Host-guest complexes of a water soluble cucurbit[6]uril derivative with some dications of 1,ω-alkyldipyridines:~1H NMR and X-ray structures

Interactions between a symmetrical tetramethyl-substituted cucurbit[6]uril (host:TMeQ[6]) and 1,ω-alkylenedipyridine (ω = 2,4,6,8,10) dicationic guests were investigated using 1H NMR spectroscopy and single crystal X-ray crystallography. In these inclusion complexes,combined cavity and portal binding in TMeQ[6] were observed,and the length of the bridged alkylene was found to play an important role not only in balancing the overall hydrophilic/hydrophobic interaction between the host and the guest,but also ...     

<Superscript>1</Superscript>H NMR study of complexation of α- and β-cyclodextrins with some biologically active acids

Reactions of - and -cyclodextrins with some biologically active acids were studied by ¹H NMR spectroscopy. Inclusion complexes are found to be formed only with aromatic amino acids (phenylalanine and tryptophan) and ascorbic acid. The complexes of cyclodextrin with citric acid are obtained through interactions between the polar groups of the guest molecule and the OH groups of the host molecule located on the outside.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 3, 2005, pp. 234–236.Original Russian Text Copyright © 2005 by Terekhova, Kulikov, Kumeev, Nikiforov, Alper.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Molecular photonics of inclusion complexes of cucurbit[7]uril with 3,3′-diethylthiazolinocarbocyanine iodide

The effect of cucurbit[7]uril (Cb7) on the photonics of 3,3′-diethylthiazolinocarbocyanine iodide (Car) in water was studied by spectrofluorimetry, ns-laser kinetic spectroscopy, and quantum chemistry. The formation of an inclusion complex of Car with Cb7 was established, and the binding constant and composition of the Car@Cb7 (1 : 2) complex were determined. It was shown that Car and Car@Cb7 are able to undergo trans → cis-photoisomerization. The lifetime of the cis-isomer of free Car was found to be much shorter than that of the cis-Car form localized inside the cavity of Cb7. The energies of formation of complexes Car@Cb7 were found and the structure of the complex in the lowest excited singlet state was determined according to the quantum chemical calculations by the DFT method with the PBE functional. The trans → cis-isomerization was found to proceed via the excited singlet S1 state having the “perpendicular” conformation.     

Triplet states of 3,3′-alkylsubstituted thiacarbocyanine dimers and dimeric complexes with cucurbit[8]uril in water

Alkylsubstituted thiacarbocyanines (3,3′-diethylthiacarbocyanine, D1, and 3,3′-disulfopropylthiacarbocyanine, D2), existing in water as monomers and dimers, manifest the ability to transition to the triplet state. The spectrum of triplet-triplet (T–T) absorption of the D2 dimers is shifted in the range higher than 590 nm by 20 nm to the red in comparison with the T–T spectrum of monomers. The D1 dimers in the presence of cucurbit[8]uril form a dimeric complex with two bands in the differential absorption spectrum. The band at 550 nm belongs to the triplet-triplet absorption of the dimeric complexes, and the band in the range of 620–700 nm is the result of charge transfer in the triplet state. The rate constants of deactivation for these triplet states coincide.     

<Superscript>13</Superscript>C-labeled bilirubin: synthesis of 3<Superscript>1</Superscript>(3<Superscript>2</Superscript>),17<Superscript>1</Superscript>(17<Superscript>2</Superscript>)-di-[<Superscript>13</Superscript>C]-mesobilirubin-XIIIα

Abstract  The title compound, labeled with ¹³C in the ethyl groups was synthesized from K¹³CN and low-molecular-weight components. The synthetic relay compound was 3¹(3²)[¹³C]-xanthobilirubinic acid methyl ester in a synthetic route that leads to a label in the ethyl β-substituent of a dipyrrinone model for bilirubin. This labeled dipyrrinone was oxidatively coupled to the dimethyl ester of mesobiliverdin-XIIIα, thereby providing a route to a ¹³C-labeled mesobiliverdin and mesobilirubin, with one carbon of each ethyl being 98% ¹³C-enriched. Graphical Abstract        

Synthesis of the [<Superscript>2</Superscript>H,<Superscript>15</Superscript>N]-labeled antiviral drug “triazavirine”

Selective methods for the incorporation of stable isotopes ¹⁵N and ²H into the structure of antiviral medicine “triazavirine” 1 were developed. The synthesized isotopically modified “triazavirine” 1– ² H ₃ , ¹⁵ N ₃ contained the labeled atoms in both the azole and the azine rings. ¹³C and ¹⁵N NMR spectra of the isotope-containing sample 1– ² H ₃ , ¹⁵ N ₃ were thoroughly analyzed.     

