Effects of surfactant head group modification on vertically oriented mesoporous silica produced by the electrochemically assisted surfactant assembly method.

Production of mesoporous silica films with vertically oriented pores has been a challenge since interest in such systems developed in the 1990s. Vertical orientation can be achieved by the electrochemically assisted surfactant assembly (EASA) method using cationic surfactants such as cetyltrimethylammonium bromide (C16TAB). The synthesis of porous silicas using a series of surfactants with increasing head sizes is described, from octadecyltrimethylammonium bromide (C18TAB) to octadecyltriethylammonium bromide (C18TEAB). These increase pore size, but the degree of hexagonal order in the vertically aligned pores reduces as the number of ethyl groups increases. Pore accessibility is also reduced with the larger head groups.

Correct specific retention volume determination in inverse gas chromatography.

Inverse Gas Chromatography (IGC) is an important technique for characterization of solids. Determining the specific retention volume of the injected probe molecule is the basis of the analysis for all the physico-chemical properties that the technique can determine, most importantly in Heat of Sorption, Glass Transition Temperature, Gibbs Adsorption Free Energy. Two equations have been used in the literature to calculate the specific retention volume; one normalizes the retention volume to 0 °C (standard temperature), which was previously proven to be thermodynamically incorrect, while the other calculates the retention volume at the measurement temperature. Here, we compare the heat of sorption for a series of alkanes on two substrates, micro crystalline cellulose and natural graphite, calculated using these two equations. This study shows that the specific retention volume is strongly dependent on the column temperature. Using the retention volume values normalised to 0 °C consistently overestimates the heats of sorption by up to 10%. Most importantly, correcting the retention volume to standard temperature will misrepresent the effect of temperature on the retention volume and the thermodynamic parameters derived from it.

Prediction of peptides retention behavior in reversed-phase liquid chromatography based on their hydrophobicity.

Hydrophobicity is an important physicochemical property of peptides and proteins. It is responsible for their conformational changes, stability, as well as various chemical intramolecular and intermolecular interactions. Enormous efforts have been invested to study the extent of hydrophobicity and how it could influence various biological processes, in addition to its crucial role in the separation and purification endeavor as well. Here, we have reviewed various studies that were carried out to determine the hydrophobicity starting from (i) simple amino acids solubility behavior, (ii) experimental approach that was undertaken in the reversed-phase liquid chromatography mode, and ending with (iii) some examples of more advanced computational and machine learning models.

Successful synthesis of a glial-specific blood-brain barrier shuttle peptide following a fragment condensation approach on a solid-phase resin.

Successful manual synthesis of the TD2.2 peptide acting as a blood-brain barrier shuttle was achieved. TD2.2 was successfully synthesised by sequential condensation of four protected peptide fragments on solid-phase settings, after several unsuccessful attempts using the stepwise approach. These fragments were chosen to minimise the number of demanding amino acids (in terms of coupling, Fmoc removal) in each fragment that are expected to hamper the overall synthetic process. Thus, the hydrophobic amino acids as well as Arg(Pbf) were strategically spread over multiple fragments rather than having them congested in one fragment. This study shows how a peptide that shows big challenges in the synthesis using the common stepwise elongation methodology can be synthesised with an acceptable purity. It also emphasises that choosing the right fragment with certain amino acid constituents is key for a successful synthesis. It is worth highlighting that lower amounts of reagents were required to synthesise the final peptide with an identical purity to that obtained by the automatic synthesiser.

Greener Cleavage of Protected Peptide Fragments from Sieber Amide Resin.

Following the successful introduction of two benign solvents for cleaving protected acid peptide fragments from 2-chlorotrityl chloride (2-CTC) resin, there is a need to green the cleavage process for obtaining protected peptide amide fragments. In this work, p-xylene and toluene are introduced as greener alternates to dichloromethane (DCM) for preparing protected peptide amide fragments from a Sieber amide resin. The N-dealkylation is a demanding chemical reaction, requiring that the cleavage protocol be optimised to ensure complete cleavage from the resin. After a 30 min reaction time, only 66 % of the final peptide product was retrieved even with the conventional dichloromethane solvent. Therefore, 120 min was considered sufficient to fully cleave the peptide from the Sieber amide resin. This work reaffirms the fact that greening strategies are far from detrimental, with green alternatives often outperforming their replaced counterparts.

