Isolation and crystallographic characterization of solvate- and anion-stabilized PCP pincer complexes of palladium(II)

Pincer PCP-Pd(II) complex [PdCl(PCP)] (1) (PCP = ^?CH(CH₂CH₂PPh₂)₂) reacts with AgNO₃ to give [Pd(NO₃)(PCP)] (2). Similar reaction with AgBF₄ gives the aqua complex [Pd(OH₂)(PCP)][BF₄] (3) and the dinuclear complex [{Pd(PCP)}₂(μ-Cl)][BF₄] (4) with singly bridging chloro ligand. All new complexes were characterized by NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. Complex 1 and the triflate complex [Pd(OTf)(PCP)] (5) are active towards Suzuki–Miyaura coupling between aryl bromides and phenyl boronic acid.     

Visible-Light-Induced Control over Reversible Single-Chain Nanoparticle Folding

We introduce a class of single-chain nanoparticles (SCNPs) that respond to visible light (λ_max=415 nm) with complete unfolding from their compact structure into linear chain analogues. The initial folding is achieved by a simple esterification reaction of the polymer backbone constituted of acrylic acid and polyethylene glycol carrying monomer units, introducing bimane moieties, which allow for the photochemical unfolding, reversing the ester-bond formation. The compaction and the light driven unfolding proceed cleanly and are readily followed by size exclusion chromatography (SEC) and diffusion ordered NMR spectroscopy (DOSY), monitoring the change in the hydrodynamic radius (R_H). Importantly, the folding reaction and the light-induced unfolding are reversible, supported by the high conversion of the photo cleavage. As the unfolding reaction occurs in aqueous systems, the system holds promise for controlling the unfolding of SCNPs in biological environments.     

Microwave survey of the conformational landscape exhibited by the propeller molecule triethyl amine

Conformational studies with quantum chemical methods yielded for the most stable conformer of triethyl amine a propeller-like structure belonging to the point group C(3), which corresponds to an oblate top. The microwave spectrum of this conformer with (14)N hyperfine splitting of all rotational transitions was assigned and molecular parameters were determined. The rotational constants were found to be A = B = 2.314873978(11) GHz, the (14)N quadrupole coupling constant χ(cc) = -5.2444(07) MHz. The observed spectrum could be reproduced within experimental accuracy. The standard deviation of a global fit with 48 rotational transitions is 1.5 kHz. The propeller-like structure seems to be energetically favorable and therefore also typical for related systems like triethyl phosphine, triisopropyl amine, tri-n-propyl amine, and tri-tert-butyl amine. Furthermore, the rotational transitions of two isotopologues, (13)C(2) and (13)C(5), could be measured in natural abundance and fitted with an excellent standard deviation. The C rotational constants could be determined to be 1.32681(96) GHz and 1.32989(18) GHz for the (13)C(2) and (13)C(5) isotopologues, respectively.     

The Scent of Maibowle – π Electron Localization in Coumarin from Its Microwave-Determined Structure

The microwave spectra of the natural substance coumarin, a planar aromatic molecule with the specific scent of maibowle, a popular fruit punch served in spring and early summer, were recorded using a molecular jet Fourier transform microwave spectrometer working in the frequency range from 4.0 to 26.5 GHz. The rotational constants and centrifugal distortion constants were determined with high precision, reproducing the spectra to experimental accuracy. The spectra of all singly-substituted ¹³C and ¹⁸O isotopologues were observed in their natural abundances to determine the experimental heavy atom substitution r_s and semi-experimental equilibrium r_e^SE structures. The experimental bond lengths and bond angles were compared to those obtained from quantum chemical calculations and those of related molecules reported in the literature with benzene as the prototype. The alternation of the C−C bond lengths to the value of 1.39 Å found for benzene reflects the localization of π electrons in coumarin, where the benzene ring and the lactone-like chain −CH=CH−(C=O)−O− are fused. The large, negative inertial defect of coumarin is consistent with out-of-plane vibrations of the fused rings.     

Integration of the primer vector in a central force field

This paper examines the primer vector which governs optimal solutions for orbital transfer when the central force field has a more general form than the usual inverse-square-force law. Along a null-thrust are that connects two successive impulses, the two sets of state and adjoint equations are decoupled. This allows the reduction of the problem to the integration of a linear first-order differential equation, and hence the solution of the optimal coasting are in the most general central force field can be obtained by simple quadratures. Immediate applications of the results can be seen in solving problems of escape in the equatorial plane of an oblate planet, satellite swing by, or station keeping around Lagrangian points in the three-body problem.This work has been sponsored by the Air Force Office of Scientific Research, under Grant No. AF-AFOSR-71-2129.     

