Decrease In Surface Pressure Research Articles

Hydrolysis of milk phospholipid and phospholipid–protein monolayers by pancreatic phospholipase A2

Recently, phospholipids have been used for the liposomal encapsulation of drugs and bioactive compounds. Pancreatic phospholipase A2 is responsible for the hydrolysis of phospholipids in the intestines. Using fluorescence microscopy, Langmuir monolayers at the air–water interface and atomic force microscopy, the aim of this work was to obtain preliminary data on the effect of the liquid-ordered domains and proteins on the hydrolysis of phospholipids by pancreatic phospholipase A2. Increasing the enzyme:substrate ratio (1:40 to 1:2) and the temperature (30°C to 37°C) increased phospholipid hydrolysis as seen by a decrease in surface pressure and change in the surface area corresponding to the formation and desorption of hydrolytic products. Hydrolysis occurred rapidly in the phase coexistence region and led to the clustering of the liquid-ordered domains likely through reduction of electrostatic forces. Atomic force microscopic images of the monolayers under simulated intestinal conditions revealed the presence of packing defects in the liquid-ordered domains where phospholipase A2 could adsorb. Hydrolysis took place starting in the center of the liquid-ordered domains and proceeded towards their edges. It did not lead to any measurable height changes by atomic force microscopy within the domains but it was evident that mechanical changes took place during hydrolysis. The presence of β-casein appeared to increase the rate of hydrolysis, possibly through interaction with phospholipase A2 at the interface.

Surface response to stratospheric aerosol changes in a coupled atmosphere–ocean model

AbstractPrevious work with a simple climate model has suggested a global cooling impact of increasing stratospheric aerosol. Here we use a comprehensive Earth System Model including coupled atmosphere and ocean components to show that increasing stratospheric aerosol since the late 1990s has reduced global warming by at least 0.07 C to present and that a further global cooling impact will occur if the observed stratospheric aerosol trend continues to the end of this decade. This result confirms the previous work and suggests that climate models that do not account for stratospheric aerosol increase will overestimate global warming to a small but notable degree. An additional new finding is that increasing stratospheric aerosol since the late 1990s has reduced the rise in global mean precipitation.Finally, regional patterns of change in simulations with stratospheric aerosol increase to year 2020 show ~40% less equatorial precipitation increase and ~60% greater surface pressure decrease around Antarctica, relative to simulations without such stratospheric aerosol changes.

Visualizing a multidrug resistance protein, EmrE, with major bacterial lipids using Brewster angle microscopy

Understanding lipid–protein interactions to enhance our knowledge of membrane architecture is a critical step in the development of novel therapeutic measures to respond to the drastic rise of drug resistant microorganisms. Escherichia coli contains a small archetypal inner membrane multidrug resistance protein, EmrE, that must multimerize to be functional but this multimerization is difficult to demonstrate in vivo. We studied three major E. coli lipids (phosphatidylethanolamine, phosphatidylglycerol and cardiolipin) that varied in head group structure, acyl chain length and saturation. These were investigated both in the presence and absence of EmrE to determine which lipid(s) EmrE influenced most strongly. Langmuir monolayers and Brewster angle microscopy demonstrated that varying each head group, acyl chain length and saturation contributed to differences in membrane packing and affected lipid–protein associations. Long unsaturated anionic lipids were influenced most strongly by EmrE. Shorter acyl chains initiated string-like formations of EmrE clusters, whereas longer chains contributed to enhance protein clustering. Longer partially unsaturated acyl chains in phosphatidylglycerol showed a significant surface pressure decrease in the presence of the protein, indicating that the monolayer was destabilized. Interestingly, longer unsaturated chains of cardiolipin formed the most stable monolayer in the presence of EmrE. These studies indicate cardiolipin acyl chains that hydrophobically match protein helical lengths stabilize EmrE structural forms.

