Differential Adsorption Research Articles

Microfluidic deposition for resolving single-molecule protein architecture and heterogeneity

Scanning probe microscopy provides a unique window into the morphology, mechanics, and structure of proteins and their complexes on the nanoscale. Such measurements require, however, deposition of samples onto substrates. This process can affect conformations and assembly states of the molecular species under investigation and can bias the molecular populations observed in heterogeneous samples through differential adsorption. Here, we show that these limitations can be overcome with a single-step microfluidic spray deposition platform. This method transfers biological solutions to substrates as microdroplets with subpicoliter volume, drying in milliseconds, a timescale that is shorter than typical diffusion times of proteins on liquid–solid interfaces, thus avoiding surface mass transport and change to the assembly state. Finally, the single-step deposition ensures the attachment of the full molecular content of the sample to the substrate, allowing quantitative measurements of different molecular populations within heterogeneous systems, including protein aggregates.

Motile bacteria in a critical fluid mixture.

We studied the swimming of Escherichia coli bacteria in the vicinity of the critical point in a solution of the nonionic surfactant C_{12}E_{5} in buffer solution. In phase-contrast microscopy, each swimming cell produces a transient trail behind itself lasting several seconds. Comparing quantitative image analysis with simulations show that these trails are due to local phase reorganization triggered by differential adsorption. This contrasts with similar trails seen in bacteria swimming in liquid crystals, which are due to shear effects. We show how our trails are controlled, and use them to probe the structure and dynamics of critical fluctuations in the fluid medium.

A flow-pulse adsorption-microcalorimetry system for studies of adsorption processes on powder catalysts.

A pulse chemisorption system combining a Tian-Calvet microcalorimeter (Setaram Sensys EVO 600) and an automated chemisorption apparatus (Micromeritics Autochem II 2920) was established to accurately measure differential adsorption heats of gas molecules' chemisorption on solid surfaces in a flow-pulse mode. Owing to high sensitivity and high degree of automation in a wide range of temperatures from -100 to 600 °C, this coupled system can present adsorption heats as a function of adsorption temperature and adsorbate coverage. The functions of this system were demonstrated by successful measurements of CO adsorption heats on Pd surfaces at various temperatures and also at different CO coverages by varying the CO concentration in the pulse dose. Key parameters, including adsorption amounts, integral adsorption heats, and differential adsorption heats of CO adsorption on a Pd/CeO2 catalyst, were acquired. Our adsorption-microcalorimetry system provides a powerful technique for the investigation of adsorption processes on powder catalysts.

Specific Interaction Sites Determine Differential Adsorption of Protein Structural Isomers on Nanoparticle Surfaces.

In biological systems, nanoparticles (NPs) elicit bioactivity upon interaction with proteins. As a result of post-translational modification, proteins occur in a variety of alternative covalent forms, including structural isomers, which present unique molecular surfaces. We aimed at a detailed description of the recognition of protein isomeric species by NP surfaces. The transient adsorption of isomeric ubiquitin (Ub) dimers by NPs was investigated by solution NMR spectroscopy. Lys63- and Lys48-linked Ub2 were adsorbed by large anionic NPs with different affinities, whereas the binding strength was similar in the cases of smaller particles. After the incorporation of paramagnetic tags into NPs, the observed site-resolved paramagnetic footprints provided a high-resolution map of the different protein surfaces binding to NPs. The approach described could be extended to further protein isoforms and more specialized NP systems to allow better control of the interactions between NPs and protein targets.

Salt effects in surfactant-free microemulsions.

The weakly associated micellar aggregates found in the so-called "pre-ouzo region" of the surfactant-free microemulsion water/ethanol/1-octanol are sensitive to changes in the system composition and also to the presence of additives like salt. In this work, we study the influence of two salts, sodium iodide and lithium chloride, on aggregates in water/ethanol/1-octanol by molecular dynamics simulations. In both cases, ethanol concentration in the nonpolar phase and at the interface is increased due to a salting out effect on ethanol in the aqueous pseudo-phase. In addition, minor charging of the interface as a consequence of differential adsorption of anions and cations occurs. However, this charge separation is overall weakened by the erratic surface of octanol aggregates, where polar hydroxyl groups and hydrophobic patches are both present. Furthermore, ethanol at the interface shields hydrophobic patches and reduces the preferential adsorption of iodide and lithium.

