-mononitroalkyl derivatives of indium

Dealkylation of trialkylindium by -mononitroalkane leads to the formation of the previously unknown -nitroalkyl derivatives of indium. An investigation of the chemical properties and of the ¹¹⁵In nuclear quadrupole resonance spectra of these compounds has been undertaken. An analysis of the data obtained from these investigations suggests the existence of intramolecular O→In coordination in the -nitroalkyl derivatives of indium.     

-Fluoro decalones as chiral epoxidation catalysts: fluorine effect

Three rigid monofluorinated trans-decalones 4a, 5e, and 6e (90% ee) have been synthesized from commercially available (−)-(R)-methyl naphthalenone (90% ee). Their structures have been fully characterized (NMR, X-ray): ketones 4a and 5e are Me,F-disubstituted to the carbonyl with the fluorine axial and equatorial, respectively, while ketone 6e is F-monosubstituted to the carbonyl with the fluorine equatorial. The use of these ketones as chiral catalysts for the epoxidation of trans-olefins (such as stilbene, β-methylstyrene and p-methoxy cinnamate) through the formation of dioxiranes shows (i) that dioxiranes with an equatorial fluorine to the dioxirane ring are less reactive and provide lower ee’s than dioxiranes with an axial fluorine and having the same chirality and (ii) that an axial methyl to the dioxirane ring is significantly less efficient than a fluorine. The results corroborate Armstrong and Houk’s theoretical model and our first hypothesis to rationalize the inverted enantioselectivities observed using -fluorinated cyclohexanones having the same chirality, i.e.: rapid ring inversion (Curtin–Hammett principle) allows the dioxirane conformation to have the fluorine axial (even if less populated than the other) to contribute significantly to the epoxidation reaction.     

-Halogenoketones—XIII Chromone epoxides; their synthesis and acid-catalysed rearrangement

The chromone epoxide ring system has been synthesised. Base-catalysed cyclization and dehydrobromination of -bromo-o-acyl (aroyl) oxyacetopheones or 2-bromo-1, 3-diones yielded 3-substituted chromone epoxides. Acid-catalysed rearrangement of a 2-methylchromone epoxide in an aprotic solvent gave a 2-methylenech-romanonol, while a 3-methoxymethylchromone epoxide fragmented to chromonol under these conditions; in alchols, chromone epoxides gave 2-alkoxychromanonols.     

-Halogenoketones—XIV Studies in the chemistry of 2'-hydroxyacrylophenones

An initial study of the side-chain unsubstituted 2'-hydroxyacrylophenone system shows it to have a considerably greater propensity for intermolecular addition than the comparable 2'-hydroxychalcone system, readily undergoing base-catalysed addition of, for example, alcohol and thereby diverting typical chalcone reactions requiring alcoholic alkali. 2'-Acetoxyacrylophenone dibromides and bromoalkoxides cyclize with base to chromone epoxides as do 2'-acetoxy--bromoacrylophenones in alcoholic alkali.     

-(1-phenylhydrazino)-alkanone phenylhydrazones: The reaction with carbonyl compounds

The unsymmetrically disubstituted hydrazines 1 were condensed with carbonyl compounds. Some of the expected condensation products were isolated, but some were formed as unstable intermediates which underwent 1,4-elimination: The phenylhydrazone of the carbonyl compound used was obtained, together with the corresponding phenylazo-alkene 11 or alternatively, the 1,4-addition product of a different protic nucleophile to 11.     

-Cyclisation of tertiary amines. Part 4. Cyano-imidoyl substituted furans from captodative enamines and dibenzoylacetylene

-Cyano-enamines and dibenzoylacetylene lead to dienes (via [2+2] cycloaddition followed by ringopening). Their -Cyclisation to oxygen produces the title compounds.     

,β-unsaturated oximes Isoxazoline formation by thermal cyclisation of compounds related to benzalacetophenone oxime and isoxazoline thermal cycloreversion reactions

At about 300° the title compounds yield fragments attributed to cyclisation to isoxazolines and subsequent cycloreversion. Isoxazolines are formed at about 200° and can usually be isolated. At 300° they yield the same products as the oximes.

