On the dissolution state of cellulose in cold alkali solutions

We have characterized the dissolved state of microcrystalline cellulose (MCC) in cold alkali [2.0 M NaOH(aq)] solutions using a combination of small angle X-ray (SAXS) and static light scattering (SLS), \(^1\)H NMR, NMR self-diffusion, and rheology experiments. NMR and SAXS data demonstrate that the cellulose is fully molecularly dissolved. SLS, however, shows the presence of large concentration fluctuations in the solution, consistent with significant attractive cellulose-cellulose interactions. The scattering data are consistent with fractal cellulose aggregates of micrometre size having a mass fractal dimension \(D\sim 1.5\). At 25\(\,^{\circ }\mathrm {C}\) the solution structure remains unchanged on the time scale of weeks. However, upon heating the solutions above 35\(\,^{\circ }\mathrm {C}\) additional aggregation occurs on the time scale of minutes. Decreasing or increasing the NaOH concentration away from the “optimum” 2 M also leads to additional aggregation. This is seen as an increase of the SAXS intensity at lower q values. Addition of urea (1.8 and 3.6 M, respectively) does not significantly influence the solution structure. With these examples, we will discuss how scattering methods can be used to assess the quality of solvents for cellulose.     

An extrapolation procedure to obtain the total fringe number from Gouy fringe pattern data

A rapid new procedure is described for getting the total number of fringes J from Gouy fringe pattern data. This PQ method is exact and the results excellent (within 0.01–0.03 fringe) for ideal systems (_j=0 for all j, Q₀=0). Such systems include most binaries; for these, the diffusion coefficient is either constant or a polynomial function of concentration with small concentration differences. For multicomponent systems and some binaries, Q₀ can be significantly different from 0. In these cases, the PQ method unambiguously gives the integer number of fringes. If in addition Q₀/Q₁ is larger than 2.0, then J obtained from a second extrapolation procedure is also good.     

N^N^C platinum(II) and palladium(II) cyclometallates of 6,6′-diphenyl-2,2′-bipyridine, L: Crystal and molecular structure of [Pd(L-H)Cl]

Reaction of K₂[PtCl₄] or Na₂[PdCl₄] with 6,6′-diphenyl-2,2′-bipyridine, L, gives the cyclometallated species [Pt(L-H)Cl], 1, and [Pd(L-H)Cl], 2, respectively, where L-H is a terdentate N^N^C anionic ligand originated by direct activation of a C(sp²)-H bond. The crystal structure of 2 has been solved by X-ray diffraction and compared to that of the analogous complex [Pd(L′-H)Cl] L′ = 6-phenyl-2,2′-bipyridine. The second phenyl ring in 2 entails a considerable distortion of the coordination around the metal. A similar distortion is also to be expected in the analogous compound 1, due to the almost equal covalent radii of palladium(II) and platinum(II).From the complexes 1 and 2 the chloride can be displaced with AgBF₄ and substituted by CO or PPh₃ to give the corresponding cationic species. By reaction of 1 with Na[BH₄] substitution of H⁻ for Cl⁻ can be achieved: the rare hydrido complex [Pt(L-H)H], stabilized only by nitrogen ligands, was isolated in the solid state and fully characterized in solution. It is noteworthy that in the case of the 6-phenyl-2,2′-bipyridine the analogous terminal hydride [Pd(L′-H)H] is unstable. In platinum chemistry the reaction of 6-substituted 2,2′-bipyridines is known to give either N^N^C or N′^C(3) rollover cyclometallation, depending on the nature of the metal precursor. In the case of 6,6′-Ph₂-2,2′-bipy cyclometallation was also shown to undergo multiple C-H activation giving the C^N^C pincer complex [Pt(L-2H)(DMSO)]. The latter species can be related to complex 1: indeed its reaction with HCl produces complex 1 and [Pt(L-H)(DMSO)Cl], a rollover species with a pendant phenyl substituent.     

