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An investigation of the interactions between clay nanoplatelets in the presence of monovalent and divalent salts, as well as cationic peptides utilising atomistic molecular dynamics

Koder Hamid, Mona LU (2020) KEMR20 20192
Department of Chemistry
Abstract
Clays are negatively charged nanoplatelets with a layered silicate structure. It has been
observed from small angle X-ray scattering measurements, and coarse-grained molecular
dynamics simulations (CG-MD) that clay nanoplatelets are able to form stacks, known
as tactoids, in the presence of divalent or multivalent counterions [8, 5]. In this thesis, the
interactions between clay nanoplatelets and counterions of varying valency was studied
by the use of atomistic MD, which are of higher resolution than CG-MD. The particular
systems studied here are the clay mineral montmorillonite (MMT) with sodium or calcium
as counterions, as well as the addition of deca-arginine (Arg10), which is a cationic
antimicrobial peptide (CAMP).... (More)
Clays are negatively charged nanoplatelets with a layered silicate structure. It has been
observed from small angle X-ray scattering measurements, and coarse-grained molecular
dynamics simulations (CG-MD) that clay nanoplatelets are able to form stacks, known
as tactoids, in the presence of divalent or multivalent counterions [8, 5]. In this thesis, the
interactions between clay nanoplatelets and counterions of varying valency was studied
by the use of atomistic MD, which are of higher resolution than CG-MD. The particular
systems studied here are the clay mineral montmorillonite (MMT) with sodium or calcium
as counterions, as well as the addition of deca-arginine (Arg10), which is a cationic
antimicrobial peptide (CAMP). Experimental studies and CG-MD, have shown that
clays are able to sequester CAMPs within tactoids, thus indicating that it can be used
as drug delivery vehicles for CAMPs [5]. The aim of this thesis was to investigate
whether atomistic MD can be applied to study freely moving clay nanoplatelets and
their interactions with CAMPs, to aid in the acquisition of knowledge of such systems.
For this purpose the thesis is comprised of three studies of increasing complexity, simu-
lating MMT systems with atomistic MD using the force field CLAYFF with the SPCE
water model. In the first study, the distribution of sodium and calcium ions in the inter-
layer between MMT surfaces was studied, where a qualitative agreement was found with
previous studies. In the second study, two freely moving MMT nanoplatelets were simu-
lated in the presence of either sodium or calcium ions. It was seen that the platelets had
attractive edge-to-face interactions regardless of the cation valency, however attractive
face-to-face interactions only occurred at high calcium content, above 100 mM, for the
platelets that were initially placed in close proximity. Lastly, in the third study, systems
of MMT and Arg10 were studied. The Arg10 chains were modelled with the CHARMM
force field, and two water models were used, SPCE and TIP3P. The number of Arg10
chains that adsorb to the platelets increased with concentration until saturation occurred,
where the total charge of the Arg10 chains exceeded the platelet charge, resulting in over-
charging, in agreement with experiments and CG-MD [5]. In addition, it is seen that
individual Arg10 chains are able to interact with multiple platelets simultaneously, which
may lead to intercalation within tactoids. However, atomistic MD of multiple platelets
with Arg10, did not exhibit tactoidal formation. Therefore, the process behind tactoidal
formation is likely more complex than what CG-MD suggests. Although, the simula-
tions here indicate that atomistic MD may capture tactoidal formation given the right
circumstances, such as the initial configuration. Further research is required to receive
conclusive results of these systems, however, this thesis has shown that atomistic MD
is a promising method for studying clay minerals and CAMPs, and may elucidate the
complex interactions involved, which is difficult to capture with experiments and not
available at atomistic resolution with CG-MD. (Less)
Popular Abstract (Swedish)
Lera har vi alla kommit i kontakt med på ett eller annat sätt, men det vi kanske inte
vetat om är att lera har flera fantastiska egenskaper som gör att det kan användas i
många olika applikationer. De som sysslat med keramik är bekanta med att lera blir
mjukt och formbart när det är blandat med vatten, men kan sedan hårdna när det
värms och torkas, och då behålla den form den formats till. Det är denna egenskap
som är själva definitionen av lera. Lera har även andra viktiga egenskaper som gör att
det kan används i andra syften än inom keramik och bygge. Lera består av negativt
laddade plattor av nanostorlek. Då lika laddning repellerar, så tenderar torr lera att ta
upp vatten och svälla så att vattenlager kan sätta sig mellan... (More)
Lera har vi alla kommit i kontakt med på ett eller annat sätt, men det vi kanske inte
vetat om är att lera har flera fantastiska egenskaper som gör att det kan användas i
många olika applikationer. De som sysslat med keramik är bekanta med att lera blir
mjukt och formbart när det är blandat med vatten, men kan sedan hårdna när det
värms och torkas, och då behålla den form den formats till. Det är denna egenskap
som är själva definitionen av lera. Lera har även andra viktiga egenskaper som gör att
det kan används i andra syften än inom keramik och bygge. Lera består av negativt
laddade plattor av nanostorlek. Då lika laddning repellerar, så tenderar torr lera att ta
upp vatten och svälla så att vattenlager kan sätta sig mellan plattorna och då minska
deras repulsion. Dessutom, så adsorberar gärna positivt laddade joner och molekyler
till ytan av lerplattorna för att neutralisera deras laddning. Flera farliga tungmetaller
är positivt laddade, och därför används lera för att ta upp dessa metaller i rening av
bland annat vatten. Lera används även för att förvara farligt radioaktivt avfall då dessa
farliga ämnena också tenderar att fastna mellan lerplattor. På grund av leras spännande
egenskaper finns ännu fler applikationer än de ovan nämnda, till exempel används lera
som en komponent i plast och papper, och även i kosmetika och färgmedel. Lera är
ett hett forskningsområde då lera är billigt och miljövänligt, och det finns möjlighet att
användas i ännu fler applikationer.
