Chlorin–Bacteriochlorin Energy‐transfer Dyads as Prototypes for Near‐infrared Molecular Imaging Probes: Controlling Charge‐transfer and Fluorescence Properties in Polar Media

The photophysical properties of two energy‐transfer dyads that are potential candidates for near‐infrared (NIR) imaging probes are investigated as a function of solvent polarity. The dyads ( FbC‐FbB and ZnC‐FbB ) contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. The dyads were studied in toluene, chlorobenzene, 1,2‐dichlorobenzene, acetone, acetonitrile and dimethylsulfoxide (DMSO). In both dyads, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of ～(5–10 ps)^?1 and a yield of >99% in nonpolar and polar media. In toluene, the fluorescence yields (Φ _f = 0.19) and singlet excited‐state lifetimes (τ～5.5 ns) are comparable to those of the benchmark bacteriochlorin. The fluorescence yield and excited‐state lifetime decrease as the solvent polarity increases, with quenching by intramolecular electron (or hole) transfer being greater for FbC‐FbB than for ZnC‐FbB in a given solvent. For example, the Φ _f and τ values for FbC‐FbB in acetone are 0.055 and 1.5 ns and in DMSO are 0.019 and 0.28 ns, whereas those for ZnC‐FbB in acetone are 0.12 and 4.5 ns and in DMSO are 0.072 and 2.4 ns. The difference in fluorescence properties of the two dyads in a given polar solvent is due to the relative energies of the lowest energy charge‐transfer states, as assessed by ground‐state redox potentials and supported by molecular‐orbital energies derived from density functional theory calculations. Controlling the extent of excited‐state quenching in polar media will allow the favorable photophysical properties of the chlorin–bacteriochlorin dyads to be exploited in vivo. These properties include very large Stokes shifts (85 nm for FbC‐FbB , 110 nm for ZnC‐FbB ) between the red‐region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (λ _f = 760 nm), long bacteriochlorin excited‐state lifetime (～5.5 ns), and narrow (≤20 nm) absorption and fluorescence bands. The latter will facilitate selective excitation/detection and multiprobe applications using both intensity‐ and lifetime‐imaging techniques.     

Crystal Structure and Spectroscopic Properties of Bis[trans‐dichlorobis(2,2‐dimethylpropane‐1,3‐diamine)chromium(III)] Tetrachlorozincate

The structure of trans‐[Cr(Me₂tn)₂Cl₂]₂ZnCl₄ (Me₂tn = 2,2‐dimethylpropane‐1,3‐diamine) was determined by a single‐crystal X‐ray diffraction study at 173 K. The analysis reveals that there are three crystallographically independent chromium(III) complex cations in the title compound. The chromium(III) atoms are coordinated by four nitrogen atoms of Me₂tn and two chlorine atoms in a trans arrangement, displaying a distorted octahedral geometry. The two six‐membered chelate rings in three complex cations are oriented in an anti chair–chair conformation with respect to each other. The Cr–N and Cr–Cl bond lengths average 2.0862(2) and 2.3112(6) Å, respectively. The ZnCl₄^2– have slightly distorted tetrahedral arrangement with Zn–Cl lengths and the Cl–Zn–Cl angles are influenced by hydrogen bonding. The resolved absorption maxima in the electronic d–d spectrum were fitted with a secular determinant for a quartet energy state of the d³ configuration in a tetragonal field. It is confirmed that the nitrogen atoms of the Me₂tn ligand are strong σ donors, but the chloro ligands have weak σ‐ and π donor properties toward the chromium(III) ion.     

