Plastics of the Future? The Impact of Biodegradable Polymers on the Environment and on Society

In recent years the littering of plastics and the problems related to their persistence in the environment have become a major focus in both research and the news. Biodegradable polymers like poly(lactic acid) are seen as a suitable alternative to commodity plastics. However, poly(lactic acid) is basically non‐degradable in seawater. Similarly, the degradation rate of other biodegradable polymers also crucially depends on the environments they end up in, such as soil or marine water, or when used in biomedical devices. In this Minireview, we show that biodegradation tests carried out in artificial environments lack transferability to real conditions and, therefore, highlight the necessity of environmentally authentic and relevant field‐testing conditions. In addition, we focus on ecotoxicological implications of biodegradable polymers. We also consider the social aspects and ask how biodegradable polymers influence consumer behavior and municipal waste management. Taken together, this study is intended as a contribution towards evaluating the potential of biodegradable polymers as alternative materials to commodity plastics.     

New Organic Salt from Levofloxacin-Citric Acid: What Is the Impact on the Stability and Antibiotic Potency?

This research dealt with the composition, structure determination, stability, and antibiotic potency of a novel organic salt composed of levofloxacin (LF) and citric acid (CA), named levofloxacin-citrate (LC). After a stoichiometric proportion screening, the antibiotic-antioxidant reaction was conducted by slow and fast evaporation methods. A series of characterizations using thermal analysis, powder X-ray diffractometry, vibrational spectroscopy, and nuclear magnetic resonance confirmed LC formation. The new organic salt showed a distinct thermogram and diffractogram. Next, Fourier transform infrared indicated the change in N-methylamine and carboxylic stretching, confirmed by ¹H nuclear magnetic resonance spectra to elucidate the 2D structure. Finally, single-crystal diffractometry determined LC as a new salt structure three-dimensionally. The attributive improvements were demonstrated on the stability toward the humidity and lighting of LC compared to LF alone. Moreover, the antibiotic potency of LF against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) enhanced ~1.5–2-fold by LC. Hereafter, LC is a potential salt antibiotic-antioxidant combination for dosage formulas development.     

Hexaazatriphenylene (HAT) versus tri‐HAT: The Bigger the Better?

A new hexaazatriphenylene (HAT) derivative formed by the fusion of three HAT units has been prepared and its electronic and molecular structures have been fully characterized by optical and vibrational Raman spectroscopy, electrochemistry, solid-state UV and inverse photoemission spectroscopy (UPS and IPES), and by quantum-chemical calculations. A comparative HAT versus tri-HAT study was performed. The fusion of three HAT molecules causes modifications in the optical and electrochemical properties consistent with enhanced π-electron delocalization attained in a bigger planar core. Such combined experimental and theoretical studies are useful to balance chemical design with supramolecular engineering directed to find enhanced characteristics for new organic semiconductor applications.     

Is the alignment of nematics on a polymer slab always along the rubbing direction? A molecular dynamics study

ABSTRACT

We have studied the alignment and molecular organisation within a thin film of the popular nematic 5CB sandwiched between two flat polymer slabs, examining the effect of polymer chemical nature and morphology with atomistic molecular dynamics simulations. We have chosen two common polymers: polystyrene (PS) and polymethylmethacrylate (PMMA), either with their chains in random coil conformation (disordered) or with chains unidirectionally stretched (ordered). We found that, independently on the arrangement of the chains, both surfaces align planarly the liquid crystal, in accord with experimental observation. Moreover, while 5CB molecules align along the chains stretching direction of the PMMA ordered surface, on the combed PS surface they arrange on average perpendicularly to the stretching direction. This behaviour is attributed to the chemically specific interactions between the respective aromatic moieties of PS and 5CB.     

Is Phytomelatonin Complex Better Than Synthetic Melatonin? The Assessment of the Antiradical and Anti-Inflammatory Properties

