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The synthesis and evaluation of three novel bis‐1,2,4‐triazine ligands containing five‐membered aliphatic rings are reported. Compared to the more hydrophobic ligands 1–3 containing six‐membered aliphatic rings, the distribution ratios for relevant f‐block metal ions were approximately one order of magnitude lower in each case. Ligand 10 showed an efficient, selective and rapid separation of AmIII and CmIII from nitric acid. The speciation of the ligands with trivalent f‐block metal ions was probed using NMR titrations and competition experiments, time‐resolved laser fluorescence spectroscopy and X‐ray crystallography. While the tetradentate ligands 8 and 10 formed LnIII complexes of the same stoichiometry as their more hydrophobic analogues 2 and 3, significant differences in speciation were observed between the two classes of ligand, with a lower percentage of the extracted 1:2 complexes being formed for ligands 8 and 10. The structures of the solid state 1:1 and 1:2 complexes formed by 8 and 10 with YIII, LuIII and PrIII are very similar to those formed by 2 and 3 with LnIII. Ligand 10 forms CmIII and EuIII 1:2 complexes that are thermodynamically less stable than those formed by ligand 3, suggesting that less hydrophobic ligands form less stable AnIII complexes. Thus, it has been shown for the first time how tuning the cyclic aliphatic part of these ligands leads to subtle changes in their metal ion speciation, complex stability and metal extraction affinity., Calling all actinides! Bis‐1,2,4‐triazine ligands bearing five‐membered rings were synthesized and evaluated as actinide‐selective extractants. Tuning the size of the aliphatic ring leads to subtle changes in actinide‐extraction properties. The origins of these changes were elucidated at the molecular level, paving the way for the rational design of improved actinide‐selective extractants for reprocessing of spent nuclear fuel.

We construct efficient ring signatures (RS) from isogeny and lattice assumptions. Our ring signatures are based on a logarithmic OR proof for group actions. We instantiate this group action by either the CSIDH group action or an MLWE-based group action to obtain our isogeny-based or lattice-based RS scheme, respectively. Even though the OR proof has a binary challenge space and therefore requires a number of repetitions which is linear in the security parameter, the sizes of our ring signatures are small and scale better with the ring size N than previously known post-quantum ring signatures. We also construct linkable ring signatures (LRS) that are almost as efficient as the non-linkable variants. The isogeny-based scheme produces signatures whose size is an order of magnitude smaller than all previously known logarithmic post-quantum ring signatures, but it is relatively slow (e.g. 5.5 KB signatures and 79 s signing time for rings with 8 members). In comparison, the lattice-based construction is much faster, but has larger signatures (e.g. 30 KB signatures and 90 ms signing time for the same ring size). For small ring sizes our lattice-based ring signatures are slightly larger than state-of-the-art schemes, but they are smaller for ring sizes larger than \(N \approx 1024\).

External fields effects on hole energies and effective g-factor of an infinite confining potential quantum ring are theoretically investigated. Based on envelope-function approach within the cylindrical polar coordinates, four band k ⋅ p method was used. We then derive the effective holes Hamiltonian and because of the ring geometry, we solve the problem as a 2-D grid ( ρ , z ) set of equations and finally valence band (VB) energy eigenvalues and g-factor of the system are estimated by using the finite difference method (FDM). Numerical results for different values of applied fields as well as various geometrical dimensions are presented. We find that our results are in good agreement with the results reported in experimental works. Our results highlight the role of external fields and the ring size for an accurate description of these two dimensional systems.

We report here the synthesis, characterization and kinetic studies of [RuL2(mac)]n+ complexes [mac = 1,4,8,11-tetraazacyclotetradecane (cyclam) or 1,4,7,10-tetraazacyclododecane (cyclen); and L = Cl−, OH−, OH2]. The dichloride complexes release one Cl− producing [RuCl(L)(mac)]n+ or two Cl− producing [Ru(L)2(mac)]n+ (L = OH2, OH−) in aqueous solution within pH 1–7. The product of these reactions were characterized by ultraviolet–visible (UV–Vis) spectroscopy. The chloride affinity of Ru(III) depends on the macrocyclic ring size and geometric structure. The k1 and thermodynamic activation parameters (at pH 4.4, T = 25 °C) of cis-[RuCl2(cyclen)]+ complex are k1 = 3.6 × 10−3 s−1 (25 °C); ΔH# = 40.2 kJ mol−1 and ΔS# = − 138 J K mol−1; under similar conditions, for cis-[RuCl2(cyclam)]+ these values are 2.4 × 10−3 s−1, ΔH# = 50.8 kJ mol−1 and ΔS# = − 119 J K mol−1. The rate of chloride aquation reactions for cis-[RuCl2(cyclen)]+ is about 1.5 times faster than for the cyclam complex. The reactivity difference could be due to a combination of the σ-trans effect, the nephelauxetic effect and the effect of solvation.

