Isomeric Complexes Research Articles

Theoretical study of oxoborate complexes with MO 4 n− tetraoxo anions in the inner and outer spheres of the B20O30 cluster

The energies and structural and spectroscopic characteristics of endohedral (MO4©B20O 30 − ) and exohedral (MO4 · B20O 30 − ) isomers of oxoborate complexes with MO 4 − tetraoxo anions with 32 valence electrons located in the inner and outer spheres of the B20O30 cluster have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, among the endohedral MO4©B20O 30 − clusters with strong multiply charged anions (VO 4 3− , CrO 4 2− , PO 4 3− , SO 4 2− , AsO 4 3− , SeO 4 2− , etc.), the isomer in which a “guest” tetrahedron MO4 is located at the center of the B20O30 cage and bonded to it through internal oxygen bridges M-O*-B is the most favorable one. Among the exohedral analogues MO4 · B20O 30 − , two most favorable isomers contain the “capping” MO4 tetrahedron bonded to the B20O30 cage through two and three external M-O-B bridges. For the complexes with doubly charged SO 4 2− and SeO 4 2− anions, the third exohedral isomer in which the sulfite or selenite group MO3 is bidentately coordinated to the oxidized B20O29(OO) cage with one peroxide bridge turns out to be close in energy to the above two isomers. For the systems with high negative charge n, the exohedral isomers are much more favorable than the endohedral isomer; however, with decreasing charge, the difference in energy between them decreases to ~10–18 kcal/mol, so that the exo–endo transition between them can require moderate energy inputs. For the endohedral complexes with singly charged ClO 4 − and BrO 4 − anions, two isomers with close energies are preferable in which the central atoms of the guest tetrahedra are reduced to the state of singly charged ions, while the oxoborate cage is oxidized to B20O26(OO)4 with four peroxide groups B-O-O-B and retains its closed (closo) structure. In the most favorable isomer of the complexes with multicharged ortho-anions BO 4 5− , CO 4 4− , and NO 4 3− , the outersphere anion is reduced to, respectively, borate, carbonate, and nitrate bidentately coordinated to the oxidized B20O29(O)2 cage with an open structure and two strongly elongated terminal B-O bonds. The results are compared with the data of previous calculations of endohedral and exohedral vanadate complexes MO4©V20O 50 − and MO4 · V20O 50 − with the same guest anions MO 4 − .

Transfer Reagent for Bonding Isomers of Iron Complexes.

The cothermolysis of As4 and [Cp″2Zr(CO)2] (Cp″ = η5-C5H3tBu2) results in the formation of [Cp″2Zr(η1:1-As4)] (1) in high yields and the arsenic-rich complex [(Cp″2Zr)(Cp″Zr)(μ,η2:2:1-As5)] (2) as a minor product. In contrast to yellow arsenic, 1 is a light-stable, weighable and storable arsenic source for subsequent reactions. The transfer reaction of 1 with [Cp‴Fe(μ-Br)]2 (Cp‴ = η5-C5H2tBu3) yields the unprecedented bond isomeric complexes [(Cp‴Fe)2(μ,η4:4-As4)] (3a) and [(Cp‴Fe)2(μ,η4:4-cyclo-As4)] (3b). In contrast, the analogous reaction with the CpBn derivative [CpBnFe(μ-Br)]2 (CpBn = η5-C5(CH2(C6H5)5) leads exclusively to the triple decker complex [(CpBnFe)2(μ,η4:4-As4)] (4) possessing the tetraarsabutadiene-type ligand analogous to 3a. To elucidate the stability of the bonding isomers 3a and 3b, DFT calculations were performed. The oxidation of 4 with AgBF4 affords [(CpBnFe)2(μ,η5:5-As5)][BF4] (5), which is a product expanded by one arsenic atom, instead of the expected complex [(CpBnFe)2(μ,η4:4-cyclo-As4)]+.

