Pure Palmitic Acid Research Articles

Synergistic enhancement of metal–organic framework-derived hierarchical porous materials towards photothermal conversion and storage properties of phase change materials

The design and synthesis of composite phase change materials that integrate photothermal conversion and latent heat storage have guiding significance for the efficient development and utilisation of solar energy. In this study, taking into consideration the advantages of metal–organic frameworks (MOFs) with adjustable structure and properties, HKUST-1-derived CuO/hierarchical porous carbon materials were employed and integrated with palmitic acid (PA) to synthesise composite phase change materials that exhibit exceptional comprehensive properties. The effects of different carbonation temperatures on HKUST-1-derived CuO/hierarchical porous carbon were analysed through a series of characterisations. The hierarchical porous structure in the blended system offers abundant pore structure and high specific surface area to prevent leakage of phase change materials. Composite phase change materials can maintain good shape stability and excellent thermal energy storage capacity. The thermal storage efficiency and photothermal conversion efficiency are 98.28% and 81.83%, respectively. Meanwhile, the thermal conductivity of the composite phase change material is 3.65 times that of pure PA. In conclusion, the MOFs derivative-based composite phase change materials designed in this study exhibited potential for thermal energy storage and can be applied to the field of solar energy conversion and storage systems.

Highly dispersed Ag quantum dots anchored on palmitic acid/ graphitic carbon nitride composite phase change materials for enhanced photo-thermal storage

Phase change materials (PCM) have attracted much attention in the field of thermal energy storage because of exceptional heat storage capacity, stable operating temperature, and recyclability. However, organic phase change materials, represented by palmitic acid (PA), are limited by inherent leakage problem, unsatisfactory thermal responsiveness and inefficient photo-thermal storage capacity, which severely hamper the development of PCMs technology. As a means of addressing these challenges, we developed one novel support material with 2D/0D structure for palmitic acid via thermal polymerization, specifically, in which highly dispersed Ag quantum dots (Ag QDs) was firmly anchored on graphitic carbon nitride (g-C3N4). PA was further infiltrated into the layered structure of nanoporous g-C3N4/Ag QDs to successfully synthesize novel shape-stabilized PA/g-C3N4/Ag QDs composite phase change materials (CPCM). On the one hand, benefiting from the tightly stacked porous structure of g-C3N4/Ag QDs, PA is effectively encapsulated to avoid leakage problem during the solid-liquid transition with a superior adsorption capacity up to 65 %. On the other hand, the combination of g-C3N4 and Ag QDs in PA/g-C3N4/Ag QDs CPCM demonstrated a synergistic effect resulting in faster heat transfer capability and more efficient solar energy capture capability compared to pure PA, which is capable of dual utilization of heat and solar energy. The newly developed PA/g-C3N4/Ag QDs CPCM features a high melting latent heat and an appropriate phase change temperature, which are 128.35 J/g and 61.92 °C, respectively. The corresponding solidification enthalpy and temperature are 121.70 J/g and 60.02 °C. The photo-thermal conversion efficiency of the material is improved to 78.6 %, facilitating a rapid capture and storage of solar energy. Furthermore, through the optimization of the preparation process, Ag QDs are densely anchored on the surface of g-C3N4, which retains the excellent properties of metallic silver while eliminates the metal agglomeration phenomenon after repeated utilization of CPCMs. PA/g-C3N4/Ag QDs CPCM is proved to be extremely recyclable and thermally stable after massive thermal cycles. This innovative and operational encapsulation modified method significantly optimizes the practicality of phase change materials. The obtained shape-stabilized PA/g-C3N4/Ag QDs CPCM is more versatile, and its unique comprehensive properties can provide high-quality materials for photo-thermal storage systems.

Palmitic acid at high concentration modifies the nanoscale structure of anhydrous milk fat

We performed a nanoscale study based on X-ray scattering to understand the impact of a promotor of crystallization, palmitic acid (PA), at high concentration, on the networks of triacylglycerols (TAGs) in anhydrous milk fat (AMF). Melted blends containing 10 wt% PA were quenched at 25 °C. X-ray scattering data were compared with those obtained for pure AMF, pure PA, and AMF containing 1 wt% PA. While PA at low concentration did not modify the nanostructure of TAG crystals (direct crystallization in the β’-2L form), a high concentration of this promotor favored the formation of polymorphic forms suggesting that PA first crystallizes and then directs crystallization of AMF TAGs towards α and β forms.