Strategies for Improving Peptide Stability and Delivery.

Peptides play an important role in many fields, including immunology, medical diagnostics, and drug discovery, due to their high specificity and positive safety profile. However, for their delivery as active pharmaceutical ingredients, delivery vectors, or diagnostic imaging molecules, they suffer from two serious shortcomings: their poor metabolic stability and short half-life. Major research efforts are being invested to tackle those drawbacks, where structural modifications and novel delivery tactics have been developed to boost their ability to reach their targets as fully functional species. The benefit of selected technologies for enhancing the resistance of peptides against enzymatic degradation pathways and maximizing their therapeutic impact are also reviewed. Special note of cell-penetrating peptides as delivery vectors, as well as stapled modified peptides, which have demonstrated superior stability from their parent peptides, are reported.

Development of efficient aqueous organic redox flow batteries using ion-sieving sulfonated polymer membranes.

Redox flow batteries using aqueous organic-based electrolytes are promising candidates for developing cost-effective grid-scale energy storage devices. However, a significant drawback of these batteries is the cross-mixing of active species through the membrane, which causes battery performance degradation. To overcome this issue, here we report size-selective ion-exchange membranes prepared by sulfonation of a spirobifluorene-based microporous polymer and demonstrate their efficient ion sieving functions in flow batteries. The spirobifluorene unit allows control over the degree of sulfonation to optimize the transport of cations, whilst the microporous structure inhibits the crossover of organic molecules via molecular sieving. Furthermore, the enhanced membrane selectivity mitigates the crossover-induced capacity decay whilst maintaining good ionic conductivity for aqueous electrolyte solution at pH 9, where the redox-active organic molecules show long-term stability. We also prove the boosting effect of the membranes on the energy efficiency and peak power density of the aqueous redox flow battery, which shows stable operation for about 120 h (i.e., 2100 charge-discharge cycles at 100 mA cm-2) in a laboratory-scale cell.

Increasing the Diameter of Vertically Aligned, Hexagonally Ordered Pores in Mesoporous Silica Thin Films.

The variation in pore size in mesoporous films produced by electrochemically assisted self-assembly (EASA) with the surfactant chain length is described. EASA produces a hexagonal array of pores perpendicular to the substrate surface by using an applied potential to organize cationic surfactants and the resultant current to drive condensation in a silica sol. Here, we show that a range of pore sizes between 2 and 5 nm in diameter is available with surfactants of the form [Me3NCnH2n+1]Br, with alkyl chain lengths between C14 and C24. The film quality, pore order, pore size, and pore accessibility are probed with a range of techniques.

Product selectivity and mass transport in levulinic acid transfer hydrogenation by monolithic MIL-100, MIL-88B and ZIF-8@Pd MOFs.

The diffusion processes between adsorbent and adsorbate naturally play a significant role in the efficiency and selectivity of the heterogenous catalytic process. This paper considers the importance of diffusion processes in the transfer hydrogenation reaction of levulinic acid to γ-valerolactone by MIL-88B, MIL-100, and ZIF8@Pd monolithic catalysts. Over a period of five catalytic cycles, it was shown that the Fe-based catalysts can achieve similar conversions to the ZIF-8 supported Pd, with the only current limitation being the lower aqueous stability of these MOFs. Diffusion constants were calculated using the ZLC method, with micropore diffusion limitation found for ZIF-8 and MIL-100 monolithic frameworks at 2.7 x 10-8 and 4.6 x 10-8 cm2 s-1 respectively. This diffusion limitation was also confirmed by IR spectroscopy with an increasing concentration of C-H bands on the MOF substrate post-reaction. Mass transfer coefficients, also calculated by ZLC, revealed increased mass transport for the hydrophobic ZIF-8 framework, which perhaps aids in the γ-valerolactone selectivity over side products that are produced in the absence of catalytic material, as seen for MIL-88B and MIL-100 after multiple uses.

