Dual role of Vascular Endothelial Growth Factor-C (VEGF-C) in post-stroke recovery.

Using a mouse model of ischemic stroke, this study characterizes stroke-induced lymphangiogenesis at the cribriform plate (CP). While blocking CP lymphangiogenesis with a VEGFR-3 inhibitor improves stroke outcome, administration of VEGF-C induced larger brain infarcts. Abstract: Cerebrospinal fluid (CSF), antigens, and antigen-presenting cells drain from the central nervous system (CNS) into lymphatic vessels near the cribriform plate and dural meningeal lymphatics. However, the pathological roles of these lymphatic vessels surrounding the CNS during stroke are not well understood. Using a mouse model of ischemic stroke, transient middle cerebral artery occlusion (tMCAO), we show that stroke induces lymphangiogenesis near the cribriform plate. Interestingly, lymphangiogenesis is restricted to lymphatic vessels at the cribriform plate and downstream cervical lymph nodes, without affecting the conserved network of lymphatic vessels in the dura. Cribriform plate lymphangiogenesis peaks at day 7 and regresses by day 14 following tMCAO and is regulated by VEGF-C/VEGFR-3. These newly developed lymphangiogenic vessels transport CSF and immune cells to the cervical lymph nodes. Inhibition of VEGF-C/VEGFR-3 signaling using a blocker of VEGFR-3 prevented lymphangiogenesis and led to improved stroke outcomes at earlier time points but had no effects at later time points following stroke. Administration of VEGF-C after tMCAO did not further increase post-stroke lymphangiogenesis, but instead induced larger brain infarcts. The differential roles for VEGFR-3 inhibition and VEGF-C in regulating stroke pathology call into question recent suggestions to use VEGF-C therapeutically for stroke.

Websites Selling Direct-to-Consumer Anti-Mullerian Hormone Tests.

Importance: The recent provision of direct-to-consumer (DTC) Anti-Mullerian Hormone (AMH) testing in several countries has been contentious, particularly due to concerns about judicious testing and informed consent. Objective: To describe and analyze information on websites that sell DTC AMH tests. Design, Setting, and Participants: Qualitative study including content analysis of text information from websites in multiple countries that sell AMH tests DTC. The top 50 search results from 4 different internet search strings were captured and reviewed for eligibility. Data were extracted in March 2022 and analyzed from April 2022 to July 2023. Main outcomes and measures: Themes and categories were derived from the website content using a conventional inductive approach, with a particular focus on information content, quality and accuracy, as well as the tone and language used. Results: Twenty-seven websites across 7 different countries formed the sample for analysis. Information varied considerably across websites and was organized into 6 overarching categories: (1) whether a test description was included (25 websites [93%]); (2) statements about what the test can do, which included indicating ovarian reserve (26 websites [96%]) and indicating likelihood of conceiving (20 websites [74%]); (3) statements about the usefulness of the test result, which included enabling women to adjust their reproductive timeline (11 websites [41%]) and determining whether egg freezing was a viable option (8 websites [30%]); (4) blood collection method (ie, through a laboratory or an at-home sample); (5) promotion tactics, such as stating the convenience of testing (24 websites [89%]) and using language promoting empowerment and control (7 websites [26%]); and (6) statements about limitations of the test, which included polycystic ovary syndrome falsely inflating AMH levels (13 websites [48%]) and that it cannot accurately predict chances of conceiving (9 websites [33%]). Conclusion and relevance: In this qualitative study including content analysis, most websites selling DTC AMH tests included false and misleading claims which might lead consumers to purchase an AMH test in the belief that it can reliably predict fertility potential and age of menopause. Depending on the test result, this may in turn lead to misplaced anxiety or reassurance about one's fertility and modifications to subsequent conception or contraceptive plans and behavior.

Active-Feedback 3D Single-Molecule Tracking Using a Fast-Responding Galvo Scanning Mirror.

