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1.
Nat Commun ; 15(1): 5106, 2024 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-38877029

RESUMO

Publicly available electric vehicle (EV) infrastructure is pivotal for the United States EV transition by 2030. Existing infrastructure lacks equitably distribution to low-income and underrepresented communities, impeding mass adoption. Our study, utilizing 2021 micro-level data from 121 million United States households, comprehensively examines income and racial disparities in EV infrastructure accessibility. Our analysis of national averages indicates that lower-income groups face less accessibility to public EV infrastructure in both urban and rural geographies. Black households experience less rural accessibility, but greater urban accessibility compared to White households conditioning on income. However, our localized analysis uncovers significant variations in accessibility gaps among counties, rural and urban settings, and dwelling types. While Black households experience greater urban accessibility nationally, a closer look at the county level reveals diminishing advantages. This study identifies areas with pronounced inequality and urgent needs for enhanced accessibility, emphasizing the necessity for tailored solutions by local governments to enhance equitable access to EV infrastructure.

2.
J Clin Med ; 13(8)2024 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-38673552

RESUMO

Background/Objectives: Lateral spine surgery offers effective minimally invasive deformity correction, but traditional approaches often involve separate anterior, lateral, and posterior procedures. The prone lateral technique streamlines this process by allowing single-position access for lateral and posterior surgery, potentially benefiting from the lordosing effect of prone positioning. While previous studies have compared prone lateral to direct lateral for adult degenerative diseases, this retrospective review focuses on the outcomes of adult deformity patients undergoing prone lateral interbody fusion. Methods: Ten adult patients underwent single-position prone lateral surgery for spine deformity correction, with a mean follow-up of 18 months. Results: Results showed significant improvements: sagittal vertical axis decreased by 2.4 cm, lumbar lordosis increased by 9.1°, pelvic tilt improved by 3.3°, segmental lordosis across the fusion construct increased by 12.2°, and coronal Cobb angle improved by 6.3°. These benefits remained consistent over the follow-up period. Correlational analysis showed a positive association between improvements in PROs and SVA and SL. When compared to hybrid approaches, prone lateral yielded greater improvements in SVA. Conclusions: Prone lateral surgery demonstrated favorable outcomes with reasonable perioperative risks. However, further research comparing this technique with standard minimally invasive lateral approaches, hybrid, and open approaches is warranted for a comprehensive evaluation.

3.
J Clin Med ; 13(7)2024 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-38610887

RESUMO

Cervical endoscopic spine surgery is rapidly evolving and gaining popularity for the treatment of cervical radiculopathy and myelopathy. This approach significantly reduces muscular damage and blood loss by minimizing soft tissue stripping, leading to less postoperative pain and a faster postoperative recovery. As scientific evidence accumulates, the efficacy and safety of cervical endoscopic spine surgery are continually affirmed. Both anterior and posterior endoscopic approaches have surfaced as viable alternative treatments for various cervical spine pathologies. Newer techniques, such as endoscopic-assisted fusion, the anterior transcorporeal approach, and unilateral laminotomy for bilateral decompression, have been developed to enhance clinical outcomes and broaden surgical indications. Despite its advantages, this approach faces challenges, including a steep learning curve, increased radiation exposure for both surgeons and patients, and a relative limitation in addressing multi-level pathologies. However, the future of cervical endoscopic spine surgery is promising, with potential enhancements in clinical outcomes and safety on the horizon. This progress is fueled by integrating advanced imaging and navigation technologies, applying regional anesthesia for improved and facilitated postoperative recovery, and incorporating cutting-edge technologies, such as augmented reality. With these advancements, cervical endoscopic spine surgery is poised to broaden its scope in treating cervical spine pathologies while maintaining the benefits of minimized tissue damage and rapid recovery.

