Maximal Surface Coverage Research Articles

Whole-genome sequence of the filamentous diazotrophic cyanobacterium Tolypothrix sp. PCC 7712 and its comparison with non-diazotrophic Tolypothrix sp. PCC 7601.

Cyanobacteria are highly promising microorganisms in forthcoming biotechnologies. Besides the systematic development of molecular tools for genetic engineering, the design of chassis strains and novel reactor concepts are in focus. The latter includes capillary biofilm reactors (CBR), which offer a high surface area-to-volume ratio and very high cell densities. In this context, Tolypothrix sp. PCC 7712 was found to be highly suited for this reactor system due to maximal surface coverage, extraordinarily strong biofilm attachment, and high biomass formation. Here, we provide the genome sequence of Tolypothrix sp. PCC 7712 to potentially allow targeted strain engineering. Surprisingly, it was almost identical to an available incomplete genome draft of Tolypothrix sp. PCC 7601. Thus, we completely sequenced this strain as well and compared it in detail to strain PCC 7712. Comparative genome analysis revealed 257 and 80 unique protein-coding sequences for strains PCC 7601 and PCC 7712, respectively. Clustering genomes based on average nucleotide identity (ANI) and 16S rRNA homology showed 99.98% similarity and only minor distance, respectively, between the two strains in contrast to 21 other cyanobacterial genomes. Despite these high similarities, both strains differ in the ability to fix atmospheric nitrogen and show specific sequence variations, which are discussed in the paper.

Aesculus hippocastanum seeds extract as eco-friendly corrosion inhibitor for desalination plants: Experimental and theoretical studies

In this work, Aesculus Hippocastanum Seeds (AHS) extract has been used as a sustainability and environmentally corrosion inhibitor to reduce the risk of copper alloy corrosion during the acid cleaning process in desalination plants. This extract contains mostly Quercetin 3,4-diglucoside, Aesculin, escin Ia, escin Ib, isoescin Ia, isoescin Ib, Leucocyanidin, Fraxin, Procyanidin A2, Quercetin, and Kaempferol, according to HPLC analysis. At 100 ppm, the AHS extract showed a 96.1 percent inhibitory efficacy as a corrosion inhibitor. The findings demonstrate that AHS is an effective mixed–type corrosion inhibitor. The AHS extract solution has a greater activation energy value (i.e. 7.32 kJ mol−1) than the blank system (i.e. 15.65 kJ mol−1), indicating a physical adsorption process. Furthermore, the Langmuir adsorption pattern is applied to describe AHS extract adsorption. The electron dispersion in inhibitor compounds was revealed by quantum calculations, revealing their capacity to accept/donate charges from Cu-Ni atoms in vacuum and in water solvation. The extract molecules adsorbed on the copper alloy surface in a nearly flat orientation to acquire maximal surface coverage and contact, according to a molecular dynamics simulation.

Optimal Wells Placement to Maximize the Field Coverage Using Derivative-Free Optimization

Abstract Mining optimization in oil and gas industry has been an important task. The production volume of oil and gas crucially depends on many factors. One of them is wells location. This study contributes to the domain of oil and gas exploration and extraction. We solve the problem of optimal wells placement on 2-D surface. We have developed a set of criteria and chosen a proportion of the field covered as objective function. In order to find the best solution satisfying these criteria, we compared different optimization algorithms. Such as, Nelder-Mead method, simulated annealing, Bayesian optimization and genetic algorithm in order to reach the maximal surface coverage with minimal number of wells in a region. To test the application of the developed algorithm on complex polygons (oil fields), we have made a generator of synthetic polygons. In this study we also compare the efficiency of regular and irregular wells placement.

Matter-tag: A universal immobilization platform for enzymes on polymers, metals, and silicon-based materials.

