The viscosity of dilute carbon nanotube (1D) and graphene oxide (2D) nanofluids.

Controlling the physicochemical properties of nanoparticles in fluids directly impacts on their liquid phase processing and applications in nanofluidics, thermal engineering, biomedicine and printed electronics. In this work, the temperature dependent viscosity of various aqueous nanofluids containing carbon nanotubes (CNTs) or graphene oxide (GO), i.e. 1D and 2D nanoparticles with extreme aspect ratios, is analyzed by empirical and predictive physical models. The focus is to understand how the nanoparticle shape, concentration, motion degrees and surface chemistry affect the viscosity of diluted dispersions. To this end, experimental results from capillary viscosimeters are first examined in terms of the energy of viscous flow and the maximum packing fraction applying the Maron-Pierce model. Next, a comparison of the experimental data with predictive physical models is carried out in terms of nanoparticle characteristics that affect the viscosity of the fluid, mostly their aspect ratio. The analysis of intrinsic viscosity data leads to a general understanding of motion modes for carbon nanoparticles, including those with extreme aspect ratios, in a flowing liquid. The resulting universal curve might be extended to the prediction of the viscosity for any kind of 1D and 2D nanoparticles in dilute suspensions.

The mechanochemical synthesis of PbTe nanostructures: following the Ostwald ripening effect during milling.

A fundamental understanding of the Ostwald ripening effect (ORE) during the mechanochemical synthesis of PbTe nanostructures is presented. The ripening process involves the coarsening of larger particles from those of smaller size; this phenomenon was systematically evaluated at different stages of milling by microscopy analyses (AFM, TEM, STEM and HRTEM). At the early stage of milling, smaller particles and quantum dots are eventually dissolved to lower the total energy assciated with their surfaces. The ripening process - during milling - involves short-range mass transfer among particles. HRTEM analyses allowed us to identify that coarsening occurs by thermo-mechanically activated cooperative mechanisms. The detachment of the atoms from smaller particles to form bigger ones plays a major role in the particle coarsening. It was found that the coarsening process was not limited to crystalline nanostructures; so grain boundaries, edge dislocations and boundaries among crystalline and amorphous phases also play an important role to determine how species migration contributes to generate coarse particles. Those serve as sites for inducing coarsening in an equivalent way as surfaces do. Secondary ion mass spectrometry and elemental chemical mapping (EDX-STEM) revealed that both the purity and the chemical homogeneity of the PbTe nanostructures are prominent features of this material. Additionally, a direct band gap enhancement (780 nm) compared to bulk PbTe (3859 nm) was detected. It occurred due to the quantum confinement effect, lattice imperfections and even surface properties of the nanostructures. It is important to point out that the whole optical behaviour of the PbTe nanostructures was dependent upon the embedded nanoparticles and quantum dots in the clusters and coarse particles ranging from 15 nm to 35 nm.

Tailored SWCNT functionalization optimized for compatibility with epoxy matrices.

We have modified single walled carbon nanotubes (SWCNTs) with well defined matrix-based architectures to improve interface interaction in SWCNT/epoxy composites. The hardener and two pre-synthesized oligomers containing epoxy and hardener moieties were covalently attached to the SWCNT walls by in situ diazonium or carboxylic coupling reactions. In this way, SWCNTs bearing amine or epoxide-terminated fragments of different molecular weights, which resemble the chemical structure of the cured resin, were synthesized. A combination of characterization techniques such as Raman and infrared absorption (FTIR) spectroscopy, elemental analysis and coupled thermogravimetry-FTIR spectroscopy were used to identify both the functional groups and degree of functionalization of SWCNTs synthesized by the laser ablation and arc-discharge methods. Depending on the type of reaction employed for the chemical functionalization and the molecular weight of the attached fragment, it was possible to control the degree of functionalization and the electronic properties of the functionalized SWCNTs. Improved dispersion of SWCNTs in the epoxy matrix was achieved by direct integration without using solvents, as observed from optical microscopy and rheology measurements of the SWCNT/epoxy mixtures. Composite materials using these fillers are expected to exhibit improved properties while preserving the thermosetting architecture.

Intrinsic and selective activity of functionalized carbon nanotube/nanocellulose platforms against colon cancer cells.

