Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 50
Filtrar
Mais filtros

Base de dados
País como assunto
Tipo de documento
Intervalo de ano de publicação
1.
Mol Pharm ; 20(9): 4546-4558, 2023 09 04.
Artigo em Inglês | MEDLINE | ID: mdl-37578286

RESUMO

Delamanid (DLM) is a hydrophobic small molecule therapeutic used to treat drug-resistant tuberculosis (DR-TB). Due to its hydrophobicity and resulting poor aqueous solubility, formulation strategies such as amorphous solid dispersions (ASDs) have been investigated to enhance its aqueous dissolution kinetics and thereby improve oral bioavailability. However, ASD formulations are susceptible to temperature- and humidity-induced phase separation and recrystallization under harsh storage conditions typically encountered in areas with high tuberculosis incidence. Nanoencapsulation represents an alternative formulation strategy to increase aqueous dissolution kinetics while remaining stable at elevated temperature and humidity. The stabilizer layer coating the nanoparticle drug core limits the formation of large drug domains by diffusion during storage, representing an advantage over ASDs. Initial attempts to form DLM-loaded nanoparticles via precipitation-driven self-assembly were unsuccessful, as the trifluoromethyl and nitro functional groups present on DLM were thought to interfere with surface stabilizer attachment. Therefore, in this work, we investigated the nanoencapsulation of DLM via emulsification, avoiding the formation of a solid drug core and instead keeping DLM dissolved in a dichloromethane dispersed phase during nanoparticle formation. Initial emulsion formulation screening by probe-tip ultrasonication revealed that a 1:1 mass ratio of lecithin and HPMC stabilizers formed 250 nm size-stable emulsion droplets with 40% DLM loading. Scale-up studies were performed to produce nearly identical droplet size distribution at larger scale using high-pressure homogenization, a continuous and industrially scalable technique. The resulting emulsions were spray-dried to form a dried powder, and in vitro dissolution studies showed dramatically enhanced dissolution kinetics compared to both as-received crystalline DLM and micronized crystalline DLM, owing to the increased specific surface area and partially amorphous character of the DLM-loaded nanoparticles. Solid-state NMR and dissolution studies showed good physical stability of the emulsion powders during accelerated stability testing (50 °C/75% RH, open vial).


Assuntos
Nanopartículas , Tuberculose Bucal , Humanos , Emulsões , Nanopartículas/química , Solubilidade , Excipientes/química , Água/química , Tamanho da Partícula
2.
Molecules ; 28(5)2023 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-36903366

RESUMO

Silk from silkworms and spiders is an exceptionally important natural material, inspiring a range of new products and applications due to its high strength, elasticity, and toughness at low density, as well as its unique conductive and optical properties. Transgenic and recombinant technologies offer great promise for the scaled-up production of new silkworm- and spider-silk-inspired fibres. However, despite considerable effort, producing an artificial silk that recaptures the physico-chemical properties of naturally spun silk has thus far proven elusive. The mechanical, biochemical, and other properties of pre-and post-development fibres accordingly should be determined across scales and structural hierarchies whenever feasible. We have herein reviewed and made recommendations on some of those practices for measuring the bulk fibre properties; skin-core structures; and the primary, secondary, and tertiary structures of silk proteins and the properties of dopes and their proteins. We thereupon examine emerging methodologies and make assessments on how they might be utilized to realize the goal of developing high quality bio-inspired fibres.


Assuntos
Bombyx , Fibroínas , Aranhas , Animais , Animais Geneticamente Modificados , Elasticidade , Aranhas/química , Fibroínas/química
3.
Angew Chem Int Ed Engl ; 62(23): e202303001, 2023 06 05.
Artigo em Inglês | MEDLINE | ID: mdl-37019840

RESUMO

Selecting a suitable support material for enzyme immobilization with excellent biocatalytic activity and stability is a critical aspect in the development of functional biosystems. The highly stable and metal-free properties of covalent-organic frameworks (COFs) make them ideal supports for enzyme immobilization. Herein, we constructed three kinds of COFs via a biofriendly and one-pot synthetic strategy at room temperature in aqueous solution. Among the three developed COFs (COF-LZU1, RT-COF-1 and ACOF-1), the horseradish peroxidase (HRP)-incorporated COF-LZU1 is found to retain the highest activity. Structural analysis reveals that a weakest interaction between the hydrated enzyme and COF-LZU1, an easiest accessibility by the COF-LZU1 to the substrate, as well as an optimal conformation of enzyme together promote the bioactivity of HRP-COF-LZU1. Furthermore, the COF-LZU1 is revealed to be a versatile nanoplatform for encapsulating multiple enzymes. The COF-LZU1 also offers superior protection for the immobilized enzymes under harsh conditions and during recycling. The comprehensive understanding of interfacial interactions of COF host and enzyme guest, the substrate diffusion, as well as the enzyme conformation alteration within COF matrices represents an opportunity to design the ideal biocatalysts and opens a broad range of applications of these nanosystems.


