Effect of hydroxypropyl-β-cyclodextrin complexation on the aqueous solubility, structure, thermal stability, antioxidant activity, and tyrosinase inhibition of paeonol

The objective of this paper is to study the effect of hydroxypropyl-β-cyclodextrin (HP-β-CD) complexation on the aqueous solubility, structure, thermal stability, antioxidant activity, and tyrosinase inhibition of paeonol (PAE). The inclusion complex (PAE-HP-β-CD complex) of HP-β-CD and PAE was prepared by a freeze-drying method. Phase solubility tests showed that the stability constant of the inclusion complex was about 33.8?M^?1 at 25?°C. The experimental results of proton nuclear magnetic resonance (H-NMR) spectroscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) suggested that PAE was included by HP-β-CD to form the PAE-HP-β-CD complex. Furthermore, the thermogravimetric analysis (TGA) results showed that the thermal stability of PAE was improved when it was complexed with HP-β-CD. Comparing the antioxidant activity of PAE with that of the PAE-HP-β-CD complex at the same concentration revealed that the complex of PAE with HP-β-CD was better able to eliminate radical. Furthermore, the experimental results revealed that the formation of a complex with HP-β-CD increased the water solubility of PAE, improving its apparent inhibitive activity of tyrosinase.     

Is the FeC cluster linear? Theoretical study of the equilibrium structure and bonding of FeC

Ab initio electron correlation methods and density functional theory are used to investigate the structure, bonding, and stability of FeC. Theoretical calculations show that the ground state of the FeC anion strongly depends on the level of theory. The linear ⁴Σ^? state with an open configuration δ²σ¹ is predicted to be the ground state of FeC at the coupled‐cluster theory restricted to single, double, and noniterative triple excitations (CCSD[T])//CISD and multireference (MR) second‐order Moller–Plesset (MP2)//CAS self‐consistent field (SCF) levels. Next stable conformations are a C_2V ring structure II (⁴B₂) and a C_2V structure III (⁴A₂) in which Fe is bonded to one carbon atom of a triangular C₃. However, CISD and CCSD//CISD calculations show that the C_2V ring structure II and the C_2V structure III are more slightly stable than is the linear structure I of FeC. The harmonic vibrational frequencies and relevant vertical electron binding energies are reported. Possible detachment transitions in the photoelectron spectrum of FeC are discussed on the basis of current calculations. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 275–279, 2003     

Theoretical study of the substituent effects on structure and dissociation of RNSi and RSiN (R = H, Li)

The effects of substituent on stability, structural properties and dissociation of HSiN, LiSiN and their isomers have been studied in detail using ab initio MP2, CCSD and CCSD(T) and density functional B3LYP methods. After dissociation of HNSi, LiNSi, HSiN and LiSiN, the fragmented atoms have been considered to be either in their ground state or in their valence excited state in various dissociation channels. Only allowed dissociations of these molecules are considered. Various dissociation channels of HSiN and LiSiN and their isomers have been explored and an interesting trend has been observed for the dissociation of stable isomers HNSi and LiNSi and less stable isomers HSiN and LiSiN. The effect of substituents on dipole moment has been discussed. The potential energy surfaces for the RSiN ↔ RNSi isomerization reactions have been analyzed. The structural properties of these molecules agree well with the theoretical and experimental values wherever available.     

Theoretical studies on structures and UV-Vis spectra of C_(70)O

Systematic studies on eight isomers of C70O were performed by means of INDO methods It has been indicated that the O atom is mainly added to the C1-C2 or C3-C3 bond and an epoxide feature with C1 symmetry is formed.Based on the optimized geometries,the UV-Vis spectra were calculated.It has been found that the main peaks of C70O resemble those of C70 and the characteristic absorptions beyond 460 nm are produced,which is m agree ment with the experimental results.Theoretical assignments about the absorptions were carried out and the reason for the red-shift of the absorptions was discussed.C70O is probably composed of four isomers according to the calculated results.     

Sorption of Am(Ⅲ) on Na-bentonite:Effect of pH,ionic strength,temperature and humic acid

Sorption of Am(Ⅲ) on Na-bentonite as a function of contact time,pH,ionic strength,humic acid(HA) and temperature was investigated under ambient conditions.The results showed that the sorption was strongly dependent on pH and ionic strength. Am(Ⅲ) sorption can be described well by pseudo-second-order model.The presence of HA takes a positive effect at low pH;but a negative influence under high pH range.Enthalpy,entropy and Gibbs free energy(i.e.,△H~0,△S~0 and△G~0) calculated from sorption isotherms suggested that sorption process of Am(Ⅲ) was spontaneous and endothermic.     

