Cyanobacterial Biocrust on Biomineralized Soil Mitigates Freeze-Thaw Effects and Preserves Structure and Ecological Functions.

Biocrust inoculation and microbially induced carbonate precipitation (MICP) are tools used in restoring degraded arid lands. It remains unclear whether the ecological functions of the two tools persist when these methods are combined and subjected to freeze-thaw (FT) cycles. We hypothesized a synergetic interaction between MICP treatment and biocrust under FT cycles, which would allow both components to retain their ecological functions. We grew cyanobacterial (Nostoc commune) biocrusts on bare soil and on MICP (Sporosarcina pasteurii)-treated soil, subjecting them to repeated FT cycles simulating the Mongolian climate. Generalized linear modeling revealed that FT cycling did not affect physical structure or related functions but could increase the productivity and reduce the nutrient condition of the crust. The results confirm the high tolerance of MICP-treated soil and biocrust to FT cycling. MICP treatment + biocrust maintained higher total carbohydrate content under FT stress. Our study indicates that biocrust on biomineralized soil has a robust enough structure to endure FT cycling during spring and autumn and to promote restoration of degraded lands.

Elucidating the enhanced role of carbonate radical in propranolol degradation by UV/peroxymonosulfate system.

Carbonate radical (CO3•-) has been proved to be an important secondary radical in advanced oxidation processes due to various radical reactions involved HCO3-/CO32-. However, the roles and contributions of CO3•- in organic micropollutant degradation have not been explored systematically. Here, we quantified the impact of CO3•- on the degradation kinetics of propranolol, a representative pollutant in the UV/peroxymonosulfate (PMS) system, by constructing a steady-state radical model. Substantially, the measured values were coincident with the predictive values, and the contributions of CO3•- on propranolol degradation were the water matrix-dependent. Propranolol degradation increased by 130% in UV/PMS system containing 10 mM HCO3-, and the contribution of CO3•- was as high as 58%. Relatively high pH values are beneficial for propranolol degradation in pure water containing HCO3-, and the contributions of CO3•- also enhanced, while an inverse phenomenon was shown for the effects of propranolol concentrations. Dissolved organic matter exhibited significant scavenging effects on HO•, SO4•-, and CO3•-, substantially retarding the elimination process. The developed model successfully predicted oxidation degradation kinetics of propranolol in actual sewage, and CO3•- contribution was up to 93%, which in indicative of the important role of CO3•- in organic micropollutant removal via AOPs treatment.

Sulfate-reducing bacteria (SRB) mediated carbonate dissolution and arsenic release: Behavior and mechanisms.

Carbonate bound arsenic act as an important reservoir for arsenic (As) in nature aquifers. Sulfate-reducing bacteria (SRB), one of the dominant bacterial species in reductive groundwater, profoundly affects the biogeochemical cycling of As. However, whether and how SRB act on the migration and transformation of carbonate bound arsenic remains to be elucidated. Batch culture experiment was employed using filed collected arsenic bearing calcite to investigate the release and species transformation of As by SRB. We found that arsenic in the carbonate samples mostly exist as inorganic As(V) (93.92 %) and As(III). The present of SRB significantly facilitated arsenic release from carbonates with a maximum of 22.3 µg/L. The main release mechanisms of As by SRB include 1) calcite dissolution and the liberate of arsenic in calcite lattices, and 2) the break of H-bonds frees arsenic absorbed on carbonate surface. A redistribution of arsenic during culture incubation took place which may due to the precipitation of As2Sx or secondary FeAl minerals. To our best knowledge, it is the first experimental study focusing on the release of carbonate bound arsenic by SRB. This study provides new insights into the fate and transport of arsenic mediated by microorganism within high arsenic groundwater-sediment system.

Effects of different oxidants on the behaviour of microplastic hetero-aggregates.