The first meteorological measurements in the Iberian Peninsula: evaluating the storm of November 1724

Early instrumental series can play a key role in the study of recent climate change or assessments of specific extreme events. Unfortunately in the Iberian Peninsula few series are available relative to the 18th century. In this article we retrieved and make available the first daily instrumental series obtained in Iberia. The observations were made in Lisbon between 1 November 1724 and 11 January 1725 by Diogo Nunes Ribeiro. While pressure and temperature values were registered twice a day, the remaining variables, i.e. the state of the sky, wind direction and force, have only one value per day. Despite the relatively short period covered by this series, we were very fortunate to discover that it helps to characterize one of the strongest storms that struck Lisbon since the early 17th century. In particular, the data provide evidence for an outstanding pressure drop of 28.61 hPa from 1010.76 hPa on the 18 November to just 982.15 hPa on the 19 November. Using recently digitized pressure data for Lisbon since 1863, we can state that this 24 h decrease of surface pressure has been surpassed only once on the 28 November 1879. Moreover, the extreme winds associated with this “bomb” affected severely the entire Lisbon area as well as large sections of central and northern Portugal during the afternoon of 19 November and caused important damage in the eastern coast of Madeira the night before (18 November). This storm resembles the rare tropical storms that have reached the Iberian Peninsula as a tropical storm (Vince 2005) or the low intense hurricane that occurred in 1842.

The predictability of precipitation episodes during the West African dry season

AbstractPrecipitation episodes in tropical West Africa (7–15°N, 10°W–10°E) during the dry season from November to March are rare, but can have significant impacts on human activities reaching from greening of pastures to spoiling harvests and health implications. Previous work has shown a link between these unseasonal rainfalls and extratropical disturbances via a decrease of surface pressure over the Sahara/Sahel and a subsequent inflow of moist air from the Gulf of Guinea. This paper supports the previously stated hypothesis that the extratropical influence leads to a high rainfall predictability through a careful analysis of operational 5 day forecasts from the European Centre for Medium‐Range Weather Forecasts' (ECMWF) ensemble prediction system (EPS), which are evaluated using Global Precipitation Climatology Project (GPCP) and Tropical Rainfall Measuring Mission (TRMM) precipitation estimates for the 11 dry seasons 1998/99‐2008/09. The long‐term regional average of ensemble‐mean precipitation lies between the two observational datasets, with GPCP being considerably wetter. Temporal correlations between the ensemble mean and observations are 0.8. Standard probabilistic evaluation methods such as reliability and relative operating characteristic (ROC) diagrams indicate remarkably good reliability, sharpness and skill across a range of precipitation thresholds. However, a categorical verification focusing on the most extreme ensemble mean values indicates too many false alarms. Despite the considerable observational uncertainty the results show that the ECMWF EPS is capable of predicting winter rainfall events in tropical West Africa with good accuracy, at least on regional spatial and synoptic time‐scales, which should encourage West African weather services to capitalize more on the valuable information provided by ensemble prediction systems during the dry season. Copyright © 2012 Royal Meteorological Society

Surface pressure record of Tibetan Plateau warming since the 1870s

AbstractThe Tibetan Plateau (TP) is the world's highest and largest plateau. By acting as an elevated thermal source as well as a topographic barrier, the TP has a profound impact on both local weather and global climate. The TP has recently been warming at a faster rate than the entire Northern Hemisphere. However, the lack of instrumental records prior to the 1950s limits our ability to place this recent warming in a longer‐term context. Here we show that over the plateau, because of its high elevation, the surface pressure is a proxy for surface air temperature and that since the 1870s there has been a statistically significant increase in surface pressure over the TP, that has undergone an acceleration since the 1980s. There is also a compensatory decrease in surface pressure in the surrounding lower elevation region. Furthermore, we show that since the 1870s the surface pressure over the plateau is correlated with the Northern Hemisphere temperature record at a statistical significance that exceeds the 99 percentile. Finally, the trend in surface pressure over the plateau is consistent with an increase in annual mean surface air temperature of ∼0.4°C since the 1870s and an increase of ∼1°C since the 1980s. The long‐term warming over the TP derived from the surface pressure trend is of the same order as the long‐term hemispheric warming. This suggests that the increased rate of warming recently observed over the plateau is not a long‐term phenomenon. Copyright © 2012 Royal Meteorological Society

