Nitrogen-water Interface Research Articles

Hydroxide and Hydronium Ions Modulate the Dynamic Evolution of Nitrogen Nanobubbles in Water.

It has been widely recognized that the pH environment influences the nanobubble dynamics and hydroxide ions adsorbed on the surface may be responsible for the long-term survival of the nanobubbles. However, understanding the distribution of hydronium and hydroxide ions in the vicinity of a bulk nanobubble surface at a microscopic scale and the consequent impact of these ions on the nanobubble behavior remains a challenging endeavor. In this study, we carried out deep potential molecular dynamics simulations to explore the behavior of a nitrogen nanobubble under neutral, acidic, and alkaline conditions and the inherent mechanism, and we also conducted a theoretical thermodynamic and dynamic analysis to address constraints related to simulation duration. Our simulations and theoretical analyses demonstrate a trend of nanobubble dissolution similar to that observed experimentally, emphasizing the limited dissolution of bulk nanobubbles in alkaline conditions, where hydroxide ions tend to reside slightly farther from the nanobubble surface than hydronium ions, forming more stable hydrogen bond networks that shield the nanobubble from dissolution. In acidic conditions, the hydronium ions preferentially accumulating at the nanobubble surface in an orderly manner drive nanobubble dissolution to increase the entropy of the system, and the dissolved nitrogen molecules further strengthen the hydrogen bond networks of systems by providing a hydrophobic environment for hydronium ions, suggesting both entropy and enthalpy effects contribute to the instability of nanobubbles under acidic conditions. These results offer fresh insights into the double-layer distribution of hydroxide and hydronium near the nitrogen-water interface that influences the dynamic behavior of bulk nanobubbles.

Polymerization of Oriented Monolayers of Octadecyl Acrylate: 1. Characterization of the Reaction Products

Octadecyl acrylate monolayers were polymerized at the nitrogen–water interface. The reaction was initiated by UV radiation and followed by measurement of surface potentials, relative surface viscosities and infrared spectra. Product behavior suggested a high molecular weight and cross-linked polymer. There were some indications that the interfacially polymerized material was stereoregular. The reaction was complicated by UV induced degradation of poly(octadecyl acrylate) monolayers to a product which showed many of the characteristics of poly(acrylic acid).

Methanofullerenes with mesogenic groups: Bulk properties and Langmuir films

New C 60 derivatives functionalized with mesogenic groups have been synthesized. Their behaviour at the nitrogen-water interface was investigated and appeared to depend on the nature of their functional group: if it contains a fluorinated chain, a stable monomolecular film is obtained; if not, then a multilayer organization is observed. In the bulk state, the structural organization of the methanofullerenes has been studied by polaried optical microscopy, DSC and X-ray diffraction experiments. At room temperature, a non-crystalline periodic structure is shown, and a phase transition leading to a viscous liquid state occurs when temperature increases.

Synthesis, Physical Characterizations, and Langmuir Films of New Methanofullerenes

Various methanofullerenes functionalized with either hydrophobic or polar groups have been synthesized. Studies of such compounds by surface pressure measurements and in situ UV-visible spectroscopy in Langmuir films show that these two types of functionalizations do not prevent the formation of aggregates at the nitrogen-water interface. Except for one compound studied in the present work, it appears that the aggregation occurs as soon as the spreading of the fullerenes solutions. However, the aggregates obtained appear to have different characteristics than those obtained with pure C{sub 60}. 26 refs., 9 figs., 2 tabs.

Intramolecular excimer fluorescence kinetics of 1,2-bis(4-pyrenylbutanoyl)phosphatidylcholine as a probe of molecular organization in spread monolayers at the nitrogen-water interface

Intramolecular excimer kinetics in a lipid containing two pyrene moieties, 1,2-bis(4-pyrenylbutanoyl)-phosphatidylcholine, have been examined by steady-state and time-resolved fluorescence in spread monolayers of several lipids to determine the effects of molecular organization on lipid dynamics. It is found that excimer formation responds markedly to compression in monolayers of unsaturated lipids, such as dioleoylphosphatidylcholine (DOL) and dielaidoylphosphatidylcholine (DEL). As expected, excimer decay was found to be little affected by lipid packing. For dipalmitoylphosphatidylcholine (DPL) systems, discontinuous changes in photophysical behavior are seen at the lipid phase transition. These types of behavior are consistent with those observed for dipyrenyl compounds in vesicles and lend themselves to a parallel data treatment. The kinetics of this probe were also measured in bulk solutions of known viscosity to provide some comparison with the data found in monolayers. 10 refs., 8 figs.

