X-ray spectral study of the nature of electronic interactions in transition metal dithiocarbamates

SK_β spectra are studied for a series of nickel(II), zinc(II), and cadmium(II) dithiocarbamate complexes. Model quantum chemical calculations of the electronic structure of planar chelate rings are reported. It is shown that the metal-ligand interaction forming a coordination bond between the dithiocarbamate ligand and the metal mainly involves the nonbonding n-electrons and the weakly bonding π-electrons localized on the sulfur atoms. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1121–1126, November–December, 1998.     

Spatial structure of β-cyclodextrin clathrates with 1,4-benzodiazepine derivatives

Understanding the mechanisms of mutual recognition and complementary binding of molecules in guest-host complexes is based on analysis of their spatial structure. As guest-host complexes, we have synthesized inclusion compounds of 1,4-benzodiazepine anxiolytic agents gidazepam and cinazepam with β-cyclodextrin, in which these anxiolytic agents manifest increased biological accessibility. The spatial structure of the complexes was determined from the two-dimensional NOESY spectra and analysis of the fragmentary mobility of the guest and host molecules, characterized by spin-lattice relaxation times T₁ of the¹³C nuclei. An analysis of d-contacts showed that the 5-phenyl ring is completely enclosed in the inner hydrophobic cavity of β-CD [(C^2′ H-C^4′ H)-CIIH(CIVH), CVH (CIIIH, CVIH₂), CVIOH]. For the 1:1 complex, intense d-contracts of C⁸H with CVIOH indicate that C⁸H is located in the vicinity of both wide and narrow bases of the bracelet. This is only possible for the 2:2 complex, in which both β-CD molecules approach each other by their wide and narrow bases. A comparison between the schemes of d-contacts for the 2:2 and 2:1 associates proves that the β-CD molecules have the same spatial orientation in the dimer. The difference is in the fact that the hydrazinocarbonyl fragment of gidazepam and the hemisuccinate fragment of cinazepam penetrate into an empty molecule of the 2:1 β-CD complex (NH₂-CIH contact). The intensities of the cross peaks were measured, due to which the interatomic distances between the guest and host molecules were calculated and the spatial structure of the clathrates was established. The benzodiazepine derivatives are embedded differently into the clathrate molecule, as shown by the value of the angle between the symmetry axis of β-CD and the axis through the centers of the aromatic rings: 0° for gidazepam and 60° for cinazepam. This is a consequence of the fact that the substituents forming hydrogen bonds with hydroxyl groups at the wide base of the β-CD bracelet lie in different positions: the hydrazinocarbonylmethyl fragment of gidazepam lies at N¹, and the hemisuccinate fragment of cinazepam is at C³. A. V. Bogatskii Physicochemical Institute, Ukrainian National Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 876–890, September–October, 1996. Translated by L. Smolina     

Study of the NpO

A new neptunium(VI) complex [(NpO₂)(CrO₄)(H₂O)] ⋅ 4H₂O (I) was synthesized, its crystal structure was determined, and the IR and near-IR absorption spectra were measured. The unit cell parameters are: a = 8.634(4) Å, b = 11.119(4) Å, c = 9.410(3) Å, β = 92.40(3)°, space group P2₁/c, Z = 4, V = 902.6(6) ų, R = 0.048, wR(F ²) = 0.054. The crystal structure of the compound is composed of the [(NpO₂)(CrO₄)(H₂O)] _n layers and the crystal water molecules located between the layers. The coordination polyhedron of neptunium is a pentagonal bipyramid whose equatorial plane is formed by the oxygen atoms of two bridging water molecules and three chromate ions. The Np(VI) complexation with the chromate ions in an aqueous solution at μ = 1 was studied by spectrophotometry. The stability constants for 1 : 1 and 1 : 2 complexes were calculated, logβ₁ = 3.19(2), logβ₂ = 3.93(2), respectively. __________ Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 11, 2005, pp. 848–852. Original Russian Text Copyright ? 2005 by Budantseva, Andreev, Fedoseev, Astafurova, Antipin.     

