Electric Field Distribution of an Optical Nanocavity Embedded with a Single Molecule

Using state-of-the-art quantum mechanical calculations, we investigate the spatial profile of the electric field enhancements induced within an optical cavity embedded with a variety of organic molecules. We observed marked differences in the spectral positions, spectral intensities, maximum achievable electric field, and spatial profile of the electric field with a remarkable sensitivity to the embedded molecular type. In a broader perspective, our quantum mechanical calculations provide quantitative access to the molecule-dependent electric field distributions and unveil intricate and rich optical features.

     

Neural cell recognition molecule F11: membrane interaction by covalently attached phosphatidylinositol

The mode of membrane insertion of F11 130 kDa protein, a neural chick cell surface glycoprotein involved in neurite fasciculation, has been investigated. Up to 41% of total F11 130 kDa is released from adult chick brain plasma membranes by phosphatidylinositol specific phospholipase C (PI-PLC), whereas no release is mediated by lecithin/cephalin specific phospholipase C (PLC). PI-PLC dependent release of F11 is also observed from embryonal chick brain plasma membranes and from the surface of intact retinal cells. Biosynthetic labelling experiments demonstrate that F11 contains ethanolamine. Taken together, these results suggest that F11 interacts with the plasma membrane at least partially through covalently linked glycosyl-phosphatidylinositol (GPI) or a structurally similar lipid.     

IR spectroscopic studies of major cellular components. III. Hydration of protein,nucleic acid,and phospholipid films

The IR absorption spectra of protein, DNA, RNA, and phospholipid films as a function of the water content are reported. We find that the hydration of protein films affects the peak intensity of amide I and amide II bands and the shape of the amide III band. For nucleic acids, the symmetric (nu(S) PO(2) (-)) and antisymmetric (nu(AS) PO(2) (-)) stretching vibrations of the phosphate linkage are the most affected by hydration, because both intensity changes and frequency shifts are observed. The spectra of phospholipid films are also sensitive to hydration, and they exhibit changes in the peak intensities and frequencies of both nu(S) PO(2) (-) and nu(AS) PO(2) (-) vibrations. We interpret the spectral differences between water saturated and dried films both in terms of structural changes and the change in the local dielectric in the vicinity of the polar and solvent exposed groups. In addition, we observe that the most significant change in the absorption intensity, frequency, and shape of the water sensitive vibrations occurs at high hydration levels. The principal component analysis of hydration results and the kinetics of water removal from sample films are also discussed. In addition, protein spectra acquired using film and KBr pellet sampling techniques are compared.     

A theoretical model of the temperature- and pressure-induced phase transition of phospholipid bilayers

A statistical thermodynamic model of phospholipid bilayers is developed. In the model, a new concept of a closely packed system is applied, i.e., a system of hard cylinders of equal radii, the radius being a function of the average number of gauche rotations in a hydrocarbon chain. Using this concept of a closely packed system, reasonable values are obtained for the change in specific volume at the order-disorder transition of lecithin bilayers. In addition to interactions between the lipid matrix and water molecules, between the head groups themselves and between hydrocarbon chains, as well as the intramolecular energy associated with chain conformation, the Hamiltonian of the membrane also includes the energy of the pressure field. Thus, the phase transition of phospholipid membranes induced not only by temperature hut also by hydrostatic pressure is described by this model simultaneously. In accordance with the experimental results, a linear relationship is obtained between the phase transition temperature and phase transition pressure. The other calculated phase transition properties of lecithin homologues. e.g., changes in enthalpy, surface area. thickness and gauche number per chain are in agreement with the available experimental data. The ratio of kink to interstitial conduction of bilayers is also estimated.     

