Groups Of Organic Molecules Research Articles

Behavior of Trapped Molecules in Lantern-Like Carcerand Superphanes.

Superphanes are a group of organic molecules from the cyclophane family. They are characterized by the presence of two parallel benzene rings joined together by six bridges. If these bridges are sufficiently long, the superphane cavity can be large enough to trap small molecules or ions. Using ab initio (time scale of 80 ps) and classical (up to 200 ns) molecular dynamics (MD) methods, we study the behavior of five fundamental molecules (M = H2O, NH3, HF, HCN, MeOH) encapsulated inside the experimentally reported lantern-like superphane and its two derivatives featuring slightly modified side bridges. The main focus is studying the dynamics of hydrogen bonds between the trapped M molecule and the imino nitrogen atoms of the side chains of the host superphane. The length of the N···H hydrogen bond increases in the following order: HF < HCN < H2O < MeOH < NH3. The mobility of the trapped molecule and its preferred position inside the superphane cage depend not only on the type of this molecule but also largely on the in/out conformational arrangement of the imino nitrogens in the side chains of the superphane. Their inward-pointing positions allow the formation of strong N···H hydrogen bonds. For this reason, these nitrogens are the preferred sites of interaction. The mobility of the molecules and their residence times on each side of the superphane have been explained by referring to the symmetry and conformation of the given superphane cage. All force field MD simulations have shown that the encapsulated molecule remained inside the superphane cage for 200 ns without any escape event to the outside. Moreover, our simulations based on some endohedral complexes in the water box also showed no exchange event. Thus, the superphanes we study are true carcerand molecules. We attribute this property to the hydrophobic side chains and their pinwheel arrangement, which makes the side walls of the studied superphanes fairly impenetrable to small molecules.

Palladium and copper co-catalyzed chloro-arylation of gem-difluorostyrenes - use of a nitrite additive to suppress β-F elimination.

The installation of fluorine and fluorinated functional groups in organic molecules perturbs the physicochemical properties of those molecules and enables the development of new therapeutics, agrichemicals, biological probes and materials. However, current synthetic methodologies cannot access some fluorinated functional groups and fluorinated scaffolds. One such group, the gem-difluorobenzyl motif, might be convergently synthesized by reacting a nucleophilic aryl precursor and an electrophilic gem-difluoroalkene. Previous attempts have relied on forming unstable anionic or organometallic intermediates that rapidly decompose through a β-F elimination process to deliver monofluorovinyl products. In contrast, we report a fluorine-retentive palladium and copper co-catalyzed chloro-arylation of gem-difluorostyrenes that takes advantage of a nitrite (NO2 -) additive to avoid the favorable β-F elimination pathway that forms monofluorinated products, instead delivering difluorinated products.

Alkyl groups in organic molecules are NOT inductively electron-releasing.

It is commonly stated that alkyl groups exert an inductive electron-releasing effect when compared to hydrogen. This information has been given in numerous organic chemistry textbooks over the last 75 years. The evidence for this position is weak, and does not withstand scrutiny, and there is some evidence for the contrary position. We provide a significant body of computational data that clearly show that alkyl groups exert an inductive electron-withdrawing (-I) effect when compared to hydrogen. This revised position is not in conflict with experimental data, since alkyl group inductive effects are small and are likely to be masked by hyperconjugation/polarizability effects (particularly in charged species), and also by solvent effects.

Surface Polarity Induced Simultaneous Enhancement of Nanopore Accessibility and Metal Utilization in Metal and Nitrogen Co-Doped Carbon Electrocatalysts for CO2 Reduction

