Papers by Gregory Holland
Microscopy and Microanalysis, Aug 1, 2019
MRS Advances, Jun 28, 2016
ABSTRACT At the MRS Fall 2014 Meeting, Symposium E, we reported on morphologies, fragmentation, a... more ABSTRACT At the MRS Fall 2014 Meeting, Symposium E, we reported on morphologies, fragmentation, and hardness in synthetic hydrogen urate monohydrate (monosodium urate monohydrate, MSUM, or MSU) crystals. We are now presenting further characterization results, including some from the biomaterial that forms in humans with gout disease: The fanning of radiating blades (needles) in spherulitic grains of synthetic MSUM was examined by microscopy techniques. These and previous data are consistent with an interpretation in terms of the crystallographic parameters in the unit cell, and the presence of dislocation arrays at low angle boundaries. The kinetics of such branched growth is here related to thermodynamic properties and super-saturation levels. Secondary nucleation is an additional mechanism leading to more complex morphologies. Differences in overall growth rates, under conditions of either branched or single needle growth, are considered in relation to gout. Novel powder XRD and solid state NMR data show, respectively, preferred orientation in the biomaterial, and the potential of NMR for identifying and characterizing MSUM in specific environments, helping to resolve pending questions in gout. Present results are anticipated to be useful for designing bio-inspired and bio-mimetic materials, regarding morphologies, overall growth rates, and mechanical properties.
Chemistry of Materials, Jul 25, 2002
Lithium ions were electrochemically inserted into V 2 O 5 ‚0.5H 2 O xerogel and studied with 7 Li... more Lithium ions were electrochemically inserted into V 2 O 5 ‚0.5H 2 O xerogel and studied with 7 Li magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Two distinct lithium environments were resolved and assigned to lithium ions occupying either interfacial or intercalated sites in the V 2 O 5 ‚0.5H 2 O xerogel matrix. Lithium chemical shifts, relaxation measurements, and variable-temperature (VT) MAS NMR are used to determine the mobility of both interfacial and intercalated lithium ions and the associated coupling to paramagnetic sites on the V 2 O 5 xerogel lattice. From spin-lattice relaxation (T 1) data, a minimum is observed, yielding an average polaron correlation time in excellent agreement with a value based independently on conductivity measurements. Thus, revealing that the dominant relaxation mechanism is associated with the nuclear dipole coupling to polaron motion.
The quantitative analysis of ammonia binding sites in the Davison (Type 3A) zeolite desiccant usi... more The quantitative analysis of ammonia binding sites in the Davison (Type 3A) zeolite desiccant using solid-state 15 N MAS NMR spectroscopy is reported. By utilizing 15 Nenriched ammonia (15 NH 3) gas, the different adsorption/binding sites within the zeolite were investigated as a function of NH 3 loading. Using 15 N MAS NMR multiple sites were resolved that have distinct cross-polarization dynamics and chemical shift behavior. These differences in the 15 N NMR were used to characterize the adsorption environments in both the pure 3A zeolite and the silicone-molded forms of the desiccant.
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services, Directorate (0704-0188). Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.
Proceedings of the National Academy of Sciences of the United States of America, Oct 22, 2018
ChemInform, Aug 19, 2008
ABSTRACT
Scientific Reports, 2019
A major challenge in liposomal research is to minimize the leakage of encapsulated cargo from eit... more A major challenge in liposomal research is to minimize the leakage of encapsulated cargo from either uncontrolled passive permeability across the liposomal membrane or upon fusion with other membranes. We previously showed that liposomes made from pure Archaea-inspired bipolar tetraether lipids exhibit exceptionally low permeability of encapsulated small molecules due to their capability to form more tightly packed membranes compared to typical monopolar lipids. Here, we demonstrate that liposomes made of synthetic bipolar tetraether lipids can also undergo membrane fusion, which is commonly accompanied by content leakage of liposomes when using typical bilayer-forming lipids. Importantly, we demonstrate calcium-mediated fusion events between liposome made of glycerolmonoalkyl glycerol tetraether lipids with phosphatidic acid headgroups (GMGTPA) occur without liposome content release, which contrasts with liposomes made of bilayer-forming EggPA lipids that displayed ~80% of content ...
Science Advances, 2019
Restricted rotation through tethering of lipids as found in archaea helps maintain barrier functi... more Restricted rotation through tethering of lipids as found in archaea helps maintain barrier function at elevated temperatures.
Organic Chemistry Frontiers, 2019
Guest dynamics inside pyrogallol[4]arene hexamers in the solid state are sensitive to structure e... more Guest dynamics inside pyrogallol[4]arene hexamers in the solid state are sensitive to structure external to the host.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2019
Investigating the interaction of Grammostola rosea venom peptides and model lipid bilayers with s... more Investigating the interaction of Grammostola rosea venom peptides and model lipid bilayers with solid-state NMR and electron microscopy techniques
Chem. Sci., 2017
Ball milling mixtures of pyrogallol[4]arene and guests gives direct access to encapsulation compl... more Ball milling mixtures of pyrogallol[4]arene and guests gives direct access to encapsulation complexes and can be monitored by solid-state NMR.
