Interactions of L-cysteine ethyl ester hydrochloride (CE), a bioactive cysteine derivative, with dipalmitoylphosphatidylcholine (DPPC) were investigated. To gain a deeper insight into analyzing L-cysteine ethyl ester HCl interaction with liposomes of DPPC in anhydrous and hydrated states, we performed experimental studies by infrared (Fourier transform infrared spectroscopy) and Raman spectroscopies. The results revealed that the interaction of CE with the phospholipid head groups was the same in absence or presence of water. In both states, the wavenumber of the PO 2 À group and C-N bond of the choline group decreased. This behavior can be ascribed to the replacement of hydration water and binding to the phosphate group. In the Raman spectrum results for the anhydrous and gel states, the S-H stretching band of the CE shifted to lower frequencies with a decrease in its force constant. Biologically active lipophilic molecules such as CE should be studied in terms of their interaction with lipid bilayers prior to the development of advanced lipid carrier systems such as liposomes. The results of these studies provide information on membrane integrity and physicochemical properties that are essential for the rational design of lipidic drug delivery systems.

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The aim of this study is to analyze the consequences of water redistribution on the structure and stability of phospholipid bilayers induced by cysteine (Cys). This interaction is studied with 1,2-dipalmitoyl- sn-glycero-3-phosphatidylcholine (DPPC) multilamellar vesicles in gel (30 °C) and liquid crystalline (50 °C) state; experimental studies were performed by means of Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and differential scanning calorimetry (DSC). The polar head sites of the lipid molecules to which water can bind are identified by competition with compounds that form hydrogen bonds, such as Cys. FTIR spectroscopy results revealed that there is a Cys interaction with the phospholipid head groups in the gel and liquid crystalline phases. Raman spectra were measured in the gel state. They were dominated by vibrations of the fatty acyl chains, with superposition of a few bands from the head group, and clearly showed that the S-H stretching band of Cys shifted to lower frequencies with a decrease in its force constant. DSC disclosed an overview of the behavior of the multilamellar vesicles in the working temperature range (30-50 °C) and showed how the increase of the molar ratios modified the environment of the polar head and the hydrocarbon chains. A loss of the pretransition ( T) and an increase in the temperature of main transition ( T) with increasing Cys/DPPC molar ratio were observed.

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Albendazole (ALB) is a broad-spectrum anthelmintic, which exhibits two solid-state forms (Forms I and II). The Form I is the metastable crystal at room temperature, while Form II is the stable one. Because the drug has poor aqueous solubility and Form II is less soluble than Form I, it is desirable to have a method to assess the solid-state form of the drug employed for manufacturing purposes. Therefore, a Partial Least Squares (PLS) model was developed for the determination of Form I of ALB in its mixtures with Form II. For model development, both solid-state forms of ALB were prepared and characterized by microscopic (optical and with normal and polarized light), thermal (DSC) and spectroscopic (ATR-FTIR, Raman) techniques. Mixtures of solids in different ratios were prepared by weighing and mechanical mixing of the components. Their Raman spectra were acquired, and subjected to peak smoothing, normalization, standard normal variate correction and de-trending, before performing the PLS calculations. The optimal spectral region (1396-1280cm(-1)) and number of latent variables (LV=3) were obtained employing a moving window of variable size strategy. The method was internally validated by means of the leave one out procedure, providing satisfactory statistics (r(2)=0.9729 and RMSD=5.6%) and figures of merit (LOD=9.4% and MDDC=1.4). Furthermore, the method's performance was also evaluated by analysis of two validation sets. Validation set I was used for assessment of linearity and range and Validation set II, to demonstrate accuracy and precision (Recovery=101.4% and RSD=2.8%). Additionally, a third set of spiked commercial samples was evaluated, exhibiting excellent recoveries (94.2±6.4%). The results suggest that the combination of Raman spectroscopy with multivariate analysis could be applied to the assessment of the main crystal form and its quantitation in samples of ALB bulk drug, in the routine quality control laboratory.

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N-acetylcysteine is a commonly used mucolytic and antioxidant agent. Knowledge of the interactions of NAC with the cell membrane is important to understand its mechanism of pharmacological action at the...