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1.
Comput Biol Med ; 171: 108216, 2024 Mar.
Article in English | MEDLINE | ID: mdl-38442555

ABSTRACT

Despite being one of the most prevalent forms of cancer, prostate cancer (PCa) shows a significantly high survival rate, provided there is timely detection and treatment. Computational methods can help make this detection process considerably faster and more robust. However, some modern machine-learning approaches require accurate segmentation of the prostate gland and the index lesion. Since performing manual segmentations is a very time-consuming task, and highly prone to inter-observer variability, there is a need to develop robust semi-automatic segmentation models. In this work, we leverage the large and highly diverse ProstateNet dataset, which includes 638 whole gland and 461 lesion segmentation masks, from 3 different scanner manufacturers provided by 14 institutions, in addition to other 3 independent public datasets, to train accurate and robust segmentation models for the whole prostate gland, zones and lesions. We show that models trained on large amounts of diverse data are better at generalizing to data from other institutions and obtained with other manufacturers, outperforming models trained on single-institution single-manufacturer datasets in all segmentation tasks. Furthermore, we show that lesion segmentation models trained on ProstateNet can be reliably used as lesion detection models.


Subject(s)
Prostate , Prostatic Neoplasms , Male , Humans , Prostate/diagnostic imaging , Imaging, Three-Dimensional/methods , Retrospective Studies , Algorithms , Prostatic Neoplasms/diagnostic imaging , Magnetic Resonance Imaging/methods
3.
Heliyon ; 10(4): e25765, 2024 Feb 29.
Article in English | MEDLINE | ID: mdl-38390118

ABSTRACT

This article presents the results and main conclusions of a quasi-experimental study after the implementation of an innovative project extended as a multi-year programme, called 'MusMotion', applied in compulsory secondary education, which is based on the relationship between music and emotions, as well as its effects on the academic performance of adolescents. The research analysed and tested an educational innovation project that improves students' academic performance, as well as the classroom climate between teachers and students (N = 444). A key strand of this research concerns the use of music to support students' emotional development and awareness. As we will explain, the results of this research have shown positive outcomes that have direct implications for pedagogy and classroom practice. The results confirm that there is a relationship between emotions and students' academic performance, and the innovative educational programme MusMotion can help to improve students' academic performance and the classroom climate by improving their state of mind. Educational systems, through the management of emotions via music, could help many children who today may have difficulty with their emotions.

4.
Chembiochem ; 25(11): e202400057, 2024 Jun 03.
Article in English | MEDLINE | ID: mdl-38390661

ABSTRACT

Halophilic organisms have adapted to multi-molar salt concentrations, their cytoplasmic proteins functioning despite stronger attraction between hydrophobic groups. These proteins, of interest in biotechnology because of decreasing fresh-water resources, have excess acidic amino acids. It has been suggested that conformational fluctuations - critical for protein function - decrease in the presence of a stronger hydrophobic effect, and that an acidic proteome would counteract this decrease. However, our understanding of the salt- and acidic amino acid dependency of enzymatic activity is limited. Here, using solution NMR relaxation and molecular dynamics simulations for in total 14 proteins, we show that salt concentration has a limited and moreover non-monotonic impact on protein dynamics. The results speak against the conformational-fluctuations model, instead indicating that maintaining protein dynamics to ensure protein function is not an evolutionary driving force behind the acidic proteome of halophilic proteins.


Subject(s)
Molecular Dynamics Simulation , Solutions , Electrolytes/chemistry , Proteins/chemistry , Proteins/metabolism , Hydrophobic and Hydrophilic Interactions , Protein Conformation , Nuclear Magnetic Resonance, Biomolecular
5.
Biophys J ; 122(12): 2577-2589, 2023 06 20.
Article in English | MEDLINE | ID: mdl-37179455