4.
J Neurol Phys Ther ; 48(2): 102-111, 2024 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-38441461

RESUMO

BACKGROUND/PURPOSE: Gait impairments in Parkinson disease (PD) contribute to decreased quality of life. This randomized controlled trial examined immediate- and longer-term effects of a single joint robotic exoskeleton device (EXOD), the Honda Walking Assist device, on gait. METHODS: Participants (n = 45) with PD (Hoehn and Yahr stages 1-3) were randomized to a robotic-assisted gait training (RAGT) group (n = 23) or control (CON) group (n = 22). The RAGT group was tested with and without the EXOD at baseline and then received supervised in-home and community training with the EXOD twice weekly for 8 weeks. The CON group received no interventions. Outcome measures included gait speed (primary), gait endurance (6-minute walk test), perceived ease of walking, and questionnaires and logs assessing performance of daily activities, freezing of gait, and daily activity levels. RESULTS: Forty participants completed the study. No significant immediate impact of EXOD usage on participants' gait measures was found. Differences in gait speed and secondary outcome measures postintervention were not significantly different between the RAGT and CON groups. Participants with greater disease severity (worse baseline motor scores) had greater improvements in stride length during unassisted walking after the intervention than those with lower severity (mean difference: 3.22, 95% confidence interval: 0.05-6.40; P = 0.04). DISCUSSION AND CONCLUSIONS: All RAGT participants could use the EXOD safely. The RAGT treatment used in this mostly low impairment population of people with PD may be ineffective and/or was insufficiently dosed to see a positive treatment effect. Our findings suggest that RAGT interventions in PD may be more effective in individuals with greater motor impairments.


Assuntos
Transtornos Neurológicos da Marcha , Doença de Parkinson , Procedimentos Cirúrgicos Robóticos , Humanos , Transtornos Neurológicos da Marcha/etiologia , Qualidade de Vida , Marcha , Caminhada , Terapia por Exercício
5.
J Clin Med ; 13(4)2024 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-38398424

RESUMO

The Prone Transpsoas (PTP) approach to lumbar spine surgery, emerging as an evolution of lateral lumbar interbody fusion (LLIF), offers significant advantages over traditional methods. PTP has demonstrated increased lumbar lordosis gains compared to LLIF, owing to the natural increase in lordosis afforded by prone positioning. Additionally, the prone position offers anatomical advantages, with shifts in the psoas muscle and lumbar plexus, reducing the likelihood of postoperative femoral plexopathy and moving critical peritoneal contents away from the approach. Furthermore, operative efficiency is a notable benefit of PTP. By eliminating the need for intraoperative position changes, PTP reduces surgical time, which in turn decreases the risk of complications and operative costs. Finally, its versatility extends to various lumbar pathologies, including degeneration, adjacent segment disease, and deformities. The growing body of evidence indicates that PTP is at least as safe as traditional approaches, with a potentially better complication profile. In this narrative review, we review the historical evolution of lateral interbody fusion, culminating in the prone transpsoas approach. We also describe several adjuncts of PTP, including robotics and radiation-reduction methods. Finally, we illustrate the versatility of PTP and its uses, ranging from 'simple' degenerative cases to complex deformity surgeries.

6.
Am J Hosp Palliat Care ; 41(3): 288-294, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-37115718

RESUMO

Long driving times from hospice providers to patients lead to poor quality of care, which may exacerbate in rural and highly isolated areas of Appalachia. This study aimed to investigate geographic patterns of pediatric hospice care across Appalachia. Using person-level Medicaid claims of 1,788 pediatric hospice enrollees who resided in the Appalachian Region between 2011 and 2013. A database of boundaries of Appalachian counties, postal addresses of hospices, and population-weighted county centroids of residences of hospice enrollees driving times from the nearest hospices were calculated. A choropleth map was created to visualize rural/urban differences in receiving hospice care. The average driving time from hospice to child residence was 28 minutes (SD = 26). The longest driving time was in Eastern Kentucky-126 minutes (SD = 32), and the shortest was in South Carolina-11 min (SD = 9.1). The most significant differences in driving times between rural and urban counties were found in Virginia 28 (SD = 7.5) and 5 minutes (SD = 0), respectively, Tennessee-43 (SD = 28) and 8 minutes (SD = 7), respectively; and West Virginia-49 (SD = 30) and 12 minutes (SD = 4), respectively. Many pediatric hospice patients reside in isolated counties with long driving times from the nearest hospices. State-level policies should be developed to reduce driving times from hospice providers.


