Calculating the hydrodynamic volume of poly(ethylene oxylated) single-walled carbon nanotubes and hydrophilic carbon clusters.

Poly(ethylene glycol) (PEG) functionalization of carbon nanotubes (CNTs) is widely used to render CNTs suitable as vectors for targeted drug delivery. One recently described PEGylated version uses an oxidized single-walled carbon nanotube called a hydrophilic carbon cluster (HCC). The resulting geometric dimension of the hybrid PEG-CNT or PEG-HCC is an important factor determining its ability to permeate the cellular membrane and to maintain its blood circulation. Molecular dynamics (MD) simulations were performed to estimate the maximum length and width dimensions for a PEGylated single-walled carbon nanotube in water solution as a model for the PEG-HCC. We ensured maximum PEGylation by functionalizing each carbon atom in a CNT ring with an elongated PEG molecule, avoiding overlapping between PEGs attached to different CNT rings. We suggest that maximum PEGylation is important to achieve an optimal drug delivery platform.

Self-assembly of DNA on a gapped carbon nanotube.

We perform molecular dynamics simulations to analyze the wrapping process of a single-stranded (ss) DNA around a gapped CNT immersed in a bath of water. We observe the formation of a stable molecular junction with the ssDNA adopting a helical or circular conformation around one CNT electrode and a linear conformation around the opposite electrode. We find that DNA undergoes several conformational changes during equilibration of the self-assembled molecular junction. This process would allow a higher yield of successful CNT-DNA interconnections, which constitutes a novel structure of interest in chemical and biological sensing at the single-molecule level.

DNA origami impedance measurement at room temperature.

The frequency response of triangular DNA origami is obtained at room temperature. The sample shows a high impedance at low frequencies, e.g., at zero frequency 20 Gohms, which decreases almost linearly with the logarithm of the frequency reaching a low and flat value at 100 kHz where the impedance turns from capacitive to resistive, concluding that DNA can be used for transmission of signals at frequencies larger than 100 kHz. It is also found that characteristics of DNA cannot be completely disentangled from the characteristics of the substrate on which it is deposited, making the design of molecular circuits more challenging than the design of circuits with present lumped devices; this is a natural feature at the nanoscale.

Current-voltage-temperature characteristics of DNA origami.

The temperature dependences of the current-voltage characteristics of a sample of triangular DNA origami deposited in a 100 nm gap between platinum electrodes are measured using a probe station. Below 240 K, the sample shows high impedance, similar to that of the substrate. Near room temperature the current shows exponential behavior with respect to the inverse of temperature. Sweep times of 1 s do not yield a steady state; however sweep times of 450 s for the bias voltage secure a steady state. The thermionic emission and hopping conduction models yield similar barriers of approximately 0.7 eV at low voltages. For high voltages, the hopping conduction mechanism yields a barrier of 0.9 eV and the thermionic emission yields 1.1 eV. The experimental data set suggests that the dominant conduction mechanism is hopping in the range 280-320 K. The results are consistent with theoretical and experimental estimates of the barrier for related molecules.

Tetralogía de Fallot asociada a conexión anómala total infradiafragmática de venas pulmonares y persistencia de conducto arterial: presentación de un caso / Tetralogy of Fallot, total anomalous pulmonary venous conection of the infracardiac variety, patent ductus arteriousus: a case report

Se presenta un caso de tetralogía de Fallot(TF) asociada a conexión anómala total infracardiaca de las venas pulmonares y a persistencia del conducto arterial. El diagnóstico se realizó por ecocardiografía y se corroboró con cateterismo y angiocardiografía. Lo peculiar del caso es que cayó en insuficiencia cardiaca, lo que nunca ocurre en la TF aislada. Se operó a la edad de dos meses y medio. No toleró la intervención y falleció. No obtuvo permiso para la necropsia. Se discuten las características clínicas y fisiopatológicas y se revisa la literatura sobre esta rara asociación

Agenesia e hipoplasia de una arteria pulmonar / Agenesis and hypoplasia of a pulmonary artery

La agenesia y la hipoplasia de una arteria pulmonar son poco frecuente. De 2,800 estudios hemodinámicos de cardiopatías, 10 fueron de agenesia y 7 de hipoplasia de una arteria pulmonar. Pueden sospecharse por la posición anómala del corazón, habitualmente desalojado a la derecha o a la izquierda en las radiografías frontales de tórax y por la asimetría torácica, con espacios intercostales disminuido del lado afectado. La mayoría se acompañan de malformaciones congénitas agregadas. Por lo general se complican de hipertensión pulmonar. Se expectúan los casos con tetralogía de Fallot o con estenosis pulmonar que obviamente no tienen hipertensión pulmonar. La demostración del problema se obtiene con angiocardiografía, pero es muy valiosa la información de la gammagrafía pulmonar, como estudio no invasivo. La agenesia de la arteria pulmonar derecha desplaza el corazón al lado homólogo (dextroposición). El electrocardiograma muestra que las aurículas y los ventrículos ocupan posición recíproca normal en situs solitus. La correlación de las anomalías asociadas no garantiza la mejoría de la hipertensión pulmonar. Se deben operar con neumonectomía cuando las condiciones del paciente lo permitan por la hipertensión pulmonar y porque el pulmón no funcionante es más susceptible a las infecciones que el pulmón normal. En esta corta serie, de 3 pacientes operados, dos mejoraron con la neumonectomía. El tercero falleció por complicaciones en el post-operatorio