Propidium iodide
[CAS# 25535-16-4]

Identification

• Name: Propidium iodide
• Synonyms: 3,8-Diamino-5-[3-(diethylmethylammonio)propyl]-6-phenylphenanthridinium diiodide
• Molecular Formula: C₂₇H₃₄I₂N₄
• Molecular Weight: 668.39
• CAS Registry Number: 25535-16-4
• EC Number: 247-081-0
• SMILES: CC[N+](C)(CC)CCC[N+]1=C2C=C(C=CC2=C3C=CC(=CC3=C1C4=CC=CC=C4)N)N.[I-].[I-]

Properties

• Solubility: 5 mM (water)
• Melting point: 220-225 ºC (decomp.

Safety Data

• Hazard Symbols: GHS07;GHS08 Warning
• Hazard Statements: H315-H319-H335-H341
• Precautionary Statements: P203-P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P318-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Germ cell mutagenicity	Muta.	2	H341
Specific target organ toxicity - single exposure	STOT SE	3	H336

Discovory and Applicatios

Propidium iodide (PI) is a red fluorescent dye that is widely used in the field of molecular biology due to its ability to bind to DNA. The discovery of propidium iodide revolutionized the study of cell viability, apoptosis, and cell cycle analysis. PI is particularly useful due to its special properties: it intercalates into double-stranded DNA but cannot penetrate living cells, making it an excellent marker for dead cells or cells with damaged membranes.

Propidium iodide was first synthesized in the mid-20th century during the exploration of new fluorescent dyes for biological applications. Its development was part of a broader effort to create tools that could provide insight into cellular processes through fluorescence microscopy and flow cytometry. The ability of the dye to fluoresce red upon binding to DNA was quickly recognized as a powerful feature for a variety of applications.

One of the main applications of propidium iodide is in cell viability assays. In these assays, PI is used to distinguish between live and dead cells. Because PI cannot penetrate the intact cell membrane of living cells, it selectively stains only cells with damaged cell membranes, which are typically dead or dying cells. When combined with other fluorescent dyes that stain live cells, such as calcein-AM, researchers can visualize live and dead cells simultaneously under a fluorescence microscope or analyze them using flow cytometry. This dual staining approach is essential for evaluating the effectiveness of cytotoxic agents, such as drugs or environmental toxins, in killing cells.

In addition to viability assays, propidium iodide is widely used to study apoptosis, the process of programmed cell death. During apoptosis, cells undergo a series of morphological and biochemical changes, including DNA fragmentation. PI staining allows researchers to detect these changes by binding to fragmented DNA, which indicates that cells are undergoing apoptosis. This application is particularly important in cancer research, as understanding and inducing apoptosis in cancer cells is a key therapeutic strategy.

Another important application of propidium iodide is cell cycle analysis. By staining the DNA of cells in a population, propidium iodide can be used to determine the distribution of cells in different phases of the cell cycle (G0/G1, S, and G2/M phases). In flow cytometry, cells are treated with propidium iodide and then passed through a laser, which excites the dye and causes it to fluoresce. The fluorescence intensity is proportional to the amount of DNA in each cell, allowing researchers to quantify the number of cells in each phase of the cell cycle. This information is essential for studying cell proliferation and the effects of various treatments on cell cycle progression.

Propidium iodide is also used in microbiology to assess the viability of bacterial cells. Similar to its use in eukaryotic cells, propidium iodide can distinguish between live and dead bacteria by staining only those with damaged membranes. This is particularly useful for evaluating the effectiveness of antibiotics and disinfectants.

In the field of clinical diagnostics, propidium iodide plays an important role in cytogenetics and can be used to stain chromosomes for karyotyping. This application helps identify chromosomal abnormalities and is valuable for diagnosing genetic diseases and cancer.

Despite its wide range of applications, propidium iodide also has some limitations to its use. For example, propidium iodide cannot distinguish between different types of dead cells or specific causes of cell death. In addition, due to its nonspecific binding to DNA, propidium iodide staining must be carefully controlled to avoid background fluorescence interfering with data interpretation.