Difference In Chain Length Research Articles

Exploring the thermochromic properties of fluoran-based complexes: Synthesis, structural influence, and application in temperature sensing

Fluoran dyes are extensively used as key components of thermochromic materials. To expand the scope of fluoran-based thermochromic systems, we conducted a comprehensive study to explore the relationships between the thermochromic properties of three-component complexes and the types and ratios of their constituents: fluoran dyes, developers, and solvents. We synthesized twenty-one fluoran dyes with varied chemical structures, including differences in the carbon chain length of the dialkylamino group, substitutions with electron-donating and electron-withdrawing groups, and the enlargement of conjugation systems. By combining these dyes with several phenolic developers and three long-chain alcohols, we prepared numerous thermochromic complexes and evaluated their color-changing behaviors under temperature variations. Complexes utilizing developers, bisphenol (BPA), bisphenol S (BPS), 4-hydroxy-4′-isopropoxydiphenylsulfone (D-8), 2,4′-dihydroxydiphenyl sulfone (2, 4′-BPS), and octyl gallate (OG) exhibited a red-to-colorless transition with increasing temperature, whereas those with developer lauryl gallate (LG) displayed a colorless-to-red transition upon heating. The chain length and conjugation extension of fluoran dyes influenced the optimal ratio of the three components. Additionally, substituents on the xanthene moiety of fluoran dyes didn't impact their complex performance. Finally, we demonstrated the fabrication of these thermochromic complexes on filter papers, showcasing their sensitivity to temperature fluctuations and highlighting their potential application as temperature sensors.

Temperature dependence of structural evolution and fragility of glass-forming monohydroxy alcohols

The dynamic, structural, and thermodynamic properties of thirty-four monohydroxy alcohols with varying molecular architectures, including differences in alkyl chain length, OH group position, and presence/type of carbon ring, were investigated. Results of dielectric spectroscopy, temperature-modulated differential scanning calorimetry, and X-ray diffraction, were analyzed to verify correlations between the glass transition temperature (Tg), molar mass (M), boiling temperature (Tb), dynamic and thermodynamic fragility (mα and m), and the structurally related parameter (S). The collected data revealed that primary and secondary alcohols generally adhere to the correlations Tg ∝ M0.51 and Tb = 132 + 2.2Tg, while alcohols with phenyl ring deviate from these trends. Moreover, it was found that the changes in the width of the main diffraction peak normalized by the peak position ΔQM/QM over temperature scaled by Tg correspond to the variable m. However, the extent and course of this relationship varies across alcohols belonging to different structural groups. The weakest correlation and largest scatter between S and m occur for phenyl alcohols exhibiting the greatest structural heterogeneity. This study underscores the challenges of establishing universal correlations between physical variables within the diverse group of monohydroxy alcohols and emphasizes the importance of considering specific molecular features in predicting glass-forming behaviour.

Interaction mechanism of soy protein isolate with aldehyde flavor compounds: Differences in carbon chain length and unsaturation

Soy protein isolate (SPI) can interact with volatile compounds, which affect flavor perception and limit its application in liquid foods. This study aimed to elucidate the interaction mechanism between SPI and six main flavors of bean (aldehyde flavor compounds with different carbon chain length and unsaturation). The results showed that carbon chain length and unsaturation of compounds influenced the combining ability with SPI. (E, E)-2,4-decadienal and (E, E)-2,4-nonadienal with longer carbon chain length and higher unsaturation showed higher affinity with SPI. Multi-spectroscopy showed that aldehyde flavor compounds could induce the unfolding of SPI structure and expose hydrophobic groups. The presence of CC enhanced the hydrogen bonding between the carbonyl group and SPI. Thermodynamic analysis revealed that complexes mainly relied on hydrophobic interaction and hydrogen bonding-driven interactions. Molecular simulations further confirmed that aldehyde flavor compounds maintained binding stability with SPI the high-flexibility key amino acid residues (Leu79, Pro82, Lys113, Glu358, etc.). This study improves the understanding of interactions between SPI and volatile compounds at the molecular level and provides a theoretical basis for SPI flavor improvement.

