DNA Cyclization: Suppression or Enhancement by Electrostatic Repulsions?

The theory of molecular and equivalent orbitals developed in previous papers of this series is used to discuss the spatial distribution of lone-pair electrons in molecules such as H 2 O and NH 3 and the part they play in determining the equilibrium configuration. Previous treatments of H 2 O have assumed that the lone pairs are essentially unaltered by molecular formation. It is shown here, on the other hand, that they will be displaced so as to be mainly concentrated on the side of the O-nucleus remote from the hydrogen atoms. An important consequence of this is that the lone-pair electrons will make a contribution to the total dipole moment. Comparison of the experimentally observed moment with an approximate quantitative treatment suggests that, as a result of this, transfer of electrons from the hydrogen atoms to the oxygen does not occur to the extent that has previously been believed. The variation of the spatial distribution of the orbitals of H 2 O with changes of nuclear configuration is examined and it is shown that, in the equilibrium position, the electronic structure can be described approximately by two sets of two equivalent orbitals pointing in nearly tetrahedral directions. The dependence of total energy on bond angle is discussed and it is shown that electrostatic repulsions between the equivalent orbitals are major factors in determining the equilibrium configuration. Similar considerations apply to NH 3 .

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Partial denaturation of small chromatin fragments: direct evidence for the radial distribution of nucleosomes in folded chromatin fibers

Journal of Cell Science ◽

10.1242/jcs.111.12.1707 ◽

1998 ◽

Vol 111 (12) ◽

pp. 1707-1715

Author(s):

A. Bermudez ◽

S. Bartolome ◽

J.R. Daban

Keyword(s):

Radial Distribution ◽

Direct Evidence ◽

Dna Loops ◽

Entry Points ◽

Partial Denaturation ◽

Chromatin Fibers ◽

High Concentrations ◽

Chicken Erythrocytes ◽

Top View ◽

Electrostatic Repulsions

To examine the internal structure of chromatin fibers, we have developed procedures for partial denaturation of small chromatin fragments (8–30 nucleosomes) from chicken erythrocytes. Electron micrographs of samples prepared under conditions that cause nucleosome dissociation show rods and loops projecting from short compact fibers fixed by glutaraldehyde in 1.7 mM Mg2+. According to previous studies in our laboratory, these images correspond to the top view of partially denatured fibers. Our results indicate that rods and loops consist of extended duplex DNA of different lengths. DNA in loops is nicked, as demonstrated by experiments performed in the presence of high concentrations of ethidium bromide. Length measurements indicate that the radial projections of DNA are produced by unfolding of nucleosomal units. Loops are formed by DNA from denatured nucleosomes in internal positions of the fiber; DNA from denatured nucleosomes in terminal positions form rods. Our micrographs show clearly a radial distribution of DNA loops and rods projecting from fibers. Rods are orthogonal to the surface of the chromatin fragments. Considering that the high ionic strength used in this study (0.8-2.0 M NaCl) neutralizes the electrostatic repulsions between rods and fiber, this observation suggests that rods are extensions of nucleosomes radially organized inside the fiber. The position of the entry points of DNA loops into the fiber could be influenced by constraint on loops, but our results showing that the arc that separates these points in dinucleosome loops is relatively short suggest that consecutive nucleosomes are relatively close to each other in the folded fiber.

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The Influence of Electrostatic Repulsions on Micellar Diffusivities Obtained by Dynamic Light Scattering: Experiment vs Theory

Surfactants in Solution ◽

10.1007/978-1-4613-1831-6_14 ◽

1986 ◽

pp. 203-216

Author(s):

D. F. Nicoli ◽

V. Athanasakis ◽

J. R. Moffat ◽

R. B. Dorshow ◽

C. A. Bunton ◽

...

Keyword(s):

Light Scattering ◽

Dynamic Light Scattering ◽

Scattering Experiment ◽

Electrostatic Repulsions

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Liquid Crystal Behavior of V2O5·nH2O Gels

MRS Proceedings ◽

10.1557/proc-547-363 ◽

1998 ◽

Vol 547 ◽

Cited By ~ 1

Author(s):

J. Livage ◽

P. Davidson ◽

X. Commeinhes ◽

O. Pelletier

Keyword(s):

Liquid Crystal ◽

Vanadium Pentoxide ◽

Colloidal Particles ◽

Organic Molecules ◽

Polarized Light ◽

Colloidal Suspensions ◽

Acid Dissociation ◽

Polymeric Particles ◽

Nematic Phases ◽

Electrostatic Repulsions

AbstractMost liquid crystals are made of organic molecules, very few of them are based on mineral compounds. Vanadium pentoxide gels and sols have been shown to give mesophases. They are made of ribbon-like polymeric particles of vanadium pentoxide dispersed in water. Ansitropic xerogel layers are formed when these gels are deposited and dried onto flat substrates. Dehydration is reversible and fluid phases are again obtained via a swelling process when water is added to the xerogel.When observed by polarized light microscopy, colloidal suspensions of V2O5 ribbons display defects typical of lyotropic nematic phases. Dilute nematic suspensions can even be oriented by applying a magnetic field of about 0.5 Tesla. Such a liquid crystal behavior is mainly due to the highly anisotropic shape of vanadium oxide colloidal particles. Acid dissociation at the oxide/water interface gives rise to surface electrical charges and electrostatic repulsions should also be responsible for the stabilization of the nematic phase.

