An AAV capsid reprogrammed to bind human transferrin receptor mediates brain-wide gene delivery.

Developing vehicles that efficiently deliver genes throughout the human central nervous system (CNS) will broaden the range of treatable genetic diseases. We engineered an adeno-associated virus (AAV) capsid, BI-hTFR1, that binds human transferrin receptor (TfR1), a protein expressed on the blood-brain barrier. BI-hTFR1 was actively transported across human brain endothelial cells and, relative to AAV9, provided 40 to 50 times greater reporter expression in the CNS of human TFRC knockin mice. The enhanced tropism was CNS-specific and absent in wild-type mice. When used to deliver GBA1, mutations of which cause Gaucher disease and are linked to Parkinson's disease, BI-hTFR1 substantially increased brain and cerebrospinal fluid glucocerebrosidase activity compared with AAV9. These findings establish BI-hTFR1 as a potential vector for human CNS gene therapy.

Free-Standing DNA Origami Superlattice to Facilitate Cryo-EM Visualization of Membrane Vesicles.

Technological breakthroughs in cryo-electron microscopy (cryo-EM) methods open new perspectives for highly detailed structural characterizations of extracellular vesicles (EVs) and synthetic liposome-protein assemblies. Structural characterizations of these vesicles in solution under a nearly native hydrated state are of great importance to decipher cell-to-cell communication and to improve EVs' application as markers in diagnosis and as drug carriers in disease therapy. However, difficulties in preparing holey carbon cryo-EM grids with low vesicle heterogeneities, at low concentration and with kinetic control of the chemical reactions or assembly processes, have limited cryo-EM use in the EV study. We report a straightforward membrane vesicle cryo-EM sample preparation method that assists in circumventing these limitations by using a free-standing DNA-affinity superlattice for covering holey carbon cryo-EM grids. Our approach uses DNA origami to self-assemble to a solution-stable and micrometer-sized ordered molecular template in which structure and functional properties can be rationally controlled. We engineered the template with cholesterol-binding sites to specifically trap membrane vesicles. The advantages of this DNA-cholesterol-affinity lattice (DCAL) include (1) local enrichment of artificial and biological vesicles at low concentration and (2) isolation of heterogeneous cell-derived membrane vesicles (exosomes) from a prepurified pellet of cell culture conditioned medium on the grid.

Mechanical DNA Origami to Investigate Biological Systems.

The ability to self-assemble DNA nanodevices with programmed structural dynamics that can sense and respond to the local environment can enable transformative applications in fields including mechanobiology and nanomedicine. The responsive function of biomolecules is often driven by alterations in conformational distributions mediated by highly sensitive interactions with the local environment. In this review, the current state-of-the-art in constructing complex DNA geometries with dynamic and mechanical properties to enable a molecular scale force measurement is first summarized. Next, an overview of engineering modular DNA devices that interact with cell surfaces is highlighted detailing examples of mechanosensitive proteins and the force-induced dynamic molecular interaction on the downstream biochemical signaling. Finally, the challenges and an outlook on this promising class of DNA devices acting as nanomachines to operate at a low piconewton range suitable for a majority of biological effects or as hybrid materials to achieve higher tension exertion required for other biological investigations, are discussed.

An AAV capsid reprogrammed to bind human Transferrin Receptor mediates brain-wide gene delivery.

Developing vehicles that efficiently deliver genes throughout the human central nervous system (CNS) will broaden the range of treatable genetic diseases. We engineered an AAV capsid, BI-hTFR1, that binds human Transferrin Receptor (TfR1), a protein expressed on the blood-brain barrier (BBB). BI-hTFR1 was actively transported across a human brain endothelial cell layer and, relative to AAV9, provided 40-50 times greater reporter expression in the CNS of human TFRC knock-in mice. The enhanced tropism was CNS-specific and absent in wild type mice. When used to deliver GBA1, mutations of which cause Gaucher disease and are linked to Parkinson's disease, BI-hTFR1 substantially increased brain and cerebrospinal fluid glucocerebrosidase activity compared to AAV9. These findings establish BI-hTFR1 as a promising vector for human CNS gene therapy.

