Revisiting salicylidene-based anion receptors

Several salicylidene-based colorimetric and fluorimetric anion sensors are known in the literature. However, our ¹H-NMR experimental results (in DMSO-d₆) showed hydrolysis of imine (–N CH–) bonds in salicylidene-based receptors (SL, CL1 and CL2) in the presence of quaternary ammonium salts (n-Bu₄N⁺) of halides (Cl⁻ and Br⁻) and oxo-anions (H₂PO₄⁻, HSO₄⁻ and CH₃COO⁻). The mono-salicylidene compound CL1 showed the most extensive –N CH– bond hydrolysis in the presence of anions. In contrast, the di-salicylidene compound CL2 and the tris-salicylidene compound SL showed comparatively slow hydrolysis of –N CH– bonds in the presence of anions. Anion-induced imine bond cleavage in salicylidene compounds could easily be detected in ¹H-NMR due to the appearance of the salicylaldehyde –CHO peak at 10.3 ppm which eventually became more intense over time, and the –N CH– peak at 8.9–9.0 ppm became considerably weaker. Furthermore, the formation of the salicylidene O–H⋯X⁻ (X⁻ = Cl⁻/Br⁻) hydrogen-bonded complex, peak broadening due to proton-exchange processes and keto–enol tautomerism have also been clearly observed in the ¹H-NMR experiments. Control ¹H-NMR experiments revealed that the presence of moisture in the organic solvents could result in gradual hydrolysis of the salicylidene compounds, and the rate of hydrolysis has further been enhanced significantly in the presence of an anion. Based on ¹H-NMR results, we have proposed a general mechanism for the anion-induced hydrolysis of imine bonds in salicylidene-based receptors.

Salicylidene Schiff bases undergo imine bond hydrolysis in the presence of halides and oxo-anions in aprotic media, raising fundamental questions on the applicability of salicylidene-based receptors as anion sensors.     

Theoretical screening of bistriazole-derived energetic salts with high energetic properties and low sensitivity

We designed four series of energetic anions by replacing nitro group (NO₂) with trinitromethyl group (C(NO₂)₃) or by inserting N-bridging groups (–NH–, –NH–NH–, –N N–, –N N(O)–) into the bistriazole frameworks. The properties of 40 energetic salts, based on the bistriazole-derived anions and hydroxylammonium cation, were studied by density functional theory (DFT) and volume-based thermodynamics calculations (VBT). It is found that the newly designed energetic salts have good detonation properties due to their larger nitrogen content and better oxygen balance. And one of their corresponding hydroxylammonium salts exhibits better detonation performance (D = 10.06 km s⁻¹ and P = 48.58 GPa) than CL-20 (D = 9.54 km s⁻¹ and P = 43.36 GPa). Moreover, 10 energetic salts not only exhibit excellent energetic properties superior to CL-20, but also have lower sensitivity than CL-20 (h₅₀ = 13.81 cm). In addition, we rationally selected salt B6 from the 10 salts to predict its crystal structure under pressures. By converting energetic molecules with excellent detonation properties into energetic ions, some highly bistriazole-derived energetic salts with both excellent performance and low sensitivity could be developed strategically.

We designed four series of energetic anions by replacing nitro group (NO₂) with trinitromethyl group (C(NO₂)₃) or by inserting N-bridging groups (–NH–, –NH–NH–, –N N–, –N N(O)–) into the bistriazole frameworks.     

Correction: Mid-infrared spectroscopy and microscopy of subcellular structures in eukaryotic cells with atomic force microscopy – infrared spectroscopy

Correction for ‘Mid-infrared spectroscopy and microscopy of subcellular structures in eukaryotic cells with atomic force microscopy – infrared spectroscopy’ by Luca Quaroni et al., RSC Adv., 2018, 8, 2786–2794.

