Critical role of the structure of the mineral-water interface in the zeta potential measured by streaming potential method

2020 ◽  
Author(s):  
Shuai Li ◽  
Matthew Jackson
Keyword(s):  
Zeta Potential ◽  
High Salinity ◽  
Critical Role ◽  
Streaming Potential ◽  
Potential Method ◽  
Fontainebleau Sandstone ◽  
Constant Potential ◽  
First Time ◽  
Polarity Change

<p><span>In this study, zeta potential has been measured by using the streaming potential method for the intact sandstone in contact with CaCl<sub>2</sub> electrolytes. The experimental results show that a positive zeta potential has been observed for the first time for the intact Fontainebleau sandstone under high salinity of CaCl<sub>2</sub>, and its magnitude increases with increasing ionic strength. It cannot be explained by the Gouy-Chapman theory anticipating a constant potential for high salinities due to the collapse of the electrical double layer. Meanwhile, the brine effluents after the completion of the streaming potential measurements were collected and then pH and brine composition were analysed suggesting that those variations of pH and chemical composition are negligible and cannot explain the polarity change at high salinity. The anomalous positive potential of the intact Fontainebleau sandstone is due to that overcharge of calcium ions sorbed into the mineral surface, which is consistence with previous literature data.</span></p>

The Determination of Electrokinetic Coupling-Coefficient and Zeta Potential of Rock Samples by Electrokinetic Measurements

2012 ◽  
Vol 516-517 ◽  
pp. 1870-1873 ◽  
Author(s):  
Jun Wang ◽  
Heng Shan Hu
Keyword(s):  
Zeta Potential ◽  
Coupling Coefficient ◽  
Streaming Potential ◽  
Potential Method ◽  
Surface Conductivity ◽  
Reliable Estimate ◽  
Surface Conductance ◽  
Streaming Current ◽  
Low Concentrations

The electrokinetic effects are important in the understanding of electric properties in porous medium. In this study, the streaming potential and streaming current of saturated samples are measured at different concentrations, then three methods are applied to obtain the zeta-potential and electrokinetic coupling coefficient. The study shows that the results obtained from streaming potential and streaming current methods agree well with each other, but the results obtained from simplified streaming potential method become seriously inaccurate at low concentrations due to the influence of surface conductance. This experimental study also provides a reliable estimate of the surface conductivity and its contribution to zeta-potential at given concentrations.

scholarly journals Isolation and Characterization of Cryptococcus neoformans Spores Reveal a Critical Role for Capsule Biosynthesis Genes in Spore Biogenesis

2009 ◽  
Vol 8 (4) ◽  
pp. 595-605 ◽  
Author(s):  
Michael R. Botts ◽  
Steven S. Giles ◽  
Marcellene A. Gates ◽  
Thomas R. Kozel ◽  
Christina M. Hull
Keyword(s):  
Cryptococcus Neoformans ◽  
Fungal Pathogens ◽  
Critical Role ◽  
Spore Formation ◽  
Yeast Cells ◽  
Isolation And Characterization ◽  
Specific Configuration ◽  
First Time

ABSTRACT Spores are essential particles for the survival of many organisms, both prokaryotic and eukaryotic. Among the eukaryotes, fungi have developed spores with superior resistance and dispersal properties. For the human fungal pathogens, however, relatively little is known about the role that spores play in dispersal and infection. Here we present the purification and characterization of spores from the environmental fungus Cryptococcus neoformans. For the first time, we purified spores to homogeneity and assessed their morphological, stress resistance, and surface properties. We found that spores are morphologically distinct from yeast cells and are covered with a thick spore coat. Spores are also more resistant to environmental stresses than yeast cells and display a spore-specific configuration of polysaccharides on their surfaces. Surprisingly, we found that the surface of the spore reacts with antibodies to the polysaccharide glucuronoxylomannan, the most abundant component of the polysaccharide capsule required for C. neoformans virulence. We explored the role of capsule polysaccharide in spore development by assessing spore formation in a series of acapsular strains and determined that capsule biosynthesis genes are required for proper sexual development and normal spore formation. Our findings suggest that C. neoformans spores may have an adapted cell surface that facilitates persistence in harsh environments and ultimately allows them to infect mammalian hosts.

