Reactive Bond Research Articles

Photocured polyacrylate coatings modified by polybutadiene derivatives with multiunsaturated reactive bonds

Photocured polyacrylate coatings modified by polybutadiene derivatives with multiunsaturated reactive bonds

Synthesis and spectral properties of H acid-containing dyes and their Mannich-type dyeing performances on silk fibroin

The colouration of silk fibroin through a Mannich-type reaction with aromatic primary amine-containing dyes (APADs), named Mannich-type dyeing, is a novel dyeing method with the advantages of moderate conditions, high selectivity, and high wet fastness. In this study, three novel APADs, including an H acid structure, D1-D3, were designed and synthesized. A similar dye, C1, without an aromatic primary amine group, was selected as the control. Their spectral and colour fastness properties in aqueous solutions and on silk fabrics were measured and evaluated. In addition, their Mannich-type reactivity to silk fabric was evaluated via experiments and simulated calculations. It was revealed that for the H acid-containing dye with the same chromosome structure, the electron accepting/donating properties of the diazo and coupling components affect the colour of the dye after the Mannich-type dyeing. The substituent effect of dyes C1–D3 demonstrated that with the changing properties of electron donation and acceptance in the case of the diazonium component, the absorption spectrum (λmax) of the neutral aqueous dye solution changed from reddish-orange (505 nm) to bluish-violet (541 nm). The λmax of Mannich-type dyed fabrics was generally red-shifted in comparison with that of dyed fabrics by acidic dyeing, which implied the formation of a reactive bond between the dye and the silk fibroin. The presence of aromatic primary amine groups in dyes is the prerequisite for Mannich-type reactivity. The primary amine groups on both benzene and naphthalene rings have Mannich-type reactivity, which is related to the electron cloud density of amino N atoms. With the increase in electron cloud density of the amino N atom, the colour fixation of the dye and the fibre was improved. After the Mannich-type dyeing, the colour fastness of the dyed fabrics and DMF stripping resistance significantly improved, also indicating the formation of a covalent bond between the dye and the fibre. The simulated calculation predicted the colour of APAD in an aqueous solution and on dyed silk fabric after Mannich-type dyeing, which guides the design and enrichment of APADs’ chromatography.

Carbon-titanium dioxide heterogeneous (photo)catalysts (C–TiO2) for highly efficient visible light photocatalytic application

In this paper, a novel one-step method for the synthesis of a heterogeneous carbon-titanium dioxide (photo)catalyst (C–TiO2) is first reported. This synthesis method was performed at room temperature and atmospheric pressure using underwater plasma treatment for 15 min over various ratios of titanium and carbon sources. The resulting C–TiO2 had anatase/brookite polycrystalline phases with turbostratic carbon and large surface areas. The bandgap energies were narrowed by the generation of reactive oxygen species and carbon bonds in the lattice of TiO2, extending optical absorption into the visible range. C60–TiO2, which had optimal ratios of carbon and TiO2, exhibited superior photocatalytic activities for methylene blue ([k] = 4.61 h−1) under artificial solar irradiation due to its enhanced optical properties and numerous adsorption sites, which were approximately 10 times higher than those of commercial TiO2 ([k] = 0.41 h−1). This study represents a milestone of rapid and convenient methods to produce C–TiO2 with high photocatalytic performance for environmental applications.

Cellulose allylcarbamate with high content of reactive double bonds for thiol-ene reaction

Polysaccharide phenylcarbonates react with amines to form carbamates with high efficiency and can be used to introduce reactive CC bonds into a biopolymer, which may be converted by thiol-ene click reactions. Thus, cellulose phenylcarbonates are allowed react with allylamine by nucleophilic reaction to yield cellulose allylcarbamate of very high degree of substitution (DS). The DS of allylcarbamate moieties could be controlled by the molar ratio of allylamine to phenylcarbonate groups. Pure products without remaining phenylcarbonate substituents were accessible. The allylcarbamate moieties are reactive regarding the radical thiol-ene reaction that was exemplified by the reaction of cellulose allylcarbamate with 2-(diethylamino)ethane-1-thiol hydrochloride (DEAET) in dimethyl sulfoxide using a photoinitiator under mild conditions. The phenylcarbonates- and allylcarbamates of cellulose as well as the DAEAET adduct were characterized by elemental analysis, NMR- and FTIR spectroscopy.

