How Many Glucan Chains Form Plant Cellulose Microfibrils? A Mini Review.

Assessing the number of glucan chains in cellulose microfibrils (CMFs) is crucial for understanding their structure-property relationships and interactions within plant cell walls. This Review examines the conclusions and limitations of the major experimental techniques that have provided insights into this question. Small-angle X-ray and neutron scattering data predominantly support an 18-chain model, although analysis is complicated by factors such as fibril coalescence and matrix polysaccharide associations.

Ultrafast Two-Color X-Ray Emission Spectroscopy Reveals Excited State Landscape in a Base Metal Dyad.

Effective photoinduced charge transfer makes molecular bimetallic assemblies attractive for applications as active light-induced proton reduction systems. Developing competitive base metal dyads is mandatory for a more sustainable future. However, the electron transfer mechanisms from the photosensitizer to the proton reduction catalyst in base metal dyads remain so far unexplored.

From Ultrafast Photoinduced Small Polarons to Cooperative and Macroscopic Charge-Transfer Phase Transition.

We study by femtosecond infrared spectroscopy the ultrafast and persistent photoinduced phase transition of the RbMnCo[Fe(CN)] ⋅ 0.2HO material, induced at room temperature by a single laser shot. This system exhibits a charge-transfer based phase transition with a 75 K wide thermal hysteresis, centred at room temperature, from the low temperature Mn-N-C-Fe tetragonal phase to the high temperature Mn-N-C-Fe cubic phase.

Bridging molecular-scale interfacial science with continuum-scale models.

Solid-water interfaces are crucial for clean water, conventional and renewable energy, and effective nuclear waste management. However, reflecting the complexity of reactive interfaces in continuum-scale models is a challenge, leading to oversimplified representations that often fail to predict real-world behavior. This is because these models use fixed parameters derived by averaging across a wide physicochemical range observed at the molecular scale.

A multi-scale assessment of the impact of salinity on the desorption of chromate from hematite: Sea level rise implications.

The solubility and transport of Cr(VI) is primarily controlled by adsorption-desorption reactions at the surfaces of soil minerals such as iron oxides. Environmental properties such as pH, ionic strength, and ion competition are expected to affect the mobility and fate of Cr(VI). Sea level rise (SLR), and consequent seawater intrusion, is creating a new biogeochemical soil environment at coastal margins, potentially impacting Cr(VI) retention at contaminated sites.

Distinguishing different surface interactions for nucleotides adsorbed onto hematite and goethite particle surfaces through ATR-FTIR spectroscopy and DFT calculations.

Geochemical interfaces can impact the fate and transport of aqueous species in the environment including biomolecules. In this study, we investigate the surface chemistry of adsorbed nucleotides on two different minerals, hematite and goethite, using infrared spectroscopy and density functional theory (DFT) calculations. Attenuated total reflectance-Fourier transform infrared spectroscopy is used to probe the adsorption of deoxyadenosine monophosphate (dAMP), deoxyguanosine monophosphate (dGMP), deoxycytidine monophosphate (dCMP), and deoxythymidine monophosphate (dTMP) onto either hematite or goethite particle surfaces.

Oxide- and Silicate-Water Interfaces and Their Roles in Technology and the Environment.

Interfacial reactions drive all elemental cycling on Earth and play pivotal roles in human activities such as agriculture, water purification, energy production and storage, environmental contaminant remediation, and nuclear waste repository management. The onset of the 21st century marked the beginning of a more detailed understanding of mineral aqueous interfaces enabled by advances in techniques that use tunable high-flux focused ultrafast laser and X-ray sources to provide near-atomic measurement resolution, as well as by nanofabrication approaches that enable transmission electron microscopy in a liquid cell. This leap into atomic- and nanometer-scale measurements has uncovered scale-dependent phenomena whose reaction thermodynamics, kinetics, and pathways deviate from previous observations made on larger systems.

Grazing-incidence diffraction reveals cellulose and pectin organization in hydrated plant primary cell wall.

The primary cell wall is highly hydrated in its native state, yet many structural studies have been conducted on dried samples. Here, we use grazing-incidence wide-angle X-ray scattering (GIWAXS) with a humidity chamber, which enhances scattering and the signal-to-noise ratio while keeping outer onion epidermal peels hydrated, to examine cell wall properties. GIWAXS of hydrated and dried onion reveals that the cellulose ([Formula: see text]) lattice spacing decreases slightly upon drying, while the (200) lattice parameters are unchanged.

Public safety redefined: Mitigating trauma by centering the community in community mental health.