Functional role of a polymorphism in the Pannexin1 gene in collageninduced platelet aggregation

2015 ◽  
Vol 114 (08) ◽  
pp. 325-336 ◽  
Author(s):  
Filippo Molica ◽  
Jean-François Denis ◽  
Paul Bradfield ◽  
Silvia Penuela ◽  
Anne Zufferey ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Platelet Reactivity ◽  
Critical Role ◽  
Atp Release ◽  
Human Platelets ◽  
Immune Synapse ◽  
Cardiovascular Patients ◽  
Exogenous Expression ◽  
First Time

SummaryPannexin1 (Panx1) forms ATP channels that play a critical role in the immune response by reinforcing purinergic signal amplification in the immune synapse. Platelets express Panx1 and given the importance of ATP release in platelets, we investigated Panx1 function in platelet aggregation and the potential impact of genetic polymorphisms on Panx1 channels. We show here that Panx1 forms ATP release channels in human platelets and that inhibiting Panx1 channel function with probenecid, mefloquine or specific 10Panx1 peptides reduces collagen-induced platelet aggregation but not the response induced by arachidonic acid or ADP. These results were confirmed using Panx1-/- platelets. Natural variations have been described in the human Panx1 gene, which are predicted to induce non-conservative amino acid substitutions in its coding sequence. Healthy subjects homozygous for Panx1–400C, display enhanced platelet reactivity in response to collagen compared with those bearing the Panx1–400A allele. Conversely, the frequency of Panx1–400C homozygotes was increased among cardiovascular patients with hyper-reactive platelets compared with patients with hypo-reactive platelets. Exogenous expression of polymorphic Panx1 channels in a Panx-deficient cell line revealed increased basal and stimulated ATP release from cells transfected with Panx1–400C channels compared with Panx1–400A expressing transfectants. In conclusion, we demonstrate a specific role for Panx1 channels in the signalling pathway leading to collagen-induced platelet aggregation. Our study further identifies for the first time an association between a Panx1–400A>C genetic polymorphism and collagen-induced platelet reactivity. The Panx1–400C variant encodes for a gain-of-function channel that may adversely affect atherothrombosis by specifically enhancing collagen-induced ATP release and platelet aggregation.

ADF/n-cofilin–dependent actin turnover determines platelet formation and sizing

Blood ◽  
2010 ◽  
Vol 116 (10) ◽  
pp. 1767-1775 ◽  
Author(s):  
Markus Bender ◽  
Anita Eckly ◽  
John H. Hartwig ◽  
Margitta Elvers ◽  
Irina Pleines ◽  
...  
Keyword(s):  
Actin Filament ◽  
Molecular Mechanisms ◽  
Critical Role ◽  
Actin Dynamics ◽  
Complex Process ◽  
First Time ◽  
Late Stages ◽  
Platelet Formation

Abstract The cellular and molecular mechanisms orchestrating the complex process by which bone marrow megakaryocytes form and release platelets remain poorly understood. Mature megakaryocytes generate long cytoplasmic extensions, proplatelets, which have the capacity to generate platelets. Although microtubules are the main structural component of proplatelets and microtubule sliding is known to drive proplatelet elongation, the role of actin dynamics in the process of platelet formation has remained elusive. Here, we tailored a mouse model lacking all ADF/n-cofilin–mediated actin dynamics in megakaryocytes to specifically elucidate the role of actin filament turnover in platelet formation. We demonstrate, for the first time, that in vivo actin filament turnover plays a critical role in the late stages of platelet formation from megakaryocytes and the proper sizing of platelets in the periphery. Our results provide the genetic proof that platelet production from megakaryocytes strictly requires dynamic changes in the actin cytoskeleton.

scholarly journals Siderophore-Mediated Iron Acquisition Plays a Critical Role in Biofilm Formation and Survival of Staphylococcus epidermidis Within the Host

2021 ◽  
Vol 8 ◽  
Author(s):  
Fernando Oliveira ◽  
Tânia Lima ◽  
Alexandra Correia ◽  
Ana Margarida Silva ◽  
Cristina Soares ◽  
...  
Keyword(s):  
Staphylococcus Epidermidis ◽  
Iron Acquisition ◽  
Critical Role ◽  
Siderophore Production ◽  
Restricted Environment ◽  
Underlying Mechanisms ◽  
First Time ◽  
Comprehensive Study

Iron acquisition through siderophores, a class of small, potent iron-chelating organic molecules, is a widely spread strategy among pathogens to survive in the iron-restricted environment found in the host. Although these molecules have been implicated in the pathogenesis of several species, there is currently no comprehensive study addressing siderophore production in Staphylococcus epidermidis. Staphylococcus epidermidis is an innocuous skin commensal bacterium. The species, though, has emerged as a leading cause of implant-associated infections, significantly supported by an inherent ability to form biofilms. The process of adaptation from skin niche environments to the hostile conditions during invasion is yet not fully understood. Herein, we addressed the possible role of siderophore production in S. epidermidis virulence. We first identified and deleted a siderophore homolog locus, sfaABCD, and provided evidence for its involvement in iron acquisition. Our findings further suggested the involvement of siderophores in the protection against oxidative stress-induced damage and demonstrated the in vivo relevance of a siderophore-mediated iron acquisition during S. epidermidis infections. Conclusively, this study addressed, for the first time in this species, the underlying mechanisms of siderophore production, highlighting the importance of a siderophore-mediated iron acquisition under host relevant conditions and, most importantly, its contribution to survival within the host.

