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C–C Bond Cleavage: Retro-Aldol Reaction

C–C Bond Cleavage: Retro-Aldol Reaction

The reverse of the aldol addition reaction is called the retro-aldol reaction. Here, the carbon–carbon bond in the aldol product is cleaved under acidic or basic conditions to form two molecules of carbonyl compounds. The mechanism of the reaction consists of three steps.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.

Cleavage and Blastulation

Cleavage and Blastulation

After a large-single-celled zygote is produced via fertilization, the process of cleavage occurs while zygotes travel through the uterine tube. Cleavage is a mitotic cell division that does not result in growth. With each round of successive cell division, daughter cells get increasingly smaller.

Bond Energies and Bond Lengths

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, that is, the energy necessary to separate the bonded atoms. Separating any pair of bonded atoms requires energy — the stronger a bond, the greater the energy required to break it.

Peptide Bonds

Peptide Bonds

A peptide bond covalently attaches amino acids through a dehydration reaction. One amino acid's carboxyl group and another amino acid's amino group combine, releasing a water molecule. The resulting bond is the peptide bond. The products that such linkages form are peptides. As more amino acids join this growing chain, the resulting chain is a polypeptide. Each polypeptide has a free amino group at one end. This end has the N-terminal, or the amino-terminal, and the other end has a free...

Bonding in Metals

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Drüde called the “Electron Sea Model”.

Ionic Bonds

Ionic Bonds

Overview
When atoms gain or lose electrons to achieve a more stable electron configuration they form ions. Ionic bonds are electrostatic attractions between ions with opposite charges. Ionic compounds are rigid and brittle when solid and may dissociate into their constituent ions in water. Covalent compounds, by contrast, remain intact unless a chemical reaction breaks them.
Opposing Charges Hold Ions Together in Ionic Compounds
Ionic bonds are reversible electrostatic interactions between ions...

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Updated: Feb 4, 2026

Programming Stem Cells for Therapeutic Angiogenesis Using Biodegradable Polymeric Nanoparticles

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Published on: September 27, 2013

Biodegradable Silica-Based Nanoparticles: Dissolution Kinetics and Selective Bond Cleavage.

Jonas G Croissant¹, C Jeffrey Brinker¹

¹Chemical and Biological Engineering, University of New Mexico, Albuquerque, NM, United States; Center for Micro-Engineered Materials, Advanced Materials Laboratory, University of New Mexico, Albuquerque, NM, United States.

|September 25, 2018

Summary

Silica nanomaterials exhibit diverse toxicity and biodegradability profiles, contrary to common assumptions. Tailoring silica hybrid materials allows for controlled degradation, enhancing their safe application in biomedical research and industry.

Keywords:

Biodegradability Dissolution Mesoporous silica nanoparticles Organosilica Silica hybrid Silsesquioxanes

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Area of Science:

Materials Science
Nanotechnology
Biomedical Engineering

Background:

Silica-based nanomaterials are widely utilized in industry and biomedical research.
Assessing their toxicity and biodegradability is crucial for safe application.
Existing literature presents conflicting data on silica's environmental and biological fate.

Purpose of the Study:

To clarify the complex nature of silica toxicity and biodegradability.
To challenge the simplistic view of silica as a uniform material.
To highlight the potential of silica hybrids in modulating degradation.

Main Methods:

Review and synthesis of existing literature on silica behavior.
Kinetic analysis of silica dissolution in aqueous environments.
Exploration of silica hybrid design for tunable degradation mechanisms.

Main Results:

Silica is not a monolithic entity; diverse silica and silica hybrid materials possess varied biocompatibility and biodegradability.
All silica forms degrade in water via dissolution, following established kinetic principles.
Tuning silica hybrid composition enables control over degradation pathways.

Conclusions:

A nuanced understanding of 'silicas' and 'silica hybrids' is necessary, moving beyond a singular 'silica' model.
The inherent degradability of silica by dissolution provides a foundation for predictable behavior.
Engineered silica hybrids offer promising avenues for developing advanced materials with tailored degradation for specific applications.