Cu-W bimetallic nanoparticles decorated g-C3N4 sheets: Facile construction and characterization for perception of dopamine in sensing application.

In this study, we present the development and analysis of electrochemical sensors utilizing graphitic carbon nitride copper-tungsten nanoparticles (g-C3N4 @Cu-W Nps) capped with various cationic surfactants of differing chain lengths and counter ions. The fabricated nanoparticles underwent thorough characterization to assess their morphological, structural, and compositional attributes, revealing their uniformity, spherical morphology, and monoclinic crystal phases. Subsequently, these nanoparticles were employed in the fabrication of electrochemical sensors for hydrazine detection. A comprehensive comparison of the electrochemical responses, evaluated via cyclic voltammetry, was conducted between sensors utilizing bare nanoparticles and those capped with surfactants.

Sourcing and long-range transport of particulate organic matter in river bedload: Río Bermejo, Argentina

Abstract. Fluvial transport of organic carbon from the terrestrial biosphere to the oceans is an important term in the global carbon cycle. Traditionally, the long-term burial flux of fluvial particulate organic carbon (POC) is estimated using river suspended sediment flux; however, organic carbon can also travel in river bedload as coarse particulate organic matter (POMBed). Estimates of fluvial POC export to the ocean are highly uncertain because few studies document POMbed sources, flux, and evolution during long-range fluvial transport from uplands to ocean basins. This knowledge gap limits our ability to determine the global terrestrial organic carbon burial flux. In this study we investigate the flux, sources, and transformations of POMBed during fluvial transport over a ∼1300 km long reach of the Río Bermejo, Argentina, which has no tributary inputs. To constrain sourcing of POMBed, we analyzed the composition and stable hydrogen and carbon isotope ratios (δ2H, δ13C) of plant wax biomarkers from POMBed at six locations along the Río Bermejo and compared this to samples of suspended sediment, soil, leaf litter, and floating organic debris (POMfloat) from both the lowland and headwater river system. Across all samples, we found no discernible differences in n-alkane average chain length or nC29 δ13C, indicting a common origin for all sampled POMBed. Leaf litter and POMfloat nC29 δ2H values decrease with elevation, making it a useful proxy for POMBed source elevation. Biomarker δ2H values suggest that POMBed is a mix of distally derived headwater and locally recruited floodplain sources at all sampling locations. These results indicate that POMBed can be preserved during transport through lowland rivers for hundreds of kilometers. However, the POMBed flux decreases with increasing transport distance, suggesting mechanical comminution of these coarse organic particles and progressive transfer into the suspended load. Our provisional estimates suggest that the carbon flux from POMBed comprises less than 1 % of the suspended load POC flux in the Río Bermejo. While this represents a small portion of the river POC flux, this coarse, high-density material likely has a higher probability of deposition and burial in sedimentary basins, potentially allowing it to be more effective in long-term CO2 drawdown relative to fine suspended particles. Because the rate and ratio of POMBed transport versus comminution likely vary across tectonic and climatic settings, additional research is needed to determine the importance of POMBed in the global carbon cycle.

Ionic Twin Nanostructural Comparison: Propylammonium Butanoate vs. Butylammonium Propanoate and Their Interactions with Water.

This study investigates the nanostructure of two protic ionic liquids (PILs), [N0 0 0 3][C3CO2] and [N0 0 0 4][C2CO2], with similar polar head groups but varying alkyl chain lengths. An X-ray scattering technique and molecular dynamics simulations have been utilized to characterize the bulk and interfacial properties of these PILs. The findings suggest that the nanostructure of the PILs is primarily determined by the electrostatic forces between charged functional groups playing a dominant role. Despite differences in the alkyl chain lengths, the PILs possess remarkably similar nanostructures. Extending our investigation, we report the impact of water on the nanostructure. Our findings reveal that the addition of water disrupts interactions between cations and anions, weakening Coulombic forces. The disruptive behavior is attributed to the establishment of hydrogen bonds between water and ions. This comprehensive approach provides valuable insights into the nuanced factors shaping the nanostructure of these PILs, which are crucial for tailoring their applications in synthetic chemistry, catalysis, and beyond.

