Search

In this theoretical study, we investigate the impact of density differences between the growing new phase and the parent phase on the overall transformation degree. By extending Kolmogorov's formalism, we derive an expression for the overall volume transformation degree, which becomes relevant when density differences are not negligible. We demonstrate that the volume and mass transformation degrees differ in the presence of density differences and provide an expression for the mass transformation degree.

We use femtosecond transient broadband absorption spectroscopy (TAS) to characterize Rose Bengal in water/methanol solutions and reveal a continuous tunability of intersystem crossing (ISC) times by changing the mole fraction of the solvents. We find that the transients of excited state absorptions (ESAs) in Rose Bengal at ∼430 nm can be attributed to transitions from the singlet state S 1 , with decay times of 74 ps via ISC in pure water and up to 405 ps in pure methanol. TA measurements at near-infrared wavelengths, on the other hand, reveal the rise of an ESA at ∼1080 nm from the triplet state T 1 with time constants of 68 and 491 ps in pure water and methanol, respectively, strongly supporting the associated UV-vis TAS data. Solvent mixtures show a quasi-linear rise of the ISC times with increasing mole fractions of methanol and indicate that Rose Bengal in varying solvent mixtures can be used as a model system to study their influence on excited state photophysics.

Nitroxide radicals have found wide applications as spin labels or probes, and their guest-host interactions with cyclodextrins exhibit enhanced applications in electron spin resonance (ESR) spectroscopy and imaging due to improved biostability toward reducing agents. Although the computational prediction of the guest-host binding has become increasingly common for small ligands, molecular simulations regarding the conformational preferences of hosted spin probes have not been conducted. Here we present molecular dynamics simulations at an atomistic level for a set of four TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl) spin probes and thereafter develop coarse-grained models compatible with the recent version of the Martini force field (v 3.0) to tackle their encapsulation in the cavity of β-cyclodextrin (βCD) for which experimental ESR data are available. The results indicate that the atomistic descriptions perform well in relation to the structural parameters derived from X-ray diffraction as well as hydrogen bonding and hydrogen patterns and predict that the guest-host complexation is hydrophobically driven by the presence of a methyl group pair of the spin probe at the cavity center of βCD. The spin probe mobility at the binding site reveals the nitroxide group orientation toward the secondary rim of the cyclodextrin and the alternating presence of the two methyl group pairs inside the cavity, features in agreement with the experimental behavior of the ESR parameters. The coarse-grained parameterizations of TEMPO probes and βCD rely on optimizing the bonded and nonbonded parameters with references to the atomistic simulation results, and they are capable of recovering the orientation and location of the spin probe inside the cyclodextrin cavity predicted by the atomistic guest-host complexes. The results suggest the cyclodextrin host-guest system as a powerful validation suite to evaluate new coarse-grained parameterizations of small ligands and future extensions to functionalized cyclodextrins in inclusion complexes.

Options to improve the extrapolation power of the neural network designed using the SchNetPack package with respect to top docking scores prediction are presented. It is shown that hyperparameter tuning of the atomistic model representation (in the schnetpack.representation) improves the prediction of the top scoring compounds, which have characteristically a low incidence in randomized data sets for training of machine learning models. The prediction robustness is evaluated according to the mean square error (MSE) and the entropy of the average loss landscape decrease. Admittedly, the improvement of the top scoring compounds' prediction accuracy comes with the penalty of worsening the overall prediction power. It is revealed that the most impactful hyperparameter is the cutoff (5 Å is reported as the optimal choice). Other parameters (e.g., number of radial basis functions, number of interaction layers of the neural network, feature vector size or its batch size) are found to not affect the prediction robustness of the top scoring compounds in any comparable way relative to the cutoff. The MSE of the best docking score prediction (below -13 kcal/mol) improves from ca. 3.5 to 0.9 kcal/mol, while the prediction of less potent compounds (-13 to -11 kcal/mol) shows a lesser improvement, i.e., a decrease of MSE from 1.6 to 1.3 kcal/mol. Additionally, oversampling and undersampling of the training set with respect to the top scoring compounds' abundance is presented. The results indicate that the cutoff choice performs better than over - or undersampling of the training set, with undersampling performing better than oversampling .

The anion-selective transport through subnanoporous liquid-crystalline (LC) water treatment membranes was quantitatively detected by the deposition and electrochemical analysis of the LC membrane on the GaN electrode. The time course of the capacitance and Warburg resistance of the LC membrane suggest that the interaction of the LC membrane with monovalent Cl - ions is distinctly different from that with SO 4 ions. A continuous decay in capacitance suggests the condensation of Cl 2- ions. A continuous decay in capacitance suggests the condensation of Cl - ions and the inner wall of subnanopores is much weaker. The chronoamperometry data further suggest that SO 4 2- ions and the inner wall of subnanopores is much weaker. The chronoamperometry data further suggest that SO 4 ions, which possess similar hydrogen-bonded structures to the hydrogen-bonded networks inside the subnanopores, can exchange the associated water molecules and hop along the network of water molecules, but Cl 2- ions bind and accumulate inside subnanopores. The well-controlled supramolecular self-assembly of LC building blocks opens a large potential toward the fine adjustment of hydrogen-bonding networks in nanospace providing materials new functions, which cannot be realized by bulk water.- ions. These results, together with the previous X-ray emission spectroscopy, suggest that SO 4 2- ions, which possess similar hydrogen-bonded structures to the hydrogen-bonded networks inside the subnanopores, can exchange the associated water molecules and hop along the network of water molecules, but Cl - ions bind and accumulate inside subnanopores. The well-controlled supramolecular self-assembly of LC building blocks opens a large potential toward the fine adjustment of hydrogen-bonding networks in nanospace providing materials new functions, which cannot be realized by bulk water.

A study of charge transport mechanisms in an electric field was conducted on nonstoichiometric protic ionic liquids (PIL) based on triethylamine (TEA), in combination with an excess of either trifluoroacetic acid (TFA) or trifluoromethanesulfonic acid (TfO). The addition of excess precursor acid adds proton-donor sites to the system to support potential structural proton transport, which could, for example, enable the use in fuel cells. Transport measurements by pulsed field gradient (PFG) NMR diffusion and, in particular, electrophoretic NMR (eNMR) are supported by NMR chemical shifts and Raman spectroscopy, where the latter techniques elucidate the local solvation structures. Migration of the acidic proton of the excess acid in the electric field occurs toward the cathode with a velocity larger than that of the anions. This intriguing feature of a rapid drift of a neutral molecule is explained by the interplay of strong correlations between anion and cation as well as between anion and acid. The neutral acid is subject to vehicular transport with the anion, while the anion is partitioning between anion-acid and anion-cation clusters, resulting in a lower average drift velocity. The negative drift direction of the neutral acid and its proton is superimposed to and thus counteracts the vehicular transport of protons with the cation. The study sheds light on the role of excess acid in PIL and reveals the versatile interactions between anion, cation, and excess acid within a PIL determining its charge transport properties.