Binding of cationic pentapeptides with modified side chain lengths to negatively charged lipid membranes: Complex interplay of electrostatic and hydrophobic interactions

Basic amino acids play a key role in the binding of membrane associated proteins to negatively charged membranes. However, side chains of basic amino acids like lysine do not only provide a positive charge, but also a flexible hydrocarbon spacer that enables hydrophobic interactions. We studied the influence of hydrophobic contributions to the binding by varying the side chain length of pentapeptides with ammonium groups starting with lysine to lysine analogs with shorter side chains, namely ornithine (Orn), α,γ-diaminobutyric acid (Dab) and α, β-diaminopropionic acid (Dap). The binding to negatively charged phosphatidylglycerol (PG) membranes was investigated by calorimetry, FT-infrared spectroscopy (FT-IR) and monolayer techniques. The binding was influenced by counteracting and sometimes compensating contributions. The influence of the bound peptides on the lipid phase behavior depends on the length of the peptide side chains. Isothermal titration calorimetry (ITC) experiments showed exothermic and endothermic effects compensating to a different extent as a function of side chain length. The increase in lipid phase transition temperature was more significant for peptides with shorter side chains. FTIR-spectroscopy revealed changes in hydration of the lipid bilayer interface after peptide binding. Using monolayer techniques, the contributions of electrostatic and hydrophobic effects could clearly be observed. Peptides with short side chains induced a pronounced decrease in surface pressure of PG monolayers whereas peptides with additional hydrophobic interactions decreased the surface pressure much less or even lead to an increase, indicating insertion of the hydrophobic part of the side chain into the lipid monolayer.

Hovmöller diagrams of climate anomalies in NCEP/NCAR reanalysis from 1948 to 2009

Atmospheric and oceanic reanalysis data of the past 60 years are visualized by time–latitude cross sections which inform about temporal and latitudinal variability, changes, and meridional circulation of the climate system on time scales from years to decades. The diagrams ease the understanding of climate dynamics in a similar way as the Hovmoller diagram has clarified the zonal propagation of synoptic-scale waves in a latitude band. Thus the time–latitude cross sections are referred to as Hovmoller diagrams of climate anomalies. Various parameters are selected at the Earth’s surface level: air temperature, pressure, sea surface temperature, column-integrated atmospheric water vapour (IWV), surface relative humidity, and surface wind. Contour lines of one parameter are overlayed on the color image of the other parameter so that relations and coincidences of trends, oscillations, and sudden changes of the climate are revealed. Temporal variations of IWV and surface relative humidity appear to be related to the strength of the Southern polar front jet. In case of ENSO 1997/1998, the equatorial IWV enhancement is accompanied by acceleration of the meridional circulation cells of the Southern Hemisphere. Meridional surface wind data suggest the existence of double polar cells in both hemispheres. The Southern polar cells switched to a higher circulation speed in 1997, and surface relative humidity increased over Antarctica. A sudden and persistent decrease of surface pressure occurred in Antarctica around 1980. Since 2000, a rapid increase of surface air temperature, sea surface temperature, and IWV occurs in the Northern Hemisphere. These results of NCEP/NCAR reanalysis have to be cross-validated with other reanalyses, climate models, and pure observations which will be a major endeavour.

Instability of Adsorbed Films of 1-Dodecanol and is Mixture with Sodium Dodecyl Sulfate at the Air/Water Interface

Properties and structures of adsorbed films on mixed aqueous solutions of sodium dodecyl sulfate (SDS) and a trace amount of 1-dodecanol (DD) were investigated by film balance experiments, a Brewster angle microscopy (BAM), and a quick X-ray reflectometry (q-XR) at 20 C. Pouring the aqueous solutions of the surfactants into a trough, the surface pressure first increased up to certain maximum values due to adsorption of the surfactants at the air/solution interface, but after a while it started to decrease probably due to evaporation of DD. BAM observation showed formation of holes of fluid phase in homogeneous condensed-phase monolayers in the course of surface pressure decrease. The q-XR technique was applied to the adsorbed films at the beginning stage of destabilization in order to characterize the film structures at the molecular level.

