Search

Cobalt complexes with multiproton- and multielectron-responsive ligands are of interest for challenging catalytic transformations. The chemical and redox noninnocence of pentane-2,4-dione bis( S -methylisothiosemicarbazone) (PBIT) in a series of cobalt complexes has been studied by a range of methods, including spectroscopy [UV-vis, NMR, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS)], cyclic voltammetry, X-ray diffraction, and density functional theory (DFT) calculations. Two complexes [Co III (H 2 L SMe )I]I and [Co III ( L SMe )I 2 ] were found to act as precatalysts in a Wacker-type oxidation of olefins using phenylsilane, the role of which was elucidated through isotopic labeling. Insights into the mechanism of the catalytic transformation as well as the substrate scope of this selective reaction are described, and the essential role of phenylsilane and the noninnocence of PBIT are disclosed. Among the several relevant species characterized was an unprecedented Co(III) complex with a dianionic diradical PBIT ligand ([Co III (L SMe•• )I])., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Protein-based hydrogels have attracted growing attention for pharmaceutical and biomedical applications. Ovalbumin (OVA), the hen egg white albumin, possessing good foaming and gelling properties and being widely used in the food industry, has recently been indicated as a potential pharmaceutical vehicle. In this study, the binding and release properties of pure OVA hydrogels were investigated by electron paramagnetic resonance (EPR) spin labeling. The comparative analysis between OVA and serum albumin (SA) hydrogels revealed the same release kinetics of hydrophilic 3-carbamoyl-proxyl and 3-carboxy-proxyl, suggesting the diffusion-dominated release of small probes from both hydrogel types. The results obtained with the amphiphilic 16-doxylstearate (16-DS) indicate that OVA, unlike SAs, does not possess a specific fatty acid binding site. However, the OVA hydrogels were able to accommodate a two-fold excess of 16-DS, resulting from protein thermally induced conformational changes, as confirmed by Raman spectroscopy. Similarly, the hydrophobic modified paullone ligand HL , which was initially free in the OVA solution, was bound in the hydrogel. The hydrogels were found to retain a significant amount of 16-DS and HL after 7-day dialysis in physiological saline. The observed facilitated binding of amphiphilic/hydrophobic molecules in OVA hydrogels compared to the solution, and their sustained release, demonstrate the applicability of OVA hydrogels in pharmaceutics.

Unprecedented self-assembly of a novel 14-membered cyclic bis-thiosemicarbazone or/and a 28-membered cyclic tetrakis-thiosemicarbazone upon acid-promoted cyclooligomerization of 4-(4-thiosemicarbazido)butan-2-one hydrazone has been discovered. A thorough study of the influence of various factors on the direction of macrocyclization provided the optimal conditions for the highly selective formation of each of the macrocycles in excellent yields. Plausible pathways for macrocyclizations have been discussed. The macrocycle precursor was prepared by the reaction of readily available 4-isothiocyanatobutan-2-one with an excess of hydrazine.

In the title hydrated mol-ecular salt, [Cu(C 7 H 20 N 4 )(H 2 O) 2 ](C 8 H 4 O 4 )·H 2 O, the metal ion is coordinated by the two primary and two secondary N atoms of the amine ligand and the mutually trans O atoms of the water mol-ecules in a tetra-gonally distorted octa-hedral geometry. The average equatorial Cu-N bond lengths (2.013 and 2.026 Å for Cu-N prim and Cu-N sec , respectively) are substanti-ally shorter than the average axial Cu-O bond length (2.518 Å). The tetra-amine ligand adopts its energetically favored conformation with its five- and six-membered chelate rings in gauche and chair conformations, respectively. In the crystal, the N-H donor groups of the tetra-amine, the acceptor carboxyl-ate groups of the isophthalate dianion and both the coordinated water mol-ecules and the water mol-ecule of crystallization are involved in numerous N-H⋯O and O-H⋯O hydrogen bonds, resulting in the formation of electroneutral layers oriented parallel to the ac plane., (© Tsymbal et al. 2022.)