Assuntos
Enzimas Imobilizadas , Estruturas Metalorgânicas , Biocatálise , Difusão , Peroxidase do Rábano Silvestre
4.
J Am Chem Soc ; 144(39): 17865-17875, 2022 10 05.
Artigo em Inglês | MEDLINE | ID: mdl-36075889

RESUMO

Enhancing the enzymatic activity inside metal-organic frameworks (MOFs) is a critical challenge in chemical technology and bio-technology, which, if addressed, will broaden their scope in energy, food, environmental, and pharmaceutical industries. Here, we report a simple yet versatile and effective strategy to optimize biocatalytic activity by using MOFs to rapidly "lock" the ultrasound (US)-activated but more fragile conformation of metalloenzymes. The results demonstrate that up to 5.3-fold and 9.3-fold biocatalytic activity enhancement of the free and MOF-immobilized enzymes could be achieved compared to those without US pretreatment, respectively. Using horseradish peroxidase as a model, molecular dynamics simulation demonstrates that the improved activity of the enzyme is driven by an opened gate conformation of the heme active site, which allows more efficient substrate binding to the enzyme. The intact heme active site is confirmed by solid-state UV-vis and electron paramagnetic resonance, while the US-induced enzyme conformation change is confirmed by circular dichroism spectroscopy and Fourier-transform infrared spectroscopy. In addition, the improved activity of the biocomposites does not compromise their stability upon heating or exposure to organic solvent and a digestion cocktail. This rapid locking and immobilization strategy of the US-induced active enzyme conformation in MOFs gives rise to new possibilities for the exploitation of highly efficient biocatalysts for diverse applications.


Assuntos
Estruturas Metalorgânicas , Metaloproteínas , Enzimas Imobilizadas/química , Heme , Peroxidase do Rábano Silvestre , Estruturas Metalorgânicas/química , Solventes
5.
Small ; 18(22): e2201449, 2022 06.
Artigo em Inglês | MEDLINE | ID: mdl-35557499

RESUMO

Rechargeable aqueous proton batteries are promising competitors for the next generation of energy storage systems with the fast diffusion kinetics and wide availability of protons. However, poor cycling stability is a big challenge for proton batteries due to the attachment of water molecules to the electrode surface in acid electrolytes. Here, a hydrogen-bond disrupting electrolyte strategy to boost proton battery stability via simultaneously tuning the hydronium ion solvation sheath in the electrolyte and the electrode interface is reported. By mixing cryoprotectants such as glycerol with acids, hydrogen bonds involving water molecules are disrupted leading to a modified hydronium ion solvation sheaths and minimized water activity. Concomitantly, glycerol absorbs on the electrode surface and acts to protect the electrode surface from water. Fast and stable proton storage with high rate capability and long cycle life is thus achieved, even at temperatures as low as -50 °C. This electrolyte strategy may be universal and is likely to pave the way toward highly stable aqueous energy storage systems.


Assuntos
Glicerol , Prótons , Eletrólitos/química , Ligação de Hidrogênio , Água/química
6.
Small ; 18(45): e2202992, 2022 11.
Artigo em Inglês | MEDLINE | ID: mdl-36156409

RESUMO

Proton electrochemistry is promising for developing post-lithium energy storage devices with high capacity and rate capability. However, some electrode materials are vulnerable because of the co-intercalation of free water molecules in traditional acid electrolytes, resulting in rapid capacity fading. Here, the authors report a molecular crowding electrolyte with the usage of poly(ethylene glycol) (PEG) as a crowding agent, achieving fast and stable electrochemical proton storage and expanded working potential window (3.2 V). Spectroscopic characterisations reveal the formation of hydrogen bonds between water and PEG molecules, which is beneficial for confining the activity of water molecules. Molecular dynamics simulations confirm a significant decrease of free water fraction in the molecular crowding electrolyte. Dynamic structural evolution of the MoO3 anode is studied by in-situ synchrotron X-ray diffraction (XRD), revealing a reversible multi-step naked proton (de)intercalation mechanism. Surficial adsorption of PEG molecules on MoO3 anode works in synergy to alleviate the destructive effect of concurrent water desolvation, thereby achieving enhanced cycling stability. This strategy offers possibilities of practical applications of proton electrochemistry thanks to the low-cost and eco-friendly nature of PEG additives.


