Neutral Molecules Research Articles

Voltage‐Mediated Water Dynamics Enables On‐Demand Transport of Sugar Molecules in Two‐Dimensional Channels

AbstractThe constructing of artificial channels with gating functions is an important undertaking for gaining insight into biological process and achieving efficient bionic functions. Typically, controllable transport within such channels relies on either electrostatic or specific interactions between the transporting species and the channel. However, for molecules with weak interactions with the channel, achieving precise gating of the transport remains a significant challenge. In this regard, this study proposes a voltage gating membrane of two‐dimensional channels that selectively transport of neutral molecules glucose with a dimension of 0.60 nm. The permeation of glucose is switched on/off by electrochemically manipulating the water dynamics in the nanochannel. Voltage driven‐intercalation of ion into the two‐dimensional channel causes water to stratify and move closer to the channel walls, thereby resulting in the channel center being emptier for glucose diffusion. Due to the sub‐nanometer size dimension of the channel, selective permeation of glucose over sucrose is also achieved in this approach.

In-situ rapid construction of aliphatic amine combined polyamide seawater reverse osmosis membrane for efficient boron removal

Polyamide (PA) reverse osmosis membranes are commonly employed in seawater desalination owing to their effective salt rejection and water permeability; however, the elimination of small and neutral boron molecules from seawater remains a significant hurdle in energy-efficient and cost-effective desalination processes. In this work, a seawater reverse osmosis (SWRO) membrane with powerful boron removal competence was designed by adopting an in-situ rapid integration protocol, which utilized aliphatic amines as hydrophobic barriers by bonding the residual chloride groups upon the membrane surface and as molecular plugs by embedding in the PA networks. Consequently, it resulted in a notable improvement in the rejection of neutral boron molecules due to enhanced steric hindrance caused by immobilized amine plugs and synergistically tunned hydrophobic interactions. The permeability coefficient of boron decreased from 4.8 to 0.9 L m−2 h−1, and the boron rejection increased from 80.7 to 90.5% under the modification conditions with the optimal type and concentration of amines, while displaying a NaCl rejection of 99.8% and an acceptable water permeability of 0.55 L m−2 h−1 bar−1. Meanwhile, the alteration of membrane chemical compositions and structure properties was kept to a minimum. This study offers intuitive insights into the critical roles played by the aliphatic amines in the selective layer of the membrane for the removal of neutral boron molecules and salts, thereby enabling the fabrication of highly selective SWRO membranes, which may have significant implications for more efficient membrane-based seawater desalination and boron removal.

Charge transfer transitions of the O2+-Ar and O2+-N2 complexes.

Electronic transitions are observed for the O2+-Ar and O2+-N2 complexes over the 225-350nm range. The transitions are not associated with recognized electronic band systems of the respective atomic and diatomic constituents (Ar+, Ar, O2+, O2, N2+, and N2) but rather are due to charge transfer transitions. Onsets of the O2+-Ar and O2+-N2 band systems occur at 3.68 and 3.62eV, respectively, corresponding to the difference in the ionization potentials of Ar and O2 (3.69eV), and N2 and of O2 (3.51eV), suggesting the band systems arise from intramolecular charge transfer transitions to states correlating with O2(X3Σg-) + Ar+ (2Pu) and O2(X3Σg-) + N2+(X2Σg+) limits, respectively. The dominant vibronic progressions have ωe values of 1565 cm-1 for O2+-Ar and 1532 cm-1 for O2+-N2, reasonably close to the value for the neutral O2 molecule in its X3Σg- state (1580 cm-1). Higher energy band systems for O2+-Ar and O2+-N2 are assigned to transitions to states correlating with the O2 (a1Δg) + Ar+ (2Pu) and O2 (a1Δg) + N2+(X2Σg+) limits, respectively.

CH3 CN@open-C60 : An Effective Inner-Space Modification and Isotope Effect Inside a Nano-Sized Flask.

