Browsing by Subject "Ions"

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Open Access
Alkali metal intercalation in MXene/Graphene heterostructures: a new platform for ion battery applications
(American Chemical Society, 2019) Demiroğlu, İ.; Peeters, F. M.; Gülseren, Oğuz; Çakır, D.; Sevik, C.
The adsorption and diffusion of Na, K, and Ca atoms on MXene/graphene heterostructures of MXene systems Sc2C(OH)2, Ti2CO2, and V2CO2 are systematically investigated by using first-principles methods. We found that alkali metal intercalation is energetically favorable and thermally stable for Ti2CO2/graphene and V2CO2/graphene heterostructures but not for Sc2C(OH)2. Diffusion kinetics calculations showed the advantage of MXene/graphene heterostructures over sole MXene systems as the energy barriers are halved for the considered alkali metals. Low energy barriers are found for Na and K ions, which are promising for fast charge/discharge rates. Calculated voltage profiles reveal that estimated high capacities can be fully achieved for Na ion in V2CO2/graphene and Ti2CO2/graphene heterostructures. Our results indicate that Ti2CO2/graphene and V2CO2/graphene electrode materials are very promising for Na ion battery applications. The former could be exploited for low voltage applications while the latter will be more appropriate for higher voltages.
Open Access
Amphiphilic peptide coated superparamagnetic iron oxide nanoparticles for in vivo MR tumor imaging
(Royal Society of Chemistry, 2016) Ozdemir, A.; Ekiz, M. S.; Dilli, A.; Güler, Mustafa O.; Tekinay, A. B.
Magnetic resonance imaging (MRI) is a noninvasive imaging technique that provides high spatial resolution and depth with pronounced soft-tissue contrast for in vivo imaging. A broad variety of strategies have been employed to enhance the diagnostic value of MRI and detect tissue abnormalities at an earlier stage. Superparamagnetic iron oxide nanoparticles (SPIONs) are considered to be suitable candidates for effective imaging due to their small size, versatile functionality and better biocompatibility. Here, we demonstrate that coating SPIONs with proline-rich amphiphilic peptide molecules through noncovalent interactions leads to a water-dispersed hybrid system suitable as an MRI contrast agent. Cellular viability and uptake of amphiphilic peptide coated SPIONs (SPION/K-PA) were evaluated with human vascular endothelial cells (HUVEC) and estrogen receptor (ER) positive human breast adenocarcinoma (MCF-7) cells. The efficiency of SPION/K-PA as MRI contrast agents was analyzed in Sprague-Dawley rats with mammary gland tumors. MR imaging showed that SPION/K-PA effectively accumulated in tumor tissues, enhancing their imaging potential. Although nanoparticles were observed in reticuloendothelial system organs (RES) and especially in the liver and kidney immediately after administration, the MR signal intensity in these organs diminished after 1 h and nanoparticles were subsequently cleared from these organs within two weeks. Histological observations also validated the accumulation of nanoparticles in tumor tissue at 4 h and their bioelimination from the organs of both healthy and tumor-bearing rats after two weeks.
Open Access
Bias in bonding behavior among boron, carbon, and nitrogen atoms in ion implanted a-BN, a-BC, and diamond like carbon films
(2011) Genisel, M. F.; Uddin, M. N.; Say, Z.; Kulakci, M.; Turan, R.; Gulseren, O.; Bengu, E.
In this study, we implanted Nþ and Nþ 2 ions into sputter deposited amorphous boron carbide (a-BC) and diamond like carbon (DLC) thin films in an effort to understand the chemical bonding involved and investigate possible phase separation routes in boron carbon nitride (BCN) films. In addition, we investigated the effect of implanted Cþ ions in sputter deposited amorphous boron nitride (a-BN) films. Implanted ion energies for all ion species were set at 40 KeV. Implanted films were then analyzed using x-ray photoelectron spectroscopy (XPS). The changes in the chemical composition and bonding chemistry due to ion-implantation were examined at different depths of the films using sequential ion-beam etching and high resolution XPS analysis cycles. A comparative analysis has been made with the results from sputter deposited BCN films suggesting that implanted nitrogen and carbon atoms behaved very similar to nitrogen and carbon atoms in sputter deposited BCN films. We found that implanted nitrogen atoms would prefer bonding to carbon atoms in the films only if there is no boron atom in the vicinity or after all available boron atoms have been saturated with nitrogen. Implanted carbon atoms also preferred to either bond with available boron atoms or, more likely bonded with other implanted carbon atoms. These results were also supported by ab-initio density functional theory calculations which indicated that carbon-carbon bonds were energetically preferable to carbon-boron and carbon-nitrogen bonds.
