NASC 2023: Showcasing Diversity in North American Supramolecular Chemistry.

Diversity in supramolecular chemistry can showcase itself in many ways. This includes the diversity of thought and topics covered in research (from fundamental science to applications in biology and materials), as well as the diversity of people (e.g., diversity in race, gender, sexual orientation, country of origin, type of higher education institute, career stage,…). At the North American Supramolecular Chemistry (NASC) meetings, we aim to bring together the best that supramolecular chemistry has to offer in North America, create a sense of community and provide a platform for researchers at any stage of their career to present their work. NASC 2023 was the successful second edition of the NASC meeting series, and this proceedings article highlights the research and impressions of some of the speakers at NASC 2023.

Structural Insight on Supramolecular Polyion Salts: Inositol Hexaphosphate Enclosed in Cationic Macrocyclic Clusters.

Supramolecular macrocyclic forces have been used to trap phytate, myo-inositol-1,2,3,4,5,6-hexakisphosphate, a key bioanion with multiple roles in metabolic processes. Due to the complex chemistry of six multivalent phosphates surrounding the small, cyclic inositol framework, crystallographic information of simple phytate salts has been elusive. This report represents a combined crystallographic, theoretical, and solution binding investigation of a supramolecular macrocyclic complex of phytate. Together, the results provide significant insight to phytate's intramolecular and intermolecular interactions at the microenvironment level. The macrocycle-phytate aggregates consist of phytate anionic pairs, each partly sandwiched by two 24-membered, amide/amine-based cationic macrocycles. The phytate ion pairs hold the tetrameric macrocyclic array together by six strong intermolecular hydrogen bonds. Both phytates crystallize in 1a5e phosphate conformations (one axial (P2) and five equatorial phosphates). Solution NMR binding studies in 1 : 1 DMSO-d6 : D2 O indicate 2 : 1 macrocycle:phytate associations, suggesting that the sandwich-like nature of the complex holds together in solution. DFT studies indicate the likely occurrence of dynamic intramolecular interchange of phosphate protons, as well as important roles for the axial (P2) phosphate in both intramolecular and intermolecular hydrogen bonding interactions.

State of the Service: Pediatric Palliative and Hospice Community-Based Service Coverage in the United States.

Background: The pediatric literature describes reliance on community-based organizations for home-based palliative and hospice care for children. Objective: To quantify and describe the inclusion of children in services, staffing, and care scope offered by community-based hospice organizations in the United States. Design and Subjects: This study utilized an online survey distributed to organizational members of the National Hospice and Palliative Care Organization (NHPCO) in the United States. Results: A total of 481 hospice organizations from 50 states, Washington DC, and Puerto Rico responded. Twenty percent do not provide services for children. Nonmetro geographies are less likely to provide services for children. Pediatric services provided include home-based pediatric hospice (57%), home-based palliative care (31%), inpatient pediatric hospice (23%), and inpatient pediatric palliative care (14%). Hospice annual pediatric census is an average of 16.5 children, while palliative care annual census is an average of 36. Less than half (48%) of responding agencies have a team that is dedicated to only pediatric care. Medicaid and the Children's Health Insurance Program are the most common forms of reimbursement, with 13% depicting "no reimbursement" for provision of care for children and many relying on philanthropy coverage. Lack of trained personnel, discomfort, and competing priorities were depicted as the most common barriers. Conclusions: Children remain underrepresented in the extension of care offered through community-based hospice organizations in the United States particularly in nonmetro settings. Further research into strong training, staffing, and reimbursement models is warranted.

Challenges and Opportunities of Providing Pediatric Funeral Services: A National Survey of Funeral Professionals.

BACKGROUND: Funeral professionals offer a unique opportunity to support, educate, and advocate for grieving families after the death of a child. From the initial point of contact to the burial, funeral professionals shape the final moments and memories of a family and a community. And yet, little is known about the needs of funeral professionals to provide high quality services when a child dies. OBJECTIVES: To conduct a needs assessment among funeral professionals in conducting funeral services for children. METHODS: Active National Funeral Directors Association members were surveyed on their experience and needs in providing pediatric funeral services. The survey contained 41 questions about experience, skills, and knowledge in providing pediatric funerals. The survey included multiple choice, yes/no, and open-ended questions. Descriptive statistics were generated from the survey items and comments/open-ended questions were coded and assessed for themes. RESULTS: More than 200 responses were received. The respondents conducted 43 pediatric funeral services in a 5-year period (approx. 8 services/year). The top 5 self-identified training needs included grieving parents, grieving siblings, memorials, comforting the community, and outreach. Themes from the open-ended questions were (a) maintaining professionalism, (b) managing emotions and experiences, (c) assessing family dynamics, (d) managing professional skills, and (e) building collaborative networks. CONCLUSIONS: Specific training needs were identified that will inform the development of targeted training for funeral professionals to improve their skills and knowledge of pediatric funeral services.