Prescription Modification by Pharmacists in a Hospital Setting: Are Ontario Pharmacists Ready?

BACKGROUND: Under Ontario's Public Hospitals Act, the scope of professional practice of hospital pharmacists is approved by each hospital's medical advisory committee. Some Ontario hospitals have adopted policies or medical directives related to prescription modification, allowing pharmacists to broadly adapt, discontinue, hold, or renew prescriptions as part of their clinical scope of practice. OBJECTIVES: The primary objective of this study was to describe Ontario hospital pharmacists' perception of their readiness to independently modify prescriptions. The secondary objectives of this study were to gather opinions on the perceived benefits, drawbacks, facilitators, and barriers to prescription modification by pharmacists and to determine how various factors affect perceived readiness. METHODS: A confidential web-based survey with Likert-type quantitative questions and qualitative open-ended questions was distributed to 936 hospital pharmacists in Ontario between May and July 2019. Mean scores were calculated for the following constructs affecting prescription modification: self-efficacy, support from the practice environment, and support from interprofessional relationships. Independent t tests were conducted to compare responses between subgroups of interest. The answers to open-ended questions were analyzed thematically. RESULTS: The survey had a 29% response rate (n = 271). The mean self-efficacy score was 5.2 out of 7 (standard deviation [SD] 1.0, Cronbach α = 0.88), equivalent to "quite sure". The mean score for support from the practice environment was 3.3 out of 5 (SD 0.4, Cronbach α = 0.75), equivalent to "not a factor". The mean score for support from interprofessional relationships was 4.2 out of 5 (SD 0.1, Cronbach α = 0.80), equivalent to "weak support". Improved efficiency of care, timelier interventions to improve medication safety and efficacy, and improved interprofessional collaboration were cited as benefits of prescription modification by pharmacists. Potential for inappropriate decision-making and miscommunication were cited as concerns. Respondents in hospitals who were already performing prescription modification reported higher self-efficacy to modify prescriptions in clinical areas of both familiarity and unfamiliarity and greater support from prescribers. CONCLUSIONS: A large proportion of respondents to a survey of Ontario hospital pharmacists expressed an encouraging level of readiness to independently modify prescriptions. Responses to open-ended questions in this study provided valuable insights to inform widespread adoption of this practice change.

