Biomedical applications of functionalised carbon nanotubes

The organic functionalisation of carbon nanotubes can improve substantially their solubility and biocompatibility profile; as a consequence, their manipulation and integration into biological systems has become possible so that functionalised carbon nanotubes hold currently strong promise as novel systems for the delivery of drugs, antigens and genes.     

Theoretical modeling of vibroelectronic quantum states in complex molecular systems: solvated carbon monoxide, a test case

In this paper we extend the perturbed matrix method by explicitly including the nuclear degrees of freedom, in order to treat quantum vibrational states in a perturbed molecule. In a previous paper we showed how to include, in a simple way, nuclear degrees of freedom for the calculation of molecular polarizability. In the present work we extend and generalize this approach to model vibroelectronic transitions, requiring a more sophisticated treatment.     

Mechanochemical assembly of hydrogen bonded organic-organometallic solid compounds

Solvent-free reactions with molecular systems have been exploited to prepare hybrid organic-organometallic solids: grinding of the complex [Fe(eta 5-C5H4COOH)2] with solid bases B generates quantitatively the corresponding hydrogen bonded salts [Fe(eta 5-C5H4COOH)(eta 5-C5H4COO)][HB] (B = 1,4-diazabicyclo[2.2.2]octane, 1,4-phenylenediamine); gas-solid reactions are also possible with volatile bases.     

Experimental and DFT studies of the conversion of ethanol and acetic acid on PtSn-based catalysts

Reaction kinetics studies were conducted for the conversions of ethanol and acetic acid over silica-supported Pt and Pt/Sn catalysts at temperatures from 500 to 600 K. Addition of Sn to Pt catalysts inhibits the decomposition of ethanol to CO, CH4, and C2H6, such that PtSn-based catalysts are active for dehydrogenation of ethanol to acetaldehyde. Furthermore, PtSn-based catalysts are selective for the conversion of acetic acid to ethanol, acetaldehyde, and ethyl acetate, whereas Pt catalysts lead mainly to decomposition products such as CH4 and CO. These results are interpreted using density functional theory (DFT) calculations for various adsorbed species and transition states on Pt(111) and Pt3Sn(111) surfaces. The Pt3Sn alloy slab was selected for DFT studies because results from in situ (119)Sn M?ssbauer spectroscopy and CO adsorption microcalorimetry of silica-supported Pt/Sn catalysts indicate that Pt-Sn alloy is the major phase present. Accordingly, results from DFT calculations show that transition-state energies for C-O and C-C bond cleavage in ethanol-derived species increase by 25-60 kJ/mol on Pt3Sn(111) compared to Pt(111), whereas energies of transition states for dehydrogenation reactions increase by only 5-10 kJ/mol. Results from DFT calculations show that transition-state energies for CH3CO-OH bond cleavage increase by only 12 kJ/mol on Pt3Sn(111) compared to Pt(111). The suppression of C-C bond cleavage in ethanol and acetic acid upon addition of Sn to Pt is also confirmed by microcalorimetric and infrared spectroscopic measurements at 300 K of the interactions of ethanol and acetic acid with Pt and PtSn on a silica support that had been silylated to remove silanol groups.     

The state of conservation of painted surfaces in the presence of accelerated ageing processes monitored by use of FT-Raman spectroscopy and multivariate control charts

A new method has been developed for monitoring the degradation of paintings. Two inorganic pigments (ultramarine blue and red ochre) were blended with linseed oil and spread on canvas. Each canvas was subjected to simulated accelerated ageing in the presence of typical degradation agents (UV radiation and acidic solution). Periodically the painted surfaces were analysed by FT-Raman, to investigate the status of the surface. The data obtained were analysed by principal component analysis (PCA). Finally the Shewhart and cumulative sum control charts based on the relevant principal components (PC) and the so called scores monitoring and residuals tracking (SMART) charts were built. The method based on the use of PC to describe the process was found to enable identification of the presence of relevant modification occurring on the surface of the samples studied.Electronic supplementary material Supplementary material is available for this article at     

