Preparation of telechelic oligomers by controlled thermal degradation of isotactic poly(1-butene) and poly(propylene-ran-1-butene)

It was found that telechelic isotactic oligo(1-butene) and telechelic oligo(propylene-ran-1-butene) could be isolated as nonvolatile oligomers from polymer residues resulting from the thermal degradation of isotactic poly(1-butene) and poly(propylene-ran-1-butene), respectively. Their structures were determined by ¹H and ¹³C NMR with attention being paid to their reactive end groups. The maximum average number of terminal vinylidene groups per molecule (f_TVD) was 1.8, indicating that about 80 mol% were α,ω-diene oligomers having two terminal vinylidene groups. This useful new telechelic oligomer had a lower polydispersity than the original polymer, in spite of its lower molecular weight and T_m. The composition of end groups of nonvolatile oligomers obtained by thermal degradation of poly(propylene-ran-1-butene) could be explained by the differences in bond dissociation energy and activation energy of elementary reactions during thermal degradation, based on the monomer composition of the original polymer.     

Synthesis and characterization of novel silica gel supported N-pyrazole ligand for selective elimination of Hg(II)

The polar organic molecule N-(2-hydroxyethyl)-3,5-dimethylpyrazole reacted with a 3-glycidoxypropyltrimethoxysilane silylant agent, previously anchored on a silica surface in a heterogeneous way to yield the product SiPz. The epoxide group was opened yielding chelating pendant group bonded to the inorganic surface. The product was characterized through elemental analysis, infrared spectroscopy, ¹³C NMR, surface area and thermogravimetry. The binding and adsorption abilities of SiPz was investigated for Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Zn²⁺, K⁺, Na⁺ and Li⁺ cations and compared to results of classical liquid-liquid extraction with the unbound N-pyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the SiPz exhibits a high selectivity toward Hg²⁺ ion with no complexation being observed towards Zinc and alkali metals. The extracted and the complexing cation percentage were determined by atomic absorption measurements.     

Spectral modulation of charge transfer fluorescence probe encapsulated inside aqueous and non-aqueous β-cyclodextrin nanocavities

In this work, we report the spectral modulations of a intramolecular charge transfer (ICT) molecule ethyl ester of N,N-dimethylaminonaphthyl-(acrylic)-acid (EDMANA) when encapsulated in the water and N,N-dimethylformamide (DMF) solution of β-CD nanocavities. From the nature of the Benesi-Hildebrand (B-H) plots, the stoichiometry of the host guest inclusion complexes are found to be 1:1 in water β-CD solution and both 1:1 and 1:2 in DMF β-CD solution. The preferential location and difference in orientation of EDMANA molecule inside the β-CD cavity has been accessed by analysis of the effect of acid and metal cation Ni²⁺ on the spectral characteristics in both the media. In case of 1:1 complex, the polar donor group prefers to expose to bulk aqueous phase capable of binding with H⁺ and Ni²⁺ ions and the acceptor to the hydrophobic interior. On the other hand, the acceptor group remains exposed to the non-polar bulk phase and the donor group is orientated preferentially inside the non-polar core in 1:2 inclusion complexes.     

Toward the controlled production of oligoesters by microwave-assisted degradation of poly(3-hydroxyalkanoate)s

The degradation of poly(3-hydroxyalkanoate)s (PHAs) could be performed in a rapid, inexpensive and straightforward way via microwave irradiation with good potential for further scale-up. One such degradation was compared to that induced by conventional heating at 190 °C. The experimental results showed that PHA oligomers with varying molar masses, characterized by a terminal crotonic double bond and a carboxyl group on the other chain end, could be effectively obtained from native PHAs in the bulk by both degradation approaches. The kinetics of PHA oligomer production was monitored by size exclusion chromatography and ¹H NMR. The influence of temperature as well as microwave irradiation time and power was investigated, and the optimal conditions of degradation are described. It turned out that this treatment was much more efficient than a conventional thermally-induced degradation, as oligomers with similar molar masses were formed with an about 100 times faster rate corresponding to very short irradiation times (maximum 15 min). Two microwave-assisted procedures could be advantageously used: an irradiation with constant temperature was appropriate to afford PHA oligomers with molar masses lower than 1000 g.mol⁻¹ and high yields, while irradiation under constant power was more convenient to provide oligoesters with higher molar masses.     