A dynamic Stern layer model to explain high salinity zeta potential measurements on sandstones

2020 ◽  
Author(s):  
Philippe Leroy ◽  
Shuai Li
Keyword(s):  
Electrical Properties ◽  
Zeta Potential ◽  
Water Flow ◽  
High Salinity ◽  
Surface Complexation ◽  
Streaming Potential ◽  
Shear Plane ◽  
Mineral Surface ◽  
Stern Layer ◽  
Counter Ions

<p>Exploring the electrical properties of the mineral-water interface for interpreting geophysical electrical measurements is a very challenging work because of the low specific surface area of minerals such as quartz or calcite. Only few methods exist to probe the properties of the electrical double layer (EDL) compensating the surface charge of minerals. Among them, there is the streaming potential (SP) method where the applied water pressure difference generates a pore water flow displacing the mobile counter-ions in excess in the EDL, hence creating a measurable electrical potential difference, the streaming potential. During SP measurements, the exact position of the shear plane from the mineral surface is not known and it is widely accepted that the shear plane is located between the compact Stern layer and the diffuse layer. In our study, we show that the assumption that there is no water flow in the Stern layer has no physical basis for sandstones in contact with a NaCl electrolyte because water molecules around counter-ions in the Stern layer may have bulk-like properties. Using a basic Stern model to simulate surface complexation reactions and considering water flow in the Stern layer, we reproduced the zeta potential measurements on sandstones over a large salinity range from about 10<sup>-2</sup> to 5.5 M NaCl. The “anomalous” high salinity zeta potential data can not be reproduced by a surface complexation model considering water flow only in the diffuse layer. Our ability to explain these measurements suggests that the shear plane may be located between the mineral surface and the Stern layer, i.e. closer to the surface than previously thought, which may have strong implications for the modelling of the surface electrical properties of the minerals.</p>

scholarly journals Streptavidin-coated gold nanoparticles: critical role of oligonucleotides on stability and fractal aggregation

2017 ◽  
Vol 8 ◽  
pp. 1-11 ◽  
Author(s):  
Roberta D'Agata ◽  
Pasquale Palladino ◽  
Giuseppe Spoto
Keyword(s):  
Gold Nanoparticles ◽  
Critical Role ◽  
Medical Diagnostics ◽  
Nanoparticle Dispersion ◽  
One Dimensional ◽  
Fundamental Properties ◽  
Biochemical Sensing ◽  
Highly Sensitive ◽  
First Time

Gold nanoparticles (AuNPs) exhibit unique properties that can be modulated through a tailored surface functionalization, enabling their targeted use in biochemical sensing and medical diagnostics. In particular, streptavidin-modified AuNPs are increasingly used for biosensing purposes. We report here a study of AuNPs surface-functionalized with streptavidin-biotinylated oligonucleotide, focussing on the role played by the oligonucleotide probes in the stabilization/destabilization of the functionalized nanoparticle dispersion. The behaviour of the modified AuNP dispersion as a consequence of the competitive displacement of the biotinylated oligonucleotide has been investigated and the critical role of displaced oligonucletides in triggering the quasi one-dimensional aggregation of nanoparticles is demonstrated for the first time. The thorough understanding of the fundamental properties of bioconjugated AuNPs is of great importance for the design of highly sensitive and reliable functionalized AuNP-based assays.

scholarly journals DUAL-tDCS Treatment over the Temporo-Parietal Cortex Enhances Writing Skills: First Evidence from Chronic Post-Stroke Aphasia

Life ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 343
Author(s):  
Francesca Pisano ◽  
Carlo Caltagirone ◽  
Chiara Incoccia ◽  
Paola Marangolo
Keyword(s):  
Parietal Cortex ◽  
Critical Role ◽  
Writing Skills ◽  
Double Blind ◽  
Post Stroke ◽  
Lexical Route ◽  
Left And Right ◽  
Cathodal Current ◽  
First Time

