In chemistry , pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a P−O−P linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate ( Na 2 H 2 P 2 O 7 ) and tetrasodium pyrophosphate ( Na 4 P 2 O 7 ), among others. Often pyrophosphates are called diphosphates . The parent pyrophosphates are derived from partial or complete neutralization of pyrophosphoric acid . The pyrophosphate bond is also sometimes referred to as a phosphoanhydride bond, a naming convention which emphasizes the loss of water that occurs when two phosphates form a new P−O−P bond, and which mirrors the nomenclature for anhydrides of carboxylic acids . Pyrophosphates are found in ATP and other nucleotide triphosphates, which are important in biochemistry. The term pyrophosphate is also the name of esters formed by the condensation of a phosphorylated biological compound with inorganic phosphate , as for dimethylallyl pyrophosphate . This bond is also referred to as a high-energy phosphate bond.
47-448: PPI may refer to: Science and technology [ edit ] Biochemistry [ edit ] PP i , the anion P 2 O 7 , a pyrophosphate Polyproline I helix Protein–protein interaction Medicine [ edit ] Patient and public involvement Prepulse inhibition , of a later pulse Proton-pump inhibitor , a medication Psychopathic Personality Inventory ,
94-402: A {\displaystyle K_{a}} ) is a quantitative measure of the strength of an acid in solution . It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid–base reactions . The chemical species HA is an acid that dissociates into A , called the conjugate base of the acid, and a hydrogen ion , H . The system
141-430: A is the exponent (−5), giving p K a = 5. For acetic acid , K a = 1.8 x 10 , so p K a is about 5. A higher K a corresponds to a stronger acid (an acid that is more dissociated at equilibrium). The form p K a is often used because it provides a convenient logarithmic scale , where a lower p K a corresponds to a stronger acid. The acid dissociation constant for an acid
188-477: A news agency Other uses [ edit ] Pareto priority index , to prioritize projects Payment protection insurance Positive polarity item Producer price index Pulse Polio , immunisation campaign in India Port Pirie Airport , IATA airport code "PPI" Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with
235-404: A values of all acids and bases are known; conversely, it is possible to calculate the equilibrium concentration of the acids and bases in solution when the pH is known. These calculations find application in many different areas of chemistry, biology, medicine, and geology. For example, many compounds used for medication are weak acids or bases, and a knowledge of the p K a values, together with
282-404: A values range from about −2 for a strong acid to about 12 for a very weak acid (or strong base). A buffer solution of a desired pH can be prepared as a mixture of a weak acid and its conjugate base. In practice, the mixture can be created by dissolving the acid in water, and adding the requisite amount of strong acid or base. When the p K a and analytical concentration of the acid are known,
329-506: A concentration c i {\displaystyle c_{i}} is simply proportional to mole fraction x i {\displaystyle x_{i}} and density ρ {\displaystyle \rho } : and since the molar mass M {\displaystyle M} is a constant in dilute solutions, an equilibrium constant value determined using (3) will be simply proportional to
376-402: A dibasic acid the relationship between stepwise and overall constants is as follows Note that in the context of metal-ligand complex formation, the equilibrium constants for the formation of metal complexes are usually defined as association constants. In that case, the equilibrium constants for ligand protonation are also defined as association constants. The numbering of association constants
423-482: A natural inhibitor of hydroxyapatite formation in extracellular fluid (ECF). Cells may channel intracellular PP i into ECF. ANK is a nonenzymatic plasma-membrane PP i channel that supports extracellular PP i levels. Defective function of the membrane PP i channel ANK is associated with low extracellular PP i and elevated intracellular PP i . Ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) may function to raise extracellular PP i . From
470-434: A p K a value of less than 0 is almost completely deprotonated and is considered a strong acid . All such acids transfer their protons to water and form the solvent cation species (H 3 O in aqueous solution) so that they all have essentially the same acidity, a phenomenon known as solvent leveling . They are said to be fully dissociated in aqueous solution because the amount of undissociated acid, in equilibrium with
517-400: A particular example of an equilibrium constant . The dissociation of a monoprotic acid , HA, in dilute solution can be written as The thermodynamic equilibrium constant K ⊖ {\displaystyle K^{\ominus }} can be defined by where { X } {\displaystyle \{X\}} represents the activity , at equilibrium, of