Microplastic hetero-aggregates are stable forms of microplastics in the aqueous environment. However, when disinfecting water containing microplastic hetero-aggregates, the response of them in water to different oxidizing agents and the effect on water quality have not been reported. Our results showed that Ca(ClO)2, K2S2O8, and sodium percarbonate (SPC) treatment could lead to the disaggregation of microplastic hetero-aggregates as well as a rise in cell membrane permeability, which caused a large amount of organic matter to be released. When the amount of oxidant dosing is insufficient, the oxidant cannot completely degrade the released organic matter, resulting in DOC, DTN, DTP and other indicators being higher than before oxidation, thus causing secondary pollution of the water body. In comparison, K2FeO4 can purify the water body stably without destroying the microplastic hetero-aggregates, but it only weakly inhibits the toxic cyanobacteria Microcystis and Pseudanabaena, which may cause cyanobacterial bloom as well as algal toxin and odorant contamination in practical application. Compared with the other oxidizers, K2S2O8 provides better inhibition of toxic cyanobacteria and has better ecological safety. Therefore, when treating microplastic-containing water bodies, we should consider both water purification and ecological safety, and select appropriate oxidant types and dosages to optimize the water treatment.

Deterioration phenomenon of Pb-contaminated aqueous solution remediation and enhancement mechanism of nano-hydroxyapatite-assisted biomineralization.

Modern metallurgical and smelting activities discharge the lead-containing wastewater, causing serious threats to human health. Bacteria and urease applied to microbial-induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) are denatured under high Pb2+ concentration. The nano-hydroxyapatite (nHAP)-assisted biomineralization technology was applied in this study for Pb immobilization. Results showed that the extracellular polymers and cell membranes failed to secure the urease activity when subjected to 60 mM Pb2+. The immobilization efficiency dropped to below 50% under MICP, whereas it due to a lack of extracellular polymers and cell membranes dropped to below 30% under EICP. nHAP prevented the attachment of Pb2+ either through competing with bacteria and urease or promoting Ca2+/Pb2+ ion exchange. Furthermore, CO32- from ureolysis replaced the hydroxyl (-OH) in hydroxylpyromorphite to encourage the formation of carbonate-bearing hydroxylpyromorphite of higher stability (Pb10(PO4)6CO3). Moreover, nHAP application overcame an inability to provide nucleation sites by urease. As a result, the immobilization efficiency, when subjected to 60 mM Pb2+, elevated to above 80% under MICP-nHAP and to some 70% under EICP-nHAP. The findings highlight the potential of applying the nHAP-assisted biomineralization technology to Pb-containing water bodies remediation.

Microbial-induced carbonate precipitation effectively prevents Pb2+ migration through the soil profile: Lab experiment and model simulation.

Due to the inappropriate disposal of waste materials containing lead (Pb) and irrigation with sewage containing Pb, the migration of Pb2+ within the soil profile has been extensively investigated. The conventional Pb2+ block method is challenging to implement due to its complex operational procedures and high construction costs. To address this issue, this study introduces the microbial-induced carbonate precipitation (MICP) technique as a novel approach to impede the migration of Pb2+ in the soil profile. Soil acclimatization with urea resulted in an increased proportion of urease-producing microorganisms, including Bacillus, Paenibacillus, and Planococcaceae, along with heightened expression of urea-hydrolyzing genes (UreA, UreB, UreC, and UreG). This indicates that urea-acclimatized soil (Soil-MICP) possesses the potential to induce carbonate precipitation. Batch Pb2+ fixation experiments confirmed that the fixation efficiency of Soil-MICP on Pb2+ exceeded that of soil without MICP, attributed to the MICP process within the Soil-MICP group. Dynamic migration experiments revealed that the MICP reaction transformed exchangeable lead into carbonate-bound Pb, effectively impeding Pb2+ migration in the soil profile. Additionally, the migration rate of Pb2+ in Soil-MICP was influenced by varying urea amounts, pH levels, and pore flow rates, leading to a slowdown in migration. The Two-site sorption model aptly described the Pb2+ migration process in the Soil-MICP column. This study aims to elucidate the MICP biomineralization process, uncover the in-situ blocking mechanism of MICP on lead in soil, investigate the impact of Pb on key genes involved in urease metabolism, enhance the comprehension of the chemical morphology of lead mineralization products, and provide a theoretical foundation for MICP technology in preventing the migration of Pb2+ in soil profiles.

Controllable synthesis of barium carbonate nano- and microparticles for SPECT and CT imaging.