In the article the assignment of two IR absorption bands, at 3010 and at 3070 cm⁻¹ has been confused by us in the text, resulting in two incorrect statements. The misstatement does not change any of the conclusions of the work, and can be corrected by restating the following sentences.The following sentence (p. 2790, column 1, line 10):A weak but sharp band can be seen at 3010 cm⁻¹, corresponding to the stretching mode of C–H bonds on unsaturated C C bonds in acyl chains.must be corrected to:A weak but sharp band can be seen at 3010 cm⁻¹, corresponding to the stretching mode of C–H₃ bonds on choline headgroups.In addition, the following sentence (p. 2792, column 1, line 25):Observation of a sharp band at 3010 cm⁻¹ indicates that at least part of the acyl chains have unsaturated C C bonds.must be changed to:Observation of a band at 3070 cm⁻¹, corresponding to the stretching mode of C–H bonds on unsaturated C C bonds in acyl chains, indicates that at least part of the acyl chains have unsaturated C C bonds.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Insights into the nucleophilic substitution of pyridine at an unsaturated carbon center

Bimolecular nucleophilic substitution (S_N2) is a fundamental reaction that has been widely studied. So far, the nucleophiles are mainly anionic species in S_N2 reactions. In this study, we use density functional theory calculations to assess the mechanisms of substitution of carbonyl, imidoyl, and vinyl compounds with a neutral nucleophile, pyridine. Charge decomposition analysis is performed to explore the main components of the transition state''s LUMO. For reactions of imidoyl or carbonyl compounds with pyridine or Cl⁻, the LUMOs of the transition states are composed of mixed orbitals originating from the nucleophile and the substrate. Considering the unique mixed nature of the orbitals, the reaction mode is termed S_Nm (m means mix). Moreover, the main components of the transition state''s LUMO are pure σ*_C–Cl MO in the reactions of H₂C CHCl with pyridine or Cl⁻. Computations were also performed for RY CHX substrates with different X and Y groups (X= Cl⁻, Br⁻, or F⁻; Y = O, N, or C).

The nucleophilic substitution of carbonyl, imidoyl, and vinyl carbon centers with pyridine or halides is investigated in this paper.     

A theoretical study of the hydrolysis mechanism of A-234; the suspected novichok agent in the Skripal attack

A-234, [EtO–P( O)(F)–N C(Me)–N(Et)₂], is the suspected A-type nerve agent used in the Skripal attack on the 4th of March 2018. Studies related to the structure and reactivity of this compound are limited. We, therefore, aimed at understanding the underlying hydrolysis mechanism of A-234 within the DFT framework. The attack of the water molecule can occur at the phosphinate and acetoamidine reactive centres. Our theoretical findings indicate that the hydrolysis at the acetoamidine centre is thermodynamically favoured compared to the hydrolysis at the phosphinate centre. The hydrolysis at the acetoamidine moiety may proceed via two pathways, depending on the nitrogen atom participating in the hydrolysis. The main pathway consists of four distinct channels to reach the final product, with the concerted 1,3-proton shift favoured kinetically and thermodynamically in the gas phase and water as solvent. The results are in good agreement with the literature, although some differences in the reaction mechanism were observed.

A theoretical study of the hydrolysis mechanism of A-234 [EtO–P( O)(F)–N C(Me)–N(Et)₂]; the suspected novichok agent in the Skripal attack.     

The enhanced reduction of bromate by highly reactive and dispersive green nano-zerovalent iron (G-NZVI) synthesized with onion peel extract

In this study, novel green nano-zerovalent iron (G-NZVI) is synthesized for the first time using onion peel extract for the prevention of rapid surface oxidation and the enhancement of particle dispersibility with a high reductive capacity. The results from various surface analyses revealed that the spherical shape of G-NZVI was fully covered by the onion peel extract composed of polyphenolic compounds with C C–C C unsaturated carbon, C C, C–O, and O–H bonds, resulting in high mobility during column chromatography. Furthermore, the obtained G-NZVI showed the complete removal of 50 mg L⁻¹ of bromate (BrO₃⁻) in 2 min under both aerobic (k = 4.42 min⁻¹) and anaerobic conditions (k = 4.50 min⁻¹), showing that G-NZVI had outstanding oxidation resistance compared to that of bare NZVI. Moreover, the observed performance of G-NZVI showed that it was much more reactive than other well-known reductants (e.g., Fe and Co metal organic frameworks), regardless of whether aerobic or anaerobic conditions were used. The effects of G-NZVI loading, the BrO₃⁻ concentration, and pH on the BrO₃⁻ removal kinetics using G-NZVI were also investigated in this study. The results provide the novel insight that organic onion peel waste can be reused to synthesize highly reactive anti-oxidative nanoparticles for the treatment of inorganic chemical species and heavy metals in water and wastewater.

