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J L Skinner - One of the best experts on this subject based on the ideXlab platform.
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vibrational spectroscopy of water in hydrated Lipid multi bilayers ii two dimensional infrared and peak shift observables within different theoretical approximations
Journal of Chemical Physics, 2011Co-Authors: Scott M Gruenbaum, Piotr A Pieniazek, J L SkinnerAbstract:In a previous report, we calculated the infrared absorption spectrum and both the isotropic and anisotropic pump-probe signals for the OD stretch of isotopically dilute water in dilauroylphosphatidylcholine (DLPC) multi-bilayers as a function of the Lipid Hydration level. These results were then compared to recent experimental measurements and are in generally good agreement. In this paper, we will further investigate the structure and dynamics of Hydration water using molecular dynamics simulations and calculations of the two-dimensional infrared and vibrational echo peak shift observables for Hydration water in DLPC membranes. These observables have not yet been measured experimentally, but future comparisons may provide insight into spectral diffusion processes and Hydration water heterogeneity. We find that at low Hydration levels the motion of water molecules inside the Lipid membrane is significantly arrested, resulting in very slow spectral diffusion. At higher Hydration levels, spectral diffusion is more rapid, but still slower than in bulk water. We also investigate the effects of several common approximations on the calculation of spectroscopic observables by computing these observables within multiple levels of theory. The impact of these approximations on the resulting spectra affects our interpretation of these measurements and reveals that, for example, the cumulant approximation, which may be valid for certain systems, is not a good approximation for a highly heterogeneous environment such as Hydration water in Lipid multi-bilayers.
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vibrational spectroscopy of water in hydrated Lipid multi bilayers i infrared spectra and ultrafast pump probe observables
Journal of Chemical Physics, 2011Co-Authors: Scott M Gruenbaum, J L SkinnerAbstract:The vibrational spectroscopy of Hydration water in dilauroylphosphatidylcholine Lipid multi-bilayers is investigated using molecular dynamics simulations and a mixed quantum/classical model for the OD stretch spectroscopy of dilute HDO in H2O. FTIR absorption spectra, and isotropic and anisotropic pump-probe decay curves have been measured experimentally as a function of the Hydration level of the Lipid multi-bilayer, and our goal is to make connection with these experiments. To this end, we use third-order response functions, which allow us to include non-Gaussian frequency fluctuations, non-Condon effects, molecular rotations, and a fluctuating vibrational lifetime, all of which we believe are important for this system. We calculate the response functions using existing transition frequency and dipole maps. From the experiments it appears that there are two distinct vibrational lifetimes corresponding to HDO molecules in different molecular environments. In order to obtain these lifetimes, we consider a simple two-population model for Hydration water hydrogen bonds. Assuming a different lifetime for each population, we then calculate the isotropic pump-probe decay, fitting to experiment to obtain the two lifetimes for each Hydration level. With these lifetimes in hand, we then calculate FTIR spectra and pump-probe anisotropy decay as a function of Hydration. This approach, therefore, permits a consistent calculation of all observables within a unified computational scheme. Our theoretical results are all in qualitative agreement with experiment. The vibrational lifetime of Lipid-associated OD groups is found to be systematically shorter than that of the water-associated population, and the lifetimes of each population increase with decreasing Hydration, in agreement with previous analysis. Our theoretical FTIR absorption spectra successfully reproduce the experimentally observed red-shift with decreasing Lipid Hydration, and we confirm a previous interpretation that this shift results from the hydrogen bonding of water to the Lipid phosphate group. From the pump-probe anisotropy decay, we confirm that the reorientational motions of water molecules slow significantly as Hydration decreases, with water bound in the Lipid carbonyl region undergoing the slowest rotations.
Scott M Gruenbaum - One of the best experts on this subject based on the ideXlab platform.
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vibrational spectroscopy of water in hydrated Lipid multi bilayers ii two dimensional infrared and peak shift observables within different theoretical approximations
Journal of Chemical Physics, 2011Co-Authors: Scott M Gruenbaum, Piotr A Pieniazek, J L SkinnerAbstract:In a previous report, we calculated the infrared absorption spectrum and both the isotropic and anisotropic pump-probe signals for the OD stretch of isotopically dilute water in dilauroylphosphatidylcholine (DLPC) multi-bilayers as a function of the Lipid Hydration level. These results were then compared to recent experimental measurements and are in generally good agreement. In this paper, we will further investigate the structure and dynamics of Hydration water using molecular dynamics simulations and calculations of the two-dimensional infrared and vibrational echo peak shift observables for Hydration water in DLPC membranes. These observables have not yet been measured experimentally, but future comparisons may provide insight into spectral diffusion processes and Hydration water heterogeneity. We find that at low Hydration levels the motion of water molecules inside the Lipid membrane is significantly arrested, resulting in very slow spectral diffusion. At higher Hydration levels, spectral diffusion is more rapid, but still slower than in bulk water. We also investigate the effects of several common approximations on the calculation of spectroscopic observables by computing these observables within multiple levels of theory. The impact of these approximations on the resulting spectra affects our interpretation of these measurements and reveals that, for example, the cumulant approximation, which may be valid for certain systems, is not a good approximation for a highly heterogeneous environment such as Hydration water in Lipid multi-bilayers.