Enzyme immobilization is extensively studied to improve enzyme properties in catalysis and analytical applications. Here, we introduce a simple and versatile enzyme immobilization platform based on adhesion-promoting peptides, namely Matter-tags. Matter-tags immobilize enzymes in an oriented way as a dense monolayer. The immobilization platform was established with three adhesion-promoting peptides; Cecropin A (CecA), liquid chromatography peak I (LCI), and Tachystatin A2 (TA2), that were genetically fused to enhanced green fluorescent protein and to two industrially important enzymes: a phytase (from Yersinia mollaretii) and a cellulase (CelA2 from a metagenomic library). Here, we report a universal and simple Matter-tag-based immobilization platform for enzymes on various materials including polymers (polystyrene, polypropylene, and polyethylene terephthalate), metals (stainless steel and gold), and silicon-based materials (silicon wafer). The Matter-tag-based enzyme immobilization is performed at ambient temperature within minutes (<10 min) in an aqueous solution harboring the phytase or cellulase by immersing the targeted material. The peptide LCI was identified as universal adhesion promoter; LCI immobilized both enzymes on all investigated materials. The attachment of phytase-LCI onto gold was characterized with surface plasmon resonance spectroscopy obtaining a dissociation constant value (KD ) of 2.9·10-8 M and a maximal surface coverage of 504 ng/cm².

Thermal stability of hydrophilic PEO-silane modified ceramic membranes

Industrial oily wastewaters often contain many recalcitrant species, such as dissolved metal ions, salts, bitumen, clays and humics. These species possess surface charges due to acidic, basic and amphoteric groups, thus leading to severe ceramic membrane fouling. To address this problem, ceramic membrane surfaces were chemically modified with highly hydrophilic PEO-based organosilanes. Three different membrane surface layers (ZrO2-TiO2, ZrO2 and TiO2) were modified at varying silane concentrations and reaction times to test their reactivity and stability. All modified membranes maintained hydrophilic behavior, as shown by water contact angles of <25° and pure water fluxes of 500–600 Lmh. Modified TiO2 membranes exhibited superhydrophilicity with contact angles <10°. It was found that TiO2 membranes were the most reactive, achieving maximal silane surface coverage at lower concentrations and reaction times, followed by ZrO2 and ZrO2-TiO2 membranes. The silylated TiO2 membrane was also the most thermally stable surface at 130 °C and 160 °C. Increasing the length of the PEO chain in the silane was also found to increase the thermal stability of the silane surface. TiO2 membranes modified with the higher molecular weight silane maintained 97% of the silane at the membrane surface when exposed to heat at 130 °C. In enhancing the suitability of ceramic membranes in challenging applications; titania membranes over zirconia and zirconia-titania should be used and modified with PEO-silanes containing 9–12 repeat units to ensure maximal surface coverage and enhanced thermal stability.

Fabrication of Photoreactive Biocomposite Coatings via Electric Field-Assisted Assembly of Cyanobacteria.

We report how dielectrophoresis (DEP) can be used as a tool for the fabrication of biocomposite coatings of photoreactive cyanobacteria (Synechococcus PCC7002) on flexible polyester sheets (PEs). The PE substrates were precoated by a layer-by-layer assembled film of charged polyelectrolytes. In excellent agreement between experimental data and numerical simulations, the directed assembly process driven by external electric field results in the formation of 1D chains and 2D sheets by the cells. The preassembled cyanobacteria chains and arrays became deposited on the substrate and remained in place after the electric field was turned off due to the electrostatic attraction between the negatively charged cell surfaces and the positively charged polyelectrolyte-coated PE. The DEP-assisted packing of cyanobacteria is close to the maximal surface coverage of ∼70% estimated from convectively assembled monolayers. Confocal laser scanning microscopy and spectrophotometry confirm that the photosynthetic pigment integrity of the Synechococcus cells is preserved after DEP immobilization. The significant decrease of the light scattering and the enhanced transmittance of these field-assembled cyanobacteria coatings demonstrate reduced self-shading compared to suspension cultures. Thus, we achieved the assembly of structured cyanobacteria coatings that optimize cell surface coverage and preserve cell viability after immobilization. This is a step toward the development of flexible multilayered cell-based photoabsorbing biomaterials that can serve as components of "biomimetic leaves" for utilizing solar energy to recycle CO2 into fuels or chemicals.

