Nanocrystallization of Rare Tolbutamide Form V in Mesoporous MCM-41 Silica

Encapsulation of pharmaceuticals inside nanoporous materials is of increasing interest due to their possible applications as new generation therapeutics, theranostic platforms, or smart devices. Mesoporous silicas are leading materials to be used as nanohosts for pharmaceuticals. Further development of new generation of nanoscale therapeutics requires complete understanding of the complex host−guest interactions of organic molecules confined in nanosized chambers at different length scales. In this context, we present results showing control over formation and phase transition of nanosize crystals of model flexible pharmaceutical molecule tolbutamide confined inside 3.2 nm pores of the MCM-41 host. Using low loading levels (up to 30 wt %), we were able to stabilize the drug in highly dynamic amorphous/disordered state or direct the crystallization of the drug into highly metastable nanocrystalline form V of tolbutamide (at loading levels of 40 and 50 wt %), providing first experimental evidence for crystallization of pharmaceuticals inside the pores as narrow as 3.2 nm

Spatially Resolved STD-NMR Applied to the Study of Solute Transport in Biphasic Systems. Application to Protein-Ligand Interactions

Fluid biphasic systems are one of the most interesting dynamic systems in chemistry and biochemistry. In NMR spectroscopy, the study of the solute dynamics across fluid biphasic systems requires the introduction of dedicated NMR methods, due to their intrinsic heterogeneity. Diffusion and spatially resolved NMR techniques represent a useful approach for dealing with the study of solutes in biphasic systems and have been applied lately with success. Nevertheless, other potential applications of NMR spectroscopy for biphasic systems remain to be explored. In this proof of concept communication, we specifically aimed to investigate whether solute exchange between two immiscible phases can be followed by NMR experiments involving transfer of magnetization. To that aim, we have used Spatially Resolved Saturation Transfer Difference NMR (SR-STD NMR) experiments to analyze solute exchange by transfer of saturation from one phase to the other in a biphasic system and have explored which are the underlying mechanisms leading to the transfer of magnetization between phases and the limits of the approach. We hereby demonstrate that SR-STD NMR is feasible and that it might be implemented in pharmacological screening for binders of biological receptors or in the study of chemical and biochemical reactions occurring at interfaces

Mechanistic and kinetic insight into spontaneous cocrystallisation of isoniazid and benzoic acid

Solid-state cocrystallisation is of contemporary interest, because it offers an easy and efficient way to produce cocrystals, which are recognized as prospective pharmaceutical materials. Research explaining solid-state cocrystallisation mechanisms is important, but still too scarce to give a broad understanding of factors governing and limiting these reactions. Here we report an investigation of the mechanism and kinetics of isoniazid cocrystallisation with benzoic acid. This reaction is spontaneous; however its rate is greatly influenced by environmental conditions (humidity and temperature) and pre-treatment (milling) of the sample. The acceleration of cocrystallisation in the presence of moisture is demonstrated by kinetic studies at elevated humidity. The rate dependence on humidity stems from moisture facilitated rearrangements on the surface of isoniazid crystallites, which lead to cocrystallisation in the presence of benzoic acid vapour. Furthermore, pre-milling the mixture of the cocrystal ingredients eliminated the induction time of the reaction and considerably increased its rate

Self-Correcting Method for the Measurement of Free Calcium and Magnesium Concentrations by 1H NMR

A method for the direct measurement of free Ca2+ and Mg2+ concentrations in the range of 1–100 mM by NMR spectroscopy is demonstrated. The method automatically corrects for the effect of ionic strength on the activity of the species in solution and works satisfactorily even when significant concentrations of competitive ions are present. The method requires only the measurement of the 1H chemical shifts of our reporter ligands, glycolate and sulfoacetate, and is easily implemented using NMR imaging techniques. As a proof of concept, we extract the thermodynamic binding constants and conformer distributions of analyte ligands using an in situ ion gradient. Existing approaches for the measurement of free Ca2+ or Mg2+ concentrations by NMR operate only at very low ion concentrations or else require careful recalibration for different sample conditions. By providing the free Ca2+ or Mg2+ concentrations, the proposed methodology significantly enhances the information obtainable via NMR investigations of ion-responsive systems

Mesoporous aluminosilicate nanofibers with a low Si/Al ratio as acidic catalyst for hydrodeoxygenation of phenol

Mesoporous aluminosilicate nanofibers (mASNF) were prepared using hard and soft dual templates approach. The mesoporous material was fully characterized and its acidic nature was confirmed by FTIR spectroscopy of pyridine adsorption and 27Al/29Si solid state NMR. Thanks to the incorporated aluminum atoms, the acidic material showed high hydrothermal stability which is an essential property for biomass conversion applications. The catalytic performance of Pd supported on mASNF for hydrodeoxygenation (HDO) of lignin model compound was also investigated. A complete conversion and a high selectivity towards cyclohexane (up to 95%) starting from phenol were achieved with this bifunctional catalyst. In comparison, no cyclohexane has been produced with a non-acidic material which underlines the importance of acidic sites in HDO process selectivity control. Moreover, the catalyst can be recycled without losing its initial structure

Solvent driven phase transitions of acyclovir-the role of water and solvent polarity