Assuntos
Cuidados Paliativos na Terminalidade da Vida , Hospitais para Doentes Terminais , Estados Unidos , Humanos , Criança , Sistemas de Informação Geográfica , População Urbana , Acessibilidade aos Serviços de Saúde , Região dos Apalaches
7.
J Am Geriatr Soc ; 72(2): 512-519, 2024 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-37974544

RESUMO

BACKGROUND: Millions of older US adults fall annually, leading to catastrophic injuries, over 32,000 deaths and healthcare costs of over $55 billion. This study evaluated perceived benefits and limitations of using community paramedicine for fall prevention strategies from the lens of older adults, caregivers, and healthcare providers. METHODS: Semi-structured focus groups were held with individuals from three stakeholder groups: (1) community-dwelling older adults (age ≥60), (2) caregivers, and (3) healthcare providers. The Strengths-Weaknesses-Opportunities-Threats (SWOT) framework was used to quantitatively analyze stakeholder perceptions of using community paramedicine for fall prevention strategies. RESULTS: A total of 10 focus groups were held with 56 participants representing older adults (n = 15), caregivers (n = 16), and healthcare providers (n = 25). Community paramedicine was supported as a model of fall prevention by older adults, caregivers, and healthcare providers. Participants identified strengths such as visibility to the home environment, ability to implement home modifications, implicit trust in emergency medical services (EMS), and capacity to redirect resources toward prevention. Additionally, participants acknowledged opportunities such as providing continuity of care across the healthcare spectrum, improving quality and safety of care and potentially reducing unnecessary emergency department use. Participants endorsed weaknesses and threats such as funding, concerns of patients about stigma, and struggles with medical data integration. CONCLUSIONS: The results of this study illuminate the opportunity to leverage community paramedicine to address a variety of perceived barriers in order to design and implement better solutions for fall prevention efforts.


Assuntos
Serviços Médicos de Emergência , Paramedicina , Humanos , Adulto , Pessoa de Meia-Idade , Idoso , Pessoal de Saúde , Cuidadores , Grupos Focais
9.
Nat Commun ; 14(1): 7904, 2023 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-38036553

RESUMO

Within coastal communities, sea level rise (SLR) will result in widespread intermittent flooding and long-term inundation. Inundation effects will be evident, but isolation that arises from the loss of accessibility to critical services due to inundation of transportation networks may be less obvious. We examine who is most at risk of isolation due to SLR, which can inform community adaptation plans and help ensure that existing social vulnerabilities are not exacerbated. Combining socio-demographic data with an isolation metric, we identify social and economic disparities in risk of isolation under different SLR scenarios (1-10 ft) for the coastal U.S. We show that Black and Hispanic populations face a disproportionate risk of isolation at intermediate levels of SLR (4 ft and greater). Further, census tracts with higher rates of renters and older adults consistently face higher risk of isolation. These insights point to significant inequity in the burdens associated with SLR.


Assuntos
Inundações , Elevação do Nível do Mar , Estados Unidos , Meios de Transporte , Demografia
10.
Neurosurg Focus ; 54(6): E16, 2023 06.
Artigo em Inglês | MEDLINE | ID: mdl-37552666

