Molecular Machines: Delving into the world of

Supramolecular Chemistry

Shreesha .V. Bhat

3rd Sem, Dept of Medicinal Chemistry

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Contents

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1.Molecular Machines – Introduction

2.Supramolecular Chemistry and Mechanical Bond

3.Catenanes and rotaxanes

- Introduction

- Synthesis

- Molecular Shuttling

4. Applications

Molecular machines

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What is a molecular machine?

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Molecular Machines

What is a molecular machine?

“An assembly of a discrete number of molecularcomponents designed to perform mechanical-like

movements as a consequence of appropriateexternal stimuli”

Angew. Chem. Int. Ed. 2000, 39, 3348-3391.5

Natural Molecular Machines-

Biomotors

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Artificial Molecular Motors

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Artificial Molecular Motors

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Supramolecular Chemistry

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Molecular Machines

Supramolecular Chemistry

Non-covalent Interactions

Mechanical Bond

Macromolecules

Mechanical Bond

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Non-covalent interactions

Mainly observed in mechanically intertwined

molecules like catenanes and rotaxanes.

Each component is intrinsically linked to the

other resulting in a mechanical bond which

prevents dissociation without cleavage of one or

more covalent bonds.

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James Bond- Sir Fraser Stoddart

Third most cited chemist with more than 14,000

citations

Has trained more than 300 Ph.Ds and postdoctorates13

Catenanes and Rotaxanes

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Catenanes and Rotaxanes

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Construction of Rotaxanes

and Catenanes

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DNA Catenanes & Rotaxanes

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Synthesis of Catenanes and

Rotaxanes

1) Active template Strategy Hydrophobic Interactions

Hydrogen Bonding

Metal ligand co-ordination π donor- π acceptor interaction

2) Click Chemistry

3) Ring Closing Metathesis

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First Synthesis of Catenanes and

Rotaxanes

•Solely based on statistical probability

•Molecules were allowed to self-assemble

•Less than 1 % yield

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How can we make complex

efficiently?

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Template Effects for efficient

synthesis

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Template Effects for efficient

synthesis

1) Hydrogen Bonding

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Template Effects for efficient

synthesis

2) Metal Co-ordination

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Template Effects for efficient

synthesis

Chem. Lett. 1996,503-504

3) Hydrophobic Interactions

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Template Effects for efficient

synthesis

Cyclodextrins (CDs) are cyclic oligosaccharides consisting of six

or more α-1,4-linked D-glucopyranose rings.

The conformation of CDs is a rigid, well-defined cavity with a

conical shape.

They have a Hydrophilic exterior, Hydrophobic Interior

The binding interaction is based on a summation of weak effects,

namely Van der Waals interactions and hydrophobic binding.

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Template Effects for efficient

synthesis

PNAS, 104, 2007, 234

4) π – donor π- acceptor Interactions

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Click Chemistry As an Approach for

Catenane/ Rotaxane synthesis

Click Chemistry is the chemistry tailored to generate

substances quickly and reliably by joining units together.

It is a modular reaction which gives very high yields and

has high atom economy

Azide Alkyne Cycloaddition using Copper as a catalyst is

one of the widely used click reactions

1,2,3 triazole

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Click Chemistry

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J. AM. CHEM. SOC. 2006, 128, 10388-10390

End Capping by Click Reactions

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Tetrahedron, 57, 2001, 3799-3808

Bis-p-phenylene-34-crown -10(BPP34C10)

Synthesis of macrocycle

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Catenane Synthesis

Bipyridinium CyclophaneBPPC34C10 dvts Catenanes

Tetrahedron, 57, 2001, 3799-380834

Functions- Molecular Switches

and Molecular Shuttles

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Incorporation of different

stations for switching

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Molecular Shuttling

External Stimuli

1)Chemical-Acid-

Base

2) Photochemical

3) Electrochemical-

Redox

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Principle Behind Shuttling

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External Stimuli for Switching

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Chemically Driven Stimuli

JACS 1998, 120, 11932-11942.40

Photochemically Driven

Switches

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Photochemically Driven

Switches

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Applications in Drug Delivery

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Macroscopic Transporters

NanoElevators

Nano Valves

Molecular Rotors

Macroscopic Transport by

synthetic Molecular Machines

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Tetraflourosuccinamidestation

Maleamide station

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Implications

Liquid transportation using photo-responsive

surfaces may prove useful for delivering

analytes in lab-on-a-chip environments,

Performing chemical reactions on a tiny

scale without reaction vessels by bringing

individual drops containing different reactants

together.

In the Future, maybe you can move solid

objects just through a Laser Pointer!!!!!

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Molecular Elevator

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Molecular Elevator

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MSNP- Mesoporous Silica

Nanoparticles -Targeted Drug

Delivery

Nanoscale, 2009, 1, 16–39 53

In Step 1, the CBPQT4+ rings encircles the TTF units, constitutes the open position of

the MSNPs and allows the cargo molecules to be loaded.

In Step 2, the nanovalves are closed by oxidizing the TTF units with Fe(ClO4)3 to the

TTF2+ dications and as a consequence of Coulombic repulsion, the tetracationic

CBPQT4+ rings move to the DNP units.

In Steps 3 and 4, the nanovalves are opened by reducing the dications back to the

neutral TTF units whereupon the CBPQT4+ rings move back to the TTF units, thus

releasing the cargo 54

Conclusions

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The Beauty of Supramolecular Chemistry, with its

Interlocked molecules converts a Chemist into an

Artist who delves into the world of catenanes and

rotaxanes.

Synthetic Molecular Machines have really wide

applications in the field of electronics, sensors and

drug delivery.

The Molecular shuttling mechanisms of rotaxanes

have wide implications in targeted drug delivery,

and can be explored further.

http://www.catenane.net/home/linksnew.h

tml

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Acknowledgements

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My Sincere thanks to Mr. Mohit Tyagi (Phd Scholar)

for introducing me to this wonderful topic, and

answering my innocent questions with great

patience.

Thank You

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QUIZ

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