Styliani Consta - electrospray
http://www.theory.chem.uwo.ca/?q=taxonomy/term/6
en_CAStar-shaped droplets
http://www.theory.chem.uwo.ca/?q=node/65
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Droplets subject to electric fields may obtain spectacular morphologies. Starting from the seminal works of Rayleigh (1882), Zeleny (1917) and G. I. Taylor (1964), the behaviour of droplets in an electric field continues to fascinate scientists due to their numerous applications. Charged droplets are often generated by electrospray ionization methods. We have found by molecular simulations that when a nano-drop comprising a single spherical central ion and dielectric solvent is charged above a well-defined threshold, it acquires a stable star morphology [S. Consta, Journal of Physical Chemistry B v. 114, pp. 5263--5268 (2010); Soft Matter v. 13 , pp. 8781-8795 (2017)] . Currently, we establish the principles of the formation of star-shaped droplets and their extensions to the formation of highly non-convex nano-particles. </p>
<div class="figure">
<img src="sites/default/files/H2OQ18_3Spikes.jpg" /><p>A three-point star comprised water and a macroion</p>
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<img src="sites/default/files/H2OQ22_4Spikes.jpg" /><p>A four-point star comprised water and a macroion</p>
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<img src="sites/default/files/H2OQ27_6Spikes.jpg" /><p>A six-point star comprised water and macroion</p>
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</div></div></div><div class="field field-name-taxonomy-vocabulary-1 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Topics: </div><div class="field-items"><div class="field-item even"><a href="/?q=taxonomy/term/3">simulations</a></div><div class="field-item odd"><a href="/?q=taxonomy/term/20">theory</a></div><div class="field-item even"><a href="/?q=taxonomy/term/26">droplets</a></div><div class="field-item odd"><a href="/?q=taxonomy/term/6">electrospray</a></div></div></div>Sun, 31 Dec 2017 23:40:43 +0000Styliani Constas65 at http://www.theory.chem.uwo.caMyong In Oh article made it to the cover of November issue of JASMS
http://www.theory.chem.uwo.ca/?q=node/62
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><div class="tex2jax"><div class="figure">
<img alt="Journal Cover" src="sites/default/files/November2017CoverProof.jpg" /><p>Journal Cover in JASMS</p>
</div>
<bold>Charging and Release Mechanisms of Flexible Macromolecules in Droplets</bold><it>Myong In Oh and Styliani Consta</it>
Journal of The American Society for Mass Spectrometry
November 2017, Volume 28, Issue 11, pp 2262–2279
We study systematically the charging and release mechanisms of a flexible macromolecule, modeled by poly(ethylene glycol) (PEG), in a droplet by using molecular dynamics simulations. We compare how PEG is solvated and charged by sodium Na+ ions in a droplet of water ($\mathrm{H_2O}$), acetonitrile (MeCN), and their mixtures. Initially, we examine the location and the conformation of the macromolecule in a droplet bearing no net charge. It is revealed that the presence of charge carriers do not affect the location of PEG in aqueous and MeCN droplets compared with that in the neutral droplets, but the location of the macromolecule and the droplet size do affect the PEG conformation. PEG is charged on the surface of a sodiated aqueous droplet that is found close to the Rayleigh limit. Its charging is coupled to the extrusion mechanism, where PEG segments leave the droplet once they coordinate a $\mathrm{Na^+}$ ion or in a correlated motion with $\mathrm{Na^+}$ ions. In contrast, as PEG resides in the interior of a MeCN droplet, it is sodiated inside the droplet. The compact macro-ion transitions through partially unwound states to an extended conformation, a process occurring during the final stage of desolvation and in the presence of only a handful of MeCN molecules. For charged $\mathrm{H_2O/MeCN}$ droplets, the sodiation of PEG is determined by the H2O component, reflecting its slower evaporation and preference over MeCN for solvating $\mathrm{Na^+}$ ions. We use the simulation data to construct an analytical model that suggests that the droplet surface electric field may play a role in the macro-ion–droplet interactions that lead to the extrusion of the macro-ion. This study provides the first evidence of the effect of the surface electric field by using atomistic simulations.</div></div></div></div><div class="field field-name-taxonomy-vocabulary-1 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Topics: </div><div class="field-items"><div class="field-item even"><a href="/?q=taxonomy/term/6">electrospray</a></div><div class="field-item odd"><a href="/?q=taxonomy/term/24">publications</a></div></div></div>Fri, 20 Oct 2017 01:36:58 +0000Styliani Constas62 at http://www.theory.chem.uwo.caComputer modelling and simulations
