Low Dissociation Energy Research Articles

Highly efficient and irreversible removal of cadmium through the formation of a solid solution

Sulfur-containing materials are very attractive for the efficient decontamination of some heavy metals. However, the effective and irreversible removal of Cd2+, coupled with a high uptake efficiency, remains a great challenge due to the relatively low bond dissociation energy of CdS. Herein, we propose a new strategy to overcome this challenge, by the incorporation of Cd2+ into a stable ZnxCd1-xS solid solution, rather than into CdS. This can be realised through the adsorption of Cd2+ by ZnS nanoparticles, which have exhibited a Cd2+ uptake capacity of approximate 400 mg g−1. Through this adsorption mechanism, the Cd2+ concentration in a contaminated solution could effectively be reduced from 50 ppb to <3 ppb, a WHO limit acceptable for drinking water. In addition, ZnS continued to exhibit this noteworthy uptake capacity even in the presence of Cu2+, Pb2+, and Hg2+. ZnS displayed high chemical stability. Particles aged in air for 3 months still retained a> 80% uptake capacity for Cd2+, compared with only 9% uptake capacity for similarly-aged FeS particles. This work reveals a new mechanism for Cd2+ removal with ZnS and establishes a valuable starting point for further studies into the formation of solid solutions for hazardous heavy metal removal applications.

Gold-Catalyzed C-H Functionalization with Aryl Germanes.

The development of orthogonal Csp2–Csp2 coupling regimes to the omnipresent Pd-catalysis class would enable an additional dimension of modularity in the construction of densely functionalized biaryl motifs. In this context, the identification of potent functional groups for selective transformations is in high demand. Although organogermanium compounds are generally believed to be of low reactivity in homogenous catalysis, this report discloses the highly efficient and orthogonal reactivity of aryl germanes with arenes under gold catalysis. The method is characterized by mildness, the employment of an air- and moisture-stable gold catalyst, and robustness. Our mechanistic studies show that aryl germanes are highly reactive with Au(I) and Au(III). Our computational data suggest that the origin of this reactivity primarily lies in the relatively low bond dissociation energy and as such low distortion energy to reach the key bond activating transition state.

Bismuth Compounds in Radical Catalysis: Transition Metal Bismuthanes Facilitate Thermally Induced Cycloisomerizations.

The controlled radical chemistry of bismuth compounds is still in its infancy. Further developments are fueled by the properties of these complexes (e.g., low toxicity, high functional group tolerance, low homolytic bond dissociation energies, and reversible homolytic bond dissociations), which are highly attractive for applications in synthetic chemistry. Here we report the first catalytic application of transition metal bismuthanes (i.e. compounds with a Bi-TM bond; TM=transition metal). Using the catalyzed radical cyclo-isomerization of δ-iodo-olefins as a model reaction, characteristics complementary or superior to known B, Mn, Cu, Zn, Sn, and alkali metal reagents are demonstrated (including a different crucial intermediate), establishing transition metal bismuthanes as a new class of (pre-)catalysts for controlled radical reactions.

Fast pyrolysis of guaiacol to simple phenols: Experiments, theory and kinetic model

This study is focused on both experimental and theoretical analysis of fast pyrolysis of guaiacol, a major pyrolysate and a model monomeric compound of lignin. Fast pyrolysis experiments were performed in an analytical pyrolyzer coupled with gas chromatograph/mass spectrometer in the temperature range of 450–650 °C. Thermodynamics and kinetics of 19 elementary reactions of 17 species were investigated using quantum chemical density functional theory calculations. Reaction pathways for the formation of four major phenols, viz. phenol, catechol, o-hydroxybenzaldehyde and o-cresol, were proposed. The homolytic cleavage of OCH3 bond, with low bond dissociation energy of 57.7 kcal/mol, is shown to be the primary reaction for the generation of free radicals. The generation of o-hydroxyphenyl radical is found to be vital for the formation of phenol and cresol, while o-hydroxybenzyloxy radical is the key intermediate for the formation of o-hydroxybenzaldehyde. Multiple pathways for the formation of catechol were evaluated. A kinetic model was developed using the elementary reactions and their Arrhenius rate parameters. The concentration of the major products at different temperatures obtained from the model reasonably matched the trends in product yields from the experiments.