In this study, novel green nano-zerovalent iron (G-NZVI) is synthesized for the first time using onion peel extract for the prevention of rapid surface oxidation and the enhancement of particle dispersibility with a high reductive capacity.     

tBuOK-triggered bond formation reactions

Recently, inexpensive and readily available tBuOK has seen widespread use in transition-metal-free reactions. Herein, we report the use of tBuOK for S–S, S–Se, N N and C N bond formations, which significantly extends the scope of tBuOK in chemical synthesis. Compared with traditional methods, we have realized mild and general methods for disulfide, azobenzenes imine etc. synthesis.

Inexpensive and readily available ^tBuOK can trigger a series of bond formation reactions, including S–S, S–Se, Se–Se, and N N and C N bonds.     

Probing the supramolecular features via π–π interaction of a di-iminopyrene-di-benzo-18-crown-6-ether compound: experimental and theoretical study

A novel DPyDB-C N-18C6 compound was synthesised by linking a pyrene moiety to each phenyl group of dibenzo-18-crown-6-ether, the crown ether, through –HC N– bonds and characterized by FTIR, ¹H-NMR, ¹³C-NMR, TGA, and DSC techniques. The quantitative ¹³C-NMR analysis revealed the presence of two position isomers. The electronic structure of the DPyDB-C N-18C6 molecule was characterized by UV-vis and fluorescence spectroscopies in four solvents with different polarities to observe particular behavior of isomers, as well as to demonstrate a possible non-bonding chemical association (such as ground- and excited-state associations, namely, to probe if there were forming dimers/excimers). The interpretation of the electronic structure was realized through QM calculations. The TD-CAM-B3LYP functional, at the 6-311+G(d,p) basis set, indicated the presence of predominant π → π* and mixed π → π* + n → π* transitions, in line with the UV-vis experimental data. Even though DPyDB-C N-18C6 computational studies revealed a π-extended conjugation effect with predominantly π → π* transitions, thorough fluorescence analysis was observed a weak emission, as an effect of PET and ACQ. In particular, the WAXD analysis of powder and thin films obtained from n-hexane, 1,2-dichloroethane, and ethanol indicated an amorphous organization, whereas from toluene a smectic ordering was obtained. These results were correlated with MD simulation, and it was observed that the molecular geometry of DPyDB-C N-18C6 molecule played a defining role in the pyrene stacking arrangement.

Herein, we report the formation of a potential supramolecular arrangement mediated by inter- and intra-molecular interactions between di-iminopyrene-dibenzo-18-crown-6-ether molecules.     

Formation of bicyclic polycyclic aromatic hydrocarbons (PAHs) from the reaction of a phenyl radical with cis-3-penten-1-yne

The formation of polycyclic aromatic hydrocarbons (PAHs) on the C₁₁H₁₁ potential energy surface involved in the reactions of a phenyl radical (C₆H₅) with cis-3-penten-1-yne (cis-C¹H C²–C³H C⁴H–C⁵H₃, referred to as C₅H₆) and its three radicals (CH C–Ċ CH–CH₃, CH C–CH Ċ–CH₃, and cis-CH C–CH CH–ĊH₂, referred to as the C³-, C⁴-, and C⁵-radicals with the same chemical components, C₅H₅) assisted by H atoms is investigated by performing combined density functional theory (DFT) and ab initio calculations. Five potential pathways for the formation of PAHs have been explored in detail: Pathways I–II correspond to the reaction of C₆H₅ with C₅H₆ at the C¹ and C² position, and Pathways III–V involve the reaction of C₆H₅ with the C³-, C⁴-, and C⁵-radicals with the assistance of H atoms. The initial association of C₆H₅ with C₅H₆ or C₅H₅ is found to be highly exothermic with only minor barriers (1.4–7.1 kcal mol⁻¹), which provides a large driving force for the formation of PAHs. The hydrogen atom is beneficial for the ring enlargement and ring formation processes. The present calculations predict 9 potential PAHs, six (CS6, CS10, CS13, CS26, CS28 and CS29) of which are indicated to be energetically more favorable along Pathways I, III, IV and V at low temperature. The calculated barriers for the formation of these PAHs are around 19.2–38.0 kcal mol⁻¹. All PAHs products could be formed at flame temperature, for the medium barriers are easily overcome in various flame conditions. The theoretical results supplement the PAH formation pathway and provide help to understand PAH growth mechanism.