Metal ions binding to tri- n-octylphosphine oxide (TOPO) monolayer spread at the air/water interface

Our recent investigations proved excellent film-forming properties of tri- n-octylphosphine oxide (TOPO) spread at the free surface of water (K. Hąc-Wydro, P. Wydro, P. Dynarowicz-Łątka, Pol. J. Chem., 79 (2005) 773). Since TOPO is known for its affinity to metal ions, it is of interest to study the behavior of TOPO monolayers spread on aqueous subphases containing different ions. For our investigation we have selected mono- and divalent alkali metal ions, differing in nuclear charge and size. Additionally, the influence of La 3+ and VO 2+ on TOPO monolayer has been studied. In order to characterize the monolayers we have applied the Langmuir monolayer technique and recorded surface pressure–area ( π– A) isotherms and analyzed the stability by monitoring the decrease of surface pressure (at constant area) vs time. Moreover, the stability of monolayers was examined by comparing the collapse pressure values. Quantitatively, the changes in the Gibbs free energy in passing from water to metal ion-containing subphase were determined from the isotherms datapoints. Our results indicate that TOPO shows the highest affinity towards La 3+ and VO 2+ and among alkali metals — towards magnesium and lithium ions, which posses the smallest ionic radius among investigated cations. Our results, based on the Langmuir monolayer technique, are in good agreement with the extraction efficiency results.

Impact of Reductive Cleavage of an Intramolecular Disulfide Bond Containing Cationic Gemini Surfactant in Monolayers and Bilayers

The properties of a novel disulfide-bond-containing gemini surfactant bis[N,N-dimethyl-N-hexadecyl-N-(2-mercaptoethyl)ammonium bromide] disulfide (DSP) were studied using a Langmuir balance, supported monolayers, differential scanning calorimetry, giant vesicles, and LUVs. In 150 mM NaCl the cmc for DSP was 7.5 microM whereas that of the monomer N,N-dimethyl-N-hexadecyl-N-(2-mercaptoethyl)ammonium bromide (MSP) was 12.1 microM. Both surfactants exhibited single endotherms upon DSC, with peak temperatures Tm at 21.7 and 20.1 degrees C for DSP and MSP, respectively. The endotherm for MSP was significantly broader indicating less cooperative melting. Both in monolayers and in vesicles reductive cleavage of the disulfide bond of DSP could be obtained by glutathione (GSH). For Langmuir films of DSP the addition of GSH into the subphase led to a decrease in surface pressure pi as well as surface dipole potential psi. Although the cleavage by GSH was significantly slower in the presence of a charge saturating concentration of DNA, it did not prevent the reaction. The resulting monomers detached from supported monolayers, leading to loss of affinity of the surface for DNA. Disruption of giant vesicles containing DSP within approximately 30 s following a local injection of GSH was observed, revealing membrane destabilization.

The Multi-scale Structure and Development Mechanism of Mesoscale Cyclones over the Sea of Japan in Winter

The western Sea of Japan is a region in which mesoscale cyclones are frequently observed as cold polar air breaks out over the sea. In this region, mesoscale cyclones occasionally develop along a convergence zone that forms on the lee side of the mountains north of the Korean Peninsula. A meso-a-scale cyclone (MaC), in which two meso-b-scale cyclones (MbCs) were embedded, was observed in the western Sea of Japan on 23 January 1990. This structure is referred to as a ‘‘multi-scale structure’’ of a mesoscale cyclone. A simulation experiment and a number of sensitivity experiments with respect to several forcing factors were performed to elucidate the development mechanism of mesoscale cyclones. Stably stratified air flows around the mountains north of the Korean Peninsula and the convergence zone forms on the lee side of the mountains. Large amounts of sensible heat and latent heat are supplied from the sea to the atmosphere. The diabatic heating due to condensation and vertical diffusion of the sensible heat and horizontal advection of the potential temperature y are almost in balance with the negative vertical advection of y. This results in an intense upward motion in the convergence zone. Since baroclinicity is intense in this region, an upward transfer of the horizontal momentum around the convergence zone intensifies the upper-level (800@600 hPa) divergence. Consequently, the surface pressure decreases, and the MaC develops. The upward motion and vorticity are concentrated mostly in the MbCs, which are considered to be the cores of the MaC. On the other hand, the MaC provides an environment for the formation and development of the MbCs and affects their movements.