The design and synthesis of nano- and microcarriers for preclinical and clinical imaging are highly attractive due to their unique features, for example, multimodal properties. However, broad translation of these carriers into clinical practice is postponed due to the unknown biological reactivity of the new components used for their synthesis. Here, we have developed microcarriers (∼2-3 µm) and  nanocarriers (<200 nm) made of barium carbonate (BaCO3) for multiple imaging applications in vivo. In general, barium in the developed carriers can be used for X-ray computed tomography, and the introduction of a diagnostic isotope (99mTc) into the BaCO3 structure enables in vivo visualization using single-photon emission computed tomography. The bioimaging has shown that the radiolabeled BaCO3 nano- and microcarriers had different biodistribution profiles and tumor accumulation efficiencies after intratumoral and intravenous injections. In particular, in the case of intratumoral injection, all the types of used carriers mostly remained in the tumors (>97%). For intravenous injection, BaCO3 microcarriers were mainly localized in the lung tissues. However, BaCO3 NPs were mainly accumulated in the liver. These results were supported by ex vivo fluorescence imaging, direct radiometry, and histological analysis. The BaCO3-based micro- and nanocarriers showed negligible in vivo toxicity towards major organs such as the heart, lungs, liver, kidneys, and spleen. This study provides a simple strategy for the design and fabrication of the BaCO3-based carriers for the development of dual bioimaging.

The interplay between crystallinity and the levels of Zn and carbonate in synthetic microcalcifications directs thyroid cell malignancy.

One of the key challenges in diagnosing thyroid cancer lies in the substantial percentage of indeterminate diagnoses of thyroid nodules that have undergone ultrasound-guided fine-needle aspiration (FNA) biopsy for cytological evaluation. This delays the definitive diagnosis and treatment plans. We recently demonstrated that hydroxyapatite microcalcifications (MCs) aspirated from thyroid nodules may aid nodule diagnosis based on their composition. In particular, Zn-enriched MCs have emerged as potential cancer biomarkers. However, a pertinent question remains: is the elevated Zn content within MCs a consequence of cancer, or do the Zn-enriched MCs encourage tumorigenesis? To address this, we treated the human thyroid cancer cell line MDA-T32 with synthetic MC analogs comprising hydroxyapatite crystals with varied pathologically relevant Zn fractions and assessed the cellular response. The MC analogs exhibited an irregular surface morphology similar to FNA MCs observed in cancerous thyroid nodules. These MC analogs displayed an inverse relationship between Zn fraction and crystallinity, as shown by X-ray diffractometry. The zeta potential of the non-Zn-bearing hydroxyapatite crystals was negative, which decreased once Zn was incorporated into the crystal. The MC analogs were not cytotoxic. The cellular response to exposure to these crystals was evaluated in terms of cell migration, proliferation, the tendency of the cells to form multicellular spheroids, and the expression of cancer markers. Our findings suggest that, if thyroid MCs play a role in promoting cancerous behavior in vivo, it is likely a result of the interplay of crystallinity with Zn and carbonate fractions in MCs.

Porous Nano-Fiber Structure of Modified Electrospun Chitosan GBR Membranes Improve Osteoblast Calcium Phosphate Deposition in Osteoblast-Fibroblast Co-Cultures.

Desirable characteristics of electrospun chitosan membranes (ESCM) for guided bone regeneration are their nanofiber structure that mimics the extracellular fiber matrix and porosity for the exchange of signals between bone and soft tissue compartments. However, ESCM are susceptible to swelling and loss of nanofiber and porous structure in physiological environments. A novel post-electrospinning method using di-tert-butyl dicarbonate (tBOC) prevents swelling and loss of nanofibrous structure better than sodium carbonate treatments. This study aimed to evaluate the hypothesis that retention of nanofiber morphology and high porosity of tBOC-modified ESCM (tBOC-ESCM) would support more bone mineralization in osteoblast-fibroblast co-cultures compared to Na2CO3 treated membranes (Na2CO3-ESCM) and solution-cast chitosan solid films (CM-film). The results showed that only the tBOC-ESCM retained the nanofibrous structure and had approximately 14 times more pore volume than Na2CO3-ESCM and thousands of times more pore volume than CM-films, respectively. In co-cultures, the tBOC-ESCM resulted in a significantly greater calcium-phosphate deposition by osteoblasts than either the Na2CO3-ESCM or CM-film (p < 0.05). This work supports the study hypothesis that tBOC-ESCM with nanofiber structure and high porosity promotes the exchange of signals between osteoblasts and fibroblasts, leading to improved mineralization in vitro and thus potentially improved bone healing and regeneration in guided bone regeneration applications.

