University of Talca

Certain dietary fibers exhibit prebiotic effects on gut microbiota, but their influence on oral health remains unclear. This study conducted a systematic review across four databases to examine the potential effects of dietary fibers on dental caries. Data selection and extraction were conducted independently and in duplicate. From 962 found titles, twenty studies were included, of which 13 were in vitro. The substances identified as prebiotics included fructo‐oligosaccharides (FOS), galacto‐oligosaccharides (GOS), inulin, pectin, raffinose, polydextrose, sialyllactose, and short‐chain fatty acids. Outcomes were assessed at biofilm (n = 14), saliva (n = 5), and tooth (n = 1) levels, with only six studies evaluating pH changes. Fifteen studies (75%) reported potential benefits, primarily attributed to the capacity of prebiotic fibers to limit the growth or adhesion of bacteria. Only two studies (10%) reported an increase in pH. Overall, the quality of the evidence was judged as moderate. In conclusion, certain dietary fibers may help limit caries development by modulating biofilm and pH levels. However, further clinical studies are needed to confirm the protective role of dietary fibers in dental caries. © 2025 Society of Chemical Industry.

Importance Mental health stigma is a considerable barrier to help-seeking among young people. Objective To systematically review and meta-analyze randomized clinical trials (RCTs) of interventions aimed at reducing mental health stigma in young people. Data Sources Comprehensive searches were conducted in the CENTRAL, CINAHL, Embase, PubMed, and PsycINFO databases from inception to February 27, 2024. Search terms included “stigma,” “mental health,” “mental disorders,” “adolescents,” “youth,” and “randomized controlled trial.” Study Selection Inclusion criteria encompassed RCTs involving interventions aimed at reducing mental health stigma among young people (aged 10-24 years). Studies had to report outcomes related to stigma or help-seeking behaviors. Exclusion criteria included grey literature and studies without results. Data Extraction and Synthesis Data were extracted independently by 7 authors (M.A.C., D.N., F.B., S.C., Á.I.L., J.C., V.M.) using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Risk of bias was assessed with the Cochrane risk-of-bias tool. Three-level multivariate meta-analyses were conducted to account for within-study correlations and to maximize data use. Standardized mean differences (SMDs) (Hedges g ) and odds ratios (ORs) with 95% CIs were calculated. The data analysis was conducted from May 30 through July 4, 2024. Main Outcomes and Measures Primary outcomes included stigma-related knowledge, attitudes, behaviors, and general stigma. Help-seeking outcomes were categorized into attitudes, intentions, and behaviors. Secondary outcomes included self-efficacy and empowerment. Results A total of 97 studies were included in the systematic review, representing 43 852 young people (mean [IQR] age, 18.7 [15.8-21.3] years; mean [IQR] females, 59.2% [49.4%-72.0%]), and 74 studies were included in 3-level multivariate meta-analyses. Significant short-term effect sizes were found for stigma-related knowledge (SMD, 0.66; 95% CI, 0.43-0.89), attitudes (SMD, 0.38; 95% CI, 0.20-0.56), behaviors (SMD, 0.29; 95% CI, 0.13-0.45), and general stigma (SMD, 0.20; 95% CI, 0.06-0.34) and for help-seeking attitudes (SMD, 0.18; 95% CI, 0.09-0.28) and intentions (SMD, 0.14; 95% CI, 0.07-0.21). Social contact interventions had a greater influence on stigma-related behaviors than did educational approaches. Conclusions and Relevance These findings suggest that interventions to reduce mental health stigma among youth are beneficial in the short term. Further high-quality RCTs with long-term follow-up are needed to better understand and enhance these interventions’ outcomes.