Open Access
Coarse-grained electrostatic model including ion-pairing equilibrium that explains DC and AC X-ray photoelectron spectroscopy measurements on ionic liquids
(American Chemical Society, 2019) Uzundal, Can Berk; Aydoğan-Göktürk, Pınar; Süzer, Şefik; Ülgüt, Burak
The dynamics of the electrochemical double layer in ionic liquids can be experimentally probed by a number of experimental techniques. Earlier, we reported on the results of an X-ray photoelectron spectroscopic investigation under applied square-wave bias of two distinct frequencies. Our studies had revealed counterintuitive properties involving the physical and temporal progression of the effect of the electrochemical double layer that could not be modeled with conventional equivalent-circuit approaches. Herein, we present a new coarse-grained modeling methodology that accounts for particle diffusion, migration, and ion-association equilibrium. Our model is computationally efficient enough to be used to predict and match the results at extended time scales and distances of the experiment. Modeling efforts predict that a crucial component of the behavior is controlled by the ion-pairing equilibrium, an often overlooked aspect of ionic liquids.
Open Access
Contraction of atomic orbitals in the oxygen anion network and superconductivity in metal oxide compounds
(TÜBİTAK, 1996) Kulik, Igor Orestovich
Anion network in the CuO2 plane of metal-oxide compound is considered as an intrinsic-hole metal with holes rather than electrons comprising a Fermi liquid immersed in the background of negative O2- ions. Due to the contraction of p-orbital of oxygen as a result of occupation by a hole, hole hopping between nearest neighbor sites (i, j) is dependent upon hole occupation as tij,σ = to + Vni,-σnj,-σ = W(ni,-σ + nj,-σ). Coupling parameters W and V (additive and multiplicative "contraction interaction" terms) result in the binding of holes into singlet, on-site configuration, or into triplet, nearest-neighbor-site configuration, due to W and V respectively. In the weak coupling limit, W results in the BCS type of superconductive pairing (singlet, s-wave), whereas multiplicative contraction V provides for either singlet, d-wave, or triplet, p-wave-like pairing states. It is concluded that the latter state may result in a plausible mechanism for high-Tc superconductivity in metal oxide compounds. The superconducting p-phase is shown to be in accord with recently published symmetry tests of the order parameter in oxides.
Open Access
Design strategies for ratiometric chemosensors: modulation of excitation energy transfer at the energy donor site
(2009) Guliyev, R.; Coskun, A.; Akkaya, E. U.
Excitation energy transfer, when coupled to an ion-modulated ICT chromophore, creates novel opportunities in sensing. The direction of energy transfer and the point of ICT modulation can be varied as desired. In our previous work, we have shown that energy transfer efficiency between two energetically coupled fluorophores will be altered by the metal ion binding to the ICT chromophore carrying a ligand. There are two beneficial results: increased pseudo-Stokes shift and expanded dynamic range. Here, we explored the consequences of the modulation of energy transfer efficiency at the energy donor site, in a molecular design which has an ICT type metal ion-sensitive chromophore placed as the energy donor in the dyad. Clear advantages emerge compared to the acceptor site modulation: unaltered emission wavelength in the red end of the visible spectrum, while keeping a large Stokes shift and the ratiometric character. © 2009 American Chemical Society.
Open Access
Detection of Calcium-induced morphological changes on RBCs by digital holographic microscopy and blinking optical tweezers
(IEEE, 2016) Rad, V. F.; Tavakkoli, R.; Moradi, Ali-Reza; Anand, A.; Javidi, B.