A quantitative study on the terrestrial input to the tropical Northeast Atlantic.

Eolian dust and riverine discharge are identified as two key components of terrestrial input to the oceans. They supply micronutrients to the oceans and modify marine carbon biogeochemistry and global climate through dust-land-ocean interactions. However, it is challenging to accurately constrain regional terrestrial inputs in the past, with currently available models and geochemical proxies. The present study utilizes sedimentary wtCaCO3% records to estimate lithogenic fluxes. The depth-dependance of CaCO3 preservation in the Holocene and Last Glacial Maximum (LGM) sediments in two major basins of the tropical Northeast Atlantic Ocean is described using a carbonate dissolution model. Results show that during the LGM, reduced dust deposition and slight drops of fluvial input are found in the Canary Basin and Cape Verde margins, respectively. To supplement, carbonate deposition during the LGM indicates that the deep subtropical Northeast Atlantic is seized by more sluggish deep waters relative to today.

Evaluating the multiple sulfur isotope signature of Eoarchean rocks from the Isua Supracrustal Belt (Southwest-Greenland) by MC-ICP-MS: Volcanic nutrient sources for early life.

On the anoxic Archean Earth, prior to the onset of oxidative weathering, electron acceptors were relatively scarce, perhaps limiting microbial productivity. An important metabolite may have been sulfate produced during the photolysis of volcanogenic SO2 gas. Multiple sulfur isotope data can be used to track this sulfur source, and indeed this record indicates SO2 photolysis dating back to at least 3.7 Ga, that is, as far back as proposed evidence of life on Earth. However, measurements of multiple sulfur isotopes in some key strata from that time can be challenging due to low sulfur concentrations. Some studies have overcome this challenge with NanoSIMS or optimized gas-source mass spectrometry techniques, but those instruments are not readily accessible. Here, we applied an aqua regia leaching protocol to extract small amounts of sulfur from whole rocks for analyses of multiple sulfur isotopes by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Measurements of standards and replicates demonstrate good precision and accuracy. We applied this technique to meta-sedimentary rocks with putative biosignatures from the Eoarchean Isua Supracrustal Belt (ISB, >3.7 Ga) and found positive ∆33S (1.40-1.80‰) in four meta-turbidites and negative ∆33S (-0.80‰ and -0.66‰) in two meta-carbonates. Two meta-basalts do not display significant mass-independent fractionation (MIF, -0.01‰ and 0.16‰). In situ Re-Os dating on a molybdenite vein hosted in the meta-turbidites identifies an early ca. 3.7 Ga hydrothermal phase, and in situ Rb-Sr dating of micas in the meta-carbonates suggests metamorphism affected the rocks at ca. 2.2 and 1.7 Ga. We discuss alteration mechanisms and conclude that there is most likely a primary MIF-bearing phase in these meta-sediments. Our new method is therefore a useful addition to the geochemical toolbox, and it confirms that organisms at that time, if present, may indeed have been fed by volcanic nutrients.

Calcium isotope fractionation by intracellular amorphous calcium carbonate (ACC) forming cyanobacteria.

