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Related Concept Videos

Solvating Effects02:12

Solvating Effects

An understanding of the solvating effect helps rationalize the relation between solvation and acidity of the compound. In addition, this also explains the relative stability of conjugate bases for compounds with different pKa values. This lesson details, in-depth, the principle of solvating effects. The strength of an acid and the stability of its corresponding conjugate base are determined using pKa values. This observed relationship is a consequence of solvation, which is the interaction...
Extraction: Effects of pH00:53

Extraction: Effects of pH

Consider a neutral form of an amine, B, with a partition coefficient, K, in a liquid mixture containing organic and aqueous phases. The pH of the aqueous phase affects the charge on acidic and basic solutes, and the charged form is usually more soluble in the aqueous phase. Suppose the conjugate acid form of the amine is soluble only in the aqueous phase while the base form is soluble in both phases. Then the distribution coefficient, D, can be given as the ratio of amine concentration in the...
Basicity of Aliphatic Amines01:21

Basicity of Aliphatic Amines

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 higher...
Solubility03:00

Solubility

Solution, Solubility, and Solubility Equilibrium
A solution is a homogeneous mixture composed of a solvent, the major component, and a solute, the minor component. The physical state of a solution—solid, liquid, or gas—is typically the same as that of the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
In a solution, the solute particles (molecules, atoms, and/or ions)...
Titration in Nonaqueous Solvents01:16

Titration in Nonaqueous Solvents

Most acid-base titrations are performed in an aqueous medium. In aqueous titrations, water competes with weaker acids or bases for proton donation or acceptance, leading to ambiguous endpoints in the titration curve. Water also affects the partial ionization of weak acids or bases. For example, water accepts a proton from acetic acid to form hydronium and acetate ions. The hydronium ion formed is a stronger acid than acetic acid, and the acetate ion is a stronger base than water. As a result,...
Basicity of Heterocyclic Aromatic Amines01:25

Basicity of Heterocyclic Aromatic Amines

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).

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Related Experiment Video

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Solubility of Hydrophobic Compounds in Aqueous Solution Using Combinations of Self-assembling Peptide and Amino Acid
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Preferential solvation in urea solutions at different concentrations: properties from simulation studies.

Hironori Kokubo1, B Montgomery Pettitt

  • 1Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA.

The Journal of Physical Chemistry. B
|April 24, 2007
PubMed
Summary

Urea solutions maintain stable hydrogen bonding locally, regardless of concentration. Different urea models affect simulation accuracy, with KBFF in TIP3P water best matching experimental data for density and diffusion.

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Area of Science:

  • Physical Chemistry
  • Computational Chemistry
  • Solution Chemistry

Background:

  • Urea solutions are crucial in biological and chemical systems.
  • Understanding urea's effect on water structure is key to explaining solution properties.
  • Previous studies have explored urea-water interactions with varying models.

Purpose of the Study:

  • To investigate the structural basis of urea solution thermodynamic properties using molecular dynamics simulations.
  • To compare the performance of two urea models (OPLS and KBFF) in reproducing experimental data.
  • To analyze hydrogen bonding characteristics and clustering behavior across different urea concentrations.

Main Methods:

  • Molecular dynamics simulations of urea solutions at various concentrations.
  • Utilized two urea models: OPLS and KBFF.
  • Analyzed hydrogen bond properties, density, diffusion constants, and preferential solvation.

Main Results:

  • Hydrogen bonding (number and lifetime) remained constant across concentrations, indicating local, not global, ideal behavior.
  • The KBFF urea model in TIP3P water accurately reproduced experimental density and diffusion data.
  • No persistent or large clusters of urea molecules were observed; molecules frequently changed clusters.

Conclusions:

  • Urea concentration affects how hydrogen bonds are satisfied locally, not the propensity for hydrogen bonding itself.
  • The KBFF model offers better agreement with experimental thermodynamic and transport properties of urea solutions.
  • Urea solutions exhibit dynamic local interactions rather than stable, large-scale aggregations.