Real-time three-dimensional single-particle tracking (RT-3D-SPT) allows continuous detection of individual freely diffusing objects with high spatiotemporal precision by applying closed-loop active feedback in an optical microscope. However, the current tracking speed in RT-3D-SPT is primarily limited by the response time of the control actuators, impeding long-term observation of fast diffusive objects such as single molecules. Here, we present an RT-3D-SPT system with improved tracking performance by replacing the XY piezoelectric stage with a galvo scanning mirror with an approximately 5 times faster response rate (∼5 kHz). Based on the previously developed 3D single-molecule active real-time tracking (3D-SMART), this new implementation with a fast-responding galvo mirror eliminates the mechanical movement of the sample and allows a more rapid response to particle motion. The improved tracking performance of the galvo mirror-based implementation is verified through simulation and proof-of-principle experiments. Fluorescent nanoparticles and ∼1 kB double-stranded DNA molecules were tracked via both the original piezoelectric stage and new galvo mirror implementations. With the new galvo-based implementation, notable increases in tracking duration, localization precision, and the degree to which the objects are locked to the center of the detection volume were observed. These results suggest that faster control response elements can expand RT-3D-SPT to a broader range of chemical and biological systems.

The Alzheimer's disease risk factor INPP5D restricts neuroprotective microglial responses in amyloid beta-mediated pathology.

INTRODUCTION: Mutations in INPP5D, which encodes for the SH2-domain-containing inositol phosphatase SHIP-1, have recently been linked to an increased risk of developing late-onset Alzheimer's disease. While INPP5D expression is almost exclusively restricted to microglia in the brain, little is known regarding how SHIP-1 affects neurobiology or neurodegenerative disease pathogenesis. METHODS: We generated and investigated 5xFAD Inpp5dfl/fl Cx3cr1Ert2Cre mice to ascertain the function of microglial SHIP-1 signaling in response to amyloid beta (Aß)-mediated pathology. RESULTS: SHIP-1 deletion in microglia led to substantially enhanced recruitment of microglia to Aß plaques, altered microglial gene expression, and marked improvements in neuronal health. Further, SHIP-1 loss enhanced microglial plaque containment and Aß engulfment when compared to microglia from Cre-negative 5xFAD Inpp5dfl/fl littermate controls. DISCUSSION: These results define SHIP-1 as a pivotal regulator of microglial responses during Aß-driven neurological disease and suggest that targeting SHIP-1 may offer a promising strategy to treat Alzheimer's disease. HIGHLIGHTS: Inpp5d deficiency in microglia increases plaque-associated microglia numbers. Loss of Inpp5d induces activation and phagocytosis transcriptional pathways. Plaque encapsulation and engulfment by microglia are enhanced with Inpp5d deletion. Genetic ablation of Inpp5d protects against plaque-induced neuronal dystrophy.

The innate immune response in tauopathies.

Tauopathies, which include frontotemporal dementia, Alzheimer's disease, and chronic traumatic encephalopathy, are a class of neurological disorders resulting from pathogenic tau aggregates. These aggregates disrupt neuronal health and function leading to the cognitive and physical decline of tauopathy patients. Genome-wide association studies and clinical evidence have brought to light the large role of the immune system in inducing and driving tau-mediated pathology. More specifically, innate immune genes are found to harbor tauopathy risk alleles, and innate immune pathways are upregulated throughout the course of disease. Experimental evidence has expanded on these findings by describing pivotal roles for the innate immune system in the regulation of tau kinases and tau aggregates. In this review, we summarize the literature implicating innate immune pathways as drivers of tauopathy.

RNA-Seq of Phenotypically Distinct Eimeria maxima Strains Reveals Coordinated and Contrasting Maturation and Shared Sporogonic Biomarkers with Eimeria acervulina.

