Chemistry
Solubility
Solubility refers to the ability of a substance to dissolve in a solvent to form a homogeneous solution. It is typically expressed as the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature. Solubility is an important concept in chemistry and is influenced by factors such as temperature, pressure, and the nature of the solute and solvent.
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eBook - ePubPharmaceutical Dissolution Testing, Bioavailability, and Bioequivalence
Science, Applications, and Beyond
- Umesh V. Banakar(Author)
- 2021(Publication Date)
- Wiley(Publisher)
2020 ). Solubility is defined as the maximum quantity of a substance that can be solubilized in another. It is the maximum amount of solute that can be solubilized in a solvent at equilibrium, which produces a saturated solution.- Solubilization: Solubilization is the formation of a thermodynamically stable, isotropic solution of a substance (the solute), normally insoluble or slightly soluble in water, by the addition of a solubilizer, such as a surfactant (Tadros 2003 ).
- Solvation: It is any stabilizing interaction of a solute and the solvent or a similar interaction of groups of an insoluble material with solvent that generally involve electrostatic forces and van der Waals forces and chemically more specific effects such as hydrogen bond formation (Muller 1994 ).
- Dissolution: Solvation or dissolution is a kinetic process that is represented by an interaction of a solute (solid) with the solvent (liquid), which leads to the stabilization of the solute species in the solution. In the dissolved state, the solute species in the solution is surrounded or complexed by solvent molecules (IUPAC 1997 ). Dissolution is quantified by its rate.
- Diffusion: The movement of atoms or molecules from a region of higher concentration to a region of lower concentration. Atoms and small molecules can move across a cell membrane by diffusion (Amer. Heritage Sci. Dict. 2011 ). The rate of flow of the diffusing substance is found to be proportional to the concentration gradient.
- Diffusivity: Diffusivity is how easily a particular solute will move in a particular solvent for a particular gradient in concentration. It is also referred to as diffusion coefficient and is a proportionality constant between the molar flux due to molecular diffusion and the concentration gradient, i.e., the driving force for diffusion. Diffusivity is encountered in Fick's law(s) and numerous other equations of physical chemistry (CRC 2010
eBook - PDFOral Bioavailability and Drug Delivery
From Basics to Advanced Concepts and Applications
- Ming Hu, Xiaoling Li, Ming Hu, Xiaoling Li(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
When a solute is placed in contact with a solvent, a mixing process occurs due to the propensity of all molecules toward randomization, resulting in an increase in overall entropy of the system. The solute molecules start to break away from the surface and pass into the solvent system. The detached solute molecules are free to move randomly throughout the solvent and eventually form a uniform solution. Solubility is defined as the concentration of the solute in a saturated solution at a certain temperature and pressure. It is important to realize that “saturated” implies phase equilibrium in the processes of solute dissolution from solid phase and crystallization from liquid phase for a solid in a liquid [34]. As per the USP <1236>, Solubility is defined as the concentration limit, at thermodynamic equilibrium, to which a solute may be uniformly mixed into a solvent. This is referred to as equilibrium or saturated Solubility. Because of the aqueous environment in the biological system and most of the drugs being solid at room temperature, pharma- ceutically relevant Solubility typically deals with solids in an aqueous system. Solubility can be expressed by a qualitative, semi- quantitative, or quantitative relationship between the solute and the solvent or solution. Quantitative expres- sion of Solubility gives an accurate ratio of the amount of solute to solvent or solution at a certain temperature. In qualitative terms, Solubility can be divided into either soluble or insoluble based on a visual inspection of the dissolution of a compound in a given solvent at given temperature. The semiquantitative expression of Solubility adopts descriptive terms to express the relationship between the solute and the solvent. The U.S. Pharmacopeia and National formulary describes the Solubility of a compound in seven different cate- gories (e.g. very soluble, freely soluble, etc.), as shown in Table 2.1.