Recycling of unseparated construction and demolition waste (UCDW) through geopolymer technology

Geopolymer technology has been recognized as an ideal option for recycling construction and demolition waste (CDW) streams as new value-added products. However, most research efforts have been devoted to the geopolymer derived from the individual fraction separated from CDW. Given the technological complexity presented in separating CDW fractions on a commercial scale, using unseparated CDW (UCDW) in geopolymer application can achieve higher environmental and economic benefits. This paper investigated the feasibility of using UCDW consisting of various constituents, i.e., unbound aggregates (UA), red clay bricks (RCB), waste concrete (WC), waste glass (WG), and waste tiles (WT), in geopolymer production. The effects of these constituents on the reactivity of UCDW and the performance of the resulting geopolymer paste were studied. Results showed that all UCDW constituents can provide reactive phases and highly reactive bonds. RCB, WG, and WT can serve as the aluminosilicate source, while UA and WC mainly offer silica and calcium. The changes in constituents affected the mechanical performance of the UCDW-based geopolymer by conditioning the content of reactive Si, Al, and Ca in the precursor. A Si/Al molar ratio of 5–8 and a Ca/Si of 1.5 were found to achieve the higher compressive strength (up to 29.7 MPa) of geopolymer. In addition, a fitting formula was proposed to predict the compressive strength of UCDW-based geopolymer paste. This work contributes to understanding the alkali-activated performance of UCDW and promotes its utilization as a mineral precursor in geopolymer production.

Gold-Aluminyl and Gold-Diarylboryl Complexes: Bonding and Reactivity with Carbon Dioxide.

The unconventional carbon dioxide insertion reaction of a gold-aluminyl [tBu3PAuAl(NON)] complex has been recently shown to be related to the electron-sharing character of the Au–Al bond that acts as a nucleophile and stabilizes the insertion product through a radical-like behavior. Since a gold-diarylboryl [IPrAuB(o-tol)2] complex with similar reactivity features has been recently reported, in this work we computationally investigate the reaction of carbon dioxide with [LAuX] (L = phosphine, N-heterocyclic carbene (NHC); X = Al(NON), B(o-tol)2) complexes to get insights into the Al/B anionic and gold ancillary ligand effects on the Au–Al/B bond nature, electronic structure, and reactivity of these compounds. We demonstrate that the Au–Al and Au–B bonds possess a similar electron-sharing nature, with diarylboryl complexes displaying a slightly more polarized bond as Au(δ+)–B(δ–). This feature reduces the radical-like reactivity toward CO2, and the Al/B anionic ligand effect is found to favor aluminyls over boryls, despite the greater oxophilicity of B. Remarkably, the ancillary ligand of gold has a negligible electronic trans effect on the Au–X bond and only a minor impact on the formation of the insertion product, which is slightly more stable with carbene ligands. Surprisingly, we find that the modification of the steric hindrance at the carbene site may exert a sizable control over the reaction, with more sterically hindered ligands thermodynamically disfavoring the formation of the CO2 insertion product.

Cryo-EM structures show the mechanistic basis of pan-peptidase inhibition by human α2-macroglobulin

Human α2-macroglobulin (hα2M) is a multidomain protein with a plethora of essential functions, including transport of signaling molecules and endopeptidase inhibition in innate immunity. Here, we dissected the molecular mechanism of the inhibitory function of the ∼720-kDa hα2M tetramer through eight cryo–electron microscopy (cryo-EM) structures of complexes from human plasma. In the native complex, the hα2M subunits are organized in two flexible modules in expanded conformation, which enclose a highly porous cavity in which the proteolytic activity of circulating plasma proteins is tested. Cleavage of bait regions exposed inside the cavity triggers rearrangement to a compact conformation, which closes openings and entraps the prey proteinase. After the expanded-to-compact transition, which occurs independently in the four subunits, the reactive thioester bond triggers covalent linking of the proteinase, and the receptor-binding domain is exposed on the tetramer surface for receptor-mediated clearance from circulation. These results depict the molecular mechanism of a unique suicidal inhibitory trap.

