S309-CAR-NK cells bind the Omicron variants in vitro and reduce SARS-CoV-2 viral loads in humanized ACE2-NSG mice.

Recent progress on chimeric antigen receptor (CAR)-NK cells has shown promising results in treating CD19-positive lymphoid tumors with minimal toxicities [including graft versus host disease (GvHD) and cytokine release syndrome (CRS) in clinical trials. Nevertheless, the use of CAR-NK cells in combating viral infections has not yet been fully explored. Previous studies have shown that CAR-NK cells expressing S309 single-chain fragment variable (scFv), hereinafter S309-CAR-NK cells, can bind to SARS-CoV-2 wildtype pseudotyped virus (PV) and effectively kill cells expressing wild-type spike protein in vitro. In this study, we further demonstrate that the S309-CAR-NK cells can bind to different SARS-CoV-2 variants, including the B.1.617.2 (Delta), B.1.621 (Mu), and B.1.1.529 (Omicron) variants in vitro. We also show that S309-CAR-NK cells reduce virus loads in the NOD/SCID gamma (NSG) mice expressing the human angiotensin-converting enzyme 2 (hACE2) receptor challenged with SARS-CoV-2 wild-type (strain USA/WA1/2020). Our study demonstrates the potential use of S309-CAR-NK cells for inhibiting infection by SARS-CoV-2 and for the potential treatment of COVID-19 patients unresponsive to otherwise currently available therapeutics. IMPORTANCE: Chimeric antigen receptor (CAR)-NK cells can be "off-the-shelf" products that treat various diseases, including cancer, infections, and autoimmune diseases. In this study, we engineered natural killer (NK) cells to express S309 single-chain fragment variable (scFv), to target the Spike protein of SARS-CoV-2, hereinafter S309-CAR-NK cells. Our study shows that S309-CAR-NK cells are effective against different SARS-CoV-2 variants, including the B.1.617.2 (Delta), B.1.621 (Mu), and B.1.1.529 (Omicron) variants. The S309-CAR-NK cells can (i) directly bind to SARS-CoV-2 pseudotyped virus (PV), (ii) competitively bind to SARS-CoV-2 PV with 293T cells expressing the human angiotensin-converting enzyme 2 (hACE2) receptor (293T-hACE2 cells), (iii) specifically target and lyse A549 cells expressing the spike protein, and (iv) significantly reduce the viral loads of SARS-CoV-2 wild-type (strain USA/WA1/2020) in the lungs of NOD/SCID gamma (NSG) mice expressing hACE2 (hACE2-NSG mice). Altogether, the current study demonstrates the potential use of S309-CAR-NK immunotherapy as an alternative treatment for COVID-19 patients.

Dental practice workforce challenges in rural England: survey into recruitment and retention in Devon and Cornwall.

Introduction Devon and Cornwall have been identified as 'dental deserts' with limited NHS dental access and high levels of oral health inequality. Challenges around recruitment and retention of the dental workforce have been acknowledged as an important contributory factor.Aims The aim of this research was to explore the experiences of dental practices within Devon and Cornwall in relation to recruitment and retention of the dental workforce.Method A self-administered, online questionnaire was used to explore various aspects of workforce recruitment and retention. The questionnaire included categorical rating scale and free-text question formats providing quantitative and qualitative data.Results In total, 106 dental practices responded to the survey, providing a response rate of 36%. The vast majority of respondents (94%) considered recruitment and retention to be a major barrier to delivering NHS services. Additionally, 77% of practices had a current staff vacancy, 57% had a dentist vacancy and 48% had a vacancy for dental nurses. Thematic analysis led to identification of four main themes which were considered to influence recruitment and retention: NHS system; economic challenges; logistics; and support networks.Conclusion A large number of dental practices in Devon and Cornwall are failing to operate at capacity due to workforce shortages, which is affecting access to services in both NHS and private practices. Recruitment and retention of dentists and dental nurses appears to be the most challenging factor, with NHS practices affected more than the private sector.

The dental workforce recruitment and retention crisis in the UK.