RESUMO

OBJECTIVE: The goal of this work was to methodically evaluate, optimize, and validate a self-supervised machine learning algorithm capable of real-time automatic registration and fluoroscopic localization of the spine using a single radiograph or fluoroscopic frame. METHODS: The authors propose a two-dimensional to three-dimensional (2D-3D) registration algorithm that maximizes an image similarity metric between radiographic images to identify the position of a C-arm relative to a 3D volume. This work utilizes digitally reconstructed radiographs (DRRs), which are synthetic radiographic images generated by simulating the x-ray projections as they would pass through a CT volume. To evaluate the algorithm, the authors used cone-beam CT data for 127 patients obtained from an open-source de-identified registry of cervical, thoracic, and lumbar scans. They systematically evaluated and tuned the algorithm, then quantified the convergence rate of the model by simulating C-arm registrations with 80 randomly simulated DRRs for each CT volume. The endpoints of this study were time to convergence, accuracy of convergence for each of the C-arm's degrees of freedom, and overall registration accuracy based on a voxel-by-voxel measurement. RESULTS: A total of 10,160 unique radiographic images were simulated from 127 CT scans. The algorithm successfully converged to the correct solution 82% of the time with an average of 1.96 seconds of computation. The radiographic images for which the algorithm converged to the solution demonstrated 99.9% registration accuracy despite utilizing only single-precision computation for speed. The algorithm was found to be optimized for convergence when the search space was limited to a ± 45° offset in the right anterior oblique/left anterior oblique, cranial/caudal, and receiver rotation angles with the radiographic isocenter contained within 8000 cm3 of the volumetric center of the CT volume. CONCLUSIONS: The investigated machine learning algorithm has the potential to aid surgeons in level localization, surgical planning, and intraoperative navigation through a completely automated 2D-3D registration process. Future work will focus on algorithmic optimizations to improve the convergence rate and speed profile.


Assuntos
Imageamento Tridimensional , Tomografia Computadorizada por Raios X , Humanos , Imageamento Tridimensional/métodos , Radiografia , Tomografia Computadorizada por Raios X/métodos , Coluna Vertebral/diagnóstico por imagem , Coluna Vertebral/cirurgia , Algoritmos , Aprendizado de Máquina
11.
Am J Ind Med ; 66(9): 713-727, 2023 09.
Artigo em Inglês | MEDLINE | ID: mdl-37329208

RESUMO

BACKGROUND: Meatpacking plants were major sources of COVID-19 outbreaks, posing unprecedented risks to employees, family members, and local communities. The effect on food availability during outbreaks was immediate and staggering: within 2 months, the price of beef increased by almost 7% with documented evidence of significant meat shortages. Meatpacking plant designs, in general, optimize on production; this design approach constrains the ability to enhance worker respiratory protection without reducing output. METHODS: Using agent-based modeling, we simulate the spread of COVID-19 within a typical meatpacking plant design under varying levels of mitigation measures, including combinations of social distancing and masking interventions. RESULTS: Simulations show an average infection rate of close to 99% with no mitigation, 99% with the policies that US companies ultimately adopted, 81% infected with the combination of surgical masks and distancing policies, and 71% infected with N95 masks and distancing. Estimated infection rates were high, reflecting the duration and exertion of the processing activities and lack of fresh airflow in an enclosed space. CONCLUSION: Our results are consistent with anecdotal findings in a recent congressional report, and are much higher than US industry has reported. Our results suggest current processing plant designs made rapid transmission of the virus during the pandemic's early days almost inevitable, and implemented worker protections during COVID-19 did not significantly affect the spread of the virus. We argue current federal policies and regulations are insufficient to ensure the health and safety of workers, creating a justice issue, and jeopardizing food availability in a future pandemic.


Assuntos
COVID-19 , Animais , Bovinos , Humanos , Pandemias/prevenção & controle , Surtos de Doenças , Distanciamento Físico , Arquitetura de Instituições de Saúde
12.
Neurosurg Focus ; 54(3): E14, 2023 03.
Artigo em Inglês | MEDLINE | ID: mdl-36857787