Bioorganometallic chemistry: biocatalytic oxidation reactions with biomimetic NAD/NADH co-factors and [Cp*Rh(bpy)H] for selective organic synthesis

The biocatalytic, regioselective hydroxylation of 2-hydroxybiphenyl to the corresponding catechol was accomplished utilizing the monooxygenase 2-hydroxybiphenyl 3-monooxygenase (HbpA). The necessary natural 1,4-dihydronicotinamde adenine dinucleotide (NADH) co-factor for this biocatalytic process was replaced by a biomimetic co-factor, N-benzyl-1,4-dihydronicotinamide, 1b. The interaction between the flavin (FAD) containing HbpA enzyme and the corresponding biomimetic NADH compound, N-benzyl-1,4-dihdronicotinamide, 1b, for hydride transfer, was shown to readily occur. The in situ recycling of the reduced NADH biomimic 1b from 1a was accomplished with [Cp*Rh(bpy)H](Cl); however, productive coupling of this regeneration reaction to the enzymatic hydroxylation reaction was not totally successful, due to a deactivation process concerning the HbpA enzyme peripheral groups; i.e., -SH or -NH₂ possibly reacting with the precatalyst, [Cp*Rh(bpy)(H₂O)](Cl)₂, and thus inhibiting the co-factor regeneration process. The deactivation mechanism was studied, and a promising strategy of derivatizing these peripheral -SH or -NH₂ groups with a polymer containing epoxide was successful in circumventing the undesired interaction between HbpA and the precatalyst. This latter strategy allowed tandem co-factor regeneration using 1a or 2a, [Cp*Rh(bpy)(H₂O)](Cl)₂, and formate ion, in conjunction with the polymer bound, FAD containing HbpA enzyme to provide the catechol product.     

An o-iminothioquinone: its cycloaddition to produce an indologlycoside and its self-dimerization to form a dithio-diazocycloctane, the structure assignment of which is based on the DFT prediction of its IR spectrum

An unusual heterodiene, an indolothiono quinone, undergoes cycloaddition with a glycal to form an indole-N-glycoside. A novel dimer of the indolothionoquinone is assigned its structure on the basis of a match between its predicted and observed IR spectrum.     

Study on the isomeric ratios of (γ,p) photonuclear reactions with isotopes 40 92 Zr and 74 183 W in the giant dipole resonance region

We have carried out the study on the isomeric ratios in (γ,p) photonuclear reactions with isotopes ₄₀ ⁹² Zr and ₇₄ ¹⁸³ W in the giant dipole resonance (GDR) region. The targets were irradiated with bremsstrahlungs produced by electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, Russia. Spectra of the irradiated samples were measured with a spectroscopic system consisting of 8192-channel analyzer CANBERRA and high-energy resolution semiconductor detector CANBERRA. The results were discussed and compared with those of other authors. The text was submitted by the authors in English.     

Microstructural impact of anodic coatings on the electrochemical chlorine evolution reaction

Sol-gel Ru(0.3)Sn(0.7)O(2) electrode coatings with crack-free and mud-crack surface morphology deposited onto a Ti-substrate are prepared for a comparative investigation of the microstructural effect on the electrochemical activity for Cl(2) production and the Cl(2) bubble evolution behaviour. For comparison, a state-of-the-art mud-crack commercial Ru(0.3)Ti(0.7)O(2) coating is used. The compact coating is potentially durable over a long term compared to the mud-crack coating due to the reduced penetration of the electrolyte. Ti L-edge X-ray absorption spectroscopy confirms that a TiO(x) interlayer is formed between the mud-crack Ru(0.3)Sn(0.7)O(2) coating and the underlying Ti-substrate due to the attack of the electrolyte. Meanwhile, the compact coating shows enhanced activity in comparison to the commercial coating, benefiting from the nanoparticle-nanoporosity architecture. The dependence of the overall electrode polarization behaviour on the local activity and the bubble evolution behaviour for the Ru(0.3)Sn(0.7)O(2) coatings with different surface microstructure are evaluated by means of scanning electrochemical microscopy and microscopic bubble imaging.     

Channel effect in isomeric ratio of 137m,gCe produced in different nuclear reactions

This work presents the experimental study of the isomeric ratio of ^137mCe–^137gCe produced in ¹³⁸Ce(γ, n) ^137m,gCe photonuclear reaction, in neutron capture reaction ¹³⁶Ce(n, γ) ^137m,gCe and in the two simultaneous reactions ¹³⁸Ce(γ, n) ^137m,gCe and ¹³⁶Ce(n, γ) ^137m,gCe in the mixed photon—neutron field by the activation method. The investigated samples were irradiated at the bremsstrahlung photon flux, in the epithermal and thermal-epithermal neutron beam and in the mixed photon-neutron field constructed at the electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia. The results were analyzed, discussed and compared with those of other authors to examine the role of the channel effect in nuclear reaction and provide the nuclear data for theoretical model interpretation of nuclear reactions.