ABSTRACT

The cytoplasmic proteins of some halophilic organisms remain stable and functional at multimolar concentrations of KCl, i.e., under conditions that most mesophilic proteins cannot withstand. Their stability arises from their unusual amino acid composition. The most dramatic difference between halophilic and mesophilic proteins is that the former are rich in acidic amino acids. It has been proposed that one of the evolutionary driving forces for this difference is the occurrence of synergistic interactions between multiple acidic amino acids at the surface of the protein, the potassium cations in solution, and water. We investigate this possibility with molecular dynamics simulations, using high-quality force fields for the protein-water, protein-ion, and ion-ion interactions. We create a rigorous thermodynamic definition of interactions between acidic amino acids on proteins that can be used to distinguish between synergistic, noninteracting and interfering interactions. Our results demonstrate that synergistic interactions between neighboring acidic amino acids in halophilic proteins are frequent at multimolar KCl concentration. Synergistic interactions have an electrostatic origin, and are associated with stronger water-to-carboxylate hydrogen bonds than for acidic amino acids without synergistic interactions. Synergistic interactions are not observed in minimal systems of carboxylates, indicating that the protein environment is critical for their emergence. Our results demonstrate that synergistic interactions are neither associated with rigid amino acid orientations nor with highly structured and slow moving water networks, as had been originally proposed. Moreover, synergistic interactions can also be found in unfolded protein conformations. However, because these conformations are only a small subset of the unfolded state ensemble, synergistic interactions should contribute to the net stabilization of the folded state.


Subject(s)
Proteins , Water , Prevalence , Amino Acids , Carboxylic Acids , Cations , Amino Acids, Acidic
6.
Macromol Biosci ; 23(5): e2200563, 2023 05.
Article in English | MEDLINE | ID: mdl-36861255

ABSTRACT

Coiled coils (CCs) are key building blocks of biogenic materials and determine their mechanical response to large deformations. Of particular interest is the observation that CC-based materials display a force-induced transition from α-helices to mechanically stronger ß-sheets (αßT). Steered molecular dynamics simulations predict that this αßT requires a minimum, pulling speed-dependent CC length. Here, de novo designed CCs with a length between four to seven heptads are utilized to probe if the transition found in natural CCs can be mimicked with synthetic sequences. Using single-molecule force spectroscopy and molecular dynamics simulations, these CCs are mechanically loaded in shear geometry and their rupture forces and structural responses to the applied load are determined. Simulations at the highest pulling speed (0.01 nm ns-1 ) show the appearance of ß-sheet structures for the five- and six-heptad CCs and a concomitant increase in mechanical strength. The αßT is less probable at a lower pulling speed of 0.001 nm ns-1 and is not observed in force spectroscopy experiments. For CCs loaded in shear geometry, the formation of ß-sheets competes with interchain sliding. ß-sheet formation is only possible in higher-order CC assemblies or in tensile-loading geometries where chain sliding and dissociation are prohibited.


Subject(s)
Molecular Dynamics Simulation , Protein Conformation, beta-Strand , Protein Conformation, alpha-Helical , Protein Structure, Secondary , Protein Domains
7.
Clin Kidney J ; 15(11): 2039-2045, 2022 Nov.
Article in English | MEDLINE | ID: mdl-36320365

ABSTRACT

Coronavirus disease 2019 (COVID-19) in kidney transplant recipients has a high risk of complications and mortality, especially in older recipients diagnosed during the early period after transplantation. Management of immunosuppression has been challenging during the pandemic. We investigated the impact of induction immunosuppression, either basiliximab or thymoglobulin, on the clinical evolution of kidney transplant recipients developing COVID-19 during the early period after transplantation. We included kidney transplant recipients with ˂6 months with a functioning graft diagnosed with COVID-19 from the initial pandemic outbreak (March 2020) until 31 July 2021 from different Spanish centres participating in a nationwide registry. A total of 127 patients from 17 Spanish centres developed COVID-19 during the first 6 months after transplantation; 73 (57.5%) received basiliximab and 54 (42.5%) thymoglobulin. Demographics were not different between groups but patients receiving thymoglobulin were more sensitized [calculated panel reactive antibodies (cPRAs) 32.7 ± 40.8% versus 5.6 ± 18.5%] and were more frequently retransplants (30% versus 4%). Recipients ˃65 years of age treated with thymoglobulin showed the highest rate of acute respiratory distress syndrome [64.7% versus 37.1% for older recipients receiving thymoglobulin and basiliximab (P < .05), respectively, and 23.7% and 18.9% for young recipients receiving basiliximab and thymoglobulin (P > .05)], respectively, and the poorest survival [mortality rate 64.7% and 42.9% for older recipients treated with thymoglobulin and basiliximab, respectively (P < .05) and 8.1% and 10.5% for young recipients treated with thymoglobulin and basiliximab (P > .05), respectively]. Older recipients treated with thymoglobulin showed the poorest survival in the Cox regression model adjusted for comorbidities. Thus thymoglobulin should be used with caution in older recipients during the present pandemic era.