Chemistry – A European Journal, 2017
Supporting information and the ORCID identification number for the authorofthis article can be fo... more Supporting information and the ORCID identification number for the authorofthis article can be found under
The Journal of Physical Chemistry C, 2016
Catechol on TiO 2 is a model system for a class of molecules that bind and interact very strongly... more Catechol on TiO 2 is a model system for a class of molecules that bind and interact very strongly with metal oxides. This interaction gives rise to a marked charge-transfer absorption band that can be used to sensitize the complex to visible light. In solar cells, these are called type-II sensitizers in contrast with type I sensitizers where an excitation of the molecule with subsequent charge injection is the main mechanism for placing an electron in the conduction band of the semiconductor. The adsorption geometry of these molecules is critical in their functioning. Nuclear magnetic resonance (NMR) spectroscopic methods can be used to elucidate structural information about the local geometry at the substrate-molecule interface. NMR methods coupled with Density Functional Theory (DFT), allow for the detailed characterization of molecular binding modes. In the present work, we report a solid-state NMR and DFT study of catechol on TiO 2 . DFT-GIPAW chemical shift predictions for the 13 C CP-MAS experiments unambiguously indicate the presence of a chelated geometry. 1 H→ 13 C cross polarization build-up kinetics were used to determine the protonation state of additional geometries and point towards the presence of molecular species. The most stable adsorption modes on regular slab models were found to be bidentate and it is only in the presence of defective surfaces where the chelated mode stabilizes in the presence of undercoordinated titanium surface sites. The combined NMR and DFT approach allows thus to characterise the binding geometry, which is a stepping stone in the design of more complex light-harvesting architectures. This work constitutes, to the best of our knowledge, the first detailed instance of combined solid-state NMR and DFT studies on this class of materials.
Biomacromolecules, Dec 12, 2016
The molecular interactions of silk materials plasticized using glycerol were studied, as these ma... more The molecular interactions of silk materials plasticized using glycerol were studied, as these materials provide options for biodegradable and flexible protein-based systems. Plasticizer interactions with silk were analyzed by thermal, spectroscopic, and solid-state NMR analyses. Spectroscopic analysis implied that glycerol was hydrogen bonded to the peptide matrix, but may be displaced with polar solvents. Solid-state NMR indicated that glycerol induced β-sheet formation in the dried silk materials, but not to the extent of methanol treatment. Fast scanning calorimetry suggested that β-sheet crystal formation in silk-glycerol films appeared to be less organized than in the methanol treated silk films. We propose that glycerol may be simultaneously inducing and interfering with β-sheet formation in silk materials, causing some improper folding that results in less-organized silk II structures even after the glycerol is removed. This difference, along with trace residual glycerol, al...
MRS Advances, 2016
ABSTRACTTo achieve the goal of biocompatibility in nano-based materials we must first obtain a fu... more ABSTRACTTo achieve the goal of biocompatibility in nano-based materials we must first obtain a fundamental understanding of the physical and chemical behavior of biomolecules at the interfaces of nanomaterials. A first step towards understanding protein interactions with nanomaterials is to understand how individual amino acids interact at the interfaces. In this paper, we investigated the lysine adsorption behavior on fumed silica nanoparticles by solid-state NMR spectroscopy. We use1H,13C and15N solid-state magic angle spinning (MAS) NMR techniques to elucidate how lysine is adsorbed on silica nanoparticles surfaces via strong hydrogen-bonding interaction between the protonated side-chain amine group and silanol group on silica nanoparticles surfaces.*
Chemistry (Weinheim an der Bergstrasse, Germany), Jun 3, 2016
This paper examines the effects of four different polar headgroups on small-ion membrane permeabi... more This paper examines the effects of four different polar headgroups on small-ion membrane permeability from liposomes comprised of Archaea-inspired glycerolmonoalkyl glycerol tetraether (GMGT) lipids. We found that the membrane-leakage rate across GMGT lipid membranes varied by a factor of ≤1.6 as a function of headgroup structure. However, the leakage rates of small ions across membranes comprised of commercial bilayer-forming 1-palmitoyl-2-oleoyl-sn-glycerol (PO) lipids varied by as much as 32-fold within the same series of headgroups. These results demonstrate that membrane leakage from GMGT lipids is less influenced by headgroup structure, making it possible to tailor the structure of the polar headgroups on GMGT lipids while retaining predictable leakage properties of membranes comprised of these tethered lipids.
The Journal of Physical Chemistry C, 2015
Investigating the interface between biomolecules and nanoparticles has attracted considerable att... more Investigating the interface between biomolecules and nanoparticles has attracted considerable attention in recent years since it has great significance in numerous fields including nanotechnology, biomineralization, cancer therapy, and origin of life. In this paper, we present a thorough solid-state NMR study on alanine adsorption and thermal condensation on fumed silica nanoparticles. The structure and dynamics at the interface between alanine and fumed silica nanoparticles were probed with a combination of 1H, 13C, and 15N one- and two-dimensional (2D) magic angle spinning (MAS) solid-state NMR methods at different alanine surface coverages and hydration levels. It is illustrated at high surface coverages both crystalline and adsorbed states of alanine exist in the samples while only adsorbed alanine is observed at low surface coverage (approximately a monolayer). At high hydration levels, the adsorbed alanine exhibits enhanced mobility, and both the carboxyl and amine group interact with mobile water m...
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Papers by Gregory Holland