Pure Buffer Research Articles

Improvement in the hole collection of polymer solar cells by utilizing gold nanoparticle buffer layer

Insertion of gold nanoparticles (GNPs) layer between the indium tin oxide (ITO) and the photoactive polymer by simple spin-coating method is found to improve the photovoltaic effects of solar cells significantly. Cross sectional SEM image provides direct evidence that GNPs layer acts as a pure buffer layer in our devices. The improvement of the device performance is due to good transmission, high work function, good conductivity, and ultra-smooth surface roughness of GNPs layer. GNPs layer can act as a promising buffer layer to facilitate hole collection from polymer donor towards ITO anode.

Internal Structure of Nanoporous TiO2/Polyion Thin Films Prepared by Layer-by-Layer Deposition

The internal structure of porous TiO2 films prepared by electrostatic layer-by-layer deposition was investigated. The films were prepared by alternate dipping of solid substrates into dispersions of TiO2 nanoparticles and polycations, polyanions, or pure buffer solution, respectively. The surface charge of the amphoteric TiO2 particles was controlled by the pH of the aqueous dispersions. The morphology of the film surface was investigated by means of scanning electron microscopy. It was found that the surface roughness strongly depends on the polymeric material used for the deposition process but is independent of the ionic strength of the solution or the molecular weight of the polyions. The samples with rough surfaces feature strong light scattering. The porosity and internal structure of the TiO2/polyelectrolyte films were investigated by adsorption/desorption of dye molecules. A crude estimate yields an internal surface that is up to 160 times the plane surface of the substrate for a film thickness of 1 microm. The composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). Detection of the XPS signal after each deposition step of the first three dipping cycles shows a significant increase of the relative surface coverage of Ti after the TiO2 deposition step and of PSS after the PSS deposition step. For later dipping cycles, such an increase was also detectable but less prominent.

Synthesis, Characterization, and Biodegradation of Novel Poly(ether ester amide)s Based on l-Phenylalanine and Oligoethylene Glycol

A new family of novel biodegradable poly(ether ester amide)s (PEEAs) consisting of three building blocks (L-phenylalanine, oligoethylene glycol, and aliphatic acid dichloride) were synthesized by solution polycondensation. Using N,N-dimethylacetamide as the solvent, these PEEA polymers were obtained with fairly good yields with reduced viscosity (eta(red)) ranging from 0.13 to 0.61 dL/g. The chemical structures of the PEEAs were confirmed by IR, NMR spectra, and elemental analysis. The PEEAs had Tg values lower than that of the saturated poly(ester amide)s (PEAs) of similar structures due to the incorporation of ether bonds in the backbones. An increase in the number of ether bonds in PEEA resulted in a lower Tg value. The solubility of the PEEA polymers in a wide range of common organic solvents was significantly improved when compared with unsaturated PEAs. The preliminary in vitro biodegradation behaviors of PEEA polymers were investigated in both pure PBS buffer and alpha-chymotrypsin solution of different concentrations. The polymers showed a significantly faster weight loss in an enzyme solution (alpha-chymotrypsin) but a very slow biodegradation rate in pure PBS buffer. The enzymatic hydrolysis rates of PEEAs (in terms of weight loss) were found to be much faster than those of saturated and unsaturated polyesteramides reported in previous studies. The zero-order-like biodegradation kinetics and molecular weight data also suggested surface erosion biodegradation mechanisms for these PEEAs.

An ELISA for apolipoprotein M reveals a strong correlation to total cholesterol in human plasma

Apolipoprotein M (apoM) is a 188 amino acid, 25 kDa protein belonging to the lipocalin protein superfamily. Although predominantly associated with high density lipoprotein, apoM is found in all major lipoprotein classes. To facilitate clinical studies of apoM, we have developed a sandwich ELISA for the measurement of apoM in human plasma. This method has been used to investigate normal apoM variation and to establish reference values for healthy individuals through the measurement of 598 samples from the Nordic Reference Interval Project Bio-bank and Database (NOBIDA) biobank. For women 18-49 years old, the reference interval for apoM was 0.58-1.18 micromol/l, whereas for women 50+ years and for men, the reference range was 0.61-1.30 micromol/l. Correlation studies of apoM with 26 common clinical chemical analytes from the NOBIDA database revealed a marked positive correlation with plasma total cholesterol (r = 0.52) and LDL and HDL cholesterol (r = 0.43 and 0.36, respectively). There was no statistically significant correlation with HDL/total cholesterol ratio or body mass index. In conclusion, a sandwich ELISA for the measurement of apoM in human plasma shows that apoM concentration is strongly correlated to total cholesterol in healthy individuals.

