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PubMedDate not supplied

Probing nanoscale surface enhanced Raman-scattering fluctuation dynamics using correlated AFM and confocal ultramicroscopy.

We have studied the laser-excitation-intensity-dependent and Ag-nanocluster interstitial-site-dependent SERS intensity fluctuations under low molecule surface coverage of rhodamine 6G and cytochrome c. A new two-channel photon time-stamping system coupled with atomic force microscopic (AFM), Raman spectroscopic, and imaging microscopy was developed and applied to record Raman intensity fluctuation trajectories at sub-microsecond resolution correlated with in situ characterization of the nanoparticle clusters. Our experimental results suggest that the nanoconfinement of the local electromagnetic-field enhancement and the interaction of the local field with the molecules, presumably under rotational motions, result in nano-Raman fluctuations. The SERS spectral fluctuation was pertinent to the nanoscale local enhancement and local interaction of the molecules with the surface when the surface coverage of the nanoparticles was less than a monolayer, and the nanoscale interstitial space controlled the finite number of molecules to contribute the microscopic Raman signal collected from a diffraction-limited focus spot. The fluctuation amplitude significantly decreased with the number of molecules confined at the nanolocal field. The nano-SERS fluctuation dynamics were both photo-induced and spontaneous for rhodamine 6G, but only the photo-induced component was observable for cytochrome c. The fluctuation dynamics were also found to be highly inhomogeneous at interstitial sites with heterogeneous geometries. To interpret the observed nano-SERS fluctuation dynamics, we used computer simulation of optical multiple scattering, based on multi-sphere scattering Mie theory, and rotational diffusion of molecules at an interstitial site, based on a random walk in orientation space.

Journal Article↗
PubMedDate not supplied

New ways of probing surface nuclear relaxation and microdynamics of water and oil in porous media.

The microdynamics of water and oil in macroporous media with SiO2 or CaCO3 surfaces has been probed at various temperatures by magnetic field-cycling measurements of spin-lattice relaxation rates. These measurements and an original theory of surface diffusion allow us to obtain surface dynamical parameters such as surface correlation times, residence times and diffusion coefficients. A coefficient of affinity of the liquids for the pore surface is deduced.

Calcium Carbonate↗
PubMed1999

Evaluating the implementation of a pain management flow sheet.

This study evaluated the outcome of implementing a pain flow sheet, using protocols derived from the Agency for Health Care Policy and Research (AHCPR) guidelines for pain management, for children recovering from surgery. Findings indicated the flow sheet was not used as designed; thus, implementing the flow sheet did not result in increased documentation of pain assessments, interventions, and outcomes, except in the increased documentation of nonpharmacological interventions for pain management. Rogers' Diffusion of Innovation Theory gives insight as to why this occurred and provides rationale for more intensive in-service education when new innovations are implemented.

Analgesics↗
PubMed2001

The physical chemistry of ligand-receptor binding identifies some limitations to the analysis of receptor images.

The biophysical chemistry of ligand-receptor interactions imposes some restrictions on the characteristics of a radioligand if it is to be a useful tracer for accurately measuring the in vivo concentration of a specific cellular membrane receptor. This review discusses thermodynamic and kinetic rate constant considerations in selecting a ligand for radiolabeling and imaging. When radioligands of only modest specific activity are injected, one is able to use kinetic analysis to calculate the rate constant for the bimolecular binding reaction as well as the receptor concentration. Images of regional receptor density can be constructed from analysis of emission imaging data when the binding occurs at a rate that is slower than the collision frequency. A tracer that reacts with each collision cannot distinguish receptor density from blood flow. The theory of diffusion-limited reactions is reviewed and individual ligand-receptor examples are presented to demonstrate conditions where, even for very fast forward reactions, the binding of radioligand to receptor is controlled by local biochemistry rather than by the purely physical process of diffusion.

Animals↗
PubMed2006

General HETP equation for the study of mass-transfer mechanisms in RPLC.

