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Related Concept Videos

Basicity of Aliphatic Amines01:21

Basicity of Aliphatic Amines

7.3K
Amines can behave as Brønsted–Lowry bases by accepting a proton from the acid to form corresponding conjugate acids. Due to a lone pair of nonbonding electrons, aliphatic amines can also act as Lewis bases by forming a covalent bond with an electrophile.
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates...
7.3K
Acid and Bases: Ka, pKa, and Relative Strengths02:35

Acid and Bases: Ka, pKa, and Relative Strengths

37.1K
This lesson delves into a critical aspect of the relative strengths of acids and bases. The strength of an acid is evaluated by the acid dissociation into its conjugate base and a hydronium ion in water. The complete dissociation of a strong acid is confirmed with a very high concentration of hydronium ions. As a result, an incomplete dissociation process affirms a weak acid. Therefore, the equilibrium is in the forward direction for strong acids and backward for weak acids in these reactions.
37.1K
Basicity of Aromatic Amines01:18

Basicity of Aromatic Amines

8.4K
The basicity of aromatic amines is much weaker than that of aliphatic amines due to the involvement of the lone pair of electrons over the N atom in resonance with the aryl rings. Generally, the electron-donating ability of any substituents on the aryl ring of aromatic amines increases the basicity of the amine by increasing electron density, and hence the availability of lone pair on the nitrogen. On the other hand, electron-withdrawing functional groups on the aryl ring of amines decrease the...
8.4K
Basicity of Heterocyclic Aromatic Amines01:25

Basicity of Heterocyclic Aromatic Amines

7.2K
Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
7.2K
Weak Base Solutions03:21

Weak Base Solutions

27.6K
Some compounds produce hydroxide ions when dissolved by chemically reacting with water molecules. In all cases, these compounds react only partially and so are classified as weak bases. These types of compounds are also abundant in nature and important commodities in various technologies. For example, global production of the weak base ammonia is typically well over 100 metric tons annually, being widely used as an agricultural fertilizer, a raw material for chemical synthesis of other...
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Buffer Effectiveness02:19

Buffer Effectiveness

58.5K
Buffer solutions do not have an unlimited capacity to keep the pH relatively constant . Instead, the ability of a buffer solution to resist changes in pH relies on the presence of appreciable amounts of its conjugate weak acid-base pair. When enough strong acid or base is added to substantially lower the concentration of either member of the buffer pair, the buffering action within the solution is compromised.
The buffer capacity is the amount of acid or base that can be added to a given volume...
58.5K

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Related Experiment Video

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Determination of the Gas-phase Acidities of Oligopeptides
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Arginine: Its pKa value revisited.

Carolyn A Fitch1, Gerald Platzer, Mark Okon

  • 1Department of Biophysics, Johns Hopkins University, Baltimore, Maryland, 21218.

Protein Science : a Publication of the Protein Society
|March 27, 2015
PubMed
Summary

The arginine guanidinium group

Keywords:
NMR spectroscopyequilibrium acid dissociation constantguanidiniumpH titrationpKa valuepotentiometryprotein electrostaticstautomer

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Area of Science:

  • Biochemistry
  • Chemical Physics

Background:

  • The arginine guanidinium group's pKa is crucial for understanding protein electrostatics.
  • Previous estimates of arginine's pKa are commonly cited in biochemistry but may be inaccurate.

Purpose of the Study:

  • To accurately determine the intrinsic acid dissociation constant (pKa) of the arginine guanidinium group.
  • To reconcile the discrepancy between theoretical calculations and experimental observations of arginine's charge state in proteins.

Main Methods:

  • Potentiometry
  • Nuclear Magnetic Resonance (NMR) spectroscopy

Main Results:

  • The equilibrium acid dissociation constant (pKa) of the arginine guanidinium group was determined to be 13.8 ± 0.1.
  • This value is significantly higher than the commonly accepted value of approximately 12.

Conclusions:

  • The revised, higher pKa explains why arginine side chains are predominantly charged across a wide pH range.
  • Arginine side chains remain protonated under physiological conditions, even in hydrophobic environments.
  • This finding has significant implications for structure-based electrostatics calculations and protein function.