Ionic complexes simultaneously containing fullerene anions and coordination structures of metal phthalocyanines with I<Superscript>−</Superscript> and EtS<Superscript>−</Superscript> anions

The ionic complexes simultaneously containing negatively charged coordination structures of metal phthalocyanines and fullerene anions, viz., {Mn^IIPc(CH₃CH₂S^?) _x ·(I^?)_1?x }·(C₆₀ ^·?)· ·(PMDAE⁺)₂·C₆H₄Cl₂ (PMDAE is N,N,N′,N′,N′-pentamethyldiaminoethane, x = 0.87, 1) and {Zn^IIPc(CH₃CH₂S^?)_y·(I^?)_1?y }₂·(C₆₀ ^?)₂·(PMDAE⁺)₄·(C₆H₄Cl₂) (y = 0.5, 2) were synthesized. The both compounds were obtained as single crystals, which made it possible to study their crystal structures. In complex 1, the fullerene radical anions form honeycomb-like layers in which each fullerene has three neighbors with center-to-center interfullerene distances of 10.13–10.29 Å. Rather long distances between the C₆₀ ^·? radical anions results in the retention of monomeric C₆₀ ^·? in this complex down to the temperature of 110(2) K. In complex 2, fullerenes form dimers (C₆₀ ^?)₂ bonded by one C-C bond. The dimers are packed in corrugated honeycomb-like layers with interfullerene center-to-center distances of 9.90–10.11 Å. Manganese(II) and zinc(II) phthalocyanines coordinate iodide and ethanethiolate anions to the central metal atom to form unusual negatively charged coordination structures M^IIPc(An^?) (An^? is anion) packed in dimers {M^IIPc(An^?)}₂ with a short distance between the phthalocyanine planes (3.14 Å in 1 and 3.27 Å in 2). The pthalocyanine dimers also form layers with the PMDAE⁺ cations, and these layers alternate with the fullerene layers. The packing of spherical fullerenes with planar phthalocyanine molecules is attained by the insertion of fullerenes between the phenylene groups of phthalocyanines. The π-π-interactions of the porphyrin macrocycle with five- or six-membered fullerene rings are characteristic of the earlier studied ionic porphyrin and fullerene complexes. Such interactions are not observed for ionic complexes 1 and 2.     

Generation of peptide radical dications via low-energy collision-induced dissociation of [Cu<Superscript>II</Superscript>(terpy)(M + H)]<Superscript>·3+</Superscript>

The first example of the formation of hydrogen-deficient radical cations of the type [M + H](.2+) is demonstrated to occur through a one-electron-transfer mechanism upon low-energy collision-induced dissociation (CID) of gas-phase triply charged [Cu(II)(terpy)(M + H)](.3+) complex ions (where M is an angiotensin III or enkephalin derivative; terpy = 2,2':6',2'-terpyridine). The collision-induced dissociation of doubly charged [M + H](.2+) radical cations generates similar product ions to those prepared through hot electron capture dissociation (HECD). Isomeric isoleucine and leucine residues were distinguished by observing the mass differences between [z(n) + H](.+) and w(n)(+) ions (having the same residue number, n) of the Xle residues. The product ion spectrum of [z(n) + H](.+) reveals that the w(n)(+) ions are formed possibly from consecutive fragmentations of [z(n) + H](.+) ions. Although only the first few [M + H](.2+) species have been observed using this approach, these hydrogen-deficient radical cations produce fragment ions that have more structure-informative patterns and are very different from those formed during the low-energy tandem mass spectrometry of protonated peptides.     