Assuntos
Fontes de Energia Elétrica , Prótons , Eletrólitos/química , Lítio/química , Água
7.
Phys Chem Chem Phys ; 23(25): 14075-14092, 2021 Jun 30.
Artigo em Inglês | MEDLINE | ID: mdl-34160000

RESUMO

Copolymeric organo-sulfur based electrodes provide a unique framework to explore and subsequently improve lithium-sulfur (Li-S) cells. There is a general difference in the way copolymers trap lithium during cell function compared to inorganic carbon-sulfur composites. Using a chain-like polyterpene copolymeric architecture involving the copolymerization of squalene monomer with sulfur (poly(S-r-squalene)), the first evidence for distinguishable differences in the entrapment of lithiated species, when using different copolymeric architectures, is provided. Investigation of poly(S-r-squalene) as an active cathode material via X-ray Absorption Near-Edge Structure (XANES) spectroscopy and high-resolution solid-state Nuclear Magnetic Resonance (NMR) reveal notable differences compared to previously studied poly(S-r-DIB) (proposed to have a less branched architecture) between the lithium environments present during electrochemistry that can be directly linked to the copolymeric structural features. Subtle but pertinent effects based on the copolymeric architecture related to the solid-electrolyte interphase (SEI) formed from the electrolytic components are also uncovered through these techniques. This work offers a comprehensive study on poly(S-r-squalene) and reveals that foundational inverse vulcanisation conditions such as choice of crosslinking monomer can dramatically impact lithium transport and SEI formation for the copolymeric electrode.

8.
Angew Chem Int Ed Engl ; 60(10): 5421-5428, 2021 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-33258208

RESUMO

Metal-organic frameworks (MOFs) have recently emerged as excellent hosting matrices for enzyme immobilization, offering superior physical and chemical protection for biocatalytic reactions. However, for multienzyme and cofactor-dependent biocatalysis, the subtle orchestration of enzymes and cofactors is largely disrupted upon immobilizing in the rigid crystalline MOF network, which leads to a much reduced biocatalytic efficiency. Herein, we constructed hierarchically porous MOFs by controlled structural etching to enhance multienzyme and cofactor-dependent enzyme biocatalysis. The expanded size of the pores can provide sufficient space for accommodated enzymes to reorientate and spread within MOFs in their lower surface energy state as well as to decrease the inherent barriers to accelerate the diffusion rate of reactants and intermediates. Moreover, the developed hierarchically porous MOFs demonstrated outstanding tolerance to inhospitable surroundings and recyclability.


Assuntos
Biocatálise/efeitos dos fármacos , Enzimas Imobilizadas/química , Estruturas Metalorgânicas/química , Armoracia/enzimologia , Glucose/química , NAD/química , Oxirredução , Fenazinas/síntese química , Fenilenodiaminas/química , Porosidade
9.
Small ; 16(12): e1903397, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31496028

RESUMO

An unprecedented microwave-based strategy is developed to facilitate solid-phase, instantaneous delamination and decomposition of graphite fluoride (GF) into few-layer, partially fluorinated graphene. The shock reaction occurs (and completes in few seconds) under microwave irradiation upon exposing GF to either "microwave-induced plasma" generated in vacuum or "catalyst effect" caused by intense sparking of graphite at ambient conditions. A detailed analysis of the structural and compositional transformations in these processes indicates that the GF experiences considerable exfoliation and defluorination, during which sp2 -bonded carbon is partially recovered despite significant structural defects being introduced. The exfoliated fluorinated graphene shows excellent electrochemical performance as anode materials in potassium ion batteries and as catalysts for the conversion of O2 to H2 O2 . This simple and scalable method requires minimal energy input and does not involve the use of other chemicals, which is attractive for extensive research in fluorine-containing graphene and its derivatives in laboratories and industrial applications.