Background Mental health disorders are one of the leading causes of illness globally. The importance of psychosocial skills acquired in early childhood, such as executive functions, inhibitory control, emotional regulation, and social problem-solving, in preventing mental disorders has been reported. Furthermore, mental health care delivery is evolving, and mobile technology is becoming the medium for assessment and intervention. We have developed Japi 2.0, the second iteration of a gaming platform, to stimulate cognitive and non-cognitive skills in early childhood, supported by early years educators using a web-based dashboard integrated into one system. This study aims to assess the acceptability and feasibility of this gaming platform and web-based dashboards. Methods This is a pilot randomized controlled trial, parallel-group type, where the school-based implementation of “Japi 2.0” training is compared to standard school curricula in control schools. A total of six schools with low socio-economic status located in the city of Santiago, Chile, are expected to be recruited and randomized with 1:1 allocation. Japi 2.0 has 24 sessions, and 2 sessions of 15 min per week are delivered for 12 weeks. Measures will be conducted using different instruments with children, parents, and early years educators to gain insight into their acceptance of the intervention and the development of cognitive and non-cognitive skills. Discussion This is a randomized control trial to assess the acceptability and feasibility of a gaming platform called “Japi 2.0” among preschoolers in Chile. This platform stimulates cognitive and non-cognitive skills with the final objective of reducing emotional and behavioral problems in early childhood. Evaluating the acceptability and feasibility of this technological solution for children is expected to produce relevant information about these novel designs. It may help guide future studies, such as a randomized controlled trial on a larger scale. Trial registration Clinical Trials NCT06420544, May 20, 2024 [https://www.clinicaltrials.gov/study/NCT06420544].

Suicide prevention programs delivered in school settings have been shown to reduce suicide attempts and ideation among adolescents. School-based digital interventions targeting at-risk youth are a promising avenue for suicide prevention, and some evidence has shown that blending digital and face-to-face components may improve the effectiveness. However, further evidence on its acceptability, feasibility, and effectiveness is needed, especially in Latin America, where mental health support is limited. Reframe-IT is an internet-based Cognitive Behavioral Therapy (CBT) program to reduce youth suicidal ideation in school settings. We created four complementary face-to-face CBT sessions and, through a pilot study, tested the acceptability, feasibility, and effectiveness of a blended intervention (Reframe-IT +) in adolescents (N = 52) from 6 public schools in Chile, randomized into two groups: Reframe-IT + (N = 33) and Control (N = 19). We found that the intervention was acceptable and feasible, with high degrees of satisfaction and adherence. We also observed a significant reduction in suicidal ideation and depressive symptoms in the intervention group compared to the control group at post-intervention. Our results suggest that the Reframe-IT + could be delivered as a suitable, acceptable, and effective intervention to reduce suicide ideation in adolescents in school settings. Further research is needed to confirm these preliminary results.

Prejudice and anti-immigrant attitudes are strongly motivated by more general ideological attitudes. Considering the current situation of migration in Chile, we conducted two studies on the ideologies underlying rejection of the affirmation of the rights of the Latin American migrant population in Chile. The first study (n = 1,103) examined the associations between right-wing authoritarianism (RWA) and social dominance orientation (SDO) on the one hand and opposition to the affirmation of rights on the other. Subsequently, Study 2 (n = 1,046) analysed the moderating role of perceptions of criminal threat in the relationship between RWA and opposition to the affirmation of rights. The results show that there is a distinct effect of both variables on the dependent variable, and that the relationship between RWA and the affirmation of immigrants’ rights in Chile is conditioned upon the perception of criminal threat.

Currently, the breeding programs focus their efforts on identifying and developing tolerant genotypes to adverse conditions, such as drought and high temperatures. In this context, the physiological approach, which involves phenotyping several traits, is useful for breeding programs. Leaf photosynthetic traits have become one of the main objectives to be evaluated for breeders due to their relationship with improving grain yield and biomass production. Gas exchange (Ge) and chlorophyll “a” fluorescence (Chf) are the main tools to characterize the photosynthetic activity in real time at the leaf level. Consequently, several association studies using proximal and nonproximal sensing (e.g., RGB, thermography) have been developed. However, for the correct application of this breeding approach, it is essential to have a basic knowledge of both the physiological principles involved in the readings and the limitations of phenotyping due to the characteristics of the devices available on the market. This revision also covers other traits, such as the morphological and anatomical characteristics of leaves and roots, and the use of isotopes complementing Ge and Chf measurements.

