The RW4 peptide, part of the (RW)_n series, is a synthetic cationic antimicrobial peptide composed of four repeats of arginine (R) and tryptophan (W) residues, with a C-terminal amidation. This peptide exhibits a strong interaction with negatively charged phospholipid bilayers, such as those containing phosphatidylglycerol (POPG), as demonstrated by circular dichroism spectroscopy and tryptophan fluorescence studies. The RW4 peptide shows enhanced antimicrobial activity with increasing chain length, attributed to its ability to partition into lipid membranes and disrupt bilayer integrity. Spectroscopic data indicate that RW4 undergoes conformational changes upon binding to lipid vesicles, suggesting a mechanism involving membrane intercalation.

Fluorescence studies reveal that the tryptophan residues in RW4 are more protected in POPG vesicles compared to zwitterionic phosphatidylcholine (POPC) vesicles, highlighting its preferential interaction with negatively charged membranes. The peptide's antimicrobial efficacy correlates with its chain length, with longer peptides like RW4 demonstrating greater activity. These findings underscore the importance of arginine and tryptophan residues in mediating peptide-lipid interactions and membrane disruption, providing insights into the design of short, potent antimicrobial peptides.

• Strøm et al (2002) Antimicrobial activity of short arginine- and tryptophan-rich peptides. J. Pept. Sci. 8(8) 431 PMID: 12212806
• Liu et al (2007) Length effects in antimicrobial peptides of the (RW)n series. Antimicrob. Agents Chemother. 51(2) 597 PMID: 17145799
• Mohan et al (2014) Enhanced antimicrobial activity of peptide-cocktails against common bacterial contaminants of ex vivo stored platelets. Clin. Microbiol. Infect. 20(1) O39 PMID: 23926880

三氟乙酸（TFA）是一种强酸，常用于从固相树脂中裂解合成的多肽，也可用于提高多肽纯化步骤中的HPLC性能。默认情况下，定制的多肽是以冻干的TFA盐的形式交付的，其中TFA的含量可能高达10-45%。

定制多肽中的TFA可能会导致后续检测数据出现无法解释的差异。例如，nM浓度的TFA已被证明会干扰细胞实验，在某些情况下会抑制细胞增殖，而在其他情况下会增加细胞活力。

TFA去除服务推荐用于:

• 将用于细胞试验的多肽
• 将被用作原料药或制成品的多肽
• 含有大量碱性残基的亲水多肽

干品多肽的重量中不仅仅包含多肽，还包含有一些非肽的组份，如水、被吸收的溶剂、配位离子和盐等。肽的净含量是指肽在其中的重量百分比，这个百分比的数值范围很大，可能从50%到90%，取决于纯度、序列以及合成和纯化的方法，不要将肽的净含量和肽的纯度混为一谈，他们是两个完全不同的概念。纯度通常是通过HPLC测定的。纯度定义的是多肽样品中含正确序列的组分的百分比，而肽的净含量是指样品中肽类物质相对于总物质所占的百分比，肽的净含量通常是氨基酸组分分析或紫外分光法测定的，这个信息主要是在一些对肽的浓度很敏感的实验中，对计算肽的浓度是很重要的。