Urea-SCR 시스템의 NH3흡·탈착 특성 및 모델기반 제어 연구

Urea-SCR system is currently regarded as promising NOx reduction technology for diesel engines. SCR system has to achieve maximal NOx conversion in combination with minimal NH3 slip. In this study, model based open loop control for urea injection was developed and assessed in the European Transient Cycle (ETC) for heavy duty diesel engine. On the basis of the transient modeling, the kinetic parameters of the NH3 adsorption and desorption are calibrated with the experimental results performed over the zeolite based catalyst. NH3 storage or surface coverage of SCR catalyst can not be measured directly and has to be calculated, which is taken into account as a control parameter in this model. In order to reduce NH3 slip while maintaining NOx reduction, NH3 storage control algorithm was applied to correct the basic urea quantity. If the actual NH3 surface coverage is higher than the maximal NH3 surface coverage, the urea injection quantity is significantly reduced in the ETC cycle. By applying this logic, the resulting NH3 slip peak can be avoided effectively. With optimizing the kinetic parameters based on standard SCR reaction, it suggests that a simplified, less accurate model can be effective to evaluate the capability of model based control in the ETC cycle.

Discrete Complexes Immobilized onto Click-SBA-15 Silica: Controllable Loadings and the Impact of Surface Coverage on Catalysis

Azidopropyl functionalized mesoporous silica SBA-15 were prepared with variable azide loadings of 0.03-0.7 mmol g(-1) (~2-50% of maximal surface coverage) through a direct synthesis, co-condensation approach. These materials are functionalized selectively with ethynylated organic moieties through a copper-catalyzed azide alkyne cycloaddition (CuAAC) or "click" reaction. Specific loading within a material can be regulated by either the azide loading or limiting the alkyne reagent relative to the azide loading. The immobilization of ferrocene, pyrene, tris(pyridylmethyl)amine (TPA), and iron porphyrin (FeTPP) demonstrates the robust nature and reproducibility of this two-step synthetic attachment strategy. Loading-sensitive pyrene fluorescence correlates with a theoretically random surface distribution, rather than a uniform one; site-isolation of tethered moieties ~15 Å in length occurs at loadings less than 0.02 mmol g(-1). The effect of surface loading on reactivity is observed in the oxygenation of SBA-15-[Cu(I)(TPA)]. SBA-15-[Mn(II)(TPA)]-catalyzed epoxidation exhibits a systematic dependence on surface loading. A comparison of homogeneous, site-isolated and site-dense complexes provides insight into catalyst speciation and ligand activity.

Cationized albumin-biocoatings for the immobilization of lipid vesicles

Tethered lipid membranes or immobilized lipid vesicles are frequently used as biomimetic systems. In this article, the authors presented a suitable method for efficient immobilization of lipid vesicles onto a broad range of surfaces, enabling analysis by quantitative methods even under rigid, mechanical conditions-bare surfaces such as hydrophilic glass surfaces as well as hydrophobic polymer slides or metal surfaces such as gold. The immobilization of vesicles was based on the electrostatic interaction of zwitterionic or negatively charged lipid vesicles with two types of cationic chemically modified bovine serum albumin (cBSA) blood plasma proteins (cBSA-113 and cBSA-147). Quantitative analysis of protein adsorption was performed as the cBSA coatings were characterized by atomic force microscopy, surface zeta potential measurement, fluorescence microscopy, and surface plasmon spectroscopy, revealing a maximal surface coverage 270-280 ng/cm(2) for 0.02 mg/ml cBSA on gold. Small unilamellar vesicles as well as giant unilamellar vesicles (GUVs) were readily immobilized (∼15 min) on cBSA coated surfaces. GUVs with 5-10 mol% negatively charged 1,2,-dipalmitoyl-sn-glycero-3-phosphoglycerol remained stable in liquid for at least 5 weeks.