Ischaemic stroke is a leading cause of death and disability. Circulating extracellular vesicles (EVs) post‐stroke may help brain endothelial cells (BECs) counter ischaemic injury. However data on how EVs from ischaemic stroke patients, considering injury severity, affect these cells are limited. The aims were to characterize the inflammatory and angiogenic components of circulating EVs in acute ischaemic stroke patients, considering stroke severity, and to investigate whether these circulating EVs differentially influence the proangiogenic properties and blood–brain barrier (BBB) integrity of human BECs. Eighteen ischaemic stroke patients (acute phase: 24–48 h) and nine controls matched by age, sex, and blood pressure were studied. Stroke severity was classified as severe (n = 9) or mild (n = 9). Plasma EVs were analysed for size, concentration, and protein markers (CD63, Alix, CD81, TSG101, HSP70), as well as proinflammatory and angiogenic proteins. EV uptake, cell viability, proangiogenic capacity, electrical resistance [TEER (transendothelial electrical resistance)], and dextran‐70 kD permeability were assessed using human brain microvascular endothelial cells (hCMEC/D3). Stroke patients had lower EV concentrations than controls (p = 0.075), with mild‐stroke patients having the smallest EVs. Stroke‐derived EVs had higher levels of interleukin 6 (IL‐6), tumour necrosis factor α (TNF‐α), nitrotyrosine, and vascular endothelial growth factor (VEGF) but lower placental growth factor (PLGF) compared to controls. IL‐6 was higher in mild strokes (p = 0.0025), and VEGF was higher in severe strokes (p = 0.048). EVs from severe‐stroke cases enhanced proangiogenic capacity and minimally disrupted the BBB. Stroke severity influences EV number, size, and composition. EVs from severe strokes may promote BBB restoration and cerebral angiogenesis, suggesting their role in intercellular communication and homeostasis in ischaemic tissue. image Key points Ischaemic stroke is one of the leading causes of death worldwide. After an ischaemic stroke several physiological processes are triggered to recover the injured tissue. Increasing evidence has suggested that extracellular vesicles (EVs) present in the bloodstream could play a role in brain recovery, but their specific impact, especially concerning stroke severity, was unclear. This study demonstrates that plasma‐derived EVs from first‐ever ischaemic stroke patients have distinctive characteristics and effects over brain angiogenesis and blood–brain barrier (BBB) integrity. Our study proposes that circulating EVs from patients with severe stroke may carry protective factors to initiate brain endothelial cell recovery after acute episodes. These findings underscore the role of EVs as potential effectors of BBB recovery and biomarkers in severe ischaemic stroke.

Oral squamous cell carcinoma (OSCC) is the most common manifestation of oral cancer. It has been proposed that periodontal pathogens contribute to OSCC progression, mainly by their virulence factors. However, the main periodontal pathogen and its mechanism to modulate OSCC cells remains not fully understood. In this study we investigate the main host-pathogen pathways in OSCC by computational proteomics and the mechanism behind cancer progression by the oral microbiome. The main host-pathogen pathways were analyzed in the secretome of biopsies from patients with OSCC and healthy controls by mass spectrometry. Then, functional assays were performed to evaluate the host-pathogen pathways highlighted in oral cancer. Host proteins associated with LPS response, cell migration/adhesion, and metabolism of amino acids were significantly upregulated in the human cancer proteome, whereas the complement cascade was downregulated in malignant samples. Then, the microbiome analysis revealed large number and variety of peptides from Fusobacterium nucleatum ( F. nucleatum ) in OSCC samples, from which several enzymes from the L-glutamate degradation pathway were found, indicating that L-glutamate from cancer cells is used as an energy source, and catabolized into butyrate by the bacteria. In fact, we observed that F. nucleatum modulates the cystine/glutamate antiporter in an OSCC cell line by increasing SLC7A11 expression, promoting L-glutamate efflux and favoring bacterial infection. Finally, our results showed that F. nucleatum and its metabolic derivates promote tumor spheroids growth, spheroids-derived cell detachment, epithelial-mesenchymal transition and Galectin-9 upregulation. Altogether, F. nucleatum promotes pro-tumoral mechanism in oral cancer.