Recent trends for clean fuel production by deoxygenation of pure palmitic acid using Ni/C catalyst.

Deoxygenation of triglycerides is one of key processes making possible a convenient production of high quality automotive fuels components (sulfur-, oxygen- and aromatics-free). This reaction was studied over non noble metal catalysts 20wt%Ni/C and performed in batch reactor system (autoclave) by using pure palmitic acid, n-hexane as a solvent and 200 psi pressure. The effect of different atmospheres (pure hydrogen, pure nitrogen, and mixture of 50 psiH2/150psiN2) and different temperature range (300 oC-350 oC) under a mixed atmosphere (50 psiH2/150psiN2) were studied in this paper. The main product was n-pentadecane (C15) which the catalyst Ni/C has lower cracking selectivity to light hydrocarbons. The total conversion of carboxylic groups of palmitic acid and the selectivity to C15 in case of pure nitrogen are (22.29% and 12.38%) respectively and in case of hydrogen they are (75.16% and 80.07%) respectively. In case of using H2/N2 as a mixture the total conversion and the selectivity are (81.18% and 75.32%) respectively for Ni/C catalyst. The total conversion increases from 81.18% to 99.99% by increase the temperature from 300 oC to 350 oC. The deoxygenation of palmitic acid over 20wt%Ni/C catalyst indicated that the high selectivity for n-alkane (C15) (75.32%) at 300 oC and reach maximum value (98.11%) at 350oC. Analysis of liquid products by gas chromatography (GC) was used to determine n-alkane (C15) yield and other products (isomeres, olefins and dimers). Insights pertaining to the reaction scheme and an assessment of the reaction products as liquid transportation fuels are also provided in this contribution.

Palmitic acid–carbon dot hybrid vesicles for absorption of uric acid

Human health is always sensitive to the effect of toxin developed due to various reason like metabolic activities, excessive material uptake etc. in the body. Hence, there is a need to develop ways to remove such toxin. In this work, we successfully fabricated a Carbon dot–palmitic acid hybrid vesicles and demonstrated that it can absorb uric acid (UA) which is taken in this work as a model toxin. Interestingly, the nanohybrid was found to be efficient UA absorber (~ 80%) compare to pure palmitic acid vesicles (~ 60%) confirming the role of carbon dot in absorption and hence removal of uric acid. The electrostatic interaction operated between carbon dot and uric acid inside the palmitic acid vesicles is the prime factor for the UA absorption. Development of such nanohybrid vesicles system will lead to system which can be used as toxin removal from our body.

Fabrication of a novel shape-stabilized composite phase change material based on multivariate supporting materials by using typical solid wastes

In this study, palmitic acid (PA)/hybrid multivariate typical solid wastes (MTSW) phase change materials (PCMs) were fabricated by integrating PA into MTSW via a facile direct impregnation method to overcome the leakage of PA. The hybrid MTSW was composed of biomass solid wastes (BSW), iron tailings (IT) and diatomite (DT) at different mass ratios. Simultaneously, carbon nanotubes (CNT) was employed to enhance the thermal conductivity of the PCMs, and then the novel PA/MTSW/CNT composite was firstly prepared. The preparation, shape-stabilization level, morphologies, chemical compatibility, thermal properties and thermal conductivity of these composite PCMs were systematically characterized by tableting leakage tests, scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hot dist and cooling test method. It was found that the MTSW could adsorb 30 wt% PA without any PA leakage and the composites can keep form-stable with mass fraction proportion of 3:2:2:3 for PA, BSW, IT and DT, respectively. The SEM images showed PA was well infiltrated into pore structure of MTSW which had good loading capacity to adsorb PA. FTIR analysis indicated that no chemical reaction had occurred among the components of composite PCMs. The DSC results suggested that the melting points were 63.65 °C and 63.08 °C for PA/MTSW and PA/MTSW/CNT (4 wt%) form-stable phase change materials (FSPCM), respectively. Correspondingly, the latent heats were 55.36 J/g and 53.10 J/g for PA/MTSW and PA/MTSW/CNT FSPCM, respectively. The TGA results showed that PA/MTSW/CNT FSPCM exhibited better thermal stability than pure PA. Compared with pure PA, the thermal conductivities of PA/MTSW/CNT were increased by 25.71%, 36.44% and 91.35% by CNT doping 2, 4 and 6 wt%, respectively. In addition, the heat storage and discharge time of PA/MTSW/CNT were reduced appreciably. In Conclusion, the as-prepared FSPCM has very good properties and a good application prospect in the field of energy-saving building.

