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The biobased polyester poly(ethylene 2,4-furanoate) (2,4-PEF) is a potentially interesting yet insufficiently studied polymer whose resistance to crystallization fundamentally stems from the asymmetric nature of the 2,4-furandicarboxylic acid monomer. A combination of vibrational spectroscopy (infrared, Raman and inelastic neutron scattering) and ab initio calculations has been used to assess the conformational and regiochemistry preferences of 2,4-PEF. The latter polymerizes following a random distribution of monomer orientation, thereby rendering the formation of periodic interchain C-H···O contacts wholly unfeasible and ultimately favoring the formation of randomly coiled chains based on gauche-ethylene glycol segments. In the absence of C-H···O stabilization, the ordered crystalline arrangement is disfavored and polymer chains - adopting several quasi iso-energetic structures - prefer to solidify into an amorphous mess.

A thorough vibrational spectroscopy and molecular modeling study on poly(ethylene 2,5-furandicarboxylate) (PEF) explores its conformational preferences, in the amorphous and crystalline regions, while clarifying structure–property correlations. Despite the increasing relevance of PEF as a sustainable polymer, some of its unique characteristics are not yet fully understood and benefit from a deeper comprehension of its microstructure and intermolecular bonding. Results show that in the amorphous domains, where intermolecular interactions are weak, PEF chains favor a helical conformation. Prior to crystallization, polymeric chains undergo internal rotations extending their shape in a zigzag pattern—an energetically unfavorable geometry which is stabilized by C–H···O bonds among adjacent chain segments. The zigzag conformation is the crystalline motif present in the α and β PEF polymorphs. The energy difference among the amorphous and crystalline chains of PEF is higher than in PET poly(ethylene terephthalat...

MoO2 nanoparticles with tremella-like morphology have been synthesized and characterized. Characterization by powder X-ray diffraction (XRD) and transmission electron micrographs (TEM) microscopy made possible to estimate that the nanosheets have ca. 12 nm and aggregate to form tremella-like structures. The resulting MoO2 nanoparticles were used as catalyst for epoxidation of several olefins. The use of tert-butylhydroperoxide (tbhp), H2O2 and cumenehydroperoxide (chp) as oxygen sources was screened under different reaction conditions, namely, solvent and temperature. The results from the catalytic experiments show that this catalyst was very efficient leading to very high conversion and product selectivity levels. In addition, the use of oxidant:olefin ratios close to 1 show that this catalyst is very efficient conducting olefin epoxidation. Further details are discussed in the work. The catalyst showed overall excellent performance with tbhp. When using H2O2, the catalyst showed good activity, which is very relevant as well. All these achievements contribute with a step forward in the development of more environmentally friendly processes.

Bacterial nanocellulose (BC)-based composites containing poly(2-hydroxyethyl methacrylate) (PHEMA), poly(methacroylcholine chloride) (PMACC) or poly(methacroylcholine hydroxide) (PMACH) were characterized by inelastic neutron scattering (INS) spectroscopy, combined with DFT (density functional theory) calculations of model systems. A reasonable match between calculated and experimental spectral lines and their intensities was used to support the vibrational assignment of the observed bands and to validate the possible structures. The differences between the spectra of the nanocomposites and the pure precursors indicate that interactions between the components are stronger for the ionic poly(methacrylate) derivatives than for the neutral counterpart. Displaced anions interact differently with cellulose chains, due to the different ability to compete with the O&ndash, H&middot, &middot, O hydrogen bonds in cellulose. Hence, the INS is an adequate technique to delve deeper into the structure and dynamics of nanocellulose-based composites, confirming that they are true nanocomposite materials instead of simple mixtures of totally independent domains.

The present work emphasizes the value of periodic density functional theory (DFT) calculations in the assessment of the vibrational spectra of molecular crystals. Periodic calculations provide a nearly one-to-one match between the calculated and observed bands in the inelastic neutron scattering (INS) spectrum of crystalline 4-phenylbenzaldehyde, thus validating their assignment and correcting previous reports based on single molecule calculations. The calculations allow the unambiguous assignment of the phenyl torsional mode at ca. 118&ndash, 128 cm&minus, 1, from which a phenyl torsional barrier of ca. 4000 cm&minus, 1 is derived, and the identification of the collective mode involving the antitranslational motion of CH&middot, &middot, O bonded pairs, a hallmark vibrational mode of systems where C-H&middot, O contacts are an important feature.

