Synthesis of a new type of dibenzopyrromethene-boron complex with near-infrared absorption property

A new type of π-extended 4-bora-3a,4a-diaza-s-indacene (BODIPY dye), bis(isoindole)-derived benzo[1,3,2]oxazaborinine 1, has been synthesized by seven-step procedure from 2-methoxybenzoic acid methyl ester. The benzannulation of the pyrrole ring and the formation of a structurally strained intramolecular B-O ring enable the dye to absorb near-infrared light at ca. 750 nm with a molecular extinction coefficient (ε) of ca 8.3 × 10⁴ M⁻¹ cm⁻¹ in THF. The absorption properties are discussed on the basis of DFT calculations. Interestingly, a film of 5,5-dihexyloxy derivative 1b, which was fabricated by a spin-coating procedure on a glass plate, exhibited a dramatic bathochromic shift of absorbance as compared to the solution, with λ_max of 922 nm.     

Anti to syn isomerization of oxacalix[4]arene bearing two methyl groups at the intra-annular distal positions

The thermal isomerization of anti to syn stereoisomers of oxacalix[4]arene bearing two methyl groups at the intra-annular distal positions was investigated by temperature-dependent NMR spectroscopy. The conversion followed a first-order kinetics, and very slowly proceeded at 473 K in nitrobenzene-d₅ with a half-life of 7.2 h. The free energy of activation (ΔG^≠ 139 kJ mol⁻¹) is much higher than those for the ring inversion of related calix[4]arene derivatives.     

A practical method to access enantiopure β-perfluoroalkyl-β-amino acids: diastereoselective reduction of cyclic enamino-esters

A highly practical method to access enantiopure β-perfluoroalkyl-β-amino acids was developed, which could be conducted without any expensive reagent, special apparatus/technique, nor tedious chromatographic separation. The condensation of methyl 4,4,4-trifluoro-3-oxobutanoate with (S)-2-amino-2-phenylethanol, followed by an intramoleculer transesterification, gave an enamino-ester with a seven-membered ring structure. The hydride reduction of the cyclic enamino-ester proceeded with excellent diastereoselectivity (dr = 95:5-97:3) to give the corresponding cyclic amino-ester. The major isomer of the cyclic amino-ester was readily separated from the minor one and successfully converted into (S)-3-amino-4,4,4-trifluorobutanoic acid (five steps, 38% overall yield, >99% ee). Concerning the key step of this synthesis, the same strategy was applicable to another substrate; the asymmetric hydride reduction of a cyclic enamino-ester with a pentafluoroethyl group also proceeded in excellent diastereoselectivity (dr = 96:4).     

The electronic structures of all trans form of permethyl-oligosilane radical cation with longer chain: A density functional theory study

Hybrid density functional theory (DFT) calculations have been carried out for neutral, radical cation and dication of permethyl-oligosilane, Si_n(CH₃)_2n+2 (n = 4-30), to elucidate the electronic structures at ground and low-lying excited states. It was found that a hole is distributed in both the Si-Si skeleton (main chain) and methyl group (side chain) in the case of shorter chain-lengths below n = 6, whereas the spin density (hole) in the methyl group becomes significantly smaller in longer chain-lengths (n > 7). The IR-band of radical cation were assigned on the basis of theoretical calculations.     

Free radical copolymerization of methyl substituted stilbenes with maleic anhydride

Stilbene-maleic anhydride is a well-known donor-acceptor comonomer pair which undergoes free radical copolymerization to form an alternating copolymer. A series of methyl substituted stilbenes were synthesized and copolymerized with maleic anhydride. A conversion versus time study was undertaken to understand the methyl substituent effect on copolymerization rates. Methyl substituents on the phenyl ring of stilbene can change the reactivity of stilbene by changing the resonance stability of the propagating radical and steric hindrance in the propagation step and thereby change the copolymerization rate. Methyl substituted stilbene-maleic anhydride copolymers were determined by quantitative ¹³C 1D NMR to be alternating copolymers. Size exclusion chromatography (SEC) measurements showed that the weight-average molecular weights of these copolymers varied from 3000 to over 1,000,000 g/mol. Interchain aggregation was observed in poly((E)-4-methylstilbene-alt-maleic anhydride) by dynamic light scattering (DLS). The SEC trace for poly((E)-4-methylstilbene-alt-maleic anhydride) exhibited bimodal peaks. No glass transition temperature or crystalline melting temperature was observed between 0 °C and 250 °C by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) showed that these polymers have 5% weight loss around 290 °C.     

