Size-dependent Fractionation Research Articles

An innovative isotopic method to identify the volcanic source of distal tephra

Identifying the sources of distal tephra in marine sediments or polar ice provides clues on the dynamic and large-scale impact of major volcanic eruptions. However, determination of the volcanic source of distal tephra is challenging due to size-dependent fractionation during atmospheric transport that modifies the mineral, chemical and even isotope composition of the transported and settled tephra. The composition of distal fine ash may thus be different from the coarser proximal products of the same eruption. Identifying the volcanic source of distal ash using the compositional data may therefore prove difficult. To get around this modification of distal composition, we propose here a new isotopic method to identify the source of distal tephra that is not based on raw transport-dependent isotope ratios but on two-dimension Pb isotope mixing lines, which account for atmospheric fractionation processes. To demonstrate the robustness of our method, we used the extensive database of Pb isotope compositions of volcanic products from the Northern Andean arc, to which we append 68 new Pb isotopic analyses obtained on proximal and distal eruptive tephra. We show for the first time that proximal products define a straight line in the 208Pb/206Pb-207Pb/206Pb space, whose equation is specific to each volcanic source. We then show that distal co-genetic tephra plot on the same line as proximal products, implying that the isotopic lines are robust fingerprints of volcanic sources that do not depend on the age, mineral assemblage, and nature of the emitted products. This new method uses bulk rock analyses and therefore provides a new perspective on distal tephra correlation and source identification in the Andes and probably other volcanic arcs with significant Pb isotopic variations.

Carbon sources driven supernatant micro-particles differentiate in submerged anaerobic membrane bioreactors (AnMBRs)

Recently, micro-particles with a size range of 0.45–10 μm in anaerobic membrane bioreactors (AnMBRs), were rich in microorganisms and characterized as a significant source to membrane fouling. Nevertheless, little is known about the formation of the micro-particles associated microorganisms as well as their metabolic functions, which could be largely impacted by carbon sources in the influent. Here, protein and glucose were chosen to be two different carbon sources fed into two identical AnMBRs (i.e., AnMBR-P and AnMBR-G), and a comprehensive comparison of the micro-particles formed in corresponding reactors was made. Size-dependent fractionation and fluorescent staining assay showed that micro-particles with the size range of 0.45–1 μm possessed the highest contents (41.4%) in the AnMBR-P and presented as vibrios and coccus, while the 5–10 μm micro-particles with filamentous morphologies were the prevailing fraction (61.9%) in the AnMBR-G. According to the results of high-throughput 16S rRNA gene sequencing, the Lentimicrobiaceae, D8A-2 and Syntrophorhabdus prevailed in the AnMBR-P micro-particles, while the SJA-15 showed overwhelming predominance than the other genera in the AnMBR-G micro-particles. Metagenomic sequencing further revealed that the micro-particles in the AnMBR-P possessed higher abundance in specific functional genes for nitrogen metabolism (nirB), sulfur metabolism (cysK) and cysteine and methionine metabolism (mtaD), as well as in the cell mobility as chemotaxis (rbsB) and flagellar assembly (fliC). In comparison, the micro-particles obtained from the AnMBR-G encoded abundant genes for converting glucose to metabolites in the next level, such as glk (glucokinase), pfk (ATP-dependent phosphofructokinase), and PGK (phosphoglycerate kinase). Overall, our findings provided new insights into the formation of micro-particles in the supernatant of AnMBRs, which could facilitate to propose related fouling alleviation methods from the perspective of carbon sources regulation and/or pretreatment of the influent.

A new data set of soil mineralogy for dust-cycle modeling

Abstract. The mineralogy of airborne dust affects the impact of dust particles on direct and indirect radiative forcing, on atmospheric chemistry and on biogeochemical cycling. It is determined partly by the mineralogy of the dust-source regions and partly by size-dependent fractionation during erosion and transport. Here we present a data set that characterizes the clay and silt-sized fractions of global soil units in terms of the abundance of 12 minerals that are important for dust–climate interactions: quartz, feldspars, illite, smectite, kaolinite, chlorite, vermiculite, mica, calcite, gypsum, hematite and goethite. The basic mineralogical information is derived from the literature, and is then expanded following explicit rules, in order to characterize as many soil units as possible. We present three alternative realizations of the mineralogical maps, taking the uncertainties in the mineralogical data into account. We examine the implications of the new database for calculations of the single scattering albedo of airborne dust and thus for dust radiative forcing.

