Measurement of Residual Dipolar Couplings of Organic Molecules in Multiple Solvent Systems Using a Liquid‐Crystalline‐Based Medium

Residual dipolar coupling (RDC), a robust anisotropic NMR parameter for structural elucidation of organic molecules, is only accessible in an anisotropic environment. Herein, we introduce a novel alignment medium based on the molecular self‐assembly of oligopeptide amphiphile (OPA). This medium is compatible with different intermediate and polar solvent systems, such as CD₃OD, [D₆]DMSO, and D₂O. The preparation of the OPA‐based medium is simple and rapid, while only very weak background signals were observed from OPAs. Furthermore, we show that the purity of OPA has only a minor influence on the quality of the RDC data. These advantages allow RDC measurements of organic molecules with different polarities and solubilities with high efficiency and accuracy.     

A Self‐Assembled Oligopeptide as a Versatile NMR Alignment Medium for the Measurement of Residual Dipolar Couplings in Methanol

Residual dipolar coupling (RDC) is a powerful structural parameter for the determination of the constitution, conformation, and configuration of organic molecules. Herein, we report the first liquid crystal‐based orienting medium that is compatible with MeOH, thus enabling RDC acquisitions of a wide range of intermediate to polar organic molecules. The liquid crystals were produced from self‐assembled oligopeptide nanotubes (AAKLVFF), which are stable at very low concentrations. The presented alignment medium is highly homogeneous, and the size of RDCs can be scaled with the concentration of the peptide. To assess the accuracy of the RDC measurement by employing this new medium, seven bioactive natural products from different classes were chosen and analyzed. The straightforward preparation of the anisotropic alignment sample will offer a versatile and robust protocol for the routine RDC measurement of natural products.     

An Alignment Medium for Measuring Residual Dipolar Couplings in Pure DMSO: Liquid Crystals from Graphene Oxide Grafted with Polymer Brushes

Residual dipolar couplings (RDCs) have attracted attention in light of their great impact on the structural elucidation of organic molecules. However, the effectiveness of RDC measurements is limited by the shortage of alignment media compatible with widely used organic solvents, such as DMSO. Herein, we present the first liquid crystal (LC) based alignment medium that is compatible with pure DMSO, thus enabling RDC measurements of polar and intermediate polarity molecules. The liquid crystals were obtained by grafting polymer brushes onto graphene oxide (GO) using free radical polymerization. The resulting new medium offers several advantages, such as absence of background signals, narrow line shapes, and tunable alignment. Importantly, this medium is compatible with π‐conjugated molecules. Moreover, sonication‐induced fragmentation can reduce the size of GO sheets. The resulting anisotropic medium has moderate alignment strength, which is a prerequisite for an accurate RDC measurement.     

RDC‐enhanced structure calculation of a β‐heptapeptide in methanol

Residual dipolar couplings (RDCs) are a rich source of structural information that goes beyond the range covered by the nuclear Overhauser effect or scalar coupling constants. They can only be measured in partially oriented samples. RDC studies of peptides in organic solvents have so far been focused on samples in chloroform or DMSO. Here, we show that stretched poly(vinyl acetate) can be used for the partial alignment of a linear β‐peptide with proteinogenic side chains in methanol. ¹D_CH, ¹D_NH, and ²D_HH RDCs were collected with this sample and included as restraints in a simulated annealing calculation. Incorporation of RDCs in the structure calculation process improves the long‐range definition in the backbone of the resulting 3₁₄‐helix and uncovers side‐chain mobility. Experimental side‐chain RDCs of the central leucine and valine residues are in good agreement with predicted values from a local three‐state model. Copyright © 2016 John Wiley & Sons, Ltd.     

Abnormal Thermal Expansion of Clathrate Hydrates Induced by Asymmetric Guest Molecules

We investigated for the first time the abnormal thermal expansion induced by an asymmetric guest structure using high‐resolution neutron powder diffraction. Three dihydrogen molecules (H₂, D₂, and HD) were tested to explore the guest dynamics and thermal behavior of hydrogen‐doped clathrate hydrates. We confirmed the restricted spatial distribution and doughnut‐like motion of the HD guest in the center of anisotropic sII‐S (sII‐S=small cages of structure II hydrates). However, we failed to observe a mass‐dependent relationship when comparing D₂ with HD. The use of asymmetric guest molecules can significantly contribute to tuning the cage dimension and thus can improve the stable inclusion of small gaseous molecules in confined cages.     