Given their large surface area and versatile chemical reactivity, single-walled carbon nanotubes (SWCNTs) are regarded as the basis of new pharmacological complexes. In this study, SWCNTs are chemically functionalized with fluorescein, folic acid, and capecitabine, a drug that is commonly used against colorectal cancer. These functionalized SWCNTs are dispersed in water by taking advantage of their synergistic interaction with type-II nanocrystalline cellulose (II-NCC), and the resulting colloidal system is tested in vitro on both normal (differentiated) and cancerous (proliferative) human colon cells (Caco-2). The functionalized SWCNT/II-NCC hybrids show a higher activity than the reference (capecitabine) against the Caco-2 cancer cell line. However, this effect appears to be intrinsically associated with the SWCNT/II-NCC complex, particularly boosted by fluorescein, as the presence of capecitabine is not required. In addition, confocal microscopy fluorescence imaging using cell cultures highlights the enormous potential of this nanohybrid platform for colon cancer theranostics.

Differential properties and effects of fluorescent carbon nanoparticles towards intestinal theranostics.

Given the potential applications of fluorescent carbon nanoparticles in biomedicine, the relationship between their chemical structure, optical properties and biocompatibility has to be investigated in detail. In this work, different types of fluorescent carbon nanoparticles are synthesized by acid treatment, sonochemical treatment, electrochemical cleavage and polycondensation. The particle size ranges from 1 to 6 nm, depending on the synthesis method. Nanoparticles that were prepared by acid or sonochemical treatments from graphite keep a crystalline core and can be classified as graphene quantum dots. The electrochemically produced nanoparticles do not clearly show the graphene core, but it is made of heterogeneous aromatic structures with limited size. The polycondensation nanoparticles do not have CC double bonds. The type of functional groups on the carbon backbone and the optical properties, both absorbance and photoluminescence, strongly depend on the nanoparticle origin. The selected types of nanoparticles are compatible with human intestinal cells, while three of them also show activity against colon cancer cells. The widely different properties of the nanoparticle types need to be considered for their use as diagnosis markers and therapeutic vehicles, specifically in the digestive system.

The influence of a compatibilizer on the thermal and dynamic mechanical properties of PEEK/carbon nanotube composites.

The effect of polyetherimide (PEI) as a compatibilizing agent on the morphology, thermal, electrical and dynamic mechanical properties of poly(ether ether ketone) (PEEK)/single-walled carbon nanotube (SWCNT) nanocomposites, has been investigated for different CNT loadings. After a pre-processing step based on ball milling and pre-mixing under mechanical treatment in ethanol, the samples were prepared by melt extrusion. A more homogeneous distribution of the CNTs throughout the matrix is found for composites containing PEI, as revealed by scanning electron microscopy. Thermogravimetric analysis demonstrates an increase in the matrix degradation temperatures under dry air and nitrogen atmospheres with the addition of SWCNTs; the level of thermal stability of these nanocomposites is maintained when PEI is incorporated. Both differential scanning calorimetry and synchrotron x-ray scattering studies indicate a slight decrease in the crystallization temperatures of the compatibilized samples, and suggest the existence of reorganization phenomena during the heating, which are favoured in the composites incorporating the compatibilizer, due to their smaller crystal size. Dynamic mechanical studies show an increase in the glass transition temperature of the nanocomposites upon the addition of PEI. Furthermore, the presence of PEI causes an enhancement in the storage modulus, and hence in the rigidity of these systems, attributed to an improved interfacial adhesion between the reinforcement and the matrix. The electrical and thermal conductivities of these composites decrease with the incorporation of PEI. Overall, the compatibilized samples exhibit improved properties and are promising for their use in industrial applications.

Block copolymer assisted dispersion of single walled carbon nanotubes and integration into a trifunctional epoxy.