Efficient preparative separation of 6‐(4‐aminophenyl)‐5‐methyl‐4, 5‐dihydro‐3(2H)‐pyridazinone enantiomers on polysaccharide‐based stationary phases in polar organic solvent chromatography and supercritical fluid chromatography

6‐(4‐Aminophenyl)‐5‐methyl‐4,5‐dihydro‐3(2H)‐pyridazinone is a key synthetic intermediate for cardiotonic agent levosimendan. Very few studies address the use of chiral stationary phases in chromatography for the enantioseparation of this intermediate. This study presents two efficient preparative methods for the isolation of (R)(?)‐6‐(4‐aminophenyl)‐5‐methyl‐4,5‐dihydro‐3(2H)‐pyridazinone in polar organic solvent chromatography and supercritical fluid chromatography using polysaccharide‐based chiral stationary phases and volatile organic mobile phases without additives in isocratic mode. Under optimum conditions, Chiralcel OJ column showed the best performance (α = 1.71, Rs = 5.47) in polar organic solvent chromatography, while Chiralpak AS column exhibited remarkable separations (α = 1.81 and Rs = 6.51) in supercritical fluid chromatography with an opposite enantiomer elution order. Considering the sample solubility, runtime and solvent cost, the preparations were carried out on Chiralcel OJ column and Chiralpak AS column (250 × 20 mm i.d.; 10 µm) in polar organic mode and supercritical fluid chromatography mode with methanol and CO₂/methanol as mobile phases, respectively. By utilizing the advantages of chromatographic techniques and polysaccharide‐based chiral stationary phases, this work provides two methods for the fast and economic preparation of (R)(?)‐6‐(4‐aminophenyl)‐5‐methyl‐4,5‐dihydro‐3(2H)‐pyridazinone, which are suitable for the pharmaceutical industry.     

Retracted: Acid‐Catalyzed Aquation of Ni(II)‐Hydrazone Complexes: Kinetics and Solvent Effect

Complexes of the type [Ni(L)(H₂O)]Cl₂·nH₂O, where L = 2‐pyridyl‐3‐isatinbishydrazone ligands, have been synthesized and characterized on the bases of elemental analysis, molar conductance, IR, electronic spectra, and thermal analysis (TGA and DTA). Acid‐catalyzed aquation of the Ni(II) isatin‐bishydrazone complexes was followed spectrophotometrically in various water–methanol and water–acetone mixtures at temperature 298 K. Kinetic behavior of the acid aquation is a linear rate law, indicating that the acid‐catalyzed aquation of these complexes in water–methanol and water–acetone mixtures follows a rate law with k_obs = k₂[H⁺]. The effect of the mole fraction of the ganic solvent, i.e., methanol and acetone, on the acid aquation has been analyzed; the decrease in the rate constant values with increasing of the methanol or acetone ratios is attributable to the effect of the co‐organic solvent on the initial states of the acid aquation by the destabilization of the H⁺ ion.     

Preparation of benzoylchitosans and their chiroptical properties in dilute solutions

Two benzoyl substituted chitosan derivatives, 3,6‐O‐dibenzoylchitosan (DBC) and 2‐N‐3,6‐O‐tribenzoylchitosan (TBC), were prepared, and their optical activities in organic solvent were investigated by circular dichroism (CD). For TBC, two splitting bands (a negative one at 288 nm and a positive one at 274 nm) corresponding to the ¹L_b transition of the benzoyl group were observed in chloroform and dichloromethane, while only a negative CD band was recorded in N, N‐dimethylformamide (DMF). These results indicated that the transition moments of benzoyl groups were orderly arranged along the helical polymer chain when TBC was dissolved in a solvent with low polarity, but the same ordered structure did not appear in a polar solvent of DMF. For DBC, only negative CD signals corresponding to the ¹L_b transition of the benzoyl group were observed, regardless of the solvent property, which indicated that the chromophores were not arranged in an ordered fashion with appropriate geometry to interact with one another to induce bi‐signate CD signals. Adding methanol or DMF to the solution of TBC/chloroform resulted in a progressive decrease of the intensity of the positive split band at 274 nm. The intensity of the positive band was weakened upon heating a solution of TBC/chloroform from 20 to 60 °C. The results suggested that the ordered arrangement of the chromophores in the TBC system was dependent on solvent and sensitive to temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4107–4115, 2004     

Crystal Structure and Spectroscopic Properties of cis‐β‐Diazido(1,4,7,11‐tetraazaundecane)chromium(III) Bromide

