Ethanol exposure perturbs sea urchin development and disrupts developmental timing.

Ethanol is a known vertebrate teratogen that causes craniofacial defects as a component of fetal alcohol syndrome (FAS). Our results show that sea urchin embryos treated with ethanol similarly show broad skeletal patterning defects, potentially analogous to the defects associated with FAS. The sea urchin larval skeleton is a simple patterning system that involves only two cell types: the primary mesenchymal cells (PMCs) that secrete the calcium carbonate skeleton and the ectodermal cells that provide migratory, positional, and differentiation cues for the PMCs. Perturbations in RA biosynthesis and Hh signaling pathways are thought to be causal for the FAS phenotype in vertebrates. Surprisingly, our results indicate that these pathways are not functionally relevant for the teratogenic effects of ethanol in developing sea urchins. We found that developmental morphology as well as the expression of some ectodermal and PMC genes was delayed by ethanol exposure. Temporal transcriptome analysis revealed significant impacts of ethanol on signaling and metabolic gene expression, and a disruption in the timing of GRN gene expression that includes both delayed and precocious gene expression throughout the specification network. We conclude that the skeletal patterning perturbations in ethanol-treated embryos likely arise from a loss of temporal synchrony within and between the instructive and responsive tissues.

Collective dynamics of molecular rotors in periodic mesoporous organosilica: a combined solid-state 2H-NMR and molecular dynamics simulation study.

Molecular rotors offer a platform to realize controlled dynamics and modulate the functions of solids. The motional mechanisms in arrays of rotors have not been explored in depth. Crystal-like porous organosilicas, comprising p-phenylene rotators pivoted onto a siloxane scaffold, were modelled using molecular dynamics (MD) simulations. Long simulations, on a microsecond scale, allowed to follow the reorientation statistics of rotor collections and single out group configurations and frequency distributions as a function of temperature. The motions observed in the MD simulations support a multiple-site model for rotor reorientations. Computed motional frequencies revealed a complex rotatory phenomenon combining an ultra-fast libration motion (oscillation up to 30°) with a slow and fast 180° flip reorientation. Adopting a multiple-site model provides a more accurate simulation of the 2H-NMR spectra and a rationalization of their temperature dependence. In particular, rotators endowed with distinct rates could be explained by the presence of slower rings locked in a T-shaped conformation.

A Molecular Interpretation of the Dynamics of Diffusive Mass Transport of Water within a Glassy Polyetherimide.

The diffusion process of water molecules within a polyetherimide (PEI) glassy matrix has been analyzed by combining the experimental analysis of water sorption kinetics performed by FTIR spectroscopy with theoretical information gathered from Molecular Dynamics simulations and with the expression of water chemical potential provided by a non-equilibrium lattice fluid model able to describe the thermodynamics of glassy polymers. This approach allowed us to construct a convincing description of the diffusion mechanism of water in PEI providing molecular details of the process related to the effects of the cross- and self-hydrogen bonding established in the system on the dynamics of water mass transport.

In vitro and in silico anti-dengue activity of compounds obtained from Psidium guajava through bioprospecting.

BACKGROUND: For decades, bioprospecting has proven to be useful for the identification of compounds with pharmacological potential. Considering the great diversity of Colombian plants and the serious worldwide public health problem of dengue-a disease caused by the dengue virus (DENV)-in the present study, we evaluated the anti-DENV effects of 12 ethanolic extracts derived from plants collected in the Colombian Caribbean coast, and 5 fractions and 5 compounds derived from Psidium guajava. METHODS: The cytotoxicity and antiviral effect of 12 ethanolic extracts derived from plants collected in the Colombian Caribbean coast was evaluated in epithelial VERO cells. Five fractions were obtained by open column chromatography from the ethanolic extract with the highest selectivity index (SI) (derived from P. guajava, SI: 128.2). From the fraction with the highest selectivity (Pg-YP-I-22C, SI: 35.5), five compounds were identified by one- and two-dimensional nuclear magnetic resonance spectroscopy. The antiviral effect in vitro of the fractions and compounds was evaluated by different experimental strategies (Pre- and post-treatment) using non-toxic concentrations calculated by MTT method. The DENV inhibition was evaluated by plate focus assay. The results were analyzed by means of statistical analysis using Student's t-test. Finally the antiviral effect in Silico was evaluated by molecular docking. RESULTS: In vitro evaluation of these compounds showed that three of them (gallic acid, quercetin, and catechin) were promising antivirals as they inhibit the production of infectious viral particles via different experimental strategies, with the best antiviral being catechin (100% inhibition with a pre-treatment strategy and 91.8% with a post-treatment strategy). When testing the interactions of these compounds with the viral envelope protein in silico by docking, only naringin and hesperidin had better scores than the theoretical threshold of - 7.0 kcal/mol (- 8.0 kcal/mol and - 8.2 kcal/mol, respectively). All ligands tested except gallic acid showed higher affinity to the NS5 protein than the theoretical threshold. CONCLUSION: Even though bioprospecting has recently been replaced by more targeted tools for identifying compounds with pharmacological potential, our results show it is still useful for this purpose. Additionally, combining in vitro and in silico evaluations allowed us to identify promising antivirals as well as their possible mechanisms of action.