Phosphatidylcholine Vesicle-Mediated Decomposition of Hydrogen Peroxide

The decomposition of hydrogen peroxide (H2O2) was examined in aqueous solution (50 mM Tris-HCl buffer, pH 7.4, containing 100 mM NaCl) at 25 degrees C in pure buffer or in the presence of either vesicles or micelles formed from various phosphatidylcholines (PCs). In the absence of PCs, more than 90% of the initially added H2O2 (1.0 mM) remained intact after incubation for 120 h. The effect of the PCs on the decomposition of H2O2 was studied by using different PCs that varied in terms of number of carbon atoms in the two acyl chains n as well as in terms of the degree of unsaturation. PCs with short hydrocarbon chains (n = 4, 6-8) were dissolved in the buffer solution in the form of nonassociated monomers or as micelles in equilibrium with monomers at a fixed PC concentration of 10 mM. The presence of these short-chain PCs slightly enhanced the H2O2 decomposition rate. Micelles formed by non-lipid detergents (sodium cholate, Triton X-100, and sodium dodecylsulfate) had a similar effect. In marked contrast, PCs with long hydrocarbon chains (n > or = 10) dispersed in buffer solution as vesicles (liposomes) significantly enhanced the rate of H2O2 decomposition, with the most effective PC being 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at 25 degrees C. This indicates that the packing density of the PC molecules influences the reactivity, presumably through the direct interaction of the PC assemblies with H2O2 molecules. Furthermore, in the case of vesicles formed from PCs with unsaturated acyl chains (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC; 1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC), carbon-carbon double bond oxidation did not occur extensively under the conditions used. This indicates that the observed effect of PCs on the decomposition of H2O2 is indeed related to the assembly structure (vesicle vs micelles vs monomers) and is clearly not related to the presence of unsaturated hydrocarbon chains. Fluorescence polarization measurements of two fluorescent probes embedded either in the acyl chain region of the vesicles (DPH, 1,6-diphenyl-1,3,5-hexatriene) or on the surface of the vesicles (TMA-DPH, 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene iodide) show that the presence of H2O2 leads to a decrease in the fluidity of the lipid-water surface and not to a change in the fluidity of the hydrophobic region of the vesicle bilayer. This indicates that the decomposition of H2O2 is triggered through interactions between H2O2 and the polar head group area of PC vesicles.

Solute effects on the irreversible aggregation of serum albumin

Thermal stress on bovine serum albumin (BSA) promotes protein aggregation through the formation of intermolecular β-sheets. We have used light scattering and chromatography to study effects of (< 1 M) Na 2SO 4, NaSCN, sucrose, sorbitol and urea on the rate of the thermal aggregation. Both salts were strong inhibitors of BSA aggregation and they reduced both the size and number (concentration) of aggregate particles compared to non-ionic solutes (or pure buffer). Hence, the salts appear to suppress both nucleation- and growth rate. The non-electrolyte additives reduced the initial aggregation rate (compared to pure buffer), but did not significantly limit the extent of aggregation in samples quenched after 27 min. heat exposure (40–50% aggregation in all samples). The non-electrolytes did, however, modify the aggregation process as they consistently brought about smaller but more concentrated aggregates than pure buffer. The results are discussed along the lines of linkage- and transition state theories. In this framework, the rate of the aggregation process is governed by the equilibrium between a thermally denatured state (D) and the transition state D ≠. Thus, the effect of a solute relies on its preferential interactions with respectively D and D ≠. The current results do not show any correlation between the solutes' preferential interactions with native BSA and their effect on the rate of aggregation. This suggests that non-specific, “Hofmeister-type” interactions, which scale with the solvent accessible surface area, are of minor importance. Rather, salt induced suppression of aggregation is suggested to depend on the modulation of specific electrostatic forces in the D ≠ state.

