Search

A novel series of double-decker lanthanide(III) bis(phthalocyaninato)-C(60) dyads [Ln(III)(Pc)(Pc')]-C(60) (M=Sm, Eu, Lu; Pc=phthalocyanine) (1 a-c) have been synthesized from unsymmetrically functionalized heteroleptic sandwich complexes [Ln(III)(Pc)(Pc')] (Ln=Sm, Eu, Lu) 3 a-c and fulleropyrrolidine carboxylic acid 2. The sandwich complexes 3 a-c were obtained by means of a stepwise procedure from unsymmetrically substituted free-base phthalocyanine 5, which was first transformed into the monophthalocyaninato intermediate [Ln(III)(acac)(Pc)] and further reacted with 1,2-dicyanobenzene in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). (1)H NMR spectra of the bis(phthalocyaninato) complexes 3 a-c and dyads 1 a-c were obtained by adding hydrazine hydrate to solutions of the complexes in [D(7)]DMF, a treatment that converts the free radical double-deckers into the protonated species, that is, [Ln(III)(Pc)(Pc')H] and [Ln(III)(Pc)(Pc')H]-C(60). The electronic absorption spectra of 3 a-c and 1 a-c in THF exhibit typical transitions of free-radical sandwich complexes. In the case of dyads 1 a-c, the spectra display the absorption bands of both constituents, but no evidence of ground-state interactions could be appreciated. When the UV/Vis spectra of 3 a-c and 1 a-c were recorded in DMF, typical features of the reduced forms were observed. Cyclic voltammetry studies for 3 a-c and 1 a-c were performed in THF. The electrochemical behavior of dyads 1 a-c is almost the exact sum of the behavior of the components, namely the double-decker [Ln(III)(Pc)(Pc')] and the C(60) fullerene, thus confirming the lack of ground-state interactions between the electroactive units. Photophysical studies on dyads 1 a-c indicate that only after irradiation at 387 nm, which excites both C(60) and [Ln(III)(Pc)(Pc')] components, a photoinduced electron transfer from the [Ln(III)(Pc)(Pc')] to C(60) occurs.

When a sample of as-made single-walled carbon nanotubes (SWNTs) is treated with nitric acid, oxidation debris are formed due to the functionalization (mainly carboxylation) of the amorphous carbon present in the sample and a continuous coating along the carbon nanotube walls is created preventing the sidewall functionalization of the SWNTs. This oxidation debris can be easily removed by an aqueous base wash leaving behind a sample with a low degree of functionality. After removal of the amorphous carbon (by steam purification) from a sample of as-made SWNTs, the resulting purified SWNTs are readily carboxylated on the walls by nitric acid treatment. The use of steam for the purification of SWNTs samples allows the removal of the amorphous carbon and graphitic layers coating the metal particles present in the sample without altering the tubular structure of the SWNTs. The exposed metal particles can then be easily removed by an acid wash. Comparison between the steam treatment and molten sodium hydroxide treatment is made.

Steam purified, carboxylic and ester functionalized single-walled carbon nanotube (SWNT) and multi-walled carbon nanotube (MWNT) films with homogeneous distribution and flexible control of thickness and area were fabricated on polymeric and metallic substrates using a modified spray deposition technique. By employing a pre-sprayed polyelectrolyte, the adhesion of the carbon nanotube (CNT) films to the substrates was significantly enhanced by electrostatic interaction. Carboxylic and ester functionalization improved electrochemical performance when immersed in 0.1 M H(2)SO(4) and the specific capacitance reached 155 and 77 F g(-1) for carboxylic functionalized SWNT and MWNT films respectively. Compared with existing techniques such as hot pressing, vacuum filtration and dip coating, the ambient pressure spray deposition technique is suggested as particularly well suited for preparing CNT films at large scale for applications including providing electrodes for electrochemical supercapacitors and paper batteries.