eBook - ePub- Britannica Educational Publishing, Erik Gregersen(Authors)
- 2010(Publication Date)
- Britannica Educational Publishing(Publisher)
CHAPTER 5 LIQUID SOLUTIONS AND SOLUBILITYT he ability of liquids to dissolve solids, other liquids, or gases has long been recognized as one of the fundamental phenomena of nature encountered in daily life. The practical importance of solutions and the need to understand their properties have challenged numerous writers since the Ionian philosophers and Aristotle. Many physicists and chemists have devoted themselves to a study of solutions.A solution is a mixture of two or more chemically distinct substances that is said to be homogeneous on the molecular scale—the composition at any one point in the mixture is the same as that at any other point. This is in contrast to a suspension (or slurry), in which small discontinuous particles are surrounded by a continuous fluid. Although the word solution is commonly applied to the liquid state of matter, solutions of solids and gases are also possible. Brass, for example, is a solution of copper and zinc, and air is a solution primarily of oxygen and nitrogen with a few other gases present in relatively small amounts.The ability of one substance to dissolve another depends always on the chemical nature of the substances, frequently on the temperature, and occasionally on the pressure. Water, for example, readily dissolves methyl alcohol but does not dissolve mercury; it barely dissolves benzene at room temperature but does so increasingly as the temperature rises. While the Solubility in water of the gases present in air is extremely small at atmospheric pressure, it becomes appreciable at high pressures where, in many cases, the Solubility of a gas is (approximately) proportional to its pressure. Thus, a diver breathes air (four-fifths nitrogen) at a pressure corresponding to the pressure around him, and, as he goes deeper, more air dissolves in his blood. If he ascends rapidly, the Solubility of the gases decreases so that they leave his blood suddenly, forming bubbles in the blood vessels. This condition (known as the bends) is extremely painful and may cause death; it can be alleviated by breathing, instead of air, a mixture of helium and oxygen because the Solubility of helium in blood is much lower than that of nitrogen.
eBook - ePubOral Bioavailability
Basic Principles, Advanced Concepts, and Applications
- Xiaoling Li, Ming Hu(Authors)
- 2011(Publication Date)
- Wiley(Publisher)
A qualitative description of Solubility divides the Solubility into either soluble or insoluble based on a visual inspection of the dissolution of a compound in a given solvent. The semiquantitative expression of Solubility uses descriptive terms to describe the relationship between the solute and the solvent. The US Pharmacopeia describes the Solubility of a compound in seven different categories, as shown in Table 3.1. Table 3.1 United States Pharmacopeia Solubility Definitions Descriptive Term Parts of Solvent Required for One Part of Solute Very soluble <1 Freely soluble From 1 to 10 Soluble From 10 to 30 Sparingly soluble From 30 to 100 Slightly soluble From 100 to 1000 Very slightly soluble From 1000 to 10,000 Practically insoluble 10,000 and over In pharmaceutical sciences, the Solubility values have traditionally been expressed quantitatively by using the concentration of solute in solution or the ratio of solute in solvent at saturation. Units of Solubility include mass per unit volume of solution, percentage, molarity and molality, mole fraction, volume fraction, etc. Commonly used units are microgram or milligram or gram per milliliter. 3.2.2 Thermodynamics of Solubility Solubility is a thermodynamic property of a substance. The system related to the Solubility is at equilibrium and the equilibrium is established for a given solute between two phases: that is, a pure drug in solid phase and its dissolved form in liquid phase. At equilibrium, the chemical potentials of both phases are equal. In addition to the equal chemical potentials, each phase in the equilibrium system must also be in thermal equilibrium (uniform temperature, T) and mechanical equilibrium (uniform pressure, p)
eBook - PDFHandbook of Property Estimation Methods for Chemicals
Environmental Health Sciences
- Donald Mackay, Robert S. Boethling, Donald Mackay, Robert S. Boethling(Authors)
- 2000(Publication Date)
- CRC Press(Publisher)
131 7.5.3 Molecular Connectivity ......................................................................................... 134 7.5.4 Solvatochromic or Linear Solvation Energy Methods ...................................... 134 7.5.5 UNIFAC ................................................................................................................... 135 7.6 Summary ............................................................................................................................. 135 7.7 Appendix ............................................................................................................................. 135 References ................................................................................................................... 136 7.1 Introduction Solubility in water is one of the most important physical chemical properties of a substance, having numerous applications to the prediction of its fate and its effects in the environ-ment. It is a direct measurement of hydrophobicity, i.e., the tendency of water to “exclude” the substance from solution. It can be viewed as the maximum concentration which an aqueous solution will tolerate before the onset of phase separation. Substances which are readily soluble in water, such as lower molecular weight alcohols, will dissolve freely in water if accidentally spilled and will tend to remain in aqueous solu-tion until degraded. On the contrary, sparingly soluble substances dissolve more slowly and, when in solution, have a stronger tendency to partition out of aqueous solution into other phases. They tend to have larger air-water partition coefficients or Henry’s law 126 Handbook of Property Estimation Methods for Chemicals constants, and they tend to partition more into solid and biotic phases such as soils, sedi-ments, and fish. As a result, it is common to correlate partition coefficients from water to these media with Solubility in water, as other chapters discuss.
