Effect of variation in the chain length and number in modulating the interaction of an immunogenic lipopeptide with biomembrane models

A differential scanning calorimetry study was carried out to investigate the effect exerted by immunogenic synthetic lipopeptides obtained by the conjugation of LCMV_33–41 peptide with lipoamino acids (Laas) bearing different alkyl chain lengths (C₁₂ and C₁₆) and number of chains (2 × C₁₂) on the thermotropic behaviour of dimyristoylphosphatidylcholine (DMPC) liposomes. The aim of this work was to study the ability of these compounds to be carried by a liposomal system and released to a biomembrane model.

The examined compounds caused variations of the thermotropic parameters that characterise the liposomal system (transition temperature, T_m and enthalpy variation, ΔH), and interacted with the biomembrane models in different way. The interaction was found to be modulated by the length and number of chains present in the examined compounds. In fact, the compounds with higher number of lipid chain showed a stronger interaction with the biomembrane models with respect to the pure peptide and the compounds with a single lipid chain. These results suggest that the lipoamino acid moiety could favour the peptide to be carried by the liposomal system and released to biomembrane.     

Freeze-fracture electron microscopic and calorimetric studies on microscopic states of surface-modified liposomes with poly(ethylene glycol) chains

The differential scanning calorimetry (DSC) and the freeze-fracture electron microscopy of dipalmitoyl phosphatidylcholine (DPPC) liposomes containing distearoyl-N-monomethoxy poly(ethylene glycol)-succinyl-phosphatidylethanolamines (PEG-DSPE) were carried out. The DSC peak of DPPC liposomes containing PEG-DSPE had a shoulder. The main phase transition temperature of DPPC bilayer membranes containing PEG-DSPE whose molecular weight of PEG is less than 3000 was slightly shifted to a higher temperature, while that containing PEG-DSPE whose molecular weight of PEG is more than 5000 was slightly shifted to a lower temperature. The electron micrographs of freeze-fracture replicas of DPPC liposomes containing PEG-DSPE quenched from 37±2°C exhibited banded and planar textures, suggesting the lateral phase separation in the bilayer membranes.     

A DSC study of paeonol-encapsulated liposomes, comparison the effect of cholesterol and stigmasterol on the thermotropic phase behavior of liposomes

Thermotropic phase behaviors of paeonol-encapsulated liposomes containing stigmasterol or cholesterol have been investigated by differential scanning calorimetry. We compared the thermotropic phase behavior of pure dipalmitoylphosphatidylcholine (DPPC) liposomes, sterol/DPPC liposomes, and paeonol/sterol/DPPC liposomes increasing the ratio of paeonol to sterol from 0 to 1, by analyzing the calorimetric parameters of main phase transition of liposomes including phase transition temperature (onset temperature and peak temperature) and phase transition cooperativity. The results showed that paeonol could incorporate into the hydrophobic region of DPPC, thus, decrease phase transition temperature of DPPC. Though stigmasterol interacts with DPPC less favorably than cholesterol, thermotropic phase behavior of paeonol/cholesterol/DPPC liposomes and that of paeonol/stigmasterol/DPPC liposomes are very similar. A phase separation occurred when the molar ratio of paeonol to sterol reached 1:1 in paeonol-encapsulated liposomes, where a paeonol-rich domain coexisted with a sterol-rich domain. The packing order of acyl chains of DPPC in sterol-rich domain is a little higher than that in paeonol-rich domain.     

The effect of sample mass and heating rate on DSC results when studying the fractional composition and oxidative stability of lube base oils

The method of dynamic microdistillation instrumented through DSC has been further elaborated and validated using distillate and residual base oils as model systems. The two major experimental factors of the method—sample mass and heating rate were varied to determine the optimal (standard) experimental conditions for better fraction resolution and thus more reliable quality assessment of petroleum products (lube oils). If these are increased, the fraction resolution ability of the method is reduced—the lighter fractions evaporate at temperatures close to those of the heavier ones, and generally all the fractions evaporate/oxidize at higher temperatures. Two major types of reactions in the heated sample were identified—the one occurring on the metal surface of the crucible leading to a polymer (lacquer) film formation and the other the oxidative cracking in the bulk of the sample leading to the formation of gaseous products. The extent of the lacquer film formation on the crucible metal surface can be reduced by increasing the heating rate and/or the sample mass, while their reduction results in better fraction resolution.     