Asymmetric flow field-flow fractionation of superferrimagnetic iron oxide multicore nanoparticles

Magnetic nanoparticles are very useful for various medical applications where each application requires particles with specific magnetic properties. In this paper we describe the modification of the magnetic properties of magnetic multicore nanoparticles (MCNPs) by size dependent fractionation. This classification was carried out by means of asymmetric flow field-flow fractionation (AF4). A clear increase of the particle size with increasing elution time was confirmed by multi-angle laser light scattering coupled to the AF4 system, dynamic light scattering and Brownian diameters determined by magnetorelaxometry. In this way 16 fractions of particles with different hydrodynamic diameters, ranging between around 100 and 500 nm, were obtained. A high reproducibility of the method was confirmed by the comparison of the mean diameters of fractions of several fractionation runs under identical conditions. The hysteresis curves were measured by vibrating sample magnetometry. Starting from a coercivity of 1.41 kA m−1 for the original MCNPs the coercivity of the particles in the different fractions varied from 0.41 to 3.83 kA m−1. In our paper it is shown for the first time that fractions obtained from a broad size distributed MCNP fluid classified by AF4 show a strong correlation between hydrodynamic diameter and magnetic properties. Thus we state that AF4 is a suitable technology for reproducible size dependent classification of magnetic multicore nanoparticles suspended as ferrofluids.

A microfluidic spiral for size-dependent fractionation of magnetic microspheres

Magnetic microspheres (MMS) are useful tools for a variety of medical and pharmaceutical applications. Typically, commercially manufactured MMS exhibit broad size distributions. This polydispersity is problematic for many applications. Since the direct synthesis of monodisperse MMS is often fraught with technical challenges, there is considerable interest in and need associated with the development of techniques for size-dependent fractionation of MMS. In this study we demonstrated continuous size-dependent fractionation of sub-micron scale particles driven by secondary (Dean effect) flows in curved microfluidic channels. Our goal was to demonstrate that such techniques can be applied to MMS containing superparamagnetic nanoparticles. To achieve this goal, we developed and tested a microfluidic chip for continuous MMS fractionation. Our data address two key areas. First, the densities of MMS are typically in the range 1.5–2.5g/cm3, and thus they tend be non-neutrally buoyant. Our data demonstrate that efficient size-dependent fractionation of MMS entrained in water (density 1g/cm3) is possible and is not significantly influenced by the density mismatch. In this context we show that a mixture comprising two different monodisperse MMS components can be separated into its constituent parts with 100% and 88% success for the larger and smaller particles, respectively. Similarly, we show that a suspension of polydisperse MMS can be separated into streams containing particles with different mean diameters. Second, our data demonstrate that efficient size-dependent fractionation of MMS is not impeded by magnetic interactions between particles, even under application of homogeneous magnetic fields as large as 35kA/m. The chip is thus suitable for the separation of different particle fractions in a continuous process and the size fractions can be chosen simply by adjusting the flow velocity of the carrier fluid. These facts open the door to size dependent fractionation of MMS.

A microfluidic chip for size dependent fractionation of magnetic microspheres for magnetic drug targeting

A microfluidic chip for size dependent fractionation of magnetic microspheres for magnetic drug targeting

Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide

Abstract. We sampled interstitial air from the perennial snowpack (firn) at a site near the West Antarctic Ice Sheet Divide (WAIS-D) and analyzed the air samples for a wide variety of gas species and their isotopes. We find limited convective influence (1.4–5.2 m, depending on detection method) in the shallow firn, gravitational enrichment of heavy species throughout the diffusive column in general agreement with theoretical expectations, a ~10 m thick lock-in zone beginning at ~67 m, and a total firn thickness consistent with predictions of Kaspers et al. (2004). Our modeling work shows that the air has an age spread (spectral width) of 4.8 yr for CO2 at the firn-ice transition. We also find that advection of firn air due to the 22 cm yr−1 ice-equivalent accumulation rate has a minor impact on firn air composition, causing changes that are comparable to other modeling uncertainties and intrinsic sample variability. Furthermore, estimates of Δage (the gas age/ice age difference) at WAIS-D appear to be largely unaffected by bubble closure above the lock-in zone. Within the lock-in zone, small gas species and their isotopes show evidence of size-dependent fractionation due to permeation through the ice lattice with a size threshold of 0.36 nm, as at other sites. We also see an unequivocal and unprecedented signal of oxygen isotope fractionation within the lock-in zone, which we interpret as the mass-dependent expression of a size-dependent fractionation process.