Photoredox-Mediated Generation of gem-Difunctionalized Ketones: Synthesis of α,α-Aminothioketones.

A photoredox-mediated gem-difunctionalization of alkynes leading to the synthesis of α,α-aminothio-substituted carbonyl compounds is reported. The work presents concomitant introduction of α-C-N and C-S bonds as a key enabling advance. Furthermore, the low bond dissociation energy of the C-S bond compared to that of C-N or C-C bonds has been exploited for selective functionalization using different nucleophiles to build diverse α,α-disubstituted carbonyl scaffolds. Mild reaction conditions, broad substrate scope, and good yields are some of the added advantages of this reaction.

Modular and Processable Fluoropolymers Prepared via a Safe, Mild, Iodo-Ene Polymerization.

Fluoropolymers have infiltrated society as coatings and insulators. However, low processability, few opportunities for polymer functionalization, and explosive monomers hampering academic investigation of these materials have precluded the extension of the unique properties of perfluorocarbons to the cutting edge of material science. Here, we present semifluorinated iodo–ene polymers as a scaffold to overcome fluoropolymer limitations. A sodium dithionate initiated polymerization of perfluorodiiodides and dienes allows for high-molecular-weight polymers (>100 kDa) to be prepared in the presence of oxygen and water with up to 59 wt % fluorine content. These conditions are sufficiently mild to enable the polymerization of functional dienes, leading to biodegradable fluoropolymers. The iodo–ene polymerization results in the addition of polarizable iodine atoms, which improve polymer processability; yet, these atoms can be removed after processing for enhanced stability. Displacement of the iodine atoms with thiols or azides facilitates covalent surface modification and cross-linking. Finally, the low bond dissociation energy of the C–I bond allows allyl group addition as well as photo-cross-linking. Collectively, the simple synthesis and modular nature of the semifluorinated iodo–ene polymers will enable the convergence of perfluorocarbons and advanced materials.

Ultralow-intensity NIR light triggered on-demand drug release by employing highly emissive UCNP and photocleavable linker with low bond dissociation energy.

Background: The design of novel nanoparticles with higher therapeutic efficacy and lower side effects, is still difficult but encouraging in cancer therapy. Specifically, for upconversion nanoparticles (UCNP)-based drug release, a high intensity of NIR light (1.4~5.0 W/cm2) above the maximum permissible exposure (0.33 W/cm2 for 980 nm) is commonly used and severely limits its practical application.Methods: The highly emissive UCNP is first synthesized and then coated with mesoporous silica (MS) shell (UCMS). Next, the surface of UCMS is modified with the thioether (-S-BP) linker, leading to UCMS-S-BP nanoparticles. Finally, after the drug doxorubicin (Dox) is loaded into the pore channels of UCMS, the pore openings are blocked by the β-cyclodextrin (β-CD) gatekeeper through the association with the -S-BP linker (UCMS(Dox)-S-BP@β-CD).Results: Upon 980 nm NIR light irradiation with an ultralow intensity of 0.30 W/cm2, it is found that the loaded Dox can be released through the cleavage of thioether linkers triggering dissociation of β-CD gatekeepers. The in vitro results exhibited significantly therapeutic efficacy with 85.2% of HeLa cells killed in this study.Conclusions: An ultralow-intensity NIR light triggered on-demand drug release system has been developed by employing highly emissive UCNP and photocleavable linker with low bond dissociation energy to avoid the potential photodamage on healthy neighbor cells.