Tricarbonyl-6,6′-dimethylfulvene chromium(0) - Structural properties

The crystal structure of tricarbonyl-6,6′-dimethylfulvene chromium(0) was determined using X-ray diffraction at room temperature and at 120 K. The title compound crystallizes in the centrosymmetric, monoclinic space group P2₁/n (no. 14) with one complete molecule in the asymmetric unit. The deviation of the chromium(0) complex from C_s(m) symmetry is negligible in agreement with results derived from density functional calculations using three different methods as well as ab initio calculations (MP2). The 6,6′-dimethylfulvene ligand is bent by 30.9° as a result of the π-η²:π-η²:π-η² coordination to the Cr(0) metal. In addition, the chromium(0) complex was studied by IR and Raman spectroscopy and selected vibrational data are compared to values derived from DFT calculations.     

Synthesis of (+)-anatoxin-a using enyne metathesis

Synthesis of N-tosylanatoxin-a was achieved by metathesis of enyne in cis-substituents on a pyrrolidine derivative. Metathesis reactions of enyne having terminal alkyne using various ruthenium-carbene complexes did not give a good results. However, when the terminal alkyne was protected with a TMS group, the reaction proceeded smoothly using a second-generation ruthenium-carbene complex to give the desired cyclized compound in high yield. Oxymercuration followed by Dess-Martin oxidation afforded N-tosylanatoxin-a.     

Synthesis and in vitro studies of Gd-DTPA derivatives as new potential MRI contrast agents

A new type of dendritic molecules, Gd-DTPA derivatives, which work as a functionalized ligand coordinating gadolinium(III) ion at the center of their frameworks with different terminal moieties on the molecular surfaces, was readily synthesized with high yield. The structures were established by ¹H, ¹³C NMR, and mass spectral studies. In vitro studies showed them to have enhanced r₁ value in albumin medium and good potentiality as MRI contrast agent.     

Large variations in acidity of terminal amide bonds in histamine-containing peptides as measured by proton DNMR

The main objective of these studies is to quantitatively estimate pK variations of individual amide bonds as a function of the ionization state of end groups in peptides, determined on measuring macro- and micro- (if any) ionization constants. ¹H NMR spectra of aqueous solutions of eight model substrates were consequently recorded using a water suppression sequence, within large pH ranges. A set of programs was devised to treat NMR data over the entirety of pH-dependent NMR patterns, in order to smooth out errors arising in handling individual spectra. Rates of amide proton abstraction by hydroxide ions were obtained from the coalescence of methylene coupled protons and the decrease of NH bond signal intensities, allowing us to estimate and discuss peptide pKs on assuming back reprotonation at a diffusion-limited rate. Cis–trans isomerization rates in two substrates bearing a tert-Butyloxycarbonyl terminal group were put in parallel with the acidity of carbamic protons.     

On the conformational characteristics of the O,O,O-trimethyl selenophosphate molecule

Spectroscopic and theoretical studies were carried out for O,O,O-trimethyl selenophosphate molecule. DFT structural and vibrational calculations were performed at 6-311++G^∗∗ level. Ar/matrix-FTIR spectra were recorded. A coexistence of different conformers with C₃ and C₁ symmetries was detected at different temperatures. Spectral evidence of a lower energy C_s conformer was found. These conclusions are consistent with the results from DFT calculations. A tentative assignment of the features observed in the Ar/matrix-FTIR spectra is proposed.     

Synthesis and optical properties of C3-ethynylated chlorin and π-extended chlorophyll dyads

A C3-ethynylated chlorophyll derivative was prepared from methyl pyropheophorbide-d possessing a 3-formyl group by treatment of Bestmann-Ohira reagent. The mono-substituted acetylene was subjected to coupling reactions at the terminal acetylenic carbon atom to form a series of π-extended chlorophyll derivatives. Replacement of the terminal hydrogen to phenyl, phenylethynyl and C3-chlorin-ethynyl caused red-shifts of their Q_y (0,0) maxima from 675 to 679, 686, and 696 nm, respectively. Optical properties of C3²-substituted 3-ethynyl-chlorophyll derivatives including chlorophyll dyads were investigated in comparison with those of their related compounds. Partial quenching of the fluorescence emission (Φ_flu=0.14) was observed for ortho-substituted dyad, compared to meta- (Φ=0.27) and para-dyads (Φ=0.29), suggesting a through-space interaction between the two chlorin macrocycles in a molecule.     