Preparation and thermal properties of palmitic acid/expanded graphite/carbon fiber composite phase change materials for thermal energy storage

Using palmitic acid (PA), expanded graphite (EG), and carbon fiber (CF) as raw materials, PA/EG/CF composite phase change materials (CPCMs) with diverse CF contents were invented by melt blending approach. The effects of different ratios on thermal properties were studied by experimental characterization and testing. Scanning electron microscopy images displayed that PA was adsorbed in the pores of the EG surface, while CF was disorderly but uniformly embedded in the interior and surface of pores. The chemical stability and thermal decomposition stability of CPCM at low temperature were proved by Fourier transform infrared spectrometer and thermogravimetric analyzer results, respectively. According to the law of heat storage/release time and latent heat variation, the optimal ratio scheme was determined, and its heat storage/release time was 65% and 59% lower than pure PA, respectively. The form-stable materials were prepared by compression forming method, and thermal cycling experiment results demonstrated that the higher the content of CF, the stronger the inhibition of mass loss. Based on the experimental results, the PA/EG/CF CPCM has the advantages of stable phase transition, strong stability, and fast heat storage and release rate, so it has a marvelous application prospect in the field of low-temperature heat storage engineering.

A promising form-stable phase change material prepared using cost effective pinecone biochar as the matrix of palmitic acid for thermal energy storage

A promising new form-stable phase change material (PA/PB) was fabricated using pinecone biochar (PB) as the supporting material of palmitic acid (PA). The biochar of PB with large surface area was produced by forest residue of pinecone, and it was cheap, environment friendly and easy to prepare. The PB was firstly utilized as the supporter of PA and the characterizations of PA/PB were analyzed by the BET, SEM, XRD, DSC, TGA, FT-IR and thermal conductivity tester. The results demonstrated that the PA was physically absorbed by the PB and the crystal structure of the PA was not destroyed. The results of DSC showed that the fusing and crystallization points of the form-stable phase change material with the maximum content of PA (PA/PB-4) were 59.25 °C and 59.13 °C, and its fusing and freezing latent heat were 84.74 kJ/kg and 83.81 kJ/kg, respectively. The results of TGA suggested that the thermal stability of the PA/PB-4 composite was excellent, which could be used for the applications of thermal energy storage. Furthermore, the thermal conductivity of PA/PB-4 was 0.3926 W/(m∙K), which was increased by 43.76% compared with that of the pure PA. Thus, the study results indicated that the PA/PB-4 had great potential for thermal energy storage applications.

Establishing the impact of model surfactants on cloud condensation nuclei activity of sea spray aerosol mimics