This study shows the potential of a thermally induced human serum albumin (HSA) hydrogel to serve as a drug depot for sustained release of a highly cytotoxic modified paullone ligand bearing a TEMPO free radical ( HL ). The binding of HL to HSA was studied by electron paramagnetic resonance (EPR) spectroscopy and imaging. The EPR protocol was also implemented for the study of matrix degradation, and ligand diffusion rate, in two additional spin-labeled hydrogels, containing 5-doxylstearate and 3-carbamoyl-proxyl. The results showed that the hydrogel is an efficient HL reservoir as it retained 60% of the ligand during 11 days of dialysis in physiological saline. Furthermore, upon incubation with Colo 205 human colon adenocarcinoma cells for 3 days, the HL /HSA hydrogel did not exhibit cytotoxic activity, demonstrating that it is also an efficient ligand depot in the presence of living cells. It was observed that the percentage of HL release is independent of its initial concentration in the hydrogel, suggesting that HSA possesses a specific binding site for the ligand, most likely Sudlow site 2, as predicted by molecular docking. The intrinsic property of albumin to bind and transport various substances, including hydrophobic drugs, may be fine-tuned by appropriate physical/chemical hydrogel preparation procedures, providing optimal drug delivery.

The proton dissociation processes of two tridentate salicylidene aminoguanidine Schiff bases (SISC, Pro-SISC-Me), the solution stability and electrochemical properties of their Cu(II), Fe(II) and Fe(III) complexes were characterized using pH-potentiometry, cyclic voltammetry and UV-visible, 1 H NMR and electron paramagnetic resonance spectroscopic methods. The structure of the proline derivative (Pro-SISC-Me) was determined by X-ray crystallography. The conjugation of L-proline to the simplest salicylidene aminoguanidine Schiff base (SISC) increased the water solubility due to its zwitterionic structure in a wide pH range. The formation of mono complexes with both ligands was found in the case of Cu(II) and Fe(II), while bis complexes were also formed with Fe(III). In the complexes these tridentate ligands coordinate via the phenolato O, azomethine N and the amidine N, except the complex [Fe(III)L 2 ] + of Pro-SISC-Me in which the (O,N) donor atoms of the proline moiety are coordinated beside the phenolato O, confirmed by single crystal X-ray crystallographic analysis. This binding mode yielded a stronger Fe(III) preference for Pro-SISC-Me over Fe(II) in comparison to SISC. This finding is also reflected in the lower redox potential value of the iron-Pro-SISC-Me complexes. The ligands alone were not cytotoxic against human colon cancer cell lines, while complexation of SISC with Cu(II) resulted in moderate activity, unlike the case of its more hydrophilic counterpart.

Paullone isomers are known as inhibitors of tubulin polymerase and cyclin dependent kinases (Cdks), which are potential targets for cancer chemotherapy. Herein we report an efficient and clean pathway to the fourth isomer, which remained elusive so far, namely 7,8-dihydroindolo[2,3- d ][1]benzazepin-6(5 H )-one. Moreover, we demonstrate the generality of our pathway by synthesizing two closely related analogues, one containing a bromo substituent and the other one incorporating an 8-membered instead of a 7-membered ring. The key transformation in this four-step synthesis, with an overall yield of 29%, is the Fischer indole reaction of 2-nitrophenylacetyl acetoacetate with 1-benzyl-1-phenylhydrazine in acetic acid that delivers methyl 2-(1-benzyl-3-(2-nitrophenyl)-1 H -indol-2-yl)acetate in 55% yield., (Copyright © 2022, Kuznetcova et al.)