Structure affecting dissociation energy in polycyclic aromatic hydrocarbon ions

Steric interference of two bay-hydrogen atoms causes the benzo[c]phenanthrene radical cation to be non-planar. The energy required to remove one of these H atoms (2.8 ± 0.1 eV, from iPEPICO spectroscopy) is 1.5 eV lower than that required from the planar tetracene ion due to the formation of a new CC bond. This low dissociation energy precludes benzo[c]phenanthrene ions losing C2H2 (observed from tetracene with an energy of 4.2 eV). The B3-LYP/6-311++G(2d,p) reaction pathways to C2H2 loss are presented and found to be mediated by azulene-containing intermediates. The second IE of tetracene was measured to be 19.0 ± 0.2 eV.

Adsorption and dissociation of H2O molecule on the doped monolayer MoS2 with B/Si

Adsorption and dissociation of H2O on monolayer MoS2 surface doped with B/Si explored by first principle calculations coupled with climb image nudged elastic band method. The impurity B/Si atoms are more likely to occupy sulfur atom lattice positions with lower formation energies, which results in the breaking of surface chemically inertness of the MoS2 (001) plane. Free H2O molecules can be adsorbed on doped surfaces with lower adsorption energies, and form chemical bonds between oxygen and impurity atoms. Adsorbed H2O can be separated into OH radical and hydrogen adatom with a lower dissociation energy barrier on these doped systems (including impurity B/Si single doped, B and Si co-doped). Furthermore, the adsorbed OH radical can be further dissociated into oxygen and hydrogen adatoms on the surface of B and Si co-doped MoS2. Our theoretical study suggests that substrate of monolayer MoS2 doped with impurity B, Si may be a potential alternative choice for hydrogen evolution reaction.

Highly-effective mechanochemical destruction of hexachloroethane and hexachlorobenzene with Fe/Fe3O4 mixture as a novel additive

In this study, Fe/Fe3O4 mixture was first applied as an additive to achieve the highly-effective mechanochemical destruction (MCD) of two halogenated organic pollutants (HOPs), hexachloroethane (HCE) and hexachlorobenzene (HCB). The MCD of HCE was more effective than that of HCB in virtue of the lower dissociation energy of CCl bond. The MCD of HOPs occurred mainly via the reduction by Fe, Fe3O4 and Fe/Fe3O4. The oxidation of Fe3O4 and reduction of FeO (formed on account of the oxidation of Fe by oxygen-containing species) may also contribute to the HOP destruction. Fe/Fe3O4 mixture exhibited a higher dechlorination rate (DR) than other three effective additives (i.e., Fe/SiO2, Al/Al2O3 and Mg/Al2O3 mixture), owing to the electrical property of Fe3O4 and its electron transfer with Fe. The HOP destruction was significantly impacted by the mass fraction of Fe3O4 (MFmag) and achieved the maximum level with an MFmag of 70%. The DR of HOPs in the atmosphere of air was higher than those of pure oxygen and nitrogen because of the oxygen vacancy in Fe3O4 and oxidation of Fe. The presence of water dramatically inhibited the HOP destruction due to the decrease of collision energy and its competition for the active sites in both Fe and Fe3O4. As expected, the DR of HOPs increased with rotation speed, and the mass ratio of ball to reactant and additive to pollutant. The analysis of intermediates indicates that HCB destruction was mainly via dechlorination and polymerization, while HCl cleavage also played an important role in HCE destruction. The results demonstrate that Fe/Fe3O4 mixture is a suitable additive for MCD process.

Role of asymmetry in the physiochemical and electrochemical behaviors of perfluorinated sulfonimide anions for lithium batteries: A DFT study

Lithium salts based on perfluorinated sulfonimide anions (PSAs) are promising new electrolyte components for application in next-generation lithium batteries. Several typical symmetric ([(n-CmF2m+1SO2)2N]−, m = 0, 1, 2, 3, and 4) and asymmetric ([(FSO2) (n-CmF2m+1SO2)N], m = 1, 2, 4, 6, and 8) PSAs have been extensively investigated in recent years. Yet little is known about the role of asymmetry in the physicochemical and electrochemical properties at the molecular level. Here we use first-principle density functional theory calculations to thoroughly examine such fundamental structure-activity relationship. Compared to symmetric PSAs, asymmetric isomers show intrinsically better internal flexibility of the S─N bond, lower dissociation energy of Li+ cation, and thereby they can be promising candidates for polymer electrolytes. We also observe that more than four C atoms in the perfluorinated chain results in negligible improvements in terms of dissociation energy, thermal stability, and anodic stability. These results provide an in-depth understanding of the impact of the molecular structure on PSAs, helping design new robust anions for lithium batteries in the future.

