Search results for "chemical science"
showing 10 items of 9771 documents
Sur la piste des matériaux organiques grâce à la spectrométrie de masse
2018
Identifying the organic materials present, establishing their origin and degree of preservation, understanding their manufacturing process and their use, all of which require interdisciplinary studies involving closely specialists in materials and human sciences. In this very specific context, mass spectrometry has become a key tool to improve knowledge of past civilizations but also to better preserve and restore the discrete remains of archaeomaterials. The identification of diagnostic molecular markers of natural substances is now a recognized strategy for characterizing amorphous organic materials (fats, beeswaxes, vegetable substances such as resins and tars). New advances have also ma…
Polymorphism and Metallic Behavior in BEDT-TTF Radical Salts with Polycyano Anions
2012
Up to five different crystalline radical salts have been prepared with the organic donor BEDT-TTF and three different polynitrile anions. With the polynitrile dianion tcpd2− (=C[C(CN)2]32−), two closely related radical salts: α'-(ET)4tcpd·THF (1) (THF = tetrahydrofurane) and α'-(ET)4tcpd·H2O (2) have been prepared, depending on the solvent used in the synthesis. With the mono-anion tcnoetOH− (=[(NC)2CC(OCH2CH2OH)C(CN)2]−) two polymorphs with similar physical properties but different crystal packings have been synthesized: θ-(ET)2(tcnoetOH) (3) and β''-(ET)2(tcnoetOH) (4). Finally, with the mono-anion tcnoprOH− (=[(NC)2CC(OCH2CH2CH2OH)C(CN)2]−) we have prepared a metallic…
Chemoselective, Substrate-directed Fluorination of Functionalized Cyclopentane β-Amino Acids
2016
This work describes a substrate-directed fluorination of some highly functionalized cyclopentane derivatives. The cyclic products incorporating CH2 F or CHF2 moieties in their structure have been synthesized from diexo- or diendo-norbornene β-amino acids following a stereocontrolled strategy. The synthetic study was based on an oxidative transformation of the ring carbon-carbon double bond of the norbornene β-amino acids, followed by transformation of the resulted "all cis" and "trans" diformyl intermediates by fluorination with "chemodifferentiation".
Monitoring Biological Damage on Paper-based Documents in the Historical Archive of the Palermo Astronomical Observatory
2017
Libraries and archives house a wide variety of documents made of materials of vegetal and animal origin: unbound papers and books, manuscripts and printed books, photographs (negative and positive), prints, maps, available to the public for reading needs, study and information. These materials are often subject to fluctuations in environmental and micro-environmental parameters. For this reason, it is essential to implement constant monitoring and control of environmental conditions and potential deteriogens in order to slow down deterioration processes. The monitoring of the microbial degradation of paper documents in the Historical Archives of Palermo Astronomical Observatory has revealed…
A magnetic look into the protecting layer of Au25 clusters
2016
The field of molecular metal clusters protected by organothiolates is experiencing a very rapid growth. So far, however, a clear understanding of the fine interactions between the cluster core and the capping monolayer has remained elusive, despite the importance of the latter in interfacing the former to the surrounding medium. Here, we describe a very sensitive methodology that enables comprehensive assessment of these interactions. Pulse electron nuclear double resonance (ENDOR) was employed to study the interaction of the unpaired electron with the protons of the alkanethiolate ligands in four structurally related paramagnetic Au25(SR)0 18 clusters (R ¼ ethyl, propyl, butyl, 2-methylpro…
Enhancing Light Emission in Interface Engineered Spin-OLEDs through Spin-Polarized Injection at High Voltages
2019
The quest for a spin-polarized organic light-emitting diode (spin-OLED) is a common goal in the emerging fields of molecular electronics and spintronics. In this device, two ferromagnetic (FM) electrodes are used to enhance the electroluminescence intensity of the OLED through a magnetic control of the spin polarization of the injected carriers. The major difficulty is that the driving voltage of an OLED device exceeds a few volts, while spin injection in organic materials is only efficient at low voltages. The fabrication of a spin-OLED that uses a conjugated polymer as bipolar spin collector layer and ferromagnetic electrodes is reported here. Through a careful engineering of the organic/…
Functional Extrapolations to Tame Unbound Anions in Density-Functional Theory Calculations
2019
Standard flavors of density-functional theory (DFT) calculations are known to fail in describing anions, due to large self-interaction errors. The problem may be circumvented using localized basis sets of reduced size, leaving no variational flexibility for the extra electron to delocalize. Alternatively, a recent approach exploiting DFT evaluations of total energies on electronic densities optimized at the Hartree-Fock (HF) level has been reported, showing that the self-interaction-free HF densities are able to lead to an improved description of the additional electron, returning affinities in close agreement with the experiments. Nonetheless, such an approach can fail when the HF densitie…
Structures and energetic properties of 4-halobenzamides
2018
The amide bond represents one of the most fundamental functional groups in chemistry. The properties of amides are defined by amidic resonance (nN→π*C=O conjugation), which enforces planarity of the six atoms comprising the amide bond. Despite the importance of 4-halo-substituted benzamides in organic synthesis, molecular interactions and medicinal chemistry, the effect of 4-halo-substitution on the properties of the amide bond in N,N-disubstituted benzamides has not been studied. Herein, we report the crystal structures and energetic properties of a full series of 4-halobenzamides. The structures of four 4-halobenzamides (halo = iodo, bromo, chloro and fluoro) in the N-morpholinyl series h…
Rational Chemical Multifunctionalization of Graphene Interface Enhances Targeted Cancer Therapy
2020
The synthesis of a drug delivery platform based on graphene was achieved through a step‐by‐step strategy of selective amine deprotection and functionalization. The multifunctional graphene platform, functionalized with indocyanine green, folic acid, and doxorubicin showed an enhanced anticancer activity. The remarkable targeting capacity for cancer cells in combination with the synergistic effect of drug release and photothermal properties prove the great advantage of a combined chemo‐ and phototherapy based on graphene against cancer, opening the doors to future therapeutic applications of this type of material.
Indirect chronology method employing rare earth elements to identify Sagunto Castle mortar construction periods
2017
A novel indirect chronology method has been developed to identify Sagunto Castle construction periods. The method is based on the use of inductively coupled plasma mass spectrometry (ICP-MS) to determine rare earth elements (REE) and other trace elements in mortars. Additionally, a no destructive geochemical analysis based on X-ray fluorescence (XRF) was employed for major elements determination. Collected chemical data were processed through Principal Component Analysis (PCA) to highlight any differences among the mortars belonging to different buildings and construction periods. The results show that PCA analysis permits to discriminate construction periods according to mortar sample REE …