Molecules In Aqueous Solution Research Articles

Solvation of Methyl Lactate in Water: Molecular Dynamics Studies.

Methyl lactate (ML), a chiral α-hydroxy ester, has been probed widely to understand the competition between two types of intramolecular H-bonds in solvents of different polarities. Recent experimental and high-level quantum chemical studies have revealed the predominant existence of ML-water insertion complexes over addition complexes in aqueous solution. Although the stability of monohydrate insertion conformer was studied accurately, ab initio quantum chemical calculations failed to predict the most stable dihydrate conformer in analogy with the experimental spectroscopic search. Atomistic molecular dynamics simulations of aqueous solution of methyl lactate predict that the population and lifetime of different H-bonded ML-water addition complexes are dictated by their interaction energies. Although the population of dihydrate insertion complexes is higher than that of the monohydrate complexes, the lifetime of the former is smaller than the latter, which is in good agreement with the experimental result. The nature of intramolecular H-bonds within a methyl lactate molecule in aqueous solution is opposite to that in the gas phase due to the solvation process in water by intermolecular H-bonding interactions.

The property study of sodium dodecyl benzenesulfonate and polyvinylpyrrolidone complexes

In this paper, the physicochemical properties between sodium dodecylbenzenesulfonate (SDBS) and polyvinylpyrrolidone (PVP) in aqueous solutions were studied at 25 °C by Ubbelohde viscometer, conductivity analyzer, and fluorescence spectrophotometer. It was found that viscosity, conductivity, steady-state fluorescence, and Rayleigh scattering curve for SDBS-PVP system could be divided into three regions by two characteristic concentrations: the critical aggregation concentration (cac) and the polymer saturation point (psp). The results revealed that interactions between SDBS and PVP molecules in aqueous solutions could be explained by “necklace and bead” model. Micelle-like surfactant aggregates, formed by SDBS-free molecules, associated with PVP chains mainly by hydrophobic interaction.

Easy-separative MoS2-glue sponges with high-efficient dye adsorption and excellent reusability for convenient water treatment

This study demonstrated high-efficient dye adsorption for wastewater using MoS2-glue sponge as an easy-separative and regenerative adsorbent. Flower-like molybdenum disulfide (MoS2) nanopowders with rich polar edge sites were firstly synthesized by a facile one-pot hydrothermal method. Chemical and morphological features of MoS2 nanoflowers were then examined by XRD, XPS, SEM and TEM. Afterwards, different concentrations of the MoS2-glue sponges with easy separability were successfully fabricated by a convenient two-step dip-coating method. The adsorption performance was estimated by the removal of Rhodamine B (RhB) dyes. The results proved that the maximum adsorption capacity of MoS2-glue sponge was 127.39 mg RhB/g product in 60 min. The RhB uptake behaviors can be well described by the Sips isotherm model and pseudo-second-order kinetic model, indicating a multilayer and chemical adsorption process. The adsorption mechanism proposed that the zwitterionic RhB molecules in aqueous solution would aggregate on the surface of negative charged MoS2 in a head-to-tail way through electrostatic interaction. Furthermore, RhB dyes could desorb easily from MoS2-glue sponges when changing the polarity of solvent and the reusability experiment showed that the MoS2-3% glue sponge could be reused for 15 times with above 85.8% of the adsorption capacity retained. Thus, the novel MoS2-glue sponge is considered as a competitive adsorbent for treatment of dyestuff waste water.

Synergistic host-guest hydrophobic and hydrogen bonding interactions in the complexation between endo-functionalized molecular tube and strongly hydrophilic guest molecules in aqueous solution.