Abstract. Surface-active compounds present in aerosols can increase their cloud condensation nuclei (CCN) activation efficiency by reducing the surface tension (σ) in the growing droplets. However, the importance of this effect is poorly constrained by measurements. Here we present estimates of droplet surface tension near the point of activation derived from direct measurement of droplet diameters using a continuous flow streamwise thermal gradient chamber (CFSTGC). The experiments used sea spray aerosol (SSA) mimics composed of NaCl coated by varying amounts of (i) oleic acid, palmitic acid or myristic acid, (ii) mixtures of palmitic acid and oleic acid, and (iii) oxidized oleic acid. Significant reductions in σ relative to that for pure water were observed for these mimics at relative humidity (RH) near activation (∼ 99.9 %) when the coating was sufficiently thick. The calculated surface pressure (π = σH2O − σobserved) values for a given organic compound or mixture collapse onto one curve when plotted as a function of molecular area for different NaCl seed sizes and measured RH. The observed critical molecular area (A0) for oleic acid determined from droplet growth was similar to that from experiments conducted using macroscopic solutions in a Langmuir trough. However, the observations presented here suggest that oleic acid in microscopic droplets may exhibit larger π values during monolayer compression. For myristic acid, the observed A0 compared well to macroscopic experiments on a fresh subphase, for which dissolution has an important impact. A significant kinetic limitation to water uptake was observed for NaCl particles coated with pure palmitic acid, likely as a result of palmitic acid (with coating thicknesses ranging from 67 to 132 nm) being able to form a solid film. However, for binary palmitic-acid–oleic-acid mixtures there was no evidence of a kinetic limitation to water uptake. Oxidation of oleic acid had a minor impact on the magnitude of the surface tension reductions observed, potentially leading to a slight reduction in the effect compared to pure oleic acid. A CCN counter was also used to assess the impact on critical supersaturations of the substantial σ reductions observed at very high RH. For the fatty-acid-coated NaCl particles, when the organic fraction (εorg) was > 0.90 small depressions in critical supersaturation were observed. However, when εorg < 0.90 the impact on critical supersaturation was negligible. Thus, for the fatty acids considered here, the substantial σ reductions observed at high RH values just below activation have limited impact on the ultimate critical supersaturation. A surface film model is used to establish the properties that surface-active organic molecules must have if they are to ultimately have a substantial impact on the activation efficiency of SSA. To influence activation, the average properties of surface-active marine-derived organic molecules must differ substantially from the long-chain fatty acids examined, having either smaller molecular volumes or larger molecular areas. The model results also indicate that organic-compound-driven surface tension depression can serve to buffer the critical supersaturation against changes to the organic-to-salt ratio in particles in which the organic fraction is sufficiently large.

Solid-acid catalyzed biodiesel production, part I: biodiesel synthesis from low quality feedstock

A series of catalysts containing phosphotungstic acid (PTA) supported on periodic mesoporous silica were prepared and evaluated for the production of biodiesel from used cooking oil. The catalytic and physical properties of the prepared catalysts were investigated. Mesoporous catalyst, KIT-5 (Korea Institute of Technology 5) loaded with 26% PTA showed high activity for single step esterification, resulting in the successful elimination of a second transesterification step. The yield of fatty acid methyl esters was 93% from used (waste) cooking oil and ∼100% from pure palmitic acid. In addition, the solid acid catalyst retained a proportion of its original catalytic activity after repeated recycling steps. Thus, the prepared solid acid catalyst has the potential to be used for the production of biodiesel from feedstock that contain high amounts of free fatty acids.

Preparation of nitrogen-doped graphene/palmitic acid shape stabilized composite phase change material with remarkable thermal properties for thermal energy storage

Palmitic acid (PA) is one of the main phase change materials (PCMs) for medium temperature thermal energy storage systems. In order to stabilize the shape and enhance the thermal conductivity of PA, the effects of adding nitrogen-doped graphene (NDG) as a carbon nanofiller were examined experimentally. NDG was dispersed in liquid PA at various mass fractions (1–5wt%) using high power ultrasonication. The dropping point test shows that there was clearly no liquid leakage through the phase change process at the operating temperature range of the composite PCMs. The thermal stability and thermal properties of composite PCM were investigated with a thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC), respectively. The thermal conductivity of the PA/NDG composite was determined by the laser flash method. The thermal conductivity at 35°C increased by more than 500% for the highest loading of NDG (5wt%). The electrical conductivity of composite PCMs was increased significantly by using NDG. The thermal cycling test proved that the PA/NDG composites PCMs had good thermal reliability and chemical durability after 1000 cycles of melting and freezing. The thermal effusivity of the PA/NDG composite PCMs was larger than that of pure PA, which is advantageous for latent heat thermal energy storage (LHTES).