Enantiomeric Separation of Triacylglycerols Consisting of Three Different Fatty Acyls and Their Chiral Chromatographic Elution Behavior.

Chromatographic separation of triacylglycerol (TG) enantiomers is a highly challenging task of analytical chemistry because of the similar physicochemical properties. The analysis of chiral TGs is crucial for improving the knowledge of lipid biochemistry and for understanding the nutritional properties of fats and oils. Thus, this study aimed to systematically investigate the chiral resolution of TGs consisting of three different fatty acyls (FAs). Thirty-three asymmetric TG enantiopairs, including 49 synthesized enantiopure TGs and racemic TGs, were analyzed with a recycling chiral HPLC system. Twenty-six enantiopairs were successfully separated. Overall, having both unsaturated and saturated FAs in the outer positions or a difference in carbon chain length between two saturated FAs at the outer positions favored the separation of enantiomers. The retention time at separation correlated negatively with the sn-3 carbon number of the early eluting enantiomer and positively with the carbon number difference between sn-1 and sn-3. When the samples were studied in separate groups based on unsaturation and regioisomers, both the acyl carbon number and the degree of unsaturation of FAs in all three positions influenced the separation and elution behavior of chiral TGs, indicating an active role of both intermolecular interactions and steric hindrances. This is the first systematic study of the chiral separation of TGs consisting of three different FAs using a large number of enantiopairs. The novel findings on the behavior of TG enantiomers in a chiral environment provide important guidance and reference for a stereospecific study of the chemistry and biochemistry of natural lipids.

Improving interactions at the electrochromic polymer‐transparent oxide electrode interface using alkyl phosphonic acid modifiers

AbstractAs new synthetic methods for the preparation of solution processable electrochromic polymers are explored, including increasing synthetic scale beyond that of the research laboratory, it is expected that polymer intermolecular and intramolecular interactions will be affected. In this study, we explore the use of four different alkyl phosphonic acids of differing chain lengths as an interfacial treatment on ITO transparent electrodes to improve the polymer‐electrode interactions to mitigate the loss of film integrity and resulting electrochromic properties (current density, optical properties, and effective switch rates) during repeated oxidation/reduction and swelling/deswelling of the film. It was found that the phosphonic acid layer allows for a compatibilization of the polarity of the electrode surface with the polymer layer while also improving surface energy uniformity. We evaluated two electrochromic polymers (ECPs), and while a near complete delamination was observed on untreated ITO, film integrity was maintained beyond 25 repeated cycles, with polymer optical contrast maintained at all switching rates when coated onto dodecylphosphonic acid. Additionally, we show that electrochromic polymer film integrity is maintained over a range of film thicknesses. This method can be extended to applications using a variety of solution processable electroactive polymers in contact with metal oxide surfaces.

The perception interaction of complex fruits aroma system: Including binary, ternary, quaternary, and with different chain length, functional groups and substituent positions compounds

The perceptual interactions between key aroma compounds (binary, ternary, and quaternary) of fruits were comprehensively evaluated using thresholds, odor activity values, Feller's additive model (S-curve), σ-τ diagram, and U model. Meanwhile, support vector machine (SVM) was initially introduced to evaluate and compare the 5 methods for selecting the most appropriate approach for investigating fruits aroma interaction. Finally, the effects of aroma molecular structure characteristics (chain length, functional group and substituent site) on the interaction was investigated. The results showed that S-curve, σ-τ diagram and U model are suitable for the binary and ternary systems, and σ-τ diagram and U model are suitable for quaternary systems. Furthermore, the functional groups strongly (P < 0.05) influenced the perception interactions. Especially, the greater the difference in carbon chain length, the more significant the synergistic effect of aldehydes and alcohols with similar chains, and the substituent site had no significant effect on aroma interactions.