Anisotropic viscoelasticity and molecular diffusion in nematic wormlike micelles

Using rheo-NMR, pulsed-field-gradient NMR diffusometry and solution rheology, we observe temperature- and composition-dependent orientational order as well as director dynamics and molecular transport in a nematic wormlike micelle (WLM) system composed of cetyltrimethylammonium bromide in D₂O. We measure, for the first time over a comprehensive nematic range in WLMs, four of the five independent anisotropic viscosities by fitting nonlinear rheo-NMR director realignment data and comparing with traditional solution rheology measurements. Additionally, we extract self-diffusion coefficients in three orthogonal directions for the aligned WLM unimers as well as for the D₂O solvent molecules. Continued study and enhanced understanding of complex fluid dynamics in these anisotropic shear-modulated fluid systems can lead to advances in lubricants, coatings, oil extraction, drug delivery and tissue engineering.     

Simultaneous Sensing of H2O,D2O and HOD through Peroxo Vibrations

Detection of HOD simultaneously in the presence of a mixture of H₂O and D₂O is still an experimental challenge. Till date, there is no literature report of simultaneous detection of H₂O, D₂O and HOD based on vibrational spectra. Herein we report simultaneous quantitative detection of H₂O, D₂O and HOD in the same reaction mixture with the help of bridged polynuclear peroxo complex in absence and presence of Au nanoparticles on the basis of a peroxide vibrational mode in resonance Raman and surface enhanced resonance Raman spectrum. We synthesize bridged polynuclear peroxo complex in different solvent mixture of H₂O and D₂O. Due to the formation of different nature of hydrogen bonding between peroxide and solvent molecules (H₂O, D₂O and HOD), vibrational frequency of peroxo bond is significantly affected. Mixtures of different H₂O and D₂O concentrations produce different HOD concentrations and that lead to different intensities of peaks positioned at 897, 823 and 867 cm⁻¹ indicating H₂O, D₂O and HOD, respectively. The lowest detection limits (LODs) were 0.028 mole fraction of D₂O in H₂O and 0.046 mole faction of H₂O in D₂O. In addition, for the first time the results revealed that the cis-peroxide forms two hydrogen bonds with solvent molecules.     

Electroreductive Cross-Electrophile Coupling (eXEC) Reactions

Electrochemistry utilizes electrons as a potent, controllable, and traceless alternative to chemical oxidants or reductants, and typically offers a more sustainable option for achieving selective organic synthesis. Recently, the merger of electrochemistry with readily available electrophiles has been recognized as a viable and increasingly popular methodology for efficiently constructing challenging C−C and C-heteroatom bonds in a sustainable manner for complex organic molecules. In this mini-review, we have systematically summarized the most recent advances in electroreductive cross-electrophile coupling (eXEC) reactions during the last decade. Our focus has been on readily available electrophiles, including aryl and alkyl organic (pseudo)halides, as well as small molecules such as CO₂, SO₂, and D₂O.     

Synthesis and photophysical properties of semiconductor molecules of D<Subscript>1</Subscript>–A–D<Subscript>2</Subscript>–A–D<Subscript>1</Subscript> structure on the basis of quinoxaline and dithienosilole derivatives for organic solar cells

new DTS(FCT₂)₂ organic semiconductor of the D₁–A–D₂–A–D₁ structure containing dithienosilole and quinoxaline chromophores as electron-donating and electron-accepting moieties, respectively, has been synthesized. The study of optical and electrochemical properties shows that the material absorbs light in a wide range of the solar spectrum through 700 nm and has an appropriate arrangement of energy levels for the efficient dissociation of excitons. The obtained results demonstrate that this approach to the design of semiconductor molecules of the D₁–A–D₂–A–D₁ structure is promising for high-performance organic solar cells.     

Effect of molecular adsorption on water permeability of microporous membranes

The rate of water permeation through a microporous membrane is affected markedly by adsorption of hydrocarbon impurities and/or trace amounts of organic ions such as H(CH₂₁₇CO₂^- and H(CH₂)₁₆NR₃⁺. Neutral and cationic hydrocarbon impurities are physisorbed primarily at the microcapillary outlets on the low-pressure side of an electropositive filter. Adsorption of the former at these critical sites causes flow through the affected capillaries to stop, and total flow to decrease accordingly, whereas adsorption of the latter at these sites causes a marked increase in total flow. Organic anions and molecules with electron donor substituents are chemisorbed on the high-pressure side of an electropositive filter. Those molecules that are held only by monodentate adsorption migrate through the microcapillaries to the low-pressure side of the filter as in ion-exchange chromatography, during which time water permeation is impeded significantly. Multidentate adsorbed molecules, such as gelatin or polyvinyl alcohol, are relatively immobile. Filters modified on one side only by such molecules exhibit marked anisotropic permeability, i.e., flow in one direction is much greater than in the other.     