Diguanidinium hydrogenarsenate monohydrate and its deuterated analogue vibrational, DSC and X-ray investigations

The crystal structure of diguanidinium hydrogenarsenate monohydrate has been found to belong to the P42(1)/c space group of the tetragonal system, with Z = 8, a = 17.114(2) A, c = 7.3500(10) A. In this complex, a network of hydrogen bonds links water molecules and hydrogenarsenate ions. The hydrogenarsenate ions form hydrogen-bonded chains along the crystallographic c-axis. Detailed vibrational studies have been carried out (FTIR and FT-Raman on powder samples, polarized FTIR microscope on a small single crystal at room temperature). The vibrational spectra are discussed in relation to the crystal structure. Calorimetric (DSC) studies have been performed, but no phase transition was found in the temperature range 100-350 K.     

Continous gradient temperature Raman Spectroscopy identifies flexible sites in proline and alanine peptides

Continuous gradient temperature Raman spectroscopy (GTRS) applies the temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a straightforward technique to identify molecular rearrangements that occur near phase transitions. Herein we apply GTRS and DSC to the solid dipeptides Ala-Pro, Pro-Ala, and the mixture Ala-Pro/Pro-Ala 2:1. A simple change in residue order resulted in dramatic changes in thermal stability and properties. Characteristic Pro vibrations were observed at ∼75 °C higher temperature in Pro-Ala than Ala-Pro. The appearance/disappearance of characteristic vibrational modes with increasing temperature showed that a double peak in the Ala-Pro major phase transition (174–184 °C) was due to a gauche to anti 165° rotation of H₃CC*NH₃ about C*. CH₂ rocking and wagging frequencies present in Pro-Ala were not observed in Ala-Pro. For Ala-Pro, the Ala ⁺NH_3, and Pro COO⁻ sites were flexible whereas the Pro ring moiety was not; since the OCN (C)₂ amide bond is planar the CNC moiety keeps the Pro ring rigid. For Pro-Ala, CH₂ sites in the Pro ring were flexible and the OCNH amide bond is perpendicular to the Pro ring. Since the mass of the Pro ring is significantly larger than the mass of the flexible Ala ⁺NH₃ moiety, Pro-Ala absorbs more thermal energy, corresponding to a higher phase transition temperature (240–260 °C). Ala-Pro, Pro-Ala, and Ala-Pro/Pro-Ala 2:1 exhibited α-helix, β-sheet, α-helix secondary structure conformations, respectively.     

Melting behavior of pure polyethylene glycol 6000 and polyethylene glycol 6000 in solid dispersions containing diazepam or temazepam: a DSC study

The purpose of the present study was to investigate the melting behavior of polyethylene glycol 6000 (PEG 6000) as such as well as in solid dispersions containing diazepam or temazepam, prepared by solvent and fusion methods, using differential scanning calorimetry (DSC). It was shown that the melting behavior of pure PEG 6000 is influenced by the crystallization procedure applied. Fusion at 80°C followed by cooling always yielded three different crystal modifications. The rate of cooling (under controlled conditions) was found to have a significant influence on the relative distribution of the three modifications: the lower the cooling rate, the higher the relative amount of the extended modification. Crystallization from organic solution yielded mainly the once folded form. The presence of diazepam and temazepam influenced the relative amount of the different PEG 6000 modifications. Both drugs decreased the formation of the more stable modification, while the formation of the twice folded form was induced. However, in the case of temazepam the contribution of the extended form at higher drug levels increased in dispersions obtained from organic solutions.     

Crystallization and melting behavior of a main-chain thermotropic copolyester

The crystallization and melting behavior of a main-chain thermotropic copolyester has been investigated by differential scanning calormetry (DSC). The effect of annealing time and temperature on the transition temperatures and enthalpies has been evidenced. Two melting peaks are observed and the first one clearly develops on annealing. Hypotheses are suggested about the crystallization mechanism.     