10.
Photochem Photobiol Sci ; 19(10): 1410-1422, 2020 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-32966538

RESUMO

The remarkable properties of deuterium have led to many exciting and favourable results in enhancing material properties, for applications in the physical, medical, and biological sciences. Deuterated isotopologues of avobenzone, a sunscreen active ingredient, were synthesised to examine for any changes to the equilibrium between the diketone and enol isomers, as well as their UV photostability and photoprotective properties. Prior to UV irradiation, deuteration of the diketone methylene/enol moiety (i.e. avobenzone-d2) led to an increase in the % diketone compared to non-deuterated, determined by 1H NMR experiments in CDCl3 and C6D12. This can be rationalised from two angles; mechanistically by a deuterium kinetic isotope effect for the CH vs. CD abstraction step during tautomerisation from the diketone to the enol, and a weaker chelating hydrogen bond for the enol when deuterated allowing increased equilibration to the diketone. Avobenzone-d2 was further examined by solid state 13C NMR. The higher % diketone for avobenzone-d2 was postulated to favour increased photodegradation by a non-reversible pathway. This was investigated by UV irradiation of the avobenzone isotopologues in C6D12, both in real time in situ within the NMR by fibre optic cable as well as ex situ using sunlight. An increase in the relative amount of photoproducts for avobenzone-d2 compared to non-deuterated was observed by 1H NMR upon UV irradiation ex situ. Overall, the study demonstrates that deuteration can be applied to alter complex equilibria, and has potential to be manifested as changes to the properties and behaviour of materials.


Assuntos
Álcoois/química , Deutério/química , Cetonas/química , Propiofenonas/química , Protetores Solares/química , Estrutura Molecular , Processos Fotoquímicos , Raios Ultravioleta
11.
Inorg Chem ; 59(17): 12143-12155, 2020 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-32808781

RESUMO

Sodium-ion batteries (NIBs) are an emerging alternative to lithium-ion batteries because of the abundance of sodium resources and their potentially lower cost. Here we report the Na0.7MnO2 solid state synthesized at 1000 °C that shows two distinct phases; one adopts hexagonal P2-type P63/mmc space group symmetry, and the other adopts orthorhombic Pbma space group symmetry. The phase ratio of P2 to the orthorhombic phase is 55.0(5):45.0(4). A single-phase P2 structure is found to form at 1000 °C after modification with alkali metals Rb and Cs, while the K-modified form produces an additional minor impurity. The modification is the addition of the alkali elements during synthesis that do not appear to be doped into the crystal structure. As a cathode for NIBs, parent Na0.7MnO2 shows a second charge/discharge capacity of 143/134 mAh g-1, K-modified Na0.7MnO2 a capacity of 184/178 mAh g-1, Rb-modified Na0.9MnO2 a capacity of 159/150 mAh g-1, and Cs-modified Na0.7MnO2 a capacity of 171/163 mAh g-1 between 1.5 and 4.2 V at a current density of 15 mA g-1. The parent Na0.7MnO2 is compared with alkali metal (K, Rb, and Cs)-modified NaxMnO2 in terms of surface morphology using scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, scanning electron microscopy, 23Na solid-state nuclear magnetic resonance, and X-ray photoelectron spectroscopy and in terms of electrochemical performance and structural electrochemical evolution using in situ or operando synchrotron X-ray diffraction.

