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

عادة ، عندما تتغير المواد المتفاعلة إلى منتجات ، يعرف الاختلاف في طاقتها باسم المحتوى الحراري للتفاعل ، والذي يمكن أن يكون إما طاردا للحرارة ، حيث يتم إطلاق الحرارة ، أو ماص للحرارة ، حيث يتم امتصاص الحرارة. 
في تفاعل كيميائي ، تشكل المواد المتفاعلة وسيطا ، وهو في حالة إثارة إلكترونيا. هذا الوسيط غير مستقر. عندما يرتاح إلى الحالة الأرضية ، تطلق الإلكترونات الموجودة في الوسيط الطاقة في انبعاث الضوء المرئي بدلا من الحرارة 
هذه الظاهرة تشبه الفلورة. تذكر أن الإلكترونات في الجزيء تشغل الحالة الأرضية. عندما تمتص الطاقة ، كما هو الحال عند تعرضها لطول موجي معين من الضوء ، فإنها تصبح متحمسة وتنتقل إلى مستوى طاقة أعلى ومتحمس. عندما تسترخي الحالة المثارة مرة أخرى إلى الحالة الأرضية ، تنبعث الطاقة الزائدة على شكل ضوء مرئي. 
ومع ذلك ، من المهم التمييز بين الاثنين. الفرق هو كيفية إثارة إلكترونات الجزيئات. في التلألؤ الكيميائي ، تثير الطاقة المتولدة من تفاعل كيميائي الإلكترونات ... بينما في التألق ، يتم إثارة الإلكترونات عن طريق الامتصاص المباشر للطاقة الضوئية أو الإشعاع الكهرومغناطيسي الآخر. عندما تسترخي الإلكترونات إلى الحالة الأرضية ، يطلق كلا النوعين من اللمعان الطاقة كضوء منبعث. 
دعونا نلقي نظرة على مثال لكل منها. عندما تضيء ضوء الأشعة فوق البنفسجية على زجاجة من الماء المنشط ، فإن الإلكترونات الموجودة في الكينين تمتص الطاقة وتتحمس إلى مستوى طاقة أعلى. عندما تسترخي الإلكترونات ، فإنها تطلق الطاقة على شكل ضوء أزرق. 
الآن ، ضع في اعتبارك عصا التوهج ، التي تحتوي على أنبوب خارجي يحتوي على أكسالات ثنائي الفينيل وصبغة ، وأنبوب داخلي يحتوي على بيروكسيد الهيدروجين. عندما تثني عصا التوهج ، ينكسر الأنبوب الداخلي ، مما يسمح للمواد المتفاعلة بالاختلاط. يؤكسد بيروكسيد الهيدروجين أكسالات ثنائي الفينيل لتكوين الفينول والبيروكسيد الدوري. يتحلل البيروكسيد الدوري إلى ثاني أكسيد الكربون ، مما يطلق الطاقة التي تثير الصبغة إلى مستوى طاقة أعلى. عندما ترتاح الصبغة إلى الحالة الأرضية ، يتم إطلاق فوتون من الضوء. هنا ، العملية هي التلألؤ الكيميائي لأن الطاقة المقدمة لإثارة الصبغة تأتي من تفاعل كيميائي. 
في هذا المختبر ، ستقوم بتصنيع 3-أمينوفثالهيدرازيد ، المعروف أيضا باسم اللمينول ، عن طريق إجراء سلسلة من التفاعلات. سوف تتفاعل بعد ذلك مع ثنائي ميثيل سلفوكسيد على هيدروكسيد البوتاسيوم الصلب لمراقبة تلألؤه الكيميائي.