Molecular interaction and partitioning in α-keratin using 1H NMR spin-lattice (T1) relaxation times.

The interactions between small molecules and keratins are poorly understood. In this paper, a nuclear magnetic resonance method is presented to measure changes in the 1H T1 relaxation times of small molecules in human hair keratin to quantify their interaction with the fibre. Two populations of small-molecule compounds were identified with distinct relaxation times, demonstrating the partitioning of the compounds into different keratin environments. The changes in relaxation time for solvent in hair compared with bulk solvent were shown to be related to the molecular weight (MW) and the partition coefficient, LogP, of the solvent investigated. Compounds with low MWs and high hydrophilicities had greater reductions in their T1 relaxation times and therefore experienced increased interactions with the hair fibre. The relative population sizes were also calculated. This is a significant step towards modelling the behaviour of small molecules in keratinous materials and other large insoluble fibrous proteins.

On the Origins of Some Spectroscopic Properties of "Purple Iron" (the Tetraoxoferrate(VI) Ion) and Its Pourbaix Safe-Space.

In this work, the authors attempt to interpret the visible, infrared and Raman spectra of ferrate(VI) by means of theoretical physical-inorganic chemistry and historical highlights in this field of interest. In addition, the sacrificial decomposition of ferrate(VI) during water treatment will also be discussed together with a brief mention of how Rayleigh scattering caused by the decomposition of FeVIO42- may render absorbance readings erroneous. This work is not a compendium of all the instrumental methods of analysis which have been deployed to identify ferrate(VI) or to study its plethora of reactions, but mention will be made of the relevant techniques (e.g., Mössbauer Spectroscopy amongst others) which support and advance this overall discourse at appropriate junctures, without undue elaboration on the foundational physics of these techniques.

SO2 Capture by Two Aluminum-Based MOFs: Rigid-like MIL-53(Al)-TDC versus Breathing MIL-53(Al)-BDC.

Metal-organic frameworks MIL-53(Al)-TDC and MIL-53(Al)-BDC were explored in the SO2 adsorption process. MIL-53(Al)-TDC was shown to behave as a rigid-like material upon SO2 adsorption. On the other hand, MIL-53(Al)-BDC exhibits guest-induced flexibility of the framework with the presence of multiple steps in the SO2 adsorption isotherm that was related through molecular simulations to the existence of three different pore opening phases narrow pore, intermediate pore, and large pore. Both materials proved to be exceptional candidates for SO2 capture, even under wet conditions, with excellent SO2 adsorption, good cycling, chemical stability, and easy regeneration. Further, we propose MIL-53(Al)-TDC and MIL-53(A)-BDC of potential interest for SO2 sensing and SO2 storage/transportation, respectively.

Fluorinated MIL-101 for carbon capture utilisation and storage: uptake and diffusion studies under relevant industrial conditions.

Carbon capture utilisation and storage (CCUS) using solid sorbents such as zeolites, activated carbon and Metal-Organic Frameworks (MOFs) could facilitate the reduction of anthropogenic CO2 concentration. Developing efficient and stable adsorbents for CO2 capture as well as understanding their transport diffusion limitations for CO2 utilisation plays a crucial role in CCUS technology development. However, experimental data available on CO2 capture and diffusion under relevant industrial conditions is very limited, particularly for MOFs. In this study we explore the use of a gravimetric Dynamic Vapour Sorption (DVS) instrument to measure low concentration CO2 uptake and adsorption kinetics on a novel partially fluorinated MIL-101(Cr) saturated with different water vapour concentrations, at ambient pressure and temperature. Results show that up to water P/P 0 = 0.15 the total CO2 uptake of the modified material improves and that the introduction of small amounts of water enhances the diffusion of CO2. MIL-101(Cr)-4F(1%) proved to be a stable material under moist conditions compared to other industrial MOFs, allowing facile regeneration under relevant industrial conditions.

Polymer-assisted modification of metal-organic framework MIL-96 (Al): influence of HPAM concentration on particle size, crystal morphology and removal of harmful environmental pollutant PFOA.