Strains of Eimeria maxima, an enteric parasite of poultry, vary in virulence. Here, we performed microscopy and RNA sequencing on oocysts of strains APU-1 (which exhibits more virulence) and APU-2. Although each underwent parallel development, APU-1 initially approached maturation more slowly. Each strain sporulated by hour 36; their gene expression diverged somewhat thereafter. Candidate biomarkers of viability included 58 genes contributing at least 1000 Transcripts Per Million throughout sporulation, such as cation-transporting ATPases and zinc finger domain-containing proteins. Many genes resemble constitutively expressed genes also important to Eimeria acervulina. Throughout sporulation, the expression of only a few genes differed between strains; these included cyclophilin A, EF-1α, and surface antigens (SAGs). Mature and immature oocysts uniquely differentially express certain genes, such as an X-Pro dipeptidyl-peptidase domain-containing protein in immature oocysts and a profilin in mature oocysts. The immature oocysts of each strain expressed more phosphoserine aminotransferase and the mature oocysts expressed more SAGs and microneme proteins. These data illuminate processes influencing sporulation in Eimeria and related genera, such as Cyclospora, and identify biological processes which may differentiate them. Drivers of development and senescence may provide tools to assess the viability of oocysts, which would greatly benefit the poultry industry and food safety applications.

Examining drivers of coronavirus disease 2019 (COVID-19) vaccine hesitancy among healthcare workers.

OBJECTIVE: To assess characteristics and perceptions associated with vaccine hesitancy among healthcare workers to increase coronavirus disease 2019 (COVID-19) vaccine uptake in this population. DESIGN: Cross-sectional quantitative survey. SETTING: A not-for-profit healthcare system in southwestern Virginia. PARTICIPANTS: A convenience sample of 2,720 employees of a not-for-profit healthcare system. METHODS: Between March 15 and 29, 2021, we conducted an Internet-based survey. Our questionnaire assessed sociodemographic and work-related characteristics, vaccine experience and intentions, agreement with vaccine-related perceptions, the most important reasons for getting or not getting vaccinated, and trusted sources of information about COVID-19. We used χ2 analyses to assess the relationship between vaccine hesitancy and both HCW characteristics and vaccine-related perceptions. RESULTS: Overall, 18% of respondents were classified as vaccine hesitant. Characteristics significantly associated with hesitancy included Black race, younger age, not having a high-risk household member, and prior personal experience with COVID-19 illness. Vaccine hesitancy was also significantly associated with many vaccine-related perceptions, including concerns about short-term and long-term side effects and a belief that the vaccines are not effective. Among vaccine-acceptant participants, wanting to protect others and wanting to help end the pandemic were the most common reasons for getting vaccinated. Personal physicians were cited most frequently as trusted sources of information about COVID-19 among both vaccine-hesitant and vaccine-acceptant respondents. CONCLUSIONS: Educational interventions to decrease vaccine hesitancy among healthcare workers should focus on alleviating safety concerns, emphasizing vaccine efficacy, and appealing to a sense of duty. Such interventions should target younger adult audiences. Personal physicians may also be an effective avenue for reducing hesitancy among their patients through patient-centered discussions.

The presentation of spontaneous coronary artery dissection in the emergency department: Signs and symptoms in an unsuspecting population.

OBJECTIVES: Spontaneous coronary artery dissection (SCAD) has emerged as a common cause of acute coronary syndrome (ACS) in young women, although it is rarely discussed in the differential diagnosis for chest pain in the emergency department (ED). In a population otherwise considered low risk for myocardial infarction, there is a danger of incomplete workup and missed diagnosis. In this study, we aim to describe the clinical presentation of those who present to the ED with SCAD to increase awareness of this potentially fatal diagnosis among emergency practitioners. METHODS: Data were queried from the Mayo Clinic "Virtual" Multicenter SCAD Registry, a large multisite international disease registry. The registry includes demographic information as well as data from both medical records and surveys administered following the SCAD event. Symptom presentation was abstracted from survey narrative responses. Data analysis was performed using descriptive statistics. RESULTS: Of 1196 subjects included, chest pain was reported during initial SCAD event in 95.7%. Most common chest symptoms descriptors were pain, pressure/weight, and tightness, with radiation most often in one or both arms/shoulders. Other common symptoms included nausea, shortness of breath, and diaphoresis. Most common electrocardiogram (ECG) findings reported were ST elevation, T-wave abnormality, and normal ECG. Initial troponin values were within normal range in 20.1% of patients. CONCLUSION: With young healthy women often considered "low risk" for ACS, it is important to understand that SCAD is a cause of ACS, and familiarity with presentation can improve awareness among emergency physicians. Our data can provide insight in helping to identify young women who present with chest pain due to SCAD so they can be appropriately evaluated.