Despite several small molecules being encapsulated inside cage-opened fullerene derivatives, such species have not considerably affected the structures and properties of the outer carbon cages. Herein, we achieved an effective inner-space modification for an open-cage C60 derivative by insertion of a neutral CH3 CN molecule into the cavity. The CH3 CN@open-C60 thus obtained showed an enhanced polarity, thus affording an easy separation from a mixture containing the empty cage by column chromatography on silica gel, without the preparative HPLC that was needed for previous cases. The less negative reduction potentials with respect to those of empty cage reflect the decreased energy level of the LUMO, which is supported by the DFT calculations. NMR spectroscopy, single-crystal X-ray analysis, and theoretical calculations revealed that both the presence of the encapsulated CH3 CN and cage deformation caused by the CH3 CN play an essential role in the change of the electronic properties. Furthermore, the favored binding affinity of deuterated acetonitrile CD3 CN with internal C60 surface is discussed.

Proton-Tunneling Dynamics along Low-Barrier Hydrogen Bonds: A Full-Dimensional Instanton Study of 6-Hydroxy-2-formylfulvene.

Understanding the dynamics of proton transfer along low-barrier hydrogen bonds remains an outstanding challenge of great fundamental and practical interest, reflecting the central role of quantum effects in reactions of chemical and biological importance. Here, we combine ab initio calculations with the semiclassical ring-polymer instanton method to investigate tunneling processes on the ground electronic state of 6-hydroxy-2-formylfulvene (HFF), a prototypical neutral molecule supporting low-barrier hydrogen-bonding. The results emerging from a full-dimensional ab initio instanton analysis reveal that the tunneling path does not pass through the instantaneous transition-state geometry. Instead, the tunneling process involves a multidimensional reaction coordinate with concerted reorganization of the heavy-atom skeletal framework to substantially reduce the donor-acceptor distance and drive the ensuing intramolecular proton-transfer event. The predicted tunneling-induced splittings for HFF isotopologues are in good agreement with experimental findings, leading to percentage deviations of only 20-40%. Our full-dimensional results allow us to characterize vibrational contributions along the tunneling path, highlighting the intrinsically multidimensional nature of the attendant hydron-migration dynamics.

Low‐cost Photoactive Hybrid Materials: From Green Synthesis to Multi‐technique Analytical Characterization

AbstractLow‐cost photoactive hybrid materials for light management, based on neutral organic molecules intercalated into saponite, were prepared by facile green methods and characterized. TPBI (2‐(2’‐tosylaminophenyl)benzimidazole) was chosen as an organic host dye, envisioning its application as a downconverter in silicon or dye‐sensitized photovoltaic modules. Mixed with a cationic surfactant, the neutral molecule was intercalated with a sort of “trojan horse” approach by an easy, almost solvent‐free method, thus limiting its aggregation. The obtained material was characterized by combining spectroscopic, diffractometric, and microscopic techniques. Moreover, the intercalation of the dye, the species present in the interlayer, their stability and mutual interactions were assessed by TGA‐GC‐MS. We obtained a material containing a fluorescent dye in the solid state and stabilized by intercalation and dispersion into saponite. At last, this material was used to prepare a photoactive polymer by melt blending, obtaining materials with the desired optical properties, with Stokes shifts larger than 100 nm and an emission yield above 50%.

Synthesis of Stable Neutral Homoaromatic Hydrocarbons

AbstractWe report the synthesis of a variety of stable neutral homoaromatic molecules. The homoaromatic character is supported by bond length analysis (from crystal structure analysis data) and spectroscopic characteristics in NMR experiments. The influence of substitution on these homoannulenes is investigated and their reactivity with electrophiles is shown. First approaches to further functionalization via cross-coupling are demonstrated. The present work lays out a general approach to stable neutral homoaromatic hydrocarbon molecules.