تخليق لومينول

Synthesis of Luminol

يمكن تصنيف التفاعلات الكيميائية على أنها ماص للحرارة أو طاردة للحرارة اعتمادا على ما إذا كانت التفاعلات تمتص الحرارة أو تطلقها عندما تتغير إلى منتجات. يعرف الفرق في الطاقة بين المواد المتفاعلة والمنتجات بالمحتوى الحراري للتفاعل. يتم العثور على ذلك عن طريق حساب الفرق في الطاقات بين المنتجات والمتفاعلات ، أو ΔH. إذا كان ΔH موجبا ، يكون التفاعل ماصة للحرارة. إذا كان سلبيا ، يكون رد الفعل طاردا للحرارة. بينما ينظر إلى التفاعلات الكيميائية تقليديا على أنها تحويل للمواد المتفاعلة إلى منتجات ، فإن العديد من التفاعلات تحدث في خطوات متعددة ، وتشكل مواد وسيطة. في التفاعلات الكيميائية ، تنتقل هذه المواد الوسيطة من حالة الطاقة العالية إلى الحالة الأرضية ، وتطلق فوتونا من الضوء قد يكون مرئيا مع تقدم التفاعل. 
<h4>مستويات الطاقة الذرية</h4>
اقترح نيلز بور ، الفيزيائي الدنماركي ، النظرية القائلة بأن الإلكترون الذي يدور حول نواة الذرة يمكن أن يشغل مدارات أو مستويات طاقة معينة فقط. يقال إن الذرة التي تحتوي على كل إلكتروناتها في أدنى مستوى طاقة ممكن تكون في حالتها الأرضية. عندما يشغل الإلكترون مستوى طاقة أعلى من الحالة الأرضية ، تكون الذرة في حالتها المثارة. 
الافتراض الرئيسي في نظرية بور هو أن الإلكترون يبقى في الحالة الأرضية حتى يتم إزعاجه. وبالتالي ، يتم رفع الإلكترون إلى حالة الإثارة فقط عن طريق امتصاص الطاقة. عندما يرتاح الإلكترون مرة أخرى إلى الحالة الأرضية ، فإنه يطلق تلك الطاقة. غالبا ما يكون هذا على شكل فوتون من الضوء ، يرتبط طوله الموجي ارتباطا مباشرا بفرق الطاقة بين الحالة المثارة والأرضية. 
عندما يتم إثارة الإلكترون إلى مستوى طاقة أعلى عن طريق امتصاص الضوء بطاقة أو طول موجي معين ، فإن هذه الظاهرة تسمى التألق. يمكن ملاحظة هذا التأثير إذا قمت بتعريض قميص أبيض مغسول لضوء أسود أو ضوء الأشعة فوق البنفسجية. يحدث التوهج المميز بسبب تألق المنظفات ومركبات التبييض في القميص ، مما يجعله يبدو أبيض تحت الضوء العادي. 
<h4>التلألؤ الكيميائي</h4>
في تفاعل المضيء الكيميائي ، يتم إثارة الإلكترون عن طريق امتصاص الحرارة المنبعثة أثناء التفاعل. بعد ذلك ، يتم إطلاق الضوء عندما يرتاح الإلكترون مرة أخرى إلى الحالة الأرضية. يتمثل الاختلاف الرئيسي بين التلألؤ الكيميائي والتألق في أن الطاقة التي تثير الإلكترونات في التلألؤ الكيميائي تأتي مباشرة من التفاعل. 
أحد التطبيقات العملية للتلألؤ الكيميائي هو في عصي التوهج التجارية. تحتوي عصا التوهج على محلولين منفصلين: أحدهما يحتوي على بيروكسيد والآخر يحتوي على أكسالات ثنائي الفينيل وصبغة ملونة. عندما يتم خلط المحلولين ، والذي يحدث عند تنشيط عصا التوهج ، ينتج التفاعل الناتج بين البيروكسيد وأكسالات ثنائي الفينيل طاقة تثير الصبغة إلى حالة طاقة أعلى. عندما يتم استنفاد المواد المتفاعلة ، تعود الصبغة إلى الحالة الأرضية وتطلق الضوء. هذا ما يعطي العصي المتوهجة لونها المميز. 
<h4>لومينول</h4>
Luminol هي مادة كيميائية تظهر خصائص كيميائية وتستخدم في مجموعة واسعة من التطبيقات ، وعلى الأخص في الطب الشرعي. Luminol (C8H7N3O2) ينبعث منه اللون الأزرق عند خلطه مع عامل مؤكسد. في حالة الطب الشرعي ، يتفاعل اللومينول مع الحديد الموجود في الهيموجلوبين ، مما يمكن علماء الطب الشرعي من تحديد آثار الدم الصغيرة جدا. 
يتم تصنيع Luminol عن طريق تفاعل الجفاف لحمض 3-nitrophthalic مع الهيدرازين. يتم تسخين التفاعل لإزالة الماء ، ويضاف ثلاثي إيثيلين جلايكول لزيادة درجة الحرارة. ثم يتم تقليل مجموعة النيترو من 3-nitrophthalhydrazide باستخدام ثنائي ثيونيت الصوديوم لتشكيل مجموعة أمينية عند درجة حموضة عالية. في الظروف الأساسية ، يكون 3-nitrophthalhydrazide قابلا للذوبان. تؤدي إضافة حمض الخليك الجليدي إلى ترسيب اللومينول. 
مع هيدروكسيد البوتاسيوم ، يشكل اللمينول دياليون. تقوم أنيونات الهيدروكسيد بتفكيك البروتونين للهيدروجين المرتبطين بالنيتروجين الموجود في اللومينول. يؤكسد غاز الأكسجين اللوميني إلى حالته المثارة. عندما يرتاح مرة أخرى إلى الحالة الأرضية ، فإنه يطلق ضوءا أزرق أبيض. 
<h4>المراجع</h4>
<ol>
	<li style="font-size:17px">كوتز ، جي سي ، تريتشيل جونيور ، بي إم ، تاونسند ، جي آر (2015). الكيمياء والتفاعل الكيميائي. بلمونت ، كاليفورنيا: بروكس / كول ، Cengage Learning. </li>
</ol>

يمكن تصنيف التفاعلات الكيميائية على أنها ماص للحرارة أو طاردة للحرارة اعتمادا على ما إذا كانت التفاعلات تمتص الحرارة أو تطلقها عندما تتغير إلى منتجات. ...

Education

JoVE Lab Manual

Chemistry

الكيمياء

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

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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

Comprehensive, curriculum-focused videos for both instructors and students in introductory chemistry lab courses.

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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

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Luminol Chemiluminescence in Forensics

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