The precarious state of NHS dentistry is widely acknowledged, yet there is limited progress in addressing the underlying issues. Further delays will undoubtedly impact patient care, leading to oral health deterioration and unnecessary suffering. This will predominantly affect the most vulnerable in society, resulting in greater oral health inequalities.The underlying issues contributing to the current NHS dental crisis are many, and they include: prolonged delays in contract reform; long-term underinvestment; private sector growth; and fewer dentists working full-time and/or in the NHS. In England, an NHS dental contract that fails to promote prevention or equality of access continues to have a deep and pernicious impact on the future of NHS dentistry. The devastating impact of the COVID-19 pandemic on access cannot be underestimated and neither should the effect of Brexit on the availability of workforce.The recruitment and retention of dentists, and other members of the dental team, is undoubtedly a major issue in terms of capacity and access to NHS dental care. These problems, seen across the UK, are a particular issue in England, with acute challenges within rural and coastal areas.There is an urgent necessity to develop coherent, multifaceted strategies, aided by the collection of clear and accurate workforce data, to tackle these issues.

Recruitment and retention in dentistry in the UK: a scoping review to explore the challenges across the UK, with a particular interest in rural and coastal areas.

Introduction There is currently reduced access to NHS dental services in the UK, particularly in England, with rural and coastal areas significantly affected. Recruitment and retention in dentistry has been highlighted as an issue contributing to the problem.Objectives To explore what is known or unknown about recruitment and retention of the dental workforce in the UK, with a particular focus on rural and coastal areas. We were keen to gain information relating to factors affecting recruitment and retention, geographical distribution of the workforce, anticipated challenges, strategies or proposals to assist workforce planning and the extent of empirical research.Methods Searches for peer-reviewed literature and reports were undertaken and included when they met the eligibility criteria. Data were extracted and the findings narratively synthesised.Discussion The findings suggested wide ranging recruitment and retention issues of the dental workforce in the UK. Most issues were associated with NHS dentists, followed by dental nurses across both the NHS and private sectors. The worst affected parts of the country were rural and coastal areas.Conclusion It appears from the evidence that there are many dental professionals discussing recruitment and retention issues, followed by stakeholders. However, there is limited research and data to initiate change.

Development of a novel human CD147 knock-in NSG mouse model to test SARS-CoV-2 viral infection.

BACKGROUND: An animal model that can mimic the SARS-CoV-2 infection in humans is critical to understanding the rapidly evolving SARS-CoV-2 virus and for development of prophylactic and therapeutic strategies to combat emerging mutants. Studies show that the spike proteins of SARS-CoV and SARS-CoV-2 bind to human angiotensin-converting enzyme 2 (hACE2, a well-recognized, functional receptor for SARS-CoV and SARS-CoV-2) to mediate viral entry. Several hACE2 transgenic (hACE2Tg) mouse models are being widely used, which are clearly invaluable. However, the hACE2Tg mouse model cannot fully explain: (1) low expression of ACE2 observed in human lung and heart, but lung or heart failure occurs frequently in severe COVID-19 patients; (2) low expression of ACE2 on immune cells, but lymphocytopenia occurs frequently in COVID-19 patients; and (3) hACE2Tg mice do not mimic the natural course of SARS-CoV-2 infection in humans. Moreover, one of most outstanding features of coronavirus infection is the diversity of receptor usage, which includes the newly proposed human CD147 (hCD147) as a possible co-receptor for SARS-CoV-2 entry. It is still debatable whether CD147 can serve as a functional receptor for SARS-CoV-2 infection or entry. RESULTS: Here we successfully generated a hCD147 knock-in mouse model (hCD147KI) in the NOD-scid IL2Rgammanull (NSG) background. In this hCD147KI-NSG mouse model, the hCD147 genetic sequence was placed downstream of the endogenous mouse promoter for mouse CD147 (mCD147), which creates an in vivo model that may better recapitulate physiological expression of hCD147 proteins at the molecular level compared to the existing and well-studied K18-hACE2-B6 (JAX) model. In addition, the hCD147KI-NSG mouse model allows further study of SARS-CoV-2 in the immunodeficiency condition which may assist our understanding of this virus in the context of high-risk populations in immunosuppressed states. Our data show (1) the human CD147 protein is expressed in various organs (including bronchiolar epithelial cells) in hCD147KI-NSG mice by immunohistochemical staining and flow cytometry; (2) hCD147KI-NSG mice are marginally sensitive to SARS-CoV-2 infection compared to WT-NSG littermates characterized by increased viral copies by qRT-PCR and moderate body weight decline compared to baseline; (3) a significant increase in leukocytes in the lungs of hCD147KI-NSG mice, compared to infected WT-NSG mice. CONCLUSIONS: hCD147KI-NSG mice are more sensitive to COVID-19 infection compared to WT-NSG mice. The hCD147KI-NSG mouse model can serve as an additional animal model for further interrogation whether CD147 serve as an independent functional receptor or accessory receptor for SARS-CoV-2 entry and immune responses.