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vibrational spectroscopy of water in hydrated Lipid multi bilayers i infrared spectra and ultrafast pump probe observables
Journal of Chemical Physics, 2011Co-Authors: Scott M Gruenbaum, J L SkinnerAbstract:The vibrational spectroscopy of Hydration water in dilauroylphosphatidylcholine Lipid multi-bilayers is investigated using molecular dynamics simulations and a mixed quantum/classical model for the OD stretch spectroscopy of dilute HDO in H2O. FTIR absorption spectra, and isotropic and anisotropic pump-probe decay curves have been measured experimentally as a function of the Hydration level of the Lipid multi-bilayer, and our goal is to make connection with these experiments. To this end, we use third-order response functions, which allow us to include non-Gaussian frequency fluctuations, non-Condon effects, molecular rotations, and a fluctuating vibrational lifetime, all of which we believe are important for this system. We calculate the response functions using existing transition frequency and dipole maps. From the experiments it appears that there are two distinct vibrational lifetimes corresponding to HDO molecules in different molecular environments. In order to obtain these lifetimes, we consider a simple two-population model for Hydration water hydrogen bonds. Assuming a different lifetime for each population, we then calculate the isotropic pump-probe decay, fitting to experiment to obtain the two lifetimes for each Hydration level. With these lifetimes in hand, we then calculate FTIR spectra and pump-probe anisotropy decay as a function of Hydration. This approach, therefore, permits a consistent calculation of all observables within a unified computational scheme. Our theoretical results are all in qualitative agreement with experiment. The vibrational lifetime of Lipid-associated OD groups is found to be systematically shorter than that of the water-associated population, and the lifetimes of each population increase with decreasing Hydration, in agreement with previous analysis. Our theoretical FTIR absorption spectra successfully reproduce the experimentally observed red-shift with decreasing Lipid Hydration, and we confirm a previous interpretation that this shift results from the hydrogen bonding of water to the Lipid phosphate group. From the pump-probe anisotropy decay, we confirm that the reorientational motions of water molecules slow significantly as Hydration decreases, with water bound in the Lipid carbonyl region undergoing the slowest rotations.
Xianli Chen - One of the best experts on this subject based on the ideXlab platform.
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preparation in vitro and in vivo evaluation of liposomal niosomal gel delivery systems for clotrimazole
Drug Development and Industrial Pharmacy, 2005Co-Authors: Meiying Ning, Yingzhi Guo, Huaizhong Pan, Xianli ChenAbstract:Clotrimazole, which is an imidazole derivative antifungal agent, was widely used for the treatment of mycotic infections of the genitourinary tract. To develop alternative formulation for the vaginal administration of clotrimazole to provide sustained and controlled release of appropriate drug for local vaginal therapy, liposomes/niosomes were evaluated as delivery vehicles. To optimize the preparation of liposomes/niosomes with regard to size and entrapment efficiency, multilamellar liposomes/niosomes containing drug were prepared by Lipid Hydration method. The prepared liposomes/niosomes were incorporated into 2% carbopol gel, and the systems were evaluated for drug stability in phosphate-buffered saline (pH 7.4) and simulated vaginal fluid at 37 ± 1°C. Further, the vesicle gel system was evaluated by antifungal activity and tolerability on tissue level in rat.
Emma Sparr - One of the best experts on this subject based on the ideXlab platform.
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thermodynamics of membrane Lipid Hydration
Pure and Applied Chemistry, 2003Co-Authors: Hakan Wennerstrom, Emma SparrAbstract:Zwitterionic or polar Lipids that form lamellar phases swell in the presence of water to take up between 10 and 30 water molecules per Lipid. The degree of the water uptake de- pends both on the state of the alkyl chains, liquid or solid, and on the nature of the polar group. The swelling behavior has been extensively characterized on the free-energy level through measuring the relation between the chemical potential of the water and the degree of swelling. In spite of the extensive studies of this type, consensus is still lacking concerning the molecular mechanism causing the swelling. The two main ideas that explain the existence of the effectively repulsive force between two opposing bilayers are (i) a water structure ef- fect and (ii) thermal excitations of the Lipid molecules. The first is from a thermodynamic per- spective caused by a negative partial molar enthalpy of the water, whereas for the second, the repulsion is caused by positive entropy. A further insight into the swelling behavior is obtained by simultaneously measuring the partial molar free energy and the partial molar enthalpy using a twin double calorimeter. Such measurements show for binary Lipid-water and for ternary Lipid-cholesterol-water sys- tems that the first four water molecules enter the bilayer driven by a favorable enthalpic in- teraction, whereas for higher water contents, the partial free energy and the partial enthalpy have opposite signs. In spite of the fact that the partial free energy varies with water content in a similar way, the partial enthalpies depend strongly on the nature of the Lipid sample. Thus, it is obvious that a molecular interpretation of the enthalpy values has to involve the Lipid degrees of freedom. This is a strong indication that the interpretation of the free ener- gies should also include the same degrees of freedom. This gives experimental evidence in favor of an interpretation of the molecular mechanism causing the swelling that involves changes in the thermal excitation of the Lipid degrees of freedom.
