Subcooled flow boiling of R-134a in vertical channels of small diameter

Subcooled flow boiling heat transfer for refrigerant R-134a in vertical cylindrical tubes with 0.83, 1.22 and 1.70 mm internal diameter was experimentally investigated. The effects of the heat flux, q″ = 1–26 kW/m², mass flux, G = 300–700 kg/m² s, inlet subcooling, ΔT_sub,i = 5–15 °C, system pressure, P = 7.70–10.17 bar, and channel diameter, D, on the subcooled boiling heat transfer were explored in detail. The results are presented in the form of boiling curves and heat transfer coefficients. The boiling curves evidenced the existence of hysteresis when increasing the heat flux until the onset of nucleate boiling, ONB. The wall superheat at ONB was found to be essentially higher than that predicted with correlations for larger tubes. An increase of the mass flux leads, for early subcooled boiling, to an increase in the heat transfer coefficient. However, for fully developed subcooled boiling, increases of the mass flux only result in a slight improvement of the heat transfer. Higher inlet subcooling, higher system pressure and smaller channel diameter lead to better boiling heat transfer. Experimental heat transfer coefficients are compared to predictions from classical correlations available in the literature. None of them predicts the experimental data for all tested conditions.     

Analysis of HIV-1 fusion peptide inhibition by synthetic peptides from E1 protein of GB virus C

The aim of this study was to identify proteins that could inhibit the activity of the peptide sequence representing the N-terminal of the surface protein gp41 of HIV, corresponding to the fusion peptide of the virus (HIV-1 FP). To do this we synthesized and studied 58 peptides corresponding to the envelope protein E1 of the hepatitis G virus (GBV-C). Five of the E1 synthetic peptides: NCCAPEDIGFCLEGGCLV (P7), APEDIGFCLEGGCLVALG (P8), FCLEGGCLVALGCTICTD (P10), QAGLAVRPGKSAAQLVGE (P18) and AQLVGELGSLYGPLSVSA (P22) were capable of inhibiting the leakage of vesicular contents caused by HIV-1 FP. A series of experiments were carried out to determine how these E1 peptides interact with HIV-1 FP. Our studies analyzed the interactions with and without the presence of lipid membranes. Isothermal titration calorimetry revealed that the binding of P7, P18 and P22 peptides to HIV-1 FP is strongly endothermic, and that binding is entropy-driven. Gibbs energy for the process indicates a spontaneous binding between E1 peptides and HIV-1 FP. Moreover, confocal microscopy of Giant Unilamellar Vesicles revealed that the disruption of the lipid bilayer by HIV-1 FP alone was inhibited by the presence of any of the five selected peptides. Our results highlight that these E1 synthetic peptides could be involved in preventing the entry of HIV-1 by binding to the HIV-1 FP. Therefore, the continued study into the interaction between GBV-C peptides and HIV-1 FP could lead to the development of new therapeutic agents for the treatment of AIDS.     

Lipolysis by phospholipase A2 of monomolecular mixed films of natural lipids

A study is made of the enzymatic lipolysis by pancreatic phospholipase A₂ and by phospholipase A₂ of Vipera berus on monomolecular films of mixture of natural lipids: cholesterol-egg lecithin and triolein-egg lecithin, by adding serumalbumin to the aqueous subphase in order to imitate the physiological conditions. The influence of the composition of the mixed film and the quantity of the added serumalbumin exerts on the velocity of lipolysis is studied, as well as the surface pressure of the film and the type and the quantity of the injected enzyme. The results obtained are discussed.     

On the definition of a probabilistic normed space

Summary In this paper we give a new definition of a probabilistic normed space. This definition, which is based on a characterization of normed spaces by means of a betweenness relation, includes the earlier definition of A. N. erstnev as a special case and leads naturally to the definition of the principal class of probabilistic normed spaces, the Menger spaces.     