Glia limitans superficialis oxidation and breakdown promote cortical cell death after repetitive head injury.

Repetitive mild traumatic brain injuries (mTBI) disrupt CNS barriers, the erosion of which has been linked to long-term neurodegenerative and psychiatric conditions. Although much attention has been devoted to CNS vasculature following mTBI, little is known about the glia limitans superficialis - a barrier of surface-associated astrocytes that helps protect the CNS parenchyma and maintain homeostasis. Here, we identify the glia limitans superficialis as a crucial barrier surface whose breakdown after acute repeat mTBI facilitates increased cell death and recruitment of peripheral myelomonocytic cells. Using intravital microscopy, we show that brain-resident microglia fortify this structure after a single mTBI, yet they fail to do so following secondary injury, which triggers massive recruitment of myelomonocytic cells from the periphery that contribute to further destruction of the glia limitans superficialis but not cortical cell death. We demonstrate, instead, that reactive oxygen species (ROS) generated in response to repetitive head injury are largely responsible for enhanced cortical cell death, and therapeutic administration of the antioxidant glutathione markedly reduces this cell death, preserves the glia limitans, and prevents myelomonocytic cells from entering the brain parenchyma. Collectively, our findings underscore the importance of preserving the glia limitans superficialis after brain injury and offer a therapeutic means to protect this structure and the underlying cortex.

SEROPREVALENCE OF TOXOPLASMA GONDII IN MARKET HOGS COLLECTED FROM U.S. SLAUGHTERHOUSES.

Foodborne pathogens continue to pose a public health risk and can cause serious illness and outbreaks of disease in consumers. The consumption of raw or undercooked infected meat, such as pork containing infectious stages of Toxoplasma gondii, may be a major route of transmission to humans. Given the occasional presence of T. gondii in pork meat and the frequent use of pork for products not intended to be cooked, such as dry-cured ham, a potential risk exists for T. gondii transmission to consumers of these products. The purpose of this study was to determine the seroprevalence of T. gondii in U.S. market hogs and sows at slaughter. A total of 20,209 sera samples collected from 22 U.S. slaughterhouses, including 15 of the top 25 largest slaughter plants in the United States, were tested for T. gondii antibodies using a commercial ELISA assay. Seroprevalence in this study was 0.74%, with a herd prevalence of 10.86%. We compared seroprevalence of T. gondii in market hogs vs. sows from a separate but geographically similar set of slaughterhouse locations, with serum samples screened using the T. gondii modified agglutination test. This set of market hogs demonstrated 0% seroprevalence for T. gondii, while sows from geographically similar but separate slaughter facilities demonstrated a seroprevalence of 1.03%. Overall, both analyses show low seroprevalence of T. gondii in U.S market hogs and sows, respectively, and a marked drop in prevalence in market hogs and sows compared to previous studies.

Cancer as Communal: Understanding Communication and Relationships from the Perspectives of Survivors, Family Caregivers, and Health Care Providers.