This article conceptualizes systems thinking from the perspective of mental models. It portrays systems thinking as a combination of perception, prior knowledge and reasoning processes for guiding decision‐making in complex, dynamic situations. Systems thinking is mostly considered as a skill, and assessment instruments are based on the observable products of thinking. However, there is a lack of research on the cognitive processes involved in generating mental representations of complex dynamic systems, deriving possible behaviours and decisions. Thus, we propose a conceptual framework that combines mental models of dynamic systems and the cognitive theory of reasoning with mental models of possibilities . This theory identifies an intuitive and a deliberative reasoning process describing how the deliberative process influences the mental model of the perceived situation. While remaining compatible with the existing literature on systems thinking, this framework addresses this gap. Through examples, the study illustrates how the distinct levels of systems thinking knowledge of three stylized agents lead to different models, even when the reasoning process is identical. Boundary mismatch errors in the represented structure lead to errors in judging‐system behaviours as necessary, possible or impossible, leading to different decisions. Based on this finding, several new research questions are proposed concerning the dynamics of the cognitive processes and mental models over the iterations of dynamic decision‐making in laboratory experiments. We close with a call for more research to move beyond the current limitations.

Background The International Index of Erectile Function (IIEF) stands out for its utility and widespread use to measure sexual function in men. However, it lacks consistency in its internal latent structure across studies, has not been evaluated for measurement invariance, and has not undergone psychometric validation for its 15-item form in Spanish among South American countries. Aim To examine the IIEF’s psychometric evidence (ie, structural/criterion validity and reliability) in a sample of adult men and determine its measurement invariance across relationship status (single vs in a relationship) and age generations (generations Z, Y/millennials, and X). Methods A sample of 650 sexually active males was derived from a broader Chilean study (Chilean Sex and Sexuality Study). We used a confirmatory factor analysis to determine the IIEF’s structural validity, sexual satisfaction dimensions to establish its criterion-related validity, and Cronbach alpha and McDonald omega to assess the reliability of its scores. Outcomes Measures of goodness of fit. Results The evidence supported the 5-factor latent solution. Meanwhile, criterion-related validity revealed subtle yet significant differences in sexual satisfaction, with younger men displaying higher satisfaction in various sexual domains. In contrast, middle-aged men and those in a relationship showed better sexual function. Finally, the IIEF was invariant across age groups and relationship status at the factor covariance level. Clinical Translation This study provides evidence that the IIEF is a valid, reliable, and invariant tool for the clinical practice in men’s sexual health, particularly that associated with their sexual function and dysfunction. Strengths and Limitations The study included a comprehensive validity analysis of the IIEF’s psychometric properties, demonstrating its reliability and validity across diverse Chilean male subpopulations. The study also offered the IIEF’s first assessment of measurement invariance and confirmed its suitability for clinical and research use in the Chilean population. Meanwhile, the study’s limitations include a lack of clinical population and a sample predominantly younger, cisgender, and heterosexual. Conclusion Our study provides evidence of the IIEF’s 5-factor structure and measurement invariance across age generations and relationship status in Chilean men, supporting its validity for clinical use and research and broadening its applicability in global sexual health studies, particularly in the Spanish-speaking South American male population.

Antimicrobial resistance (AMR) poses a significant global health challenge, necessitating advanced predictive models to support clinical decision-making. In this study, we explore multi-label classification as a novel approach to predict antibiotic resistance across four clinically relevant bacteria: E. coli, S. aureus, K. pneumoniae, and P. aeruginosa. Using multiple datasets from the DRIAMS repository, we evaluated the performance of four algorithms – Multi-Layer Perceptron, Support Vector Classifier, Random Forest, and Extreme Gradient Boosting – under both single-label and multi-label frameworks. Our results demonstrate that the multi-label approach delivers competitive performance compared to traditional single-label models, with no statistically significant differences in most cases. The multi-label framework naturally captures the complex, interconnected nature of AMR data, reflecting real-world scenarios more accurately. We further validated the models on external datasets (DRIAMS B and C), confirming their generalizability and robustness. Additionally, we investigated the impact of oversampling techniques and provided a reproducible methodology for handling MALDI-TOF data, ensuring scalability for future studies. These findings underscore the potential of multi-label classification to enhance predictive accuracy in AMR research, offering valuable insights for developing diagnostic tools and guiding clinical interventions.