This work aims to assess the recently established anti-inflammatory and antioxidant potential of melatonin of plant origin extracted from the plant matrix as a phytomelatonin complex (PHT-MLT), and compare its activity with synthetic melatonin (SNT-MLT) when used on its own or with vitamin C. For this purpose, a COX-2 enzyme inhibitory activity test, an antiradical activity in vitro and on cell lines assays, was performed on both PHT-MLT and SNT-MLT products. COX-2 inhibitory activity of PHT-MLT was found to be ca. 6.5 times stronger than that of SNT-MLT (43.3% and 6.7% enzyme inhibition, equivalent to the activity of acetylsalicylic acid in conc. 30.3 ± 0.2 and 12.0 ± 0.3 mg/mL, respectively). Higher antiradical potential and COX-2 inhibitory properties of PHT-MLT could be explained by the presence of additional naturally occurring constituents in alfalfa, chlorella, and rice, which were clearly visible on the HPLC-ESI-QTOF-MS fingerprint. The antiradical properties of PHT-MLT determined in the DPPH test (IC₅₀ of 21.6 ± 1 mg of powder/mL) were found to originate from the presence of other metabolites in the 50% EtOH extract while SNT-MLT was found to be inactive under the applied testing conditions. However, the antioxidant studies on HaCaT keratinocytes stimulated with H₂O₂ revealed a noticeable activity in all samples. The presence of PHT-MLT (12.5, 25 and 50 µg/mL) and vitamin C (12.5, 25 and 50 µg/mL) in the H₂O₂-pretreated HaCaT keratinocytes protected the cells from generating reactive oxygen species. This observation confirms that MLT-containing samples affect the intracellular production of enzymes and neutralize the free radicals. Presented results indicated that MLT-containing products in combination with Vitamin C dosage are worth to be considered as a preventive alternative in the therapy of various diseases in the etiopathogenesis, of which radical and inflammatory mechanisms play an important role.     

Impact of the ΔPhe configuration on the Boc-Gly-ΔPhe-NHMe conformation: experiment and theory

Conformational propensities of N-t-butoxycarbonyl-glycine-(E/Z)-dehydrophenylalanine N′-methylamides (Boc-Gly-(E/Z)-ΔPhe-NHMe) in chloroform were investigated by NMR and IR techniques. The low-temperature crystal structure of the E isomer was determined by single crystal X-ray diffraction and the experimental data were elaborated by theoretical calculations using DFT (B3LYP, M06-2X) and MP2 approaches. The β-turn tendencies for both isomers were determined in the gas phase and in the presence of solvent. The obtained results reveal that the configuration of ΔPhe residue significantly affects the conformations of the studied dehydropeptides. The tendency to adopt β-turn conformations is significantly lower for the E isomer (Boc-Gly-(E)-ΔPhe-NHMe), both in gas phase and in chloroform solution.

     

Theoretical Study on the Mechanism of Sonogashira Coupling Reaction

The mechanism of palladium-catalyzed Sonogashira cross-coupling reaction has been studied theoretically by DFT （density functional theory） calculations. The model system studied consists of Pd（PH3）2 as the starting catalyst complex, phenyl bromide as the substrate and acetylene as the terminal alkyne, without regarding to the co-catalyst and base. Mechanistically and energetically plausible catalytic cycles for the cross-coupling have been identified. The DFT analysis shows that the catalytic cycle occurs in three stages： oxidative addition of phenyl bromide to the palladium center, alkynylation of palladium（Ⅱ） intermediate, and reductive elimination to phenylacetylene. In the oxidative addition, the neutral and anionic pathways have been investigated, which could both give rise to cis-configured palladium（Ⅱ） diphosphine intermediate. Starting from the palladium（Ⅱ） diphosphine intermediate, the only identifiable pathway in alkynylation involves the dissociation of Br group and the formation of square-planar palladium（Ⅱ） intermediate, in which the phenyl and alkynyl groups are oriented cis to each other. Due to the close proximity of phenyl and alkynyl groups, the reductive elimination of phenylacetylene proceeds smoothly.     

Impact of Zeolite Framework Composition and Flexibility on Methanol-To-Olefins Selectivity: Confinement or Diffusion?

The methanol-to-olefins reaction catalyzed by small-pore cage-based acid zeolites and zeotypes produces a mixture of short chain olefins, whose selectivity to ethene, propene and butene varies with the cavity architecture and with the framework composition. The product distribution of aluminosilicates and silicoaluminophosphates with the CHA and AEI structures (H-SSZ-13, H-SAPO-34, H-SSZ-39 and H-SAPO-18) has been experimentally determined, and the impact of acidity and framework flexibility on the stability of the key cationic intermediates involved in the mechanism and on the diffusion of the olefin products through the 8r windows of the catalysts has been evaluated by means of periodic DFT calculations and ab initio molecular dynamics simulations. The preferential stabilization by confinement of fully methylated hydrocarbon pool intermediates favoring the paring pathway is the main factor controlling the final olefin product distribution.     

Development of C?N Coupling Using Mechanochemistry: Catalytic Coupling of Arylsulfonamides and Carbodiimides

Reported herein is the mechanochemical synthesis of sulfonyl guanidines, a family of molecules which are relevant as pharmaceuticals and herbicides, by direct coupling of sulfonamides and aromatic or aliphatic carbodiimides. Attempts to conduct the coupling in solution have either failed or given very low conversions, thus demonstrating mechanochemistry as the necessary component for the discovery of this synthetic strategy.     