Phase behavior and structure of aqueous dispersions of sphingomyelin

The phase behavior of bovine brain sphingomyelin in water has been determined by polarizing light microscopy, differential scanning calorimetry, and X-ray diffraction. Lamellar phases, in which water is intercalated between sheets of lipid molecules arranged in the classical bilayer fashion, are present over much of the phase diagram. An order-disorder transition separates the high temperature, liquid crystalline, lamellar phase from a more ordered lamellar phase at low temperatures. The hydration characteristics of sphingomyelin are similar to the structurally related lecithin in that only limited amounts of water are incorporated above and below the transition. Above the transition at 47 degrees C, a maximum of 35% by weight of water can be incorporated between the lipid bilayers, the total thickness at maximum hydration being 60.2 A, the lipid thickness 38 A, and the surface area per lipid molecule at the interface 60 A(2). Water in excess of 35% by weight is present as a separate phase. Below the phase transition, at 25 degrees C a maximum of 42% by weight of water may be incorporated between the lipid bilayers. On increasing the hydration, the lamellar repeat distance increases from 63.5 A to a limiting value of 76 A. Within this hydration range the calculated lipid thickness decreases from 63.5 to 42.5 A, and the surface area per lipid molecule increases from 36.1 to 53.6 A(2). Although these changes may be accounted for by a structure in which the hexagonally packed ordered hydrocarbon chains tilt progressively with respect to the normal to the bilayer plane on increasing hydration, it is possible that changes in other more complex lamellar structures may be responsible for these variations in lipid thickness and surface area.     

Interaction of alamethicin with lecithin bilayers: a 31P and 2H NMR study

The interaction of alamethicin with artificial lecithin multilamellar dispersions was investigated by nuclear magnetic resonance (NMR) and Raman spectroscopies. 31P NMR studies revealed perturbation of the lipid head groups in the presence of the icosapeptide. Simulation of the 31P NMR spectra indicated that the observed spectral changes could be attributed to slight variations in the average tilt angle of the head groups. In contrast, no noticeable effect of the peptide on the segmental order of the hydrophobic acyl chains of the lipid molecules was detected by 2H NMR and Raman spectroscopic measurements. Taken together, these results indicated that, in the absence of a transmembrane electric potential, alamethicin interacts primarily at the water-lipid interface without significant insertion or incorporation into the bilayer leaflet.     

A Computational Study of the Giant Local Electric Field Enhancement in Al-Au-Ag Trimetallic Three-Layered Nanoshells

The surface plasmon resonance (SPR)-induced local field effect in Al-Au-Ag trimetallic three-layered nanoshells has been studied theoretically. Because of having three kinds of metal, three plasmonic bands have been observed in the absorption spectra and the local electric field factor spectra. The local electric field enhancement and the corresponding resonance wavelength for different plasmon coupling modes and spatial positions of the Al-Au-Ag nanoshells with various geometry dimensions are investigated to find the maximum local electric field enhancement. The calculation results indicate that the giant local electric field enhancement could be stimulated by the plasmon coupling in the middle Au shell or the outer Ag shell and could be optimized by increasing the Ag shell thickness and decreasing the Au shell thickness. What is more, the local electric field enhancement also nonmonotonously depends on the dielectric constant of the environment; the local electric field intensity will be weakened when the surrounding dielectric constant is too small or too large.

     

Effect of phospholipase D on micellar phospholipids and the role of calcium ions]

The rates of the reaction products formation under simultaneous phospholipase D effect on phosphatidyl ethanolamine and phosphatidyl choline were studied. The hydrolysis of cephalin, unlike the phospholipase D effect on lecithin, does not require Ca2+ ions. Ca2+ does not affect the enzymatic degradation of lecithin and inhibits the reaction with cephalin in "inorganized" phospholipid emulsions. The hydrolysis of micellar phospholipids by phospholipase D (in the presence of the anionic detergent sodium dodecyl sulfate) is accelerated by Ca2+ ions for both substrates. The apparent Km value is equal to 1.5 mM and does not depend on the phospholipid type. In contrast, the value of kcat for lecithin is twice as high as that for cephalin. It was demonstrated that the phase state of the phospholipids and the chemical nature of the alcohol residue in the phospholipid molecule are essential for the substrate specificity of phospholipase D.     

Organizational changes in phospholipid multibilayers induced by uncouplers of oxidative phosphorylation: a spin label study

A cholestane spin probe was used to study the effect of uncouplers of oxidative phosphorylation (2,4-dinitrophenol, pentachlorophenol and dicumarol) on the degree of organization of phospholipids in hydrated multibilayers. Disruptive effects were observed—their magnitude depending on pH, time and the presence of cholesterol. A correlation between changes in probe organization and ion conductivity, with maximum effects at the pH corresponding to the pK of the uncoupler, could be demonstrated in the films containing cholesterol. Egg lecithin films containing no cholesterol were disordered maximally at pH 4.0 irrespective of the uncoupler used. The effect of uncouplers on the probe disorganization varied with time after exposure. These time effects indicated that relative movement of uncoupler, probe and lipid molecules occur to produce lipid organizations differing from those after initial exposure to uncoupler. The results show that even in a simple model system uncoupler effects may be complex, and suggest that changes in bilayer lipid organization parameters may play a role in uncoupling oxidative phosphorylation.     