The two-tier tissue reinforcing and toughening mechanism caused by dual-granularity Si powders ingredient, and dielectric properties in reaction bonded and sintered reaction bonded Si3N4 porous ceramics

With the rapid development of hypersonic vehicles and broadband wave-transparent radome, Si3N4 porous ceramics (Si3N4-PC) have attracted attention due to their excellent intrinsic properties of Si3N4 and high porosity. However, its high porosity results in low strength and toughness, which are fundamental properties for radome. Reaction bonded (RB) Si3N4-PC has advantages of dielectric properties and cost over general phase transformation sintering (PTS) and sintered reaction bonded (SRB) Si3N4-PC while it has been neglected in recent years. In this study, RB and SRB Si3N4-PC prepared by non-aqueous gelcasting and the influence of Si powders ingredient on their properties are discussed in order to illuminate the potential of RB Si3N4-PC in wave-transparent materials. The results show that RB Si3N4-PC with dual-granularity ingredients of 5 μm & 45 μm produces a two-tier tissue of framework of coarse whiskers enhanced by a network of tiny whiskers. SRB Si3N4-PC evolves into a two-tier tissue of framework of columnar and rod-like grains joining together to brace each other. The two-tier microscopic tissue strongly reinforces and toughens the structure and results in higher σF and γwof. As a result, the RB and SRB Si3N4-PC of dual-granularity of 5 μm & 45 μm obtain the maximum σF of 109.94 MPa and 119.56 MPa as well as maximum γwof of 990.74 J m-2 and 1167.88 J m-2, respectively. Furthermore, the ε′ and tanδ of RB and SRB Si3N4-PC of dual-granularity of 5 μm & 45 μm are about 4.20 and 4.52 as well as 7.01 × 10-3 and 22.90 × 10-3, respectively. It is concluded that RB Si3N4-PC of dual-granularity has good mechanical and dielectric properties, which are favorable for radome.

Structure and reactivity of germylene-bridged digold complexes

The bonding between gold and main-group metallic elements (M) featuring Auδ−−Mδ+ polarity, has been studied recently. The gold in the bonds is expected to have the oxidation number of −1, and hence, nucleophilic. However, the knowledge of the reactivity of the gold-metal bonds remains limited. Here, we report digold-substituted germanes of the form of R’2Ge(AuPR3)(AuGeR’2) (3a; R = Me, 3b; R = Et), featuring two Au-Ge(IV) and one Au-Ge(II) bonds. DFT calculations of 3a revealed the existence of high-lying σ(Ge-Au) type HOMO and low-lying LUMO with germylene pπ nature. A pendular motion of AuPR3 group between Ge(IV) and Ge(II) of 3 occurs in the NMR time scale, suggesting that the Ge(II) center has an enhanced electrophilicity to be attacked by the nucleophilic gold (−I) atom. 3a reacts with nucleophilic Cl− and electrophilic MeOTf reagents at Ge(II) and Ge(IV) centers, respectively.

Structural Dynamics Support Electrostatic Interactions in the Active Site of Adenylate Kinase.

Electrostatic preorganization as well as structural and dynamic heterogeneity are often used to rationalize the remarkable catalytic efficiency of enzymes. However, they are often presented as incompatible because the generation of permanent electrostatic effects implies that the protein structure remains rigid. Here, we use a metric, electric fields, that can treat electrostatic contributions and dynamics effects on equal footing, for a unique perspective on enzymatic catalysis. We find that the residues that contribute the most to electrostatic interactions with the substrate in the active site of Adenylate Kinase (our working example) are also the most flexible residues. Further, entropy-tuning mutations raise flexibility at the picosecond timescale where more conformations can be visited on short time periods, thereby softening the sharp heterogeneity normally visible at the microsecond timescale.

Vibrational spectra and molecular docking studies of bergapten isolated from Melicopedenhamii leaves as anti-breast cancer agents

This paper highlights the notable bioactivity and pharmaceutical significance of the natural furocoumarin viz. Bergapten (BG), extracted from the medicinal plant Melicopedenhamii. The equilibrium geometry, chemical reactivity and Natural Bond Orbital analysis to understand the charge transfer interactions of BG have been carried out aided by density functional theoretical calculations at the B3LYP/6–311++G(d,p) level. Vibrational spectral analysis of the extracted Bergapten, brings to light the vibrational wavenumbers and intensities of the compound. The analysis of the electron density of HOMO and LUMO gives an idea of the delocalization in the molecule and the low value of the energy gap aids in electron transport and thereby bioactivity of the molecule. Molecular docking studies which reveal the best binding sites with target proteins, particularly its inhibiting activity against carcinoma type proteins, manifest Bergapten as a promising agent for breast cancer therapy.