Acyclovir, an antiviral purine derivative listed on the WHO's Model List of Essential Medicines, is commonly used in several different dosage forms from tablets to gels, oleogels and suspensions. Although temperature driven phase transitions of its commercially available 3 : 2 hydrate have been known since 2011, information on the solvent driven phase transitions of this drug has been limited. This study identifies the pathways of transformations of acyclovir forms I and V induced by organic solvents and water using the method of solution mediated phase transformation. The 3 : 2 hydrate, form V, undergoes dehydration to anhydrous form I in methanol, ethanol and N,N-dimethylformamide. Form I converts to anhydrous form II in dry methanol and N,N-dimethylformamide, while increased water content in the solvent prevents the transformation of form I to form II. Both forms I and V yield a gel-like material in dimethyl sulfoxide, composed of highly crystalline form II and reported here for the first time. Furthermore, significant differences in the thermal dehydration process of forms V and VI were observed using VT FTIR, including the first time report on a novel metastable ACV form VII formed upon dehydration of ACV dihydrate (form VI). High resolution solid-state NMR spectra of two anhydrous polymorphs (forms I and II) and two hydrates (forms V and VI) supported by DFT calculations using the CASTEP code are also presented

Mechanically robust gels formed from hydrophobized cellulose nanocrystals

Cellulose nanocrystals (CNCs) that bind to each other through associative hydrophobic interactions have been synthesized by modifying sulfated CNCs (sCNCs) with hydrophobic moieties. These octyl-CNCs form gels at significantly lower concentrations than parent sCNCs, producing extremely strong hydrogels. Unlike sCNCs, these octyl-CNCs do not form ordered liquid crystalline phases indicating a random association into a robust network driven by hydrophobic interactions. Furthermore, involvement of the octyl-CNCs into multicomponent supramolecular assembly was demonstrated in combination with starch. AFM studies confirm favorable interactions between starch and octyl-CNCs, which is thought to be the source of the dramatic increase in gel strength

Sidechain control of porosity closure in multiple peptide-based porous materials by cooperative folding

Porous materials find application in separation, storage and catalysis. We report a crystalline porous solid formed by coordination of metal centres with a glycylserine dipeptide. We prove experimentally that the structure evolves from a solvated porous into a non-porous state as result of ordered displacive and conformational changes of the peptide that suppress the void space in response to environmental pressure. This cooperative closure, which recalls the folding of proteins, retains order in three-dimensions and is driven by the hydroxyl groups acting as H-bond donors in the peptide sequence through the serine residue. This ordered closure is also displayed by multipeptide solid solutions in which the combination of different sequences of amino acids controls their guest response in a non-linear way. This functional control can be compared to the effect of single point mutations in proteins, where the exchange of single amino acids can radically alter structure and functio

Thermosensitive supramolecular and colloidal hydrogels via self-assembly modulated by hydrophobized cellulose nanocrystals

Utilization of reversible non-covalent interactions is a versatile design strategy for the development of stimuli responsive soft materials. In this study, hydrophobic interactions were harnessed to assemble water-soluble macromolecules and nanoparticles into a transient hybrid network forming thermosensitive hydrogels with tunable rheological properties. Hybrid hydrogels were built of biopolymer derived components: cellulose nanocrystals (CNCs), nanoparticles of high aspect ratio, and hydroxypropyl methylcellulose (HPMC). To enable polymer/CNC assembly via hydrophobic interactions, the surface of highly hydrophilic CNCs was modified by binding octyl moieties (octyl-CNCs). The amphiphilicity of octyl-CNCs was confirmed by surface tension measurements. The molecular and particulate amphiphiles assemble into hybrid networks, which result in stiffer and stronger hydrogels compared to HPMC hydrogels and hydrogels reinforced with hydrophilic CNCs. Hybrid hydrogels retain the ability of HPMC hydrogels to flow under applied shear stress. However, significantly higher viscosity was achieved for HPMC/octyl-CNCs compared with HPMC/CNCs hydrogels. The inherent thermal response of rheological properties of HPMC hydrogels was further amplified in combination with octyl-CNCs due to temperature-induced polymer/nanoparticle association via hydrophobic interactions. Saturation transfer difference NMR spectroscopy demonstrated the growth of network-bound water with an increase in temperature, which correlates with the increase of stiffness and viscosity of hydrogels upon heating. Rheological properties of these hybrid hydrogels are defined by the content of the soluble polymer and the CNCs, and it is shown that they can be finely adjusted for a required application

Unravelling cationic cellulose nanofibril hydrogel structure: NMR spectroscopy and small angle neutron scattering analyses

Stiff, elastic, viscous shear thinning aqueous gels are formed upon dispersion of low weight percent concentrations of cationically modified cellulose nanofibrils (CCNF) in water. CCNF hydrogels produced from cellulose modified with glycidyltrimethylammonium chloride, with degree of substitution (DS) in the range 10.6(3)–23.0(9)%, were characterised using NMR spectroscopy, rheology and small angle neutron scattering (SANS) to probe the fundamental form and dimensions of the CCNF and to reveal interfibrillar interactions leading to gelation. As DS increased CCNF became more rigid as evidenced by longer Kuhn lengths, 18–30 nm, derived from fitting of SANS data to an elliptical cross-section, cylinder model. Furthermore, apparent changes in CCNF cross-section dimensions suggested an “unravelling” of initially twisted fibrils into more flattened ribbon-like forms. Increases in elastic modulus (7.9–62.5 Pa) were detected with increased DS and 1H solution-state NMR T1 relaxation times of the introduced surface –N+(CH3)3 groups were found to be longer in hydrogels with lower DS, reflecting the greater flexibility of the low DS CCNF. This is the first time that such correlation between DS and fibrillar form and stiffness has been reported for these potentially useful rheology modifiers derived from renewable cellulose