The asymmetric unit of the title compound, trans -di-aqua-(1,4,8,11-tetra-aza-undecane-κ 4 N 1 , N 4 , N 8 , N 11 )nickel(II) bis-(pyridine-2,6-di-carboxyl-ato-κ 3 O 2 , N , O 6 )nickel(II) {[Ni( L )(H 2 O) 2 ][Ni(pdc) 2 ] where L = 1,4,8,11-tetra-aza-undecane (C 7 H 20 N 4 ) and pdc = the dianion of pyridine-2,6-di-carb-oxy-lic acid (C 7 H 3 NO 4 2- )} consists of an [Ni( L )(H 2 O) 2 ] 2+ complex cation and a [Ni(pdc) 2 ] 2- anion. The metal ion in the cation is coordinated by the four N atoms of the tetra-amine ligand and the mutually trans O atoms of the water mol-ecules in a tetra-gonally elongated octa-hedral geometry with the average equatorial Ni-N bond length slightly shorter than the average axial Ni-O bond [2.087 (4) versus 2.128 (4) Å]. The ligand L adopts its energetically favored conformation with five-membered and six-membered chelate rings in gauche and chair conformations, respectively. In the complex anion, the Ni II ion is coordinated by the two tridentate pdc 2- ligands via their carboxyl-ate and nitro-gen atom donors in a distorted octa-hedral trans -NiO 4 N 2 geometry with nearly orthogonal orientation of the planes defining the carboxyl-ate rings and the average Ni-N bond length [1.965 (4) Å] shorter than the average Ni-O bond distance [2.113 (7) Å]. In the crystal, the NH donor groups of the tetra-amine, the carb-oxy-lic groups of the pdc 2- anion and the coordinated water mol-ecules are involved in numerous N-H⋯O and O-H⋯O hydrogen bonds, leading to electroneutral sheets oriented parallel to the (001) plane., (© Andriichuk et al. 2021.)

Two 15-membered octaazamacrocyclic nickel(II) complexes are investigated by theoretical methods to shed light on their affinity forwards binding and reducing CO 2 . In the first complex 1 [ Ni II L ] 0 , the octaazamacrocyclic ligand is grossly unsaturated (π-conjugated), while in the second 1 [ Ni II LH ] 2+ one, the macrocycle is saturated with hydrogens. One and two-electron reductions are described using Mulliken population analysis, quantum theory of atoms in molecules, localized orbitals, and domain averaged fermi holes, including the characterization of the Ni-C CO2 bond and the oxidation state of the central Ni atom. It was found that in the [ NiLH ] complex, the central atom is reduced to Ni 0 and/or Ni I and is thus able to bind CO 2 via a single σ bond. In addition, the two-electron reduced 3 [ NiL ] 2- species also shows an affinity forwards CO 2 .

A series of thiosemicarbazone-coumarin hybrids ( HL 1 -HL 3 and H 2 L 4 ) has been synthesised in 12 steps and used for the preparation of mono- and dinuclear copper(II) complexes, namely Cu(HL 1 )Cl 2 ( 1 ), Cu(HL 2 )Cl 2 ( 2 ), Cu(HL 3 )Cl 2 ( 3 ) and Cu 2 (H 2 L 4 )Cl 4 ( 4 ), isolated in hydrated or solvated forms. Both the organic hybrids and their copper(II) and dicopper(II) complexes were comprehensively characterised by analytical and spectroscopic techniques, i.e., elemental analysis, ESI mass spectrometry, 1D and 2D NMR, IR and UV-vis spectroscopies, cyclic voltammetry (CV) and spectroelectrochemistry (SEC). Re-crystallisation of 1 from methanol afforded single crystals of copper(II) complex with monoanionic ligand Cu(L 1 )Cl , which could be studied by single crystal X-ray diffraction (SC-XRD). The prepared copper(II) complexes and their metal-free ligands revealed antiproliferative activity against highly resistant cancer cell lines, including triple negative breast cancer cells MDA-MB-231, sensitive COLO-205 and multidrug resistant COLO-320 colorectal adenocarcinoma cell lines, as well as in healthy human lung fibroblasts MRC-5 and compared to those for triapine and doxorubicin. In addition, their ability to reduce the tyrosyl radical in mouse R2 protein of ribonucleotide reductase has been ascertained by EPR spectroscopy and the results were compared with those for triapine.