The propensity of complex formation of a host, an endo-functionalized naphthotube that has bisnaphthalene cleft architecture (host-1b), with four different strongly neutral hydrophilic guest molecules, namely 1,4-dioxane (14D), acetone, DMSO and DMF, in water is examined using classical molecular dynamics simulations. This type of molecular tube has received significant attention recently due to its usefulness as a supramolecular catalyst and for its ability to selectively recognise biologically and environmentally important neutral molecules in aqueous solution. We sequentially address the role of the different guest molecules in the structural change of host-1b, the role of the host-inserted guest and the water-inserted guest hydrogen bond properties and the host-guest binding free energies in the complex. The derivatives of our findings are: (a) the host changes its shape upon the insertion of a guest molecule and the magnitude of the shape change depends on the type and the nature of the guest molecule; (b) the complete insertion of a guest into the cavity of host-1b is only observed for guest 14D; and (c) the complete removal of water molecules from the host cavity is observed for guest 14D and the presence of a single water molecule is observed for all other guest molecules. The PMF and MM-PBSA calculations reveal that host-1b/14D complexation is the most energetically stable and the synergistic host-guest hydrophobic and hydrogen bonding interactions play a profound role in the stability of these host-guest complexes. Specifically, as the host cavity contains a small hydrophilic part and a large hydrophobic part, guest molecules with both these parts can form hydrogen bonds with the hydrophilic part of the host as well as forming a favorable hydrophobic interaction with the hydrophobic part of the host at the time of complexation.

Novel morphologies of poly(allyamine hydrochloride)-methotrexate nanoassemblies for methotrexate delivery.

Poly(allylamine hydrochloride)–methotrexate (PAH–MTX) nanoassemblies with novel morphologies (i.e. nanostrips, nanorolls, nanosheets, and nanospheres) were achieved for the first time via supramolecular self-assembly directed by the synergistic action of various non-covalent interactions between PAH and MTX molecules in aqueous solution. Herein, MTX acted in a versatile manner as both a morphology-regulating agent and a small molecular hydrophobic anticancer drug. Moreover, different morphologies presented diverse drug release profiles, which may be caused by the distinctive interactions between PAH and MTX molecules. Synergistically non-covalent interactions, including electrostatic interactions, van der Waals forces, and hydrogen bonding, favored easier matrix corrosion and more rapid drug release of non-spherical structures (i.e. nanostrips, nanorolls, and nanosheets) through the ligand exchange process. On the other hand, the highly sealed encapsulation mode for hydrophobic MTX molecules made the nanospheres exhibit slower and better controlled release. In addition, in vitro bioassay tests showed that nanostrips displayed the most obvious suppression on the viability of cancer cells among other morphologies, especially after a longer duration. The strategy of using small molecular anticancer drugs not as passively delivered cargoes but as effective molecular building blocks, opens up a new way to develop self-delivering drugs for anticancer therapy.

Effective computational route towards vibrational optical activity spectra of chiral molecules in aqueous solution.

We present a computational methodology based on a polarizable Quantum Mechanical (QM)/Molecular Mechanics (MM) approach to accurately compute the Vibrational Optical Activity (VOA) spectra of chiral systems. This approach is applied for the calculation of Infrared (IR), Vibrational Circular Dichroism (VCD), Raman and Raman Optical Activity (ROA) spectra of aqueous solutions of (l)-methyl lactate and (S)-glycidol. Remarkable agreement between calculations and experiments is reported, showing the reliability and accuracy of the methodology, especially with respect to standard continuum solvation approaches.

Disassembly-driven signal turn-on probes for bimodal detection of DNA with 19F NMR and fluorescence

To image DNAs in vivo, molecular probes that can detect DNA with a highly transparent signal are required. In this study, we designed and synthesized amphiphilic molecular probes that can detect DNA with a highly transparent 19F NMR signal in a signal turn-on manner based on the self-assembly and target-dependent-disassembly of the probe molecules in aqueous solution. Fluorescence and dynamic light scattering studies revealed that these amphiphilic probes consisting of bisbenzimide H 33258 and 3,5-bis(trifluoromethyl)benzene are assembled and form aggregates in aqueous solution, and that the aggregates are collapsed when the probes bind to double-stranded DNA via selective interaction between the bisbenzimide H 33258 moiety and AATT double-stranded region of DNA. Since the target-dependent-disassembly of the probes caused turn-on of 19F NMR and fluorescence signals, bimodal detection of double-stranded DNA was successfully achieved.