Regioselective Sequential Additions of Nucleophiles and Electrophiles to Perfluoroalkylfullerenes: Which Cage C Atoms Are the Most Reactive and Why?

The sequential addition of CN^? or CH₃^? and electrophiles to three perfluoroalkylfullerenes (PFAFs), C_s‐C₇₀(CF₃)₈, C₁‐C₇₀(CF₃)₁₀, and C_s‐p‐C₆₀(CF₃)₂, was carried out to determine the most reactive individual fullerene C atoms (as opposed to the most reactive C?C bonds, which has previously been studied). Each PFAF reacted with CH₃^? or CN^? to generate metastable PFAF(CN)^? or PFAF(CH₃)₂^2? species with high regioselectivity (i.e., one or two predominant isomers). They were treated with electrophiles E⁺ to generate PFAF(CN)(E) or PFAF(CH₃)₂(E)₂ derivatives, also with high regioselectivity (E⁺=CN⁺, CH₃⁺, or H⁺). All of the predominant products, characterized by mass spectrometry and ¹⁹F NMR spectroscopy, are new compounds. Some could be purified by HPLC to give single isomers. Two of them, C₇₀(CF₃)₈(CN)₂ and C₇₀(CF₃)₁₀(CH₃)₂(CN)₂, were characterized by single‐crystal X‐ray diffraction. DFT calculations were used to propose whether a particular reaction is under kinetic or thermodynamic control.     

The Reactivity of Ambident Nucleophiles: Marcus Theory or Hard and Soft Acids and Bases Principle?

The model reactions CH₃X + (NH—CH=O)M ➔ CH₃—NH—NH═O or NH═CH—O—CH₃ + MX (M = none, Li, Na, K, Ag, Cu; X = F, Cl, Br) are investigated to demonstrate the feasibility of Marcus theory and the hard and soft acids and bases (HSAB) principle in predicting the reactivity of ambident nucleophiles. The delocalization indices (DI) are defined in the framework of the quantum theory of atoms in molecules (QT-AIM), and are used as the scale of softness in the HSAB principle. To react with the ambident nucleophile NH═CH—O⁻, the carbocation H₃C⁺ from CH₃X (F, Cl, Br) is actually a borderline acid according to the DI values of the forming C…N and C…O bonds in the transition states (between 0.25 and 0.49), while the counter ions are divided into three groups according to the DI values of weak interactions involving M (M…X, M…N, and M…O): group I (M = none, and Me₄N) basically show zero DI values; group II species (M = Li, Na, and K) have noticeable DI values but the magnitudes are usually less than 0.15; and group III species (M = Ag and Cu(I)) have significant DI values (0.30–0.61). On a relative basis, H₃C⁺ is a soft acid with respect to group I and group II counter ions, and a hard acid with respect to group III counter ions. Therefore, N-regioselectivity is found in the presence of group I and group II counter ions (M = Me₄N, Li, Na, K), while O-regioselectivity is observed in the presence of the group III counter ions (M = Ag, and Cu(I)). The hardness of atoms, groups, and molecules is also calculated with new functions that depend on ionization potential (I) and electron affinity (A) and use the atomic charges obtained from localization indices (LI), so that the regioselectivity is explained by the atomic hardness of reactive nitrogen atoms in the transition states according to the maximum hardness principle (MHP). The exact Marcus equation is derived from the simple harmonic potential energy parabola, so that the concepts of activation free energy, intrinsic activation barrier, and reaction energy are completely connected. The required intrinsic activation barriers can be either estimated from ab initio calculations on reactant, transition state, and product of the model reactions, or calculated from identity reactions. The counter ions stabilize the reactant through bridging N- and O-site of reactant of identity reactions, so that the intrinsic barriers for the salts are higher than those for free ambident anions, which is explained by the increased reorganization parameter Δr. The proper application of Marcus theory should quantitatively consider all three terms of Marcus equation, and reliably represent the results with potential energy parabolas for reactants and all products. For the model reactions, both Marcus theory and HSAB principle/MHP principle predict the N-regioselectivity when M = none, Me₄N, Li, Na, K, and the O-regioselectivity when M = Ag and Cu(I). © 2019 Wiley Periodicals, Inc.     