Theoretical studies of photovoltaic properties of five new silol dithiophene based D2-A-D1-A-D2 donors

Organic solar cell of silol dithiophene based D₂-A-D₁-A-D₂/PC₇₁BM (D: donor part; A: acceptor part; 1 and 2 denote different units) possesses promising power conversion efficiency. Researchers have studied D₂-A-D₁-A-D₂ molecules carefully, including the effects of the different number of terminal thiophenes, the different central moiety (D₁), and the length of the alkyl chain. However, there are few investigations, especially theoretical studies, on the influences of different A (acceptor) units on the properties of D₂-A-D₁-A-D₂ molecule. In the present work, we have designed and modeled five new D₂-A-D₁-A-D₂ (D₂ = bithiophene and D₁ = silol dithiophene) donors by changing A units (A = diketopyrrolopyrrole, naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole, 5-fluoro-2,1,3-benzoselenadiazole, benzobisthiadiazole, and thiazolo[5,4-d]thiazole). We have applied density functional theory (DFT) and time-dependent DFT to predict their ground-state electronic structures and the UV–vis spectra, and the open circuit voltages (Vocs) of organic solar cells of D₂-A-D₁-A-D₂/PC₇₁BM. Based on the calculated results, we find that bithiophene thiazolo[5,4-d]thiazole siloldithiophene (BTTS) (D₂ = bithiophene, A = thiazolo[5,4-d]thiazole, D₁ = silol dithiophene) possesses the highest lowest unoccupied molecular orbital (−2.60 eV) and the lowest highest occupied molecular orbital (−5.33 eV) energies, and the strongest absorption in the visible region. Besides, the solar cell of BTTS/PC₇₁BM has the highest Voc of 1.02 V. These results indicate that it may be a promising donor. In contrast, bithiophene benzobisthiadiazole siloldithiophene (BBBS) (A = benzobisthiadiazole) has low absorption strength in the visible region, which indicates that it may not be a suitable donor material.     

Rotational dynamics of a discotic liquid crystal studied by deuteron spin relaxation

We report on measurements of deuteron quadrupolar splitting and spin-lattice relaxation times T_1Q and T_1Z in the columnar phase of a ring-deuteriated hexaoctyloxyrufigallol at 46 MHz as a function of temperature. To describe small-step rotations of these molecules within each column in the columnar phase, a space-fixed frame is used to diagonalize the molecular diffusion tensor. The principal diffusion constants in this so called 'anisotropic viscosity' model D_alpha and D_beta are for rotations of a molecule around and perpendicular to the columnar axis, respectively. A global target analysis of the spectral densities at seven temperatures in a minimization procedure was carried out. We found that D_alpha > D_beta, which is consistent with the picture that the motion towards or away from the local director tends to disrupt the packing of molecules within the column.     

Investigation of a Simple Pickup Method for Doping Molecules into Water Clusters

A capillary pickup method was investigated for doping molecules into water clusters, which were produced by supersonic expansion, and underwent a sticking collision with a crossed beam from the capillary. This method was applied to H₂O clusters in a beam with pickup of DCl, CH₃OH, NH₃, CO₂ and D₂O molecules, however, we found only molecule of DCl can be picked up by water clusters with the capillary configuration in those tested dopants. Meanwhile, two different distances between the capillary to the nozzle were investigated based on the collected mass spectra, and we found that the smaller distance can obtain the stronger mixed cluster intensity.     

Determination of rotational diffusion constants of liquid benzene from measurements of infrared and raman line widths

Line widths are measured for the Raman v₁, v₁₅ and infrared v₁₂ of C₆ll₆ in C₆D₆ solution. Rotational diffusion constants are determined from the observed line widths, and compared with literature values. A rather anisotropic rotation of benzene molecules is suggested.     