Multiwall WS(2) nanotube templates were used as hosts to prepare core-shell PbI(2)@WS(2) nanotubes by a capillary-wetting method. Conformal growth of PbI(2) layers on the inner wall of the relatively wide WS(2) nanotubes (i.d. ca. 10 nm) leads to nanotubular structures which were not previously observed in narrow carbon nanotube templates. Image simulation after structural modeling (see picture) showed good agreement with the experimental HRTEM image.

Purification and shortening of single-walled carbon nanotubes (SWNTs) is carried out by treatment with steam. During the steam purification the graphitic shells coating the catalytic metal particles are removed. Consequently, the exposed catalytic particles can be easily dissolved by treatment with hydrochloric acid. No damage to the carbon nanotube tubular structure is observed, even after prolonged treatment with steam. Samples are characterized by HRTEM, TGA, magnetic measurements, Raman spectroscopy, AFM, and XPS.

We describe the functionalization of single-wall carbon nanotubes (SWNTs) with 4-(2-trimethylsilyl)ethynylaniline and the subsequent attachment of a zinc-phthalocyanine (ZnPc) derivative using the reliable Huisgen 1,3-dipolar cycloaddition. The motivation of this study was the preparation of a nanotube-based platform which allows the facile fabrication of more complex functional nanometer-scale structures, such as a SWNT-ZnPc hybrid. The nanotube derivatives described here were fully characterized by a combination of analytical techniques such as Raman, absorption and emission spectroscopy, atomic force and scanning electron microscopy (AFM and SEM), and thermogravimetric analysis (TGA). The SWNT-ZnPc nanoconjugate was also investigated with a series of steady-state and time-resolved spectroscopy experiments, and a photoinduced communication between the two photoactive components (i.e., SWNT and ZnPc) was identified. Such beneficial features lead to monochromatic internal photoconversion efficiencies of 17.3% when the SWNT-ZnPc hybrid material was tested as photoactive material in an ITO photoanode.

The sidewall functionalisation of carbon nanotubes using the standard nitric acid treatment can be greatly enhanced by first removing the amorphous carbon present in the sample.

We report the synthesis, characterization and photophysical features of a new nanometer scale carbon nanostructure, that is, a single-wall carbon nanotube bearing phthalocyanine chromophores.

HiPco single-walled carbon nanotubes (SWNTs) have been sidewall-functionalized with phthalocyanine addends following two different approaches: a straightforward Prato reaction with N-octylglycine and a formyl-containing phthalocyanine, and a stepwise approach that involves a former Prato cycloaddition to the double bonds of SWNTs using p-formyl benzoic acid followed by esterification of the derivatized nanotubes with an appropriate phthalocyanine molecule. The two materials obtained by these routes comprise different carbon/Pc-addenda ratios, as evidenced by Raman, TGA, and photophysical studies. The occurrence of electron transfer from photoexcited phthalocyanines to the nanotube framework in these ZnPc-SWNT ensembles is observed in transient absorption experiments, which confirm the absorption of the one-electron oxidized ZnPc cation and the concomitant bleaching of the van Hove singularities typical from SWNTs. Charge-separation (i.e., 2.0 x 1010 s(-1)) and charge-recombination (i.e., 1.5 x 106 s(-1)) dynamics reveal a notable stabilization of the radical ion pair product in dimethylformamide.

A newly constructed chamber/Fourier transform infrared system was used to determine the relative rate coefficient, k(i), for the gas-phase reaction of Cl atoms with 2-butanol (k(1)), 2-methyl-2-butanol (k(2)), 3-methyl-2-butanol (k(3)), 2,3-dimethyl-2-butanol (k(4)) and 2-pentanol (k(5)). Experiments were performed at (298 +/- 2) K, in 740 Torr total pressure of synthetic air, and the measured rate coefficients were, in cm(3) molecule(-1) s(-1) units (+/-2sigma): k(1)=(1.32 +/- 0.14) x 10(-10), k(2)=(7.0 +/- 2.2) x 10(-11), k(3)=(1.17 +/- 0.14) x 10(-10), k(4)=(1.03 +/- 0.17) x 10(-10) and k(5)=(2.18 +/- 0.36) x 10(-10), respectively. Also, all the above rate coefficients (except for 2-pentanol) were investigated as a function of temperature (267-384 K) by pulsed laser photolysis-resonance fluorescence (PLP-RF). The obtained kinetic data were used to derive the Arrhenius expressions: k(1)(T)=(6.16 +/- 0.58) x 10(-11)exp[(174 +/- 58)/T], k(2)(T)=(2.48 +/- 0.17) x 10(-11)exp[(328 +/- 42)/T], k(3)(T)=(6.29 +/- 0.57) x 10(-11)exp[(192 +/- 56)/T], and k(4)(T)=(4.80 +/- 0.43) x 10(-11)exp[(221 +/- 56)/T](in units of cm(3) molecule(-1) s(-1) and +/-sigma). Results and mechanism are discussed and compared with the reported reactivity with OH radicals. Some atmospheric implications derived from this study are also reported.