Rhodium Indenyl NHC and Fluorenyl-Tethered NHC Half-Sandwich Complexes: Synthesis,Structures and Applications in the Catalytic C−H Borylation of Arenes and Alkanes

Indenyl (Ind) rhodium N-heterocyclic carbene (NHC) complexes [Rh(η⁵-Ind)(NHC)(L)] were synthesised for 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) with L=C₂H₄ ( 1 ), CO ( 2 a ) and cyclooctene (COE; 3 ), for 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (SIMes) with L=CO ( 2 b ) and COE ( 4 ), and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) with L=CO ( 2 c ) and COE ( 5 ). Reaction of SIPr with [Rh(Cp*)(C₂H₄)₂] did not give the desired SIPr complex, thus demonstrating the “indenyl effect” in the synthesis of 1 . Oxidative addition of HSi(OEt)₃ to 3 proceeded under mild conditions to give the Rh silyl hydride complex [Rh(Ind){Si(OEt)₃}(H)(SIPr)] ( 6 ) with loss of COE. Tethered-fluorenyl NHC rhodium complexes [Rh{(η⁵-C₁₃H₈)C₂H₄N(C)C₂H_xNR}(L)] (x=4, R=Dipp, L=C₂H₄: 11 ; L=COE: 12 ; L=CO: 13 ; R=Mes, L=COE: 14 ; L=CO: 15 ; x=2, R=Me, L=COE: 16 ; L=CO: 17 ) were synthesised in low yields (5–31 %) in comparison to good yields for the monodentate complexes (49–79 %). Compounds 3 and 1 , which contain labile alkene ligands, were successful catalysts for the catalytic borylation of benzene with B₂pin₂ (Bpin=pinacolboronate, 97 and 93 % PhBpin respectively with 5 mol % catalyst, 24 h, 80 °C), with SIPr giving a more active catalyst than SIMes or IMes. Fluorenyl-tethered NHC complexes were much less active as borylation catalysts, and the carbonyl complexes were inactive. The borylation of toluene, biphenyl, anisole and diphenyl ether proceeded to give meta substitutions as the major product, with smaller amounts of para substitution and almost no ortho product. The borylation of octane and decane with B₂pin₂ at 120 and 140 °C, respectively, was monitored by ¹¹B NMR spectroscopy, which showed high conversions into octyl and decylBpin over 4–7 days, thus demonstrating catalysed sp³ C−H borylation with new piano stool rhodium indenyl complexes. Irradiation of the monodentate complexes with 400 or 420 nm light confirmed the ready dissociation of C₂H₄ and COE ligands, whereas CO complexes were inert. Evidence for C−H bond activation in the alkyl groups of the NHC ligands was obtained.     

Studies on the Neodymium-induced Pinacol Coupling of Aromatic Aldehydes and Ketones in Aqueous Media

1,2-Diols are very useful synthons for a variety of organic synthesis1, which have been used as intermediates for the construction of the skeletons of the biologically important natural products2. Within the last several years, various metals, such as Mg3…     

Impact of Arsenic Trioxide on LS-174T Cell Growth and the Activity of Telomerase

The therapeutic action of arsenic trioxide（ As203 ） on solid tumors has aroused widespread interest among scholars. To study the impact of As2O3 on human colorectal carcinoma cells（ LS-174T cell） and the activity of telomerase, the methods of PCR-ELISA, flow cytometry （FCM） and MTT assay in vitro were utilized. The results show that （1） with an increase in the concentration of As2O3, the ratio of living the cells to dead cells decreases significantly, and the IC50 value is 5.23 μg/mL; （2） the cells of the experimental groups can endure a series of morphological changes similar to the features of apoptosis ; （3） the apoptotic curves of FCM pictures appear after 24 h, and the cells show the apoptosis in a time-dependent manner; （4） As2O3 can inhibit the activity of telomerase of the cell extraction obviously in a concentration-dependent and time-dependent manner after 24 h. It can be concluded from the experiment results in vitro that As2O3 can induce the apoptosis of LS-174T cells and inhibit the telomerase activity. Therefore, it has been proposed, for the first time, that these two factors （the apoptosis of LS-174T cells and the inhibition to the telomerase activity） are important causes of the LS-174T cell death caused by As2O3.     

Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?