The efficient utilization of active centers for the emerging class of metal (M) and nitrogen (N) co-doped carbon (M–N–C) catalysts remains a research hotspot for electrochemical synthesis such as the reduction reactions of CO2, O2, N2, or functional groups in organic molecules. However, keeping sufficient accessibility to these active centers upon thermal treatment at high temperatures can be challenging due to possible nanopore blocking issues. To tackle this limitation, this work presents a precise surface modulation approach based on a kind of porous carbon support with an ultrapolar surface, over which the unusual enhancement of nanopore accessibility and metal utilization is achieved. The strategy is well applicable to transition metals, precious metals, and rare earth metals. Experimental evidence revealed that the ultrapolar pore walls can be spontaneously wetted by hydrated metal ions. The unprecedented wettability ensured a unique metal-support interaction, which not only warrants the anchoring metal species in a dispersed manner but also induces the development of transport nanopores by dynamical etching of the polar carbon walls during thermal treatment. By this way, this strategy addresses the trade-off issue between metal utilization efficiency and accessibility to the active centers for the M–N–C type catalysts.

Studying the governing factors on the photo(electro)catalytic activity of surface-modified photocatalysts under visible light illumination

The nature of the interaction at the interface of dye molecules and TiO2 surface has paramount importance in their photosensitization properties for photo(electro)catalytic application. To address this issue, two groups of organic molecules i.e., catechol and salicylic derivatives were used for the surface modification of titania. These hybrid materials were then thoroughly analyzed employing XRD, SEM, UV–Vis, FTIR, Raman, and impedance spectroscopies. The photoactivity was studied using the photoelectrochemical analysis and photocatalytic hydroxylation of terephthalic acid. Moreover, applying principal component analysis on Raman spectra indicated a significant change in the bond strength of Ti–O (B1g band) as a consequence of the chemical bond of adsorbed dye. This study links the nature of the interaction of dye and titania and the photoactivity of materials, which is thoroughly discussed in the presented work.

Chalcones: Versatile intermediates in heterocyclic synthesis

AbstractChalcones are a fascinating and well‐studied group of organic molecules. Synthesis of chalcones has been one of the essential areas of organic synthesis over the last few decades because of their immense therapeutic and excellent photophysical properties. Furthermore, these chalcone derivatives can be utilized to make a variety of heterocyclic compounds, especially five‐ and six‐membered heterocycles. Heterocyclic compounds have a long history in chemistry, primarily in pharmaceuticals. However, synthesizing some specific heterocyclic molecules remains challenging and requires multistep processes with few possible intermediates. Chalcones can be considered as one of the most useful, readily available intermediates in heterocyclic synthesis. Herein, the synthesis of various potential heterocyclic compounds using chalcones as an intermediate is elaborated. This review shows the untapped potential of chalcones in organic synthesis. Also, it will assist the chemist in designing new heterocycles by adopting these strategies.

Automatic materials characterization from infrared spectra using convolutional neural networks.

Infrared spectroscopy is a ubiquitous technique used to characterize unknown materials in the form of solids, liquids, or gases by identifying the constituent functional groups of molecules through the analysis of obtained spectra. The conventional method of spectral interpretation demands the expertise of a trained spectroscopist as it is tedious and prone to error, particularly for complex molecules which have poor representation in the literature. Herein, we present a novel method for automatically identifying functional groups in molecules given the corresponding infrared spectra, which requires no recourse to database-searching, rule-based, or peak-matching methods. Our model employs convolutional neural networks that are capable of successfully classifying 37 functional groups which have been trained and tested on 50 936 infrared spectra and 30 611 unique molecules. Our approach demonstrates its practical relevance in the autonomous analytical identification of functional groups in organic molecules from infrared spectra.

Antioxidant activity of methanol extract of cassava leaves (Manihot esculenta Crantz) using CUPRAC method

Background: Antioxidants are a group of organic molecules and enzymes that work synergistically to enhance cellular defenses and combat oxidative stress. Antioxidants can come from plants because they contain many groups of phytochemical compounds and vitamins. One of the plants that has compounds with antioxidant activity is cassava. Objective: To measure the antioxidant activity of methanol extract of cassava leaves using the CUPRAC method. Methods: Cassava leaves were extracted by maceration using methanol as a solvent with the addition of 5% H2SO4. Phytochemical screening of flavonoids with Mg and HCl, while phenol with the addition of FeCl3. The antioxidant activity based on the reaction of the test solution with CUPRAC reagent. Antioxidant activity can be determined by IC50 value by using x value as concentration and y value as absorbance. Results: The results of phytochemical screening showed that the methanol extract of cassava leaves contained flavonoids and phenolic groups. The antioxidant capacity of the methanol extract of cassava leaves obtained an IC50 value of 156.03 ppm, while quercetin has a very strong capacity as an antioxidant with an IC50 of 9.83 ppm. Conclusion: The methanol extract of cassava leaves has a weak antioxidant capacity in reducing metal ions. Keywords: Cassava leaves, Manihot esculenta Crantz, methanol extract, antioxidants, CUPRAC.

