Recent developments in asymmetric cyclopropanation

I am really glad to have this opportunity to write to you, specially about a subject in which I have worked for half a century. When I was your age, if somebody had told me that I would be working in chemistry of materials most of my life, I would not have believed it. At that time, chemistry of materials meant studying something about cement, steel, sand and asbestos. It was indeed dull. I never didwell in school and college exams on questions related to this subject. Much later in my life, I got greatly interested in the subject for various reasons. First, inmy study of chemistry, I was influenced by Linus Pauling who ismy academic grandfather. His book titled ‘Nature of the Chemical Bond’ which I read when I was young made a great impression. It taught me how the structure of molecules and materials is an extremely important aspect of chemistry, and how the understanding of structure and bonding provides a basis to understand chemistry and to do new chemistry. It is because of this terrific inspiration that I started studying chemistry. It was clear at the end of my undergraduate career that I wanted to be a chemist.

Chemistry of materials

Brucellosis is an endemic zoonotic disease in most of the developing world that causes devastating losses to the livestock industry and small-scale livestock holders. Infected animals exhibit clinical signs that are of economic significance to stakeholders and include reduced fertility, abortion, poor weight gain, lost draught power, and a substantial decline in milk production. In humans, brucellosis typically manifests as a variety of non-specific clinical signs. Chronicity and recurring febrile conditions, as well as devastating complications in pregnant women are common sequelae. In regions where the disease is endemic, brucellosis has far-reaching and deleterious effects on humans and animals alike. Deeply entrenched social misconceptions and fear of government intervention contribute to this disease continuing to smolder unchecked in most of the developing world, thereby limiting economic growth and inhibiting access to international markets. The losses in livestock productivity compromise food security and lead to shifts in the cognitive competency of the working generation, influence the propagation of gender inequality, and cause profound emotional suffering in farmers whose herds are affected. The acute and chronic symptoms of the disease in humans can result in a significant loss of workdays and a decline in the socioeconomic status of infected persons and their families from the associated loss of income. The burden of the disease to society includes significant human healthcare costs for diagnosis and treatment, and non-healthcare costs such as public education efforts to reduce disease transmission. Brucellosis places significant burdens on the human healthcare system and limits the economic growth of individuals, communities, and nations where such development is especially important to diminish the prevalence of poverty. The implementation of public policy focused on mitigating the socioeconomic effects of brucellosis in human and animal populations is desperately needed. When developing a plan to mitigate the associated consequences, it is vital to consider both the abstract and quantifiable effects. This requires an interdisciplinary and collaborative, or One Health, approach that consists of public education, the development of an infrastructure for disease surveillance and reporting in both veterinary and medical fields, and campaigns for control in livestock and wildlife species.

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Brucellosis remains a neglected disease in the developing world: a call for interdisciplinary action

Nitrogen adsorption/desorption isotherms are used to investigate the Brunauer, Emmett, and Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) pore size distribution of physically modified, thermally annealed, and octadecanethiol functionalized np-Au monoliths. We present the full adsorption-desorption isotherms for N2 gas on np-Au, and observe type IV isotherms and type H1 hysteresis loops. The evolution of the np-Au under various thermal annealing treatments was examined using scanning electron microscopy (SEM). The images of both the exterior and interior of the thermally annealed np-Au show that the porosity of all free standing np-Au structures decreases as the heat treatment temperature increases. The modification of the np-Au surface with a self-assembled monolayer (SAM) of C18-SH (coverage of 2.94 × 1014 molecules cm−2 based from the decomposition of the C18-SH using thermogravimetric analysis (TGA)), was found to reduce the strength of the interaction of nitrogen gas with the np-Au surface, as reflected by a decrease in the ‘C’ parameter of the BET equation. From cyclic voltammetry studies, we found that the surface area of the np-Au monoliths annealed at elevated temperatures followed the same trend with annealing temperature as found in the BET surface area study and SEM morphology characterization. The study highlights the ability to control free-standing nanoporous gold monoliths with high surface area, and well-defined, tunable pore morphology.