Changing Pediatric Hospice and Palliative Care Through Medicaid Partnerships.

Since its inception in 2010, the Concurrent Care for Children Provision of the Affordable Care Act has enabled seriously ill pediatric patients and their families to access comprehensive, supportive hospice services while simultaneously receiving ongoing treatment-directed therapies. Although this groundbreaking federal legislation has resulted in improvements in care for vulnerable pediatric patients, the implementation of the law has varied from state to state through Medicaid programming. The pediatric professional community is called to consider how Medicaid services can more effectively be delivered by leveraging legislative mandates and collaborative relationships between clinicians, Medicaid administrators, and policy makers. In this article, we examine ways concurrent care has been executed in 3 different states and how key stakeholders in care for children with serious illness advocated to ensure effective implementation of the legislation. The lessons learned in working with state Medicaid programs are applicable to any advocacy issue impacting children and families .

Hydrophilic and hydrophobic carboxamide pincers as anion hosts.

Hydrophobic and hydrophilic, monotopic and ditopic carboxamide pincer hosts containing ethyl, hexyl, 2-hydroxyethyl and 2-hydroxyethyl ethyl ether pendant arms were synthesized. Solubility trends indicated that solubilities in water or hydrocarbon solvents varied depending on the nature of the pendant arms. Binding constants for hydrophilic pincers were larger in general than their hydrophobic analogs. Significant synergistic binding effects for the ditopic hosts were not observed.

MR method for measuring microscopic histologic soft tissue textures.

PURPOSE: Provide a direct, non-invasive diagnostic measure of microscopic tissue texture in the size scale between tens of microns and the much larger scale measurable by clinical imaging. This paper presents a method and data demonstrating the ability to measure these microscopic pathologic tissue textures (histology) in the presence of subject motion in an MR scanner. This size range is vital to diagnosing a wide range of diseases. THEORY/METHODS: MR micro-Texture (MRµT) resolves these textures by a combination of measuring a targeted set of k-values to characterize texture-as in diffraction analysis of materials, performing a selective internal excitation to isolate a volume of interest (VOI), applying a high k-value phase encode to the excited spins in the VOI, and acquiring each individual k-value data point in a single excitation-providing motion immunity and extended acquisition time for maximizing signal-to-noise ratio. Additional k-value measurements from the same tissue can be made to characterize the tissue texture in the VOI-there is no need for these additional measurements to be spatially coherent as there is no image to be reconstructed. This method was applied to phantoms and tissue specimens including human prostate tissue. RESULTS: Data demonstrating resolution <50 µm, motion immunity, and clearly differentiating between normal and cancerous tissue textures are presented. CONCLUSION: The data reveal textural differences not resolvable by standard MR imaging. As MRµT is a pulse sequence, it is directly translatable to MRI scanners currently in clinical practice to meet the need for further improvement in cancer imaging.

Snapshots of "crystalline" salt-water solutions of inositol hexaphosphate conformers.

Supramolecular insight to intra- and inter-ionic interactions in two inositol hexaphosphate conformers as a function of pH was enabled by NMR and crystallographic studies. These findings also shed light on the complex interactive roles of extended salt-water arrays through the crystal "solution" lattice.

Supramolecular traps for highly phosphorylated inositol sources of phosphorus.

Structurally elusive inositol hexakisphosphates have been trapped in host-guest sandwiches between two picolinamide macrocycles that remain intact in solution, aided by hydrogen bonds and electrostatic interactions. This first report of macrocyclic complexes of inositol hexakisphosphates provides structural insight to significant biosources of phosphorus that impact the global phosphorus cycle.

Novel magnetic resonance technique for characterizing mesoscale structure of trabecular bone.