Thus benzalacetophenone oxime gives 3,5-diphenylisoxazoline which then largely undergoes two distinct cycloreversions: (a) 1,3-cleavage (numbers refer to isoxazoline bonds) yielding benzonitrile and acetophenone and (b) reductive 1,4-cleavage yielding benzaldehyde and 1-phenylethylimine hydrolysis products. By-products are 2,4,6-triphenylpyridine, water and ammonium benzoate. With -methylchalcone oxime reductive 1,4-cleavage is suppressed and with β-methylchalcone oxime both modes of cleavage are suppressed and 5-methyl-3,5-diphenylisoxazole is the stable product. An analogue of -methylchalcone oxime, 2-methyl-1-phenyl-3-(2-thienyl)prop-2-ene-1-one oxime gives fragments attributed to both cleavage modes of an unisolatable and hitherto unknown isoxazoline.

Possible mechanisms for the cyclisation and cycloreversions are discussed and the reductive 1,4-cleavage is believed to be a cycloreversion of a vinyl-nitrene.     

- and β-cyclodextrin complexes with n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates. A molecular mechanics study of 1:1 and 1:2 associations

Molecular mechanics (MM) methods were employed to evaluate stabilization upon formation of inclusion compounds between two different guest molecules and - and β-cyclodextrins (CDs) for two different stoichiometries 1:1 and 1:2. The two guest molecules studied were n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates with variety of chain lengths. The computed stability for the inclusion compounds between -CDs and n-alkyl carboxylic acids reproduced experimental data reported in the literature. The transition between 1:1/1:2 complexes occurred at an alkyl chain length of n_C=9. It was previously demonstrated by diffusion coefficients measures that a stable 1:2 stoichiometry inclusion compound could be formed between n-alkyl p-hydroxy benzoates and -CD for the chain length n_C>4. The computed results reproduced the experimental ones. The combination between OPLS and GB/SA resulted in better agreements with experiments than those obtained with MM2 and MM3.     

Blue-shifting intramolecular CH O(S) contacts in sterically strained systems

A group of model systems which may form chelate-type structures with intramolecular CH  Y (Y = O, S) contact is investigated computationally. The existence of several conformers permits to identify a reference molecule without the CH  Y intramolecular contact and to establish the blue-shifting character of this interaction. The CH stretching frequency in chelate forms is found to increase with respect to its value in the reference system. A parallel decrease of the CH bond distance is also established. The blue-shifting character of the intramolecular CH  Y contact is interpreted in terms of the sterically enforced repulsion between the hydrogen atom in CH and the electron donor Y. This interpretation is supported by the negative (repulsive) estimates of the energy contribution due to CH  Y contacts.     

Boron trifluoride-catalyzed degradation of poly--caprolactone at ambient temperature

Poly--caprolactone (PCL) can be accelerated to degrade in the presence of boron trifluoride at ambient temperature. The degradation behaviors were studied by using the inherent viscosity measurement, gel permeation chromatography (GPC), infrared analysis (FTIR), nuclear magnetic resonance analysis (NMR), and thermal analysis (DSC). With increasing the addition amount of boron trifluoride, the molecular weight of PCL decreases; the molecular weight distribution is broadened; and the degree of crystallinity of PCL increases at first at low BF₃ level, then decreases when BF₃ content exceeds to 2.64 wt%. The results of IR, ¹HNMR and GPC reveal that -caprolactone monomer does not occur and the main degradation products are the oligomers of PCL with low molecular weight. The mechanism for boron trifluoride-catalyzed degradation of PCL is discussed.     