Synthesis and structures of Cu<Superscript>I,II</Superscript> complexes with a 2,2´-bipyridine derivative bearing a (+)-3-carene moiety

The complex salt {[CuL₂][Cu₄I₆]?MeCN}_n (1) and the compound [Cu₄L₃I₄]?3 MeCN (2) (L is a chiral ligand bearing a natural monoterpene (+)-3-carene moiety) were synthesized. The crystal structures of compounds 1 and 2 were determined by X-ray diffraction. The structure of compound 1 consists of complex cations [CuL₂]²⁺ (N₃O₂ polyhedron is a trigonal bipyramid) and Cu^I coordination polymers (CuI₄ polyhedron is a tetrahedron) as anions. The experimental magnetic moment μ_eff at 300 K is 1.90 μ_B, which is consistent with the X-ray diffraction data and the assumption that compound 1 is mixed-valence. The structure of compound 2 comprises a tetranuclear Cu^I complex, in which three Cu atoms are coordinated by two N atoms of the ligand L and two I atoms, and the fourth Cu atom is coordinated by four I atoms (coordination polyhedra are distorted tetrahedra). Compounds L and 2 were found to influence the viability of human laryngeal carcinoma cells (Hep2). The IC₅₀ value for complex 2 (13.0±1.7 μM) is substantially smaller than IC₅₀ for compound L (30.5±0.5 μM).     

Host–guest complexes of the antituberculosis drugs pyrazinamide and isoniazid with cucurbit[7]uril

The potential use of cucurbit[7]uril (CB[7]) as an excipient in oral formulations for improved drug physical stability or for improved drug delivery was examined with the antituberculosis drugs pyrazinamide (pyrazine-2-carboxamide) and isoniazid (isonicotinohydrazide). Both drugs form 1:1 host–guest complexes with CB[7] as determined by ¹H nuclear magnetic resonance spectrometry, electrospray ionisation mass spectrometry and molecular modelling. Drug binding is stabilised by hydrophobic effects between the pyridine and pyrazine rings of isoniazid and pyrazinamide, respectively, to the inside cavity of the CB[7] macrocycle as well as hydrogen bonds between the hydrazide and amide groups of each drug to the CB[7] carbonyl portals. At pH 1.5, isoniazid binds CB[7] with a binding constant of 5.6 × 10⁵ M^?1, whilst pyrazinamide binds CB[7] at pH 7 with a much smaller binding constant (4.8 × 10³ M^?1). Finally, CB[7] prevents drug melting through encapsulation. Where previously pyrazinamide displays a typical melting point of 189 °C and isoniazid 171 °C, by differential scanning calorimetry, no melting or degradation at temperatures up to 280 °C is observed for either drug once bound by CB[7].     

Primary photophysical and photochemical processes upon UV excitation of PtBr<Subscript>6</Subscript><Superscript>2–</Superscript> and PtCl<Subscript>6</Subscript><Superscript>2–</Superscript> complexes in water and methanol

Primary photophysical and photochemical processes were studied for Pt^IVBr₆ ^2– and Pt^IVCl₆ ^2– complexes in water and methanol by ultrafast kinetic spectroscopy upon excitation in the band region of charge transfer from the ligand-centered group π-orbitals to the e_g*-orbital of Pt^IV complex anion (LMCT bands). The data obtained earlier upon excitation in the region of d—d bands were compared. Irrespective of the excitation wavelength, the photochemical properties of complexes are caused by the reactions of intermediates proceeding in the picosecond time range. These intermediates were identified as Pt^IVBr₅ ^– upon photolysis of Pt^IVBr₆ ^2– and, presumably, the Adamson radical pair [Pt^IIICl₅ ^2–(C _4v )...Cl?] upon photolysis of Pt^IVCl₆ ^2–. The difference in the exciting light wavelengths has an impact only on the first step of these processes, i.e., transition from the Franck—Condon excited state to intermediates.     

Analogs of ecdysteroids with a tetrasubstituted Δ<Superscript>8,14</Superscript>-bond

By hydrogenation of (20R,22R)-6α,14α,25-trihydroxy-and (20R,22R)-6β,14α,25-trihydroxy-2,3:20,22-bis(isopropylidenedioxy)-5α-cholest-7-enes on a catalyst (Raney nickel) the corresponding (5α,6α)-and (5β,6β)-epimers of previously unknown Δ^8,14-6-hydroxy derivatives of ecdysteroids were synthesized.     

