NMR Reveals That a Highly Reactive Nonheme FeIV=O Complex Retains Its Six-Coordinate Geometry and S=1 State in Solution

The [Fe^IV(O)(Me₃NTB)]²⁺ (Me₃NTB=tris[(1-methyl-benzimidazol-2-yl)methyl]amine) complex 1 has been shown by Mössbauer spectroscopy to have an S=1 ground state at 4 K, but is proposed to become an S=2 trigonal-bipyramidal species at higher temperatures based on a DFT model to rationalize its very high C−H bond-cleavage reactivity. In this work, ¹H NMR spectroscopy was used to determine that 1 does not have C₃-symmetry in solution and is not an S=2 species. Our results show that 1 is unique among nonheme Fe^IV=O complexes in retaining its S=1 spin state and high reactivity at 193 K, providing evidence that S=1 Fe^IV=O complexes can be as reactive as their S=2 counterparts. This result emphasizes the need to identify factors besides the ground spin state of the Fe^IV=O center to rationalize nonheme oxoiron(IV) reactivity.     

Synthesis and Biological Evaluation of Novel Tetracyclic Benzothiazepines

6-Arylidene-2,3-dimethyl-6,7,8,9-tetrahydro-benzocyclohepten-5-one 2a–l were obtained by the condensation of 2,3-dimethyl/3-methyl benzocyclohepten-5-one 1 with appropriate aromatic aldehydes, and upon condensation with 2-aminothiophenol in ethyl alcohol yielded 1,5-benzothiazepine derivatives 3a–l, respectively. Compounds 3d and 3h were found to possess antimicrobial activity when tested against B. Subtilis. Compounds 3i and 3j were found to possess moderate anti-inflammatory activity. Compound 3b was found to possess comparable antifungal activity when compared to clotrimazole against Trichomonas species.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Synthesis and Antioxidant Activity of New Thiazole Analogues Possessing Urea,Thiourea, and Selenourea Functionality

A new series of urea, thiourea, and selenourea derivatives with thiazole moieties were synthesized by the nucleophilic addition reaction of (2-amino-4-(3-chlorophenyl)thiazol-5-yl)(2-chlorophenyl)methanone with various substituted isocyanates/ isothiocyanates/isoselenocynates in acetone having a catalytic amount of sodium hydroxide at room temperature with good yields. All the synthesized compounds were fully characterized by spectroscopic data and screened for their in vitro antioxidant activity using 1,1-diphenylpicrylhydrazyl (DPPH), nitric oxide (NO), and hydrogen peroxide (H₂O₂) radical scavenging methods. A preliminary study of the structure–activity relationship revealed that the compounds containing selenourea functionality along with halogen group have exhibited potent activity (IC₅₀ ≤ 0.0309 µmol/mL) compared to the standards (IC₅₀ ≤ 0.0814 µmol/mL). Thus the title compounds are a new class of potent antioxidant agents and worthy of further investigation.     

A Non‐Heme Iron Photocatalyst for Light‐Driven Aerobic Oxidation of Methanol

Non‐heme (L)Fe^III and (L)Fe^III‐O‐Fe^III(L) complexes (L=1,1‐di(pyridin‐2‐yl)‐N,N‐bis(pyridin‐2‐ylmethyl)ethan‐1‐amine) underwent reduction under irradiation to the Fe^II state with concomitant oxidation of methanol to methanal, without the need for a secondary photosensitizer. Spectroscopic and DFT studies support a mechanism in which irradiation results in charge‐transfer excitation of a Fe^III?μ‐O?Fe^III complex to generate [(L)Fe^IV=O]²⁺ (observed transiently during irradiation in acetonitrile), and an equivalent of (L)Fe^II. Under aerobic conditions, irradiation accelerates reoxidation from the Fe^II to the Fe^III state with O₂, thus closing the cycle of methanol oxidation to methanal.     

Modified complex method for constrained design and optimization of optical multilayer thin-film devices

A new computer design program based on the modified-complex method has been developed for constrained optimization and refinement of optical thin-film multilayer devices. This program is having a provision to include both limiting constraints as well as constraint equations. Constraints are suitably accommodated to generate designs which are practicable and withstand high laser power. Various rapid convergent processes like dynamic contraction and expansion of feasible vertices are incorporated for efficient scanning of the constraint parametric space. A broad band IR antireflection coating has been designed to test its relative efficiency with respect to other available methods. A wide varieties of highly useful multilayer devices have been successfully developed using this method.     

Heat transfer augmentation and pumping power in double-pipe heat exchangers

One of the criteria for evaluating the performance of a heat exchanger with extended surfaces is the pumping power required for a specified heat duty. The results of an experimental project to relate the pumping power to heat transfer augmentation in a double-pipe heat exchanger are reported. The inner, electrically heated pipe was provided with external, rectangular, axial extended surfaces with interruptions. Heat transfer augmentation and friction factors were determined for different configurations with air as the fluid. Starting with continuous fins, cuts were introduced in the fins to give four ratios of the finssegment length to the gap between the segments, and finally all the fins were removed, which resulted in smooth pipes. Five different mass flow rates in two different inner pipes were employed. Lengths, surface areas, and pumping powers for finned pipes are compared with those for smooth pipes. The average heat transfer coefficient increases with an increase in the frequency of the interruptions. For equal heat transfer rates a significant reduction in the lengths can be achieved by interrupted fins. In many cases the reduction in the length is also accompanied by a reduction in the pumping power.     

A mechanism for pulsar radiation

The methods available for the determination of the stability constants of non-extractable complexes by solvent extraction are reviewed. The method proposed by Connick and McVey is valid only when no complexes of the auxiliary-ligand exist in the aqueous phase. This is applicable only at very low concentrations of the auxiliary-ligand. Hence, the stability constants calculated by this method decrease with increasing concentration and approach the theoretical values only at low concentrations of the auxiliary-ligand. It is essential, therefore, to apply the rigorous method incorporating the constants for the metal-auxiliary-ligand to calculate the stability constants which are independent of the changes in the experimental conditions. This is illustrated by few typical calculations.     

The propagation in space of cosmic-ray helium nuclei and the slope of their energy spectrum

Cosmic-ray helium nuclei, along with heavier nuclei, traverse interstellar and interplanetary matter during their propagation from their “source” to the earth. Ionisation and spallation losses during this traversal modify the energy spectra with which they started. Taking these effects into account, a calculation has been made of the abundance of helium nuclei relative to that of heavier nuclei (charge Z?6) as a function of energy and the amount of matter traversed. A comparison of the results with the experimental observations suggests that the exponents of the energy spectra of the helium and heavier nuclei should differ by ～0·25 at the “source”.     

Production of X-radiation in the Crab nebula

It is suggested that the X-rays from the Crab nebula are due to the synchrotron radiation of electrons of energy ～4×10¹² eV in the magnetic field of the central region of the nebula, the magnetic field being enhanced by hydromagnetic waves. The consistency of the model with experimental X-ray observations and the energetics of the nebula are shown.