The formation of intracellular amorphous calcium carbonate (ACC) by various cyanobacteria is a widespread biomineralization process, yet its mechanism and importance in past and modern environments remain to be fully comprehended. This study explores whether calcium (Ca) isotope fractionation, linked to ACC-forming cyanobacteria, can serve as a reliable tracer for detecting these microorganisms in modern and ancient settings. Accordingly, we measured stable Ca isotope fractionation during Ca uptake by the intracellular ACC-forming cyanobacterium Cyanothece sp. PCC 7425. Our results show that Cyanothece sp. PCC 7425 cells are enriched in lighter Ca isotopes relative to the solution. This finding is consistent with the kinetic isotope effects observed in the Ca isotope fractionation during biogenic carbonate formation by marine calcifying organisms. The Ca isotope composition of Cyanothece sp. PCC 7425 was accurately modeled using a Rayleigh fractionation model, resulting in a Ca isotope fractionation factor (Δ44Ca) equal to -0.72 ± 0.05‰. Numerical modeling suggests that Ca uptake by these cyanobacteria is primarily unidirectional, with minimal back reaction observed over the duration of the experiment. Finally, we compared our Δ44Ca values with those of other biotic and abiotic carbonates, revealing similarities with organisms that form biogenic calcite. These similarities raise questions about the effectiveness of using the Ca isotope fractionation factor as a univocal tracer of ACC-forming cyanobacteria in the environment. We propose that the use of Δ44Ca in combination with other proposed tracers of ACC-forming cyanobacteria such as Ba and Sr isotope fractionation factors and/or elevated Ba/Ca and Sr/Ca ratios may provide a more reliable approach.

New Oldowan locality Sare-Abururu (ca. 1.7 Ma) provides evidence of diverse hominin behaviors on the Homa Peninsula, Kenya.

The Homa Peninsula, in southwestern Kenya, continues to yield insights into Oldowan hominin landscape behaviors. The Late Pliocene locality of Nyayanga (∼3-2.6 Ma) preserves some of the oldest Oldowan tools. At the Early Pleistocene locality of Kanjera South (∼2 Ma) toolmakers procured a diversity of raw materials from over 10 km away and strategically reduced them in a grassland-dominated ecosystem. Here, we report findings from Sare-Abururu, a younger (∼1.7 Ma) Oldowan locality approximately 12 km southeast of Kanjera South and 18 km east of Nyayanga. Sare-Abururu has yielded 1754 artifacts in relatively undisturbed low-energy silts and sands. Stable isotopic analysis of pedogenic carbonates suggests that hominin activities were carried out in a grassland-dominated setting with similar vegetation structure as documented at Kanjera South. The composition of a nearby paleo-conglomerate indicates that high-quality stone raw materials were locally abundant. Toolmakers at Sare-Abururu produced angular fragments from quartz pebbles, representing a considerable contrast to the strategies used to reduce high quality raw materials at Kanjera South. Although lithic reduction at Sare-Abururu was technologically simple, toolmakers proficiently produced cutting edges, made few mistakes and exhibited a mastery of platform management, demonstrating that expedient technical strategies do not necessarily indicate a lack of skill or suitable raw materials. Lithic procurement and reduction patterns on the Homa Peninsula appear to reflect variation in local resource contexts rather than large-scale evolutionary changes in mobility, energy budget, or toolmaker cognition.

Phenolate-thiazole based reversible "turn-on" chemosensor for the selective detection of carbonate anion: X-ray crystallography, DFT/TDFT, and cell study.

A new phenolate-thiazole derivative (L) has been synthesized and structurally characterized.The chemo-sensing activity of L is detected by the naked eye for the aqueous carbonate anion in the pH range of 4 to 8. The selective 'turn-on' fluorescence occurs through the formation of a stable intermediate L∙CO32-(1) following the PET mechanism. The limit of detection (LOD) is found 0.18 µM based on the absorbance-based assay.The quinonoid form of bromophenol unit binds strongly with CO32- through thiazole nitrogen and hydrazinic nitrogen. Further, the selective holding of CO32- anion over other planar tetranuclear anions (e.g., SO32-, NO3-) happens with several intra and intermolecular hydrogen bonds as envisaged by the DFT/TDFT study. The formation mechanism of L∙CO32- is proposed based on experimental and theoretical studies. The biological experiments (MTT and cell imaging)reveal the non-cytotoxicity nature of L and the biocompatible uptake of L mostly in the cytoplasm at physiological pH.

Insight into the key factors and mechanism of excellent tetracycline adsorption on amorphous cobalt carbonate nanosheets.