Isomeric ruthenium(II) complexes for cancer therapy and cellular imaging

Two isomeric ruthenium(II) complexes, [Ru-m-OH]2+ and [Ru-o-OH]2+ with two hydroxyl substituents at different positions of ligands, had been designed and synthesized. We found that the cellular uptake efficiency of Ru-o-OH]2+ was much better than Ru-m-OH]2+, and it exhibited higher toxicity toward cancer cell (BEL-7402) than its isomeric compound, [Ru-m-OH]2+. Importantly, [Ru-o-OH]2+ showed great selectivity between cancer cells and human normal cell (HBMEC). Confocal microscopy and inductively coupled plasma mass spectrometry (ICP-MS) indicated that [Ru-o-OH]2+ mainly accumulated in mitochondria. It could up-grade the expression of Bax and down-grade the level of Bcl-2, which trigger in mitochondrial apoptotic pathway. This study suggests that isomeric metal complexes might make differences in the field of medicine for anti-cancer.

The attractive isomers of 1,1′-bis(verdazyl)ferrocene diradical on structure-property relationship

In 2006, the interesting π-stacks diradical 1,1′-bis(verdazyl)ferrocene (20) with two-electron multicenter (2e/mc) bonding were synthesized and investigated (J. Am. Chem. Soc.2006,128, 690–691). Based on the 20, two attractive isomeric complexes(319 and 4144) are designed by a piece of radical rotating along iron-Cp axis about 19° and 144°, respectively. Among these three diradicals, a unique two-electron eight-center (2e/8c) π–π bonding is obtained in the 20 due to the overlap of SOMOs of the two pieces of radicals, the 319 has a σ-covalent bonding, and two separate radicals are shown in the 4144. Further, the UV-visible absorption spectrum of 20 and 319 arise a new absorption feature at 566 and 530 nm, respectively, which may be assigned to π-π stacking (20) and σ-covalent (319) bonding of two pieces of radicals, although this absorption feature not exist in experimental UV-visible absorption spectrum. Fortunately, the UV-visible absorption spectrum of 4144 is similar to experimental results, which demonstrate that the 20 with 2e/8c bonding may transform to be 4144 with two separate radicals in solution. These three diradicals may transform to each other, which is beneficial to understanding their magnetic properties in solution and crystal and designing new complexes with excellent magnetic property.

Ancillary Ligand Effects upon the Photochemistry of Mn(bpy)(CO)3X Complexes (X = Br-, PhCC-).

The photochemistry of two Mn(bpy)(CO)3X complexes (X = PhCC-, Br-) has been studied in the coordinating solvents THF (terahydrofuran) and MeCN (acetonitrile) employing time-resolved infrared spectroscopy. The two complexes are found to exhibit strikingly different photoreactivities and solvent dependencies. In MeCN, photolysis of 1-(CO)(Br) [1 = Mn(bpy)(CO)2] affords the ionic complex [1-(MeCN)2]Br as a final product. In contrast, photolysis of 1-(CO)(CCPh) in MeCN results in facial to meridional isomerization of the parent complex. When THF is used as solvent, photolysis results in facial to meridional isomerization in both complexes, though the isomerization rate is larger for X = Br-. Pronounced differences are also observed in the photosubstitution chemistry of the two complexes where both the rate of MeCN exchange from 1-(MeCN)(X) by THFA (tetrahydrofurfurylamine) and the nature of the intermediates generated in the reaction are dependent upon X. DFT calculations are used to support analysis of some of the experiments.

Synthesis of an Electron-Deficient Triruthenium Hydrido Complex Having a Bridging Carbonyl Ligand: Influence of a CO Ligand on the Properties and Reactivities of a Hydrido Cluster

