Structural Changes Research Articles

Condition of the cardiovascular system in Wistar rats with experimental renal dysfunction

The aim: to evaluate functional and structural changes in blood vessels and myocardium in Wistar rats at different stages of the formation of experimental kidney dysfunction.Materials and Methods. Four groups of animals were studied. The first two groups consisted of rats subjected to 5/6 nephrectomy (NE). The period after NE is 2 or 4 months. The third and fourth groups included sham-operated (SO) animals of a similar observation period. After the end of the experiment, blood pressure was measured in rats, the left ventricular mass index (LVMI) was calculated, a biochemical blood test, histological, immunohistochemical and electron microscopic examination of the myocardium were performed, and the contractile activity of the portal vein was recorded for a period of 2 months (in vitro).Results. 2 months after NE, an increase in blood pressure, LVMI, and a decrease in the autorhythmic contractile activity of the portal vein were detected in rats. At the histological level, thickening of cardiomyocytes and arterial vessel walls and the presence of perivascular fibrosis were noted. After 4 months, in rats with NE, the increase in blood pressure, cardiomyocyte hypertrophy and perivascular fibrosis progressed. The thickness of cardiomyocytes was 14.1±3.11 μm, which was significantly greater than in the group with NE for 2 months (12.5±1.5 μm; p=0.008). At this period of observation, electron microscopic examination revealed deintegration of myofibrils, disruption of myofibril stacking and z-disk structure, and changes in the shape of mitochondria. 2 months after NE, an increase in the area of open capillaries was detected in rats (1902.8±202.9 μm²) compared to the corresponding LO animals (730.4±58.2 μm²; p=0.000). As renal dysfunction develops, the capillary area tends to increase (2139.1±396.5 μm²; p =0.120).Conclusion. In Wistar rats with renal dysfunction, changes were detected not only in the level of blood pressure, but also in the functional activity of the intravenous fluid, as well as in the structural components of the myocardium – cardiomyocytes, stroma and blood vessels. The increase in myocardial mass at the histological level was manifested by a significant increase in the thickness of cardiomyocytes, the volume of connective tissue, and the thickness of the wall of arterial vessels, reaching a maximum value at a longer period after NE.

Synthesis of β-cyclodextrin derivatives substituted at larger or smaller rims via amine-catalyzed ring-opening oligomerization of ε-caprolactone

The involvement of cyclodextrins in transesterification reactions with active esters has been described to mimic enzyme-catalyzed reactions, making cyclodextrin molecules suitable as enzyme models. Cyclodextrin-catalyzed ring-opening of cyclic esters in bulk reaction conditions was considered to proceed similarly. However, the mechanism of activating cyclic esters through inclusion in the cyclodextrin cavity remains incompletely understood to date. The present research is focused on observing the transesterification of ε-caprolactone in the presence of β-cyclodextrin and additional amine organocatalysts within dimethyl sulfoxide solutions. The conducted experiments provide insights into the structural changes caused by various catalytic conditions in terms of the substitution pattern of the cyclodextrins. Our results are supported by a deep structural characterization through NMR and MALDI MS, which revealed the prospect of promoting rim-selective substitution of β-cyclodextrin at either secondary or primary hydroxyl groups using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) organocatalysts. This offers the possibility to prepare cyclodextrin derivatives with specific substitution patterns. Based on the acquired structural information, the particular pathway in which β-cyclodextrin influences the ring-opening of ε-caprolactone is delineated as follows: monomer complexation, substitution at the larger rim, chain elongation, and intramolecular transfer toward the smaller rim.

Ercc1 DNA repair deficiency results in vascular aging characterized by VSMC phenotype switching, ECM remodeling, and an increased stress response.