Classical HETP equations including the Van Deemter and the Knox equations, are semiempirical, approximate equations that provide apparent mass-transfer coefficients with little sound physical justifications. The conventional A and B coefficients are revisited, the former through the use of the fundamental theory of eddy diffusion due to Giddings, the latter by taking into account the intraparticle diffusion (pore and surface diffusion). Our work confirms that eddy diffusion originated from three different sources in RPLC: trans-channel, short-range interchannel, and long-range interchannel velocity biases. Accordingly, the eddy diffusion term is given by the ratio of two third-degree polynomials. Finally, the C term is the sum of two terms corresponding to the resistance to mass transfer due to diffusion through the external stationary film of liquid phase surrounding the silica particles and to the classical resistances to mass transfer due to diffusion through the silica particles. It is easily related to the physical characteristics of the phenomena involved. Experimental HETP data were derived from moment analysis for phenol on a C(18)-Sunfire column, with a mixture of acetonitrile and water as the mobile phase (15/85, v/v). The linear interstitial velocity ranged between 0.027 cm/s and 4.7 mL/min, and six temperature (21, 36, 45, 55, 67, and 77 degrees C) were applied successively. The HETP equation obtained was tested to study the mass-transfer mechanism. An excellent agreement was found between the experimental and theoretical HETP. The model allows the precise calculation of the activation energy for surface diffusion (E(S) = 31.3 kJ/mol) and the coefficient beta that relates the restriction energy for molecular diffusion on the C(18)-bonded surface to the isosteric heat of adsorption Q(st) (beta = 0.80).

Chemical Phenomena↗
PubMed1985

Motion of myosin cross-bridges in skeletal muscle fibers studied by time-resolved fluorescence anisotropy decay.

The time-resolved fluorescence polarization anisotropy signal has been measured from fluorescent-labeled myosin cross-bridges in single glycerinated muscle fibers in the relaxed and rigor states. In one experimental configuration, the polarization of the excitation light and the fiber axis are aligned, and the anisotropy is sensitive to rotational motions of the probes about axes other than the fiber axis. The rotational correlation times are approximately 1000 ns for relaxed fibers and greater than 7000 ns for rigor fibers. In another experimental configuration, the excitation light polarization is perpendicular to the fiber axis, and its propagation vector has a component parallel to the fiber axis so that the anisotropy is sensitive to probe rotational motion about different axes, including the fiber axis. In this configuration, the rotational correlation times are approximately 300 ns for both relaxed and rigor fibers. The theory of rotational diffusion in a potential described in a related paper [Burghardt, T.P. (1985) Biophys. J. (in press)] is applied to the relaxed fiber data.

Animals↗
PubMed1976

Ionic influences on the phase transition of dipalmitoylphosphatidylserine.

The ionization and phase behavior of 1,2-dipalmitoyl-sn-glycero-3-phosphoserine have been investigated under a variety of condtions by several different methods. As measured by turbidity changes, the temperature of the crystal-liquid crystal phase transition of this lipid is influenced by pH and mono- and divalent cation concentrations. The pH-transition temperature curve is congruent with the curve relating temperature to the degree of ionization of the carboxyl group of the crystalline form. The transition temperature falls from an upper plateau of 72 degrees C at low pH values, where the carboxyl group is fully protonated, to a lower plateau of 55 degrees C at high pH values, where this group is fully ionized. The apparent pK (pH at 50% ionization) of the crystalline form shifts from 6.0 to 4.6 to 3.7 with an increase of NaCl concentration from 10(-3) to 0.1 to l.0 M, respectively. These observations are in accord with a simple theoretical analysis that utilizes diffuse double layer theory and the influence of surface potential on surface concentration of protons. In qualitative terms, an increase in electrolyte concentration reduces the surface potential, the result of which is a diminution of the surface-bulk pH difference and a lowering of the apparent pK. Assuming an area of 50 A2/molecule, the intrinsic pKa (apparent pK corrected for surface pH) of the carboxyl group is 2.7. A 1000-fold change of NaCl concentration produces a very large change in surface potential without influencing the transition temperature of the ionized form of the lipid.

Calorimetry↗
PubMed1976

The hydrophobic adsorption of charged molecules to bilayer membranes: a test of the applicability of the stern equation.