Assessing the potential of nanoporous carbon adsorbents from polyethylene terephthalate (PET) to separate CO2 from flue gas

A series of nanoporous carbons was obtained by physical activation of polyethylene terephthalate and investigated for the separation of CO2 from flue gas. The prepared carbons exhibited extremely low functionalization—negligible content in oxygen and other heteroatoms—accompanied by well-developed porous networks consisting of gradually increasing surface areas and micropore volumes. Such features allowed to study the role of nanopore confinement in the separation of carbon dioxide in CO2/N2 gas mixtures. The analysis of the adsorption isotherms of individual gases and their mixtures revealed different trends for the CO2 uptake and the selectivity. Whereas CO2 uptake was larger in the carbons with higher burn-off degree, the selectivity of CO2 over N2 was favored in the carbons with a higher fraction of narrow micropores. The differential adsorption enthalpy curves are typical of highly microporous samples reaching values close to those found in zeolites for low loadings. Data also show that the choice of the best adsorbent for cyclic gas adsorption and separation processes should consider a broad context, taking into account various parameters simultaneously such as gas selectivity, working capacity, adsorption enthalpy and energy consumption in the synthesis of the adsorbent.

Pore structure characteristics of low- and medium-rank coals and their differential adsorption and desorption effects

The pores and methane adsorption-desorption characteristics are different between low- and medium-rank coal. For this paper, mercury intrusion porosimetry and isothermal adsorption experiments were carried out on thirteen coal samples with Ro,max between 0.22% and 0.98%. To evaluate the effect of the pore structure on coal permeability, we calculated the multi-scale fractal dimensions according to classic geometry models and discussed factors influencing pore fractals, including metamorphism degree, ash yield, and the content of vitrinite (huminite). Three key pressures in the stage of depressurization were calculated on the basis of Langmuir adsorption theory, and the influencing factors were discussed, including metamorphism degree, fractal dimension, and moisture content. The results show that pores of the coal can be divided into three types according to the pore diameter boundaries of 6,000 nm and 100 nm.The multi-scale fractal dimensions of coal pores (D1, D2, D3) are in the range of 2.341–2.836, 2.041 to 2.476, 2.237 to 2.656, respectively. The pore fractal dimension (D1) is controlled by the degree of metamorphism, and D3 is mainly affected by ash yield, the content of vitrinite (huminite), and the degree of metamorphism. The adsorption of low- and medium-rank coal is a step-by-step control mode under the control of coal metamorphism, in which lignite mainly depends on the moisture content, and long-flame coal-gas coal mainly depends on the adsorption-diffusion hole (<100 nm) pore structure. The lower the fractal dimension of adsorption pore, the better the adsorption. The higher the fractal dimension of the seepage pore, the better the seepage. Four desorption stages of the desorption process are subdivided according to three critical pressure points (starting pressure, transition pressure, and depletion pressure). The different critical pressure points are mainly affected by the degree of coal metamorphism, the pore structure characteristics of the primary seepage pore, and the moisture content. Larger Langmuir volume (VL) and ratio of Langmuir constants (1/PL) are beneficial to earlier advent of steady production stage, whereas it is also possible that the declining production stage may occur ahead of schedule.

