Interaction between cucurbit[6]uril and bispyridinecarboxamide

The interaction between cucurbit[6]uril and N,N′-(m-bispyridinecarboxamide)-1,n-alkane (m = 2, 3, 4; n = 4, 6, 8) has been investigated by ¹H-NMR, ESI-MS and single crystal X-ray diffraction method. The results show that cucurbit[6]uril can form pseudorotaxanes with N,N′-(m-bispyridinecarboxamide)-1,6-hexane (m = 2, 3, 4) easily. When the alkyl chain length increases (n = 8), the binding mode is identical, but the binding ability of the host towards guest decreases. In both two cases cucurbit[6]uril shows no selectivity towards positional isomers. However, in the case of n = 4, the binding mode is different, having relations with positional substitution of the guest. Only N,N′-(m-bispyridinecarboxamide)-1,4-butane (m = 2) can form pseudorotaxane with cucurbit[6]uril, while the other two (m = 3, m = 4) form external complex with cucurbit[6]uril. The possible reason for the difference has been discussed.     

Electrochemistry of nickel(II) and copper(II) N,N′-ethylenebis(acetylacetoniminato) complexes and their electrocatalytic activity for reduction of carbon dioxide and carboxylic acid protons

The effect of the metal center of [ML] complexes [M = Ni(II), Cu(II); L = N,N′-ethylenebis(acetylacetoniminato)] on their electrochemistry and electrocatalytic activity for the reduction of CO₂ and protons has been studied using cyclic voltammetry and bulk electrolysis. The two complexes exhibit different electrochemistries, which are not significantly dependent on the nature of the solvent. The electrocatalytic activity of [NiL] is significantly higher than that of [CuL] for CO₂ reduction, due to the higher stability of the electrochemically generated [Ni(I)L] complex, relative to the Cu(I) analog. The diffusion coefficient of [NiL] calculated from the steady-state diffusion limiting current is 3.0 × 10^?6 cm² s^?1. The catalytic efficiency of [NiL] in non-aqueous solvents in terms of i _p(CO₂)/i _p(N₂) per nickel center is smaller than that of [Ni(cyclam)]²⁺, but greater than those of sterically hindered mononuclear [Ni(1,3,6,8,10, 13,15-heptaazatricyclo(11.3.1.1) octadecane)]²⁺ or multinuclear [Ni₃ (X)]⁶⁺ where X = 8,8′,8″-{2,2′,2″(-nitrilotriethyl)-tris(1,3,6,8,10,13,15-heptaazatricyclo(11.3.1.1) octadecane}. Both [NiL] and [CuL] are also electrocatalysts for the reduction of carboxylic acid protons, with the catalytic pathway being different for acetic and trifluoroacetic acids in MeCN.     

Effect of the glutaraldehyde derivatives of Calix[n]arene as cross-linker reagents on lipase immobilization

Synthesis of the glutaraldehyde derivatives calix[n]arene (n = 4,6,8) (Calix[n]-GA) and using as cross-linkers for immobilization of Candida rugosa lipase (CRL) have been discussed in this paper. The amino functional calix[n]arene derivatives (Calix[n]-NH ₂) were synthesized via reduction of dinitrile, hexanitrile and octanitrile derivatives of calix[n]arenes. These amino functional calix[n]arene derivatives (Calix[n]-NH ₂) were converted to their aldehyde derivativatives with glutaraldehyde. The calix[n]arene derivatives were used in lipase immobilization in order to see the role of calix[n]arene binding site on the lipase activitiy and stability. The activity recovery of calix[n]arene-supported lipases (Calix[n]-CRL) based on the Calix[4]-CRL, Calix[6]-CRL and Calix[8]-CRL reaches to 53.5, 66.1 and 76.4%, respectively.     

Solvent extraction of europium trifluoromethanesulfonate into nitrobenzene in the presence of p-tert-butylcalix[6]arene and p-tert-butylcalix[8]arene

From extraction experiments and ??-activity measurements, the extraction constants corresponding to the general equilibrium Eu³⁺(aq) + 3A^?(aq) + L(nb) ? EuL³⁺(nb) + 3A^?(nb) taking part in the two-phase water?Cnitrobenzene system (A^? = CF₃SO₃ ^?; L = p-tert-butylcalix[6]arene, p-tert-butylcalix[8]arene; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the EuL³⁺ complexes in nitrobenzene saturated with water were calculated for a temperature of 25 °C as log ?? _nb(EuL³⁺) = 6.4 ± 0.1 (L = p-tert-butylcalix[6]arene) and log ?? _nb(EuL³⁺) = 11.3 ± 0.1 (L = p-tert-butylcalix[8]arene).     