The absolute rate coefficients for the reactions of hydroxyl radical (OH) with 2-butanol (k(1)), 2-methyl-2-butanol (k(2)), and 2,3-dimethyl-2-butanol (k(3)) were measured as a function of temperature (263-354 K) and pressure (41-193 Torr of He, Ar, and N(2)) by the pulsed laser photolysis/laser-induced fluorescence technique. This work represents the first absolute determination of k(1)(-)k(3) and their temperature dependence. No pressure dependence of the rate coefficients was observed in the range studied. Thus, k(i)(298 K) values (x10(-12) cm(3) molecule(-1) s(-1) with an uncertainty of +/-2sigma) were averaged over the pressure range studied yielding 8.77 +/- 1.46, 3.64 +/- 0.60, and 9.01 +/- 1.00 for 2-butanol (k(1)), 2-methyl-2-butanol (k(2)), and 2,3-dimethyl-2-butanol (k(3)), respectively. k(1) and k(3) exhibit a slightly negative temperature dependence over the temperature range studied. In contrast, the rate coefficient for the reaction of OH with 2-methyl-2-butanol (k(2)) did not show any temperature dependence. Some deviation of the conventional Arrhenius behavior was clearly observed for k(3). In this case, the best fit to our data was found to be described by the three-parameter expression k(T) = A + B exp(-C/T). The UV absorption cross sections of 2-butanol, 2-methyl-2-butanol, and 2,3-dimethyl-2-butanol have also been measured at room temperature between 208 and 230 nm. The values reported constitute the first determination of the UV cross sections of those alcohols. Our results are compared with previous studies, when possible, and are discussed in terms of the H-abstraction by OH radicals. The atmospheric implications of these reactions and the photochemistry of these alcohols are also discussed.

The absolute rate coefficients for the tropospheric reactions of hydroxyl radical (OH) with a series of linear aliphatic ketones (2-butanone (k1), 2-pentanone (k2), 2-hexanone (k3), and 2-heptanone (k4)) were measured as a function of temperature (228-405 K) and pressure (45-600 Torr of He) by the pulsed laser photolysis/laser induced fluorescence technique. These studies are essential to model the atmospheric chemistry of these ketones and their impact in the air quality. No pressure dependence of the rate coefficients was observed in the range studied. Thus, k1(298 K) (x10(-12) cm3 molecule(-1) s(-1)) were averaged over the pressure range studied yielding the following: (1.04+/-0.74), (3.14+/-0.40), (6.37+/-1.40), and (8.22+/-1.10), for 2-butanone (k1), 2-pentanone (k2), 2-hexanone (k3), and 2-heptanone (k4), respectively. k1 exhibits a slightly positive temperature dependence over the temperature range studied. A conventional Arrhenius expression describes the observed behavior. In contrast, the temperature dependence of k2-k4 shows a distinct deviation from the Arrhenius behavior. The best fit to our data was found to be described by the three-parameter expression: k(T) = A + B exp(-C/T) in cm3 molecule(-1) s(-1). This work constitutes the first determination of the temperature dependence of k2-k4. Our results are compared with previous studies, when possible, and are discussed in terms of the H-abstraction by OH radicals. The atmospheric implications of these reactions are also discussed.