http://www.theory.chem.uwo.ca/?q=node/59
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><div>
<h3>Protein complex dissociation in a droplet</h3>
<p><embed src="sites/all/libraries/mediaplayer/mediaplayer.swf?file=/sites/default/files/video/new-frag.mp4" width="256" height="256" allowfullscreen="true" autoplay="true" currenttime="1.0"></embed></p>
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<div>
<h3>Formation of spines in droplets with DNA complex</h3>
<p><embed src="sites/all/libraries/mediaplayer/mediaplayer.swf?file=/sites/default/files/video/spine-shape-small.mp4" width="256" height="256" allowfullscreen="true" autoplay="true" currenttime="1.0"></embed></p>
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<div>
<h3>PEG interaction with calcium in droplets</h3>
<p><embed src="sites/all/libraries/mediaplayer/mediaplayer.swf?file=/sites/default/files/video/sm-calcium.mp4" width="256" height="256" wmode="transparent" allowfullscreen="true" autoplay="true" currenttime="1.0"></embed></p>
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<h3>PEG interaction with lithium in droplets</h3>
<p><embed src="sites/all/libraries/mediaplayer/mediaplayer.swf?file=/sites/default/files/video/sm-lithium.mp4" width="256" height="256" allowfullscreen="true" autoplay="true" currenttime="1.0"></embed></p>
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<h3>Constant volume droplet oscillation along l=2,m=0 spherical mode</h3>
<p><embed src="sites/all/libraries/mediaplayer/mediaplayer.swf?file=/sites/default/files/video/sm-l20.mp4" width="256" height="256" allowfullscreen="true" autoplay="true" currenttime="1.0"></embed></p>
</div></div></div><div class="field field-name-taxonomy-vocabulary-1 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Topics: </div><div class="field-items"><div class="field-item even"><a href="/?q=taxonomy/term/6">electrospray</a></div><div class="field-item odd"><a href="/?q=taxonomy/term/21">research</a></div><div class="field-item even"><a href="/?q=taxonomy/term/22">dna</a></div><div class="field-item odd"><a href="/?q=taxonomy/term/23">spines</a></div></div></div>Tue, 18 Aug 2015 21:01:41 +0000Styliani Constas59 at http://www.theory.chem.uwo.caManifestations of Charge Induced Instability in Droplets Effected by Charged Macromolecules
http://www.theory.chem.uwo.ca/?q=node/47
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><div class="tex2jax"><p style="font-weight:bold">
Phys. Rev. Lett. 109, 148301 (2012)
</p>
<p style="font-weight:bold;font-style:italic;padding:2em">Ion-release processes from droplets that contain excess charge are of central importance in determining the charge-state distributions of macromolecules in electrospray ionization methods. We develop an analytical theory to describe the mechanism of contiguous extrusion of a charged macromolecule from a droplet. We find that the universal parameter determining the system behavior is the ratio of solvation energy per unit length to the square of the ion charge density per unit length. Systems with the same value of the ratio will follow the same path in the course of droplet evaporation. The analytical model is compared with molecular simulations of charged polyethylene glycol macroion in aqueous droplets, and the results are in excellent agreement.</p>
<div>
<p>
We illustrate the mechanism of extrusion and define the parameters critical to a theoretical examination of the mechanism. The parameters of the model contributing to the energy are the solvation energy of the linear macromolecule and its charge. In the considered model we assume that the droplet has spherical shape. As the droplet shape remains spherical the surface energy is constant and the surface tension term does not enter equation \eqref{eq:ener-total}. Based on the above considerations we express the total energy of the system as<br />
\begin{equation}<br />
E_{\mathrm{total}} = E_{\mathrm{elec}} + (L-{\lambda}) v_{0} .<br />
\label{eq:ener-total}<br />
\end{equation}<br />
where $L$ is the length of the macromolecule, $\lambda$ is the length of the extruded segment of the macromolecule and $v_0$ the solvation energy per unit length of the macromolecule. Electrostatic energy of the straight rigid segment in vacuum is set to zero and the corresponding change in the self-interaction energy upon solvation is accounted for by the solvation energy contribution.