Using a modified version of the Tavis–Cummings–Hubbard model to simulate the formation of neutral hydrogen molecule

Using a modified version of the Tavis–Cummings–Hubbard model to simulate the formation of neutral hydrogen molecule

Soft X-Ray-induced Dimerization of Methane

Carbon 1s excitation of methane, CH4, has been studied in the gas phase using the ion trap integrated with the photon–ion instrument at PETRA III/DESY and soft X-rays from the beamline P04. The created photoions are stored within the ion trap so that in further steps the photoions can undergo reactions with neutral methane molecules. The ionic photoproducts as well as reaction products created thereby are mass-over-charge analyzed by an ion time-of-flight spectrometer. Besides the photoions, product ions with up to three carbon atoms are found. In contrast to experiments using vacuum ultraviolet radiation, especially highly reactive product ions with a small number of hydrogen atoms such as and are found, which are important precursors for larger hydrocarbons such as C6H6. Possible production routes of the product ions are analyzed on the basis of a model that considers the probabilities for photofragmentation and the first subsequent chemical reaction step. The model indicates that the high degree of fragmentation by photons with energies around 280 eV is favoring these products. The results of the measurements show that the products like and can be generated by a single collision of the ionization product with neutral methane. The results suggest that soft X-rays might be important for chemical reactions in planetary atmospheres, which has usually not been taken into account. However, due to the high degree of fragmentation and large cross sections involved, they can have a large influence even when the corresponding photon flux is rather small.

Investigation of vibrational changes due to adsorption of glycine on gold

The affinity of glycine to gold nanoparticles in aqueous environments is of importance in a wide range of applications including protein engineering and wet chemical synthesis. In an aqueous environment, glycine exists predominantly as a zwitterion, however, the adsorption of zwitterionic glycine on gold and its impact on the vibrational spectra has not been well studied. This work uses density functional theory to investigate the adsorption of neutral and zwitterionic glycine molecules on two-, four-, six- and 20-atom gold clusters. The neutral glycine molecule preferentially binds to gold via the amine group rather than via the carboxyl group, with interaction energies ranging from 21 down to ≈11 kcalmol−1 for two to 20 atom gold clusters, respectively. For the zwitterion in an implicit solvent medium, binding can only occur via the carboxyl group. The interaction energy ranges from 23 to 13 kcalmol−1 for two to 20-atom gold clusters, respectively. Bader charges analysis and charge difference density maps show that electronic charge is transferred to the gold cluster. Vibrational frequencies and IR intensities were calculated for neutral and zwitterionic glycine and for all binding configurations on the gold clusters. The IR spectra of both neutral and zwitterion glycine molecules show the sharpest peak for C–O stretching modes. This C–O stretching mode redshifts by around 100 cm−1 neutral glycine binds via carboxyl group. In the case of the zwitterion, the sharpest peak remains at the same position after adsorption. The size of the gold cluster has a negligible impact on the vibrational IR spectra for both neutral and zwitterion glycine molecules.

Synthesis, Characterization, and Trapping of a Cyclic Diborylcarbene, an Electrophilic Carbene.

A carbene bearing two geminal boryl substituents, called diborylcarbene (DBC), has been predicted to be highly Lewis acidic in sharp contrast to the well-studied persistent carbenes stabilized by π-donating substituents. Studies on DBC have been limited to either the base-trapping or theoretical calculations. Herein, we developed chemical equivalents for DBC, namely, K/X-diborylcarbenoids 2X (X = F or Cl). Treatment of 2F with Al(C6F5)3 yielded [AlF(C6F5)3]--stabilized DBC 1-FAl, which showed a significant low-field shift of the carbenoid carbon from 169 ppm (doublet, coupling with 19F) to 242 ppm (singlet). The loss of halogen was also detected through electrospray ionization time-of-flight mass spectrometry analysis of 2X only in the presence of Al(C6F5)3. Generated DBC 1 from 1-FAl or 2Cl was successfully trapped with excess amounts of trialkylphosphines (PR3, R = Me or Et), which afforded the corresponding DBC-PR3 adducts. In addition, the Lewis acidity of DBC 1 was evaluated both experimentally and theoretically to reveal that 1 is one of the most Lewis acidic species among neutral molecules.