On the calculation of the potential of mean force between atomistic nanoparticles.

We study the potential of mean force (PMF) between atomistic silica and gold nanoparticles in the vacuum by using molecular dynamics simulations. Such an investigation is devised in order to fully characterize the effective interactions between atomistic nanoparticles, a crucial step to describe the PMF in high-density coarse-grained polymer nanocomposites. In our study, we first investigate the behavior of silica nanoparticles, considering cases corresponding to different particle sizes and assessing results against an analytic theory developed by Hamaker for a system of Lennard-Jones interacting particles (H.C. Hamaker, Physica A 4, 1058 (1937)). Once validated the procedure, we calculate effective interactions between gold nanoparticles, which are considered both bare and coated with polyethylene chains, in order to investigate the effects of the grafting density [Formula: see text] on the PMF. Upon performing atomistic molecular dynamics simulations, it turns out that silica nanoparticles experience similar interactions regardless of the particle size, the most remarkable difference being a peak in the PMF due to surface interactions, clearly apparent for the larger size. As for bare gold nanoparticles, they are slightly interacting, the strength of the effective force increasing for the coated cases. The profile of the resulting PMF resembles a Lennard-Jones potential for intermediate [Formula: see text], becoming progressively more repulsive for high [Formula: see text] and low interparticle separations.

Biomembrane solubilization mechanism by Triton X-100: a computational study of the three stage model.

The solubilization mechanism of lipid membranes in the presence of Triton X-100 (TX-100) is investigated at molecular resolution using molecular dynamics (MD) simulations. Thanks to the large time and length scales accessible by the hybrid particle-field formulation of the models employed here, the complex process of membrane solubilization has been studied, with the goal of verifying the three stage model reported in the literature. DPPC lipid bilayers and vesicles have been studied at different concentrations of the TX-100 detergent employing coarse grained (CG) models. Systems up to ∼600.000 beads, corresponding to more than 2 millions heavy atoms, have been simulated. Moreover, in order to clarify several experimental pieces of evidence, both slow and fast detergent partition scenarios have been investigated. Flat and curved (vesicles) lipid bilayer surfaces, interacting with TX-100, have been considered to study the curvature effects on the detergent partition rate in the membrane. Shape and conformational changes of mixed DPPC/TX-100 vesicles, as a function of TX-100 content, have also been studied. In particular, high curvature surfaces, corresponding to a higher local TX-100 content, promote a membrane rupture. In flat lipid surfaces, on the time scale simulated the detergent partition is almost absent, following a different pathway of the solubilization membrane mechanism.

MicroRNA-21 predicts response to preoperative chemoradiotherapy in locally advanced rectal cancer.

PURPOSE: The treatment of choice for locally advanced rectal cancer is preoperative chemoradiotherapy. Despite half of patients do not respond and suffer unnecessary toxicities and surgery delays, there are no biomarkers to guide preoperative CRT outcome. MicroRNA-21 has been related to acquisition of 5-fluorouracil resistance; however, its potential predictive value of response to preoperative chemoradiotherapy in locally advanced rectal cancer remains unknown. METHODS: Nighty-two patients diagnosed with locally advanced rectal cancer who were preoperatively treated with chemoradiotherapy were selected for this study. Moreover, microRNA-21 expression was quantified in formalin-fixed paraffin-embedded biopsies from this cohort, and the results obtained were correlated with clinical and molecular characteristics, pathological response, and outcome. RESULTS: MicroRNA-21 was found overexpressed in 77.6% cases, and significantly correlated with tumor grade after preoperative chemoradiotherapy (P = 0.013) and with pathological response (P = 0.013). The odds ratio of having miR-21 overexpression and not getting a respond to chemoradiotherapy resulted in 9.75 CI 2.24 to 42. Sensitivity, specificity, negative predictive values, and positive predictive value were 86.6, 60, 42.8, and 92%, respectively. Multivariate analysis confirmed the clinical significance of miR-21 determining preoperative chemoradiotherapy response. CONCLUSIONS: MicroRNA-21 expression efficiently predicts preoperative chemoradiotherapy pathological response in locally advanced rectal cancer.

