Rational Design of Pore Size and Functionality in a Series of Isoreticular Zwitterionic Metal-Organic Frameworks

The isoreticular expansion and functionalization of charged-polarized porosity has been systematically explored by the rational design of 11 isostructural zwitterionic metal-organic frameworks (ZW-MOFs). This extended series of general structural composition {[M3F(L1)3(L2)1.5]·guests}n was prepared by employing the solvothermal reaction of Co and Ni tetrafluoroborates with a binary ligand system composed of zwitterionic pyridinium derivatives and traditional functionalized ditopic carboxylate auxiliary ligands (HL1·Cl = 1-(4-carboxyphenyl)-4,4′-bipyridinium chloride, Hcpb·Cl; or 1-(4-carboxyphenyl-3-hydroxyphenyl)-4,4′-bipyridinium chloride, Hchpb·Cl; and H2L2 = benzene-1,4-dicarboxylic acid, H2bdc; 2-aminobenzene-1,4-dicarboxylic acid, H2abdc; 2,5-dihydroxy-1,4-benzenedicarboxylic acid, H2dhbdc; biphenyl-4,4′-dicarboxylic acid, H2bpdc; or stilbene-4,4′-dicarboxylic acid, H2sdc). Single-crystal structure analyses revealed cubic crystal symmetry (I-43m, a = 31-36 Å) with a 3D pore system of significant void space (73-81%). The pore system features three types of pores being systematically tunable in size ranging from 17.4 to 18.8 Å (pore I), 8.2 to 12.8 Å (pore II), and 4.8 to 10.4 Å (pore III) by the choice of auxiliary ligands. All members of this series have noninterpenetrating structures and exhibit robust architectures, as evidenced by their permanent porosity and high thermal stability (up to 300 °C). The structural integrity and specific surface areas could be systematically optimized using supercritical CO2 exchange methods for framework activation resulting in BET surface areas ranging from 1250 to 2250 m2/g. Most interestingly, as a structural landmark, we found the pore surfaces lined with charge gradients employed by the pyridinium ligands. This key feature results in significant adsorption of carbon dioxide and methane which is attributed to polarization effects. With this contribution we pioneer the reticulation of pyridinium building blocks into extended zwitterionic networks in which specific properties can be targeted

Observation of reduced thermal conductivity in a metal-organic framework due to the presence of adsorbates

Whether the presence of adsorbates increases or decreases thermal conductivity in metal-organic frameworks (MOFs) has been an open question. Here we report observations of thermal transport in the metal-organic framework HKUST-1 in the presence of various liquid adsorbates: water, methanol, and ethanol. Experimental thermoreflectance measurements were performed on single crystals and thin films, and theoretical predictions were made using molecular dynamics simulations. We find that the thermal conductivity of HKUST-1 decreases by 40 – 80% depending on the adsorbate, a result that cannot be explained by effective medium approximations. Our findings demonstrate that adsorbates introduce additional phonon scattering in HKUST-1, which particularly shortens the lifetimes of low-frequency phonon modes. As a result, the system thermal conductivity is lowered to a greater extent than the increase expected by the creation of additional heat transfer channels. Finally, we show that thermal diffusivity is even more greatly reduced than thermal conductivity by adsorption

How reproducible are surface areas calculated from the BET equation?

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called "BET surface identification" (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible

Current trend in synthesis, Post-Synthetic modifications and biological applications of Nanometal-Organic frameworks (NMOFs)

Since the early reports of MOFs and their interesting properties, research involving these materials has grown wide in scope and applications. Various synthetic approaches have ensued in view of obtaining materials with optimised properties, the extensive scope of application spanning from energy, gas sorption, catalysis biological applications has meant exponentially evolved over the years. The far‐reaching synthetic and PSM approaches and porosity control possibilities have continued to serve as a motivation for research on these materials. With respect to the biological applications, MOFs have shown promise as good candidates in applications involving drug delivery, BioMOFs, sensing, imaging amongst others. Despite being a while away from successful entry into the market, observed results in sensing, drug delivery, and imaging put these materials on the spot light as candidates poised to usher in a revolution in biology. In this regard, this review article focuses current approaches in synthesis, post functionalization and biological applications of these materials with particular attention on drug delivery, imaging, sensing and BioMOFs

Perigraft to right atrial shunt by using autologous pericardium for control of bleeding in acute type A dissections