The new complex, cis‐β‐[Cr(2,2,3‐tet)(N₃)₂]Br (2,2,3‐tet = 1,4,7,11‐tetraazaundecane), was prepared and its structure was determined by single‐crystal X‐ray diffraction. The chromium(III) atom is in a distorted octahedral environment coordinated by four nitrogen atoms of 2,2,3‐tet and two azido ligands in a cis‐β arrangement, with bent Cr–N₃ linkages at the coordinating azide nitrogen atoms. The mean Cr–N(2,2,3‐tet) and Cr–N(azide) bond lengths are 2.084(5) and 2.021(5) Å, respectively. The crystal structure is stabilized by ionic interactions, supported by N–H ··· N(azide) and N–H ··· Br hydrogen bonds. The IR and electronic spectroscopic properties are also discussed.     

Novel fluorescent 2‐(2‐aminofluorophenyl)benzoxazoles: Syntheses and photophysical properties

2‐(2‐Amino‐3,4,5,6‐tetrafluorophenyl)benzoxazole ( 2 ) absorbs in long wavelength band (λ_abs^max = 346 nm in methanol) and in the normal wavelength band (λ_abs^max = 285.5 nm), and emits blue fluorescence. The emission intensity is highly affected by the solvent polarity and is large in a polar solvent such as methanol. 2‐(2‐Pentafluorobenzamido‐3,4,5,6‐ tetrafluorophenyl)benzoxazole ( 5 ) emits green fluorescence along with the short wavelength emission around 380 nm and their relative intensity depends on the solvent polarity. Green fluorescence is enhanced in nonpolar solvents such as chloroform and toluene, resulting in the considerably large Stokes shift.     

Electrochemical Impedance Spectroscopy and Cyclic Voltammetry of <Emphasis Type="Italic">cis</Emphasis>-[Cr(bipy)<Subscript>2</Subscript>(SCN)<Subscript>2</Subscript>]I (where bipy: 2,2′-Bipyridine) in Polar Solvents

Cyclic voltammetric studies (CV) on the complex cis-bis(2,2′-bipyridine)bis(thiocyanate)chromium(III) iodide [Cr(bipy)₂(SCN)₂]I (where bipy: 2,2′-bipyridine, C₁₀H₈N₂) were recorded on platinum (Pt) and glassy carbon (GC) electrodes in either acetonitrile (ACN) or acetone (ACE) solvent media including n-tetrabutylammonium hexafluorophosphate (NBu₄PF₆) as supporting electrolyte, at scan rates (v) ranging from 0.05 to 0.12 V⋅s⁻¹. In addition, electrochemical impedance spectroscopic (EIS) measurements in the frequency (f) range from 0.1 Hz to 50 kHz were carried out on GC and Pt electrodes. The half-wave potential (E _1/2) of the redox couple Cr(III)/Cr(II) was determined as −0.84 V and −0.79 V (versus Ag/AgCl) in ACN and ACE, respectively. The heterogeneous electron transfer rate constant (k _s) corresponding to the couple Cr(III)/Cr(II) was found to be greater on GC compared to the Pt electrode. The nature of the solvent medium also affects the kinetics of the investigated couple, to be exact, k _s increases remarkably upon replacement of ACE by ACN. The EIS results indicate that the GC electrode is a better capacitor and provides the smaller charge transfer resistance in ACN.     

Solvent and temperature effects on the conformational equilibria of a dihydrobenzo[h]quinolinium fluoroborate

Spectra of the N‐phenyl‐5,6‐dihydro‐2,4‐diphenylbenzo[h]quinolinium tetrafluoroborate (1) and of the N‐phenyl‐5,6,8,9‐tetrahydro‐7‐phenyldibenzo[c,h]acridinium tetrafluoroborate (2) were recorded in various solvents and temperatures. The analysis of the ¹H‐NMR spectra of the tetrafluoroborate salt 1, recorded in acetone, acetonitrile, 1,1,2,2‐tetrachloroethane and chloroform, revealed the existence of an equilibrium between two conformers in solution. Tight ion‐pairing in chloroform led to a smaller barrier for interconversion between the two conformers. In more polar solvents, where the dihydrobenzoquinolinium exists as a free cation, theoretical calculations predicted larger barriers. The spectra of 1 in 1,1,2,2‐tetrachloroethane also varied with temperature, resembling at higher temperatures the spectrum in CDCl₃ and at 300K spectra in more polar media. Spectra of 2 did not vary with the solvent or the temperature, in an indication of a much higher barrier to conformational interconversion, because of a greater steric hindrance between the N‐phenyl substituent and the dihydrobenzo rings. Copyright © 2009 John Wiley & Sons, Ltd.     