Flexible Alkali-Halogen Bonding in Two Dimensional Alkali-Metal Organic Frameworks.

On-surface fabrication of two-dimensional (2D) metal organic frameworks (MOFs) has been continuously attracting attentions for years. However, the synthesis of 2D MOFs with large-amplitude flexibility was rarely carried out since the bonding configurations in the coordination nodes are typically highly directional. Here we demonstrate that single alkali ions, which are fully isotropic in ionic bonding, can act as pivot joints for constructing tunable 2D MOFs by bonding to dihalogen groups in organic molecules. We take 2,3,6,7,10,11-hexabromotriphenylene, a 3-fold polycyclic molecule with three ortho-dibromo groups, and sodium (Na) atoms as a model system and successfully construct Na-based MOFs on Au(111) surface. The deflection angle of the Na coordination nodes is variable in an unprecedentedly large range between ±36° that allows the construction of multiple 2D MOF architectures. Such a flexible alkali-halogen bonding may provide a unique toolbox for designing and constructing more tunable MOFs by choosing various alkali atoms and halogen moieties.

New insights into the accessibility of native cellulose to environmental contaminants toward tritium behavior prediction

Tritium speciation and behavior in the environment directly rely on accessible OH groups of organic molecules and their hydrogen exchangeability properties. As one of the most widespread biomolecule, cellulose role in reducing the exchange capacity of the hydrogen atom has been previously highlighted experimentally in various environmental matrices. In this paper, a robust and reliable T/H gas-solid isotopic exchange procedure has been implemented to assess the OH group accessibility of native celluloses with an increasing degree of crystallinity. A linear relationship was found between hydroxyl reactivity and the crystallinity index (CrI) of native celluloses, as determined by the analysis of their crystalline structure from XRD characterization. The application of the obtained linear experimental model to cellulosic materials was then evaluated and an acceptable minimum value of 12% for the CrI parameter on environmental matrices could thus be established. The authors have therefore proposed an environmental matrices relevant and efficient analytical process in order to determine the accessibility of native cellulose hydroxyl groups to tritium in the environment from a single and quick sample characterization procedure.

The Room-Temperature Planar Type Gas Sensor Based on DPA-Ph-Dbpzdcn/TPA-Dcpp for NH3 Monitoring Application