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#1732773144179564-510: A personality test Psychophysiological Interaction , fMRI analysis technique Computing [ edit ] Parallel Peripheral Interface , of the Blackfin processor Programmable Peripheral Interface, Intel 8255 chip Programmable Peripheral Interconnect , in Nordic nRF microcontrollers Pixels per inch , of a display Productivity Products International , commercializer of
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658-411: A proton and forming the conjugate acid SH . In solution chemistry, it is common to use H as an abbreviation for the solvated hydrogen ion, regardless of the solvent. In aqueous solution H denotes a solvated hydronium ion rather than a proton. The designation of an acid or base as "conjugate" depends on the context. The conjugate acid BH of a base B dissociates according to which
705-400: A proton donor, but it has been confirmed by Raman spectroscopy that this is due to the hydrolysis equilibrium: Similarly, metal ion hydrolysis causes ions such as [Al(H 2 O) 6 ] to behave as weak acids: According to Lewis 's original definition, an acid is a substance that accepts an electron pair to form a coordinate covalent bond . An acid dissociation constant is
752-406: A proton exchange reaction: The acid loses a proton, leaving a conjugate base; the proton is transferred to the base, creating a conjugate acid. For aqueous solutions of an acid HA, the base is water; the conjugate base is A and the conjugate acid is the hydronium ion. The Brønsted–Lowry definition applies to other solvents, such as dimethyl sulfoxide : the solvent S acts as a base, accepting
799-416: A reaction is itself a function of temperature, according to Kirchhoff's law of thermochemistry : where Δ C p {\displaystyle \Delta C_{p}} is the heat capacity change at constant pressure. In practice Δ H ⊖ {\displaystyle \Delta H^{\ominus }} may be taken to be constant over
846-537: A small temperature range. In the equation K a appears to have dimensions of concentration. However, since Δ G = − R T ln K {\displaystyle \Delta G=-RT\ln K} , the equilibrium constant, K {\displaystyle K} , cannot have a physical dimension. This apparent paradox can be resolved in various ways. The procedures, (1) and (2), give identical numerical values for an equilibrium constant. Furthermore, since
893-460: A weak acid. p K a values for strong acids have been estimated by theoretical means. For example, the p K a value of aqueous HCl has been estimated as −9.3. After rearranging the expression defining K a , and putting pH = −log 10 [H ] , one obtains This is the Henderson–Hasselbalch equation , from which the following conclusions can be drawn. In water, measurable p K
940-427: Is a direct consequence of the underlying thermodynamics of the dissociation reaction; the p K a value is directly proportional to the standard Gibbs free energy change for the reaction. The value of the p K a changes with temperature and can be understood qualitatively based on Le Châtelier's principle : when the reaction is endothermic , K a increases and p K a decreases with increasing temperature;
987-495: Is a substance that dissociates in aqueous solution, releasing the hydrogen ion H (a proton): The equilibrium constant for this dissociation reaction is known as a dissociation constant . The liberated proton combines with a water molecule to give a hydronium (or oxonium) ion H 3 O (naked protons do not exist in solution), and so Arrhenius later proposed that the dissociation should be written as an acid–base reaction : Brønsted and Lowry generalised this further to
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#17327731441791034-735: Is a tetraprotic acid, with four distinct p K a 's: The pKa's occur in two distinct ranges because deprotonations occur on separate phosphate groups. For comparison with the p K a 's for phosphoric acid are 2.14, 7.20, and 12.37. At physiological pH 's, pyrophosphate exists as a mixture of doubly and singly protonated forms. Disodium pyrophosphate is prepared by thermal condensation of sodium dihydrogen phosphate or by partial deprotonation of pyrophosphoric acid. Pyrophosphates are generally white or colorless. The alkali metal salts are water-soluble. They are good complexing agents for metal ions (such as calcium and many transition metals) and have many uses in industrial chemistry. Pyrophosphate
1081-473: Is an example of a polyprotic acid as it can lose three protons. When the difference between successive p K values is about four or more, as in this example, each species may be considered as an acid in its own right; In fact salts of H 2 PO 4 may be crystallised from solution by adjustment of pH to about 5.5 and salts of HPO 2− 4 may be crystallised from solution by adjustment of pH to about 10. The species distribution diagram shows that
