Why Is Hematine Important Biology Essay

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The Malaria disease can be carried by five types of the plasmodium parasite, but the most important of which attack humans, Plasmodium Falciparum. The malaria cycle begins when a female Anopheles mosquito bites a person. When a female mosquito bites a person infected with malaria, it receives a certain amount of the parasite including the blood drawn. Some time later, when the mosquito bites another person, part of the parasites is injected into the blood of the person bitten. After a time, from weeks and months, malaria begins to reproduce itself and multiply causing symptoms such as headache, fever and even death.

When a mosquito bites a person, sporozoites mixed in the mosquito's saliva, they pass into the bloodstream and reach the liver. 

Shortly after, the sporozoites infecthepatocytes and they start to multiply in the liver reproducing to yield lots of merozoites. When they break the host cells, pass into the bloodstream again, starting the erythrocytic stage of the malaria cycle.

When they infect the red blood cells, they begin to multiply, breaking out their host to infect more red blood cells.

The enzyme Heme Polymerase, is which polymerizes the Ferriprotoporphyrin that has been released from hemoglobin as substrate for biosynthesis of Hemozoin, to β-hematin (main component of Hemozoin). Incorporation of Ferriprotoporphyrin into Hemozoin is believed to be a protective measure by the parasite against self-destruction. The molecules of ferriprotoporphyrin that has not been polymerized are very toxic because damage proteases and cell membranes.

Some antimalarial drugs as chloroquine, inhibits the polymeration of ferriprotoporphyrin. Although has been checked that the chloroquine kills Plasmodium Falciparum, the parasite creates crystals of β-hematine to protect itself against it.

3.2) Crystals and Crystallization:

A crystal is a solid formed by the linking together of atoms, ions, or molecules. The pattern-like structure of crystal formation can result in the development of faces on the surface of the crystal, provided its growth is uninhibited. Crystals can thus be categorized in classes which are determined by their external symmetry. {Donals Bloss, 1994 #25}

A crystal is defined by the unit cell, concretely for the repetition of it. To know the size and shape of the unit cell, there are some lattice parameters described below. {Putnis,1992 #34}. The unit cell can be described by the vectors a, b, c that define the structure of a parallelepiped, which correspond with the X, Y, Z crystallographic axes. The angles that describe the unit cell are α , β, and γ. α is opposite to a, β is opposite to b, and γ is opposite to c. This is shown in the picture below:

Figure 3.1: Unit celd of a crystalline structure{Putnis, 1992 #34}:

The crystallization technique is commonly used in chemistry and chemical engineering for separation processes. These processes consist in the union of a certain group of molecules, atoms and even ions, to form a tridimensional structure that is know as crystal.

The properties of the crystals often depend of the direction. Generally, crystals general can grow and dissolve. Some of the properties of the crystals as the thermal expansion coefficients, the refractive indices and the electrical conductivity or mechanical properties in general depend of the direction. The size of the rystals can vary from from nanometers (similar to our case), up to several millimeters (sugar, salt…). {Davey, 2000 #27}

3.2.1) Supersaturation:

It it is required to perform crystal growth, it is necessary to carry the solute molecules to an state thermodynamically unstable, exceeding the solubility limit of the compound to be growing.

Supersaturation occurs when the solute concentration exceeds the solubility limit, leaving the system is an stare of not equilibrium.

The supersaturation is determinated by σ = ln(C/Co). Co is the solubility of the solute at defined conditions and C is the concentration of the solute.{Keel, 2004 #30}

The following solubility diagram in the Figure 3.2 explains the supersaturation of a system. The continuos line in the diagram (B) determines the limit of the solute in the solvent.  D region is prone to have nucleation because the system is supersaturated and crystal growth can happen. However, at any point below the line B (A region), the system is under saturated and crystal growth cannot happen.

Figure 3.2 Variation of the solute concentration when it is raised the temperature of the system.{Keel, 2004 #31}

Crystallization processes consist of two major events, nucleation and crystal growth:

3.2.2) Nucleation:

Nucleation process consist in the creation of a new solid phase from a supersaturated homogeneous phase.{Davey, 2000 #27} . The first part of the crystal growth requires having small clusters in a supersaturated phase. In it, the molecules have to be oriented in a fixed lattice and too have to resist the tendency to dissolve.

There is an attachment and detachment of individual units in which occurs a series of bimolecular reactions that lead to growth and decay of the groups that contain a certain number of molecules. There must be a state of supersaturation for that the process can happen.{Meza, 2006 #2}

The liquids called supercooled are which are in a temperature below the temperature of heterogeneous nucleation (melting). They are in a temperature above the freezing temperature of the pure substance, that can be called too, temperature of homogeneous nucleation temperature.

To create a nucleus is necessary to form an interface in the limits of the new state. If we have a nucleus too small, is needed an extra energy and there will not take place the nucleation. Attending to the size of a nucleus, if r = r * (r critical), the process of the nucleation occurs. Furthermore, a thermal activation gives the needed energy for that an stable nucleus could be formed. Then the crystal can grows until reach a thermodynamic equilibrium.

For example, if it treats of pure water the temperature at which it freezes is not the melting temperature (0°C) , it is -42 ° C. {Wikipedia, #28}

3.2.3) Crystal Growth:

Crystal growth is the process in which it develops a solid phase with an order structure through an irregular and disordered state. The branch which studies this process is thermodynamic. Can be said that has been reached the equilibrium if the system remains a long period without changes in any condition. If an external force causes changes in the equilibrium state forming a nucleus, the crystal growth takes place. The ambient phases in which a crystal can grows are vapor, melt, solid and solution.{Sunagawa, 2005 #26}

The processes of mass and heat transfer are related in crystal growth. To know how grows a crystal is necessary to know the degree of contribution of the different transport processes and know the phase in which is working.

If it is wanted growing a crystal in a liquid state, there are two possible phases, dissolved or condensed. To work in a dissolved phase it is necessary before a condensation and it is very important the mass transfer. The role of heat is not so important in this case. However, in we are working in a condense phase, heat transfer has an important role, and the mass transfer contribution is very small.

Recrystallization, is the process in which as the initial and the final product have the same crystal structure.

The crystallization from vapor, melt and solution phases which are the ambient phases having random structures, can be differentiated into diluted and condensed phases. The diluted phase can be vapor and solution. In them, the condensation process of mass transfer has an extra importance. However, in the condensed melt phase, the important role is carried out by heat transfer. In addition, it has to be taken into account the interaction between the solute and the solvent.

3.2.3.1) Crystal Growth Mechanisms:

In crystal grow processes, the steps and kink sites on the surface are very important. The fact of knowing the height of the steps and know how the steps begin to appear, are important aspects to understand the growth mechanism. Although there are a few numbers of lesser-observed mechanisms in crystal growth, predominately are considered three growth mechanisms. Continuous growth, surface nucleation and spiral growth. These are all summarized below:

Continuous growth

Continuous or normal growth as it is also called happens when the energy required to form a step on the crystal surface is low. Due to it, the surface of the crystal will contain some kinks and step sites.

.Figure 3.3: Diagram showing the layer by layer growth

Surface nucleation

This type of mechanism occurs if the different growth units do not find quickly a growth site. It they do not find it, what can occurs is that they join to other adsorbed molecules to form other structures or that they come back to the fluid phase. The adsorbed growth units can continue adding themselves to the kinks formed until all the crystal surface will be covered completing a monomolecular layer. If the growth follows proceeding, it makes that the supersaturation of the solution decrease due to the loss of solute molecules in the crystalline surface.

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