With cancer increasing in prevalence and high priorities placed on concurrent oncological and palliative care to help meet the familial, spiritual, and individual needs of stakeholders in cancer, research is needed that assesses the factors that facilitate coping across stakeholders in cancer care. We were interested in synthesizing our understanding of communication and relationships among patients, caregivers, and providers based on the reasoning that illness is relational, but often conceptualized and researched from the individual perspectives of various stakeholders. The current study examined the experiences of relational and communication opportunities and challenges during cancer for current and former family caregivers, cancer survivors, and palliative and oncology health care practitioners. The thematic analysis of 30 semi-structured interviews revealed an overarching theme on the benefits of orienting toward cancer as communal, which was, in turn, facilitated or impeded by four additional themes/sets of behaviors: support, presence, perspective-taking, and reframing hope. Results of a cross-case data matrix analysis reveal that stakeholders in different roles experience qualitative differences in their experience of cancer as communal, isolated, or ambivalent. Implications for education, palliative care, and interventions are discussed.

Analysis of Posttraumatic Stress Disorder, Depression, Anxiety, and Resiliency Within the Unique Population of Spontaneous Coronary Artery Dissection Survivors.

Background Mental health after spontaneous coronary artery dissection (SCAD), a cause of myocardial infarction in young women, remains largely unexplored. We assessed the prevalence and severity of psychiatric symptoms after SCAD. Methods and Results Individuals with confirmed SCAD who consented to the Mayo Clinic "Virtual" Multicenter SCAD Registry were sent the Posttraumatic Stress Disorder Diagnostic Scale for Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Patient Health Questionnaire-9, Generalized Anxiety Disorder-7, Anxiety Sensitivity Index, Connor-Davidson Resilience Scale, 36-Item Short-Form Health Survey, and an SCAD-specific questionnaire. Among 782 patients contacted, 512 surveys were returned. Most respondents were women (97.5%), with median age at time of SCAD and survey completion of 47 and 52 years, respectively. Eighty-two percent had at least one trauma, with mild or more posttraumatic stress disorder symptoms in 28%. Symptoms of anxiety and depression were observed in 41% and 32%, respectively. On multivariable analysis, those of younger age at first SCAD and low resiliency scored higher on measures of trauma, anxiety, and depression. Those with higher anxiety sensitivity had more severe anxiety and posttraumatic stress disorder symptoms. Emotional and social quality of life was higher in those with high resiliency scores. Time from SCAD event to survey completion was associated with lower Generalized Anxiety Disorder-7 score severity. Conclusions Survivors of SCAD have significant rates of posttraumatic stress disorder, depression, and anxiety, which are associated with lower quality of life specifically among those with lower resiliency. Given the prevalence and potential impact, screening and treatment for the psychological distress is advised. Behavioral interventions targeted toward resiliency training may be beneficial for this patient population.

A Microporous Co-MOF for Highly Selective CO2 Sorption in High Loadings Involving Aryl C-H···O═C═O Interactions: Combined Simulation and Breakthrough Studies.

In the context of porous crystalline materials toward CO2 separation and capture, a new 2-fold interpenetrated 3D microporous Co-MOF, IITKGP-11 (IITKGP denotes Indian Institute of Technology Kharagpur), has been synthesized consisting of a 1D channel of ∼3.6 × 5.0 Å2 along the [101] direction with a cavity volume of 35.20%. This microporous framework with a BET surface area of 253 m2g-1 shows higher uptake of CO2 (under 1 bar, 3.35 and 2.70 mmol g-1 at 273 and 295 K, respectively), with high separation selectivities for CO2/N2 and CO2/CH4 gas mixtures under ambient conditions as estimated through IAST calculation. Moreover, real time dynamic breakthrough studies reveal the high adsorption selectivity toward CO2 for these binary mixed gases at 295 K and 1 bar. Besides high gas separation selectivity, capacity considerations in mixed gas phases are also important to check the performance of a given adsorbent. CO2 loading amounts in mixed gas phases are quite high as predicted through IAST calculation and experimentally determined from dynamic breakthrough studies. In order to get insight into the phenomena, GCMC simulation was performed demonstrating that the CO2 molecules are electrostatically trapped via interactions between oxygen on CO2 and hydrogen on pyridyl moieties of the spacers.