tert-Butyl 2,5-diaryl-3-oxopent-4-ynoates, obtained from arylacetylenes and the acid chloride of tert-butyl 2-phenylmalonate, represent strongly enolized β-ketoesters. Their C≡C bonds were activated by Ag(I) salts so that de-tert-butylating π-cyclizations occurred. The latter followed a 6-endo-dig mode giving 3,6-diaryl-4-hydroxy-2-pyrones, or a 5-exo-dig mode giving (Z)-configured 2-aryl-4-(arylmethylidene)tetronic acids (“pulvinones”). Perfectly selective pyrone formations were induced by AgSbF6 in methanol and equally selective pulvinone formations by Ag2CO3 and DABCO in acetonitrile.

Lithium bis(trifluoromethanesulfonyl)imide (LiNTf2) doped ionic liquids (ILs) are investigated herein, as potential electrolytes for lithium-ion batteries, via scaled-charge molecular dynamics simulations. Four model ILs based on the [NTf2]− anion and heterocyclic ammonium cations were studied with varying concentrations, ranging from 0 to 1 M solutions, of the dissolved lithium salt. The pyrrolidinium ([pyrHH]+), piperidinium ([pipHH]+), N-butyl-pyrrolidinium ([pyrH4]+), and N-butyl-N-methyl-pyrrolidinium ([pyr14]+) cations were considered to evaluate the combined effects of increased ring size, as well as the introduction of apolar groups on the nitrogen atom of the cations, on the liquid structure properties of the electrolytes. Among the investigated ILs, [pyr14][NTf2] is the only aprotic IL allowing for a comparison of protic and aprotic ILs. The lithium coordination shell is seen to be quite different in the various IL-based systems; networks of lithium ions bridged by [NTf2]− ions have interesting ...

Recently, a number of fentanyl analogs have been implicated in overdose deaths in Europe and in the US. So far, little is known of the molecular behavior of the structurally related subgroup; the alicyclic fentanyls. In this study, reference standards of cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and 2,2,3,3-tetramethylcyclopropyl fentanyl (TMCPF) at a final concentration of 5 µM were incubated with cryopreserved human hepatocytes (1 × 106 cells/mL) for 0, 1, 3 and 5 h. The metabolites formed were identified by liquid chromatography–quadrupole time-of-flight mass spectrometry analysis. The most abundant biotransformation found was N-dealkylation (formation of normetabolites) and oxidation of the alicyclic rings. As ring size increased, the significance of N-dealkylation decreased in favor of alicyclic ring oxidation. An example of this was cyclopropyl fentanyl, with a three-carbon ring, whose normetabolite covered 82% of the total metabolic peak area and no oxidation of the alicyclic ring was observed. In contrast, TMCPF, with a seven-carbon ring structure, rendered as much as 85% of its metabolites oxidized on the alicyclic ring. Other biotransformations found included oxidation of the piperidine ethyl moiety and/or the phenethyl substructure, glucuronidation as well as amide hydrolysis to form metabolites identical to despropionyl fentanyl. Taken together, this study provides a base for understanding the metabolism of a number of structurally related fentanyl analogs formed upon intake. Electronic supplementary material The online version of this article (10.1007/s00204-018-2330-9) contains supplementary material, which is available to authorized users.

Nanocluster models were investigated to explore the diversity of metallacycle intermediates for ethylene dimerization over NiMCM-41 at B3LYP/6-311+G* and M06/Def2-TZVP. The thermodynamic favorability of the formation of matallacycle with respect to the ring size of silica varied in the sequence of 6T

Monomers possessing two functionalities suitable for polymerization are often designed and utilized in syntheses directed to the formation of cross-linked macromolecules. In this review, we give an account of recent developments related to the use of such monomers in cyclopolymerization processes, in order to form linear, soluble macromolecules. These processes can be activated by means of radical, ionic, or transition-metal mediated chain-growth polymerization mechanisms, to achieve cyclic moieties of variable ring size which are embedded within the polymer backbone, driving and tuning peculiar physical properties of the resulting macromolecules. The two functionalities are covalently linked by a "tether", which can be appropriately designed in order to "imprint" elements of chemical information into the polymer backbone during the synthesis and, in some cases, be removed by postpolymerization reactions. The two functionalities can possess identical or even very different reactivities toward the polymerization mechanism involved; in the latter case, consequences and outcomes related to the sequence-controlled, precision synthesis of macromolecules have been demonstrated. Recent advances in new initiating systems and polymerization catalysts enabled the precision syntheses of polymers with regulated cyclic structures by highly regio- and/or stereoselective cyclopolymerization. Cyclopolymerizations involving double cyclization, ring-opening, or isomerization have been also developed, generating unique repeating structures, which can hardly be obtained by conventional polymerization methods.

