Differences In Adsorption Rates Research Articles

Enantiomer Recognition by the Difference in Adsorption Rates on the Surfaces of Chiral Crystals.

The chirality of biopolymers remains one of the mysteries of Life. For such objects, the phenomenon of supramolecular chirality (SMC) is vital. Enantiomers can be recognized by the adsorption on surfaces with SMC. However, the mechanisms of such chiral recognition are still unknown. In this work, the adsorption kinetics of menthol test enantiomers on the surfaces of γ-glycine and NiSO4•6H2O chiral crystals was studied. It was found that the difference in adsorption was observed in nonequilibrium state more often than in equilibrium. If the enantioselectivity in equilibrium state was observed, the enantioselectivity coefficient α at nonequilibrium conditions was higher. The maximum α in nonequilibrium state was 2.44 for γ-glycine crystals and 2.12 for NiSO4•6H2O crystals. Even if no differences in adsorption were observed under adsorption-desorption equilibrium conditions, a significant enantioselectivity at nonequilibrium conditions was found. This has proved the possibility of chiral recognition on surfaces with SMC by the differences in adsorption rates. Such novel chiral recognition mechanism can provide enhanced enantioselectivity in adsorption, catalysis, chromatographic separation, and chemical sensing.

Performance Evaluation of a Desiccant Dehumidifier with a Heat Recovery Unit

In order to effectively increase the drying rate and reduce the energy consumption, a dryer which reduces the air humidity at the dryer inlet using desiccant and regenerates the desiccant by recovering waste heat using a heat pipe heat exchanger was developed in this study. Both the adsorption rate and desorption rate of the dryer were measured at several ambient temperatures ranging from 15 °C to 35 °C, relative humidity levels of air ranging from 20% to 85%, and airflow rates ranging from 30 m3/h to 150 m3/h. The results showed that the adsorption rate in an environment of high relative humidity of air was 4.89 times higher than that of low relative humidity of air at 15 °C. Moreover, the difference in adsorption rate between two given relative humidity of air increased as the ambient temperature decreased. The specific energy consumption estimated with both energy consumption during desorption and the desorption rate indicated that the energy consumption was 8.27 kJ/g H2O without using recovered heat, while the energy consumption was 4.77 kJ/g H2O using recovered heat at 130 °C.

Capturing Conformation-Dependent Molecule-Surface Interactions When Surface Chemistry Is Heterogeneous.

Molecular building blocks, such as carbon nanotubes and DNA origami, can be fully integrated into electronic and optical devices if they can be assembled on solid surfaces using biomolecular interactions. However, the conformation and functionality of biomolecules depend strongly on the local chemical environment, which is highly heterogeneous near a surface. To help realize the potential of biomolecular self-assembly, we introduce here a technique to spatially map molecular conformations and adsorption, based on single-molecule fluorescence microscopy. On a deliberately patterned surface, with regions of varying hydrophobicity, we characterized the conformations of adsorbed helicogenic alanine-lysine copeptides using Förster resonance energy transfer. The peptides adopted helical conformations on hydrophilic regions of the surface more often than on hydrophobic regions, consistent with previous ensemble-averaged observations of α-helix surface stability. Interestingly, this dependence on surface chemistry was not due to surface-induced unfolding, as the apparent folding and unfolding dynamics were usually much slower than desorption. The most significant effect of surface chemistry was on the adsorption rate of molecules as a function of their initial conformational state. In particular, regions with higher adsorption rates attracted more molecules in compact, disordered coil states, and this difference in adsorption rates dominated the average conformation of the ensemble. The correlation between adsorption rate and average conformation was also observed on nominally uniform surfaces. Spatial variations in the functional state of adsorbed molecules would strongly affect the success rates of surface-based molecular assembly and can be fully understood using the approach developed in this work.

Properties and uses of chlorpyrifos in the United States.