Identification and Characterization of a Novel Nuclear Protein Complex Involved in Nuclear Hormone Receptor-mediated Gene Regulation

NRC/NCoA6 plays an important role in mediating the effects of ligand-bound nuclear hormone receptors as well as other transcription factors. NRC interacting factor 1 (NIF-1) was cloned as a novel factor that interacts in vivo with NRC. Although NIF-1 does not directly interact with nuclear hormone receptors, it enhances activation by nuclear hormone receptors presumably through its interaction with NRC. To further understand the cellular and biological function of NIF-1, we identified NIF-1-associated proteins by in-solution proteolysis followed by mass spectrometry. The identified components revealed factors involved in histone methylation and cell cycle control and include Ash2L, RbBP5, WDR5, HCF-1, DBC-1, and EMSY. Although the NIF-1 complex contains Ash2L, RbBP5, and WDR5, suggesting that the complex might methylate histone H3-Lys-4, we found that the complex contains a H3 methyltransferase activity that modifies a residue other than H3-Lys-4. The identified components form at least two distinctly sized NIF-1 complexes. DBC-1 and EMSY were identified as integral components of an NIF-1 complex of approximately 1.5 MDa and were found to play an important role in the regulation of nuclear receptor-mediated transcription. Stimulation of the Sox9 and HoxA1 genes by retinoic acid receptor-alpha was found to require both DBC-1 and EMSY in addition to NIF-1 for maximal transcriptional activation. Interestingly, NRC was not identified as a component of the NIF-1 complex, suggesting that NIF-1 and NRC do not exist as stable in vitro purified complexes, although the separate NIF-1 and NRC complexes appear to functionally interact in the cell.

Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements

We present elemental and isotopic measurements of noble gases (He, Ne, Ar, Kr, and Xe), oxygen and nitrogen of firn air from two sites. The first set of samples was taken in 1998 at the summit of the Devon Ice Cap in the eastern part of Devon Island. The second set was taken in 2001 at NGRIP location (North Greenland). He and Ne are heavily enriched relative to Ar with respect to the atmosphere in the air near the close-off depth at around 50–70 m. The enrichment increases with depth and reaches the maximum value in the deepest samples just above the zone of impermeable ice where no free air could be extracted anymore. Similarly, elemental ratios of O 2 / N 2, O 2 / Ar and Ar / N 2 are increasing with depth. In contrast but in line with expectations, isotopic ratios of 15N / 14N, 18O / 16O, and 36Ar / 40Ar show no significant enrichment near the close-off depth. The observed isotopic ratios in the firn air column can be explained within the uncertainty ranges by the well-known processes of gravitational enrichment and thermal diffusion. To explain the elemental ratios, however, an additional fractionation process during bubble inclusion has to be considered. We implemented this additional process into our firn air model. The fractionation factors were found by fitting model profiles to the data. We found a very similar close-off fractionation behavior for the different molecules at both sites. For smaller gas species (mainly He and Ne) the fractionation factors are linearly correlated to the molecule size, whereas for diameters greater than about 3.6 Å the fractionation seems to be significantly smaller or even negligible. An explanation for this size dependent fractionation process could be gas diffusion through the ice lattice. At Devon Island the enrichment at the bottom of the firn air column is about four times higher compared to NGRIP. We explain this by lower firn diffusivity at Devon Island, most probably due to melt layers, resulting in significantly reduced back diffusion of the excess gas near the close-off depth. The results of this study considerably increase the understanding of the processes occurring during air bubble inclusion near the close-off depth in firn and can help to improve the interpretation of direct firn air measurements, as well as air bubble measurements in ice cores, which are used in numerous studies as paleo proxies.

Size Sorting of Protein Assemblies Using Polymeric Gradient Surfaces

We report on a novel approach for the size-dependent fractionation of protein assemblies on polymeric surfaces. Using a simple temperature gradient method to generate one-dimensional gradients of grafted poly(ethylene glycol), we fabricated silicon-oxide chips with a gradually changing surface density of kinesin motor molecules. We demonstrate that such a bioactive surface can be used to sort gliding microtubules according to their length. To our knowledge, this is the first example of the self-organized sorting of protein assemblies on surfaces.