Ca+2 level in the circulating red blood cells (RBCs) takes part not only in controlling biophysical properties, but also affects the membrane composition, and its morphological and rheological properties. Excessive accumulation of Ca2+ within the cells is associated with a number of important pathological diseases. In this paper, by the use of digital holographic microscopy (DHM), we quantitatively analyzed the volumetric behavior of RBC membrane under influence of excess Calcium ions. DHM in a transmission mode is an effective tool for quantitative visualization of phase objects. By deriving the associated phase changes 3D information on the morphology variation of the cells at arbitrary time scales is obtained. Individual cells are immobilized by the use of optical tweezers and are monitored live with DHM system, while the concentration of Ca2+ ions in the buffer is changed simultaneously. We utilized blinking optical tweezers, by inserting an optical chopper to modulate intensity of the trapping laser beam. Blinking optical tweezers, while keeping the cell trapped during the experiments, ensures of minimizing the photo-damage of trapping laser beam on the cell. Our experimental results are in agreement with previous biological studies and predictions, and experimental observations of living RBCs under Ca2+ influence.
Open Access
Effects of temperature, pH and counterions on the stability of peptide amphiphile nanofiber structures
(Royal Society of Chemistry, 2016) Ozkan A.D.; Tekinay, A. B.; Güler, Mustafa O.; Tekin, E. D.
Peptide amphiphiles are a class of self-assembling molecules that are widely used to form bioactive nanostructures for various applications in bionanomedicine. However, peptide molecules can exhibit distinct behaviors under different conditions, suggesting that environmental variables such as temperature, pH, electrolytes and the presence of biological factors may greatly affect the self-assembly process. In this work, we used united-atom molecular dynamics simulations to understand the effects of three counterions (Na+, Ca2+ at pH 7 and Cl- at pH 2) and temperature change on the stability of the lauryl-VVAGERGD peptide amphiphile self-assembly. This molecule contains a bioactive RGD peptide sequence and has been shown to support cellular adhesion and proliferation in vitro. A 19-layered peptide nanostructure, containing 12 peptide amphiphile molecules per layer, was previously shown to exhibit optimal stability and it was used as the model nanofiber system. Peptide backbone stability was studied under increasing temperatures (300-358 K) using the number of hydrogen bonds and root-mean-square deviations of nanofiber size. At higher temperatures, fiber disintegration was observed to be dependent on the type of counter-ion used for nanofiber formation. Interestingly, rapid heating to higher temperatures could sometimes reestablish the integrity of the nanofiber backbone, possibly by allowing the system to bypass an energy barrier and assuming a more thermodynamically stable configuration. As counterion identity was observed to exhibit remarkable effects on the thermal stability of peptide nanofibers, we suggest that these behaviors should be considered while developing new materials for potential applications.
Open Access
Electrostatic interactions in charged nanoslits within an explicit solvent theory
(Institute of Physics Publishing, 2015) Buyukdagli, S.
Within a dipolar Poisson-Boltzmann theory including electrostatic correlations, we consider the effect of explicit solvent structure on solvent and ion partition confined to charged nanopores. We develop a relaxation scheme for the solution of this highly non-linear integro-differential equation for the electrostatic potential. The scheme is an extension of the approach previously introduced for simple planes (Buyukdagli and Blossey 2014 J. Chem. Phys. 140 234903) to nanoslit geometry. We show that the reduced dielectric response of solvent molecules at the membrane walls gives rise to an electric field significantly stronger than the field of the classical Poisson-Boltzmann equation. This peculiarity associated with non-local electrostatic interactions results in turn in an interfacial counterion adsorption layer absent in continuum theories. The observation of this enhanced counterion affinity in the very close vicinity of the interface may have important impacts on nanofluidic transport through charged nanopores. Our results indicate the quantitative inaccuracy of solvent implicit nanofiltration theories in predicting the ionic selectivity of membrane nanopores.
Open Access
FTIR spectroscopic study on nickel(II)-exchanged sulfated alumina: nature of the active sites in the catalytic oligomerization of ethene
(Springer, 2002) Davydov, A. A.; Kantcheva, M.; Chepotko, M. L.
The nature of the active sites in nickel(II)-exchanged sulfated alumina in the reaction of ethene oligomerization has been studied by means of FTIR spectroscopy of adsorbed CO. It has been established that isolated nickel(I) species are the active sites in this process. These sites are formed by a reduction process, in which protonic centers are involved. The latter are due to the presence of covalently-bonded sulfate ions on the catalyst surface.