The increased safety of salt-in-ionic liquid electrolytes compared with established carbonate-based systems has promoted intense research in this field, but low conductivities, slow lithium transport, and unfavorable lithium anion correlations still prevent a mass market application. In particular, strong Li-anion correlations lead to dominant vehicular Li transport with the same drift direction for anions and lithium in the electric field. Here, three different strategies and their mutual interplay are evaluated, which could reduce Li-anion coordination, i.e., high salt concentration, a mixed-anion composition, as well as an ether functionalization of the organic cation. To this end, two series of highly concentrated IL-based electrolytes, based on either ethylmethylimidazolium (EMIM) or the ether-functionalized 1-methoxyethyl-1-methylpyrrolidinium (Pyr 12O1 ) organic cation, and employing mixed bis(fluorosulfonyl)imide/bis(trifluoromethylsulfonyl)imide (FSI/TFSI) anions are investigated. Measurements of conductivities, diffusion coefficients, and electrophoretic mobilities reveal no beneficial effect due to the increased heterogeneity of the FSI/TFSI-based electrolyte matrix, generally showing improved transport properties with increasing FSI share. However, a combination of both the ether-functionalized cation and high FSI content is proven successful, as lithium mobilities are positive, and vehicular transport is overcome by structural Li transport. Our study demonstrates the decisive role of synergy of the different approaches: While the single effect of a high salt concentration, weakly lithium-coordinating anions, or organic cations with lithium-affine functional groups is too weak to prevent vehicular transport, their joint effect can overcome vehicular Li transport, leading to improved Li conduction in ionic liquids.

The effect of the degree of isotopic substitution of the aqueous medium on the adsorption kinetics and the surface dilational rheological behavior at the water/air interface of the globular protein β-lactoglobulin was investigated. Aqueous solutions with fixed concentrations of 1 μM protein and 10 mM hydrogenous buffer with controlled pH 7 were prepared in H 2 O, D 2 O, and an isotopic mixture of 8.1% v/v D 2 O in H 2 O (called air contrast matched water, ACMW). Using a bubble shape analysis tensiometer, we obtained various experimental dependencies of the dilational viscoelasticity modulus E as a function of the dynamic surface pressure and of the frequency and amplitude of bubble surface area oscillations, either in the course of adsorption or after having reached a steady state. In general, the results revealed virtually no effect from substituting H 2 O by ACMW but distinct albeit relatively weak effects for intermediate adsorption times for D 2 O as the aqueous phase. In the final stage of adsorption, established after around 10 h, the equilibrium adsorption and the dilational rheological behavior of all protein layers under investigation are only very weakly affected by the presence of D 2 O. The obtained results help to design experimental protocols for protein adsorption studies, for example, by neutron reflectivity.

Electron transfer (ET) between neutral and cationic tryptophan residues in the azurin construct [Re I (H126)(CO) 3 (dmp)](W124)(W122)Cu I (dmp = 4,7-Me 2 -1,10-phenanthroline) was investigated by Born-Oppenheimer quantum-mechanics/molecular mechanics/molecular dynamics (QM/MM/MD) simulations. We focused on W124 •+ ← W122 ET, which is the middle step of the photochemical hole-hopping process *Re II (CO) 3 (dmp •- ) ← W124 ← W122 ← Cu I , where sequential hopping amounts to nearly 10,000-fold acceleration over single-step tunneling ( ACS Cent. Sci . 2019 , 5 , 192-200). In accordance with experiments, UKS-DFT QM/MM/MD simulations identified forward and reverse steps of W124 •+ ↔ W122 ET equilibrium, as well as back ET Re I (CO) 3 (dmp •- ) → W124 •+ that restores *Re II (CO) 3 (dmp •- ). Strong electronic coupling between the two indoles (≥40 meV in the crossing region) makes the productive W124 •+ ← W122 ET adiabatic. Energies of the two redox states are driven to degeneracy by fluctuations of the electrostatic potential at the two indoles, mainly caused by water solvation, with contributions from the protein dynamics in the W122 vicinity. ET probability depends on the orientation of Re(CO) 3 (dmp) relative to W124 and its rotation diminishes the hopping yield. Comparison with hole hopping in natural systems reveals structural and dynamics factors that are important for designing efficient hole-hopping processes.

The activation mechanism of thiamine diphosphate (ThDP) in enzymes has long been the subject of intense research and controversial discussion. Particularly contentious is the formation of a carbene intermediate, the first one observed in an enzyme. For the formation of the carbene to take place, both intramolecular and intermolecular proton transfer pathways have been proposed. However, the physiologically relevant pH of ThDP-dependent enzymes around neutrality does not seem to be suitable for the formation of such reactive chemical species. Herein, we investigate the general mechanism of activation of the ThDP cofactor in human transketolase (TKT), by means of electronic structure methods. We show that in the case of the human TKT, the carbene species is accessible through a p K shift induced by the electrostatics of a neighboring histidine residue (H110), whose protonation state change modulates the p a of ThDP and suppresses the latter by more than 6 pH units. Our findings highlight that ThDP enzymes activate the cofactor beyond simple geometric constraints and the canonical glutamate. Such observations in nature can pave the way for the design of biomimetic carbene catalysts and the engineering of tailored enzymatic carbenes.K a of ThDP and suppresses the latter by more than 6 pH units. Our findings highlight that ThDP enzymes activate the cofactor beyond simple geometric constraints and the canonical glutamate. Such observations in nature can pave the way for the design of biomimetic carbene catalysts and the engineering of tailored enzymatic carbenes.

Molecular dynamics simulations can provide the means to visualize and understand the role of intermolecular interactions in the mechanisms involved in molecular aggregation. Along these lines, simulations can allow the study of how surface chemical modifications can influence nanomaterial assembly at the molecular level. Layered silicate clays have been of significant interest for some time, particularly with regard to their use in organic/inorganic nanocomposites. However, despite numerous reports on the covalent linkage of organic moieties via silanol condensation, the theoretical understanding of these systems has heretofore been limited to noncovalent interactions, specifically ionic interactions at the charged basal surfaces. Herein, a model for edge-functionalized layered aluminosilicate clay, based on the siloxane linkage, is presented. In addition to reproducing experimentally observed degrees of molecular aggregation of clay-linked perylene diimide derivatives with different terminal functional groups as a function of solvent composition, a molecular-level understanding of the role of van der Waals interactions and hydrogen bonding of the different end-groups on the aggregation state in different water/ N , N -dimethylformamide mixtures is obtained. The reported model provides a means to simulate organic moieties covalently bound to the layered silicate edge, which will enable future simulations of nanocomposites and organic/inorganic hybrids based on this system.

Immunoglobulin G (IgG) is the most common type of antibody found in blood and extracellular fluids and plays an essential role in our immune response. However, studies of the dynamics and reaction kinetics of IgG-antigen binding under physiological crowding conditions are scarce. Herein, we develop a coarse-grained model of IgG consisting of only six beads that we find minimal for a coarse representation of IgG's shape and a decent reproduction of its flexibility and diffusion properties measured experimentally. Using this model in Brownian dynamics simulations, we find that macromolecular crowding affects only slightly the IgG's flexibility, as described by the distribution of angles between the IgG's arms and stem. Our simulations indicate that, contrary to expectations, crowders slow down the translational diffusion of an IgG less strongly than they do for a smaller Ficoll 70, which we relate to the IgG's conformational size changes induced by crowding. We also find that crowders affect the binding kinetics by decreasing the rate of the first binding step and enhancing the second binding step.

Misfolding and aggregation of transthyretin (TTR) cause several amyloid diseases. Besides being an amyloidogenic protein, TTR has an affinity for bicyclic small-molecule ligands in its thyroxine (T4) binding site. One class of TTR ligands are trans-stilbenes. The trans-stilbene scaffold is also widely applied for amyloid fibril-specific ligands used as fluorescence probes and as positron emission tomography tracers for amyloid detection and diagnosis of amyloidosis. We have shown that native tetrameric TTR binds to amyloid ligands based on the trans-stilbene scaffold providing a platform for the determination of high-resolution structures of these important molecules bound to protein. In this study, we provide spectroscopic evidence of binding and X-ray crystallographic structure data on tetrameric TTR complex with the fluorescent salicylic acid-based pyrene amyloid ligand (Py1SA), an analogue of the Congo red analogue X-34. The ambiguous electron density from the X-ray diffraction, however, did not permit Py1SA placement with enough confidence likely due to partial ligand occupancy. Instead, the preferred orientation of the Py1SA ligand in the binding pocket was determined by molecular dynamics and umbrella sampling approaches. We find a distinct preference for the binding modes with the salicylic acid group pointing into the pocket and the pyrene moiety outward to the opening of the T4 binding site. Our work provides insight into TTR binding mode preference for trans-stilbene salicylic acid derivatives as well as a framework for determining structures of TTR-ligand complexes.

