712 research outputs found
Direct Observation of Quantum Coherence in Single-Molecule Magnets
Direct evidence of quantum coherence in a single-molecule magnet in frozen
solution is reported with coherence times as long as T2 = 630 ns. We can
strongly increase the coherence time by modifying the matrix in which the
single-molecule magnets are embedded. The electron spins are coupled to the
proton nuclear spins of both the molecule itself and interestingly, also to
those of the solvent. The clear observation of Rabi oscillations indicates that
we can manipulate the spin coherently, an essential prerequisite for performing
quantum computations.Comment: 5 Pages, 4 Figures, final version published in PR
Magnetic ground state and 2D behavior in pseudo-Kagome layered system Cu3Bi(SeO3)2O2Br
Anisotropic magnetic properties of a layered kagome-like system
Cu3Bi(SeO3)2O2Br have been studied by bulk magnetization and magnetic
susceptibility measurements as well as powder and single-crystal neutron
diffraction. At T_N = 27.4 K the system develops an alternating
antiferromagnetic order of (ab) layers, which individually exhibit canted
ferrimagnetic moment arrangement, resulting from the competing ferro- and
antiferro-magnetic intralayer exchange interactions. A magnetic field B_C ~ 0.8
T applied along the c axis (perpendicular to the layers) triggers a
metamagnetic transition, when every second layer flips, i.e., resulting in a
ferrimagnetic structure. Significantly higher fields are required to rotate the
ferromagnetic component towards the b axis (~7 T) or towards the a axis (~15
T). The estimates of the exchange coupling constants and features indicative of
an XY character of this quasi-2D system are presented.Comment: 7 pages, 6 figures, final versio
Aza- and Mixed Thia/Aza-Macrocyclic Receptors with Quinoline-Bearing Pendant Arms for Optical Discrimination of Zinc(II) or Cadmium(II) Ions
The synthesis and coordination properties of two fluorescent chemosensors, featuring [9]aneN3 (1,4,7-triazacyclononane; L1) and [12]aneNS3 (1-aza-4,7,10-trithiacyclododecane; L2) as receptor units, and a quinoline pendant arm with an amide group as a functional group spacer are described. The optical responses of L1 and L2 in the presence of several metal ions were analysed in MeCN/H2O (1 : 4 v/v) solutions. A selective chelation enhancement of fluorescence (CHEF) effect was observed in the presence of Zn2+ in the case of L1, and in the presence of Cd2+ in the case of L2, following the formation of a 1 : 1 and a 1 : 2 metal/ligand complex, respectively, which was also confirmed by potentiometric measurements. 1H and 13C NMR measurements in CD3CN/CDCl3 in combination with molecular mechanics calculations show that for both complexes of L1 and L2 with Zn2+ and Cd2+, respectively, the coordination of the carbonyl group from the pendant arm could be the origin of the observed optical selectivity
Colorimetric response to anions by a "robust" copper(II) complex of a [9]aneN3 pendant arm derivative: CN- and I- selective sensing
The 1 : 1 complex [Cu(L)](BF4)2MeCN (1) of the tetradentate ligand 1-(2-quinolinylmethyl)-1,4,7-triazacyclononane (L) selectively changes its colour in the presence of CN in H2O and MeCN (without undergoing decomplexation from the macrocyclic ligand). The same complex in MeCN assumes different colours in the presence of CN or I
High-field Electron Spin Resonance of Cu_{1-x}Zn_{x}GeO_{3}
High-Field Electron Spin Resonance measurements were made on powder samples
of Cu_{1-x}Zn_{x}GeO_{3} (x=0.00, 0.01, 0.02, 0.03 and 0.05) at different
frequencies (95, 110, 190, 220, 330 and 440 GHz) at low temperatures. The
spectra of the doped samples show resonances whose positions are dependent on
Zn concentration, frequency and temperature. The analysis of intensity
variation of these lines with temperature allows us to identify them as
originating in transitions within states situated inside the Spin Peierls gap.
A qualitative explanation of the details of the spectra is possible if we
assume that these states in the gap are associated with "loose" spins created
near the Zn impurities, as recently theoreticaly predicted. A new phenomenon of
quenching of the ESR signal across the Dimerized to Incommensurate
phase-boundary is observed.Comment: 4 pages, 5 ps figures in the text, submitted to Phys. Rev. Let
Magnetic and thermal properties of 4f-3d ladder-type molecular compounds
We report on the low-temperature magnetic susceptibilities and specific heats
of the isostructural spin-ladder molecular complexes L[M(opba)]_{3\cdot
xDMSOHO, hereafter abbreviated with LM (where L =
La, Gd, Tb, Dy, Ho and M = Cu, Zn). The results show that the Cu containing
complexes (with the exception of LaCu) undergo long range magnetic
order at temperatures below 2 K, and that for GdCu this ordering is
ferromagnetic, whereas for TbCu and DyCu it is probably
antiferromagnetic. The susceptibilities and specific heats of TbCu
and DyCu above have been explained by means of a model
taking into account nearest as well as next-nearest neighbor magnetic
interactions. We show that the intraladder L--Cu interaction is the predominant
one and that it is ferromagnetic for L = Gd, Tb and Dy. For the cases of Tb, Dy
and Ho containing complexes, strong crystal field effects on the magnetic and
thermal properties have to be taken into account. The magnetic coupling between
the (ferromagnetic) ladders is found to be very weak and is probably of dipolar
origin.Comment: 13 pages, 15 figures, submitted to Phys. Rev.
