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Biomedical subjects

S M Ma

Publications and source records attributed to S M Ma.

At least 19 recordsLinked to original sources
PubMed1990

Anesthesia cutoff phenomenon: interfacial hydrogen bonding.

Anesthesia "cutoff" refers to the phenomenon of loss of anesthetic potency in a homologous series of alkanes and their derivatives when their sizes become too large. In this study, hydrogen bonding of 1-alkanol series (ethanol to eicosanol) to dipalmitoyl-L-alpha-phosphatidylcholine (DPPC) was studied by Fourier transform infrared spectroscopy (FTIR) in DPPC-D2O-in-CCl4 reversed micelles. The alkanols formed hydrogen bonds with the phosphate moiety of DPPC and released the DPPC-bound deuterated water, evidenced by increases in the bound O-H stretching signal of the alkanol-DPPC complex and also in the free O-D stretching band of unbound D2O. These effects increased according to the elongation of the carbon chain of 1-alkanols from ethanol (C2) to 1-decanol (C10), but suddenly almost disappeared at 1-tetradecanol (C14). Anesthetic potencies of these alkanols, estimated by the activity of brine shrimps, were linearly related to hydrogen bond-breaking activities below C10 and agreed with the FTIR data in the cutoff at C10.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

Infrared spectra of phospholipid membranes: interfacial dehydration by volatile anesthetics and phase transition.

Fourier-transform infrared attenuated total reflection (ATR) spectroscopy was used to study the effect of volatile anesthetics on fully hydrated dipalmitoylphosphatidylcholine (DPPC) vesicle membranes. The main phase transition was monitored by the change in the C-H2 asymmetric stretching frequencies of the lipid tails. The surface property was analyzed by the changes in the P = O stretching, (CH3)3-N+ stretching of the hydrophilic head, and C = O stretching of the glycerol skeleton. The partial pressures of those agents that decreased the transition temperature 1.0 C degree were halothane 0.75, enflurane 1.90 and CCl4 0.85 kPa. At a 2:1 lipid/anesthetic mole ratio, the polar anesthetics, halothane and enflurane, increased the ratio of (P = O stretching band area)/((CH3)3-N+ stretching band area) by 26.3% and 21.1%, respectively, whereas apolar CCl4 increased it 10.5%. The water molecules bound to the P = O moiety are apparently replaced by the anesthetic molecules. The deconvoluted C = O spectra showed two peaks: free sn-1 that is closer to the lipid core and hydrogen-bonded sn-2 that is closer to the polar head. Addition of halothane and enflurane, but not CCl4, increased the number of peaks to three. The third peak is free sn-2, formed by disrupting hydrogen-bonding to water. Because the temperature-induced spectral change was limited to C-H2 stretching at the main phase transition, the effects of anesthetics on the lipid membrane structure are not identical to temperature elevation. Among anesthetics, the effects of apolar and polar molecules on the interfacial properties are different.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1988

Membrane-buffer partition coefficients of tetracaine for liquid-crystal and solid-gel membranes estimated by direct ultraviolet spectrophotometry.

The membrane-buffer partition coefficient of tetracaine was measured by direct ultraviolet spectrophotometry in dimyristoylphosphatidylcholine unilamellar liposomes at temperatures above and below the main phase transition. The partition coefficients of uncharged tetracaine to solid-gel (18 degrees C) and liquid-crystal (30 degrees C) membranes were 6.9 x 10(4) and 1.2 x 10(5), respectively. Despite the general assumption that local anesthetic binding to the solid membrane is negligible, this study showed that the solid membrane binding amounts to 57.5% of the liquid membrane binding. Binding of the charged form to the liquid or solid membrane was not detectable under the present experimental condition of 0.03 mM tetracaine bulk concentration. The present method measures metachromasia of local anesthetics when bound to lipid membranes. Its advantage is that the separation of the vesicles from the solution is not required. A linearized equation is presented that estimates the partition coefficient or binding constant graphically from a linear plot of the absorbance data. The method is applicable for estimation of drug partition when a measurable spectral change occurs due to complex formation.

Buffers↗
PubMed1987

Fourier transform infrared studies on phospholipid hydration: phosphate-oriented hydrogen bonding and its attenuation by volatile anesthetics.