A study of the electrophoretic mobility of a very small inert gas bubble suspended in aqueous inorganic electrolyte and cationic surfactant solutions.

On the basis of the experimental technique proposed by one of present authors, this work is devoted to the measurement of the electromobility of a very small nitrogen bubble suspended in a few aqueous electrolyte solutions. It was confirmed that the isoelectric point (i.e.p.) of a bubble in water exists in a pH range between 2 and 3 irrespective of bubble size in light of the experimental results previously reported.When the mono- and divalent inorganic salts NaCl and MgSO4 were added to water, the negative mobility at a pH of 5.6 was monotonically depressed with increasing concentration of each salt.As for the trivalent salts AlCl3 and Al2(SO4)3, a charge reversal was observed at a certain concentration of each salt which agreed with previous data reported by other workers.Four n-alkyltrimethylammonium bromides of different n-alkyl chain length were also examined and it was observed that the i.e.p. of a surfactant with a smaller total number of carbon atoms in the n-alkyl chain of a n-alkyltrimethylammonium bromide tends to shift to a higher concentration. When the concentration giving the i.e.p. is plotted against the number of carbon atoms, a good linear correlation on a semilogarithmic scale was obtained. Incorporating the Stern-Graham double-layer model and the above linear correlation, the transfer energy required by the n-alkyltrimethylammonium ion when it is brought from the water phase to the nitrogen-water interface was estimated and the result was found to be reasonable.

Mixed monolayer studies of chlorophyll a and plastoquinone 9 at the nitrogen-water interface

Mixed monolayer studies of chlorophyll a and plastoquinone 9 at the nitrogen-water interface

Monolayer properties of mixed chlorophyll a-digalactosyldiacylglycerol at the nitrogen–water interface

Surface pressure, surface potential, and ellipsometric–area isotherms have been measured to investigate the properties of chlorophyll a – digalactosyldiacylglycerol monolayers at the nitrogen – water interface. The surface pressure – area isotherms of the mixed film show a pronounced negative deviation with respect to ideality, whereas the surface potential isotherms follow the additivity law for mixed films. As the mole fraction of Chl a increases from 0.1 to 0.5, each of the corresponding ellipsometric isotherm is shifted towards more negative values in the liquid expanded region. As the mole fraction is increased above 0.5, the ellipsometric δΔ values become more positive, with this trend continuing throughout the 0.5 to 0.9 mole fraction range. The combined effects of anisotropy in both the refractive indices and the absorption coefficient can explain the turnover observed in the ellipsometric δΔ isotherms as the mole fraction of Chl a becomes larger than 0.5.Hydrophilic interactions have been ruled out on the basis of the agreement with the additivity law, which is observed for surface potentials of the mixed monolayers. The observed deviation exhibited in the π–A isotherms is interpreted in terms of the intermolecular cavity effect. Key words: chlorophyll a, digalactosyldiacylglycerol, mixed monolayer, ellipsometry.

Purification of galactofipids by high-performance liquid chromatography for monolayer and Langmuir—Blodgett film studies

In order to obtain pure galactolipids usable for monolayer work at the nitrogen—water interface, and also for fluorescence intensity measurements in Langmuir—Blodgett films when mixed with chlorophyll a, purification procedures for mono- and digalactosyldiacylglycerol were established using high-performance liquid chromatography. The rapid and efficient methods described were applied to commercial samples and enriched extracted fractions of lipids obtained by preparative liquid chromatography. Surface pressure—area isotherms at the nitrogen—water interface of purified and unpurified samples are also reported. The fluorescence spectra of chlorophyll a mixed with purified and unpurified galactolipids in Langmuir—Blodgett films clearly show the necessity for the purification.