</p>
<div class="figure">
<img src="sites/default/files/illustr-01.png" /><p>Illustration of a system consisting of a partially extruded macromolecule (PEG) in a droplet. Model parameters are defined. The droplet radius is $R$ and the length of the extruded segment is $\lambda$. In a conducting droplet the electric charges (denoted by ``+'') are transferred to the isopotential surface of the droplet.</p>
</div>
<p>
We evaluate the electrostatic energy of a conducting sphere and a linear charged macromolecule using macroscopic description of the constituent parts. Using the general formula for the electrostatic energy \cite[see p. 57]{electrostatics}<br />
\begin{equation}<br />
E_{\mathrm{elec}} = \sum \frac{1}{2} \phi'_i q_i<br />
\label{eq:elec-def}<br />
\end{equation}<br />
where $q_i$ are charges and $\phi'_i$ are electrostatic potentials at the positions of the corresponding charges without that of the charge $q_i$.
</p>
<p>
Using the technique of electrostatic images the electrostatic field from charge $q$ at distance $x$ from the conducting droplet is equivalent to field created by the system of three charges $q$, $-\frac{qR}{R+x}$ at distance $\frac{R}{R+x}$ from the center of the sphere and $\frac{qR}{R+x}$ at the center of the sphere.
</p>
<p>
Using equation \eqref{eq:elec-def} we write the contribution to the electrostatic energy from charges in the droplet (which are distributed on the surface) as<br />
\begin{equation}<br />
E_{\mathrm{elec}} (Q_1) = \frac{1}{2}\frac{1}{4\pi\epsilon_0 R}<br />
\left( Q_1 + Q_c \right) Q_1<br />
\label{eq:ee-surf}<br />
\end{equation}<br />
where $\gamma$ is the charge per unit length of the macromolecule, $Q_1 = \gamma (L - \lambda)$ is the charge inside the droplet and $Q_c$ is the total induced image charge in the center of the droplet given by<br />
\begin{equation}<br />
Q_c = \int\limits_0^{\lambda} \frac{R \gamma d x}{R+x} .<br />
\label{eq:elec-charge-induced}<br />
\end{equation}<br />
Note, that there is no contribution to the electrostatic energy from the pairs of charges $(q, -\frac{qR}{R+x})$ as they compensate each other exactly on the surface of the sphere.
</p>
<p>
Contribution to the electrostatic energy from the charges on the extruded part of the macromolecule is<br />
\begin{equation}<br />
E_{\mathrm{elec}} (Q_2)<br />
= \frac{1}{2}\frac{1}{4\pi\epsilon_0}<br />
\left[ \left( Q_1 + Q_c \right) \int\limits_0^{\lambda} \frac{\gamma<br />
d x}{R+x} - \int\limits_0^{\lambda} \int\limits_0^{\lambda}<br />
\frac{\gamma dx}{ R + x - \frac{R^2}{R+y} } \frac{R \gamma dy}{ R<br />
+ y } \right] .<br />
\label{eq:ee-macr}<br />
\end{equation}
</p>
<p>
Adding energies given by equations \eqref{eq:ee-surf} and \eqref{eq:ee-macr} and after some algebra we arrive at<br />
\begin{equation}<br />
E_{\mathrm{elec}} = \frac{1}{2}\frac{1}{4\pi\epsilon_0} \biggl[<br />
\frac{1}{R} \left( Q_1 + Q_c \right)^2 - \gamma^2 R<br />
\int\limits_0^{\lambda} \int\limits_0^{\lambda} \frac{dx<br />
dy}{(R+x)(R+y)-R^2} \biggr] .<br />
\label{eq:ee-total}<br />
\end{equation}
</p>
<p>
We analyze stability of the system given by equation \eqref{eq:ee-total}. The central property is the location of the minima of the energy as a function of macromolecule extrusion $\lambda$. The locations of the minima are given by the solutions of the following equations<br />
\begin{equation}<br />
0 = - \frac{\partial E_{\mathrm{total}} } {\partial \lambda} = v_{0}<br />