The in situ spectroelectrochemical cyclic voltammetric studies of the antimony-monocapped nickel(II) and iron(II) tris-pyridineoximates with a labile triethylantimony cross-linking group and Zr(IV)/Hf(IV) phthalocyaninate complexes were performed in order to understand the nature of the redox events in the molecules of heterodinuclear zirconium(IV) and hafnium(IV) phthalocyaninate-capped derivatives. Electronic structures of their 1e-oxidized and 1e-electron-reduced forms were experimentally studied by electron paramagnetic resonance (EPR) spectroscopy and UV-vis-near-IR spectroelectrochemical experiments and supported by density functional theory (DFT) calculations. The investigated hybrid molecular systems that combine a transition metal (pseudo)clathrochelate and a Zr/Hf-phthalocyaninate moiety exhibit quite rich redox activity both in the cathodic and in the anodic region. These binuclear compounds and their precursors were tested as potential catalysts in oxidation reactions of cyclohexane and the results are discussed.

Recognition of elements of protein tertiary structure is crucial for biotechnological and biomedical tasks; this makes the development of optical sensors for certain protein surface elements important. Herein, we demonstrated the ability of iron(II) clathrochelates ( 1 - 3 ) functionalized with mono-, di- and hexa-carboxyalkylsulfide to induce selective circular dichroism (CD) response upon binding to globular proteins. Thus, inherently CD-silent clathrochelates revealed selective inducing of CD spectra when binding to human serum albumin (HSA) ( 1 , 2 ), beta-lactoglobuline ( 2 ) and bovine serum albumin (BSA) ( 3 ). Hence, functionalization of iron(II) clathrochelates with the carboxyalkylsulfide group appears to be a promising tool for the design of CD-probes sensitive to certain surface elements of proteins tertiary structure. Additionally, interaction of 1 - 3 with proteins was also studied by isothermal titration calorimetry, protein fluorescence quenching, electrospray ionization mass spectrometry (ESI-MS) and computer simulations. Formation of both 1:1 and 1:2 assemblies of HSA with 1 - 3 was evidenced by ESI-MS. A protein fluorescence quenching study suggests that 3 binds with both BSA and HSA via the sites close to Trp residues. Molecular docking calculations indicate that for both BSA and HSA, binding of 3 to Site I and to an "additional site" is more favorable energetically than binding to Site II.

Thiosemicarbazones continue to attract the interest of researchers as potential anticancer drugs. For example, 3-aminopyridine-2-carboxaldehyde thiosemicarbazone, or triapine, is the most well-known representative of this class of compounds that has entered multiple phase I and II clinical trials. Two new triapine derivatives HL 1 and HL 2 were prepared by condensation reactions of 2-pyridinamidrazone and S-methylisothiosemicarbazidium chloride with 3- N -( tert -butyloxycarbonyl) amino-pyridine-2-carboxaldehyde, followed by a Boc-deprotection procedure. Subsequent reaction of HL 1 and HL 2 with CuCl 2 ·2H 2 O in 1:1 molar ratio in methanol produced the complexes [Cu II (HL 1 )Cl 2 ]·H 2 O ( 1·H 2 O ) and [Cu II (HL 2 )Cl 2 ] ( 2 ). The reaction of HL 2 with Fe(NO 3 ) 3 ∙9H 2 O in 2:1 molar ratio in the presence of triethylamine afforded the complex [Fe III (L 2 ) 2 ]NO 3 ∙0.75H 2 O ( 3∙0.75H 2 O ), in which the isothiosemicarbazone acts as a tridentate monoanionic ligand. The crystal structures of HL 1 , HL 2 and metal complexes 1 and 2 were determined by single crystal X-ray diffraction. The UV-Vis and EPR spectroelectrochemical measurements revealed that complexes 1 and 2 underwent irreversible reduction of Cu(II) with subsequent ligand release, while 3 showed an almost reversible electrochemical reduction in dimethyl sulfoxide (DMSO). Aqueous solution behaviour of HL 1 and 1, as well as of HL 2 and its complex 2 , was monitored as well. Complexes 1 - 3 were tested against ovarian carcinoma cells, as well as noncancerous embryonic kidney cells, in comparison to respective free ligands, triapine and cisplatin. While the free ligands HL 1 and HL 2 were devoid of antiproliferative activity, their respective metal complexes showed remarkable antiproliferative activity in a micromolar concentration range. The activity was not related to the inhibition of ribonucleotide reductase (RNR) R2 protein, but rather to cancer cell homeostasis disturbance-leading to the disruption of cancer cell signalling.

