Ring polymers as model bacterial chromosomes: confinement, chain topology, single chain statistics, and how they interact

Soft Matter ◽  
2012 ◽  
Vol 8 (7) ◽  
pp. 2095-2102 ◽  
Author(s):  
Youngkyun Jung ◽  
Chanil Jeon ◽  
Juin Kim ◽  
Hawoong Jeong ◽  
Suckjoon Jun ◽  
...  
Keyword(s):  
Single Chain ◽  
Bacterial Chromosomes ◽  
Ring Polymers

scholarly journals A method to estimate the size of single-chain nanoparticles under severe crowding conditions

RSC Advances ◽  
2022 ◽  
Vol 12 (3) ◽  
pp. 1571-1575
Author(s):  
Isabel Asenjo-Sanz ◽  
Ester Verde-Sesto ◽  
José A. Pomposo
Keyword(s):  
Single Chain ◽  
Ring Polymers

A method to estimate the size of single-chain nanoparticles (SCNPs), ring polymers and nanostructured Janus-shaped SCNPs under crowding.

scholarly journals Effects of precursor topology and synthesis under crowding conditions on the structure of single-chain polymer nanoparticles

Soft Matter ◽  
2017 ◽  
Vol 13 (37) ◽  
pp. 6430-6438 ◽  
Author(s):  
Maud Formanek ◽  
Angel J. Moreno
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Polymer Nanoparticles ◽  
Cross Linking ◽  
Single Chain ◽  
Chain Polymer ◽  
Ring Polymers ◽  
Concentrated Solution ◽  
Dynamics Simulations

By means of molecular dynamics simulations, we investigate the formation of single-chain nanoparticles through intramolecular cross-linking of linear and ring polymers, in the presence of their precursors acting as purely steric crowders in concentrated solution.

Cryo-electron microscopy of two-dimensional crystals of reduced type B botulinum neurotoxin

1992 ◽  
Vol 50 (1) ◽  
pp. 530-531
Author(s):  
P. F. Flicker ◽  
V.S. Kulkarni ◽  
J. P. Robinson ◽  
G. Stubbs ◽  
B. R. DasGupta
Keyword(s):  
Disulfide Bonds ◽  
Clostridium Botulinum ◽  
Structural Changes ◽  
Two Dimensional ◽  
Type B ◽  
Single Chain ◽  
Muscle Paralysis ◽  
Cryo Electron Microscopy ◽  
Disulfide Linkages ◽  
Intracellular Action

Botulinum toxin is a potent neurotoxin produced by Clostridium botulinum. The toxin inhibits release of neurotransmitter, causing muscle paralysis. There are several serotypes, A to G, all of molecular weight about 150,000. The protein exists as a single chain or or as two chains, with two disulfide linkages. In a recent investigation on intracellular action of neurotoxins it was reported that type B neurotoxin can inhibit the release of Ca++-activated [3H] norepinephrine only if the disulfide bonds are reduced. In order to investigate possible structural changes in the toxin upon reduction of the disulfide bonds, we have prepared two-dimensional crystals of reduced type B neurotoxin. These two-dimensional crystals will be compared with those of the native (unreduced) type B toxin.

Fine structure and properties of defects in naturally occurring silicates and oxides

1990 ◽  
Vol 48 (4) ◽  
pp. 460-461
Author(s):  
David R. Veblen
Keyword(s):  
Chemical Reactions ◽  
High Resolution Electron Microscopy ◽  
Extended Defects ◽  
Single Chain ◽  
Naturally Occurring ◽  
Resolution Electron ◽  
Fine Structures ◽  
Image Simulations ◽  
Similar Crystal Structure

Extended defects and interfaces control many processes in rock-forming minerals, from chemical reactions to rock deformation. In many cases, it is not the average structure of a defect or interface that is most important, but rather the structure of defect terminations or offsets in an interface. One of the major thrusts of high-resolution electron microscopy in the earth sciences has been to identify the role of defect fine structures in reactions and to determine the structures of such features. This paper will review studies using HREM and image simulations to determine the structures of defects in silicate and oxide minerals and present several examples of the role of defects in mineral chemical reactions. In some cases, the geological occurrence can be used to constrain the diffusional properties of defects.The simplest reactions in minerals involve exsolution (precipitation) of one mineral from another with a similar crystal structure, and pyroxenes (single-chain silicates) provide a good example. Although conventional TEM studies have led to a basic understanding of this sort of phase separation in pyroxenes via spinodal decomposition or nucleation and growth, HREM has provided a much more detailed appreciation of the processes involved.

