Acetylation of cellulose in LiCl-N,N-dimethylacetamide: first report on the correlation between the reaction efficiency and the aggregation number of dissolved cellulose

The acylation of three cellulose samples by acetic anhydride, Ac(2)O, in the solvent system LiCl/N,N-dimethylacetamide, DMAc (4 h, 110 A degrees C), has been revisited in order to investigate the dependence of the reaction efficiency on the structural characteristics of cellulose, and its aggregation in solution. The cellulose samples employed included microcrystalline, MCC; mercerized cotton linters, M-cotton, and mercerized sisal, M-sisal. The reaction efficiency expresses the relationship between the degree of substitution, DS, of the ester obtained, and the molar ratio Ac(2)O/AGU (anhydroglucose unit of the biopolymer); 100% efficiency means obtaining DS = 3 at Ac(2)O/AGU = 3. For all celluloses, the dependence of DS on Ac(2)O/AGU is described by an exponential decay equation: DS = DS(o) - Ae(-[(Ac2O/AGU)/B]); (A) and (B) are regression coefficients, and DS(o) is the calculated maximum degree of substitution, achieved under the conditions of each experiment. Values of (B) are clearly dependent on the cellulose employed: B((M-cotton)) > B((M-sisal)) > B((MCC)); they correlate qualitatively with the degree of polymerization of cellulose, and linearly with the aggregation number, N(agg), of the dissolved biopolymer, as calculated from static light scattering measurements: (B) = 1.709 + 0.034 N(agg). To our knowledge, this is the first report on the latter correlation; it shows the importance of the physical state of dissolved cellulose, and serves to explain, in part, the need to use distinct reaction conditions for MCC and fibrous celluloses, in particular Ac(2)O/AGU, time, temperature.

Formation and decomposition of N-alkyinaphthalimides: experimental evidences and ab initio description of the reaction pathways

The kinetics of hydrolysis of 1,8-N-butyl-naphthalimide (1,8-NBN) to 1,8-N-butyl-naphthalamide (1,8-NBAmide) and of 2,3-N-butyl-naphthalimide (2,3-NBN) to 2,3-N-butyl-naphthalamide (2,3-NBAmide), as well as the formation of the respective anhydrides from the amides were investigated in a wide acidity range. 1,8-NBN equilibrates with 1,8-NBAmide in mild alkali. Under the same conditions 2,3-NBN quantitatively yields 2,3-NBAmide. Over a wide range of acidities the reactions of the 1,8- and 2,3-N-butyl-naphthalamides (or imides) yield similar products but with widely different rates and at distinct pH`s. Anhydride formation in acid was demonstrated for 1,8-NBAmide. The reactions mechanisms were rationalized in the manifold pathways of ab initio calculations. The differences in rates and pH ranges in the reactions of the 1,8- and 2,3-N-butyl-naphthalamides were attributed to differences in the stability of the tetrahedral intermediates in alkali as well as the relative stabilities of the five and six-membered ring intermediates. The rate of carboxylic acid assisted 1,8-N-Butyl-naphthalamide hydrolysis is one of the largest described for amide hydrolysis models. Copyright (C) 2010 John Wiley & Sons, Ltd.

An insight into the beginning stage of the aqueous ring opening metathesis polymerization of exo,exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid with Ru(III) compounds: the consumption of Ru(III) species in the presence of carboxylic acids monitored by ESR spectroscopy

The presence of paramagnetic species in the aqueous ring opening metathesis polymerizations of the exo,exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid monomer with RuCl(3) and K(2)[RuCl(5)H(2)O] compounds was studied using ESR techniques. It was observed that the intensities of the Ru(III) signals in the ESR spectra decrease on the time scale of the induction period so that the ROMP can take place. The intensity of the Ru(III) signal almost disappeared 50 min after reacting with K(2)[RuCl(5)H(2)O] and after 100 mm in the case of RuCl(3). Reactions of the cis-[Ru(NH(3))(4)(H(2)O)(2)](tfms)(3) and [Ru(NH(3))(5)H(2)O](tfms)(3) complexes with the monomer and different organic compounds representing the organic functions in the monomer (furan, norbornene, but-2-ene-1,4-diol and formic, acetic, oxalic and maleic acids) were also monitored by ESR and UV/vis spectra. It was deduced that the organic acids provide the disappearance of the Ru(III) signal. The proton NMR relaxation times of the residual water in D(2)O for reactions with oxalic acid suggested that the presence of paramagnetic ions in the solution decreases along with

Removal of Zn(2+) from Electroplating Wastewater Using Modified Wood Sawdust and Sugarcane Bagasse

This paper describes the preparation of new adsorbents derived from sugarcane bagasse and wood sawdust (Manilkara sp.) to remove zinc (II) ions from electroplating wastewater. The first part deals with the chemical modification of sugarcane bagasse and wood sawdust, using succinic anhydride to introduce carboxylic acid functions into the material. The obtained materials (modified sugarcane bagasse MB2 and modified wood sawdust MS2) were then characterized by infrared spectroscopy (IR) and used in adsorption experiments. The adsorption experiments evaluates Zn(2+) removal from aqueous single metal solution and real electroplating wastewater on both batch and continuous experiments using fixed-bed columns prepared in laboratorial scale with the obtained adsorbents. Adsorption isotherms were then developed using Langmuir model and the Thomas kinetic model. The calculated Zn(2+) adsorption capacities were found to be 145 mg/g for MS2 and 125 mg/g for MB2 in single metal aqueous solution, whereas for the industrial wastewater these values were 61 mg/g for MS2 and 55 mg/g for MB2.