A theoretical study of the lowest electronic states of azobenzene: the role of torsion coordinate in the cis–trans photoisomerization

In the present paper we report the results of a multiconfigurational computational study on potential-energy curves of azobenzene along the NN twisting to clarify the role of this coordinate in the decay of the S₂(*) and S₁(n*) states. We have found that there is a singlet state, S₃ at the trans geometry, on the basis of the doubly excited configuration n²*², that has a deep minimum at about 90° of twisting, where it is the lowest excited singlet state. The existence of this state provides an explanation for the short lifetime of S₂(*) and for the wavelength-dependence of azobenzene photochemistry. We have characterized the S₁(n*) state by calculating its vibrational frequencies, which are found to correspond to the recently observed transient Raman spectrum. We have also computed the potential-energy curve for the triplet T₁(n*) at the density functional theory B3LYP level, which indicates that in this state the isomerization occurs along the twisting coordinate.Acknowledgement The financial support from MIUR (project Modellistica delle proprietà spettroscopiche di sistemi molecolari complessi funds ex 60% and project Dinamiche molecolari in sistemi di interesse chimico funds ex 40%), from the University of Bologna (Funds for Selected Research Topics) is gratefully acknowledged.Contribution to the Jacopo Tomasi Honorary Issue     

4-Amino-1-oxyl-2,2,6,6-tetramethylpiperidine-3-carboxylic acid (β-TOAC), the first spin-labelled, cyclic, chiral β-amino acid resolved in an enantiomerically pure state

Amination of 3-carboxymethyl-1-oxyl-2,2,6,6-tetramethyl-4-piperidone with (R)-α-methylbenzylamine, NaBH₃CN reduction of the resulting enamine and removal of the chiral auxiliary from the separated diastereoisomers, led to enantiomerically pure (3S,4S) and (3R,4R) methyl 4-amino-1-oxyl-2,2,6,6-tetramethylpiperidine-3-carboxylates.     

A new enzyme model for enantioselective esterases based on molecularly imprinted polymers

An efficient enzyme model exhibiting enantioselective esterase activity was prepared by using molecular imprinting techniques. The enantiomerically pure phosphonic monoesters 4 L and 5 L were synthesized as stable transition-state analogues. They were used as templates connected by stoichiometric noncovalent interactions to two equivalents of the amidinium binding site monomer 1. After polymerization and removal of the template, the polymers were efficient catalysts for the hydrolysis of certain nonactivated amino acid phenylesters (2 L, 2 D, 3 L, 3 D) depending on the template used. Imprinted catalyst IP4 (imprinted with 4 L) enhanced the hydrolysis of the corresponding substrate 2 L by a factor of 325 relative to that of a buffered solution. Relative to a control polymer containing the same functionalities, prepared without template 4 L, the enhancement was still about 80-fold, showing the highest imprinting effect up to now. In cross-selectivity experiments a strong substrate selectivity of higher than three was found despite small differences in the structure of the substrate and template. Plots of initial velocities of the hydrolysis versus substrate concentration showed typical Michaelis-Menten kinetics with saturation behavior. From these curves, the Michaelis constant K(M) and the catalytic constant k(cat) can be calculated. The enantioselectivity shown in these values is most interesting. The ratio of the catalytic efficiency k(cat)/K(M), between the hydrolysis of 2 L- and 2 D-substrate with IP4, is 1.65. This enantioselectivity derives from both selective binding of the substrate (K(M)L/K(M)D=0.82), and from selective formation of the transition state (k(cat)L/k(cat)D=1.36). Thus, these catalysts give good catalysis as well as high imprinting and substrate selectivity. Strong competitive inhibition is caused by the template used in imprinting. This behavior is also quite similar to the behavior of natural enzymes, for which these catalysts are good models.     