Background Suicide prevention programs delivered in school settings have been shown to reduce suicide attempts and ideation among adolescents. School-based digital interventions targeting at-risk youth are a promising avenue for suicide prevention, and some evidence has shown that blending digital and face-to-face components may improve the effectiveness. However, further evidence is needed, especially in Latin America, where mental health support is limited. We tested the effectiveness of the Reframe-IT+, a blended cognitive behavioral indicated intervention to reduce suicidal ideation, designed to be delivered in school settings. It includes 13 sessions, combining eight internet-based sessions and five face-to-face sessions. Methods We conducted a cluster RCT and delivered the Reframe-IT + among secondary students attending Years 9–11. We recruited 21 schools that were randomized into two groups: (1) Intervention Reframe-IT + Group (IG) (n = 863) and (2) Control Group (CG) (n = 683). All consented students completed online screening self-reported questionnaires at baseline. The primary outcome was suicidal ideation . Additionally, we tested the impact of the intervention on depressive and anxiety symptoms, hopelessness, and emotion regulatory strategies, including social solving-problems skills, behavioral activation, cognitive reappraisal, and emotion suppression. A total of 303 students (IG, n = 164; CG, n = 139) were identified as at risk and eligible for inclusion in the study. From those, 224 students (IG, n = 123; CG, n = 101) and their caregivers were interviewed to confirm inclusion and exclusion criteria. Finally, 48 and 47 students were allocated to control and intervention groups, respectively, and answered the online questionnaires at post-intervention. We performed an intention-to-treat analysis using repetitive measures and multilevel regression analyses. Results We found a significant reduction in suicidal ideation (b=-6.7, p = 0.015, Cohen´s d = 0.49), depressive (b=-3.1, p = 0.002, Cohen´s d = 0.81) and anxiety (b=-2.60, p < 0.001, Cohen´s d = 0.72) symptoms, and hopelessness (b=-3.7, p < 0.001, Cohen´s d = 0.70) in the intervention group compared to the control group at post-intervention. We also found improvement in solving-problems skills (b=-1.6, p = 0.002, Cohen´s d = 0.58), behavioral activation (b = 2.8, p = 0.019, Cohen´s d = 0.47), and cognitive reappraisal (b = 2.2, p = 0.029, Cohen´s d = 0.53). In the exploration of the intervention mechanisms concerning suicidal ideation, the total indirect effect of the intervention (b = -5.727923; p = 0.008) was significant, whereas the direct effect (b = − 0.03195473, p = 0.903) was not significant (Suppl 2, Table 1). Problem-solving skill (b=-2.84, p = 0.016) was a significant mediator of intervention effects on suicidal ideation (Path a*b). Conclusions This is the first clustered RCT evaluation of the effectiveness of a blended indicated intervention to prevent suicidality in school settings in Latin America. This is the first step to informing policymakers to scale up an effective intervention for an important public health problem. Trial registration Clinical Trials NCT05229302. Registered on January 27th, 2022.

Accurately predicting the diverse bound-state conformations of small molecules is crucial for successful drug discovery and design, particularly when detailed protein-ligand interactions are unknown. Established tools exist, but efficiently exploring the vast conformational space remains challenging. This work introduces Moltiverse, a novel protocol using enhanced sampling molecular dynamics (MD) simulations for conformer generation. The extended adaptive biasing force (eABF) algorithm combined with metadynamics, guided by a single collective variable (radius of gyration, RDGYR), efficiently samples the conformational landscape of a small molecule. Moltiverse demonstrates comparable accuracy and, in some cases, superior quality when benchmarked against established software like RDKit, CONFORGE, ConfGenX, Torsional diffusion, and Conformator. We present an exhaustive ranking based on eight quantitative metrics and statistical analysis for robust conformer generation algorithms comparison and provide recommendations for their improvement based on our findings. We introduce the Cofactorv1 dataset, a complementary resource for conformer generator evaluation. Unlike traditional datasets with thousands of single-conformer molecules, the Cofactorv1 dataset features only seven small molecule cofactors but with hundreds to thousands of experimental conformers per molecule (sourced from the PDB). This diversity, encompassing 15-29 rotatable bonds, poses a significant challenge for conformer generation benchmarks. Cofactorv1 is a complementary dataset that serves as a valuable resource for developing and evaluating conformer generation methods like Moltiverse, pushing the boundaries of accuracy and diversity in this relevant field.

