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Silvia Giordani

Publications and source records attributed to Silvia Giordani.

10 recordsLinked to original sources
PubMed2006

Linear and nonlinear optical characterization of a tetraphenylporphyrin-carbon nanotube composite system.

We present a study of tetraphenylporphyrin composites formed with single-walled carbon nanotubes (SWNTs). Stable porphyrin/SWNT composite solutions were obtained by non-covalent bonding between the carbon nanotubes and conjugated tetraphenylporphyrin molecules. Transmission electron microscopy reveals porphyrin molecules adhering to the nanotube surface. We report on the first complete linear and nonlinear optical characterization of these nanocomposite materials. The composite solutions were found to be superior optical limiters to nanotubes alone, and to all porphyrin systems studied, including metalloporphyrins.

Journal Article↗
PubMed2006

Debundling of single-walled nanotubes by dilution: observation of large populations of individual nanotubes in amide solvent dispersions.

Large-scale debundling of single-walled nanotubes has been demonstrated by dilution of nanotube dispersions in the solvent N-methyl-2-pyrrolidone (NMP). At high concentrations some very large (approximately 100 s of micrometers) nanotube aggregates exist that can be removed by mild centrifugation. By measurement of the absorbance before and after centrifugation as a function of concentration the relative aggregate and dispersed nanotube concentrations can be monitored. No aggregates are observed below CNT approximately 0.02 mg/mL, suggesting that this can be considered the nanotube dispersion limit in NMP. After centrifugation, the dispersions are stable against sedimentation and further aggregation for a period of weeks at least. Atomic force microscopy (AFM) studies on deposited films reveal that the bundle diameter distribution decreases dramatically as concentration is decreased. Detailed data analysis suggests the presence of an equilibrium bundle number density and that the dispersions self-arrange themselves to always remain close to the dilute/semidilute boundary. A population of individual nanotubes is always observed that increases with decreasing concentration until almost 70% of all dispersed objects are individual nanotubes at a concentration of 0.004 mg/mL. The number density of individual nanotubes peaks at a concentration of approximately 10(-2) mg/mL. Both the mass fraction and the partial concentration of individual nanotubes can also be measured and behave in similar fashion. Comparison of the number density and partial concentration also of individual nanotubes reveals that the individual nanotubes have average molar masses of approximately 700,000 g/mol. The presence of individual nanotubes in NMP dispersion was confirmed by photoluminescence spectroscopy. Concentration dependence of the photoluminescence intensity confirms that the AFM measurements reflect the diameter distributions in situ. In addition, Raman spectroscopy confirms the presence of large quantities of individual nanotubes in the deposited films. Finally, the nature of the solvent properties required for dispersion are discussed.

Amides↗
PubMed2005

Does rTMS hasten the response to escitalopram, sertraline, or venlafaxine in patients with major depressive disorder? A double-blind, randomized, sham-controlled trial.

BACKGROUND/OBJECTIVE: Repetitive transcranial magnetic stimulation (rTMS) has been mainly studied as adjunctive treatment for drug-resistant patients. We assessed the effectiveness of rTMS started concomitantly with antidepressant medications in non-drug-resistant major depressive disorder patients. We also evaluated if, among the 3 antidepressants administered, one had a better synergy with rTMS. METHOD: In this 5-week, double-blind, randomized, sham-controlled study, we recruited 99 inpatients suffering from a major depressive episode (DSM-IV criteria). They were randomly assigned to receive venlafaxine, sertraline, or escitalopram in combination with a 2-week period of sham or active 15-Hz rTMS on the left dorso-lateral prefrontal cortex. Data were gathered from February 2004 to June 2005. RESULTS: The active rTMS group showed a significantly faster reduction in Hamilton Rating Scale for Depression (HAM-D) scores compared with the sham group (p = .0029). The response and remission rates were significantly greater in the active rTMS group after the stimulation period (p = .002 and p = .003, respectively), but not at the endpoint. We found no significant difference in HAM-D score reduction among the 3 drugs administered, either in the active or in the sham group. CONCLUSION: These findings support the efficacy of rTMS in hastening the response to antidepressant drugs in patients with major depressive disorder. The effect of rTMS seems to be unaffected by the specific concomitantly administered drug.

Adult↗
PubMed2004

Neuropsychological investigation of decision-making in anorexia nervosa.

Anorexia nervosa (AN) could be considered a form of obsessive-compulsive disorder in which an impairment of the cognitive domain related to decision-making was found. We explored this function in AN patients, as well as possible differences between restricting type and binge/purge type, with the aim of examining the hypothesis that AN is part of the obsessive-compulsive spectrum. Decision-making was assessed in 59 inpatients with AN and 82 control subjects using the Gambling task, which simulates real-life decision-making by assessing the ability to balance immediate rewards against long-term negative consequences. We confirmed the supposed deficit of decision-making in AN. However, restricting and binge eating/purge subtypes showed different patterns of decision-making impairment. Poor performance on the Gambling task is not a mere consequence of starvation and does not appear to be related to illness severity. The decision-making deficiency that some AN patients show is linked to those individual features that contribute to the phenomenological expression of the disorder.