Phytic acid is a polyphosphate whose ionized form is used as a cross-linking agent to formulate chitosan-based nanoparticles and hydrogels as carriers with remarkable adhesivity and biocompatibility. To predict the underlying cross-linking pattern responsible for the structural arrangement in the chitosan hydrogels, we put forth coarse-grained parametrization of the phytic acid compatible with the Martini 2.3P force field. The bonded parameters giving the distinctive representation of the phosphate substitutes to the myo -inositol ring of phytic acid are optimized by a structural comparison to the conformation sampled with the GROMOS 56A CARBO force field. The chitosan strand is coarse-grained following a similar approach, and the cross-interaction terms are optimized to reproduce the atomistic features of phytate-mediated cross-linking. The predicted binding motifs of the phytic acid-chitosan complexation enable us to rationalize the structural characteristics of the reticulated chitosan in a semi-dilute solution. The model describes a network topology affected by the phytic acid concentration and a nonmonotonous behavior of the mean pore size caused by a poor predilection for the parallel strand alignment near the charge neutralization of the phytic acid-chitosan complex.

Ethylenediaminetetraacetic acid (EDTA) is frequently used in lipid experiments to remove redundant ions, such as Ca 2+ , from the sample solution. In this work, combining molecular dynamics (MD) simulations and Langmuir monolayer experiments, we show that on top of the expected Ca 2+ depletion, EDTA anions themselves bind to phosphatidylcholine (PC) monolayers. This binding, originating from EDTA interaction with choline groups of PC lipids, leads to the adsorption of EDTA anions at the monolayer surface and concentration-dependent changes in surface pressure as measured by monolayer experiments and explained by MD simulations. This surprising observation emphasizes that lipid experiments carried out using EDTA-containing solutions, especially of high concentrations, must be interpreted very carefully due to potential interfering interactions of EDTA with lipids and other biomolecules involved in the experiment, e.g., cationic peptides, that may alter membrane-binding affinities of studied compounds.

Overtones and combinational modes frequently play essential roles in ultrafast vibrational energy relaxation in liquid water. However, these modes are very weak and often overlap with fundamental modes, particularly in isotopologues mixtures. We measured VV and HV Raman spectra of H 2 O and D 2 O mixtures with femtosecond stimulated Raman scattering (FSRS) and compared the results with calculated spectra. Specifically, we observed the mode at around 1850 cm -1 and assigned it to H-O-D bend + rocking libration. Second, we found that the H-O-D bend overtone band and the OD stretch + rocking libration combination band contribute to the band located between 2850 and 3050 cm -1 . Furthermore, we assigned the broad band located between 4000 and 4200 cm -1 to be composed of combinational modes of high-frequency OH stretching modes with predominantly twisting and rocking librations. These results should help in a proper interpretation of Raman spectra of aqueous systems as well as in the identification of vibrational relaxation pathways in isotopically diluted water.

Macromolecular crowding has profound effects on the mobility of proteins, with strong implications on the rates of intracellular processes. To describe the dynamics of crowded environments, detailed molecular models are needed, capturing the structures and interactions arising in the crowded system. In this work, we present OPEPv7, which is a coarse-grained force field at amino-acid resolution, suited for rigid-body simulations of the structure and dynamics of crowded solutions formed by globular proteins. Using the OPEP protein model as a starting point, we have refined the intermolecular interactions to match the experimentally observed dynamical slowdown caused by crowding. The resulting force field successfully reproduces the diffusion slowdown in homogeneous and heterogeneous protein solutions at different crowding conditions. Coupled with the lattice Boltzmann technique, it allows the study of dynamical phenomena in protein assemblies and opens the way for the in silico rheology of protein solutions.

We investigate the glass polymorphism of dilute LiCl-H 2 O in the composition range of 0-5.8 mol % LiCl. The solutions are vitrified at ambient pressure (requires hyperquenching with ∼10 6 K s -1 ) and transformed to their high-density state using a special high-pressure annealing protocol. Ex situ characterization was performed via isobaric heating experiments using X-ray diffraction and differential scanning calorimetry. We observe signatures from a distinct high-density and a distinct low-density glass for all solutions with a mole fraction x of ≤ 4.3 mol %, where the most notable are (i) the jumplike polyamorphic transition from high-density to low-density glass and (ii) two well-separated glass-to-liquid transitions LiCl of ≤ 4.3 mol %, where the most notable are (i) the jumplike polyamorphic transition from high-density to low-density glass and (ii) two well-separated glass-to-liquid transitions T g,1 ≥ 5.8 mol %, which show only continuous densification and relaxation behavior. That is, a switch from water-dominated to solute-dominated region occurs between 4.3 mol % LiCl and 5.8 mol % LiCl. For the water-dominated region, we find that LiCl has a huge impact only on the low-density form. This is manifested as a shift in halo peak position to denser local structures, a lowering of T , and a significant change in relaxation dynamics. These effects of LiCl are observed both for hyperquenched samples and low-density samples obtained via heating of the high-density glasses, suggesting path independence. Such behavior further necessitates that LiCl is distributed homogeneously in the low-density glass. This contrasts earlier studies in which structural heterogeneity is claimed: ions were believed to be surrounded by only high-density states, thereby enforcing a phase separation into ion-rich high-density and ion-poor low-density glasses. We speculate the difference arises from the difference in cooling rates, which are higher by at least 1 order of magnitude in our case.g,2 , each pertaining to one glass polymorph. These features are absent for solutions with x LiCl ≥ 5.8 mol %, which show only continuous densification and relaxation behavior. That is, a switch from water-dominated to solute-dominated region occurs between 4.3 mol % LiCl and 5.8 mol % LiCl. For the water-dominated region, we find that LiCl has a huge impact only on the low-density form. This is manifested as a shift in halo peak position to denser local structures, a lowering of T g,1 , and a significant change in relaxation dynamics. These effects of LiCl are observed both for hyperquenched samples and low-density samples obtained via heating of the high-density glasses, suggesting path independence. Such behavior further necessitates that LiCl is distributed homogeneously in the low-density glass. This contrasts earlier studies in which structural heterogeneity is claimed: ions were believed to be surrounded by only high-density states, thereby enforcing a phase separation into ion-rich high-density and ion-poor low-density glasses. We speculate the difference arises from the difference in cooling rates, which are higher by at least 1 order of magnitude in our case.

Coherent Raman scattering microscopy utilizing bioorthogonal tagging approaches like isotope or alkyne labeling allows for a targeted monitoring of spatial distribution and dynamics of small molecules of interest in cells, tissues, and other complex biological matrices. To fully exploit this approach in terms of real-time monitoring of several Raman tags, e.g., to study drug uptake dynamics, extremely fast tunable lasers are needed. Here, we present a laser concept without moving parts and fully electronically controlled for the quasi-simultaneous acquisition of coherent anti-Stokes Raman scattering images at multiple Raman resonances. The laser concept is based on the combination of a low noise and spectrally narrow Fourier domain mode-locked laser seeding a compact four wave mixing-based high-power fiber-based optical parametric amplifier.