The suitability of porous materials to immobilize and release under control bioactive molecules prompted us to design and study delivery systems of Vitamin A (VitA). This molecule, relevant in several physiological functions, is easily oxidized. Commercial VitA was immobilized in two different clays, montmorillonite K-10 (MMT) and sepiolite (SEP), and in MCM-41, by impregnation. Characterization of the resulting hybrid materials by XRD, FTIR and 13C and 29Si (MAS) NMR spectroscopies revealed its presence. The photo-stability tests showed decreased degradation of VitA in the clays, compared to MCM-41 and the pure VitA, while thermostability is observed until ∼100 °C. The kinetics of the release depended on the structural features of the support material and the pH. Sepiolite originated a classic profile of increasing amount of VitA with time, indicating that no oxidation was taking place. In both montmorillonite and MCM-41 the amount of released VitA dropped after ∼2 hours, reflecting oxidation. Oxidation and degradation products obtained when VitA was immobilized in MCM-41, both under nitrogen and in air, were identified by mass spectrometry experiments. Sepiolite is therefore a suitable material to use in controlled release of VitA, since it appears to prevent oxidation.

The organometallic fragment [MoI 2 (CO) 3 ] was coordinated to magnetic iron oxide nanoparticles of different sizes (average size of 11 and 30 nm) which have been previously coated with a silica shell and grafted with a pyridine derivative ligand. The Mo loading was found to be approximately 0.37 wt-% Mo and 0.57 wt-% Mo, corresponding to 0.150 mmol Mo g −1 and 0.230 mmol Mo g −1 for materials MNP 30 -Si-inic-Mo and MNP 11 -Si-inic-Mo , respectively. Preparation of these organometallic decorated magnetic nanoparticles was further confirmed by evidence obtained from extensive characterization by powder XRD, SEM/TEM analysis, as well as from data of 57 Fe Mossbauer and FTIR spectroscopy. Olefin epoxidation of a variety of substrates promoted by these organometallic nano-hybrid materials using tbhp as oxidant, was performed with very good results. The catalytic studies show that the catalysts yield selectively the desired epoxides of a series of olefins. In addition, these catalysts are found to work under a wide temperature range and over several catalytic cycles without notorious performance loss in most cases.

Glucuronolactones were used as precursors for N9 and N7 purine nucleosides containing glucuronic acid derivatives in their structures. Acetylated N-benzylglucofuran- and glucopyranuronamides were synthesized in a few steps from glucofuranurono-6,3-lactone. They were converted into the corresponding furanosyl and pyranosyl uronamide-based nucleosides by N-glycosylation with silylated 2-acetamido-6-chloropurine in the presence of trimethylsilyl triflate. The triacetylated bicyclic lactone was coupled itself with the nucleobase to give bicyclic N9,N7 nucleosides. Tri-O-acetylglucopyranurono-6,1-lactone was used for the first time as a glycosyl donor for N-glycosylation, and led to β-configured N9- and N7-linked purinylglucuronides under reaction conditions similar to those used with the 1-O-acetyl-substituted glycosyl donors. The cholinesterase inhibitory profiles of the synthetic nucleosides bearing glucuronic acid derivatives as glycons were evaluated, and they showed moderate selective acetylcholinesterase inhibitory activities (Ki = 14.78–50.53 μM). The best inhibition was shown by the furanosyl N9-linked uronamide-based purine nucleoside.

Helical mesoporous materials of the MCM-41 type are important materials that can be prepared by onepot synthesis procedures with a co-surfactant. A control of the characteristics at a local level is of the most important in the view of the applications of such materials. However, there are not many studies relating such features with synthetic approaches. In this work, we prepared both helical and regular channel materials from Si-based MCM-41 type. Afterward, a bpy derivative was used as ligand to coordinate MoII/VI. The complexes and the new materials were tested as the catalytic precursors in the epoxidation of cis-cyclooctene, styrene, 1-octene, R-(+)-limonene and trans-hex-2-en-1-ol, using tert-butylhydroperoxide (TBHP) as oxidant. Although almost all the catalysts were 100% selective toward the epoxide, the conversions were in general good. The major achievement of these catalysts is an outstanding stereocontrol of the reaction products. In addition, these catalysts were found to be very effective under several circumstances. This is certainly an important contribution for such concept and may render such materials further applications where chiral recognition is important.