Development of a Novel Human CD147 Knock-in NSG Mouse Model to Test SARS-CoV-2 Viral Infection.

Background: An animal model that can mimic the SARS-CoV-2 infection in humans is critical to understanding the rapidly evolving SARS-CoV-2 virus and for development of prophylactic and therapeutic strategies to combat emerging mutants. Studies show that the spike proteins of SARS-CoV and SARS-CoV-2 bind to human angiotensin-converting enzyme 2 (hACE2, a well-recognized, functional receptor for SARS-CoV and SARS-CoV-2) to mediate viral entry. Several hACE2 transgenic (hACE2Tg) mouse models are being widely used, which are clearly invaluable. However, the hACE2Tg mouse model cannot fully explain: 1) low expression of ACE2 observed in human lung and heart, but lung or heart failure occurs frequently in severe COVID-19 patients; 2) low expression of ACE2 on immune cells, but lymphocytopenia occurs frequently in COVID-19 patients; and 3) hACE2Tg mice do not mimic the natural course of SARS-CoV-2 infection in humans. Moreover, one of most outstanding features of coronavirus infection is the diversity of receptor usage, which includes the newly proposed human CD147 (hCD147) as a possible co-receptor for SARS-CoV-2 entry. It is still debatable whether CD147 can serve as a functional receptor for SARS-CoV-2 infection or entry. Results: Here we successfully generated a hCD147 knock-in mouse model (hCD147KI) in the NOD- scid IL2Rgamma null (NSG) background. In this hCD147KI-NSG mouse model, the hCD147 genetic sequence was placed downstream of the endogenous mouse promoter for mouse CD147 (mCD147), which creates an in vivo model that may better recapitulate physiological expression of hCD147 proteins at the molecular level compared to the existing and well-studied K18-hACE2-B6 (JAX) model. In addition, the hCD147KI-NSG mouse model allows further study of SARS-CoV-2 in the immunodeficiency condition which may assist our understanding of this virus in the context of high-risk populations in immunosuppressed states. Our data show 1) the human CD147 protein is expressed in various organs (including bronchiolar epithelial cells) in hCD147KI-NSG mice by immunohistochemical staining and flow cytometry; 2) hCD147KI-NSG mice are marginally sensitive to SARS-CoV-2 infection compared to WT-NSG littermates characterized by increased viral copies by qRT-PCR and moderate body weight decline compared to baseline; 3) a significant increase in leukocytes in the lungs of hCD147KI-NSG mice, compared to infected WT-NSG mice. Conclusions: hCD147KI-NSG mice are more sensitive to COVID-19 infection compared to WT-NSG mice. The hCD147KI-NSG mouse model can serve as an additional animal model for further interrogation whether CD147 serve as an independent functional receptor or accessory receptor for SARS-CoV-2 entry and immune responses.

Controlled and Selective Photo-oxidation of Amyloid-ß Fibrils by Oligomeric p-Phenylene Ethynylenes.