8.
Nefrologia (Engl Ed) ; 42(1): 85-93, 2022.
Article in English | MEDLINE | ID: mdl-36153903

ABSTRACT

Living donor kidney transplantation (LDKT) is the best treatment option for end stage renal disease in terms of both patient and graft survival. However, figures on LDKT in Spain that had been continuously growing from 2005 to 2014, have experienced a continuous decrease in the last five years. One possible explanation for this decrease is that the significant increase in the number of deceased donors in Spain during the last years, both brain death and controlled circulatory death donors, might have generated the false idea that we have coped with the transplant needs. Moreover, a greater number of deceased donor kidney transplants have caused a heavy workload for the transplant teams. Furthermore, the transplant teams could have moved on to a more conservative approach to the information and assessment of patients and families considering the potential long-term risks for donors in recent papers. However, there is a significant variability in the LDKT rate among transplant centers and regions in Spain independent of their deceased donor rates. This fact and the fact that LDKT is usually a preemptive option for patients with advanced chronic renal failure, as time on dialysis is a negative independent factor for transplant outcomes, lead us to conclude that the decrease in LDKT depends on other factors. Thus, in the kidney transplant annual meeting held at ONT site in 2018, a working group was created to identify other causes for the decrease of LDKT in Spain and its relationship with the different steps of the process. The group was formed by transplant teams, a representative of the transplant group of the Spanish Society of Nephrology (SENTRA), a representative of the Spanish Society of Transplants (SET) and representatives of the Spanish National Transplant Organization (ONT). A self-evaluation survey that contains requests about the phases of the LDKT processes (information, donor work out, informed consent, surgeries, follow-up and human resources) were developed and sent to 33 LDKT teams. All the centers answered the questionnaire. The analysis of the answers has resulted in the creation of a national analysis of strengths, weaknesses, opportunities, threats (SWOT) of the LDKT program in Spain and the development of recommendations targeted to improve every step of the donation process. The work performed, the conclusions and recommendations provided, have been reflected in the following report: Spanish living donor kidney transplant program assessment: recommendations for optimization. This document has also been reviewed by a panel of experts, representatives of the scientific societies (Spanish Society of Urology (AEU), Spanish Society of Nephrology Nursery (SEDEN), Spanish Society of Immunology (SEI/GETH)) and the patient association ALCER. Finally, the report has been submitted to public consultation, reaching ample consensus. In addition, the transplant competent authorities of the different regions in Spainhave adopted the report at institutional level. The work done and the recommendations to optimize LDKT are summarized in the present manuscript, organized by the different phases of the donation process.


Subject(s)
Kidney Failure, Chronic , Kidney Transplantation , Graft Survival , Humans , Kidney , Kidney Failure, Chronic/surgery , Living Donors
9.
J Phys Chem B ; 126(16): 2943-2945, 2022 04 28.
Article in English | MEDLINE | ID: mdl-35477251
10.
J Phys Chem B ; 125(49): 13552-13564, 2021 12 16.
Article in English | MEDLINE | ID: mdl-34875166

