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What are adsorption isotherms?

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The Ecomaterials and Environment Laboratory is located at the University of de Oriente in Maturn, Venezuela.

Simn Bolvar University has a laboratory for organic chemistry. E-mail:


The effect of pH on the adsorption of nucleic acid constituents was studied. Langmuir and Freundlich isotherms were used to describe the process. The neutral pH favored the adsorption of the nucleic acid components. The binding capacity of nucleobases and their derivatives depends on the structure of the adsorbed species. The order in which the biomolecules are adsorbed on the catalyst is: Nucleotides > Nucleosides > Nucleobases.

The highest values ​​of the maximum adsorption capacity (Xm) were obtained for the nucleotides, finding at pH 7 that CMP5 (Xm = 64.94 mg/L) > UMP5 (Xm = 54.64 mg/L ) GMP5 (Xm = 54.35 mg/L) > AMP5 (Xm = 45.05 mg/L). The constants ranged from 4 to 7.

The active sites of the catalyst are equivalent, except for the one at pH 7. The neutral pH is the best for modifying the WO3 surface.

There are biomolecules, including nitrogenous base.

There is aTRACT

We studied the effect of pH on the adsorption of nucleic acid constituents onWO3 in this paper. Langmuir and Freundlich were used to describe the processes. It was noted that neutral pH favors the adsorption of nucleic acid components. The binding capacity of the nucleobases and their derivatives depends on the structure of the adsorbed species. The sequence of the biomolecules that are being adsorption onto the catalyst has been found.

The highest values ​​of the maximum adsorption capacity (Xm) were obtained for nucleotides, finding that at pH 7 the CMP'5 (Xm = 64.94 mg/L) > UMP'5 (Xm = 54.64 mg/L) GMP'5 (Xm = 54.35 mg/L) > AMP'5 (Xm = 45.05 mg/L). The constants ranged between 4 and 7. The active sites of catalyst are equivalent, except for the AMP'5 at pH 7 which has a value of 2.16. The neutral pH is best for altering the surface of the WO3.

Key words are nucleotide, nitrogenous base, biomolecules.

August of 2013). November 2013).

The final version was released in January.

The introduction

There are a variety of roles for chondrites in cellular metabolism.

They act as chemical signals in cellular systems and are also structural components of a series of cofactors. They are the components of nucleic acids, which are the source of genetic information. The structure of all the biomolecules and the cellular components is the result of the information that is programmed into the nucleus of the cell.

Nitrogenous base, pentose and aphosphate group are components of nanchotides. The molecule is called a nucleoside because it doesn't have thephosphate group. pyrimidine and purine are the two parent compounds of nitrogenous bases.

Heterocycles are the bases and pentoses in common nucleotides.

The compound that contains oxygen and the transition metal tungsten is known as the chemical compound, Tungsten trioxide.

WO3 is obtained as an intermediate product in the purification of tungsten from its minerals; tungstite or hydrated tungsten oxide WO3·H2O, meymacite or dihydrated tungsten oxide WO3·2H2O and hydrotungstite or tungstic acid H2WO4. The minerals are treated with alkaline solutions.

In recent years, several studies have shown that zinc oxide and iron oxide can be removed from the surface of a piece of electronics. Cleaves et al. used various types of nucleic acid components to remove it from the TiO2 surface. There is a significant difference between the biomolecules, which are dependent on the architecture of the adsorbed species. They determined the order of the adsorption on TiO2 Nucleotide.

The isotherm describes the adsorption.

When the adsorption process reaches an equilibrium state, the adsorbed molecules are distributed between the liquid and solid phases. Many models describe the phenomenon of adsorption, however researchers usually use the models proposed by Langmuir and Freundlich to understand it.

In order to understand the role of the tungsten trioxide (WO3) surface, the effect of pH during the adsorption of nucleic acid components (nucleobases, nucleosides and nucleotides) on the semiconductor oxide was studied using the Langmuir and Freundlich isotherms. .

There are methods and materials.

There are materials.