A Brief Study of Organic &amp; Perovskite-Type Solar Cells

In this paper, a brief study is conducted between organic and perovskite-type solar cells, which are a possible replacement for inorganic Si semiconductor solar cells. As the need for renewable energy is increasing, there is more and more emphasis being laid on utilizing solar radiations for meeting the energy requirements. As inorganic solar cells reaching their saturation point of energy conversion, we rely more and more on organic and hybrid ways of converting solar radiation into energy. There are two leading contenders for this which are organic and hybrid or Perovskite-type materials. The main problem with both is power conversion efficiency and stability. Perovskite solar cells have a better and promising future ahead of them because of low dissociation energy required which increases the Power conversion efficiency. Organic solar cells can be implemented on a wide variety of object making possibilities for the various design pattern.

Reactivity of phosphorus mononitride and interstellar formation of molecules containing phospazo linkage: A computational study on the reaction between HSi (X2Π) and PN (X1Σ+)

Phosphorus mononitride (PN) shows some interesting chemistry due to its low dissociation energy (compared to N2) and small dipole moment (zero dipole moment for N2). In this work, a reaction between HSi ([Formula: see text]) and PN ([Formula: see text]) has been studied using various computational methods. Analysis of the doublet surface of the [Formula: see text] reaction indicates that the reaction is exothermic in nature leading to the formation of various products. In view of the barrierless association of the reactants and exothermic nature for the product formation, it is suggested that species like HPNSi, cyclic-SiN(H)P (these two most stable isomers have phosphazo linkage) and HSiNP (third most stable isomer has phosphdiazo linkage) can possibly be detected in the interstellar medium. In view of the potential applications of phosphazo compounds in amide synthesis and pervasive nature of amide linkages in the nature, possible interstellar prebiotic applications can be advocated for these compounds.

Controlling the structure of sequence-defined poly(phosphodiester)s for optimal MS/MS reading of digital information.

Digital polymers are monodisperse chains with a controlled sequence of co-monomers, defined as letters of an alphabet, and are used to store information at the molecular level. Reading such messages is hence a sequencing task that can be efficiently achieved by tandem mass spectrometry. To improve their readability, structure of sequence-controlled synthetic polymers can be optimized, based on considerations regarding their fragmentation behavior. This strategy is described here for poly(phosphodiester)s, which were synthesized as monodisperse chains with more than 100units but exhibited extremely complex dissociation spectra. In these polymers, two repeating units that differ by a simple H/CH3 variation were defined as the 0 and 1bit of the ASCII code and spaced by a phosphate moiety. They were readily ionized in negative ion mode electrospray but dissociated via cleavage at all phosphate bonds upon collisional activation. Although allowing a complete sequence coverage of digital poly(phosphodiester)s, this fragmentation behavior was not efficient for macromolecules with more than 50 co-monomers, and data interpretation was very tedious. The structure of these polymers was then modified by introducing alkoxyamine linkages at appropriate location throughout the chain. A first design consisted of placing these low dissociation energy bonds between each monomeric bit: while cleavage of this sole bond greatly simplified MS/MS spectra, efficient sequencing was limited to chains with up to about 50units. In contrast, introduction of alkoxyamine bonds between each byte (i.e. a set of eight co-monomers) was a more successful strategy. Long messages (so far, up to 8 bytes) could be read in MS3 experiments, where single-byte containing fragments released during the first activation stage were further dissociated for sequencing. The whole sequence of such byte-truncated poly(phosphodiester)s could be easily re-constructed based on a mass tagging system which permits to determine the original location of each byte in the chain. Copyright © 2017 John Wiley & Sons, Ltd.