ABSTRACT

The interplay between the local hydration shell structure, the length of hydrophobic solutes, and their identity (perfluorinated or not) remains poorly understood. We address this issue by combining Raman-multivariate curve resolution (Raman-MCR) spectroscopy, simulation, and quantum-mechanical calculations to quantify the thermodynamics and the first principle interactions behind the formation of defects in the hydration shell of alkyl-diol and perfluoroalkyl-diol chains. The hydration shell of the fluorinated diols contains substantially more defects than that of the nonfluorinated diols; these defects are water hydroxy groups that do not donate hydrogen bonds and which either point to the solute (radial-dangling OH) or not (nonradial-dangling OH). The number of radial-dangling OH defects per carbon decreases for longer chains and toward the interior of the fluorinated diols, mainly due to less favorable electrostatics and exchange interactions; nonradial-dangling OH defects per carbon increase with chain length. In contrast, the hydration shell of the nonfluorinated diols only contains radial-dangling defects, which become more abundant toward the center of the chain and for larger chains, predominantly because of more favorable dispersion interactions. These results have implications for how the folding of macromolecules, ligand binding to biomacromolecules, and chemical reactions at water-oil interfaces could be modified through the introduction of fluorinated groups or solvents.


Subject(s)
Halogenation , Water , Hydrogen Bonding , Hydrophobic and Hydrophilic Interactions , Solutions , Thermodynamics
11.
Front Psychol ; 12: 648592, 2021.
Article in English | MEDLINE | ID: mdl-34504455

ABSTRACT

The effects of the pandemic have affected and continue to affect education methods every day. The education methods are not immune to the pandemic periods we are facing, so teachers must know how to adapt their methods in such a way that teaching, and its quality, is not negatively affected. This study provides an overview of different types of teaching methodology before, during, and after the coronavirus disease 2019 (COVID-19) pandemic. This study describes the different types of teaching (e.g., presence learning, blended learning, and distance education) used in two Spanish Universities (i.e., one private and one public) during the pandemic. A new teaching methodology is proposed. The purpose of this study report is to share what we learned about the response to COVID-19. Results provide a basis for reflection about the pros and cons of teaching and learning modalities in higher education. The current situation demands that we continue to rethink what is the best methodology for teaching so that the education of students is not affected in any way. This study is useful for learning about different teaching methods that exist and which ones may suit us best depending on the context, situation, and needs of our students.

12.
Nefrologia (Engl Ed) ; 2021 Jul 19.
Article in English, Spanish | MEDLINE | ID: mdl-34294484

ABSTRACT

Living donor kidney transplantation (LDKT) is the best treatment option for end stage renal disease in terms of both patient and graft survival. However, figures on LDKT in Spain that had been continuously growing from 2005 to 2014, have experienced a continuous decrease in the last five years. One possible explanation for this decrease is that the significant increase in the number of deceased donors in Spain during the last years, both brain death and controlled circulatory death donors, might have generated the false idea that we have coped with the transplant needs. Moreover, a greater number of deceased donor kidney transplants have caused a heavy workload for the transplant teams. Furthermore, the transplant teams could have moved on to a more conservative approach to the information and assessment of patients and families considering the potential long-term risks for donors in recent papers. However, there is a significant variability in the LDKT rate among transplant centers and regions in Spain independent of their deceased donor rates. This fact and the fact that LDKT is usually a preemptive option for patients with advanced chronic renal failure, as time on dialysis is a negative independent factor for transplant outcomes, lead us to conclude that the decrease in LDKT depends on other factors. Thus, in the kidney transplant annual meeting held at ONT site in 2018, a working group was created to identify other causes for the decrease of LDKT in Spain and its relationship with the different steps of the process. The group was formed by transplant teams, a representative of the transplant group of the Spanish Society of Nephrology (SENTRA), a representative of the Spanish Society of Transplants (SET) and representatives of the Spanish National Transplant Organization (ONT). A self-evaluation survey that contains requests about the phases of the LDKT processes (information, donor work out, informed consent, surgeries, follow-up and human resources) were developed and sent to 33 LDKT teams. All the centers answered the questionnaire. The analysis of the answers has resulted in the creation of a national analysis of strengths, weaknesses, opportunities, threats (SWOT) of the LDKT program in Spain and the development of recommendations targeted to improve every step of the donation process. The work performed, the conclusions and recommendations provided, have been reflected in the following report: Spanish living donor kidney transplant program assessment: recommendations for optimization. This document has also been reviewed by a panel of experts, representatives of the scientific societies (Spanish Society of Urology (AEU), Spanish Society of Nephrology Nursery (SEDEN), Spanish Society of Immunology (SEI/GETH)) and the patient association ALCER. Finally, the report has been submitted to public consultation, reaching ample consensus. In addition, the transplant competent authorities of the different regions in Spain have adopted the report at institutional level. The work done and the recommendations to optimize LDKT are summarized in the present manuscript, organized by the different phases of the donation process.