A new synthesis method was developed to prepare an aluminum-based metal organic framework (MIL-96) with a larger particle size and different crystal habits. A low cost and water-soluble polymer, hydrolyzed polyacrylamide (HPAM), was added in varying quantities into the synthesis reaction to achieve >200% particle size enlargement with controlled crystal morphology. The modified adsorbent, MIL-96-RHPAM2, was systematically characterized by SEM, XRD, FTIR, BET and TGA-MS. Using activated carbon (AC) as a reference adsorbent, the effectiveness of MIL-96-RHPAM2 for perfluorooctanoic acid (PFOA) removal from water was examined. The study confirms stable morphology of hydrated MIL-96-RHPAM2 particles as well as a superior PFOA adsorption capacity (340 mg/g) despite its lower surface area, relative to standard MIL-96. MIL-96-RHPAM2 suffers from slow adsorption kinetics as the modification significantly blocks pore access. The strong adsorption of PFOA by MIL-96-RHPAM2 was associated with the formation of electrostatic bonds between the anionic carboxylate of PFOA and the amine functionality present in the HPAM backbone. Thus, the strongly held PFOA molecules in the pores of MIL-96-RHPAM2 were not easily desorbed even after eluted with a high ionic strength solvent (500 mM NaCl). Nevertheless, this simple HPAM addition strategy can still chart promising pathways to impart judicious control over adsorbent particle size and crystal shapes while the introduction of amine functionality onto the surface chemistry is simultaneously useful for enhanced PFOA removal from contaminated aqueous systems.

A Robust and Biocompatible Bismuth Ellagate MOF Synthesized Under Green Ambient Conditions.

The first bioinspired microporous metal-organic framework (MOF) synthesized using ellagic acid, a common natural antioxidant and polyphenol building unit, is presented. Bi2O(H2O)2(C14H2O8)·nH2O (SU-101) was inspired by bismuth phenolate metallodrugs, and could be synthesized entirely from nonhazardous or edible reagents under ambient aqueous conditions, enabling simple scale-up. Reagent-grade and affordable dietary supplement-grade ellagic acid was sourced from tree bark and pomegranate hulls, respectively. Biocompatibility and colloidal stability were confirmed by in vitro assays. The material exhibits remarkable chemical stability for a bioinspired MOF (pH = 2-14, hydrothermal conditions, heated organic solvents, biological media, SO2 and H2S), attributed to the strongly chelating phenolates. A total H2S uptake of 15.95 mmol g-1 was recorded, representing one of the highest H2S capacities for a MOF, where polysulfides are formed inside the pores of the material. Phenolic phytochemicals remain largely unexplored as linkers for MOF synthesis, opening new avenues to design stable, eco-friendly, scalable, and low-cost MOFs for diverse applications, including drug delivery.

Functionalized NU-1000 with an Iridium Organometallic Fragment: SO2 Capture Enhancement.

A new material, MOF-type [Ir]@NU-1000, was accessed from the incorporation of the iridium organometallic fragment [Ir{κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)2}] into NU-1000. The new material incorporates less than 1 wt % of Ir(III) (molar ratio Ir to NU-1000, 1:11), but the heat of adsorption for SO2 is significantly enhanced with respect to that of NU-1000. Being a highly promising adsorbent for SO2 capture, [Ir]@NU-1000 combines exceptional SO2 uptake at room temperature and outstanding cyclability. Additionally, it is stable and can be regenerated after SO2 desorption at low temperature.

Reversible and efficient SO2 capture by a chemically stable MOF CAU-10: experiments and simulations.

The adsorption of sulphur dioxide (SO2) in CAU-10 is obtained with the use of advanced experimental and computational tools to gain insight into the molecular mechanisms responsible for the adsorption of SO2. It is shown that the adsorption by CAU-10 is highly energy efficient and that van der Waals interactions are the driving force that controls adsorption in this system.

Surface Energy Mapping of Modified Silica Using IGC Technique at Finite Dilution.