The formation of PAHs within 4-, 5-, 6- and 7-membered rings on the C₆H₅ + C₅H₆ potential energy surface.     

Insights into the promotion role of phosphorus doping on carbon as a metal-free catalyst for low-temperature selective catalytic reduction of NO with NH3

The catalytic reduction of NO with NH₃ (NH₃-SCR) on phosphorus-doped carbon aerogels (P-CAs) was studied in the temperature range of 100–200 °C. The P-CAs were prepared by a one-pot sol–gel method by using phosphoric acid as a phosphorus source followed by carbonization at 600–900 °C. A correlation between catalytic activity and surface P content is observed. The P-CA-800_vac sample obtained via carbonization at 800 °C and vacuum treatment at 380 °C shows the highest NO conversion of 45.6–76.8% at 100–200 °C under a gas hourly space velocity of 500 h⁻¹ for the inlet gas mixture of 500 ppm NO, 500 ppm NH₃ and 5.0 vol% O₂. The coexistence of NH₃ and O₂ is essential for the high conversion of NO on the P-CA carbon catalysts, which can decrease the spillover of NO₂ and N₂O. The main Brønsted acid sites derived from P-doping and contributed by the C–OH group at edges of carbon sheets are beneficial for NH₃ adsorption. In addition, the C₃–P O configuration seems to have the most active sites for favorable adsorption and dissociation of O₂ and facilitates the formation of NO₂. Therefore, the simultaneous presence of acidic groups for NH₃ adsorption and the C₃–P O active sites for NO₂ generation due to the activation of O₂ molecules is likely responsible for the significant increase in the NH₃-SCR activity over the P–CAs. The transformation of C₃–P O to C–O–P functional groups after the reaction is found, which could be assigned to the oxidation of C₃–P O by the dissociated O*, resulting in an apparent decrease of catalytic activity for P-CAs. The C–O–P based functional groups are also active in the NH₃-SCR reaction.

P species can effectively enhance the catalytic activity of carbon aerogels for NO reduction at low temperature.     

Nitrogen–phosphorus doped graphitic nano onion-like structures: experimental and theoretical studies

Onion-like graphitic structures are of great importance in different fields. Pentagons, heptagons, and octagons are essential features of onion-like graphitic structures that could generate important properties for diverse applications such as anodes in Li metal batteries or the oxygen reduction reaction. These carbon nanomaterials are fullerenes organized in a nested fashion. In this work, we produced graphitic nano onion-like structures containing phosphorus and nitrogen (NP-GNOs), using the aerosol assisted chemical vapor deposition method. The NP-GNOs were grown at high temperature (1020 °C) using ferrocene, trioctylphosphine oxide, benzylamine, and tetrahydrofuran precursors. The morphology, structure, composition, and surface chemistry of NP-GNOs were characterized using different techniques. The NP-GNOs showed diameters of 110–780 nm with Fe-based nanoparticles inside. Thermogravimetric analysis showed that NP-GNOs are thermally stable with an oxidation temperature of 724 °C. The surface chemistry analysis by FTIR and XPS revealed phosphorus–nitrogen codoping, and several functionalities containing C–H, N–H, P–H, P–O, P O, C O, and C–O bonds. We show density functional theory calculations of phosphorus–nitrogen doping and functionalized C₂₄₀ fullerenes. We present the optimized structures, electronic density of states, HOMO, and LUMO wave functions for P-doped and OH-functionalized fullerenes. The P O and P–O bonds attributed to phosphates or hydroxyl groups attached to phosphorus atoms doping the NP-GNOs could be useful in improving supercapacitor function.

Nitrogen–phosphorus doped graphitic nano onion-like structures.     