RESUMO

OBJECTIVE: The Goel-Harms atlantoaxial screw fixation technique for the treatment of atlantoaxial instability and unstable odontoid fractures is reliable and reproducible for a variety of anatomies. The drawbacks of the technique are the potential for significant bleeding from the C2 nerve root venous plexus and the risks associated with posterior midline exposure and retraction, such as pain and wound complications. The authors developed a minimally invasive surgical (MIS) modification of the Goel-Harms technique using intra-articular grafting to facilitate placement of percutaneous lateral mass and pars screws with extended tabs for minimally invasive subfascial rod placement. The objective of this study was to present the authors' first series of 5 patients undergoing minimally invasive modification in comparison with 51 patients undergoing open atlantoaxial fusion. METHODS: A retrospectiveanalysis of patient comorbid conditions, blood loss, length of surgery, and length of stay was performed on patients undergoing Goel-Harms instrumented fusion (GHIF) for unstable odontoid fractures performed between 2016 and 2021. RESULTS: Patients undergoing the minimally invasive procedure showed significantly less blood loss than those undergoing the open atlantoaxial fusion procedure, with a median blood loss of 30 ml compared with 150 ml using the open technique (p < 0.01). The patients showed no significant differences in length of stay (2 days for MIS vs 4 days for open atlantoaxial fusion, p = 0.25). There were no significant differences in length of surgery for MIS, but a possible trend toward increased operative duration (234 vs 151 minutes, p = 0.112). CONCLUSIONS: In this small pilot study, it was shown that MIS-GHIF can be performed with decreased blood loss in atlantoaxial instability and odontoid fractures. This technique may allow for greater and safer application of the procedure in the elderly and infirm.


Assuntos
Pesquisa , Doenças da Coluna Vertebral , Idoso , Humanos , Projetos Piloto , Dor
13.
J Huntingtons Dis ; 11(4): 435-453, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36155527

RESUMO

BACKGROUND: In 2020, our group published physical therapy clinical practice guidelines (CPG) for people with Huntington's disease (HD). The guideline recommendations were categorized according to six primary movement impairment classifications. OBJECTIVE: To facilitate implementation of this CPG, we have developed guideline-based algorithms for physical therapy assessments and interventions and recommendations for therapists to overcome barriers to CPG implementation for people with HD. METHODS: We conducted a literature review of papers that evaluated physical therapy interventions in individuals with HD (n = 26) to identify assessments for each of the primary movement impairment classifications, and then searched for papers (n = 28) that reported their clinometric/psychometric properties in HD. Assessments were evaluated using modified Movement Disorder Society Committee on Rating Scales criteria and other relevant criteria. RESULTS: We identified a "core set" of physical therapy assessments for persons with HD, including the Six Minute Walk Test, Timed Up and Go Test, Berg Balance Scale, and the Medical Outcomes Study Short Form 36 (SF-36). We then developed guideline-based decision trees to assist in decision making and implementation of the CPG into practice for persons with HD across the continuum of care. Finally, we developed strategies for overcoming barriers to implementation, such as seeking specialized training in HD, engaging caretakers or family members to help the person with HD to exercise, and establishing clinical pathways that support early physical therapy referrals. CONCLUSION: Knowledge translation documents such as this are essential to promoting implementation of the physical therapy CPGs into clinical practice.


Assuntos
Doença de Huntington , Humanos , Doença de Huntington/reabilitação , Equilíbrio Postural , Estudos de Tempo e Movimento , Modalidades de Fisioterapia , Árvores de Decisões
14.
J Craniovertebr Junction Spine ; 13(2): 198-200, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35837421

RESUMO

Treatment of atlantoaxial pathology is often associated with significant morbidity and mortality. While surgical techniques for fixation are well established, approaches that minimize blood loss and muscle dissection are advantageous for expediting recovering and minimizing surgical risk. We present a 34-year-old female who presented with a Type III odontoid fracture requiring surgical fixation. She underwent a C1-2 fusion employing a novel minimally invasive modification of the Goel-Harms atlantoaxial fusion using percutaneous screws and intra-articular cage.