Elemental mass loss in silicate minerals during x-ray analysis

1990 ◽  
Vol 48 (4) ◽  
pp. 804-805
Author(s):  
P.E. Champness ◽  
R.W. Devenish
Keyword(s):  
Mass Loss ◽  
Current Density ◽  
Damage Mechanism ◽  
Beam Current ◽  
Single Chain ◽  
Plagioclase Feldspar ◽  
X Ray ◽  
Alkali Ions ◽  
Structural Order ◽  
Sheet Silicate

It has long been recognised that silicates can suffer extensive beam damage in electron-beam instruments. The predominant damage mechanism is radiolysis. For instance, damage in quartz, SiO2, results in loss of structural order without mass loss whereas feldspars (framework silicates containing Ca, Na, K) suffer loss of structural order with accompanying mass loss. In the latter case, the alkali ions, particularly Na, are found to migrate away from the area of the beam. The aim of the present study was to investigate the loss of various elements from the common silicate structures during electron irradiation at 100 kV over a range of current densities of 104 - 109 A m−2. (The current density is defined in terms of 50% of total current in the FWHM probe). The silicates so far ivestigated are:- olivine [(Mg, Fe)SiO4], a structure that has isolated Si-O tetrahedra, garnet [(Mg, Ca, Fe)3Al2Si3AO12 another silicate with isolated tetrahedra, pyroxene [-Ca(Mg, Fe)Si2O6 a single-chain silicate; mica [margarite, -Ca2Al4Si4Al4O2O(OH)4], a sheet silicate, and plagioclase feldspar [-NaCaAl3Si5O16]. Ion- thinned samples of each mineral were examined in a VG Microscopes UHV HB501 field- emission STEM. The beam current used was typically - 0.5 nA and the current density was varied by defocussing the electron probe. Energy-dispersive X-ray spectra were collected every 10 seconds for a total of 200 seconds using a Link Systems windowless detector. The thickness of the samples in the area of analysis was normally 50-150 nm.

Fibrin-specificity of a Plasminogen Activator Affects the Efficiency of Fibrinolysis and Responsiveness to Ultrasound: Comparison of Nine Plasminogen Activators In Vitro

1999 ◽  
Vol 81 (04) ◽  
pp. 605-612 ◽  
Author(s):  
Dmitry V. Sakharov ◽  
Marrie Barrett-Bergshoeff ◽  
Rob T. Hekkenberg ◽  
Dingeman C. Rijken
Keyword(s):  
Thrombolytic Therapy ◽  
Plasminogen Activator ◽  
Tissue Type ◽  
Bolus Administration ◽  
High Frequency Ultrasound ◽  
Single Chain ◽  
Response Curves ◽  
Maximal Speed ◽  
Frequency Ultrasound

SummaryIn a number of cases, thrombolytic therapy fails to re-open occluded blood vessels, possibly due to the occurrence of thrombi resistant to lysis. We investigated in vitro how the lysis of hardly lysable model thrombi depends on the choice of the plasminogen activator (PA) and is accelerated by ultrasonic irradiation. Lysis of compacted crosslinked human plasma clots was measured after addition of nine different PAs to the surrounding plasma and the effect of 3 MHz ultrasound on the speed of lysis was assessed.Fibrin-specific PAs showed bell-shaped dose-response curves of varying width and height. PAs with improved fibrin-specificity (staphylokinase, the TNK variant of tissue-type PA [tPA], and the PA from the saliva of the Desmodus rotundus bat) induced rapid lysis in concentration ranges (80-, 260-, and 3,500-fold ranges, respectively) much wider than that for tPA (a 35-fold range). However, in terms of speed of lysis, these three PAs exceeded tPA only slightly. Reteplase and single-chain urokinase were comparable to tPA, whereas two-chain urokinase, anistreplase, and streptokinase were inferior to tPA. In the case of fibrin-specific PAs, ultrasonic treatment accelerated lysis about 1.5-fold. For streptokinase no acceleration was observed. The effect of ultrasound correlated with the presence of plasminogen in the outer plasma, suggesting that it was mediated by facilitating the transport of plasminogen to the surface of the clot.In conclusion, PAs with improved fibrin-specificity induce rapid lysis of plasminogen-poor compacted plasma clots in much wider concentration ranges than tPA. This offers a possibility of using single-or double-bolus administration regimens for such PAs. However, it is not likely that administration of these PAs will directly cause a dramatic increase in the rate of re-opening of the occluded arteries since they are only moderately superior to tPA in terms of maximal speed of lysis. Application of high-frequency ultrasound as an adjunct to thrombolytic therapy may increase the treatment efficiency, particularly in conjunction with fibrin-specific PAs.

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