Highly photostable NV centre ensembles in CVD diamond produced by using N2O as the doping gas

High density Nitrogen-Vacancy (NV) centre ensembles incorporated in plasma assisted chemical vapour deposition (CVD) diamond are crucial to the development of more efficient sensing devices that use the properties of luminescent defects. Achieving high NV doping with N2 as the dopant gas source during diamond growth is, however, plagued by the formation of macroscopic and point defects that quench luminescence. Moreover, such NVs are found to exhibit poor photostability under high laser powers. Although this effect can be harnessed to locally and durably switch off NV luminescence for data storage, it is usually undesirable for most applications. In this work, the use of N2O as an alternative doping source is proposed. Much higher amounts of the doping gas can be added without significantly generating defects, which allows the incorporation of perfectly photostable and higher density NV ensembles. This effect is believed to be related to the lower dissociation energy of the N2O molecule together with the beneficial effect of the presence of a low and controlled amount of oxygen near the growing surface.

Research on surface nano-texturation and wet-chemical passivation of multi-crystalline silicon wafer

Surfaces nano-texturing has triggered off much attention for trapping sunlight to improve the efficiency of solar cells. Silicon nanowire (SiNWs) arrays, with excellent antireflection performance, will hopefully improve photoelectric conversion of solar cells, however, the deteriorated effective carrier lifetime seriously limits efficiency enhancement of solar devices. Until now, the effect of SiNWs structure on effective carrier lifetime remains unexplored. Herein, the effects of fabrication parameters on the morphology structure and effective carrier lifetime of textured mc-Si were studied in detail. We also firstly discover that the relationship of SiNWs arrays length and effective carrier lifetime shows the negative exponential relation. Moreover, the effects of ethanolic iodine (I–E) concentration, immersion time, and surface pre-conditioning (with and without native oxide) on surface passivation of SiNWs arrays were investigated. It is found that more effective surface passivation could be achieved for the SiNWs arrays with shorter length. Meanwhile, the HF dipping pretreatment is conducive for SiNWs passivation, and which is attributed to Si–Hx termination with lower dissociation energy.

Study of the interface stability of the metal (Mo, Ni, Pd)/HfO2/AlN/InGaAs MOS devices

The degeneration of the metal/HfO2 interfaces for Mo, Ni, and Pd gate metals was studied in this paper. An unstable PdOx interfacial layer formed at the Pd/HfO2 interface, inducing the oxygen segregation for the Pd/HfO2/InGaAs metal oxide capacitor (MOSCAP). The low dissociation energy for the Pd-O bond was the reason for oxygen segregation. The PdOx layer contains O2− and OH− ions which are mobile during thermal annealing and electrical stress test. The phenomenon was not observed for the (Mo, Ni)/HfO2/InGaAs MOSCAPs. The results provide the guidance for choosing the proper metal electrode for the InGaAs based MOSFET.

Computational Study of Ni-Catalyzed C-H Functionalization: Factors That Control the Competition of Oxidative Addition and Radical Pathways.

The mechanisms of Ni-catalyzed C-H arylation, alkylation, and sulfenylation with N,N-bidentate directing groups are investigated using density functional theory (DFT) calculations. While the C-H cleavage occurs via the concerted metalation-deprotonation (CMD) mechanism in all types of reactions, the subsequent C-C and C-X bond formation steps may occur via either oxidative addition to form a Ni(IV) intermediate or radical pathways involving Ni(III) complexes generated from homolytic dissociation of disulfides/peroxides or halide-atom transfer from alkyl halides. DFT calculations revealed that radical mechanisms are preferred in reactions with sterically hindered coupling partners with relatively low bond dissociation energies (BDE) such as dicumyl peroxide, heptafluoroisopropyl iodide and diphenyl disulfide. In contrast, these radical processes are highly disfavored when generating unstable phenyl and primary alkyl radicals. In such cases, the reaction proceeds via an oxidative addition/reductive elimination mechanism involving a Ni(IV) intermediate. These theoretical insights into the substrate-controlled mechanisms in the C-H functionalizations were employed to investigate a number of experimental phenomena including substituent effects on reactivity, chemo- and regioselectivity and the effects of oxidant in the intermolecular oxidative C-H/C-H coupling reactions.

