Phase transitions in crystals of racemic long chain 2-amino alcohols

Characterizations on the Stability and Release Properties of β-ionone Loaded Thermosensitive Liposomes (TSLs)

Liposomes with phase transition temperatures, T_m, near pathogenic site temperature are potential chemoprophylactic delivery vehicles. We prepared and characterized the thermal properties of liposomes composed of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) and hydrogenated soy phosphatidylcholine (HSPC) incorporating β-ionone with T_m at 42 °C. Liposomes with β-ionone/lipid ratio (w/w) of 1:20 and 1:8 had the necessary stability and released most of the β-ionone. The molecular architecture surrounding T_m was studied by fluorescent probes, Raman spectroscopy, and differential scanning calorimeter (DSC). β-Ionone was found to be preferentially located in the deep regions of the lipid bilayer (toward the long chain alkyl of the lipid) at moderate loading. The results showed that β-ionone encapsulated liposomes have a superior release at higher loading amount. Increasing β-ionone leads to disorder in the liquid crystalline state and accelerates the release rate. These studies provide information on the membrane structural properties of β-ionone loaded liposomes that guide rational bioactive molecular delivery systems design for health products.

Solid-solid phase transitions in DL-norvaline studied by differential scanning calorimetry and Raman spectroscopy

The structural modifications of the amino acid DL-Norvaline have been studied using differential scanning calorimetry (DSC) and Raman spectroscopy. DSC results showed that this amino acid undergoes two solid-solid phase transitions at -116.9 and -76.1 degrees C in the temperature range -130 to +300 degrees C. Raman spectroscopy was applied to complement DSC results. The combination of the two methodologies point out that the observed phase transitions correspond to an increment of disordering in the aliphatic side chain of amino acid, an augmentation of the rotational motion of the amino group and a decrease of the strength of the intramolecular hydrogen bonding of the initial dimers at low temperatures. The observed phase transitions of DL-norvaline are compared with those found in DL-norleucine.

A DSC and Raman spectroscopy study on the effect of PAMAM dendrimer on DPPC model lipid membranes

The interaction between PAMAM (polyamidoamine) dendrimer generation 4 (G4) and 3,5 (G3,5) with model lipid membranes composed of dipalmytoylphosphatidylcholine (DPPC) has been investigated. Differential scanning calorimetry (DSC) and Raman spectroscopy were applied to assess the thermodynamic changes caused by PAMAM G4 and G3,5 and to specify the exact location of these dendrimers into the DPPC lipid bilayer. DSC thermograms indicated that the maximum percentages of PAMAM G4 and of G3,5 that can be incorporated in the DPPC membrane without deranging its integrity were 5% and 3%, respectively. The Raman intensity ratios I(2935/2880), I(2844/2880) and I(1090/1130) cm(-1) showed the degree of the fluidity of the lipid bilayer, while the absorption at 715 cm(-1) showed a strong interaction of PAMAM G4 and G3,5 with the polar head group of phospholipid. The results showed that the incorporation of the PAMAM G4 and G3,5 dendrimers in DPPC bilayers causes a concentration dependent increase of the membrane fluidity and that the bilayers interact strongly with both the lipophilic part and the polar head group of the phospholipids. Due to the current weak knowledge relating to the mechanism(s) under which dendrimers interact with lipidic membranes and transport through cells, these results may justify the tendency of dendrimers to disrupt biological membranes. The findings from this study could also prove helpful to rationally design new liposomal drug carriers for bioactive molecules by combining dendrimeric and liposomal technologies.