Fractionated stereotactic radiotherapy for acoustic neuromas: preservation of function versus size

For larger acoustic neuromas the preservation of cranial nerve function following radiosurgery remains a challenge. Fractionated stereotactic radiotherapy (FSR) for acoustic neuromas offers both higher total tumour dose (Gy) and potential sparing of the facial motor, sensory and auditory cranial nerves. Eighty consecutive patients (45 M, 35 F) (age 56.8±1.7 years) received FSR for AN and have a median follow up of 1.1 years. A prospective schedule permitted increased fractionation vs. size. For FSR 70 patients having AN <3.0 cm in diameter had 5 daily fractions of 5 Gy (25 Gy total) and 10 patients having AN ⩾3 cm had 10 daily fractions of 3 Gy (30 Gy total). All treatments were prescribed to the 80% isodose and given via the dedicated 10 MeV accelerator. For both the larger and smaller AN, the percentage decrease in volume was similar. No tumour increased in size, no patient developed facial weakness and hearing was preserved. Using size-dependent fractionation, FSR may result in both tumour control and preservation of normal cranial nerve functions for both large and small AN.

Polydispersity of liposome preparations as a likely source of peak width in capillary zone electrophoresis

Negatively charged liposomes consisting of phosphatidylcholine/phosphatidylglycerol/cholesterol in various ratios when subjected to capillary zone electrophoresis (CZE) in Tris–HCl (pH 8) buffer of different concentrations have been shown previously to exhibit a size-dependent migration rate at low ionic strength. The present study, focusing on the peak width under those conditions, shows that the polydispersity of liposomes correlated with, and appears to be a dominant source of, the peak width of the liposomes in CZE in a buffer of low ionic strength (2 to 5 m M Tris–HCl buffer, pH 8) at moderate electric field strengths (200 V cm −1 or less). This finding, beyond allowing for the analysis of liposome polydispersity by CZE, suggests that the size-dependent fractionation of liposome preparations by a preparative electrophoretic technique such as free-flow electrophoresis is potentially feasible.

Slalom chromatography: size-dependent separation of DNA molecules by a hydrodynamic phenomenon

Slalom chromatography, a size-dependent DNA fractionation method based on a new principle [Hirabayashi, J., & Kasai, K. (1989) Anal. Biochem. 178, 336-341], was systematically studied in detail. In this method, larger DNA fragments are eluted much later than smaller ones from columns packed with spherical microbeads. Elution of a series of DNA fragments was systematically examined by using columns packed with polymer-based packings of different diameter and different pore size for high-performance gel permeation chromatography. Packings of smaller diameter proved to be superior for resolving the smaller size range of DNA, while the reverse was the case for larger DNAs. Application of a faster flow rate led to larger retardation of every DNA fragment, while at the lowest flow rate applied (0.067 cm/min), all the fragments were eluted almost at the void volume. When the column temperature was lowered, retardation of DNA became larger. On the other hand, differences in the chemical nature and the pore size of packings, or in the hydrophobicity of the eluting solvent, had little effect on DNA retardation. Size-dependent fractionation of DNA was also achieved even on columns packed with nonporous packings having anionic groups (cation exchangers). In conclusion, these results confirmed the previous conclusion that slalom chromatography is not based on an adsorption or equilibrium phenomenon but should be attributed to a hydrodynamic phenomenon.

Size-dependent, chromatographic separation of double-stranded DNA which is not based on gel permeation mode

A new procedure for size-dependent fractionation of DNA was investigated. DNA fragments ranging from 10 to 40 kbp were separated by using columns for high-performance gel permeation chromatography. However, the order of elution was opposite to that which would be expected for gel permeation chromatography, i.e., smaller fragments were eluted faster than larger fragments, though separation based on normal gel permeation chromatography was observed when smaller DNA fragments (less than 5 kbp) were applied. The size range of DNA which can be resolved by this new procedure was found to depend on both particle size and flow rate; the use of a column packed with smaller particles or the application of a faster flow rate enabled us to resolve smaller DNA fragments, but the pore size or chemical nature of the column packing had scarcely any effect on the resolution. This mode of separation was attained by using both silica and polymer packings. The results suggest that the separation is based on a hydrodynamic phenomenon.