Name: luminol chemiluminescence in forensics
Uploaded: 2020-03-26T07:22:29.000Z
Duration: 3 min 2 s
Channel: JoVE

通常、反応物が生成物に変化するとき、そのエネルギーの差は反応のエンタルピーとして知られており、熱が放出される発熱性、または熱が吸収される吸熱性のいずれかです。
化学発光反応では、反応物は中間体を形成し、中間体は電子的に励起された状態にあります。この中間体は不安定です。基底状態までリラックスすると、中間体の電子は熱の形でではなく、可視光の放出でエネルギーを放出します。
この現象は蛍光に似ています。分子内の電子が基底状態を占めていることを思い出してください。特定の波長の光にさらされたときなど、エネルギーを吸収すると、興奮して、より高い励起エネルギーレベルに移行します。励起状態が基底状態に戻ると、過剰なエネルギーが可視光の形で放出されます。
ただし、2つを区別することが重要です。違いは、分子の電子がどのように励起されるかです。化学発光では、化学反応から発生するエネルギーで電子が励起されますが、蛍光では、光エネルギーなどの電磁放射を直接吸収することで電子が励起されます。電子が基底状態までリラックスすると、どちらのタイプの発光も放出された光としてエネルギーを放出します。
それぞれの例を見てみましょう。 トニックウォーターのボトルにUVライトを当てると、キニーネの電子がエネルギーを吸収し、より高いエネルギーレベルに励起されます。電子がリラックスすると、青色光の形でエネルギーを放出します。
次に、シュウ酸ジフェニルと染料を含む外側のチューブと、過酸化水素を含む内側のチューブがあるグロースティックを考えてみましょう。グロースティックを曲げると、インナーチューブが壊れて反応物が混ざり合います。過酸化水素はシュウ酸ジフェニルを酸化して、フェノールと環状過酸化物を形成します。環状過酸化物は二酸化炭素に分解し、エネルギーを放出して染料をより高いエネルギーレベルに励起します。色素が基底状態に弛緩すると、光子が放出されます。ここで、色素を励起するために供給されるエネルギーは化学反応から来るため、プロセスは化学発光です。
このラボでは、一連の反応を行うことにより、3-アミノフタルヒドラジド(ルミノールとも呼ばれる)を合成します。次に、ルミノールを固体の水酸化カリウムの上でジメチルスルホキシドと反応させて、その化学発光を観察します。

ルミノールの合成

Synthesis of Luminol

化学反応は、反応が生成物に変化したときに熱を吸収するか放出するかによって、吸熱性または発熱性に分類できます。反応物と生成物の間のエネルギー差は、反応のエンタルピーとして知られています。これは、生成物と反応物との間のエネルギー差、つまりΔHを計算することによって求められます。ΔHが正の場合、反応は吸熱性です。陰性の場合、反応は発熱性です。化学反応は伝統的に反応物を生成物に変換すると考えられてきましたが、多くの反応は複数のステップで行われ、中間体を形成します。化学発光反応では、これらの中間体は高エネルギー状態から基底状態に遷移し、反応が進行するにつれて見える光子を放出します。
<h4>原子力レベル</h4>
デンマークの物理学者であるニールス・ボーアは、原子核を周回する電子は特定の軌道またはエネルギー準位しか占められないという理論を提唱しました。すべての電子が可能な限り低いエネルギー準位にある原子は、基底状態にあると言われます。電子が基底状態よりも高いエネルギー準位を占めるとき、原子は励起状態になります。
ボーアの理論の重要な仮定は、電子は攪乱されるまで基底状態に留まるということです。したがって、電子はエネルギーを吸収することによってのみ励起状態に上昇します。電子が基底状態に戻ると、そのエネルギーが放出されます。多くの場合、これは光子の形をしており、その波長は励起状態と基底状態との間のエネルギー差に直接関係しています。
電子が特定のエネルギーまたは波長の光を吸収することによってより高いエネルギーレベルに励起されるとき、この現象は蛍光と呼ばれます。この効果は、洗濯した白いTシャツをブラックライトまたはUVライトにさらすと確認できます。特徴的な輝きは、シャツに含まれる洗剤と漂白剤の蛍光によって引き起こされ、通常の光の下では白く見えます。
<h4>化学 発光</h4>
化学発光反応では、反応中に放出される熱を吸収することにより、電子が励起されます。その後、電子が基底状態に戻ると光が放出されます。化学発光と蛍光の主な違いは、化学発光で電子を励起するエネルギーが反応から直接得られることです。
化学発光の実用化の1つは、市販のグロースティックです。グロースティックには、過酸化物を含む溶液とシュウ酸ジフェニルと着色染料を含む溶液の2つの別々の溶液が含まれています。2つの溶液を混合すると、これはグロースティックを作動させたときに起こり、過酸化物とシュウ酸ジフェニルとの間の反応により、色素をより高いエネルギー状態に励起するエネルギーが生成されます。反応物が使い果たされると、色素は基底状態に戻り、光を放出します。これがグロースティックに特徴的な色を与えている理由です。
<h4>ルミノール</h4>
ルミノールは化学発光特性を示す化学物質であり、特に法医学など幅広い用途で利用されています。ルミノール(C8H7N3O2)は、酸化剤と混合すると青色を放出します。法医学の場合、ルミノールはヘモグロビン中の鉄と反応するため、法医学者は非常に小さな微量の血液を特定することができます。
ルミノールは、3-ニトロフタル酸とヒドラジンの脱水反応によって合成されます。反応を加熱して水分を取り除き、トリエチレングリコールを加えてさらに温度を上げます。次に、3-ニトロフタルヒドラジドのニトロ基をジチオン酸ナトリウムを使用して還元し、高pHでアミノ基を形成します。基本的な条件では、3-ニトロフタルヒドラジドは可溶性です。氷酢酸を添加すると、ルミノールが沈殿します。
水酸化カリウムを使用すると、ルミノールはジアニオンを形成します。水酸化物アニオンは、ルミノール中の窒素に結合している2つの水素を脱プロトン化します。酸素ガスはルミノールを励起状態に酸化します。基底状態に戻ると、青白色の光を放出します。
<h4>参照</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2015).化学および化学反応性。カリフォルニア州ベルモント:ブルックス/コール、Cengage Learning。</li>
</ol>