Interaction between cetyltrimethylammonium bromide and β-cyclodextrin: surface tension and interfacial dilational viscoelasticity studies

The interaction between cetyltrimethylammonium bromide (CTAB) and β-cyclodextrin (β-CD) was studied via surface tension and dilational viscoelasticity methods. The effect of sodium bromide and sodium chloride on the interaction between CTAB and β-CD were studied as well. The surface tension isotherms provided a series of parameters, including apparent critical micelle concentration (cmc*), surface tension at the cmc* (γ_cmc), stoichiometry of the complex (R), and the efficiency of adsorption (pC ₂₀ ). The addition of NaBr and NaCl decreases the cmc* of CTAB/β-CD solution. CTAB molecules enter the cavities of β-CD molecules thus formed both 1:1 and 1:2 inclusion complexes. From the change of γ_cmc, it can be seen that the CTAB/β-CD complexes (1:1) act as short-chain alcohol, which decrease γ_cmc, but the depression of cmc* is too small to be detected. R first decreases then increases as a function of NaBr and NaCl. Compared to NaCl, NaBr increases R more efficiently. The presence of NaBr and NaCl increases pC ₂₀ of CTAB/β-CD solution. The results obtained from the dilational viscoelasticity measurements at low dilational frequencies (0.005–0.1 Hz) reveal that the dilational modulus passes through a maxium value with increasing concentration of β-CD at a given concentration of CTAB. The addition of both NaBr and NaCl decreases the dilational modulus of a given concentration CTAB/β-CD solution. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Phosphorescence of aromatic molecules in complexes with crystalline β-cyclodextrin at room temperature

The rate constants for the quenching by oxygen of triplet states of aromatic molecules (naphthalenes-d₈ and-h₈, phenanthrene) forming inclusion complexes with crystalline β-cyclodextrin in water at 290 K are equal to 900–1300 L mol⁻¹s⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1450–1453, August, 1997.     

Photoelectron spectroscopy of transition metal complexes. Effect of electron relaxation on spectrum informativity

Orbital ionization energies are compared with the results of ab initio calculations for three-atomic linear BeCl₂, XeF₂, CrCl₂ and five-atomic tetrahedral TiCl₄, RuO₄ molecules to investigate the effect of electron relaxation in ions on the informativity of photoelectron spectra of molecules and complex compounds. For all compounds except CrCl₂ there is satisfactory agreement between theory and experiment in respect of the sequence and character of electronic levels and the orbital nature of chemical bonds. In the series of 3d metal tris-β-diketonates, for metal complexes of the second half of the series there are wide discrepancies between the photoelectron, X_α-DV, and ab initio data on the electronic structure of the complexes, which are due to electron relaxation in the ions. The calculations exaggerate the mixing of levels between the metal and ligands, since the energy splitting of the corresponding spin-orbitals (spin polarization) considerably exceeds the multiplet splitting of states corresponding to a vacancy on the ligand MO estimated from the photoelectron spectra. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1113–1120, November–December, 1998.     

Host–Guest Interaction Study of Resveratrol With Natural and Modified Cyclodextrins

The aim of this work is to increase the stability and water solubility of resveratrol by complexation with different cyclodextrins. Furthermore, physical–chemical properties of each inclusion compound were investigated. Complexes of resveratrol with cyclodextrins both native (α, β, γ) and modified (2-hydroxypropyl-β-cyclodextrin, dimethyl-β-cyclodextrin) were obtained by using the suspension method. An inclusion complex with β-cyclodextrin was also prepared by using the microwave. Solid state characterization of the products was carried out using Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (DRX); solution studies were performed by UV–Vis spectrophotometry and ¹H-NMR spectroscopy. Phase solubility profiles with all cyclodextrins employed were classified as A_N type, indicating the formation of 1:1 stoichiometric inclusion complexes. Stability constants (K _c) from the phase solubility diagrams were calculated. Stability studies in the solid state and in solution were performed; the photodegradation by UV–Vis spectrophotometry was monitored. The isomerization rate trans to cis, in ethanol solution, decreased with inclusion. The dissolution studies revealed that resveratrol dissolution rate was improved by the formation of inclusion complexes.     

Complexes of Ca2+ and Mg2+ withN-acetyl-α,β-dehydrodipeptides: the state in an alcoholic solution and its relationship with asymmetric induction upon diastereoselective hydrogenation

In an alcoholic solution,N-acetyl-α,β-dehydrodipeptides interact with Ca²⁺ and Mg²⁺ ions to form complex particles containing several dehydrodipeptide molecules per metal ion. The composition of these particles and steric interactions in them determine the acidity of the carboxyl groups and the degree of asymmetric induction upon diastereoselective hydrogenation. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp.904–907, May, 1999.     