A comprehensive study of the reactions of chelating phosphines with Ni(cod)2 to form (phosphine)Ni(cod), (phosphine)2Ni, or mixtures thereof is presented. A series of (phosphine)Ni(cod) complexes were isolated and characterized. The structural differences between the (phosphine)Ni(cod) and (phosphine)2Ni complexes were examined using X-ray crystallography and 1H and 31P NMR spectroscopy. In addition, the effects of ring size, rigidity, and bulk of the phosphine backbone on the formation of either (phosphine)Ni(cod) or (phosphine)2Ni were investigated. These studies show that the Ni–P bond lengths in both the (phosphine)Ni(cod) and (phosphine)2Ni complexes and the size of the ring formed by the chelating phosphine and Ni are crucial in determining whether or not (phosphine)Ni(cod) complexes can be isolated. Other factors such as π-stacking interactions were found to have marginal influence.

The one-pot synthesis and modification of cyclic peptides through a self-cleaving on-resin protocol is described. We apply Dawson's MeDbz linker to achieve direct intramolecular peptide cyclization by thioesterification followed by S → N acyl shift. This native chemical ligation approach requires no activating additive and allows direct modification of the crude cyclic peptides in one-pot. The strategy was applied to synthesize 5 cyclic peptide natural products of varying ring size. Finally, one-pot modifications include desulfurization, fluorophore conjugation, and intramolecular disulfide formation.

Cyclophilins are a family of peptidyl-prolyl isomerases that are implicated in a wide range of diseases including hepatitis C. Our aim was to discover through total synthesis an orally bioavailable, non-immunosuppressive cyclophilin (Cyp) inhibitor with potent anti-hepatitis C virus (HCV) activity that could serve as part of an all oral antiviral combination therapy. An initial lead 2 derived from the sanglifehrin A macrocycle was optimized using structure based design to produce a potent and orally bioavailable inhibitor 3. The macrocycle ring size was reduced by one atom, and an internal hydrogen bond drove improved permeability and drug-like properties. 3 demonstrates potent Cyp inhibition (Kd = 5 nM), potent anti-HCV 2a activity (EC50 = 98 nM), and high oral bioavailability in rat (100%) and dog (55%). The synthetic accessibility and properties of 3 support its potential as an anti-HCV agent and for interrogating the role of Cyp inhibition in a variety of diseases.

Six examples of α,α′-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridine-cobalt(II) chlorides, [2,3:5,6-{C4H8C(NAr)}2C5HN]CoCl2 (Ar = 2-(C5H9)-6-MeC6H3 Co1, 2-(C6H11)-6-MeC6H3 Co2, 2-(C8H15)-6-MeC6H3 Co3, 2-(C5H9)-4,6-Me2C6H2 Co4, 2-(C6H11)-4,6-Me2C6H2 Co5, 2-(C8H15)-4,6-Me2C6H2 Co6), containing N-aryl groups that differ in either the ring size of the ortho-cycloalkyl substituents or the para-R group (R = H, Me), have been synthesized using a one-pot template approach. The molecular structure of Co1 highlights the ring puckering of both the ortho-cyclopentyl substituents and the two pyridine-fused seven-membered rings; a square-based pyramidal geometry is conferred about the metal center. On activation with either methylaluminoxane (MAO) or modified MAO (MMAO), all six complexes afforded strictly linear polyethylene (all Tm's > 130 °C) with high molecular weight (Mw up to 64.3 kg mol−1). Furthermore, all precatalysts displayed high activities (up to 2 × 106 g PE mol-1 (Co) h−1) at temperatures between 20 and 60 °C with the catalytic activities correlating with the type of ortho-cycloalkyl substituent: cyclohexyl (Co2, Co5) > cyclopentyl (Co1, Co4) > cyclooctyl (Co6, Co3) for either R = H or Me. The narrow unimodal distributions of the resulting polymers are consistent with single-site active species for the catalysts.

A gold-catalyzed oxidative coupling of alkynes was developed as an efficient approach for the synthesis of challenging cyclic conjugated diynes (CCD). Compared to the classical copper-promoted oxidative coupling reaction of alkynes, this gold-catalyzed process exhibits a faster reaction rate due to the rapid reductive elimination from the Au(III) intermediate. This unique reactivity thus allowed a challenging diyne macrocyclization to take place in high efficiency. Condition screening revealed a [(n-Bu)(4)N](+)[Cl-Au-Cl](−) salt as the optimal pre-catalyst. Macrocycles with ring size between 13 to 28 atoms were prepared in moderate to good yields, which highlighted the broad substrate scope of this new strategy. Furthermore, the synthetic utilities of the cyclic conjugated diynes for copper-free click chemistry have been demonstrated, which showcased the potential application of this strategy in biological systems.