To describe the hydrophobic adsorption of charged molecules to bilayer membranes, one must recognize that the adsorption produces a change in the electrostatic potential at the surface of the membrane. The surface potential produced by the adsorption of the charged molecules can be described most simply by the Gouy equation from the theory of the diffuse double layer. This potential will tend to lower the concentration of the adsorbing ions in the aqueous phase immediately adjacent to the membrane, a phenomenon which can be described by the Boltzmann relation. The number of adsorbed ions is, in turn, a function of the aqueous concentration of these ions at the membrane solution interface and can be described, in the simplest case, by a Langmuir adsorption isotherm. If the ions are regarded as point charges, the combination of the Gouy, Boltzmann, and Langmuir relations may be considered a simplified Stern equation. To test experimentally the applicability of this equation, one should measure both the charge density and surface potential as a function of the concentration of adsorbing molecules in the bulk aqueous phases. Direct, accurate measurements of one of these parameters, the number of moles of 2, 6-toluidinylnaphthalenesulfonate ions bound to vesicles formed from phosphatidylcholine, are available in the literature (Huang, C., and Charlton, J.P. (1972), Biochemistry 11, 735). We estimated the change in the surface potential in two independent ways; by means of conductance measurements with "probe" molecules on planar black lipid membranes and by means of electrophoresis measurements on multilaminar unsonicated vesicles. The two estimates agreed with one another and all of the data could be adequately described by the Stern equation, assuming, at 25 degrees C, a dissociation constant of 2 X 10(-4) M and a maximum number of binding sites of 1/70 A2.

Adsorption↗
PubMedDate not supplied

Osmotic forces and gap junctions in spreading depression: a computational model.

In a computational model of spreading depression (SD), ionic movement through a neuronal syncytium of cells connected by gap junctions is described electrodiffusively. Simulations predict that SD will not occur unless cells are allowed to expand in response to osmotic pressure gradients and K+ is allowed to move through gap junctions. SD waves of [K+]out approximately 25 to approximately 60 mM moving at approximately 2 to approximately 18 mm/min are predicted over the range of parametric values reported in gray matter, with extracellular space decreasing up to approximately 50%. Predicted waveform shape is qualitatively similar to laboratory reports. The delayed-rectifier, NMDA, BK, and Na+ currents are predicted to facilitate SD, while SK and A-type K+ currents and glial activity impede SD. These predictions are consonant with recent findings that gap junction poisons block SD and support the theories that cytosolic diffusion via gap junctions and osmotic forces are important mechanisms underlying SD.

Computer Simulation↗
PubMed1998

HIV prevention with male prostitutes and patrons of hustler bars: replication of an HIV preventive intervention.

The core objectives of this study were to document the process by which a community-based organization replicated and adapted an experimentally developed intervention to its own use and to explore the effectiveness of that HIV prevention program for male prostitutes and other patrons in New York City "hustler" bars. The intervention model employed was based on previous research with gay men (Kelly, St. Lawrence, Diaz, et al., 1991; Kelly, St. Lawrence, Stevenson, et al., 1992) and inspired by diffusion of innovation theory (Rogers, 1995). The effects of the current intervention were assessed on a sample of 1,741 male prostitutes and bar patrons. Analyses indicated significant reductions in paid, unprotected sexual intercourse and oral sex following the intervention. Analyses further indicated that the data were partially consistent with the program's model, which specified that norms were the putative mediator of behavior change in the intervention. Also, the intervention's effects varied by bar and by participants' race/ethnicity. Data support the utility of the intervention model for an urban sample of men at high risk for HIV infection. The importance of exploring the mechanisms that underlie the intervention is discussed.

Adolescent↗
PubMed1981

Charge screening by cations affects the conformation of the mitochondrial inner membrane. A study of exogenous MAD(P)H oxidation in plant mitochondria.

Cations caused a decrease in the apparent Km and an increase in the Vmax. for the oxidation of exogenous NADH by both Jerusalem-artichoke (Helianthus tuberosus) and Arum maculatum (cuckoo-pint) mitochondria prepared and suspended in a low-cation medium (approximately or equal to 1 mM-K+). In Arum mitochondria the addition of cations caused a much greater stimulation of the oxidation of NAD(P)H via the cytochrome oxidase pathway than via the alternative, antimycin-insensitive, pathway. This shows that cations affected a rate-limiting step in the electron-transport chain at or beyond ubiquinone, the branch-point of electron transport in plant mitochondria. The effects were only dependent on the valency of the cation (efficiency C3+ greater than C2+ greater than C+) and not on its chemical nature, which is consistent with the theory of the diffuse layer. The results are interpreted to show that the screening of fixed negative membrane changes on lipids and protein complexes causes a conformational change in the mitochondrial inner membrane, leading to a change in a rate-limiting step of NAD(P)H oxidation. More specifically, it is proposed that screening removes electrostatic restrictions on lateral diffusion and thus accelerates diffusion-limited steps in electron transport.