化学反応は、反応が生成物に変化したときに熱を吸収するか放出するかによって、吸熱性または発熱性に分類できます。...

Education

JoVE Lab Manual

Chemistry

化学

luminol chemiluminescence in forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic.

Many reactions do not happen in a single step. They can pass through intermediates along the way. In chemiluminescent reactions, these intermediates move from a high-energy state to the ground state and release a photon of light. That light can be seen as the reaction continues.

Atomic energy levels help explain why this glow happens. Niels Bohr proposed that electrons can occupy only certain orbits, or energy levels, around the nucleus. An atom is in the ground state when its electrons are in the lowest possible energy level. When an electron moves to a higher level, the atom is in an excited state. The electron must absorb energy to move up, and it releases that energy when it falls back down. This release is often a photon of light, and the light wavelength depends on the energy gap. When light causes this kind of excitation, the process is called fluorescence, such as the glow seen under a black light on a white T-shirt washed with detergent and bleach compounds.

Chemiluminescence is related to fluorescence, but the energy comes from the chemical reaction itself. In glow sticks, one solution contains peroxide and the other contains diphenyl oxalate and a color dye. When the solutions mix, the reaction produces energy that excites the dye. As the reactants are used up, the dye returns to the ground state and gives off light. This is why glow sticks have their characteristic color.

Luminol is a chemiluminescent chemical with an important forensic use. It emits blue light when mixed with an oxidizing agent. In forensic science, luminol reacts with the iron in hemoglobin, which helps detect very small traces of blood. Luminol is made by dehydrating 3-nitrophthalic acid with hydrazine. The reaction is heated to remove water, and triethylene glycol is added to raise the temperature further. Next, the nitro group in 3-nitrophthalhydrazide is reduced with sodium dithionite to form an amino group at high pH. The compound is soluble in basic conditions, and glacial acetic acid is added to precipitate the luminol. With potassium hydroxide, luminol forms a dianion because hydroxide ions remove the two hydrogens attached to the nitrogens. Oxygen gas then oxidizes luminol to its excited state. When it relaxes back to the ground state, it gives off a blue-white light.

Luminol Chemiluminescence in Forensics

lab techniques

Measuring with Accuracy in the Lab

Measuring with accuracy in the lab starts with careful records, the right tools, and correct reading of data. Scientists use lab notebooks to record how an experiment was done. These notes include the amounts of materials used and each step of the procedure. Without that record, an experiment cannot be repeated in the same way. Balances and glassware are used to measure solids and liquids for experiments. The precision of a measurement depends on the equipment used. Digital balances show the...

scientific measurement and lab skills

Graphs, Curve Fit, and Standard Deviation

Two-dimensional graphs help students compare an independent variable with a dependent variable in science data. In a chemistry example, temperature is the independent variable and volume is the dependent variable. After data are collected, the relationship between the two measurements must be quantified so it can be evaluated and compared with other relationships. A graph can also show when no relationship exists between the two variables. To make a two-dimensional graph, each data point needs...