IntroductionAmmonia (NH3) gas sensor is the indispensable element in safety, air quality monitoring and respiratory analysis fields. The chemoresistor sensors are mainly focused in the investigation of NH3 sensors attributing to the high stability, simple sensing structure, low cost and portable device. However, solving the high working temperature issue and achieving reproducible and stable gas sensing properties by designing novel sensitive material is highly desirable for widespread development of ammonia sensor [1]. Here, the planar room-temperature NH3 sensors are fabricated through spin-coating DPA-Ph-DBPzDCN/TPA-DCPP organic semiconductor materials onto the Al2O3 substrate with Au interdigital electrodes. The two sensors exhibit favorable sensing response as 72.73%/76.4% to 100 ppm NH3 under 98% RH, respectively, also demonstrates the low detection limits, good reproducibility, selectivity and long-term stability. The DFT calculation results further demonstrate that the excellent NH3 sensing characteristics are attributed to the enhanced absorption between NH3 and the N groups of organic molecules, which formed the H2O pre-adsorption under the high RH. This work is expected it can offer some guidance and inspiration for the rational design of sensing materials and further development of room temperature gas sensor. Results and Conclusions The synthesis process of DPA-Ph-DBPzDCN/TPA-DCPP were detailed reported previously [2, 3]. The sensor devices were successful fabricated via spin-coated sensitive materials onto the Al2O3 substrate with Au interdigital electrodes and illustrated in Figure 1. It was illustrated from scanning electron microscopy (SEM) image that the organic sensing films were formed uniformly and tightly. Then, the response transients of sensors in different NH3 concentration under 98% and 25% RH were monitored (Figure 2). The response value improved alone with the increasing of NH3 concentration and performed the highest response value as 72.73%/76.4% to 100 ppm NH3 under the 98% RH, respectively. Furthermore, there had a decreasing trend of the lowest detectable NH3 concentration along with the increasing RH, especially, the TPA-DCPP sensor exhibited the lowest detection limit as 500 ppb under 98% RH.Accordingly, the density functional theory (DFT) calculations were performed to gain further insight into the interaction between gas molecules and the sensitive materials, also the enhanced ammonia sensing properties under the high RH. The three most likely ammonia adsorbing sites (A: trihpenylamine-ortho C on the benzene ring; B: pyrazine-N; C: cyano-N) were selected due to the negative charge was mainly located. The configuration and the charge density difference after NH3 adsorption (Figure 3) demonstrated that the charge transfer occurred through the NH3 given electrons to organic compounds, thereby the conductivity of organic semiconductors increased until to an equilibrium state. Simultaneously, the NH3, H2O, NH3-H2O adsorption energies of the corresponding adsorbing sites were given in Table 1. It was shown that the NH3 adsorbing to organic compounds after H2O pre-adsorption were more capable compared with the NH3 adsorption only. Meanwhile, the NH3 adsorption energy before and after H2O pre-adsorption of the pyrazine-N on TPA-DCPP (-0.1809 eV, -0.4011 eV) was obviously higher than the DPA-Ph-DBPZdCN molecule (-0.14362 eV, -0.15679 eV), resulting in the response value of TPA-DCPP sensor was apparently improved compared to the DPA-Ph-DBPZdCN sensor under the low/high RH, that were attributed to the increasing of the negative charge on pyrazine-N owing to the directly link between and the pyrazine the cyano group, the change of molecular structure leading to a significantly stronger coulombic effect between pyrazine-N with NH3. Taken together, the excellent NH3 sensing characteristics were attributed to the enhanced absorption between NH3 and H2O pre-adsorption organic molecules under the high RH [4]. The DPA-Ph-DBPZdCN/TPA-DCPP could be the promising NH3 organic sensitive materials for the room temperature sensor, meanwhile, the discussion of sensing mechanism bring the further understanding of the organic gas sensors, providing the new concept of organic materials which has potential application value in gas monitoring of production and daily life at room temperature.

Spontaneous Grafting of OH-Terminated Molecules on Si−H Surfaces via Si–O–C Covalent Bonding

The surface functionalization of oxide-free hydrogen-terminated silicon (Si−H) enables predictably tuning its electronic properties, by incorporating tailored functionality for applications such as photovoltaics, biosensing and molecular electronics devices. Most of the available chemical functionalization approaches require an external radical initiator, such as UV light, heat or chemical reagents. Here, we report forming organic monolayers on Si–H surfaces using molecules comprising terminal alcohol (–OH) groups. Self-assembled monolayer (SAM) formation is spontaneous, requires no external stimuli–and yields Si–O–C covalently bound monolayers. The SAMs were characterized by X-ray photoelectron spectroscopy (XPS) to determine the chemical bonding, by X-ray reflectometry (XRR) to determine the monolayers thicknesses on the surface and by atomic force microscopy (AFM) to probe surface topography and surface roughness. The redox activity and the electrochemical properties of the SAMs were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The availability and the ease of incorporating OH groups in organic molecules, makes this spontaneous grafting as a reliable method to attach molecules to Si surfaces in applications ranging from sensing to molecular electronics where incorporating radical initiator setups is not accessible.