12.
Soft Matter ; 15(11): 2400-2410, 2019 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-30776040

RESUMO

More than 40% of newly developed drug molecules are highly hydrophobic and, thus, suffer from low bioavailability. Kinetically trapping the drug as a nanoparticle in an amorphous state enhances solubility. However, enhanced solubility can be compromised by subsequent recrystallization from the amorphous state during drying processes. We combine Flash NanoPrecipitation (FNP) to generate nanoparticles with spray-drying to produce stable solid powders. We demonstrate that the continuous nanofabrication platform for nanoparticle synthesis and recovery does not compromise the dissolution kinetics of the drug. Lumefantrine, an anti-malaria drug, is highly hydrophobic with low bioavailability. Increasing the bioavailability of lumefantrine has the potential to reduce the dose and number of required administrations per treatment, thus reducing cost and increasing patient compliance. The low melting temperature of lumefantrine (Tm = 130 °C) makes the drying of amorphous nanoparticles at elevated temperatures potentially problematic. Via FNP, we produced 200-400 nm nanoparticles using hydroxypropyl methylcellulose acetate succinate (HPMCAS), lecithin phospholipid, and zein protein stabilizers. Zein nanoparticles were spray-dried at 100 °C and 120 °C to study the effect of the drying temperature. For zein powders, at two hours the dissolution kinetics under fasted conditions reached 85% release for the 100 °C sample, but only 60% release for the 120 °C sample. Powder X-ray diffraction, differential scanning calorimetry, and solid state nuclear magnetic resonance indicate that the lumefantrine in the nanoparticle core is amorphous for samples spray-dried at 100 °C. Dissolution under fed state conditions showed similar release kinetics for both temperatures, with 90-95% release at two hours. Zein and HPMCAS nanoparticles spray-dried at 100 °C showed release profiles in fasted and fed state media that are identical to those of lyophilized samples, i.e. those dried at cryogenic conditions where no transformation to the crystalline state can occur. Thus, spray drying 30 °C below the melting transition of lumefantrine is sufficient to maintain the amorphous state. These inexpensive formulations have potential to be developed into future therapies for malaria, and the results also highlight the potential of combining FNP and spray-drying as a versatile platform to assemble and rapidly recover amorphous nanoparticles in a solid dosage form.

13.
Phys Chem Chem Phys ; 21(34): 18667-18679, 2019 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-31417991

RESUMO

Composite organo-sulfur cathodes provide a unique platform for the realization of lithium-sulfur (Li-S) cells. However, difficulties arise in the interpretation of the function of these electrodes in Li-S cells and the role they play in suppressing the so-called 'shuttle effect'. This work focuses on monitoring in detail the structural evolution and lithium environments during charge-discharge cycles in a lithium half-cell of an organo-sulfur cathode, which was synthesised by inverse vulcanisation with 1,3-diisopropenylbenzene. For the first-time in organo-sulfur materials, high resolution solid state 7Li-1H and 13C-1H double resonance NMR spectroscopy coupled with X-ray absorption near-edge structure (XANES) and X-ray diffraction (XRD) are used to develop a detailed structural model of the cathode material and its lithium environments as a function of cycle number. This work provides the first experimental evidence via 2D NMR spectroscopy of distinct molecular proximities of the lithium species with respect to the sulfur, the organic skeleton and the electrolyte in the cathode material. This approach enables us to develop unparalleled understanding of the mechanisms of the high charge capacity of 607 mA h g-1, rationalising initial capacity drop and suppression of capacity fade with cycling. These results also show new possibilities on how to better understand electrode function to further increase the lithium capacities of organo-sulfur cathode materials, which can in turn lead to performance-enhanced Li-S cells.

14.
Mol Pharm ; 15(2): 495-507, 2018 02 05.
Artigo em Inglês | MEDLINE | ID: mdl-29244515

RESUMO

We report the development of a new spray-drying and nanoparticle assembly process (SNAP) that enables the formation of stable, yet rapidly dissolving, sub-200 nm nanocrystalline particles within a high Tg glassy matrix. SNAP expands the class of drugs that spray-dried dispersion (SDD) processing can address to encompass highly crystalline, but modestly hydrophobic, drugs that are difficult to process by conventional SDD. The process integrates rapid precipitation and spray-drying within a custom designed nozzle to produce high supersaturations and precipitation of the drug and high Tg glassy polymer. Keeping the time between precipitation and drying to tens of milliseconds allows for kinetic trapping of drug nanocrystals in the polymer matrix. Powder X-ray diffraction, solid state 2D NMR, and SEM imaging shows that adding an amphiphilic block copolymer (BCP) to the solvent gives essentially complete crystallization of the active pharmaceutical ingredient (API) with sub-200 nm domains. In contrast, the absence of the block copolymer results in the API being partially dispersed in the matrix as an amorphous phase, which can be sensitive to changes in bioavailability over time. Quantification of the API-excipient interactions by 2D 13C-1H NMR correlation spectroscopy shows that the mechanism of enhanced nanocrystal formation is not due to interactions between the drug and the BCP, but rather the BCP masks interactions between the drug and hydrophobic regions of the matrix polymers. BCP-facilitated SNAP samples show improved stability during aging studies and rapid dissolution and release of API in vitro.