Physical properties and use data provide the basis for estimating environmental exposures to chlorpyrifos (CPY) and for assessing its risks. The vapor pressure ofCPY is low, solubility in water is <1 mg L-1, and its log Kow is 5. Chlorpyrifos has short to moderate persistence in the environment as a result of several dissipation pathways that may proceed concurrently. Primary mechanisms of dissipation include volatilization, photolysis, abiotic hydrolysis, and microbial degradation.Volatilization dominates dissipation from foliage in the initial 12 h after application,but decreases as CPY adsorbs to foliage or soil. In the days after application, CPY adsorbs more strongly to soil, and penetrates more deeply into the soil matrix,becoming less available for volatilization. After the first 12 h, other processes of degradation, such as chemical hydrolysis and catabolism by microbiota become important. The half-life of CPY in soils tested in the laboratory ranged from 2 toI ,575 d (N = 126) and is dependent on properties of the soil and rate of application.At application rates used historically for control of termites, the degradation rate is much slower than for agricultural uses. In agricultural soils under field conditions,half-lives are shorter (2 to 120 d, N=58). The mean water-soil adsorption coefficient(Koc) of CPY is 8,216 mL g-1; negligible amounts enter plants via the roots,and it is not translocated in plants. Half-lives for hydrolysis in water are inversely dependent on pH, and range from 16 to 73 d. CPY is an inhibitor of acetylcholinesterase and is potentially toxic to most animals. Differences in susceptibility result from differences in rates of adsorption,distribution, metabolism, and excretion among species. CPY is an important tool in management of a large number of pests (mainly insects and mites) and is used on a wide range of crops in the U.S. Estimates of annual use in the U.S. from 2008 to 2012 range from 3.2 to 4.1 M kg y-1, which is about 50% less than the amount used prior to 2000. Applications to corn and soybeans accounts for 46-50%of CYP's annual use in the U.S.

Study of the spontaneous attachment of polycyclic aryldiazonium salts onto amorphous carbon substrates

Diazonium salts of two nitro-substituted polycyclic aromatic compounds were synthesized and their spontaneous covalent attachment onto amorphous carbon surfaces was studied via electrochemical and spectroscopic techniques. In situ spectroscopic monitoring of the grafting of these compounds at amorphous carbon surfaces via attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR) highlighted a marked difference in adsorption rates, which was also evident via ex situ electrochemical analysis. We show that adsorption rate differences cannot be explained based on differences in the solvolysis rates of these two molecules. It was found instead that the relative position of the –N2+ groups with respect to the –NO2 groups affected the reduction potential of the diazonium cations and in turn their adsorption rate at amorphous carbon surfaces. We conclude that differences in the electron density at the carbon atom bound to the diazonium group are responsible for the differences observed in the spontaneous attachment at carbon.

Integrated carbon nanotube fibre–quartz tuning fork biosensor

We report on a novel label-free biosensor for in situ measurements in liquid. It is comprised of a porous carbon nanotube (CNT) fibre attached to one prong of a quartz tuning fork (QTF) resonator. Only the protruding CNT fibre is immersed into a liquid, while the QTF is kept above the liquid to avoid short circuit of its electrodes. The low density and large surface area of the CNT fibre assure sufficient sensitivity without affecting the performance of the QTF significantly. Efficiency of the sensor was demonstrated experimentally by comparison of the adsorption rate of bovine serum albumin to the CNT fibre at two different pH values; differences in adsorption rates were clearly distinguishable.

Mesoporous carbide-derived carbon for cytokine removal from blood plasma

Porous carbons can be used for purification of bio-fluids due to their excellent biocompatibility with blood. Since the ability to adsorb a range of inflammatory cytokines within the shortest possible time is crucial to stop the progression of sepsis, the improvement of the adsorption rate is a key factor to achieving efficient removal of cytokines. Here, we demonstrate the effect of synthesis temperatures (from 600°C to 1200°C), carbon particle sizes (from below 35μm to 300μm), and annealing conditions (Ar, NH3, H2, Cl2, and vacuum annealing) that determine the surface chemistry, on the ability of carbide-derived carbons (CDCs) to remove cytokines TNF-α, IL-6, and IL-1β from blood plasma. Optimization of CDC processing and structure leads to up to two orders of magnitude increase in the adsorption rate. Mesoporous CDCs that were produced at 800°C from Ti2AlC with the precursor particle size of <35μm and annealed in NH3, displayed complete removal of large molecules of TNF-α in less than an hour, with >85% and >95% TNF-α removal in 5 and 30min, respectively. This is a very significant improvement compared to the previously published results for CDC (90% TNF-α removal after 1h) and activated carbons. Smaller interleukin IL-6 and IL-1β molecules can be completely removed within 5min. These differences in adsorption rates show that carbons with controlled porosity can also be used for separation of protein molecules.