Effect of a fluorinated surfactant on Langmuir monolayer properties of minimal-linker gemini surfactants

A new class of carboxylic acid-terminated gemini surfactants which contain the smallest possible headgroup linker (a single bond) has recently been reported in the literature. In this current work, we have explored how Langmuir monolayers of two different alkyl tail chain length variants (n = 12, n = 16) of these surfactants, dubbed Cn-0-Cn, are impacted by mixing with a benchmark perfluorinated surfactant, perfluorotetradecanoic acid (PF). Pure PF and C16-0-C16 monolayers share similar general characteristics, yielding compact, incompressible, solid-like films at the air-water interface. In contrast, the shorter tail chain variant, C12-0-C12 forms expanded, compressible liquid-like films. While both tail chain variants formed mixed films with PF that were generally expanded in comparison with their pure components, and were also phase-separated, the extent of interactions between film components and the resulting micron-scale morphology of the mixed films were different for the two alkyl chain lengths. Overall, PF induces different packing behavior in both the systems and the observations are attributed to the difference in the dispersion forces originating from the tail chain length differences.

Plasma Lipidomic Profiles in cART-Treated Adolescents with Perinatally Acquired HIV Compared to Matched Controls.

Children with perinatally acquired human immunodeficiency virus (PHIV) are growing into adulthood with HIV and treatment-associated comorbidities, such as dyslipidemia and insulin resistance. HIV is identified as independent risk factor for cardiovascular disease (CVD). The hypothesis behind increased CVD risk associated with HIV includes vascular inflammation, dyslipidemia and combination antiretroviral therapy (cART) metabolomic toxicity. To investigate differences in lipid profiles and pathophysiological mechanisms of CVD risk in adolescents with PHIV, we compared the plasma lipidome of PHIV adolescents and HIV-negative controls. We additionally investigated the influence of current cART regimens and increased lipoprotein(a) (Lp(a)) levels on the plasma lipidome. We included 20 PHIV-infected adolescents and 20 HIV-negative controls matched for age, sex, ethnic origin and socio-economic status. Plasma lipidome was measured using Thermo Scientific Ultimate 3000 binary high-performance liquid chromatography (HPLC)-mass spectrometry. We evaluated the plasma lipidome in PHIV adolescents using different cART regimens (including those known to be associated with lipid alterations). The median age was 17.5 years (15.5-20.7) and 16.5 years (15.7-19.8) for PHIV adolescents and controls, respectively. Of PHIV adolescents, 45% used a non-nucleotide reverse transcriptase inhibitor (NNRTI)-based (25%) or protease inhibitor (PI)-based (20%) cART regimen. In this pilot study, we observed no significant differences between lipidomic profiles between PHIV adolescents and controls. We observed no differences in the plasma lipidome in participants with increased versus normal Lp(a) levels. Different cART regimens appear to influence chain length differences in the plasma lipidome of PHIV adolescents; however, the significance and causality of this observation remains undetermined. Further research on the influence of cART on lipid composition could further identify these alterations.

Stable isotopes delineate regional pelagic food web structure in British Columbia’s coastal ocean

The pelagic food webs of British Columbia’s (BC) coastal oceans have never had a comprehensive review of their trophic structure. In this study, we analyzed carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of pelagic food web components collected from four regions in southern BC: Juan de Fuca Strait, the Strait of Georgia, Queen Charlotte Strait, and Queen Charlotte Sound during an August 2019 survey. In addition, conductivity, temperature, and depth (CTD), chlorophyll, and nutrient data were collected to assess the oceanographic basis for regionalization. Between regions, we observed differences in the isotopic baseline driven by regional oceanography. Likewise, we also observed oceanography-driven differences in regional food chain length, carbon range, and isotopic overlap. Species-specific trophic level and isotopic niche were determined. For common pelagic species, we described how trophic level varied regionally, was not always in line with previously published dietary data, and instead largely tracked regional changes in food chain length. We conclude that variable food web properties and trophic ecology can manifest across the small spatial scales of the BC coast’s discrete regions.