Open Access
Hierarchical self-assembly of histidine-functionalized peptide amphiphiles into supramolecular chiral nanostructures
(American Chemical Society, 2017) Koc, M. H.; Ciftci, G. C.; Baday, S.; Castelletto, V.; Hamley, I. W.; Güler, Mustafa O.
Controlling the hierarchical organization of self-assembling peptide amphiphiles into supramolecular nanostructures opens up the possibility of developing biocompatible functional supramolecular materials for various applications. In this study, we show that the hierarchical self-assembly of histidine- (His-) functionalized PAs containing d- or l-amino acids can be controlled by both solution pH and molecular chirality of the building blocks. An increase in solution pH resulted in the structural transition of the His-functionalized chiral PA assemblies from nanosheets to completely closed nanotubes through an enhanced hydrogen-bonding capacity and π-π stacking of imidazole ring. The effects of the stereochemistry and amino acid sequence of the PA backbone on the supramolecular organization were also analyzed by CD, TEM, SAXS, and molecular dynamics simulations. In addition, an investigation of chiral mixtures revealed the differences between the hydrogen-bonding capacities and noncovalent interactions of PAs with d- and l-amino acids.
Open Access
Ionic current inversion in pressure-driven polymer translocation through nanopores
(American Physical Society, 2015) Buyukdagli, S.; Blossey, R.; Ala-Nissila, T.
We predict streaming current inversion with multivalent counterions in hydrodynamically driven polymer translocation events from a correlation-corrected charge transport theory including charge fluctuations around mean-field electrostatics. In the presence of multivalent counterions, electrostatic many-body effects result in the reversal of the DNA charge. The attraction of anions to the charge-inverted DNA molecule reverses the sign of the ionic current through the pore. Our theory allows for a comprehensive understanding of the complex features of the resulting streaming currents. The underlying mechanism is an efficient way to detect DNA charge reversal in pressure-driven translocation experiments with multivalent cations. © 2015 American Physical Society.
Open Access
Like-Charge Attraction And Opposite-Charge Decomplexation Between Polymers and DNA Molecules
(American Physical Society, 2017) Buyukdagli, S.
We scrutinize the effect of polyvalent ions on polymer-DNA interactions. We extend a recently developed test-charge theory [S. Buyukdagli, Phys. Rev. E 94, 042502 (2016)1539-375510.1103/PhysRevE.94.042502] to the case of a stiff polymer interacting with a DNA molecule in an electrolyte mixture. The theory accounts for one-loop level electrostatic correlation effects such as the ionic cloud deformation around the strongly charged DNA molecule as well as image-charge forces induced by the low DNA permittivity. Our model can reproduce and explain various characteristics of the experimental phase diagrams for polymer solutions. First, the addition of polyvalent cations to the electrolyte solution results in the attraction of the negatively charged polymer by the DNA molecule. The glue of the like-charge attraction is the enhanced shielding of the polymer charges by the dense counterion layer at the DNA surface. Second, through the shielding of the DNA-induced electrostatic potential, mono- and polyvalent cations of large concentration both suppress the like-charge attraction. Within the same formalism, we also predict a new opposite-charge repulsion effect between the DNA molecule and a positively charged polymer. In the presence of polyvalent anions such as sulfate or phosphate, their repulsion by the DNA charges leads to the charge screening deficiency of the region around the DNA molecule. This translates into a repulsive force that results in the decomplexation of the polymer from DNA. This opposite-charge repulsion phenomenon can be verified by current experiments and the underlying mechanism can be beneficial to gene therapeutic applications where the control over polymer-DNA interactions is the key factor.
Open Access
Local electric fields in aqueous electrolytes
(American Chemical Society, 2021-07-27) Drexler, C. I.; Cracchiolo, O. M.; Myers, R. L.; Okur, Halil İbrahim; Serrano, A. L.; Corcelli, S. A.; Cremer, P. S.