In Situ Study of the Surface Oxidation of FeCr Alloys Using Grazing Incidence X‐ray Absorption Spectroscopy (GIXAS)

The surface oxidation of FeCr alloys with 18, 28, and 43 mass‐% Cr was investigated in situ using grazing‐incidence X‐ray absorption spectroscopy (GIXAS) at the chromium and iron K‐edges. Oxidation in air was monitored in situ in the temperature range from 290 K to 680 K. The standard GIXAS data analysis is extended for the treatment of a single layer model in order to estimate the chromium concentrations of the oxide layer and of the near‐interface substrate as well as the oxide layer thickness. XANES analysis shows transitions from b.c.c. Fe to corundum type Fe₂O₃ and from b.c.c. Cr to corundum type Cr₂O₃. The initial oxide layers are 1.1‐1.4 nm thick and contain 60‐90 mass‐% chromium, while the near‐interface substrate is depleted in Cr. During heating, iron oxide growth dominates up to 560‐600 K. Then the chromium oxide layer loses its passivation effect and Cr oxidation sets in.     

Long‐Lived Room‐Temperature Deep‐Red‐Emissive Intraligand Triplet Excited State of Naphthalimide in Cyclometalated IrIII Complexes and its Application in Triplet‐Triplet Annihilation‐Based Upconversion

Cyclometalated Ir^III complexes with acetylide ppy and bpy ligands were prepared (ppy=2‐phenylpyridine, bpy=2,2′‐bipyridine) in which naphthal ( Ir‐2 ) and naphthalimide (NI) were attached onto the ppy ( Ir‐3 ) and bpy ligands ( Ir‐4 ) through acetylide bonds. [Ir(ppy)₃] ( Ir‐1 ) was also prepared as a model complex. Room‐temperature phosphorescence was observed for the complexes; both neutral and cationic complexes Ir‐3 and Ir‐4 showed strong absorption in the visible range (ε=39600 M ^?1 cm^?1 at 402 nm and ε=25100 M ^?1 cm^?1 at 404 nm, respectively), long‐lived triplet excited states (τ_T=9.30 μs and 16.45 μs) and room‐temperature red emission (λ_em=640 nm, Φ_p=1.4 % and λ_em=627 nm, Φ_p=0.3 %; cf. Ir‐1 : ε=16600 M ^?1 cm^?1 at 382 nm, τ_em=1.16 μs, Φ_p=72.6 %). Ir‐3 was strongly phosphorescent in non‐polar solvent (i.e., toluene), but the emission was completely quenched in polar solvents (MeCN). Ir‐4 gave an opposite response to the solvent polarity, that is, stronger phosphorescence in polar solvents than in non‐polar solvents. Emission of Ir‐1 and Ir‐2 was not solvent‐polarity‐dependent. The T₁ excited states of Ir‐2 , Ir‐3 , and Ir‐4 were identified as mainly intraligand triplet excited states (³IL) by their small thermally induced Stokes shifts (ΔE_s), nanosecond time‐resolved transient difference absorption spectroscopy, and spin‐density analysis. The complexes were used as triplet photosensitizers for triplet‐triplet annihilation (TTA) upconversion and quantum yields of 7.1 % and 14.4 % were observed for Ir‐2 and Ir‐3 , respectively, whereas the upconversion was negligible for Ir‐1 and Ir‐4 . These results will be useful for designing visible‐light‐harvesting transition‐metal complexes and for their applications as triplet photosensitizers for photocatalysis, photovoltaics, TTA upconversion, etc.     