Selective PEGylation of Parylene-C/SiO2 Substrates for Improved Astrocyte Cell Patterning

Controlling the spatial distribution of glia and neurons in in vitro culture offers the opportunity to study how cellular interactions contribute to large scale network behaviour. A recently developed approach to cell-patterning uses differential adsorption of animal-serum protein on parylene-C and SiO2 surfaces to enable patterning of neurons and glia. Serum, however, is typically poorly defined and generates reproducibility challenges. Alternative activation methods are highly desirable to enable patterning without relying on animal serum. We take advantage of the innate contrasting surface chemistries of parylene-C and SiO2 to enable selective bonding of polyethylene glycol SiO2 surfaces, i.e. PEGylation, rendering them almost completely repulsive to cell adhesion. As the reagents used in the PEGylation protocol are chemically defined, the reproducibility and batch-to-batch variability complications associated with the used of animal serum are avoided. We report that PEGylated parylene-C/SiO2 substrates achieve a contrast in astrocyte density of 65:1 whereas the standard serum-immersion protocol results in a contrast of 5.6:1. Furthermore, single-cell isolation was significantly improved on PEGylated substrates when astrocytes were grown on close-proximity parylene-C nodes, whereas isolation was limited on serum-activated substrates due tolerance for cell adhesion on serum-adsorbed SiO2 surfaces.

Theoretical and Experimental Studies of the Controlled Release of Tetracycline Incorporated into Bioactive Glasses.

Several authors have studied the release profile of drugs incorporated in different devices. However, to the best of our knowledge, although many studies have been done on the release of tetracycline, in these release devices, no study has investigated if the released compound is actually the tetracycline, or, instead, a degraded product. This approach is exploited here. In this work, we analyse the influence of two drying methods on the tetracycline delivery behaviour of synthesised glasses using the sol-gel process. We compare the drying methods results using both theoretical models and practical essays, and analyse the chemical characteristic of the released product in order to verify if it remains tetracycline. Samples were freeze-dried or dried in an oven at 37°C and characterised by several methods such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TG), differential thermogravimetric analysis (DTG), differential thermal analyses (DTA) and gas adsorption analysis (BET). The released concentration of tetracycline hydrochloride was studied as a function of time, and it was measured by ultraviolet spectrophotometry in the tetracycline wavelength. The drug delivery profiles were reasonably consistent with a diffusion model analysis. In addition, we observed higher release rates for the freeze-dried compared to those dried in an oven at 37°C. This higher release can be attributed to larger pore size for the freeze-dried sample systems with tetracycline, which promoted more water penetration, improving the drug diffusion. The analysis of the solution obtained in the release tests using high-performance liquid chromatography- mass spectrometry (HPLC-MS) confirmed that tetracycline was being released.

Efficient purification of a highly active H-subunit of tyrosinase from Agaricus bisporus

A highly-active tyrosinase (H subunit) isoform has been purified from a commercial crude extract of Agaricus bisporus by a specific, two step-hydrophobic chromatography cascade process based on the differential adsorption of the proteins from the extract to hydrophobic-functionalized supports.At first, commercial, crude tyrosinase from Agaricus bisporus (AbTyr) dissolved in aqueous media was added to octadecyl-Sepabeads matrix at 25 °C. Under these conditions, the support specifically adsorbed a protein with a molecular weight of 47 kDa which showed no tyrosinase activity. The known H subunit of tyrosinase from Agaricus bisporus (45 kDa, H-AbTyr) and another protein of 50 kDa were present in the supernatant. Sodium phosphate buffer was added to adjust the ionic strength of the solution up to 100 mM and Triton X-100 was added (final concentration of 0.07% v/v) to control the hydrophobicity effect for both proteins. This solution was offered again to fresh octadecyl-Sepabeads support, immobilizing selectively the H-AbTyr and leaving exclusively the 50 kDa protein as a pure sample in the supernatant. This tyrosinase isoform of 50 kDa was almost 4-fold more active than the known H-TyrAb, with a specific tyrosinase activity of more than 38,000 U/mg.

Adsorption Properties of a Silicagel Surface with Grafted Transition Metal Acetylacetonate Complexes

The adsorption properties of a Silipore 200 surface and chemically modified sorption materials containing nickel, cobalt, and copper acetylacetonates are studied via gas chromatography. n-Alkanes (C6–C9) and adsorbates, the molecules of which have different electron-donating and electron-acceptor properties, are used as test compounds. From experimental data on the retention of adsorbates; their differential molar adsorption heats \(\bar q_{dif,1}\); changes in standard differential molar entropy \(\Delta \bar S_{1,C}^S\); and, for polar adsorbates, contributions \(\Delta \bar q_{dif,1(specific)}\) to the energy of dispersive and specific interactions, are calculated. The effect the metal ion in the structure of acetylacetonate has on the characteristics of thermodynamic retention is shown.

