Bonding and electronic structure in consanguineous and conjugal iron and rhenium sp carbon chain complexes [MC4M'](n)+: computational analyses of the effect of the metal

Density functional theory has been used to probe the bonding and electronic properties of the homo- and heterobimetallic sp carbon chain complexes (ML(m), = (eta(5)-C(5)R(5))(eta(2)-R(2)PCH(2)CH(2)PR(2))Fe, (eta(5)-C(5)R(5))(NO)(PR(3))Re; z = 0-4). All neutral complexes are best described by MCtbd1;CCtbd1;CM electronic structures, in accord with much experimental data. The singlet dications are best described by cumulenic (+)M=C=C=C=C=M(+) valence formulations. However, the diiron and rhenium/iron dications are found to possess triplet states of nearly identical energy, clarifying experimental magnetic data. Their electronic structures have dominant *(+)MCtbd1;CCtbd1;CM(+)* character, with some spin delocalization onto the carbon chain. The mixed valence monocation radicals exhibit delocalized unpaired electrons, in accord with class III (strongly coupled) and II (weakly coupled) assignments made from experimental data earlier, with some spin density on the carbon chain. An isolable diiron trication has a doublet ground state, but some computational data suggest a close-lying quartet. For the unknown diiron tetracation, a bis(carbyne) or (2+)Fetbd1;CCtbd1;CCtbd1;Fe(2+) electronic structure is predicted. Calculated adiabatic ionization potentials show the iron endgroup to be more electron-releasing than rhenium, in accord with electrochemical data. This polarizes the electronic structures of the rhenium/iron complexes. To help validate the computed model structures, crystal structures of ((eta(5)-C(5)Me(5))Fe(eta(2)-dppe))(2)(mu-C(4)) and [((eta(5)-C(5)Me(5))Fe(eta(2)-dippe))(2)(mu-C(4))](3+) 3PF(6)(-) are determined. Data are analyzed with respect to related diruthenium and dimanganese complexes.     

Crystal Structures and Characterizations of Bis（1-benzoyl-methyl-benzotriazole-N^3）dichoro Metal（Ⅱ） Complex： [MCl2（C6H4N3CH2COPh）2] [M=Zn（Ⅱ），Co（Ⅱ）]

The structures of [MCl₂(C₆H₄B₃CH₂COPh)₂] [M=Zn(II) (1), Co(II) (2)] have been determined by X‐ray crystallography. They were characterized by elemental analysis, IR spectrum, electronic spectrum and thermogravimetric‐differential thermal analysis. They all crystallize in the triclinic system, space pup Pi, with lattice parameters a=0.9449(2) nm, b=1.1291(2) nm, c=1.3637(3) nm, α=111.70(3)°, β= 94.33(3)°, y=90.97(3), Z=2 for compound 1; a=0.9437(2) nm, b= 1.1277(2) nm, c= 1.3650(3) nm, a=111.76(3)°, β=94.50(3)°, y=90.80(3)°, Z=2 for compound 2. The metal ions are all coordinated by two C1^?‐ anions and two nitrogen atoms of 1‐benzoylmethyl‐bentriazole ligands. forming the distorted tetrahedral geometry. The Zn—Cl and Zn—N bond lengths are 0.2209(2), 0.2210(2) nm and 0.2059(4), 0.2067(4) nm. respectively. The CO‐Cl 3 and Co–N bond lengths are 0.2215(2). 0.2222(2) nm and 0.2028(5), 0.2045(5) nm. respectively. The thermogravimetric (TG) data indicate that they are nearly similar in TG curve, and there are not structural transitions in the two compounds. They all have a high thd stability. But, there is little difference in DTG (differential thermogravimetric) curves of those two compounds. Elemental analysis, electronic and IR spectra are in agreement with the structural data.     