CONTEXTE: En vertu de la Loi sur les hôpitaux publics de l'Ontario, le comité consultatif de chaque hôpital approuve l'élargissement de la pratique professionnelle des pharmaciens d'hôpitaux. Certains hôpitaux de l'Ontario ont adopté des politiques ou des directives médicales concernant la modification de la prescription. Celles-ci autorisent les pharmaciens à adapter, cesser, suspendre ou renouveler largement les prescriptions dans le cadre de leur champ de pratique. OBJECTIFS: L'objectif principal de cette étude visait à décrire la perception des pharmaciens d'hôpitaux de l'Ontario de leur degré de préparation à modifier des prescriptions de manière indépendante. Les objectifs secondaires consistaient à recueillir les opinions sur les avantages, les inconvénients, les éléments de facilitation et les obstacles perçus par les pharmaciens au sujet de la modification de la prescription et de définir comment divers facteurs influençaient la perception de leur degré de préparation. MÉTHODES: Entre mai et juillet 2019, 936 pharmaciens d'hôpitaux en Ontario ont reçu une enquête confidentielle menée sur Internet comportant des questions quantitatives de type Likert et des questions ouvertes qualitatives. Les scores médians ont été calculés pour les concepts suivants liés à la modification de la prescription : l'autoefficacité, le soutien de l'environnement de pratique et le soutien des relations interprofessionnelles. Des tests t indépendants ont été menés pour comparer les réponses entre les sous-groupes sous-groupes qui intéressaient les auteurs. Les réponses aux questions ouvertes ont été analysées par thème. RÉSULTATS: Le taux de réponses à l'enquête se montait à 29 % (n = 271). Le score moyen pour le thème « Autoefficacité ¼ était de 5,2 sur 7 (écart type [ET] 1, Cronbach α = 0,88), ce qui équivaut à la réponse « Assez certain ¼. Le score moyen pour le thème « Soutien de l'environnement de pratique ¼ était de 3,3 sur 5 (ET 0,4, Cronbach α = 0,75), ce qui équivaut à la réponse « N'est pas un facteur ¼. Le score moyen pour le thème « Relations interprofessionnelles ¼ était de 4,2 sur 5 (ET 0,1, Cronbach α = 0,80), ce qui équivaut à la réponse « Soutien faible ¼. Les pharmaciens ont cité l'amélioration de l'efficacité des soins, les interventions en temps opportun visant à améliorer l'innocuité et l'efficacité des médicaments ainsi que l'amélioration de la collaboration interprofessionnelle comme étant des avantages de la modification indépendante des prescriptions. Ils ont aussi indiqué que le risque de prise de décision inappropriée ainsi que la mauvaise communication constituaient pour eux un sujet de préoccupation. Les répondants qui pratiquaient déjà la modification de la prescription en milieu hospitalier ont indiqué un gain d'autoefficacité de la modification des prescriptions dans des domaines cliniques qui leur sont familiers ou non, ainsi qu'un plus grand soutien de la part des prescripteurs. CONCLUSIONS: Une grande partie des répondants à une enquête menée auprès de pharmaciens d'hôpitaux de l'Ontario ont jugé que leur degré de préparation à la modification indépendante des ordonnances était prometteur. Les réponses aux questions ouvertes de cette étude fournissent des éclaircissements précieux sur l'adoption généralisée de ce changement de pratique.

An Exploratory Screening Study for Type 2 Diabetes in Hospitalized Adult Medicine Patients.

OBJECTIVES: Literature from stroke and cardiac hospital admissions demonstrate a higher prevalence of undiagnosed type 2 diabetes compared with the general population. Fewer diabetes screening studies exist in the general medicine population, none of which have been based in Canada. Our primary objective in this study was to determine the prevalence of probable undiagnosed diabetes (glycated hemoglobin [A1C]≥6.5%) in hospitalized medicine patients. Secondary objectives were to identify the prevalence of undiagnosed dysglycemia (A1C≥6.0%) and the subsequent management of emergent cases. METHODS: In this prospective cohort study, adult patients admitted to internal medicine at a tertiary hospital in Ontario were screened for diabetes using an A1C test over a 3-month period. Baseline demographics and outcomes were compared using t tests, chi-square tests and Fisher's exact tests for normoglycemia, undiagnosed dysglycemia and probable undiagnosed diabetes. A regression analysis was performed to identify any relationships between various cardiovascular-related risk factors and A1C. RESULTS: A total of 53 adult patients were enrolled. The prevalence of probable undiagnosed diabetes and undiagnosed dysglycemia was 7.5% (n=4) and 30.2% (n=16), respectively. Implementation of diabetes management strategies and/or documentation of the finding occurred in 4 of 16 patients. Regression analysis showed no relationship between either cardiovascular-related risk factors or admission glucose with A1C. CONCLUSIONS: A broader screening approach may capture previously undiagnosed cases of diabetes that do not belong to traditionally at-risk populations. Future studies should focus on identifying risk factors for undiagnosed dysglycemia in hospitalized patients, including ethnicity and barriers to community access, so that appropriate screening programs can be developed.

Modular Imaging Scaffold for Single-Particle Electron Microscopy.