Influence of ultrasonic waves on phosphate determination by the molybdenum blue method

Polymeric bonds between molybdate monomeric ions in acidic medium were broken by 40 kHz ultrasonic wave irradiation, improving the reaction kinetics with o-phosphate in the presence of ascorbic acid. It could be assumed that the ultrasonic wave irradiation of molybdate solution in acidic medium during 1.0 min was sufficient to increase the rate of the molybdenum blue formation. The approach was applied to the o-phosphate determination in natural waters. Precise results were obtained in the range from 0.05 to 0.50 μg ml⁻¹ (r=0.9994; N=6), and the detection limit was estimated as 0.027 μg ml⁻¹ PPO₄. Advantages over the classical analogous procedure are emphasised.     

Quantum-chemical calculations of the IR absorption spectra of modified polytetrafluoroethylene forms

DFT(B3LYP) (basis set 6–31 + G(d)) and HF (basis set 6–31G) calculations were performed to determine the geometric structure and vibrational spectra of the C_nF_2n and C_nF_2n O molecules (n = 3–13). The IR spectra of chain C_nF_2n O molecules with the terminal carbonyl group (-COF) were found to contain a band at 1885 cm^?1. The C=C and C=O stretching vibrations of the-CF=CF₂ and COF terminal groups were independent, and there was no mutual influence of their frequencies starting with the seven-fragment molecule. In the presence of chain branching, the sensitivity of the ν(C=C) and ν(C=O) frequencies in the olefin and carbonyl groups depended on where branching occurred. The chain configuration was found to be energetically favorable compared with branched structures.     

Synthesis and structure of N-salicylidene-o-aminophenolato gallium(III) complexes

The reactions of Ga(acac)₃ with N-salicylidene-o-aminophenol (saphH₂) and its 5-methyl (5MesaphH₂) and 5-bromo (5BrsaphH₂) derivatives in alcohols afforded the complexes [Ga(acac)(saph)(EtOH)] (1), [Ga(acac)(5Mesaph)(MeOH)] (2) and [Ga(acac)(5Brsaph)(EtOH)] (3), respectively, in good yields. The crystal structures of 1 and 2 have been solved by single-crystal X-ray crystallography. All three complexes are mononuclear with the Ga^III atoms being surrounded by a dianionic tridentate Schiff base ligand, one bidentate acac⁻ ligand and a terminal alcohol molecule. Characteristic IR data are discussed in terms of the nature of bonding and the structures of the three complexes.     

Thermo- and pH-sensitive comb-type grafted poly(N,N-diethylacrylamide-co-acrylic acid) hydrogels with rapid response behaviors

Poly(N,N-diethylacrylamide) with a terminal hydroxyl end group (PDEA-OH) was synthesized by radical telomerization of N,N-diethylacrylamide (DEA) monomer using 2-hydroxyethanethiol as a chain transfer agent. Macromonomer of thermo-sensitive PDEA was synthesized by condensation reaction of PDEA-OH with acryloyl chloride. The macromonomer was characterized by FTIR and ¹H NMR, and the molecular weight was determined by GPC. Thermo- and pH-sensitive comb-type grafted poly(N,N-diethylacrylamide-co-acrylic acid) (PDEA-co-AA) hydrogels (GHs) were successfully prepared by grafting PDEA chains with freely mobile ends onto the backbone of a cross-linked (PDEA-co-AA) network. The results showed that the deswelling behavior of the hydrogels was dependent on the test temperature. At 45 °C (beneath the VPTT of the hydrogels), both the normal-type hydrogels (NHs) and comb-type grafted P(DEA-co-AA) hydrogels had lower deswelling rates. While at 60 °C (far beyond the VPTT of the hydrogels), the deswelling rates of the GHs were faster than that of the NHs. Furthermore, pulsatile stimuli-responsive studies indicated that the GHs had excellent thermo-reversibility and were superior to the NHs in the magnitude of their swelling ratios to temperature changes. However, the reversibility to pH changes was poor for both the NHs and the GHs.     