Determination of triptolide and triptonide in human plasma by high-performance liquid chromatography

An isocratic high-performance liquid chromatographic method for determination of triptolide and triptonide in human plasma is described. Plasma samples were extracted with OasisHLB solid-phase extraction (SPE) cartridges. After pretreatment, they were separated on a SymmetryShieldRP(18) column with a mobile phase of acetonitrile-water (40:60,v/v) at 40 degrees C. The effluent was monitored at UV 217 nm. Linearity (0.010-1.0 mg/L) was good, and the lower limit of detection was 3 ng/mL for triptolide and 4.5 ng/mL for triptonide (S/N = 3). The relative standard deviations of intra- and inter-day assay were less than 15% and the recoveries were better than 80%. The developed method was applied to the determination of triptolide and triptonide concentration in a patient's plasma after taking the medicament containing Tripterygium wilfordii Hook. F.     

Hyperconjugation effect in substituted methyl boranes: an orbital deletion procedure analysis

The hyperconjugation effect in the substituted methyl boranes, XCH(2)BH(2) (X = H, CH(3), NH(2), PH(2), OH, SH, F, Cl, Br), has been quantitatively evaluated by using the orbital deletion procedure (ODP), where the p(pi) orbital on boron is deactivated. Except for the case of X = NH(2), which forms a three-membered ring, the magnitude of the hyperconjugative stabilization in all other substituted methylborane ranges from 6.8 to 3.4 kcal/mol. Significant structural changes are observed, particularly the shortening of the central B-C bond distance and the reducing of the corresponding XCB and HCB bond angles. In general, the strength of the hyperconjugative interaction between the occupied sigma(C-X) bond and the vacant p(pi) orbital on boron is correlated to the electronegativity of X, and the competition between the donation ability of the sigma(C-X) and the sigma(C-H) bonds determines the preference of the staggered or eclipsed structure as the energy minimum state. When the donation abilities of the C-X and C-H bonds are comparable, other factors such as electron correlation and steric effect may play elaborate roles in the geometrical propensity of the most stable structures.     

Electron impact mass spectral fragmentation patterns of 2a,4-disubstituted 5-benzoyl-2-chloro-2a,3,4,5-tetrahydroazeto[1,2-a][1,5]benzodiazepin-1( 2H)-ones

The mass spectrometric behaviour of six 2a,4-disubstituted 5-benzoyl-2-chloro-2a,3,4,5-tetrahydroazeto[1,2-a][1,5]benzodia zepin-1(2H)-ones has been studied with the aid of mass-analysed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a chlorine atom, a chlorine atom plus benzaldehyde, benzoyl radical, chloroketene or chlorine atom plus CO and H2O molecules to yield, respectively, [M-Cl]+ ions, 2a,4-disubstituted 2a,3-dihydroazeto[1,2-a][1,5]benzodiazepin-1(2H)-one ions, [M-PhCO]+ ions, 2,4-disubstituted 1-benzoyl-2,3-dihydro-1H-1,5-benzodiazepine ions, or 1,2,4-trisubstituted 1H-1,7-benzodiazonine ions, which could also be formed from [M-Cl]+ ions by loss of CO and H2O molecules simultaneously. The [M-Cl]+ ions could further lose benzoyl radical to form [M-Cl-PhCO]+ ions, or lose benzoyl amide and undergo a rearrangement to form 4,6-disubstituted 1-benzoazocine-2(1H)-one ions. The [M-PhCO]+ ions could eliminate NH to produce 2a,4-disubstituted 2,2a,3,4-tetrahydroazeto[1,2,-a]quinolin-1-one ions, which could further eliminate chloroketene, CO and/or HCl to produce some important ions, respectively. 2,4-Disubstituted 1-benzoyl-2,3-dihydro-1H-1,5-benzodiazepine ions could lose benzoyl radical to yield 2,4-disubstituted 2,3-dihydro-1H-1,5-benzodiazepine ions, which could further yield other small fragment ions by loss of propene/styrene or small fragments.     

Surface structure and energetics of hydrogen adsorption on the Fe(111) surface

Spin-polarized density functional theory calculations have been performed to characterize the hydrogen adsorption and diffusion on the Fe(111) surface at 2/3-, 1-, and 2-monolayer (ML) coverages. It is found that the most favored adsorption site for atomic hydrogen (H) is the top-shallow bridge site (tsb), followed by the quasi 4-fold site (qff) with the energy difference of about 0.1 eV, while the top site (t) is not competitive. Furthermore, the adsorbed atomic hydrogen (H) has a high mobility, as indicated by the small diffusion barriers. The local density of state (LDOS) analysis reveals that the Fe-H (tsb or qff) bond involves mainly the Fe 4s and 4p and H 1s orbitals with less contribution of the Fe 3d orbital, while the Fe 4s, 4p, and 3d orbitals all participate in the Fe-H (top) bond. In addition, the coverage effects on the adsorption configurations and adsorption energies are addressed.     