Ab Initio Simulations of Water Dynamics in Aqueous TMAO Solutions: Temperature and Concentration Effects.

We use ab initio molecular dynamics simulation to study the effect of hydrophobic groups on the dynamics of water molecules in aqueous solutions of trimethylamine N-oxide (TMAO). We show that hydrophobic groups induce a moderate (<2-fold) slowdown of water reorientation and hydrogen-bond dynamics in dilute solutions, but that this slowdown rapidly increases with solute concentration. In addition, the slowdown factor is found to vary very little with temperature, thus suggesting an entropic origin. All of these results are in quantitative agreement with prior classical molecular dynamics simulations and with the previously suggested excluded-volume model. The hydrophilic TMAO headgroup is found to affect water dynamics more strongly than the hydrophobic moiety, and the magnitude of this slowdown is very sensitive to the strength of the water-solute hydrogen-bond.

Preparation and detection of progesterone by molecularly imprinted film based on reversible addition fragmentation chain transfer polymerization

Molecularly imprinted technique is a versatile and straightforward way to produce artificial receptors for a given target molecule. The molecularly imprinted polymers (MIPs) have received widespread attention and application, owing to their high physical stability, remarkable robustness and low cost. Despite the tremendous progress made in this field, many changes still remain to be solved. In general, MIPs are prepared by traditional free radical polymerization. However, this approach causes problems such as low-affinity binding, high diffusion barrier, low-rate mass transfer. In particular, it has been demonstrated that most of the MIPs fail to exhibit specific recognition towards the target molecules in aqueous environments although they can be successfully applied to recognize the target molecules in organic solvent media, which severely limits their potential application in some fields. In this work, a new method to prepare MIPs film for the detection of progesterone based on reversible addition-fragmentation chain transfer (RAFT) polymerization is presented. 2-Methyl-2-[(dodecylsulfanylthiocarbonyl)sulfanyl]propanoic acid (DDMAT) was employed as the sole control agent in the UV polymerization. The SPR sensor chip with 50 nm Au was firstly immersed in an ethanol solution of cysteamine (5 mmol/L) for 24 h. The cysteamine modificated chip was washed by pure ethanol solvent repeatedly and dried under a stream of nitrogen. Then the chip was placed in 40 mL acetonitrile solution with 14.6 mg DDMAT and 16.5 mg N , N ′-dicyclohexylcarbodiimide (DCC) for 24 h. After that, the chip was washed with acetonitrile several times and dried under a stream of nitrogen. The MIPs film was grafted by UV irradiated without adding additional photo initiator or catalyst in the presence of progesterone (31.4 mg), methacrylic acid (33.4 μL), ethylene glycol dimethacrylate (338.5μL) and DDMAT (15 mg) in 4 mL acetonitrile. The growth process of the MIPs film was monitored by surface plasmon resonance (SPR) in situ . A mixture of PBS (pH 7.4) buffer and acetic acid (v:v=9:1) was used as a washing solution to remove the template molecules from the MIPs film. Results indicated that DDMAT acted as both photo initiator and chain transfer agent during the polymerization. The MIPs film was characterized by contact angle measurements, infrared spectroscopy and scanning electron microscope (SEM). Analysis of SPR spectroscopy showed that the MIPs film coated sensor displayed good sensitivity and selectivity to progesterone compared to other analytes with a similar structure. The response of the progesterone ranged from 10−12 to 10−7 mol/L with a limit of detection (LOD) of 3.24×10−13 mol/L ( S / N =3) in PBS buffer (pH 7.4). The MIPs film coated sensor also showed good reusability and stability, and kept about 81% of its original response after 30 d of storage under N2 protection at room temperature. In addition, the SPR sensor was successfully used to determine progesterone in tap water, underground water and artificial urine samples with recoveries from 92.9% to 96.5%, which indicated the SPR sensor can be applied for the real sample detection. This method will expand the surface modification of the MIPs film on the surface of different sensors and is a great candidate for rapid, simple and label-free detection of molecules in aqueous solution. Finally, this study opens a door to re-know the roles of chain transfer agents (DDMAT, in this study) in synthesizing MIPs and we believe that the properties of various chain transfer agents will be excavated and utilized in future study.