Arc discharge single walled carbon nanotubes were processed by acid treatment, dispersion in a Pluronic F68 block copolymer aqueous solution and centrifugation. The as-prepared material was characterized by transmission electron microscopy, X-ray diffraction and Raman spectroscopy, showing an important degree of debundling as well as the removal of most of the graphitic and metallic impurities from pristine nanotubes. The nanotube-Pluronic material was integrated into an advanced trifunctional epoxy resin, triglycidyl p-aminophenol, using 4,4'-diaminodiphenylsulfone as the curing agent. The material was incorporated into the epoxy system (0.1, 0.25, 0.50, 1.0, 2.0 wt%) throughout hot magnetic stirring and ultrasonication. Curing kinetics was studied using differential scanning calorimetry, applying the Vyazovkin's isoconversional method. In the early stages of curing, the kinetic study revealed a decrease in the activation energy for samples containing Pluronic, suggesting that Pluronic induced an improvement in the mobility of reactants. The cured composites were characterized by Raman spectroscopy, thermogravimetric analysis and scanning electron microscopy. Micrographs revealed successful integration and homogeneous distribution of the nanotube-Pluronic material in the epoxy matrix, while direct integration of bare nanotubes originated aggregates and inhomogeneity.

Production and stability of mechanochemically exfoliated graphene in water and culture media.

The preparation of graphene suspensions in water, without detergents or any other additives is achieved using freeze-dried graphene powders, produced by mechanochemical exfoliation of graphite. These powders of graphene can be safely stored or shipped, and promptly dissolved in aqueous media. The suspensions are relatively stable in terms of time, with a maximum loss of ∼25% of the initial concentration at 2 h. This work provides an easy and general access to aqueous graphene suspensions of chemically non-modified graphene samples, an otherwise (almost) impossible task to achieve by other means. A detailed study of the stability of the relative dispersions is also reported.

Peptide-based biomaterials. Linking l-tyrosine and poly l-tyrosine to graphene oxide nanoribbons.

Peptide-based biomaterials are being studied actively in a variety of applications in materials science and biointerface engineering. Likewise, there has been ongoing exploration over the last few decades into the potential biological applications of carbon nanomaterials, motivated by their size, shape, structure and their unique physical and chemical properties. In recent years, the functionalization of carbon nanotubes and graphene has led to the preparation of bioactive carbon nanomaterials that are being used in biomedicine as structural elements and in gene therapy and biosensing. The present study proposes different strategies for the bonding of l-tyrosine and the homopolypeptide poly-l-tyrosine to graphene oxide nanoribbons (GONRs). The covalent attachment of l-tyrosine was undertaken by amidation of the α-amine group of tyrosine with the existing carboxylic groups in GONR and by means of esterification through phenol nucleophiles contained in their side chains. In both cases use was made of protective groups to address the functionalization with the desired reactive groups. The linking of GONRs to the PTyr was attempted according to two different strategies: either by ester bonding of commercial PTyr through its phenol side groups or by in situ ring-opening polymerization of an N-carboxyanhydride tyrosine derivative (NCA-Tyr) with Tyr-functionalized GONRs. These biofunctionalized nanomaterials were characterized by Raman and infrared spectroscopies, X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission electron microscopy, fluorescence and electrochemical techniques. On the basis of their properties, prospects for the potential utilization of the prepared hybrid nanomaterials in different applications are also given.

First Report and Epidemics of Buffelgrass Blight Caused by Pyricularia grisea in South Texas.