Technological breakthroughs in electron microscopy (EM) have made it possible to solve structures of biological macromolecular complexes and to raise novel challenges, specifically related to sample preparation and heterogeneous macromolecular assemblies such as DNA-protein, protein-protein, and membrane protein assemblies. Here, we built a V-shaped DNA origami as a scaffolding molecular system to template proteins at user-defined positions in space. This template positions macromolecular assemblies of various sizes, juxtaposes combinations of biomolecules into complex arrangements, isolates biomolecules in their active state, and stabilizes membrane proteins in solution. In addition, the design can be engineered to tune DNA mechanical properties by exerting a controlled piconewton (pN) force on the molecular system and thus adapted to characterize mechanosensitive proteins. The binding site can also be specifically customized to accommodate the protein of interest, either interacting spontaneously with DNA or through directed chemical conjugation, increasing the range of potential targets for single-particle EM investigation. We assessed the applicability for five different proteins. Finally, as a proof of principle, we used RNAP protein to validate the approach and to explore the compatibility of the template with cryo-EM sample preparation.

The Peptidisc, a simple method for stabilizing membrane proteins in detergent-free solution.

Membrane proteins are difficult to work with due to their insolubility in aqueous solution and quite often their poor stability in detergent micelles. Here, we present the peptidisc for their facile capture into water-soluble particles. Unlike the nanodisc, which requires scaffold proteins of different lengths and precise amounts of matching lipids, reconstitution of detergent solubilized proteins in peptidisc only requires a short amphipathic bi-helical peptide (NSPr) and no extra lipids. Multiple copies of the peptide wrap around to shield the membrane-exposed part of the target protein. We demonstrate the effectiveness of this 'one size fits all' method using five different membrane protein assemblies (MalFGK2, FhuA, SecYEG, OmpF, BRC) during 'on-column', 'in-gel', and 'on-bead' reconstitution embedded within the membrane protein purification protocol. The peptidisc method is rapid and cost-effective, and it may emerge as a universal tool for high-throughput stabilization of membrane proteins to advance modern biological studies.

Lipopolysaccharides promote binding and unfolding of the antibacterial colicin E3 rRNAse domain.

Nuclease colicins are antibacterial proteins produced by certain strains of E. coli to reduce competition from rival strains. These colicins are generally organized with an N-terminal transport (T)-domain, a central receptor binding (R)-domain, and a C-terminal cytotoxic nuclease domain. These colicins are always produced in complex with an inhibitory immunity protein, which dissociates prior entrance of the cytotoxic domain in the target cell. How exactly colicins traverse the cell envelope is not understood, yet this knowledge is important for the design of new antibacterial therapies. In this report, we find that the cytotoxic rRNAse domain of colicin E3, lacking both T- and R-domains, is sufficient to inhibit cell growth provided the immunity protein Im3 has been removed. Thus, while the T-domain is needed for dissociation of Im3, the rRNAse alone can associate to the cell surface without R-domain. Accordingly, we find a high affinity interaction (Kd ~1-2µM) between the rRNAse domain and lipopolysaccharides (LPS). Furthermore, we show that binding of ColE3 to LPS destabilizes the secondary structure of the toxin, which is expectedly crucial for transport through the narrow pore of the porin OmpF. The effect of LPS on binding and unfolding of ColE3 may be indicative of a broader role of LPS for transport of colicins in general.

TonB-dependent ligand trapping in the BtuB transporter.

TonB-dependent transporters are ß-barrel outer membrane proteins occluded by a plug domain. Upon ligand binding, these transporters extend a periplasmic motif termed the TonB box. The TonB box permits the recruitment of the inner membrane protein complex TonB-ExbB-ExbD, which drives import of ligands in the cell periplasm. It is unknown precisely how the plug domain is moved aside during transport nor have the intermediate states between TonB recruitment and plug domain movement been characterized biochemically. Here we employ nanodiscs, native gel electrophoresis, and scintillation proximity assays to determine the binding kinetics of vitamin B12 to BtuB. The results show that ligand-bound BtuB recruits a monomer of TonB (TonB∆1-31), which in turn increases retention of vitamin B12 within the transporter. The TonB box and the extracellular residue valine 90 that forms part of the vitamin B12 binding site are essential for this event. These results identify a novel step in the TonB-dependent transport process. They show that TonB binding to BtuB trap the ligand, possibly until the ExbB-ExbD complex is activated or recruited to ensure subsequent transport.