A series of four water-soluble salicylaldehyde thiosemicarbazones with a positively charged trimethylammonium moiety ([H 2 L R ]Cl, R = H, Me, Et, Ph) and four copper(II) complexes [Cu(HL R )Cl]Cl ( 1 - 4 ) were synthesised with the aim to study (i) their antiproliferative activity in cancer cells and, (ii) for the first time for thiosemicarbazones, the interaction with membrane transport proteins, specifically organic cation transporters OCT1-3. The compounds were comprehensively characterised by analytical, spectroscopic and X-ray diffraction methods. The highest cytotoxic effect was observed in the neuroblastoma cell line SH-5YSY after 24 h exposure and follows the rank order: 3 > 2 > 4 > cisplatin > 1 >>[H 2 L R ]Cl. The copper(II) complexes showed marked interaction with OCT1-3, comparable to that of well-known OCT inhibitors (decynium 22, prazosin and corticosterone) in the cell-based radiotracer uptake assays. The work paves the way for the development of more potent and selective anticancer drugs and/or OCT inhibitors., Competing Interests: The authors declare no conflict of interest.

The asymmetric unit of the title com-pound, catena -poly[[[(perchlorato-κ O )copper(II)]-μ-3-(3-carb-oxy-prop-yl)-1,5,8,12-tetra-aza-3-azonia-cyclo-tetra-decane-κ 4 N 1 , N 5 , N 8 , N 12 ] bis-(per-chlorate)], {[Cu(C 13 H 30 N 5 O 2 )(ClO 4 )](ClO 4 ) 2 } n , (I), consists of a macrocyclic cation, one coordinated per-chlorate anion and two per-chlorate ions as counter-anions. The metal ion is coordinated in a tetra-gonally distorted octa-hedral geometry by the four secondary N atoms of the macrocyclic ligand, the mutually trans O atoms of the per-chlorate anion and the carbonyl O atom of the protonated carb-oxy-lic acid group of a neighbouring cation. The average equatorial Cu-N bond lengths [2.01 (6) Å] are significantly shorter than the axial Cu-O bond lengths [2.379 (8) Å for carboxyl-ate and average 2.62 (7) Å for disordered per-chlorate]. The coordinated macrocyclic ligand in (I) adopts the most energetically favourable trans -III conformation with an equatorial orientation of the substituent at the protonated distal 3-position N atom in a six-membered chelate ring. The coordination of the carb-oxy-lic acid group of the cation to a neighbouring com-plex unit results in the formation of infinite chains running along the b -axis direction, which are cross-linked by N-H⋯O hydrogen bonds between the secondary amine groups of the macrocycle and O atoms of the per-chlorate counter-anions to form sheets lying parallel to the (001) plane. Additionally, the extended structure of (I) is consolidated by numerous intra- and interchain C-H⋯O contacts., (© Tsymbal et al. 2019.)