Low-temperature selective transformation of diethylbenzene to isobutane and cyclohexanes via the interplay of Pt and acid centres in Pt/H-*BEA zeolites

The hydrocracking of aromatic hydrocarbons on bifunctional catalysts comprises parallel reactions that provide a wide distribution of products and byproducts. This work demonstrates on diethylbenzene (DEB) hydrotreatment that Pt/H-Al-rich *BEA zeolite catalysts can significantly reduce the hydrocracking temperature so that only the selected reaction mechanisms prevail in the process, providing high selectivity. The interplay of high activity of Pt clusters in hydrogenation/dehydrogenation and Brønsted acid sites in acid-catalysed reactions allows selective hydrocracking of DEB to isobutane and methylcyclopentane by the paring reaction at 200 °C. Low-temperature hydrocracking consists of hydrogenation of DEB to diethylcyclohexane, its rapid skeletal hydroisomerization to C10 branched alkylcycloalkanes followed by their A type β scission providing isobutane and methylcyclopentane with 80% selectivity at 68% DEB conversion, practically without subsequent reactions of the formed products. The reactive CC bond in tribranched alkylcycloalkanes selectively undergoes A type β scission, while more stable CC bonds in less or unbranched hydrocarbon chains or rings do not crack to a substantial extent at low temperatures. The study demonstrates that the low-temperature hydrotreatment of aromatics over highly active catalysts allows controlling the involvement of individual reaction mechanisms in the complex hydrocracking process and provides tailored selectivity.

Alkali Metal Ions Dictate the Structure and Reactivity of an Iron(II) Imido Complex.

The presence of redox innocent metal ions has been proposed to modulate the reactivity of metal ligand multiple bonds; however, insight from structure/function relationships is limited. Here, alkali metal reduction of the Fe(III) imido complex [Ph2B(tBuIm)2Fe═NDipp] (1) provides the series of structurally characterized Fe(II) imido complexes [Ph2B(tBuIm)2Fe═NDippLi(THF)2] (2), [Ph2B(tBuIm)2Fe═NDippNa(THF)3] (3), and [Ph2B(tBuIm)2Fe═NDippK]2 (4), in which the alkali metal cations coordinate the imido ligand. Structural investigations demonstrate that the alkali metal ions modestly lengthen the Fe═N bond distance from that in the charge separated complex [Ph2B(tBuIm)2Fe═NDipp][K(18-C-6)THF2] (5), with the longest bond observed for the smallest alkali metal ion. In contrast to 5, the imido ligands in 2-4 can be protonated and alkylated to afford Fe(II) amido complexes. Combined experimental and computational studies reveal that the alkali metal polarizes the Fe═N bond, and the basicity of imido ligand increases according to 5 < 4 ≈ 3 < 2. The basicity of the imido ligands influences the relative rates of reaction with 1,4-cyclohexadiene, specifically by gating access to complex 5, which is the species that is active for HAT. All complexes 2-4 react with benzophenone form metastable Fe(II) intermediates that subsequently eliminate the metathesis product Ph2C═NDipp, with relative rates dependent on the alkali metal ion. By contrast, the same reaction with 5 does not lead to the formation of Ph2C═NDipp. These results demonstrate that the coordination of alkali metal ions dictate both the structure and reactivity of the imido ligand and moreover can direct the reactivity of reaction intermediates.