Estimation of disk membrane lateral pressure and molecular area of rhodopsin by the measurement of its orientation at the nitrogen-water interface from an ellipsometric study

The internal lateral pressure of a bilayer has been estimated by numerous investigators. Most of these measurements were made by using the monolayer technique. In our approach, the disk membrane lateral pressure was estimated by assuming that this value is equal to the surface pressure necessary to maintain the transmembrane orientation of rhodopsin. The orientation of rhodopsin at the nitrogen-water interface was determined by using ellipsometry, which can measure the thickness of the film. By examining surface pressure and ellipsometric isotherms of intact and partially hydrolyzed rhodopsin, we have determined that a lateral pressure of 38 mN/m is necessary to give rhodopsin its natural transmembrane orientation and that surface pressures exceeding 45 mN/m lead to the formation of multilayers in the disk membrane film. At 38 mN/m, pure rhodopsin is found to have a molecular area of 2300 A2.

Properties of mixed chlorophyll a-glycolipid monolayers

Surface pressure, ellipsometric and surface potential-area isotherms have been measured to investigate the properties of chlorophyll a-digalactosyldiacyglycerol (Chl a-DGDG) and Chl a-sulfoquinovosyldiacylglycerol (SQDG) monolayers at the nitrogen-water interface. The surface pressure-area isotherms of Chl a-DGDG exhibit a pronounced negative deviation with respect to ideality, whereas ellipsometric and surface potential isotherms of the mixed monolayers fall between those of the pure components. Hydrophilic interactions have been ruled out on the basis of the additivity law followed by the surface dipole moment of the mixed monolayers. The observed deviation exhibited by the π- A isotherms is interpreted in terms of an intermolecular cavity effect.

The binding of G-protein to rod outer segment phospholipids at the nitrogen–water interface

In the visual process, one photoexcited rhodopsin (R*) catalyzes the activation of hundreds of G-proteins. It remains to be determined whether G-protein and R* find one another by membrane surface diffusion of these components (diffusion model) or by diffusion of G-protein through the aqueous phase (hopping model). A monolayer of each main rod outer segment (ROS) phospholipid interacting with a subphase containing G-protein, has been used to simulate the interaction of G-protein with the cytoplasmic surface of discal membranes. The possible diffusion of G-protein through the aqueous phase was then measured by observing its adsorption-desorption in the monolayer of each main ROS phospholipid. From examination of surface pressure and ellipsometric isotherms at the nitrogen-water interface, we have determined that once incorporated into the monolayer, the G-protein remains associated, independent of surface pressure, thus providing evidence against the hopping model.

Effects of molecular organization on photophysical and photochemical behavior: Quenching by subphase iodide of fluorescence in pyrene-bearing probes at the nitrogen-water interface

The quenching by subphase iodide of pyrene covalently bound to amphiphatic molecules in spread monolayers has been measured. The probes employed were 2-(6-pyreneylhexanoyl)-3-palmitoyl-sn-glycero-1-phosphorylcholine, 10-(6(8)-octadecylpyrenyl) decanoic acid and 1-pyrenedocosanoic acid; the host lipids utilized were dioleoylphosphatidylcholine (DOL) and dipalmitoylphosphatidylcholine (DPL). It has been observed in all cases that pyrene fluorescence is significantly quenched in the uncompressed layer and that this quenching diminishes markedly as the surface pressure is increased over the liquid expanded region. Beyond this range a plateau in the fluorescence decay is reached in DOL, while in DPL changes in quenching are related to phase transitions. These findings indicate significant probe-water interaction at low surface pressure. Residual iodide quenching in DOL above 10 dyn cm −1 indicates some continued water-probe contact which may be due to the liquid character of the host layer and the double-bond character of the lipid while the very small residual quenching in DPL suggests tight packing in the non-liquid phases.

Measurement of fluorescence depolarization for chlorophyll-a and chlorophyll-b in spread monolayers at the nitrogen-water interface

Fluorescence polarization has been measured for chlorophyll-a (Chl-a) and chlorophyll-b (Chl-b) in spread monolayers of dioleoylphosphatidylcholine as functions of monolayer compression in the surface pressure range 2–30 dyn cm −1. Concentrations of chlorophyll from a mole fraction of 0.0025 to pure chlorophyll were used. Polarization in Chl-b was found to be 3–4 times greater than in Chl-a under similar conditions and to exhibit a marked dependence on surface pressure. The polarization of Chl-a was only marginally affected by surface pressure.