Agarose‐based hydrogels with tunable, charge‐selective permeability properties

AbstractPhysiologically, a hallmark of biological hydrogels is their ability to selectively trap diffusing molecules and particles. And indeed, there is now increasing interest in using selective hydrogel barriers for applications in biomedicine and medical engineering. However, when employing synthetic polymers to create hydrogels with selective permeabilities, controlling the type and strength of the ensuing filtration process is difficult. Here, we generate hybrid gels with adjustable selectivity profiles by mixing a series of (bio‐)macromolecules with agarose. Depending on the type and concentration of the incorporated macromolecules, those hybrid gels achieve a selective retardation of the diffusive translocation of either positively or negatively charged dextrans at both, acidic and neutral pH. Furthermore, we demonstrate three strategies that provide hydrogels with sequestered patches of both, cationic and anionic binding sites, thus creating symmetric charge (i.e., electrostatic bandpass) filters which still allow neutral molecules to pass. Moreover, such agarose matrices offer a high level of versatility as their permeability profiles can be tailored at will by integrating macromolecules with desired physico‐chemical properties. Thus, those agarose‐based hybrid gels may serve as a powerful platform to engineer adjustable and versatile materials for a broad range of future applications in the field of biomedical engineering.

Synthesis, Crystal Structure, and Luminescent Sensing Properties of a Supramolecular 3D Zinc(II) Metal–Organic Framework with Terephthalate and Bis(imidazol-1-yl)methane Linkers

Supramolecular 3D Zn(II) coordination polymer {[Zn(bim)(bdc)]⋅0.8DMF⋅0.4EtOH⋅0.1H2O }n (Zn-MOF), constructed from Zn2+ ions, bis(imidazol-1-yl)methane (bim) and terephthalate (bdc2−) anions, was synthesized and structurally characterized. Zn-MOF crystallizes in the tetragonal crystal system, space group P42/n. Each Zn(II) ion coordinates two neutral bim molecules in a bridging bidentate coordination mode via nitrogen atoms at position 3 of the imidazole rings and two bdc2− anions, with monodentate coordination of the carboxylate group for one of them and bidentate coordination for another. Zn(II) cations are in a distorted square pyramidal ZnN2O3 coordination environment. Metal cations are alternately linked by the bim and bdc2− ligands, forming a two-dimensional layered structure along the crystallographic plane ab. As a result of layer interpenetration, a supramolecular 3D network is formed. Zn-MOF demonstrated blue (aquamarine) emission with a maximum at 430 nm upon excitation at 325 nm. The luminescence lifetime of 6 ns is characteristic for ligand-centered fluorescence. The luminescent sensing properties of Zn-MOF in ethanol suspension toward inorganic cations and anions were evaluated and an emission quenching response was observed for Fe3+ and chromate/dichromate ions. Photoinduced electron transfer from Zn-MOF to Fe3+ was elucidated as a possible quenching mechanism on the basis of DFT calculations.

Impedance data as a possible basis for finding stability constants of cucurbituril complexes with inorganic cations

An analysis of the array of impedance data for the interface the Hg-electrode/salt solutions of macrocyclic cavitands of the cucurbituril family containing their supramolecular cationic complexes was performed. A significant change in the properties of the adsorption layer was established with a change in the charge of the electrode surface and the concentrations of the components of the complex formation reaction. The existence of two types of adsorption layer was found, one of which (with positive charges on the electrode surface) is formed with the participation of neutral cavitand molecules. The high sensitivity of the impedance data to the presence of these molecules in solution made it possible to establish the corresponding quantitative dependences for systems with known values of the stability constants of cationic complexes. It is shown that these data can be used to find previously unknown stability constants of cationic complexes of a given cavitand formed in other similar salt systems. The applicability of the proposed method was demonstrated using impedance data for systems with known stability constants of cationic complexes (cucurbit[6]uril + Me2 SO4, Me+ = K+, Na+).

FEATURES OF THE DECAY OF EXCITED STATES OF IONIC DYES IN THE NEAR FIELD OF METAL NANOPARTICLES

The influence factor of silver nanoparticles on the intramolecular processes of deactivation of the electronically excited state of polymethine dyes (PD) of different ionicity has been studied. It has been demonstrated that the optical density forcationic 1 and anionic 2 dyes does not change under the action of the plasmon field of Ag nanoparticles. Whereas an increase in absorbance by almost 18% was observed for neutral dye 3. A decrease in the enhancement in fluorescence intensity in the series of anionic–cationic–neutral dyes was registered upon addition of Ag nanoparticles to their solutions. The fluorescence lifetime practically does not change for all PDs under study.Data processing within the framework of the model of the influence of a plasmonic nanoparticle on radiative transitions in a dye molecule showed that the values of plasmon-enhanced rates of radiative decay of molecules decreases from neutral to cationic and, finally, to anionic dye. The rates of energy transfer from PD to plasmonic nanoparticles decrease in the reverse sequence of dyes, i.e. anionic-cationic-neutral PD. This is expressed in a decrease in the proportion of neutral dye molecules that were deactivated by fluorescence.