A novel triruthenium hydrido cluster, (Cp*Ru)3(μ3-H)(μ-H)2(μ-CO) (4; Cp* = η5-C5Me5), having a bridging CO ligand was synthesized by the reaction of {Cp*Ru(μ-H)}3(μ3-O) (3) with methanol. Upon introduction of a CO ligand, the cyclic voltammogram of 4 demonstrated a significant shift of the redox potential in the positive direction in comparison to a pentahydrido complex, {Cp*Ru(μ-H)}3(μ3-H)2 (1), which adopts the same 44-electron configuration. Owing to its coordinatively unsaturated nature, 4 readily reacted with butadiene, terminal alkynes, and alkenes similarly to the parent pentahydrido complex 1. However, the reactivity was slightly different from that of 1, and the influence of the CO ligand at the triruthenium site was evaluated by the reaction of various unsaturated hydrocarbons. The reaction of 4 with 1,3-dienes yielded a diene adduct, {Cp*Ru(μ-H)}3(μ-η2:η2-s-cis-H2C═CRCH═CH2)(CO) (5a, R = H; 5b, R = Me) without elimination of dihydrogen. In the same manner as for 1, 4 reacted with phenylacetylene to yield a μ3-η2:η2(⊥)-alkyne complex, (Cp*Ru)3(μ-H){μ3-η2:η2(⊥)-PhCCH}(μ3-CO) (7a); in contrast, an isomeric μ3-pentenylidene complex, (Cp*Ru)3(μ-H){μ3-η2-C═C(nPr)H}(μ-CO) (9b), was obtained by reaction with 1-pentyne. A series of products was obtained by the reaction of 4 with ethylene molecules. A μ3-ethylidyne complex, (Cp*Ru)3(μ-H)2(μ3-CMe)(μ-CO) (11), was initially formed, accompanied by the formation of ethane at ambient temperature. The treatment of 11 with ethylene resulted in the removal of hydrido ligands, affording a μ3-vinylidene complex, (Cp*Ru)3(μ-H)(μ3-η2-C═CH2)(μ-CO) (9a). At higher temperatures, a second ethylene molecule was incorporated in the triruthenium plane and an equilibrated mixture of a μ3-ethylidyne−μ-ethylidyne complex, (Cp*Ru)3(μ-H)(μ-CMe)(μ3-CMe)(μ-CO) (13), and μ3-ethylidyne−μ-vinyl complex, (Cp*Ru)3(μ-H)(μ3-CMe)(μ-η2-CH═CH2)(μ-CO) (12), was obtained. The formation of a μ3-η3-C3 ring on the Ru3 plane was observed upon the thermolysis of the equilibrated mixture at 180 °C, which clearly demonstrates the coupling of the two C2 moieties placed on each face of the triruthenium plane.

N‐Heterocyclic Phosphenium Dihalido‐Aurates: On the Borderline between Classical Coordination Compounds and Ion Pairs

2‐Bromo‐ and 2‐chloro‐1,3,2‐diazaphospholenes react with (tht)AuCl to afford isolable N‐heterocyclic phosphenium (NHP) dihalido‐aurates, which were characterized by analytical and spectroscopic data and in one case by a single‐crystal X‐ray diffraction study. The T‐shaped metal coordination sphere found in the crystal consists of a pseudo‐linear AuX2 unit that is perturbed by a weakly bound NHP unit. DFT studies indicate that the subunits interact mainly through electrostatic and dispersion forces, with negligible covalent contributions, and that the phosphenium dibromido‐aurate is slightly more stable than an isomeric complex with an intact bromophosphane ligand. NMR studies reveal that the NHP‐AuX2 pairs persist in solution but are kinetically labile and readily undergo halide scrambling. The hydride/fluoride exchange reaction between a secondary phosphane‐AuCl complex and [Ph3C][BF4] implies that a gold complex with an intact 2‐halogeno‐1,3,2‐diazaphospholene ligand may be more stable than its phosphenium dihalido‐aurate isomer when covalent P–X bonding contributions are strengthened.

Thermally Activated Delayed Fluorescence in CuI Complexes Originating from Restricted Molecular Vibrations.

The mechanism of thermally activated delayed fluorescence (TADF) in molecules in aggregated or condensed solid states has been rarely studied and is not well understood. Nevertheless, many applications of TADF emitters are strongly affected by their luminescence properties in the aggregated state. In this study, two new isomeric tetradentate CuI complexes which simultaneously show aggregation induced emission (AIE) and TADF characteristics are reported for the first time. We provide direct evidence that effectively restricting the vibrations of individual molecules is a key requisite for TADF in these two CuI complexes through in‐depth photophysical measurements combined with kinetic methods, single crystal analysis and theoretical calculations. These findings should stimulate new molecular engineering endeavours in the design of AIE–TADF active materials with highly emissive aggregated states.