Intramolecular hydrogen bonding allows simple enaminones to structurally mimic the i, i + 4, and i + 7 residues of an α-helix

An intramolecularly hydrogen bonded enaminone scaffold was designed and synthesized in order to mimic the i, i + 4, and i + 7 residues of an α-helix. The resonance stabilized vinylogous amide group serves as an aromatic ring isostere and allows the positioning and angular projection of the R-groups in a manner similar to an α-helix.     

Excess and deviation properties for the binary mixtures of methylcyclohexane with benzene, toluene, p-xylene, mesitylene, and anisole at T = (298.15, 303.15, and 308.15) K

Experimental data on density, viscosity, and refractive index at T = (298.15, 303.15, and 308.15) K, while speed of sound values at T = 298.15 K are presented for the binary mixtures of (methylcyclohexane + benzene), methylbenzene (toluene), 1,4-dimethylbenzene (p-xylene), 1,3,5-trimethylbenzene (mesitylene), and methoxybenzene (anisole). From these data of density, viscosity, and refractive index, the excess molar volume, the deviations in viscosity, molar refraction, speed of sound, and isentropic compressibility have been calculated. The computed values have been fitted to Redlich-Kister polynomial equation to derive the coefficients and estimate the standard errors. Variations in the calculated excess quantities for these mixtures have been studied in terms of molecular interactions between the component liquids and the effects of methyl and methoxy group substitution on benzene ring.     

A novel method for the synthesis of 2,2-diaryl-1,1-difluoroethenes

β,β-Difluoro-α-phenylvinylstannane 3 was prepared in 60% yield from the reaction of β,β-difluoro-α-phenylvinylsulfone 2 with tributyltin hydride in refluxing benzene for 5 h. The cross-coupling reaction of 3 with aryl iodides bearing substituents such as proton, fluoro, chloro, bromo, methoxy, methyl, trifluoromethyl, and nitro on ortho, meta, para positions of the benzene ring in the presence of 10 mol % Pd(PPh₃)₄/10 mol % CuI afforded the corresponding 2,2-diaryl-1,1-difluoroethenes 4 in 22-82% yields.     

Preparation of a multi-hapten antigen and broad specificity polyclonal antibodies for a multiple pesticide immunoassay

A multi-determinant artificial antigen was prepared by haptens of four pesticides (chlorpyrifos, triazophos, carbofuran and parathion methyl) conjugating to the carrier protein BSA in turn. Male New Zealand white rabbits were immunized with this multi-determinant immunogen to produce the polyclonal antibodies (PAbs), which can recognize the four pesticides. The PAbs displayed high level for each relative hapten-OVA conjugate, with the favorable titers of 4.49 × 10⁴, 8.98 × 10⁴, 2.24 × 10⁴ and 1.86 × 10⁴, for CHBu-OVA, THHe-OVA, BFNB-OVA and MP5-OVA, respectively. Characterization studies of the PcAbs showed that it has high affinity and specificity to the four relative pesticides. An indirect competitive ELISA was developed for multi-residue determination. The I₅₀ value for the four pesticides was 0.290, 0.065, 0.582 and 2.824 μg mL⁻¹, with the detection limit (I₁₀) of 0.022, 0.005, 0.015 and 0.115 μg mL⁻¹ for carbofuran, triazophos, chlorpyrifos and parathion methyl, respectively. The linear rang was 0.016-2.000, 0.005-0.500, 0.010-2.000 and 0.063-5.000 μg mL⁻¹, respectively, for carbofuran, triazophos, chlorpyrifos and parathion methyl. Results indicated that, this study provided a new strategy to develop immunoassays through artificial antigen design for pesticides multi-residue determination.     