Water-phospholipid (dimyristoylphosphatidylcholine) interaction was analyzed in a water-in-oil(benzene) reversed micellar system using Fourier transform infrared spectroscopy, and the effects of inhalation anesthetics (halothane, enflurane, chloroform, and carbon tetrachloride) on the interaction were studied. The O-H stretching frequency, representing water, increased from 3369 cm-1 to a steady 3430 cm-1 when the water/phospholipid mole ratio exceeded 18. The value did not quite reach the frequency of free water of 3490 cm-1 at the water/phospholipid mole ratio of 30. The O-H bending frequency of water did not appear until the water/phospholipid mole ratio exceeded 9. The P=O stretching frequency in the polar head group of unhydrated dimyristoylphosphatidylcholine was 1262 cm-1 and decreased with the addition of water, reaching a steady value of 1238 cm-1 at the water/phospholipid mole ratio of 9. However, the (CH3)3N+ stretching of the choline head, as well as the C-H stretching of the hydrocarbon tail and the C=O stretching of the ester linkage, showed little change by the addition of water. The present results suggest that the primary hydration site of dimyristoylphosphatidylcholine is the phosphate moiety, and up to 18 water molecules are restricted at the polar head group. Apparently, the choline head has a minor role in the hydration of phospholipids despite the positive electrostatic charge. Among the water molecules interacting with the phospholipid head group, about 9 water molecules are strongly bound. The water content in the micelles correlated linearly with the ratio of the absorbance band area between O-H and C=O stretching. The addition of polar anesthetics (halothane, enflurane, and chloroform) increased the O-H stretching frequency and elevated the ratio of the absorbance band area between O-H and C=O stretching, implying that the anesthetics released the structured water molecules bound at the phospholipid-water interface. The anesthetics disrupted the hydrogen bond between the phosphate moiety of the phospholipid and water. Although apolar carbon tetrachloride also released bound water molecules, the magnitude was less than that of the polar anesthetics, as expected. The anesthetics did not affect the C-H stretching or C=O stretching bands, indicating that the disordering action upon the hydrocarbon core of phospholipid membranes is minimal at low water content. These results support our view that the primary site of action of inhalation anesthetics is the membrane-water interface, releasing bound water molecules.

Anesthetics↗
PubMed1986

Dose-dependent nonlinear response of the main phase-transition temperature of phospholipid membranes to alcohols.

The effect of 1-alkanols upon the main phase-transition temperature of phospholipid vesicle membranes between gel and liquid-crystalline phases was not a simple monotonic function of alkanol concentration. For instance, 1-decanol decreased the transition temperature at low concentrations, but increased it at high concentrations, displaying a minimal temperature. This concentration-induced biphasic effect cannot be explained by the van't Hoff model on the effect of impurities upon the freezing point. To explain this nonlinear response, a theory is presented which treats the effect of 1-alkanols (or any additives) on the transition temperature of phospholipid membranes in a three-component mixture. By fitting the experimental data to the theory, the enthalpy of the phase transition delta H* and the interaction energy, epsilon*AB between the additive and phospholipid molecules may be estimated. The theory predicts that when epsilon*AB greater than 2 (where epsilon*AB = epsilon AB/RT0, T0 being the transition temperature of phospholipid), both minimum and maximum transition temperatures should exist. When epsilon*AB = 2, only one inflection point exists. When epsilon*AB less than 2, neither maximum nor minimum exists. The alkanol concentration at which the transition temperature is minimum (Xmin) depends on the epsilon*AB value: the larger the epsilon*AB values, the smaller the Xmin. When epsilon*AB is large enough, Xmin values become so small that the plot delta T vs. X shows positive delta T in almost all alkanol concentrations. The interaction energy between 1-alkanols and phospholipid molecules increased with the increase in the carbon chain-length of 1-alkanols. In the case of the dipalmitoylphosphatidylcholine vesicle membrane, the carbon chain-length of 1-alkanols that caused predominantly positive delta T was about 12.

Alcohols↗
PubMed1986

Anesthetics release unfreezable and bound water in partially hydrated phospholipid lamellar systems and elevate phase transition temperature.