A FRET-based fluorescent Zn2+ sensor: 3D ratiometric imaging,flow cytometric tracking and cisplatin-induced Zn2+ fluctuation monitoring

Monitoring labile Zn²⁺ homeostasis is of great importance for the study of physiological functions of Zn²⁺ in biological systems. Here we report a novel ratiometric fluorescent Zn²⁺ sensor, CPBT, which was constructed based on chelation-induced alteration of FRET efficiency. CPBT was readily cell membrane permeable and showed a slight preferential localization in the endoplasmic reticulum. With this sensor, 3D ratiometric Zn²⁺ imaging was first realized in the head of zebra fish larvae via Z-stack mode. CPBT could track labile Zn²⁺ in a large number of cells through ratiometric flow cytometric assay. More interestingly, both ratiometric fluorescence imaging and flow cytometric assay demonstrated that the labile Zn²⁺ level in MCF-7 cells (cisplatin-sensitive) decreased while that in SKOV3 cells (cisplatin-insensitive) increased after cisplatin treatment, indicating that Zn²⁺ may play an important role in cisplatin induced signaling pathways in these cancer cells.

A Zn²⁺ sensor exhibiting 3D ratiometric imaging and flow cytometric ability was constructed based on the FRET mechanism, and cisplatin-induced endogenous labile Zn²⁺ fluctuations were monitored in real time.     

Are oxocarbon dianions aromatic?

Assessment of the cyclic electron delocalization of the oxocarbon dianions, C(n)()O(n)()(2)(-) and their neutral counterparts C(n)()O(n)() (n = 3-6), by means of structural, energetic, and magnetic criteria, shows that C(3)O(3)(2)(-) is doubly aromatic (both sigma and pi cyclic electron delocalization), C(4)O(4)(2)(-) is moderately aromatic, but C(5)O(5)(2)(-), as well as C(6)O(6)(2)(-), are less so. Localized orbital contributions, computed by the individual gauge for localized orbitals method (IGLO), to the nucleus-independent chemical shifts (NICS) allow pi effects to be disected from the sigma single bonds and other influences. The C-C(pi) contribution to (NICS(0,pi) (i.e., at the center of the ring) in oxocarbon dianions decreases with ring size but shows little ring size effect at points 1.0 A above the ring. On the basis of the same criteria, C(4)O(4) exhibits cyclic electron delocalization due to partial occupancy of the sigma CC bonds. However, the dissociation energies of all the neutral oxocarbons, C(n)()O(n)(), are highly exothermic.     

Electrochemical studies of 1,5-dihydroxynaphthalene as substrate for voltammetric enzyme immunoassay

Immunoassay is one of the biochemical analytical techniques using the specific antigen antibody com-plexation for analytical purposes. It has extensive ap-plication in clinical diagnostics, prevention and cure of diseases, and virus diagnostics. The presentation and progress of immunoassay methodology are one of the greatest achievements of bioanalytical chemistry. It is estimated that several-hundred millions of immuno-analytical determinations are carried out every year all over the world. E…     

An industrially viable catalyst system for palladium-catalyzed telomerizations of 1,3-butadiene with alcohols

The telomerization reaction of 1,3-butadiene with alcohols to give alkyl octadienyl ethers in the presence of palladium-carbene catalysts has been studied in detail. Unprecedented catalyst efficiency with turnover numbers (TON) up to 1,500,000 and turnover frequencies (TOF) up to 100,000 h(-1) have been obtained after optimization for the reaction of methanol in the presence of an excess of in situ generated carbene ligands. High yields (75-97 %) and catalyst productivities (TON 15,000-100,000) are observed for other aliphatic alcohols and phenols. For comparison five carbene-palladium(0) complexes have been synthesized and characterized by X-ray crystallography. Both electronic and steric effects on the stability and reactivity of the catalysts have been discussed on the basis of density functional theory calculations.