Nanomaterials, specifically silver nanoparticles (AgNPs), have demonstrated great potential in biomedical applications due to their unique properties, such as antimicrobial activity and conductivity. One promising strategy to improve their biocompatibility...

Allergic rhinitis (AR) and asthma (AS) are two of the most common chronic respiratory diseases and a major public health concern. Multiple studies have demonstrated the role of the nasal bacteriome in AR and AS, but little is known about the airway mycobiome and its potential association to airway inflammatory diseases. Here we used the internal transcriber spacers (ITS) 1 and 2 and high-throughput sequencing to characterize the nasal mycobiome of 339 individuals with AR, AR with asthma (ARAS), AS and healthy controls (CT). Seven to ten of the 14 most abundant fungal genera (Malassezia, Alternaria, Cladosporium, Penicillium, Wallemia, Rhodotorula, Sporobolomyces, Naganishia, Vishniacozyma, and Filobasidium) in the nasal cavity differed significantly (p ≤ 0.049) between AS, AR or ARAS, and CT. However, none of the same genera varied significantly between the three respiratory disease groups. The nasal mycobiomes of AR and ARAS patients showed the highest intra-group diversity, while CT showed the lowest. Alpha-diversity indices of microbial richness and evenness only varied significantly (p ≤ 0.024) between AR or ARAS and CT, while all disease groups showed significant differences (p ≤ 0.0004) in microbial structure (i.e., beta-diversity indices) when compared to CT samples. Thirty metabolic pathways (PICRUSt2) were differentially abundant (Wald’s test) between AR or ARAS and CT patients, but only three of them associated with 5-aminoimidazole ribonucleotide (AIR) biosynthesis were over abundant (log2 Fold Change >0.75) in the ARAS group. AIR has been associated to fungal pathogenesis in plants. Spiec-Easi fungal networks varied among groups, but AR and ARAS showed more similar interactions among their members than with those in the CT mycobiome; this suggests chronic respiratory allergic diseases may disrupt fungal connectivity in the nasal cavity. This study contributes valuable fungal data and results to understand the relationships between the nasal mycobiome and allergy-related conditions. It demonstrates for the first time that the nasal mycobiota varies during health and allergic rhinitis (with and without comorbid asthma) and reveals specific taxa, metabolic pathways and fungal interactions that may relate to chronic airway disease.

Global climate change exacerbates abiotic stresses, as drought, heat, and salt stresses are anticipated to increase significantly in the coming years. Plants coexist with a diverse range of microorganisms. Multiple inter-organismic relationships are known to confer benefits to plants, including growth promotion and enhanced tolerance to abiotic stresses. In this study, we investigated the mutualistic interactions between three fungal endophytes originally isolated from distinct arid environments and an agronomically relevant crop, Solanum lycopersicum. We demonstrated a significant increase in shoot biomass under drought conditions in co-cultivation with Penicillium chrysogenum isolated from Antarctica, Penicillium minioluteum isolated from the Atacama Desert, Chile, and Serendipita indica isolated from the Thar Desert, India. To elucidate plant gene modules commonly induced by the different endophytes that could explain the observed drought tolerance effect in tomato, a comprehensive transcriptomics analysis was conducted. This analysis led to the identification of a shared gene module in the fungus-infected tomato plants. Within this module, gene network analysis enabled us to identify genes related to abscisic acid (ABA) signaling, ABA transport, auxin signaling, ion homeostasis, proline biosynthesis, and jasmonic acid signaling, providing insights into the molecular basis of drought tolerance commonly mediated by fungal endophytes. Our findings highlight a conserved response in the mutualistic interactions between endophytic fungi isolated from unrelated environments and tomato roots, resulting in improved shoot biomass production under drought stress.