The extensive use of tetracyclines (TCs) has led to their widespread distribution in the environment, causing serious harm to ecosystems because of their toxicity and resistance to decomposition. Adsorption is presently the principal approach to dispose of TCs, and the development of excellent adsorbents is crucial to TC removal. Herein, a novel amorphous cobalt carbonate hydroxide (ACCH) was successfully prepared by a one-step solvothermal method, which was identified as Co(CO3)0·63(OH)0.74·0.07H2O. The ultimate adsorption capacity of ACCH for TC reaches 2746 mg g-1, and the excellent adsorption performance can be maintained over a wide pH (3.0-11.0) and temperature (10-70 °C) range. Moreover, ACCH also exhibits a wonderful adsorption performance for other organic contaminants, such as ciprofloxacin and Rhodamine B. The TC adsorption process can be reasonably described by the pseudo-second-order kinetic model, intraparticle model and Langmuir isothermal model. The experimental results in this work suggest that the excellent adsorption performance of ACCH is ascribed to the large specific surface area, alkaline characteristics and numerous functional groups of ACCH. Accordingly, this work provides a promising strategy for the development of highly-efficient adsorbents and demonstrates their application prospects in environmental remediation.

Advanced remediation in the presence of ferrous iron and carbonate-containing water by oxygen-induced oxidation of organic contaminants.

Mechanistic investigations of an environmentally friendly and easy-to-implement oxidation method in the remediation of contaminated anoxic waters, i.e. groundwater, through the sole use of oxygen for the oxygen-induced oxidation of pollutants were the focus of this work. This was achieved by the addition of O2 under anoxic conditions in the presence of ferrous iron which initiated the ferrous oxidation and the simultaneous formation of reactive •OH radicals. The involvement of inorganic ligands such as carbonates in the activation of oxygen as part of the oxidation of Fe2+ in water was investigated, too. The formation of •OH radicals, was confirmed in two different, indirect approaches by a fluorescence-based method involving coumarin as •OH scavenger and by the determination of the oxidation products of different aromatic VOCs. In the latter case, the oxidation products of several typical aromatic groundwater contaminants such as BTEX (benzene, toluene, ethylbenzene, xylenes), indane and ibuprofen, were determined. The influence of other ligands in the absence of bicarbonate and the effect of pH were also addressed. The possibility of activation of O2 in carbonate-rich water i.e. groundwater, may also potentially contribute to oxidation of groundwater contaminants and support other primary remediation techniques.

A conserved asparagine residue stabilizes iron binding in Manduca sexta transferrin-1.

Transferrin 1 (Tsf1) is an insect-specific iron-binding protein that is abundant in hemolymph and other extracellular fluids. It binds iron tightly at neutral pH and releases iron under acidic conditions. Tsf1 influences the distribution of iron in the body and protects against infection. Elucidating the mechanisms by which Tsf1 achieves these functions will require an understanding of how Tsf1 binds and releases iron. Previously, crystallized Tsf1 from Manduca sexta was shown to have a novel type of iron coordination that involves four iron-binding ligands: two tyrosine residues (Tyr90 and Tyr204), a buried carbonate anion, and a solvent-exposed carbonate anion. The solvent-exposed carbonate anion was bound by a single amino acid residue, a highly conserved asparagine at position 121 (Asn121); thus, we predicted that Asn121 would be essential for high-affinity iron binding. To test this hypothesis, we analyzed the iron-binding and -release properties of five forms of recombinant Tsf1: wild-type, a Y90F/Y204F double mutant (negative control), and three Asn121 mutants (N121A, N121D and N121S). Each of the Asn121 mutants exhibited altered spectral properties, confirming that Asn121 contributes to iron coordination. The N121D and N121S mutations resulted in slightly lower affinity for iron, especially at acidic pH, while iron binding and release by the N121A mutant was indistinguishable from that of the wild-type protein. The surprisingly minor consequences of mutating Asn121, despite its high degree of conservation in diverse insect species, suggest that Asn121 may play a role that is essential in vivo but non-essential for high affinity iron binding in vitro.

Sizeable net export of base cations from a Carpathian flysch catchment indicates their geogenic origin while the 26Mg/24Mg, 44Ca/40Ca and 87Sr/86Sr isotope ratios in runoff are indistinguishable from atmospheric input.