Periprosthetic joint infections in femoral neck fracture patients treated with hemiarthroplasty - should we use antibiotic-loaded bone cement?

BACKGROUND: Hemiarthroplasty is the most common treatment in elderly patients with displaced intra-capsular femoral neck fracture (FNF). Prosthetic joint infection (PJI) is one of the most feared and frequent complications post-surgery because of the frail health status of these patients and the need for fast track surgery. Therefore, priorities should lie in effective preventive strategies to mitigate this burden. AIM: To determine how much the implementation of the routine use of antibiotic-loaded bone cement (ALBC) as a relatively easy-to-apply amendment to the surgical practice reduces the infection rate in our hemiarthroplasty cohort. METHODS: We retrospectively assessed all demographic, health status and treatment-related data of our FNF patients undergoing cemented hemiarthroplasty in the period from 2011 to 2017; 241 patients were further analyzed after exclusion of patients with cancer-related sequelae and those who died before the end of the 1-year observation period. The PJI rate as diagnosed on basis of the Musculoskeletal Infection Society (MSIS) criteria 2011 was determined for each included patient and compared in function of the bone cement used for hip stem fixation. Patients were split into a group receiving a plain bone cement in the period from January 2011 to June 2013 (non-ALBC group) and into a group receiving an ALBC in the period July 2013 to December 2017 (ALBC group). Data analysis was performed with statistical software. We further calculated the cost-efficacy of the implementation of routine use of ALBC in the second group balancing the in-hospital infection related treatment costs with the extra costs of use of ALBC. RESULTS: In total 241 FNF patients who received cemented hemiarthroplasty in the period from January 2011 to January 2017 were eligible for inclusion in this retrospective study. There were 8 PJI cases identified in the ALBC group among n = 94 patients, whereas 28 PJI cases were observed in the non-ALBC group among n = 147 patients. The statistical analysis showed an infection risk reduction of 55.3% (in particular due to the avoidance of chronic delayed infections) in the ALBC group (95%CI: 6.2%-78.7%; P = 0.0025). The cost-evaluation analysis demonstrated a considerable cost saving of 3.500 € per patient, related to the implementation of routine use of ALBC in this group. CONCLUSION: Use of ALBC is a potent infection preventive factor in FNF patients receiving cemented hemiarthroplasties. It was further found to be highly cost-effective.

N-heterocyclic carbene complexes of au, pd, and pt as effective catalysts in organic synthesis.

N-Heterocyclic carbenes (NHC) have been developed in the last 20 years as effective alternatives to classical tertiary phosphines in transition metal-catalyzed transformations. The rapid development of this area is a result of synergistic interactions between experimental and computational chemists. Indeed, computer modeling has proven extremely useful in rationalizing large amount of experimental data, and thus has permitted to accelerate the pace at which this chemistry has been developed. In this review, we will discuss catalytic transformations involving NHC-containing gold, platinum, and palladium complexes. Particular attention is drawn to the fundamental insights that computational chemistry provided to rationalize mechanistic aspects of these processes.

Traumatic quadruple amputee rehabilitation: from amputation to prosthetic functionality: a case report.