Influence of flaxseed flour as a partial replacement for wheat flour on the characteristics of Chinese steamed bread

This study investigated the effects of partially replacing wheat flour with flaxseed flour (FF) on the quality parameters of Chinese Steamed Bread (CSB). FF was utilized as a functional ingredient of CSB at varying levels. The pasting properties of flour blends, the rheological and microstructural characteristics of dough, the textural and quality characteristics and functional group structure of CSB were analyzed. Results showed that FF addition influenced the pasting characteristics of wheat flour by decreasing the final viscosity, breakdown and setback values, but had little effect on the rheological properties of the dough. The microstructure of the dough indicated that the disruption degree of the gluten matrix increased with the increase of FF. Besides, FF addition increased the hardness and chewiness of CSB, while decreasing the cohesiveness and springiness. Additional characteristic peaks were observed at 1745, 2854, and 3006 cm⁻¹ and associated with –C O, –CH₂, and cis-C CH bond stretching vibrations of flaxseed. Results suggested 12% FF exhibited the best acceptability.

Chinese steamed bread supplemented with flaxseed flour can be recommended as a dietary product with health benefits.     

A sorbent containing pH-responsive chelating residues of aspartic and maleic acids for mitigation of toxic metal ions,cationic, and anionic dyes

t-Butyl hydroperoxide-initiated cycloterpolymerization of diallylaminoaspartic acid hydrochloride [(CH₂ CHCH₂)₂NH⁺CH(CO₂H)CH₂CO₂H Cl⁻] (I), maleic acid (HO₂CH CHCO₂H) (II) and cross-linker tetraallylhexane-1,6-diamine dihydrochloride [(CH₂ CHCH₂)₂NH⁺(CH₂)₆NH⁺ (CH₂CH CH₂)₂ 2Cl⁻] (III) afforded a new pH-responsive resin (IV), loaded with four CO₂H and a chelating motif of NH⁺⋯CO₂⁻ in each repeating unit. The removal of cationic methylene blue (MB) (3000 ppm) at pH 7.25 and Pb(ii) (200 ppm) at pH 6 by IV at 298, 313, and 328 K followed second-order kinetics with E_a of 33.4 and 40.7 kJ mol⁻¹, respectively. Both MB and Pb(ii) were removed fast, accounting for 97.7% removal of MB within 15 min at 313 K and 94% of Pb(ii) removal within 1 min. The super-adsorbent resin gave respective q_max values of 2609 mg g⁻¹ and 873 mg g⁻¹ for MB and Pb(ii). IV was also found to trap anionic dyes; it removed 91% Eriochrome Black T (EBT) from its 50 ppm solutions at pH 2. The resin was found to be effective in reducing priority metal contaminants (like Cr, Hg, Pb) in industrial wastewater to sub-ppb levels. The synthesis of the recyclable resin can be easily scaled up from inexpensive starting materials. The resin has been found to be better than many recently reported sorbents.

Cycloterpolymerization of diallylaminoaspartic acid hydrochloride (I), maleic acid (II) and a cross-linker (III) afforded a new pH-responsive resin (IV), loaded with four CO₂H and a chelating motif of NH⁺⋯CO₂⁻ in each repeating unit.     

Reactions of triosmium and triruthenium clusters with 2-ethynylpyridine: new modes for alkyne C–C bond coupling and C–H bond activation

The reaction of the trimetallic clusters [H₂Os₃(CO)₁₀] and [Ru₃(CO)₁₀L₂] (L = CO, MeCN) with 2-ethynylpyridine has been investigated. Treatment of [H₂Os₃(CO)₁₀] with excess 2-ethynylpyridine affords [HOs₃(CO)₁₀(μ-C₅H₄NCH=CH)] (1), [HOs₃(CO)₉(μ₃-C₅H₄NC CH₂)] (2), [HOs₃(CO)₉(μ₃-C₅H₄NC CCO₂)] (3), and [HOs₃(CO)₁₀(μ-CH CHC₅H₄N)] (4) formed through either the direct addition of the Os–H bond across the C C bond or acetylenic C–H bond activation of the 2-ethynylpyridine substrate. In contrast, the dominant pathway for the reaction between [Ru₃(CO)₁₂] and 2-ethynylpyridine is C–C bond coupling of the alkyne moiety to furnish the triruthenium clusters [Ru₃(CO)₇(μ-CO){μ₃-C₅H₄NC CHC(C₅H₄N) CH}] (5) and [Ru₃(CO)₇(μ-CO){μ₃-C₅H₄NCCHC(C₅H₄N)CHCHC(C₅H₄N)}] (6). Cluster 5 contains a metalated 2-pyridyl-substituted diene while 6 exhibits a metalated 2-pyridyl-substituted triene moiety. The functionalized pyridyl ligands in 5 and 6 derive via the formal C–C bond coupling of two and three 2-ethynylpyridine molecules, respectively, and 5 and 6 provide evidence for facile alkyne insertion at ruthenium clusters. The solid-state structures of 1–3, 5, and 6 have been determined by single-crystal X-ray diffraction analyses, and the bonding in the product clusters has been investigated by DFT. In the case of 1, the computational results reveal a rare thermodynamic preference for a terminal hydride ligand as opposed to a hydride-bridged Os–Os bond (3c,2e Os–Os–H bond).