Inclusion complexes of 2-phenoxyethanol and alkoxyethanols in cyclodextrins: an 1H NMR study

The association in aqueous solutions of small amphiphilic molecules [2-phenoxyethanol, PhE₁, and some α-n-alkyl-ω-hydroxyoligo(oxiethylenes], C₄E₁, C₄E₂ and C₆E₂) with β-cyclodextrin (βCD), heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TRIMEB) was investigated by ¹H NMR spectroscopy. The upfield shifts observed for the H3 and H5 NMR signals due to anisotropic shielding confirm that the host–guest associations are of inclusion type. The stoichiometries and the apparent inclusion constants, K _app, were determined by ¹H NMR spectroscopy using the H5 and H3 signals. The relative differences in the K _app values for βCD inclusion complexes seem to reflect the hydrophobic/hydrophilic balance of the guests. The K _app values for the PhE₁ inclusion complexes can be related to the degree of methylation and hydrophobicity variation within the considered hosts. In addition, a comparative study between βCD and TRIMEB inclusion complexes using 2D ROESY (Rotating-frame Overhauser Enhancement SpectroscopY) NMR spectra provides structural features for these complexes which are inaccessible by other experimental methods.     

Thermodynamics of Nicotinic Acid Interactions with Some Saccharides

The interactions of nicotinic acid with α-D-glucose and maltose, and with α-, β-, hydroxypropyl-α- and hydroxypropyl-β-cyclodextrins were studied by using solution calorimetry at T = 298.15 K and pH = 3.4. The thermodynamic parameters (log₁₀ K, Δ G∘_c, Δ H∘_c and Δ S∘_c) were calculated for the systems in which complex formation was observed. Systems with weak interparticle interactions lacking complex formation were characterized by enthalpic virial coefficients calculated on the basis of the McMillan–Mayer theory. It was found that the complexation affinity of α-cyclodextrin to nicotinic acid is stronger in comparison to β-cyclodextrin and the mono- and disaccharides. The influence of different factors, such as the availability of the macrocyclic hydrophobic cavity, the relationship of the sizes of guest molecule to the host cavity, the presence of bulky hydroxypropyl substitutes and their structure, and the solvation of guest molecules on the stability of complexes and their thermodynamic parameters of interaction is discussed.     

Effect of Solvents and pH on <Emphasis Type="Italic">β</Emphasis>-Cyclodextrin Inclusion Complexation of 2,4-Dihydroxyazobenzene and 4-Hydroxyazobenzene

The spectral characteristics of 2,4-dihydroxyazobenzene (DHAB, sudan orange G) and 4-hydroxyazobenzene (HAB) have been studied in various solvents, different hydrogen ion and β-cyclodextrin (β-CD) concentrations, and are compared with azobenzene (AB). The inclusion complexes of the above molecules with β-CD were analyzed by UV-vis spectrometry, flourometry, FT-IR, ¹H NMR, SEM and DFT methods. The solvent study shows that only the azo form is present in DHAB and HAB molecules. The unusually large red shift observed in acidic solutions indicates both molecules exhibit azo-hydrazo tautomerization. In the β-CD solutions, the increase in fluorescence intensity and large bathochromic shift in the S₁ state indicates that DHAB and HAB form 2:2 inclusion complexes, whereas AB forms a 1:1 inclusion complex.     

Synthesis of mixed-ligand managanese(II) complexes with alkyl xanthate ions and nitrogen-containing heterocycles. Crystal and molecular structure of the [Mn(S2COC3H7−i )2(2,2′-Bipy)] complex

We have synthesized high-spin mixed-ligand Mn²⁺ complexes Mn(S₂COR)₂L where R=i−C₃H₇, i−C₄H₉; [L=1,10-phenanthroline (Phen), 2,2′-bipyridyl (2,2′-Bipy), 4,4′-bipyridyl (4,4′-Bipy)]. As solids, the compounds are stable to oxidation by atmospheric oxygen. An X-ray structural study of the [Mn(S₂COC₃H₇−i)₂(2,2′-Bipy)] complex was carried out. The structure is composed of discrete monomeric molecules. The corrdination polyhedron of the Mn atom is a distorted [4S+2N] octahedron. The molecules are bonded by van der Waals interactions. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 2, pp. 106–111, March–April, 1994. Translated by T. Yudanova     

Structure of molecular complexes in liquid CO2 solutions of water

The calculated anharmonic frequencies and intensities of simultaneous vibrational transitions in CO₂−H₂O and (CO₂)₂−H₂O hydrogen-bonded complexes are compared with known experimental data. Hydrogen-bonded complexes form in liquid CO₂ solutions of water under normal conditions, unlike the gas phase in which the CO₂ and H₂O molecules are coupled by van der Waals bonds. The majority of these complexes are 2∶1 complexes. N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 375–379, March–April, 1995. Translated from E. Taskaeva     