Pressure-induced correlation field splitting of vibrational modes: structural and dynamic properties in lipid bilayers and biomembranes.

Correlation field splittings of the vibrational modes of methylene chains in lipid bilayers, isolated lipid molecules in perdeuterated lipid bilayers, crystalline lipid, and interdigitated lipid bilayers have been investigated by pressure-tuning Fourier-transform infrared spectroscopy. The correlation field splittings of these modes are originating from the vibrational coupling interactions between the fully extended methylene chains with different site symmetry along each bilayer leaflet. The interchain-interactions of the methylene chains with the same site symmetry only contribute to frequency shift of the vibrational modes. The magnitude of the correlation field splitting is a measure of the strength of the interchain-interactions, and the relative intensities of the correlation field component bands provide information concerning the relative orientation of the zig-zag planes of the interacting methylene chains. It has been demonstrated in the present work that the correlation field splitting of the CH2 bending and rocking modes commonly observed in the vibrational spectra of lipid bilayers is the result of the intermolecular interchain-interactions among the methylene chains of the neighboring molecules. The intramolecular interchain-interactions between the sn-1 and sn-2 methylene chains within each molecule are weak. The correlation field splitting resulting from the intramolecular interchain-interactions exhibits a much smaller magnitude than that from the intermolecular interchain-interactions and is observed only at very high pressure. Interdigitation of the opposing bilayer leaflets disturbs significantly the intermolecular interchain-interactions and results in dramatic changes in the pressure profiles of the correlation field component bands of both the CH2 bending and rocking modes. The relative intensities of the correlation field component bands of these modes and the magnitude of the splitting are also altered significantly. These results provide further evidence that the correlation field splitting of the CH2 bending and rocking modes in the vibrational spectra of lipid bilayers is due to the intermolecular interchain-interactions. The present work has also demonstrated that the correlation field splitting of the vibrational modes in lipid bilayers is mainly contributed by the intermolecular interchain-interactions among the nearest neighboring molecules and that the long-range correlation interactions beyond the second neighboring molecules are insignificant.     

Serum and thyroid tissue lipids in patients with thyroid tumors in euthyroidism

Plasma lipids of 24 euthyroid subjects with thyroid adenoma and non-toxic primary differentiated thyroid carcinoma (papillary and follicular types) were assessed and compared with a similar investigation conducted on 20 normal subjects. A parallel study with thyroid tumor tissues examined the lipid changes which occurred in the same group of patients. These were compared with the picture seen in 5 normal thyroids. The investigations examined the changes in total lipids; total, free and esterified cholesterol; total phospholipids; lecithin; cephalin and sphingomyelin; triglycerides and free fatty acids in both serum and thyroid tissue. Compared with normal subjects, the serum lipids were almost identical except for the concentration of free fatty acids which showed significantly lower values in the group with neoplastic changes. Tissue analysis of the cancerous thyroid however revealed a marked rise in virtually all lipid fractions but the cholesterol seemed to dominate the picture. The differential studies of total phospholipids for thyroid tissue membrane lipids further revealed a significant increase in the lecithin and sphingomyelin components of total phospholipids as well as the esterified cholesterol fraction in thyroid carcinoma. The changes in thyrophospholipids were more marked in females normal thyroids than males. An attempt has been made through evaluation of the results derived from differential lipid studies to elucidate the role of some of the various fractions determined and the possible effect of the changes described on thyroid hormone metabolism.     

LIPID CLASS AND FATTY ACID COMPOSITION OF PERIPHERAL NERVE FROM NORMAL AND ORGANOPHOSPHORUS-POISONED CHICKENS*

The demyelination which attends tri-ortho-cresyl phosphate (TOCP) or di-isopropyl-fluorophosphonate (DFP) administration in chickens has been well characterized histologically (Fenton , 1955; Cavanaugh , 1954) as resembling Wallerian degen- eration. However, no study of lipid class composition of chicken nerve degenerating after TOCP poisoning has been reported comparable to classical studies of Johnson , Mcnab band Rossiter (1949a) and of Brante ,(1949) who described the lipid class changes in transected sciatic nerve. Webster (1954) observed no change in lipid phosphorus concentration or rZP]- phosphate incorporation into lipids in the sciatic nerves of TOCP-poisoned hens, while NELSONand BARNUM(1960) noted a decrease in [32P]phosphate incorporation into the brain lipids of DFP-poisoned mice. These findings were in contrast to those of Magee and Rossiter (1954) who noted an increase in the incorporation of p2P]- inorganic phosphate into the lipids of sciatic nerve degenerating after section. In the present study, individual lipid classes were isolated, identified, quantitated, and their fatty acid compositions determined in normal and organophosphorus- poisoned chickens. These results are compared with a parallel study (Berry , Cevallos and Wade , 1965) on normal and sectioned cat sciatic nerve in order to determine whether the two types of demyelination were chemically similar.     

