Force-controlled release of small molecules with a rotaxane actuator.

Force-controlled release of small molecules offers great promise for the delivery of drugs and the release of healing or reporting agents in a medical or materials context1-3. In polymer mechanochemistry, polymers are used as actuators to stretch mechanosensitive molecules (mechanophores)4. This technique has enabled the release of molecular cargo by rearrangement, as a direct5,6 or indirect7-10 consequence of bond scission in a mechanophore, or by dissociation of cage11, supramolecular12 or metal complexes13,14, and even by 'flex activation'15,16. However, the systems described so far are limited in the diversity and/or quantity of the molecules released per stretching event1,2. This is due to the difficulty in iteratively activating scissile mechanophores, as the actuating polymers will dissociate after the first activation. Physical encapsulation strategies can be used to deliver a larger cargo load, but these are often subject to non-specific (that is, non-mechanical) release3. Here we show that a rotaxane (an interlocked molecule in which a macrocycle is trapped on a stoppered axle) acts as an efficient actuator to trigger the release of cargo molecules appended to its axle. The release of up to five cargo molecules per rotaxane actuator was demonstrated in solution, by ultrasonication, and in bulk, by compression, achieving a release efficiency of up to 71% and 30%, respectively, which places this rotaxane device among the most efficient release systems achieved so far1. We also demonstrate the release of three representative functional molecules (a drug, a fluorescent tag and an organocatalyst), and we anticipate that a large variety of cargo molecules could be released with this device. This rotaxane actuator provides a versatile platform for various force-controlled release applications.

Mechanical scission of a knotted polymer.

Molecular knots and entanglements form randomly and spontaneously in both biological and synthetic polymer chains. It is known that macroscopic materials, such as ropes, are substantially weakened by the presence of knots, but until now it has been unclear whether similar behaviour occurs on a molecular level. Here we show that the presence of a well-defined overhand knot in a polymer chain substantially increases the rate of scission of the polymer under tension (≥2.6× faster) in solution, because deformation of the polymer backbone induced by the tightening knot activates otherwise unreactive covalent bonds. The fragments formed upon severing of the knotted chain differ from those that arise from cleavage of a similar, but unknotted, polymer. Our solution studies provide experimental evidence that knotting can contribute to higher mechanical scission rates of polymers. It also demonstrates that entanglement design can be used to generate mechanophores that are among the most reactive described to date, providing opportunities to increase the reactivity of otherwise inert functional groups.

Antiviral Activity of Lenacapavir Against HIV-2 Isolates and Drug-resistant HIV-2 Mutants.

The activity of lenacapavir against HIV-1 has been extensively evaluated in vitro, but comparable data for HIV-2 are scarce. We determined the anti-HIV-2 activity of lenacapavir using single-cycle infections of MAGIC-5A cells and multicycle infections of a T cell line. Lenacapavir exhibited low-nanomolar activity against HIV-2, but was 11- to 14-fold less potent against HIV-2 in comparison to HIV-1. Mutations in HIV-2 that confer resistance to other antiretrovirals did not confer cross-resistance to lenacapavir. Although lenacapavir-containing regimens might be considered for appropriate patients with HIV-2, more frequent viral load and/or CD4 testing may be needed to assess clinical response.

Intrinsic resistance of HIV-2 and SIV to the maturation inhibitor GSK2838232.

GSK2838232 (GSK232) is a novel maturation inhibitor that blocks the proteolytic cleavage of HIV-1 Gag at the junction of capsid and spacer peptide 1 (CA/SP1), rendering newly-formed virions non-infectious. To our knowledge, GSK232 has not been tested against HIV-2, and there are limited data regarding the susceptibility of HIV-2 to other HIV-1 maturation inhibitors. To assess the potential utility of GSK232 as an option for HIV-2 treatment, we determined the activity of the compound against a panel of HIV-1, HIV-2, and SIV isolates in culture. GSK232 was highly active against HIV-1 isolates from group M subtypes A, B, C, D, F, and group O, with IC50 values ranging from 0.25-0.92 nM in spreading (multi-cycle) assays and 1.5-2.8 nM in a single cycle of infection. In contrast, HIV-2 isolates from groups A, B, and CRF01_AB, and SIV isolates SIVmac239, SIVmac251, and SIVagm.sab-2, were highly resistant to GSK232. To determine the role of CA/SP1 in the observed phenotypes, we constructed a mutant of HIV-2ROD9 in which the sequence of CA/SP1 was modified to match the corresponding sequence found in HIV-1. The resulting variant was fully susceptible to GSK232 in the single-cycle assay (IC50 = 1.8 nM). Collectively, our data indicate that the HIV-2 and SIV isolates tested in our study are intrinsically resistant to GSK232, and that the determinants of resistance map to CA/SP1. The molecular mechanism(s) responsible for the differential susceptibility of HIV-1 and HIV-2/SIV to GSK232 require further investigation.

Isotope Effect in the Activation of a Mechanophore.

In mechanochemistry, molecules under tension can react in unexpected ways. The reactivity of mechanophores (mechanosensitive molecules) can be controlled using various geometric or electronic factors. Often these factors affect the rate of mechanical activation but sometimes give rise to alternative reaction pathways. Here we show that a simple isotope substitution (H to D) leads to a reversal of selectivity in the activation of a mechanophore. Remarkably this isotope effect is not kinetic in nature but emerges from dynamic effects in which deuteration reduces the ability of the reactant to follow a post-transition-state concerted trajectory on the bifurcated force-modified potential energy surface. These results give a new insight into the reactivity of molecules under tension.