Tuning the magnetic ground state of a novel tetranuclear Nickel(II) molecular complex by high magnetic fields
Electron spin resonance and magnetization data in magnetic fields up to 55 T
of a novel multicenter paramagnetic molecular complex [L_2Ni_4(N_3)(O_2C
Ada)_4](Cl O_4) are reported. In this compound, four Ni centers each having a
spin S = 1 are coupled in a single molecule via bridging ligands (including a
\mu_4-azide) which provide paths for magnetic exchange. Analysis of the
frequency and temperature dependence of the ESR signals yields the relevant
parameters of the spin Hamiltonian, in particular the single ion anisotropy gap
and the g factor, which enables the calculation of the complex energy spectrum
of the spin states in a magnetic field. The experimental results give
compelling evidence for tuning the ground state of the molecule by magnetic
field from a nonmagnetic state at small fields to a magnetic one in strong
fields owing to the spin level crossing at a field of ~25 T.Comment: revised version, accepted for publication in Physical Review
Exploring the ability of luminescent metal assemblies to bind and sense anionic or ionizable analytes a ru(Phen)2bipy-based dizinc complex for bisphenol a (bpa) recognition
The anti-ageing and whitening potential of a cosmetic serum containing 3-o-ethyl-l-ascorbic acid
Skin ageing has many manifestations such as wrinkles, dryness, hyperpigmentation, and uneven skin tone. Extrinsic and intrinsic factors, especially solar ultraviolet light (UVB), contribute to skin ageing; its main features are brown spots, alterations in melanin pigmentation, and a decrease in collagen and hyaluronic acid linked to oxidative stress. Several studies showed that topical products containing ingredients with antioxidant activity can reduce oxidative damage; to provide a maximum anti-ageing effect to the skin, topical products can combine various ingredients. C-SHOT SERUM contains a combination of two molecules with a proven anti-ageing activity: a high percentage (30%) of a more stable vitamin C derivative, 3-O-ethyl-L-ascorbic acid, and lactic acid (1%). The product showed a high biocompatibility, assessed through an MTT assay on keratinocytes and on Reconstructed Human Epidermis (RHE, SkinEthic); the anti-ageing activity was demonstrated on human dermal fibroblasts and keratinocytes by a statistically significant increase in collagen production and a reduction of a UVB-induced DNA damage marker (\u3b3-H2AX histone), indicating DNA protection. Moreover, a depigmenting activity, shown by a highly significant decrease in melanin content on treated Reconstructed Human Pigmented Epidermis (RHPE), was assessed. According to the data of our study, the tested product contrasts the effect of skin ageing and irregular pigmentation due to the physiological decline of the skin
A practical approach for the in vitro safety and efficacy assessment of an anti-ageing cosmetic cream enriched with functional compounds
(1) Background: Cosmeceuticals are topical products applied to human skin to prevent skin ageing and maintain a healthy skin appearance. Their effectiveness is closely linked to the compounds present in a final formulation. In this article, we propose a panel of in vitro tests to support the efficacy assessment of an anti-ageing cream enriched with functional compounds. (2) Methods: biocompatibility and the irritant effect were evaluated on reconstructed human epidermis (RHE) and corneal epithelium (HCE) 3D models. After a preliminary MTT assay, normal human dermal fibroblasts (NHDF) and keratinocytes (HaCaT) were used to evaluate the extracellular matrix (ECM) protein synthesis, and interleukin-6 (IL-6) and metalloproteinase-1 (MMP-1) production. (3) Results: data collected showed good biocompatibility and demonstrated the absence of the irritant effect in both 3D models. Therefore, we demonstrated a statistical increase in collagen and elastin productions in NHDF cells. In HaCaT cells, we highlighted an anti-inflammatory effect through a reduction in IL-6 levels in inflammatory stimulated conditions. Moreover, the reduction of MMP-1 production after UV-B radiation was demonstrated, showing significant photo-protection. (4) Conclusion: a multiple in vitro assays approach is proposed for the valid and practical assessment of the anti-ageing protection, anti-inflammatory and biocompatible claims that can be assigned to a cosmetic product containing functional compounds
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