Cardiovascular diseases are the number one cause of death globally. The most important determinant of cardiovascular health is a person's age. Aging results in structural changes and functional decline of the cardiovascular system. DNA damage is an important contributor to the aging process, and mice with a DNA repair defect caused by Ercc1 deficiency display hypertension, vascular stiffening, and loss of vasomotor control. To determine the underlying cause, we compared important hallmarks of vascular aging in aortas of both Ercc1Δ/- and age-matched wildtype mice. Additionally, we investigated vascular aging in 104 week old wildtype mice. Ercc1Δ/- aortas displayed arterial thickening, a loss of cells, and a discontinuous endothelial layer. Aortas of 24 week old Ercc1Δ/- mice showed phenotypical switching of vascular smooth muscle cells (VSMCs), characterized by a decrease in contractile markers and a decrease in synthetic markers at the RNA level. As well as an increase in osteogenic markers, microcalcification, and an increase in markers for damage induced stress response. This suggests that Ercc1Δ/- VSMCs undergo a stress-induced contractile-to-osteogenic phenotype switch. Ercc1Δ/- aortas showed increased MMP activity, elastin fragmentation, and proteoglycan deposition, characteristic of vascular aging and indicative of age-related extracellular matrix remodeling. The 104 week old WT mice showed loss of cells, VSMC dedifferentiation, and senescence. In conclusion, Ercc1Δ/- aortas rapidly display many characteristics of vascular aging, and thus the Ercc1Δ/- mouse is an excellent model to evaluate drugs that prevent vascular aging in a short time span at the functional, histological, and cellular level.

Alginate Silver Nanoparticles and Their Effect on Sperm Parameters of the Domestic Rabbit

Silver nanoparticles possess valuable physical, chemical, and biological properties, rendering them widely applied as bioactive agents in the industry. Nonetheless, their influence on the natural environment and on living organisms remains unclear. Therefore, this study aims to investigate the impact of polymer composites containing silver nanoparticles on sperm cells. The nanosilver polymer composites were chemically synthesized, employing sodium alginate as the stabilizer. The reducing agents employed were solutions comprising sodium borohydride and xylose. The concentration of silver nanoparticles obtained after synthesis was 100 parts per million. The examined biological species were rabbit sperm cells. The impact of nanosilver on the sperm was assessed through the elucidation of the toxicity profile, comet test, and analysis of morphological characteristics of the animal cells. The results of the study demonstrate a twofold impact of polymer composites infused with silver nanoparticles on domestic rabbit sperm when obtained through chemical synthesis using two reducing agents (xylose and sodium borohydride) at a 10 ppm concentration. The comet test showed no harmful effect on the DNA integrity of rabbit sperm by the tested compounds. Twenty-four-hour exposure of rabbit spermatozoa to silver nanoparticles, obtained by reducing xylose and borohydride, induced significant secondary changes in the morphological structure of male reproductive cells. These findings indicate the potential reproductive toxicity of silver nanoparticles.

Reorganization of 3D genome architecture provides insights into pathogenesis of early fatty liver disease in laying hens

BackgroundFatty liver disease causes huge economic losses in the poultry industry due to its high occurrence and lethality rate. Three-dimensional (3D) chromatin architecture takes part in disease processing by regulating transcriptional reprogramming. The study is carried out to investigate the alterations of hepatic 3D genome and H3K27ac profiling in early fatty liver (FLS) and reveal their effect on hepatic transcriptional reprogramming in laying hens.ResultsResults show that FLS model is constructed with obvious phenotypes including hepatic visible lipid deposition as well as higher total triglyceride and cholesterol in serum. A/B compartment switching, topologically associating domain (TAD) and chromatin loop changes are identified by high-throughput/resolution chromosome conformation capture (HiC) technology. Targeted genes of these alternations in hepatic 3D genome organization significantly enrich pathways related to lipid metabolism and hepatic damage. H3K27ac differential peaks and differential expression genes (DEGs) identified through RNA-seq analysis are also enriched in these pathways. Notably, certain DEGs are found to correspond with changes in 3D chromatin structure and H3K27ac binding in their promoters. DNA motif analysis reveals that candidate transcription factors are implicated in regulating transcriptional reprogramming. Furthermore, disturbed folate metabolism is observed, as evidenced by lower folate levels and altered enzyme expression.ConclusionOur findings establish a link between transcriptional reprogramming changes and 3D chromatin structure variations during early FLS formation, which provides candidate transcription factors and folate as targets for FLS prevention or treatment.