Molecular dynamics (MD) simulations are reported for [polyethylene glycol (PEG)200], a polydisperse mixture of ethylene glycol oligomers with an average molar weight of 200 g·mol -1 . As a first step, available force fields for describing ethylene glycol oligomers were tested on how accurately they reproduced experimental properties. They were found to all fall short on either reproducing density, a static property, or the self-diffusion coefficient, a dynamic property. Discrepancies with the experimental data increased with the increasing size of the tested ethylene glycol oligomer. From the available force fields, the optimized potential for liquid simulation (OPLS) force field was used to further investigate which adjustments to the force field would improve the agreement of simulated physical properties with experimental ones. Two parameters were identified and adjusted, the (HO)-C-C-O proper dihedral potential and the polarity of the hydroxy group. The parameter adjustments depended on the size of the ethylene glycol oligomer. Next, PEG200 was simulated with the OPLS force field with and without modifications to inspect their effects on the simulation results. The modifications to the OPLS force field significantly decreased hydrogen bonding overall and increased the propensity of intramolecular hydrogen bond formation at the cost of intermolecular hydrogen bond formation. Moreover, some of the tri- and more so tetraethylene glycol formed intramolecular hydrogen bonds between the hydroxy end groups while still maintaining strong intramolecular interactions with the ether oxygen atoms. These observations allowed the interpretation of the obtained RDFs as well as structural properties such as the average end-to-end distances and the average radii of gyration. The MD simulations with and without the modifications showed no evidence of preferential association of like-oligomers to form clusters nor any evidence of long-range ordering such as a side-by-side stacking of ethylene glycol oligomers. Instead, the simulation results support the picture of PEG200 being a random mixture of its ethylene glycol oligomer components. Finally, additional MD simulations of a binary mixture of tri-and hexaethylene glycol with the same average molar weight as PEG200 revealed very similar structural and physical properties as for PEG200.

Triazole hosts allow cooperative binding of anions via hydrogen bonds, which makes them versatile systems for application in anion binding catalysis to be performed in organic solvents. The anion binding behavior of a tetratriazole host is systematically studied by employing a variety of salts, including chloride, acetate, and benzoate, as well as different cations. Classical nuclear magnetic resonance ( 1 H NMR) titrations demonstrate a large influence of cation structures on the anion binding constant, which is attributed to poor dissociation of most salts in organic solvents and corrupts the results of classical titration techniques. We propose an approach employing electrophoretic NMR (eNMR), yielding drift velocities of each species in an electric field and thus allowing a distinction between charged and uncharged species. After the determination of the dissociation constants K D . Interestingly, dependence of K on salt concentration occurs, which is attributed to cation aggregation with the anion-host complex. Finally, by the extrapolation to zero salt concentration, the true anion-host binding constant is obtained. Thus, the approach by eNMR allows a fully quantitative analysis of two factors that might impair classical anion binding studies, namely, an incomplete salt dissociation as well as the occurrence of larger aggregate species.A . Interestingly, dependence of K A on salt concentration occurs, which is attributed to cation aggregation with the anion-host complex. Finally, by the extrapolation to zero salt concentration, the true anion-host binding constant is obtained. Thus, the approach by eNMR allows a fully quantitative analysis of two factors that might impair classical anion binding studies, namely, an incomplete salt dissociation as well as the occurrence of larger aggregate species.

Pore-spanning membranes (PSMs) are a versatile tool to investigate membrane-confined processes in a bottom-up approach. Pore sizes in the micrometer range are most suited to visualize PSMs using fluorescence microscopy. However, the preparation of these PSMs relies on the spreading of giant unilamellar vesicles (GUVs). GUV production faces several limitations. Thus, alternative ways to generate PSMs starting from large or small unilamellar vesicles that are more reproducibly prepared are highly desirable. Here we describe a method to produce PSMs obtained from large unilamellar vesicles, making use of droplet-stabilized GUVs generated in a microfluidic device. We analyzed the lipid diffusion in the free-standing and supported parts of the PSMs using z -scan fluorescence correlation spectroscopy and fluorescence recovery after photobleaching experiments in combination with finite element simulations. Employing atomic force indentation experiments, we also investigated the mechanical properties of the PSMs. Both lipid diffusion constants and lateral membrane tension were compared to those obtained on PSMs derived from electroformed GUVs, which are known to be solvent- and detergent-free, under otherwise identical conditions. Our results demonstrate that the lipid diffusion, as well as the mechanical properties of the resulting PSMs, is almost unaffected by the GUV formation procedure but depends on the chosen substrate functionalization. With the new method in hand, we were able to reconstitute the syntaxin-1A transmembrane domain in microfluidic GUVs and PSMs, which was visualized by fluorescence microscopy.

Protic ionic liquids (PILs) are potential candidates as electrolyte components in energy storage devices. When replacing flammable and volatile organic solvents, PILs are expected to improve the safety and performance of electrochemical devices. Considering their technical application, a challenging task is the understanding of the key factors governing their intermolecular interactions and physicochemical properties. The present work intends to investigate the effects of the structural features on the properties of a promising PIL based on the 1,8-diazabicyclo[5.4.0]undec-7-ene (DBUH + ) cation and the (trifluoromethanesulfonyl)(nonafluorobutanesulfonyl)imide (IM14 - ) anion, the latter being a remarkably large anion with an uneven distribution of the C-F pool between the two sides of the sulfonylimide moieties. For comparison purposes, the experimental investigations were extended to PILs composed of the same DBU-based cation and the trifluoromethanesulfonate (TFO - ) or bis(trifluoromethanesulfonyl)imide (TFSI - ) anion. The combined use of multiple NMR methods, thermal analyses, density, viscosity, and conductivity measurements provides a deep characterization of the PILs, unveiling peculiar behaviors in DBUH-IM14, which cannot be predicted solely on the basis of differences between aqueous p K values of the protonated base and the acid (Δp a ). Interestingly, the thermal and electrochemical properties of DBUH-IM14 turn out to be markedly governed by the size and asymmetric nature of the anion. This observation highlights that the structural features of the precursors are an important tool to tailor the PIL's properties according to the specific application.K a ). Interestingly, the thermal and electrochemical properties of DBUH-IM14 turn out to be markedly governed by the size and asymmetric nature of the anion. This observation highlights that the structural features of the precursors are an important tool to tailor the PIL's properties according to the specific application.

Systems with short-range attraction and long-range repulsion can form ordered microphases in bulk and under confinement. Using grand canonical Monte Carlo simulations, we study a colloidal system with competing interactions under confinement in narrow spherical shells at thermodynamic conditions at which the hexagonal phase of cylindrical clusters is stable in bulk. We observe spontaneous formation of different ordered structures. The results of the simulations are in a very good agreement with the predictions of a simple mathematical model based on the geometry and optimal packing of colloidal clusters. The results of the simulations and the explanation provided by a relatively simple geometric model may be helpful in manufacturing copolymer nanocapsules and may indicate possible ways of coiling DNA strands on spherical objects.

We present a novel decomposition scheme for electronic interaction energies based on the flexible formulation of fragmentation schemes through fragment combination ranges (FCRs; J. Chem. Phys. , 2021 , 155 , 164105). We devise a clear additive decomposition with contribution of nondisjoint fragments and correction terms for overlapping fragments and apply this scheme to the metalloenzyme-substrate complex of a lytic polysaccharide monooxygenase (LPMO) with an oligosaccharide. By this, we further illustrate the straightforward adaptability of the FCR-based schemes to novel systems. Our calculations suggest that the description of the electronic structure is a larger error source than the fragmentation scheme. In particular, we find a large impact of the basis set size on the interaction energies. Still, the introduction of three-body interaction terms in the fragmentation setup improves the agreement to the supermolecular reference. Yet, the qualitative results for the decomposition scheme with two-body terms only largely agree within the investigated electronic-structure approaches and basis sets, which are B97-3c, DFT (TPSS and B3LYP), and MP2 methods. The overlap contributions are found to be small, allowing analysis of the interaction energy into individual amino acid residues: We find a particularly strong interaction between the substrate and the LPMO copper active site.