Host–guest complexes of some cucurbit[n]urils with the hydrochloride salts of some imidazole derivatives

Interaction between the normal cucurbit[n]urils (n = 6,7,8; Q[6], Q[7], Q[8]) and a sym-tetramethyl-substituted cucurbit[6]uril derivative (TMeQ[6]) with the hydrochloride salts of some imidazole derivatives N-(4-hydroxylphenyl)imidazole (g1), N-(4-aminophenyl)imidazole (g2), 2-phenylimidazole (g3) in aqueous solution was investigated by using ¹H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy, as well as by using a single crystal X-ray diffraction determination. The ¹H NMR spectra analysis established a basic interaction model in which inclusion complexes with a host:guest ratio of 1:1 forms for the Q[6]s and Q[7] cases, while with a host:guest ratio of 1:2 form for the Q[8] cases. It was common that the hosts selectively bound the phenyl moiety of the guests. Absorption spectrophotometric and fluorescence spectroscopic analysis in aqueous solution defined the stability of the host–guest inclusion complexes at pH 5.8 with a host:guest ratio of 1:1 form quantitatively as logK values between 4 and 5 for the smaller hosts Q[6 or 7]s, while with a host:guest ratio of 1:2 form quantitatively as logK values between 11 and 12 for the host Q[8]. Two single crystal X-ray structures of the inclusion complexes TMeQ[6]-g2 · HCl and TMeQ[6]-g3 · HCl showed the phenyl moiety of these two guests inserted into the host cavity, which supported particularly the ¹H NMR spectroscopic study in solution.     

Structural organization of silver(I) complexes with O,O′-dialkyl dithiophosphates: Solid-state <Superscript>13</Superscript>C and <Superscript>31</Superscript>P CP/MAS NMR and single-crystal X-ray diffraction studies

Silver(I) complexes with four symmetrically substituted O,O′-dialkyl derivatives of dithiophosphoric acid of the general formula [Ag{S₂P(OR)₂}] _n (R = C₂H₅, i-C₃H₇, C₄H₉, and s-C₄H₉) were obtained. Their structures and spectroscopic characteristics were studied by solid-state ¹³C and ³¹P CP/MAS NMR spectroscopy and X-ray diffraction analysis. The parameters of the anisotropy of the ³¹P chemical shift ³¹P-δ _aniso and η (δ _aniso is the chemical shift anisotropy and η is the asymmetry parameter) calculated from the diagrams of the x ²-statistic revealed that the (RO)₂PS₂ groups act as bridging ligands in all the silver(I) complexes obtained. The hexanuclear complex [Ag₆{S₂P(O-i-C₃H₇)₂}₆] was found to form two modifications α and β. According to the X-ray diffraction data, the silver(I) complex with O,O′-di-s-butyl dithiophosphate exists as discrete hexanuclear molecules [Ag₆{S₂P(O-s-C₄H₉)₂}₆]. In the clear molecules β-[Ag₆{S₂P(O-i-C₃H₇)₂}₆], the signals for the phosphorus atoms were assigned to their positions determined from the X-ray diffraction data.     

Conjugate halo- and mercuroazidation of 1-phenyltricyclo-[4.1.0.0<Superscript>2.7</Superscript>]heptane. Synthesis of a conformationally rigid α-amino acid with a bicyclo[3.1.1]heptane skeleton

1-Phenyltricyclo[4.1.0.0^2.7]heptane reacted with N-bromo-, N-chloro-, and N-iodosuccinimides and with mercury(II) acetate in the presence of sodium azide as external nucleophile to give conjugate addition products to the central C¹–C⁷ bicyclobutane bond with a norpinane structure, where the azido group and the phenyl were attached to the same carbon atom (C⁶). The bromo- and chloroazidation showed anti-stereo-selectivity, and the iodoazidation, moderate syn-stereoselectivity; the mercuroazidation afforded exclusively the corresponding syn-addition product. Hydro-, bromo- and chlorodemercuration of the mercury adduct with sodium tetrahydridoborate and elemental bromine and chlorine, respectively, did not involve the azido group, and the original configuration was retained. The reduction of the hydrodemercuration product with LiAlH₄ gave 6-exo-phenylbicyclo[3.1.1]heptan-6-amine which was transformed in three steps into conformationally rigid 6-endo-(acetamido)bicyclo[3.1.1]heptane-6-carboxylic acid.     