1128-416: Is said to be in equilibrium when the concentrations of its components do not change over time, because both forward and backward reactions are occurring at the same rate. The dissociation constant is defined by where quantities in square brackets represent the molar concentrations of the species at equilibrium. For example, a hypothetical weak acid having K a = 10 , the value of log K
1175-413: Is the first member of an entire series of polyphosphates . The anion P 2 O 4− 7 is abbreviated PP i , standing for i norganic p yro p hosphate . It is formed by the hydrolysis of ATP into AMP in cells . For example, when a nucleotide is incorporated into a growing DNA or RNA strand by a polymerase , pyrophosphate (PP i ) is released. Pyrophosphorolysis is the reverse of
1222-442: Is the reverse of the equilibrium The hydroxide ion OH , a well known base, is here acting as the conjugate base of the acid water. Acids and bases are thus regarded simply as donors and acceptors of protons respectively. A broader definition of acid dissociation includes hydrolysis , in which protons are produced by the splitting of water molecules. For example, boric acid ( B(OH) 3 ) produces H 3 O as if it were
1269-425: Is the reverse of the numbering of dissociation constants; in this example log β 1 = p K a 2 {\displaystyle \log \beta _{1}=\mathrm {p} K_{{\ce {a2}}}} When discussing the properties of acids it is usual to specify equilibrium constants as acid dissociation constants, denoted by K a , with numerical values given
1316-528: The Objective-C language Other science and technology [ edit ] Gabarit passe-partout international , in railways Picks per inch, a unit of textile measurement Plan position indicator , radar display Polymethylene polyphenylene isocyanate Business and organizations [ edit ] Italian People's Party (1919) (Partito Popolare Italiano), a political party Italian People's Party (1994) (Partito Popolare Italiano),
1363-423: The octanol-water partition coefficient , can be used for estimating the extent to which the compound enters the blood stream. Acid dissociation constants are also essential in aquatic chemistry and chemical oceanography , where the acidity of water plays a fundamental role. In living organisms, acid–base homeostasis and enzyme kinetics are dependent on the p K a values of the many acids and bases present in
1410-473: The polymerization reaction in which pyrophosphate reacts with the 3′-nucleosidemonophosphate ( NMP or dNMP), which is removed from the oligonucleotide to release the corresponding triphosphate ( dNTP from DNA, or NTP from RNA). The pyrophosphate anion has the structure P 2 O 4− 7 , and is an acid anhydride of phosphate . It is unstable in aqueous solution and hydrolyzes into inorganic phosphate: or in biologists' shorthand notation: In
1457-619: The absence of enzymic catalysis, hydrolysis reactions of simple polyphosphates such as pyrophosphate, linear triphosphate, ADP , and ATP normally proceed extremely slowly in all but highly acidic media. (The reverse of this reaction is a method of preparing pyrophosphates by heating phosphates.) This hydrolysis to inorganic phosphate effectively renders the cleavage of ATP to AMP and PP i irreversible , and biochemical reactions coupled to this hydrolysis are irreversible as well. PP i occurs in synovial fluid , blood plasma , and urine at levels sufficient to block calcification and may be
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1504-601: The cell and in the body. In chemistry, a knowledge of p K a values is necessary for the preparation of buffer solutions and is also a prerequisite for a quantitative understanding of the interaction between acids or bases and metal ions to form complexes . Experimentally, p K a values can be determined by potentiometric (pH) titration , but for values of p K a less than about 2 or more than about 11, spectrophotometric or NMR measurements may be required due to practical difficulties with pH measurements. According to Arrhenius 's original molecular definition , an acid
1551-432: The chemical species X. K ⊖ {\displaystyle K^{\ominus }} is dimensionless since activity is dimensionless. Activities of the products of dissociation are placed in the numerator, activities of the reactants are placed in the denominator. See activity coefficient for a derivation of this expression. Since activity is the product of concentration and activity coefficient ( γ )
1598-592: The definition could also be written as where [ HA ] {\displaystyle [{\text{HA}}]} represents the concentration of HA and Γ {\displaystyle \Gamma } is a quotient of activity coefficients. To avoid the complications involved in using activities, dissociation constants are determined , where possible, in a medium of high ionic strength , that is, under conditions in which Γ {\displaystyle \Gamma } can be assumed to be always constant. For example,