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a calorimetric study of phosphoLipid Hydration simultaneous monitoring of enthalpy and free energy
Journal of Physical Chemistry B, 2000Co-Authors: Natalia Markova, Emma Sparr, Lars Wadso, Hakan WennerstromAbstract:We present a novel method for monitoring isothermal Lipid Hydration using a sorption microcalorimeter. A measuring cell of the double-twin calorimeter consists of two vessels connected by a stainless steel tube. The upper vessel contains pure water, and the bottom vessel is loaded with the Lipid sample. This calorimeter allows for simultaneous measurement of the partial molar enthalpy and the chemical potential (or the partial molar free energy) of the water. The versatility of the method is demonstrated by studies of the Hydration of the phosphoLipids dipalmitoyl phosphatyl choline (DPPC), dimyristoyl phosphatidyl choline (DMPC), and dilauroyl phosphatidyle choline (DLPC) at 25 and 27 C. The measurements provide a relation between water content and water chemical potential, which, in these lamellar systems, is often recast as a force-distance relation and has been called the Hydration force. Through the simultaneously monitored calorimetric values, the partial molar enthalpy of water is also obtained. The method consequently provides a rather unique combination of information on both partial molar enthalpy and partial molar free energy and thus also the partial molar entropy of the process. We find that the incorporation of the first three to four water molecules per Lipid is exothermic. These water molecules presumably interact directly with oxygen atoms on the phosphate of the Lipid headgroup. When the first waters have been added, the remaining ones are incorporated endothermically. This applies to the water molecules taken up both in the gel phase and in the liquid crystalline state. We also observe that the sorption process triggers a first-order phase change from a gel (L') to a liquid crystalline (L) phase. For DLPC, this occurs at 25 C at a relative humidity of 0.79 with an endothermic transition enthalpy of 42 ± 2 kJ/mol (DLPC) and, for DMPC, at 27 C at 0.93 relative humidity with H = 56 ± 5 kJ/mol (DMPC). We use a previously established model to quantitatively interpret these phase transitions. Furthermore, the observed endothermic nature of the sorption process above three to four waters per Lipid is fully consistent with the suggestion that the negative free energy of the sorption (swelling) is due to increased thermal excitations and thus a positive entropy. It is more problematic to reconcile the data with models proposing structuring effects in the water as the main cause of the swelling. (Less)
Meiying Ning - One of the best experts on this subject based on the ideXlab platform.
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preparation in vitro and in vivo evaluation of liposomal niosomal gel delivery systems for clotrimazole
Drug Development and Industrial Pharmacy, 2005Co-Authors: Meiying Ning, Yingzhi Guo, Huaizhong Pan, Xianli ChenAbstract:Clotrimazole, which is an imidazole derivative antifungal agent, was widely used for the treatment of mycotic infections of the genitourinary tract. To develop alternative formulation for the vaginal administration of clotrimazole to provide sustained and controlled release of appropriate drug for local vaginal therapy, liposomes/niosomes were evaluated as delivery vehicles. To optimize the preparation of liposomes/niosomes with regard to size and entrapment efficiency, multilamellar liposomes/niosomes containing drug were prepared by Lipid Hydration method. The prepared liposomes/niosomes were incorporated into 2% carbopol gel, and the systems were evaluated for drug stability in phosphate-buffered saline (pH 7.4) and simulated vaginal fluid at 37 ± 1°C. Further, the vesicle gel system was evaluated by antifungal activity and tolerability on tissue level in rat.
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preparation and in vitro evaluation of liposomal niosomal delivery systems for antifungal drug clotrimazole
Indian Journal of Experimental Biology, 2005Co-Authors: Meiying Ning, Zhongwei Gu, Heming Yu, Kai XiaoAbstract:: Clotrimazole, an imidazole derivative antifungal agent is widely used for the treatment of mycotic infections of the genitourinary tract. In order to develop alternative formulation for the vaginal administration of clotrimazole to provide sustained and controlled release of appropriate drug for local vaginal therapy, liposomes/niosomes were evaluated as delivery vehicles. To optimize the preparation of liposomes/niosomes with regards to size and entrapment efficiency, multilamellar liposomes/niosomes containing drug were prepared by Lipid Hydration method. The ability of the systems to deliver clotrimazole into and through the mucosa was evaluated in vitro using rabbit vaginal mucosa with vertical Franz diffusion cells. The in vitro permeation data showed that the liposomes/niosomes system increased the clotrimazole total penetration through the vaginal mucosa by 1.6, 1.5-fold, the accumulation of clotrimazole into the mucosa was increased by 3.1, 2.3-fold, respectively, as compared with control during 24 hr. These results suggest that the studied liposomes/niosomes systems may be appropriate vesicles for the vaginal mucosa delivery of clotrimazole for local vaginal therapy.