A silsesquioxane cage polymer functionalized with eight chloropropyl arms (1, T8-PrCl) reacted with 2,2′-dipyridiylamine (DPA) to afford a new derivative with eight pendant linear chains (2, T8-Pr-DPA). Further reaction with [Mo(η3-C3H5)Br(CO)2(NCMe)2] afforded another derivative containing three molybdenum units (3, T8-Pr-DPA-Mo), after substitution of the two nitrile ligands in each complex. These are the first silsesquioxane species containing DPA and the Mo(η3-C3H5)Br(CO)2 fragment. The three materials were characterized by 1H, 13C, 29Si, and 95Mo NMR, FTIR, XRD, and elemental analysis, and T8-PrCl (1) was also structurally characterized by single-crystal X-ray diffraction. It was identified as a low-temperature polymorph of this material. Elemental analysis indicated that all Cl atoms in the parent material T8-PrCl (1) were substituted by the deprotonated DPA group in T8-Pr-DPA (2). However, only three [Mo(η3-C3H5)Br(CO)2(DPA)] units were detected in T8-Pr-DPA-Mo (3). A comprehensive NMR study, compl...

The [Mo VI O 2 Cl 2 (thf) 2 ] and [Mo II I 2 (CO) 3 (MeCN) 2 ] precursor complexes, were immobilized in a hybrid periodic mesoporous organosilicas (PMO)-type material. These new hybrid matrix materials were prepared in one pot synthesis, containing the bidentate N , N ′-ligand ( glypy ) in the material. In a second approach, the ordered mesoporous silica MCM- glypy was prepared using a tethered approach by a stepwise procedure. The metal complexes were grafted in both types of materials to obtain heterogeneous pre-catalysts. The modified materials have been characterized by powder X-ray diffraction, N 2 adsorption, and solid-state CP MAS NMR ( 13 C, 29 Si). All metal containing materials were tested as catalysts in epoxidation of 1-octene, cyclooctene and styrene with tert -butylhydroperoxide (TBHP) at 328 K. Selectivity to octene and cyclooctene epoxides was complete. The new PMO materials described in this work are outstanding catalysts for any of the transformations described. In fact, cyclooctene selectivity based on TBHP consumption is found to be almost independent of the mol ratio attesting the efficiency of the catalysts. They are also effective under stoichiometric olefin/oxidant ratio. In addition, a mechanism for acid catalyzed benzaldehyde formation is proposed as well as the conversion of Mo(II) to Mo(VI) under catalysis.

Dioxygenated cyclopentenones are versatile building blocks for the synthesis of several natural products. Herein we report a direct asymmetric synthesis of trans-4,5-dioxygenated cyclopentenone derivatives through base-catalyzed rearrangement of pyranones followed by dynamic kinetic resolution. Milder conditions than previously reported for this rearrangement have been found regarding amine base catalysis, solvent and temperature effects. All data supports a mechanism involving cyclization of an intermediate formed by electrocyclic ring opening of a pyranone-derived enol. We have developed conditions for asymmetric synthesis of trans-4-tert-butoxy-5-hydroxycyclopent-2-enone, in 81% yield and 95% ee, and analogous dioxygenated cyclopentenones, via a lipase induced dynamic kinetic resolution.

[Mo(η3-C3H5)X(CO)2(NCCH3)2] (X = Br, 1a; X = Cl, 1b) complexes reacted with the bidentate ligand RN C(Ph)–C(Ph) NR, R = (CH2)2CH3 (DAB, 2) affording [Mo(η3-C3H5)X(CO)2(DAB)] (X = Br, 4a; X = Cl, 4b), which were characterized by elemental analysis, FTIR and 1H and 13C NMR spectroscopy. The modified silylated ligand RN C(Ph) C(Ph) NR, R = (CH2)3Si(OCH2CH3)3 (DAB–Si, 3), was used to immobilize the two complexes in MCM-41 (MCM) mesoporous silica. The new materials were characterized by powder X-ray diffraction, N2 adsorption analysis, FTIR and 29Si and 13C CPMAS solid state NMR spectroscopy. Both the materials and the complexes were tested in the oxidation of cyclooctene and styrene and behaved as active catalyst precursors for cyclooctene and styrene epoxidation with TBHP (t-butylhydroperoxide), leading selectively to epoxides with high conversions and TOFs. Although the homogeneous systems reach 100% conversion of cyclooctene and slightly less for styrene, the loss of catalytic activity in the heterogeneous systems is small, with a 98% conversion of styrene achieved by the chloride containing material.