Monomer insertion mechanism of ring-opening polymerization of -caprolactone with yttrium alkoxide intermediate: A DFT study

The mechanism of -caprolactone (CL) insertion into a Y–OCH₃ bond was investigated using density functional theory (DFT) calculations. The optimized geometries and corresponding Gibbs-free energies of the intermediates were obtained, which confirmed a four-step coordination-insertion mechanism. The coordination of CL onto yttrium center led to a nucleophilic addition of the carbonyl group of CL, followed by an intramolecular alkoxide ligand exchange. A monomer insertion was completed by the CL ring opening via acyl–oxygen bond cleavage. The formation of the five-coordinated yttrium intermediate, 3, was found to be the rate-determining step. This study could be applicable to ring-opening polymerisation (ROP) of CL initiated by lanthanide metal complexes.     

Ion transfer across liquidliquid interfaces from transition-state theory and stochastic molecular dynamics simulations

We investigate the kinetics and dynamics of ion transfer across liquidliquid interfaces. We calculate the potential of mean force (pmf) of ion transfer from Monte Carlo simulations of a lattice–gas model, assuming independent chemical and electrostatic contributions. The shape of the pmf justifies considering the transfer as activated. The kinetics are obtained from transition-state theory and independently from stochastic molecular dynamics simulations. Both methods yield consistent results, with straight Tafel plots and friction effects in line with Kramers’ theory, but stronger than for a diffusing particle. A higher friction makes barrier recrossing more likely.     

A two-plasmid system for the glycosylation of polyketide antibiotics: bioconversion of -rhodomycinone to rhodomycin D

Background: The biological activity of many microbial products requires the presence of one or more deoxysugar molecules attached to agylcone. This is especially prevalent among polyketides and is an important reason that the antitumor anthracycline antibiotics are avid DNA-binding drugs. The ability to make different deoxyaminosugars and attach them to the same or different aglycones in vivo would facilitate the synthesis of new anthracyclines and the quest for antitumor drugs. This is feasible using the numerous bacterial genes for deoxysugar biosynthesis that are now available. Results: Production of thymidine diphospho (TDP)- -daunosamine (dnm), the aminodeoxysugar present in the anthracycline antitumor drugs daunorubicin (DNR) and doxorubicin (DXR), and its attachment to -rhodomycinone to generate rhodomycin D has been achieved by bioconversion with a strain of Streptomyces lividans that bears two plasmids. One contained the Streptomyces peucetius dnmJVUZTQS genes plus dnmW (previously named dpsH and considered to be a polyketide cyclase gene), dnrH, which is not required for the formation of rhodomycin D, and dnrl, a regulatory gene required for expression of the dnm and drr genes. The other plasmid had genes encoding glucose-1-phosphate thymidylyltransferase and TDP-glucose-4,6-dehydratase (dnmL and dnmM, respectively, or mtmDE, their homologs from Streptomyces agrillaceus) plus the drrAB DNR/DXR resistance genes. Conclusions: The high-yielding glycosylation of the aromatic polyketide -rhodomycinone using plasmid-borne deoxysugar biosynthesis genes proves that the minimal information for -daunosamine biosynthesis and attachment in the heterologous host is encoded by the dnmLMJVUTS genes. This is a general approach to making both known and new glycosides of anthracyclines, several of which have medically important antitumor activity.     

Patterning of biomolecules on a poly(-caprolactone) film surface functionalized by ion implantation

Biomolecule patterning is important due to its potential applications in biodevices, tissue engineering, and drug delivery. In this study, we developed a new method for a biomolecular patterning on poly(-caprolactone) (PCL) films based on ion implantation. Ion implantation on a PCL film surface resulted in the formation of carboxylic acid groups. The generated carboxylic acid groups were used for the covalent immobilization of amine-functionalized p-DNA, followed by hybridization with fluorescently tagged c-DNA. Biotin-amine was also covalently immobilized on the carboxylic acid generated PCL surfaces. Successful biotin-specific binding of streptavidin further confirmed the potential of this strategy for patterning of various biomolecules.     