Platinum(II) complexes containing pyridyl-substituted thiourea dianion and monoanion ligands: Synthesis, structural chemistry, and theoretical investigations

Reactions of cis-[PtCl2(PPh3)2] with the 2-pyridyl-substituted thioureas py(CH2)nNHC(S)NHC6H4R (R = H, OMe or NO2; n = 0, 1 or 2) in methanol with Et3N base, followed by precipitation with water gave good yields of the complexes [Pt{SC(NC6H4R)(N(CH2)npy)}(PPh3)2]. The compounds were characterised 1H NMR, 31P{1H} NMR, FTIR and single crystal X-ray crystallography. The initial NMR investigation indicated the possibility of isomerism in the complexes. 31P{1H} NMR investigations revealed the presence of an initial distal isomer for the dianion complexes, which underwent solution phase isomerization into the proximal isomeric forms of the complexes and/or a mixture of the proximal and distal isomers. The opposite trend was recorded for the monoanionic complex with the formation of an initial proximal isomer and subsequent isomerisation into 1:3 mixture of the distal and proximal isomeric forms of the complex. The degree of isomerization was observed to be related to the difference in energy between the two isomeric forms of the complex and the nature and size of the R substituents in the complex. The molecular geometries of a number of the compounds showed a distorted square-planar geometry defined by a NP2S donor set. The thiourea ligand acts as (N,S)-chelating dianionic ligand so that each donor atom is opposite a phosphane-P atom; a trans-influence is evident on the Pt-P bonds. In each complex, the pyridyl-substituted nitrogen is coordinated to platinum. The cationic complex [Pt{SC(NPh)(NHCH2py)}(PPh3)2]+ was also isolated as its BF4- salt by addition of excess NaBF4 to the reaction mixture. In this complex, the thiourea monoanion coordinates in a distal manner, with the NHCH2py group remote from the platinum centre. Charge-assisted ammonium-NH…N(pyridyl) bonding leads to dimeric aggregates. These, along with the neutral molecules [Pt{SC(Np-C6H4R2)(N(CH2)npy)}(PPh3)2] are assembled into the three-dimensional crystal via weak non-covalent interactions. Characterisation by 31P{1H} NMR spectroscopy showed the presence of several isomeric species in solution.

Dynamic polyiodide anions formation in cationic covalent organic framework for efficient iodine capture

Rapid and efficient capture of iodine is very important for the treatment of radioactive nuclear waste, but the traditional iodine adsorbents have the disadvantages, including the slow adsorption rate and the low adsorption capacity. To address these problems, herein, a new cationic vinyl-based covalent organic framework (COF) with abundant dissociative iodide anions was synthesized by Knoevenagel condensation and the post-ionization modification (PIM) reaction. The resulting ionic COF (iCOF-TMPT) has high specific surface area, excellent chemical stability, as well as the high-density pyridine cations and abundant dissociative iodide anions, which is beneficial for the highly efficient iodine adsorption. The iCOF-TMPT not only has the outstanding iodine adsorption capacity for iodine vapor and solution (6.61 g g−1 for iodine vapor and 1.55 g g−1 for iodine solution), but also possesses the remarkable iodine adsorption rate of 2.81 g h−1, which surpasses any other reported COF absorbents. The adsorption mechanism indicated that the dissociative iodide ions in iCOF-TMPT can induce neutral iodine molecules to generate polyiodide anions, and the pyridine cations in iCOF-TMPT can form strong Coulomb interaction with the formed polyiodide anions. This work not only provides a novel cationic vinyl-based two-dimensional COF with ultra-high chemical stability by Knoevenagel condensation and PIM reaction, the high-density pyridine cations and extra-framework iodide ions can achieve efficient I2 capture by inducing the formation of polyiodide.