Clustering of transmembrane proteins underlies a multitude of fundamental biological processes at the plasma membrane (PM) such as receptor activation, lateral domain formation, and mechanotransduction. The self-association of the respective transmembrane domains (TMDs) has also been suggested to be responsible for the micron-scaled patterns seen for integral membrane proteins in the budding yeast PM. However, the underlying interplay between the local lipid composition and the TMD identity is still not mechanistically understood. In this work, we combined coarse-grained molecular dynamics simulations of simplified bilayer systems with high-resolution live-cell microscopy to analyze the distribution of a representative helical yeast TMD from the PM sensor Slg1 within different lipid environments. In our simulations, we specifically evaluated the effects of acyl chain saturation and anionic lipid head groups on the association of two TMDs. We found that weak lipid-protein interactions significantly affect the configuration of TMD dimers and the free energy of association. Increased amounts of unsaturated phospholipids (PLs) strongly reduced the helix-helix interaction, while the presence of anionic phosphatidylserine (PS) hardly affected the dimer formation. We could experimentally confirm this surprising lack of effect of PS using the network factor, a mesoscopic measure of PM pattern formation in yeast cells. Simulations also showed that the formation of TMD dimers in turn increased the order parameter of the surrounding lipids and induced long-range perturbations in lipid organization. In summary, our results shed new light on the mechanisms of lipid-mediated dimerization of TMDs in complex lipid mixtures.

Excited-state character and dynamics of two 6-(dimethylamino)-2-acylnaphthalene dyes (Prodan and Badan-SCH 2 CH 2 OH) were studied by picosecond time-resolved IR spectroscopy (TRIR) in solvents of different polarity and relaxation times: hexane, CD 3 OD, and glycerol- d 8 . In all these solvents, near-UV excitation initially produced the same S 1 (ππ*) excited state characterized by a broad TRIR signal. A very fast decay (3, ∼100 ps) followed in hexane, whereas conversion to a distinct IR spectrum with a ν(C═O) band downshifted by 76 cm -1 occurred in polar/H-bonding solvents, slowing down on going from CD 3 OD (1, 23 ps) to glycerol- d 8 (ICT) by comparing experimental and TDDFT-calculated spectra. TRIR conversion kinetics are comparable to those of early stages of multiexponential fluorescence decay and dynamic fluorescence red-shift. This work presents a strong evidence that Prodan-type dyes undergo solvation-driven charge separation in their S 2 state, which is responsible for the dynamic fluorescence Stokes shift observed in polar/H-bonding solvents. The time evolution of the optically prepared S 1 (ICT) by comparing experimental and TDDFT-calculated spectra. TRIR conversion kinetics are comparable to those of early stages of multiexponential fluorescence decay and dynamic fluorescence red-shift. This work presents a strong evidence that Prodan-type dyes undergo solvation-driven charge separation in their S 1 (ICT) final state reflects environment relaxation and solvation dynamics. This finding rationalizes the widespread use of Prodan-type dyes as probes of environment dynamics and polarity.1 (ππ*) state to the S 1 (ICT) final state reflects environment relaxation and solvation dynamics. This finding rationalizes the widespread use of Prodan-type dyes as probes of environment dynamics and polarity.

The bi-thiophene-vinylene-benzothiazole (bTVBT4) ligand developed for Alzheimer's disease (AD)-specific detection of amyloid tau has been studied by a combination of several theoretical methods and experimental spectroscopies. With reference to the cryo-EM tau structure of the tau protofilament ( Nature 2017, 547, 185), a periodic model system of the fibril was created, and the interactions between this fibril and bTVBT4 were studied with nonbiased molecular dynamics simulations. Several binding sites and binding modes were identified and analyzed, and the results for the most prevailing fibril site and ligand modes are presented. A key validation of the simulation work is provided by the favorable comparison of the theoretical and experimental absorption spectra of bTVBT4 in solution and bound to the protein. It is conclusively shown that the ligand-protein binding occurs at the hydrophobic pocket defined by the residues Ile360, Thr361, and His362. This binding site is not accessible in the Pick's disease (PiD) fold, and fluorescence imaging of bTVBT4-stained brain tissue samples from patients diagnosed with AD and PiD provides strong support for the proposed tau binding site.

Ice XIX represents the latest discovery of ice polymorphs and exists in the medium pressure range near 1-2 GPa. Ice XIX is a partially hydrogen-ordered phase, by contrast to its disordered mother phase ice VI, which shares the same oxygen-atom network with ice XIX. Ice XIX differs in terms of the ordering of the hydrogen-atom sublattice, and hence the space group, from its hydrogen-ordered sibling ice XV, which also features the same type of oxygen network. Together, ice VI, XV, and XIX form the only known trio of ice polymorphs, where polymorphic transformations from order to order, order to disorder, and disorder to order are possible, which also compete with each other depending on the thermodynamic path taken and the cooling/heating rates employed. These transitions in the H-sublattice have barely been investigated, so we study here the unique triangular relation in the ice VI/XV/XIX trio based on calorimetry experiments. We reveal the following key features for H-sublattice transitions: (i) upon cooling ice VI, domains of ice XV and XIX develop simultaneously, where pure ice XV forms at ≤0.85 GPa and pure ice XIX forms at ≥1.60 GPa, (ii) ice XIX transforms into ice XV via a transient disordered state, (iii) ice XV recooled at ambient pressure features a complex domain structure, possibly containing an unknown H-ordered polymorph, (iv) recooled ice XV partly transforms back into ice XIX at 1.80 GPa, and (v) partial deuteration slows down domain reordering strongly. These findings not only are of interest in understanding possible hydrogen-ordering and -disordering processes in the interior of icy moons and planets but, more importantly, also provide a challenging benchmark for our understanding and parameterizing many-body interactions in H-bonded networks.

Halogenated and alkylated BODIPY derivatives are reported as suitable candidates for their use as photosensitizers in photodynamic therapy due to their efficient intersystem crossing (ISC) between states of different spin multiplicities. Spin-orbit couplings (SOCs) are evaluated using an effective one-electron spin-orbit Hamiltonian for brominated and alkylated BODIPY derivatives to investigate the quantitative effect of alkyl and bromine substituents on ISC. BODIPY derivatives containing bromine atoms have been found to have significantly stronger SOCs than alkylated BODIPY derivatives outside the Frank-Condon region while they are nearly the same at local minima. Based on calculated time-dependent density functional theory (TD-DFT) vertical excitation energies and SOCs, excited-state dynamics of three BODIPY derivatives were further explored with TD-DFT surface hopping molecular dynamics employing a simple accelerated approach. Derivatives containing bromine atoms have been found to have very similar lifetimes, which are much shorter than those of the derivatives possessing just the alkyl moieties. However, both bromine atoms and alkyl moieties reduce the HOMO/LUMO gap, thus assisting the derivatives to behave as efficient photosensitizers.