Stability‐indicating HPTLC method for quantitative estimation of silybin in bulk drug and pharmaceutical dosage form

In the present study a novel stability‐indicating high‐performance thin‐layer chromatography (HPTLC) method for quantitative determination of silybin in bulk drug and nanoemulsion formulation has been developed and validated on silica using solvent chloroform–acetone–formic acid (9 : 2 : 1 v/v/v) (R_f of silybin 0.46 ± 0.05) in the absorbance mode at 296 nm. The method showed a good linear relationship (r² ± 0.999) in the concentration range 25–1500 ng per spot. It was found to be linear, accurate, precise, specific, robust and stability‐indicating and can be applied for quality control and standardization of several multi‐component hepatoprotective formulations as well as for stability testing of different dosage forms. The method proposed was also used to investigate the kinetics of acidic and alkaline degradation processes by quantification of drug at different temperature to calculate the activation energy and half‐life for silymarin degradation. Copyright © 2009 John Wiley & Sons, Ltd     

Ultrasonic assisted deep eutectic solvent liquid–liquid microextraction using azadipyrromethene dye as complexing agent for assessment of chromium species in environmental samples by electrothermal atomic absorption spectrometry

A novel type of solvent named deep eutectic solvent (DES) has been considered as a green ionic liquid analogue. A novel method was developed for enrichment and speciation of chromium ion from water and food samples based on deep eutectic solvent and ultrasonic extraction. The procedure for this method was comprised of Cr(III) complex formation with a hydrophobic complexing agent (Z)‐N‐(3,5‐diphenyl‐1H‐pyrrol‐2‐yl)‐3,5‐diphenyl‐2H‐pyrrol‐2‐imine (azadipyrromethene dye). Metal complex was entrapped in a deep eutectic solvent as an extracting solvent. While Cr(III) recovery was quantitative, the recovery of Cr(VI) was found 5%. After reduction of Cr(VI) to Cr(III), the method was applied for determination of total chromium(III) ion. The amount of Cr(VI) was calculated as subtracting of Cr(III) from total chromium ion. Various analytical parameters were optimized. The certified reference materials were analyzed and standard addition method also carried out to real samples to check the accuracy of the developed method. Preconcentration factor was found to be 50. The limit of detection of chromium(III) was found to be 4.3 ng l^‐1. The precision of developed method as the relative standard deviation (RSD) was found as 3.5 %. The developed method was applied successfully for the speciation of chromium ions in water and food samples.     

Polymerization of aniline derivatives by K2Cr2O7 and production of Cr2O3 nanoparticles

Oxidative polymerization of aniline, anthranilic acid, and aniline‐co‐anthranilic acid by potassium dichromate Cr(VI) as an oxidant in acidic medium was investigated. In this study, the polymerization process of aniline, o‐anthranilic acid as well as aniline/o‐anthranlic acid using K₂Cr₂O₇ produced, coordinated Cr(III)/polyaniline (PANI), Cr(III)/polyanthranilic acid (PAA) and Cr(III)/poly aniline‐co‐anthranilic acid (PANAA). The mechanism of polymerization reaction in the presence of dichromate was hypothesized. The precursor chromium doped polymers were characterized by TGA, FT‐IR, UV‐visible, XRD analyses. Cr₂O₃ nanoparticles size were determined using TEM analysis. The calcinations process of synthesized chromium doped PANI, PAA and PANAA yields Cr₂O₃ nanoparticles 26%, 31%, and 34% wt. respectively. Rhombohedral phase of Cr₂O₃ particles in the range from 33 to 61 nm was produced from chromium/polyanthranilic acid (PAA) and chromium/poly(aniline‐co‐anthranilic acid) PANAA. UV‐ visible analysis showed that optical band gaps (E_g) of doped poly aniline and its derivatives are in the range from1.55 to 1.80 using Tacu's law. The band gap values reveal that the doped chromium emeraldine base can be used as semiconductor materials. Copyright © 2016 John Wiley & Sons, Ltd.     