Surface area and pore size characteristics of nanoporous gold subjected to thermal, mechanical, or surface modification studied using gas adsorption isotherms, cyclic voltammetry, thermogravimetric analysis, and scanning electron microscopy

Nanoporous gold with networks of interconnected ligaments and highly porous structure holds stimulating technological implications in fuel cell catalysis. Current syntheses of nanoporous gold mainly revolve around de-alloying approaches that are generally limited by stringent and harsh multistep protocols. Here we develop a one-step solution phase synthesis of zero-dimensional hollow nanoporous gold nanoparticles with tunable particle size (150-1,000 nm) and ligament thickness (21-54 nm). With faster mass diffusivity, excellent specific electroactive surface area and large density of highly active surface sites, our zero-dimensional nanoporous gold nanoparticles exhibit ~1.4 times enhanced catalytic activity and improved tolerance towards carbonaceous species, demonstrating their superiority over conventional nanoporous gold sheets. Detailed mechanistic study also reveals the crucial heteroepitaxial growth of gold on the surface of silver chloride templates, implying that our synthetic protocol is generic and may be extended to the synthesis of other nanoporous metals via different templates.

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One-step synthesis of zero-dimensional hollow nanoporous gold nanoparticles with enhanced methanol electrooxidation performance

HPLC-Assisted Automated Oligosaccharide Synthesis

A new route to synthesize septanoside derivatives from protected 2-hydroxyglycals is reported. Ring expansion of a pyranoside to a septanoside was achieved through key reactions of a cyclopropanation, ring opening, oxidation, and reduction. Methyl septanoside derivatives, namely, methyl \alpha-D-glycero-Dtalo- septanoside and methyl \alpha-D-glycero-L-altro-septanoside, were synthesized in an overall yield of 35% and 46%, respectively, from the corresponding protected 2-hydroxy glycals.

Synthesis of septanosides through an oxyglycal route.

Nanoporous gold (NPG), made by dealloying low carat gold alloys, is a relatively new nanomaterial finding application in catalysis, sensing, and as a support for biomolecules. NPG has attracted considerable interest due to its open bicontinuous structure, high surface-to-volume ratio, tunable porosity, chemical stability and biocompatibility. NPG also has the attractive feature of being able to be modified by self-assembled monolayers. Here we use scanning electron microscopy (SEM) and atomic force microscopy (AFM) to characterize a highly efficient approach for protein immobilization on NPG using N-hydroxysuccinimide (NHS) ester functionalized self-assembled monolayers on NPG with pore sizes in the range of tens of nanometres. Comparison of coupling under static versus flow conditions suggests that BSA (Bovine Serum Albumin) and IgG (Immunoglobulin G) can only be immobilized onto the interior surfaces of free standing NPG monoliths with good coverage under flow conditions. AFM is used to examine protein coverage on both the exterior and interior of protein modified NPG. Access to the interior surface of NPG for AFM imaging is achieved using a special procedure for cleaving NPG. AFM is also used to examine BSA immobilized on rough gold surfaces as a comparative study. In principle, the general approach described should be applicable to many enzymes, proteins and protein complexes since both pore sizes and functional groups present on the NPG surfaces are controllable.

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Characterization of protein immobilization on nanoporous gold using atomic force microscopy and scanning electron microscopy.

A ring-expansion methodology for the preparation of aryl septanosides, arabinofuranosyl and glucopyranosyl septanoside disaccharides, and azido septanosides is reported. A cyclopropanated adduct Of the oxyglycal upon reaction with phenols, sugars, and azide led to the formation of ring-expanded septanoside derivatives. The ring expansion was found to be stereoselective with sugars, whereas phenols and the azide afforded an anomeric mixture of the ring expanded product. It was observed further that the conversion of the intermediate diketones to the diols, using NaBH4, occurred with high diastereoselectivities for the alpha-anomers of the septanosides. This report consolidates further the generality of the oxyglycal ring-expansion method to prepare septanosides, possessing different substituents at their reducing ends.

N. Vijaya Ganesh

Papers

Surface area and pore size characteristics of nanoporous gold subjected to thermal, mechanical, or surface modification studied using gas adsorption isotherms, cyclic voltammetry, thermogravimetric analysis, and scanning electron microscopy

HPLC-Assisted Automated Oligosaccharide Synthesis

Synthesis of septanosides through an oxyglycal route.

Characterization of protein immobilization on nanoporous gold using atomic force microscopy and scanning electron microscopy.

Synthesis of Aryl, Glycosyl, and Azido Septanosides through Ring Expansion of 1,2-Cyclopropanated Sugars