Synthesis, characterization and thermal properties of nanoencapsulated phase change materials via sol–gel method

This study focuses on preparing PCM (phase change material) nanocapsules which contain PA (palmitic acid) as core and SiO2 as shell materials. For the first time encapsulation of phase change materials is synthesized in nano scale via the sol–gel method by changing the value of pH in the range of 11–12. The morphology and the mean size of three samples are compared and the influences of different pH values on the particle size studied. This investigation reveals that the encapsulation ratio of PA is increased from 83.25 to 89.55 percent by increasing the pH value in the range of 11–12. The nanoencapsulated PCMs are arranged uniformly and spherically with mean diameter sizes 183.7, 466.4 and 722.5 nm for pH values of 11, 11.5 and 12, respectively. A thermal cycling test is done by 2500 melting/freezing cycles to determine thermal reliability and chemical stability of the nanoencapsulated PCMs. The thermal conductivity of the encapsulated PA is significantly improved compared to pure PA. As a result, the prepared PA/SiO2 nanocapsules are appropriate PCMs for slurry thermal energy storage applications because of their acceptable thermal properties, good thermal reliability, chemical stability, uniform morphology and thermal conductivities.

Ichthyotoxicity of gymnodinioid dinoflagellates: PUFA and superoxide effects in sheepshead minnow larvae and rainbow trout gill cells

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 426:213-224 (2011) - DOI: https://doi.org/10.3354/meps09036 Ichthyotoxicity of gymnodinioid dinoflagellates: PUFA and superoxide effects in sheepshead minnow larvae and rainbow trout gill cells Ben D. Mooney1,*, Juan José Dorantes-Aranda1, Allen R. Place2, Gustaaf M. Hallegraeff1 1University of Tasmania, Institute for Marine and Antarctic Studies, Private Bag 55, Hobart, Tasmania 7001, Australia 2Institute of Marine and Environmental Technology, University of Maryland Center for Environmental Sciences, Baltimore, Maryland 21202, USA *Email: ben.mooney@utas.edu.au ABSTRACT: While 24 h exposure of sheepshead minnow fish larvae to purified monogalactosyl diglyceride (MGDG) lipids, containing octadecapentaenoic acid (OPA) exclusively or as a mixture of octadecatetraenoic acid, eicosapentaenoic acid, and OPA (OTA-EPA-OPA), caused sluggish swimming and gulping, it produced no mortalities even at concentrations up to 120 mg l–1. In contrast, comparable concentrations and exposure times caused significant reductions in viability of rainbow trout gill cells. Pure EPA was the most harmful to gill cells (up to 98.5% viability loss in 60 h) followed by OPA-rich MGDG (45% loss), with OTA-rich MGDG (37% loss) the least toxic. OPA-pure MGDG was non-toxic to rainbow trout gill cells; however, surprisingly, pure palmitic acid was harmful (40% viability loss), and we conclude that gill cell line toxicity of the OPA-rich MGDG fraction was caused by admixture with palmitic acid. Screening of 15 Kareniaceae dinoflagellate species demonstrated that these species are low (on average 10 times less) producers of superoxide compared to the ichthyotoxic raphidophyte Chattonella marina. No mortality of sheepshead minnow fish larvae occurred when exposed to superoxide alone or superoxide combined with either OPA-rich MGDG or OTA-rich MGDG. Superoxide showed a slight impact on viability of rainbow trout gill cells. In conclusion, synergistic interactions between free fatty acids and reactive oxygen species as previously claimed for raphidophytes could not be confirmed. Gill damaging effects from EPA were conclusively demonstrated, however; when these co-occurred with OTA, a higher loss of viability was observed (up to 37%), suggesting a magnified toxic effect. Contradictory literature claims as to the ichthyotoxicity of OPA (nontoxic in our work) may relate to the presence of chemical impurities. KEY WORDS: Kareniaceae · Ichthyotoxicity · Octadecapentaenoic acid · OPA · Polyunsaturated fatty acid · PUFA· Superoxide Full text in pdf format PreviousNextCite this article as: Mooney BD, Dorantes-Aranda JJ, Place AR, Hallegraeff GM (2011) Ichthyotoxicity of gymnodinioid dinoflagellates: PUFA and superoxide effects in sheepshead minnow larvae and rainbow trout gill cells. Mar Ecol Prog Ser 426:213-224. https://doi.org/10.3354/meps09036 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 426. Online publication date: March 28, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Catalytic Deoxygenation of Stearic Acid and Palmitic Acid in Semibatch Mode

The deoxygenation experiments of different reactants, i.e., pure palmitic acid, stearic acid, and a technical grade stearic acid containing a mixture of 59% of palmitic and 40% of stearic acid were successfully performed over 4 wt% Pd/C mesoporous catalyst at 300 °C under 17 bar of 5% H2 in argon. The main product in catalytic deoxygenation of saturated fatty acids, C16 and C18, were aliphatic chain length hydrocarbons containing one less carbon than the corresponding acid. Additionally it was found that the deoxygenation rates of different reactant were independent on carbon chain length of its fatty acids.

