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Quinaldine Red

Properties
Quinaldine red (pronounced kwin′al-dēn red) is an indicator. It has a 95% dye content composition. Free Quinaldine red does not have fluorescence in solution when it is not bound to anything. Quinaldine red is only visible by fluorescence when it is bound. It has 2 H- Bond acceptors.

Oxidation
The quinaldine red is cationic and undergoes oxidation at different levels of pH. The rate of oxidation of Quinaldine red is in the first order with respect to the concentration of hydrogen peroxide, the oxidizing agent. Other factors that increases the rate of oxidation includes increasing pH and increased sodium carbonate concentration. The reaction rate eventually levels off due to the maximum formation of peroxide anions within the oxidation process.

Phosphate detection
A pale pink mixture of quinaldine red can be used to detect free phosphate. PVA must be dissolved to 0.14% in water by boiling. Ammonium molybdate should then be dissolved to 12.3 mM in 1.2 M sulfuric acid. Quinaldine red dye is then dissolved in DMSO and added to the PVA solution to 0.1 mg/ml, 1% DMSO final concentration. PVA–dye would be mixed with molybdate–acid mix resulting in a very pale pink to colorless solution. The Quinaldine red dye mix can then be dispensed into the sample in question. The amount of dye added to different volumes of the sample should be determined using solutions containing increasing concentrations of inorganic phosphate. The lower detection limit and the linear dynamic range of the phosphate detection can be found through fluorescence quench absorbance. Any phosphate ions in the sample solution would react with 12 molybdate molecules to form a phosphomolybdate complex ion. This would subsequently be stained with the quinaldine red dye to form a red product. After the products are stained, the samples can then be read using excitation wavelength at 430 nm and emission at 530 nm. These results are useful for monitoring the activity of many enzymes such as phosphatases, ATPases, and GTPases.

Characteristics

 * CH4 + H2O → CO + 3 H2


 * 2 CH4 + O2 → 2 CO + 4 H2

Fluorescence activity
Quinaldine red (abbreviated as QR) does not exhibit fluorescence unless bounded to nucleic acids, which then emit radiation between 580-650 nm. Maximum fluorescence was detected from 557 nm to 607 nm. The results were produced when tested with Calf thymus DNA (CT-DNA) and yeast RNA separated, where the QR and the nucleic acids reacted quickly under room temperature. The resulting QR-nucleic acid complex was then stable for 1.5 hours, where the fluorescence would decrease afterwards. Maximum fluorescence between QR and DNA was found to lie within the pH range of 3.2-3.6, with a maxima at pH 3.5. The volume of 2.3 x 10-5 QR solution that allowed maximum and constant fluorescence effect was found to be from 1.0 - 2.0 ml. The amount of fluorescence was found to be linearly related to the concentrations of CT DNA or RNA. These findings prove useful for determining amounts of nucleic acids in a solution even as they replicate. Additionally, the use of QR is relatively safe, inexpensive and sensitive method compared with other fluorescence probes like ethidium bromide or dimeric cyanine dyes.

Quantative analysis of specific nucleic acids
During leukemia, the human body enters acute-phase response in which it increases concentrations of specific proteins in the plasma such as α1-acid glycoprotein (AAG) which decreasing others like human serum albumin (HSA). Quinaldine red can bind onto the carrier proteins in plasma, where the concentration of the QR- nuclei acid complex can be measured through spectrofluorometer due to the fluorescent property of QR complex. Leukemia increased Quinaldine red binding by 65%. The binding ability of cationic Quinaldine red onto the carrier proteins in plasma was measured using a spectrofluorometer with an emission wavelength of 520/610 nm. Samples of constant concentrations of the Quinaldine red but increasing concentrations of blood plasma can then be used in order to find the apparent dissociation constant (Kd )of the dye. The Kd value for the QR-AAG glycoprotein binding, of about 1 μM, indicate a considerably higher affinity of the QR to AAG than to albumin (for QR-HSA complex, Kd value is ~500 μM). Consequently, in plasma QR binds predominantly to AAG, even if the molar concentration of AAG is 1-2 orders of magnitude lower than albumin.