INTRODUCTION: Traumatic quadruple amputations limit daily living activities; however, the current literature regarding rehabilitation treatment for multi-limb amputations is scant. The patient showed adaptation to prosthetic fittings, acquiring a level of functional independence that enabled the patient to lead a nearly independent life. METHODS: The patient's therapeutic intervention was divided into a pre-prosthetic phase, which consisted of functional physical adaptation to the amputation and preparation for the prostheses, and a prosthetic phase, in which different myoelectric and microprocessor limb prostheses were integrated to be used functionally. Its functional use was favored by the training with contact electromyography feedback carried out with the Biometrics E-Link System® for the upper extremities that has made it possible to obtain many grip options in a natural way, for the lower extremities the use of the intelligent passive prostheses has overcome the functional capacity achieved in this type of patients referenced in the literature who had used prostheses of previous generations such as mechanical passive prostheses. RESULTS: With rehabilitation, the patient showed improvements in the following scales and questionnaires (initial vs. final values): Disabilities of the Arm, Shoulder, and Hand Questionnaire; Functional Independence Measure; Berg Balance Scale; Locomotor Capabilities Index in Amputees (an assessment of overall motor capacity); and Special Interest Group in Amputee Medicine scale (an assessment of the degree of mobility). CONCLUSIONS: The patient's age, psychological status, and family and personal support, in addition to technical and economic resources used for next-generation prostheses adapted to this clinical case, were crucial for his progress. IMPLICATIONS FOR REHABILITATION The use of next-generation myoelectric and microprocessor prostheses makes it possible to achieve greater end functionality in quadruple amputees. Proximal amputation levels present greater difficulty in achieving good functionality. Early and intensive rehabilitation could favour and contribute towards improving psychological states. Age, psychological status, and pain management are aspects to take into account during the rehabilitation process.

Mechanistic insights into the cis-trans isomerization of ruthenium complexes relevant to catalysis of olefin metathesis.

The mechanism of the trans to cis isomerization in Ru complexes with a chelating alkylidene group has been investigated by using a combined theoretical and experimental approach. Static DFT calculations suggest that a concerted single-step mechanism is slightly favored over a multistep mechanism, which would require dissociation of one of the ligands from the Ru center. This hypothesis is supported by analysis of the experimental kinetics of isomerization, as followed by (1)H NMR spectroscopy. DFT molecular dynamics simulations revealed that the variation of geometrical parameters around the Ru center in the concerted mechanism is highly uncorrelated; the mechanism actually begins with the transformation of the square-pyramidal trans isomer, with the Ru==CHR bond in the apical position, into a transition state that resembles a metastable square pyramidal complex with a Cl atom in the apical position. This high-energy structure collapses into the cis isomer. Then, the influence of the N-heterocyclic carbene ligand, the halogen, and the chelating alkylidene group on the relative stability of the cis and trans isomers, as well as on the energy barrier separating them, was investigated with static calculations. Finally, we investigated the interconversion between cis and trans isomers of the species involved in the catalytic cycle of olefin metathesis; we characterized an unprecedented square-pyramidal metallacycle with the N-heterocyclic carbene ligand in the apical position. Our analysis, which is relevant to the exchange of equatorial ligands in other square pyramidal complexes, presents evidence for a remarkable flexibility well beyond the simple cis-trans isomerization of these Ru complexes.

International trends of Down syndrome 1993-2004: Births in relation to maternal age and terminations of pregnancies.

BACKGROUND: The aim of this study was to examine trends of Down syndrome (DS) in relation to maternal age and termination of pregnancies (ToP) in 20 registries of the International Clearinghouse for Birth Defects Surveillance and Research (ICBDSR). METHODS: Trends of births with DS (live-born and stillborn), ToP with DS, and maternal age (percentage of mothers older than 35 years) were examined by year over a 12-year period (1993-2004). The total mean number of births covered was 1550,000 annually. RESULTS: The mean percentage of mothers older than 35 years of age increased from 10.9% in 1993 to 18.8% in 2004. However, a variation among the different registers from 4-8% to 20-25% of mothers >35 years of age was found. The total mean prevalence of DS (still births, live births, and ToP) increased from 13.1 to 18.2/10,000 births between 1993 and 2004. The total mean prevalence of DS births remained stable at 8.3/10,000 births, balanced by a great increase of ToP. In the registers from France, Italy, and the Czech Republic, a decrease of DS births and a great increase of ToP was observed. The number of DS births remained high or even increased in Canada Alberta, and Norway during the study period. CONCLUSIONS: Although an increase in older mothers was observed in most registers, the prevalence of DS births remained stable in most registers as a result of increasing use of prenatal diagnostic procedures and ToP with DS.

DENV and ZIKV detection in patients with acute febrile syndrome in Córdoba, Colombia.