The asymmetric units of the title compounds, trans -di-aqua-(3-benzyl-1,3,5,8,12-penta-aza-cyclo-tetra-decane-κ 4 N 1 , N 5 , N 8 , N 12 )copper(II) isophthalate monohydrate, [Cu(C 16 H 29 N 5 )(H 2 O) 2 ](C 8 H 4 O 4 )·H 2 O, (I), and trans -di-aqua-[3-(pyridin-3-ylmeth-yl)-1,3,5,8,12-penta-aza-cyclo-tetra-decane-κ 4 N 1 , N 5 , N 8 , N 12 ]copper(II) iso-phthalate 0.9-hydrate, [Cu(C 15 H 28 N 6 )(H 2 O) 2 ](C 8 H 4 O 4 )·0.9H 2 O, (II) consist of one di-aqua macrocyclic cation, one di-carboxyl-ate anion and uncoordinated water mol-ecule(s). In each compound, the metal ion is coordinated by the four secondary N atoms of the macrocyclic ligand and the mutually trans O atoms of the water mol-ecules in a tetra-gonally distorted octa-hedral geometry. The average equatorial Cu-N bond lengths are significantly shorter than the average axial Cu-O bond lengths [2.020 (9) versus 2.495 (12) Å and 2.015 (4) versus 2.507 (7) Å for (I) and (II), respectively]. The coordinated macrocyclic ligand in the cations of both compounds adopts the most energetically favorable trans -III conformation. In the crystals, the complex cations and counter-anions are connected via hydrogen-bonding inter-actions between the N-H groups of the macrocycles and the O-H groups of coordinated water mol-ecules as the proton donors and the O atoms of the carboxyl-ate as the proton acceptors. Additionally, as a result of O-H⋯O hydrogen bonding with the coordinated and water mol-ecules of crystallization, the isophthalate dianions form layers lying parallel to the (01) and (100) planes in (I) and (II), respectively.

The asymmetric unit of the title compound, trans -di-aqua-(3,10-dimethyl-1,3,5,8,10,12-hexa-aza-cyclo-tetra-decane-κ 4 N 1 , N 5 , N 8 , N 12 )copper(II) 4,4'-methyl-ene-bis(3-hy-droxy-naphthalene-2-carboxyl-ate), [Cu(C 10 H 26 N 6 )(H 2 O) 2 ](C 23 H 14 O 6 ) {[Cu( L )(H 2 O) 2 ](pam), where L = 3,10-dimethyl-1,3,5,8,10,12-hexa-aza-cyclo-tetra-decane and pam = dianion of pamoic acid} consists of two independent halves of the [Cu( L )(H 2 O) 2 ] 2+ cation and one di-carboxyl-ate anion. The Cu II atoms, lying on inversion centres, are coordinated by the four secondary N atoms of the macrocyclic ligands and the mutually trans O atoms of the water mol-ecules in a tetra-gonally elongated octa-hedral geometry. The average equatorial Cu-N bond length is significantly shorter than the average axial Cu-O bond length [2.007 (10) and 2.486 (18) Å, respectively]. The macrocyclic ligand in the complex cations adopts the most energetically stable trans -III conformation. The complex cations and anions are connected via hydrogen-bonding inter-actions between the N-H groups of the macrocycles and the O-H groups of coordinated water mol-ecules as the proton donors and the O atoms of the carboxyl-ate as the proton acceptors into layers lying parallel to the (11) plane.

X- and Q-band electron paramagnetic resonance (EPR) spectroscopy was used to characterize polycrystalline Cu(II) complexes that contained sodium 5-sulfonate salicylaldehyde thiosemicarbazones possessing a hydrogen, methyl, ethyl, or phenyl substituent at the terminal nitrogen. The ability of thiosemicarbazone proligands to generate superoxide radical anions and hydroxyl radicals upon their exposure to UVA irradiation in aerated aqueous solutions was evidenced by the EPR spin trapping technique. The UVA irradiation of proligands in neutral or alkaline solutions and dimethylsulfoxide (DMSO) caused a significant decrease in the absorption bands of aldimine and phenolic chromophores. Mixing of proligand solutions with the equimolar amount of copper(II) ions resulted in the formation of 1:1 Cu(II)-to-ligand complex, with the EPR and UV-Vis spectra fully compatible with those obtained for the dissolved Cu(II) thiosemicarbazone complexes. The formation of the complexes fully inhibited the photoinduced generation of reactive oxygen species, and only subtle changes were found in the electronic absorption spectra of the complexes in aqueous and DMSO solutions upon UVA steady-state irradiation. The dark redox activity of copper(II) complexes and proligand/Cu(II) aqueous solutions towards hydrogen peroxide which resulted in the generation of hydroxyl radicals, was confirmed by spin trapping experiments., Competing Interests: The authors declare no conflict of interest.