A Dimeric NHC–Silicon Monotelluride: Synthesis, Isomerization, and Reactivity

AbstractThe reaction of the NHC–disilicon(0) complex [(IAr)Si=Si(IAr)] (1, IAr=:C{N(Ar)C(H)}2, Ar=2,6‐iPr2C6H3) with two equiv of elemental Te in toluene at room temperature for three days afforded a mixture of the first dimeric NHC–silicon monotelluride [(IAr)Si=Te]2 (2) and its isomeric complex [(IAr)Si(μ‐Te)Si(IAr)=Te] (3). When the same reaction was performed for ten days, only 3 was isolated from the reaction mixture. Compound 1 reacted with four equiv of elemental Te in toluene for four weeks, which proceeded through the formation of 2, 3 and the NHC–disilicon tritelluride complex [{(IAr)Si(=Te)}2Te] (5‐Te), to form the dimeric NHC–silicon ditelluride [(IAr)Si(=Te)(μ‐Te)]2 (4). The reactions are in line with theoretical mechanistic studies for the formation of 4. Compound 3 reacted with one equiv of elemental sulfur in toluene to form the first NHC–disilicon sulfur ditelluride complex [{(IAr)Si(=Te)}2S] (5‐S).

A Dimeric NHC–Silicon Monotelluride: Synthesis, Isomerization, and Reactivity

The reaction of the NHC-disilicon(0) complex [(IAr )Si=Si(IAr )] (1, IAr =:C{N(Ar)C(H)}2 , Ar=2,6-iPr2 C6 H3 ) with two equiv of elemental Te in toluene at room temperature for three days afforded a mixture of the first dimeric NHC-silicon monotelluride [(IAr )Si=Te]2 (2) and its isomeric complex [(IAr )Si(μ-Te)Si(IAr )=Te] (3). When the same reaction was performed for ten days, only 3 was isolated from the reaction mixture. Compound 1 reacted with four equiv of elemental Te in toluene for four weeks, which proceeded through the formation of 2, 3 and the NHC-disilicon tritelluride complex [{(IAr )Si(=Te)}2 Te] (5-Te), to form the dimeric NHC-silicon ditelluride [(IAr )Si(=Te)(μ-Te)]2 (4). The reactions are in line with theoretical mechanistic studies for the formation of 4. Compound 3 reacted with one equiv of elemental sulfur in toluene to form the first NHC-disilicon sulfur ditelluride complex [{(IAr )Si(=Te)}2 S] (5-S).

Multiple isomerization of structural units in ion-polymeric heteronuclear gold(III)–zinc(II) complex ([Au{S2CN(C4H9)2}2]2[ZnCl4])n: Chemisorption-based synthesis, supramolecular structure (self-organization of long-period cation–cationic polymer chains), and thermal behavior

Chemisorption of gold(III) from solutions in 2 M HCl with freshly precipitated binuclear zinc dithiocarbamate [Zn2{S2CN(C4H9)2}4] resulted in the formation of a polymeric heteronuclear gold(III)–zinc(II) dithiocarbamato-chlorido complex ([Au{S2CN(C4H9)2}2]2[ZnCl4]) n (I), which was characterized by MAS 13C NMR, X-ray diffraction (CIF file CCDC no. 1526616), and simultaneous thermal analysis. Compound I isolated on a preparative scale was found to have a highly intricate supramolecular structure composed of 13 centrosymmetric and non-centrosymmetric isomeric complex cations, [Au{S2CN(C4H9)2}2]+, with 24 structurally non-equivalent BuDtc ligands, and six isomeric [ZnCl4]2– anions. The isomeric gold(III) cations perform different structural functions. Four and six cations are involved in the formation of two sorts of long-period cation–cationic chains (via pair non-valence secondary Au···S bonds): (···A···B···C···D···C···B···) n and (···F···G···H···I···J···K···) n . The discrete E, L, and M cations and the [ZnCl4]2– complex anions are located alongside of the polymer chains and do not take part in the secondary interactions. According to simultaneous thermal analysis, thermolysis of I includes destruction of the dithiocarbamate moiety with reduction of gold to the metal in the cation and liberation of zinc chloride with partial conversion to ZnS in the anion.

Remarkable differences and similarities between the isomeric Mn(II)- cis - and trans- 1,2-diaminocyclohexane- N , N , N ′, N ′-tetraacetate complexes