stoichiometry, product yield, and limiting reactants

stoichiometry-product-yield-and-limiting-reactants

Balancing Equations and Reactant Limits

Chemical equations show how reactants change into products during a reaction. Stoichiometry is the study of the relative amounts of reactants and products. It is based on the Law of Conservation of Mass, which says matter is neither created nor destroyed. Because atoms are only rearranged, the number and identity of atoms must match on both sides of a reaction. That is why a chemical equation must be balanced. A balanced equation has the same number of atoms for each element in the reactants...

redox reactions

Oxidation States in Redox Reactions

Oxidation states help identify redox reactions. In a redox reaction, oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons. These reactions are often tracked by changes in oxidation state, also called oxidation number. Each atom in a molecule has an oxidation state. This number shows how oxidized an atom is compared with its free elemental form. It is written as the charge an atom would have if every bond were purely ionic. In that model, bonding...

ideal gas law

Gas Laws Behind the Ideal Gas Equation

The ideal gas equation brings together the main gas laws used in chemistry. Gases have molecules that are far apart, so their behavior is described with four measurable variables: pressure, volume, number of moles, and temperature. The ideal gas law links these variables with the gas constant, R, which equals 8.314 J·K−1 mol−1. Boyle’s law describes the link between pressure and volume. When temperature and the number of moles stay constant, pressure and volume change in opposite directions.

acid and base concentrations

Acids, Bases, and pH in Titration

Acids, bases, and pH explain how acidic or basic a solution is. An Arrhenius acid releases hydrogen ions when it dissolves in water, while an Arrhenius base releases hydroxide ions. These reactions also create conjugate partners: an acid forms a conjugate base after losing hydrogen, and a base forms a conjugate acid after losing hydroxyl. Every acid has a conjugate base, and every base has a conjugate acid. pH measures the amount of hydrogen ions in a solution. The pH scale runs from 0 to 14...

buffers

Buffer pH and the Common Ion Effect

Buffer solutions help keep pH steady when acids or bases are added. In water, an Arrhenius acid (HA) dissociates into hydrogen ions, H+, and a conjugate base, A-. More hydrogen ions make a solution more acidic and lower its pH. An Arrhenius base (BOH) dissociates into a conjugate acid, B+, and hydroxide ions, OH-. Strong acids and strong bases usually change pH a lot because they react completely in water and raise the amount of H+ or OH-. Buffers reduce those pH changes. A buffer usually...

enthalpy of reaction

Reaction Heat, Hess’s Law, and Calorimetry

Reaction heat is explained through enthalpy, Hess’s law, and calorimetry. These ideas show how heat moves during chemical reactions and how scientists measure it. Thermodynamics is the study of heat energy and other forms of energy, such as work. Its laws are used across science, from biology to physics. The first law says energy is conserved in an isolated system. Energy can change form, such as thermal energy becoming work, but it cannot be created or destroyed. The second law of...

solubility

Solubility in Water and Other Solvents

Solubility describes how much of a solute can dissolve in a specific solvent. It is usually reported as solute mass per solvent volume or as solute mass per solvent mass. For example, sodium chloride has a solubility of 36 g per 100 mL of water at room temperature. If solubility is given by solvent mass, that mass must be converted to volume for later calculations. Temperature changes solubility. Sodium carbonate dissolves at about 7 g per 100 mL of water at 0 °C, 22 g per 100 mL at room...

metal flame emission

Flame Test Metal Color Clues

Flame testing uses a metal sample and a flame to identify a substance by its color. Each element gives off a characteristic light emission in the flame, so the color can help distinguish one element from another. This same idea appears in fireworks, where different metal components create different colors. The color comes from energy absorbed by the metallic component. When a species absorbs energy, that energy can go into translation, vibration, rotation, or electron excitement. Electron...

balmer series

Hydrogen Emission Lines

Hydrogen emission lines show how electrons move between fixed energy levels in the Bohr model. Niels Bohr proposed this model for the hydrogen atom in 1913. In this model, an electron can only occupy certain orbits, and it cannot exist between them. These energy states are labeled with the quantum number n. The ground state is n = 1. Higher values, such as n = 2, 3, 4, and so on, are excited states. An electron changes state only by absorbing or emitting energy equal to the difference between...

beer's law

Absorbance Spectra and Beer-Lambert Analysis

Absorbance spectra and the Beer-Lambert Law show how light can be used to study molecules in solution. When light hits a substance, it may be absorbed, transmitted, or reflected. A substance often interacts with a range of wavelengths, and each wavelength can affect the molecules or atoms in a different way. When a molecule absorbs light, that energy can be used for translation, vibration, rotation, or electron excitement. Electron excitement is especially important in spectroscopy because it...

concentration dependence

Reaction Order and Rate Constants

Chemical kinetics describes the speed of a chemical reaction. The rate depends on the reaction mechanism, the complexity of the reaction, and the number of reactants involved. Reactant concentration also affects how fast a reaction happens. The rate law is the experimental relationship that connects these factors to reaction rate. In the rate law, each reactant contributes through a reaction order. The general form is r = k[A]^m[B]^n for aA + bB + ... → cC. Here, r is the reaction rate, k is...