We report on the investigation of Bismuth-doped pure silica glass without other co-dopant by the tech- nique of magnetic circular dichroism (MCD), which allows the direct probing of the ground state of optical centres. Taking into account the results of conventional optical spectroscopy, we show that the observed MCD bands belong to the centre responsible for the red photoluminescence in this material. Measurements of the temperature and field dependences indicate that the MCD effect is caused by the even-electron system. This, however, opposes the widespread opinion that Bi 2+ ions are the origin of red photoluminescence in Bismuth-doped silica glasses. On the other hand, the lasing centre responsi- ble for the near infrared photoluminescence does not exhibit any magnetic optical activity connected to its ground state. As a consequence, we conclude that the ground state of lasing centre is a magnetic singlet with the effective spin S = 0.

endo-Tricyclo[3.2.1.0(2,4)]oct-8-ylidene is a foiled carbene reaction intermediate. It was generated by thermolyzing Δ(3)-1,3,4-oxadiazoline precursors dissolved in benzaldehyde and acetophenone. The products appear to stem from direct insertion of the carbene's divalent C atom into the α-bonds of the carbonyl compounds; however, this is only superficial. The strict stereochemistry observed is due to the topologies of the reaction intermediates of the proposed two-step mechanism. Bimolecular nucleophilic addition generates bent 1,3-zwitterions. The neutral reaction intermediates undergo pinacolic rearrangements to form the observed adducts. Product ratios reflect the migratory aptitudes of the carbonyl compounds' α-substituents. The carbene reaction was modeled using DFT. The singlet carbene's bicoordinate C atom bends 31° toward the endo-fused cyclopropane bond, elongating it to r = 1.69 Å. The resulting trishomocyclopropyl HOMO{-1} is a three-center two-electron bond responsible for the electron-deficient carbene's nucleophilicity. Its calculated properties are consistent with this assertion: (1) singlet-triplet (ΔE(S-T)) energy gap of -25 kcal/mol, (2) gas-phase proton affinity (PA) value of 272 kcal/mol, (3) hard and soft acid and base (HSAB) ΔN value of -0.2 in its initial reaction with the carbonyl compounds, and (4) negative frontier orbital interaction values ΔΔE(PhC(O)H) = -4.38 eV and ΔΔE(PhC(O)Me) = -3.97 eV.

3-Aminomethylation of salicylalkylamides afforded hybrids with a Mannich base. In addition, it triggered the rotation of the amide bond. The observed conformational switch is driven by strong intramolecular hydrogen bonding between the Mannich base and phenolic group. Crystal structure analysis reveals the stabilization of the hybrid molecules by double hydrogen bonding of the phenolic OH, which acts as an acceptor and donor simultaneously. The molecules contain an amide site and a Mannich base site in an orthogonal spatial arrangement. The intramolecular hydrogen bonds are persistent in a nonpolar solvent (e.g., chloroform). The conformational change can be reversed upon protection or protonation of the Mannich base nitrogen.

Bismuth-Gallium co-doped silica glass fiber preform was prepared from nano-porous silica xerogels using a conventional solution doping technique with a heterotrinuclear complex and subsequent sintering. Ga-connected optical Bismuth active center (BAC) was identified as the analogue of Al-connected BAC. Visible and infrared photoluminescence (PL) were investigated in a wide temperature range of 1.46 - 300 K. Based on the results of the continuous wave (CW) and time resolved (TR) spectroscopy we identify the centers emitting in the spectral region of 480 - 820 nm as Bi(+) ions. The near infrared (NIR) PL around 1100 nm consists of two bands. While the first one can be ascribed to the transition in Bi(+) ion, the second band is presumably associated to defects. We put in evidence the energy transfer (ET) between Bi(+) ions and the second NIR emitting center via quadrupole-quadrupole and dipole-quadrupole mechanisms of interactions. Finally, we propose the energy level diagram of Bi(+) ion interacting with this defect.