15.
J Craniovertebr Junction Spine ; 12(3): 302-305, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34728998

RESUMO

INTRODUCTION: Correction of cervical deformity can be achieved using anterior cervical fixation and fusion techniques. However, supplemental posterior fixation is a critical component for ensuring biomechanical longevity and favorable patient outcomes. We present a novel percutaneous technique for posterior cervical fixation in patients where cervical pedicle (CP) screws may not be feasible and midline muscle dissection is not needed. METHODS: Three patients presented to our hospital with cervical pathology amendable to circumferential cervical fusion. After adequate deformity correction was performed through an anterior cervical decompression and fusion, staged posterior supplemental fixation was achieved using percutaneous CP inlet (CPI) screws using a percutaneous muscle-sparing approach. RESULTS: All three patients underwent CPI screw placement without postoperative neurovascular complications. Postoperative radiographic follow-up showed the desired, proper screw placement, with continued maintained cervical alignment. CONCLUSIONS: CPI screw placement may be alternative hybrid screw that achieves a advantageous safety profile while also avoiding an open midline exposure.

16.
Gait Posture ; 86: 186-191, 2021 05.
Artigo em Inglês | MEDLINE | ID: mdl-33756407

RESUMO

BACKGROUND: Treadmill training may improve gait disorders associated with neurodegenerative diseases. In Parkinson's disease (PD), treadmill training alters gait patterns after one session, and long-term training improves gait parameters, fall risk, and quality of life. RESEARCH QUESTION: What is the feasibility and safety of using this intervention for people with Lewy body dementia (LBD) or Huntington's disease (HD)? METHODS: In this observational study, 10 individuals with HD, 8 individuals with LBD, and 10 control individuals walked for 20 min on a treadmill using a speed dependent protocol starting at a slow comfortable speed and increasing incrementally toward their normal overground speed. Feasibility was determined by compliance to protocol and safety by no incidents of abnormal vital signs or expressions of distress. Changes in gait measures, Timed Up and Go (TUG) scores and quantitative motor function measures (Q-Motor; precision grasp force variability, finger and foot tapping frequency) before and after treadmill walking were analyzed using linear models. RESULTS: Treadmill training is feasible and safe in LBD and HD; although, participants could not initiate treadmill walking at their comfortable overground speeds, and only 3 participants with HD were able to achieve their overground walking speed within the 20-minute session. No changes in gait measures, TUG times, and Q-Motor measures were found among LBD and HD participants after treadmill walking, although control participants demonstrated significant increases in several gait measures, and foot tap frequency (estimated difference = 0.290; p = 0.026). SIGNIFICANCE: Longer and more frequent treadmill sessions may be needed to see gait and motor function effects in LBD and HD. Motor and cognitive impairments associated with these diseases may make them less amenable to the effects of treadmill training.


Assuntos
Terapia por Exercício , Transtornos Neurológicos da Marcha/terapia , Doença de Huntington/fisiopatologia , Doença por Corpos de Lewy/fisiopatologia , Caminhada/fisiologia , Idoso , Idoso de 80 Anos ou mais , Estudos de Viabilidade , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Projetos Piloto , Resultado do Tratamento
17.
Global Spine J ; 11(1): 71-75, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32875842

RESUMO

STUDY DESIGN: Retrospective cohort study. OBJECTIVES: Gender appears to play in important role in surgical outcomes following acute cervical spine trauma, with current literature suggesting males have a significantly higher mortality following spine surgery. However, no well-adjusted population-based studies of gender disparities in incidence and outcomes of spine surgery following acute traumatic axis injuries exist to our knowledge. We hypothesized that females would receive surgery less often than males, but males would have a higher 1-year mortality following isolated traumatic axis fractures. METHODS: We performed a retrospective cohort study using Medicare claims data that identified US citizens aged 65 and older with ICD-9 (International Classification of Diseases, Ninth Revision) code diagnosis corresponding to isolated acute traumatic axis fracture between 2007 and 2014. Our primary outcome was defined as cumulative incidence of surgical treatment, and our secondary outcome was 1-year mortality. Propensity weighted analysis was performed to balance covariates between genders. Our institutional review board approved the study (IRB #16-0533). RESULTS: There was no difference in incidence of surgery between males and females following acute isolated traumatic axis fractures (7.4 and 7.5 per 100 fractures, respectively). Males had significantly higher 1-year weighted mortality overall (41.7 and 28.9 per 100 fractures, respectively, P < .001). CONCLUSION: Our well-adjusted data suggest there was no significant gender disparity in incidence of surgical treatment over the study period. The data also support previous observations that males have worse outcomes in comparison to females in the setting of axis fractures and spinal trauma regardless of surgical intervention.