Active cyano groups to coordinate AlCl2+ cation for rechargeable aluminum batteries

Rechargeable aluminum batteries, owing to the abundant Al resources and high safety guarantee, have been exploited as the ideal power sources for large-scale energy storage. However, the application of aluminum batteries is still restricted by the unsatisfactory positive electrodes due to low capacity, electrode variation or poor cycle stability of inorganic materials. As an alternative route for addressing the critical issues, multi-cyano organic molecules are proposed as the positive electrode materials for stable rechargeable aluminum batteries. With the first-principle calculation of the electron distribution, molecular energy levels and theoretical specific capacity, the results suggest that the electron-deficient cyano groups in organic molecules can reversibly coordinate/dissociate with positively charged Al-complex ions (i.e. AlCl2+). According to the molecule design and experiment results, tetracyanoquinodimethane (TCNQ) with high conductivity is identified as the optimized cyano-organic positive electrode material. The as-assembled cell delivers a high specific capacity of 180 mAh g−1 at first cycle and a discharge plateau ~1.6 V, along with long-term operation beyond 2000 cycles and coulombic efficiency of ~100%. The design principle here opens a new platform to utilize stable cyano-organic molecules as positive electrode materials for high-energy-density aluminum batteries, offering opportunities to design and exploit high-performance rechargeable Al-organic batteries.

Effect of Gelation Temperature on the Molecular Structure and Physicochemical Properties of the Curdlan Matrix: Spectroscopic and Microscopic Analyses.

In order to determine the effect of different gelation temperatures (80 °C and 90 °C) on the structural arrangements in 1,3-β-d-glucan (curdlan) matrices, spectroscopic and microscopic approaches were chosen. Attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) and Raman spectroscopy are well-established techniques that enable the identification of functional groups in organic molecules based on their vibration modes. X-ray photoelectron spectroscopy (XPS) is a quantitative analytical method utilized in the surface study, which provided information about the elemental and chemical composition with high surface sensitivity. Contact angle goniometer was applied to evaluate surface wettability and surface free energy of the matrices. In turn, the surface topography characterization was obtained with the use of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Described techniques may facilitate the optimization, modification, and design of manufacturing processes (such as the temperature of gelation in the case of the studied 1,3-β-d-glucan) of the organic polysaccharide matrices so as to obtain biomaterials with desired characteristics and wide range of biomedical applications, e.g., entrapment of drugs or production of biomaterials for tissue regeneration. This study shows that the 1,3-β-d-glucan polymer sample gelled at 80 °C has a distinctly different structure than the matrix gelled at 90 °C.

The Room-Temperature Planar Type Gas Sensor Based on DPA-Ph-Dbpzdcn/TPA-Dcpp for NH3 Monitoring Application