Micellar structure of nonenyl succinic anhydride modified pullulan in aqueous solution

A polydisperse pullulan (PUL) sample was hydrophobically modified by nonenyl succinic anhydride (NSA) with four different degree of substitution (DS) samples (PUL-NSA). Small-angle X-ray scattering functions and pyrene-probe fluorescence were measured for PUL-NSA samples in 0.05 M aqueous NaCl. Both the SAXS and fluorescence results can be explained by the loose flower necklace model well. The SAXS results of PUL-NSA was different from that of the random copolymer of octenyl succinic anhydride hydrophobically modified PUL (PUL-OSA) with approximate DS. The stiffness of the flower necklace qFN for PUL-NSA was lower than PUL-OSA, probably due to the differences in the alkyl chain length.

Mechanisms of lipotoxicity-induced dysfunction and death of human pancreatic beta cells under obesity and type 2 diabetes conditions.

The term "pancreatic beta-cell lipotoxicity" refers to the detrimental effects of free fatty acids (FFAs) on a wide variety of cellular functions. Basic research in the field has primarily analyzed the effects of palmitic acid and oleic acid. The focus on these two physiological FFAs, however, ignores differences in chain length and degree of saturation. In order to gain a comprehensive understanding of the lipotoxic mechanisms, a wide range of structurally related FFAs should be investigated. Structure-activity relationship analyses of FFAs in the human EndoC-βH1 beta-cell line have provided a deep insight into the mechanisms of beta-cell lipotoxicity. This review focuses on the effects of a wide range of FFAs with crucial structural determinants for the development of lipotoxicity in human beta cells and documents an association between increased triglyceride stores in obesity and in type 2 diabetes.

Определение взаимосвязи генотипов SNP с содержанием жирных кислот различной пространственной конфигурации в молоке коров

Abstract. Milk fat is the third main source of lipids for human nutrition. Fatty acids in milk fat have a heterogeneous composition due to differences in chain length, degree of saturation, etc. It has been scientifically proven that long-term consumption of trans-fatty acids causes various diseases of the human body; according to WHO recommendations, their maximum consumption should not exceed 1 % of total energy. A comprehensive study of the composition of fatty acids in cattle milk gives scientists the opportunity to use this trait in breeding work by selecting genotypes with a low content of trans-isomers and saturated fatty acids harmful to human health. The scientific novelty lies in the study of molecular genetic mechanisms for regulating the quantitative content of fatty acids and their trans-isomers in the fat fraction of cow's milk. The purpose of the work is to identify allelic variants of SNPs associated with the fatty acid composition of cow's milk and the content of trans isomers of unsaturated fatty acids in it. Research methods. The studies were carried out on cows of the Holstein black-and-white breed. The genetic profile of animals of the Holstein black-and-white breed was studied, SNPs significantly associated with the quantitative and qualitative content of fatty acids and their trans-isomers in the fat fraction of cow's milk were identified. The fatty acid composition of cows' milk was determined using a multiparameter automatic analyzer MilkoScan 7/Fossomatic 7 FT+ / DC (FOSS, Denmark). Results. Whole-genome genotyping was performed. Analyzing the content of fatty acids with different saturation of hydrogen bonds, a significant difference between the amount of fatty acids and genotypes, reliable values were established only for 5 SNPs. It was found that for four SNPs, the highest values of the content of fatty acids and trans-isomers were in homozygous genotypes ARS-BFGL-NGS-41348GG; BTA-115852-no-rsAA; BTB-00771463GG; Hapmap46159-BTA-70956TT. A significant difference in the content of trans-fatty acid isomers in milk between genotypes was found only for SNP ARS-BFGL-NGS-5502. The largest mass fraction of trans-isomers of unsaturated fatty acids was found in the milk fat of cows with the heterozygous genotype AG, which amounted to 0.076 g/100 g and was 0.011 g/100 g and 0.032 g/100 g (P≤0.01) more compared to heterozygous genotypes GG and AA, respectively.