OBJECTIVE: To determine simultaneous circulation of DENV serotypes and ZIKV in Córdoba, Colombia, during 2015 and 2016. MATERIAL AND METHODS: A total of 294 samples from patients with clinical diagnosis of febrile syndrome compatible with dengue were collected between June 2015 and December 2016. All samples were tested for DENV and ZIKV by RT-PCR using C6/36 cells culture supernatant. RESULTS: Thirty-three percent of the samples were positive (97/294); from these, 61.8% were positive for DENV and 31% were positive for Zika. The predominant serotype was DENV-2 (70.1%), followed by DENV-3 (8.9%), DENV-4 (6%), and DENV-1 (3%). DENV/ZIKV coinfection was identified in 7.2% of the cases associated with DENV-1 and DENV-3 serotypes. The confirmed cases of dengue, Zika, and DENV/ZIKV coinfections were clinically mild and self-limited. CONCLUSIONS: We reported the co-circulation of all four DENV serotypes, with a higher frequency of DENV-2, and ZIKV introduction in Córdoba department-Colombia in August 2015. This scenario favored the appearance of DENV/ZIKV coinfections.

Exploring the reactivity of Ru-based metathesis catalysts with a pi-acid ligand trans to the Ru-ylidene bond.

In this work we explore the reactivity induced by coordination of a CO molecule trans to the Ru-ylidene bond of a prototype Ru-olefin metathesis catalyst bearing the N-heterocyclic carbene (NHC) ligand SIMes. Static DFT calculations indicate that CO binding to the Ru center promotes a cascade of reactions with very low energy barriers that lead to the final crystallographically characterized product, in which the original methylidene group has attacked the proximal aromatic ring of the SIMes ligand leading to a cycloheptatriene through a Buchner ring expansion. Analysis of the relevant molecular orbitals, supported by ab initio molecular dynamics simulations, illuminate the key role of the pi-acid CO coordinated trans to the Ru-methylidene bond to promote this reactivity. Based on this result, we investigated to which extent a large set of pi-acid groups could promote this deactivating reaction. Results clearly indicate that almost any sufficiently pi-acidic group that can approach the Ru center in the sterically crowded position trans to the Ru-methylidene bond can promote this deactivation route.

Chemodivergent metathesis of dienynes catalyzed by ruthenium-indenylidene complexes: an experimental and computational study.

A study on the enyne metathesis reaction leading to the formation cyclic compounds using ruthenium-indenylidene complexes is presented. Several 1,11-dien-6-ynes have been subjected to ruthenium metathesis cyclization by using ruthenium-indenylidene complexes bearing various phosphine and N-heterocyclic carbene (NHC) ligands. Interestingly, for some substrates chemodivergent metathesis occurs and is a function of the catalyst employed. This led us to investigate the competing "ene-then-yne" or "yne-then-ene" reaction pathways apparently at play in these systems using both experimental observations and DFT calculations. Experimental and computational studies were found in good agreement and permit to conclude that for phosphine-containing catalysts, the "ene-then-yne" pathway is exclusively adopted. On the other hand, for catalysts bearing NHC ligands, both pathways are possible.

Gold- and platinum-catalyzed cycloisomerization of enynyl esters versus allenenyl esters: an experimental and theoretical study.

Ester-way to heaven: Unexpected formation of bicyclo[3.1.0]hexene 4 was the main focus of combined experimental and theoretical studies on the Au-catalyzed cycloisomerization of branched dienyne 1 (see scheme), which provided better understanding of the mechanistic details governing the cyclization of enynes bearing a propargylic ester group.Experimental and theoretical studies on Au- and Pt-catalyzed cycloisomerization of a branched dienyne with an acetate group at the propargylic position are presented. The peculiar architecture of the dienyne precursor, which has both a 1,6- and a 1,5-enyne skeleton, leads, in the presence of alkynophilic gold catalysts, to mixtures of bicyclic compounds 3, 4, and 5. Formation of unprecedented bicyclo[3.1.0]hexene 5 is the main focus of this study. The effect of the ancillary ligand on the gold center was examined and found to be crucial for formation of 5. Further mechanistic studies, involving cyclization of an enantioenriched dienyne precursor, (18)O-labeling experiments, and DFT calculations, allowed an unprecedented reaction pathway to be proposed. We show that bicyclo[3.1.0]hexene 5 is likely formed by a 1,3-OAc shift/allene-ene cyclization/1,2-OAc shift sequence, as calculated by DFT and supported by Au-catalyzed cyclization of isolated allenenyl acetate 7, which leads to improved selectivity in the formation of 5. Additionally, the possibility of OAc migration from allenyl acetates was supported by a trapping experiment with styrene that afforded the corresponding cyclopropane derivative. This unprecedented generation of a vinyl metal carbene from an allenyl ester supports a facile enynyl ester/allenenyl ester equilibrium. Further examination of the difference in reactivity between enynyl acetates and their corresponding [3,3]-rearranged allenenyl acetates toward Au- and Pt-catalyzed cycloisomerization is also presented.