Redox-Active Glyconanoparticles as Electron Shuttles for Mediated Electron Transfer with Bilirubin Oxidase in Solution.

We demonstrate self-assembly, characterization and bioelectrocatalysis of redox-active cyclodextrin-coated nanoparticles. The nanoparticles with host-guest functionality are easy to assemble and permit entrapment of hydrophobic redox molecules in aqueous solution. Bis-pyrene-ABTS encapsulated nanoparticles were investigated electrochemically and spectroscopically. Their use as electron shuttles is demonstrated via an intraelectron transfer chain between neighboring redox units of clustered particles (Dh,DLS = 195 nm) and the mono- and trinuclear Cu sites of bilirubin oxidases. Enhanced current densities for mediated O2 reduction are observed with the redox nanoparticle system compared to equivalent bioelectrode cells with dissolved mediator. Improved catalytic stability over 2 days was also observed with the redox nanoparticles, highlighting a stabilizing effect of the polymeric architecture. Bioinspired nanoparticles as mediators for bioelectrocatalysis promises to be valuable for future biofuel cells and biosensors.

Self-Assembly of Long-Chain Betaine Surfactants: Effect of Tailgroup Structure on Wormlike Micelle Formation.

Long-chain amidopropyl betaines are known for their ability to self-assemble into viscoelastic wormlike micellar structures. Here, we explore the effect of tailgroup molecular architecture on this process, comparing five molecules, each with C18 chains but different levels of unsaturation and branching. The surfactants are synthesized from stearic, oleic, linoleic, linolenic, and isostearic acids. The self-assembly of these molecules in aqueous solutions is explored using small- and ultra-small-angle neutron scattering (SANS and USANS). It is seen that optimum wormlike micelle formation is achieved for the oleic-chained surfactant, and the alignment of self-assembled structures is further explored using rheo-SANS. The more highly unsaturated molecules form rodlike micelles, whereas the stearic-tailed molecule shows a pronounced Krafft point and the isostearic-chained surfactant is entirely water-insoluble. These results demonstrate the critical importance of tailgroup geometry on surfactant properties and self-assembly for this industrially important class of surfactants.

Custom Glycosylation of Cells and Proteins Using Cyclic Carbamate-Derivatized Oligosaccharides

The structural complexity of glycosylation restrains the functional characterization of glycans. We present a versatile carbohydrate ligation technique based on the reaction of cyclic carbamates with primary amines. Cyclic-carbamate-derivatized carbohydrates can be added to primary amine-containing molecules in aqueous solution to yield glycoconjugates. This method enabled the presentation of carbohydrate epitopes on live animal cells, as shown by the acquisition of E-selectin binding sites on mouse MC-38 cells decorated with 3-fucosyllactose or 3-fucosyl-3-sialyllactose. Ligation of 3- and 6-sialyllactose to Escherichia coli demonstrated theimportance of sialic acid linkages in regulating complement factor H binding. Proteins were modified with oligosaccharides to study their role in stimulating cytokine secretion by dendritic cells, thus pointing to interactions between glycoproteins and phosphoinositide 3-kinase signaling in controlling interleukin-12, tumor necrosis factor alpha and interleukin-1β release. Overall, cyclic-carbamate-mediated ligation is useful to study the biology ofcarbohydrate epitopes on proteins and on cell membranes.

Flexible Microsphere-Embedded Film for Microsphere-Enhanced Raman Spectroscopy.

