CSIR NET Chemical Sciences Interdisciplinary Topics Syllabus

Differentiate the 'lock-and-key' model from the 'induced-fit' model of recognition.

Lock-and-key (Emil Fischer): host and guest are rigidly complementary in shape. Induced-fit (Koshland): the host (or guest) changes conformation upon binding to achieve complementarity.

What is the chelate effect and the macrocyclic effect in molecular recognition?

Chelate effect: enhanced stability of complexes with multidentate (chelating) ligands due to favorable entropy. Macrocyclic effect: even greater stability/selectivity when the binding ligand is a preorganized ring (e.g., crown ethers vs open-chain analogues).

Define preorganization in supramolecular chemistry.

The principle (Cram) that a host which is already organized for binding (low conformational/solvation reorganization needed) before complexation binds guests more strongly than a flexible host.

Define self-assembly in supramolecular chemistry.

The spontaneous, reversible organization of molecular components into ordered, well-defined aggregates/structures through non-covalent interactions, without external direction.

What is the difference between thermodynamic and kinetic control in self-assembly?

Self-assembly is usually under thermodynamic control — reversible interactions allow error correction so the system reaches the most stable (lowest free energy) structure, unlike kinetically trapped covalent synthesis.

Give two classic examples of self-assembled structures.

Lipid bilayers/micelles from amphiphiles, the DNA double helix from base pairing, and metal-organic frameworks/cages from metal-ligand self-assembly.

What drives micelle formation in water, and what is the CMC?

The hydrophobic effect drives amphiphiles to aggregate with tails inward. CMC (critical micelle concentration) is the surfactant concentration above which micelles spontaneously form.

Define host-guest chemistry.

A branch of supramolecular chemistry in which a larger 'host' molecule possesses a cavity that selectively binds a smaller 'guest' molecule/ion via non-covalent interactions to form a host-guest complex.

What are crown ethers and what do they selectively bind?

Cyclic polyethers (e.g., 18-crown-6) whose oxygen atoms line a cavity that selectively binds alkali/alkaline-earth metal cations by size match — 18-crown-6 binds K+, 15-crown-5 binds Na+, 12-crown-4 binds Li+.

What are cryptands and how do they differ from crown ethers?

Cryptands are bicyclic/three-dimensional polyether-polyamine hosts that encapsulate cations in a 3D cavity (forming 'cryptates'), giving higher binding strength and selectivity than the 2D crown ethers.

What are cyclodextrins and what type of guests do they bind?

Cyclic oligosaccharides (alpha-, beta-, gamma- with 6,7,8 glucose units) with a hydrophilic outer surface and hydrophobic inner cavity that binds non-polar/organic guest molecules in water — used in drug delivery.

What are calixarenes?

Cup-shaped macrocyclic hosts made of phenol units linked by methylene bridges (n = 4,6,8), with a tunable cavity used to bind ions and neutral molecules.

Distinguish the top-down and bottom-up approaches to nanomaterial synthesis.

Top-down: carving bulk material down to nanoscale (e.g., ball milling, lithography, etching). Bottom-up: building nanostructures from atoms/molecules (e.g., sol-gel, CVD, self-assembly, colloidal synthesis).

Describe the sol-gel process for nanomaterial synthesis.

A bottom-up wet-chemical route where a 'sol' (colloidal suspension of metal alkoxide/precursor) undergoes hydrolysis and condensation to form a 'gel' network, which is dried/calcined to give oxide nanoparticles (e.g., SiO2, TiO2).

What is Chemical Vapour Deposition (CVD) used for in nanotech?

A bottom-up gas-phase method where volatile precursors react/decompose on a heated substrate to deposit thin films or grow nanostructures such as carbon nanotubes and graphene.

What is the principle behind the citrate (Turkevich) synthesis of gold nanoparticles?

Sodium citrate reduces Au3+ (from HAuCl4) to Au0 and also acts as a stabilizing/capping agent, producing monodisperse colloidal gold nanoparticles.

Why do gold and silver nanoparticles show intense colors not seen in the bulk metal?

Due to Localized Surface Plasmon Resonance (LSPR) — collective oscillation of conduction electrons resonant with visible light, giving size/shape-dependent colors (e.g., red colloidal gold).

How does the surface-area-to-volume ratio change at the nanoscale and why does it matter?

It increases dramatically as size decreases, so a large fraction of atoms sit at the surface. This raises reactivity, catalytic activity, and surface energy compared with bulk material.

Explain quantum confinement and its effect on semiconductor quantum dots.

When particle size approaches the exciton Bohr radius, electron energy levels become discrete and the band gap widens as size decreases. Smaller quantum dots emit higher-energy (blue-shifted) light; larger ones emit red-shifted light.

Why do nanoparticles often have lower melting points than the bulk material?

Melting point depression: the high fraction of high-energy, less-coordinated surface atoms reduces the cohesive energy, so nanoparticles melt at lower temperatures than the bulk.

Compare the structures and key properties of fullerene (C60), carbon nanotubes, and graphene.

C60: spherical cage of 60 carbons (0D). CNTs: rolled graphene cylinders (1D), can be metallic or semiconducting with high tensile strength. Graphene: single 2D sheet of sp2 carbon, excellent conductor with very high electron mobility.

What determines whether a single-walled carbon nanotube is metallic or semiconducting?

Its chirality (the (n,m) rolling vector). It is metallic when (n - m) is divisible by 3; otherwise it is semiconducting.

Name two biomedical applications of nanotechnology.

Targeted drug delivery using nanoparticle/liposome carriers, cancer hyperthermia using magnetic nanoparticles, contrast/imaging agents (quantum dots), and biosensors/diagnostics.

How are TiO2 nanoparticles applied in environment and consumer products?

As photocatalysts for degrading pollutants and self-cleaning/antibacterial surfaces, and as UV-blocking agents in sunscreens (also in solar cells and paints).

What is rational drug design?

The targeted design of drug molecules based on knowledge of the biological target (e.g., enzyme/receptor structure or mechanism), as opposed to random screening, to achieve optimal binding and activity.

What is a pharmacophore?

The specific 3D arrangement of essential steric and electronic features of a molecule required to ensure optimal interaction with the biological target and to trigger/block its response.

Define a prodrug and give an example.

A pharmacologically inactive (or less active) compound that is metabolically converted in the body to the active drug, improving absorption/targeting. Example: aspirin (to salicylate) or levodopa converting to dopamine; enalapril to enalaprilat.

Differentiate an agonist from an antagonist in drug action.

An agonist binds a receptor and activates it to produce a biological response. An antagonist binds the receptor but produces no response and blocks the agonist's effect (can be competitive or non-competitive).

What is the difference between affinity and efficacy (intrinsic activity) of a drug?

Affinity is how tightly a drug binds its receptor. Efficacy/intrinsic activity is the drug's ability to produce a response once bound (agonist efficacy = 1, antagonist = 0, partial agonist between 0 and 1).

What do the ADME steps of pharmacokinetics stand for?

Absorption, Distribution, Metabolism, and Excretion — the processes describing what the body does to a drug over time.

Define the elimination half-life (t1/2) of a drug and its formula for first-order kinetics.

The time required for the plasma drug concentration to fall by half. For first-order elimination, t1/2 = 0.693 / k (k = elimination rate constant), and t1/2 = 0.693 x Vd / Cl.

What is bioavailability (F) and what is its value for an intravenous drug?

The fraction of an administered dose of unchanged drug that reaches the systemic circulation. By definition, IV drugs have F = 1 (100%); oral bioavailability is reduced by incomplete absorption and first-pass metabolism.