Equilibrium, kinetic (solvent exchange and dissociation of the complex) and relaxometric studies (1H and 17O NMR) have been performed with the [M(II)(c-cdta)]2− complexes (c-cdta = cis-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, M(II) = Mn(II), Zn(II), Cu(II),Ca(II), Mg(II)) and the physico-chemical data are compared to the isomeric complexes with trans-1,2-cdta (t-cdta) with the aim of searching appropriate ligands for Mn(II) complexation for safe MRI contrast agents. The total basicity (Σ log KiH) of the c-cdta ligand appears to be very similar to that of the trans-derivative under the conditions applied (I = 0.15 M NaCl and 25 °C), but the first two protonation constants notably differ. log K1H is 1.5 log units higher, while the log K2H is 0.8 log units lower than those determined for the trans-derivative. Similar basicity of the ligands results in similar complex stability (log K[Mn(L)] values are 14.19(2) and 14.32), whereas the conditional stabilities near to physiological pH are different (pMn values are 7.82 and 8.68) for the [Mn(c-cdta)]2− and the [Mn(t-cdta)]2− derivatives, respectively. Dissociation kinetic studies revealed that the [Mn(c-cdta)]2− dissociates 250 times faster than the [Mn(t-cdta)]2− complex. The water exchange rate (kex298) of [Mn(c-cdta)]2− is ca. 60% higher than that of [Mn(t-cdta)]2−. The differences can likely be attributed to the different distances between the individual donor atoms, and the arrangement of the donor atoms around the metal ions in the cis- and trans- isomers. Interestingly, the relaxivity values of the Mn(II) complexes are very close (r1p = 3.79 mM−1 s−1 and 3.62 mM−1 s−1; 20 MHz, 25 °C for the cis- and trans-isomers, respectively). DFT calculations were used to gain insight into the different properties of the [Mn(c-cdta)]2− and the [Mn(t-cdta)]2− complexes. The results gained in our studies confirm that the trans-1,2-cyclohexanediamine “building block” displays better features for further ligand development.

H-π Landscape of the Phenylacetylene-HCl System: Does This Provide the Gateway to the Markovnikov Addition?

Non covalently bonded complexes of phenylacetylene-HCl were studied using matrix isolation infrared spectroscopy and ab initio calculations. Phenylacetylene (PhAc) is an interesting hydrogen bond precursor as it has multiple sites for weak interactions, and it was therefore considered worthwhile to study PhAc-HCl landscape. The interactions in PhAc-HCl were identified using the shifts in the infrared frequencies of the precursor molecules, as a result of complex formation. Our experiments unambiguously revealed spectral signatures of two types of H-π complexes, in both of which HCl was the proton donor. In one complex, the acetylenic π cloud (H-πAc) was the proton acceptor, while in the second, the role of the proton acceptor was played by the phenyl π cloud (H-πPh). The H-πAc and H-πPh complexes were evidenced by a 124 and 80 cm-1 red shift respectively, in the fundamental HCl stretch, relative to that of the uncomplexed HCl monomer. Ab initio calculations performed at M06-2X and MP2 level of theory using 6-311++G(d,p) and aug-cc-pVDZ basis functions indicated the H-πAc complex to be the global minimum and the H-πPh complex to be a local minimum; thus corroborating our experimental results. These conclusions were also confirmed by calculations at MP2/CBS and CCSD(T)/CBS limits. Interestingly, there were two isomers for the H-πAc complex, and it appears from an analysis of the charge densities, that one of the two isomers may serve as the gateway complex for the Markovnikov addition reaction. Computations identified a number of other minima, characterized by n-σ* and possibly Cl-π bonded structures, on the PhAc-HCl potential surface. AIM, NBO, and LMO-EDA analyses were also performed to characterize the non covalent interactions in the PhAc-HCl heterodimer.

Reversible isomerization of a novel [FeFe]‑hydrogenase model complex and water-promoted electrocatalytic proton reduction

μ-(SCH(CH2CH3)CH2S)-Fe2(CO)4(κ2-DPPE) (complex 1, DPPE is 1,2-bis (diphenylphosphor) ethane), which can be regarded as a model of the [FeFe]‑hydrogenase active site, was synthesized and characterized. The reversible isomerization of complex 1 under N2 and CO atmosphere was demonstrated by cyclic voltammetry, IR spectroscopy and 31P NMR. Furthermore, we discovered that both the presence of a CO atmosphere and the addition of H2O can independently trigger the same inversion of configuration of complex 1. The electrocatalytic proton reduction capacity of 1 was evaluated under varying conditions. It was found that addition of a little H2O to CH3CN can facilitate its efficiency of electrocatalytic proton reduction. The possible mechanism of transition between axial/basal and dibasal isomers and the function of H2O in the electrocatalytic reaction are discussed.

In Vitro Anticancer Evaluation of Platinum(II/IV) Complexes with Diisoamyl Ester of (S,S)-ethylenediamine-N,N'-di-2-propanoic Acid.