Effect of Heating/Cooling Rate on the Local Electronic Structure of Amorphous Calcium Carbonate

Here, in the impact of heating/cooling rate was investigated on the formation of amorphous calcium carbonate (calcite) during sol-gel synthesis by probing local electronic structure. The amorphous calcium carbonate was synthesized by annealing precursor at 400oC at different heating/cooling rates i.e., 1.5 and 3oC /min. X-ray diffraction studies revealed amorphous nature at both heating/cooling rates. Fourier transformed infrared spectroscopic measurements characteristics bands in the spectra of both materials. Near edge X-ray absorption fine structure measurements at Ca L-edge, C K-edge and O K-edge were utilized to reveal the associated changes in the local electronic structure during synthesis. Local electronic structure investigation using near edge X-ray absorption fine structure measurements shows onset of moisture absorption on the surface particles when kept in the open environment.

Unraveling the Nano-Bio Interface Interactions of a Lipase Adsorbed on Gold Nanoparticles under Laser Excitation.

The complex nature and structure of biomolecules and nanoparticles and their interactions make it challenging to achieve a deeper understanding of the dynamics at the nano-bio interface of enzymes and plasmonic nanoparticles subjected to light excitation. In this study, circular dichroism (CD) and Raman spectroscopic experiments and molecular dynamics (MD) simulations were used to investigate the potential changes at the nano-bio interface upon plasmonic excitation. Our data showed that photothermal and thermal heating induced distinct changes in the secondary structure of a model nanobioconjugate composed of lipase fromCandida antarcticafraction B (CALB) and gold nanoparticles (AuNPs). The use of a green laser led to a substantial decrease in the α-helix content of the lipase from 66% to 13% and an increase in the β-sheet content from 5% to 31% compared to the initial conformation of the nanobioconjugate. In contrast, the differences under similar thermal heating conditions were only 55% and 11%, respectively. This study revealed important differences related to the enzyme secondary structure, enzyme-nanoparticle interactions, and the stability of the enzyme catalytic triad (Ser105-Asp187-His224), influenced by the instantaneous local temperature increase generated from photothermal heating compared to the slower rate of thermal heating of the bulk. These results provide valuable insights into the interactions between biomolecules and plasmonic nanoparticles induced by photothermal heating, advancing plasmonic biocatalysis and related fields.

Ganglioside GM1 Drives Hemin and Protoporphyrin Adsorption in Phospholipid Membranes: A Structural Study.

Monosialoganglioside (GM1), a ubiquitous component of lipid rafts, and hemin, an integral part of heme proteins such as hemoglobin, are essential to the cell membranes of brain neurons and erythrocyte red blood cells for regulating cellular communication and oxygen transport. Protoporphyrin IX (PPIX) and its derivative hemin, on the contrary, show significant cytotoxic effects when in excess causing hematological diseases, such as thalassemia, anemia, malaria, and neurodegeneration. However, the in-depth molecular etiology of their interactions with the cell membrane has so far been poorly understood. Herein, the structure of the polymer cushion-supported lipid bilayer (SLB) of the binary mixture of phospholipid and GM1 in the presence of PPIX and its derivative hemin has been investigated to predict the molecular interactions in model phospholipid membranes. A high-resolution synchrotron-based X-ray scattering technique has been employed to explore the out-of-plane structure of the assembly at different compositions and concentrations. The structural changes have been complemented with the isobaric changes in the mean molecular area obtained from the Langmuir monolayer isotherm to predict the additive-induced membrane condensation and fluidization. PPIX-induced fluidization of phospholipid SLB without GM1 was witnessed, which was reversed to condensation with 2-fold higher structural changes in the presence of GM1. A hemin concentration-dependent linear condensing effect was observed in the pristine SLB. The effect was significantly reduced, and the linearity was observed to be lost in the mixed SLB containing GM1. Our study shows that GM1 alters the interaction of hemin and PPIX with the membrane, which could be explained with the aid of hydrophobic and electrostatic interactions. Our study indicates favorable and unfavorable interactions of GM1 with PPIX and hemin, respectively, in the membrane. The observed structural changes in both SLB and the underlying polymer cushion layer lead to the proposal of a molecule-specific interaction model that can benefit the pharmaceutical industries specialized for drug designing. Our study potentially enriches our fundamental biophysical understanding of neurodegenerative diseases and drug-membrane interactions.