Dielectric microspheres with extraordinary microscale optical properties, such as photonic nanojets, optical whispering-gallery modes (WGMs), and directional antennas, have drawn interest in many research fields. Microsphere-enhanced Raman spectroscopy (MERS) is an alternative approach for enhanced Raman detection by dielectric microstructures. Unfortunately, fabrication of microsphere monolayer arrays is the major challenge of MERS for practical applications on various specimen surfaces. Here we report a microsphere-embedded film (MF) by immersing a highly refractive microsphere monolayer array in the poly(dimethylsiloxane) (PDMS) film as a flexible MERS sensing platform for one- to three-dimensional (1D to 3D) specimen surfaces. The directional antennas and wave-guided whispering-gallery modes (WG-WGMs) contribute to the majority of Raman enhancement by the MFs. Moreover, the MF can be coupled with surface-enhanced Raman spectroscopy (SERS) to provide an extra >10-fold enhancement. The limit of detection is therefore improved for sensing of crystal violet (CV) and Sudan I molecules in aqueous solutions at concentrations down to 10-7 M. A hybrid dual-layer microsphere enhancer, constructed by depositing a MF onto a microsphere monolayer array, is also demonstrated, wherein the WG-WGMs become dominant and boost the enhancement ratio >50-fold. The present work opens up new opportunities for design of cost-effective and flexible MERS sensing platforms as individual or associated techniques toward practical applications in ultrasensitive Raman detection.

Comparison of a quantum random number generator with pseudorandom number generators for their use in molecular Monte Carlo simulations.

Four pseudorandom number generators were compared with a physical, quantum-based random number generator using the NIST suite of statistical tests, which only the quantum-based random number generator could successfully pass. We then measured the effect of the five random number generators on various calculated properties in different Markov-chain Monte Carlo simulations. Two types of systems were tested: conformational sampling of a small molecule in aqueous solution and liquid methanol under constant temperature and pressure. The results show that poor quality pseudorandom number generators produce results that deviate significantly from those obtained with the quantum-based random number generator, particularly in the case of the small molecule in aqueous solution setup. In contrast, the widely used Mersenne Twister pseudorandom generator and a 64-bit Linear Congruential Generator with a scrambler produce results that are statistically indistinguishable from those obtained with the quantum-based random number generator. © 2017 Wiley Periodicals, Inc.

Primary Formation Path of Formaldehyde in Hydrothermal Vents.

Formaldehyde is abundant in the universe and one of the fundamental molecules for life. Hydrothermal vents produce a substantial amount of hydrogen molecules by serpentinization and promote reductive reactions of single carbon compounds. The abundance of formaldehyde is expected to be low due to the high Gibbs free energy in hydrothermal vents. We consider two competing formation pathways of formaldehyde: (1) the reduction of CO by H2 and (2) the reduction of HCOOH by H2 to form a methanediol, followed by the dehydration of the methanediol. We performed a number of quantum chemical simulations to examine the formation of formaldehyde in the gas phase as well as in aqueous solution. The energy barrier is significantly reduced by the catalytic effect of water molecules in aqueous solution and becomes lowest when a water cluster consisted of 5 water molecules catalyzes the reduction. The energy barrier to form a methanediol by the reduction of HCOOH is lower by 17.5 kcal/mol than that to form a formaldehyde by the reduction of CO. Considering the low energy barrier to dehydrate methanediol, the primary pathway to form formaldehyde in hydrothermal vents is concluded to be the reduction of HCOOH by H2, followed by the dehydration of methanediol.

An Ultrastable Metal–Organic Framework with Open Coordinated Sites Realizing Selective Separation toward Cationic Dyes in Aqueous Solution

A novel Zn-based metal–organic framework (MOF) was synthesized from the mixed ligands, 3,3′,5,5′-azoxybenzenetetracarboxylic acid (H4AOBTC) and 1,4-bis(1H-benzo[d]imidazol-1-yl)benzene (phenDIB) ligand. The crystal structure of the complex exhibits an interpenetrated three-dimensional framework that can be simplified as a (4,4)-connected 2-nodal bbf net. This MOF displays extraordinary thermostability in boiling water for 12 h and chemical stability in a wide pH range of 2–13. The most intriguing feature is that it can successfully separate cationic dyes from mixed dye molecules in aqueous solution with high effectivity and selectivity, even for rhodamine B molecule with a large size. Furthermore, this material is reusable, and the adsorbed dye molecules can be released and recovered completely. It is very important for the practical application from a view of environmental protection and resource recycling.