Introduction Ammonia (NH3) gas sensor is the indispensable element in safety, air quality monitoring and respiratory analysis fields. The chemoresistor sensors are mainly focused in the investigation of NH3 sensors attributing to the high stability, simple sensing structure, low cost and portable device. However, solving the high working temperature issue and achieving reproducible and stable gas sensing properties by designing novel sensitive material is highly desirable for widespread development of ammonia sensor [1]. Here, the planar room-temperature NH3 sensors are fabricated through spin-coating DPA-Ph-DBPzDCN/TPA-DCPP organic semiconductor materials onto the Al2O3 substrate with Au interdigital electrodes. The two sensors exhibit favorable sensing response as 72.73%/76.4% to 100 ppm NH3 under 98% RH, respectively, also demonstrates the low detection limits, good reproducibility, selectivity and long-term stability. The DFT calculation results further demonstrate that the excellent NH3 sensing characteristics are attributed to the enhanced absorption between NH3 and the N groups of organic molecules, which formed the H2O pre-adsorption under the high RH. This work is expected it can offer some guidance and inspiration for the rational design of sensing materials and further development of room temperature gas sensor. Results and Conclusions The synthesis process of DPA-Ph-DBPzDCN/TPA-DCPP were detailed reported previously [2, 3]. The sensor devices were successful fabricated via spin-coated sensitive materials onto the Al2O3 substrate with Au interdigital electrodes and illustrated in Figure 1. It was illustrated from scanning electron microscopy (SEM) image that the organic sensing films were formed uniformly and tightly. Then, the response transients of sensors in different NH3 concentration under 98% and 25% RH were monitored (Figure 2). The response value improved alone with the increasing of NH3 concentration and performed the highest response value as 72.73%/76.4% to 100 ppm NH3 under the 98% RH, respectively. Furthermore, there had a decreasing trend of the lowest detectable NH3 concentration along with the increasing RH, especially, the TPA-DCPP sensor exhibited the lowest detection limit as 500 ppb under 98% RH.Accordingly, the density functional theory (DFT) calculations were performed to gain further insight into the interaction between gas molecules and the sensitive materials, also the enhanced ammonia sensing properties under the high RH. The three most likely ammonia adsorbing sites (A: trihpenylamine-ortho C on the benzene ring; B: pyrazine-N; C: cyano-N) were selected due to the negative charge was mainly located. The configuration and the charge density difference after NH3 adsorption (Figure 3) demonstrated that the charge transfer occurred through the NH3 given electrons to organic compounds, thereby the conductivity of organic semiconductors increased until to an equilibrium state. Simultaneously, the NH3, H2O, NH3-H2O adsorption energies of the corresponding adsorbing sites were given in Table 1. It was shown that the NH3 adsorbing to organic compounds after H2O pre-adsorption were more capable compared with the NH3 adsorption only. Meanwhile, the NH3 adsorption energy before and after H2O pre-adsorption of the pyrazine-N on TPA-DCPP (-0.1809 eV, -0.4011 eV) was obviously higher than the DPA-Ph-DBPZdCN molecule (-0.14362 eV, -0.15679 eV), resulting in the response value of TPA-DCPP sensor was apparently improved compared to the DPA-Ph-DBPZdCN sensor under the low/high RH, that were attributed to the increasing of the negative charge on pyrazine-N owing to the directly link between and the pyrazine the cyano group, the change of molecular structure leading to a significantly stronger coulombic effect between pyrazine-N with NH3. Taken together, the excellent NH3 sensing characteristics were attributed to the enhanced absorption between NH3 and H2O pre-adsorption organic molecules under the high RH [4]. The DPA-Ph-DBPZdCN/TPA-DCPP could be the promising NH3 organic sensitive materials for the room temperature sensor, meanwhile, the discussion of sensing mechanism bring the further understanding of the organic gas sensors, providing the new concept of organic materials which has potential application value in gas monitoring of production and daily life at room temperature.

Experimental methods in chemical engineering: Fourier transform infrared spectroscopy—FTIR

AbstractWhen molecules absorb infrared radiation (IR), their vibrational mode—stretching and bending of the electric dipole—changes to an excited state. Functional groups in organic molecules absorb IR related to their characteristic vibrational modes. A Fourier transform infrared absorption (FTIR) analyzer measures the absorbed IR to identify molecular composition of surfaces, structural and geometric isomers, orientation in polymers and solutions, and quantify impurities. We describe the power of FTIR instruments and their basic operating principles, including the main experimental setups available: transmission, diffuse reflectance (DRIFTS), reflection adsorption infrared spectroscopy (RAIRS), and attenuated total reflection (ATR), including the recent advances related to time‐resolved and operando applications. In catalytic studies, FTIR spectroscopy has demonstrated its versatility over the last several decades to understand reaction mechanisms, measure gas phase composition, and identify active sites. Over 3000 articles include catalysis and FTIR as keywords but 50 000 articles per year mention IR. We generated a bibliometric map of keywords in articles that Web of Science indexed in 2016 and 2017. The map identified four broad clusters of research related to or applying FTIR: nano‐composites, composites, and mechanical properties; nano‐particles, degradation, graphene oxide, and photo‐catalysis; adsorption, aqueous solutions, and waste water; and drug delivery, silver and gold nano‐particles, green synthesis, and antibacterial activity. Together with a synopsis of the principals of IR spectroscopy and a review of the applications, we discuss uncertainties and limitations of the technique.