The twisted lateral tetraalkyloxy ortho‐terphenyl units in dibenzo[18]crown‐6 ethers 1 a – f were readily converted into the flat tetraalkyloxytriphenylene systems 2 a – f by oxidative cyclization with FeCl₃ in nitromethane. Reactions of the latter with potassium salts gave complexes KX ?2 , which displayed mesomorphic properties. The aromatization increased both the clearing and melting points; the mesophase stabilities, however, were mainly influenced by the respective anions upon complexation with various potassium salts. In contrast, the alkyl chain lengths played only a secondary role. Among the potassium complexes of triphenylene‐substituted crown ethers KX ?2 , only those with the soft anions I^? and SCN^? displayed mesophases with expanded phase temperature ranges of 93 °C and 132 °C (for KX ?2 e ), respectively, as compared to the corresponding o‐terphenyl‐substituted crown ether complexes KI ?1 e (ΔT=51 °C) and KSCN ?1 e (plastic crystal phase). Anions such as Br^?, Cl^?, and F^? decreased the mesophase stability, and PF₆^? led to complete loss of the mesomorphic properties of KPF₆ ?2 although not for KPF₆ ?1 . For crown ether complexes KX ?2 (X=F, Cl, Br, I, BF₄, and SCN), columnar rectangular mesophases of different symmetries (c2 mm, p2 mg, and p2 gg) were detected. In contrast to findings for the twisted o‐terphenyl crown ether complexes KX ?1 , the complexation of the flat triphenylene crown ethers 2 with KX resulted in the formation of organogels. Characterization of the organogel of KI ?2 e in CH₂Cl₂ revealed a network of fibers.     

Theoretical and Experimental Study on Reaction Coupling： Dehydrogenation of Ethylbenzene in the Presence of Carbon Dioxide

Dehydrogenation of ethylbenzene (EB) to styrene (ST) in the presence of CO2, in which EB dehydrogenation is coupled with the reverse water-gas shift (RWGS), was investigated extensively through both theoretical analysis and experimental characterization. The reaction coupling proved to be superior to the single dehydrogenation in several respects. Thermodynamic analysis suggests that equilibrium conversion of EB can be improved greatly by reaction coupling due to the simultaneous elimination of the hydrogen produced from dehydrogenation. Catalytic tests proved that iron and vanadium supported on activated carbon or Al2O3 with certain promoters are potential catalysts for this coupling process. The catalysts of iron and vanadium are different in the reaction mechanism, although ST yield is always associated with CO2 conversion over various catalysts. The two-step pathway plays an important role in the coupling process over Fe/Al2O3, while the one-step pathway dominates the reaction over V/Al2O3. Coke deposition and deep reduction of active components are the major causes of catalyst deactivation. CO2 can alleviate the catalyst deactivation effectively through preserving the active species at high valence in the coupling process, though it can not suppress the coke deposition.     

Synthesis of (NHC)Rh(cod)Cl and (NHC)RhCl(CO)2 complexes – Translation of the Rh- into the Ir-scale for the electronic properties of NHC ligands

Twenty-three different Rh complexes of the (NHC)RhCl(cod) and (NHC)RhCl(CO)₂ type were synthesized from [RhCl(cod)]₂. The electron donating nature of the NHC ligands was changed in a systematic manner. The redox potentials of the various (NHC)RhCl(cod) and the ν(CO) of the various (NHC)RhCl(CO)₂ were determined. A correlation of the Rh redox potentials and the Rh ν(CO), respectively, with the related data from analogous (NHC)IrCl(cod) and (NHC)IrCl(CO)₂ complexes established two linear relationships. The linear regression (R² = 0.993) of the Rh and the Ir redox potentials results in an equation for the redox potential transformation: E_1/2(Ir) = 1.016 · E_1/2(Rh) ? 0.076 V. The linear regression (R² = 0.97) of the Rh and Ir ν_av(CO) results in an equation for the ν_av(CO) transformation: ν_av(CO)Ir = 0.8695 · ν_av(CO)Rh + 250.7 cm^?1. In this manner the Rh and the Ir-scale for the determination of the electron donating properties of NHC ligands are unified.     

Effect of Steam on the Oxidative Coupling of Methane over La-Ba System Catalysts

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Impact of the nature and shape of cellulosic nanoparticles on the isothermal crystallization kinetics of poly(ε-caprolactone)

Polycaprolactone (PCL)/cellulose nanocomposites were prepared by mixing PCL with surface modified sisal nanowhiskers (CNW) and microfibrillated cellulose (MFC) extracted from sisal fibers. The influence of cellulosic nanoparticles on the crystallization behavior of PCL was investigated by differential scanning calorimetry. Isothermal crystallization data were modeled with Avrami’s kinetics, Lauritzen–Hoffman secondary nucleation theory and equilibrium melting points were determined with the Hoffman–Weeks method. The cellulose nanoparticles, acting as nucleating agents, drastically accelerate the crystallization of PCL while depressing its equilibrium melting by 9–10 °C. The crystallization of MFC-nanocomposites is slightly faster than that of CNW-nanocomposites, in agreement with the slightly lower bulk activation energy for crystallization and nucleation parameter in the former. The results are discussed based on the differences of specific surface area and surface chemistry of nanoparticles, as well as the confinement phenomenon.