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The Journal of Physical Chemistry. A Sep 2017Coherent exciton delocalization in dye aggregate systems gives rise to a variety of intriguing optical phenomena, including J- and H-aggregate behavior and Davydov...
Coherent exciton delocalization in dye aggregate systems gives rise to a variety of intriguing optical phenomena, including J- and H-aggregate behavior and Davydov splitting. Systems that exhibit coherent exciton delocalization at room temperature are of interest for the development of artificial light-harvesting devices, colorimetric detection schemes, and quantum computers. Here, we report on a simple dye system templated by DNA that exhibits tunable optical properties. At low salt and DNA concentrations, a DNA duplex with two internally functionalized Cy5 dyes (i.e., dimer) persists and displays predominantly J-aggregate behavior. Increasing the salt and/or DNA concentrations was found to promote coupling between two of the DNA duplexes via branch migration, thus forming a four-armed junction (i.e., tetramer) with H-aggregate behavior. This H-tetramer aggregate exhibits a surprisingly large Davydov splitting in its absorbance spectrum that produces a visible color change of the solution from cyan to violet and gives clear evidence of coherent exciton delocalization.
Topics: Biomimetic Materials; Carbocyanines; DNA; Energy Transfer; Fluorescent Dyes; Kinetics; Light; Magnesium Chloride; Models, Chemical; Temperature; Thermodynamics
PubMed: 28813152
DOI: 10.1021/acs.jpca.7b04344 -
Biophysical Journal Apr 2006Parameters determining ionic transport numbers in transdermal iontophoresis have been characterized. The transport number of an ion (its ability to carry charge) is key...
Parameters determining ionic transport numbers in transdermal iontophoresis have been characterized. The transport number of an ion (its ability to carry charge) is key to its iontophoretic delivery or extraction across the skin. Using small inorganic ions, the roles of molar fraction and mobility of the co- and counterions present have been demonstrated. A direct, constant current was applied across mammalian skin in vitro. Cations were anodally delivered from either simple M(+)Cl(-) solutions (single-ion case, M(+) = sodium, lithium, ammonium, potassium), or binary and quaternary mixtures thereof. Transport numbers were deduced from ion fluxes. In the single-ion case, maximum cationic fluxes directly related to the corresponding ionic aqueous mobilities were found. Addition of co-ions decreased the transport numbers of all cations relative to the single-ion case, the degree of effect depending upon the molar fraction and mobility of the species involved. With chloride as the principal counterion competing to carry current across the skin (the in vivo situation), a maximum limit on the single or collective cation transport number was 0.6-0.8. Overall, these results demonstrate how current flowing across the skin during transdermal iontophoresis is distributed between competing ions, and establish simple rules with which to optimize transdermal iontophoretic transport.
Topics: Administration, Cutaneous; Ammonium Chloride; Animals; Cations; Electric Conductivity; In Vitro Techniques; Ion Transport; Iontophoresis; Lithium Chloride; Magnesium Chloride; Permeability; Skin; Sodium Chloride; Swine
PubMed: 16443654
DOI: 10.1529/biophysj.105.074609 -
Biochimica Et Biophysica Acta.... May 2022Cells are dynamic systems with complex mechanical properties, regulated by the presence of different species of proteins capable to assemble (and disassemble) into...
Cells are dynamic systems with complex mechanical properties, regulated by the presence of different species of proteins capable to assemble (and disassemble) into filamentous forms as required by different cells functions. Giant unilamellar vesicles (GUVs) of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) are systems frequently used as a simplified model of cells because they offer the possibility of assaying separately different stimuli, which is no possible in living cells. Here we present a study of the effect of acting protein on mechanical properties of GUVs, when the protein is inside the vesicles in either monomeric G-actin or filamentous F-actin. For this, rabbit skeletal muscle G-actin is introduced inside GUVs by the electroformation method. Protein polymerization inside the GUVs is promoted by adding to the solution MgCl and the ion carrier A23187 to allow the transport of Mg ions into the GUVs. To determine how the presence of actin changes the mechanical properties of GUVs, the vesicles are deformed by the application of an AC electric field in both cases with G-actin and with polymerized F-actin. The changes in shape of the vesicles are characterized by optical microscopy and from them the bending stiffness of the membrane are determined. It is found that G-actin has no appreciable effect on the bending stiffness of DMPC GUVs, but the polymerized actin makes the vesicles more rigid and therefore more resistant to deformations. This result is supported by evidence that actin filaments tend to accumulate near the membrane.