Salmonella Rapidly Regulates Membrane Permeability To Survive Oxidative Stress.

UNLABELLED: The outer membrane (OM) of Gram-negative bacteria provides protection against toxic molecules, including reactive oxygen species (ROS). Decreased OM permeability can promote bacterial survival under harsh circumstances and protects against antibiotics. To better understand the regulation of OM permeability, we studied the real-time influx of hydrogen peroxide in Salmonella bacteria and discovered two novel mechanisms by which they rapidly control OM permeability. We found that pores in two major OM proteins, OmpA and OmpC, could be rapidly opened or closed when oxidative stress is encountered and that the underlying mechanisms rely on the formation of disulfide bonds in the periplasmic domain of OmpA and TrxA, respectively. Additionally, we found that a Salmonella mutant showing increased OM permeability was killed more effectively by treatment with antibiotics. Together, these results demonstrate that Gram-negative bacteria regulate the influx of ROS for defense against oxidative stress and reveal novel targets that can be therapeutically targeted to increase bacterial killing by conventional antibiotics. IMPORTANCE: Pathogenic bacteria have evolved ways to circumvent inflammatory immune responses. A decrease in bacterial outer membrane permeability during infection helps protect bacteria from toxic molecules produced by the host immune system and allows for effective colonization of the host. In this report, we reveal molecular mechanisms that rapidly alter outer membrane pores and their permeability in response to hydrogen peroxide and oxidative stress. These mechanisms are the first examples of pores that are rapidly opened or closed in response to reactive oxygen species. Moreover, one of these mechanisms can be targeted to artificially increase membrane permeability and thereby increase bacterial killing by the antibiotic cefotaxime during in vitro experiments and in a mouse model of infection. We envision that a better understanding of the regulation of membrane permeability will lead to new targets and treatment options for multidrug-resistant infections.

Canadian health care institution resource utilization resulting from skeletal-related events.

PURPOSE: We describe the types of major institution health care resources consumed as a result of skeletal-related events (SREs) [ie, pathological fracture, bone surgery, radiation to bone, spinal cord compression]. METHODS: A retrospective multicenter chart review of cancer patients with bone metastases who experienced SREs was conducted. Patients with multiple SREs occurring during the same hospitalization within 21 days of each other were grouped into SRE clusters. RESULTS: We reviewed 156 patient charts from 4 Canadian institutions, accounting for 358 SREs and 259 SRE clusters. Of the total patients, 63% experienced 1 SRE; 19%, 2 SREs; 10%, 3 SREs; and 8%, ≥ 4 events. Health care resource utilization was captured for ≥ 90 days following each SRE: 54% of all SRE events resulted in an inpatient stay; 34% in an emergency visit; 85% of SREs required the use of diagnostic procedures (including radiography, magnetic resonance imaging, Computerized Axial Tomography scans, and radio scans); 57% required radiation treatment; 34% required a surgical procedure; 35% received outpatient treatment visits (ie, physiotherapy or occupational therapy). Bone surgery and spinal cord compression were more often associated with hospitalization than were other SRE types. Spinal cord compression was associated with the greatest number of inpatients stays (1.09 per SRE), longest duration of hospital stay (mean 26.18 days per SRE), and more outpatient visits, relative to other SRE types. CONCLUSION: Results of our Canadian retrospective study clearly demonstrate that SREs occur in cancer patients and each SRE is associated with considerable institutional consumption of health care resources.

FhuA interactions in a detergent-free nanodisc environment.