Study on Inclusion Complex Formation of <Emphasis Type="Italic">m</Emphasis>-Aminobenzoic Acid with Native and Substituted <Emphasis Type="Italic">β</Emphasis>-Cyclodextrins

The complex formation of native and substituted β-cyclodextrins with m-aminobenzoic acid in water was characterized by calorimetry, ¹H NMR and UV spectroscopic studies. These studies showed that β-, hydroxypropyl-β- and methyl-β-cyclodextrins form 1:1 inclusion complexes with m-aminobenzoic acid. The thermodynamic properties of complex formation (K,Δ_c G ^o,Δ_c H ^o,Δ_c S ^o) were calculated. It was found that the processes of complexation are mainly favorable entropically. Introduction of hydroxypropyl- and methyl-substituents into the β-CD molecule results in negligible enhancement of stability of the complexes formed. The structure of these substituents has no influence on the stability constant values. The insertion of the carboxylic group of m-aminobenzoic acid into the cyclodextrin cavity was confirmed by ¹H NMR data.     

Analysis of the interaction of ethidium bromide with a DNA octamer 5’-d(GpApCpApTpGpTpC) in aqueous solution using1H NMR data

Complexation of a phenanthridine dye ethidium bromide with a desoxyoligonucleotide 5’-d(GpApCpAp-TpGpTpC) in aqueous salt solution is studied by one- and two-dimensional¹H NMR spectroscopy. Two-dimensional correlated homonuclear PMR spectroscopy (2D-TOCSY and 2D-N0ESY) was used for complete assignment of the proton signals of molecules in solution and for qualitative analysis of the character of interaction between ethidium bromide and desoxyoctanucleotide. The concentration dependences of the proton chemical shifts of the molecules were measured at three temperatures (T₁ = 298 K, T₂ = 308 K, and T₃ = 318 K); the temperature dependences were measured in the temperature range 278–358 K. Different schemes of dye complexation with an octamer duplex involving different molecular associates in solution are considered. The equilibrium constants of the reactions, the corresponding thermodynamic parameters (δH⁰, δS₀), and the limiting values of the chemical shifts of ethidium bromide protons in the complexes are determined. The relative contents of complexes of different types in solution (dye complexes with desoxyoctanucleotide in duplex form) are analyzed, and peculiarities of the dynamic equilibrium depending on the ratio of dye and octamer concentrations and temperature are established. The most probable structures of the 1:2 and 2:2 intercalated complexes corresponding to dye intercalation into the pyrimidine-purine sites of the desoxyoctanucleotide duplex are derived using the calculated values of the induced proton chemical shifts of ethidium bromide and two-dimensional PMR data. Translated fromZhurnal Strukturnoi Khimii, Vol.40, No. 2, pp. 265–275, March–April, 1999.     

A Study of Haloperidol Inclusion Complexes with <Emphasis Type="Italic">β</Emphasis>-Cyclodextrin Using Phase Solubility,NMR Spectroscopy and Molecular Modeling Techniques

Guest-host interactions of haloperidol (Halo) with β-cyclodextrin (β-CD) have been investigated using several techniques including phase solubility diagrams (PSD), proton nuclear magnetic resonance (¹H-NMR), X-ray powder diffractometry (XRPD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and molecular mechanical modeling (MM⁺). From an analysis of the PSDs, both protonated and neutral Halo (pK _a=8.5) form soluble 1:1 and 1:2 Halo/β-CD complexes, while the insoluble complex has 1:2 (Halo:β-CD) stoichiometry (B_S-type PSD). Ionization of Halo reduces its tendency to complex with β-CD, where the protonated species at pH=4.6 and 6.0 have K ₁₁ values of 100 L⋅mol⁻¹ and 298 L⋅mol⁻¹, respectively, compared with 2000 L⋅mol⁻¹ for neutral species at pH=10.6. The hydrophobic character of Halo was found to provide 32% of the driving force for complex stability, whereas other factors including specific interactions contribute −15 kJ⋅mol⁻¹. ¹H-NMR and MM⁺ studies indicate the formation of isomeric 1:1 and 1:2 complexes, where the chlorophenyl, flurophenyl, piperidine and butanone moieties become included into separate β-CD cavities. The dominant driving force for complexation is evidently van der Waals with very little electrostatic contribution. PSD, ¹H-NMR, XRPD, DSC and SEM studies indicate the formation of inclusion complexes in solution and in the solid state.     