The reinforcing silica filler, which can be more than 40% of an elastomer composite, plays a key role to achieve the desired mechanical properties in elastomer vulcanizates. However, the highly hydrophilic nature of silica surface causes silica particle aggregation. It remained a challenge for many tire manufacturers when using silica-filled elastomer compounds. Here, the silica surface energy changes when the surface is modified with coupling or noncoupling silanes; coupling silanes can covalently bond the silica to the elastomers. The surface energy of silica was determined using inverse gas chromatography (IGC) at finite dilution (FD-IGC) and found to be reduced by up to 50% when the silica surface was silanized. The spatial distribution of silica aggregates within the tire matrix is determined by transmission electron microscopy (TEM) and a direct correlation between aggregate size (silica microdispersion) and work of cohesion from IGC is reported, highlighting surface energy and work of cohesion being excellent indicators of the degree of dispersion of silica aggregates.

The Influence of Moisture Content and Temperature on the Long-Term Storage Stability of Freeze-Dried High Concentration Immunoglobulin G (IgG).

High protein concentration products for targeted therapeutic use are often freeze-dried to enhance stability. The long-term storage stability of freeze-dried (FD) plasma-derived Immunoglobulin G (IgG) from moderate to high concentrations (10-200 mg/mL) was assessed. Monomer content, binding activity and reconstitution times were evaluated over a 12-month period under accelerated and real-term storage conditions. In the first case study it was shown that FD IgG from 10 to 200 mg/mL had minimal monomer/activity losses at up to ambient temperature after 12 months of storage. However, at 45 °C the sucrose-to-protein ratio played a significant impact on IgG stability above 50 mg/mL. All IgG concentrations witnessed moisture ingress over a 12-month period. The impact of moisture ingress from environmental exposure (between 0.1% and 5% w/w moisture) for IgG 50 mg/mL was assessed, being generated by exposing low moisture batches to an atmospheric environment for fixed time periods. Results showed that at -20 °C and 20 °C there was no significant difference in terms of monomer or antigen-binding activity losses over 6 months. However, at 45 °C, there were losses in monomer content, seemingly worse for higher moisture content samples although model binding activity indicated no losses. Finally, the difference between a low moisture product (0.1-1% w/w) and a moderately high moisture (3% w/w) product generated by alternative freeze-drying cycles, both stoppered under low oxygen headspace conditions, was evaluated. Results showed that at -20 °C and 20 °C there was no difference in terms of binding activity or monomer content. However, at 45 °C, the low moisture samples had greater monomer and binding activity losses than samples from the highest moisture cycle batch, indicating that over-drying can be an issue.

The influence of the closure format on the storage stability and moisture content of freeze-dried influenza antigen.

Low moisture content is seen as crucial to achieving long term stability of freeze dried biologics and reference materials. Highly hygroscopic freeze-dried material are susceptible to moisture ingress over time which can lead to degradation and loss of biological potency. This study compared vials with unprocessed stoppers, vials with vacuum-oven dried stoppers and glass ampoules in order to determine the superior long term storage format in terms of moisture ingress and potency. B/Phuket influenza antigen was chosen as the model biological standard and the lyophilized antigen was stored at -20, 25 and 45 °C over a 1 year period. Ampoules had no significant moisture change across all storage temperatures as would be anticipated. Moisture content results at -20 °C showed no significant differences between ampoules, vials with vacuum-oven dried stoppers and vials with unprocessed stoppers over 12 months. Vials with vacuum-oven dried stoppers performed similarly to ampoules at -20 °C and 20 °C, but had a small increase in moisture content after 6 months at 45 °C. Vials with unprocessed stoppers preformed the worst and exhibited the largest moisture ingress after just 3 months at both 20 °C and 45 °C. Single radial immunodiffusion (SRD) potency assays showed at -20 °C and 20 °C there was no significant difference between all closure formats. At 45 °C there was a drop in potency for all closure formats, but ampoules and vials with vacuum-oven dried stoppers retained higher potency than vials with unprocessed stoppers. Thus, while ampoules are still considered to be the gold standard format for long term storage stability, using vials with vacuum-oven dried stoppers provides comparable stability and moisture integrity at -20 °C and 20 °C storage.