Multiarm star nanocarriers containing a poly(ethylene imine) core and polylactide arms

Star polymers (SPs) containing a hyperbranched poly(ethylene imine) (PEI; number‐average molecular weight = 10,000) core and polylactide arms were synthesized via the ring‐opening polymerization of lactide. PEI was used as a multifunctional macroinitiator for the ring‐opening polymerization of lactide. Different lactide monomer/amino‐functional group (LA/NH_n; n = 1 or 2) ratios were used for preparing SPs with different molecular weights. SPs were able to encapsulate small guest molecules such as Rose Bengal; they also transported small, hydrophilic molecules from water to the organic phase. The transport capacity of all the nanocarriers depended on the LA/NH_n ratio used for synthesizing the SPs. Nanocarriers with a higher LA/NH_n ratio had higher transport capacities. The size of all the nanocarriers depended on the type of solvent. In chloroform, these nanoparticles had several sizes that were related to the self‐assembly of these nanocarriers, but in acetone, they were monodisperse, and their size was smaller than that in chloroform. Also, the transport of polar dyes from water to the chloroform phase was possible. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5740–5749, 2006     

Hexavalent Chromium Reduction by Free and Immobilized Cell-free Extract of <Emphasis Type="Italic">Arthrobacter rhombi-RE</Emphasis>

In the present study, hexavalent chromium (Cr(VI)) reduction potential of chromium reductase associated with the cell-free extracts (CFE) of Arthrobacter rhombi-RE species was evaluated. Arthrobacter rhombi-RE, an efficient Cr(VI) reducing bacterium, was enriched and isolated from a chromium-contaminated site. Chromium reductase activity of Arthrobacter rhombi-RE strain was associated with the cell-free extract and the contribution of extracellular enzymes to Cr(VI) reduction was negligible. NADH enhanced the chromium reductase activity. The enzyme activity was optimal at a pH of 5.5 and a temperature of 30 °C. Among the ten electron donors screened, sodium pyruvate was the most effective one followed by NADH and propionic acid. Michaelis–Menten constant, K _m, and maximum reaction rate, V _max, obtained from the Lineweaver–Burk plot were 48 μM and 4.09 nM/mg protein/min, respectively, in presence of NADH as electron donor and 170.5 μM and 4.29 nM/mg protein/min, respectively, in presence of sodium pyruvate as electron donor. Ca²⁺ enhanced the enzyme activity while Hg²⁺, Cd²⁺, Ba²⁺, and Zn²⁺ inhibited the enzyme activity. Among the various immobilization matrices screened, calcium alginate beads seemed to be the most effective one. Though immobilized enzyme system was able to reduce Cr(VI), the performance was not very encouraging in continuous mode of operation.     

Photodecomposition of Chloroform Catalyzed by Unmodified MCM‐41 Mesoporous Silica

Unactivated MCM‐41 mesoporous silica catalyzes the photodecomposition of chloroform to phosgene and hydrogen chloride under near‐UV (λ > 360 nm) irradiation. The rate of photodecomposition increases toward an asymptotic limit as the O₂ partial pressure is increased. Deuterochloroform does not decompose under the same experimental conditions. Low concentrations of both cyclohexane and ethanol quench the photodecomposition, whereas water, up to its solubility limit, does not. Dissolved tetraalkylammonium salts suppress photodecomposition. The data are consistent with a mechanism in which light absorption by an SiO₂ defect yields an electron‐deficient oxygen atom, which then abstracts hydrogen from chloroform. The resulting CCl₃ radicals react with oxygen to form a peroxy radical that decomposes, eventually yielding phosgene and hydrogen chloride.     

Two biologically active thio­phene‐3‐carbox­amide derivatives

The compounds 2‐{[(E)‐(4‐methoxy­phenyl)­methyl­ene]­amino}‐N‐(3‐methyl­phenyl)‐4,5,6,7‐tetra­hydro‐1‐benzo­thio­ph­ene‐3‐carbox­amide, C₂₄H₂₄N₂O₂S, (I), and N‐(4‐meth­yl­phenyl)‐2‐{[(E)‐(4‐methyl­phenyl)­methyl­ene]­amino}‐4,5,6,7‐tetra­hydro‐1‐benzo­thio­phene‐3‐carbox­amide, C₂₄H₂₄N₂OS, (II), show antibacterial and antifungal activities. The m‐toluidine ring in (I) and the p‐toluidine ring in (II) are coplanar with their respective thio­phene rings. In (I), an intermolecular C—H⋯O hydrogen bond is present, whereas (II) does not exhibit any significant intermolecular interactions. However, in both compounds, an intramolecular N—H⋯N hydrogen bond forms a pseudo‐six‐membered ring, thus locking the molecular conformation and eliminating conformational flexibility.     