Verbindungen A3M5 (A = Erdalkalimetall,M = Triel/Tetrel): Eine Fallstudie zur strukturellen und elektronischen Stabilität polarer intermetallischer Phasen

Compounds A₃M₅ (A = alkaline earth, M = triel/tetrel): A Case Study on Structural and Electronic Factors Stabilizing Polar Intermetallics Starting from the non electron precise binary compounds Ca₃Ga₅/Sr₃In₅ (Hf₃Ni₂Si₃ type) and Ba₃Al₅ at one hand and Ba₃Pb₅ (Pu₃Pd₅ type) at the other hand, a series of new ternary intermetallics of the general formula A₃M₅ (A: alkaline earth, M: triel/tetrel) has been synthesized, structurally characterized and studied by band structure calculations. The chemical substitution of M in A₃M₅ allows, via the continous variation of the radius ratio (r_A:r_M) and the valence electron number (VE/M) the detection of the geometrically and electronically determined stability ranges of the three structure types formed by the binary compounds. At values of r_A:r_M between 1.30 and 1.52 in the triel rich region of A₃M′_xM″_5?x the Hf₃Ni₂Si₃ type (orthorhombic, space group Cmcm) is formed: In Ca₃Ga₅ up to 1.8 Ga can be substituted by Al, in Sr₃In₅ similar amount of In can be replaced by either Al or Ga. The mixed trielide Sr₃Al_2.6Ga_2.4 (a = 468.4(1), b = 1132.5(1), c = 1570.0(2) pm, R1 = 0.0261) can be obtained, although both corresponding binary phases are not known. At larger values of the ratio r_A/r_M as in Ba₃Al₃Ga₂ (Ba₃Al₅ type, hexagonal, space group P6₃/mmc, a = 598.9(1), c = 1456.0(3) pm, R1 = 0.0353) layers of condensed M₅ building blocks with Al‐Al partial bonds are formed. Substituting one In position in Sr₃In₅ against Pb results in the isotypic, but electron precise Zintl compound Sr₃In₄Pb (a = 506.1(1), b = 1191.8(3), c = 1650.2(4) pm, R1 = 0.0286), where the Fermi level in shifted into a distinct minimum of the density of states. Conversely, at the tetrele rich end of the series A₃In_xPb_5?x, characterized by compounds of the Pu₃Pd₅ type (orthorhombic, space group Cmcm) with almost isolated nido clusters M₅, a minimum of the DOS can be reached, if Pb is partially substituted by In (A₃In_xPb_5?x with A = Sr/Ba: x = 0.7/0.6; a = 1084.6(2)/1118.6(2), b = 867.1(2)/904.4(1), c = 1104.8(2)/1133.9(2) pm, R1 = 0.0394/0.0434).     

Evaluation of a synergetic effect between Rh as permanent chemical modifier and acetylacetone as complexing agent in Sc determination in sediment slurry samples by ETAAS

In the present work, scandium was determined in sediment slurry samples (from three different rivers) by electrothermal atomic absorption spectrometry (ETAAS). Slurries were prepared by weighting 100 mg of dry sediment samples (≤53 μm particle sizes) and adding 6 ml of HCl:HNO₃:HF (3:1:2, v/v). Accurate results were only possible due to the synergetic effect between Rh as permanent chemical modifier and acetylacetone (Acac) as complexing agent. The same platform was used for 400 heating cycles. The performance of the chemical modification was evaluated by using scanning electron microscopy (SEM), synchrotron radiation X-ray fluorescence (SRXRF) and some figures of merit (precision and detectability). The best analytical conditions were attained using 1500 and 2550 °C as pyrolysis and atomization temperatures. The scandium content in the liquid phase of the slurries ranged from 61 to 73%, thus indicating, in this study, that both liquid and solid phases play an important role in slurry analyses. An amount of 5.0–20.0 μg l⁻¹ Sc linear range as well as LOD and LOQ of 0.19 and 0.62 μg l⁻¹, respectively, were obtained under these conditions. The accuracy was checked by using microwave-assisted decomposition, and the results compared to those obtained with the proposed methodology (slurry analysis). By checking both sets of the results, there is no statistical difference at the 95% confidence levels.