The reactivity of 2-ethynylpyridine at low-valent triosmium and triruthenium centers has been investigated.     

FTIR product study of the Cl-initiated oxidation products of CFC replacements: (E/Z)-1,2,3,3,3-pentafluoropropene and hexafluoroisobutylene

A product study of the reactions of (E/Z)-1,2,3,3,3-pentafluoropropene ((E/Z)-CF₃CF CHF) and hexafluoroisobutylene ((CF₃)₂C CH₂) initiated by Cl atoms were developed at 298 ± 2 K and atmospheric pressure. The experiments were carried out in a 1080 L quartz-glass environmental chamber coupled via in situ FTIR spectroscopy to monitor the reactants and products. The main products observed and their yields were as follows: CF₃C(O)F (106 ± 9)% with HC(O)F (100 ± 8)% as a co-product for (E/Z)-CF₃CF CHF, and CF₃C(O)CF₃ (94 ± 5)% with HC(O)Cl (90 ± 7)% as a co-product for (CF₃)₂C CH₂. Atmospheric implications of the end-product degradation are assessed in terms of their impact on ecosystems to help environmental policymakers consider HFOs as acceptable replacements.

An experimental product distribution study and the atmospheric implications of the reactions of Cl with two fluorinated alkenes is provided.     

Boron-doped graphene as a metal-free catalyst for gas-phase oxidation of benzyl alcohol to benzaldehyde

Boron-doped graphene samples (BGs) with tunable boron content of 0–2.90 at% were synthesized and directly used in the gas-phase oxidation of benzyl alcohol to benzaldehyde, and showed excellent performance. XPS results indicated that the graphitic sp² B species (BC₃) is the mainly boron dopant species incorporated in the graphene lattice, which could significantly improve the content of ketone carbonyl groups (C O) on the graphene. For instance, the contents of C O jumped from 1.93 to 4.19 at% while BC₃ doped into the graphene lattice was only 0.35 at%. The C O is the active site of catalytic reaction, so BG has significantly improved catalytic activity. Compared to the un-doped graphene (G), the conversion of benzyl alcohol over BGs increased 2.35 times and the selectivity of benzaldehyde increased from 77.3% to 99.2%. Aerobic–anaerobic exchange experiments revealed that the superior catalytic performance of BG was achieved only under aerobic conditions. The study of the boron-doped carbocatalyst may also provide guidance for the design of surface modified carbon-based catalysts for the selective oxidation dehydrogenation of alcohols by regulating doping elements and their types.

Boron doped graphene for the oxidative dehydrogenation reactions.     

Spectral evidence for generic charge → acceptor interactions in carbamates and esters

The correlations of the ¹H NMR, ¹³C NMR and FT-IR spectral data from the R–O–C O groups in the alkyl carbamates and esters of homologous alcohols reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and their donation to generic acceptors at C^α of even alkyl alcohols (R), which explains several of their apparently anomalous properties.

NMR, FT-IR spectral correlations of the R–O–C O groups in carbamates and esters of homologous alcohols (R) reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and its donation to generic acceptors at Cα of even alkyl R.