Stigma-related access barriers and violence against trans women in the Colombian healthcare system.

Drawing from qualitative research conducted in a participatory action research framework with 28 transgender women in Colombia, this paper presents the stigma-related barriers to healthcare experienced by trans women and their experiences of multi-level violence within the healthcare system. The authors also discuss how advocacy work was conducted as part of the research process and how trans community leaders were involved throughout the project in order to promote policy-relevance and community-based implementation of findings. The paper concludes with a discussion of how the experiences of violence and stigmatisation within the health care system is linked to broader processes of structural stigma reproduced within Colombian society.

Structural Characterization of Electron Donors in Ziegler-Natta Catalysts.

Ziegler-Natta catalysis is a very important industrial process for the production of polyolefins. However, the catalysts are not well-understood at the molecular level. Yet, atomic-scale structural information is of pivotal importance for rational catalyst development. We applied a solid-state NMR/density functional theory tandem approach to gain detailed insight into the interactions between the catalysts' support, MgCl2, and organic electron donors. Because of the heterogeneity of the samples, large line widths are observed in the carbon spectra. Despite this, good agreement between experimental and computational values was reached, and this shows that 1,3-diether based donors coordinate at (110) surface sites, while phthalates are less selective and coordinate at both (104) and (110) surface sites.

Identification of an alpha-amylase inhibitor from Pterodon pubescens with ability to inhibit cowpea weevil digestive enzymes.

Cowpea seeds (Vigna ungiculata) are widely cultivated by poor farmers in Latin America and Africa and are often severely damaged by the cowpea weevil Callosobruchus maculatus. A proteinaceous inhibitor of cowpea weevil digestive enzymes, PpAI, was purified from white sucupira seeds (Pterodon pubescens) and biochemically characterized in this study. Proteins were extracted from seeds and precipitated with ammonium sulfate at 100% saturation. This fraction was applied onto a Red-sepharose CL-6B column, and the retained peak showed 70% inhibitory activity toward larval C. maculatus digestive alpha-amylases. The retained peak was then purified using an analytical reversed-phase HPLC column. Purified PpAI showed 65% inhibitory activity against larval C. maculatus enzymes. Enzymatic assays also showed that the purified P. pubescens inhibitor was unable to reduce the activity of mammalian alpha-amylases, suggesting specificity toward insect enzymes. Moreover, artificial seeds containing PpAI were able to reduce larval weight by 36% and cause 55% mortality. Mass spectrometry and SDS-PAGE analyses indicated that PpAI showed a molecular mass of approximately 5.0 kDa. This alpha-amylase inhibitor, coming from a native Cerrado plant, could be used to construct a genetically engineered cowpea with enhanced resistance against weevil pests.

Local Structure and Dynamics of Water Absorbed in Poly(ether imide): A Hydrogen Bonding Anatomy.

Hydrogen bonding (HB) interactions play a major role in determining the behavior of macromolecular systems absorbing water. In fact, functional and structural properties of polymer-water mixtures are affected by the amount and type of these interactions. This contribution aims at a molecular level understanding of the interactional scenario for the technologically relevant case of the poly(ether imide)-water system. The problem has been tackled by combining different experimental and theoretical approaches which, taken together, provide a comprehensive physical picture. Relevant experimental data were gathered by in situ FTIR spectroscopy, while molecular dynamics (MD) and statistical thermodynamics approaches were used as modeling theoretical tools. It was found that, among the possible configurations, some are strongly prevailing. In particular, water molecules preferentially establish water bridges with two carbonyl groups of the same PEI repeating unit. Water self-interactions were also detected, giving rise to a "second shell" species in the prevalent form of dimers. The population of the different water species was evaluated spectroscopically, and a remarkable agreement with theoretical predictions was found.