The summer of 2020 marked a shift in public perception of police brutality and racism in the United States. Following the police murder of George Floyd and ensuing social unrest, the appropriate role and function of the police in communities have been a frequent topic of debate. Of particular concern is the intersection of policing and mental health where we see a pattern of police using excessive force disproportionately against persons with disabilities, especially mental health disabilities (Autistic Self Advocacy Network, 2017).

Microbial Denitrification: Active Site and Reaction Path Models Predict New Isotopic Fingerprints.

The study of isotopic fingerprints in nitrate (δN, δO, ΔO) has enabled pivotal insights into the global nitrogen cycle and revealed new knowledge gaps. Measuring populations of isotopic homologs of intact NO ions (isotopologues) shows promise to advance the understanding of nitrogen cycling processes; however, we need new theory and predictions to guide laboratory experiments and field studies. We investigated the hypothesis that the isotopic composition of the residual nitrate pool is controlled by the N-O bond-breaking step in Nar dissimilatory nitrate reductase using molecular models of the enzyme active sites and associated kinetic isotope effects (KIEs).

A perspective on iron (Fe) in the atmosphere: air quality, climate, and the ocean.

As scientists engage in research motivated by climate change and the impacts of pollution on air, water, and human health, we increasingly recognize the need for the scientific community to improve communication and knowledge exchange across disciplines to address pressing and outstanding research questions holistically. Our professional paths have crossed because our research activities focus on the chemical reactivity of Fe-containing minerals in air and water, and at the air-sea interface. (Photo)chemical reactions driven by Fe can take place at the surface of the particles/droplets or within the condensed phase.

Connecting Thermodynamics of Alkali Ion Exchange on the Quartz (101) Surface with Density Functional Theory Calculations.

Periodic plane-wave density functional theory (DFT) calculations were performed on the α-quartz (SiO) (101) surface to model exchange of adsorbed Li and either Na, K, or Rb in inner- and outer-sphere adsorbed, and aqueous configurations, which are charge-balanced with 2 Cl. SiO or SiOH groups represented the adsorption surface sites. The SiO models included 58 HO and 2 HO molecules to approximate an aqueous environment, whereas the SiOH models had 59 HO and 1 HO molecules.

Effect of Dimer Structure and Inhomogeneous Broadening of Energy Levels on the Action of Flavomononucleotide in Rigid Polyvinyl Alcohol Films.

The results of time-resolved fluorescence measurements of flavin mononucleotide (FMN) in rigid polyvinyl alcohol films (PVA) demonstrate that fluorescence intensity decays are strongly accelerated in the presence of fluorescent dimers and nonradiative energy transfer processes. The fluorescence decay originating both from H and J dimer states of FMN was experimentally observed for the first time. The mean fluorescence lifetimes for FMN dimers were obtained: τfl = 2.

Fundamental Characterization, Photophysics and Photocatalysis of a Base Metal Iron(II)-Cobalt(III) Dyad.

A new base metal iron-cobalt dyad has been obtained by connection between a heteroleptic tetra-NHC iron(II) photosensitizer combining a 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine with 2,6-bis(3-methyl-imidazol-2-ylidene)-4,4'-bipyridine ligand, and a cobaloxime catalyst. This novel iron(II)-cobalt(III) assembly has been extensively characterized by ground- and excited-state methods like X-ray crystallography, X-ray absorption spectroscopy, (spectro-)electrochemistry, and steady-state and time-resolved optical absorption spectroscopy, with a particular focus on the stability of the molecular assembly in solution and determination of the excited-state landscape. NMR and UV/Vis spectroscopy reveal dissociation of the dyad in acetonitrile at concentrations below 1 mM and high photostability.

and Real-Time ATR-FTIR Temperature-Dependent Adsorption Kinetics Coupled with DFT Calculations of Dimethylarsinate and Arsenate on Hematite Nanoparticles.

Temperature-dependent kinetic studies of the adsorption of critical pollutants onto reactive components in soils and removal technologies provide invaluable rate information and mechanistic insight. Using attenuated total internal reflection Fourier transform infrared spectroscopy, we collected spectra as a function of time, concentration, and temperature in the range of 5-50 °C (278-323 K) for the adsorption of arsenate (iAs) and dimethylarsinate (DMA) on hematite nanoparticles at pH 7. These experimental data were modeled with density functional theory (DFT) calculations on the energy barriers between surface complexes.

Adsorption of Organic Acids and Phosphate to an Iron (Oxyhydr)oxide Mineral: A Combined Experimental and Density Functional Theory Study.