In vitro biomineralization potential in simulated wound fluid and antibacterial efficacy of biologically-active glass nanoparticles containing B2O3/ZnO

In the present study, SiO2-CaO-B2O3-ZnO (SCBZ), SiO2-CaO-B2O3 (SCB), SiO2-CaO-ZnO (SCZ) and SiO2-CaO (SC) silicate-based glasses were synthesized by the sol-gel method to elucidate the influence of B2O3 and ZnO substitution on glass characteristics aiming to further use in wound healing applications. The amorphous nature, spherical-shaped morphology and nano-sized primary particles of glasses were revealed by XRD and SEM analysis. Moreover, investigating the antibacterial activity of glasses against E.coli and S.aureus bacteria indicated the improved antibacterial properties of SCBZ glass against both bacterial strains compared with SCB and SCZ glasses. Assessment of ion release revealed that the incorporation of zinc induces a more stable glass network with a lower tendency to dissolution contrary to the incorporation of boron, which facilitated the dissolution of glass by the formation of more reactive SiOB and BO bonds. Glasses were immersed in Simulated Wound Fluid (SWF) to predict their mineralization susceptibility. Morphological studies and FTIR analysis showed the formation of cauliflower-like hydroxy-carbonated apatite on the surface of SCB and SC glasses after 14 days. In contrast, the presence of Zn in SCBZ and SCZ glasses inhibited the formation of crystalline apatite and induced the deposition of spherical-shaped amorphous apatite. Our study suggests that the co-incorporation of B and Zn in SCBZ glass make this material a potential multifunctional candidate for accelerating the healing of skin wounds.

A crossed molecular beams and computational study on the unusual reactivity of banana bonds of cyclopropane (c-C3H6; ) through insertion by ground state carbon atoms (C(3Pj)).

The mechanism and chemical dynamics of the reaction of ground electronic state atomic carbon C(3Pj) with cyclopropane c-C3H6 have been explored by combining crossed molecular beams experiments with electronic structure calculations of the pertinent triplet C4H6 potential energy surface and statistical computations of product branching ratios under single-collision conditions. The experimental findings suggest that the reaction proceeds via indirect scattering dynamics through triplet C4H6 reaction intermediate(s) leading to C4H5 product(s) plus atomic hydrogen via a tight exit transition state, with the overall reaction exoergicity evaluated as 231 ± 52 kJ mol-1. The calculations indicate that C(3Pj) can easily insert into one of the three equivalent C-C 'banana' bonds of cyclopropane overcoming a low barrier of only 2 kJ mol-1 following the formation of a van der Waals reactant complex stabilized by 15 kJ mol-1. The carbon atom insertion into one of the six C-H bonds is also feasible via a slightly higher barrier of 5 kJ mol-1. These results highlight an unusual reactivity of cyclopropane's banana C-C bonds, which behave more like unsaturated C-C bonds with a π-character than saturated σ C-C bonds, which are known to be generally unreactive toward the ground electronic state atomic carbon such as in ethane (C2H6). The statistical theory predicts the overall product branching ratios at the experimental collision energy as 50% for 1-butyn-4-yl, 33% for 1,3-butadien-2-yl, i-C4H5, and 11% for 1,3-butadien-1-yl, n-C4H5, with i-C4H5 (230 kJ mol-1 below the reactants) favored by the C-C insertion providing the best match with the experimentally observed reaction exoergicity. The C(3Pj) + c-C3H6 reaction is predicted to be a source of C4H5 radicals under the conditions where its low entrance barriers can be overcome, such as in planetary atmospheres or in circumstellar envelopes but not in cold molecular clouds. Both i- and n-C4H5 can further react with acetylene eventually producing the first aromatic ring and hence, the reaction of the atomic carbon with c-C3H6 can be considered as an initial step toward the formation of benzene.

Rapid synthesis of polyester based single-chain polymeric nanoparticles via an intra-molecular aza-Michael addition reaction

An alternative method to produce single-chain polymeric nanoparticles using the aza-Michael addition reaction of a linear polyester containing in-chain reactive triple bonds is introduced.

Unraveling the reactivity of a cationic iminoborane: avenues to unusual boron cations.

A cationic terminal iminoborane [Mes*N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> B ← IPr2Me2][AlBr4] (3+[AlBr4]−) (Mes* = 2,4,6-tri-tert-butylphenyl and IPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) has been synthesized and characterized. The employment of an aryl group and N-heterocyclic carbene (NHC) ligand enables 3+[AlBr4]− to exhibit both B-centered Lewis acidity and BN multiple bond reactivities, thus allowing for the construction of tri-coordinate boron cations 5+–12+. More importantly, initial reactions involving coordination, addition, and [2 + 3] cycloadditions have been observed for the cationic iminoborane, demonstrating the potential to build numerous organoboron species via several synthetic routes.