Study of Monoclonal Antibody Aggregation at the Air-Liquid Interface under Flow by ATR-FTIR Spectroscopic Imaging.

Throughout bioprocessing, transportation, and storage, therapeutic monoclonal antibodies (mAbs) experience stress conditions that may cause protein unfolding and/or chemical modifications. Such structural changes may lead to the formation of aggregates, which reduce mAb potency and may cause harmful immunogenic responses in patients. Therefore, aggregates need to be detected and removed or ideally prevented from forming. Air-liquid interfaces, which arise during various stages of bioprocessing, are one of the stress factors causing mAb aggregation. In this study, the behavior of an immunoglobulin G (IgG) at the air-liquid interface was investigated under flow using macro attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging. This chemically specific imaging technique allows observation of adsorption of IgG to the air-liquid interface and detection of associated secondary structural changes. Chemical images revealed that IgG rapidly accumulated around an injected air bubble under flow at 45 °C; however, no such increase was observed at 25 °C. Analysis of the second derivative spectra of IgG at the air-liquid interface revealed changes in the protein secondary structure associated with increased intermolecular β-sheet content, indicative of aggregated IgG. The addition of 0.01% w/v polysorbate 80 (PS80) reduced the amount of IgG at the air-liquid interface in a static setup at 30 °C; however, this protective effect was lost at 45 °C. These results suggest that the presence of air-liquid interfaces under flow may be detrimental to mAb stability at elevated temperatures and demonstrate the power of ATR-FTIR spectroscopic imaging for studying the structural integrity of mAbs under bioprocessing conditions.

Disturbance in the Composition of the Intestinal Microflora in the Mechanisms of the Formation of Clinical Manifestations in Patients with Chronic Pancreatitis

To determine the role of a violation of the composition of the intestinal microflora in the formation of clinical manifestations and in structural changes of COD in patients with CP and to evaluate the effect of therapy aimed at restoring intestinal microbiosenosis on the course of the disease

SPINAL ANATOMY AND BEYOND: INVESTIGATING DEGENERATIVE DISC DISEASE

Degenerative disc disease is a common manifestation in routine spine imaging; this finding is partly attributable to physiological aging and partly to a pathological condition, and sometimes, this distinction is simply not clear. The study's main objective is to find the spinal anatomy and investigate degenerative disc disease in spinal patients. This mixed-methods study was conducted in a public hospital in Karachi, Pakistan from March 2023 to September 2023. Fifty patients diagnosed with DDD are enrolled, with comprehensive clinical assessments conducted to evaluate symptomatology, functional impairment, and radiological findings. Additionally, advanced imaging modalities, including MRI and CT scans, elucidate structural changes within the spinal column. Preliminary analysis reveals a mean disc height loss of 3.2 mm (±0.8) across the study cohort, with significant variability observed among individual patients. Annular tears are prevalent in 70% of cases, predominantly localized to the lumbar spine. Furthermore, facet joint degeneration is evident in 85% of patients, with a mean grade of 2.4 (±0.6) on the Pfirrmann scale. Correlation analysis demonstrates a moderate positive correlation (r = 0.56, p < 0.001) between disc height loss and severity of clinical symptoms. It is concluded that this study provides the complex pathology of degenerative disc disease (DDD) and its impact on spinal anatomy. Through a comprehensive investigation involving clinical assessments and advanced imaging techniques, we have elucidated the spectrum of degenerative changes within the intervertebral discs and facet joints.

