Synthesis of Boc-protected 4,5-methano-β-proline

An efficient method for the preparation of Boc-protected 4,5-methano-β-proline—a novel bicyclic cyclopropane-containing β-amino acid—was developed, starting from readily available itaconic acid. A modified Simmons–Smith reaction was used for the construction of the cyclopropane ring. The method allowed for the synthesis of both cis and trans isomers of the title compound in 49% total yield and can be employed for gram-scale preparations. An approach to the preparation of methyl 5-oxopyrrolidine-3-carboxylate, which is one of the key intermediates in the synthetic scheme, on a multigram scale was also developed.     

On the Ultrafilter Semigroup of a Topological Group

The ultrafilter semigroup Ult(G) of a topological group G consists of all nonprincipal ultrafilters on G converging to the identity and is a closed subsemigroup in the Stone-Cech compactification βG_d of G as a discrete semigroup. We show that it is consistent with ZFC that for every countable nondiscrete topological group G, Ult(G) can be partitioned into closed right ideals each of which admits a continuous homomorphism onto the Bohr compactification of the integers.     

Finite groups in Stone-Cech compactifications

Let be an infinite cardinal and let G = ₂. Now let β Gbe the Stone–ech compactification of G as a discrete semigroup,and let =_<c_{β G} {xG\{0}:minsupp (x)}. We show that thesemigroup contains no nontrivial finite group.     

The Rb7Bi3−3xSb3xCl16 Family: A Fully Inorganic Solid Solution with Room-Temperature Luminescent Members

Low-dimensional ns²-metal halide compounds have received immense attention for applications in solid-state lighting, optical thermometry and thermography, and scintillation. However, these are based primarily on the combination of organic cations with toxic Pb²⁺ or unstable Sn²⁺, and a stable inorganic luminescent material has yet to be found. Here, the zero-dimensional Rb₇Sb₃Cl₁₆ phase, comprised of isolated [SbCl₆]³⁻ octahedra and edge-sharing [Sb₂Cl₁₀]⁴⁻ dimers, shows room-temperature photoluminescence (RT PL) centered at 560 nm with a quantum yield of 3.8±0.2 % at 296 K (99.4 % at 77 K). The temperature-dependent PL lifetime rivals that of previous low-dimensional materials with a specific temperature sensitivity above 0.06 K⁻¹ at RT, making it an excellent thermometric material. Utilizing both DFT and chemical substitution with Bi³⁺ in the Rb₇Bi_3−3xSb_3xCl₁₆ (x≤1) family, we present the edge-shared [Sb₂Cl₁₀]⁴⁻ dimer as a design principle for Sb-based luminescent materials.     

Formyl MIDA Boronate: C1 Building Block Enables Straightforward Access to α-Functionalized Organoboron Derivatives

Formyl MIDA boronate has been known to be an elusive type of acylboronate that has not been obtained to date. In this work, an approach to the one-pot preparation and chemical transformations of formyl MIDA boronate were developed to provide new types of α-functionalized organoboron compounds. Among them are acylboronate reagents which present boron-substituted analogues of ynones and β-dicarbonyl compounds. The developed synthetic procedures, utilizing formyl MIDA boronate, are tolerant to diverse functional groups, making this reagent an advantageous C₁ building block for extending the scope of organoboron chemistry.     

Advective–diffusive mass transfer in binary regular structures in the steady-state regime

Having analyzed the stationary processes of admixture transfer in two-phase regular structures with taking into account periodical character of advective phenomena, we propose a method of constructing exact analytic solutions for such class of boundary value problems. This technique is based on the application of integral transformations individually for each contacting domain. The relation between these corresponding integral transformations is obtained from the nonideal boundary conditions. We have obtained the analytic solution of a diffusion problem for a two-phase layer of a regular structure with advective mass transfer mechanism in one of its phases. The expressions describing admixture flow through a certain body surface are derived, mass flows through the interface is investigated. Having analyzed the concentration of migrating particles in the structural elements of the body and the admixture flow through the given body surface, we present results graphically. The conditions of the existence of a limit passage from the contact boundary value problem of advective diffusion in regular structures to the continual model of advective two-way heterodiffusion are determined. A natural dimensionless form is introduced.     

Impact of Electrospinning Parameters and Post-Treatment Method on Antibacterial and Antibiofilm Activity of Chitosan Nanofibers

Chitosan, a natural biopolymer, is an ideal candidate to prepare biomaterials capable of preventing microbial infections due to its antibacterial properties. Electrospinning is a versatile method ideally suited to process biopolymers with minimal impact on their physicochemical properties. However, fabrication parameters and post-processing routine can affect biological activity and, therefore, must be well adjusted. In this study, nanofibrous membranes were prepared using trifluoroacetic acid and dichloromethane and evaluated for physiochemical and antimicrobial properties. The use of such biomaterials as potential antibacterial agents was extensively studied in vitro using Staphylococcus aureus and Escherichia coli as test organisms. The antibacterial assay showed inhibition of bacterial growth and eradication of the planktonic cells of both E. coli and S. aureus in the liquid medium for up to 6 hrs. The quantitative assay showed a significant reduction in bacteria cell viability by nanofibers depending on the method of fabrication. The antibacterial properties of these biomaterials can be attributed to the structural modifications provided by co-solvent formulation and application of post-treatment procedure. Consequently, the proposed antimicrobial surface modification method is a promising technique to prepare biomaterials designed to induce antimicrobial resistance via antiadhesive capability and the biocide-releasing mechanism.     

Exploring the Strength of the H‐Bond in Synthetic Models for Heme Proteins: The Importance of the N−H Acidity of the Distal Base

The distal hydrogen bond (H‐bond) in dioxygen‐binding proteins is crucial for the discrimination of O₂ with respect to CO or NO. We report the preparation and characterization of a series of Zn^II porphyrins, with one of three meso‐phenyl rings bearing both an alkyl‐tethered proximal imidazole ligand and a heterocyclic distal H‐bond donor connected by a rigid acetylene spacer. Previously, we had validated the corresponding Co^II complexes as synthetic model systems for dioxygen‐binding heme proteins and demonstrated the structural requirements for proper distal H‐bonding to Co^II‐bound dioxygen. Here, we systematically vary the H‐bond donor ability of the distal heterocycles, as predicted based on pK_a values. The H‐bond in the dioxygen adducts of the Co^II porphyrins was directly measured by Q‐band Davies‐ENDOR spectroscopy. It was shown that the strength of the hyperfine coupling between the dioxygen radical and the distal H‐atom increases with enhanced acidity of the H‐bond donor.