Photodynamic therapy (PDT) has been explored as a therapeutic strategy to clear toxic amyloid aggregates involved in neurodegenerative disorders such as Alzheimer's disease. A major limitation of PDT is off-target oxidation, which can be lethal for the surrounding cells. We have shown that a novel class of oligo-p-phenylene ethynylenes (OPEs) exhibit selective binding and fluorescence turn-on in the presence of prefibrillar and fibrillar aggregates of disease-relevant proteins such as amyloid-ß (Aß) and α-synuclein. Concomitant with fluorescence turn-on, OPE also photosensitizes singlet oxygen under illumination through the generation of a triplet state, pointing to the potential application of OPEs as photosensitizers in PDT. Herein, we investigated the photosensitizing activity of an anionic OPE for the photo-oxidation of Aß fibrils and compared its efficacy to the well-known but nonselective photosensitizer methylene blue (MB). Our results show that, while MB photo-oxidized both monomeric and fibrillar conformers of Aß40, OPE oxidized only Aß40 fibrils, targeting two histidine residues on the fibril surface and a methionine residue located in the fibril core. Oxidized fibrils were shorter and more dispersed but retained the characteristic ß-sheet rich fibrillar structure and the ability to seed further fibril growth. Importantly, the oxidized fibrils displayed low toxicity. We have thus discovered a class of novel theranostics for the simultaneous detection and oxidization of amyloid aggregates. Importantly, the selectivity of OPE's photosensitizing activity overcomes the limitation of off-target oxidation of traditional photosensitizers and represents an advancement of PDT as a viable strategy to treat neurodegenerative disorders.

Computational Investigation of the Binding Dynamics of Oligo p-Phenylene Ethynylene Fluorescence Sensors and Aß Oligomers.

Amyloid protein aggregates are pathological hallmarks of neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's (PD) diseases and are believed to be formed well before the onset of neurodegeneration and cognitive impairment. Monitoring the course of protein aggregation is thus vital to understanding and combating these diseases. We have recently demonstrated that a novel class of fluorescence sensors, oligomeric p-phenylene ethynylene (PE)-based electrolytes (OPEs) selectively bind to and detect prefibrillar and fibrillar aggregates of AD-related amyloid-ß (Aß) peptides over monomeric Aß. In this study, we investigated the binding between two OPEs, anionic OPE12- and cationic OPE24+, and to two different ß-sheet rich Aß oligomers using classical all-atom molecular dynamics simulations. Our simulations have revealed a number of OPE binding sites on Aß oligomer surfaces, and these sites feature hydrophobic amino acids as well as oppositely charged amino acids. Binding energy calculations show energetically favorable interactions between both anionic and cationic OPEs with Aß oligomers. Moreover, OPEs bind as complexes as well as single molecules. Compared to free OPEs, Aß protofibril bound OPEs show backbone planarization with restricted rotations and reduced hydration of the ethyl ester end groups. These characteristics, along with OPE complexation, align with known mechanisms of binding induced OPE fluorescence turn-on and spectral shifts from a quenched, unbound state in aqueous solutions. This study thus sheds light on the molecular-level details of OPE-Aß protofibril interactions and provides a structural basis for fluorescence turn-on sensing modes of OPEs.

Computational Study of the Driving Forces and Dynamics of Curcumin Binding to Amyloid-ß Protofibrils.

Oligomeric aggregates of the amyloid-ß (Aß) peptide are believed to be the primary toxic species that initiate events leading to neurodegeneration and cognitive decline in Alzheimer's disease (AD). Small molecules that interfere with Aß aggregation and/or neurotoxicity are being investigated as potential therapeutics for AD, including naturally occurring polyphenols. We have recently shown that curcumin exerts a neuroprotective effect against Aß40-induced toxicity on cultured neuronal cells through two possible concerted pathways, ameliorating Aß oligomer-induced toxicity and inducing the formation of nontoxic Aß oligomers, both of which involve curcumin binding to Aß oligomers. To gain molecular-level insights into curcumin's interaction with Aß oligomers, we use all-atom molecular dynamics (MD) simulations to study the dynamics and energetics of curcumin binding to an Aß protofibril composed of 24 peptides. Our results show that curcumin binds to specific hydrophobic sites on the protofibril surface and that binding is generally associated with the concomitant complexation of curcumin into dimers, trimers, or tetramers. Curcumin also binds to the protofibril growth axis ends but without complexation. Analysis of the energetics of the binding process revealed that curcumin complexation contributes in an additive fashion to curcumin-Aß protofibril interactions. Favorable curcumin-protofibril binding is driven by a combination of hydrophobic interactions between curcumin and protofibril, curcumin self-aggregation, and solvation effects. These interactions are likely critical in blocking Aß oligomer toxicity and inducing the growth of the protofibrils into "off-pathway" wormlike fibrils observed experimentally.