Interaction of C-phycocyanin with lipid monolayers under nitrogen and in the presence of air

The surface interaction of C-phycocyanin with lipids was studied using the monolayer technique. The surface activity of the protein was found to be higher at the lipid-water interface than at the nitrogen-water interface, particularly at high surface pressures of the lipid monolayer. The maximum initial surface pressures beyond which phycocyanin could not penetrate the dipalmitoylphosphatidylcholine and monogalactosyldiglycerol monolayers were 27 and 30 mN m −1, respectively. Below these values the protein demonstrated preferential interaction with the monogalactosyldiglycerol monolayer. The surface properties of the unfolded protein at pH 2.5 at the lipid-water interface were compared with those of the protein at pH 7.0. Higher affinity of the three-dimensional structure of the protein to lipid monolayers was observed, in particular by high sub-phase protein concentration. When the lipid films were subjected to oxidation stress by exposure to air, the surface properties of C-phycocyanin and dipalmitoylphosphatidylcholine were not greatly affected but the surface activity of monogalactosyldiacylglycerol was reduced dramatically by autoxidation. The oxidation of monogalactosyldiacylglycerol could not be prevented by the introduction of C-phycocyanin molecules at the lipid-water interface.

Direct evidence for the formation of a monolayer from a bilayer. An ellipsometric study at the nitrogen-water interface

Direct evidence for the formation of a monolayer from a bilayer was measured by ellipsometry after spreading unilamellar vesicles of dioleoyl phosphatidylcholine (DOPC) at the nitrogen-water interface. The ellipsometric isotherms of DOPC vesicles and DOPC spread from an organic solvent were compared and found similar. From the observed ellipsometric angle (delta delta) in the plateau region (-1.04 degrees) and literature data for refractive indices of an anisotropic film similar to DOPC, we have calculated a thickness of 20 +/- 1 A. These results strongly suggest that, similarly to DOPC spread from an organic solvent, DOPC vesicles form a monolayer when spread at the nitrogen-water interface.

Ellipsometric studies of rod outer segment phospholipids at the nitrogen-water interface

Ellipsometry is an optical method which uses the principle that the state of polarization of polarized light changes on reflection at an interface. We have constructed a null ellipsometer for the study of the optical properties of monomolecular films of biological interest at the nitrogen-water interface. With this apparatus we have reproduced the known ellipsometric properties of arachidic acid spread on acidic aqueous solution. Then, we have performed surface potential, surface pressure and ellipsometric measurements of PC (18:1) and rod outer segment phospholipids, i.e. PE ros , PC ros and PS ros , at the nitrogen-water interface. Based on literature refractive indices data, results provide information about the thickness of a lipid film in the close-packed region. Pertinent information about molecular organization of the film is deduced from the close relationship observed between surface potential and ellipsometric isotherms. The importance of these results on the discal membrane structure and function is discussed.

Effects of molecular organization on photophysical behavior. Excimer kinetics and diffusion of 1-pyrenedecanoic acid in lipid monolayers at the nitrogen-water interface

The time resolved behavior of pyrenedecanoic acid excimers in spread phospholipid monolayers at the air-water interface is reported herein. Interactions of the pyrene-bearing probe, 1-pyrenedecanoic (PDecA) have been compared as functions of probe concentration and hydrocarbon structure of the host liquid to the character of the lipid environment. The time resolved fluorescence measurements of mixed PDecA-lipid monolayers exhibit two features at 480 nm: a very fast rise in excimer intensity and a dependence of the excimer decay on PDecA mole fraction in the layer. 9 references, 3 figures.

Effects of molecular organization on photophysical behavior: lifetime and steady-state fluorescence of chlorophyll a singlets in monolayers of dioleoylphosphatydylcholine at the nitrogen-water interface

Effects of molecular organization on photophysical behavior: lifetime and steady-state fluorescence of chlorophyll a singlets in monolayers of dioleoylphosphatydylcholine at the nitrogen-water interface

Effects of molecular organization on photophysical and photochemical behavior. Exciplex formation in 1-pyrenedodecanoic acid and 4-dodecylaniline at the nitrogen-water interface

Effects of molecular organization on photophysical and photochemical behavior. Exciplex formation in 1-pyrenedodecanoic acid and 4-dodecylaniline at the nitrogen-water interface