Isotopic Distribution Coefficient of Tritiated Water Adsorbed on Faujasite-Type Zeolite

The fixed-bed adsorption processusing zeolite has been studied as one of the promising processes for the recovery of tritiated water in the field of nuclear fusion. In H2O-HTO binary systems, the difference in adsorption rate must be considered to obtain the isotopic distribution coefficient of tritiated water adsorbed on zeolite. The static method is probably the best approach to measure the distribution coefficient considering the difference in adsorption rate. In this study, the influence of framework SiO2/Al2O3 ratio ranging from 2.0 to 10.0 and of cations (K+, Na+, Ca2+) on isotopic distribution coefficient of tritiated water adsorbed on faujasite-type zeolite was systematically examined. The isotopic distribution coefficient of tritiated water between water adsorbed on zeolite absorbent was 1.1˜1.4. The effect of framework SiO2 to Al2O3 ratio of the X/Y type zeolite on the isotopic distribution coefficient depended on the content of cation in zeolite. The framework SiO2 to Al2O3 ratio of the NaX/NaY zeolite had negligible effect on the isotopic distribution coefficient. The considerable effect of framework SiO2 to Al2O3 ratio was found in the case of KX/KY and CaX/CaY zeolite.

Nisin adsorption to hydrophobic surfaces coated with the PEO–PPO–PEO triblock surfactant Pluronic ® F108

The adsorption and elution of the antimicrobial peptide nisin at hydrophobic, silanized silica surfaces coated with the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) surfactant Pluronic ® F108 were measured in situ, with ellipsometry. While such layers are known to inhibit protein adsorption, nisin was observed to adsorb in multilayer quantities, to an extent similar to its adsorption at uncoated, hydrophobic surfaces. The rates of nisin adsorption and elution were generally slower at F108-coated surfaces. And, the sequential adsorption of nisin, including two adsorption–elution cycles at each surface, showed greater differences in adsorption rates between the first and second adsorption cycles, when evaluated at identical mass density, for uncoated relative to F108-coated surfaces. These results indicate that nisin adsorption occurs via “entrapment” within the PEO brush layer at F108-coated surfaces, in this way slowing adsorption and spontaneous elution, and inhibiting post-adsorptive molecular rearrangements by reducing the lateral mobility of nisin. While F108-coated layers rejected adsorption of serum albumin, sequential adsorption experiments carried out with nisin and albumin showed a low level of albumin adsorption when nisin was present at the interface.

Protein concentration and adsorption time effects on fibrinogen adsorption at heparinized silica interfaces

Heparin was modified with adipic dihydrazide and covalently linked to surface-activated silica wafers. X-ray photoelectron spectroscopy was used at each stage of derivatization and showed that successful immobilization had taken place. Surfaces were imaged with atomic force microscopy to determine the uniformity of the heparin layer as well as its thickness. In situ ellipsometry was used to estimate layer thickness as well, and to study protein concentration and adsorption time effects on the adsorption and elution kinetics exhibited by human plasma fibrinogen. The adsorbed amount of fibrinogen increased with time and concentration on each type of surface. Under all experimental conditions, fibrinogen adsorbed at a lower rate and to a lower extent on heparinized as compared to unheparinized silica. In addition, buffer elution experiments showed that fibrinogen was less tightly bound to heparinized silica. In order to examine behavior relative to fibrinogen mobility at these interfaces, the sequential adsorption of fibrinogen was recorded. The difference in adsorption rates between the first and second adsorption cycles, evaluated at identical mass density, indicated that post-adsorptive molecular rearrangements had taken place. In general, higher solution concentration and longer adsorption time in the first adsorption step led to more rearrangement, and these history dependent effects were more pronounced on the heparinized silica. These rearrangements are suggested to involve clustering of adsorbed fibrinogen, in this way increasing the amount of unoccupied area at the interface. These rearrangements were presumably facilitated on the heparinized silica by enhanced lateral mobility of fibrinogen at this negatively charged, highly hydrophilic interface.

Comparative Study of Electrochemically Directed Assembly versus Conventional Self-Assembly of Thioacetyl-Terminated Oligo(phenylene ethynylene)s on Gold and Platinum Surfaces

The assembly of thioacetyl-terminated oligo(phenylene ethynylene)s (OPEs) on Au and Pt surfaces under an electric potential (electrochemical assembly, EA) was compared to assembly at an open circuit (conventional self-assembly, CSA). Cyclic voltammetry and ellipsometry were used to characterize the adsorption kinetics of self-assembled monolayers formed by these two techniques. The adsorption rate of the EA was remarkably faster at positive potentials but slower at negative potentials than that of the CSA, The EA at 400 mV proceeded about 800 times faster than the CSA when exposed to the same solution concentrations. The adsorption rates of both EA and CSA were found to be dependent on the molecular structures of OPEs. OPEs containing electron-donating groups assemble faster than those with electron-withdrawing groups. The amount of time that the thioacetyl-terminated OPE is in the presence of the base, for removal of the acetyl group to generate the thiolate, is called the deprotection time. Deprotection times play a critical role in achieving the maximum difference in adsorption rates between the EA and the CSA. The assembly must be initiated no later than 5 min after the basic deprotection is commenced so that the thiolate concentration remains low. The difference in the adsorption rates between EA and CSA might enable selective deposition of certain OPEs onto specific electrodes.