Oligomeric Conjugated Polyelectrolytes Display Site-Preferential Binding to an MS2 Viral Capsid.

Opportunistic bacteria and viruses are a worldwide health threat prompting the need to develop new targeting modalities. A class of novel synthetic poly(phenylene ethynylene) (PPE)-based oligomeric conjugated polyelectrolytes (OPEs) have demonstrated potent wide-spectrum biocidal activity. A subset of cationic OPEs display high antiviral activity against the MS2 bacteriophage. The oligomers have been found to inactivate the bacteriophage and perturb the morphology of the MS2 viral capsid. However, details of the initial binding and interactions between the OPEs and the viruses are not well understood. In this study, we use a multiscale computational approach, including random sampling, molecular dynamics, and electronic structure calculations, to gain an understanding of the molecular-level interactions of a series of OPEs that vary in length, charge, and functional groups with the MS2 capsid. Our results show that OPEs strongly bind to the MS2 capsid protein assembly with binding energies of up to -30 kcal/mol. Free-energy analysis shows that the binding is dominated by strong van der Waals interactions between the hydrophobic OPE backbone and the capsid surface and strong electrostatic free energy contributions between the OPE charged moieties and charged residues on the capsid surface. This knowledge provides molecular-level insight into how to tailor the OPEs to optimize viral capsid disruption and increase OPE efficacy to target amphiphilic protein coats of icosahedral-based viruses.

Diblock copolymer micelles and supported films with noncovalently incorporated chromophores: a modular platform for efficient energy transfer.

We report generation of modular, artificial light-harvesting assemblies where an amphiphilic diblock copolymer, poly(ethylene oxide)-block-poly(butadiene), serves as the framework for noncovalent organization of BODIPY-based energy donor and bacteriochlorin-based energy acceptor chromophores. The assemblies are adaptive and form well-defined micelles in aqueous solution and high-quality monolayer and bilayer films on solid supports, with the latter showing greater than 90% energy transfer efficiency. This study lays the groundwork for further development of modular, polymer-based materials for light harvesting and other photonic applications.

Enzyme-specific sensors via aggregation of charged p-phenylene ethynylenes.

Chemical and biological sensors are sought for their ability to detect enzymes as biomarkers for symptoms of various disorders, or the presence of chemical pollutants or poisons. p-Phenylene ethynylene oligomers with pendant charged groups have been recently shown to have ideal photophysical properties for sensing. In this study, one anionic and one cationic oligomer are combined with substrates that are susceptible to enzymatic degradation by phospholipases or acetylcholinesterases. The photophysical properties of the J-aggregated oligomers with the substrate are ideal for sensing, with fluorescence quantum yields of the sensors enhanced between 30 and 66 times compared to the oligomers without substrate. The phospholipase sensor was used to monitor the activity of phospholipase A1 and A2 and obtain kinetic information, though phospholipase C did not degrade the sensor. The acetylcholinesterase sensor was used to monitor enzyme activity and was also used to detect the inhibition of acetylcholinesterase by three different inhibitors. Phospholipase A2 is a biomarker for heart and circulatory disease, and acetylcholinesterase is a biomarker for Alzheimer's, and indicative of exposure to certain pesticides and nerve agents. This work shows that phenylene ethynylene oligomers can be tailored to enzyme-specific sensors by careful selection of substrates that induce formation of a molecular aggregate, and that the sensing of enzymes can be extended to enzyme kinetics and detection of inhibition. Furthermore, the aggregates were studied through all-atom molecular dynamics, providing a molecular-level view of the formation of the molecular aggregates and their structure.

