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.     

Host–guest complexes of cucurbit[7]uril with albendazole in solid state

The inclusion complex of cucurbit[7]uril (CB7) and albendazole (ABZ) in solid state was prepared by freeze-drying. The formation of a host–guest complex was confirmed by microanalysis, ¹H-nuclear magnetic resonance spectroscopy, and fourier transformed-infrared spectroscopy (FT-IR) techniques. The shifts in the NMR peaks supported the encapsulation from the propylthio and not the carbamate site, in agreement with the previously reported results in solution. The N₂ adsorption–desorption isotherms indicated no change in the calculated surface area or the pore size distribution for the unbound and CB7-bound ABZ solid drugs. Freeze-drying produced a system with a higher degree of amorphisation as confirmed by the X-ray powder diffraction (XRD) technique. Thermal analysis of the drug-loaded CB7 by using differential scanning calorimetry and thermogravimetry demonstrated the possibility of dehydration at temperature 100 °C beyond the melting point of unbound ABZ since no melting of the samples was observed until the CB7 itself begins to decompose around 300 °C. Putting it all together, the results supported that CB7 imparts significant thermal/physical stability on the ABZ drug in the solid state.     

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.     

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.     

<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        

σ<Superscript>H</Superscript>-Adducts of <Emphasis Type="Italic">N</Emphasis>-alkylpyrazinium and quinoxalinium salts with nucleophiles. The <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR spectra and the crystal structures of P-adducts

The previously unknown addition products of P-nucleophiles to 5-aryl- and 5-hetaryl- 2,3-dicyano-1-ethylpyrazinium salts and to 5-aryl- and 5-hetaryl-14nethylquinoxalinium salts were synthesized. The three-dimensional structures of the P- σ^H-adducts of the 1,4-diazine series were established by X-ray diffraction.     

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.     

Stabilization of [Sc(NCS)<Subscript>6</Subscript>]<Superscript>3−</Superscript> anion by [M(18C6)]<Superscript>+</Superscript> complexes in solvation systems

The [M(18C6)]₄[Sc(NCS)₆]Cl · nH₂O complexes were established to form in the solutions ScCl _x -Solv-MNCS-18C6, where Solv is ethanol, THF, acetonitrile, or isopropyl alcohol; M = Na, K; 18C6 is 1,4,7,10,13,16-hexaoxocyclooctadecane. X-ray diffraction analysis of [K(18K6)]₄[Sc(NCS)₆]Cl · 3.33H₂O showed that the thiocyanate ion was coordinated by Sc through the N atom. The structure consists of octahedral Sc(NCS) ₆ ^3? that are united via nonvalent K-S interaction with macrocyclic dimers [M(18C6)]₂ into chains. Each 18C6 molecule coordinates one K atom.     

Bond variations in the complexes [CuCl<Subscript>6</Subscript>]<Superscript>4−</Superscript>

An extended version of the angular overlap model developed from the fourth-order variational perturbation theory was used to explain why sd mixing for [CuCl₆]^4? and other pseudooctahedral complexes [CuL₆]^n? with the split ground state ² E is responsible for strong softening of the vibrational E mode, which results in lengthening and even cleavage of the bonds between the metal atom and the axial ligands.     

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.     

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.     

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.