Osteoporosis, characterized by increased fracture risk and bone fragility, impacts millions of adults worldwide, but effective, non-invasive and easily accessible diagnostic tests of the disease remain elusive. We present a magnetic resonance (MR) technique that overcomes the motion limitations of traditional MR imaging to acquire high-resolution frequency-domain data to characterize the texture of biological tissues. This technique does not involve obtaining full two-dimensional or three-dimensional images, but can probe scales down to the order of 40 µm and in particular uncover structural information in trabecular bone. Using micro-computed tomography data of vertebral trabecular bone, we computationally validate this MR technique by simulating MR measurements of a 'ratio metric' determined from a few k-space values corresponding to trabecular thickness and spacing. We train a support vector machine classifier on ratio metric values determined from healthy and simulated osteoporotic bone data, which we use to accurately classify osteoporotic bone.

Characterizing Hydrogen-Bond Interactions in Pyrazinetetracarboxamide Complexes: Insights from Experimental and Quantum Topological Analyses.

Experimental and topological analyses of dipalladium(II) complexes with pyrazinetetracarboxamide ligands containing tetraethyl (1), tetrahexyl (2), and tetrakis(2-hydroxyethyl) ethyl ether (3) are described. The presence of two very short O---O distances between adjacent amide carbonyl groups in the pincer complexes revealed two protons, which necessitated two additional anions to satisfy charge requirements. The results of the crystal structures indicate carbonyl O---O separations approaching that of low barrier hydrogen bonds, ranging from 2.413(5) to 2.430(3) Å. Solution studies and quantum topological analyses, the latter including electron localization function, noncovalent interaction, and Bader's quantum theory of atoms in molecules, were carried out to probe the nature of the short hydrogen bonds and the influence of the ligand environment on their strength. Findings indicated that the ligand field, and, in particular, the counterion at the fourth coordination site, may play a subtle role in determining the degree of covalent association of the bridging protons with one or the other carbonyl groups.

Pyrazinetetracarboxamide: A Duplex Ligand for Palladium(II).

Tetraethylpyrazine-2,3,5,6-tetracarboxamide forms a dipalladium(II) complex with acetates occupying the fourth coordination sites of the two bound metal ions. Crystallographic results indicate that the "duplex" dipincer has captured two protons that serve as the counterions. The protons lie between adjacent amide carbonyl groups with very short O···O distances of 2.435(5) Å. In the free base, the adjacent carbonyl groups are farther apart, averaging 3.196(3) Å. While the dipalladium(II) complexes stack in an ordered stepwise fashion along the a axis, the free base molecules stack on top of each other, with each pincer rotated by about 60° from the one below.

Chelate effects in sulfate binding by amide/urea-based ligands.

The influence of chelate and mini-chelate effects on sulfate binding was explored for six amide-, amide/amine-, urea-, and urea/amine-based ligands. Two of the urea-based hosts were selective for SO4(2-) in water-mixed DMSO-d6 systems. Results indicated that the mini-chelate effect provided by a single urea group with two NH binding sites appears to provide enhanced binding over two amide groups. Furthermore, additional urea binding sites incorporated into the host framework appeared to overcome to some extent competing hydration effects with increasing water content.

Macrocyclic influences in CO2 uptake and stabilization.

Two 24-member diamine-tetraamido macrocycles (R = H and CH3), readily synthesized in one or two steps, were found to react with CO2 rapidly and efficiently (100% conversion within 1 min at rt). The resulting carbamate formation was demonstrated by (1)H, (13)C NMR, ESI-MS, and X-ray crystallography. The crystal structure clearly showed the carbamate group (N-CO2(-)) formed was tightly bound within the macrocyclic cavity, held by five internal hydrogen bonds, and stabilized by intramolecular carbamate-ammonium salt-bridge formation.

Chemical mustard containment using simple palladium pincer complexes: the influence of molecular walls.

Six amide-based NNN palladium(II) pincer complexes Pd(L)(CH3CN) were synthesized, characterized, and examined for binding the sulfur mustard surrogate, 2-chloroethyl ethyl sulfide (CEES). The complexes all bind readily with CEES as shown by (1)H NMR spectroscopy in CDCl3. The influence of para-substituents on the two amide phenyl appendages was explored as well as the effect of replacing the phenyl groups with larger aromatic rings, 1-naphthalene and 9-anthracene. While variations of the para-substituents had only a slight influence on the binding affinities, incorporation of larger aromatic rings resulted in a significant size-related increase in binding, possibly due to increasing steric and electronic interactions. In crystal structures of three CEES-bound complexes, the mustard binds through the sulfur atom and lies along the aromatic walls of the side appendages approximately perpendicular to the pincer plane, with increasingly better alignment progressing from phenyl to 1-naphthalene to 9-anthracene.