TonB-dependent membrane receptors from bacteria have been analyzed in detergent-containing solution, an environment that may influence the role of ligand in inducing downstream interactions. We report reconstitution of FhuA into a membrane mimetic: nanodiscs. In contrast to previous results in detergent, we show that binding of TonB to FhuA in nanodiscs depends strongly on ferricrocin. The stoichiometry of interaction is 1:1 and the binding constant KD is ~200nM; an equilibrium affinity that is ten-fold lower than reported in detergent. FhuA in nanodiscs also forms a high-affinity binding site for colicin M (KD ~3.5nM), while ferricrocin renders FhuA refractory to colicin binding. Together, these results demonstrate the importance of the ligand in regulating receptor interactions and the advantages of nanodiscs to study ß-barrel membrane proteins in a membrane-like environment.

Venous thromboembolism in elderly high-risk medical patients: time course of events and influence of risk factors.

Venous thromboembolism (VTE) causes significant morbidity and mortality in hospitalized medical populations; however, medical patients do not currently receive thromboprophylaxis beyond their hospital stay. We reviewed the real-life occurrence of VTE-related care for 100 days post-hospitalization in Calgary, Canada. Using medical visit records with a unique patient identifier number applied throughout the city's hospitals, 989 high-risk patients were selected for review. Almost three-quarters of the elderly patients received appropriate prophylaxis while in hospital, and only 2% received prophylaxis on discharge. Over the 100-day follow-up, 21% of the patients presented with clinically suspected VTE, of which 3.8% had confirmed VTE. Patients with multiple risk factors (≥ 3) had the highest frequency of confirmed VTE (≥ 6.1%). This study suggests that the actual rate of VTE-related follow-up care in patients post-hospitalization is high in the first 100 days, particularly among those who have multiple risk factors, warranting consideration of extended thromboprophylaxis in this population.

Management and adherence to VTE treatment guidelines in a national prospective cohort study in the Canadian outpatient setting. The Recovery Study.

Documenting patterns and outcomes of venous thromboembolism (VTE) management and degree of adherence by clinicians to treatment guidelines could help identify remediable gaps in patient care. Prospective, clinical practice-based data from Canadian outpatient settings on management of VTE, degree of adherence with treatment guidelines and frequency of recurrent VTE and bleeding during follow-up was obtained in a multicentre, prospective observational study. From 12 Canadian centres, we assessed 868 outpatients with acute symptomatic VTE who received the low-molecular-weight heparin (LMWH) enoxaparin alone or with vitamin K antagonists (VKA), at baseline and at six months (or at the end of treatment, whichever came first). Index VTE was limb deep venous thrombosis (DVT) in 583 (67.2%) patients, pulmonary embolism (PE) with or without DVT in 262 (30.2%) patients, and unusual site DVT in 23 (2.6%) patients. VTE was unprovoked in 399 (46.0%) patients, associated with cancer in 74 (8.5%) patients, transient risk factors in 327 (37.7%) patients and hormonal factors in 68 (7.8%) patients.With regard to guideline adherence, 58 (7.3%) patients received <5 days LMWH and 114 (14.5%) had overlap <1 day. Among patients with cancer-related VTE, 59.5% were prescribed LMWH monotherapy and 43.2% received such treatment for >3 months. Only 38.1% of patients with transient VTE risk factors had received thromboprophylaxis. Our study provides useful information on clinical presentation, management and related outcomes in Canadian outpatients with VTE. Our results suggest there may be important gaps in use of thromboprophylaxis to prevent VTE and use of LMWH monotherapy to treat cancer-related VTE.

Association Between Use of Proton Pump Inhibitors and a Clostridium difficile-Associated Disease Outbreak: Case-Control Study.