Preparation, thermal properties and thermal reliability of palmitic acid/expanded graphite composite as form-stable PCM for thermal energy storage

This study is focused on the preparation and characterization of thermal properties and thermal reliability of palmitic acid (PA)/expanded graphite (EG) composite as form-stable phase change material (PCM). The maximum mass fraction of PA retained in EG was found as 80 wt% without the leakage of PA in melted state even when it is heated over the melting point of PA. Therefore, the PA/EG (80/20 w/w%) composite was characterized as form-stable PCM. From differential scanning calorimetry (DSC) analysis, the melting and freezing temperatures and latent heats of the form-stable PCM were measured as 60.88 and 60.81 °C and 148.36 and 149.66 J/g, respectively. Thermal cycling test showed that the composite PCM has good thermal reliability although it was subjected to 3000 melting/freezing cycles. Fourier transformation infrared (FT-IR) spectroscopic investigation indicated that it has good chemical stability after thermal cycling. Thermal conductivities of PA/EG composites including different mass fractions of EG (5%, 10%, 15% and 20%) were also measured. Thermal conductivity of form-stable PA/EG (80/20 w/w%) composite (0.60 W/mK) was found to be 2.5 times higher than that of pure PA (0.17 W/mK). Moreover, the increase in thermal conductivity of PA was confirmed by comparison of the melting and freezing times of pure PA with that of form-stable composite. Based on all results, it was concluded that the form-stable PA/EG (80/20 w/w%) has considerable latent heat energy storage potential because of its good thermal properties, thermal and chemical reliability and thermal conductivity.

Thermal properties of heat storage composites containing multiwalled carbon nanotubes

Thermal performance enhanced heat storage nanocomposites consisting of palmitic acid (PA) and multiwalled carbon nanotubes (CNTs) were prepared by dispersing chemically treated CNTs into melting PA. The PA/CNT composites remain stable after repeating energy storage and release 80 times. The melting point and latent heat capacity decrease with an increase in the mass fraction of CNTs. PA/CNT composites have enhanced thermal conductivities compared to pure PA, with the enhancement ratios increasing with the mass fraction of CNTs. For PA/CNT composite containing CNTs with a mass fraction of 5.0%, the thermal conductivity enhancement ratios amount up to 36% and 56% in solid and liquid states, respectively.

Investigation of the antifouling constituents from the brown alga Sargassum muticum (Yendo) Fensholt

One of the most promising alternatives to toxic heavy metal-based paints is offered by the development of antifouling coatings in which the active ingredients are compounds naturally occurring in marine organisms and operating as natural antisettlement agents. Sessile marine macroalgae are remarkably free from settlement by fouling organisms. They produce a wide variety of chemically active metabolites in their surroundings, potentially as an aid to protect themselves against other settling organisms. In this study, a dichloromethane extract from the brown seaweed Sargassum muticum was tested in situ and, after 2 months of immersion, showed less fouling organisms on paints in which the extract was included, compared to paints containing only copper after 2 months of immersion. No barnacles or mussels have been observed on the test rack. Identification by NMR and GC/MS of the effective compound revealed the abundance of palmitic acid, a commonly found fatty acid. Pure palmitic acid showed antibacterial activity at 44 µg mL−1, and also inhibited the growth of the diatom Cylindrotheca closterium at low concentration (EC50 = 45.5 µg mL−1), and the germination of Ulva lactuca spores at 3 µg mL−1. No cytotoxicity was highlighted, which is promising in the aim of the development of an environmentally friendly antifouling paint.

