A molecular orbital rationalization of ligand effects in N2 activation

Molecular orbital theory has been used to study a series of [(micro-N2){ML3}2] complexes as models for dinitrogen activation, with M=Mo, Ta, W, Re and L=NH2, PH2, AsH2, SbH2 and N(BH2)2. The main aims of this study have been to provide a thorough electronic analysis of the complexes and to extend previous work involving molecular orbital analyses. Molecular orbital diagrams have been used to rationalize why for L=NH2 ligand rotation is important for the singlet state but not the triplet, to confirm the effect of ligand pi donation, and to rationalize the importance of the metal d-electron configuration. The outcomes of this study will assist with a more in-depth understanding of the electronic basis for N2 activation and allow clearer predictions to be made about the structure and multiplicity of systems involved in transition-metal catalysis.     

The adsorption of triethylenediamine on Al(2)O(3)-II: hydrogen bonding to Al-OH groups

The hydrogen bonding of the triethylenediamine (TEDA) molecule to isolated Al-OH groups on partially dehydroxylated high area gamma-Al(2)O(3) powder has been studied using transmission IR spectroscopy. It has been found that TEDA adsorbs both singly and as multiple species to single Al-OH groups in clearly separable equilibrium stages of adsorption at 300 K. The reversible adsorption of a single TEDA molecule to Al-OH fits the Langmuir adsorption isotherm well, and the enthalpy of adsorption is found to be -15.6 +/- 0.5 kJ mol(-1) in the range of fractional coverage of 0.5-0.6. Red shifts of the Al-OH frequency from approximately -200 cm(-1) to approximately -1000 cm(-1) are observed as a result of -OH bonding to the N lone pair in the TEDA molecule.     

Allylic amidation. An investigation of nitrosocarbonylmethane for direct allylic functionalization of olefins

Nitrosocarbonylmethane reacts with a variety of olefins $\text{via}$ an ene pathway, yielding N-substituted hydroxamic acid products in a preparatively useful reaction. With unsymmetrical olefins, observed regiochemical preferences can be rationalized by a mechanism involving electrophilic addition of nitrogen to the olefin.     

Scission of Carbon Monoxide Using TaR3, R=(N(tBu)Ph) or OSi(tBu)3: A DFT Investigation

The experimentally known reduction of carbon monoxide using a 3‐coordinate [Ta(silox)₃] (silox=OSi(tBu)₃) complex initially forms a ketenylidene [(silox)₃Ta? CCO], followed by a dicarbide [(silox)₃Ta? CC? Ta(silox)₃] structure. The mechanism for this intricate reaction has finally been revealed by using density functional theory, and importantly a likely structure for the previously unknown intermediate [(silox)₃Ta? CO]₂ has been identified. The analysis of the reaction pathway and the numerous intermediates has also uncovered an interesting pattern that results in CO cleavage, that being scission from a structure of the general form [(silox)₃Ta? C_nO] in which n is even. When n is odd, cleavage cannot occur. The mechanism has been extended to consider the effect of altering both the metal species and the ligand environment. Specifically, we predict that introducing electron‐rich metals to the right of Ta in the periodic table to create mixed‐metal dinuclear intermediates shows great promise, as does the ligand environment of the Cummins‐style 3‐coordinate amide structure. This latter environment has the added complexity of improved electron donation from amide rotation that can significantly increase the reaction exothermicity.     

On the first excited state of137Ba

The first excited state of¹³⁷Ba has been excited by the inelastic scattering of accelerator-produced neutrons. The energy of this state at 283.5 keV is not in agreement with the generally accepted value of 279.2 keV, but is in accord with other recent measurements. No evidence for a doublet of states near this energy is found.     

Reducing the computational cost of NMR crystallography of organic powders at natural isotopic abundance with the help of 13C-13C dipolar couplings

Structure determination of functional organic compounds remains a formidable challenge when the sample exists as a powder. Nuclear magnetic resonance crystallography approaches based on the comparison of experimental and Density Functional Theory (DFT)-computed ¹H chemical shifts have already demonstrated great potential for structure determination of organic powders, but limitations still persist. In this study, we discuss the possibility of using ¹³C-¹³C dipolar couplings quantified on powdered theophylline at natural isotopic abundance with the help of dynamic nuclear polarization, to realize a DFT-free, rapid screening of a pool of structures predicted by ab initio random structure search. We show that although ¹³C-¹³C dipolar couplings can identify structures possessing long range structural motifs and unit cell parameters close to those of the true structure, it must be complemented with other data to recover information about the presence and the chemical nature of the supramolecular interactions.     

Dual Gold‐Catalyzed Cycloaromatization of Unconjugated (E)‐Enediynes

A synthesis of unconjugated (E)‐enediynes from allenyl amino alcohols is reported and their gold‐catalyzed cascade cycloaromatization to a broad range of enantioenriched substituted isoindolinones has been developed. Experimental and computational studies support the reaction proceeding via a dual‐gold σ,π‐activation mode, involving a key gold‐vinylidene‐ and allenyl‐gold‐containing intermediate.     

Immobilization of a sulfide-oxidizing bacterium in a novel adsorbent biocatalyst support

Applied Biochemistry and Biotechnology - Preliminary experiments have shown thatT. denitrificans strain F can be immobilized in DuPont BIO-SEP beads and used to treat refinery spent sulfidic...     

Evidence for Multiple Binding Modes in the Initial Contact Between SARS-CoV-2 Spike S1 Protein and Cell Surface Glycans**

Infection of host cells by SARS-CoV-2 begins with recognition by the virus S (spike) protein of cell surface heparan sulfate (HS), tethering the virus to the extracellular matrix environment, and causing the subunit S1-RBD to undergo a conformational change into the ‘open’ conformation. These two events promote the binding of S1-RBD to the angiotensin converting enzyme 2 (ACE2) receptor, a preliminary step toward viral-cell membrane fusion. Combining ligand-based NMR spectroscopy with molecular dynamics, oligosaccharide analogues were used to explore the interactions between S1-RBD of SARS CoV-2 and HS, revealing several low-specificity binding modes and previously unidentified potential sites for the binding of extended HS polysaccharide chains. The evidence for multiple binding modes also suggest that highly specific inhibitors will not be optimal against protein S but, rather, diverse HS-based structures, characterized by high affinity and including multi-valent compounds, may be required.