Syntheses of chromium tricarbonyl organometals of 1-methyl-naphthalene and different polycyclic aromatic hydrocarbons,characterisation of the (C11H10)Cr(CO)3 isomers and the crystal structure of the [(η6-5,6,7,8,9,10-C11H10)Cr(CO)3] complex

The synthesis of organometal complexes from chromium hexacarbonyl with 1-methyl-naphthalene ligand is reported. Two arene-chromium-tricarbonyl isomers are formed at competitive yields, featured with the metal fragment coordinated to both the methylated and the benzenic aromatic ring. A single-crystal X-ray diffraction measurement has been performed on the [(η⁶-5,6,7,8,9,10-C₁₁H₁₀)Cr(CO)₃] isomer, which presents the metal carbonyl moiety attached to the benzenic arene ligand. The products of reaction have been studied by UV–VIS–NIR, fluorescence and ¹H NMR spectroscopies. A detailed vibrational characterisation by mean of experimental FT-IR and Raman spectroscopy and DFT calculations is reported. The electron ligand donation to the metal carbonyl system, determined by FT-IR spectroscopy, has been related to the actual decrease of resonance energy of the aromatic hydrocarbon in the complex and compared with other chromium tricarbonyl complexes of different polycyclic aromatic hydrocarbons provided with the naphthalenic moiety.     

Expeditious convergent procedure for the preparation of bis(POC) prodrugs of new (E)-4-phosphono-but-2-en-1-yl nucleosides

A series of unsaturated acyclonucleoside bis(POC) prodrugs of E configuration were synthesized through an expeditious, highly efficient and stereoselective one-step procedure from corresponding bis(POC)allylphosphonate through Ru catalyzed cross-coupling metathesis reaction. The [RuCl₂(PCy₃)(SIPr)(Indenylidene)] and [RuCl₂(PCy₃)(IMes)(benzylidene)] catalysts were employed; the unsaturated ANP were used bore C5-halovinyl uracil, C5-dihalovinyluracil or furanopyrimidine motifs. The chemical cleavage of biolabile (POC) group is a useful pathway to acid phosphonate derivatives.     

Exploiting Free‐Energy Minima to Design Novel EphA2 Protein–Protein Antagonists: From Simulation to Experiment and Return

The free‐energy surface (FES) of protein–ligand binding contains information useful for drug design. Here we show how to exploit a free‐energy minimum of a protein‐ligand complex identified by metadynamics simulations to design a new EphA2 antagonist with improved inhibitory potency.     

Effective cell uptake of nanoassemblies of a fluorescent amphiphilic cyclodextrin and an anionic porphyrin

An emitting nanoassembly composed of a novel amphiphilic cyclodextrin functionalised with a covalently appended fluorophore and an anionic porphyrin internalizes effectively in tumor cells, allowing simultaneously the detection of carrier and photosensitiser.     

Determination of the relative stereochemistry of flexible organic compounds by Ab initio methods: conformational analysis and Boltzmann-averaged GIAO 13C NMR chemical shifts

Ab initio calculations at the Hartree-Fock level with full-geometry optimization using the 6-31G(d) basis set, and GIAO (gauge including atomic orbitals) (13)C NMR chemical shifts, are presented here as a support in the study of the stereochemistry of low-polar organic compounds having an open-chain structure. Four linear stereoisomers, fragments of a natural product previously characterized by experimental (13)C NMR spectra, which possesses three stereogenic centers, 11 carbon atoms, and 38 atoms in total, were considered. Conformational searches, by empirical force-field molecular dynamics, pointed out the existence of 8-13 relevant conformers per stereoisomer. Thermochemical calculations at the ab initio level in the harmonic approximation of the vibrational modes, allowed the evaluation, at 298.15 K, of the standard Gibbs free energy of the conformers. The (13)C NMR chemical shift of a given carbon atom in each stereoisomer was considered as the average chemical shift value of the same atom in the different conformers. The averages were obtained by the Boltzmann distribution, using the relative standard free energies as weighting factors. Computed parameters related to linear correlation plots of experimental (13)C chemical shifts versus the corresponding computed average data allowed us to distinguish among the four stereoisomers.