Decamethonium Compounds↗
PubMed1999

Public health nursing practice guidelines: an evaluation of dissemination and use.

Public health nursing needs to build a practice on research-based knowledge. Public health guidelines are one strategy to achieve this goal. Using research-based knowledge, the Minnesota Practice Enhancement Project (MPEP) developed positive parenting and family violence prevention guidelines for public health nurses (PHNs). The purpose of this study was to evaluate the dissemination and use of the MPEP guidelines using a survey of PHNs and telephone interviews of public health nursing directors. Results indicated that respondents viewed the guidelines as important, but identified numerous barriers to integrating the guidelines into their practice. Major barriers included lack of time in their work day, complex guideline structure, and competing agency demands and priorities. Findings were consistent with Roger's Diffusion of Innovations theory, which describes factors associated with the adoption of a new idea or practice. Recommendations for effective dissemination include administrative support and structure to increase PHN intentional use of practice guidelines, a simplified guideline format, and mentorship in guideline use.

Attitude of Health Personnel↗
PubMed2004

Biomolecule-directed assembly of nanoscale building blocks studied via lattice Monte Carlo simulation.

We perform lattice Monte Carlo simulations to study the self-assembly of functionalized inorganic nanoscale building blocks using recognitive biomolecule linkers. We develop a minimal coarse-grained lattice model for the nanoscale building block (NBB) and the recognitive linkers. Using this model, we explore the influence of the size ratio of linker length to NBB diameter on the assembly process and the structural properties of the resulting aggregates, including the spatial distribution of NBBs and aggregate topology. We find the constant-kernel Smoluchowski theory of diffusion-limited cluster-cluster aggregation describes the aggregation kinetics for certain size ratios.

Algorithms↗
PubMed2006

Origin invariant approaches to the calculation of two-photon circular dichroism.

The origin dependence of the expression of two-photon circular dichroism in the length formulation employed by the authors in a recent computational study [B. Jansik et al., Chem. Phys. Lett. 414, 461 (2005)] is discussed in detail, and some inherently origin invariant alternative formulations are introduced. Extensive computational tests on a small reference chiral system, namely, a chiral form of H(2)O(2), are performed at the density functional theory (DFT)/B3LYP level of theory with large diffuse correlation consistent basis sets. The results indicate that the velocity formulation originally proposed by Tinoco, Jr. [J. Chem. Phys. 62, 1006 (1975)] provides the most convenient approach for an origin invariant calculation of two-photon circular dichroism.

Journal Article↗
PubMed1974

The electrostatic basis of Mg++ inhibition of transmitter release.

The inhibition by Mg(++) of stimulus-evoked transmitter release is attributed to a decrease in surface potential, Psi(0), on the outer surface of the presynaptic terminal and hence a lower surface calcium concentration, [Ca(++)](0). Data on the frog neuromuscular junction are quantitatively fit by assuming that there is a negative charge density, sigma, on the outer surface of the presynaptic terminal of 6.5 x 10(13) charges per cm(2) and that simple diffuse double layer theory is applicable. No specific binding of Mg(++) or Ca(++) is required. Without any additional assumptions, the inhibitory effect of univalent cations is also quantitatively predicted.

Acetylcholine↗
PubMed1971

Divalent ions and the surface potential of charged phospholipid membranes.

Phospholipid bilayer membranes were bathed in a decimolar solution of monovalent ions, and the conductance produced by neutral carriers of these monovalent cations and anions was used to assess the electric potential at the surface of the membrane. When the bilayers were formed from a neutral lipid, phosphatidylethanolamine, the addition of alkaline earth cations produced no detectable surface potential, indicating that little or no binding occurs to the polar head group with these ions. When the bilayers were formed from a negatively charged lipid, phosphatidylserine, the addition of Sr and Ba decreased the magnitude of the surface potential as predicted by the theory of the diffuse double layer. In particular, the potential decreased 27 mv for a 10-fold increase in concentration in the millimolar-decimolar range. A 10-fold increase in the Ca or Mg concentration also produced a 27 mv decrease in potential in this region, which was again due to screening, but it was necessary to invoke some specific binding to account for the observation that these cations were effective at a lower concentration than Ba or Sr. It is suggested that the ability of the alkaline earth cations to shift the conductance-voltage curves of a nerve along the voltage axis by 20-26 mv for a 10-fold increase in concentration may be due to essentially a screening rather than a binding phenomenon.