[MoX 2 (CO) 3 (pyca)] (X = I, Br) complexes bearing the ligand C 5 H 4 NCH N(CH 2 ) 2 CH 3 (pyca, 2 ) were prepared and characterized by elemental analysis as well as FTIR and 1 H and 13 C solution NMR spectroscopy. Using the modified ligand C 5 H 4 NCH N(CH 2 ) 3 Si(OEt) 3 (pycaSi, 3 ), they were immobilized in MCM-41 ( MCM ) and in mesoporous materials (i.e., periodic mesoporous organosilica [PMO]) and then characterized by powder X-ray diffraction, N 2 adsorption analysis, FTIR, and 29 Si MAS and CP MAS and 13 C CP MAS solid-state NMR spectroscopy. These new materials and complexes were tested in the oxidation of cyclohexene, cyclooctene, and styrene and in the polymerization of styrene and norbornene. All were good catalyst precursors for olefin epoxidation with TBHP ( t -butylhydroperoxide), leading selectively to epoxides with high conversions and TOFs and achieving high conversions in the second run. This finding, combined with the fact that the materials outperformed the homogeneous complexes, make these catalysts very attractive. They combine the selectivity and activity of the homogeneous species with the features of materials. The iodine-containing materials performed better for styrene (100% conversion), and the bromine-containing materials displayed higher conversion for cyclooctene.

Complex fac-[Re{κ3-H(µ-H)2B(timMe)}(CO)3] (1) (timMe = 2-mercapto-1-methylimidazolyl) promptly reacts with the neutral substrates PPh3, tBuNC and EtOOCCH2NC yielding fac-[Re{κ2-H2(µ-H)B(timMe)}(L)(CO)3] (L = PPh3(2), (tBuNC) (3), (EtOOCCH2NC) (4)). Complexes 2−4 have been fully characterized, including by variable-temperature NMR studies and X-ray diffraction analysis in the case of 2. Unlike 1, complexes 2−4 are fluxional in solution undergoing a dynamic process that accounts for the magnetic equivalence of all the B−H hydrogen atoms at room temperature. Compounds 1 and 2 were studied by DFT methods to explain the different solution behavior of the complexes anchored by (κ2-H,S) and (κ3-H,H′,S) soft scorpionates.

New Mo(II) diimine derivatives of [Mo(η3-allyl)X(CO)2(CH3CN)2] (allyl = C3H5 and C5H5O; X = Cl, Br) were prepared, and [Mo(η3-C3H5)Cl(CO)2(BIAN)] (BIAN = 1,4-(4-chloro)phenyl-2,3-naphthalenediazabutadiene) (7) was structurally characterized by single-crystal X-ray diffraction. This complex adopted an equatorial−axial arrangement of the bidentate ligand (axial isomer), in contrast with the precursors, found as the equatorial isomer in the solid and fluxional in solution. The new complexes of the type [Mo(η3-allyl)X(CO)2(N−N)] (N−N is a bidentate chelating dinitrogen ligand) were tested for the catalytic epoxidation of cyclooctene using tert-butyl hydroperoxide as oxidant. All catalytic systems were 100% selective toward epoxide formation. While their turnover frequencies paralleled those of related Mo(II) carbonyl compounds or Mo(VI) compounds bearing similar N-donor ligands, they exhibited similar olefin conversions in consecutive catalytic runs. The acetonitrile precursors were generally more active than...

Organic-inorganic mesoporous materials of the MCM-41 type are important materials that can be prepared by either post-synthesis or one-pot synthesis procedures. A complete control of the characteristics at a local level is of the utmost importance in view of the applications of such materials. However, there are not many studies relating such features with synthetic approaches. In this work, we prepared samples by post-synthesis derivatization of materials from Si-based MCM-41, with bidentate nitrogen ligands bearing one or two silylated arms, and by one-pot synthesis of organic-inorganic hybrid materials. The bulk properties of the two kinds of materials were comparable. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and Raman spectroscopy were used to investigate the local environment, namely, the number of OH groups and distribution of SiO 4 units (large and small ring units). Hydrophilicity correlates with both the type of organic moiety used (mono- or disily-lated), as well as with the synthetic procedure. The same vibrational studies showed how the structure in the channels changes as a function of pressure, reflecting the low mechanical stability of the mesoporous materials.

2-O-Acyl protected-d-ribo-3-uloses reacted with [(ethoxycarbonyl)methylene]triphenylphosphorane in acetonitrile to afford regio- and stereoselectively 2-(Z)-alkenes in 10–60 min under microwave irradiation. This domino reaction is proposed to proceed via tautomerization of 3-ulose to enol, acyl migration, tautomerization to the 3-O-acyl-2-ulose, and Wittig reaction. Alternatively, in chloroform, regioselective 3-olefination of 2-O-pivaloyl-3-uloses gave (E)-alkenes, key precursors for the miharamycins’ bicyclic sugar moiety.