A dimyristoylphosphatidylcholine multilamellar system with varied water content was prepared by dessiccating sonicated vesicles in vacuo. The water content in the sample was determined by gas chromatography after dissolving the multilamellar system in water-free benzene. Differential scanning microcalorimetry revealed several endothermic peaks in the heating scan at subzero temperature, ranging from -25 to -3 degrees. The peaks that appeared in the subzero temperature range indicate the existence of water molecules bound to the lipid head groups, differing from free water that freezes at 0 degrees. The difference between the amount of water molecules that froze in calorimetry and the total amount of water detected by gas chromatography indicates the presence of unfreezable, tightly bound water molecules. The relative amount of free, intermediate, and unfreezable water was estimated by comparing the differential scanning microcalorimetry data with gas chromatography measurements. The addition of halothane and 1-hexanol significantly decreased the intermediately bound water peaks. The anesthetics dehydrated the lamellar system. The phase polymorphism of partially hydrated phospholipid multilayers is well known, and the temperature that corresponds to the main phase transition of fully hydrated lipid membranes shifts to a higher temperature. The addition of anesthetics increased the phase transition temperature when the water content was less than 18 wt%. This result is the complete reverse of the depressant action of anesthetics in fully hydrated lipid membranes. The present anesthetic effect upon the elevation of the transition temperature is apparently caused by anesthetic-induced dehydration of the lipid-water interface at the present experimental condition.

Anesthetics↗
PubMed1983

Frictional torque in surface and conventional hip replacement.

UNLABELLED: The frictional torque of the Trapezoidal-28 total hip replacement and the Tharies SR-3 and SR-5 surface replacements were measured in the University of California at Los Angeles hip-joint simulator in calf serum. Loads of as much as 890 newtons were applied while the femoral component oscillated through a 60-degree arc at forty cycles per minute. Frictional torque, as measured by a ring transducer at a fixed distance from the center of rotation, was seen to diminish as the thickness of the polyethylene increased and was found to be relatively proportional to the diameter of the femoral component. The torques measured in this study were found to be twenty to 100 times smaller than the static torques to failure for acetabular fixation that have been reported in the literature. Finally, no permanent deformation of the thin acetabular shells attributable to the cementing process was apparent when the recommended technique of surgical insertion was utilized. CLINICAL RELEVANCE: Surface replacement components have been shown to generate greater frictional torques at the acetabular bone-cement interface than do smaller-diameter conventional hip replacements. This indicates that the local mechanical-loading conditions of the hip joint are not the same for both types of replacements, and this should be considered when selecting the type of arthroplasty for an individual patient.

Biomechanical Phenomena↗
PubMed1982

Revision of aseptic loose total hip arthroplasties.

Sixty-six patients were revised for aseptic loosening of their conventional hip arthroplasties; follow-up periods ranged from one to nine years. In comparing them with an overall conventional arthroplasty series, there was a higher failure rate with dysplasia and post-traumatic patients, and a lower incidence in osteoarthritic and rheumatoid patients. The average time to revision was four years. The patients were eight years younger than those in the overall UCLA conventional hip arthroplasty series. Forty-two per cent had undergone hip surgery prior to the original hip arthroplasty that failed. The average improvement, as well as the follow-up pain, walking, and function ratings, and the postoperative flexion arc were less than those in the overall conventional arthroplasty series. The quality of femoral and acetabular fixation obtained at revision was considerably inferior to that of the primary surgery. Six patients (9%) have already required re-revision of their hip arthroplasties. In a further 20%, the radiolucencies progressed substantially in extent and width, and are radiographically loose. Although these patients are relatively asymptomatic, prognosis is guarded. Forty-four per cent had no complications and are radiographically well fixed. Other complications included trochanteric migration (7.6%), dislocation (10.6%), and peroneal nerve palsy (7.6%), but there were no deaths or other serious medical complications and only one case (1.5%) of sepsis.

Acetabulum↗
PubMed1981

Reaction kinetics in living systems.

