactive ingredients.
• Maceration: Whole/coarsely powdered drug is placed in a container with a liquid solvent and allowed to stand at room temperature with frequent agitation.
• Infusion: Crude drug soaked briefly in cold or hot water to extract readily soluble components (dilute solution).
• Decoction: Crude drug is boiled in a particular amount of water to extract water-soluble, heat-stable components.
• Digestion: Similar to maceration but with slight warming to increase efficiency.
• Percolation: Moistened drug is packed in a filter-aided container with the solvent percolated through the material.

Hot Continuous Extraction (e.g., Soxhlet)

• A diagram of the apparatus and a detailed explanation of each component and stage of the process are provided.

Steam Distillation (Hydrodistillation)

• A common technique for separating aromatic compounds (essential oils) from plants.
• The steam creates a vapor mixture that is later cooled and separated into an oil layer and water layer (hydrosol), which are then collected.
• Diagrams are provided

Liquid-Liquid Extraction

• A process, also called partitioning, to transfer a solute between two immiscible or partially miscible solvents.
• A separating funnel is used to separate the two layers.

Various Novel Techniques

• Various novel extraction techniques are introduced.
  • Ultrasound-assisted extraction
  • Microwave-assisted extraction
  • Supercritical fluid extraction
  • Enzyme-assisted extraction

Ultrasound-Assisted Extraction (UAE)

• Ultrasound increases the contact surface area between solvents and samples, improving permeability of cell walls.
• Physical and chemical properties of materials are modified to disrupt plant cell walls.
• This process enhances mass transport of solvents into plant cells.
• A detailed diagram and figure are provided.

Microwave-Assisted Extraction (MAE)

• Combines microwave and classical solvent extraction.
• Electromagnetic waves cause structural changes in cells to facilitate extraction.
• Diagram of apparatus is provided

Supercritical Fluid Extraction

• Is a technique that involves using solvents at their critical temperature and pressure to extract compounds from solid matrices.
• The critical state of the solvent provides intermediary properties between gases and liquids.
• CO2 is a common solvent due to its renewability

Enzyme-Assisted Extraction

• Enzymes are used to disrupt cell walls, increasing extraction yield of bioactive compounds.
• The scanning electron microscopy diagrams show the effect of enzymes on plant cell walls before and after treatment.

Calculation of Percentage Yield

• Percentage yield measures the efficiency of extract isolation based on the ratio of crude to extracted weight.

Standardized Herbal Extracts

• Standardized herbal extracts have a consistent concentration of specific components.
• This consistency is beneficial for the consumer.
• Standardized extracts are used when there is wide variation in composition, quality, and therapeutic effects of crude extracts.

Preliminary Phytochemical Screening

• The table provides qualitative tests for alkaloids, glycosides, tannins, phenolic compounds, resins etc.

Isolation (Column Chromatography)

• Column chromatography is a highly effective method to separate plant extracts.
• A diagram illustrating the process of column chromatography is shown
• Elution, separation and collection are demonstrated in diagrams.
• The principle explaining the separation mechanism, based on affinity to the stationary phase, is described
• Elution involves separation based on components relative affinity to the mobile and stationary phase.

Spectroscopic Methods

• Various spectroscopic methods are helpful for the structure confirmation of natural compounds and the products of their degradation.
  • UV spectroscopy (conjugated dienes, α,β-unsaturated ketones)
  • IR spectroscopy (hydroxyl groups, oxo groups, isopropyl groups)
  • NMR spectroscopy (double bonds, types of functional groups, number of rings, and orientation of groups)
  • Mass spectroscopy (molecular weight, molecular formula, functional groups)

Thin Layer Chromatography (TLC)

• TLC is a technique to separate and qualitatively identify compounds in a mixture.
• A method to determine components in a mixture, the identity of components and purity is described in detail.
• Silica gel is a typical stationary phase in TLC.
• Steps in performing TLC are detailed in pictures and text, including spotting, development, visualization of spots.