A practical approach to the determination of the pore entrance size in ordered silicas with cage-like mesoporous structures (OSCMSs) is proposed. A fundamental insight into the OSCMS pore connectivity is gained, including the control of the pore entrance size by post-synthesis surface modification, and by selection of appropriate synthesis temperature. These findings show a new promise for the synthesis of mesoporous solids with molecular size- and shape-selective properties.
A new approach to pore size and surface area analysis for hydrophobic mesoporous solids is proposed. Welldefined materials with strongly hydrophobic surfaces were prepared via chemical bonding of octyldimethylsilyl (ODMS) ligands to the surface of large-pore MCM-41 samples. Nitrogen statistical film thickness curves (t-curves) were determined for hydrophobic pores. These t-curves were fitted with the nitrogen adsorption isotherm for a macroporous silica modified with ODMS groups in order to derive the reference t-curve valid in the entire range of relative pressures. An empirical expression for the reference t-curve was found. The reference t-curve and the previously derived corrected form of the Kelvin equation were used to calculate pore size distributions for hydrophobic mesoporous materials, allowing to correctly reproduce the total pore volume, average pore size, and surface area determined using independent calculation procedures. The reference nitrogen adsorption isotherm on hydrophobic materials is reported in a tabular form. Moreover, the accuracy of the BET specific surface area was discussed. Thus, this study allowed us to develop the methodology for accurate and consistent characterization of hydrophobic mesoporous materials using nitrogen adsorption.
An incorporation of 1-benzoyl-3-propylthiourea groups into siliceous mesopores of MCM-41 afforded an ordered material with open porosity. This material was prepared via a two-step modification by attachment of an aminopropyl functionality and its subsequent conversion into a thiourea ligand. About 1.5 mmol/g of 1-benzoyl-3-propylthiourea groups was attached to the silica surface, which resulted in ca. 70% conversion of amino groups. Such material has a large surface area of 380 m 2 /g and accessible mesopores of 3.0 nm in diameter. The presence of several functional groups in the thiourea structure, able to coordinate metal ions, causes a significant enhancement of the maximum capacity of this material toward mercury ions. The maximum loading of mercury ions from aqueous solution for this material was ca. 1.0 g Hg 2+ /g or 5.0 mmol Hg 2+ /g, exceeding the capacity of the previously known samples by about twice. The fit of the mercury adsorption isotherm by a two-term Langmuir-Freundlich equation suggests a two-step adsorption process characterized by different adsorption constants. A relatively weak mercury interaction with 1-benzoyl-3-propylthiourea ligands made the adsorbent's regeneration possible under mild conditions via washing the mercury-loaded samples with slightly acidified aqueous thiourea solution. The regenerated material retained over 70% of the initial adsorption capacity.
Insulin has a narrow therapeutic index, reflected in a small margin between a dose that achieves good glycemic control and one that causes hypoglycemia. Once injected, the clearance of exogenous insulin is invariant regardless of blood glucose, aggravating the potential to cause hypoglycemia. We sought to create a "smart" insulin, one that can alter insulin clearance and hence insulin action in response to blood glucose, mitigating risk for hypoglycemia. The approach added saccharide units to insulin to create insulin analogs with affinity for both the insulin receptor (IR) and mannose receptor C-type 1 (MR), which functions to clear endogenous mannosylated proteins, a principle used to endow insulin analogs with glucose responsivity. Iteration of these efforts culminated in the discovery of MK-2640, and its in vitro and in vivo preclinical properties are detailed in this report. In glucose clamp experiments conducted in healthy dogs, as plasma glucose was lowered stepwise from 280 mg/dL to 80 mg/dL, progressively more MK-2640 was cleared via MR, reducing by ∼30% its availability for binding to the IR. In dose escalations studies in diabetic minipigs, a higher therapeutic index for MK-2640 (threefold) was observed versus regular insulin (1.3-fold).
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