Photolysis of open-chain 1,2-diazidoalkenes: generation of 2-azido-2H-azirines, formyl cyanide, and formyl isocyanide

Solutions of several open-chain 1,2-diazidoethenes were photolyzed to yield 2-azido-2H-azirines, which were identified by NMR spectroscopy at low temperature. On prolonged irradiation or warm-up of the NMR solutions, these heterocycles lost a second molecule of nitrogen to be cleaved into two fragments of cyano compounds. In the case of (Z)-2,3-diazidocinnamaldehyde, the formation of formyl cyanide was detected by IR spectroscopy when the photolysis was performed in argon matrix. The latter substance was rearranged to formyl isocyanide on irradiation. This new species was characterized by comparison of its experimental and calculated (B3LYP/6-311+G^∗∗) IR spectrum.     

Photolytic decarbonylation of o-benzoquinones

It was established that photodecarbonylation of o-benzoquinones occurs by irradiation not only by UV-light, but visible light (λ>520 nm) too. Study of the series of 4,5-di-substituted 3,6-di-tert-butyl-o-benzoquinones detected that the only product of photoreaction is the corresponding 3,4-di-substituted 2,5-di-tert-butyl-cyclopentadienone, which is formed in a yield close to quantitative. NMR monitoring of reaction of photodecarbonylation of o-benzoquinones detected that this is a two-stage process. In the first stage the photoexcited molecule of quinone rearranges into bicyclo compound (bicyclo[1.3.0]hexa-3-en-2,6-dione) containing five- and three- membered cycles, which spontaneously decomposes during the following dark stage into cyclopentadienone and a molecule of CO.     

Synthesis of (Z)-1-bromo-1-alkenes and terminal alkynes from anti-2,3-dibromoalkanoic acids by microwave-induced reaction

(Z)-1-Bromo-1-alkenes were stereoselectively prepared in high yields in a short reaction time by microwave irradiation of the corresponding anti-2,3-dibromoalkanoic acids in a Et₃N/DMF system. A one-pot synthesis of terminal alkynes and enynes from 2,3-dibromoalkanoic acids were also developed by microwave-induced reaction.     

Atom transfer radical polymerization of n-octyl acrylate under microwave irradiation

The atom transfer radical polymerization (ATRP) of n-octyl acrylate (OA) was successfully carried out using ethyl-2-bromobutyrate as an initiator, and CuBr/2,2^′-bipyridine (bpy) as a catalyst under microwave irradiation (MI) at 76.8 °C. The polymerization of n-octyl acrylate under MI showed linear first-order rate plots, a linear increase of the number-average molecular weight M_n with conversion, and low polydispersities, 1.1<M_w/M_n<1.4, where M_w is weight-average molecular weight. The ATRP of n-octyl acrylate is well controlled. Under the same experimental conditions, the apparent rate constant, k_p^app, under MI is larger apparently than that under conventional heating. In addition, the effects of concentration of catalyst and other factors on polymerization are reported.     

Stille reaction over cis-halocyclohexadienediol derivatives

Stille reaction was performed with several halo cis-diol derivatives by reaction with allyltributyltin in the presence of a palladium catalyst forming allyl cis-dihydrodiol derivatives. These couplings were conducted with conventional heating as well as with microwave irradiation. Allylbenzene cis-dihydrodiol was obtained with excellent yield using mild conventional heating. However, if the diol moiety is protected with the isopropylidene group, the expected product is obtained only under microwave irradiation. The unusual reactivity observed for the polyoxygenated derivatives suggests assistance of the free hydroxyls in the catalytic cycle.     

Synthesis of 3-nitro-chlorophyll-a derivatives and their electronic absorption/emission data

The formyl group at the 3-position of methyl pyropheophorbide-d, one of chlorophyll-a derivatives, was efficiently transformed to the 3²-cis-unsubstituted/methyl- or 3²-cis-phenyl-3²-trans-nitro-vinyl groups by Henry (nitro-aldol) or nitro-Mannich (aza-Henry) reactions with nitromethane/ethane or nitrophenylmethane, respectively. The introduction of a nitro group at the terminal of the 3-ethenyl moieties directly connected with the chlorin π-system red-shifted and broadened their Qy electronic absorption and fluorescence emission bands in a solution. The fluorescence intensities were largely suppressed by the substitution with the nitro group.