eBook - ePubBiopharmaceutics
From Fundamentals to Industrial Practice
- Hannah Batchelor(Author)
- 2021(Publication Date)
- Wiley(Publisher)
4 SolubilityHannah BatchelorStrathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom4.1 Definition of Solubility
Solubility is a measurement of the amount of a substance that can stay in a solvent without precipitation. Solubility may be expressed in units of concentration, molality, mole fraction, mole ratio and other units. For the purposes of biopharmaceutics, the substance of interest is usually the API and the solvent will vary depending upon the physiological region of interest; for example the stomach, small intestine or pulmonary fluid.A drug's structure determines its Solubility as the chemical structure will also determine lipophilicity, hydrogen bonding, molecular volume, crystal energy and ionisability. Thus during lead compound optimisation, there is scope to balance potency with Solubility [1] .The Solubility of a substance can change when pressure, temperature and/or the composition of the solvent changes thus it is important to accurately detail Solubility data to provide sufficient information.4.2 The Importance of Solubility in Biopharmaceutics
Poor aqueous Solubility of a drug can lead to issues during the preclinical phase of drug development and beyond. Insufficient Solubility within the gastrointestinal lumen can limit absorption and subsequent exposure to the drug in question. Thus, the Solubility of a drug candidate will impact upon decisions and risk assessments undertaken during development.There has been an increase in the proportion of poorly water‐soluble drugs with estimates of up to 75% of candidates in development being classified as low aqueous Solubility [2] . This trend towards increasing proportions of low aqueous Solubility drugs is linked to the drive towards potent and selective drugs where candidate optimisation often adds lipophilic groups to enhance binding, yet the lipophilicity of the resulting molecule increases. However, poorly water‐soluble candidate drugs are associated with higher rates of attrition as well as higher costs during drug development [3] . Furthermore, poorly water‐soluble drugs are associated with greater inter‐individual pharmacokinetic variability as well as being susceptible to food effects [3]
eBook - ePub- Simon Gaisford, Mark Saunders(Authors)
- 2012(Publication Date)
- Wiley-Blackwell(Publisher)
4.5 ) the reason for the term equilibrium Solubility noted earlier.It appears from Equation (4.2 ) that the crystal lattice energy might affect Solubility. It also seems from Equation (4.1 ) that there should be an effect of temperature on Solubility, since the position of equilibrium will change. Both of these effects can be explored further through the concept of ideal Solubility .Summary box 4.14.2.1 Ideal Solubility- Solubility is the maximum concentration of a given solute that can be attained in a given solvent.
- Solids transition to solution by dissolution.
- Thermodynamic Solubility is a position of equilibrium.
- Dissolution governs the rate at which Solubility is achieved.
- As a general rule, Solubility below 1 mg mL−1 is likely to hinder development while Solubility above 10 mg mL−1 is acceptable.