A log buffer-based flash translation layer using fully-associative sector translation

Flash memory is being rapidly deployed as data storage for mobile devices such as PDAs, MP3 players, mobile phones, and digital cameras, mainly because of its low electronic power, nonvolatile storage, high performance, physical stability, and portability. One disadvantage of flash memory is that prewritten data cannot be dynamically overwritten. Before overwriting prewritten data, a time-consuming erase operation on the used blocks must precede, which significantly degrades the overall write performance of flash memory. In order to solve this “erase-before-write” problem, the flash memory controller can be integrated with a software module, called “flash translation layer (FTL).” Among many FTL schemes available, the log block buffer scheme is considered to be optimum. With this scheme, a small number of log blocks, a kind of write buffer, can improve the performance of write operations by reducing the number of erase operations. However, this scheme can suffer from low space utilization of log blocks. In this paper, we show that there is much room for performance improvement in the log buffer block scheme, and propose an enhanced log block buffer scheme, called FAST (full associative sector translation). Our FAST scheme improves the space utilization of log blocks using fully-associative sector translations for the log block sectors. We also show empirically that our FAST scheme outperforms the pure log block buffer scheme.

Electrical characterisation of phosphorus-doped ZnO thin films grown by pulsed laser deposition

Abstract Phosphorus-doped ZnO films were grown by pulsed laser deposition using a ZnO:P 2 O 5 -doped target as the phosphorus source with the aim of producing p-type ZnO material. ZnO:P layers (with phosphorus concentrations of between 0.01 to 1 wt%) were grown on a pure ZnO buffer layer. The electrical properties of the films were characterised from temperature dependent Hall-effect measurements. The samples typically showed weak n-type conduction in the dark, with a resistivity of 70 Ω cm, a Hall mobility of μ n ∼0.5 cm 2 V −1 s −1 and a carrier concentration of n∼3×10 17 cm −3 at room temperature. After exposure to an incandescent light source, the samples underwent a change in conduction from n- to p-type, with an increase in mobility and decrease in concentration for temperatures below 300 K.

Effects of osmolytes on hexokinase kinetics combined with macromolecular crowding: Test of the osmolyte compatibility hypothesis towards crowded systems

We investigated the effect of compatible and non-compatible osmolytes in combination with macromolecular crowding on the kinetics of yeast hexokinase. This was motivated by the fact that almost all studies concerning the osmolyte effects on enzyme activity have been performed in diluted buffer systems, which are far from the physiological conditions within cells, where the cytosol contains several hundred mg protein ml − 1 . Four organic (glycerol, betaine, TMAO and urea) and one inorganic (NaCl) osmolyte were tested. It was concluded that the effect of compatible osmolytes (glycerol, betaine and TMAO) on V max and K M was practically equivalent in pure buffer and in 200–250 mg BSA ml − 1 supporting the view that these small organic osmolytes do minimal perturbance on enzyme function in physiological solutions. The effect of urea on enzyme kinetics was not independent of protein concentration, since the presence of 250 mg BSA ml − 1 partly compensated the perturbing effect of urea. Even though the organic osmolytes glycerol, betaine and TMAO are generally considered compatible with enzyme function, especially glycerol did have a significant effect on hexokinase kinetics, decreasing both k cat, K M and k cat/ K M. The osmolytes decreased k cat/ K M in the order: NaCl > Urea > TMAO/glycerol > betaine. For the organic osmolytes this order correlates with the degree of exclusion from protein–water interfaces. Thus, the stronger the exclusion the weaker the perturbing effects on k cat/ K M.