Adsorption characteristics of clay minerals in shale

ABSTRACTBased on the adsorption potential theory, this paper describes the adsorption characteristics of four kinds of clay minerals, i.e. Montmorillonite, Kaolinite, Chlorite, and Illite, in clay shales, meanwhile adding quartzite as control sample. We focus on adsorption amount a, differential adsorption work A, characteristic energy E, characteristic coefficient n in adsorption potential analysis. The results show that the differential adsorption work decreases as the adsorption energy increases, which can generally represent the change features during each stage; the optimum value of n is around 1.5 for five kinds of inorganic minerals; E slightly decreases as the temperature increases. For clay minerals, the absolute values of adsorption heat and the result of maximum adsorption can meet that Montmorillonite> Kaolinite> Chlorite> Illite.

Morphological Effects of CuO Nanostructures on Fibrillation of Human Serum Albumin.

The influence of different morphologies of nanostructures on amyloid fibrillation has been investigated by monitoring the fibrillation of human serum albumin (HSA) in the presence of rod-, sphere-, flower-, and star-shaped copper oxide (CuO) nanostructures. The different morphologies of CuO have been synthesized from an aqueous solution-based precipitation method using various organic acids, viz., acetic acid, citric acid, and tartaric acid. The fibrillation process of HSA has been examined using various biophysical techniques, e.g., Thioflavin T fluorescence, Congo red binding studies through UV spectroscopy, circular dichroism spectroscopy, and fluorescence microscopy. The monolayer protein coverage on the CuO nanostructures has been established through DLS studies, and the well-fitted Langmuir isotherm model has been used to interpret the differential adsorption behavior of HSA molecules on the CuO nanostructures. The nanostar-shaped CuO, by virtue of their higher specific surface area (94.45 m2 g-1), presence of high indexed facets {211} and high positive surface charge potential (+16.2 mV at pH 7.0) was found to show the highest adsorption of the HSA monomers and thus was more competent to inhibit the formation of HSA fibrils compared to the other nanostructures of CuO.

Combined Reflectometric Interference Spectroscopy and Quartz Crystal Microbalance Detect Differential Adsorption of Lipid Vesicles with Different Phase Transition Temperatures on SiO2, TiO2, and Au Surfaces.

Quantitative analysis of biomolecular adsorption on a substrate is crucial for understanding biomolecular interactions. A quartz crystal microbalance (QCM) is a highly sensitive device to detect such interactions based on mass. However, the physicochemical analysis by the QCM alone often leads to overestimation of the actual adsorbed mass. Here, a combined reflectometric interference spectroscopy (RIfS) and QCM is developed to simultaneously analyze adsorption of biomolecules. RIfS detects the adsorbed mass based on the reflectance and predicts the adsorbed condition by modeling the reflection spectra using the transfer matrix method. In contrast, the QCM detects physicochemical characteristics of the adsorbed molecules along with the adsorbed mass. The combined RIfS-QCM successfully detected the adsorption of proteins with different surface properties and lipid vesicles with different phase transition temperatures. The initial stage of adsorption revealed distinct individual properties of the adsorbates. Moreover, the RIfS-QCM revealed differential adsorption of the vesicles on silicon dioxide, titania, and gold surfaces, and the differences in adsorption were further interrogated by atomic force microscopy. The results demonstrate that the RIfS-QCM serves as a useful tool to quantitatively analyze molecular adsorption on various surfaces.