差示扫描量热法研究寡糖链对糖蛋白的热力学性质的影响

报道了研究寡糖链对糖蛋白热力学性质影响的新方法;以小麦胚芽为原料,从其水溶性提取物中分离得到粗蛋白-糖复合物,经DEAE-Cellulose 52和Seplmdex G-100柱层析,得到一种糖蛋白(WGGP);采用差示扫描量热法(DSC)分别对WGGP和去糖基化的WGGP的热力学参数进行了测定,二者的tp分别为96.098℃和74.338℃,说明WGGP的寡糖链对于蛋白质具有较好的稳定和抗变性功能。     

Raman spectroscopic and DSC studies of diglycine-perchlorate (DGPCl)

Single crystals of diglycine perchlorate (DGPCl) and deuterated diglycine perchlorate (DDGPCl) are synthesized and studied using differential scanning calorimetry (DSC) and Raman spectroscopy. DSC data indicated that both DGPCl and DDGPCl undergo a reversible first-order phase transition (solid-solid) at −11.5 °C and −9.3 °C, respectively. The Raman spectra of DGPCl and DDGPCl obtained at ambient temperature are analyzed to infer on the strength of hydrogen bonding in this compound relative to the parent compounds. The occurrence of NH stretching frequency at higher value in DGPCl in comparison with glycine suggests presence of a weak N–H?O hydrogen bond in DGPCl than in glycine. The lower isotropic melting temperature of DGPCl as compared to that of glycine is understood on the basis of the relative strength of hydrogen bonding in these compounds.     

Influence of annealing and chain defects on the melting behaviour of poly(vinylidene fluoride)

The melting behaviour of poly(vinylidene fluoride) (PVDF) was investigated by differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering in order to study the influence of the chain defects content and of the temperature of annealing on the crystallization and melting behaviour.All the DSC scans show a double endotherm and the analysis of the data suggests that the low temperature endotherm is due to the melting of a population of thin lamellae, whose thickness increases during the annealing, but a high content of chain defects prevents the lamellar thickening and the main effect in this case is the crystallization of thin lamellae from a portion of polymer which did not crystallize during the quenching from the melt. Furthermore, the two melting endotherms, which are observed, can be partially ascribed to a melting-recrystallization process.Furthermore, stepwise isothermal cooling was performed in a differential scanning calorimeter followed by melting scans of fractionated PVDF samples to point out the possible presence of a series of endothermic peaks.     

A rapid quantitative method for determination of short chain branching content and branching distribution index in LLDPEs by DSC

A new method for rapid quantitative determination of short chain branching content (SCB) and branching distribution index (BDI) of ethylene/1-butene copolymers based on DSC is presented. Simple DSC thermograms of the samples are divided into small narrow slices with 1 °C width. The slice area is calculated with a program written with Mathlab software. Using the moment equations for branching distribution, the number and weight average short chain branching contents (C_n and C_w) are calculated. The values of C_w agreed well with the SCB contents obtained by ¹³C NMR (or TREF). The branching distribution index (BDI), which is equal to C_w/C_n, is an indicator of the broadness of SCB distribution. This parameter can be a good and rapid criterion for predicting the heterogeneity of branching structure of a sample.     

Nonionic urea surfactants: influence of hydrocarbon chain length and positional isomerism on the thermotropic and lyotropic phase behavior

The thermotropic and lyotropic phase behavior of 1- and 5-decyl urea, and 1-, 2-, 4-, and 6-dodecyl urea have been studied. This allowed the effect of positional isomerism to be examined. Intermolecular hydrogen bonding by the urea moiety is the dominant factor in determining the solid-state thermal behavior and crystal solubility boundary of these linear nonionic surfactants. The positional isomers where the urea moiety was not situated at the terminus of the hydrocarbon chain exhibited higher melting points than the 1-alkyl ureas. This has been rationalized by postulating interdigitated chains in the solid state. In the urea surfactant-water systems, three phases are observed, viz. crystalline solid, a dilute aqueous solution of the alkyl urea, and an isotropic liquid. The last two phases coexist in the low-surfactant, high-temperature region of the binary phase diagram. An overview of structure-property correlations for linear nonionic urea surfactants is presented in light of the new physicochemical data obtained for the decyl urea and dodecyl urea positional isomers.     