Quantitative in Vivo Microsampling for Pharmacokinetic Studies Based on an Integrated Solid-Phase Microextraction System

An integrated microsampling approach based on solid-phase microextraction (SPME) was developed to provide a complete solution to highly efficient and accurate pharmacokinetic studies. The microsampling system included SPME probes that are made of poly(ethylene glycol) (PEG) and C18-bonded silica, a fast and efficient sampling strategy with accurate kinetic calibration, and a high-throughput desorption device based on a modified 96-well plate. The sampling system greatly improved the quantitative capability of SPME in two ways. First, the use of the C18-bonded silica/PEG fibers minimized the competition effect from analogues of the target analytes in a complicated sample matrix such as blood or plasma samples, which is a common problem associated with solid coating SPME fibers for quantitative analysis. Moreover, the C18-bonded silica/PEG fibers provide high sensitivity and a large dynamic range that covers the possible sample concentration range during diazepam administration and elimination. Second, the kinetic calibration method offers more accurate quantitation than the calibration curve method for in vivo SPME, because it compensates for convection and matrix effects during sampling. Therefore, it is especially suitable as a fast sampling technique for pre-equilibrium SPME. Furthermore, with the high-throughput desorption device, the integrated system offers compactness and high efficiency. Its feasibility for in vivo sampling was demonstrated by monitoring diazepam pharmacokinetics and validated by conventional chemical assays and equilibrium SPME. In addition, we propose a simple method to determine the apparent distribution constant between an SPME fiber and a blood matix (Kfs) and the distribution constant between an SPME fiber and a pure PBS buffer sample matrix (Kfb). As a result, both total and free concentrations of the drug and its metabolites can be detected simultaneously. Accordingly, the binding constants to the blood matrix can be obtained, which are of special significance for clinical diagnosis and drug discovery.

Synthesis, characterization, and biodegradation of copolymers of unsaturated and saturated poly(ester amide)s

AbstractA new family of biodegradable copolymers of unsaturated poly(ester amide)s (UPEAs) and saturated poly(ester amide)s (SPEAs) based on L‐phenylalanine, aliphatic dicarboxylic acids, and aliphatic dialcohols was synthesized by solution polycondensation and characterized. These unsaturated/saturated poly(ester amide) copolymers (USPEAs) were obtained in fairly good yields with N,N‐dimethylacetamide as the solvent. The molecular weights (Mn and Mw) of the USPEAs measured by GPC ranged from 15 to 60 kg/mol with a molecular weight distribution of 1.07–1.63. The chemical structures of the USPEAs were confirmed by both IR and NMR spectra. The USPEA copolymers had glass transition temperatures lower than that of pure UPEA but higher than that of pure SPEA. An increase in the unsaturated component in the USPEA copolymers led to an increase in their glass transition temperatures. The solubility of the copolymers was good in N,N‐dimethylacetamide and dimethyl sulfoxide but poor in water, acetone, methanol, and ethyl acetate. The preliminary in vitro biodegradation properties of the USPEA copolymers were investigated in both pure phosphate buffered saline (PBS) buffer and α‐chymotrypsin solutions. The copolymers showed significantly faster weight loss in an enzyme solution than in a pure PBS buffer. Upon the adjustment of the unsaturated‐to‐saturated diester monomer feed ratio, the obtained USPEA copolymers could have controlled chemical and physical properties, such as glass transition temperatures, solubility, and biodegradability, which could easily extend their applications to biomedical and pharmaceutical areas. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1595–1606, 2007

The microfabricated electrokinetic pump: a potential promising drug delivery technique

Directly delivering liquid using direct current power was a dream for 40 years. Now, the electrokinetic pump can accomplish it. This review reports recent developments in microfabricated electrokinetic pump technologies and their applications, and also discusses the electrophoresis pump and elctroosmotic pump, as well as the materials and fabrication methods frequently used for the production of these pump devices. Electrokinetics pumps can be used to deliver pure water, pure polar organic solvents, inorganic buffer and biomacromolecules, with wide applications for the delivery of liquids. These devices have the potential to become drug delivery systems, for the precise, timed and/or targeted delivery of drugs. Future trends, limitations and possibilities are also discussed.

The morphology of DNA solution in an open fluidic channel studied by non-contact AFM

The morphologies of pure buffer solution and DNA-containing solution in an open fluidic channel with rectangle cross section (1 μm in width and 150 nm in depth) have been explored using non-contact AFM. A remarkable feature is that a uniform nano-scale trench (∼15 nm deep and 14 μm long) on the surface of the DNA solution has been observed. The presence of two neighboring stretched DNA molecules near the solution surface may be responsible for the configuration of the nanotrench. This new phenomenon of partially stretched DNA molecules is likely to be useful for the future designing of fluidic devices, and for the manipulation and study of single DNA molecules.