Radiosynthesis of 10-(2-[18F]fluoroethoxy)-20(S)-camptothecin as a potential positron emission tomography tracer for the imaging of topoisomerase I in cancers

The preparation of 10-(2-[¹⁸F]fluoroethoxy)-20(S)-camptothecin, a potential positron emission tomography tracer for the imaging of topoisomerase I in cancers, is described. 10-(2-[¹⁸F]Fluoroethoxy)-20(S)-camptothecin was synthesized by the [¹⁸F]fluoroalkylation of the corresponding hydroxy precursor molecule with 2-[¹⁸F]fluoroethyl bromide ([¹⁸F]FEtBr) in dimethylsulfoxide (DMSO) at 55 °C for 20 min; this was followed by purification using high performance liquid chromatography (HPLC) with a total preparation time of 60 min. The overall radiochemical yield was approximately 5.4–12 % (uncorrected), and the radiochemical purity was above 96 %.     

Immobilization of calix[6]arene bearing carboxylic acid and amide groups on aminopropyl silica gel and its sorption properties for Cr(VI)

An aminopropyl silica gel-immobilized calix[6]arene (C[6]APS) containing both amide and acid moieties was prepared from p-tert-butylcalix[6]arene hexacarboxylate derivative and aminopropyl silica gel in the presence of N,N′-diisopropyl carbodiimide coupling reagent. C[6]APS was used to evaluate the sorption properties of Cr(VI) as a sorbent material. In sorption studies, it was observed that C[6]APS was highly effective at pH 1.5 for Cr(VI). The effect of parameters such as pH, sorbent dosage, contact time, initial Cr(VI) concentration and temperature on Cr(VI) sorption; the sorption isotherms were also studied. Maximum sorption capacity was obtained as 3.1 mg g^?1 at pH 1.5 and 25 °C for 1 h and 10.4 mg L^?1 initial Cr(VI) concentration. Thermodynamic parameters such as change in free energy, enthalpy, and entropy were also determined. In the isotherm studies, Langmuir and Freundlich isotherm models were applied and it was found that the experimental data confirmed to Freundlich isotherm model, and the batch sorption capacity of C[6]APS was calculated as 37.66 mg g^?1.     

The synthesis of a new cardiac sympathetic nerve imaging agent N-[11C]CH3-dopamine and biodistribution study

In this study, we synthesized and characterized N-[¹¹C]methyl-dopamine ([¹¹C]MDA) for cardiac sympathetic nerve imaging. [¹¹C]MDA was synthesized by direct N-methylation of dopamine with [¹¹C]methyl iodide and purified by semi-preparation reverse high pressure liquid chromatography (HPLC). The total synthesis time was 45 min including HPLC purification. The radiochemical yields of [¹¹C]MDA was 20 ± 3 %, without decay correction. The radiochemical purity was >98 % and the specific activity was about 50 GBq/mmol. The biological properties of [¹¹C]MDA were evaluated by biodistribution study in normal mice. PET imaging was performed in healthy Chinese mini-swines. Biodistribution study showed that [¹¹C]MDA had high myocardium uptake. PET/CT imaging showed [¹¹C]MDA had clear and symmetrical myocardium uptake, which was blocked obviously by injecting imipramine hydrochloride. [¹¹C]MDA would be a promising candidate of radiotracer for cardiac sympathetic nervous system imaging.     

Optical Spectroscopic Studies on Structural Changes of Helical-rich Proteins in Aqueous Solutions of Ionic Liquids

We have investigated structural changes of myoglobin and cytochrome c, which are helical-rich proteins, in aqueous 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) solutions by Fourier transform infrared and circular dichroism spectroscopy. At low [bmim][Cl] concentrations {X (mol% IL) < 10}, both proteins unfold. Remarkably, at high [bmim][Cl] concentrations (X > 10), myoglobin aggregates whereas cytochrome c refolds its α-helical structure. The tertiary structures of both proteins are disrupted over the entire range of studied [bmim][Cl] concentrations. Our results suggest that, in aqueous solutions at high [bmim][Cl] concentrations, the differences in structural transitions between myoglobin and cytochrome c might be due to the difference in hydration between these proteins.     