Physicochemical Properties of Phosphatidylcholine (PC) Monolayers with Different Alkyl Chains, at the Air/Water Interface

Physicochemical properties of a series of PC monolayers with different alkyl chains (C24, C20, C16, and C8), at the air/water interface were investigated. The surface pressure is influenced mainly by the hydrophobicity of the PCs, which is confirmed by the curve shape and the on-set value of π-A isotherms at the air/water interface by increasing the number of alkyl chain. The on-set values of surface pressure were 125 Ų/molecule for DOPC(C8), 87 Ų/molecule for DPPC(C16), 75 Ų/molecule for DAPC(C20), and 55 Ų/molecule for DLPC(C24), respectively. The orientations of alkyl chains at the air/water interface are closely connected with the rigidity of the monolayers, and it was confirmed by the tendency of monolayer thickness in ellipsometry data. The temperature dependence of a series of PCs shows that the surface pressure decreases by increasing temperature, because the longer the alkyl chain length, the larger the hydrophobic interaction in surface pressure. The temperature effects and the conformational changes of unsaturated and saturated PCs were confirmed by the computer simulation study of the cis-trans transition with POPC and DPPC(C16). The cistrans conformational energy difference of POPC is 62.06 kcal/mol and that of DPPC(C16) is 6.75 kcal/mol. Due to the high conformational energy barrier of POPC, phase transition of POPC is limited in comparison with DPPC(C16).

Combined scanning electrochemical microscopy–Langmuir trough technique for investigating phase transfer kinetics across liquid/liquid interfaces modified by a molecular monolayer

The first combination of scanning electrochemical microscopy (SECM) with a Langmuir trough for liquid/liquid interfaces is described. The technique has been examined and demonstrated through investigations of the effect of monolayers of l-α-phosphatidylcholine, distearoyl (DSPC) on the kinetics of oxygen transfer from decane to water. The stability of monolayers, formed in this way, on the timescale of SECM measurements has been identified as a function of compression speed and subphase composition. Monolayers were stable over a wide range of pressures and molecular areas, but at high compression a decrease in surface pressure with time was observed. This effect was attributed to desorption of the lipid from the interface. In this situation, it was possible to perform SECM measurements (tip-interface approach curves) rapidly under surface pressure control, without causing significant disturbance to the monolayer. DSPC had no detectable effect on the oxygen transfer kinetics when the monolayer was in the liquid-expanded phase, but in the liquid-condensed phase a significant decrease in the rate of oxygen transfer was observed.

Enzymatic hydrolysis reaction of phospholipids in monolayers

The hydrolysis reaction of l-, d- and d, l-dipalmitoylphosphatidylcholine (DPPC) catalized by bee venom phospholipase A 2 was studied in spreading monolayer at the water/air interface. DPPC and the hydrolysis products, palmitic acid and l-lysophosphatidylcholine, palmitoyl were characterized at the interface by means of surface pressure, surface potential and ellipsometric measurements. Furthermore, mixed monolayers of reagents and products were investigated to ascertain their miscibility. The results show that the hydrolysis reaction can be followed by the decrease of surface pressure with time on subphases containing β-cyclodextrin, a well-known complexing agent of many amphiphilic compounds. The order of the reaction, the kinetic constant and other kinetic parameters are deduced.