WOS: 000178452500024PubMed ID: 12400747Background. We report our experience with creating a perigraft to right atrial fistula by using autologous pericardium to control the inaccessible bleeding after aortic root repair in patients with acute type A aortic dissection. Methods. Between 1994 and 2001, perigraft to right atrial fistula was used in 7 of 109 patients (mean age; 55 years) who underwent emergency operation for acute type A dissections. A chamber around the aortic graft was created by suturing a patch of pericardium to the right ventricular wall inferiorly, to the pulmonary artery medially, to the Teflon felt at the distal aortic anastomosis or innominate vein superiorly, and to the superior vena cava and right atrium laterally. A large stab wound was created on the medial aspect of the right atrium. The perigraft space was then closed expeditiously. Results. None of these patients required reexploration for bleeding and they were discharged from the hospital without complications. The average blood and fresh frozen plasma requirement was 3.4 +/- 0.9 and 2.7 +/- 0.7, respectively. All underwent echocardiographic examination before discharge and no perigraft to right atrial shunt was detected. Conclusions. If intractable bleeding is encountered after the administration of protamine and thrombotic agents and a discrete bleeding site can not be found, then a perigraft to right atrial fistula using autologous pericardium can be created as a last resort. It provides primary and definite sternal closure and avoids the detrimental effects of a second pump run and continued bleeding

Acute intraoperative arterial elongation: an experimental study

WOS: 000169992900008PubMed ID: 11461102Objectives: small arterial defects resulting from either trauma or resection of an aneurysm often present difficult problems to the vascular surgeon. Design: to demonstrate that certain arterial gaps as a result of traumatic injury or aneurysm resection could be closed with acute intraoperative arterial elongation. Materials: fifteen mongrel dogs underwent acute intraoperative arterial elongation of the right superficial femoral artery, with the left side used for a control vessel. Methods: arterial defects created surgically (median 50 (range 25 to 60 mm) mm). Appropriate length of artery was then undermined. A Foley catheter was placed proximally and distally directly beneath this undermined portion of vessel. The vessel is lengthened following 3 expansion/relaxation cycle of Foley catheter. Arterial gaps were closed by end to end anastomosis. Arterial pressure study was performed in all vessels. Results: acutely, arterial pressure differences proximal and distal to the anastomosis were seen only when arterial gaps were exceeded 55 mm. There was no occlusion either acutely or after 4 weeks follow-up period. Light microscopic examination of arterial specimens revealed partial disruption of internal elastic lamina. At the end of the follow-up period, formation of neointima with regeneration of the internal elastic lamina was demonstrated. Scanning electron microscopy revealed minimal endothelial denudation. Conclusions: we believe that, acute intraoperative elongation can be used as an alternative technique to vein grafting for the repair of small traumatic arterial defects in selected cases

Arch-first technique used with commercial T-graft: To treat subacute type-A aortic dissection in patient with Marfan syndrome

PubMed ID: 11995844Staged repair of extensive thoracic aortic aneurysms puts certain patients at risk of rupture. We report the case of a patient with Marfan syndrome who presented with subacute type-A aortic dissection and a large descending aortic aneurysm. We used the arch-first technique with a commercially available Dacron T-graft. A clamshell incision was used for exposure. A button of arch vessels was anastomosed to the T-graft. Antegrade cerebral perfusion was established through the side branch. The distal end of the graft was anastomosed to the descending aorta and the proximal end to a composite graft. The duration of cerebral ischemia was 30 minutes; antegrade cerebral perfusion lasted 52 minutes. The patient experienced no neurologic dysfunction and was discharged with no major deficit. This technique shortens brain-ischemia time and is a good option if the risk of rupture of the descending component of an extensive thoracic aortic aneurysm is high. To the best of our knowledge, this is the 1st reported case in which the arch-first technique has been used with a commercially available T-graft to treat subacute type-A aortic dissection in a patient with Marfan syndrome

Reduction of spinal cord injury with pentobarbital and hypothermia in a rabbit model

WOS: 000179554600013PubMed ID: 12443752Objectives: to evaluate the effects of hypothermia and pentobarbital on spinal cord ischaemia induced in a rabbit model. Materials and Methods: thirty-two rabbits, allocated into four equal groups, had the infrarenal aorta clamped distal to the left renal artery and above the iliac bifurcation for 40 min. Groups 3 and 4 had infusion of 15 mg/kg of pentobarbital intravenously for 5 min, 15 min before the cross-clamping. Groups 2 and 4 had infusion of 20 ml of Ringer's lactate (LR) solution at 3degreesC for 3 min during aortic cross clamp into the isolated aortic segment. Group 1 was untreated and served as control. Postoperative functions of spinal cord were assessed. Results: paraplegia occurred in all rabbits in Group 1, in one in each of Groups 2 and 3, whereas no paraplegia was observed in Group 4. In addition 2 and 3 animals of Groups 2 and 3, respectively revealed varying degree of neurological disturbances, whereas all animals of Group 4 had normal function. This difference between Groups 2, 3, and 4 vs Group 1 was significant (p < 0.002). So was the difference between Groups 2 and 4 (p = 0.03), whereas the difference between Groups 3 and 4 was not significant. Conclusions: hypothermia and pentobarbital was more effective than hypothermia alone for prevention of spinal cord ischaemia in a rabbit model