Covalent immobilization of redox protein via click chemistry and carbodiimide reaction: Direct electron transfer and biocatalysis

In this paper, a simple, facile and general strategy was proposed for the covalent biofunctionalization of Au surface with hemoglobin (Hb). Structurally well-defined azide-terminated organic self-assembled monolayers (SAMs) were formed on Au surface from a mixture solution of azidoundecanethiol and dilute thiol. 4-Pentynoic acid was used as a bifunctional linker to immobilized Hb via a selective, reliable, robust click reaction and a widely used carbodiimide reaction. The surface modification was characterized by reflectance absorption infrared (RAIR) spectroscopy, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The experimental data indicate that the proposed methodology is a highly versatile strategy for quantitative, stable and covalent attachment of biomacromolecules onto solid interface. The Hb functionalized Au electrode shows a pair of well-defined and quasi-reversible peaks at about −0.210 V (vs. SCE) in 0.1 mol/L pH 5.0 buffers, which stands for the reduction and oxidation of Hb Fe(III)/Fe(II) redox couple. The electron transfer rate constant ( k s ) was estimated to be 0.78 s −1. The maximal surface coverage ( Г) of the immobilized Hb was 8.3 × 10 −12 mol cm −2, indicating the formation of a monolayer. Moreover, the biocatalytic activity of the Hb biofunctonalized electrode was investigated and an excellent electrocatalytic reduction toward O 2 and H 2O 2 was observed.

Characterization of metal cations-complexing polymer films interactions followed with anodic stripping voltammetry

The complexing ability of thin poly(3-pyrrol-1-ylpropyl)malonic acid films coated onto glassy carbon disc electrode surfaces was evaluated towards Pb(II) and Cu(II) ions, using the chemical preconcentration-anodic stripping method. The affinity of these metal cations for the complexing film modified electrodes and their maximal surface coverage rate could be evaluated from a Langmuir isotherm model coupled to the chemical preconcentration-anodic stripping technique. Isothermal studies conducted between 293 and 308 K allowed to estimate enthalpy and entropy variations associated to the metal sorption, which expectedly proved to fit chemisorption processes. As judged from the estimated binding constants, Pb(II) ions turned out to present a higher affinity for the functionalized surface than the smaller Cu(II) species. The mobilization of a higher number of malonic acid units per metal cation upon complexation of Pb(II), as compared to Cu(II), is however believed to account for the estimated lower Pb(II) surface coverage. The combination of the Langmuir isotherm model to the chemical preconcentration-anodic stripping technique is thus revealed to be an efficient method to characterize the complexing ability of complexing film electrode surface.

The detection of HBV DNA with gold-coated iron oxide nanoparticle gene probes.

Gold-coated iron oxide nanoparticle Hepatitis B virus (HBV) DNA probes were prepared, and their application for HBV DNA measurement was studied. Gold-coated iron oxide nanoparticles were prepared by the citrate reduction of tetra-chloroauric acid in the presence of iron oxide nanoparticles which were added as seeds. With a fluorescence-based method, the maximal surface coverage of hexaethiol 30-mer oligonucleotides and the maximal percentage of hybridization strands on gold-coated iron oxide nanoparticles were (120 ± 8) oligonucleotides per nanoparticle, and (14 ± 2%), respectively, which were comparable with those of (132 ± 10) and (22 ± 3%) in Au nanoparticle groups. Large network aggregates were formed when gold-coated iron oxide nanoparticle HBV DNA gene probe was applied to detect HBV DNA molecules as evidenced by transmission electron microscopy and the high specificity was verified by blot hybridization. Our results further suggested that detecting DNA with iron oxide nanoparticles and magnetic separator was feasible and might be an alternative effective method.