Synthesis and examination of amine-cyanocarboxyboranes, the boron analogues of α-cyanocarboxylic acids: X-ray structural study of the first lactam containing a boron atom in the lactam ring

The first representatives of chiral boron atom-containing amine-cyanomethoxycarbonyl boranes (A · BH(CN)COOMe) have been synthesized either from the corresponding amine-bromocyanomethoxycarbonylborane complexes with [Bu₄N]CN or from Me₃N · BH(CN)COOMe and an amine in a base-exchange reaction. Acid hydrolyses of methyl esters generated the free acids (A · BH(CN)COOH), which are isoelectronic to the α-cyano carboxylic acids. Their pK_a values and hydrolysis half-lives in acidic medium (that is rate of proton reduction) have been determined. Similarly to the alpha cyano carboxylic acids, the cyano group attached to the boron (in alpha position to the COOH group) increased the acid strength of carboxy boranes with 2.0-2.5 orders of magnitude. Independently from the type of the amine, pK_a values of the amine-cyanocarboxyboranes (6.34-5.82) decrease consistently with the increase of pK_b values of the amines. Hydrolytic decomposition rate of the alkylamine complexes increases with increasing pK_b values of the amines while the opposite was found for pyridine base complexes. When considering both types of the amines, hydrolysis half-lives of the complexes range over several orders of magnitude from 0.005 to 400 h. Based on these observations protonation of the amine nitrogen atom appears to be the rate determining step in the hydrolysis process. With loss of methanol, 2-NH₂-py · BH(CN)COOMe transformed into a five membered lactam derivative. X-ray diffraction revealed that the pyridine ring is coplanar with the five membered lactam ring. In the crystal two molecules are connected in a head to tail arrangement by strong intermolecular H-bonds between N(2)-H and the carbonyl oxygen (O1) with a donor and acceptor distance of 2.867(3) Å. Three new cyanomethoxycarbonylborates having the composition of K[BH_n(CN)_3−nCOOMe] (n = 1, 2) and K[B(OH)(CN)₂COOMe] have also been synthesized and their properties examined.     

New one- and two-dimensional 4H-pyranylidene NLO-phores

Dipolar, V-shaped compounds derived from 4H-pyranylidene-linked acceptors have been synthesized, and their linear and nonlinear optical properties (displaying μβ values up to 3000 × 10⁻⁴⁸ esu) have been compared to those of analogous one-dimensional derivatives. The pyranylidene ring behaves strictly as a spacer, and not as a donor group.     

Carboxylic acid functional group analysis using constant neutral loss scanning-mass spectrometry

The present study describes the development of a new analytical technique for the functional group determination of the carboxylic moiety using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS/MS) operated in the constant neutral loss scanning (CNLS) mode. Carboxylic groups were first derivatized into their corresponding methyl esters by reacting with BF₃/methanol mix and the reaction mixture was then directly injected into the APCI chamber. The loss of methanol (m/z = 32 amu) resulting from the fragmentation of the protonated methyl esters was then monitored. Applying this method together with a statistical approach to reference mixtures containing 31 different carboxylic acids at randomly calculated concentrations demonstrated its suitability for quantitative functional group measurements with relative standard deviations below 15% and a detection limit of 0.005 mmol L⁻¹. Its applicability to environmental matrices was also shown through the determination of carboxylic acid concentrations inside atmospheric aerosol samples. To the best of our knowledge, it is the first time that the tandem mass spectrometry was successfully applied to functional group analysis, offering great perspectives in the characterization of complex mixtures which are prevailing in the field of environmental analysis as well as in the understanding of the chemical processes occurring in these matrices.     

X-ray diffraction and inelastic neutron scattering study of 2,6-dimethylpyrazine (DMP) chloranilic acid (CLA) complex

The DMP · CLA and DMP · CLA-d₂ crystals below 100 K are monoclinic, space group P2₁/c with four molecules in the unit cells. Infinite chains of hydrogen bonded counterparts are formed with O?N distances equal to 2.767(2) and 2.639(2) for non-deuterated DMP · CLA. Deuteration leads to the Ubbelohlde effect particularly well manifested in the second short O–H?N bridge (elongation by ca. 0.02 Å). In the IR spectra a Had?i’s trio of the broad absorption is observed characteristic of strong hydrogen bonds. In the INS spectra the vibrational density of states and methyl rotational tunnel splittings were determined. The temperature dependence of tunneling bands enabled to make mode assignments and to determine the methyl rotational potentials. Comparison of the results to the pure electron donor DMP was made and the difference found can be almost completely assigned to the steric changes of the environment. A weak isotope effect with deuteration of the OH?N bridges of the DMP · CLA complex is assigned to a charge transfer of δe/e = 0.006.     