Vibrational Stark shifts were explored in aqueous solutions of organic molecules with carbonyl- and nitrile-containing constituents. In many cases, the vibrational resonances from these moieties shifted toward lower frequency as salt was introduced into solution. This is in contrast to the blue-shift that would be expected based upon Onsager’s reaction field theory. Salts containing well-hydrated cations like Mg2+ or Li+ led to the most pronounced Stark shift for the carbonyl group, while poorly hydrated cations like Cs+ had the greatest impact on nitriles. Moreover, salts containing I– gave rise to larger Stark shifts than those containing Cl–. Molecular dynamics simulations indicated that cations and anions both accumulate around the probe in an ion- and probe-dependent manner. An electric field was generated by the ion pair, which pointed from the cation to the anion through the vibrational chromophore. This resulted from solvent-shared binding of the ions to the probes, consistent with their positions in the Hofmeister series. The “anti-Onsager” Stark shifts occur in both vibrational spectroscopy and fluorescence measurements.
Open Access
Lyotropic liquid-crystalline mesophases of [Zn(H2O)6](NO3)2-C12EO10-CTAB-H2O and [Zn(H2O)6](NO3)2-C12EO10-SDS-H2O systems
(2008) Albayrak, C.; Soylu, A. M.; Dag, Ö.
The mixture of two surfactants (C12EO10-CTAB and C 12EO10-SDS) forms lyotropic liquid-crystalline (LLC) mesophases with [Zn(H2O)6](NO3)2 in the presence of a minimum concentration of 1.75 H2O per C 12EO10. The metal ion/C12EO10 mole ratio can be increased up to 8.0, which is a record high metal ion density in an LLC mesophase. The metal ion concentration can be increased in the medium by increasing the CTAB/C12EO10 or SDS/C12EO 10 mole ratio at the expense of the stability of the LLC mesophase. The structure and some thermal properties of the new mesophase have been investigated using XRD, POM, FTIR, and Raman techniques. © 2008 American Chemical Society.
Open Access
Mn2+-doped CdSe/CdS core/multishell colloidal quantum wells enabling tunable carrier-dopant exchange interactions
(American Chemical Society, 2015) Delikanlı, S.; Akgül, M. Z.; Murphy, J. R.; Barman, B.; Tsai, Y.; Scrace, T.; Zhang, P.; Bozok, B.; Hernández-Martínez, P.L.; Christodoulides, J.; Cartwright, A. N.; Petrou, A.; Demir, Hilmi Volkan
In this work, we report the manifestations of carrier-dopant exchange interactions in colloidal Mn2+-doped CdSe/CdS core/multishell quantum wells. The carrier-magnetic ion exchange interaction effects are tunable through wave function engineering. In our quantum well heterostructures, manganese was incorporated by growing a Cd0.985Mn0.015S monolayer shell on undoped CdSe nanoplatelets using the colloidal atomic layer deposition technique. Unlike previously synthesized Mn2+-doped colloidal nanostructures, the location of the Mn ions was controlled with atomic layer precision in our heterostructures. This is realized by controlling the spatial overlap between the carrier wave functions with the manganese ions by adjusting the location, composition, and number of the CdSe, Cd1-xMnxS, and CdS layers. The photoluminescence quantum yield of our magnetic heterostructures was found to be as high as 20% at room temperature with a narrow photoluminescence bandwidth of ∼22 nm. Our colloidal quantum wells, which exhibit magneto-optical properties analogous to those of epitaxially grown quantum wells, offer new opportunities for solution-processed spin-based semiconductor devices. © 2015 American Chemical Society.
Open Access
Molecular and continuum perspectives on intermediate and flow reversal regimes in electroosmotic transport
(American Chemical Society, 2019) Çelebi, A. T.; Çetin, Barbaros; Beşkök, A.
Electroosmotic slip flows in the Debye–Hückel regime were previously investigated using molecular dynamics and continuum transport perspectives ( J. Phys. Chem. C 2018, 122, 9699). This continuing work focuses on distinct electrostatic coupling regimes, where the variations in electroosmotic flows are elucidated based on Poisson–Fermi and Stokes equations and molecular dynamics simulations. In particular, aqueous NaCl solution in silicon nanochannels are considered under realistic electrochemical conditions, exhibiting intermediate flow and flow reversal regimes with increased surface charge density. Electroosmotic flow exhibits plug flow behavior in the bulk region for channel heights as small as 5 nm. With increased surface charge density, constant bulk electroosmotic flow velocity first increases and then it begins to gradually decrease until flow reversal is observed. In order to capture the flow physics and discrete motions within electric double layer accurately, the continuum model includes overscreening and crowding effects as well as slip contribution and local variations of enhanced viscosity. After extraction of the continuum parameters based on molecular dynamics simulations, good agreement between simulation results and continuum predictions are obtained for surface charges as large as −0.37 C/m2.