Electronic interactions at the R–O–C O groups in carbamates and esters are less understood than that at the R–N–C O groups in amides. Carbamates in which both these groups are fused at the carbonyl C O bond, have several ester-like rather than amide-like features^1,2 including comparable C–O bond lengths in crystals,^3–6 favourable interactions between the dipoles of the C O and O–R bonds in the predominant s-trans rotamers of the R–O–C O groups and unfavourable lone pair repulsion between the two ester oxygens in their trace s-cis rotamers^7–10 (Fig. 1a). However, several anomalous properties of carbamates and esters cannot be explained by these dipole and repulsive forces alone. For example, despite the electronic resonance at the O–C O group in esters and additionally at the N–C O group in carbamates (both of which augment the electron density at their carbonyl oxygens), their carbonyls have remarkably lower basicities than the carbonyls of amides¹¹ and even those of ketones, which lack such resonance effects.¹² The barriers to the C–N bond rotation for carbamates are 3–4 kcal mol⁻¹ lower than those for analogous amides.^13,14 Carbamate and ester carbonyl oxygens also have poor hydrogen bond accepting propensities compared to amides.^15–20Open in a separate windowFig. 1(a) Dipole–dipole, electronic and steric interactions governing the rotamer stabilities at R–O–C O frameworks in carbamates and esters; (b) earlier report of n → π* O⋯C^α interaction in phenyl carbamates; (c) current finding of generic donor → acceptor interactions: (i) charge → HCR* (ii) charge → σ*; (d) list of carbamates (1–8), esters (9–16) and alcohols (17–20) investigated. HCR is hyperconjugative resonance along the C^α–C^β bond of alcohol groups in carbamates and esters.Of particular current interest is the apparent anomaly that in the crystals of phenyl carbamates, the phenyl ring plane is oriented perpendicular to the carbamate plane^21,22 (Fig. 1b). The presence of an extraordinary n → π* orbital overlap interaction (O⋯C^α_phenyl) between the lone-pair electrons on the carbonyl (C O) oxygen and the π* orbital of the phenyl ring has been proposed as the stabilizing force for this conformer based on natural bond orbital (NBO) analysis.²² This is interesting for several reasons: (i) despite a decrease in the stretching frequency of C O in the FT-IR spectrum for this conformer, which indicates a decrease in the bond order and concomitant improvement in the charge density at the carbonyl oxygen, a discussion on the origin and role of such charge on this O⋯C^α_alcohol interaction is lacking. Rather, the interaction is assumed to originate from the lone pair on oxygen. (ii) Our investigation of CCDC revealed that the O⋯C^α_alcohol distances at the C^α–O–C O groups are quite non-variant (2.62–2.81 Å) for both aliphatic and aromatic carbamates and esters,^{3–6,23–27} notwithstanding the variations in the structure resolutions. These invoked the following questions: is the O⋯C^α interaction specific to the π* acceptors at C^α_alcohol? Can any antibonding orbital at C^α_alcohol act as an acceptor of the electrons from carbonyl oxygen? What is the generic nature and role of this O⋯C^α interaction in the C^α–O–C O groups? Here, we present the first spectral evidence for the generic nature of the O⋯C^α interactions even with non-π* orbital acceptors (like σ* and hyperconjugative resonance bonds) at C^α in the C^α–O–C O groups (Fig. 1c) of a variety of model homologous aliphatic carbamates and esters (Fig. 1d). The charge at the carbonyl oxygen is interdependent on the alkoxy groups and forms charge → acceptor O⋯C^α interactions, which influence the rotational states of the O–C^α bonds in the carbamates and esters.To explore the possibility of the O⋯C^α interactions at C^α–O–C O in aliphatic carbamates and esters, we investigated the ¹H NMR, ¹³C NMR and FT-IR spectra of the secondary and tertiary carbamates (1–4 and 5–8), acetates (9–12) and benzoates (13–16) of homologous aliphatic alcohols (H–C^αH₂–OH, MeOH; CH₃–C^αH₂–OH, ethanol; (CH₃)₂–C^αH–OH, isopropanol; and (CH₃)₃–C^α–OH, tert-butanol, 17–20) (

The effects of green waste compost on soil N,P, K,and organic matter fractions in forestry soils: elemental analysis evaluation

