This document provides an introduction to liquid crystals including: - Their discovery in 1888 by Friedrich Reinitzer who observed two melting points in cholesteryl benzoate. - Their unique properties between solid and liquid phases termed the "mesogenic state". - Two main structural forms: thermotropic which depends on temperature and lyotropic which depends on concentration. - Examples of liquid crystals in biology like cell membranes, myelin, and spider silk which use liquid crystalline properties. - Potential medical applications of lyotropic liquid crystals like liposomes for targeted drug delivery.

1. PRESENTING BY : NABEEL.B.AZEEZ
M.Sc STUDENT AT YILDIZ TECHNIC UNIVERSITY
DEPARTMENT OF CHEMISTRY

2. Introduction to Liquid Crystals
The study of liquid crystals began in 1888 when an Austrian botanist named Friedrich Reinitzer
observed that a material known as cholesteryl benzoate had two distinct melting points. In his
experiments, Reinitzer increased the temperature of a solid sample and watched the crystal change
into a hazy liquid. As he increased the temperature further, the material changed again into a clear,
transparent liquid. Because of this early work, Reinitzer is often credited with discovering a new phase
of matter - the liquid crystal phase.
Liquid crystal materials are unique in their properties and uses., liquid crystals will play an important
role in modern technology.
What are Liquid Crystals?
Liquid crystal materials generally have several common characteristics. Among these are a rod-like
molecular structure, rigidness of the long axis, and strong dipoles and/or easily polarizable substituents.
The distinguishing characteristic of the liquid crystalline state is the tendency of the molecules a
common axis, called the director. This is in contrast to molecules in the liquid phase, which have no
intrinsic order. In the solid state, molecules are highly ordered and have little translational freedom.
The characteristic orientational order of the liquid crystal state is between the traditional solid and
liquid phases and this is the origin of the term mesogenic state, used synonymously with liquid crystal
state.

3. Structural forms of liquid crystals

4. 1. Thermotropic – the degree of order depends mainly on the temperature

5. :

6. 2. Lyotropic – the degree of order depends mainly on concentration ratio Formed
by amphiphilic molecules
the most important example of a
biological liquid crystal is the cell
membrane. The layered (lamellar)
structure can be seen in the diagram
opposite.
The lamellar structure of the cell
membrane in photoreceptors is
important in polarized light vision in fish.
There, the liquid crystal order also
orients the molecule that absorbs light

7. The role of biological membranes
• Separation of different fluid
compartments
• Selective transport of ions and
molecules
• Signal transduction
Main components of membranes
• Lipids (40-60 %)
- phospholipids
- neutral, negatively, positively charged
- saturated or unsaturated
- cholesterol
- other lipids (sphingolipids, glycolipids)
• Proteins (30-50 %)
- integrated (transmembrane) or
peripheral

8. Transport across membrane (1)
• Passive – according to concentration drop
(=towards lower concentration) → diffusion,
osmosis (water, O2, CO2)
• Facilitated diffusion – across channel, according
to concentration drop. Opening and closing of the
channel is controlled by ligand, voltage or other
factors.
Transport across membrane (2)
• Active – against concentration drop
- The energy requirement is covered
usually by ATP (e.g. Na+-K+-ATP-ase)
• Indirect active transport – a transport
process towards concentration drop and
another one against it are connected.
- symport – both processes are in the same
direction (e.g. Na+- glucose transport)
- antiport – the transprots are in opposite
direction (e.g. H+-Na+ transport in plants)
Na+-K+-ATP-ase

9. Phase transitions
The phase transitions exhibited by
biological membranes are an important
aspect of their properties and are directly
related to their structure. In a typical
case, calorimetric measurements (such
as those discussed in connection
with Differential Scanning Calorimetry)
show a rather broad specific heat
anomaly near or just below the
temperature at which the membranes
formed when the cell was grown. Studies
of a variety of membranes indicate that
this transition is related to a disordering
of the hydrocarbon chains

10. Lyotropic liquid crystal molecules
belong to a class of substances
called amphiphilic compounds.
These compounds are characterized
by a sort of split personality - one
end of the molecule is polar and
attracted to water while the other
end is nonpolar and attracted to
hydrocarbons, or lipophilic

11. Artificialmembranes
Liposomes
Lipid spheres made of one or more bilayers. Drugs,
diagnostics,
DNA can be enclosed
Advantages:
- targeted delivery
- less side effects
- lower dose, effective concentration for longer time
Classification of liposomes
1. – multilamellar (MLV) – unilamellar (SUV, LUV)
2. – conventional (C): removed from circulation by macrophages
– sterically stabilised (stealth – S): hidden from immune
system by polymer chains, longer circulation time
immunoliposomes: antibodies are attached to the surface →specific antigen –
antibody reaction on the surface of targetcells

12. Examples for medical applications of liposome.
They are used for the encapsulation of :
a) diagnostics
- X-ray contrast materials
b) therapeutic drugs (useful in case of severe side effects)
- antibiotics – against bacteria
– against fungi
Ex : citostatic (antitumoral) drugs to decrease severe side effects

13. C- drugs for local treatment (e.g. on the skin) to increase thedrug
penetration into the deeper layers of skin and toavoid the
penetration into the systemic circulation
DNA encapsulation (gene transfer)

14. examples of liquid crystals in biology
* the iridescent colors displayed by some beetles
* biological materials that form lyotropic liquid
crystals include bile acid salts, long chain fatty acids,
stereo esters, retinols and vitamins A, E and K.
* Myelin, which forms the sheath around nerve cells
and is prominent in the transmission of electrical
impulses by the nerve, is also liquid crystalline

15. examples of liquid crystals in biology
biomembrane is an enclosing or separating membrane that acts as
a selectively permeable barrier within living things. Biological
membranes, in the form of cell membranes, often consist of
a phospholipid bilayer with embedded, integral and peripheral
proteins used in communication and transportation of chemicals
and ions
Phospholipids are a class of lipids that are a
major component of all cell membranes as
they can form lipid bilayers. Most
phospholipids contain a diglyceride,
a phosphate group, and a simple organic
molecule such as choline; one exception to this
rule is sphingomyelin, which is derived
from sphingosine instead of glycerol

16. examples of liquid crystals in biology
Liquid crystalline spinning of spider silk.
Spider silk has outstanding mechanical properties
despite being spun at close to ambient temperatures
and pressures using water as the solvent. The spider
achieves this feat of benign fibre processing by
judiciously controlling the folding and crystallization of
the main protein constituents, and by adding auxiliary
compounds, to create a composite material of defined
hierarchical structure. Because the 'spinning dope' (the
material from which silk is spun) is liquid crystalline

17. REFRENCES
1. http://pubs.rsc.org/en/content/articlelanding/2010/sm/b921576j#!divAbstract
2. Liquid Crystals and Life .. Helen Gleeson, University of Manchester, 2010
3.S. V. Shiyanovskii O. D. Lavrentovich Chemical Physics Interdisciplinary Program
and Liquid Crystal Institute, Kent State University, Kent, Ohio3.
4. Applications of liquid crystals in chemical and biological detection
5. http://plc.cwru.edu/tutorial/enhanced/files/lc/intro.htm