Oxygen heterocycles are the second most common type of heterocycles that appear as structural components of U.S. Food and Drug Administration (FDA) approved pharmaceuticals. Analysis of our database of drugs approved through 2017 reveals 311 distinct pharmaceuticals containing at least one oxygen heterocycle. Most prevalent among these are pyranoses, with furanoses, macrolactones, morpholines, and dioxolanes rounding off the top five. The main body of this Perspective is organized according to ring size, commencing with three- and four-membered rings and ending with macrocycles, polymers, and unusual oxygen-containing heterocycles. For each section, all oxygen heterocycle-containing drugs are presented along with a brief discussion about structural and drug application patterns.

Three tetranuclear heterometallic ZnII‐LnIII complexes of the 30‐membered [3+3] hexaimine macrocycle (LEt)6–, with general formula ZnII3LnIII(LEt)(NO3)2OAc·5H2O (LnIII = DyIII, ErIII, YbIII), were prepared using our established one‐pot synthesis methodology, whereby the individual components of the whole system are poised to assemble themselves into a mixed 3d/f4f macrocyclic system. This uses a 3:1:3:3 reaction of ZnII acetate, the appropriate LnIII nitrate, 1,4‐diformyl‐2,3‐dihydroxybenzene, and 1,2‐diaminoethane. These ten individual building blocks readily assemble into tetrametallic complexes, analogous to our previously reported examples with larger macrocycles. Identity was confirmed by IR spectroscopy (imine), micro‐ (C, H, N) and metal‐ (Zn, Ln) analysis, TGA (solvent content), and mass spectrometry. Magnetic properties were studied down to 2 K and with ac susceptibility measurements were used to check for slow relaxation of the magnetization characteristic of Single‐Molecule Magnet (SMM) behavior. As is often the case for single ion systems (only Ln is paramagnetic) no such behavior was observed. However, under an applied dc field, an out‐of‐phase ac susceptibility signal is seen for all three complexes. We speculate that shrinkage of macrocyclic ring size (30) compared to that of the original ZnII3DyIII system (33) has led to a less favorable coordination arrangement for the DyIII and ErIII ions through a change in the imposed coordination environment of the LnIII ion.

The chemokine CC receptor subtype 2 (CCR2) has attracted intensive interest for drug development in diverse therapeutic areas, including chronic inflammatory diseases, diabetes, neuropathic pain, atherogenesis and cancer. By employing a cut-and-sew scaffold hopping strategy, we identified an active scaffold of 3,4-dihydro-2,6-naphthyridin-1(2H)-one as the central pharmacophore to derive novel CCR2 antagonists. Systematic structure–activity relationship study with respect to the ring size and the substitution on the naphthyridinone ring gave birth to 1-arylamino-6-alkylheterocycle-6,7,8,9-tetrahydro-5H-pyrido[4,3-c]azepin-5-ones as a brand new chemotype of CCR2 antagonists with nanomolar inhibitory activity. The best antagonism activity in this series was exemplified by compound 13a, which combined the optimal substitutions of 3,4-dichlorophenylamino at C-1 and 3-(4-(N-methylmethylsulfonamido)piperidin-1-yl)propyl at N-6 position, leading to an IC50 value of 61 nM and 10-fold selectivity for CCR2 over CCR5. Efficient and general synthesis was established to construct the innovative core structure and derive the compound collections. This is the first report on our designed 6,7,8,9-tetrahydro-5H-pyrido[4,3-c]azepin-5-one as novel CCR2 antagonist scaffold and its synthesis.

Cycloparaphenylenes (CPPs) are hoop-shaped conjugated hydrocarbons corresponding to partial structures of fullerenes or armchair carbon nanotubes. Here, we examined the fluorescence properties of a series of [n]cycloparaphenylene dications ([n]CPP2+, n = 5–9), which have unique in-plane aromaticity. The fluorescence peak positions of the [n]CPP2+s shifted to the longer-wavelength region with increasing ring size, reaching the near-infrared region for those with n > 5. The fluorescence quantum yield of [6]CPP2+ was the highest among the [n]CPP2+s examined in this study, and the value was on the same order as that of carbon nanotubes. The Stokes shifts of [n]CPP2+s were smaller than those of neutral [n]CPPs, which do not have in-plane aromaticity. Theoretical calculations indicate that [n]CPP2+s undergo smaller structural changes upon S0–S1 transition than [n]CPPs do, and this is responsible for the difference of the Stokes shift. Furthermore, molecular orbital analysis reveals that the S0–S1 transition of ...