The learning of writing skills involves the re-engagement of previously established independent procedures. Indeed, the writing deficit an adult may acquire after left hemispheric brain injury is caused by either an impairment to the lexical route, which processes words as a whole, to the sublexical procedure based on phoneme-to-grapheme conversion rules, or to both procedures. To date, several approaches have been proposed for writing disorders, among which, interventions aimed at restoring the sub-lexical procedure were successful in cases of severe agraphia. In a randomized double-blind crossover design, fourteen chronic Italian post-stroke aphasics underwent dual transcranial direct current stimulation (tDCS) (20 min, 2 mA) with anodal and cathodal current simultaneously placed over the left and right temporo-parietal cortex, respectively. Two different conditions were considered: (1) real, and (2) sham, while performing a writing task. Each experimental condition was performed for ten workdays over two weeks. After real stimulation, a greater amelioration in writing with respect to the sham was found. Relevantly, these effects generalized to different language tasks not directly treated. This evidence suggests, for the first time, that dual tDCS associated with training is efficacious for severe agraphia. Our results confirm the critical role of the temporo-parietal cortex in writing skills.

scholarly journals Deletion of Seipin Attenuates Vascular Function and the Anticontractile Effect of Perivascular Adipose Tissue

2021 ◽  
Vol 8 ◽  
Author(s):  
Mengyu Wang ◽  
Junhui Xing ◽  
Mengduan Liu ◽  
Mingming Gao ◽  
Yangyang Liu ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Adipose Tissue ◽  
Vascular Function ◽  
Mesenteric Artery ◽  
Critical Role ◽  
Perivascular Adipose Tissue ◽  
Vascular Homeostasis ◽  
Lipid Droplet Formation ◽  
First Time

Seipin locates in endoplasmic reticulum (ER) and regulates adipogenesis and lipid droplet formation. Deletion of Seipin has been well-demonstrated to cause severe general lipodystrophy, however, its role in maintaining perivascular adipose tissue (PVAT) and vascular homeostasis has not been directly assessed. In the present study, we investigated the role of Seipin in mediating the anticontractile effect of PVAT and vascular function. Seipin expression in PVAT and associated vessels were detected by qPCR and western-blot. Seipin is highly expressed in PVAT, but hardly in vessels. Structural and functional alterations of PVAT and associated vessels were compared between Seipin−/− mice and WT mice. In Seipin−/− mice, aortic and mesenteric PVAT were significantly reduced in mass and adipose-derived relaxing factors (ADRFs) secretion, but increased in macrophage infiltration and ER stress, as compared with those in WT mice. Aortic and mesenteric artery rings from WT and Seipin−/− mice were mounted on a wire myograph. Vasoconstriction and vasodilation were studied in vessels with and without PVAT. WT PVAT augmented relaxation but not Seipin−/− PVAT, which suggest impaired anticontractile function in PVAT of Seipin−/− mice. Thoracic aorta and mesenteric artery from Seipin−/− mice had impaired contractility in response to phenylephrine (PHE) and relaxation to acetylcholine (Ach). In conclusion, Seipin deficiency caused abnormalities in PVAT morphology and vascular functions. Our data demonstrated for the first time that Seipin plays a critical role in maintaining PVAT function and vascular homeostasis.

scholarly journals Glioblastoma Multiformе Tumour Stem Cells as Potential Therapeutic Targets

2019 ◽  
Vol 9 (3) ◽  
pp. 216-222
Author(s):  
O. A. Beylerli ◽  
I. F. Gareev ◽  
Sh. Zhao ◽  
X. Chen
Keyword(s):  
Stem Cells ◽  
Critical Role ◽  
Molecular Heterogeneity ◽  
Immune Recognition ◽  
Malignant Tumours ◽  
Phenotypic Characteristics ◽  
Malignant Brain Tumours ◽  
First Time ◽  
Original Concept

The original concept of tumour stem cells (TSC) has been questioned ten years after TSCs in glioblastoma (GBM) had been described for the first time. Our understanding of cell heterogeneity in malignant brain tumours has become more complex. The improvements in our knowledge of tumour stem cells also impact on pre-clinical research and clinical practice. Chemoresistance is one of the key obstacles to success in treating malignant tumours; it results in tumour recurrence and metastatic spread. GBM relapse is almost universal, and its prognosis remains uncertain despite significant advances in treatment over the last decade. Tumour stem cells, glioblastoma stem cells (GSC) in particular, are highly resistant to chemotherapy, radiation therapy and immune recognition. GBM shows significant intratumoural phenotypic and molecular heterogeneity containing a population of tumour stem cells that contributes to the division of tumour cells supporting the resistance to treatment. TSCs are defined functionally by their ability for self-renewal and differentiation; they present a most diverse hierarchy of cells making up the tumour. The critical role of TSCs in glioblastoma pathogenesis makes the research into their molecular and phenotypic characteristics is a therapeutic priority.

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