Cu(I) 4 H -imidazolato complexes are excellent photosensitizers with broad and intense light absorption properties, based on an earth-abundant metal, and hold great promise as photosensitizers in artificial photosynthesis and for accumulation of redox equivalents. In this study, the excited-state relaxation dynamics of three novel heteroleptic Cu(I) 4 H -imidazolato complexes with phenyl, tolyl, and mesityl side groups are systematically investigated by femtosecond and nanosecond time-resolved transient absorption spectroscopy and theoretical methods, complemented by steady-state absorption spectroscopy and (spectro)electrochemistry. After photoexcitation into the metal-to-ligand charge transfer (MLCT) and intraligand charge transfer absorption band, fast (0.6-1 ps) intersystem crossing occurs into the triplet MLCT manifold. The triplet-state population relaxes via the geometrical planarization of the N -aryl rings on the Cu(I) 4 H -imidazolato complexes. Depending on the initial Franck-Condon state, the remaining small singlet state population relaxes into two geometrically distinct minima geometries with similar energy, S 1/2,relax and S 3/4,relax . Subsequent ground-state recovery from S 1/2,relax and internal conversion from S 3/4,relax to S 1/2,relax take place on a 100 ps time scale. The internal conversion can be understood as hole transfer from a d yz -orbital to a d xz -orbital, which is accompanied with the structural reorganization of the coordination environment. Generally, the photophysical processes are determined by the steric hindrance of the side groups on the ligands. And the excited singlet-state pathways are dependent on the excitation wavelength.

Sterols have been ascribed a major role in the organization of biological membranes, in particular for the formation of liquid ordered domains in complex lipid mixtures. Here, we employed molecular dynamics simulations to compare the effects of cholesterol and ergosterol as the major sterol of mammalian and fungal cells, respectively, on binary mixtures with 1,2-dipalmitoyl- sn -glycero-3-phosphocholine (DPPC) as a proxy for saturated lipids. In agreement with previous work, we observe that the addition of sterol molecules modifies the order of DPPC both in the gel phase and in the liquid phase. When disentangling the overall tilt angle and the structure of the tail imposed by trans/gauche configurations of torsion angles in the tail, respectively, a more detailed picture of the impact of sterols can be formulated, revealing, for example, an approximate temperature-concentration superposition ranging from the liquid to the gel phase. Furthermore, a new quantitative measure to identify the presence of collective sterol effects is discussed. Moreover, when comparing both types of sterols, addition of cholesterol has a noticeably stronger impact on phospholipid properties than that of ergosterol. The observed differences can be attributed to higher planarity of the cholesterol ring system. This planarity combined with an inherent asymmetry in its molecular interactions leads to better alignment and hence stronger interaction with saturated acyl chains. Our results suggest that the high order demonstrated for ergosterol in fungal plasma membranes must therefore be generated via additional mechanisms.

Intramolecular hydrogen bonds in aprotic media were studied by combined (simultaneous) NMR and UV-vis spectroscopy. The species under investigation were anionic and featured single or coupled H-bonds between, for example, carboxylic groups and phenolic oxygen atoms (COO···H···OC) - , among phenolic oxygen atoms (CO···H···OC) - , and hydrogen bond chains between a carboxylic group and two phenolic oxygen atoms (COO···H···(OC)···H···OC) - . The last anion may be regarded as a small molecule model for the hydrogen bond system in the active site of wild-type photoactive yellow protein (PYP) while the others mimic the corresponding H-bonds in site-selective mutants. Proton positions in isolated hydrogen bonds and hydrogen bond chains were assessed by calculations for vacuum conditions and spectroscopically for the two media, CD 2 Cl 2 and the liquefied gas mixture CDClF 2 /CDF 3 at low temperatures. NMR parameters allow for the estimation of time-averaged H-bond geometries, and optical spectra give additional information about geometry distributions. Comparison of the results from the various systems revealed the effects of the formation of hydrogen bond chains and changes of medium conditions on the geometry of individual H-bonds. In particular, the proton in a hydrogen bond to a carboxylic group shifts from the phenolic oxygen atom in the system COO - ···H-OC to the carboxylic group in COO-H···(OC) - ···H-OC as a result of hydrogen bond formation to the additional phenolic donor. Increase in medium polarity may, however, induce the conversion of a structure of a type COO-H···(OC) - ···H-OC to the type COO - ···H-(OC)···H-OC. Application of these results obtained from the model systems to PYP suggests that both cooperative effects within the hydrogen bond chain and a low-polarity protein environment are prerequisites for the stabilization of negative charge on the cofactor and hence for the spectral tuning of the photoreceptor.

Mesoporous silica materials (MSMs) produced by true liquid crystal templating (TLCT) are often considered as direct inverted replicas of the initial lyotropic liquid crystal (LLC) phase. However, the predictive design of tailor-made MSMs requires the full knowledge of the TLCT process, which is still incomplete. Here, we tackle this issue by monitoring the structural evolution during the templating process by small-angle X-ray scattering, showing that after the addition of the silica source the reaction mixture is first isotropic and then an intermediary liquid crystal phase appears, which is the key to the success of the templating process, namely the formation of ordered MSMs. We analyze the structure and the formation dynamics of this intermediary phase and present a simple theoretical model, which allows us to connect the structural parameters of the initial LLC and the MSM. These results provide an enhanced understanding of the TLCT process and are an important step toward the predictable synthesis of new MSMs in the future.

Many applications of responsive microgels rely on the fast adaptation of the polymer network. However, the underlying dynamics of the de-/swelling process of the gels have not been fully understood. In the present work, we focus on the collapse kinetics of poly- N -isopropylacrylamide (pNIPAM) microgels due to cononsolvency. Cononsolvency means that either of the pure solvents, e.g., pure water or pure methanol, act as a so-called good solvent, leading to a swollen state of the polymer network. However, in mixtures of water and methanol, the previously swollen network undergoes a drastic volume loss. To further elucidate the cononsolvency transition, pNIPAM microgels with diameters between 20 and 110 μm were synthesized by microfluidics. To follow the dynamics, pure water was suddenly exchanged with an unfavorable mixture of 20 mol% methanol (solvent-jump) within a microfluidic channel. The dynamic response of the microgels was investigated by optical and fluorescence microscopy and Raman microspectroscopy. The experimental data provide unique and detailed insight into the size-dependent kinetics of the volume phase transition due to cononsolvency. The change in the microgel's diameter over time points to a two-step process of the microgel collapse with a biexponential behavior. Furthermore, the dependence between the two time constants from this biexponential behavior and the microgel's diameter in the collapsed state deviates from the square-power law proposed by Tanaka and Fillmore [ J. Chem. Phys. 1979, 70, 1214-1218]. The deviation is discussed considering the adhesion-induced deformation of the gels and the physical processes underlying the collapse.

Orientation analysis of the β-sheet structure within films of the established recombinant spider silk protein eADF4(C16) was performed using a concept based on dichroic transmission- and attenuated total reflection-Fourier transform infrared spectroscopy, lineshape analysis, assignment of amide I components to specific vibration modes, and transition dipole moment directions of β-sheet structures. Based on the experimental dichroic ratio R , the order parameter S of β-sheet structures was calculated with respect to uniaxial orientation. Films of eADF4(C16) were deposited on untexturized (Si) and unidirectionally scratched silicon substrates (Si-sc) and post-treated with MeOH vapor. Freshly cast thin and thick eADF4(C16) films out of hexafluoroisopropanol featured β-sheet contents of ≈6%, which increased to >30% after MeOH post-treatment in dependence of time. Pseudo-first order folding kinetics were obtained, suggesting a transition from an unfolded to a folded state. In MeOH post-treated thin films with diameters in the nanometer range, a significant orientation of β-sheets was obtained regardless of the texturization of the silicon substrate (Si, Si-sc). This was rationalized by dichroic ratios of the amide I component at 1696 cm -1 assigned to the (0, π) mode of antiparallel β-sheet structures, whose transition dipole moment M is located in parallel to both β-sheet plane and chain direction. The calculated high molecular order parameter S ≈ 0.40 suggested vertically (out-of-plane) oriented antiparallel β-sheet stacks with tilt angles of γ ≈ 39° to the surface normal. Microscale (thick) films, in contrast, revealed low order parameters S ≈ 0. Scanning force microscopy on thin eADF4 films at silicon substrates showed dewetted polymer film structures rather at the micro-scale. These findings give new insights in the role of the β-sheet crystallite orientation for the mechanical properties of spider silk materials.