Symptom targeted intervention webinar trainings: feedback from participants.

Professional trainings through the use of webinar format are widely used, but participant feedback is seldom studied. In the spring of 2013, 83 nephrology social workers participated in weekly webinar trainings to learn how to implement Symptom Targeted Intervention (STI) into their clinical practice. At the end of the project, participants were asked to complete an online questionnaire to provide feedback on the perceived value and effectiveness of the trainings. Sixty-eight participants completed the questionnaire. The results indicate that social workers found the webinar trainings to be very useful and wanted the trainings to continue beyond the project. Based on participant feedback, clinical training and case presentation through the use of ongoing webinars is a useful education modality for nephrology professionals, but more research is indicated to evaluate how best to utilize webinars to maximize learning.

Computational study of bacterial membrane disruption by cationic biocides: structural basis for water pore formation.

The development of biocides as disinfectants that do not induce bacterial resistance is crucial to health care since hospital-acquired infections afflict millions of patients every year. Recent experimental studies of a class of cationic biocides based on the phenylene ethynylene backbone, known as OPEs, have revealed that their biocidal activity is accompanied by strong morphology changes to bacterial cell membranes. In vitro studies of bacterial membrane mimics have shown changes to the lipid phase that are dependent on the length and orientation of the cationic moieties on the backbone. This study uses classical molecular dynamics to conduct a comprehensive survey of how oligomers with different chemical structures interact with each other and with a bacterial cell membrane mimic. In particular, the ability of OPEs to disrupt membrane structure is studied as a function of the length of the biocides and the orientation of their cationic moieties along the backbone of the molecule. The simulation results show that the structure of OPEs radically affects their interactions with a lipid bilayer. Biocides with branched cationic groups form trans-membrane water pores regardless of their backbone length, while only 1-1.5 nm of membrane thinning is observed with biocides with cationic groups on their terminal ends. The molecular dynamics simulations provide mechanistic details at the molecular level of the interaction of these biocidal oligomers and the lipid bilayer and corroborate experimental findings regarding observed differences in membrane disruption by OPEs with different chemical structures.

Calculation of iron transport through human H-chain ferritin.

Influx of ferrous ions from the cytoplasm through 3-fold pores in the shell of ferritin protein is computed using a 3-dimensional Poisson-Nernst-Planck electrodiffusion model, with inputs such as the pore structure and the diffusivity profile of permeant Fe(2+) ions extracted from all-atom molecular dynamics (MD) simulations. These calculations successfully reproduce experimental estimates of the transit time of Fe(2+) through the ferritin coat, which is on the millisecond time scale and hence much too long to be directly simulated via all-atom MD. This is also much longer than the typical time scale for ion transit in standard membrane spanning ion channels whose pores bear structural similarity to that of the 3-fold ferritin pore. The slow time scale for Fe(2+) transport through ferritin pores is traced to two features that distinguish the ferritin pore system from standard ion channels, namely, (i) very low concentration of cytoplasmic Fe(2+) under physiological conditions and (ii) very small internal diffusion coefficients for ions inside the ferritin pore resulting from factors that include the divalent nature of Fe(2+) and two rings of negatively charged amino acids surrounding a narrow geometric obstruction within the ferritin pore interior.

Cationic oligo-p-phenylene ethynylenes form complexes with surfactants for long-term light-activated biocidal applications.

Cationic oligo-p-phenylene ethynylenes are highly effective light-activated biocides that deal broad-spectrum damage to a variety of pathogens, including bacteria. A potential problem arising in the long-term usage of these compounds is photochemical breakdown, which nullifies their biocidal activity. Recent work has shown that these molecules complex with oppositely-charged surfactants, and that the resulting complexes are protected from photodegradation. In this manuscript, we determine the biocidal activity of an oligomer and a complex formed between it and sodium dodecyl sulfate. The complexes are able to withstand prolonged periods of irradiation, continuing to effectively kill both Gram-negative and Gram-positive bacteria, while the oligomer by itself loses its biocidal effectiveness quickly in the presence of light. In addition, damage and stress responses induced by these biocides in both E. coli and S. aureus are discussed. This work shows that complexation with surfactants is a viable method for long-term light-activated biocidal applications.