The detection of HBV DNA with gold nanoparticle gene probes

Objective Gold nanoparticle Hepatitis B virus(HBV) DNA probes were prepared, and their application for HBV DNA measurement was studied. Methods Alkanethiol modified oligonucleotide was bound with self-made Au nanoparticles to form nanoparticle HBV DNA gene probes, through covalent binding of Au-S. By using a fluorescence-based method, the number of thiolderivatized, single-stranded oligonucleotides and their hybridization efficiency with complementary oligonucleotides in solution was determined. With the aid of Au nanoparticle-supported mercapto-modified oligonucleotides serving as detection probes, and oligonucleotides im-mobilized on a nylon membrane surface acting as capturing probes, HBV DNA was detected visually by sandwich hybridization based on highly sensitive aggregation and silver staining. The modified nanoparticle HBV DNA gene probes were also used to detect the HBV DNA extracted from serum in patients with hepatitis B. Results Compared with bare Au nanoparticles, oligonucleotide modified nanoparticles had a higher stability in NaCl solution or under high temperature environment and the absorbance peak of modified Au nanoparticles shifted from 520 nm to 524 nm. For Au nanoparticles, the maximal oligonucleotide surface coverage of hexaethiol 30-mer oligonucleotide was(132 ± 10) oligonucleotides per nanoparticle, and the percentage of hybridization strands on nanoparticles was(22 ± 3%). Based on a two-probe sandwich hybridization/nanoparticle amplification/silver staining enhancement method, Au nanoparticle gene probes could detect as low as 10 −11 mol/L composite HBV DNA molecules on a nylon membrane and the PCR products of HBV DNA visually. As made evident by transmission electron microscopy, the nanoparticles assembled into large network aggregates when nanoparticle HBV DNA gene probes were applied to detect HBV DNA molecules in liquid. Conclusion Our results showed that successfully prepared Au nanoparticle HBV DNA gene probes could be used to detect HBV DNA directly. The detection-visuallized method has many advantages, including high sensitivity, simple operation and low cost. This technique has potential applications in many fields, especially in multi-gene detection chips.

Thermodynamic Roles of Basic Amino Acids in Statherin Recognition of Hydroxyapatite

Salivary statherin is a highly acidic, 43 amino acid residue protein that functions as an inhibitor of primary and secondary crystallization of the biomineral hydroxyapatite. The acidic domain at the N-terminus was previously shown to be important in the binding of statherin to hydroxyapatite surfaces. This acidic segment is followed by a basic segment whose role is unclear. In this study, the role of the basic amino acids in the hydroxyapatite adsorption thermodynamics has been determined using isothermal titration calorimetry and equilibrium adsorption isotherm analysis. Single point mutations of the basic side chains to alanine lowered the binding affinity to the surface but did not perturb the maximal surface coverage and the adsorption enthalpy. The structural and dynamic properties of the single point mutants as characterized by solid-state NMR techniques were not altered either. Simultaneous replacement of all four basic amino acids with alanine lowered the adsorption equilibrium constant by 5-fold and the maximal surface coverage by nearly 2-fold. The initial exothermic phase of adsorption exhibited by native statherin is preserved in this mutant, along with the alpha-helical structure and the dynamic properties of the N-terminal domain. These results help to refine the two binding site model of statherin adsorption proposed earlier in our study of wild-type statherin (Goobes, R., Goobes, G., Campbell, C.T., and Stayton, P.S. (2006) Biochemistry 45, 5576-5586). The basic charges function to reduce protein-protein charge repulsion on the HAP surface, and in their absence, there is a considerable decrease in statherin packing density on the surface at binding saturation.

Structure–Function Analysis of the Emulsifying and Interfacial Properties of Apomyoglobin and Derived Peptides

Apomyoglobin was chosen as a model to study the emulsifying properties of proteins. It was cleaved into three peptides using cyanogen bromide and these peptides were purified and tested for emulsifying and interfacial properties. Two of the peptides had improved emulsifying activity compared to the whole protein. The peptide (residues 1–55) with the highest emulsifying activity and whole apomyoglobin were studied further. The amount of protein or peptide adsorbed at the oil–water interface of an emulsion was measured and the surface area occupied per molecule was calculated. For apomyoglobin, at maximal surface coverage each molecule occupied a surface area of ∼8 nm2. This is consistent with a packed monolayer, based on the approximate dimensions of apomyoglobin. For peptide (1–55), at maximal surface coverage each molecule occupied a surface area of ∼3 nm2. This is consistent with the area that the two amphipathic α-helices which are potentially present in this molecule would cover, if they were aligned along the oil–water interface. The different structural characteristics of these molecules responsible for their emulsifying properties are discussed.