+ \frac{1}{4\pi\epsilon_0}<br />
\biggl[ \frac{Q_1 + Q_c} {R} \frac{\gamma \lambda}{R+{\lambda}}<br />
+ \gamma^2 R \int\limits_0^{\lambda}<br />
\frac{dx}{(R+x)(R+{\lambda})-R^2} \biggr]<br />
\label{eq:minima}<br />
\end{equation}
</p>
<p>
Equation \eqref{eq:minima} can be explicitly evaluated and recast in the following form<br />
\begin{equation}<br />
-\frac{4\pi\epsilon v_0}{\gamma^2} = \biggl[ \frac{L-\lambda}{R} +<br />
\ln{\frac{R+\lambda}{R}} \biggr] \frac{\lambda}{R+{\lambda}} +<br />
\frac{R}{R+{\lambda}} \ln{\frac{2R+\lambda}{R}},<br />
\label{eq:min-simpl}<br />
\end{equation}<br />
with dimensionless parameters on both sides of the equation. The universal parameter $B_{\mathrm{ex}}$<br />
\begin{equation}<br />
B_{\mathrm{ex}} = \frac{4\pi\epsilon v_0}{\gamma^2} =<br />
\biggl[L v_0\biggr] \cdot \biggl[ \frac{Q^2}{4\pi\epsilon L} \biggr]^{-1}<br />
\label{eq:univ}<br />
\end{equation}<br />
determines the position of the minima for a specific system. $B_{\mathrm{ex}}$ is the ratio of the total solvation energy over a measure of electrostatic energy of the macromolecule and could have been obtained from dimensional analysis as the only combination of two characteristic quantities of the system. The systems with the same ratios of solvation energy to the square of the charge density will follow the same path in the course of droplet evaporation on the $(\lambda/R, L/R)$ diagram.
</p>
<div class="figure">
<img src="sites/default/files/phas-diag-il.png" /><p>Regions of the phase diagram in the system of $\xi = \lambda/L$ and $L/R$ coordinates. Contiguous lines correspond to constant values of the interaction parameter $B_{\mathrm{ex}}$. The gray region in all subplots indicates location of the restricted domain (see details in the text). The plot shows an overall view of the minima of the droplet energy. Representative snapshots of simulations of charged PEG in water droplets that correspond to the various regions of the phase diagram are also shown. </p>
</div>
<p>
Following the approach used to describe gas-liquid boundary lines of the van der Waals equation of state we solved the system of equations $\bigl\{ \frac{\partial E_{\mathrm{total}} } {\partial \lambda} = 0 \wedge \frac{\partial^2 E_{\mathrm{total}} } {\partial \lambda^2} = 0 \bigr\}$ and determined that the allowed region of parameters lie on the r.h.s. of the dashed curve shown in \figref{fig:phas-diag} and given by<br />
\begin{equation}<br />
\frac{L}{R} = \frac{\lambda}{R} + \frac{\lambda^2}{R^2} -<br />
\ln\frac{R+\lambda}{2R+\lambda} - \frac{R+\lambda}{2R+\lambda}.<br />
\label{eq:allowed}<br />
\end{equation}
</p>
<p>
Equations \eqref{eq:minima} and \eqref{eq:allowed} are conveniently presented in the ($\xi = \lambda/L$, $L/R$) system of coordinates. The system of equations were solved numerically and the results of calculations are presented in \figref{fig:phas-diag}. On the phase diagram (\figref{fig:phas-diag}) the dashed line delineates the region of $(\xi, L/R)$ values with the solutions corresponding to the maxima of the total energy (equation \ref{eq:ener-total}). In this region the fully solvated chain (corresponding to $\xi = 0$) and an extruded state lying on the boundary of the allowed region are in dynamic equilibrium as illustrated in \figref{fig:phas-diag}a lower insert. On the phase diagram we identified two distinct regions that correspond to different extrusion mechanisms.