Hydrophobic Forces and Hydrogen Bonds in the Adhesion between Retinoid-Coated Surfaces

Interactions between hydrophobic chains of lipid monolayers and interactions between hydrophilic headgroups of lipid bilayers (with or without a molecular recognition step) are now well documented, especially for commonly used lipids. Here, we report force measurements between a new class of fluorinated lipid layers whose headgroups (synthetic ligands of retinoid receptors) display a very unusual polar/apolar character and can interact via a combination of hydrophobic forces and hydrogen bonds. Although these two interactions produce adhesion and are therefore not easily distinguishable, we show that it is possible to extract both contributions unambiguously. Experiments are performed both in pure water, where the adhesion is a combination of hydrophobic forces and hydrogen bonds, and in Tris buffer, where the hydrophobic effect is the dominant short-range attractive force. The contribution of hydrophobic forces scaled down to molecular interactions is deduced from force versus distance profiles, and the same value is found independently in pure water and Tris buffer, about 1 kBT. We also show that retinoid lipid layers attract each other through a very long-range (100 nm) exponential force, which is insensitive to the pH and the salinity. The origin of this long-range attraction is discussed on the basis of previously proposed mechanisms.

Controlled release of paclitaxel from biodegradable unsaturated poly(ester amide)s/poly(ethylene glycol) diacrylate hydrogels

Biodegradable hydrogels (FPBe-G) were synthesized by the photopolymerization of two precursors: FPBe, a fumurate-based unsaturated poly(ester amide) (UPEA), and poly(ethylene glycol) diacrylate (PEG-DA). Depending on the feed ratio of these two precursors, the resultant FPBe-G hydrogels showed different crosslinking levels of network structure, mesh sizes (ξ) and matrix morphology. When a lipophilic drug, paclitaxel, was preloaded into FPBe-G hydrogels, the two-month drug-release kinetics from FPBe-G hydrogels in both pure PBS buffer and α-chymotrypsin media were measured. The paclitaxel-preloaded FPBe-G hydrogels in a α-chymotrypsin solution had significantly faster drug release rate than the corresponding hydrogels in a pure PBS buffer due to an enzyme catalyzed biodegradation of FPBe-G hydrogels. Sustained paclitaxel releases over a two-month period without initial burst release were also achieved by using hydrogels having certain feed ratios of hydrogel precursors. These paclitaxel release data correlated well with the molecular mesh size (ξ), molecular weight between cross-links (M c) and matrix morphological structure of FPBe-G hydrogels.

Master equation simulations of competing unimolecular and bimolecular reactions: application to OH production in the reaction of acetyl radical with O2

Master equation calculations were carried out to simulate the production of hydroxyl free radicals initiated by the reaction of acetyl free radicals (CH3(C=O).) with molecular oxygen. In particular, the competition between the unimolecular reactions and bimolecular reactions of vibrationally excited intermediates was modeled by using a single master equation. The vibrationally excited intermediates (isomers of acetylperoxyl radicals) result from the initial reaction of acetyl free radical with O2. The bimolecular reactions were modeled using a novel pseudo-first-order microcanonical rate constant approach. Stationary points on the multi-well, multi-channel potential energy surface (PES) were calculated at the DFT(B3LYP)/6-311G(2df,p) level of theory. Some additional calculations were carried out at the CASPT2(7,5)/6-31G(d) level of theory to investigate barrierless reactions and other features of the PES. The master equation simulations are in excellent agreement with the experimental OH yields measured in N2 or He buffer gas near 300 K, but they do not explain a recent report that the OH yields are independent of pressure in nearly pure O2 buffer gas.

Embedding a Reporter

CHEMISTRY The nitrile (CN) group can be a useful infrared reporter in proteins because it has a strong stretching vibration near ∼2200 cm−1, a spectral region usually free from interfering absorptions in a biochemical environment. Schultz et al. have devised a protocol to introduce the non-naturally occurring amino acid para- cyano-l-phenylalanine (pCNPhe) into proteins during bacterial synthesis, using an orthogonal nonsense suppressor transfer RNA (tRNA) paired with an aminoacyl tRNA synthetase derived from Methanococcus janannaschi. They apply this system to incorporate the pCNPhe reporter in place of a histidine residue (His64) near the ligand-binding site of the heme group in myoglobin. When water was bound in the active site, they observed an 11-cm−1 shift in frequency relative to pCNPhe absorption in pure water or buffer solution, a change consistent with increased water polarity in the binding pocket. Changes in the observed CN stretching frequency were also consistent with the bent conformations of Fe(II)-bound NO and O2, as well as the linear CO-Fe(II) complex. — PDS J. Am. Chem. Soc. 128 , 10.1021/ja0636690 (2006).