Topics: Actin Cytoskeleton; Actins; Animals; Calcimycin; Dimyristoylphosphatidylcholine; Electricity; Magnesium Chloride; Microscopy; Muscle, Skeletal; Rabbits; Surface Tension; Unilamellar Liposomes; Viscosity
PubMed: 35181295
DOI: 10.1016/j.bbamem.2022.183883 -
Molecules (Basel, Switzerland) Jan 2019Developing phase change materials (PCMs) with suitable phase change temperatures and high latent heat is of great significance for accelerating the development of latent...
Developing phase change materials (PCMs) with suitable phase change temperatures and high latent heat is of great significance for accelerating the development of latent heat storage technology to be applied in solar water heating (SWH) systems. The phase change performances of two mixtures, NH₄Al(SO₄)₂·12H₂O-MgCl₂·6H₂O (mixture-A) and KAl(SO₄)₂·12H₂O-MgCl₂·6H₂O (mixture-B), were investigated in this paper. Based on the DSC results, the optimum contents of MgCl₂·6H₂O in mixture-A and mixture-B were determined to be 30 wt%. It is found that the melting points of mixture-A (30 wt% MgCl₂·6H₂O) and mixture-B (30 wt% MgCl₂·6H₂O) are 64.15 °C and 60.15 °C, respectively, which are suitable for SWH systems. Moreover, two mixtures have high latent heat of up to 192.1 kJ/kg and 198.1 kJ/kg as well as exhibit little supercooling. After 200 cycles heating-cooling experiments, the deviations in melting point and melting enthalpy of mixture-A are only 1.51% and 1.20%, respectively. Furthermore, the XRD patterns before and after the cycling experiments show that mixture-A possesses good structure stability. These excellent thermal characteristics make mixture-A show great potential for SWH systems.
Topics: Alum Compounds; Aluminum Compounds; Calorimetry, Differential Scanning; Magnesium Chloride; Molecular Structure; Phase Transition; Potassium Compounds; Sulfates; Thermogravimetry; X-Ray Diffraction
PubMed: 30669591
DOI: 10.3390/molecules24020363 -
The Journal of Biological Chemistry Nov 1990We have recently shown that the Ca.EGTA and Mg.EDTA complexes, but not free Ca2+ or Mg2+, inhibit the liver glucose-6-phosphatase (Mithieux, G., Vega, F. V., Beylot, M.,...
The liver glucose-6-phosphatase of intact microsomes is inhibited and displays sigmoid kinetics in the presence of alpha-ketoglutarate-magnesium and oxaloacetate-magnesium chelates.
We have recently shown that the Ca.EGTA and Mg.EDTA complexes, but not free Ca2+ or Mg2+, inhibit the liver glucose-6-phosphatase (Mithieux, G., Vega, F. V., Beylot, M., and Riou, J. P. (1990) J. Biol. Chem. 265, 7257-7259). In this work, we report that, when complexed with Mg2+, two endogenous dicarboxylic keto acids (alpha-ketoglutarate (alpha-KG) and oxaloacetate (OAA] inhibit the glucose-6-phosphatase activity at low concentrations of substrate. This phenomenon is specific for complexes of Mg2+ with alpha-KG and OAA since 1) the complexes of Mg2+ with a number of other di- or tricarboxylic acids having high structural analogy with alpha-KG and OAA (oxalate, malate, succinate, citrate, aspartate, and glutamate) do not inhibit the glucose-6-phosphatase activity and 2) the Ca.alpha-KG and Ca.OAA chelates do not inhibit the glucose-6-phosphatase activity. In the presence of Mg.alpha-KG or Mg.OAA chelates, the enzyme displays sigmoid kinetics; the Hanes plots deviate from linearity, indicating the positive cooperative dependence of the velocity upon the substrate concentration. Hill coefficients (equal to 1 in the absence of the chelates) of 1.23 and 1.33 have been determined in the presence of Mg.alpha-KG and Mg.OAA complexes, respectively. The disruption of microsomal integrity by detergents abolishes the effect of Mg.alpha-KG and Mg.OAA, suggesting that the magnesium chelates inhibit the translocase component of the glucose-6-phosphatase system.