Radioiodination of 4-benzyl-1-(3-iodobenzylsulfonyl)piperidine, 4-(3-iodobenzyl)-1-(benzylsulfonyl)piperazine and their derivatives via isotopic and non-isotopic exchange reactions

A mild and simple technique for preparing of 4-benzyl-1-(3-[¹²⁵I]iodobenzylsulfonyl)piperidine, 4-(3-[¹²⁵I]iodobenzyl)-1-(benzylsulfonyl)piperazine and their derivatives, as sigma-1 receptor ligands, with relatively high radiochemical yields via nucleophilic substitution reaction by means of isotopic and non-isotopic exchange reactions is described. Some factors affecting the radiochemical yield were commonly studied in presence of acidic medium at elevated temperature. Unfortunately, the radiochemical yields were weak. Some attempts were carried out in presence of polar aprotic solvents to enhance the radiochemical yield. N,N-Dimethylformamide was proved highly efficient for preparing of radioiodinated 4-benzyl-1-(3-iodobenzylsulfonyl)piperidine (4-B-[¹²⁵I]-IBSP, 70 ± 5.7 %) and 4-(3-iodobenzyl)-1-(benzylsulfonyl)piperazine (4-[¹²⁵I]-IBBSPz, 72 ± 6.0 %) at moderate temperature (100–105 °C) within 8 h. The specific activities of 4-B-[¹²⁵I]-IBSP and 4-[¹²⁵I]-IBBSPz (6,534.2 and 5,927.4 MBq/mmol) were obtained respectively.     

Synthesis,crystal structure,and FET characteristics of thieno[2,3-b]thiophene-based bent-thienoacenes

Two novel bent-shaped thienoacenes, naphtho[2,3-b]naphtho[2′,3′:4,5]thieno[3,2-d]thiophene (bent-DNTT) and anthra[2,3-b]anthra[2′,3′:4,5]thieno[3,2-d]thiophene (bent-DATT) were synthesized from thieno[2,3-b]thiophene and their corresponding aromatic anhydrides by three steps: Friedel–Crafts acylation, acid-promoted cyclization, and reductive aromatization. The structural curvature improved the solubility of these thienoacenes in organic solvents. The bent-DNTT based FET device was fabricated by the spin-coating method. The device exhibited p-type characteristics with a mobility of 5.1 × 10^?5 cm² V^?1 s^?1. Its thin-film structure was fully characterized as an edge-on orientation with large intermolecular orbital coupling.     

Synthesis and structures of two novel indolo[3,2-b] carbazole derivatives

Indolocarbazole derivatives have already been reported to be good organic semiconductor candidates. The knowledge of the relationship between the structure and packing of molecules in crystal is indispensable in design of high performance organic semiconductor materials. Two new indolocarbazole derivatives, 2,8-dibromo-5,11-di-[4-(isoindole-1,3-dione-2-yl)butyl]indolo[3,2-b]carbazole (I) and 2,8,6,12-tetrabromo-5,11-di-(4-chlorobutyl)indolo[3,2-b]carbazole (II) have been synthesized and the crystal structures have been studied. The dichloromethane solvate of (I), C₄₂H₃₂Br₂N₄O₄ · 2CH₂Cl₂, is monoclinic, space groups P2₁/n. Unit cell parameters are a = 11.6847(2), b = 12.6942(2), c = 13.7899(2) Å, β = 91.8220(10)°. Unlike other indolo[3,2-b]carbazole derivatives, there is no any π–π stacking between the indolocarbazole backbone of two adjacent molecules in the crystal. Since the isoindole-1,3-dione-2-yl is introduced in 5- and 11-positions in the molecule, the intermolecular short contacts mainly localize in between the pendant groups of the neighboring indolocarbazole molecules. The compound (II) is also monoclinic with P2₁/c space groups. Unit cell parameters are a = 4.6427(9), b = 11.425(2), c = 24.511(4) Å, β = 93.47(1)°. In contrast with compound (I), the molecules of (II) possess strong face-to-face π–π stacking. The crystal structures were studied in detail. It is concluded that linear pedant groups benefit to co-facial π–π interaction. Additionally, the molecule electronic spectra were studied by quantum chemistry theoretical calculation.     

Diversity-oriented synthesis of 1,2,3,5-tetrahydrobenzo[e][1,2,4]oxadiazepines and 2,3-dihydro-1H-benzo[e][1,2,4]triazepines by base-induced [4 + 3] annulation reactions

The base-induced formal [4 + 3] annulation reactions of N-(ortho-chloromethyl)aryl amides with nitrones or hydrazonoyl chlorides have been reported. When nitrones are used as the 1,3-dipole, the corresponding reaction afforded a series of 1,2,3,5-tetrahydrobenzo[e][1,2,4]oxadiazepine derivatives. Highly functionalized 2,3-dihydro-1H-benzo[e][1,2,4]triazepine derivatives were also synthesized via an unprecedented tandem aza-Michael addition/rearrangement aromatization between N-(ortho-chloromethyl)aryl amides and hydrazonoyl chlorides.     