Zinc Recovery from Wulagen Sulfide Flotation Plant Tail by Applying Ether Amine Organic Collectors

Separating oxidized zinc minerals from flotation tailings is always a challenge. In this study, a flotation tailing from Wulagen zinc mine in China (Zn grade < 1%) was processed using froth flotation with combinations of amines (OPA 10, OPA 1214, OPA 13, DDA) and Na₂S to study the effects of these amines on the zinc recovery as well as their interactions with other reagents, aiming to screen out a proper reagent scheme to improve zinc separation from extremely low-grade zinc flotation tailings. The results show that different amines led to different flotation performance, and the collectors were ranked as OPA 1214, OPA 13, OPA 10 and DDA in a decreasing order based on flotation collectivity and selectivity. An increase in the concentration of each collector increased the zinc recovery but reduced the concentrate zinc grade. Interactions were also observed between different amines and Na₂S and Na₂SiO₃, and OPA 1214 outdid the others in saving the usage of both the Na₂S and Na₂SiO₃. The measured adsorption of collector onto smithsonite was found to correlate well with flotation test results. It was concluded that hydrocarbon chains can be held accountable for the difference in the flotation performance with different amines. The longer the hydrocarbon chain, the stronger the hydrophobic association ability of amine, which is conducive to the selective amine adsorption onto sulfurized smithsonite particles and hence the smithsonite flotation.     

Two-photon spectroscopy of organic molecules recorded by the fluorescence induced by a picosecond light continuum generated in D2O

It is shown that the fluorescence of large organic molecules induced by the two-photon excitation of a picosecond light continuum generated in D₂O is a useful and sensitive new technique for two-photon spectroscopic study or excited electronic states of large organic molecules in solution This technique is tested on the first two singlet transitions of rhodamine 6G and on the first singlet transitions (430–630 nm) of naphthalene.     

Angular dependence of 1H-NMR and 2H-NMR spectra of water absorbed in cellulose film

¹H-NMR and ²H-NMR spectra of water (H₂O and D₂O) absorbed in Visking cellulose tubing have been observed as a function of the angle Θ between the film surface and the magnetic field. ¹H-NMR spectra show broad lines, and the chemical shift and the linewidth depend on Θ. From the angular dependence of the chemical shift, the anisotropic volume diamagnetic susceptibilities of the film are determined, i.e., χ_∥ in the direction longitudinal to the tubing (stretched direction) is 0.43 ppm, and χ_⊥ in the transverse direction is 0.57 ppm. The different values of χ_∥ and χ_⊥ afford an evidence of the anisotropy of the film. ²H-NMR spectra of D₂O absorbed in the film show quadrupole splitting which also depends on Θ. The angular dependences of the linewidth (¹H-NMR) and the quadrupole splitting (²H-NMR) indicate that the H? H axes of the water molecules have a tendency to orient in the direction longitudinal to the film surface.     

Mild,Selective Ru-Catalyzed Deuteration Using D2O as a Deuterium Source

A method for the selective deuteration of polyfunctional organic molecules using catalytic amounts of [RuCl₂(PPh₃)₃] and D₂O as a deuterium source is presented. Through variation of additives like CuI, KOH, and various amounts of zinc powder, orthogonal chemoselectivities in the deuteration process are observed. Mechanistic investigation indicates the presence of different, defined Ru-complexes under the given specific conditions.     

Deuteriodifluoromethylation and gem-Difluoroalkenylation of Aldehydes Using ClCF2H in Continuous Flow

The deuteriodifluoromethyl group (CF₂D) represents a challenging functional group due to difficult deuterium incorporation and unavailability of precursor reagents. Herein, we report the use of chlorodifluoromethane (ClCF₂H) gas in the continuous flow deuteriodifluoromethylation and gem-difluoroalkenylation of aldehydes. Mechanistic studies revealed that the difluorinated oxaphosphetane (OPA) intermediate can proceed via alkaline hydrolysis in the presence of D₂O to provide α-deuteriodifluoromethylated benzyl alcohols or undergo a retro [2+2] cycloaddition under thermal conditions to provide the gem-difluoroalkenylated product.     

Long‐Range Residual Dipolar Couplings: A Tool for Determining the Configuration of Small Molecules

Together with NOE and J coupling, one‐bond residual dipolar coupling (RDC), which reports on the three‐dimensional orientation of an internuclear vector in the molecular frame, plays an important role in the conformation and configuration analysis of small molecules in solution by NMR spectroscopy. When the molecule has few C? H bonds, or too many bonds are in parallel, the available RDCs may not be sufficient to obtain the alignment tensor used for structure elucidation. Long‐range RDCs that connect nuclei over multiple bonds are normally not parallel to the single bonds and therefore complement one‐bond RDCs. Herein we present a method for extracting the long‐range RDC of a chosen proton or group of protons to all remotely connected carbon atoms, including non‐protonated carbon atoms. Alignment tensors fitted directly to the total long‐range couplings (T=J+D) enabled straightforward analysis of both the long‐range and one‐bond RDCs for strychnine.