Structural basis for aggregation mode of oligo-p-phenylene ethynylenes with ionic surfactants.

In this letter, the aggregation modes of two classes of ionic p-phenylene ethynylene oligomers with oppositely charged surfactants are studied. The location of the ionic side chains was found to influence the type of aggregate formed when an equivalent number of surfactant molecules are added to solution. When the charged groups were located at the terminal ends of the molecule, strong H-aggregates were observed to form. Alternatively, when the ionic groups were both located on opposite sides of the central phenyl ring, the formation of J-aggregates was observed. Interestingly, as the surfactant concentration approaches the critical micelle concentration, the weakly bound aggregates are dissociated and the absorbance spectrum returns to what is observed in water. This study reveals the structural basis for aggregation effects between molecules based on the p-phenylene ethynylene backbone, and gives an understanding of how to influence the aggregation mode of similar compounds.

Photochemistry of "end-only" oligo-p-phenylene ethynylenes: complexation with sodium dodecyl sulfate reduces solvent accessibility.

Cationic oligo-p-phenylene ethynylenes are very effective light-activated biocides and biosensors but degrade upon exposure to light. In this study, we explore the photochemistry of a class of "end-only" compounds from this series, which have cationic moieties on the ends of the backbone. Product characterization by mass spectrometry reveals that the photoreactivity of these molecules is higher than that of a previously studied oligomer and that the primary products of photolysis result from the addition of water or oxygen across the triple bond. In addition, a product suggesting the addition of peroxide or other reactive oxygen species across the triple bond was observed. To explore avenues by which the photodegradation of these compounds can be mitigated, the effects of complexation with sodium dodecyl sulfate micelles on their photochemistry was explored. Classical molecular dynamics simulations revealed that compounds that were protected from photolysis by SDS buried their phenylene ethynylene backbones into the interior of the micelle, protecting it from contact with water. This work has revealed a molecular basis for the protection of a novel class of light-activated biocides from irradiation that is consistent with the proposed photochemistry of these compounds. This information can be useful for developing photodegradation-resistant biocidal materials and applications for current compounds and leads to new molecular design.

Metal binding sites of human H-chain ferritin and iron transport mechanism to the ferroxidase sites: a molecular dynamics simulation study.

We study via all atom classical molecular dynamics (MD) simulation the process of uptake of ferrous ions (Fe(2+)) into the human ferritin protein and the catalytic ferroxidase sites via pores ("channels") in the interior of the protein. We observe that the three-fold hydrophilic channels serve as the main entrance pathway for the Fe(2+) ions. The binding sites along the ion pathway are investigated. Two strong binding sites, at the Asp131 and Glu134 residues and two weak binding sites, at the His118 and Cys130 are observed inside the three-fold channel. We also identify an explicit pathway for an ion exiting the channel into the central core of the protein as it moves to the ferroxidase site. The diffusion of an Fe(2+) ion from the inner opening of the channel to a ferroxidase site located in the interior region of the protein coat is assisted by Thr135, His136 and Tyr137. The Fe(2+) ion binds preferentially to site A of the ferroxidase site.

Molecular dynamics simulation study of the interaction of cationic biocides with lipid bilayers: aggregation effects and bilayer damage.

A novel class of phenylene ethynylene polyelectrolyte oligomers (OPEs) has been found to be effective biocidal agents against a variety of pathogens. The mechanism of attack is not yet fully understood. Recent studies have shown that OPEs cause catastrophic damage to large unilamellar vesicles. This study uses classical molecular dynamics (MD) simulations to understand how OPEs interact with model lipid bilayers. All-atom molecular dynamics simulations show that aggregates of OPEs inserted into the membrane cause significant structural damage and create a channel, or pore, that allows significant leakage of water through the membrane on the 0.1 µs time scale.