Crosslinking is the process of chemically joining two or more molecules by a covalent bond. Crosslinking reagents contain reactive ends to specific functional groups (primary amines, sulfhydryls, etc.) on proteins or other molecules.
The availability of several chemical groups in proteins and peptides make them targets for conjugation and for studyusing crosslinking methods. Crosslinkers also are commonly used to modify nucleic acids, drugs and solid surfaces.

Photoreactive Crosslinker Chemistry
用于標記和交聯蛋白質和生物分子的試劑中可光活化的反應性化學基團包括芳基疊氮化物（苯基疊氮化物）和重氮基。本文介紹了這類試劑的反應化學和生物學研究應用。
Photo-activatable reactive chemical groups in reagents for labeling and crosslinking proteins and biomolecules include aryl azides (phenyl azides) and diazirines. This article describes the reaction chemistries and biology research applications of this class of reagents.

光反應性交聯劑反應性基團
光活化（或光化學）交聯反應需要光能來引發。光反應性基團是化學惰性的化合物，當暴露于紫外線或可見光時會發生反應。實際上，用于交聯應用的試劑中使用的所有光反應性基團品種都需要暴露于紫外光（UV光）中以進行分子活化。下圖提供了可光活化交聯劑和UV交聯應用中使用的儀器類型的示例。

Photoreactive crosslinker reactive groups
Photo-activatable (or photo-chemical) crosslinking reactions require energy from light to initiate. Photoreactive groups are chemically inert compounds that become reactive when exposed to ultraviolet or visible light. Practically all varieties of photoreactive groups used in reagents for crosslinking applications require exposure to ultraviolet light (UV light) for molecular activation. The following image provides an example of the type of instrument used with photoactivatable crosslinkers and UV-crosslinking applications.

代表紫外線燈。luyor-3410 高強度紫外線燈是緊湊的紫外燈，特別是用于與可光活化交聯劑和UV交聯方法中使用的365nm的撥號可選擇波長的設置。
Representative ultraviolet lamp. LUYOR-3410 UV Lamps are compact,  ultraviolet lamps with 365 nm dial-selectable wavelength settings especially for use with photoactivatable crosslinkers and UV-crosslinking methods.

對于與生物樣品和實驗進行交聯和標記應用，光化學反應基團比嚴格的熱化學試劑具有某些優勢。最重要的是，它們使在實驗的早期步驟中添加試劑成為可能，然后在隨后的某個步驟中引發交聯（通過暴露于紫外線），從而與目標特定生物學條件相協調。另外，這些基團中的許多基團將與它們在激活后的短時間內遇到的蛋白質中幾個常見功能基團中的任何一個綴合。此功能使它們在捕獲蛋白質相互作用中特別有用（請參見下面的討論）。已摻入用于生物共軛技術的交聯和標記化合物的光反應性基團包括芳基疊氮化物，疊氮基甲基香豆素，二苯甲酮，蒽醌，某些重氮化合物，重氮基和補骨脂素衍生物。這些蛋白質生物學研究中最有用的是芳基疊氮化物和重氮。

蛋白質交聯中使用的選定的光反應性化學基團。傳統上，最廣泛使用的是芳基疊氮化物（也稱為苯基疊氮化物，前兩行）。補骨脂素（右下圖）幾乎只與RNA或DNA反應，用于標記核酸或交聯并研究蛋白質與核酸的相互作用。Diazirines（左下）是一類新的化合物，在蛋白質研究中越來越流行和實用。花鍵代表標記試劑或具有反應性基團的交聯劑的一端。
Photochemical reactive groups have certain advantages over strictly thermochemical reagents for crosslinking and labeling applications with biological samples and experiments. Most importantly, they make it possible to add reagents at an early step in an experiment and then to initiate crosslinking (by exposure to UV light) at some later step that coordinates with the particular biological condition of interest. Additionally, many of these groups will conjugate to any one of several common functional groups in proteins that they encounter during the brief time when they are activated. This feature makes them particularly useful in capturing protein interactions (see discussion below).

Photoreactive groups that have been incorporated into crosslinking and labeling compound for use in bioconjugate techniques include aryl azides, azido-methyl-coumarins, benzophenones, anthraquinones, certain diazo compounds, diazirines, and psoralen derivatives. The most useful of these for protein biology research are aryl azides and diazirines.

Photocleavable Linker (PC Linker) often used in the design of multi-functional single-stranded nucleotide conjugates for the selection of novel DNA or RNA-based catalysts in vitro. Photocleavable PC linker modified oligonucleotide are demonstrated in Bruker Daltonik's genoSNIP, a MALDI-TOF MS based assay system for SNP detection.

 Photocleavable  PC linker contained a non-nucleosidic group that can be used to link two nucleotide sequences through a short, UV photo-cleavable C3 spacer arm. Upon irradiation by UV light, photo-cleavage released oligonucleotide contain a 5-phosphorylated group with greater hybridization affinity for a complementary DNA strand than PC spacer.

 Photocleavable PC linker can be incorporate at any position within an oligonucleotide. Contact Bio-Synthesis for service details.

Cleavage Protocol

 Cleavage occurs by irradiation with near-UV light (300-350 nm, complete cleavage occurs within 5 minutes. Try using a Black Ray LUYOR-3410 UV lamp  at a distance of 15 cm (emission peak 365 nm, 300 nm cut-off, 1.1 mW intensity at~31 cm).