Adapting the Glaser Reaction for Bioconjugation: Robust Access to Structurally Simple, Rigid Linkers

AbstractCopper‐mediated coupling between alkynes to generate a structurally rigid, linear 1,3‐diyne linkage has been known for over a century. However, the mechanistic requirement to simultaneously maintain CuI and an oxidant has limited its practical utility, especially for complex functional molecules in aqueous solution. We find that addition of a specific bpy‐diol ligand protects unprotected peptides from CuII‐mediated oxidative damage through the formation of an insoluble CuII gel which solves the critical challenge of applying Glaser coupling to substrates that are degraded by CuII. The generality of this method is illustrated through the conjugation of a series of polar and nonpolar labels onto a fully unprotected GLP‐1R agonist through a linear 7 Å diynyl linker.

Adapting the Glaser Reaction for Bioconjugation: Robust Access to Structurally Simple, Rigid Linkers.

Copper-mediated coupling between alkynes to generate a structurally rigid, linear 1,3-diyne linkage has been known for over a century. However, the mechanistic requirement to simultaneously maintain CuI and an oxidant has limited its practical utility, especially for complex functional molecules in aqueous solution. We find that addition of a specific bpy-diol ligand protects unprotected peptides from CuII -mediated oxidative damage through the formation of an insoluble CuII gel which solves the critical challenge of applying Glaser coupling to substrates that are degraded by CuII . The generality of this method is illustrated through the conjugation of a series of polar and nonpolar labels onto a fully unprotected GLP-1R agonist through a linear 7 Å diynyl linker.

An Addressable 2D Heterogeneous Nanoreactor to Study the Enzyme-Catalyzed Reaction at the Interface.

Membrane plays significant role in cellular enzymatic reactions. To better understand its function on membrane integral or bound enzymes, DNA origami and frame-guided assembly strategy are combined to construct a given-size, addressable enzyme-containing nanomembrane as a heterogeneous reactor to explore the enzymatic catalyst reaction on the membrane. The enzymes in the membrane are located precisely. This new kind of membrane can enrich hydrophobic substrate molecules in aqueous solution to the embedded enzymes. Otherwise, this nanomembrane shows the capability of substrate selectivity, which plays important role in the highly efficient and specific properties of enzymes in vivo.

Selenium-Functionalized Graphene Oxide That Can Modulate the Balance of Reactive Oxygen Species.

Graphene oxide (GO) is an important two-dimensional material since it is water-soluble and can be functionalized to adapt to different applications. However, the current covalent functionalization methods usually require hash conditions, long duration, and sometimes even multiple steps, while noncovalent functionalization is inevitably unstable, especially under a physiological environment where competing species exist. Diselenide bond is a dynamic covalent bond and can respond to both redox conditions and visible light irradiation in a sensitive manner. Thus, in this work by combining the stimuli response of diselenide bond and the oxidative/radical attackable nature of GO, we achieved the in situ covalent functionalization of GO simply by stirring GO with diselenide-containing molecules in aqueous solution. The covalent functionalization was proved by Fourier transform infrared, time-of-flight secondary ion mass spectrometry, atomic force microscopy, thermogravimetric analysis, and so forth, and the functionalization mechanism was deduced to involve both redox reaction and radical addition reaction according to the X-ray photoelectron spectrscopy, atomic emission spectroscopy, and Raman spectroscopy. Moreover, we modified GO with a biocompatible diselenide-containing polymer (mPEGSe)2 and found selenium-functionalized GO could modulate the balance of reactive oxygen species (ROS). GOSe could decrease ROS level by accelerating the reduction of peroxides when the ROS concentration is high while boosting the ROS level by in situ generating ROS when its concentration is relatively low.