Aldrich providedWO3 and several other substances.

A number of compounds were obtained from Sigma.

Adsorption is not the only thing.

The initial concentrations of the nucleic acid components were varied to keep the volume of the adsorbate and the amount of the adsorbent constant.

In the absence of light and continuous agitation for 48 hours, the adsorptions were carried out at the selected pH. The final concentrations of each solution were determined using UV-Visible spectroscopy after the solutions were filters. In order to study the nature of adsorption, adjustments were made to the various parameters of the Langmuir and Freundlich models.

There are results and findings.

The amount of biomolecule that accumulated on the WO3 was quantified by the development of adsorption isotherms.

The Langmuir and Freundlich mathematical models were used for the purpose of this investigation.

The Langmuir Adsorption model assumes that: (a) the surface is homogeneous, (b) it has a specific number where a molecule can be adsorbed, that is, when all the sites are occupied it is not possible for adsorption to continue (the system saturates), (c) the heat of adsorption is independent of the degree of coverage and (d) all sites are equivalent and the energy of the adsorbed molecules is independent of the presence of other molecules (Ortega and Núñez 2012).

Figure 2 shows an isotherm of Adenosine 5-monophosphate on a wafer. This type of behavior was obtained for all the components tested.

The biomolecules are interacting with all the active sites of WO3 and this trend is typical of the isotherm proposed by Langmuir.

The Langmuir isotherm can be described by an equation.

KL is the equilibrium constant and C is the concentration of water.

It was possible to determine the adsorptive capacity of WO3 for all the components evaluated. The maximum capacity of the monolayer is shown in Figure 3.

The different ways in which purine and pyrimidine nucleobases interact with the WO3 surface are shown in Figure 4.

The bases Adenine and Cytosine exhibited the highest binding affinities at pH 3 and 7, possibly due to potential forms of coordination with the Semiconductor oxide surface.

The exocyclic group of edinine and cysine will allow them to interact with the surface of WO3 or the water on the catalyst.

In an alkaline medium, it was observed that purine compounds have the highest Xm values ​​(Adenine = 25.71 mg/L and Guanine = 22.83 mg/L) which turned out to be approximately double when compared to pyrimidine bases (Cytosine = 11 .42 mg/L and U racil = 9.74 mg/L).

The behavior is justified because the WO3 surface is negatively charged which will allow Adenine and Guanine to interact by means of hydrogen bonding with the Semiconductor. Cleaves et al. reported a similar behavior for the adsorption of nucleobases on titanium oxide in a wide range of pH.

The behavior of the nucleosides analyzed are shown in Figure 5. The compound's binding affinity with the WO3 surface increased after the addition of the sugar fragment. Shkrob et al. show that the presence of the fragment favors the adsorption on the Semiconductor by means of the hydroxyl groups of the sugar.

All the nucleosides had their maximum capacity displayed. The net neutral charge of the nucleosides will allow them to bind on the surface of the Semiconductor oxide.

The high adsorption of Guanosine (30.49 mg/L) allows us to infer that the Nucleoside binds to the catalyst using different mechanisms, for example through the interaction of the hydroxyl groups of the carbohydrate fragment with the surface and/or the formation of a biomolecule-WO3 complex through hydrogen bonds similar to those shown in Figure 4.

When comparing the Xm values for the nucleobases and the nucleosides under the same conditions, a significant increase was observed.

In a neutral medium, Guanosine adsorbed to a greater extent than Guanine on the Semiconductor. This fact supports the idea that Ribofuranose promotes the formation of bonds between the two nucleosides.

At pH 7, the adsorption of purine nucleosides on WO3 improved by 20% compared to pH 10 (Guanosine: Xm = 30.49 mg/L at pH 7 and Xm = 25.64 mg/L at pH 10), while In the case of pyrimidine nucleosides, adsorption increased by 60% (Uridine: Xm = 21.14 mg/L at pH 7 and Xm = 13.14 mg/L at pH 10).