Compact second generation kinetically enhanced copper vapor laser at 10kHz repetition rate

A simple, compact, 60W second generation kinetically enhanced copper vapor laser (KE-CVL) optimized at repetition rate of ∼10kHz is demonstrated using a 25mm bore and a 1m length discharge tube with reduced thermal insulation. Recrystallized alumina tube (45mm bore) is used as an outer enclosure to contain a discharge tube and a thin layer of alumina fibrous thermal insulation for achieving compactness, ruggedness, and reliability in the KE-CVL. Double thyratron pulse modulator has been used for minimizing the switching stresses in the discharge circuit without using snubber circuit and magnetic assist. Specific output power of ∼122W∕liter was achieved with input power of ∼4.5kW and moderate charging voltage of ∼13.5kV (dc supply voltage ∼6.75kV). Specific output energy of ∼12mJ∕cm3 (at 10kHz repetition rate) was achieved as compared to ∼8mJ∕cm3 (at 25kHz) in a 25mm bore KE-CVLs reported previously. The design modifications and KE effects combined are the main reasons for many-fold increase in total output power and energy as compared to standard elemental copper vapor lasers of similar discharge tube and circuitry using pure neon buffer gas at ∼10kHz repetition rate. Warm-up time of about 0.25h was achieved in this compact KE-CVL.

Use of PLL-g-PEG in Micro-Fluidic Devices for Localizing Selective and Specific Protein Binding

By utilizing flow-controlled PLL-g-PEG and PLL-g-PEGbiotin modification of predefined regions of a poly(dimethylsiloxane) (PDMS) micro-fluidic device, with an intentionally chosen large (approximately 1 cm2) internal surface area, we report rapid (10 min), highly localized (6 x 10(-6) cm2), and specific surface-based protein capture from a sample volume (100 microL) containing a low amount of protein (160 attomol in pure buffer and 400 attomol in serum). The design criteria for this surface modification were achieved using QCM-D (quartz crystal microbalance with energy dissipation monitoring) of serum protein adsorption onto PLL-g-PEG-modified oxidized PDMS. Equally good, or almost as good, results were obtained for oxidized SU-8, Topas, and poly(methyl metacrylate) (PMMA), demonstrating the generic potential of PLL-g-PEG for surface modification in various micro-fluidic applications.

Cooperative Adsorption of Ezrin on PIP2-Containing Membranes

By means of the quartz crystal microbalance (QCM) and scanning force microscopy (SFM), the adsorption of ezrin, a member of the ezrin/radixin/moesin protein family, on l-alpha-phosphatidylinositol-4,5-bisphosphate (PIP(2)) containing solid-supported membranes was investigated. An increase in the PIP(2) content in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes resulted in an increased amount of bound ezrin strongly supporting the crucial role of PIP(2) for ezrin recruitment to membranes. No ezrin adsorption to membranes composed of pure POPC was detected. To characterize the binding process in more detail, the kinetics and reversibility of ezrin adsorption were investigated by the QCM technique, showing that the protein remains partly bound after rinsing with pure buffer, which we suspected to be a result of lateral interactions between the proteins. SFM images revealed the formation of two-dimensional ezrin clusters on PIP(2)-doped POPC membranes. Time-elapsed SFM images show that the growth of protein domains occurs from a few nucleation sites. The QCM data in conjunction with the results obtained by SFM led us to propose that the binding process of ezrin occurs in a positive cooperative manner. When lateral interactions of the proteins on the membrane were taken into account, we were able to simulate the kinetics obtained from time-resolved QCM readouts by employing a model developed by Minton. On the basis of the kinetic analysis, we were also able to reconstruct the adsorption isotherm.