Oxygen Selectivity on Na-A Type Zeolite at Low Temperature

Na-A type zeolite (Na-A) shows favorable selectivity for nitrogen in an oxygen-nitrogen bi-component system at room temperature and also it is known that oxygen selectivity is dominated by differences in adsorption rates. In this study, the oxygen adsorption behavior of Na-A pellets at low temperature was evaluated. When temperature decreased, oxygen selectivity was enhanced as a result of the difference in adsorption rates. It was also strongly suggested that the oxygen equilibrium adsorbed amount of Na-A pellets was larger than that of nitrogen below 213 K. Na-A pellets are expected to be a good oxygen adsorbent for oxygen-nitrogen separation from air by pressure swing adsorption (PSA).

Adsorption during Heat Treatment Related to the Thermal Unfolding/Aggregation of β-Lactoglobulins A and B

Adsorption onto chromium surfaces during heat treatment (65–68°C) of β-lactoglobulin A and B in phosphate buffer, pH 6.88, was investigated byin situellipsometry. Thermal unfolding andin situheat-induced aggregation under the same conditions were studied by differential scanning calorimetry and dynamic light scattering, respectively. A lag phase was observed for buildup of the thickness of the adsorbed layer of β-lactoglobulin A and B at 68°C. The lag period was found to increase with decreasing temperature. The difference in adsorption rate between the variants was found to be in agreement with the aggregation difference in solution, that is, the A variant aggregated more rapidly after a somewhat slower beginning. These results could be related to a difference in the thermal unfolding behavior. By applying a non-two state model the second of two transitions was suggested to involve the activation of the free sulfydryl group. The results indicated that fouling proceeds via attachment of aggregates with an activated free sulfydryl group through an interchange reaction with a disulfide bond in the adsorbed protein layer.

Replication of lactate dehydrogenase-elevating virus in cells infected with murine leukaemia viruses in vitro.

Although the majority of mouse strains infected with lactate dehydrogenase-elevating virus (LDV) do not show any particular symptoms, the virus is able to induce acute poliomyelitis in C58 or AKR mice. Murine leukaemia virus (MuLV) has been detected at a high titre in the spinal cord of affected mice. In this study, we have analysed the possible role of MuLV in the induction of neurological disease by LDV. Immunofluorescent staining, autoradiography and an infectivity assay of virus yield have shown that LDV replicated in continuous mouse and rat cell lines that had been infected with an ecotropic MuLV isolated from C58 mice, but did not replicate in cells not infected with MuLV. No significant differences in infection were observed among the various ecotropic MuLVs employed, except for Friend leukaemia virus which rendered the cells susceptible to LDV least efficiently. The infectivity of the neurovirulent strain, LDV-C, to MuLV-infected cells was 50- to 100-fold greater than that of the avirulent strains (LDV-N, -Nu, -R and -P). The infectivity to macrophages was almost the same for virulent and avirulent strains. Adsorption studies using a radiolabelled virus revealed that LDV-C was adsorbed to MuLV-infected cells more efficiently than the avirulent strain, LDV-N. The difference in infectivity to these cells, therefore, may be due in part to the difference in adsorption rate. This may suggest differences in the interaction of the viral proteins with MuLV-infected cells from those with macrophages at the initiation of virus infection. These results may be relevant to the mechanisms of paralytic disease caused by LDV infection in C58 mice.