The Xm values ​​for the purine nucleosides increased by approximately 50% when passing from pH 3 to 7 (Adenosine: Xm = 13.85 mg/L at pH 3 and Xm = 20.79 mg/L at pH 7), however for with pyrimidine nucleosides, the increase in Xm was 30% (cytosine: Xm = 20.28 mg/L at pH 3 and Xm = 26.32 mg/L at pH 7).

Purine nucleosides were more strongly adsorbed than their pyrimidine counterparts.

However, for each of the pH values ​​evaluated, there was little difference between the maximum nucleoside adsorption values ​​(Xm), which suggests that the biomolecules interact with the WO3 surface using similar forms of bonds (intermolecular bond complexes and /or interaction of the hydroxyl groups of the sugar with the catalyst).

The nucleotides that were adsorbed on the surface were adenosine 5-monophosphate (AMP5), gutanidine 5-monophosphate (GMP5), cytidine 5-monophosphate (CMP5), and uridine 5-monophosphate. UMP5 is a word. The binding affinity of ribonucleotides increased when compared to nucleobases and nucleosides.

A 100% increase in the maximum adsorption capacity was caused by the addition of a phosphate group to the nucleosides.

The Ribonucleotides were generated at neutral pH and the distribution of the Xm values present a certain degree of grouping. It was observed that the values of UMP5 and GMP5 are very close to one another. The highest value of Xm was presented by CMP5 for all the nucleotides evaluated. Arora et al. (2007) evaluated the adsorption of the nucleotides AMP5, GMP5, CMP5 and UMP5 on the surface of FeOOH (Fe2O3 precursor), they found that the maximum binding percentages were generated in a neutral medium (AMP 5 = 76.5%; GMP5 = 89.0%; CMP5 = 75.0%; UMP5 = 60.0%).

The bonding of nucleotides in the pH range 3 10 can be explained through hydrogen bonding or electrostatic interactions, as shown in Figure 7.

When comparing the Xm values obtained at pH 7 with the values obtained at pH 10, the adsorption of the nucleotides improved by 65%.

The Xm values for the nucleotides went up by 140% when they went from pH 3 to 7 The largest Xm were obtained in an acidic medium when the nucleotides CMP5 and UMP5 were removed from the surface of aluminum oxide. Purine nucleotides were adsorbed to a greater extent than pyrimidines at acidic pH.

When applying the model proposed by Langmuir, it was found that the maximum adsorption values were higher for nucleotides than for nucleosides. It was possible to show that the neutral medium is the optimal condition to promote to a greater degree the biomolecule'ssorption on the surface of WO3.

The Langmuir model assumes that the heat of adsorption is independent of the degree of coating, and that it is limited to the formation of a monolayer. The heat of adsorption varies from site to site because most surfaces are heterogeneous.

One of the adsorption isotherms for heterogeneous surfaces is the Freundlich Isotherm.

The amount of adsorbed per unit weight of the adsorbent is determined by q and kf and n is the amount of adsorption intensity which is restricted to values greater than unity. A range of n between 2 and 10 is a good indication of the intensity of the adsorption.

The model was used to analyze the equilibrium of biomolecules. The linearity of the data was adjusted to the model proposed by Freundlich in the figure 8.

The table shows the parameters for the removal of nucleic acid components. The isotherm was used to analyze the efficiency of tungsten oxide in the biomolecule adsorption process.

The values of the parameters for the nucleic acid components in the range of 3-7 pH units were found to be greater than 1, which suggests that the Adsorbent-Adsorbate interaction is physical.

At pH 7 and 10 they presented a moderate adsorption on the WO3 surface, with the exception of Uracil, which reflected a very intense interaction. In an acid medium, Uracil exhibited excellent binding capacities.

It was possible to determine that the adsorption of nucleosides and nucleotides has a moderate intensity because of the values of the parameters n and 1-6. The active sites of the catalyst are equivalent to the values of the nucleosides and nucleotides in the pH values. The only exception was the removal of AMP5 from the neutral medium.

Kavita Sivakumar