The interplay of the isotropic-nematic transition and phase separation in lyotropic solutions of two types of semiflexible macromolecules with pronounced difference in chain stiffness is studied by Density Functional Theory and Molecular Dynamics simulations. While the width of the isotropic-nematic two-phase coexistence region is narrow for solutions with a single type of semiflexible chain, the two-phase coexistence region widens for solutions containing two types of chains with rather disparate stiffness. In the nematic phase, both types of chains contribute to the nematic order, with intermediate values of the order parameter compared to the corresponding single component solutions. As the difference in bending stiffness is increased, the two chain types separate into two coexisting nematic phases. The phase behavior is rationalized by considering the chemical potentials of the two components and the Gibbs excess free energy. The geometric properties of the chain conformations under the various conditions are also discussed.

In this work, we explore the possibility of promoting the formation of ordered microphases by confinement of colloids with competing interactions in ordered porous materials. For that aim, we consider three families of porous materials modeled as cubic primitive, diamond, and gyroid bicontinuous phases. The structure of the confined colloids is investigated by means of grand canonical Monte Carlo simulations in thermodynamic conditions at which either a cluster crystal or a cylindrical phase is stable in bulk. We find that by tuning the size of the unit cell of these porous materials, numerous novel ordered microphases can be produced, including cluster crystals arranged into close packed and open lattices as well as nonparallel cylindrical phases.

We utilized fluorescence spectroscopy to learn about the molecular arrangement of naphthalene (Np) and 1-methylnaphthalene (MeNp) in frozen aqueous solutions. The freezing induces pronounced compound aggregation in the freeze-concentrated solution (FCS) in between the ice grains. The fluorescence spectroscopy revealed prevalent formation of a vitrified solution and minor crystallization of aromatic compounds. The FCS is shown as a specific environment, differing significantly from not only the pure compounds but also the ice surfaces. The results indicate marked disparity between the behavior of the Np and the MeNp; the cooling rate has a major impact on the former but not on the latter. The spectrum of the Np solution frozen at a faster cooling rate (ca 20 K/min) exhibited a temperature-dependent spectral behavior, whereas the spectrum of the solution frozen at a slower rate (ca 2 K/min) did not alter before melting. We interpret the observation through considering the varied composition of the FCS: Fast freezing leads to a higher water content expressed by the plasticizing effect, allowing molecular rearrangement, while slow cooling produces a more concentrated and drier environment. The experiments were conceived as generalizable for environmentally relevant pollutants and human-made freezing.

We study the complex mixture of a polyethylene oxide- b -polypropylene oxide- b -polyethylene oxide triblock copolymer (Pluronic F127) with ionic liquid (IL) and Li-salt, which is potentially interesting as an electrolyte system with decoupled mechanical and ion-transport properties. Small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) are employed to scrutinize the phase structures and elucidate the ternary phase diagram. These data are combined with the ion diffusivities obtained by pulsed field gradient (PFG) nuclear magnetic resonance (NMR). Analyzing the partial ternary phase diagram of F127/LiTFSI/Pyr 14 TFSI, hexagonal, lamellar, and micellar mesophases are identified, including two-phase coexistence regions. While the PPO block is immiscible with the liquid, and forms the backbone of the mesostructured aggregates, the PEO blocks are not well miscible with the IL. Poorly solvated, the latter may still crystallize. At a higher IL content, PEO is further solvated, but a major solvation effect occurs due to addition of Li-salt. Li ions promote solubilization of the PEO chains in the IL, since they coordinate to the PEO chains. This was identified as the mechanism of a transition of the mesostructures, with increasing Li-salt content changing from a hexagonal to a lamellar and further to a micellar phase. In summary, both, the amount of IL and its compatibility with the PEO block, the latter being controlled by the Li-salt amount, influence the compositions of the formed mesophases and the ion diffusion in their liquid regions.

Although the effect of ionizing radiation on prebiotic chemistry is often overlooked, primordial natural radioactivity might have been an important source of energy for various chemical transformations. Estimates of the abundances of short-lived radionuclides on early Earth suggest that the primordial intensity of endogenous terrestrial radioactivity was up to 4 × 10 3 times higher than it is today. Therefore, we assume that chemical substances in contact with radioactive rocks should therefore undergo radiolysis. The calculations are followed by research investigating the influence of ionizing γ radiation on basic prebiotic substances, including formamide mixed with various clays, which might have played the role of a catalyst and an agent that partially blocked radiation that was potentially destructive for the products. Our explorations of this effect have shown that the irradiation of formamide-clay mixtures at doses of ∼6 kGy produces significant amounts of urea (up to the maximal concentration of approximately 250 mg L -1 ), which plays a role in HCN-based prebiotic chemistry.

An experimental study is presented for the reverse micellar system of 15% by mass polydisperse hexaethylene glycol monodecylether (C 10 E 6 ) in cyclohexane with varying amounts of added water up to 4% by mass. Measurements of viscosity and self-diffusion coefficients were taken as a function of temperature between 10 and 45 °C at varying sample water loads but fixed C 10 E 6 /cyclohexane composition. The results were used to inspect the validity of the Stokes-Einstein equation for this system. Unreasonably small reverse average micelle radii and aggregation numbers were obtained with the Stokes-Einstein equation, but reasonable values for these quantities were obtained using the ratio of surfactant-to-cyclohexane self-diffusion coefficients. While bulk viscosity increased with increasing water load, a concurrent expected decrease of self-diffusion coefficient was only observed for the surfactant and water but not for cyclohexane, which showed independence of water load. Moreover, a spread of self-diffusion coefficients was observed for the protons associated with the ethylene oxide repeat unit in samples with polydisperse C 10 E 6 but not in a sample with monodisperse C 10 E 6 . These findings were interpreted by the presence of reverse micelle to reverse micelle hopping motions that with higher water load become increasingly selective toward C 10 E 6 molecules with short ethylene oxide repeat units, while those with long ethylene oxide repeat units remain trapped within the reverse micelle because of the increased hydrogen bonding interactions with the water inside the growing core of the reverse micelle. Despite the observed breakdown of the Stokes-Einstein equation, the temperature dependence of the viscosities and self-diffusion coefficients was found to follow Arrhenius behavior over the investigated range of temperatures.

As manifested in biological cell membranes, the confinement of chemical reactions at the 2D interfaces significantly improves the reaction efficacy. The interface between two liquid phases is used in various key processes in industries, such as in food emulsification and floatation. However, monitoring the changes in the mechanics and dynamics of molecules confined at the liquid/liquid interfaces still remains a scientific challenge because it is nontrivial to access the interface buried under a liquid phase. Herein, we report the in situ monitoring of the cross-linking of polyalginate mediated by Ca 2+ ions at the oil/water interface by grazing incidence X-ray photon correlation spectroscopy (GIXPCS). We first optimized the reaction conditions with the aid of interfacial shear rheology and then performed GIXPCS using a high-energy synchrotron X-ray beam (22 keV) that guarantees sufficiently high transmittance through the oil phase. The intensity autocorrelation functions implied that the formation of a percolated network of polyalginate is accompanied by increasing relaxation time. Moreover, the relaxation rate scales linearly with the momentum transfer parallel to the interface, suggesting that the process is driven by hyperdiffusive propagation but not by Brownian diffusion. Our data indicated that high-energy GIXPCS has potential for in situ monitoring of changes in the dynamics of polymers confined between two liquid phases.