Non-toxic 2D Ti[formula omitted]C[formula omitted] MXene surface-modified with Al, Ga, In alkoxides by chemical reactions with metal trialkyls

Understanding the surface chemistry and reactivity of 2D MXenes is of fundamental importance in developing more advanced functional materials. In this work, we describe multilayered Ti3C2 MXene-based materials such as Ti3C2/Al3＋, Ti3C2/In3+ and Ti3C2/Ga3+, obtained by modifying the MXene surface with aluminum-, indium- and gallium alkoxides. In the synthesis of these materials, organometallic compounds of group 13 metals (Et3Al, Me3In, and Et3Ga) were chosen as precursors for the alkoxides to modify the surface. To attach organometallic compounds to the MXene surface, their high reactivity towards the terminal OH, = O and F groups present on the MXene surface was used. In the next step, exposure of the surface-attached aluminum-, indium and gallium alkyls to air allowed their transformation into metal alkoxides due to the high reactivity of the metal-carbon bonds to oxygen and water. In our method of MXene modification, the alkoxide precursors can be extended to other organometallic compounds, such as groups 1, 2 and 12 alkyls. Microbiological studies of the developed 2D Ti3C2/Al3＋, Ti3C2/In3+ and Ti3C2/Ga3+ alkoxides showed no acute ecotoxicity to the tested microorganisms. The obtained materials did not influence bioluminescent/biosensor-type microorganisms nor reduce the viability of other types of microorganisms, such as Staphylococcus aureus, Escherichia coli or Candida albicans. The obtained results clearly indicate that the surface modification of 2D Ti3C2 MXene with group 13 metal compounds is highly prospective toward the development of various types of materials that do not show any adverse effects to living organisms.

Selective chemodosimetric ‘Turn-On’ fluorescence sensor for HSO3−: Comparing the reactivity of the exocyclic vs. non-exocyclic C[dbnd]C double bond

The present report deals with specific colorimetric (naked-eye) and fluorometric sensing of HSO3− by a pair of chemodosimetric probes, namely L1 and L2. The D-π-A structure-based probes exhibited an outstanding HSO3−-dependent response with excellent selectivity and lower detection limit values. The probes were designed to verify the reactivity of exo-cyclic vs. non-exocyclic CC bonds towards reaction-based sensing. It was proven that only activated exo-cyclic CC double bonds were responsible for selective sensing. We also reported the utility of probe-coated paper-strip analysis withL1for rapid detection of HSO3− in the experimental medium. Also, the ability to detect HSO3− in real food sample as well as in river water, lake water, and tap water were also checked by L1.

Catalytic Fields as a Tool to Analyze Enzyme Reaction Mechanism Variants and Reaction Steps.

Catalytic fields representing the topology of the optimal molecular environment charge distribution that reduces the activation barrier have been used to examine alternative reaction variants and to determine the role of conserved catalytic residues for two consecutive reactions catalyzed by the same enzyme. Until now, most experimental and conventional top-down theoretical studies employing QM/MM or ONIOM methods have focused on the role of enzyme electric fields acting on broken bonds of reactants. In contrast, our bottom-up approach dealing with a small reactant and transition-state model allows the analysis of the opposite effects: how the catalytic field resulting from the charge redistribution during the enzyme reaction acts on conserved amino acid residues and contributes to the reduction of the activation barrier. This approach has been applied to the family of histidyl tRNA synthetases involved in the translation of the genetic code into the protein amino acid sequence. Activation energy changes related to conserved charged amino acid residues for 12 histidyl tRNA synthetases from different biological species allowed to compare on equal footing the catalytic residues involved in ATP aminoacylation and tRNA charging reactions and to analyze different reaction mechanisms proposed in the literature. A scan of the library of atomic multipoles for amino acid side-chain rotamers within the catalytic field pointed out the change in the Glu83 conformation as the critical catalytic effect, providing, at low computational cost, insight into the electrostatic preorganization of the enzyme catalytic site at a level of detail that has not yet been accessible in conventional experimental or theoretical methods. This opens the way for rational reverse biocatalyst design at a very limited computational cost without resorting to empirical methods.