Enzymatic hydride transfer reactions play a crucial role in numerous metabolic pathways, yet their accurate computational modeling remains challenging due to the trade-off between accuracy and computational efficiency. Ideally, molecular dynamics simulations should sample all enzyme configurations along the reaction path using post Hartree-Fock or DFT QM/MM electrostatic embedding methods, but these are computationally expensive. Here, we introduce a simple approach to improve the third-order density functional tight binding (DFTB3) semi-empirical method to model hydride transfer reactions in enzymes. We identified deficiencies in DFTB3's description of the potential energy surface for the hydride transfer step in Crotonyl-CoA Carboxylase/Reductase (Ccr) and developed a systematic methodology to address these limitations. Our approach involves modifying DFTB3's repulsive potential functions using linear combinations of harmonic functions, guided by analysis of C-H and C-C distance distributions along the reaction path. The optimized DFTB3 Hamiltonian significantly improved the description of the hydride transfer reaction in Ccr, reproducing the reference DFT activation barrier within 0.1 kcal/mol. We also addressed the transferability of our method by applying it to another hydride transfer reaction bearing the 1,4-dihydropyridine motif but exhibiting distinct structural features of the reactant, as well as the hydride transfer reaction in Dihydrofolate Reductase (DHFR). In both cases our adapted DFTB3 Hamiltonian correctly reproduced the DFT reference and experimentally observed activation barriers. The low computational cost and transferability of our method will enable more accurate and efficient QM/MM molecular dynamics simulations of hydride transfer reactions, potentially accelerating research in enzyme engineering and drug design.

Enzymatic hydride transfer reactions play a crucial role in numerous metabolic pathways, yet their accurate computational modeling remains challenging due to the trade-off between accuracy and computational efficiency. Ideally, molecular dynamics simulations should sample all enzyme configurations along the reaction path using post Hartree-Fock or DFT QM/MM electrostatic embedding methods, but these are computationally expensive. Here, we introduce a simple approach to improve the third-order density functional tight binding (DFTB3) semi-empirical method to model hydride transfer reactions in enzymes. We identified deficiencies in DFTB3's description of the potential energy surface for the hydride transfer step in Crotonyl-CoA Carboxylase/Reductase (Ccr) and developed a systematic methodology to address these limitations. Our approach involves modifying DFTB3's repulsive potential functions using linear combinations of harmonic functions, guided by analysis of C-H and C-C distance distributions along the reaction path. The optimized DFTB3 Hamiltonian significantly improved the description of the hydride transfer reaction in Ccr, reproducing the reference DFT activation barrier within 0.1 kcal/mol. We also addressed the transferability of our method by applying it to another hydride transfer reaction bearing the 1,4-dihydropyridine motif but exhibiting distinct structural features of the reactant, as well as the hydride transfer reaction in Dihydrofolate Reductase (DHFR). In both cases our adapted DFTB3 Hamiltonian correctly reproduced the DFT reference and experimentally observed activation barriers. The low computational cost and transferability of our method will enable more accurate and efficient QM/MM molecular dynamics simulations of hydride transfer reactions, potentially accelerating research in enzyme engineering and drug design.

Coastal Maulino Forest, a biodiversity hotspot, is increasingly threatened by frequent and higher-severity wildfires. Endangered tree species, including Nothofagus spp., inhabit small, isolated native forest fragments surrounded by extensive Pinus radiata plantations, a non-native species that often colonises fire-affected areas. However, the seedling density of the native Chilean wineberry, Aristotelia chilensis, negatively correlates with the abundance of P. radiata seedlings in post-fire areas. This pattern emerged across areas burned at varying fire severities, sampled 8 and 24 months following the 2017 “Las Máquinas” megafire in Chile. The high proportion of plots lacking P. radiata seedlings, coupled with this negative relationship, suggests that A. chilensis may play a role in limiting P. radiata invasion. The negative relationship was most pronounced in areas with moderate fire severity, likely reflecting differences in shade tolerance between the species. While A. chilensis, a light-demanding species with some shade tolerance, can persist in partially shaded environments, P. radiata, a strictly light-demanding species, struggles under significant shade. In low-severity areas, no significant relationship was observed since the substantial native canopy remaining likely limits P. radiata establishment by shading. Conversely, in high-severity fire areas, the absence of a significant relationship might result from the detrimental effects on both species, including potential microbiome dependence for A. chilensis. Given the successful establishment of A. chilensis at low fire severity, enhancing its post-fire recruitment, particularly in moderately burned areas, could be a valuable strategy for mitigating P. radiata invasion and restoring fire-affected Mediterranean ecosystems.