Maurizi G, Amicosante G, Oratore A, Di Giulio A
Dipartimento di Scienze e Technologie Biomediche e di Biometria, Università degli Studi L'Aquila, Italy.
Anal Biochem. 1993 Sep;213(2):271-6. doi: 10.1006/abio.1993.1420.
Sulbactam, a beta-lactam antibiotic, absorbs uv light at 273 nm when in alkaline media, whereas at neutral or acidic pH this peak disappears. Sulbactam-loaded liposomes, prepared by reverse-phase evaporation, were spectroscopically analyzed by the derivative mode measuring the peak-through amplitude between +258 and -285 nm, so that the spectral interference of the sample is eliminated. Taking advantage of this experimental approach, we could study the influence of different parameters on the dissociation state of the drug when entrapped in dipalmitoyl phosphatidylcholine liposomes. In particular, following the time course of sulbactam peak disappearance, we found that: (i) the effectiveness of protonating the sulbactam of the chosen buffers is acetate/acetic acid > succinate/succinic acid > citrate/citric acid; (ii) the rate of signal disappearance is influenced by the externally imposed pH and can be somewhat related to the dissociation state of the organic acids; (iii) as expected, the whole phenomenon is temperature dependent. The observations reported here might be the basis for quantitative permeation studies in synthetic and/or natural membranes using this methodology.
舒巴坦是一种β-内酰胺抗生素，在碱性介质中于273nm处吸收紫外线，而在中性或酸性pH值下该峰值消失。通过反相蒸发制备的载有舒巴坦的脂质体，采用导数模式在+258至-285nm之间测量峰-谷幅度进行光谱分析，从而消除样品的光谱干扰。利用这种实验方法，我们可以研究不同参数对包裹在二棕榈酰磷脂酰胆碱脂质体中的药物解离状态的影响。特别是，通过跟踪舒巴坦峰值消失的时间过程，我们发现：（i）所选缓冲液使舒巴坦质子化的有效性为乙酸盐/乙酸＞琥珀酸盐/琥珀酸＞柠檬酸盐/柠檬酸；（ii）信号消失的速率受外部施加的pH值影响，并且可能与有机酸的解离状态有一定关系；（iii）正如预期的那样，整个现象与温度有关。此处报道的观察结果可能是使用该方法对合成和/或天然膜进行定量渗透研究的基础。