A novel synthesis of multicyclic polymers that feature ultradense arrays of cyclic polymer units has been developed by exploiting the cyclopolymerization of α,ω-norbornenyl end-functionalized macromonomers mediated by the Grubbs third-generation catalyst (G3). Owing to the living polymerization nature, the number of cyclic repeating units in these multicyclic polymers was controlled to be between 1 and approximately 70 by varying the initial macromonomer-to-G3 ratio. The ring size was also tuned by choosing the molecular weight of the macromonomer; in this way we successfully prepared multicyclic polymers that possess cyclic repeating units composed of up to about 500 atoms, which by far exceeds those prepared to date by cyclopolymerization. Specifically, cyclopolymerizations of α,ω-norbornenyl end-functionalized poly(l-lactide)s (PLLAs) proceeded homogeneously under highly dilute conditions (∼0.1 mM in CH2Cl2) to give multicyclic polymers that feature cyclic PLLA repeating units on the polynorbornene bac...

The ring-closing metathesis (RCM) of α,m,ω-triene was employed for the syntheses of four slightly different EE, EZ, ZE, and ZZ isomers of macrocycles with two greatly separated type I olefins. Kinetic control of the RCM reaction using G1 was achieved, in which secondary metathesis of the initially formed RCM product that usually afforded the thermodynamically favored product was inhibited, and a reliable model was built to differentiate the kinetic or thermodynamic control in the RCM reaction. Kinetic studies of olefin metathesis using the kinetically controlled Z-selective catalyst Cat-Z were conducted to determine its thermodynamic capability to convert (Z)-olefin to (E)-olefin. Finally, the ring size selectivity of α,ω- vs α,m-/m,ω-products in the RCM reaction of α,m,ω-triene revealed that all types of isomeric α,ω-products are favored for the 18-membered ring and above, and α,m-/m,ω-products are predominant for the rings with 14-members and less. For the 15-, 16-, and 17-membered rings, each of the E/...

Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization. This type of catalyst features six-membered chelate ring size, and can enable the copolymerizations of ethylene with a wide variety of polar monomers. In this contribution, we decide to investigate the influence of chelate ring size on the properties of phosphine-sulfonate palladium catalysts. As such, a series of phosphine-sulfonate ligands and the corresponding seven-membered ring Pd(II) complexes [ κ 2-( P , O )-2-(CH2- P R1R2)-4-methylphenyl-sulfonato]Pd(Me) (DMSO) ( Pd1 , R1=R2=Cy, Pd2 , R1=R2= o -MeO-C6H4; Pd3 , R1=Ph, R2=2-[2,6-(MeO)2C6H3]C6H4; DMSO=dimethyl sulfoxide) were designed, prepared and characterized. These palladium complexes are moderately active when they were applied in ethylene polymerization and copolymerizations with methyl acrylate and butyl vinyl ether. However, their properties are greatly reduced from those of the classic six-membered ring phosphine-sulfonate palladium complex Pd2 ′. The experimental results indicate that the bigger chelate ring size can increase the ligand flexibility and damage the catalytic properties for the phosphine-sulfonate type palladium catalysts.

The size of nitrogen heterocycle in N-allyl- and N-propargyl-α-furyl lactams, as well as the nature of the unsaturated substituent linked to the nitrogen atom affected the possibility of thermal intramolecular [4+2] cycloaddition between multiple bond and the furan ring. N-Allyl-γ-(α-furyl)butyrolactam was shown to be unreactive at temperatures from 140 to 230°С. Substituted δ-valero- and e-caprolactams underwent partial Diels–Alder cyclization, forming tautomeric mixtures that contained both the initial open-chain form and the cyclic form (diastereomeric 3a,6-epoxyisoindoles fused with an aza ring) in ratios between 19:81 and 55:45. N-Propargyl-α-furyl lactams did not participate in thermal IMDAF reaction regardless of the ring size and the temperature of the synthesis.

A series of isoquinuclidine benzamides as glycine uptake inhibitors for the treatment of schizophrenia are described. Potency, lipophilicity, and intrinsic human microsomal clearance were parameters for optimization. Potency correlated with the nature of the ortho substituents of the benzamide ring, and reductions in lipophilicity could be achieved through heteroatom incorporation in the benzamide and pendant phenyl moieties. Improvements in human CLint were achieved through changes in ring size and the N-alkyl group of the isoquinuclidine itself, with des-alkyl derivatives (40–41, 44) demonstrating the most robust microsomal stability. Dimethylbenzamide 9 was tested in a mouse MK801 LMA assay and had a statistically significant attenuation of locomotor activity at 3 and 10 μmol/kg compared to control.

Platinum nanoparticles (NPs) modified with alkylamines containing various aromatic rings (benzyl, naphtyl, anthryl, and pyrenyl) were synthesized as model cathode catalysts for fuel cells to investigate the role of aromatic surface modification agents on catalytic performance. Surface modification of Pt was confirmed by nuclear magnetic resonance spectra for NPs and thermogravimetric analysis for carbon-supported catalysts. Surface modification of Pt NPs with aromatic alkylamines improved the electrocatalytic activities for the oxygen reduction reaction, whose activity values increased by increasing the number of aromatic rings. The effect of surface modification on the electronic properties of the catalyst was evaluated by X-ray photoelectron spectroscopy. A large positive shift in the Pt 4f binding energy of surface-modified catalyst, especially for anthryl and pyrenyl modifications, was observed, indicating that one of the important factors is metal–support interaction facilitated by the aromatic groups through the π–π interactions with carbon support.