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Influence of calcium chloride on the chymosin-initiated coagulation of casein micelles

Journal of Dairy Research ◽

10.1017/s0022029900024997 ◽

1986 ◽

Vol 53 (3) ◽

pp. 371-379 ◽

Cited By ~ 30

Author(s):

Neal A. Bringe ◽

John E. Kinsella

Keyword(s):

Calcium Chloride ◽

Average Rate ◽

Casein Micelle ◽

Clotting Time ◽

Casein Micelles ◽

Casein Hydrolysis ◽

Catalysed Reaction ◽

Low Concentrations ◽

Hydrolysis Of ◽

Electrostatic Repulsions

SUMMARYCoagulation of para-casein micelles was monitored using a Platelet Aggregometer at 37·8 °C and pH 6·7. The macropeptide released by chymosin was determined quantitatively with fluorescamine. The aggregatability of para-casein micelles integrated over the complete hydrolysis of κ-casein was calculated from the amount of κ-casein hydrolysed during the clotting time (Tc). Low concentrations of CaCl2 enhanced the rate of κ-casein hydrolysis but increases in CaCl2 concentration above 8 mM caused marked decreases in this rate. Calcium chloride enhanced the ability of para-casein micelles to aggregate. Little aggregation of para-casein micelles occurred at 0·6 mM-CaCl2 even after all of the κ-casein was hydrolysed. As the concentration of CaCl2 was increased from 3 to 60 mM, aggregation of para-casein micelles took place at progressively lower levels of κ-casein hydrolysis and the percentage hydrolysis at the Tc decreased markedly from 71±7% to 26±8%. The combined influence of CaCl2 on the velocity of the chymosin-catalysed reaction and on para-casein micelle aggregatability accounted for its effect on the average rate of coagulation (calculated by the reciprocal of the Tc). Results are consistent with the hypothesis that electrostatic repulsions and ionic bonding are involved in the interaction between chymosin and κ-casein.

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Factors Influencing the Surface Functionalization of Citrate Stabilized Gold Nanoparticles with Cysteamine, 3-Mercaptopropionic Acid or l-Selenocystine for Sensor Applications

Chemosensors ◽

10.3390/chemosensors8030080 ◽

2020 ◽

Vol 8 (3) ◽

pp. 80

Author(s):

Georgia I. Sakellari ◽

Nicole Hondow ◽

Philip H.E. Gardiner

Keyword(s):

Gold Nanoparticles ◽

Co Adsorption ◽

Limiting Factor ◽

Experimental Conditions ◽

Mercaptopropionic Acid ◽

X Ray ◽

Sensor Applications ◽

Factors Influencing ◽

Electrostatic Repulsions ◽

Functionalized Aunps

Thiols and selenides bind to the surface of gold nanoparticles (AuNPs) and thus provide suitable platforms for the fabrication of sensors. However, the co-existence of adsorbed citrate on the surface of the nanoparticles can influence their functionalization behavior and potentially their sensing performance measured by the extent of particle aggregation. In this study, the functionalization of purchased (7.3 ± 1.2 nm) and in-house prepared AuNPs (13.8 ± 1.2 nm), under the same experimental conditions with either cysteamine (Cys), 3-mercaptopropionic acid (3-MPA), or l-selenocystine (SeCyst) was investigated. 1H-NMR measurements showed distinct citrate signatures on the in-house synthesized citrate-stabilized AuNPs, while no citrate signals were detected on the purchased AuNPs other than evidence of the presence of α-ketoglutaric acid. Carboxylate-containing species attributed to either citrate or α-ketoglutaric acid were identified in all functionalized AuNPs. ATR-FTIR spectroscopy confirmed the functionalization of AuNPs with Cys and 3-MPA, and energy dispersive X-ray (EDX) spectroscopy measurements suggested the formation of SeCyst functionalized AuNPs. Co-adsorption rather than displacement by the functionalizing agents and carboxylate-containing molecules was indicated, which for Cys and SeCyst functionalized AuNPs was also the aggregation limiting factor. In contrast, the behavior of 3-MPA functionalized AuNPs could be attributed to electrostatic repulsions between the functionalized groups.

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Evidence of re-entrant behavior in laponite-PEO systems

MRS Proceedings ◽

10.1557/proc-0899-n09-03 ◽

2005 ◽

Vol 899 ◽

Cited By ~ 3

Author(s):

Hossein Baghdadi ◽

Surita R. Bhatia ◽

Elizabeth E. C. Jensen ◽

Nalini Easwar

Keyword(s):

Molecular Weight ◽

Viscosity Solution ◽

High Viscosity ◽

Polymer Chains ◽

Low Viscosity ◽

End Distance ◽

Depletion Force ◽

Poly Ethylene Oxide ◽

Poly Ethylene ◽

Electrostatic Repulsions

AbstractRheology and dynamic light scattering capture re-entrant behavior of laponite-polymer systems. Neat laponite under basics conditions and concentrations of 2wt% or greater forms a viscoelastic soft glass due to electrostatic repulsions. We show that that addition of low molecular weight poly(ethylene oxide) (PEO) melts the glass due to a depletion force. The depletion force speeds up dynamics in the system resulting in a low viscosity solution. A re-entrant viscoelastic solid is formed with the addition of high molecular weight PEO due to the polymer chains bridging between laponite particles. As expected the transition from a low to high viscosity solution scales with the polymer mean square end-to-end distance and gap between laponite particles.

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