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Solvating Effects

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...

SN1 Reaction: Mechanism

S_N1 Reaction: Mechanism

Kinetic studies of ionization of a tertiary halide in a protic solvent suggest that only the substrate participates in the rate-determining step (slow step). The nucleophile is involved only after the slowest step. The SN1 reaction takes place in a multiple-step mechanism.
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a polar...

Chemical Shift: Internal References and Solvent Effects

Chemical Shift: Internal References and Solvent Effects

In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...

Nuclear Overhauser Enhancement (NOE)

Nuclear Overhauser Enhancement (NOE)

Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the nuclear Overhauser enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active...

Nucleophilic Substitution Reactions

Nucleophilic Substitution Reactions

Historical perspective
In 1896, the German chemist Paul Walden discovered that he could interconvert pure enantiomeric (+) and (-) malic acids through a series of reactions. This conversion suggested the involvement of optical inversion during the substitution reaction. Further, in 1930, Sir Christopher Ingold described for the first time two different forms of nucleophilic substitution reactions, which are known as SN1 (nucleophilic substitution unimolecular) and SN2 (nucleophilic substitution...

Conjugate Addition of Enolates: Michael Addition

Conjugate Addition of Enolates: Michael Addition

The attack of a nucleophile at the β carbon of an α,β-unsaturated carbonyl compound is called conjugate addition. Conjugate addition reactions of active methylene compounds, such as β-diketones, β-keto esters, β-keto nitriles, and α-nitro ketones, are called Michael addition reactions.

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Updated: Jul 3, 2026

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes

Published on: January 16, 2016

Microsolvation Redirects Electron-Induced Chemistry in Nucleobases.

Sejun An¹, Sang Kyu Kim¹

¹Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea.

The Journal of Physical Chemistry Letters

|July 2, 2026

Summary

Even one water molecule prevents DNA damage from low-energy electrons. Hydration redirects electron-induced chemical reactions in nucleobases, crucial for understanding biological environments.

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$Microcrystal Electron Diffraction of Small Molecules$

Microcrystal Electron Diffraction of Small Molecules

Published on: March 15, 2021

Area of Science:

Physical Chemistry
Chemical Physics
Biophysics

Background:

Low-energy electrons cause genetic material damage via bond rupture in DNA and RNA nucleobases.
Understanding electron-nucleobase interactions is vital for biological systems.

Purpose of the Study:

To investigate the effect of microsolvation on electron-induced damage to nucleobases.
To explore how water molecules alter the fragmentation dynamics of electron-attached uracil.

Main Methods:

Mass-selected hydrated uracil anions were studied.
Photoexcitation was performed over a broad energy range (0.5-5.5 eV).
Photofragment excitation spectroscopy was used to probe electronic structures.

Main Results:

A single water molecule suppresses covalent bond rupture in electron-attached uracil.
Excited clusters relax via internal conversion and sequential water evaporation, not bond cleavage.
A stochastic evaporation model accurately described solvent loss, with a binding energy of ~0.4 eV.

Conclusions:

Microsolvation fundamentally alters electron-induced damage pathways in nucleobases.
Immediate hydration redirects relaxation mechanisms, impacting electron-driven chemistry in aqueous biological environments.