Quercetin inhibits necroptosis in cardiomyocytes after ischemia-reperfusion via DNA-PKcs-SIRT5-orchestrated mitochondrial quality control.

We investigated the mechanism by which quercetin preserves mitochondrial quality control (MQC) in cardiomyocytes subjected to ischemia-reperfusion stress. An enzyme-linked immunosorbent assay was employed in the in vivo experiments to assess myocardial injury markers, measure the transcript levels of SIRT5/DNAPK-cs/MLKL during various time intervals of ischemia-reperfusion, and observe structural changes in cardiomyocytes using transmission electron microscopy. In in vitro investigations, adenovirus transfection was employed to establish a gene-modified model of DNA-PKcs, and primary cardiomyocytes were obtained from a mouse model with modified SIRT5 gene. Reverse transcription polymerase chain reaction, laser confocal microscopy, immunofluorescence localization, JC-1 fluorescence assay, Seahorse energy analysis, and various other assays were applied to corroborate the regulatory influence of quercetin on the MQC network in cardiomyocytes after ischemia-reperfusion. In vitro experiments demonstrated that ischemia-reperfusion injury caused changes in the structure of the myocardium. It was seen that quercetin had a beneficial effect on the myocardial tissue, providing protection. As the ischemia-reperfusion process continued, the levels of DNA-PKcs/SIRT5/MLKL transcripts were also found to change. In vitro investigations revealed that quercetin mitigated cardiomyocyte injury caused by mitochondrial oxidative stress through DNA-PKcs, and regulated mitophagy and mitochondrial kinetics to sustain optimal mitochondrial energy metabolism levels. Quercetin, through SIRT5 desuccinylation, modulated the stability of DNA-PKcs, and together they regulated the "mitophagy-unfolded protein response." This preserved the integrity of mitochondrial membrane and genome, mitochondrial dynamics, and mitochondrial energy metabolism. Quercetin may operate synergistically to oversee the regulation of mitophagy and the unfolded protein response through DNA-PKcs-SIRT5 interaction.

Seasonal changes of prokaryotic microbial community structure in Zhangjiayan Reservoir and its response to environmental factors

As a typical sub-deep reservoir in the upper reaches of the Yangtze River in the southwest region, Zhangjiayan Reservoir is also an important source of drinking water. Exploring the role of microorganisms in the material cycle of water bodies is of great significance for preventing the exacerbation of eutrophication in the reservoir. In this study, water samples from the overlying water of five points in the reservoir were collected four times in spring (April), summer (July), autumn (November), and winter (January) of 2022–2023 using a gas-tight water sampler. Physicochemical factors were measured, and the microbial community structure was analyzed by high-throughput MiSeq sequencing of the V3–V4 hypervariable region of 16S rRNA gene in order to explore the relationship between physicochemical factors and microbial community structure and the dominant microbial populations that affect eutrophication of the reservoir. The following results were obtained through analysis. Among the 20 overlying water samples from Zhangjiayan Reservoir, a total of 66 phyla, 202 classes, 499 orders, 835 families, 1716 genera, and 27,904 ASVs of the bacterial domain were detected. The phyla Proteobacteria and Actinobacteria were dominant in the microbial community of the overlying water in Zhangjiayan Reservoir. At the genus level, hgcI_clade and Actinobacteria had the highest abundance and was the dominant population. The microbial community in the water of Zhangjiayan Reservoir has a high level of diversity. The diversity index ranked by numerical order was winter > autumn > summer > spring. Significant differences were found in the composition and structure of the microbial community between the spring/summer and autumn/winter seasons (p < 0.05). Total phosphorus, dissolved total phosphorus, soluble reactive phosphorus, and dissolved oxygen have a significant impact on the composition and structure of the microbial community (p < 0.01). The bacterial community in the overlying water of Zhangjiayan Reservoir showed a mainly positive correlation. Sphingomonas, Brevundimonas, and Blastomonas were the central populations of the bacterial community in the overlying water of Zhangjiayan Reservoir. This study indicates that environmental factors, such as phosphorus and other nutrients, have a significant impact on the formation of the microbial community structure in different seasons. Sphingomonas, Brevundimonas, and Blastomonas are key populations that may have a significant impact on eutrophication in Zhangjiayan Reservoir.