Small size benzo-substituted crown ethers are attractive complexing agents for lithium isotope separation by solvent extraction. Low transfer of the crown ethers from solvent to water is a key point for applicability of the extractants. In the present study, 9- and 12-membered crown ethers were synthesized, and their distribution between chloroform and water was studied. Polyether ring size, benzene substituents and addition of LiCl to water were found to effect on distribution constants. Low losses of the macrocycles were observed at single-stage contact with aqueous phase. However, these losses should be taken into account in the design of multistage processes for the preparation of highly enriched lithium isotopes.

This review considers noncovalent bonds between divalent chalcogen centers. In the first part we present X-ray data taken from the solid state structures of dimethyl- and diphenyl-dichalcogenides as well as oligoalkynes kept by alkyl-sulfur, -selenium, and -tellurium groups. Furthermore, we analyzed the solid state structures of medium sized (12-24 ring size) selenium coronands and medium to large rings with alkyne and alkene units between two chalcogen centers. The crystal structures of the cyclic structures revealed columnar stacks with close contacts between neighboring rings via noncovalent interactions between the chalcogen centers. To get larger space within the cavities, rings with diyne units between the chalcogen centers were used. These molecules showed channel-like structures in the solid state. The flexibility of the rings permits inclusion of guest molecules such as five-membered heterocycles and aromatic six-membered rings. In the second part we discuss the results of quantum chemical calculations. To treat properly the noncovalent bonding between chalcogens, we use diffuse augmented split valence basis sets in combination with electron correlation methods. Our model substances were 16 dimers consisting of two Me-X-Me (X = O, S, Se, Te) pairs and dimers of Me-X-Me/Me-X-CN (X = O, S, Se, Te) pairs. The calculations show the anticipated increase of the interaction energy from (Me-O-Me)

The ene cyclization has evolved to become an indispensable tool for the synthesis of various ring size heterocyclic compounds. In the past and recent years, many exciting reports have demonstrated the broad scope and synthetic utility of ene cyclization and the versatility of oxonium ion, iminium ion and thionium ion intermediates. Moreover, the ease of regio- and stereoselectivity of ene cyclization has led to the development of new types of heterocyclic compounds. This article aims at reviewing the utilities of ene cyclization reactions for the synthesis of various ring sizes of oxygen, nitrogen and sulfur heterocycles. It also covers some applications in natural product synthesis. The mechanism of the reactions is discussed wherever necessary. The review article covers the time period from 1986 to 2017.

Morphology engineering is a decisive factor for the optoelectronic properties of nanocrystals. Differing from morphologies with a solid interior, ring-like structures have a unique internal space which is not only available for loading chemicals, but also useful for controlling the field distribution. Herein, the perovskite array family welcomes a new member – CsPbBr3 ring arrays. This work solves several fundamental problems for fabricating CsPbBr3 ring arrays: (i) developing a simple method using 2D colloidal crystal templates to achieve ring arrays of CsPbBr3, (ii) finding two ways, say changing the template size or annealing of the template, to accurately tune the ring size of the array in a wide range from 2.6 μm to 16.9 μm, and (iii) investigating the dynamics of perovskite rings, which indicates a shrinking process towards the template spheres before the crystallization of the perovskites. Finally, the application of CsPbBr3 perovskite ring arrays to the field of lasers is shown.

The oxidation potential of a test set of 21 nitroxide radicals, including a number of novel compounds, has been studied experimentally in acetonitrile and correlated with theoretical calculations. It was found that both Hammett constants (σp) of the substituents on the nitroxide radicals and hyperfine splitting constants of the respective nitrogen atoms (αN) were well correlated to their experimental oxidation potentials. Theoretical calculations, carried out at the G3(MP2,CC)(+)//M06-2X/6-31+G(d,p) level of theory with PCM solvation corrections, were shown to reproduce experiments to within a mean absolute deviation of 33 mV, with a maximum deviation of 64 mV. The oxidation potentials of the nitroxides examined varied over 400 mV, depending on ring size and substitution. This considerable variation can be rationalised by the ability of various substituents to electrostatically stabilize the oxidised oxoammonium cation. Importantly, this can be quantified by a simple predictive relationship involving the distance scaled dipole and quadrupole moments of the analogous cyclohexyl ring. This highlights the often-overlooked role of through-space electrostatic substituent effects, even in formally neutral compounds.