</p>
<p style="font-weight:bold">
</p><pre style="font-style:italic">
@article{consta2012manifestations,
title = {Manifestations of Charge Induced Instability in Droplets Effected by Charged Macromolecules},
author = {Consta, Styliani and Malevanets, Anatoly},
journal = {Phys. Rev. Lett.},
volume = {109},
issue = {14},
pages = {148301},
numpages = {5},
year = {2012},
month = {Oct},
doi = {10.1103/PhysRevLett.109.148301},
url = {http://link.aps.org/doi/10.1103/PhysRevLett.109.148301},
publisher = {American Physical Society}
}
</pre>
</div></div></div></div></div><div class="field field-name-taxonomy-vocabulary-1 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Topics: </div><div class="field-items"><div class="field-item even"><a href="/?q=taxonomy/term/5">fragmentation</a></div><div class="field-item odd"><a href="/?q=taxonomy/term/6">electrospray</a></div><div class="field-item even"><a href="/?q=taxonomy/term/20">theory</a></div></div></div>Sat, 22 Dec 2012 22:32:21 +0000Styliani Constas47 at http://www.theory.chem.uwo.caCharged nanodrops
http://www.theory.chem.uwo.ca/?q=node/23
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
My research primarily focuses on properties of ion-solvent interactions and macromolecular ion-solvent interactions in liquid droplets, in general, and properties of charged droplets, in particular. My research group uses molecular simulations and analytical methods combined with analysis of experimental data as principal techniques to study the various facets of the vast world of clusters and droplets. The droplets in question are composed of solvent and charge carriers that may be simple ions such as sodium, potassium, macromolecular ions (protonated peptides, charged polyethylene glycol) and complexes of macromolecules such as small interfering RNA (si-RNA) or complexes of proteins, or charged nanoparticles. Highly charged droplets present atypical chemical environment with distinct properties characterized by high ionic concentrations. The questions that we pose are:</p>
<dl></dl><li><a href="?q=node/53">charging mechanism of the macromolecules;</a>
</li><li><a href="?q=node/47">the origin and the manifestations of charge-induced instabilities in droplets;</a>
</li><li><a href="?q=node/53"> relation to the charge state and conformational states of macromolecules in droplet and gaseous state environment; </a>
</li><li><a href="?q=node/43">release of macromolecular ions from droplets;</a>
</li><li><a href="?q=node/7">evaporation of droplets;</a>
</li><li><a href="?q=node/54">role of acidity in the charge states of proteins;</a>
</li><li><a href="?q=node/55">classification of charge-induced instabilities in droplets;</a>
</li><li>charge states and conformational changes in the bulk solution.<br /><p>The studies of charged macromolecules in bulk and droplet environments play central role in such diverse subjects such as poly-electrolytes in solution (e.g. DNA); electrospray ionization (ESI) methods and ion-mobility spectroscopy where jets of charged nanodroplets with macromolecules is a critical intermediate state.
</p>
</li></div></div></div><div class="field field-name-taxonomy-vocabulary-1 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Topics: </div><div class="field-items"><div class="field-item even"><a href="/?q=taxonomy/term/5">fragmentation</a></div><div class="field-item odd"><a href="/?q=taxonomy/term/6">electrospray</a></div></div></div>Sun, 28 Oct 2007 01:36:53 +0000Styliani Constas23 at http://www.theory.chem.uwo.caResearch
http://www.theory.chem.uwo.ca/?q=node/18
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><div class="figure">
<img src="http://upload.wikimedia.org/wikipedia/commons/2/25/Alchemist_Thomas_Wijck.jpg" /></div>
<p>
<quote>Every attempt to employ mathematical methods in the study of chemical questions must be considered profoundly irrational and contrary to the spirit of chemistry.... if mathematical analysis should ever hold a prominent place in chemistry, an aberration which is happily almost impossible, it would occasion a rapid and widespread degeneration of that science.</quote></p>
<p>Auguste Comte, <em>Cours de philosophie positive</em>, 1830
</p>
<hr /></div></div></div><div class="field field-name-taxonomy-vocabulary-1 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Topics: </div><div class="field-items"><div class="field-item even"><a href="/?q=taxonomy/term/3">simulations</a></div><div class="field-item odd"><a href="/?q=taxonomy/term/6">electrospray</a></div><div class="field-item even"><a href="/?q=taxonomy/term/20">theory</a></div></div></div>Wed, 03 Oct 2007 20:01:44 +0000Styliani Constas18 at http://www.theory.chem.uwo.ca