Aniline Compounds↗
PubMed1981

Adsorption of divalent cations to bilayer membranes containing phosphatidylserine.

The Stern equation, a combination of the Langmuir adsorption isotherm, the Boltzmann relation, and the Grahame equation from the theory of the diffuse double layer, provides a simple theoretical framework for describing the adsorption of charged molecules to surfaces. The ability of this equation to describe the adsorption of divalent cations to membranes containing brain phosphatidylserine (PS) was tested in the following manner. Charge reversal measurements were first made to determine the intrinsic 1:1 association constants of the divalent cations with the anionic PS molecules: when the net charge of a PS vesicle is zero one-half of the available sites are occupied by divalent cations. The intrinsic association constant, therefore, is equal to the reciprocal of the divalent cation concentration at which the mobility of a PS vesicle reverses sign. The Stern equation with this association constant is capable of accurately describing both the zeta potential data obtained with PS vesicles at other concentrations of the divalent cations and the data obtained with with vesicles formed from mixtures of PS and zwitterionic phospholipids. Independent measurements of the number of ions adsorbed to sonicated PS vesicles were made with a calcium-sensitive electrode. The results agreed with the zeta potential results obtained with multilamellar vesicles. When membranes are formed at 20 degrees C in 0.1 M NaCl, the intrinsic 1:1 association constants of Ni, Co, Mn, Ba, Sr, Ca, and Mg with PS are 40, 28, 25, 20, 14, 12, and 8 M-1, respectively.

Cations, Divalent↗
PubMed1986

An experimental test of new theoretical models for the electrokinetic properties of biological membranes. The effect of UO2++ and tetracaine on the electrophoretic mobility of bilayer membranes and human erythrocytes.

For a large smooth particle with charges at the surface, the electrophoretic mobility is proportional to the zeta potential, which is related to the charge density by the Gouy-Chapman theory of the diffuse double layer. This classical model adequately describes the dependence of the electrophoretic mobility of phospholipid vesicles on charge density and salt concentration, but it is not applicable to most biological cells, for which new theoretical models have been developed. We tested these new models experimentally by measuring the effect of UO2++ on the electrophoretic mobility of model membranes and human erythrocytes in 0.15 M NaCl at pH 5. We used UO2++ for these studies because it should adsorb specifically to the bilayer surface of the erythrocyte and should not change the density of fixed charges in the glycocalyx. Our experiments demonstrate that it forms high-affinity complexes with the phosphate groups of several phospholipids in a bilayer but does not bind significantly to sialic acid residues. As observed previously, UO2++ adsorbs strongly to egg phosphatidylcholine (PC) vesicles: 0.1 mM UO2++ changes the zeta potential of PC vesicles from 0 to +40 mV. It also has a large effect on the electrophoretic mobility of vesicles formed from mixtures of PC and the negative phospholipid phosphatidylserine (PS): 0.1 mM UO2++ changes the zeta potential of PC/PS vesicles (10 mol % PS) from -13 to +37 mV. In contrast, UO2++ has only a small effect on the electrophoretic mobility of either vesicles formed from mixtures of PC and the negative ganglioside GM1 or erythrocytes: 0.1 mM UO2++ changes the apparent zeta potential of PC/GM1 vesicles (17 mol % GM1) from -11 to +5 mV and the apparent zeta potential of erythrocytes from -12 to -4 mV. The new theoretical models suggest why UO2++ has a small effect on PC/GM1 vesicles and erythrocytes. First, large groups (e.g., sugar moieties) protruding from the surface of the PC/GM1 vesicles and erythrocytes exert hydrodynamic drag. Second, charges at the surface of a particle (e.g., adsorbed UO2++) exert a smaller effect on the mobility than charges located some distance from the surface (e.g., sialic acid residues).

Electrophoresis↗