In the special case where the enthalpy of any solute–solvent interaction is equal to the enthalpy of any solvent–solvent interaction then solvation of the solute may occur with no change in enthalpy (i.e. Δmix H = 0) and dissolution is said to be ideal . Formation of an ideal solution also occurs with the following change in entropy ( ):(4.6)where R is the universal gas constant (8.314 J K−1 mol−1 ). Ideal dissolution (although unlikely, because the solute and solvent molecules would need to possess identical properties, such as size, shape and chemical nature) leads to ideal Solubility and is an interesting theoretical position because it can be described in thermodynamic terms, which allows calculation of the dependence of Solubility on temperature.From Equation (4.2 ) if Δmix H = 0 then Δf H is equal to Δsol H (note that since Δf H must be positive, i.e. endothermic, Δsol H must also be positive for ideal dissolution). For a process to occur spontaneously the Gibbs free energy (ΔG ) must be negative. The familiar thermodynamic relationship for dissolution is(4.7)where T is absolute temperature. Δsol G is most likely to be negative when Δsol H is negative but, as noted above, Δsol H is frequently positive for dissolution and must be so when dissolution is ideal. This means that for dissolution to occur spontaneously the driving force can only be a significant increase in entropy. Since the mole fractions of both solvent and solute must be less than 1, the logarithmic terms in Equation (4.6
eBook - PDFEtching of Crystals
Theory, Experiment and Application
- K. Sangwal(Author)
- 2012(Publication Date)
- North Holland(Publisher)
Solubility OF CRYSTALS AND COMPLEXES IN SOLUTION In order to pass into solution, a solid substance should possess a particular property, the Solubility, which, to a significant extent, depends on the solvation of ions in solutions. The phenomenon of solvation involves the motion of the ions in solution together with a part of the solvent and disruption of its structure. If the solvent molecules have a dipole moment, then they interact with the ions, forming a solvation shell. Solvation can occur due to electrostatistic as well as non-Coulombian chemical forces. Several salts form hydrates not only in solutions but also in solid state. Almost all salts have a tendency of this type of complex formation. For example, the formation of hydrates of copper salts is a typical process of complex formation. In these compounds the bonding between ions and water molecules is purely chemical, which is caused by the usual coordination valency typical for complex compounds. The mobility of ions depends on the viscosity of the medium and on the radius of the ions in solution, and is determined by Stoke's law. The radius of an ion in solution is different from the crystallographic radius, and depends on its charge and crystallographic radius. A smaller crystallographic radius and a higher charge favour a larger radius of the ion in solution. In the present chapter we will acquaint ourselves with the above phenomena and the relationship between Solubility, surface energy and hardness. 6.1. The structure of solvents and solutions Among liquids water has unusual properties. It has a high boiling point, a high thermal conductivity, dielectric constant and surface tension, a low enthalpy of fusion, a maximum density at 4°C, etc. These properties are due to the existence of the hydrogen bond. A water molecule is represented by an oxygen atom at the centre of a regular 196 6
eBook - PDF- J W Mullin(Author)
- 2001(Publication Date)
- Butterworth-Heinemann(Publisher)
3.9 Measurement of Solubility Innumerable techniques, of almost infinite variety, have been proposed at one time or another for the measurement of the Solubility of solids in liquids. No single method can be identified, however, as being generally applicable to all possible types of system. The choice of the most appropriate method for a given case has to be made in the light of the system properties, the availability of apparatus and analytical techniques, the skill and experience of the operators, the precision required, and so on. The accuracy required of a Solubility measurement depends greatly on the use that is to be made of the information. Requirements vary enormously. In some cases, a simple assessment of whether a substance is highly, moderately or sparingly soluble in a given solvent, with some rough quantification, may be quite sufficient. In others, very high precisions may be demanded. For most work, however, a precision of < 1% should be aimed for, and usually this is not too difficult to attain. Extensive reviews of the literature on the subject of experimental Solubility determination have been made by Vold and Vold (1949) and Zimmerman (1952). Purdon and Slater (1946) give an excellent account of the determination of Solubility in aqueous salt systems. The monographs of Blasdale (1927) and Teeple (1929) give comprehensive accounts of the problems encountered in measuring equilibria in complex multicomponent aqueous salt systems. Temperature control Constant temperature control is essential during all the experimental pro-cedures for Solubility determination, not only during equilibration, but also during the sampling of saturated solution for analysis. The allowable limits of temperature variation depend on the system under investigation and the required precision of the Solubility measurement. Much greater care has to be taken when the Solubility changes appreciably with a change in temperature.