Despite the difficulty in administering a safe dose regimen and reports of emerging resistance, warfarin (1) remains the most widely-used oral anticoagulant for the prevention and treatment of thrombosis in humans globally. Systematic substitution of the warfarin phenyl ring with either 1,3,5,7-cyclooctatetraene (COT) (2), cubane (3), cyclohexane (4) or cyclooctane (5) and subsequent evaluation against the target enzyme, vitamin K epoxide reductase (VKOR), facilitated interrogation of both steric and electronic properties of the phenyl pharmacophore. The tolerance of VKOR to further functional group modification (carboxylate 14, PTAD adduct 15) was also investigated. The results demonstrate the importance of both annulene conferred π-interactions and ring size in the activity of warfarin.

Rotaxane is a supramolecule in which ring chains are threaded on an axial chain, showing a fascinating sliding dynamics of ring chains along the axial chain. In this study, we investigated the sliding dynamics of ring chains on a knotted polymer chain in rotaxane, exhibiting a sub-diffusion at the intermediate time range resulting from the intra-strand interaction between the ring chains and the knotted axial chain in the knot crossing region. Meanwhile, the non-monotonous dependence of sliding diffusion coefficient D of ring chains on ring size Nring indicates that there exist two competing effects: one is the friction effect between the ring chains and the axial chain in which the ring chains slide fast along the knotted axial chain for large Nring, and another is the knot effect in which the ring chains move slowly along the knotted axial chain for large Nring because the knot crossing hinders ring chains to pass through for large Nring. Based on the unique sliding sub-diffusion behaviour of the threaded ring chains, we also proposed a new approach to estimate the average knot size of the knotted axial chain, and our estimation about the average knot size is in good agreement with the result according to the Alexander polynomial calculation using the free python package TOPOLY. These results may provide a fundamental view for understanding the dominant factors of the sliding dynamics of ring chains in complex polymer-based rotaxane.

Our ultimate goal is to create a library of ester-free type trimetylene carbonate derivatives, so that we can design and produce poly(trimethylene carbonate) (PTMC) derivatives that meet application needs. Herein we introduced cycloalkyl groups (cyclopentyl, cyclohexyl and cycloheptyl groups) into the side chain of an ester-free type PTMC. Previously, ester-free type PTMC derivatives with aromatic rings in the side chain have been reported from our group, but there have been no reports of aliphatic cyclic compounds introduced with ether linkage into their side chains. This research makes possible the production of more versatile ester-free PTMC derivatives using cycloalkyl groups. The effect of ring size was also investigated. All of the monomers gave homopolymers with Mn of a few thousands, improving the thermal degradation temperatures, compared to unmodified PTMC. We found a tendency towards increasing glass transition temperature with larger ring size.

To find and calibrate a robust and reliable computational protocol for mapping conformational space of medium-sized molecules, exhaustive conformational sampling has been carried out for a series of seven macrocyclic compounds of varying ring size and one acyclic analogue. While five of them were taken from the MD/LLMOD/force field study by Shelley and co-workers (Watts, K. S.; Dalal, P.; Tebben, A. J.; Cheney, D. L.; Shelley, J. C. Macrocycle Conformational Sampling with MacroModel. J. Chem. Inf. Model. 2014, 54, 2680−2696), three represent potential macrocyclic inhibitors of human cyclophilin A. The free energy values (GDFT/COSMO-RS) for all of the conformers of each compound were obtained by a composite protocol based on in vacuo quantum mechanics (DFT-D3 method in a large basis set), standard gas-phase thermodynamics, and the COSMO-RS solvation model. The GDFT/COSMO-RS values were used as the reference for evaluating the performance of conformational sampling algorithms: standard and extended MD/LLMOD...

1,1-Difluoro-1-alkenes bearing a biaryl-2-yl group effectively underwent site-selective intramolecular iodoarylation by the appropriate cationic iodine species. Iodoarylation of 2-(2-aryl-3,3-difluoroallyl)biaryls proceeded via regioselective carbon–carbon bond formation at the carbon atoms in β-position to the fluorine substituents, thereby constructing dibenzo-fused six-membered carbocycles bearing a difluoroiodomethyl group. In contrast, 2-(3,3-difluoroallyl)biaryls underwent a similar cyclization at the α-carbon atoms to afford ring-difluorinated seven-membered carbocycles.