Cobalt‐based metal coordination polymers with 4,4′‐bipyridinyl groups: highly efficient catalysis for one‐pot synthesis of 3,4‐dihydropyrimidin‐2(1H)‐ones under solvent‐free conditions

Three new metal coordination complexes, namely [Co(BPY)₂(H₂O)₂](BPY)(BS)₂(H₂O)₄ ( 1 ), [Co(BPY)₂(H₂O)₄](ABS)₂(H₂O)₂ ( 2 ) and [Co(BPY)(H₂O)₄](MBS)₂ ( 3 ) (BPY = 4,4′‐bipyridine, BS = phenylsulfonic acid, ABS = p‐aminobenzenesulfonic acid, MBS = p‐methylbenzenesulfonic acid), were obtained under hydrothermal conditions. Complexes 1 , 2 , 3 were structurally characterized using single‐crystal X‐ray diffraction and infrared spectroscopy. All of them display low‐dimensional motifs: complex 1 displays a two‐dimensional structure; and complexes 2 and 3 exhibit a one‐dimensional tape structure. Through strong intermolecular hydrogen bonding interactions and weak packing interactions, all of them further stack to generate a three‐dimensional supramolecular architecture. Catalysts 1 , 2 , 3 were involved in the green synthesis of a variety of 3,4‐dihydropyrimidin‐2(1H)‐ones under solvent‐free conditions through Biginelli reactions. The corresponding catalytic product was obtained in quantitative yields (99%) under eco‐friendly synthesis conditions for the variety of reactions. Catalysts 1 , 2 , 3 exhibit excellent efficiency for the desired product, and their catalytic performance shows the following order: 2  >  1  ≈  3 , which can be ascribed to the hydrophobic interactions of different phenylsulfonate groups. The catalytic performance for the Biginelli reaction is not only dependent on the selected solvents, but also inversely proportional to the polarities of the solvents. Copyright © 2016 John Wiley & Sons, Ltd.     

Corrosion and wear resistance properties of multilayered diamond‐like carbon nanocomposite coating

Multilayered diamond‐like carbon (DLC) nanocomposite coating has been deposited on silicon and stainless steel substrates by combination of cathodic arc evaporation and magnetron sputtering. In order to make DLC coating adhered to metal substrate, a chromium interlayer has been deposited with constant bias voltage of −150 V applied to the substrate. Dense multilayered coating consists of metallic or nonmetallic and tetrahedral carbon (ta‐C) layers with total thickness of 1.44 μm. The coating has been studied for composition, morphology, surface nature, nanohardness, corrosion resistance, and tribological properties. The composition of the coating has been estimated by energy‐dispersive spectroscopy. Field‐emission scanning electron microscopy and atomic force microscopy have been used to study the surface morphology and topography. I_D/I_G ratio of ta‐C:N layer obtained from Raman spectroscopy is 1.2, indicating the disorder in the layer. X‐ray photoelectron spectroscopy studies of individual ta‐C:N, CrN, and Cr‐doped DLC layers confirm the presence of sp²C, sp³C, CrN, Cr₂N, and carbidic carbon, and sp²C, sp³C, and Cr carbide. Nanohardness studies show the maximum penetration depth of 70 to 85 nm. Average nanohardness of the multilayered DLC coating is found to be 35 ± 2.8 GPa, and Young's modulus is 270 GPa. The coating demonstrates superior corrosion resistance with better passivation behavior in 3.5% NaCl solution, and corrosion potential is observed to move towards nobler (more positive) values. A low coefficient of friction (0.11) at different loads is observed from reciprocating wear studies. Wear volume is lower at all loads on the multilayered DLC nanocomposite coating compared to the substrate.