Assuntos
Dessecação/métodos , Composição de Medicamentos/métodos , Nanopartículas/química , Disponibilidade Biológica , Química Farmacêutica/métodos , Liberação Controlada de Fármacos , Excipientes , Interações Hidrofóbicas e Hidrofílicas , Espectroscopia de Ressonância Magnética , Polímeros/química , Solubilidade , Difração de Raios X
15.
Angew Chem Int Ed Engl ; 56(29): 8441-8445, 2017 07 10.
Artigo em Inglês | MEDLINE | ID: mdl-28570761

RESUMO

The present study highlights the importance of understanding the structural changes of micelles induced by drug loading on their physico-chemical properties. A block copolymer with attached fructose, which interacts with GLUT5 receptor, was used and conjugated with a low and a high amount of platinum drugs. Against expectations, the low-loading micelle, despite having a less defined morphology and larger nanoparticle size according to TEM, displays higher cellular uptake and higher toxicity. This behaviour can only be understood when elucidating additional information on the structure of micelles. Extensive solid-state NMR measurements were therefore employed to reveal that the drug loading affected swelling and mobility of core and shell of the micelle. The results obtained from solid-state NMR spectroscopy could explain all the observations on this system. In summary, solid-state NMR spectroscopy is an excellent tool to understand the effects of drug loading on the behavior of micelles.

16.
Environ Sci Technol ; 50(14): 7706-14, 2016 07 19.
Artigo em Inglês | MEDLINE | ID: mdl-27284608

RESUMO

Dramatic changes in molecular structure, degradation pathway, and porosity of biochar are observed at pyrolysis temperatures ranging from 250 to 550 °C when bamboo biomass is pretreated by iron-sulfate-clay slurries (iron-clay biochar), as compared to untreated bamboo biochar. Electron microscopy analysis of the biochar reveals the infusion of mineral species into the pores of the biochar and the formation of mineral nanostructures. Quantitative (13)C nuclear magnetic resonance (NMR) spectroscopy shows that the presence of the iron clay prevents degradation of the cellulosic fraction at pyrolysis temperatures of 250 °C, whereas at higher temperatures (350-550 °C), the clay promotes biomass degradation, resulting in an increase in both the concentrations of condensed aromatic, acidic, and phenolic carbon species. The porosity of the biochar, as measured by NMR cryoporosimetry, is altered by the iron-clay pretreatment. In the presence of the clay, at lower pyrolysis temperatures, the biochar develops a higher pore volume, while at higher temperature, the presence of clay causes a reduction in the biochar pore volume. The most dramatic reduction in pore volume is observed in the kaolinite-infiltrated biochar at 550 °C, which is attributed to the blocking of the mesopores (2-50 nm pore) by the nonporous metakaolinite formed from kaolinite.


Assuntos
Carbono , Carvão Vegetal/química , Biomassa , Minerais , Estrutura Molecular , Porosidade
17.
Int J Mol Sci ; 17(8)2016 Aug 09.
Artigo em Inglês | MEDLINE | ID: mdl-27517909

RESUMO

The exceptional strength and extensibility of spider dragline silk have been thought to be facilitated by two spidroins, major ampullate spidroin 1 (MaSp1) and major ampullate spidroin 2 (MaSp2), under the assumption that protein secondary structures are coupled with the expressed spidroins. We tested this assumption for the dragline silk of three co-existing Australian spiders, Argiope keyserlingi, Latrodectus hasselti and Nephila plumipes. We found that silk amino acid compositions did not differ among spiders collected in May. We extended these analyses temporally and found the amino acid compositions of A. keyserlingi silks to differ when collected in May compared to November, while those of L. hasselti did not. To ascertain whether their secondary structures were decoupled from spidroin expression, we performed solid-state nuclear magnetic resonance spectroscopy (NMR) analysis on the silks of all spiders collected in May. We found the distribution of alanine toward ß-sheet and 3,10helix/random coil conformations differed between species, as did their relative crystallinities, with A. keyserlingi having the greatest 3,10helix/random coil composition and N. plumipes the greatest crystallinity. The protein secondary structures correlated with the mechanical properties for each of the silks better than the amino acid compositions. Our findings suggested that a differential distribution of alanine during spinning could decouple secondary structures from spidroin expression ensuring that silks of desirable mechanical properties are consistently produced. Alternative explanations include the possibility that other spidroins were incorporated into some silks.