Hydrophobic Laminin-Related Peptides: Synthesis and Surface Properties

The synthesis of hydrophobic peptide derivatives related to the laminin sequence [YIGSR(NH(2))] is described. Hydrophobicity is achieved by the attachment of decanoic, myristic, or stearic acids to the amino terminal end of the peptide. Moreover, a cholesterol residue was also introduced as succinimidoyl-cholesteryl moiety at the same position. These peptidic compounds are designed to be inserted into lipid bilayers to prepare, what can be considered as, immunoliposomes to target these vesicles to tumor cells. Physicochemical aspects related to their surface activity, insertion into lipid layers, spreadibility, formation of aggregates, and haemolytic activity have been studied as a previous step in the selection of the most convenient derivative. The results obtained indicate that these peptide derivatives show a high tendency to form aggregates in aqueous media, this fact reducing their interaction with lipid mono- and bilayers. The most suitable derivatives for interacting with liposomes are myristoyl and decanoyl. Copyright 2001 Academic Press.     

Interfacial interactions of hydrophobic peptides with lipid bilayers

Four hydrophobic laminin-related peptides and their corresponding parent peptides were synthesized to use them to target liposomes to tumoral cells. The peptide sequence was YIGSR((NH(2))), and hydrophobic residues linked to the alpha-amino terminal end were decanoyl, myristoyl, stearoyl, and cholesteryl-succinoyl. Before use in biological systems, a physicochemical study was carried out in order to determine their interaction with DPPC bilayers that could compromise both the toxicity and the stability of liposomal preparations. The experiments were based on DSC, fluorescence polarization, outer-membrane destabilization, and vesicle leakage. These peptides showed in general a low interaction with the vesicles, promoting in all cases the rigidification of bilayers. This lack of strong disturbances in the ordered state of phospholipid molecules seems more likely due to the similarity of peptide acyl chains with those of lipids than to the absence of interactions. The bulkiness of cholesteryl derivative as well as its tendency toward aggregation resulted in weak interaction levels except in thermograms. The binding of peptides to the surface of liposomes loaded with doxorubicin resulted in preparations with good entrapment yields and small size, required for long circulating vesicles (especially for the myristoyl derivative). The alternative method based on the reaction of parent peptide to the surface of liposomes through an amide linkage was slightly more efficient when the peptide was linked to the carboxy-terminal end of the DSPE-PEG-COOH-containing liposomes. Nevertheless, the final decision must be made with the simplicity of the procedure and reduction in losses during all the steps of the processes taken into consideration.     

Influence of the saturation chain and head group charge of phospholipids in the interaction of hepatitis G virus synthetic peptides

Using the Langmuir technique, we have studied the properties at the air/water interface and the interaction of the hepatitis G virus synthetic peptide E1(53-66) and its palmitoyl derivative with membrane phospholipids. These phospholipids had different characteristics referring to the net charge and saturation of the acyl chain. The palmitoyl derivative was more stable at the air/water interface and in the kinetic at constant area measurements showed higher incorporation to the monolayer. The interaction was higher for saturated phospholipids and those with a negative net charge. When the peptides were in the subphase, they produced changes in the miscibility of mixed monolayers composed of DPPC/DPPG or DOPC/DOPG. It can be deduced from the results obtained that electrostatic interactions play a major role, but when the peptide is derivatized with the palmitoyl chain, hydrophobic interactions are added to the former ones. The interaction is also influenced by the saturation of the acyl chain.     

Mixed monolayers composed of PC/PS/Chol. Interaction with opioid molecules

The miscibility of phosphatidylserine, phosphatidylcholine, and cholesterol in monolayers were studied. The influence of sodium and calcium ions in this system was determined. The compression isotherms of mixed monolayers of the above cited three components spread on subphases containing opiate molecules are elucidated. Moreover, the penetration kinetics of opiate molecules in these mixed monolayers was also recorded. The results show that the presence of cholesterol always lowers the penetration of opioid molecules; this effect is weaken for meperidine, the most hydrophobic of the molecules assayed.Abreviations PS phosphatidylserine - PC phosphatidylcholine - PI phosphatidylinositol - Chol cholesterol