Cucurbit[10]uril-based chemistry

With the biggest cavity in the cucurbit[n]urils (CB[n]s) family, CB[10] has shown its unique molecular recognition properties. This review gives a brief summary of the research progresses in the CB[10]-based chemistry, involving its purification and applications in fields such as molecular recognition and molecular assembly.     

Automated synthesis of [18F]FMISO on IBA Synthera®

In cancer cells hypoxia can cause resistance to both radio- and chemo-therapy. Being able to quantify, the degree of hypoxia in the cells is a useful tool in therapy planning. The positron emitting 1-[¹⁸F]fluoro-3-(2-nitro-1H-imidazol-1-yl)propan-2-ol ([¹⁸F]FMISO) is the most extensively used tracer for imaging hypoxia. Automated synthesis of [¹⁸F]FMISO was set up on IBA Synthera^®. The precursor 1-(2′-nitro-1′-imidazolyl)-2-O-tetrahydropyranyl-3-O-p-toluenesulfonyl propanediol (NITTP) was heated at 100 °C for 10 min with [K/K 2.2.2.]⁺[¹⁸F]^? and thereafter hydrolyzed with 0.1 M hydrochloric acid at 90 °C for 2 min. Purification was performed on solid-phase extraction (SPE) cartridges. [¹⁸F]FMISO was obtained in 50 ± 3 % (n = 6) radiochemical yield (decay-corrected) in 35 min synthesis time with radiochemical purity of ≥98 %. The use of disposable Integrated Fluid Processors (IFP?:s) and cartridge purification simplifies the handling and shortens the synthesis time. This is a no frills setup based on all commercially available materials and the synthesis is performed with minor changes from the FDG time-list.     

Radiosynthesis and preliminary biological evaluation of the 2-[<Superscript>18</Superscript>F]fluoropropionic acid enantiomers for tumor PET imaging

The aim of this study was to synthesize the optically pure [¹⁸F]FPA, and to investigate the diagnostic value of different isomers. Semi-automated radiosynthesis of R-[¹⁸F]FPA or S-[¹⁸F]FPA was respectively from the chiral precursor (S)- or (R)-ethyl 2-(((trifluoromethyl)sulfonyl)oxy)propanoate via a two-step reaction and performed on the commercial FDG synthesizer. The improved radiochemical yields of R-[¹⁸F]FPA and S-[¹⁸F]FPA were 30–40% (decay-uncorrected, n = 10) in 35 min. There was no significant difference on the biodistribution of two enantiomers in normal mice (P > 0.05), but positron emission tomography imaging demonstrated that R-[¹⁸F]FPA was more suitable for PC3 tumor imaging than S-[¹⁸F]FPA and [¹⁸F]FDG.     

Heterobimetallic compounds [Ru(η<Superscript>5</Superscript>-Cp)(dppf)X] (X = Cl,Br, I and N<Subscript>3</Subscript>): synthesis,electrochemical analysis,and the crystal structure of [Ru(η<Superscript>5</Superscript>-Cp)(dppf)I] [dppf = 1,1′-bis(diphenylphosphino)ferrocene]

A series of new ruthenium-iron based derivatives [Ru(η⁵-Cp)(dppf)Cl] (1), [Ru(η⁵-Cp)(dppf)Br] (2), [Ru(η⁵-Cp)(dppf)I] (3) and [Ru(η⁵-Cp)(dppf)N₃] (4) were obtained by reactions of [Ru(η⁵-Cp)(PPh₃)₂Cl] with 1,1′-bis(diphenylphosphino) ferrocene (dppf) and characterized by IR, NMR (¹H, ¹³C and ³¹P), ⁵⁷Fe Mössbauer spectroscopy and cyclic voltammetry. Additionally, the compound (3) was structurally characterized by X-ray crystallography, and the results were as follows: orthorhombic, Pbca, a = 18.2458(10), b = 20.9192(11), c = 34.4138(19) Å, α = β = γ = 90°, V = 13135.3(12) Å³ and Z = 16.     