A blight on buffelgrass, Cenchrus ciliaris L., has been observed for several years in south Texas and Mexico. The disease did not reach epidemic proportions until 1996. The causal agent, identified as Pyricularia grisea (Cooke) Sacc., is a common pathogen of grasses and other cultivated crops. Several Pennisetum spp. have been reported as hosts of Pyricularia spp.; this is the first report of buffelgrass as a host of this pathogen (1,2). Pathogenicity of P. grisea on buffelgrass was confirmed by greenhouse inoculations of 2-month-old buffelgrass plants with conidia washed with distilled water from monoconidial isolations of the pathogen, grown on potato dextrose agar, from infected leaves collected in several locations in south Texas and Mexico. Plants were placed for 8 h every night inside a plastic enclosure with a humidifier, simulating the high relative humidity conditions prevalent during the epidemic. Typical lesions developed after 7 days. The pathogen was re-isolated from the lesions after 10 days, fulfilling Koch's postulates. Conidia harvested from the sporulating samples were hyaline, transversely septate, with one to three septa, most of them having two. Conidia were obpyriform, with hylum often protuberant, measuring 20.6 to 26.3 µm in length and 8.5 to 10.1 µm wide. These measurements are consistent with those given for Pyricularia spp. by Ellis (1). Conidiophores were hyaline, single, slender, and unbranched. Initial symptoms were dark, discolored spots on the leaf that developed into tan, round to elliptical, necrotic lesions with a dark red border and a yellow, chlorotic halo. With increasing severity, lesions can coalesce, killing the entire leaf blade. Under heat and moisture stress, leaves with few lesions and yellow discoloration will wilt completely. Except for the presence of distinct lesions, wilted plants appear to be suffering from severe drought stress or herbicide injury. Losses vary from a few lesions to wilted whole plants and entire pastures. The pathogen also reduces the quantity and quality of seed by infecting involucres of the head. In the absence of the disease, even under severe moisture or drought stress, buffelgrass is able to thrive. Common T-4464 buffelgrass, which is highly susceptible to P. grisea, was introduced into south Texas in the late 1940s and is currently grown on 8 to 10 million acres in south Texas and Mexico. Buffelgrass reproduces by obligate apomixis, in which seeds are formed without sexual fertilization. Consequently, the progeny are genetically identical to the maternal parent. The monoculture of this grass with its unique type of reproduction encompasses millions of acres with genetically identical plants. Interaction of inoculum with weather conditions (nights with 8 to 10 h of more than 75% relative humidity) in 1996, 1997, and the late summer of 1998 produced epidemics of buffelgrass blight throughout south Texas and northern Mexico. P. grisea was also isolated from lesions on grassburr Cenchrus incertus M. A. Curtis collected throughout the area. References: (1) M. B. Ellis 1971. Dematiaceous hyphomycetes. Commonwealth Mycological Institute, Kew, Surrey, England. (2) D. F. Farr et al. 1989. Fungi of Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.

[HLA DR7 as a protective factor against gold salt toxicity in rheumatoid arthritis]. / HLA DR7 como factor de protección frente a la toxicidad por sales de oro en la artritis reumatoide.

We performed a study of antigens HLA type I and II (specificity DR) in 90 patients with diagnosis of Rheumatoid Arthritis (RA) treated with Sodium Aurothiomalate (SATM) in order to detect the presence of an antigen HLA which could act as a protective factor against toxicity by SATM. Our results demonstrated a decrease in the frequency of the antigen DR7 in patients with toxicity by SATM, which suggests a protective factor of this antigen against the development of toxic reactions due to gold salts.

[Lymphocyte subpopulations in rheumatoid arthritis patients, their relatives and spouses]. / Subpoblaciones linfocitarias en pacientes con artritis reumatoide, sus familiares y cónyuges.

A study of lymphocytic sub-populations of patients with rheumatoid arthritis, their families and partners, is presented. The determination was carried out by means of monoclonal antibodies, analysing: T cells sub-population (CD3, CD4, CD8 and quotient CD4/CD8); B cells sub-population (B1); activated cells (OK1a); monocytes and NK cells (OKM1 and BMA 070). The results showed an increase of CD3 sub-population (T total lymphocytes) in patients with RA and their families. The meaning of these results is difficult to evaluate as lymphocyte sub-population is affected by several variables. The lack of modification of suppressor population, CD4/CD8 quotient and IKM1 cells in RA patients is probably due to the moderate activity of the disease.

[HLA antigens in patients with rheumatoid arthritis, their relatives, and spouses]. / Estudio de los antígenos HLA en pacientes con artritis reumatoide, sus familiares y cónyuges.

The results of the comparison between phenotypic frequency of HLA antigen classes I and II in patients afflicted with rheumatoid arthritis (RA) and their relatives (study carried out in the east of Andalusian), showed a significant increase of HLA A24, B51, B44, CW1 ans CW5 class I antigen in the group of relatives. We found a statistically significant DR4 antigen class II increase in both, patients and relative groups. The marriage parther of patients with RA did not have variations in class I or II HLA antigens compared to the control group. We concluded that RA is probably related to the following antigens: A24, B51, B44, CW1, CW5 and DR4.

[Plasma and intraerythrocytic zinc in rheumatoid arthritis and ankylosing spondylitis]. / Cinc plasmático e intraeritrocitario en la artritis reumatoide y espondilitis anquilosante.

The levels of plasmatic and intraerythrocyte zinc in our control group did not show differences in accordance with age or sex. Patients affected by rheumatoid arthritis showed a decrease of plasmatic levels of zinc and an increase of intraerythrocyte zinc level. The patients with ankylosing spondylitis did not show significant variations of zinc levels, even though the patient with increased SR after the first hour (25 mm) showed lower plasmatic zinc with statistical significance. Finally, patients with rheumatoid arthritis in treatment with NSAID, low dose of steroids, gold salts, D-penicilamin, did not show differences compared to the total group of patients with this disease.