Preparation and characterization of a porous silicate material from silica fume

A porous silicate material derived from silica fume was successfully prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, Thermogravimetry and Differential thermal gravity (TG-DTG), N2 adsorption and desorption isotherms, and scanning electron microscopy (SEM). Raw silica fume was analyzed by XRD, FT-IR and SEM. The analysis results of silica fume indicated that SiO2 in silica fume is mainly determined as amorphous state, and that the particles of raw silica fume exhibited characteristic spherical structure with a diameter of from 50 nm to 200 nm. The preparation of the porous silicate material involved two steps. The first step was the extraction of the SiO 3 2− leachate from raw silica fume. The maximum value of SiO 3 2− extraction yield was obtained under the following conditions: reaction temperature of 120 °C, reaction time of 120 min, NaOH concentration of 15%, and alkali to SiO2 molar ratio of 2. The second step was the preparation of the porous silicate material though the reaction of SiO 3 2− leachate and Ca(OH)2 suspension liquid. The optimum preparation conditions were as follows: preparation temperature of 90 °C, preparation time of 1.5 h, Si/Ca molar ratio of 1 : 1, and stirring rate of 100 r/min. The BET surface area and pore size of the porous silicate material were 220.7 m2·g−1 and 8.55 cm3/g, respectively. The porous silicate material presented an amorphous and unordered structure. The spectroscopic results indicated that the porous silicate material was mainly composed of Si, Ca, O, C, and Na, in the form of Ca2+, SiO 3 2− , CO 3 2− and Na+ ions, respectively, which agreed with the XRD, TG-DSC, and FT-IR data. The N2 adsorption-desorption isotherm mode indicates that the porous silicate material belonged to a typical mesoporous material. The porous silicate material presented efficiency for the removal of formaldehyde: it showed a formaldehyde adsorption capacity of 8.01 mg/g for 140 min at 25 °C.

Study of charcoal detoxification of acid hydrolysate from corncob and its fermentation to xylitol

In the present study, adsorption isotherms, kinetics and thermodynamics of fermentation inhibitors generated during the acid hydrolysis of corncob were investigated using activated charcoal (0.5–2.0% w/v) as the adsorbent. The results indicated that lower pH and lower temperature favor the adsorption of both furans and phenolics. The adsorption kinetic regimes were found more favorable in pseudo second order kinetics than pseudo first order kinetics. The experimental values were in good correlation with the predicted values with a regression coefficient (R2) value of more than 0.99. Moreover, the negative values of enthalpy (ΔH), and free energy (ΔG) indicated that the adsorption process was spontaneous in nature and exothermic. The detoxified corncob hydrolysate on its assessment for fermentability revealed the production of 4.8g/L and 4.3g/L xylitol from Candida tropicalis ITCC 1830 and C. tropicalis MTCC 9038. The activated charcoal adsorption has shown differential adsorption capacity and isotherms on various inhibitors under different conditions. Hence using the optimum conditions the process efficiency can be improved to make the whole process cost competitive.

High-pressure methane accumulation in a carbon fibrous sorbent

Recent data on methane adsorption on C300 carbon-fibrous sorbent obtained in the pressure range of 1 to 55 MPa and temperature range of 303 to 333 K are reported. Methane adsorption isosteres in the same ranges of pressures and temperatures were calculated on the basis of experimental isotherms of methane adsorption. Differential molar isosteric adsorption heats were calculated as a function of the value of methane adsorption and temperature. Dependences of methane adsorption on the C300 adsorbent on pressure were calculated on the basis of the Dubinin theory of volume filling of micropores and compared with experimental data. The best agreement between the results of calculations and experimental data was found at the intermediate range of pore filling.

Quantification of gene-specific DNA methylation in oesophageal cancer via electrochemistry