Adsorption Behavior of Polyelectrolytes on Barium Sulfate Crystals

For two polyphosphinoacrylates, PPAA-I and PPAA-II, and a random copolymer of maleic acid and vinyl sulfonic acid, PMA-PVS, the levels of adsorption equilibrium on BaSO4 crystals were determined as a function of their concentration and related to the formerly established growth-inhibiting effect of these compounds on BaSO4 crystallization. The best growth retarder of the two polyphosphinoacrylates, PPAA-II, reaches a higher surface coverage than PPAA-I which has a lower molecular weight. Such a relationship between inhibitor effect, maximal surface coverage, and molecular weight is only valid for structurally identical compounds. For the better growth retarder, PMA-PVS, a lower maximal surface coverage was found than for the structurally different PPAA-II. From the adsorption isotherms of PMA-PVA and PPAA-II, the equilibrium surface coverages at the PMA-PVS and PPAA-II concentrations which cause total growth blockage (0.2 ppm and 0.5 ppm, respectively) could be derived. This resulted in equilibrium surface coverages of ≈3.8 × 10-3 mg m-2 for PMA-PVS and ≈6.6 × 10-3 mg m-2 for PPAA-II.To determine whether matching between the inhibitor molecules and the crystal surface layer of BaSO4 plays a role in its performance, the shape and morphology of BaSO4 crystals were examined after long-term growth experiments in the presence of PMA-PVS and PPAA-II. The development of the {011} and {101} faces in the presence of PMA-PVS points at an easy replacement of the lattice sulfate ions with one S-O bond orientated perpendicular to the crystal surface by sulfonate ions of PMA-PVS. In the presence of PPAA-II, striations were observed in the 〈010〉 directions which might be related to a good fitting between the interatomic lattice distances in these directions and the mutual distances of the functional carboxylate groups of the inhibitor.

Human serum albumin adsorption onto octadecyldimethylsilyl-silica gradient surface

The effects of long-range electrostatic repulsion and short-range hydrophobic attraction on human serum albumin adsorption were studied as a function of the surface density of octadecyldimethylsilyl chains (C18) on silica. A C18 surface density gradient was prepared on fused silica plates. The water contact angles increased smoothly from 12° to 105° in the 12.5 mm long gradient region. The maximal fractional surface coverage of the C18 chains was calculated to be 0.92. Fluorescein-5-isothiocyanate-labeled human serum albumin (FITC-HSA) adsorption from dilute buffer solution onto the C18 gradient surface was measured using spatially resolved total internal reflection fluorescence (TIRF) spectroscopy. FITC-HSA adsorbed progressively more onto the surfaces with higher hydrophobicity. When the fractional surface coverage of C18 chains was larger than 0.42 the adsorption saturation of FITC-HSA leveled off. The adsorption kinetics of FITC-HSA changed from a transport-limited process at moderate-to-high C18 surface coverages to an adsorption-limited process at lower C18 surface coverages. The kinetics of FITC-HSA adsorption, including the convective-diffusive transport of protein to the surface, were modeled as a simple binding process with a single forward and reverse rate. The apparent binding constant, derived from the initial forward and reverse binding rates, depended more strongly on the C18 surface coverage in 0.165 M buffer than in 0.025 M buffer.

Testing protein adsorption models by off-null ellipsometry: Determination of binding constants from a single adsorption curve

The kinetics of prothrombin adsorption on planar bilayers, prepared from 40% dioleoyl phosphatidylserine and 60% dioleoyl phosphatidylcholine, are studied by off-null ellipsometry. A simple expression for the adsorption rate is derived directly from measured adsorption rates. The interpretation of this expression in terms of transport processes shows that up to a surface coverage Γ = 1.8 pmol cm −2, i.e. 50% of the maximal surface coverage Γ max, the adsorption rate appears to be regulated by diffusion-limited transport of prothrombin from the bulk solution to the adsorbing surface. The adsorption rate is proportional to the concentration difference between the bulk and the solution immediately adjacent to the surface. The latter concentration appears to be instantaneously in equilibrium with the surface excess, conforming to the classical Langmuir isotherm. For low surface coverages, below 50% of maximal adsorption, the kinetics are thus described by a simple model containing the mass transfer coefficient, the dissociation constant K d and the maximal surface coverage Γ max, With known Γ max this model allows the estimation of K d from a single adsorption curve. However, for surface coverages exceeding 60% of maximal adsorption, drastic deviations from this model are found. The intrinsic adsorption rate is substantially reduced, presumably by surface exclusion.