Synthesis of [3-<Superscript>14</Superscript>C]-L-tryptophan and 5′-hydroxy-[3-<Superscript>14</Superscript>C]-L-tryptophan

The synthesis of selectively labeled [3-¹⁴C]-L-tryptophan and its derivative 5′-hydroxy-[3-¹⁴C]-L-tryptophan using chemical and multienzymatic methods is reported. The key intermediate for this synthesis, [3-¹⁴C]-DL-alanine was obtained from ¹⁴CH₃I as a result of its condensation with N-(diphenylmethylene)glycine tert-butyl ester. Next, the mixture containing [3-¹⁴C]-DL-alanine, indole or 5-hydroxyindole has been converted to [3-¹⁴C]-L-tryptophan or 5′-hydroxy-[3-¹⁴C]-L-tryptophan, respectively, in a one-pot multienzymatic reaction using four enzymes: D-amino acid oxidase, catalase, glutamic-pyruvic transaminase and tryptophanase.     

Structure of sulfanilamide-containing cobalt(III) dioximates with the [ZrF<Subscript>6</Subscript>]<Superscript>2−</Superscript> and [BF<Subscript>4</Subscript>]<Superscript>−</Superscript> anions

The complexes [Co(DH)₂(Sam)₂]₂[ZrF₆]·5H₂O (I) and [Co(DH)₂(Sam)₂][BF₄]·H₂O (II), where DH^? is the dimethylglyoxime monoanion, and Sam is para-aminobenzenesulfamide (sulfanilamide, white streptocid), were synthesized, and their crystal structures were determined by X-ray diffraction analysis. The coordination polyhedron of the Co³⁺ atom is an N₆ octahedron formed by four nitrogen atoms of the two dimethylglyoxime residues and two nitrogen atoms of the Sam fragments. The latter are realized in virtually parallel orientation relative to the polyhedron of the metal atom and its equatorial plane; the average value of the dihedral angles is 26.8(1)°, and there is π-π interaction between the benzene rings of the Sam fragments and the π delocalized equatorial metallocycle. The deviation of the cobalt atom from the four-angle plane is up to 0.009(1) Å. The (Co-N)_DH? and (Co-N)_Sam distances in the [Co(DH)₂(Sam)₂]⁺ complex cations vary from 1.892(2) Å to 1.907(3) Å and from 2.000(2) Å to 2.012(2) Å, respectively. The [ZrF₆]^2? and [BF₄]^? complex anions play the major role in crystal formation; they produce a substantial effect on the formation of a complex system of hydrogen bonds.     

Determination of the structure of quinolone-γ-cyclodextrin complexes and their binding constants by means of UV–Vis and <Superscript>1</Superscript>H NMR

The host–guest inclusion complex structure and binding ability of two different quinolones with γ-cyclodextrin (γ-CD) were investigated in solution by means of UV–Vis and ¹H NMR spectroscopy. Competition of oxolinic and nalidixic acid molecules for the γ-CD cavity was evaluated by determination of association constants. Both quinolones form 1:1 inclusion complexes, their binding constants at room temperature (25 °C) under acidic and basic conditions were calculated using Benesi–Hildebrand equation. The stability of the complexes was dependent on the structure of the quinolone. In general, the weaker binding constants were observed for oxolinic acid-γ-CD complexes (1616 and 1765 M^?1) and the larger binding constants were obtained for nalidixic acid-γ-CD complexes (3760 and 3840 M^?1). ¹H NMR studies in D₂O were performed to elucidate the structure of each inclusion complex, nalidixic acid molecule penetrates more deeply into the γ-CD cavity and an intermolecular hydrogen bond is formed. Knowledge about structure and relative stability of quinolone-γ-CD complexes will be useful for future applications of these antimicrobial agents in medicinal chemistry.     

X-ray emission study of the electronic structure of binuclear niobium complexes with (S<Subscript>2</Subscript>)<Superscript>2</Superscript>–disulfide bridging ligands

The electronic structure of binuclear niobium complexes [Nb₂S₄(acac)₄] and K₄[Nb₂S₄(ox)4] is studied by X-ray emission fluorescent spectroscopy and quantum chemistry techniques. Data on the partial atomic composition of highest occupied molecular orbitals of the complexes are obtained. The energy positions of bonding and antibonding frontier molecular orbitals observed in the X-ray emission spectra of binuclear [Nb₂((S₂)^2–)₂]⁴⁺ clusters are determined by the analysis of overlap populations.