Theoretical studies on the spectroscopic properties and the substituent effects of pyridyl triazole Os(Ⅱ) complexes

To explore the spectroscopic properties of pyridyl triazole Os(Ⅱ) complexes and how the substituent effects affect the spectroscopic properties of [Os(ptz)2L2] (L=PH3; ptzH=(2-pyridyl)-1,2,4-triazole) (1), [Os(bptz)2L2] (bptzH=3-tert-butyl-5-(2-pyridyl)-1,2,4-triazole) (2), [Os(fptz)2L2] (fptzH=3- (trifluoreomethyl)- 5-(2-pyridyl)-1,2,4-triazole) (3), and [Os(fbtz)2L2] (fbtzH=3-(trifluoreomethyl)-5-(4-tert-butyl- 2-pyridyl)-1,2, 4-triazole) (4), the density functional theory (DFT) method at the B3LYP level ...     

Synthesis,Characterization, Optical Property and Bioactivity of the Eu(Ⅲ) Complex with Aromatic Carboxylic Triazole

A novel complex{[Eu(H_5TIA)(C_2O_4)_(0.5)(H_2O)_3]·H_2O}_(n )of Eu(Ⅲ)with aromatic carboxylic triazole(H_7TIA=5-(4H-1,2,4-triazol-4-yl)isophthalic acid,H_2C_2O_4=oxalic acid)was hydrothermally synthesized and characterized by IR,UV-Vis,emission spectra and optical activity,and its crystal structure was determined.It crystallizes in triclinic system,space group P1 with a=7.4452(13),b=10.776(2),c=11.286(2)?,α=110.546(3)°,β=106.604(3)°,γ=99.031(3)°,V=486.0,GOOF=1.096,the final R=0.0196 and w R=0.0527 for 3081 observed reflections with I≥2σ(I),R=0.0209 and wR=0.0535 for all data with(Δ/σ)_(max)=0.001,(Δρ)_(max)=0.48 and(Δρ)_(min)=–0.46 e·?~(-3).The natural bond orbital(NBO)charges,electrostatic potential(ESP)and frontier orbital of this complex were also analyzed.The results of anti-bacterial activity against Gram positive(S. aureus)and Gram negative(E. coli)bacteria reveal that the studied complex possesses a moderate inhibiting effect,and the inhibition effect on E.coli is better.     

Theoretical studies on Ru(fppz)_2(CO)L (L=N-heterocyclic ligand):Electronic structure,absorption,phosphorescence,and solvatochromism

A series of ruthenium(II) complexes Ru(fppz)2(CO)L [fppz = 3-trifluoromethyl-5(2-pyridyl)pyrazole; L = pyridine (1), 4-dimethylaminopyridine (2), 4-cyanopyridine (3)] were designed and investigated theo-retically to explore their electronic structures, absorption, and emissions as well as the solvatochrom-ism. The singlet ground state and triplet excited state geometries were fully optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ level, respectively. The HOMO of 1-3 is composed of dyz(Ru) atom and π(fppz). The LUMO of 1 and 2 is dominantly contributed by π*(fppz) orbital, but that of 3 is con-tributed by π*(L). Absorption and phosphorescence in vacuo, C6H12, and CH3CN media were calculated using the TD-DFT level of theory with the PCM model based on the optimized ground and excited state geometries, respectively. The lowest-lying absorption of 1 and 2 at 387 and 391 nm is attributed to {[dyz(Ru) π(fppz)] → [π*(fppz)]} transition, but that of 3 at 479 nm is assigned to {[dyz(Ru) π(fppz)] → [π*(L)]} transition. The phosphorescence of 1 and 2 at 436 and 438 nm originates from 3{[dyz(Ru) π(fppz)] [π*(fppz)]} excited state, while that of 3 at 606 nm is from 3{[dyz(Ru) π(fppz)] [π*(L)]} excited state. The calculation results showed that the absorption and emission transition character can be changed from MLCT/ILCT to MLCT/LLCT transition by altering the substituent on the L ligand. The phosphorescence of 1 and 2 does not have solvatochromism, but that of 3 at 606 nm (vacuo), 584 nm (C6H12), and 541 nm (CH3CN) is strongly dependent on the solvent polarity, so introducing elec-tron-withdrawing group on ligand L will induce remarkable solvatochromism.     