Det kan vara svårt att studera lera med experiment, och därför studeras det även till
stor utsträckning med datorsimuleringar. En typ av datorsimuleringar är så kallade
molekylär dynamiska (MD) simuleringar. (Less)
Please use this url to cite or link to this publication:
author
Koder Hamid, Mona LU
supervisor
organization
course
KEMR20 20192
year
type
H2 - Master's Degree (Two Years)
subject
keywords
clay, molecular dynamics simulations, physical chemistry, fysikalisk kemi, theoretical chemistry, teoretisk kemi
language
English
id
9006040
date added to LUP
2020-04-30 15:15:57
date last changed
2020-04-30 15:15:57
@misc{9006040,
  abstract     = {{Clays are negatively charged nanoplatelets with a layered silicate structure. It has been
observed from small angle X-ray scattering measurements, and coarse-grained molecular
dynamics simulations (CG-MD) that clay nanoplatelets are able to form stacks, known
as tactoids, in the presence of divalent or multivalent counterions [8, 5]. In this thesis, the
interactions between clay nanoplatelets and counterions of varying valency was studied
by the use of atomistic MD, which are of higher resolution than CG-MD. The particular
systems studied here are the clay mineral montmorillonite (MMT) with sodium or calcium
as counterions, as well as the addition of deca-arginine (Arg10), which is a cationic
antimicrobial peptide (CAMP). Experimental studies and CG-MD, have shown that
clays are able to sequester CAMPs within tactoids, thus indicating that it can be used
as drug delivery vehicles for CAMPs [5]. The aim of this thesis was to investigate
whether atomistic MD can be applied to study freely moving clay nanoplatelets and
their interactions with CAMPs, to aid in the acquisition of knowledge of such systems.
For this purpose the thesis is comprised of three studies of increasing complexity, simu-
lating MMT systems with atomistic MD using the force field CLAYFF with the SPCE
water model. In the first study, the distribution of sodium and calcium ions in the inter-
layer between MMT surfaces was studied, where a qualitative agreement was found with
previous studies. In the second study, two freely moving MMT nanoplatelets were simu-
lated in the presence of either sodium or calcium ions. It was seen that the platelets had
attractive edge-to-face interactions regardless of the cation valency, however attractive
face-to-face interactions only occurred at high calcium content, above 100 mM, for the
platelets that were initially placed in close proximity. Lastly, in the third study, systems
of MMT and Arg10 were studied. The Arg10 chains were modelled with the CHARMM
force field, and two water models were used, SPCE and TIP3P. The number of Arg10
chains that adsorb to the platelets increased with concentration until saturation occurred,
where the total charge of the Arg10 chains exceeded the platelet charge, resulting in over-
charging, in agreement with experiments and CG-MD [5]. In addition, it is seen that
individual Arg10 chains are able to interact with multiple platelets simultaneously, which
may lead to intercalation within tactoids. However, atomistic MD of multiple platelets
with Arg10, did not exhibit tactoidal formation. Therefore, the process behind tactoidal
formation is likely more complex than what CG-MD suggests. Although, the simula-
tions here indicate that atomistic MD may capture tactoidal formation given the right
circumstances, such as the initial configuration. Further research is required to receive
conclusive results of these systems, however, this thesis has shown that atomistic MD
is a promising method for studying clay minerals and CAMPs, and may elucidate the
complex interactions involved, which is difficult to capture with experiments and not
available at atomistic resolution with CG-MD.}},
  author       = {{Koder Hamid, Mona}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{An investigation of the interactions between clay nanoplatelets in the presence of monovalent and divalent salts, as well as cationic peptides utilising atomistic molecular dynamics}},
  year         = {{2020}},
}