Communicatively Constructing the Bright and Dark Sides of Hope: Family Caregivers' Experiences during End of Life Cancer Care.

(1) Background: The communication of hope is complicated, particularly for family caregivers in the context of cancer who struggle to maintain hope for themselves and their loved ones in the face of terminality. In order to understand these complexities, the current study examines the bright and dark sides of how hope is communicated across the cancer journey from the vantage point of bereaved family caregivers; (2) Methods: We analyzed interviews with bereaved family caregivers using qualitative thematic and case oriented strategies to identify patterns in the positive and negative lived experiences when communicating about hope at the end of life; (3) Results: Two overarching patterns of hope emerged. Those who experienced hope as particularized (focused on cure) cited communication about false hope, performing (faking it), and avoidance. Those who transitioned from particularized to generalized hope (hope for a good death) reported acceptance, the communication of hope as social support, prioritizing family, and balancing hope and honesty; (4) Conclusion: Family caregivers face myriad complexities in managing the bright and dark sides of hope. Interventions should encourage concurrent oncological and palliative care, increased perspective-taking among family members, and encourage the transition from particularized to generalized hope.

Reasons for, and outcomes of patients who were referred for a ventricular assist device but were declined: the recent era forgotten ones.

BACKGROUND: Ventricular assist devices (VADs) have a proven survival benefit in select patients with advanced heart failure, yet many patients considered for implantation are declined for various reasons. The outcome of these patients is obscure owing to their exclusion from recent VAD studies. We aim to compare the outcomes of patients who received a VAD to those who did not. METHODS: For this study, the Artificial Heart Program's database at Intermountain Medical Center was queried from 2006 to 2012 for patients referred for a VAD. Kaplan-Meier survival analysis was performed with log-rank test determining significance. RESULTS: Of 232 patients included, 118 patients received a VAD and 114 patients did not. The prevailing reason for VAD decline in eligible and willing patients was due to pre-existing illness (39%). Mortality was higher in non-VAD vs. VAD patients (58.8% vs. 35.6%, p < 0.001) with a median time-to-death of 67 (IQR:12-314) and 301 (IQR:136-694) d, respectively (p = 0.007). CONCLUSIONS: In the current era of non-pulsatile VADs, mortality of patients who are considered but not implanted remains high. Additionally, mortality of these patients occurred much sooner. Educational efforts ensuring timely referral for VAD therapy are important to maximize the number of patients who may benefit.

Identification of active sites in CO oxidation and water-gas shift over supported Pt catalysts.

Identification and characterization of catalytic active sites are the prerequisites for an atomic-level understanding of the catalytic mechanism and rational design of high-performance heterogeneous catalysts. Indirect evidence in recent reports suggests that platinum (Pt) single atoms are exceptionally active catalytic sites. We demonstrate that infrared spectroscopy can be a fast and convenient characterization method with which to directly distinguish and quantify Pt single atoms from nanoparticles. In addition, we directly observe that only Pt nanoparticles show activity for carbon monoxide (CO) oxidation and water-gas shift at low temperatures, whereas Pt single atoms behave as spectators. The lack of catalytic activity of Pt single atoms can be partly attributed to the strong binding of CO molecules.

Topological data analysis of Escherichia coli O157:H7 and non-O157 survival in soils.

Shiga toxin-producing E. coli O157:H7 and non-O157 have been implicated in many foodborne illnesses caused by the consumption of contaminated fresh produce. However, data on their persistence in soils are limited due to the complexity in datasets generated from different environmental variables and bacterial taxa. There is a continuing need to distinguish the various environmental variables and different bacterial groups to understand the relationships among these factors and the pathogen survival. Using an approach called Topological Data Analysis (TDA); we reconstructed the relationship structure of E. coli O157 and non-O157 survival in 32 soils (16 organic and 16 conventionally managed soils) from California (CA) and Arizona (AZ) with a multi-resolution output. In our study, we took a community approach based on total soil microbiome to study community level survival and examining the network of the community as a whole and the relationship between its topology and biological processes. TDA produces a geometric representation of complex data sets. Network analysis showed that Shiga toxin negative strain E. coli O157:H7 4554 survived significantly longer in comparison to E. coli O157:H7 EDL 933, while the survival time of E. coli O157:NM was comparable to that of E. coli O157:H7 EDL 933 in all of the tested soils. Two non-O157 strains, E. coli O26:H11 and E. coli O103:H2 survived much longer than E. coli O91:H21 and the three strains of E. coli O157. We show that there are complex interactions between E. coli strain survival, microbial community structures, and soil parameters.