Phospholipid hydration studied by deuteron magnetic resonace spectroscopy

Deuteron magnetic resonance spectra were obtained from ²H₂O in mixtures with egg lecithin, egg phosphatidylethanolamine, and ox brain sodium phosphatidylserine. The acid form of phosphatidylserine does not hydrate. Details of the different hydration “shells” were obtained by studying the spectral splittings as a function of ²H₂O concentration. Several different types of water are present, including bulk water (exchanging only slowly with water associated with the lipid), “trapped” water (not present with phosphatidylethanolamine), and up to three types of bound water. The spectral splittings characteristic of each water environment yielded information about the water binding energies and degrees of anisotropy of motion of the phospholipid polar groups; lecithin polar groups have least motional restriction and sodium phosphatidylserine most, while phosphatidylethanolamine binds water most tightly.Spectra of some lecithin and phosphatidylserine dispersions varied with time, due to a slow reorganization of randomly oriented multilamellar regions into longer, more ordered systems, with a length of about 1 μm. At ?20°C the timescales of the change were of the order of a week and a month for lecithin and phosphatidylserine respectively.Complex changes in the spectra were observed as the temperature was raised; these are interpreted in terms of changes in the motions of the phospholipid molecules.     

Reaction of Local Anesthetics with Phospholipids : A possible chemical basis for anesthesia

Local anesthetics (LA) have been found to interact with phospholipids and lipids extracted from nerve and muscle. This reaction is demonstrated by: (a) Inhibition by LA of phospholipid (and tissue lipid) facilitated transport of calcium from a methanol: water phase into chloroform. This action is dependent upon the cationic form of the LA. (b) LA increase the electrical resistance of "membranes" prepared by impregnating Millipore filters with cephalin:cholesterol or tissue lipid extracts and bathed with NaCl or KCl solutions. (c) LA coagulate aqueous dispersions of cephalin, phosphatidyl serine, phosphatidyl ethanolamine, and inositide, an action shared by calcium. The order of potency in coagulating cephalin sols is tetracaine > calcium > butacaine > procaine. Na⁺ and K⁺ do not coagulate phospholipid dispersions at 0.1 M concentration and antagonize the effect of Ca²⁺. (d) LA produce a marked fall in the pH of cephalin sols equivalent to that produced by calcium, (e) Ca²⁺ and LA form 1:2 molar complexes with phospholipids probably by ion-ion and ion-induced polar type of binding at the phosphate groups of the lipid. It is suggested that such reactions with cell membrane phospholipids may underlie inhibitory effects of LA on cellular ion fluxes and provide a chemical basis for anesthetic action.     

The bacteriochlorophyll absorption band shifts linked with the energy state of photosynthetic bacteria membranes

The uncoupler of photophosphorylation FCCP inhibits the light-induced changes in absorbancy forRhodospirillum rubrum, Ectothiorhodospira shaposhnikovii andChromatium minutissimum cells in anaerobic conditions. These changes are associated with the shifts of bacteriochlorophyll absorption bands. The superposition of these spectral shifts and the photobleaching of reaction centers P890 is observed in aerobic conditions.The light-induced shifts of bacteriochlorophyll absorption bands are suggested to be due to the electrochemical transmembrane potential and local electric field arising as a result of the primary separation of opposite charges.Abbreviations FCCP carbonylcyanide-p-trifluoromethoxy phenyl-hydrazone - TMPD tetramethyl-p-phenylenediamine     

Interaction of liposomes with black lipid membranes

Liposomes labelled with fluorescent pigments were allowed to interact with black lipid films. The transfer of label from the liposomes to the film was studied by fluorescence and photoelectric measurements. With the neutral lipid lecithin, in contrast to negatively charged phosphatidylinositol, a rapid transfer was observed. The results are discussed with respect to fusion of liposomes with black lipid films.     