Heterogeneous OH oxidation of palmitic acid in single component and internally mixed aerosol particles: vaporization and the role of particle phase

Abstract. We studied the OH oxidation of submicron aerosol particles consisting of pure palmitic acid (PA) or thin (near monolayer) coatings of PA on aqueous and effloresced inorganic salt particles. Experiments were performed as a function of particle size and OH exposure using a continuous-flow photochemical reaction chamber coupled to a chemical ionization mass spectrometer (CIMS) system, for detection of gas and particle-bound organics, and a DMA/CPC for monitoring particle size distributions. The loss rate of PA observed for pure PA aerosols and PA on crystalline NaCl aerosols indicates that the OH oxidation of PA at the gas-aerosol interface is efficient. The pure PA oxidation data are well represented by a model consisting of four main processes: 1) surface-only reactions between OH and palmitic acid, 2) secondary reactions between palmitic acid and OH oxidation products, 3) volatilization of condensed-phase mass, and 4) a surface renewal process. Using this model we infer a value of γOH between 0.8 and 1. The oxidation of palmitic acid in thin film coatings of salt particles is also efficient, though the inferred γOH is lower, ranging from ~0.3+0.1/−0.05) for coatings on solid NaCl and ~0.05 (±0.01) on aqueous NaCl particles. These results, together with simultaneous data on particle size change and volatilized oxidation products, provide support for the ideas that oxidative aging of aliphatic organic aerosol is a source of small oxidized volatile organic compounds (OVOCs), and that OH oxidation may initiate secondary condensed-phase reactions.

Role of Lactose in Modifying Gel Transition Temperature and Morphology of Self-assembled Hydrogels

Lactose, a low-value dairy byproduct, was investigated as a gelling agent that could be used to tune the gel transition temperature (Tgel) and morphology of self-assembled fatty acid and fatty amine gels prepared in a water/alcohol cosolvent. Palmitic acid−lactose and n-hexadecylamine−lactose gels were studied using Fourier transform infrared spectroscopy, atomic force microscopy, and scanning electron microscopy. Lactose was observed to lower the Tgel of the palmitic acid system while raising the Tgel of the n-hexadecylamine system. Pores ranging from ∼20 to 50 μm were observed for the n-hexadecylamine−lactose gel while ∼5−10 μm pores were observed for the palmitic acid−lactose gel. Compared to the pure palmitic acid, the infrared spectra of the palmitic acid−lactose system exhibit a 9 cm-1 shift of the carbonyl (CO) stretching vibration and up to a 29 cm-1 shift of three hydroxyl (O−H) stretching vibrations, implying strong intermolecular hydrogen bonding. In contrast, a covalent conjugation is indicated for the n-hexadecylamine−lactose system by the disappearance of a sharp peak corresponding to a primary aliphatic amine stretching vibration (3337 cm-1) and emergence of a weak peak corresponding to a secondary aliphatic amine stretching vibration (3431 cm-1). Thus, lactose, either through covalent or physical conjugation to fatty amine and fatty acid, respectively, can be used as an effective agent to control the gel transition temperature for synthesis of thermally reversible hydrogels having a broad range of gel transition temperatures.

Molecular Dynamics Simulations of a Pulmonary Surfactant Protein B Peptide in a Lipid Monolayer

Pulmonary surfactant is a complex mixture of lipids and proteins that lines the air/liquid interface of the alveolar hypophase and confers mechanical stability to the alveoli during the breathing process. The desire to formulate synthetic mixtures for low-cost prophylactic and therapeutic applications has motivated the study of the specific roles and interactions of the different components. All-atom molecular dynamics simulations were carried out on a model system composed of a monolayer of palmitic acid (PA) and a surfactant protein B peptide, SP-B 1–25. A detailed structural characterization as a function of the lipid monolayer specific area revealed that the peptide remains inserted in the monolayer up to values of specific area corresponding to an untilted condensed phase of the the pure palmitic acid monolayer. The system remains stable by altering the conformational order of both the anionic lipid monolayer and the peptide secondary structure. Two elements appear to be key for the constitution of this phase: an electrostatic interaction between the cationic peptide residues with the anionic headgroups, and an exclusion of the aromatic residues on the hydrophobic end of the peptide from the hydrophilic and aqueous regions.