Accelerated Adsorption of Bacteriophage T5 to Escherichia coli F, Resulting from Reversible Tail Fiber-Lipopolysaccharide Binding

A dual specificity for phage T5 adsorption to Escherichia coli cells is shown. The tail fiber-containing phages T5(+) and mutant hd-3 adsorbed rapidly to E. coli F (1.2 x 10(-9) ml min(-1)), whereas the adsorption rate of the tail fiber-less mutants hd-1, hd-2, and hd-4 was low (7 x 10(-11) ml min(-1)). The differences in adsorption rates were due to the particular lipopolysaccharide structure of E. coli F. Phage T4-resistant mutants of E. coli F with an altered lipopolysaccharide structure exhibited similar low adsorption for all phage strains with and without tail fibers. The same held true for E. coli K-12 and B which also differ from E. coli F in their lipopolysaccharide structures. Only the tail fiber-containing phages reversibly bound to isolated lipopolysaccharides of E. coli F. Infection by all phage strains strictly depended on the tonA-coded protein in the outer membrane of E. coli. We assume that the reversible preadsorption by the tail fibers to lipopolysaccharide accelerates infection which occurs via the highly specific irreversible binding of the phage tail to the tonA-coded protein receptor. The difference between rapid and slow adsorption was also revealed by the competition between ferrichrome and T5 for binding to their common tonA-coded receptor in tonB strains of E. coli. Whereas binding of T5(+) to E. coli K-12 and of the tail-fiber-less mutant hd-2 to E. coli F and K-12 was inhibited 50% by about 0.01 muM ferrichrome, adsorption of T5 to E. coli F was inhibited only 40% by even 1,000-fold higher ferrichrome concentrations.

Co-Evolution of a Virus-Alga System

Plectonema boryanum , a filamentous blue-green alga, was cloned and then allowed to reach a steady state in a quasi-continuous culture in the presence of the algal virus, LPP-1. The culture was maintained for a 3.5-month period during which time at least four distinct culture lysings were evident. After the fourth lysis the culture reached a steady-state level which was identical in its algal concentration to the preinfection level. Upon testing the characteristics of the evolved alga and virus variants, the following was determined: cell variants resistant to both the original virus and the derived virus had evolved, and there was no evidence of lysogeny present among these cells. The evolved virus strains still grew on the parental algal strain, though with altered plaque morphology. Furthermore, they were antigenically similar to the parental virus, and showed no significant difference in adsorption rate or growth characteristics on parental cells. However, a low-grade chronic viral infection persisted in the culture. Rapid re-establishment of a dense, stable culture is apparently the normal laboratory response of a procaryotic cell-virus system.

Co-Evolution of a Virus-Alga System

Plectonema boryanum, a filamentous blue-green alga, was cloned and then allowed to reach a steady state in a quasi-continuous culture in the presence of the algal virus, LPP-1. The culture was maintained for 3.5-month period during which time at least four distinct culture lysings were evident. After the fourth lysis the culture reached a steady-state level which was identical in its algal concentration to the preinfection level. Upon testing the characteristics of the evolved alga and virus variants, the following was determined: cell variants resistant to both the original virus and the derived virus had evolved, and there was no evidence of lysogeny present amony these cells. The evolved virus strains still grew on the parental algal strain, though with altered plaque morphology. Furthermore, they were antigenically similar to the parental virus, and showed no significant difference in adsorption rate or growth characteristics on parental cells. However, a low-grade chronic viral infection persisted in the culture. Rapid re-establishment of a dense, stable culture is apparantly the normal laboratory response of a procaryotic cell-virus system.

PURIFIED INTERFERONS: PHYSICAL PROPERTIES AND SPECIES SPECIFICITY.

The antiviral activity of highly purified preparations of chick and mouse interferons has marked species specificity. This species specificity is not explained by a demonstrable difference in adsorption rates. There is no difference in charge between the molecules as measured by combined zone electrophoresis or ion-exchange chromatography. The interferons are distinguishable by thermal inactivation studies and by precise chromatography on G-100 Sephadex columns. With the latter method, interferons produced by the same cell species (i) in vivo or in vitro, or (ii) in response to different viruses, have been shown to be identical. The same virus stimulates physically distinguishable molecules in the two different cell species. These findings indicate that interferon is a virus-induced product of the host genome

Purified Interferons: Physical Properties and Species Specificity

The antiviral activity of highly purified preparations of chick and mouse interferons has marked species specificity. This species specificity is not explained by a demonstrable difference in adsorption rates. There is no difference in charge between the molecules as measured by combined zone electrophoresis or ion-exchange chromatography. The interferons are distinguishable by thermal inactivation studies and by precise chromatography on G-100 Sephadex columns. With the latter method, interferons produced by the same cell species (i) in vivo or in vitro, or (ii) in response to different viruses, have been shown to be identical. The same virus stimulates physically distinguishable molecules in the two different cell species. These findings indicate that interferon is a virus-induced product of the host genome.