Density Functional Study of Neutral and Charged Silver Clusters Agn with n = 2-22. Evolution of Properties and Structure.

Geometries and electronic properties of neutral Agn, cationic Agn+, and anionic Agn- silver clusters with n = 2-22 were investigated by density functional theory (DFT) with M06 functional. For neutral clusters, transition from planar to "empty cage" structure occurs at n = 7, "empty cage" to "cage with one Ag atom" at n = 18, and to "cage with two Ag atoms" at n = 22. For lowest-energy Agn clusters, Ag8 and Ag18 show lowest polarizability due to closed-shell valence electron configurations 1S2/1P6 and 1S2/1P6/1D10. High stability of Ag8 is manifested in small dissociation energies of Ag9 to Ag8 plus Ag1 and Ag10 cluster to Ag8 plus Ag2. Cluster Ag20 with configuration 1S2/1P6/1D10/2S2 is stable due to low dissociation energy of Ag21 to Ag1 and Ag22 to Ag2. Cationic clusters with even n namely Ag10+ (9 valence electrons), Ag16+ (15 valence electrons), and Ag22+ (21 valence electrons) dissociate to Ag1 and closed-shell Ag9+ (1S2/1P6), Ag15+ (1S2/1D10/2S2) and Ag21+ (1S2/1P6/1D10/2S2). For odd n, Ag11+ and Ag17+ dissociate to Ag2 and closed-shell Ag9+ and Ag15+. For anionic clusters Agn-, cohesion energy Ecoh and binding energy (BE) show maxima at n = 7 and n = 17 due to stable Ag7- and Ag17- clusters. Small Agn- clusters (n = 4-11) with even n (except n = 8) have lower dissociation energy for loss of Ag1 while those with odd n have lower dissociation energy for loss of Ag2. For n = 12-22, all clusters have lower dissociation energy for loss of Ag1.

Assessment of disulfide and hinge modifications in monoclonal antibodies.

During the last years there was a substantial increase in the use of antibodies and related proteins as therapeutics. The emphasis of the pharmaceutical industry is on IgG1, IgG2, and IgG4 antibodies, which are therefore in the focus of this article. In order to ensure appropriate quality control of such biopharmaceuticals, deep understanding of their chemical degradation pathways and the resulting impact on potency, pharmacokinetics, and safety is required. Criticality of modifications may be specific for individual antibodies and has to be assessed for each molecule. However, some modifications of conserved structure elements occur in all or at least most IgGs. In these cases, criticality assessment may be applicable to related molecules or molecule formats. The relatively low dissociation energy of disulfide bonds and the high flexibility of the hinge region frequently lead to modifications and cleavages. Therefore, the hinge region and disulfide bonds require specific consideration during quality assessment of mAbs. In this review, available literature knowledge on underlying chemical reaction pathways of modifications, analytical methods for quantification and criticality are discussed. The hinge region is prone to cleavage and is involved in pathways that lead to thioether bond formation, cysteine racemization, and iso‐Asp (Asp, aspartic acid) formation. Disulfide or sulfhydryl groups were found to be prone to reductive cleavage, trisulfide formation, cysteinylation, glutathionylation, disulfide bridging to further light chains, and disulfide scrambling. With regard to potency, disulfide cleavage, hinge cleavage, disulfide bridging to further light chains, and cysteinylation were found to influence antigen binding and fragment crystallizable (Fc) effector functionalities. Renal clearance of small fragments may be faster, whereas clearance of larger fragments appears to depend on their neonatal Fc receptor (FcRn) functionality, which in turn may be impeded by disulfide bond cleavage. Certain modifications such as disulfide induced aggregation and heterodimers from different antibodies are generally regarded critical with respect to safety. However, the detection of some modifications in endogenous antibodies isolated from human blood and the possibility of in vivo repair mechanisms may reduce some safety concerns.