Open Access
Nanoengineering hybrid supramolecular multilayered biomaterials using polysaccharides and self-assembling peptide amphiphiles
(Wiley-VCH Verlag, 2017) Borges, J.; Sousa, M. P.; Cinar, G.; Caridade, S. G.; Güler, Mustafa O.; Mano, J. F.
Developing complex supramolecular biomaterials through highly dynamic and reversible noncovalent interactions has attracted great attention from the scientific community aiming key biomedical and biotechnological applications, including tissue engineering, regenerative medicine, or drug delivery. In this study, the authors report the fabrication of hybrid supramolecular multilayered biomaterials, comprising high-molecular-weight biopolymers and oppositely charged low-molecular-weight peptide amphiphiles (PAs), through combination of self-assembly and electrostatically driven layer-by-layer (LbL) assembly approach. Alginate, an anionic polysaccharide, is used to trigger the self-assembling capability of positively charged PA and formation of 1D nanofiber networks. The LbL technology is further used to fabricate supramolecular multilayered biomaterials by repeating the alternate deposition of both molecules. The fabrication process is monitored by quartz crystal microbalance, revealing that both materials can be successfully combined to conceive stable supramolecular systems. The morphological properties of the systems are studied by advanced microscopy techniques, revealing the nanostructured dimensions and 1D nanofibrous network of the assembly formed by the two molecules. Enhanced C2C12 cell adhesion, proliferation, and differentiation are observed on nanostructures having PA as outermost layer. Such supramolecular biomaterials demonstrate to be innovative matrices for cell culture and hold great potential to be used in the near future as promising biomimetic supramolecular nanoplatforms for practical applications.
Open Access
One-dimensional peptide nanostructure templated growth of iron phosphate nanostructures for lithium-ion battery cathodes
(American Chemical Society, 2016-06) Susapto, H. H.; Kudu, O. U.; Garifullin, R.; Yllmaz, E.; Güler, Mustafa O.
Template-directed synthesis of nanomaterials can provide benefits such as small crystalline size, high surface area, large surface-to-volume ratio, and structural stability. These properties are important for shorter distance in ion/electron movement and better electrode surface/electrolyte contact for energy storage applications. Here nanostructured FePO4 cathode materials were synthesized by using peptide nanostructures as a template inspired by biomineralization process. The amorphous, high surface area FePO4 nanostructures were utilized as a cathode for lithium-ion batteries. Discharge capacity of 155 mAh/g was achieved at C/20 current rate. The superior properties of biotemplated and nanostructured amorphous FePO4 are shown compared to template-free crystalline FePO4.
Open Access
Preparation of Au and Au-Pt nanoparticles within PMMA matrix using UV and X-ray irradiation
(2009) Ozkaraoglu, E.; Tunc, I.; Süzer, Şefik
Au and Au-Pt alloy nanoparticles are prepared and patterned at room temperature within the PMMA polymer matrix by the action of 254 nm UV light or X-rays. The polymer matrix enables us to entangle the kinetics of the photochemical reduction from the nucleation and growth processes, when monitored by UV-vis spectroscopy. Accordingly, increase of the temperature to 50 °C of the reaction medium increases the nucleation and growth rates of the nanoparticle formation by more than one order of magnitude, due to enhanced diffusion and nucleation at the higher temperature, but has no effect on the photochemical reduction process. Presence of Pt ions also increases the same rate, but by a factor two only. Similar photochemical reduction and particle growth take also place within the PMMA matrix, when these metal ions are subjected to prolonged exposure to X-rays, as evidenced by XPS analysis. Both angle-resolved and charge-contrast measurements using XPS reveal that the resultant Au and Pt species are in close proximity to each other, indicating the Au-Pt alloy formation to be the most likely case.