13.
Biophys J ; 120(13): 2746-2762, 2021 07 06.
Article in English | MEDLINE | ID: mdl-34087206

ABSTRACT

Proteins of halophilic organisms, which accumulate molar concentrations of KCl in their cytoplasm, have a much higher content in acidic amino acids than proteins of mesophilic organisms. It has been proposed that this excess is necessary to maintain proteins hydrated in an environment with low water activity, either via direct interactions between water and the carboxylate groups of acidic amino acids or via cooperative interactions between acidic amino acids and hydrated cations. Our simulation study of five halophilic proteins and five mesophilic counterparts does not support either possibility. The simulations use the AMBER ff14SB force field with newly optimized Lennard-Jones parameters for the interactions between carboxylate groups and potassium ions. We find that proteins with a larger fraction of acidic amino acids indeed have higher hydration levels, as measured by the concentration of water in their hydration shell and the number of water/protein hydrogen bonds. However, the hydration level of each protein is identical at low (bKCl = 0.15 mol/kg) and high (bKCl = 2 mol/kg) KCl concentrations; excess acidic amino acids are clearly not necessary to maintain proteins hydrated at high salt concentration. It has also been proposed that cooperative interactions between acidic amino acids in halophilic proteins and hydrated cations stabilize the folded protein structure and would lead to slower dynamics of the solvation shell. We find that the translational dynamics of the solvation shell is barely distinguishable between halophilic and mesophilic proteins; if such a cooperative effect exists, it does not have that entropic signature.


Subject(s)
Amino Acids, Acidic , Sodium Chloride , Ions , Potassium , Potassium Chloride , Water
14.
J. Bras. Patol. Med. Lab. (Online) ; 57: e2462021, 2021. tab, graf
Article in English | LILACS-Express | LILACS | ID: biblio-1154606

ABSTRACT

ABSTRACT The report describes the clinic of an aggressive non-Hodgkin lymphoma, primary cutaneous diffuse large-B cell lymphoma, leg type (PCDLBCL-LT), and shows its relevance for addressing the case of a rare lymphoma, with complex diagnosis and, in most cases, late as there are few studies reported on the subject. Since it is an aggressive pathology, it is essential to have the dissemination of knowledge to assist in the early diagnosis of the disease and, consequently, in the choice of a more effective treatment. Therefore, we seek to demonstrate the main clinical characteristics, as well as the diagnostic approach, staging, and the symptomatic and specific treatment of PCDLBCL-LT.


RESUMEN Este trabajo describe la clínica de un linfoma no Hodgkin extranodal agresivo, el linfoma cutáneo difuso de células B grandes, tipo pierna (LCDCGTP), y muestra su relevancia en abordar el caso de un linfoma raro, de diagnóstico complejo y, en la mayor parte de las veces, tardío ante la carencia de estudios sobre el asunto. Por ser una enfermedad agresiva, debe existir una mayor difusión de conocimiento para ayudar a su diagnóstico precoz y, consecuentemente, la selección de un tratamiento más eficaz. Por lo tanto, buscamos demostrar las principales características clínicas, así como el abordaje diagnóstico, la estadificación y el tratamiento sintomático y específico del LCDCGTP.


RESUMO Este trabalho descreve a clínica de um agressivo linfoma não Hodgkin extranodal, o linfoma cutâneo difuso de grandes células B, tipo perna (LCDCBTP) e mostra sua relevância ao abordar o caso de um linfoma raro, com diagnóstico complexo e, na maioria das vezes, tardio devido aos raros estudos sobre o assunto. Por ser uma patologia agressiva, é primordial haver maior difusão de conhecimento para auxiliar no diagnóstico precoce da doença e, consequentemente, na escolha de um tratamento mais eficaz. Portanto, buscamos demonstrar as principais características clínicas, bem como a abordagem diagnóstica, o estadiamento e o tratamento sintomático e específico do LCDCBTP.