Nutrient imbalances may negatively affect the health status of forests exposed to multiple stress factors, including drought and bark beetle calamities. We studied the origin of base cations in runoff from a small Carpathian catchment underlain by base-poor flysch turbidites using magnesium (Mg), calcium (Ca) and strontium (Sr) isotope composition of 10 ecosystem compartments. Our objective was to constrain conclusions drawn from long-term hydrochemical monitoring of inputs and outputs. Annual export of Mg, Ca and Sr exceeds 5-to-15 times their atmospheric input. Mass budgets per se thus indicate sizeable net leaching of Mg, Ca and Sr from bedrock sandstones and claystones. Surprisingly, δ26Mg, δ44Ca and 87Sr/86Sr isotope ratios of runoff were practically identical to those of atmospheric deposition and soil water but significantly different from bedrock isotope ratios. We did not find any carbonates in the studied area as a hypothetical, easily dissolvable source of base cations whose isotope composition might corroborate the predominance of geogenic base cations in the runoff. Marine carbonates typically have lower δ26 Mg and 87Sr/86Sr ratios, and silicate sediments often have higher δ26Mg and 87Sr/86Sr ratios than runoff at the study site. Mixing of these two sources, if confirmed, could reconcile the flux and isotope data.

Immature porcine cortical bone mechanical properties and composition change with maturation and displacement rate.

Computational models of mature bone have been used to predict fracture; however, analogous study of immature diaphyseal fracture has not been conducted due to sparse experimental mechanical data. A model of immature bone fracture may be used to aid in the differentiation of accidental and non-accidental trauma fractures in young, newly ambulatory children (0-3 years). The objective of this study was to characterize the evolution of tissue-level mechanical behavior, composition, and microstructure of maturing cortical porcine bone with uniaxial tension, Raman spectroscopy, and light microscopy as a function of maturation. We asked: 1) How do the monotonic uniaxial tensile properties change with maturation and displacement rate; 2) How does the composition and microstructure change with maturation; and 3) Is there a correlation between composition and tensile properties with maturation? Elastic modulus (p < 0.001), fracture stress (p < 0.001), and energy absorption (p < 0.014) increased as a function of maturation at the quasistatic rate by 110%, 86%, and 96%, respectively. Fracture stress also increased by 90% with maturation at the faster rate (p = 0.001). Fracture stress increased as a function of increasing displacement rate by 28% (newborn p = 0.048; 1-month p = 0.004; 3-month p= < 0.001), and fracture strain decreased by 68% with increasing displacement rate (newborn p = 0.002; 1-month p = 0.036; 3-month p < 0.001). Carbonate-to-phosphate ratio was positively linearly related to elastic modulus, and fracture stress was positively related to carbonate-to-phosphate ratio and matrix maturation ratio. The results of this study support that immature bone is strain-rate dependent and becomes more brittle at faster rates, contributing to the foundation upon which a computational model can be built to evaluate immature bone fracture.

Buffer-Dependent Photophysics of 2-Aminopurine: Insights into Fluorescence Quenching and Excited-State Interactions.

2-Aminopurine (2AP) is the most widely used fluorescent nucleobase analogue in DNA and RNA research. Its unique photophysical properties and sensitivity to environmental changes make it a useful tool for understanding nucleic acid dynamics and DNA-protein interactions. We studied the effect of ions present in commonly used buffer solutions on the excited-state photophysical properties of 2AP. Fluorescence quenching was negligible for tris(hydroxymethyl)aminomethane (TRIS), but significant for phosphate, carbonate, 3-(N-morpholino) propanesulfonic acid (MOPS), and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffers. Results indicate that the two tautomers of 2AP (7H, 9H) are quenched by phosphate ions to different extents. Quenching by the H2PO4- ion is more pronounced for the 7H tautomer, while the opposite is true for the HPO42- ion. For phosphate ions, the results of the time-resolved fluorescence study cannot be explained using a simple collisional quenching mechanism. Instead, results are consistent with transient interactions between 2AP and the phosphate ions. We postulate that excited-state interactions between the 2AP tautomers and an H-bond acceptor (phosphate and carbonate) result in significant quenching of the singlet-excited state of 2AP. Such interactions manifest in biexponential fluorescence intensity decays with pre-exponential factors that vary with quencher concentration, and downward curvatures of the Stern-Volmer plots.