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Related Concept Videos

Factors Affecting Solubility04:01

Factors Affecting Solubility

Compared with pure water, the solubility of an ionic compound is less in aqueous solutions containing a common ion (one also produced by dissolution of the ionic compound). This is an example of a phenomenon known as the common ion effect, which is a consequence of the law of mass action that may be explained using Le Chȃtelier’s principle. Consider the dissolution of silver iodide:
Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids02:04

Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids

Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
Factors Affecting α-Alkylation of Ketones: Choice of Base01:10

Factors Affecting α-Alkylation of Ketones: Choice of Base

α-Alkylation of ketones is achieved in the presence of alkyl halides and a base. The reaction proceeds via the formation of an enolate ion followed by nucleophilic substitution. The choice of base employed is essential as it is the key factor in determining the reaction outcome.
The reaction involving bases like EtO− whose conjugate acid EtOH (pKa = 15.9) is stronger than the ketone (pKa = 19.2) results in an equilibrium mixture with higher ketone concentration. As a consequence, side reactions...
Role of Skin in Vitamin D Synthesis01:23

Role of Skin in Vitamin D Synthesis

The skin plays a crucial role in the synthesis of vitamin D, a vital nutrient for various physiological processes in the body. Vitamin D is unique because it can be synthesized in the skin through a series of chemical reactions triggered by exposure to ultraviolet B (UVB) radiation from sunlight.
The solar UV B rays (290-315 nm) are absorbed by the skin, and 7-dehydrocholesterol (provitamin D3) photolyzes it to previtamin D3, which undergoes a rapid transformation to vitamin D3(cholecalciferol).
Pigmentation01:19

Pigmentation

The color of the skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Recall that melanin is produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The melanin is transferred to the keratinocytes via melanosomes.
Melanin occurs in two primary forms: eumelanin that provides black and brown pigment and pheomelanin that provides red color. Dark-skinned individuals produce more melanin than those with pale...
Factors Influencing Drug Absorption: Physicochemical Parameters01:22

Factors Influencing Drug Absorption: Physicochemical Parameters

The physicochemical characteristics of drugs play a crucial role in formulating stable and bioavailable drug products. The solubility of a drug, governed by the varying pH along the GI tract and its dissociation constant (pKa), is pivotal in determining its ionization state and absorption rate. Notably, weak acids and bases remain unionized and are absorbed more rapidly.
Enhanced drug absorption can be achieved by reducing particle sizes and increasing surface areas, thereby facilitating...

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Related Experiment Video

Updated: May 28, 2026

Pharmacologic Induction of Epidermal Melanin and Protection Against Sunburn in a Humanized Mouse Model
12:37

Pharmacologic Induction of Epidermal Melanin and Protection Against Sunburn in a Humanized Mouse Model

Published on: September 7, 2013

Factors influencing sunless tanning with dihydroxyacetone.

B-C Nguyen1, I E Kochevar

  • 1Wellman Laboratories of Photomedicine, Department of Dermatology, Massachusetts General Hospital, WEL-224, Harvard Medical School, 50 Blossom Street, Boston, MA 02114, USA.

The British Journal of Dermatology
|August 23, 2003
PubMed
Summary
This summary is machine-generated.

Sunless tanning reactions depend on hydration, pH, and amino acids. Optimizing these factors may enhance pigment and photoprotection from dihydroxyacetone (DHA) sunless tanners.

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Last Updated: May 28, 2026

Pharmacologic Induction of Epidermal Melanin and Protection Against Sunburn in a Humanized Mouse Model
12:37

Pharmacologic Induction of Epidermal Melanin and Protection Against Sunburn in a Humanized Mouse Model

Published on: September 7, 2013

Preparation of Keratin Hydrolysate from Chicken Feathers and Its Application in Cosmetics
08:29

Preparation of Keratin Hydrolysate from Chicken Feathers and Its Application in Cosmetics

Published on: November 27, 2017

Quantification of Hypopigmentation Activity In Vitro
06:08

Quantification of Hypopigmentation Activity In Vitro

Published on: March 6, 2019

Area of Science:

  • Dermatology
  • Cosmetic Science
  • Biochemistry

Background:

  • Sunless tanning products utilize dihydroxyacetone (DHA) to create temporary pigmentation through reactions with stratum corneum amino acids.
  • These preparations have been popular for over 50 years, mimicking a natural tan without UV exposure.

Purpose of the Study:

  • To investigate factors influencing dihydroxyacetone (DHA) reactions with amino acids in the stratum corneum.
  • The primary goal is to enhance DHA-induced pigmentation for improved photoprotection.

Main Methods:

  • Assessed the impact of hydration and oxygen on DHA-induced pigment development in vivo and ex vitro.
  • Utilized diffuse reflectance and fluorescence emission spectroscopy to quantify pigment formation.
  • Studied the reaction kinetics between DHA and nine amino acids across different pH levels (5 and 7).

Main Results:

  • Pigmentation was inhibited by occlusion but resumed post-occlusion, indicating DHA persistence.
  • High hydration levels and absence of oxygen influenced coloration; pigmentation correlated with humidity up to 75% but decreased thereafter.
  • Lysine, glycine, and histidine showed the fastest reactions with DHA, particularly at pH 7. Reaction products absorbed light up to 340 nm.

Conclusions:

  • Stratum corneum hydration, pH, and specific amino acid availability are key determinants of DHA-induced pigmentation.
  • Manipulating these factors presents an opportunity to develop sunless tanning products with enhanced photoprotective qualities.