Dilatometric and calorimetric studies of the effect of staphylococcus aureus delta-lysin on the phospholipid phase transition

The interaction of the protein -lysin from Staphylococcus aureus with model membrane of dipalmitol-sn-glycero-3-phosphocholine has been studied by the method of temperature scanning densitometry and high precision differential scanning calorimetry. The studies were performed in the range of low relative protein concentrations (between 10^–4 and 3×10^–2 moles -lysin per mole phospholipid) in order to observe those effects which may be relevant to the high efficiency of membranolysis. -lysin was found to have strong effects on the main transition as well as on the pretransition, i.e., significant reduction of the transition volume and transition enthalpy and complete abolition of the pretransition. The temperature of the main transition was nearly unaffected in this concentration range. These effects can be interpreted as long-range structural changes in the lipid bilayers caused by the protein and are discussed in terms of a cooperative cluster model. The results are in many respects qualitatively similar to those observed earlier with the bee venom protein melittin.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples, December 4–7, 1984     

磷脂DHPC和短杆菌肽D相互作用的DSC研究

Changes of the behavior of the thermotropic phase transitions of the phospholipid DHPC by the action of miniprotein gramicidin D (G.D) have been studied by differential scanning calorimetry. The experimental results demonstrated that G.D could not remove the pretransition of DHPC, but the pretransition peak and the main transition peak of DHPC were incorporated into a broad peak. The pretransition temperature and the main transition temperature of DHPC decreased to different ex-tent. The sums of the pretransition and main transition enthalpies of DHPC showed a lineally decreasing relationship with increasing the mole fraction x_g of gramicidin D.     

Effect of chain length distribution on the phase behavior of polyglycerol fatty acid ester in water

The effect of the chain length distribution on the phase behavior, the structure of liquid crystals, and physicochemical properties was investigated in water/ polyglycerol fatty acid ester. Polyglycerol fatty acid esters with sharply distributed polyglycerol (10G*0.7L) and with broadly distributed polyglycerol (10G0.7L) were used. Unreacted polyglycerol in both surfactants was removed. 10G*0.7L forms hexagonal liquid crystals at a higher concentration than 10G0.7L. The effective cross-sectional area of the lipophilic parts in the hexagonal phase of 10G0.7L is smaller than that of 10G*0.7L owing to the difference in the chain length distribution. Evidently, 10G0.7L molecules are tightly packed in aggregates; therefore, 10G0.7L decreased the surface tension more strongly and promoted emulsification. Received: 11 January 2000 Accepted: 8 March 2000     

DSC Differential Spectrum Applied in the Study of Hydrogen Bonding Interaction in Aqueous Solution

In this work, thermal signals of the interaction between urea (UR) and partly hydrolyzed polyacrylamide (HPAM) in aqueous solution were first investigated by differential scanning calorimetry (DSC) differential spectrum and 2-dimensional (2-D) differential spectrum analysis. A remarkable interaction between urea and HPAM was found when the temperature was about 40°C. Near this temperature, the hydrogen bonding between the carbonyl group of HPAM and water would dissociate partly, and another hydrogen bonding between carbonyl and amino would form simultaneously. Not only the DSC differential spectrum, but also a rheological experiment and two-dimensional correlation infrared spectrum (2-D-IR) were used to prove this result.     

二元贮冷水合盐熔解热的差示扫描量热法研究

用差示扫描量热法（differential scanning calorimetry)对二元贮冷水合盐的相变温度与熔解热进行了研究，实验结果对认识多元贮冷水合盐的相变过程的相变机理及选配贮冷水合盐材料，具有重要意义。     

DSC and Raman study on the effect of lysozyme and bovine serum albumin on phospholipids liposomes

In this paper, the effect of increasing amounts of lysozyme (Lyso) and bovine serum albumin (BSA) on the behaviour of lecithin (DMPC) and cephalin (DMPE) liposomes was investigated by means of Raman and DSC techniques. The results showed that both proteins affected, but in a different way, both lecithin and cephalin liposomes. In the samples with lower Lyso concentrations (up to 2 % w/w), a small decrease on the main transition temperature (T _m) was observed, whereas T _m increased by further addition of Lyso (up to 15.0 % w/w). At the same time, an increase of about 20 % in the ΔH of the transition was observed. Pre-transition was also affected in a greater extent by protein presence. When BSA interacted with liposomes, a smaller increase in the T _m values was observed with a contemporary increase of about 8 % in the associated ΔH. The data suggested that the BSA–liposomes interaction involves only the external surface of the bilayer, excluding thus any penetration into the liposomal hydrophobic core. On the contrary, a partial penetration into the bilayer is suggested when Lyso is added to liposomes. Both considered proteins strengthened the overall bilayer structure of DMPC liposomes, suggesting a decrease in the membrane permeability. Moreover, Lyso secondary structure changed by interaction with liposomes, as demonstrated by the Raman spectra behaviour, in particular in the case of DMPE.