The interaction of soil organic matter with mineral surfaces is a critical reaction involved in many ecosystem services, including stabilization of organic matter in the terrestrial carbon pool and bioavailability of plant nutrients. Using model organic acids typically present in soil solutions, this study couples laboratory adsorption studies with density functional theory (DFT) to provide physical insights into the nature of the chemical bonding between carboxylate functional groups and a model FeOOH cluster. Topological determination of electron density at bond critical points using quantum theory of atoms in molecules (QTAIM) analysis revealed that the presence of multiple bonding paths between the organic acid and the FeOOH cluster is essential in determining the competitive adsorption of organic acids and phosphate for FeOOH surface adsorption sites.

Evaluating Computational Chemistry Methods for Isotopic Fractionation between CO(g) and HO(g).

Quantum mechanical calculations can be useful in predicting equilibrium isotopic fractionations of geochemical reactions. However, these computational chemistry methods vary widely in their effectiveness in the prediction of various physical observables. Most studies employing the approach known as density functional theory (DFT) to model these observable quantities focus on predictive accuracy for energetics and geometries.

Gibbsite (100) and Kaolinite (100) Sorption of Cadmium(II): A Density Functional Theory and XANES Study of Structures and Energies.

Due to the potential toxicity of cadmium (Cd) and its presence in various waste products found in the environment, it is necessary to develop methods to attenuate and remediate Cd waste. Sorption of Cd to mineral surfaces is a potential route to accomplish this goal. This work focused on improving our molecular-scale understanding of the chemistry of Cd interactions with gibbsite and kaolinite mineral surfaces.

Simulations of Cellulose Synthesis Initiation and Termination in Bacteria.

The processivity of cellulose synthesis in bacterial cellulose synthase (CESA) was investigated using molecular dynamics simulations and the hybrid quantum mechanics and molecular mechanics approach. Our results suggested that cellulose synthesis in bacterial CESA can be initiated with HO molecules. The chain length or degree of polymerization (DOP) of the product cellulose is related to the affinity of the cellulose chain to the transmembrane tunnel of the enzyme.

Cyclodextrin-enhanced 1,4-dioxane treatment kinetics with TCE and 1,1,1-TCA using aqueous ozone.

Enhanced reactivity of aqueous ozone (O) with hydroxypropyl-β-cyclodextrin (HPβCD) and its impact on relative reactivity of O with contaminants were evaluated herein. Oxidation kinetics of 1,4-dioxane, trichloroethylene (TCE), and 1,1,1-trichloroethane (TCA) using O in single and multiple contaminant systems, with and without HPβCD, were quantified. 1,4-Dioxane decay rate constants for O in the presence of HPβCD increased compared to those without HPβCD.

Kinetic analysis of cellulose synthase of Gluconacetobacter hansenii in whole cells and in purified form.

The Gram-negative bacterium, Gluconacetobacter hansenii, has been long studied and is a model for cellulose synthesis. It produces cellulose, using the enzyme AcsA-AcsB, of exceptionally high crystallinity in comparison to the cellulose of higher plants. We determined the rate of cellulose synthesis in whole cells measured as moles of glucose incorporated into cellulose per second per mole of enzyme.

The Shape of Native Plant Cellulose Microfibrils.

Determining the shape of plant cellulose microfibrils is critical for understanding plant cell wall molecular architecture and conversion of cellulose into biofuels. Only recently has it been determined that these cellulose microfibrils are composed of 18 cellulose chains rather than 36 polymers arranged in a diamond-shaped pattern. This study uses density functional theory calculations to model three possible habits for the 18-chain microfibril and compares the calculated energies, structures, C NMR chemical shifts and WAXS diffractograms of each to evaluate which shape is most probable.

Initiation, Elongation, and Termination of Bacterial Cellulose Synthesis.

Cellulose is the major component of the plant cell wall and composed of β-linked glucose units. Use of cellulose is greatly impacted by its physical properties, which are dominated by the number of individual cellulose strand within each fiber and the average length of each strand. Our work described herein provides a complete mechanism for cellulose synthase accounting for its processivity and mechanism of initiation.

Stand-Off Detection of Alcohol Vapors Exhaled by Humans.

Early detection of humans under the influence of alcohol in public places (workplace, public gathering) is particularly important for safety reasons. In this article, the theoretical analysis of stand-off detection of alcohol in the air exhaled by humans as well as experimental results of the developed experimental setup is presented. The concept of differential absorption of two laser beams at different wavelengths was used.

Quantum Calculations on Plant Cell Wall Component Interactions.

Density functional theory calculations were performed to assess the relative interaction energies of plant cell wall components: cellulose, xylan, lignin and pectin. Monomeric and tetramer linear molecules were allowed to interact in four different configurations for each pair of compounds. The M05-2X exchange-correlation functional which implicitly accounts for short- and mid-range dispersion was compared against MP2 and RI-MP2 to assess the reliability of the former for modeling van der Waals forces between these PCW components.