1645-406: The dissociation products, is below the detection limit . Likewise, any aqueous base with an association constant p K b less than about 0, corresponding to p K a greater than about 14, is leveled to OH and is considered a strong base . Nitric acid , with a p K value of around −1.7, behaves as a strong acid in aqueous solutions with a pH greater than 1. At lower pH values it behaves as
1692-458: The extent of dissociation and pH of a solution of a monoprotic acid can be easily calculated using an ICE table . A polyprotic acid is a compound which may lose more than 1 proton. Stepwise dissociation constants are each defined for the loss of a single proton. The constant for dissociation of the first proton may be denoted as K a1 and the constants for dissociation of successive protons as K a2 , etc. Phosphoric acid , H 3 PO 4 ,
1739-426: The magnitude of the acid dissociation constant include inductive effects , mesomeric effects , and hydrogen bonding . Hammett type equations have frequently been applied to the estimation of p K a . The quantitative behaviour of acids and bases in solution can be understood only if their p K a values are known. In particular, the pH of a solution can be predicted when the analytical concentration and p K
1786-454: The medium might be a solution of 0.1 molar (M) sodium nitrate or 3 M potassium perchlorate . With this assumption, is obtained. Note, however, that all published dissociation constant values refer to the specific ionic medium used in their determination and that different values are obtained with different conditions, as shown for acetic acid in the illustration above. When published constants refer to an ionic strength other than
1833-419: The one required for a particular application, they may be adjusted by means of specific ion theory (SIT) and other theories. A cumulative equilibrium constant, denoted by β , {\displaystyle \mathrm {\beta } ,} is related to the product of stepwise constants, denoted by K . {\displaystyle \mathrm {K} .} For
1880-438: The opposite is true for exothermic reactions. The value of p K a also depends on molecular structure of the acid in many ways. For example, Pauling proposed two rules: one for successive p K a of polyprotic acids (see Polyprotic acids below), and one to estimate the p K a of oxyacids based on the number of =O and −OH groups (see Factors that affect p K a values below). Other structural factors that influence
1927-553: The precursor to tens of thousands of terpeness and terpenoids . Various diphosphates are used as emulsifiers , stabilisers , acidity regulators , raising agents , sequestrants , and water retention agents in food processing. They are classified in the E number scheme under E450: In particular, various formulations of diphosphates are used to stabilize whipped cream . PKa In chemistry , an acid dissociation constant (also known as acidity constant , or acid-ionization constant ; denoted K
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1974-420: The standard enthalpy change , Δ H ⊖ {\displaystyle \Delta H^{\ominus }} , is negative and K decreases with temperature. For endothermic reactions, Δ H ⊖ {\displaystyle \Delta H^{\ominus }} is positive and K increases with temperature. The standard enthalpy change for
2021-399: The standpoint of high energy phosphate accounting, the hydrolysis of ATP to AMP and PP i requires two high-energy phosphates, as to reconstitute AMP into ATP requires two phosphorylation reactions. The plasma concentration of inorganic pyrophosphate has a reference range of 0.58–3.78 μM (95% prediction interval). Isopentenyl pyrophosphate converts to geranyl pyrophosphate ,
2068-460: The symbol p K a . On the other hand, association constants are used for bases. However, general purpose computer programs that are used to derive equilibrium constant values from experimental data use association constants for both acids and bases. Because stability constants for a metal-ligand complex are always specified as association constants, ligand protonation must also be specified as an association reaction. The definitions show that
2115-458: The title PPI . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=PPI&oldid=1210399589 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Pyrophosphate Pyrophosphoric acid
2162-434: The value of an acid dissociation constant is the reciprocal of the value of the corresponding association constant: Notes All equilibrium constants vary with temperature according to the van 't Hoff equation R {\displaystyle R} is the gas constant and T {\displaystyle T} is the absolute temperature . Thus, for exothermic reactions,
2209-415: The values obtained with (1) and (2). It is common practice in biochemistry to quote a value with a dimension as, for example, " K a = 30 mM" in order to indicate the scale, millimolar (mM) or micromolar (μM) of the concentration values used for its calculation. An acid is classified as "strong" when the concentration of its undissociated species is too low to be measured. Any aqueous acid with
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