Platinum(II) and platinum(IV) complexes [PtCln{(S,S)-(i-Am)2eddip}] (n = 2, 4: 1, 2, respectively; (S,S)-(i-Am)2eddip = O,O'-diisoamyl-(S,S)-ethylenediamine-N,N'-di-2-propanoate) were synthesized and characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy and mass spectrometry. Quantum chemical calculations were used to predict formed isomers of 1 and 2. Furthermore, reduction of 2 with ascorbic acid was followed by time-dependant 13C NMR spectroscopy in order to enable assignation of the formed isomers for complex 1. In vitro cytotoxic activity was determined for 1 and 2 on a panel of five human tumor cell lines derived from cervix adenocarcinoma (HeLa), alveolar basal adenocarcinoma (A549), breast adenocarcinoma (MDA-453), colorectal cancer (LS 174), erythromyeloblastoid leukemia (K562), as well as one non-malignant human lung fibroblast cell line (MRC-5), using MTT assay. Both complexes exhibited high (2 against K562: IC50 = 5.4 μM), more active than cisplatin, to moderate activity (1). Both complexes caused considerable decrease of cell number in K562 cells in G1, S and G2 phases, concordantly increasing subpopulation in sub-G1 fraction. Morphological analysis of K562 cell death induced by platinum(II/IV) complexes indicate apoptosis.

A comparative study of α- N -pyridyl thiosemicarbazones: Spectroscopic properties, solution stability and copper(II) complexation

Abstract The effects of methyl substituents at different positions on the 2-formylpyridine thiosemicarbazone (FTSC) core structure on various physico-chemical properties were investigated. Proton dissociation processes, aqueous solution stability, isomer distribution in different solvents, fluorescence properties and lipophilic character of FTSC, pyridine-2-carboxaldehyde N 4 , N 4 -dimethylthiosemicarbazone (PTSC), 2-acetylpyridine thiosemicarbazone (AcFTSC) and 2-acetylpyridine N 4 , N 4 -dimethylthiosemicarbazone (AcPTSC) were studied and compared under the same conditions. There are more and more indications that Cu(II) ions play an important role in the biological activity of anticancer thiosemicarbazones. Therefore, the complex formation equilibria of FTSC with Cu(II) ions were studied by pH-potentiometry, UV–visible spectrophotometry and electron paramagnetic resonance (EPR) spectroscopy to determine stoichiometry, stability constants and solution structures of the complexes formed in aqueous solution (with 30% DMSO). Mono-ligand complexes in different protonation states were identified such as [CuLH] 2+ , [CuL] + and [CuL(OH)] with (N pyridyl ,N,S)(H 2 O), (N pyridyl ,N,S − )(H 2 O) and (N pyridyl ,N,S − )(OH) coordination modes, respectively. At ligand excess two kinds of isomers of a bis complex [CuL 2 ] were detected at pH > 7, in which binding of the ligands via (N pyridyl ,N,S − )(N) and (N pyridyl ,N,S − )(S − ) donor sets is probable at the equatorial positions. Based on the stability data, [CuL] + complexes of the α- N -pyridyl thiosemicarbazones are predominant at pH 7.4 at 1:1 metal-to-ligand ratio possessing such high solution stability that their decomposition is not likely even at biologically relevant micromolar concentrations. In addition, FTSC and all methylated derivatives investigated show similar Cu(II) binding abilities which is in contrast to the respective Fe(II)/(III) complexes where terminal dimethylation distinctly increases the solution stabilities.

Magnetic Solid-phase Extraction with Fe3O4/Molecularly Imprinted Polymers Modified by Deep Eutectic Solvents and Ionic Liquids for the Rapid Purification of Alkaloid Isomers (Theobromine and Theophylline) from Green Tea