Identification of SNPs associated with the content of saturated and unsaturated fatty acids in cow milk

The fatty acids in milk fat have a heterogeneous composition due to differences in chain length, their saturation degree, etc. Fatty acids with the number of carbon atoms in the chain from 10 to 14 are considered carriers of the unique taste of dairy products, in particular cheese and butter. In addition, medium-chain fatty acids are used in the treatment of newborn children, as well as adults with disorders of: triglyceride hydrolysis in the small intestine and the process of their absorption, chronic pancreatitis, congenital celiac disease, chronic enteritis, etc. A comprehensive study of the composition of fatty acids in cattle milk provides an opportunity to use this feature in breeding work by selecting genotypes to obtain raw materials with specified properties.

A new class of “structure-by-design” polymer membranes for organic solvent nanofiltration with controllable selectivity

Membrane based separations offer an inexpensive and energy efficient pathway to purification. However, their use is often stifled during separation of organics due to low selectivity. This can be attributed to the inherent limitations of the synthesis methods employed, namely, interfacial polymerization and phase inversion. In this work, a new class of structure-by-design membranes are synthesized by surface modification of crosslinked polyimide using graft polymerization with a series of methacrylate monomers with differing chain lengths and chemistries. Graft polymerization of long chain monomers resulted in increased selectivity (α∼3.7 for 80-20 mol.% MeOH-toluene and α∼6 for 95-5 mol.% toluene-triisopropyl benzene (TIPB) for both test solutions) as a result of increased stiffness and order (using GIWAXS)). The observed selectivities renders these membranes competitive for organic solvent nanofiltration applications. In addition, pure solvent permeabilities were measured. The performance of these membranes was correlated with brush properties such as degree of grafting (using ATR-FTIR), surface polarity (contact angle measurements), stiffness (using QCM-D) and brush configuration in different solvent environments (using MD Simulations). MD simulations demonstrate that in mixtures containing hydrophobic species, polymers with longer hydrophobic side chains well more and form fuller matrices leading to increased solvent accessible surface area. GIWAXS results showed increased order with longer side chain length. These tunable membranes offer promise for organics separation.

PBP and PSP promote β' form crystallization of palm oil, palm stearin, and a cocoa butter replacer

AbstractTo precisely regulate the crystallization of lipids, an in‐depth understanding of the correlation between the structures of the crystallization promoters and their functionalities is crucial. The effects of the crystallization promoters 1,3‐dipalmitoyl‐2‐behenoyl‐glycerol (PBP) and 1,3‐dipalmitoyl‐2‐stearoyl‐glycerol (PSP) on the crystallization behavior of palm oil, palm stearin, and a cocoa butter replacer were investigated by differential scanning calorimetry, polarized light microscopy, and X‐ray diffraction. The chain‐length difference between PSP and PBP resulted in different thermally stable polymorphs. PBP was stabilized in the β‐3L form, but PSP was stabilized in the β′‐2L form. The addition of PBP and PSP significantly promoted nucleation and led to an earlier onset of crystallization during cooling. After isothermal and nonisothermal crystallization, the PSP and PBP increased the melting temperatures of the palm oil and the cocoa butter replacer but decreased the melting temperature of the palm stearin, since PBP and PSP effectively promoted β′ formation but retarded the β' to β transformation. Due to the differences in chain length and subcell matching, palm stearin crystallizes on PSP and PBP via different modes.Practical Applications: PBP and PSP have potential as β'‐form crystallization promoters for plastic fats. This research indicated the possibility of regulating the nanostructures of fats by structural design of the crystallization promoters.