Assuntos
Fibroínas/química , Proteínas de Insetos/química , Seda/química , Aminoácidos/química , Animais , Cromatografia Líquida de Alta Pressão , Espectroscopia de Ressonância Magnética
18.
Phys Chem Chem Phys ; 17(34): 22195-203, 2015 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-26239510

RESUMO

A range of solid-state NMR techniques is used to characterise a molecular host:guest complex consisting of a [5]polynorbornane bisurea host binding a terephthalate dianion guest. Detailed information is obtained on the molecular dynamics and associations from the point of view of both the host and guest molecules. The formation of the complex in the solid state is confirmed using (1)H 2D exchange NMR, and the 180° flipping of the (2)H-labelled terephthalate guest and its eventual expulsion from the complex at elevated temperatures are quantified using variable-temperature (2)H spin-echo experiments. Two-dimensional (1)H-(13)C HETCOR spectra obtained under fast magic angle spinning conditions (60 kHz) show a high resolution despite the poor crystallinity of the solid complex, and clearly reveal changes in the rigidity of the host molecule when complexed. Short-range intra- and intermolecular (1)H-(1)H proximities are also detected using 2D SQ-DQ correlation methods, providing insight into the molecular packing in the solid phase.


Assuntos
Simulação de Dinâmica Molecular , Norbornanos/química , Ácidos Ftálicos/química , Ureia/química , Espectroscopia de Ressonância Magnética , Ureia/análogos & derivados
19.
Phys Chem Chem Phys ; 17(17): 11252-9, 2015 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-25835336

RESUMO

Two organic polymers containing alternating electron donating triarylamine and electron accepting thiazolo[5,4-d]thiazole (TzTz) moieties have been synthesized and their redox states investigated. When donor and acceptor units are proximal (polymer )1, electron density is delocalized, leading to a small electrical and optical band gap; these are larger with the inclusion of an adjoining alkynyl-phenyl bridge (polymer 2), where electron density is more localized due to the rotation of the monomer units. As a result, 1 and 2 display different optical and fluorescence properties in their neutral states. Upon chemical and electrochemical redox reactions, radicals form in both 1 and 2, yielding magnetic materials that display temperature-independent paramagnetism, attributable to delocalization of radical spins along the polymeric backbones. The ability to convert between diamagnetic and paramagnetic states upon chemical oxidation and/or reduction allows for the materials to display switchable magnetism and fluorescence, imparting multifunctionality to these solid-state purely organic materials.

20.
Proc Natl Acad Sci U S A ; 108(22): 8949-54, 2011 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-21562207

RESUMO

Sugar molecules adsorbed at hydrated inorganic oxide surfaces occur ubiquitously in nature and in technologically important materials and processes, including marine biomineralization, cement hydration, corrosion inhibition, bioadhesion, and bone resorption. Among these examples, surprisingly diverse hydration behaviors are observed for oxides in the presence of saccharides with closely related compositions and structures. Glucose, sucrose, and maltodextrin, for example, exhibit significant differences in their adsorption selectivities and alkaline reaction properties on hydrating aluminate, silicate, and aluminosilicate surfaces that are shown to be due to the molecular architectures of the saccharides. Solid-state (1)H, (13)C, (29)Si, and (27)Al nuclear magnetic resonance (NMR) spectroscopy measurements, including at very high magnetic fields (19 T), distinguish and quantify the different molecular species, their chemical transformations, and their site-specific adsorption on different aluminate and silicate moieties. Two-dimensional NMR results establish nonselective adsorption of glucose degradation products containing carboxylic acids on both hydrated silicates and aluminates. In contrast, sucrose adsorbs intact at hydrated silicate sites and selectively at anhydrous, but not hydrated, aluminate moieties. Quantitative surface force measurements establish that sucrose adsorbs strongly as multilayers on hydrated aluminosilicate surfaces. The molecular structures and physicochemical properties of the saccharides and their degradation species correlate well with their adsorption behaviors. The results explain the dramatically different effects that small amounts of different types of sugars have on the rates at which aluminate, silicate, and aluminosilicate species hydrate, with important implications for diverse materials and applications.


Assuntos
Silicatos de Alumínio/química , Alumínio/química , Dissacarídeos/química , Silicatos/química , Adesividade , Adsorção , Compostos de Alumínio/química , Reabsorção Óssea , Compostos de Cálcio/química , Glucose/química , Espectroscopia de Ressonância Magnética/métodos , Microscopia Eletrônica de Varredura/métodos , Conformação Molecular , Óxidos/química , Polissacarídeos/química , Sacarose/química
SELEÇÃO DE REFERÊNCIAS
Detalhe da pesquisa