Cation-mediated interaction of dextran sulfate with phospholipid vesicles: binding, vesicle surface polarity, leakage and fusion

The interaction of dextran sulfate (DS) with dimyristoylphosphatidylcholine (DMPC) large unilamellar vesicles was investigated. DS of different molecular weights (1, 8, 40 and 500 kDa) and divalent cations (Ca2+, Mg2+ and Mn2+) and the trivalent cation La3+ were used in the experiments. Binding of DS was studied by use of the microelectrophoresis and monolayer technique. Binding depends strongly on cation and NaCl concentrations in the medium and does not occur in the absence of multivalent cations. Binding is modulated by the molecular weight of the polymers; DS with lower molecular weights lead to less negative zeta potentials at identical concentrations. A comparable monomer of DS, glucose-6-sulfate, does not change the zeta potential of DMPC vesicles. Monolayer experiments revealed a decrease in surface pressure after addition of multivalent cations and DS, indicating a stronger interaction of the cation–polymer complex with the phosphatidylcholine headgroups than its penetration into the phospholipid (PL) bilayer. The cation-mediated binding of DS to the vesicles leads to aggregation of the vesicles. The tendency to promote aggregation of DMPC vesicles is La3+>Ca2+>Mn2+≥ Mg2+. The aggregated vesicles show a stacklike arrangement of the bilayers as shown by freeze-fracture electron microscopy. The strong aggregation is accompanied by lipid mixing measured by the 1,4-nitrobenzo-2-oxa-1,3-diazole–phosphatidylethanolamine (PE)/lissamine rhodamine B sulfonyl-PE assay. At low ionic strength substantial lipid mixing can be observed in the previously mentioned order of the cations. This lipid mixing is accompanied by an increase in the permeability of the vesicles as revealed by the 1-aminonaphthalene-3,6,8-trisulfonic acid/p-xylenebis (pyridiium bromide) assay. The extent of leakage is determined by the cation used and the DS molecular weight. These interaction processes between the opposing bilayers are connected with a decrease in the water content in the gap between the opposing PL bilayers. As a measure for the change of the polar properties of the vesicle surface the shift of the emission wavelength of the fluorescent probe dansylphosphatidylethanolamine was measured. The effectiveness of divalent/trivalent cations to decrease the surface dielectric constant of DMPC vesicles also followed the sequence of ions as found for binding, PL mixing and leakage. The results are discussed in terms of the changed hydration at the bilayer surface induced by DS in the presence of multivalent ions.

Tethered chains in poor solvent conditions: An experimental study involving Langmuir diblock copolymer monolayers

We have employed Langmuir monolayers of highly asymmetric polydimethylsiloxane-polystyrene (PDMS-PS) diblock copolymers on dioctyl phthalate (DOP) at temperatures ranging from 22 to −35 °C as a model system for tethered chains in poor solvent conditions. The thicknesses of the tethered PS layers extending into the DOP subphase, measured by neutron reflection, decrease with decreasing temperature (T) over this entire range. However, the variation with T becomes weak below −20 °C. At the lowest T, the layer thicknesses are 55%–75% of the values at the theta condition (Tθ=22 °C). The contraction of the layer with decreasing T is determined as a function of surface density and molecular weight, and these data are compared to universal scaling forms. The PS segments are depleted from the near surface region over the entire T range, with the thickness of the depletion layer increasing slightly with decreasing T. The free energy of the surface layer is probed by surface tension measurements. With decreasing T, negative surface pressures are observed at low coverages for both PDMS-PS and PDMS monolayers, indicating metastability toward lateral phase separation. Evidence for a transition from a dispersed phase to a condensed phase with decreasing T was observed in the reflectivity for very low PDMS-PS coverage. At high coverage where the submerged blocks are strongly interacting at 22 °C, only a modest decrease in surface pressure is observed over the experimental range of T despite the strong contraction. This latter result is discussed in terms of the relative contributions of enthalpic and entropic effects to the surface pressure.