[Zinc and osteoporosis]. / Zinc y osteoporosis.

The relevant role of zinc in osteoporosis, its correlation with nutrient intake and the modifications of its urinary and serum levels, have been demonstrated. In this paper, we have studied the plasmatic, urinary and intraerythrocitary levels of zinc in a group of patients with extended primary osteoporosis, most of them women with postmenopausic osteoporosis. No significant differences were observed in zinc levels between osteoporotic patients and controls. We think that certain aspects regarding the correlation between zinc and bone mineral content still have to be defined, as well as zinc intake and osteoporosis.

Association of HLA-DR5 with mucocutaneous lesions in patients with rheumatoid arthritis receiving gold sodium thiomalate.

OBJECTIVE: To investigate the possible association between HLA antigens and adverse reactions to gold sodium thiomalate therapy (GSTM). METHODS: Ninety consecutive patients with rheumatoid arthritis (RA) were studied for possible association between HLA antigens and adverse reactions to GSTM therapy. RESULTS: HLA-DR5 was significantly increased in patients who developed gold induced mucocutaneous lesions. On the other hand, patients with RA carrying B8 and DR3 antigens are of a high risk of developing proteinuria after gold therapy. A very interesting finding was the low incidence of DR7 antigen in patients who developed adverse reactions to GSTM. We also report the relationship between B27 antigen and chrysiasis due to gold therapy. CONCLUSION: Our results support suggestions that the DR7 antigen provides a protective effect against gold toxicity. We also found a strong association between DR5 and mucocutaneous lesions in patients with RA treated with GSTM.

HLA antigen familial study in complete Behçet's syndrome affecting three sisters.

Behçet's disease is a multisystemic disease affecting most organs. Although a tendency towards an association with a certain genetic type and with HLA-B51 is suspected, the incidence of several siblings with Behçet's disease in a single family is rare. A family, in which three sisters were affected with Behçet's disease, uveitis being the most severe manifestation, was studied. In this family all siblings were B51 positive. Only the female siblings, however, with a positive identical HLA phenotype: A2, A11, B51, B44, Cw6, Cw5, DR4, DRw13, DRw53, DRw52, DQw7, DQw6, developed the disease symptoms, whereas none of the male siblings was affected.

[Anticardiolipin antibodies in parenteral drug addicts: relationship with HIV]. / Anticuerpos anticardiolipina en adictos a drogas por vía parenteral: relación con el virus de inmunodeficiencia humana.

The IgG isotype of anticardiolipin antibodies (aCL) and its possible relationship with the immunodeficiency virus (HIV) were studied in 65 parenteral drug addicts (PDA). Thirty-seven patients were infected in the present study. Nineteen (51%) fulfilled diagnostic criteria of AIDS. Thirty-two of these 37 HIV-positive patients (86%) were IgG-aCL positive. Fourteen (50%) of the 28 HIV-negative patients were IgG-aCL positive. Our study reveals a lack of correlation between aCL and thrombocytopenia. None of the patients had thromboembolic complications. In AIDS patients no relationship was found between IgG-aCL levels and the presence of Pneumocystis carinii, other infections by opportunist microorganism, and clinical deterioration. Highly increased levels of IgG-aCL (> 80 GPL) were observed in three patients with AIDS and infectious endocarditis. In conclusion, given the non-specificity of aCL en PDA, it is our opinion that its measurement is of little help in daily clinical praxis.

[The study of zinc in osteonecrosis]. / Estudio del zinc en la osteonecrosis.

Plasmatic, urinary and intra-erythrocytic zinc levels did not modify in patients with head of femur aseptic osteonecrosis (HFAO), except for those patients with raised alkaline phosphatase who showed a diminution in zinc plasmatic levels, being found a negative correlation between plasmatic zinc levels and a raise in serum alkaline phosphatase. A raise on the latter would mean a raise on the osteoblastic activity in a repair intent from the bone of the small trabecular fractures and/or of the necrotic zone which is produced in HFAO. These results show the relationship of zinc with the increase on bone metabolic activity in patients with HFAO, but the scarce previous references force to study them in depth.