Investigation of failure mechanisms in aged aerospace composites

The effect of isothermal ageing on two high temperature, bismaleimide composite materials, a novel CSIRO CBR 320/328 composite and a commercial CIBA GEIGY Matrimid® 5292 composite, was examined at 204 and 250 °C. Delamination is a major cause of failure in composite materials, therefore, the Mode I interlaminar fracture toughness (GIC) of both materials was measured using the double cantilever beam (DCB) test. Chemical degradation of the matrix was monitored concurrently using Fourier transform infrared (FTIR) and Raman spectroscopy. Chemical changes at the core of both of these materials were found to occur concomitantly with the observed changes in interlaminar fracture toughness. FTIR analysis of both matrix materials revealed the predominant degradation mechanism to be the oxidation of the methylene group bridging two aromatic rings common to the structure of both resins, and was substantiated by the ingrowth of a broad peak centred at 1600 cm⁻¹ . In addition to this, the pyromellitic anhydride unit present only in the CBR 320/328 composites was found to be highly resistant to the effects of ageing, whereas the saturated imide, common to the cured structures of both materials, was observed to degrade. Raman spectroscopy indicated that the predominant degradation mechanism of the composites differed at the two ageing temperatures.

Modeling of enzyme–substrate complexes for the metalloproteases MMP-3, ADAM-9 and ADAM-10

The matrix metalloproteases (MMPs) and the ADAMs (A Disintegrin And Metalloprotease domain) are proteolytic enzyme families containing a catalytic zinc ion, that are implicated in a variety of normal and pathological processes involving tissue remodeling and cancer. Synthetic MMP inhibitors have been designed for applications in pathological situations. However, a greater understanding of substrate binding and the catalytic mechanism is required so that more effective and selective inhibitors may be developed for both experimental and clinical purposes. By modeling a natural substrate spanning P4-P4‘ in complex with the catalytic domains, we aim to compare substrate-specificities between Stromelysin-1 (MMP-3), ADAM-9 and ADAM–10, with the aid of molecular dynamics simulations. Our results show that the substrate retains a favourable antiparallel beta-sheet conformation on the P-side in addition to the well-known orientation of the P'-region of the scissile bond, and that the primary substrate selectivity is dominated by the sidechains in the S1' pocket and the S2/S3 region. ADAM-9 has a hydrophobic residue as the central determinant in the S1' pocket, while ADAM-10 has an amphiphilic residue, which suggests a different primary specificity. The S2/S3 pocket is largely hydrophobic in all three enzymes. Inspired by our molecular dynamics calculations and supported by a large body of literature, we propose a novel, hypothetical, catalytic mechanism where the Zn-ion polarizes the oxygens from the catalytic glutamate to form a nucleophile, leading to a tetrahedral oxyanion anhydride transition state.

Total synthesis of (±)-hyphodermins A and D

An efficient formal synthesis of (±)-hyphodermins A and D, metabolites of Hyphoderma radula, has been completed in 12 and 11 steps, respectively. The tricyclic carbon skeleton of enone 6 was rapidly assembled from diester 11 via an α brominationn−elimination sequence followed by anhydride formation. Regioselective reduction of the lactone group of enone 6 with LiAlH(t-BuO)3 gave lactol 15. Lactol 15 was converted in two steps to (±)-hyphodermin D, without the need for complex protection−deprotection strategies. Lactol 15 was converted in three steps to (±)-hyphodermin A, via the key step of epoxidation of an enone in the presence of a THP lactol. A combination of NMR and ab initio studies suggests that the structures of hyphodermin C and D should be interchanged.

Efficient formal synthesis of (±)-hyphodermin B

An efficient formal synthesis of hyphodermin B 1, a metabolite of Hyphoderma radula, has been completed in 15% overall yield. The tricyclic carbon skeleton 3 was rapidly assembled from a novel vinyl enone via a Diels−Alder reaction, followed by dehydrogenation and anhydride formation. Selective reduction of anhydride 3 with LiAlH(t-BuO)3 gave hyphodermin B 1 in 99% yield. The structure of hyphodermin B 1 was confirmed by X-ray crystallographic analysis. The anhydride 3, bearing a γ-carbonyl group, displayed unexpected reactivity with the anhydride carbonyl closest to the γ-ketone being the most electrophilic site. This was confirmed by HF/6-31G* calculations. In the presence of base, 3 underwent a rearrangement to the novel lactone 16.