Topics: Animals; Calcium Chloride; Glucose-6-Phosphatase; Ketoglutaric Acids; Kinetics; Magnesium; Magnesium Chloride; Microsomes, Liver; Oxaloacetates; Rats
PubMed: 2173703
DOI: No ID Found -
Proceedings of the National Academy of... Mar 1992When coated on bacteriological plastic at doses greater than or equal to 0.1 microgram/cm2, human and bovine angiogenin support calf pulmonary artery endothelial and...
When coated on bacteriological plastic at doses greater than or equal to 0.1 microgram/cm2, human and bovine angiogenin support calf pulmonary artery endothelial and Chinese hamster fibroblast cell adhesion and spreading, but do not affect cell adhesion when in solution. The kinetics of endothelial cell attachment to angiogenin are indistinguishable from those in the presence of gelatin. Calcium and/or magnesium ions are critical for cell adhesion or spreading onto angiogenin but protein synthesis and glycoprotein secretion are not necessary. Adhesion to angiogenin is not altered by the addition to the incubation solution of fibronectin, fibrinogen, laminin, collagen I and IV, or vitronectin. The peptide Arg-Gly-Asp-Ser inhibits endothelial cell response to angiogenin whereas the reverse peptide Ser-Asp-Gly-Arg-Gly has no effect. These findings show that angiogenin can serve as an effective substratum for cell adhesion by inducing an interaction similar to but independent from that of other extracellular matrix molecules. Induction of cell adhesion and subsequent migration may be critical steps in the process of angiogenesis.
Topics: Amino Acid Sequence; Angiogenesis Inducing Agents; Animals; Calcium Chloride; Cattle; Cell Adhesion; Cell Line; Dose-Response Relationship, Drug; Endothelium, Vascular; Fibroblasts; Humans; Kinetics; Magnesium Chloride; Molecular Sequence Data; Oligopeptides; Proteins; Pulmonary Artery; Recombinant Proteins; Ribonuclease, Pancreatic
PubMed: 1549588
DOI: 10.1073/pnas.89.6.2232 -
Carbohydrate Research Jul 2007Solid-state hydrolysis proceeded with cellulose and methyl alpha- and beta-D-glucopyranosides in the presence of hydrated magnesium chloride. This reaction was effective...
Solid-state hydrolysis proceeded with cellulose and methyl alpha- and beta-D-glucopyranosides in the presence of hydrated magnesium chloride. This reaction was effective even at >100 degrees C since the hydrated water, which is held by MgCl(2) up to >200 degrees C, is utilized as a nucleophile. Excess water made this reaction ineffective due to the competition between water and sugar oxygen atoms in coordinating with Mg(2+), a Lewis acid. Consequently, this hydrolysis reaction is characteristic of solid-state reactions.
Topics: Cellulose; Chromatography, Gel; Glucosides; Hot Temperature; Hydrolysis; Magnesium Chloride; Magnetic Resonance Spectroscopy; Molecular Structure; Pyrans; Water; X-Ray Diffraction
PubMed: 17498675
DOI: 10.1016/j.carres.2007.04.009 -
The Journal of Biological Chemistry Mar 2016Replicative DNA polymerases (DNAPs) require divalent metal cations for phosphodiester bond formation in the polymerase site and for hydrolytic editing in the exonuclease...
Replicative DNA polymerases (DNAPs) require divalent metal cations for phosphodiester bond formation in the polymerase site and for hydrolytic editing in the exonuclease site. Me(2+) ions are intimate architectural components of each active site, where they are coordinated by a conserved set of amino acids and functional groups of the reaction substrates. Therefore Me(2+) ions can influence the noncovalent transitions that occur during each nucleotide addition cycle. Using a nanopore, transitions in individual Φ29 DNAP complexes are resolved with single-nucleotide spatial precision and sub-millisecond temporal resolution. We studied Mg(2+) and Mn(2+), which support catalysis, and Ca(2+), which supports deoxynucleoside triphosphate (dNTP) binding but not catalysis. We examined their effects on translocation, dNTP binding, and primer strand transfer between the polymerase and exonuclease sites. All three metals cause a concentration-dependent shift in the translocation equilibrium, predominantly by decreasing the forward translocation rate. Me(2+) also promotes an increase in the backward translocation rate that is dependent upon the primer terminal 3'-OH group. Me(2+) modulates the translocation rates but not their response to force, suggesting that Me(2+) does not affect the distance to the transition state of translocation. Absent Me(2+), the primer strand transfer pathway between the polymerase and exonuclease sites displays additional kinetic states not observed at >1 mm Me(2+). Complementary dNTP binding is affected by Me(2+) identity, with Ca(2+) affording the highest affinity, followed by Mn(2+), and then Mg(2+). Both Ca(2+) and Mn(2+) substantially decrease the dNTP dissociation rate relative to Mg(2+), while Ca(2+) also increases the dNTP association rate.