temperature dependence

Reaction Rate, Arrhenius, and Catalysts

Chemical kinetics explains how fast a reaction happens and why that speed changes. The reaction rate is the speed of a chemical reaction. It is defined as the change in concentration of a reactant or product over time. Reaction speed depends on several factors, including the concentration of the reactants and the temperature of the reaction. Each reactant affects the rate in a specific way. That relationship is described by the rate law. The rate law is an equation that connects the...

galvanic cells

Battery Power from Redox Reactions

Electrochemistry studies how chemical change and electrical energy are linked. In this branch of chemistry, electrons move from one species to another. That movement can either produce current or be driven by an applied current. The main reaction in electrochemistry is the oxidation-reduction, or redox, reaction. A redox reaction has two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. These changes also shift the oxidation state of each substance. The...

electrolytic cells

Electroplating with Electrolytic Cells

Electrochemistry links electrical energy with chemical change, and electrolytic cells show how electricity can drive a nonspontaneous reaction. In these reactions, electrons move from one species to another. The key chemistry is a redox reaction, or oxidation-reduction reaction, which happens in two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. The substance that loses electrons is the reducing agent, and the substance that gains electrons is the...

proper lab notebook keeping

Recording a Reproducible Lab Experiment

Accurate lab notebook records are essential in science and organic chemistry labs. Without clear notes, descriptions, quantities, and observations, an experiment cannot be repeated or checked. Good record keeping supports reproducibility, which means other people can follow the same work and get similar results. A laboratory notebook is useful in school labs, research settings, and industry. It can also become a legal record when an idea, process, substance, or technique is patented and...

basic organic chemistry techniques

Organic Lab Glassware and Safe Handling

Organic chemistry labs use specific glassware, careful weighing steps, and controlled heating to keep reactions safe and accurate. Beakers and Erlenmeyer flasks are often used for mixing or holding solvents, but they are not meant for measuring volume unless only an approximate amount is needed. Volumetric glassware is used when a precise volume matters. This group includes graduated cylinders, volumetric pipettes, and volumetric flasks. A graduated cylinder is commonly used in the organic lab...

melting points

How Impurities Change Melting Points

Melting point helps identify an organic compound by showing the temperature where a solid turns into a liquid at 1 atmosphere of pressure. It is a physical property, like solubility, density, color, and electronegativity. Because the exact start of melting is hard to measure, the result is reported as a range. The lower end is when the first drops of liquid appear. The upper end is when the last solid has melted. Scientists compare this range with literature values to help identify a compound. <br...

boiling points

Boiling Point and Vapor Pressure

Boiling point and vapor pressure are key physical properties of a liquid. For a pure compound, the boiling point can help identify the substance. In experiments, the boiling point is usually recorded as a range because exact values are hard to measure and may differ by a few degrees from the literature value. Vapor pressure explains why a liquid boils. In a sealed container, some molecules at the liquid surface gain enough energy to escape into the gas phase. At the same time, some gas...

recrystallization

Purifying Crystals by Solubility

Purifying crystals by solubility is a key organic chemistry technique. Recrystallization uses differences in solubility to separate a desired solid product from starting materials, solvent, and impurities. It is one of the three standard purification methods, along with distillation and extraction. Solubility is the maximum amount of a substance that can dissolve in a fixed volume of solvent at a given temperature. Different solutes dissolve in different solvents, and their behavior can vary...

extraction

Separating Mixtures with Solvent Extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point. There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase...

simple distillation

Separating Liquids by Boiling Point

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

thin-layer chromatography

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats. A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result,...

synthesis of luminol

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary. Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical...

chemistry

入門化学ラボコースの指導者と学生のための、包括的でカリキュラムに焦点を当てたビデオ。

https://cloudfront.jove.com/files/banners/scicat/labbio.jpg

Learn how luminol chemiluminescence produces blue-white light, why glow sticks glow, and how forensic scientists use luminol to detect traces of blood.

Luminol Chemiluminescence in Forensics | JoVE K12

ルミノールの合成 を教える準備を、この 5 分間の教員向けガイドで行いましょう。JoVE Lab Manual の Chemistry ラボの主要な準備手順を解説します。

Chemistry の ルミノールの合成 教員準備 - 2.4K+ 回の視聴 | JoVE Lab Manual

この 14 分間の学生プロトコル動画で、ルミノールの合成 の手順をステップごとに学びましょう。JoVE Lab Manual の Chemistry コレクションの一部です。

Chemistry の ルミノールの合成 学生プロトコル - 9.7K+ 回の視聴 | JoVE Lab Manual

Luminol Chemiluminescence in Forensics

Description

Transcript