Hexagonal molecular "palladawheel".

A hexagonal molecular "palladawheel" consisting of six N,N'-diphenyl-2,6-pyridinedicarboxamide-Pd(II) pincer complexes held together via six Pd∙∙∙O=CAmide bonds was efficiently synthesized and crystallographically characterized. The hexameric ring possesses C3 (pseudo-S6) symmetry with up-down alternating phenyl substituents acting as interior "spokes" and exterior "propellers."

Bereavement photography for children: program development and health care professionals' response.

Reports of in-hospital bereavement photography focus largely on stillborns and neonates. Empiric data regarding the implementation of bereavement photography in pediatrics beyond the neonatal period and the impact of such programs on healthcare professionals (HCPs) is lacking. The authors describe the implementation of a pediatric intensive care unit (PICU) bereavement photography program and use questionnaire data from HCPs to describe HCPs' reflections on the program and to identify program barriers. From July 2007 through April 2070, families of 59 (36%) of the 164 patients who died in the PICU participated in our bereavement photography program. Forty questionnaires from 29 HCPs caring for 39 participating patients/families indicated that families seemed grateful for the service (n = 34; 85%) and that the program helped HCPs feel better about their role (n = 30; 70%). Many HCPs disagreed that the program consumed too much of his/her time (n = 34; 85%) and that the photographer made his/her job difficult (n = 37; 92.5%). Qualitative analysis of responses to open-ended questions revealed 4 categories: the program's general value; positive aspects of the program; negative aspects of the program; and suggestions for improvements. Implementing bereavement photography in the PICU is feasible though some barriers exist. HCPs may benefit from such programs.

Chemistry and structure of a host-guest relationship: the power of NMR and X-ray diffraction in tandem.

An amine/amide mixed covalent organic tetrahedral cage 1 (H(12)) was synthesized and characterized. The H(12) cage contains 12 amide NH groups plus four tertiary amine N groups, the latter of which are positioned in a pseudo-tetrahedral array. Crystallographic findings indicate that the tetrahedral host can adopt either a pseudo-C(3) symmetric "compressed tetrahedron" structure, or one in which there are two sets of three stacked pyridine units related by a pseudo-S(4) axis. The latter conformation is ideal for encapsulating small pentameric clusters, either a water molecule or a fluoride ion surrounded by a tetrahedral array of water molecules, i.e., H(2)O·4H(2)O or F(-)·4H(2)O, as observed crystallographically. In solution, however, (19)F NMR spectroscopy indicates that H(12) encapsulates fluoride ion through direct amide hydrogen bonding. By collectively combining one-dimensional (1)H, (13)C, and (19)F with two-dimensional (1)H-(1)H COSY, (1)H-(13)C HSQC, and (1)H-(19)F HETCOR NMR techniques, the solution binding mode of fluoride can be ascertained as consisting of four sets of independent structural subunits with C(3) symmetry. A complex deuterium exchange process for the fluoride complex can also be unraveled by multiple NMR techniques.

A case for molecular recognition in nuclear separations: sulfate separation from nuclear wastes.

In this paper, we present the case for molecular-recognition approaches for sulfate removal from radioactive wastes via the use of anion-sequestering systems selective for sulfate, using either liquid-liquid extraction or crystallization. Potential benefits of removing sulfate from the waste include improved vitrification of the waste, reduced waste-form volume, and higher waste-form performance, all of which lead to potential cleanup schedule acceleration and cost savings. The need for sulfate removal from radioactive waste, especially legacy tank wastes stored at the Hanford site, is reviewed in detail and primarily relates to the low solubility of sulfate in borosilicate glass. Traditional methods applicable to the separation of sulfate from radioactive wastes are also reviewed, with the finding that currently no technology has been identified and successfully demonstrated to meet this need. Fundamental research in the authors' laboratories targeting sulfate as an important representative of the class of oxoanions is based on the hypothesis that designed receptors may provide the needed ability to recognize sulfate under highly competitive conditions, in particular where the nitrate anion concentration is high. Receptors that have been shown to have promising affinity for sulfate, either in extraction or in crystallization experiments, include hexaurea tripods, tetraamide macrocycles, cyclo[8]pyrroles, calixpyrroles, and self-assembled urea-lined cages. Good sulfate selectivity observed in the laboratory provides experimental support for the proposed molecular-recognition approach.