A significant fraction of the cell volume is occupied by various proteins, polysaccharides, nucleic acids, etc., which considerably reduces the mobility of macromolecules. Theoretical and experimental work so far have mainly focused on the dependence of the mobility on the occupied volume, while the effect of a macromolecular shape received less attention. Herein, using fluorescence correlation spectroscopy (FCS) and Brownian dynamics (BD) simulations, we report on a dramatic slowdown of tracer diffusion by cylindrically shaped double-stranded (ds) DNAs (16 nm in length). We find, for instance, that the translational diffusion coefficient of a streptavidin tracer is reduced by about 60% for a volume fraction of dsDNA as low as just 5%. For comparison, for a spherical crowder (Ficoll70) the slowdown is only 10% at the same volume fraction and 60% reduction occurs at a volume fraction as high as 35%. BD simulations reveal that this reduction can be attributed to a larger volume excluded to a tracer by dsDNA particles, as compared with spherical Ficoll70 at the same volume fraction, and to the differences in the tracer-crowder attractive interactions. In addition, we find using BD simulations that rotational diffusion of dsDNA is less affected by the crowder shape than its translational motion. Our results show that diffusion in crowded systems is determined not merely by the occupied volume fraction, but that the shape and interactions can determine diffusion, which is relevant to the diverse intracellular environments inside living cells.

The synergistic use of blends of regioregular poly(3-hexylthiophene) (P3HT) and poly(vinylidene fluoride) (PVDF) or poly((vinylidene fluoride)-block-(methyl methacrylate)) (PVDF-PMMA) to form Langmuir and Langmuir-Schaefer (LS) films is reported. P3HT has wide applications in sensor devices because of its properties such as conductivity, luminescence, and chromism; however, the stiffness of the films and the difficulty in organizing the molecules may pose a problem in these applications. In this context, polymers based on PVDF can be used in the formation of thin P3HT films and present an alternative to improve the organization of P3HT molecules. In addition, PVDF acts as a plasticizer, making the film less rigid. The films were obtained from the blends of P3HT/PVDF and P3HT/PVDF-PMMA in a solution containing chloroform and DMAc ( N , N -dimethylacetamide). Surface pressure isotherms, in situ ultraviolet-visible (UV-vis) spectroscopy, polarization-modulation infrared reflection-absorption spectroscopy, and Brewster angle microscopy techniques were used to analyze Langmuir films. The surface morphology of LS films was characterized by atomic force microscopy and UV-vis spectroscopy, and their degradation was analyzed by UV-vis spectroscopy after exposure to natural light under atmospheric conditions. The Langmuir films containing PVDF indicate a direct formation of the ferroelectric β phase, with dipoles parallel to the water surface. The Langmuir films formed by P3HT presented dipoles of side chains parallel and aromatic groups perpendicular to the water surface. P3HT and PVDF or PVDF-PMMA films show high molecular organization compared with pure P3HT films. The results suggest that these films could be used to improve the properties of P3HT in several device applications, such as in optical and electrical sensors.

Arylazopyrazoles (AAPs) as substitutes for azobenzene derivatives have gained considerable attention due to their superior properties offering E / Z photoisomerization with high yield. In order to compare and quantify their performance, azobenzene triethylammonium (Azo-TB) and arylazopyrazole triethylammonium (AAP-TB) bromides were synthesized and characterized in the bulk (water) using NMR and UV/Vis spectroscopy. At the air-water interface, complementary information from vibrational sum-frequency generation (SFG) spectroscopy and neutron reflectometry (NR) has revealed the effects of E/Z isomerization in great detail. In bulk water the photostationary states of >89% for E / Z switching in both directions were very similar for the surfactants, while their interfacial behavior was substantially different. In particular, the surface excess Γ of the surfactants changed drastically between E and Z isomers for AAP-TB (maximum change of Γ: 2.15 μmol/m 2 ); for Azo-TB, the change was only moderate (maximum change of Γ: 1.02 μmol/m 2 ). Analysis of SFG spectra revealed that strong nonresonant contributions that heterodyned the resonant vibrational bands were proportional to Γ, enabling the aromatic C-H band to be interpreted as an indicator for changes in the interfacial molecular order. Close comparison of Γ from NR with the SFG amplitude from the aromatic C-H stretch as a function of concentrations and E / Z conformation revealed substantial molecular order changes for AAP-TB. In contrast, only Γ and not the molecular order varied for Azo-TB. These differences in interfacial properties are attributed to the molecular structure of the AAP center that enables favorable lateral interactions at the air-water interface, causing closed-packed interfacial layers and substantial changes during E / Z photoisomerization.

Structural forces within aqueous water at a solid interface can significantly change surface reactivity and the affinity of solutes toward it. We show using molecular dynamics simulations how hydrophilic and hydrophobic quartz surfaces perturb the orientational structure of aqueous water, ultimately strengthening dipolar forces between molecules in proximity to the interface. When derived as a function of distance from each surface, it was found that both surfaces indirectly enhance the long-range dipolar attraction of water for itself toward the interfacial region. This was found to be longer-ranged for water molecules solvating the hydrophobic surface than those solvating the hydrophilic surface, with a range of up to 2.5 nm from the hydrophobic surface. Our results give direct quantification of surface-induced changes in solvent-solvent attraction, ultimately providing a counterintuitive addition to the balance of hydrophobic forces at aqueous-solid interfaces.

The strong coupling of an IR-active molecular transition with an optical mode of the cavity results in vibrational polaritons, which opens a new way to control chemical reactivity via confined electromagnetic fields of the cavity. In this study, we design a voltage-tunable open microcavity and we show the formation of multiple vibrational polaritons in methyl salicylate. A Rabi splitting and polariton anticrossing behavior is observed when the cavity mode hybridizes with the C═O stretching vibration of methyl salicylate. Furthermore, the proposed theoretical model based on coupled harmonic oscillators reveals that the absorption of uncoupled molecules must also be considered to model the experimental spectra properly and that simultaneous coupling of multiple molecular vibrations to the same cavity mode has a significant influence on the transmission spectral profile.

We report the assembly of four imidazolium bromides, each of which bears a naphthyl on one side of the imidazolium cation and a branched alkyl chain on the other. This design creates a new type of amphiphilic ionic liquid with an apolar-polar-apolar structure and a low melting point ( m , <-20 °C), which has not been achieved by reported counterparts bearing linear alkyl chains. In solvent-free states, microphase segregation occurs where polar and apolar domains arrange bicontinuously as proved by molecular dynamics (MD) simulations. When dispersed in water, self-stabilized giant aggregates formed with ultrahigh colloidal stability (up to years). MD simulations provide clues of discrete bicontinuous phases within the giant aggregates. These newly discovered self-assemblies provide a heterogeneous reservoir that can accommodate guest molecules including the highly apolar fullerene C p , paving the way for a wide range of potential applications.60 , paving the way for a wide range of potential applications.

Intrinsic molecular brightness (MB) is a number of emitted photons per second per molecule. When a substrate labeled by a fluorophore and a second unlabeled substrate form a complex in solution, the MB of the fluorophore changes. Here we use this change to determine the equilibrium constant ( K ) for the formation of the complex at pM concentrations. To illustrate this method, we used a reaction of DNA hybridization, where only one of the strands was fluorescently labeled. We determined K at the substrate concentrations from 80 pM to 30 nM. We validated this method against Förster resonance energy transfer (FRET). This method is much simpler than FRET as it requires only one fluorophore in the complex with a very small (a f̃ew percent) change in MB.