Two kinds of aza[1n]paracyclophanes, tetraaza[14]paracyclophane (P4) and octaaza[18]paracyclophane (P8), were synthesized as the smallest and the largest monodisperse macrocyclic oligomers of polyaniline ever made. Herein we report the electronic nature of the cationic species of these two macrocycles with different ring size. By combining ESR spectroscopy and DFT calculations it was suggested that P4·+ was classified as delocalized class III or poised on the class II/III borderline while P8·+ was regarded as a localized class II mixed-valence system. We successfully isolated the dication of P4 as a stable dicationic salt P42+·2[SbF6]−, and the structure of P42+ was determined by X-ray crystal analysis. Variable-temperature NMR measurements for P42+·2[SbF6]− unequivocally showed that P42+ was a 22π electron system with a singlet ground state. The supercharged hexacation of P8 was also isolated as P86+·6[SbCl6]−, and X-ray crystal analysis revealed that P86+ includes one SbCl6– anion in its macrocyclic cavity.

Ring closing metathesis of acyclic trienes that can provide oxacycles or carbocycles has been investigated. It was found that a substituent on one of the alkene units determines the reaction course to provide either oxacycles or carbocyles exclusively irrespective of the ring size of the resulting compounds. Ring closing metathesis of acyclic trienes with Grubbs’ first generation (G-I) catalyst was found to be greately influenced by the presence of an alkyl substituent on one of the alkene units to provide either oxacycles or carbocyles exclusively irrespective of the ring size of the resulting compounds.

The effect of macrocycle ring size on the corrosion inhibition efficiency of dibenzo-12-crown-4 (DB12C4), dibenzo-15-crown-5 (DB15C5), dibenzo-18-crown-6 (DB18C6), dibenzo-21-crown-7 (DB21C7) and dibenzo-24-crown-8 (DB24C8) have been elucidated by mean of density functional calculation at B3LYP/6-31G(d) level of theory in the gas and aqueous environment. The quantum chemical parameters including the frontier orbital energies (EHOMO, ELUMO), ionization potential (I), electron affinity (A), the absolute electronegativity (χ), hardness (η), softness (σ), and the fraction of electron transferred (ΔN) are positively correlated to the corrosion inhibition efficiency (IE%) of the studied crown ethers. The calculation results indicate that DB24C8 exhibits the highest corrosion inhibition efficiency, whereas DB12C4 exhibits the lowest corrosion inhibition efficiency. The results of this study will contribute to design crown ethers potential as corrosion inhibitors.

We have serendipitously discovered a unique transformation of a cyclooctatetraene derivative 1 into a cycloheptatriene spirolactone 3 upon oxidation, which is the first such transformation reported in 60 years. Product 3 could be reversibly interconverted into the aromatic tropylium cation 3H+ by acid/base treatment, which was accompanied by drastic spectroscopic changes. The resultant cycloheptatriene could be further converted into benzene upon oxidation. We characterized all the key structures by X-ray studies. Eventually, the π-conjugated ring size shrinks from 8 to 7, then finally to 6 upon oxidation, in the direction of the stronger aromatization.

A series of bulky pyridine-bridged NHC-Ru complexes have been rationally designed and synthesized; these exhibited very high catalytic activity in the hydrogenation of cyclic and linear carbonates under mild reaction conditions. In the presence of catalytic amounts of a weak base, a broad range of substrates with different ring size and steric bulk were well tolerated, providing methanol and the corresponding diols in excellent yields with a catalyst loading as low as 0.5 mol %.

The complexation of molecular clips containing fragments of diphenylglycoluril and benzocrown ethers with paraquat and its derivatives has been studied both in solution and in the solid state. In this paper we studied the influence of the crown ether ring size and the nature of the substituents at the nitrogen atoms of the paraquat derivatives on the composition and stability of these complexes.

Zirconium and hafnium complexes bearing cycloheptane- or cyclononane-fused [OSSO]-type bis(phenolato) ligands ([C7] and [C9], respectively) were prepared and subjected to the polymerization of 1-hexene as the precatalyst. The polymerizations produced poly(1-hexene)s with high activities and high isospecificity, where complexes bearing [C9] were more reactive than those bearing [C7]. Their activities were compared with those of the corresponding complexes bearing cyclohexane- and cyclooctane-fused ligands ([C6] and [C8], respectively), which we reported previously, to show the order of activity [C8] > [C9] > [C7] > [C6]. The ring-size effect on the activity was investigated with the help of DFT calculations on active and dormant cationic zirconium species, π complexes of the active species with propene, and transition states for propene insertion into the Zr–C(iBu) bond. The order of activity speculated from the activation energy, that is the energy difference between the π complex and the corresponding tr...

Piperlongumine B ( 19 ), an alkaloid previously isolated from long pepper ( Piper longum ) has been synthesized for the first time in a short sequence and in good yield together with 19 analogs. Screening of these compounds in Ellman's assays showed several of them to be good inhibitors of acetylcholinesterase while being less active for butyrylcholinesterase. Activity of the compounds increased with the ring size of the heterocycle, and a maximum of activity was observed for an analog holding 12 methylene groups in the aliphatic side chain. These compounds may be regarded as promising candidates for the development of efficient inhibitors of acetylcholinesterase being useful for the treatment of Alzheimer's disease.