Dipole-switch induced modification of the emissive response of carbon nanotubes.

The interaction of carbon nanotubes with the molecular dipole switch spiropyran is expected to affect the optical response of the tubes. Until now, the need of anchor groups to immobilize the switches on the tubes has hindered the experimental observation of the effects of switching on the emission behavior of the tubes. Here we present spiropyran-carbon nanotube complexes obtained by micelle swelling. This method does not require any anchor nor sophisticated chemistry to warrant close tube-switch proximity. For the first time, we observe the shifts predicted theoretically and their effect on the tubes' excitation and emission energies.

Advanced carbon nanotubes functionalization.

Similar to graphene, carbon nanotubes are materials made of pure carbon in its sp2 form. Their extended conjugated π-network provides them with remarkable quantum optoelectronic properties. Frustratingly, it also brings drawbacks. The π-π stacking interaction makes as-produced tubes bundle together, blurring all their quantum properties. Functionalization aims at modifying and protecting the tubes while hindering π-π stacking. Several functionalization strategies have been developed to circumvent this limitation in order for nanotubes applications to thrive. In this review, we summarize the different approaches established so far, emphasizing the balance between functionalization efficacy and the preservation of the tubes' properties. Much attention will be given to a functionalization strategy overcoming the covalent-noncovalent dichotomy and to the implementation of two advanced functionalization schemes: (a) conjugation with molecular switches, to yield hybrid nanosystems with chemo-physical properties that can be tuned in a controlled and reversible way, and; (b) plasmonic nanosystems, whose ability to concentrate and enhance the electromagnetic fields can be taken advantage of to enhance the optical response of the tubes.

Relaxation lifetimes of plasmonically enhanced hybrid gold-carbon nanotubes systems.

Recently, we introduced a novel hybridization route for carbon nanotubes using gold nanoparticles, whose close proximity neatly enhances their radiative emission. Here we investigate the mechanisms behind the enhancement by monitoring the de-excitation dynamics of our π-hybrids through two-color pump-probe time-resolved spectroscopy. The de-excitation process reveals a fast component and a slow component. We find that the presence of gold prominently affects the fast processes, indicating a stronger influence of the gold nanoparticle on the intra-band non-radiative relaxation than on the inter-band recombination of the single-walled carbon nanotube. By evaluating the de-excitation times, we estimate the balance between near-field pumping and the faster metal-induced de-excitation contributions, proving the enhanced pumping to be the leading mechanism.

Tuning the interaction between carbon nanotubes and dipole switches: the influence of the change of the nanotube-spiropyran distance.

The non-covalent functionalization of carbon nanotubes with spiropyran molecules, serving as optically addressable dipole switches, is reported. Two kinds of pyrene-spiropyran-based dyads with spacers of different lengths resulting in different switch-tube distances were investigated. While both surfactants were able to form stable carbon nanotube suspensions, the different distances between the switch and the tube affected both of the components' optical properties. In the case of the shorter spacer, the nanotubes' luminescence as well as the merocyanine absorption band were red-shifted and furthermore, the rate of the merocyanine → spiropyran thermal back isomerization was decreased.

Carbon nanotubes as substrates for molecular spiropyran-based switches.

We present a joint theory-experiment study investigating the excitonic absorption of spiropyran-functionalized carbon nanotubes. The functionalization is promising for engineering switches on a molecular level, since spiropyrans can be reversibly switched between two different conformations, inducing a distinguishable and measurable change of optical transition energies in the substrate nanotube. Here, we address the question of whether an optical read-out of such a molecular switch is possible. Combining density matrix and density functional theory, we first calculate the excitonic absorption of pristine and functionalized nanotubes. Depending on the switching state of the attached molecule, we observe a red-shift of transition energies by about 15 meV due to the coupling of excitons with the molecular dipole moment. Then we perform experiments measuring the absorption spectrum of functionalized carbon nanotubes for both conformations of the spiropyran molecule. We find good qualitative agreement between the theoretically predicted and experimentally measured red-shift, confirming the possibility for an optical read-out of the nanotube-based molecular switch.

Marine diatoms as optical biosensors.

We have chemically modified the frustules of the marine diatom Coscinodiscus concinnus Wm. Smith to properly bind a highly selective bioprobe such as an antibody. By measuring the changes in the photoluminescence emission of diatoms frustules, we have monitored the molecular recognition event between the antibody and its ligand: the dissociation constant estimated is of the same order of that measured by standard Biacore. The nanostructured silica frustules, a low-cost and natural available material, have shown high sensitivity, equal to 1.2+/-0.2 nm microM(-1), and a detection limit of 100 nM, and thus are quite ideal candidates for lab-on-particle applications.