Controlled modification of the inorganic and organic bricks in an Al-based MOF by direct and post-synthetic synthesis routes

Four new porous CAU-1 derivatives CAU-1–NH2 ([Al4(OH)2(OCH3)4(BDC–NH2)3]·xH2O, BDC–NH22− = aminoterephthalate), CAU-1–NH2(OH) ([Al4(OH)6(BDC–NH2)3]·xH2O), CAU-1–NHCH3 ([Al4(OH)2(OCH3)4(BDC–NHCH3)3]·xH2O) and CAU-1–NHCOCH3 ([Al4(OH)2(OCH3)4(BDC–NHCOCH3)3]·xH2O) all containing an octameric [Al8(OH)4+y(OCH3)8−y]12+ cluster, with y = 0–8, have been obtained by MW-assisted synthesis and post-synthetic modification. The inorganic as well as the organic unit can be modified. Heteronuclear 1H–15N, 1H–13C and homonuclear 1H–1H connectivities determined by solid-state NMR spectroscopy prove the methylation of the NH2 groups when conventional heating is used. Varying reaction times and temperatures allow controlling the degree of methylation of the amino groups. Short reaction times lead to non-methylated CAU-1 (CAU-1–NH2), while longer reaction times result in CAU-1–NHCH3. CAU-1–NH2 can be modified chemically by using acetic anhydride, and the acetamide derivative CAU-1–NHCOCH3 is obtained. Thermal treatment permits us to change the composition of the Al-containing unit. Methoxy groups are gradually exchanged by hydroxy groups at 190 °C in air. Solid-state NMR spectra unequivocally demonstrate the presence of the amino groups, as well as the successful post-synthetic modification. Furthermore 1H–1H correlation spectra using homonuclear decoupling allow the orientation of the NHCOCH3 groups within the pores to be unravelled. The influence of time and temperature on the synthesis of CAU-1 was studied by X-ray powder diffraction, elemental analyses, and 1H liquid-state NMR and IR spectroscopy.

Synthesis of 4-amino substituted 1,8-naphthalimide derivatives using palladium-mediated amination

Successful amination of 4-bromo-1,8-naphthalimides with 'lengthy' imide N-functionality has been achieved using a general palladium mediated approach (conventional thermal protocols were sub-optimal). Only readily available Pd/ligand combinations were considered and the resulting Buchwald-Hartwig procedure using Pd2(dba)3, Xantphos and Cs 2CO3 is high yielding, relatively mild (40-80 °C, 24 h, yields 50-90%), requires only a modest excess of amine (3.0 equiv) and works equally well with other imide N-substituents. As such, the protocol complements existing methods but is superior for more complex substrates. Herein we compare this Pd mediated approach to the methods most commonly used and further demonstrate its utility by synthesising a number of new, highly fluorescent, 4-aminonaphthalimides. © 2014 Elsevier Ltd. All rights reserved.

Synthesis of N-substituted 4-hydroxynaphthalimides using palladium-catalysed hydroxylation

Successful implementation of a palladium-mediated hydroxylation of N-substituted 4-chloro-1,8-naphthalimides has been achieved. The methodology detailed herein utilises 4-chloro-1,8-naphthalic anhydride as a starting point and implements the catalyst/ligand combination of Pd(OAc)2/t-BuXPhos; all of which are relatively inexpensive. A range of imide substituents tolerated the reaction conditions, including acid sensitive substrates which are not compatible with other existing methodology. As such this approach is not only complimentary to existing procedures, it presents a more direct alternative to accessing 4-hydroxy-1,8-naphthalimides.

Synthesis and in vitro anti Mycobacterium tuberculosis activity of a series of phthalimide derivatives

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Ação de reguladores e estimulantes vegetais na germinação de milho e tomateiro

Reguladores e estimulantes vegetais tem sido utilizados nas condições dos trópicos sem a verificação de seus efeitos sob condições controladas, levando frequentemente ao mascaramento de seus efeitos pelas condições do agroecossistema. Com a finalidade de observar os efeitos dessas substâncias sob condições de laboratório, sementes de Zea mays cv. C-525 e Lycopersicon esculentum cv. Kada foram submetidas aos efeitos de giberelina 100 ppm, chlormequat 2000 ppm, hidrazida maleica 1000 ppm, Agrostemin 1,25 g. l-1 e Atonik 0,5 ml.1-1, além do controle, em caixas de Petri. Observações realizadas 7 e 15 dias após a instalação do ensaio mostraram que giberelina e Agrostemin promoveram aumento no crescimento da radícula e do hipocótilo de milho e tomateiro. Hidrazida maleica inibiu o desenvolvimento da radícula das plântulas de milho. Hidrazida maleica e Atonik tenderam a reduzir o crescimento da radícula e do hipocótilo de tomateiro.