Different kinds of deep eutectic solvents (DES) based on choline chloride (ChCl) and ionic liquids (ILs) based on 1-methylimidazole were used to modify Fe3O4/molecularly imprinted polymers (Fe3O4/MIPs), and the resulting materials were applied for the rapid purification of alkaloid isomers (theobromine and theophylline) from green tea with magnetic solid-phase extraction (M-SPE). The M-SPE procedure was optimized using the response surface methodology (RSM) to analyze the maximum conditions. The materials were characterized by Fourier transform infrared spectroscopy (FI-IR) and field emission scanning electron microscopy (FE-SEM). Compared to the ILs-Fe3O4/MIPs, the DESs-Fe3O4/MIPs were developed for the stronger recognition and higher recoveries of the isomers (theophylline and theobromine) from green tea, particularly DES-7-Fe3O4/MIPs. With RSM, the optimal recovery condition for theobromine and theophylline in the M-SPE were observed with ratio of methanol (80%) as the washing solution, methanol/acetic acid (HAc) (8:2) as the eluent at pH 3, and an eluent volume of 4 mL. The practical recoveries of theobromine and theophylline in green tea were 92.27% and 87.51%, respectively, with a corresponding actual extraction amount of 4.87 mg·g−1 and 5.07 mg·g−1. Overall, the proposed approach with the high affinity of Fe3O4/MIPs might offer a novel method for the purification of complex isomer samples.

The CO2-O2 van der Waals complex

Using the explicitly correlated CCSD(T)-F12 method with cc-pVXZ-F12 (VXZ-F12) and aug-cc-pVXZ (AVXZ) (up to X=Q) basis sets, various structures of the triplet CO2-O2 complex were investigated. Accordingly, the planar slipped-tilted isomer is most stable, with a binding energy (ΔE) of 230cm−1, followed by the cross-shaped C2v-X isomer, having ΔE=202cm−1 and by the in-plane T-shaped C2v-Ta isomer with ΔE=181cm−1 (energies obtained from counterpoise corrected optimizations using the VQZ-F12 basis set). Binding energies using the AVQZ basis set are similar, with 238, 211 and 188cm−1, respectively. Frequency calculations showed that C2v-Ta is a first-order saddle point. The binding energies are in line with values obtained for related CO2 complexes, although the slipped-tilted structure of the most stable isomer of the CO2-O2 complex is somewhat unexpected. To our knowledge, this is the first theoretical study of CO2-O2 complexes.

New Infrared Bands of the C-Bonded Isomer of OC-N2O and Determination of Two Intermolecular Frequencies.

Three combination bands involving intermolecular modes of the most stable isomer of the OC-N2O van der Waals complex have been observed, two in the carbon monoxide CO stretch region (∼2150 cm-1) and one in the ν3 asymmetric stretch region of N2O (∼2223 cm-1). Vibrational assignment is achieved by comparison with data recently published ( Barclay , A. ; et al. Chem. Phys. Lett. 2016 , 62 , 651 ), concerning OC-CO2. Two of these bands involve the same intermolecular mode, one with the CO stretch and the other with the ν3 asymmetric stretch of N2O. The values of intermolecular frequency deduced from these two bands agree very well, showing no significant dependence on intramolecular vibrational excitation.

Synthesis, characterization, DNA and HSA binding studies of isomeric Pd (II) antitumor complexes using spectrophotometry techniques

Two new Palladium(II) isomeric complexes, [Pd (Gly)(Leu)](I) and [Pd (Gly)(Ile)](II), where Gly is glycine, and Leu and Ile are isomeric amino acids (leucine and isoleucine), have been synthesized and characterized by elemental analysis, molar conductivity measurements, FT-IR, 1H NMR, and UV–Vis. The complexes have been tested for their In vitro cytotoxicity against cancer cell line K562 and their binding properties to calf thymus DNA (CT-DNA) and human serum albumin (HSA) have also been investigated by multispectroscopic techniques. Interactions of these complexes with CT-DNA were monitored using gel electrophoresis. The energy transfer from HSA to these complexes and the binding distance between HSA and the complexes (r) were calculated. The results obtained from these studies indicated that at very low concentrations, both complexes effectively interact with CT-DNA and HSA. Fluorescence studies revealed that the complexes strongly quench DNA bound ethidium bromide as well as the intrinsic fluorescence of HSA through the static quenching procedures. Binding constant (Kb), apparent biomolecular quenching constant (kq), and number of binding sites (n) for CT-DNA and HSA were calculated using Stern–Volmer equation. The calculated thermodynamic parameters indicated that the hydrogen binding and vander Waals forces might play a major role in the interaction of these complexes with HSA and DNA. Thus, we propose that the complexes exhibit the groove binding with CT-DNA and interact with the main binding pocket of HSA. The complexes follow the binding affinity order of I > II with DNA- and II > I with HSA-binding.