Laser-Raman study of valinomycin-doped and omega-CD3-labeled phosphatidylcholine liposomes

The relative intensities of the CH stretching vibrations are used to study the interaction of lecithin liposomes with valinomycin, a mobile carrier for alkali ions. In the case of dipalmitoyl lecithin liposomes, the lipid phase transition is not significantly affected by valinomycin. However, in dimyristoylphosphatidylcholine liposomes, the phase transition is broadened by the addition of 1 mol% valinomycin even at low K⁺ concentrations. This indicates that the carrier interacts with the hydrophobic core of the bilayer. In addition, these experiments showed that the lipid phase transitions which are reflected by the methylene groups and the terminal methyl groups are nearly equivalent. Therefore a reevaluation of the assignment of the CH stretching bands seemed necessary. Our Raman spectroscopic investigation of ω-deuterated dipalmitoyl lecithin liposomes improves the assignment of CH stretch vibrations to methylene and methyl groups. The deuteration displaces the methyl group vibrations to the 2050–2250 cm^?1 region and produces gross intensity changes of the bands at 2883 and 2936 cm^?1. These changes lead to the conclusion that both bands arise from vibrations which can be attributed simultaneously to the methylene and methyl groups of the fatty acid chains. The displacement of the CH₃ group vibrations from their original positions enhances the intensity ratios (per centimeter), $\text{2883}\text{2847}$ and $\text{2936}\text{2847}$, for the CH₂- groups which are used to monitor the lipid phase transition, and implies that the contributions of the CH₃ groups to the phase transition curves are unimportant. Our finding that the -CD₃ groups reflect no phase transition supports this statement.     

Alterations of spectral parameters of rat brain electrical activity after sciatic nerve section

Changes in electrophysiological brain characteristics accompanying the development of neurogenic pain syndrome induced by transsection of sciatic nerve were analyzed. At the maximum pain syndrome 3 weeks after the deafferentation, a reorganization of the brain electrical activity was observed in the limbic structures (hippocampus, amygdale, and nucleus accumbens), frontal cortex, and the caudate putamen. An increase in the relative spectral power of the delta and alpha bands and a decrease in the relative power of the beta2 band (as compared to baseline activity) took place. Alteration of the electrical activity in the limbic structures did not depend on manifestations of the neurogenic pain syndrome (autotomy). The increase in the relative spectral power of the alpha-band activity in all the structures under study suggests the involvement of the reticular thalamic nucleus in pathogenesis of neurogenic pain syndrome.     

Phase transitions of phospholipids in monolayers and surface viscosity

The surface pressures and the surface viscosities of lecithin, cephalin and its analogs were measured at the air—water and the oil—water interfaces. It was found that the surface viscosity of the phospholipids used in this study was very high, and was comparable to those of some polymer films at the oil—water interface as well as at the air—water interface under the conditions where the monolayers were condensed. The plateaus indicating the phase transitions in monolayers were clearly observed on the pressure-area curves at the oil—water interface in all of the specimens studied. It was found that the phase transitions exactly corresponded to the abrupt increases in surface viscosity. From the results thus obtained, an intermolecular ionic linkage between neighboring molecules in the monolayers is discussed.     

Distribution of halothane in a dipalmitoylphosphatidylcholine bilayer from molecular dynamics calculations

We report a 2-ns constant pressure molecular dynamics simulation of halothane, at a mol fraction of 50%, in the hydrated liquid crystal bilayer phase of dipalmitoylphosphatidylcholine. Halothane molecules are found to preferentially segregate to the upper part of the lipid acyl chains, with a maximum probability near the C(5) methylene groups. However, a finite probability is also observed along the tail region and across the methyl trough. Over 95% of the halothane molecules are located below the lipid carbonyl carbons, in agreement with photolabeling experiments. Halothane induces lateral expansion and a concomitant contraction in the bilayer thickness. A decrease in the acyl chain segment order parameters, S(CD), for the tail portion, and a slight increase for the upper portion compared to neat bilayers, are in agreement with several NMR studies on related systems. The decrease in S(CD) is attributed to a larger accessible volume per lipid in the tail region. Significant changes in the electric properties of the lipid bilayer result from the structural changes, which include a shift and broadening of the choline headgroup dipole (P-N) orientation distribution. Our findings reconcile apparent controversial conclusions from experiments on diverse lipid systems.