Relaxation phenomena in monoglyceride films at the air–water interface

Monoglycerides are the most commonly used surfactants in the food industry in traditional food, low-fat products and instant foods. In this work we are essentially concerned with the study of the stability in monoglyceride monolayers (monopalmitin, monoolein and monolaurin) as a function of surface pressure (10 and 20 mN.m −1) and aqueous phase pH (pH 5 and 7). Monolayer stability was determined in an automated Langmuir-type film balance at constant temperature (20 and 40°C). The rate of monolayer molecular loss increases with surface pressure, and is pH dependent. Molecular loss at the interface also depends on the lipid. In the discussion, special attention will be given to the effect of the hydrocarbon chain length and the presence of a double bond in the hydrocarbon chain. Monopalmitin monolayers are more stable than those of monoolein and monolaurin. Maximum instability was observed with monolaurin monolayers. Two kinds of experiment have been performed to analyse relaxation mechanisms. In one, the surface pressure is kept constant, and the area is measured as a function of time. In the second, the area is kept constant at monolayer collapse and the surface pressure decreases. This decrease is measured as a function of time. Various relaxation mechanisms, including monolayer molecular loss by dissolution and/or collapse, can be fitted to the results derived from these experiments.

Electron Transfer Photofragmentation Reactions in Monolayer Films at the Air/Water Interface

A series of photoinduced electron-transfer fragmentation reactions have been studied in compressed monolayer films at the air/water interface. The reactions investigated involve amphiphilic and polymeric derivatives of fragmentable amino alcohol, 1,2-diamine, and pinacol donors and light-absorbing acceptors, which are reactive in solution-phase studies from their triplet states. For intralayer studies a surfactant anthraquinone derivative was the light-absorbing acceptor. For comparable interfacial studies, the water soluble cation tris(2,2'-bipyridine)ruthenium(II)2+ (Ru(bpy) 32+) was the photoactive acceptor from the subphase. The fragmentation reactions all involve oxidative cleavage of a relatively strong C-C bond in the donor. Reaction was followed in each case by monitoring changes in surface pressure that occur when the compressed film is irradiated and maintained at a constant area. Reaction was readily observed in most cases where the donor and light-absorbing substrate are present; however the consequences were found to be quite dependent upon the specific donor substrate. Thus for simple single-chain amphiphiles containing either amino alcohol or 1,2-diamine donor sites, both intralayer and interfacial reactions result in rapid decrease in surface pressure, consistent with destruction of the film as the more hydrophilic redox products are solubilized into the subphase. For a polymeric diamine, much more complex behavior is observed, consistent with a situation where single fragmentation events do not lead to removal of material from the film but multiple fragmentation reactions culminate in film solubilization. Finally, a double-chain amphiphilic pinacol was found to undergo interfacial fragmentation with Ru(bpy) 32+ in the subphase with a concurrent increase in surface pressure to form stable films that do not dissolve' into the subphase. The isotherms observed following irradiation, decompression, and recompression are consistent with an expansion that occurs as the two-chain amphiphile undergoes redox fragmentation to produce two equivalents of a single-chain amphiphile.

A Case Study of Antarctic Katabatic Wind Interaction with Large-Scale Forcing*

Surface pressure decreases of up to 20 hPa occurred over much of the Antarctic continent during a 4-day midwinter period of 1988. The widespread change in the pressure field accompanied intense cyclonic activity to the north of the ice sheet. The equatorward mass transport across the Antarctic coastline resulted in a redistribution of atmospheric pressure that extended to the subtropics of the Southern Hemisphere. Most of the mass flux from Antarctica was the result of low-level processes and appears tied to the katabatic wind circulation. The observed surface pressure decrease over the continent reflects a perturbation of the mean meridional circulation between Antarctica and the subpolar latitudes by synoptic-scale processes. Zonally averaged circulations over Antarctica were examined using output from the European Centre for Medium-Range Weather Forecasts model. Results suggest that only a poorly defined return branch of the meridional circulation exists in the middle and upper troposphere. This southward-directed flow does not compensate for the northward mass transport provided by the katabatic wind outflow in the lower atmosphere. Isallobaric contours over the Antarctic ice sheet roughly match the area of the large-scale drainage catchment associated with katabatic wind transport through the Ross Sea sector. An intense extratropical cyclone was present in the circumpolar oceanic belt to the north of the continent. The horizontal pressure gradient associated with the cyclone prompted enhanced drainage off the high interior plateau. The resulting katabatic flow issued from the continent through a narrow corridor across the Ross Ice Shelf and out over the Southern Ocean.