Performance assessment of charge plasma based hetero‐structure VTFET biosensor for linearity enhancement

AbstractThis paper examines a charge plasma‐based hetero‐structure full gate vertical tunnel field effect transistor (CP‐FG‐VTFET) as a dielectrically modulated biosensor. It is also compared with a charge plasma‐based short gate vertical TFET (CP‐SG‐VTFET) biosensor and a charge plasma‐based asymmetrical vertical TFET (CP‐AS‐VTFET) biosensor with identical dimensions. We examine the basic physics of these biosensors and compare their ability to recognize charged and neutral molecules. It has been noted that these designs, which use GaSb as the n‐type TFET source material, are suitable for supply voltages lower than 1.2 V. The short gate device has a lower miller capacitance and a higher drive current because it has a narrow bandgap source material. Additionally, the left and right gate alignment of asymmetrical gate architectures has a considerable impact on the sensitivity of the device. Therefore, a simulation is conducted to assess the effects of gate misalignment on biosensor surface potential and drain current sensitivity. In addition, various figures of merits (FOMs) are computed for the device utilizing the dielectric constant range of 1–12, including linearity, sensitivity, and evaluation of noise characteristics. The widely available Silvaco TCAD was employed to simulate the proposed VTFET biosensors. A comprehensive evaluation of the FOM values showed that the CP‐FG‐VTFET is a promising device in terms of linearity and sensitivity.

Modelling the Performance of Electrically Conductive Nanofiltration Membranes

Electrically conductive membranes are a class of stimuli-responsive materials, which allow the adjustment of selectivity for and the rejection of charged species by varying the surface potential. The electrical assistance provides a powerful tool for overcoming the selectivity–permeability trade-off due to its interaction with charged solutes, allowing the passage of neutral solvent molecules. In this work, a mathematical model for the nanofiltration of binary aqueous electrolytes by an electrically conductive membrane is proposed. The model takes into account the steric as well as Donnan exclusion of charged species due to the simultaneous presence of chemical and electronic surface charges. It is shown that the rejection reaches its minimum at the potential of zero charge (PZC), where the electronic and chemical charges compensate for each other. The rejection increases when the surface potential varies in positive and negative directions with respect to the PZC. The proposed model is successfully applied to a description of experimental data on the rejection of salts and anionic dyes by PANi–PSS/CNT and MXene/CNT nanofiltration membranes. The results provide new insights into the selectivity mechanisms of conductive membranes and can be employed to describe electrically enhanced nanofiltration processes.

Antimicrobial activity of cold atmospheric-pressure argon plasma combined with chicory (Cichorium intybus L.) extract against P. aeruginosa and E. coli biofilms

The present study reports a significant combined antibacterial activity of Cichorium intybus L. (known as Chicory) natural extract with cold atmospheric-pressure argon plasma treatment against multi-drug resistant (MDR) Gram-negative bacteria. To detect reactive species that are generated in the argon plasma, optical emission spectra were recorded. The molecular bands were allocated to the hydroxyl radicals (OH) and neutral nitrogen molecules (N2). Moreover, the atomic lines form the emitted spectra were determined to argon atoms (Ar) and the oxygen atoms (O), respectively. The results revealed that Chicory extract treatment at a concentration of 0.043 g/ml reduced the metabolic activity of P. aeruginosa cells by 42%, while, a reduced metabolic activity of 50.6% was found for E. coli biofilms. Moreover, the combination of Chicory extract with 3 min Ar-plasma introduced a synergistic effect, so that it exhibited a significantly reduced metabolic activity of P. aeruginosa to 84.1%, and E. coli ones to 86.7%, respectively. The relationship between cell viability and membrane integrity of P. aeruginosa and E. coli biofilms treated with Chicory extract and argon plasma jet were also analyzed by CLSM. It was found that after the combined treatment, a noticeable membrane disruption was formed. Besides, it was concluded that E. coli biofilms showed a higher sensitivity to Ar-plasma than P. aeruginosa biofilm at longer plasma exposure times. This study suggests that the anti-biofilm therapy based on a combined effect of Chicory extract and cold argon plasma treatment can serve as a considerable green method for treatment of antimicrobial MDR bacteria.