Electrochemical reductive carbon-to-carbon coupling of σ-ethynyl complexes of transition metals

The electrochemical properties of σ-ethynyl complexes of chromium subgroup metals were studied by cyclic voltammetry and preparative-scale electrolysis. The redox cycle of C₅H₅(CO)₃CrC=CPh was shown to give the bis-carbyne complex (η⁵-C₅H₅)(CO)₂Cr≡C-C(Ph)=C(Ph)-C-Cr(CO)₂(η⁵-C₅H₅) formedvia the reductive C_β−C_β coupling of ethynyl moieties. The influence of the nature of the metal atom and the ligand environment on the course of this reaction was considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1955–1958, October, 1998.     

Inclusion complexes of spin-labeled indoles with cyclodextrins in aqueous solutions

Guest-host complexes of β- and γ-cyclodextrins (CDs) with two spin-labeled indole derivatives having the same molecular weights but different structures were studied by EPR spectroscopy in aqueous solutions and semiempirical quantum-chemical calculations of these systems were carried out. In the presence of CD the polarity of the NO group environment decreases and the rotational correlation time (τ) of guest molecules increases. Both indole derivatives form 1 : 1 complexes with γ-CD, the binding constants of the complexes being different more than twice. Simulation of EPR spectra made it possible to determine the indole ring orientation relative to the plane of the host molecule (at angles in the range 30–60°) and the rotational diffusion coefficients of the complexes, which corresponded to the hydrodynamic volume of one γ-CD molecule. In contrast to the complexes with γ-CD the rotational correlation times, τ, of the complexes with β-CD correspond to a hydrodynamic volume which much exceeds the volume of a single β-CD molecule. The complexes with β-CD are also characterized by more hydrophobic environment for guest molecules and absence of spin exchange with Ni²⁺ ions in the aqueous solution. There results are consistent with a dimeric structure of β-CD in the complex and with the orientation of the long axis of the guest molecule along the dimer axis. The energies and geometric parameters were calculated for all complexes by the PM3 method with a conventional set of parameters. The optimized energetically stable structures of the 1 : 1 complexes with γ-CD and of the 1 : 2 complexes with β-CD are consistent with experimental data. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1139–1147, May, 2005.     

Spectral Characteristics of Sulfa Drugs: Effect of Solvents,pH and <Emphasis Type="Italic">β</Emphasis>-Cyclodextrin

The absorption and fluorescence spectra of sulfamethoxazole (SMO), sulfisoxazole (SFO), sulfathiazole (STO) and sulfanilamide (SAM) in different solvents, pH and β-cyclodextrin (β-CD) have been analyzed. The inclusion complexes of the above sulfa drugs with β-CD were investigated by UV-visible spectroscopy, fluorometry, DFT, SEM, FT-IR and ¹H NMR. The solvent study indicates that the position of the substituent (oxazole or thiazole group) in the SAM molecule (R–SO₂–NH-group) is not the key factor to change the absorption and emission behavior of these sulpha drug molecules. In aqueous solution, a single fluorescence band (340 nm) was observed whereas in solutions of β-CD dual emission (430 nm) was noticed in sulpha drug compounds. Formation of the inclusion complex in SMO, SFO and STO should result dual emission which is due to a Twisted Intramolecular Charge Transfer band (TICT). The β-CD study indicates that (i) sulpha drugs form 1:1 inclusion complexes with β-CD and (ii) the red shift and the presence of TICT in the β-CD medium confirms heterocyclic ring encapsulated in the β-CD cavity with the aniline ring present on the out side of the β-CD cavity.     

Host–guest interactions between niobocene dichloride and α-, β-, and γ-cyclodextrins: preparation and characterization

The possible inclusion complexes of Cp₂NbCl₂ into α-, β-, and γ-CD hosts have been investigated. The existence of a true inclusion complex in the solid state was confirmed by a combination of thermogravimetric analysis, FTIR, PXRD, and ¹³C CP-MAS NMR spectroscopies. The solid-state results demonstrated that α-cyclodextrin does not form inclusion complexes with Cp₂NbCl₂ whereas β- and γ-cyclodextrins do form such complexes. PXRD, NMR, and thermal analysis showed that the organometallic molecules of Cp₂NbCl₂OH are included in the cavities of β- and γ-cyclodextrins, possibly adopting a symmetrical conformation in the complex, with each glucose unit in a similar environment. In solution, ¹H NMR experiments suggest that niobocene has a shallow penetration on the β-CD leading to upfield shift on H-3 signal with a minor perturbation on the H-5 proton while for γ-CD, both H-3 and H-5 are shifted upfield substantially. This suggests that niobocene penetrates deeper into the γ-CD cavity than in the β-CD cavity, as a result of the cavity size. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.