Molecular structure and spectroscopic properties of N-methylmorpholine betaine complex with 4-hydroxybenzoic acid

Crystal structure of the 1:1 complex of N-methylmorpholine betaine (MMB) with 4-hydroxybenzoic acid (4-HBA) has been determined by X-ray diffraction. Crystals are orthorhombic, space group Pna2₁ with a=7.933(2), b=15.336(3), and Z=4, R=0.033. The acid molecule forms two O-H?O hydrogen bonds with two betaine molecules. The COOH group of the acid forms shorter hydrogen bond with betaine (2.587(2) Å), than the hydroxyl group (2.677(2) Å). The carbonyl oxygen atom of the acid also interacts with the methylene hydrogen atom of the betaine through C-H?O hydrogen bond (3.256(2) Å). Thus formed infinite chains parallel to the z axis are connected by other C-H?O hydrogen bonds into layers perpendicular to the x axis. The morpholine ring has a chair conformation with the methyl group in the equatorial position and CH₂COO⁻ group in the axial one. The powder FTIR and Raman spectra and semiempirical calculations of the isolated molecule confirm the structure of the complex investigated. The ¹H and ¹³C spectra indicate that in DMSO-d₆ solution, protons are not transferred from the acid to the betaine molecules.     

Synthesis, X-ray crystal structure, and reactivity of Pd2(μ-dotpm)2 (dotpm = bis(di-ortho-tolylphosphino)methane)

Alkylation of PdCl₂(dotpm) (dotpm = bis(di-ortho-tolylphosphino)methane) with n-butyllithium produces the binuclear Pd(0) complex Pd₂(μ-dotpm)₂ and the elimination byproducts 1-butene, cis-2-butene, trans-2-butene, butane, and octane. The dibutyl complex, Pd(dotpm)(n-Bu)₂, is presumed to be the reaction intermediate. The crystal structure of Pd₂(μ-dotpm)₂ reveals that the methylene groups of the bridging dotpm ligands are located on opposite sides of the Pd₂P₄ unit, forming an 8-membered ring that is in an elongated chair conformation. The four phosphorus atoms are not coplanar, and the P1-P2-P3-P4 ring has a torsion angle of 13.8°, which minimizes the spatial interactions among the o-tolyl rings. The Pd-Pd bond distance is 2.8560(6) Å, which indicates that there is a weak “closed-shell” bonding interaction between the d¹⁰-d¹⁰ metal centers. Each palladium atom has a nearly linear geometry, and the eight methyl groups of the dotpm ligands shield the open coordination sites on the metal centers. Four methyl groups shield the metal atoms above and below the Pd₂P₄ ring cavity, and four methyl groups block the open metal sites outside of the Pd₂P₄ ring. The Pd₂(μ-dotpm)₂ complex readily undergoes oxidative addition of dichloromethane to form the rigid A-frame complex Pd₂Cl₂(μ-CH₂)(μ-dotpm)₂.     

Measurement and correlation of vapor–liquid equilibria for methanol + methyl laurate and methanol + methyl myristate systems near critical temperature of methanol

A flow-type method was adopted to measure the vapor–liquid equilibria for methanol + methyl laurate and methanol + methyl myristate systems at 493–543 K, near the critical temperature of methanol (T_c = 512.64 K), and 2.16–8.49 MPa. The effect of temperature and fatty acid methyl esters to the phase behavior was discussed. The mole fractions of methanol in liquid phase are almost the same for both systems. In vapor phase, the mole fractions of methanol are very close to unity at all temperatures. The present vapor–liquid equilibrium data were correlated by PRASOG. A binary parameter was introduced to the combining rule of size parameter. The binary parameters of methanol + fatty acid methyl ester systems were determined by fitting the present experimental data. The correlated results are in good agreement with the experimental data. The vapor–liquid equilibria for methanol + methyl laurate + glycerol and methanol + methyl myristate + glycerol ternary systems were also predicted using the methanol + fatty acid methyl ester binary parameters. The mole fractions of methanol in vapor phase are around unity even if glycerol is included in the systems.     