Direct role of surface oxygen vacancies in visible light emission of tin dioxide nanowires.

Tin dioxide (SnO(2)) nanowires exhibit a strong visible photoluminescence that is not observed in bulk crystalline SnO(2). To explain such effect, oxygen vacancies are often invoked without clarifying if they represent the direct origin of luminescence or if their presence triggers other radiative processes. Here we report an investigation of the nature of the visible light emission in SnO(2) nanowires, showing that both experimental and theoretical ab initio analyses support the first hypothesis. On the basis of photoluminescence quenching analysis and of first-principles calculations we show that surface bridging oxygen vacancies in SnO(2) lead to formation of occupied and empty surface bands whose transition energies are in strong agreement with luminescence features and whose luminescence activity can be switched off by surface adsorption of oxidizing molecules. Finally, we discuss how such findings may explain the decoupling between "electrical-active" and "optical-active" states in SnO(2) gas nanosensors [G. Faglia et al., Appl. Phys. Lett. 86, 011923 (2005)].

Nonlinear dynamics induced in liquid crystals in the presence of the orbital and spin angular momentum of light.

We studied the dynamical effects induced in a homeotropic nematic film when a normally incident circularly polarized light beam with an elliptical intensity profile is used. A three-dimensional dynamical model shows that, besides the spin, the orbital angular momentum of photons also plays a role in the reorientation process. Our measurements fairly reproduce the main dynamical features predicted by the model in the near threshold region. The model, however, does not work, as it is, at higher incident laser power where chaotic director rotation was reported [A. Vella, A. Setaro, B. Piccirillo, E. Santamato, Phys. Rev. E 67, 051704 (2003)].

On-off intermittency in chaotic rotation induced in liquid crystals by competition between spin and orbital angular momentum of light.

We observed on-off intermittency in the chaotic rotation induced by a cw laser beam in a thin liquid crystal film where the spin and the orbital angular momentum of light compete in reorienting the sample. We found that the azimuthal angle phi(t) of the molecular director increased linearly in time on large time scales but, occasionally, it exhibited large fluctuations about its average value omega(0)t, so that its angular velocity phi;(t) undergoes an on-off intermittent motion. The intermittent signal omega(t)=phi;(t)-omega(0) obeyed the scaling laws of on-off intermittency, including the symmetry between laminar and burst phases. The chaotic rotations were observed only when the spin and the angular momentum of light were transferred simultaneously to the sample.

Different impact of carvedilol and transdermal scopolamine on cardiovascular performance of mild-moderate chronic heart failure patients: evidence of useful effects of scopolamine on tolerance to work load.

OBJECTIVES: To verify and compare the effects respectively exercised in chronic heart failure patients by transdermal, slow release scopolamine patch and by the beta and alfa adrenoreceptor blocker carvedilol upon the main indexes derived from maximal cardiopulmonary stress test, as well as from analysis of heart rate variability. METHODS: In each of 14 patients suffering from NYHA class II chronic heart failure, admitted to study, the maximal cardiopulmonary test and heart period power spectrum assessment were performed, firstly during usual therapy, then after 7 days of continuous adjunctive treatment with scopolamine patch, and, finally after 3 months of regular administration of oral carvedilol, added to the basal therapy. The need of time enough to the adaptation of the cardiovascular system against the carvedilol pharmacodynamics, together with the need of slow, progressive dose titration, caused that the onset of therapy with carvedilol was separated from assessment of its effects on ergometric and spectral parameters by an interval period of 3 months. RESULTS: During administration of low doses of scopolamine, the values of VO2max, exercise time and double product were respectively 24 +/- 5.3 ml/kg/min, 12 +/- 3 min and 23630 +/- 3760, and resulted significantly higher than basal (p < 0.05 in all cases) and carvedilol-related readings (p < 0.01 by comparisons with VO2max and double product; p < 0.05 by comparison with exercise time). Again during scopolamine, the total variance, LF and HF powers exhibited the values reported as follows: 1255 msec2 and, respectively, 430 and 250 msec2, thus exceeding significantly the basal levels (p < 0.05 from comparison with total power, p < 0.01 from comparisons with LF and HF bands) as well as the levels reached during adrenergic blockade with carvedilol (LF scopolamine vs LF carvedilol: p < 0.01; total power and HF scopolamine vs corrispective carvedilol values p < 0.05). Compared to the basal findings, the carvedilol induced a significant reduction in VO2max (p < 0.05), double product (p < 0.01), peack of heart rate (p < 0.05) and LF power (p < 0.05), and elicited no significant decreases in exercise time; similarly a weak, not significant surge was product by carvedilol in total and HF powers. CONCLUSIONS: Therefore, in patients with left ventricle asymptomatic dysfunction, the low doses of scopolamine potentiate simultaneously the spontaneous heart rare variability and cardiopulmonary maximal testing; whereas, the carvedilol acts upon LF oscillatory component only, the effects upon total variance and HF band being negligible; moreover, this drug depress the myocardial functional capability; in fact, the carvedilol has been demonstrated to produce a remarkable fall in VO2max, this significant reduction in O2 maximal uptake involving the poor rise in cardiac output during the effort or less effective O2 removal from capillary beds or both.