The entry of HCl through soluble surfactants on sulfuric acid: effects of chain branching.

Gas-liquid scattering experiments are used to determine how a soluble, branched surfactant (2-ethylbutanol) controls the entry of gaseous HCl molecules into 60 and 68 wt % D2SO4 at 213 K. Short-chain alcohols spontaneously segregate to the surfaces of these sulfuric acid solutions, which are representative of aerosol droplets in the lower stratosphere. We find that 2-ethylbutanol enhances HCl entry at low surface coverages, most likely because it provides extra interfacial OH groups that aid HCl dissociation. This enhancement disappears at higher coverages as the alkyl chains crowd each other and block access to the acid. The branched alcohol impedes HCl entry more effectively than its unbranched isomer 1-hexanol, implying that the larger 2-ethybutanol footprint on the surface blocks more HCl molecules from reaching the alcohol-acid interface. This behavior contrasts sharply with gas transport through long-chain monolayers, where branching introduces gaps that allow more facile passage. The experiments suggest that short-chain surfactants with extended footprints may impede transport more effectively than their unbranched isomers.

Ballistic Evaporation and Solvation of Helium Atoms at the Surfaces of Protic and Hydrocarbon Liquids.

Atomic and molecular solutes evaporate and dissolve by traversing an atomically thin boundary separating liquid and gas. Most solutes spend only short times in this interfacial region, making them difficult to observe. Experiments that monitor the velocities of evaporating species, however, can capture their final interactions with surface solvent molecules. We find that polarizable gases such as N2 and Ar evaporate from protic and hydrocarbon liquids with Maxwell-Boltzmann speed distributions. Surprisingly, the weakly interacting helium atom emerges from these liquids at high kinetic energies, exceeding the expected energy of evaporation from salty water by 70%. This super-Maxwellian evaporation implies in reverse that He atoms preferentially dissolve when they strike the surface at high energies, as if ballistically penetrating into the solvent. The evaporation energies increase with solvent surface tension, suggesting that He atoms require extra kinetic energy to navigate increasingly tortuous paths between surface molecules.

HCl uptake through films of pentanoic acid and pentanoic acid/hexanol mixtures at the surface of sulfuric acid.

Molecular beam scattering experiments are used to investigate collisions and reactions of HCl with deuterated sulfuric acid containing 0-0.2 M pentanoic acid (PA) and mixtures of PA and hexanol. Surface tension measurements at 296 K indicate that PA segregates to the surface of the acid, reaching coverages of 58% and 52% of maximum packing on 60 and 68 wt % D(2)SO(4), respectively. We find that these films increase HCl entry into the acid at low PA surface coverage at 213 K. This enhancement is attributed to the dissociation of HCl molecules that come into contact with surface COOH groups and protonate them. At higher coverages, the PA film becomes more compact and impedes HCl uptake. Comparisons with films of pure hexanol and pentanoic acid/hexanol mixtures indicate that surface OH groups are more effective than COOH groups in catalyzing HCl entry. They also suggest that the PA films consist of patchy regions of tightly packed molecules, which are pushed away from the surface upon addition of the more surface active hexanol. HCl entry into the pure and mixed films can be analyzed quantitatively using a two-step model in which adsorbed HCl molecules penetrate between the alkyl chains and then dissociate at the surfactant-acid interface.