Changes in fish species diversity, size structure and distribution in the trawlable demersal zones of Lake Malawi, Malawi

Changes in fish species diversity, size structure and distribution in the trawlable demersal zones of Lake Malawi, Malawi

Pyrene-Appended Boronic Acids on Graphene Foam Electrodes Provide Quantum Capacitance-Based Molecular Sensors for Lactate.

Molecular recognition and sensing can be coupled to interfacial capacitance changes on graphene foam surfaces linked to double layer effects and coupled to enhanced quantum capacitance. 3D graphene foam film electrodes (Gii-Sens; thickness approximately 40 μm; roughness factor approximately 100) immersed in aqueous buffer media exhibit an order of magnitude jump in electrochemical capacitance upon adsorption of a charged molecular receptor based on pyrene-appended boronic acids (here, 4-borono-1-(pyren-2-ylmethyl)pyridin-1-ium bromide, or abbreviated T1). This pyrene-appended pyridinium boronic acid receptor is employed here as a molecular receptor for lactate. In the presence of lactate and at pH 4.0 (after pH optimization), the electrochemical capacitance (determined by impedance spectroscopy) doubles again. Lactic acid binding is expressed with a Hillian binding constant (Klactate = 75 mol-1 dm3 and α = 0.8 in aqueous buffer, Klactate = 460 mol-1 dm3 and α = 0.8 in artificial sweat, and Klactate = 340 mol-1 dm3 and α = 0.65 in human serum). The result is a selective molecular probe response for lactic acid with LoD = 1.3, 1.4, and 1.8 mM in aqueous buffer media (pH 4.0), in artificial sweat (adjusted to pH 4.7), and in human serum (pH adjusted to 4.0), respectively. The role of the pyrene-appended boronic acid is discussed based on the double layer structure and quantum capacitance changes. In the future, this new type of molecular capacitance sensor could provide selective enzyme-free analysis without analyte consumption for a wider range of analytes and complex environments.

Structural and chemical changes in hardwood cell walls during early stages of flash pyrolysis

Structural and chemical changes in hardwood cell walls during early stages of flash pyrolysis

Effects of economic globalization, environment-related technology innovation, and industrial structure change on the ecological footprint of top 10 Asian technological innovation countries

Effects of economic globalization, environment-related technology innovation, and industrial structure change on the ecological footprint of top 10 Asian technological innovation countries

An abrupt vegetation change on south-central Yunnan Plateau (Southwest China) during the last deglaciation