Complexation of Eu(III), Am(III) and Cm(III) with Dicarboxylates: Thermodynamics and Structural Aspects of the Binary and Ternary Complexes

The complexation of Eu(III), Am(III) and Cm(III) with dicarboxylate anions with O, N or S donor groups was measured in I=6.60 mol⋅kg⁻¹ (NaClO₄) at temperatures of 0–60 °C by potentiometry and solvent extraction. The complexation thermodynamics of these complexes show that their stability is due to highly favorable complexation entropies because the complexation enthalpies are endothermic. Luminescence studies with Eu(III) and Cm(III) were used to measure the hydration numbers of the complexes. NMR spectra of ¹H and ¹³C were used to determine the binding modes of La(III) with the ligands. The formation of 1:1:1 ternary complexes of M(EDTA)⁻ with the dicarboxylate ligands was studied to determine changes in coordination of the metal cation with formation of the ternary species. The complexation of ternary complexes changes from bidentate to monodentate as the chain length between the binding sites of the dicarboxylates increases from 1 (malonate) to 4 (adipate). DFT computations were used to confirm the structural aspects of the interaction of these complexes.     

Theoretical studies of the reactions of M+ (M = Ta,W, Re) with CS2

Gas-phase CS₂ activation by M⁺ (M = Ta, W, Re) was studied by the B3LYP density functional method.The geometries for reactants, transition states, and products were completely optimized. CS₂ activation mediated by M⁺ (M = Ta, W, Re) were found to be a spin-forbidden process as a result of the crossing among the multistate energetic profiles. On the basis of the Hammond postulate, this was a typical two-state reactivity reaction. Among the different potential energy surfaces, the crossing points had been explored. The spin–orbit coupling (SOC) was also calculated between the electronic states of different multiplicities at the crossing point to estimate the intersystem crossing probability. For CP1, CP2, and CP4, the computed SOC constants were 80.28, 128.65, and 526.77 cm^?1, which obtained by using one-electron spin–orbit Hamiltonian in Gaussian 09.     

Theoretical insights into the nature of Pt?Sn bond: Reevaluating the bonding/back‐bonding properties of trichlorostannate with comparison to the cyano ligand

The coordinating properties of the trichlorostannate ligand in hydrido platinum trichlorostannato and platinum bis‐trichlorostannato complexes, containing various phosphine ligands, have been elucidated by means of charge decomposition analysis, the Ziegler‐Rauk Energy Decomposition with the Natural Orbitals for Chemical Valence, Domain‐Averaged Fermi Hole, and natural bond orbital methods. Trichlorostannate has been found to be a strong σ‐donor and a weak π‐acceptor ligand with coordination properties not far from those of the cyano ligand. For back‐bonding, the tin‐chlorine orbitals are mostly responsible. In contrast to previous assumptions, the 5d orbitals of tin play no role at all in the interaction with the platinum center. QTAIM calculations suggest, that the platinum‐tin interaction should be interpreted as donor–acceptor, rather than covalent type. Trichlorostannate has been found to have weaker trans influence in comparison to the cyano ligand. © 2017 Wiley Periodicals, Inc.     

Theoretical studies on the mechanism of the thermal decarboxylation and decarbonylation of a number of α-keto-acids

Both processes of decarboxylation and decarbonylation of a number of acids including RCOCO2H,R=H,CH3,CH2F,CF3,CH=CH2,Ph,OH have been studied by semi-empirical MO theory AMI method to verify the reaction mechanism of each process and the effect of different substituents on them.The calculated results are consistent with the experimental reports and can be summed up as follows:(1) The decarboxylation of these acids to form aldehydes and carbon dioxide is concerted and takes place through a 4-membered ring transition state in which a partial negative charge develops on the carbon of the α-carbonyl group,so that the inductive effect of some substituents is favourable for this process.(2) Their decarbonylation into carboxylic acids and carbon monoxide however is the attack of the OH on the carbon of the alkyl portion of the acid,forming a 3-membered ring transition state.(3) The activation energy of decarbonylation is lower than that of decarboxylation,since oxygen is more nucleophilic than hydrogen and als     

Theoretical study of Aun clusters (n = 1–5) deposited on a rutile TiO2 (110) slab,concerning structure and stability

The initial nucleation of gold clusters Au_n (n = 1–5) on TiO₂ rutile (110) reduced surface is studied using density functional theory and a full-potential augmented-plane-wave method implemented in the WIEN2k code. The first two gold atoms remained tied to the surface with a bond length similar to those belonging to other well-known related materials, while the other gold atoms do not spread over the surface; they preferred to form a new layer. The occurrence of relativistic effects produced a preferential triangle geometry for Au₃ and a combination of triangular units for Au₄ and Au₅. The Au–Au average distance increased from n = 2 to n = 5, indicating an expansion with a tendency to the bond distance found in the bulk. We are reporting an early 2D→3D transition of small folding, from Au₃→Au₄, followed by an Au₄→Au₅ transition of evident 3D character.     