The structure of p-chlorophenol and barrier to internal OH rotation in the S1-state

The structure and barrier to internal rotation of 4-chlorophenol in the ground state and the electronically excited S₁-state has been examined by rotationally resolved laser induced fluorescence spectroscopy of 4-³⁵Cl-phenol, 4-³⁷Cl-phenol, 4-³⁵Cl-phenol-d₁, and 4-³⁷Cl-phenol-d₁. The overlapping spectra have been assigned simultaneously using a genetic algorithm approach. The rotationally resolved spectrum of the electronic origin of 4-chlorophenol is comprised of two subbands, which are split by 60 MHz due to the internal rotation of the hydroxy group. The torsional barrier in the electronically excited state could be estimated to be 1400 cm⁻¹, only about 250 cm⁻¹ higher than in the ground state. The CCl bond lengths decreases by approximately 6 pm upon electronic excitation and the aromatic ring is distorted quinoidally.     

Phase controllable synthesis of unusual -Ga2O3 single crystals with promising luminescence property

A new synthetic approach to unusual -Ga₂O₃ with improved luminescence properties was developed by taking advantage of a microwave-assisted synthesis followed by calcinations at appropriate temperatures. Upon control of crystallinities of GaOOH precursors and the followed calcination temperature, the single crystalline -Ga₂O₃ nanorods can be synthesized in a large scale. The resulting products were characterized by transmission electron microscopy, powder X-ray diffraction, and cathodoluminescence. The luminescence property of this unusual Ga₂O₃ phase was investigated for the first time.     

Flame retardant polyamide 6 by in situ polymerization of ε-caprolactam in the presence of melamine derivatives

An improved method for preparing melamine cyanurate （MCA） based flame retardant polyamide 6 （FRPA6） materials has been proposed. This processing method, i.e., improved in situ polymerization, was used to synthesize flame retardant PA6. In situ formed MCA nanoparticles were supposed to be linked to PA6 chains in the ε-caprolactam hydrolytic polymerization system to obtain startype polymers for the first time. Through TEM photographs, it can be found that the in situ formed MCA nanoparticles with diametric size of less than 50 nm, are nanoscaled, highly uniformly dispersed in the PA6 matrix. Synthesized flame retardant PA6 have good fire performance which can achieve UL-94 V-0 rating at 1.6 mm thickness with the presence of 7.34 wt.% MCA in the matrix.     

Degradation of copolymers obtained by ring-opening polymerization of glycolide and -caprolactone: A high resolution NMR and ESI-MS study

Electrospray ionization-mass spectrometry (ESI-MS) and proton nuclear magnetic resonance (¹H NMR) have been used to investigate the hydrolytic degradation of copolymers obtained by bulk ring-opening copolymerization of glycolide and -caprolactone with monomer ratios ranging from 70/30 to 30/70. NMR allows changes of the average sequence distribution and composition of the components to be followed. In contrast, ESI-MS is able to reveal the detailed chemical structures of various sequences despite the molecular weight limit of 2000 Da. Combination of ESI-MS with NMR can thus provide information to describe microstructure changes during degradation. The distribution of various oligomers shown in the form of planar projections is of great interest for the design of biodegradable system aimed at medical applications.     

Quantum mechanical studies of the protonation and NBr bond dissociation of the biologically important N-bromosuccinimide

N-Bromosuccinimide (NBS) is a brominating and oxidizing agent that is used as a source of bromine. The proton affinities, the tautomeric forms and NBr bond dissociation of NBS have been computed using the B3LYP functional as implemented in the density functional approach. The electronic structures of all possible tautomeric forms of NBS have been thoroughly investigated. The keto form of NBS has been shown to be more stable than any other tautomeric forms. The geometries and relative energies for various stationary structures were determined. The results indicate clearly that O-site protonation is strongly favored over N-site protonation for the studied compound in case of mono- and di-protonation. The bond dissociation energies (BDEs), involving the formation of the bromine radical, cation, and anion, of the NBr bond have been investigated. The NBr BDE of the Br radical formation is lower than that of the Br anion or cation. These conclusions are in good agreement with the experimental results.