HIV-2 Drug Resistance Genotyping from Dried Blood Spots.

The treatment of HIV-2 in resource-limited settings (RLS) is complicated by the limited availability of HIV-2-active antiretroviral drugs and inadequate access to HIV-2 viral load and drug resistance testing. Dried blood spots (DBS)-based drug resistance testing, widely studied for HIV-1, has not been reported for HIV-2 and could present an opportunity to improve care for HIV-2-infected individuals. We selected 150 DBS specimens from ongoing studies of antiretroviral therapy (ART) for HIV-2 infection in Senegal and subjected them to genotypic drug resistance testing. Total nucleic acid was extracted from DBS, reverse transcribed, PCR amplified, and analyzed by population-based Sanger sequencing, and major drug resistance-associated mutations (RAM) were identified. Parallel samples from plasma and peripheral blood mononuclear cells (PBMC) were also genotyped. We obtained 58 protease/reverse transcriptase genotypes. Plasma viral load was significantly correlated with genotyping success (P < 0.001); DBS samples with corresponding plasma viral load >250 copies/ml had a success rate of 86.8%. In paired DBS-plasma genotypes, 83.8% of RAM found in plasma were also found in DBS, and replicate DBS genotyping revealed that a single test detected 86.7% of known RAM. These findings demonstrate that DBS-based genotypic drug resistance testing for HIV-2 is feasible and can be deployed in RLS with limited infrastructure.

Three concomitant C-C dissociation pathways during the mechanical activation of an N-heterocyclic carbene precursor.

Chemical reactions usually proceed through a radical, concerted or ionic mechanism; transformations in which all three mechanisms occur are rare. In polymer mechanochemistry, a mechanical force, transduced along polymer chains, is used to activate covalent bonds in mechanosensitive molecules (mechanophores). Cleavage of a C-C bond often follows a homolytic pathway, but some mechanophores have also been designed that react in a concerted or, more rarely, a heterolytic manner. Here, using 1H- and 19F-nuclear magnetic resonance spectroscopy in combination with deuterium labelling, we show that the dissociation of a mechanophore built around an N-heterocyclic carbene precursor proceeds with the rupture of a C-C bond through concomitant heterolytic, concerted and homolytic pathways. The distribution of products probably arises from a post-transition-state bifurcation in the reaction pathway, and their relative proportion is dictated by the polarization of the scissile C-C bond.

Two-directional cross-metathesis.

Two-directional cross-metathesis of a range of alpha,omega dienes with a variety of electron deficient alkenes has been accomplished. It was found that the process is quite general and gives complete selectivity for the E,E-dienes, making this a very useful and high yielding protocol for two-directional chain elongation.

Becoming an education architect. How to design a training program that fits your department's needs.

This article has discussed the concept of instructional design and the initial processes involved in creating high-quality, comprehensive training sessions that meet the needs of the EMS organization and its employees. Conducting a training needs assessment, as well as a training needs analysis, provides essential information about the types of training necessary to enhance overall performance. Additionally, knowing the audience and location for the training will afford insight into limitations on the program. This essential information leads to the creation of behavioral or performance objectives as the developing curriculum progresses.

Recognizing imminent danger: characteristics of a suicide bomber.

By all reports, the public is at increasing risk of attack by terrorist organizations. Citizens have been asked to increase their vigilance and report suspicious individuals to reduce the chance of a suicide or homicide bombing. Terrorist groups often target their actions to inflict the most casualties and may choose mass gatherings to detonate an explosive device. Since EMS providers are frequently assigned to work special details where large numbers of people may gather, EMTs and paramedics can assist law enforcement in identifying individuals who may pose a threat to the people gathered at the event. The characteristics of suicide bombers discussed here are meant to increase your awareness level to recognize a potential problem. The astute EMS provider can then notify appropriate law enforcement personnel for further investigation and action.

Geriatrics and their meds: problems and perils.

The EMS provider often encounters the elderly patient at home, where a comprehensive medication history can be obtained. Because of the aging process, the older patient may not be able to tolerate drug therapy as well as a younger adult. When obtaining a medication history, look and ask for detailed information, including the use of dietary and herbal supplements, especially if the signs and symptoms do not match existing or known conditions. The astute EMT or paramedic may be able to recognize drug-induced illness and alert the emergency department physician. Early intervention may save the elderly patient's life.

Impact of practice arrangements on physicians' satisfaction.

This research examines the effect of practice arrangements on five dimensions of physicians' satisfaction (i.e., personal factors, resources, peer review, profession, and state regulations) and the moderating effect of job autonomy and decision making on this relationship. This research finds that physicians who work for HMOs and hospitals are more satisfied with job resources, regulatory climate, and their professions, compared with physicians who are self-employed (solo and group practices). Physicians who work for HMOs and hospitals have less autonomy and decision-making power, compared with self-employed physicians. Also, job autonomy partially moderates the relationship between organizational arrangement and physicians' satisfaction with job resources and satisfaction with the profession. Decision making does not moderate the organizational arrangement and physicians' satisfaction relationship.

How does your garden grow? Herbal remedíes EMS may encounter.

Millions of dollars are spent annually on over-the-counter herbal remedies. While most of these self-administered cures are benign, some may pose a problem for EMS professionals, either through inherent adverse effects or interactions with prescription medications. This article has highlighted several of the more popular herbal remedies and given brief information about the typical problems that EMTs and paramedics may encounter in the field.