Poly(ester imide)s possessing low coefficients of thermal expansion (CTE) and low water absorption (III). Use of bis(4-aminophenyl)terephthalate and effect of substituents

A variety of poly(ester imide)s (PEsIs) were prepared using bis(4-aminophenyl)terephthalate (BPTP) and substituted BPTP (BPTP series) for applications to novel base film materials in flexible printed circuit boards (FPC). BPTP series were all highly reactive with various tetracarboxylic dianhydrides and led to considerably high molecular weights of PEsI precursors. The thermally imidized BPTP-based PEsI films achieved lower extents of water absorption (W_A) than the corresponding 4-aminophenyl-4′-aminobenzoate (APAB)-based PEsI systems while keeping other target properties, in particular, the linear coefficient of thermal expansion (CTE) much lower than that of copper foil as a conductive layer in FPC. The lower W_A is attributed to the decreased imide contents in the structure by using BPTP. The considerably low CTE can be explained in terms of intimate stacking between the p-aromatic ester fragments with an extended conformation. The BPTP-based PEsI system also exhibited a considerably low dissipation factor (tan δ = 1.91 × 10⁻³) at a high-frequency electric field of 18.3 GHz, comparable to a liquid-crystalline polyester. An effect of substituents on the film properties was also investigated in this work. Incorporation of methyl substituents on BPTP was very effective for property improvement, whereas methoxy substituents on BPTP, as well as methyl substituents onto hydroquinone bis(trimellitate anhydride) (TAHQ), showed a trend to significantly increase the CTE. Copolymerization with an adequate amount of a typically flexible monomer, 4,4′-oxydianiline (4,4′-ODA), allowed the CTE matching with copper foil and the film toughness improvement at the same time. The PEsI copolymer prepared from TAHQ (10 mmol) with methyl-substituted BPTP (7 mmol) and 4,4′-ODA (3 mmol) achieved excellent combined properties, namely, a very high T_g at 410 °C, a slightly lower CTE (10.0 ppm/K) than that of copper foil, suppressed water absorption (0.35%), an extremely low linear coefficient of humidity expansion (CHE = 3.4 ppm/RH%), and good film toughness (the elongation at break, ε_b = 50.7%). Thus, BPTP- and methyl-substituted BPTP-based PEsI systems can be promising candidates as a next generation of FPC base film materials.     

Bioreduction of methyl o-chlorobenzoylformate at 500 g L without external cofactors for efficient production of enantiopure clopidogrel intermediate

Biocatalytic reduction of methyl o-chlorobenzoylformate (CBFM) provides a green and direct access to methyl (R)-o-chloromandelate [(R)-CMM], an intermediate for a platelet aggregation inhibitor named clopidogrel. As much as 500 g L⁻¹ of CBFM was stoichiometrically converted into enantiopure (R)-CMM at 20 °C by using a whole-cell catalyst coexpressing an aldo-keto reductase from Bacillus sp. and a glucose dehydrogenase (GDH). In addition to the high productivity of 812 g L⁻¹ d⁻¹, this new whole-cell reduction is attractive by eliminating the need of an added external cofactor.     

Catalytic effects of sulfates on thermal degradation of waste poly(methyl methacrylate)

The thermal degradation of waste poly(methyl methacrylate) (PMMA) in the presence of ferric sulfate, cupric sulfate, aluminum sulfate, magnesium sulfate, and barium sulfate was studied by using thermogravimetric analysis (TGA) in air atmosphere. The values of apparent activation energies (E_a) calculated by Flynn-Wall-Ozawa method were found to be in the order of PMMA + Fe₂(SO₄)₃ < PMMA + Al₂(SO₄)₃ < PMMA + MgSO₄ < PMMA + CuSO₄ < PMMA + BaSO₄ < PMMA. The mechanism of catalytic degradation of PMMA in presence of the sulfates was discussed and the results showed that the catalytic effects of sulfates have a relationship with the acidity of their respective metal ions.     

Efficient double bond migration of allylbenzenes catalyzed by Pd(OAc)2-HFIP system with unique substituent effect

A novel catalyst system of Pd(OAc)₂-HFIP induces double-bond migration of allylbenzenes under mild conditions with low catalytic loading to afford 1-propenylbenzenes. The reaction shows a unique substituent effect that is highly dependent on the distance of substituents from the allylic moiety. Thus, the reactivity of substrates bearing a methyl group is ordered in para > meta > ortho, whereas it is entirely reversed as ortho > meta > para for methoxy and chloro substituents.