The synthesis of new pseudo‐C‐nucleosides was accomplished starting from 3‐O‐benzyl‐1,2‐O‐isopropylidene‐α‐D‐ribo‐pentodialdo‐1,4‐furanose, aiming to build thiazole, triazole, tetrazole, and thiazolidinone derivatives. The stereochemistry of the thiazolidinone epimers was confirmed by DFT/B3LYP calculations. The well‐known diversity of biological activities exhibited by compounds with these heterocyclic moieties in their structure encouraged the investigation of the insecticidal activity against Musca domestica. The thiazole derivative was efficient as insecticide with LD50=6.7 ng/g, which is in the order of the LD50 values for pyrethroids on the same insect. All the compounds tested showed knockdown, mediated through action on the insect nervous system. The neuroactivity found in insects has motivated the evaluation of the inhibition of acetylcholinesterase and butyrylcholinesterase. The two thiazolidinone derivatives tested inhibited butyrylcholinesterase from human serum (36% and 22%), while inhibition...

Three new mononuclear oxovanadium(IV) complexes [VO(acac)(R-BIAN)]Cl (BIAN = 1,2-bis{(R-phenyl)imino} acenaphthene, R = H, 1; CH3, 2; Cl, 3) were prepared and characterized. They promoted the catalytic oxidation of olefins such as cyclohexene, cis-cyclooctene, and styrene with both tbhp (tert-butylhydroperoxide) and H2O2, and of enantiopure olefins (S(-)- and R(+)-pinene, and S(-)- and R(+)-limonene) selectively to their epoxides, with tbhp as the oxidant. The TOFs for styrene epoxidation promoted by complex 3 with H2O2 (290 mol mol(-1)V h(-1)) and for cis-cyclooctene epoxidation by 2 with tbhp (248 mol mol(V)(-1) h(-1)) are particularly good. Conversions reached 90% for several systems with tbhp, and were lower with H2O2. A preference for the internal C=C bond, rather than the terminal one, was found for limonene. Kinetic data indicate an associative process as the first step of the reaction and complex [VO(acac)(H-BIAN)](+) (1(+)) was isolated in an FTICR cell after adding tbhp to 1. EPR studies provide evidence for the presence of a V(IV) species in solution, until at least 48 hours after the addition of tbhp and cis-cyclooctene, and cyclic voltammetry studies revealed an oxidation potential above 1 V for complex 1. DFT calculations suggest that a [VO(H-BIAN)(MeOO)](+) complex is the likely active V(IV) species in the catalytic cycle from which two competitive mechanisms for the reaction proceed, an outer sphere path with an external attack of the olefin at the coordinated peroxide, and an inner sphere mechanism starting with a complex with the olefin coordinated to vanadium.

Some antioxidant mechanisms displayed by several phenolic compounds relate with OH bond dissociation energy. One way for its determination, in the gas-phase, relies on acidity measurements. Gas-phase acidities were determined experimentally, applying the kinetic method, for chromanol and four dimethoxyphenols, and theoretically through quantum chemical DFT calculations for chromanol, six dimethoxyphenols and 3,4,5-trimethoxyphenol. The experimental acidity order, 2,3-dimethoxyphenol > 3,5-dimethoxyphenol > 2,6-dimethoxyphenol > 3,4-dimethoxyphenol ≈ phenol > chromanol shows good agreement with the theoretical acidity order, 2,5-dimethoxyphenol > 2,3-dimethoxyphenol > 3,4,5-trimethoxyphenol > 3,5-dimethoxyphenol ≈ 2,4-dimethoxyphenol > 2,6-dimethoxyphenol > 3,4-dimethoxyphenol > phenol > chromanol. These acidity trends were rationalized in terms of the substituent effects on the thermodynamic stabilities both of the parent phenols and the corresponding phenoxide ions. DFT calculations also evidenced the occurrence of intramolecular C-H···O hydrogen bonds whenever there are vicinal substituents (either OH, O(-) or OCH(3)) which induce further stabilization of the geometries.

Spectroscopic evidence for C-H...O hydrogen bonding in chloroform...acetone [Cl(3)CH...O=C(CH(3))(2)] mixtures was obtained from vibrational inelastic neutron scattering (INS) spectra. Comparison between the INS spectra of pure samples and their binary mixtures reveals the presence of new bands at about 82, 130 and 170 cm(-1). Assignment of the 82 cm(-1) band to the nuO...H anti-translational mode is considered and discussed. In addition, the betaC-H mode of CHCl(3) at 1242 cm(-1) is split in the spectra of the mixtures, and the high-wavenumber component is assigned to the hydrogen-bonded complex. The plot of the integrated intensity of this component shows a maximum for x=0.5, in agreement with the 1:1 stoichiometry of the chloroformacetone complex, with a calculated complexation constant of 0.15 dm(3) mol(-1). Results also show that the complex behaves as an independent entity, that is, despite being weak, such interactions play a key role in supramolecular chemistry.