- Jan Rydberg(Author)
- 2004(Publication Date)
- CRC Press(Publisher)
The totality of these interactions is called the solvation of the solute in the particular solvent. When the solvent happens to be water, the term used is hydration. The solvation process has certain consequences pertaining to the energy, the volume, the fluidity, the electrical conductivity, and the spectroscopic properties of the solute-solvent system. The apparent molar properties of the solute ascribe to the solute itself the entire change in the properties of the system that occur when 1 mol of solute is added to an infinite amount of solution of specified composition. The solvent is treated in the calculation of the apparent molar quantities of the solute as if it had the properties of the pure solvent, present at its nominal amount in the solution. The magnitudes of quantities, such as the apparent molar volume or heat content, do convey some information on the system. However, it must be realized that both the solute and the solvent are affected by the solvation process, and more useful information is gained when the changes occurring in both are taken into account. 2.3.1 Interactions at the Molecular Scale The solvation process can be envisioned as occurring in several stages, although only the sum of the stage contributions to the overall process is measurable. First, a cavity must be created in the solvent to accommodate the solute. Then the solute is placed in the cavity and permitted to interact with its nearest neighbors, eventually forming coordinate bonds with some of them, forming a new entity, the solvated solute. Finally, this entity may interact further with its surroundings, by orienting solvent molecules, by the formation or disruption of hydrogen bonds, or by other interactions. If the solute is charged (i.e., if it is an ion), it will orient the dipoles of a polar solvent by its electrical field.
eBook - PDF- Camille Georges Wermuth(Author)
- 2011(Publication Date)
- Academic Press(Publisher)
Based on the assumption that the non-ionized form of an electrolyte is effectively a nonelectrolyte, an extension to the general Solubility equation has been proposed. 4,5 While this approach still requires the melting tem- perature of the substance in question, that is, requires its existence, the full in silico calculation based on the struc- tural formula is now possible. Several recent publications present computational programs for the prediction of solu- bility. These approaches are being used for the pre-screen- ing of candidates in advance of their synthesis, or for the design of combinatorial libraries. In a review of the differ- ent methodologies and the quality of results obtained from the most useful procedures it is concluded that viable pro- cedures now exist for the determination of Solubility with less than 1 log unit uncertainty. 6 This uncertainty is judged to be adequate for use in the above processes. In parallel with this, combination of a newly miniaturized shake flask experimental method and a computational approach for Solubility prediction has been published. 7 It may be added here, that, as extensions to these compu- tational predictors of Solubility, initial information has been published recently on the search for models for the predic- tion of drug Solubility and permeability, 8 bioavailability 9 and for the determination of the influence of some solid-state properties (melting point, enthalpy of melting and entropy of melting) on the intrinsic Solubility of drugs. 10 In any case, the Solubility is determined experimentally as soon as sufficient substance of an active compound is available. Many experimental methods have been described and are in use. The true equilibrium Solubility is the data that counts. Solubility studies are best undertaken by add- ing sufficient drug substance to the solvent until undis- solved solid is present.
eBook - PDFSoil and Water Chemistry
An Integrative Approach, Second Edition
- Michael E. Essington(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
289 6 Mineral Solubility Mineral dissolution and precipitation processes influence the distribution of inorganic substances between the soil solid and solution phases and therefore have a pronounced influence on the chemi-cal composition of soil solutions. The extent to which either process occurs is determined by the chemical properties of the soil solution (specifically ion activities) and the intrinsic stability of the minerals involved. While the misconception that insoluble minerals do indeed exist in the terres-trial environment persists, it is a fact that no mineral is insoluble in water and minerals that appear to be insoluble are in reality sparingly soluble . All minerals, indeed all solids, are soluble to some degree in water. Mineral Solubility principles are used to elucidate pedogenic processes, to predict the concentrations of elements in soil solutions, to predict trace element–bearing minerals formed in natural and waste-affected environments, and to verify the effectiveness of processes designed to enhance the in situ stabilization of trace elements that are potentially harmful to human health and the environment. 6.1 MINERAL Solubility: BASIC PRINCIPLES The dissolution of a soil mineral can be described by the following generalized reaction: M a L b (OH) c ( s ) + c H + ( aq ) → a M m+ ( aq ) + b L n− ( aq ) + c H 2 O( l ) (6.1) where M m+ is a metal cation L n− is a ligand anion The true dissolution equilibrium constant for this reaction is K dis m a n b c a b c c = + -+ ( ) ( ) ( ) ( ( ) )( ) M L H O M L OH H 2 (6.2) where the parentheses denote activities and am + c − bn = 0 is a condition of electroneutrality.
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