Influence of the type of phosphate additive and its concentration on the setting kinetics of CA cement bonded refractory castables with special regard to the resulting pH value

During the hydration of CA cement exists a dormant period, which is responsible for the setting kinetics of CA cement bonded refractory castables. The dormant period is believed to be caused by an Al–O–H passivation layer on the CA cement particles. Recent publications indicate that the dissolution (aging) of the passivation layer is closely connected to the prevailing pH value of the pore solution during setting. The higher the pH value, the faster the dissolution of the passivation layer.As phosphate additives, frequently used as dispersing agent, differ in their pH value when dissolved in water it is reasonable that they change the setting kinetics of CA cement bonded refractory castables. Commonly used sodium polyphosphate (S-PP, special case S-TPP for sodium tripolyphosphate) dispersing agents mainly differ in chain length, and therefore in Na+ and phosphate concentration, with different setting kinetics as a result.To investigate the influence of S-(T)PP on setting kinetics, sonic velocity and pH measurements were conducted on S-(T)PP/citric acid dispersed and CA cement bonded refractory castables during their setting. Different phosphates, differing in portion of Na+ to phosphate and medium chain length of the phosphate molecules, were used in varied concentrations within refractory castables to quantify the shift in setting kinetics and verify the role of the pH value during the hydration of CA cement.It was found that the chain length of the phosphate molecule of S-(T)PP influences the setting kinetics, and especially the length of the dormant period of the hydration of CA cement, in an indistinct way. Minor differences within the Na+ concentration at differing chain length S-(T)PP showed a comparable tendency to influence the hydration kinetics of CA cement as the chain length of the phosphate molecule was varied. However, an increase of the concentration of the applied S-(T)PP, which goes along with a distinctly increased Na+ concentration, resulted in a significant shorter dormant period and correspondingly an accelerated main hydration of CA cement. The corresponding pH value during the dormant period of the hydration of CA cement increased concurrently to the increase of the S-(T)PP and Na+ concentration.It is discussed that this increase of the pH value of the pore solution of the refractory castable results from an increase of the Na+ concentration from the S-(T)PP, while phosphate molecules are precipitated as Ca-phosphate. This indicates that the dissolution of the Al–O–H passivation layer accelerates with an increasing Na+ concentration (equivalent to increasing pH value) in the pore solution. Thereby, the dormant period is shorter and the hydration of CA cement starts earlier.The general tendency that additives of alkaline nature are accelerating the setting kinetics could be linked to the pH value during the dormant period. Therefore, the theory of the pH dependent aging of the Al–O–H passivation layer on CA cement particles was confirmed. As a directly applicable result, S-(T)PP may be used as accelerator (accelerating the CA cement hydration) beside their dispersing effect.

Hydroclimate variations over the last 17,000 years as estimated by leaf waxes in rodent middens from the south-central Atacama Desert, Chile

Leaf cuticular waxes are one of the most important environment-plant interaction structural systems that enable desert plants to withstand extreme climatic conditions. We present a long chain n-alkyl lipids study in fresh plant leaves and rodent palaeomiddens collected along an elevational gradient in the south-central Atacama Desert of Chile, covering six different vegetation belts: Steppe (4500-4000 m asl), Puna (4000-3300 m asl), pre-Puna (3300-2400 m asl), Absolute Desert (2400-1000 m asl) and Coastal Desert (1000-0 m asl). The 28 rodent palaeomiddens analyzed from Quebrada Incahuasi (25.6 °S, 3600 m asl) span the last 17,000 years. Modern-day distribution of long-chain n-alkanes and n-alkanoic acids varies among the dominant plant associations of the Atacama Desert. These plants show a species-specific chemotaxonomy linked to the climatic conditions. Furthermore, differences in average chain length (ACL) and carbon preference index (CPI) suggest that these plant communities are highly adapted to extreme environmental conditions. The sum of leaf wax n-alkanes was highest under wet conditions, while n-alkanoic acids (between n-C24 and n-C28) increased with hyperaridity. Similarly, analysis of n-alkane time series from palaeomiddens showed that the greatest changes in leaf wax n-alkane distributions (ACL and CPI) corresponded to the greatest increases in moisture during the Central Andean Pluvial Event (CAPE; between 18 and 9 ka cal BP) and the Late Holocene. The shift in the palaeomidden n-alkane distributions is corroborated by the relative abundance of rainfall-dependent extra-local taxa. This is the first study to report leaf wax content obtained from ancient rodent middens, and shows promising results as a robust hydroclimate proxy for the Atacama Desert region.