[The dobutamine-dopamine combination versus amrinone in congestive heart failure with a marked edematogenic sign complicated by functional kidney failure. A comparison between 2 different models of inotropic stimulation and diuresis potentiation]. / Associazione dobutamina-dopamina versus amrinone nello scompenso cardiaco congestizio a marcata impronta edemigena complicato da insufficienza renale funzionale. Confronto tra due diversi modelli di stimolazione inotropa e di potenziamento della diuresi.

BACKGROUND: We evaluated the diuretic output in patients with decompensated chronic heart failure (CHF), previously treated by i.v. infusion with dobutamine and dopamine (dob-dop) or with amrinone (amr). Our target was to identify the possible discrepancies in urinary output perhaps linked to the different type of inotropic stimulation in the two subsets. METHODS: Adjunctive therapy with dob-dop or amr was chosen because the administration of diuretics only, without cardiac support, as tested in previous hospitalizations, had been demonstrated to produce unfavourable results, mainly expressed by finding of a low output syndrome in 50% of cases or more. The administration of i.v. infusion was maintained during 17 hours (1000 min approximatively), and included infusion in separate pumps of the two amines, dobutamine at dose of 5 micrograms/kg/min and dopamine at dose of 2.8 micrograms/kg/min or, alternatively, i.v. infusion of amr, administered at dose of 7 micrograms/kg/min. Infusion volumes were similar in the two subsets. The two subsets were homogeneous relatively to renal impairment, i.e. to the parameters (urinary Na, U/P creatinine, U/P urea, urinary osmolality) we fixed as markers idoneous to demonstrate the occurrence of organic renal damage (acute tubular necrosis). RESULTS: The diuresis was recovered in all 24 patients, and the urine volume resulted more pronounced in the subset attributed to the dob-dop at both the 8th and the 17th hour readings. We found no harmful alterations in HR and AP, whereas renal function parameters have been shown to enhance in both the dob-dop and amr arms. The diuretic effectiveness of the SIEV obtained by catecholamine implementation exercised a synergistic, favourable effect on diuresis, renal flow, glomerular filtration rate, and sodium post-proximal delivery. Amr resulted less effective then dob-dop simultaneous administration relatively to the diuretic effect. No remarkable differences were found in the two subsets as regards the heart rate, whereas a decrease in arterial pressure was found after amr. A persistent shift towards a condition of chronic renal failure, was identified in 4/24 patients, the two groups despite of the prolonged treatment at optimized doses: no remarkable side effects were reported. CONCLUSIONS: Thus, the selective effect upon renal hemodynamics, as exercised by dob-dop infusion low doses of dop, together with the enhanced renal output due to dob, has been shown to be more effective than amr influence: thus, the catecholamine therapeutical approach has been demonstrated to possess the best effectiveness in excitation of diuresis, among the CHF oliguric patients.

[Hypotension during acute myocardial infarct. Different pattern of parameters of renal function in relation to the localization of necrosis]. / Ipotensione durante IMA. Diverso contegno di alcuni parametri di funzione renale in rapporto alla sede di necrosi.