The magnitude and pace of anthropogenic climate change are increasing the likelihood of abrupt changes in terrestrial ecosystems worldwide. The Last Deglacial Transition (LDT) witnessed global and regional climate change and caused vegetation change globally. The recognition and attribution of deglacial abrupt vegetation conversion would certainly enhance our understanding on the survivability and resilience of ecosystems to climate change. Here, we conducted statistical analyses for a pollen record from Yilong Lake, southwestern China, focusing on the period of the LDT. Biome changes since the Last Glacial Maximum were reconstructed numerically by using a standard approach of pollen-plant functional type-biome assignment (biomization). Principal component analysis and structure change test were applied on pollen composition and diversity data. Modern vegetation and climate relationship was analyzed to discuss climatic conditions for the vegetation conversion in Yilong region during the LDT. Our results revealed a vegetation conversion occurring around 14.3 cal kyr BP, characterized by abrupt shifts in pollen compositions and biomes and also reduction in diversity indices. We suggested that the cumulative pressure of climate warming during the LDT was probably the critical climatic variable triggering the vegetation conversion in Yilong region, while precipitation played an important role in regulating the proportions or coverages of different vegetation types after the development of evergreen broadleaved forest. By the end of tthis century, climate under intermediate to very high greenhouse gas emission scenarios were projected to reach the thresholds for vegetation transitions from evergreen broadleaved forest to (monsoon) rainforest, or to Savanna-like vegetation. However, it is still a challenge to forecast accurately when or on what spatial scale vegetation change will happen because vegetation responses to climate change are complicated and the topography and habitats on Yunnan Plateau are extremely diverse.

Thermal, structural, and conductivity properties of As14Sb26S(60−x)–(AgI)x chalcogenide glasses

The present work describes the preparation of a new series of chalcogenide glasses in an As14Sb26S(60−x) (AgI)x system intending to explore its thermal, structural, optical, mechanical, and electrical properties. The differential scanning calorimetry results of the studied glasses show the sharp decrease in glass transition temperature (Tg) with the successive incremental inclusion of AgI in the composition, implying the structural changes in the glass network. A thorough Raman analysis corroborates the occurrence of changes in the glass network due to the formation of AsI3 units and Ag–S–As bonds with increasing AgI content. Also, structural changes can be reflected with the change in the optical bandgap (Eg) that was calculated using Tauc equations where it was found that Eg is in harmony with the observed structural variations of glasses. The studied glasses possess a transmittance window (∼0.68–12 μm) with transmittance above 60% in the mid-infrared region. These structural changes are closely related to the significant enhancement of conductivity of the present glasses from 10−8 to 10−6 S/cm at 373 K with a decrease in activation energies. Impedance spectra for the glass with highest AgI revealed the presence of two different relaxation processes. AC conductivity data followed an Arrhenius behavior as well as Jonscher’s power law. The present work provides insights into glass network modifications due to silver iodide inclusion and its role in the enhancement of conductivity.

Elucidating the Changes in Molecular Structure at the Buried Interface of RTV Silicone Elastomers during Curing.

Silicone elastomers are widely used in many industrial applications, including coatings, adhesives, and sealants. Room-temperature vulcanized (RTV) silicone, a major subcategory of silicone elastomers, undergoes molecular structural transformations during condensation curing, which affect their mechanical, thermal, and chemical properties. The role of reactive hydroxyl (-OH) groups in the curing reaction of RTV silicone is crucial but not well understood, particularly when multiple sources of hydroxyl groups are present in a formulated product. This work aims to elucidate the interfacial molecular structural changes and origins of interfacial reactive hydroxyl groups in RTV silicone during curing, focusing on the methoxy groups at interfaces and their relationship to adhesion. Sum frequency generation (SFG) vibrational spectroscopy is an in situ nondestructive technique used in this study to investigate the interfacial molecular structure of select RTV formulations at the buried interface at different levels of cure. The primary sources of hydroxyl groups required for interfacial reactions in the initial curing stage are found to be those on the substrate surface rather than those from the ingress of ambient moisture. The silylation treatment of silica substrates eliminates interfacial hydroxyl groups, which greatly impact the silicone interfacial behavior and properties (e.g., adhesion). This study establishes the correlation between interfacial molecular structural changes in RTV silicones and their effect on adhesion strength. It also highlights the power of SFG spectroscopy as a unique tool for studying chemical and structural changes at RTV silicone/substrate interface in situ and in real time during curing. This work provides valuable insights into the interfacial chemistry of RTV silicone and its implications for material performance and application development, aiding in the development of improved silicone adhesives.