15.
Insights Imaging ; 11(1): 126, 2020 Nov 27.
Article in English | MEDLINE | ID: mdl-33245443

ABSTRACT

OBJECTIVES: To study the diffusion tensor-based fiber tracking feasibility to access the male urethral sphincter complex of patients with prostate cancer undergoing Retzius-sparing robot-assisted laparoscopic radical prostatectomy (RS-RARP). METHODS: Twenty-eight patients (median age of 64.5 years old) underwent 3 T multiparametric-MRI of the prostate, including an additional echo-planar diffusion tensor imaging (DTI) sequence, using 15 diffusion-encoding directions and a b value = 600 s/mm2. Acquisition parameters, together with patient motion and eddy currents corrections, were evaluated. The proximal and distal sphincters, and membranous urethra were reconstructed using the deterministic fiber assignment by continuous tracking (FACT) algorithm, optimizing fiber tracking parameters. Tract length and density, fractional anisotropy (FA), axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD) were computed. Regional differences between structures were accessed by ANOVA, or nonparametric Kruskal-Wallis test, and post-hoc tests were employed, respectively, TukeyHSD or Dunn's. RESULTS: The structures of the male urethral sphincter complex were clearly depicted by fiber tractography using optimized acquisition and fiber tracking parameters. The use of eddy currents and subject motion corrections did not yield statistically significant differences on the reported DTI metrics. Regional differences were found between all structures studied among patients, suggesting a quantitative differentiation on the structures based on DTI metrics. CONCLUSIONS: The current study demonstrates the technical feasibility of the proposed methodology, to study in a preoperative setting the male urethral sphincter complex of prostate cancer patients candidates for surgical treatment. These findings may play a role on a more accurate prediction of the RS-RARP post-surgical urinary continence recovery rate.

16.
Soft Matter ; 16(43): 9917-9928, 2020 Nov 11.
Article in English | MEDLINE | ID: mdl-33030193

ABSTRACT

Single alpha helices (SAHs) stable in isolated form are often found in motor proteins where they bridge functional domains. Understanding the mechanical response of SAHs is thus critical to understand their function. The quasi-static force-extension relation of a small number of SAHs is known from single-molecule experiments. Unknown, or still controversial, are the molecular scale details behind those observations. We show that the deformation mechanism of SAHs pulled from the termini at pull speeds approaching the quasi-static limit differs from that of typical helices found in proteins, which are stable only when interacting with other protein domains. Using molecular dynamics simulations with atomistic resolution at low pull speeds previously inaccessible to simulation, we show that SAHs start unfolding from the termini at all pull speeds we investigated. Unfolding proceeds residue-by-residue and hydrogen bond breaking is not the main event determining the barrier to unfolding. We use the molecular simulation data to test the cooperative sticky chain model. This model yields excellent fits of the force-extension curves and quantifies the distance, xE = 0.13 nm, to the transition state, the natural frequency of bond vibration, ν0 = 0.82 ns-1, and the height, V0 = 2.9 kcal mol-1, of the free energy barrier associated with the deformation of single residues. Our results demonstrate that the sticky chain model could advantageously be used to analyze experimental force-extension curves of SAHs and other biopolymers.


Subject(s)
Molecular Dynamics Simulation , Proteins , Hydrogen Bonding , Protein Conformation, alpha-Helical , Protein Folding , Protein Structure, Secondary , Protein Unfolding
17.
Phys Chem Chem Phys ; 22(40): 22997-23008, 2020 Oct 21.
Article in English | MEDLINE | ID: mdl-33034325

ABSTRACT

The ability to locally tune solute-water interactions and thus control the hydrophilic/hydrophobic character of a solute is key to control molecular self-assembly and to develop new drugs and biocatalysts; it has been a holy grail in synthetic chemistry and biology. To date, the connection between (i) the hydrophobicity of a functional group; (ii) the local structure and thermodynamics of its hydration shell; and (iii) the relative influence of van der Waals (dispersion) and electrostatic interactions on hydration remains unclear. We investigate this connection using spectroscopic, classical simulation and ab initio methods by following the transition from hydrophile to hydrophobe induced by the step-wise fluorination of methyl groups. Along the transition, we find that water-solute hydrogen bonds are progressively transformed into dangling hydroxy groups. Each structure has a distinct thermodynamic, spectroscopic and quantum-mechanical signature connected to the associated local solute hydrophobicity and correlating with the relative contribution of electrostatics and dispersion to the solute-water interactions.