BACKGROUND: The influence on renal function caused by acute myocardial infarction complicated by hypotension has been studied. Particularly, a possible difference in renal functional pattern related to different localization and/or extension of necrotic myocardial area was investigated. METHODS: The study has been performed in 12 cases of acute myocardial infarction, involving anteroseptal (7) or inferodorsal (5) myocardial wall. The score of parietal asynergy resulted 13.28 in anterior vs 7.6 in inferior localization (p < 0.001). RESULTS: The decrease in systolic pressure, conversely, resulted not significantly different in the two groups. The renal function was assessed by measuring the urinary output (V) and creatinine clearance (CrCl). During the first 24 hours, both parameters resulted more preserved in inferior than in anterior AMI (V-552 vs 214 ml; p < 0.005; CrCl 70.6 vs 33.42; p < 0.001). Thus 1) the pressure decrease resulted unrelated to the size of asynergy and 2) the markers of renal function, although the decrease in brachial pressure has been identical in the two groups, have been shown to decrease more profoundly in the anterior infarction. DISCUSSION AND CONCLUSIONS: This may depends upon the reflex interruption of efferent nervous sympathetic drive toward the renal arteriolar bed, occurring in inferior infarction, despite of the systemic hypotension, and able to exercising a beneficial influence on the glomerular filtration rate (GFR). This reflex modulation has been demonstrated as effective in the inferior, but not in the anterior localization of infarction, this different haemodynamic pattern being able to explain the more pronounced decrease in GFR and diuresis in anterior than inferior AMI, as observed in our study.

[Abnormal vasomotor response of the forearm due to propranolol-induced loss of cardiopulmonary baroreflex sensitivity: experience with seven cases of recent myocardial infarct]. / Abnorme risposta vasomotoria dell'avambraccio da perdita della sensibilità baroriflessa cardiopolmonare correlata a trattamento con propranololo: esperienza su sette casi di infarto miocardico recente.

In 7 patients suffering from acute myocardial infarction (AMI) occurring in the previous 30 days, we investigated forearm vascular reactivity to lower body negative pressure (LBNP), by the strain gauge plethysmography with simultaneous administration of negative pressure around the lower limbs. This manoeuvre has then been repeated after 10 days of oral beta-blocker therapy (propanolol 160 mg/die). A significant flow reduction derived from LBNP associated to plethysmography with respect to plethysmography alone, but this significant difference was suppressed by propranolol treatment, that prevented the reflex decrease in forearm blood flow, (forearm blood flow from 5.97 to 3.85 ml/min/100 ml in wash-out vs 5.64 to 5.75 ml/min/100 ml during propranolol treatment). We hypothesize that this phenomenon is due to the desensitizing effect of propranolol on cardiopulmonary mechanoreceptors (CPB), with the consequent loss or reduction of their functional inhibition for the efferent sympathetic outflow towards resistance vessels in skeletal muscle. Therefore, LBNP does not elicit forearm reflex sympathetic vasoconstriction, because pressure unloading of CPB areas is no longer able to modify sympathetic discharge, since the influence on it of baroreceptor activity has already been weakened by prolonged beta-blockade. Thus, the LBNP low levels, by ruling out and/or by removing the CPB activity are theorically able to elicit sympathetic "disinhibition", and to exercise, consequently, a reflex, vasoconstrictor influence upon the forearm vascular bed, whereas the same reflex behaviour by forearm resistance vessels does not appear feasible if the CPB activity has been preventively minimized by prolonged, chronic beta-blockade.

[The clinical and hemodynamic effects of propionyl-L-carnitine in the treatment of congestive heart failure]. / Effetti clinici ed emodinamici della propionil-L-carnitina nel trattamento dello scompenso cardiaco congestizio.

In order to evaluate the clinical and hemodynamic effects of propionyl-L-carnitine (PLC) a randomized, double-blind study versus placebo was performed in 50 patients of both sexes, between 48 and 69 years of age, affected by mild-moderate congestive heart failure. All patients participating in said study were on digitalis and diuretic treatment. 25 of these belonged to the control group, while the other 25 were treated with an oral dose of 1 g b.i.d of propionyl-L-carnitine. At the end of six months of treatment maximum exercise time on the treadmill increased 11.1% after 90 days and 16.4% after 180 in the group treated with PLC. From a hemodynamic standpoint, after 30, 90 and 180 days the ejection fraction increased by 7.3%, 10.7% and 12.1%. At the same time, moreover, the systemic vascular resistances were reduced by 14.9%, 20% and 20.6%. In the patients treated with placebo, however, the above-mentioned parameters showed no significant variation. Finally, no unexpected events or toxic effects were observed in any of the patients in either group. As a consequence of these results it is possible to affirm that propionyl-L-carnitine, due to its clinical and hemodynamic effects, represents a drug of notable therapeutic interest in patients with congestive heart failure, in whom it may be usefully combined with the usual pharmacological therapy.