Pressure-Induced Solidification of 1-Butyl-3-methylimidazolium Tetrafluoroborate

We have used Raman spectroscopy to investigate the high-pressure phase behavior of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), a representative ionic liquid, at pressures up to ~7.5 GPa. We have also studied how increasing pressure leads to conformational changes in the [bmim]⁺ cation. We have found that liquid [bmim][BF₄] undergoes pressure-induced solidification (freezing) into a superpressed (metastable) state at 2.5 GPa; another structural change probably occurs at ~6 GPa. Remarkably, conformational changes in the [bmim]⁺ cation between trans and gauche conformers are concordant with the metastable structural changes of [bmim][BF₄]. As the pressure is increased from ambient, the fraction of gauche conformers increases, but the gauche fraction decreases above the solidification pressure (2.5 GPa), and slope of the gauche/trans ratio changes again above 6 GPa. We interpret these results in terms of the fragility of the ionic liquid.     

Fluorescence signaling of aromatic oxoanion inclusion within metal-ion activated molecular receptor complexes formed from 2-(9-anthracenylmethylamino)ethyl-appended cyclen

Our observations that 1-[2-[(9-anthracenylmethylamino)ethyl)-4,7,10-tris[(2S)-2-hydroxy-3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, L¹, complexes Cd(II) to form fluorescent [CdL¹]²⁺ which undergoes a fluorescence change when it acts as an aromatic anion receptor complex has caused us to explore further the potential development of an interesting sequestration/sensor system. Accordingly, three new, octadentate, fluorescent, macrocyclic ligands, 1-[2-[(9-anthracenylmethyl)((2S)-2-hydroxy-3-phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L²), 1-[2-[(9-anthracenyl-methyl)((2S)-2-hydroxy-3-(4??-methyl)phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-(4??-methyl)phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L³), and 1-[2-[(9-anthracenylmethyl)((2S)-2-hydroxy-3-(4??-t-butyl)phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-(4??-t-butyl)phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L⁴), have been prepared with a view to using their metal complexes to study aromatic anion sequestration. The eight-coordinate Cd(II) complexes of L² and L³, [CdL²](ClO₄)₂·5H₂O and [CdL³](ClO₄)₂·2H₂O·2Et₂O are both capable of acting as receptors for a range of aromatic oxoanions. This is demonstrated by perturbation of the anthracene derived fluorescence emission intensity as the guest aromatic oxoanion and the receptor complex combine. In 20% aqueous 1,4-dioxane the receptor complex/aromatic oxoanion association constants are in the range of 10^3.2 M^?1 (guest = p-hydroxybenzoate) to 10^7.3 M^?1 (guest = 3,4,5-trihydroxybenzoate).     

A one-step fully automated radio-synthesis of a dopamine transporter PET imaging agent 18F-FECNT and its in vivo evaluations

2β-Carbomethoxy-3β-(4-chlorophenyl)-8-(2-[¹⁸F]fluoroethyl)nortropane ([¹⁸F]-FECNT) is a potential dopamine transporter PET imaging agent. However, its current radio-synthesis is tedious and time consuming. In this article, we reported a fully automatic method for the synthesis of [¹⁸F] FECNT through only one step, using a TRACERlab FX_N module, with decay corrected radiochemical yield of 25 ± 5 % (n = 5). The total synthesis time was 50–55 min. The synthesized [¹⁸F]FECNT was evaluated in vivo in Parkinson’s disease model rats.     

Synthesis and crystal structure of p-acylated calix[4]arene ethers

C-acylation of calix[n]arenes is an important reaction which has been primarily utilized for their further functionalization to provide conformers with varying shapes, cavity dimensions and molecular receptor characteristics that can bind ionic and neutral species in a selective and specific manner. The length of the alkyl chain at the upper or the lower rim of calixarenes can be adjusted as required to give derivatives which can span the channels and membranes and majorly influence transport phenomenon. As a part of our program to obtain calixarene based derivatives that can span and scan artificial membranes, C-acylation of calix[4]arene has been examined to yield peracylated and partially acylated calixarene ethers. 5,11,17,23-Tetraacetyl-25,26,27,28-tetramethoxycalix[4]arene has been obtained in 80 % yield by treatment of tetramethoxycalix[4]arene with acetyl chloride in the presence of aluminum chloride using dichloromethane as the solvent. The structure was established by the conversion to corresponding phenyl hydrazones and oximes. The tetraacetyltetramethoxycalix[4]arene 2a crystallized in a monoclinic lattice, space group P2₁/C with a = 10.320(2) Å, b = 18.928(4) Å, c = 18.421(4) Å, β = 95.44(3)^o, Z = 4. The corresponding methyl substituted O7 directs inwards towards the cavities of calix[4]arene to give an inward flattened partial cone conformation. Molecular packing shows the presence of intermolecular C–H···O, H-bonding interactions between methyl and methylene hydrogens and oxygens of the acetyl groups.