19.
Phys Chem Chem Phys ; 22(27): 15448-15462, 2020 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-32602482

RESUMO

The isolation of Am(iii) ion from Ln(iii) ions is very crucial for the safe disposal of nuclear wastes and thus, studies are being continuously pursued to accomplish this goal. In view of this, herein, a new conformationally rigid bitopic ligand, N,N,N',N'-tetra(2-ethylhexyl)piperazine-di-methylenecarboxamide (PIPDA) has been synthesized and studied for the separation of Am(iii) from Ln(iii) ions. The effect of structural rigidification on the selectivity of Am(iii) over Ln(iii) was compared with an open chain flexible compound, namely, N,N,N',N'-tetra(2-ethylhexyl)-3,6-(N'',N'''-dibutyl)diaza-octane-1,8-diamide (DADA). Two oxygen atoms of the diamide moiety seem to be responsible for controlling the metal ion extraction ability of PIPDA, whereas two nitrogen atoms of the piperazine moiety most probably dictate the separation factor between the Am(iii) and Eu(iii) ions in PIPDA. In addition, scalar relativistic density functional theory (DFT) in conjunction with Born-Haber thermodynamics was used herein to compliment the experimental selectivity. The experimentally observed preferential selectivity of PIPDA for Am(iii) ion over the Ln(iii) ion was corroborated by the computed extraction free energy, ΔGext. The covalent nature of bonding between the metal ions and the ligand was confirmed by analyzing the Mayer bond order and bond character analysis using the atom in molecule concept. Though the conformational rigidity of PIPDA gives stronger interaction than DADA, it does not offer a significant advantage over DADA in terms of the separation factor. The marginal increase in the separation factor for PIPDA over DADA might be attributed to the piperazine nitrogen and to the ligand architecture during complex formation.

20.
Phys Chem Chem Phys ; 22(26): 14682-14693, 2020 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-32573611

RESUMO

Isotope effect is a quantum mechanical phenomenon and thus poses a challenge for the separation of isotopes of an element of interest, especially for heavy elements. Isotopic fractionation of zinc is also quite difficult and challenging but is necessitated due to various applications of its isotopes ranging from nuclear medicine to nuclear power reactors. Here, we developed the dibenzo-18-crown-6 (DB18C6) ether-functionalized poly(methacrylic acid) (PMA) resin by exploiting the ion and isotope recognition ability of the crown ether using DFT/MD simulations followed by experiments for isotopic fractionation of zinc. The PMADB18C6 adsorbent was prepared and suitably characterized. Both computational and experimental findings demonstrate that the adsorption and isotope separation of zinc with PMADB18C6 are due to the molecular recognition effect of the "O" dipole of the crown ether. Furthermore, both MD simulations and experiments suggest Langmuir type adsorption isotherms. The adsorption of Zn2+ ions on the PMA resin is predicted to be endothermic, whereas it is exothermic on the PMADB18C6 resin, as revealed from the experimentally observed enthalpy change. A small scale fixed bed column study was demonstrated to test the scale-up application. The values of the experimental separation factors: 1.0013 for 66/64 and 1.0027 for 68/64 confirm the computationally predicted results of 1.00088 and 1.0010, respectively, thus establishing the combined strength of the theory and experiments for the identification of efficient fractionating agents for a complex quantum isotope effect which eventually helps in planning further experiments in view of medicinal and technological applications of zinc isotopes.

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