Background and Objectives: Ambulatory blood pressure (BP) monitoring has found some specific clinical indications in the treatment and control of hypertension (HT). As with other target organs exposed to vascular damage dependent on HT, ambulatory BP monitoring can be a useful tool in the prevention of cerebrovascular processes., Method: Review of published articles (Medline database) which have investigated the value of continuous recording of BP in cerebrovascular disease (CVD)., Results: Research on the BP patterns and its relationship with stroke has been carried out in subjects with no previous history of CVD (cohort studies and in patients with essential HT, differentiating between adults and elderly patients) and patients after a cerebral ischemic event. The study objectives are aimed at determining its prognostic value in the development of silent and symptomatic CVD, and its prognostic significance regarding functional recovery and the differences of the BP patterns according to the different stroke subtypes., Conclusions: BP monitoring is a useful technique with applications in the control and treatment of the pathological variations of BP in hypertensive patients, with and without a previous history of cerebral ischemia, and mainly in elderly patients, due to the deterioration of the cerebral circulation regulation mechanisms. Clinical research has confirmed the importance of factors related to the circadian rhythm of BP in the primary and secondary prevention of cerebrovascular processes., (Copyright 2004 S. Karger AG, Basel)

Enzyme-linked immunosorbent assays (ELISAs) with a high detectability have been developed for determination of the antifouling agent Irgarol 1051. The features of the resulting assays have been rationalized by using molecular mechanic calculations (MM2+) to correlate the chemical structure of different immunizing haptens and the corresponding avidities of the obtained antisera. The ability of Irgarol 1051 to compete for the antibody binding sites with 11 horseradish peroxidase enzyme tracers, differing in the chemical structures of the hapten, has been investigated. The present paper demonstrates that high-quality antibodies and, therefore, immunoassays reaching very low detection limits could be predicted by molecular modeling studies of the analyte conformations and of the immunizing haptens' geometries, hydrogen-bonding capabilities, and electronic distributions. Two of the ELISAs obtained have been optimized to obtain reproducible immunoassays. The dynamic ranges of both assays are between 30 and 200 ng/L, and the limits of detection are approximately 16 ng/L. The reported immunoassays have been evaluated and validated by analyzing spiked and real seawater samples. Irgarol 1051 has been found to be present in two of the geographical locations analyzed at concentration levels dependent on the time of year. The analytical results obtained with these immunoassays have been validated by chromatographic methods.

The ideal choice of a priming solution of the cardiopulmonary bypass (CPB) and its influence on the hemostatic system are not clear. Addition of albumin was reported to inhibit platelet damaging by blood-surface interactions ("coating"). To explore this possibility in 60 consecutive male patients undergoing elective aortocoronary bypass grafting, five different priming solutions were randomly used: (1) 1000 mL of 5% dextrose + 1000 mL of Ringer's solution (RS) + 250 mL of 5% human albumin (HA); (2) 1850 mL of RS + 400 mL of 20% HA; (3) 1750 mL of RS + 500 mL of 10% low molecular weight hydroxyethyl starch (molecular weight average: 200,000; molar substitution ratio: 0.5); (4) 1750 mL of RS + 500 mL of 3.5% gelatin; (5) 2250 mL of RS. Platelet function was studied by aggregometry (= turbidometric technique; 1.0 and 2.0 mumol/L of adenosine diphosphate (ADP), 4 microL/mL of collagen, 25 mumol/L of epinephrine) before, during, and after CPB until the first postoperative day. Blood loss and need for homologous blood was not different between the groups. During CPB, maximum platelet aggregation induced by ADP was least compromised in group 1 and group 4. At the end of the operation ADP-induced aggregation increased in group 1 (+27%), whereas aggregation was decreased in the other priming solution groups. A significant increase in maximum aggregation was found in group 1 even on the first postoperative day (+132% +/- 16%). Collagen-induced aggregation was also least compromised in group 1. Epinephrine-induced platelet aggregation did not change and was similar for all groups. Maximum gradient of aggregation was influenced in an identical way as maximum aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)