On the occasion of the 100th anniversary: Ernst Sp\xe4th and his mescaline synthesis of 1919

Characterizing plant ingredients has been the main topic of chemical research at the University of Vienna since the beginning of the last half of the nineteenth century, especially at the IInd Chemical Institute (founded in 1870). The remarkable success in many fields of natural organic product structure elucidation was in part the result of the discovery of important identifying reactions of functional groups in organic molecules by Austrian chemists, e.g., Lieben´s iodoform test, the Herzig–Meyer´s method for the determination of methylamino groups or Zeisel´s method for the determination of methoxy groups in organic compounds. Ernst Späth was the most prominent exponent of the Viennese school of phytochemistry. He and his coworkers identified more than 120 phytochemical substances. His mescaline synthesis of 1919 has marked a milestone in the chemistry of organic natural products.Graphical abstract

The Iodine Test for Reducing Sugars – A Safe, Quick and Easy Alternative to Copper(II) and Silver(I) Based Reagents

The reaction of Fehling’s and Benedicts’s test solutions with solutions of reducing sugars, e.g. glucose, is frequently misinterpreted with respect to the products formed. The tests are by no means suitable to detect aldehyde groups in organic molecules. The course of the reaction is known since long to be rather complex and the corresponding carboxylate, often assumed to be the major reaction product, does not occur at all. Both tests, as well as Tollens’ test using alkaline silver(I) solution, have some drawbacks for chemistry lessons, especially in students’ lab courses. The “iodine test”, well established to quantitatively determine glucose, could be a suitable alternative in many cases. It allows a quick detection, even of small amounts or reducing sugars at room temperature by decolourisation of a weakly alkaline iodine–starch–solution. The test is based on several coupled equilibria, and hypoiodous acid is the oxidizing agent. The complexity of the molecular description of the reaction can easily be reduced. Hence, the iodine test is suited to set different levels of difficulty, in lab work as well as in exams. The “iodine test” can even be used in Primary School, since the necessary solutions do not represent a danger.

Using differential ion mobility spectrometry to perform class-specific ion-molecule reactions of 4-quinolones with selected chemical reagents.

Gas phase ion/molecule reactions are often used in analytical applications to support the analysis of isomers or to identify specific functional groups of organic molecules. Until now, deliberate chemical reactions have not been performed in differential ion mobility spectrometry (DMS) devices except for hydrogen exchange and cluster formation. The present work extends that of Colorado and Brodbelt (Anal Chem 66:2330-5, 1994) on ion/molecule reactions in an ion trap mass spectrometer. In this study, class-specific chemical reactions of 4-quinolone antibiotics with various chemical reagents were used to demonstrate the analytical utility of ion/molecule reactions in a DMS drift cell. For these reactions, dehydrated reactive precursor ions were initially formed and made to undergo annulation reactions with selected reagents within the timescale of the DMS separation. Careful study of the energies required for dissociation of the adducts confirmed the covalent nature of the newly formed bond; thus demonstrating the analytical utility of this approach. Graphical abstract.

Dynamic Nuclear Polarization of 13 C Nuclei in the Liquid State over a 10 Tesla Field Range.

Nuclear magnetic resonance (NMR) techniques play an essential role in natural science and medicine. In spite of the tremendous utility associated with the small energies detected, the most severe limitation is the low signal-to-noise ratio. Dynamic nuclear polarization (DNP), a technique based on transfer of polarization from electron to nuclear spins, has emerged as a tool to enhance sensitivity of NMR. However, the approach in liquids still faces several challenges. Herein we report the observation of room-temperature, liquid DNP 13 C signal enhancements in organic small molecules as high as 600 at 9.4 Tesla and 800 at 1.2 Tesla. A mechanistic investigation of the 13 C-DNP field dependence shows that DNP efficiency is raised by proper choice of the polarizing agent (paramagnetic center) and by halogen atoms as mediators of scalar hyperfine interaction. Observation of sizable DNP of 13 CH2 and 13 CH3 groups in organic molecules at 9.4 T opens perspective for a broader application of this method.