In this report we treat reaction rates, equilibrium theory, and irreversible thermodynamics as different aspects of a single discipline. In biological reactions the rate is ultimately controlled by enzymes and other proteins of complex structure and high molecular weight. The needed formalism can be placed in one-to-one correspondence with appropriate electrical and mechanical networks. An enzyme molecule has zwitter ions anchored in the polypeptide chain, which enable it to distort the substrate by electrostatic polarization. Water weakens the induced or existing polar bonds and so speeds reaction. Several biological processes, such as luminescence, catalysis, nerve excitation, and anesthesia, in which enzymatic reactions play a major part are discussed from this point of view. We also have discussed the energy consumption and coupling effect in living systems. It is likely that a small fraction of bonds can become energy rich through the process of quenching and that unsymmetrical barriers in biological systems act like transistors in making the driving forces more efficient by a valve effect.

Anesthetics↗
PubMed1980

A theory of distortion of the reaction zone.

A cylindrical detonating explosive behaves like a non-Newtonian viscous fluid emerging from a cylindrical pipe. The expression for non-Newtonian viscous flow has been applied to detonating explosives. The resultant fit to emerging flame fronts from detonation is excellent for a wide variety of detonating explosives both for transients (at various times) and for steady state. The quantities k'(lambda/lambda(1))(2/B) and 1/B and the rate constant k' increase abruptly at a time supporting a change in mechanism from deflagration to detonation in the transient during initiation. All of these parameters are temperature sensitive, indicating an abrupt temperature increase as a condition or indicator in the deflagration-to-detonation transition. Furthermore, a straight line results when log particle velocity u is plotted against log radial distance r, indicating that, for the explosives studied, the hyperbolic cosine wave front can be replaced by a parabolic wave front within the accuracy of the available experimental data.

Journal Article↗
PubMed1980

Similarity and differences between conditions for initiation and failure of detonation.

A theory is proposed to study the sensitivity of cylindrical explosives. Using the equations governing the conservation of mass, energy, and momentum, the equation of state, and Newtonian mechanics, we have derived the expression D = D(o)e(-a2/d), in which the apparent length of the reaction zone, a, takes into account burned and unburned explosive and pressure release through the back and sides of the reaction zone. D is the detonation velocity and d is the diameter of the cylindrical charge. From the observed D(1/d) curves and critical energy values, we can interpret failure and other phenomena associated with detonation.

Journal Article↗
PubMed1979

Thermodynamic properties of solid CH(4).

The significant structures procedure of liquids has been used to calculate the thermodynamic properties of solid C(2)H(4). Two degeneracy terms were used to describe the behavior in the vicinities of the two phase transitions. The calculated entropy and specific heat agree well with experimental results from a few kelvins to the melting point. Less satisfactory agreement is obtained for compressibility and thermal expansion coefficients. This simple model represents surprisingly well the phase transitions in the solid state.

Journal Article↗
PubMed1978

Hysteresis effects of CH(4) and CH(4) in the regions of the solid-phase transitions.

The thermodynamic model of hysteresis in phase transitions based on the regular solution theory, previously developed, was applied to the solid phases of C(1)H(4) and C(2)H(4). The width and height of the hysteresis loops for these systems were calculated and compared with the experimental data; agreement was satisfactory.

Journal Article↗
PubMed1977

Single partition function for three phases.

The significant structures theory of liquids has been extended to take into account (i) translational degrees of freedom in the degeneracy term and (ii) the perturbation term which becomes important near the critical region. With these improvements, the calculated thermodynamic properties of argon agree very well with experimental results from the melting point through the critical point, along the coexistence curve as well as along the critical isochore and for the solid and the vapor.

Journal Article↗
PubMed1975

The significant structure theory applied to a mesophase system.

The significant structure theory of liquids is extended to the mesophase system with p-azoxyanisole as an example. This compound has two different structures, a nematic phase and an isotropic phase, in its liquid state. In this study the nematic phase is treated as subject to a second volume and temperature-dependent degeneracy formally like that due to melting. The isotropic phase is treated as a normal liquid. The specific heat, thermal expansion coefficient, compressibility, volume, entropy of transitions, and heat of transitions are calculated and compared to the observed values. This analysis differs from previous ones in including the volume dependence as well as the temperature dependence in one explicit expression for the Helmholtz free energy.

Journal Article↗
PubMed1975

Properties of molten magnesium oxide.

The Significant Structure Theory of Liquids has been used to calculate the thermodynamic properties, viscosity, self-diffusion coefficient, and specific conductance of molten magnesium oxide, taking account of the decomposition of MgO to Mg and O(2) species in the gas-like part of the partition function.

Journal Article↗