Effects of emulsifier on the bonding performance and freeze–thaw stability of starch-based wood adhesive

In this study, different emulsifiers were used to improve the bonding performance and freeze–thaw stability of renewable starch-based wood adhesive. The improved bonding performance and freeze–thaw stability were supported by the enhanced shear strength, grafted parameters, and viscosity stability after repeated freeze–thaw cycling. ζ-Potential determination, differential scanning calorimetry and pulsed nuclear magnetic resonance analysis indicated that the emulsifiers improve the grafting of vinyl acetate monomers into the starch bonds via free radical vinyl polymerization and hinder the aggregation of starch molecules. Among the emulsifiers tested, sodium dodecyl sulfate showed the highest improvement in the bonding performance and freeze–thaw stability of starch-based wood adhesives.     

Theoretical studies on the potential energy surfaces and vibrational energy levels of HXeF and HXeCl

The potential energy surfaces for the electronic ground state of the HXeCl and HXeF molecules areconstructed by using the internally contracted multi-reference configuration interaction with theDavidson correction(icMRCI Q)method and large basis sets.The stabilities and dissociation barriersare identified from the potential energy surfaces.The three-body dissociation channel is found to bethe dominate dissociation channel for HXeCl,while two dissociation channels are possible and com-petitive for HXeF.Based on the obtained potentials,vibrational energy levels of HXeCl and HXeF arecalculated using the Lanczos algorithm.Our theoretical results are in good agreement with the avail-able observed values.Particularly,the calculated fundamental frequency of the H—Xe stretching vi-bration including the Xe matrix effect of HXeCl is found to be 1666.6 cm-1,which is only 17.6 cm-1higher than the recently observed value of 1649 cm-1.     

Crystal structure and fluorescence spectrum of the complex [Eu(Ⅲ)(TTA)_3(phen)]

The title complex Eu(Ⅲ)(TTA)3(phen) (where TTA= thenoyltrifluoroacetone monoanion; phen = 1,10-phenanthroline) has been synthesized in mixed solvents of acetone and ethanol (1:1 volume ratio) and its crystal structure has been determined by X-ray diffraction. The complex crystals are triclinic, space group P1(#2) with cell dimensions of a = 1.3241 (2) nm, 6 = 1.5278(4) nm, c = 0.9755(3) nm, α = 92.49 (2)°, β=102.57(2)°, γ = 91.62(2)°, V=1.9268(8) nm3, Z = 2, μ(Mo Kα) = 18.77 cm-1, Dx = 1.720 g/cm3. The coordination geometry of Eu atom is a distorted square antiprism, and the encapsulated structure that can meet the structural requirement of the typical europium luminescent sensor. The fluorescence spectrum suggests that the complex is a strong photoluminescent material.     

Study on the synthesis and crystal structure of tetrahyhrated tetraaquotris(4-mono-chloroacetylantipyrine)samarium (Ⅲ) perchlorate

Based on the phase equilibrium study of the system Sm(ClO4)3-4-monochloroace-tylantipyrine (C13H13ClN2O2)-H2O at 30℃, we have synthesized the title complex [Sm(C13H13Cl. N2O2)3(H2O)4](C1O4)3.4H2O. The single crystal structure analysis on RASA-IIS Rigaku diffrac-tometer shows that the coordination number of the metal ion is nine and the geometry of the complex is tricapped trigonal prism. Two of the three molecules of organic ligand act as bidentate chelated through both carbonyl oxygens to the metal ion, but the other one as a monodentate coordinated only through the ring carbonyl oxygen, the side chain carbonyl is far away from the central ion. The crystal is monoclinic, space group P21, a = 18.013(4), 6 = 14.709(3), c = 10.536(3) A, β=94.69(2)°, V=2782(1) A3, Z=2.     

The influence of the nature of the solvent on the crystal structure and the character of formation of hydrogen bonds inN′-(5-nitrofurfurylidene)isonicotinehydrazide

N(5-Nitrofurfurylidene)isonicotinehydrazide (1) was synthesized in the reaction of nicotinic acid hydrazide with 5-nitrofurfurol in anhydrous or aqueous ethanol. Crystals of different shape and color were obtained depending on the conditions of synthesis and the nature of the solvent. As was established by IR spectroscopy, compound1 in the crystalline state forms solvates of various types. An X-ray study of two different crystals, one obtained by recrystallization from methanol (1a), and the other obtained from aqueous acetic acid (1b), was performed. In the crystal structure of1a intermolecular hydrogen bonds (IMHB) of the NH...N(Py) type occur; the crystals1b are built of solvates with one molecule of acetic acid in which the components are bonded by the IMHB (Ac)O-H..N(Py). The solvates are linked in an infinite chain by the amidohydrate IMHB C=O...W...H-N.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2263–2268, September, 1996.