We study the effects of green waste compost on soil fertility to provide a theoretical basis for accurately improving forestry soil quality. This study aims to investigate the effects of green waste compost on soil N, P, K, and soil organic matter (SOM) fractions using elemental and FTIR analyses. Therefore, five fertilization treatments were set up for research, including mineral fertilization (M-fert), green waste compost fertilization (G-fert), standard rate of M-fert plus G-fert (GM-fert), half the standard rate of M-fert plus G-fert (1/2 GM-fert), and a control with no fertilizer addition (N-fert). The results showed that GM-fert treatment significantly increased the content of soil NH₄–N, available phosphorus (AP), available potassium (AK), water soluble organic carbon (WSOC), humus (HE), and humic acid (HA), which were 8.53 ± 0.67, 76.1 ± 5.96, 168 ± 3.42, 0.152 ± 0.01, 5.64 ± 0.15, and 4.69 ± 0.21 mg kg⁻¹, respectively. The content of HA (36.7%, F = 7.55, P = 0.01) was positively correlated with the soil N, P, K, and the HA absorption peak. The relative intensities of the alcohol –OH, aliphatic –CH and carbohydrate C–O peaks showed the largest changes, which were 18.6 ± 0.56%, 13.1 ± 0.33%, and 16.3 ± 0.49%. –CH/C C (49.8%, F = 12.9, P < 0.01) was also significantly positively correlated with soil N, P, K. In conclusion, green waste compost significantly increased soil N, P, K, and HA in forestry soils, and the –CH/C C of HA was the main factor related to soil nutrients.

Green waste compost significantly increased soil N, P, K, and HE fractions, and the –CH/C C components of the HA structures made the biggest contribution to soil N, P, K in forestry soil.     

A mechanism of surface hardness enhancement for H+ irradiated polycarbonate

H⁺ irradiation increases the surface hardness of polycarbonate. Nano indentation measurement shows that the hardness increases up to 3.7 GPa at the dose of 5 × 10¹⁶ # cm⁻² and at the irradiation energy of 150 keV. In addition, the hardness increases with the dose and the energy of H⁺ irradiation. In accordance with the nano indentation measurement, the Fourier-transform infrared spectroscopy (FTIR) depends on the dose and energy of H⁺ irradiation. The peak at ∼1500 cm⁻¹ for the aromatic ring and the peak at ∼1770 cm⁻¹ for the C O stretch decrease with increasing dose and energy, while the increase of the dose and energy develops a new C O stretch vibration at ∼1700 cm⁻¹ and forms aromatic hydrocarbons at ∼1600 cm⁻¹. X-ray diffraction experiments are also consistent with the nano indentation measurement and FTIR spectra. Based on the experiments, we discuss a possible mechanism of the surface hardness enhancements by ion beam irradiation.

H⁺ irradiation increases the surface hardness of polycarbonate.     

Functionalization of MOF-5 with mono-substituents: effects on drug delivery behavior

Metal organic frameworks (MOFs) are widely used in drug carrier research due to their tunability. The properties of MOFs can be adjusted through incorporation of mono-substituents to obtain pharmaceutical carriers with excellent properties. In this study, different functional groups of –NH₂, –CH₃, –Br, –OH and –CH₂ CH are connected to MOF-5 to analyse the effect of mono-substituent incorporation on drug delivery properties. The resulting MOFs have similar structures, except for Br–MOF. The pore size of this series of MOFs ranges from 1.04 nm to 1.10 nm. Using oridonin (ORI) as a model drug, introduction of the functional groups appears to have a significant effect on the drug delivery performance of the MOFs. The IRMOFs can be ranked according to drug-loading capacity: MOF-5 > HO–MOF-5 > H₃C–MOF-5 = Br–MOF-5 > H₂N–MOF-5 > CH₂ CH–MOF-5. The ORI release from ORI @IRMOFs is explored at two different pH values: 7.4 and 5.5, and the ORI@IRMOFs are ranked according to the cumulative release percentage of ORI: ORI@MOF-5 > ORI@Br–MOF-5 > ORI@H₃C–MOF-5 > ORI@H₂N–MOF-5 > CH₂ CH–MOF-5 > ORI@ HO–MOF-5. In particular, the release behaviour of ORI@MOFs is described through a new model. The different drug delivery performance of MOFs may be due to the complex interactions between MOFs and ORI. In addition, the introduction of single substituents does not change the biocompatibility of MOFs. MTT in vitro experiments prove that this series of MOFs has low cytotoxicity. This study shows that the incorporation of single substituents can effectively adjust the drug delivery behaviour of MOFs, which is conducive to realization of personalized drug delivery modes. The introduction of active groups can also facilitate post-synthesis modification to achieve coupling of targeting groups. MOFs incorporated with single substituents perform favorably in terms of use as biomedical drug delivery alternative carriers in effective drug payload and flexible drug release.

Metal organic frameworks (MOFs) are widely used in drug carrier research due to their tunability.