Adult↗
PubMed2003

A switch in a cage with a memory.

[structure: see text] Chemical and optical stimulations control the interconversion of a three-state molecular switch trapped inside a silica monolith. The resulting absorbance changes in the visible region can be exploited to reproduce a sequential logic operator with one optical input and one optical output. This strategy to transfer operating principles for digital processing from bulk solutions to rigid materials can lead to the development of chemical logic gates based on functional solid components.

Journal Article↗
PubMed2003

Digital processing with a three-state molecular switch.

Certain molecular switches respond to input stimulations producing detectable outputs. The interplay of these signals can be exploited to reproduce basic logic operations at the molecular level. The transition from simple logic gates to complex digital circuits requires the design of chemical systems able to process multiple inputs and outputs. We have identified a three-state molecular switch that responds to one chemical and two optical inputs producing two optical outputs. We have encoded binary digits in its inputs and outputs applying positive logic conventions and demonstrated that this chemical system converts three-digit input strings into two-digit output strings. The logic function executed by the three-state molecular switch is equivalent to that of a combinational logic circuit integrating two AND, two NOT, and one OR gate. The three states of the molecular switch are a colorless spiropyran, a purple trans-merocyanine, and its yellow-green protonated form. We have elucidated their structures by X-ray crystallography, (1)H NMR spectroscopy, COSY and NOE experiments, as well as density functional calculations. The three input stimulations controlling the interconversion of the three states of the molecular switch are ultraviolet light, visible light, and H(+). The two outputs are the absorption bands in the visible region of the two colored states of the molecular switch. We have monitored the switching processes and quantified the associated thermodynamic and kinetic parameters with the aid of (1)H NMR and visible absorption spectroscopies.

Journal Article↗
PubMed2003

Memory effects based on intermolecular photoinduced proton transfer.

We have identified a strategy to communicate a chemical signal between two independent molecular components. One of them is a photoactive merocyanine that switches to a spiropyran, releasing a proton, when stimulated with visible light. The other is a 4,4'-pyridylpyridinium monocation that captures the released proton, producing an electroactive 4,4'-bipyridinium dication. Under the irradiation conditions employed, the photoinduced transformation requires ca. 15 min to reach a photostationary state. In the dark, the ensemble of communicating molecules reequilibrates to the original state in ca. 5 days. These processes can be monitored following the photoinduced enhancement and thermal decay, respectively, of the current for the monolectronic reduction of the 4,4'-bipyridinium dication. The pronounced difference in time scale for the current enhancement and decay steps can be exploited to implement a memory element with a bit retention time of 11 h. A bit of information can be written optically in the chemical system and it can be read electrically and nondestructively. The memory can be reset, extending its permanence in the dark beyond the bit retention time. A binary logic analysis of the signal transduction operated by the communicating molecules reveals the characteristic behavior of sequential logic operators, which are the basic components of digital memories.

Benzopyrans↗
PubMed2002

All-optical processing with molecular switches.

A gradual transition from electrical to optical networks is accompanying the rapid progress of telecommunication technology. The urge for enhanced transmission capacity and speed is dictating this trend. In fact, large volumes of data encoded on optical signals can be transported rapidly over long distances. Their propagation along specific routes across a communication network is ensured by a combination of optical fibers and optoelectronic switches. It is becoming apparent, however, that the interplay between the routing electrical stimulations and the traveling optical signals will not be able to support the terabit-per-second capacities that will be needed in the near future. Electrical inputs cannot handle the immense parallelism potentially possible with optical signals. Operating principles to control optical signals with optical signals must be developed. Molecular and supramolecular switches are promising candidates for the realization of innovative materials for information technology. Binary digits can be encoded in their chemical, electrical, or optical inputs and outputs to execute specific logic functions. We have developed a simple strategy to gate optical signals with optical signals by using a photoactive molecular switch. We have demonstrated that NAND, NOR, and NOT operations can be implemented exclusively with optical inputs and optical outputs coupling from one to three switching elements. Our remarkably simple approach to all-optical switching might lead to the development of a new generation of devices for digital processing and communication technology.

Journal Article↗
PubMed2002

Multichannel digital transmission in an optical network of communicating molecules.

In present telecommunication networks, information transfer relies on the interplay of optical and electrical signals. Data are communicated optically but processed electronically. Methods to maintain the propagating signals solely at the optical level must be developed to overcome the transmission capacities and speed limits imposed by the electronic components. We have demonstrated that molecular switches can be used to gate optical signals in response to optical signals. We have realized a simple optical network consisting of three light sources, one cell containing a solution of three fluorescent molecules, one cell containing a solution of a three-state molecular switch and a detector. The light emitted by the three fluorophores is absorbed by the three states of the molecular switch. Using this simple operating principle, we have shown that multichannel digital transmission can be implemented on an ensemble of communicating molecules relying exclusively on the interplay of optical inputs and optical outputs.

Journal Article↗