Development of simple and inexpensive method for the analysis of gene-specific DNA methylation is important for the diagnosis and prognosis of patients with cancer. Herein, we report a relatively simple and inexpensive electrochemical method for the sensitive and selective detection of gene-specific DNA methylation in oesophageal cancer. The underlying principle of the method relies on the affinity interaction between DNA bases and unmodified gold electrode. Since the affinity trend of DNA bases towards the gold surface follows as adenine (A) > cytosine (C) > guanine (G)> thymine (T), a relatively larger amount of bisulfite-treated adenine-enriched unmethylated DNA adsorbs on the screen-printed gold electrodes (SPE-Au) in comparison to the guanine-enriched methylated sample. The methylation levels were (i.e., different level of surface attached DNA molecules due to the base dependent differential adsorption pattern) quantified by measuring saturated amount of charge-compensating [Ru(NH3)6]3+ molecules in the surface-attached DNAs by chronocoulometry as redox charge of the [Ru(NH3)6]3+ molecules quantitatively reflects the amount of the adsorbed DNA confined at the electrode surface. The assay could successfully distinguish methylated and unmethylated DNA sequences at single CpG resolution and as low as 10% differences in DNA methylation. In addition, the assay showed fairly good reproducibility (% RSD= <5%) with better sensitivity and specificity by analysing various levels of methylation in two cell lines and eight fresh tissues samples from patients with oesophageal squamous cell carcinoma. Finally, the method was validated with methylation specific-high resolution melting curve analysis and Sanger sequencing methods.

ZTS-1 and ZTS-2: Novel intergrowth zeolites with AFX/CHA structure

Novel AFX/CHA aluminosilicate intergrowth zeolites ZTS-1 and ZTS-2 were synthesized using the dual structure-directing agent (dual-SDA) approach. ZTS-1 was obtained using the 1,1′-(1,4-butanediyl)bis(1-azonia-4-azabicyclo[2,2,2]octane) dication (Dab-42+) and the N,N,N-trimethyl-1-adamantylammonium cation (TMAda+) as organic structure-directing agents (OSDAs) for AFX and CHA phases, respectively. The obtained materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), electron diffraction, high-resolution transmission electron microscopy (HRTEM), solid-state 13C dipolar decoupled magic-angle-spinning nuclear magnetic resonance (13C DD/MAS NMR), thermogravimetric and differential thermal analysis (TG/DTA), CHN analysis, and N2 adsorption. The combined results of these characterizations and those of the DIFFaX simulation showed that the AFX/CHA ratio of ZTS-1 was 80–85% AFX and 15–20% CHA (based on the number of unit cells). Control of the AFX/CHA ratio by simple variation of the hydrothermal synthetic parameters proved to be challenging. The catalytic performance of Cu-loaded ZTS-1 was tested in the selective catalytic reduction of NOx with NH3 (NH3-SCR), and its higher hydrothermal stability compared to the Cu-loaded AFX catalyst was confirmed. ZTS-2 was synthesized using K+ instead of TMAda+, under synthetic conditions completely different from those used for ZTS-1. The AFX/CHA ratio of ZTS-2 was estimated as 15–20% AFX and 80–85% CHA, strongly indicating the possibility of controlling the above ratio.

New Advances in Dial-Lidar-Based Remote Sensing of the Volcanic CO2 Flux

We report here on the results of a proof-of-concept study aimed at remotely sensing the volcanic CO2 flux using a Differential Adsorption lidar (DIAL-lidar). The observations we report on were conducted on June 2014 on Stromboli volcano, where our lidar (LIght Detection And Ranging) was used to scan the volcanic plume from ~ 3 km distance from the summit vents. The obtained results prove that a remotely operating lidar can resolve a volcanic CO2 signal of a few tens of ppm (in excess to background air) over km-long optical paths. We combine these results with independent estimates of plume transport speed (from processing of UV Camera images) to derive volcanic CO2 flux time-series of ≈16-33 minutes temporal resolution. Our lidar-based CO2 fluxes range from 1.8±0.5 to 32.1±8.0 kg/s, and constrain the daily averaged CO2 emissions from Stromboli at 8.3±2.1 to 18.1±4.5 kg/s (or 718-1565 tons/day). These inferred fluxes fall within the range of earlier observations at Stromboli. They also agree well with contemporaneous CO2 flux determinations (8.4-20.1 kg/s) obtained using a standard approach that combines Multi-GAS-based in-plume readings of the CO2/SO2 ratio (≈ 8) with UV-camera sensed SO2 fluxes (1.5-3.4 kg/s). We conclude that DIAL-lidars offer new prospects for safer (remote) instrumental observations of the volcanic CO2 flux.