Foiled carbene structures comprising strong stabilizing interactions between the divalent carbon and the intramolecular double bond have been located by DFT calculations. These tetracyclic species bearing fused five-membered rings impeding intramolecular rearrangements are theoretically predicted to lie in a deep potential energy well. A suitable dibromocyclopropane precursor for this type of foiled carbene has been prepared in 12 steps. Its treatment with methyllithium led to the isolation of a product of a formal carbene dimerization, a bicyclopropylidene., (© 2011 American Chemical Society)

Bridging 2,3 and 2',3' positions in 2,2'-dihydroxy-1,1'-binaphthyl and 2,2'-diamino-1,1'-binaphthyl, respectively, resulted in formation of chiral O- and N-bis-tricyclic compounds accessible in 4 steps from known 3,3'-diiodo precursors. In both cases, 2-fold ring closing metathesis of tetraallyl intermediates proceeded regioselectively to give tetrahydrobinaphtho[2,3-b]oxepine and -azepine, respectively. In case of the N-mesyl-N-allyl precursor, three, at room temperature separable, rotamers were isolated and characterized by NMR spectroscopy and X-ray structure determination. Their interconversion (process I) was followed by NMR, yielding rate constants and thermodynamic parameters. The rotamers with either C(1) or C(2) symmetry were stereospecifically cyclized to conformatively moderately stable bis-sulfonamides. Also in this case, the kinetics of their interconversion (process II) was investigated and from two of them the crystal structure was determined. Processes I and II were investigated by a DFT method, M06-2X, to gain insight into electronic and steric peculiarities responsible for the remarkable conformative stabilities. Transition state geometries and energies were calculated and compared with empirical data., (© 2011 American Chemical Society)

Tetravinylbenzene 4 was prepared in nearly quantitative yield from commercially available tetrabromobenzene; the improved, one-step procedure now employs Suzuki-Miyaura cross-coupling conditions. Intermolecular cyclopropanation of 4 with dibromocarbene gave a series of gem-dibromide adducts. Intramolecular cyclopropanation of monoadduct 5, putatively by its methyllithium-generated cyclopropylidene(oid), produced compound 11, which features a highly distorted spiropentane having a C-C-C bond angle of 163.5°. The stability of the reported spiropentanes was investigated using DFT calculations.

The molecule of the title compound, C(10)H(6)N(24), lies on a crystallographic inversion centre located in the middle of the benzene ring. Steric overcrowding by the bulky N(3) groups is avoided by the tendency of four azide entities to be arranged parallel to the benzene ring and the other four azide groups to be arranged alternately above and below the benzene plane in a skeletal C(i) symmetry. The compound is of interest for high-energy research and as a precursor for the synthesis of carbon nanotubes, nanospheres or high-nitrogen carbon nitrides with great potential for biological and technological applications.

The chemistry of endo-tricyclo[6.2.1.0 (2.7)]undec-9-en-11-ylidene (10), an archetypal foiled carbene, has been investigated. The intermolecular reactions of 10 are most conveniently performed with oxadiazoline 6 because the corresponding diazirine can be obtained only in very low yield. Furthermore, the aziridinyl imine is difficult to decompose and the tosylhydrazone sodium salt poorly soluble in common organic solvents. Photolysis of 6 in diethylamine leads merely to a reduction of the diazo group and regeneration of acetyl hydrazone 5, whereas thermolysis cleanly affords tertiary amine 12(anti) in 77% yield. Calculations show that even stabilized-nucleophilic carbenes react with amines through an ylidic pathway and not by a concerted insertion into the N-H bond. Nevertheless, in the gas phase, norbornen-7-ylidene (13) is predicted to be stabilized by one molecule of NH3 more efficiently through a hydrogen bond than by ylide formation.

An induced circular dichroism (ICD) solution study on the orientation of ferrocenyl azide within the beta-cyclodextrin cavity is described. In DMSO, ferrocenyl azide prefers an axial inclusion, whereas in ethylene glycol and DMSO/H2O = 50/50 an equatorial alignment dominates. As shown by temperature-dependent ICD spectra, at lower temperatures ferrocenyl azide adopts preferentially an equatorial arrangement, whereas at higher temperatures an axial one is favored. Temperature and solvent effects on the co-conformation of ferrocene noncovalently bound to cyclodextrin have never been observed before.