BIOLOGICAL LIQUID CRYSTALS

PRESENTING BY : NABEEL.B.AZEEZM.Sc STUDENT AT YILDIZ TECHNIC UNIVERSITY DEPARTMENT OF CHEMISTRY

Introduction to Liquid CrystalsThe 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 .

Structural forms of liquid crystals

smectic

nematic

cholesteric

Based on thermooptical phenomenon

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

Based on electrooptical phenomenon:

2 .Lyotropic – the degree of order depends mainly on concentration ratio Formed by amphiphilic molecules

All biological liquid crystals involve lyotropic phases

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

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

Transport across membrane (1) •Passive – according to concentration drop

=(towards lower concentration )→diffusion,osmosis (water, O2, CO2)

•Facilitated diffusion – across channel, accordingto concentration drop. Opening and closing of thechannel is controlled by ligand, voltage or otherfactors.

Transport across membrane (2) •Active – against concentration drop

-The energy requirement is coveredusually by ATP (e.g. Na+-K+-ATP-ase)

•Indirect active transport – a transportprocess towards concentration drop andanother one against it are connected.

-symport – both processes are in the samedirection (e.g. Na+- glucose transport)

-antiport – the transprots are in oppositedirection (e.g. H+-Na+ transport in plants)

Na+-K+-ATP-ase

Phase transitionsThe 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

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

Artificial membranesLiposomesLipid spheres made of one or more bilayers. Drugs, diagnostics,

DNA can be enclosedAdvantages:

-targeted delivery -less side effects

-lower dose, effective concentration for longer time

Classification of liposomes1. – 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 target cells

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 fungiEx : citostatic (antitumoral) drugs to decrease severe side effects

C- drugs for local treatment (e.g. on the skin) to increase the drug penetration into the deeper layers of skin and to avoid the penetration into the systemic circulation

DNA encapsulation (gene transfer)

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

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

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

REFRENCES

1. :// . . / / / /2010/ / 9http pubs rsc org en content articlelanding sm b

21576 #!j 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