18.
Phys Chem Chem Phys ; 22(21): 12140-12153, 2020 Jun 04.
Article in English | MEDLINE | ID: mdl-32436497

ABSTRACT

We report a terahertz absorption spectroscopy study of MgSO4 aqueous solutions in the concentration range 0.1 mol dm-3 to 2.4 mol dm-3. Accompanying classical MD simulations were carried out that use a polarizable force field parameterized to reproduce the solution thermodynamics. Contrary to prior reports, we find no evidence of contact ion pairs, even close to the solubility limit. Only solvent separated and different types of solvent shared ion pairs are found, being abundant even at the lowest concentration investigated here. The structure of the solution is concentration-dependent: the number of both types of ion pairs grows with increasing salt concentration. The combined theoretical and experimental analysis of the spectra in the frequency region 50-640 cm-1 suggests that the dynamics of water directly between two ions in solvent shared configuration is very strongly perturbed, via a cooperative, supra-additive, effect arising from the two ions. At high concentrations, the results support a scenario, where the perturbations in the water dynamics extend up to the third hydration layer via a cooperative, but additive, effect involving multiple ions. The SO42- and its hydration shell are much more strongly perturbed by the presence of the counterions than the first hydration shell of Mg2+. It is further shown that our simulations and observations are in agreement with thermodynamic properties of aqueous MgSO4 solutions derived by other methods.

19.
J Am Chem Soc ; 141(40): 15856-15868, 2019 10 09.
Article in English | MEDLINE | ID: mdl-31503489

ABSTRACT

Although perfluorination is known to enhance hydrophobicity and change protein activity, its influence on hydration-shell structure and thermodynamics remains an open question. Here we address that question by combining experimental Raman multivariate curve resolution spectroscopy with theoretical classical simulations and quantum mechanical calculations. Perfluorination of the terminal methyl group of ethanol is found to enhance the disruption of its hydration-shell hydrogen bond network. Our results reveal that this disruption is not due to the associated volume change but rather to the electrostatic stabilization of the water dangling OH···F interaction. Thus, the hydration shell structure of fluorinated methyl groups results from a delicate balance of solute-water interactions that is intrinsically different from that associated with a methyl group.

20.
Phys Chem Chem Phys ; 21(4): 2029-2038, 2019 Jan 23.
Article in English | MEDLINE | ID: mdl-30633256

ABSTRACT

Fluorination can dramatically improve the thermal and proteolytic stability of proteins and their enzymatic activity. Key to the impact of fluorination on protein properties is the hydrophobicity of fluorinated amino acids. We use molecular dynamics simulations, together with a new fixed-charge, atomistic force field, to quantify the changes in hydration free energy, ΔGHyd, for amino acids with alkyl side chains and with 1 to 6 -CH → -CF side chain substitutions. Fluorination changes ΔGHyd by -1.5 to +2 kcal mol-1, but the number of fluorines is a poor predictor of hydrophobicity. Changes in ΔGHyd reflect two main contributions: (i) fluorination alters side chain-water interactions; we identify a crossover point from hydrophilic to hydrophobic fluoromethyl groups which may be used to estimate the hydrophobicity of fluorinated alkyl side-chains; (ii) fluorination alters the number of backbone-water hydrogen bonds via changes in the relative side chain-backbone conformation. Our results offer a road map to mechanistically understand how fluorination alters hydrophobicity of (bio)polymers.


Subject(s)
Amino Acids/chemistry , Fluorine/chemistry , Halogenation , Hydrogen Bonding , Hydrophobic and Hydrophilic Interactions , Molecular Conformation , Molecular Dynamics Simulation , Proteins/chemistry
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