BACKGROUND: The use of proton pump inhibitors (PPIs) has been implicated as a potential contributor to the development of Clostridium difficile-associated disease (CDAD) because of the ability of these drugs to substantially reduce the bactericidal effect of gastric acid. This study focused on the impact of PPIs, among other known risk factors, during an outbreak of CDAD in a hospital setting. OBJECTIVES: The primary objective was to determine whether there was an association between current use of a PPI and the CDAD outbreak. Secondary objectives were to evaluate any correlations between the CDAD outbreak and past use of PPIs, use of antibiotics, diabetes mellitus, enteral feeding, cancer, gastrointestinal surgery, inflammatory bowel disease, and previous care or residence in an institutional setting. METHODS: A retrospective case-control study was conducted. One hundred and fifty cases of hospital-acquired Clostridium difficile were identified. Patients were individually matched to controls for age, sex, date of admission to hospital, and hospital unit. The groups were compared with respect to each exposure. RESULTS: Eight case patients could not be matched with suitable controls. Therefore, data from 142 cases and 142 controls were analyzed. There was no association between current use of a PPI and the CDAD outbreak (odds ratio [OR] 1.0, 95% confidence interval [CI] 0.99-1.01). Similarly, there was no correlation between the CDAD outbreak and diabetes, enteral feeding, cancer, gastrointestinal surgery, inflammatory bowel disease, or previous care or residence in an institution. However, the development of CDAD was positively associated with use of antibiotics within the 30 days preceding the infection (OR 12.0, 95% CI 4.0-35.7) and with past use of a PPI (OR 2.4, 95% CI 1.4-4.3). CONCLUSIONS: The development of CDAD during a hospital outbreak was associated with use of antibiotics and with past, not current, use of PPIs.

Rh III- and Ir III-catalyzed asymmetric transfer hydrogenation of ketones in water.

Asymmetric transfer hydrogenation (ATH) of ketones by formate in neat water is shown to be viable with Rh-TsDPEN and Ir-TsDPEN catalysts, derived in situ from [Cp*MCl2]2 (M=Rh, Ir) and TsDPEN. A variety of ketones were reduced, including nonfunctionalized aryl ketones, heteroaryl ketones, ketoesters, and unsaturated ketones. In comparison with Ir-TsDPEN and the related Ru II catalyst, the Rh III catalyst is most efficient in water, affording enantioselectivities of up to 99 % ee at substrate/catalyst (S/C) ratios of 100-1000 even without working under an inert atmosphere. The aqueous phase reduction is shown to be highly pH-dependent; the optimum pH windows for TOF greater than 50 mol mol(-1) h(-1) for Rh- and Ir-TsDPEN are 5.5-10.0 and 6.5-8.5, respectively. Outside the pH window, the reduction becomes slow or stagnant depending on the pH. However, the enantioselectivities erode only under acidic conditions. At a higher S/C ratio, the aqueous ATH by Rh-TsDPEN is shown to be product- as well as byproduct-inhibited; the product inhibition appears to stem at least partly from the reaction being reversible. The aqueous phase reduction is simple, efficient and environmentally benign, thus presenting a viable alternative for asymmetric reduction.

Arylthiolate-protected silver quantum dots.

This paper describes a new, organic-soluble 4-tert-butylbenzyl mercaptan (BBT) monolayer-protected silver cluster (AgBBT MPC) as the first example of a dissolved silver nanoparticle that exhibits quantized one-electron double layer charging (QDL) voltammetry. Polydisperse AgBBT MPCs made by two different synthetic protocols, but with similar average core diameters (2.1 nm), exhibit sharply differing electrochemistry and optical absorbance spectra. A two-phase procedure (organic/aqueous, termed Prep A-AgBBT) produced MPCs exhibiting a 475 nm surface plasmon absorbance and QDL voltammetry. Neither property was seen for MPCs made by a single-phase procedure, termed Prep B-AgBBT. The difference is thought to reflect poor passivation to oxide formation in the latter Prep B procedure, which is supported by X-ray photoelectron spectroscopy results. Thermogravimetry, mass spectra, and electrochemistry results suggest an average stoichiometric formula of Ag140BBT53, but transmission electron microscopy shows that the products are also polydisperse and include polycrystalline aggregates. Dry, cast films of both Ag MPC preparations on interdigitated array electrodes exhibit low electron hopping conductivity, compared to Au MPCs.