Topics: Amino Acid Substitution; Bacteriophages; Biocatalysis; Calcium Chloride; Chlorides; DNA Replication; DNA-Directed DNA Polymerase; Deoxycytidine Monophosphate; Deoxyguanine Nucleotides; Kinetics; Magnesium Chloride; Manganese Compounds; Polymerization; Protein Binding; Viral Proteins
PubMed: 26797125
DOI: 10.1074/jbc.M115.701797 -
Nucleic Acids Research Nov 2021Liposomes are widely used as synthetic analogues of cell membranes and for drug delivery. Lipid-binding DNA nanostructures can modify the shape, porosity and reactivity...
Liposomes are widely used as synthetic analogues of cell membranes and for drug delivery. Lipid-binding DNA nanostructures can modify the shape, porosity and reactivity of liposomes, mediated by cholesterol modifications. DNA nanostructures can also be designed to switch conformations by DNA strand displacement. However, the optimal conditions to facilitate stable, high-yield DNA-lipid binding while allowing controlled switching by strand displacement are not known. Here, we characterized the effect of cholesterol arrangement, DNA structure, buffer and lipid composition on DNA-lipid binding and strand displacement. We observed that binding was inhibited below pH 4, and above 200 mM NaCl or 40 mM MgCl2, was independent of lipid type, and increased with membrane cholesterol content. For simple motifs, binding yield was slightly higher for double-stranded DNA than single-stranded DNA. For larger DNA origami tiles, four to eight cholesterol modifications were optimal, while edge positions and longer spacers increased yield of lipid binding. Strand displacement achieved controlled removal of DNA tiles from membranes, but was inhibited by overhang domains, which are used to prevent cholesterol aggregation. These findings provide design guidelines for integrating strand displacement switching with lipid-binding DNA nanostructures. This paves the way for achieving dynamic control of membrane morphology, enabling broader applications in nanomedicine and biophysics.
Topics: Cholesterol; DNA; DNA, Single-Stranded; Hydrogen-Ion Concentration; Kinetics; Liposomes; Magnesium Chloride; Nanostructures; Nucleic Acid Conformation; Phosphatidylcholines; Phosphatidylethanolamines; Sodium Chloride; Solutions; Thermodynamics
PubMed: 34614184
DOI: 10.1093/nar/gkab888 -
International Journal of Molecular... Jun 2024Biopharmaceutical products, in particular messenger ribonucleic acid (mRNA), have the potential to dramatically improve the quality of life for patients suffering from...
Biopharmaceutical products, in particular messenger ribonucleic acid (mRNA), have the potential to dramatically improve the quality of life for patients suffering from respiratory and infectious diseases, rare genetic disorders, and cancer. However, the quality and safety of such products are particularly critical for patients and require close scrutiny. Key product-related impurities, such as fragments and aggregates, among others, can significantly reduce the efficacy of mRNA therapies. In the present work, the possibilities offered by size exclusion chromatography (SEC) for the characterization of mRNA samples were explored using state-of-the-art ultra-wide pore columns with average pore diameters of 1000 and 2500 Å. Our investigation shows that a column with 1000 Å pores proved to be optimal for the analysis of mRNA products, whatever the size between 500 and 5000 nucleotides (nt). We also studied the influence of mobile phase composition and found that the addition of 10 mM magnesium chloride (MgCl) can be beneficial in improving the resolution and recovery of large size variants for some mRNA samples. We demonstrate that caution should be exercised when increasing column length or decreasing the flow rate. While these adjustments slightly improve resolution, they also lead to an apparent increase in the amount of low-molecular-weight species (LMWS) and monomer peak tailing, which can be attributed to the prolonged residence time inside the column. Finally, our optimal SEC method has been successfully applied to a wide range of mRNA products, ranging from 1000 to 4500 nt in length, as well as mRNA from different suppliers and stressed/unstressed samples.
Topics: RNA, Messenger; Chromatography, Gel; Humans; Porosity; Molecular Weight; Magnesium Chloride
PubMed: 38892442
DOI: 10.3390/ijms25116254