Why is thiol unexpectedly less reactive but more selective than alcohol in phenanthroline-catalyzed 1,2-- and -furanosylations?

The lack of catalytic stereoselective approaches for producing 1,2--furanosides emphasizes the critical need for further research in this area. Herein, we present a stereoselective -furanosylation method, utilizing a 4,7-dipiperidine-substituted phenanthroline catalyst. This developed protocol fills a gap in the field, enabling the coupling of cysteine residues and thiols with furanosyl bromide electrophiles.

Highly stereoselective synthesis of α-glycosylated carboxylic acids by phenanthroline catalysis.

Carbohydrate molecules with an α-glycosylated carboxylic acid motif provide access to biologically relevant chemical space but are difficult to synthesize with high selectivity. To address this challenge, we report a mild and operationally simple protocol to synthesize a wide range of functionally and structurally diverse α-glycosylated carboxylic acids in good yields with high diastereoselectivity. Although there is no apparent correlation between reaction conversion and p of carboxylic acids, we found that carboxylic acids with a p of 4-5 provide high selectivity while those of a p of 2.

Reducing the Cost of TD-CI Simulations of Strong Field Ionization.

Strong field ionization of molecules by intense laser pulses can be simulated by time-dependent configuration interaction (TD-CI) with a complex absorbing potential (CAP). Standard molecular basis sets need to be augmented with several sets of diffuse functions for effective interaction with the CAP. This dramatically increases the number of configurations and the cost of the TD-CI simulations as the size of the molecules increases.

Rare Events Sampling Methods for Quantum and Classical Ab Initio Molecular Dynamics.

We provide an approach to sample rare events during classical ab initio molecular dynamics and quantum wavepacket dynamics. For classical AIMD, a set of fictitious degrees of freedom are introduced that may harmonically interact with the electronic and nuclear degrees of freedom to steer the dynamics in a conservative fashion toward energetically forbidden regions. A similar approach when introduced for quantum wavepacket dynamics has the effect of biasing the trajectory of the wavepacket centroid toward the regions of the potential surface that are difficult to sample.

Mechanism of the Sharpless Epoxidation Reaction: A DFT Study.

The Sharpless reaction is an enantioselective epoxidation of prochiral allylic alcohols that employs a Ti(IV) catalyst formed from titanium tetra(isopropoxide), Ti(O--Pr), diethyl tartrate (DET), and the oxidizing agent -butyl hydroperoxide. The M06-2X DFT functional with the 6-311+G(d,p) basis set has been employed to model the structures and energetics of the Sharpless epoxidation reaction. The monomeric tetracoordinate titanium(IV) diethyltartrate is thermodynamically strongly favored to dimerize, producing a pentacoordinate catalyst, [Ti(DET)(O-i-Pr)], that is a more reactive chiral epoxidation catalyst.

Scope and Mechanistic Probe into Asymmetric Synthesis of α-Trisubstituted-α-Tertiary Amines by Rhodium Catalysis.

Asymmetric reactions that convert racemic mixtures into enantioenriched amines are of significant importance due to the prevalence of amines in pharmaceuticals, with about 60% of drug candidates containing tertiary amines. Although transition-metal catalyzed allylic substitution processes have been developed to provide access to enantioenriched α-disubstituted allylic amines, enantioselective synthesis of sterically demanding α-tertiary amines with a tetrasubstituted carbon stereocenter remains a major challenge. Herein, we report a chiral diene-ligated rhodium-catalyzed asymmetric substitution of racemic tertiary allylic trichloroacetimidates with aliphatic secondary amines to afford α-trisubstituted-α-tertiary amines.

Charge Migration in HCCI Cations Probed by Strong Field Ionization: Time-Dependent Configuration Interaction and Vibrational Wavepacket Simulations.

Strong field ionization of neutral iodoacetylene (HCCI) can produce a coherent superposition of the X and A cations and results in charge migration between the CC π orbital and the iodine π-type lone pair. This charge migration causes oscillations in the rate of strong field ionization of the cation to the dication that can be monitored using intense few-cycle probe pulses. The dynamics and strong field ionization of the coherent superposition the X and A states of HCCI have been modeled by time-dependent configuration interaction (TDCI) simulations.

Stereoselective glycosylation reactions with 2-deoxyglucose: a computational study of some catalysts.

2-Deoxy glycosides are important components of many oligosaccharides with antibiotic and anti-cancer activity, but their synthesis can be very challenging. Phenanthrolines and substituted pyridines promote stereoselective glycosylation of 1-bromo sugars via a double S2 mechanism. Pyridine reacting with α-bromo, 2-deoxyglucose was chosen to model this reaction.

Calculated p Values for a Series of Aza- and Deaza-Modified Nucleobases.

A variety of synthetic modified nucleobases have been used to investigate the structure and function of RNA and DNA or act as enzyme inhibitors. A set of these modifications involves the addition or removal of a nitrogen atom in the ring. These aza and deaza modifications have garnered interest as useful biochemical tools, but information on some of their physical characteristics is lacking.

Attosecond Imaging of Electronic Wave Packets.

An electronic wave packet has significant spatial evolution besides its temporal evolution, due to the delocalized nature of composing electronic states. The spatial evolution was not previously accessible to experimental investigations at the attosecond timescale. A phase-resolved two-electron-angular-streaking method is developed to image the shape of the hole density of an ultrafast spin-orbit wave packet in the krypton cation.

A bioinspired cobalt catalyst based on a tripodal imidazole/pyridine platform capable of water reduction and oxidation.

The prototypical drug carrier [Co(L)Cl]PF (1), where L is a tripodal amine bound to pyridine and methyl-imidazoles, had its electrocatalytic water splitting activity studied under different pH conditions. This species contains a high-spin 3d Co metal center, and is capable of generating both H from water reduction and O from water oxidation Turnover numbers reach 390 after 3 h for water reduction. Initial water oxidation activity is molecular, with TONs of 71 at pH 7 and 103 at pH 11.

Inertial Sensor-Based Sport Activity Advisory System Using Machine Learning Algorithms.

The aim of this study was to develop a physical activity advisory system supporting the correct implementation of sport exercises using inertial sensors and machine learning algorithms. Specifically, three mobile sensors (tags), six stationary anchors and a system-controlling server (gateway) were employed for 15 scenarios of the series of subsequent activities, namely squats, pull-ups and dips. The proposed solution consists of two modules: an activity recognition module (ARM) and a repetition-counting module (RCM).

Carrier-Envelope Phase Controlling of Ion Momentum Distributions in Strong Field Double Ionization of Methyl Iodide.

In strong field ionization of methyl iodide initiated by elliptically polarized few-cycle pulses, a significant correlation was observed between the carrier-envelope phases (CEPs) of the laser and the preferred ejection direction of methyl cation arising from dissociative double ionization. This was attributed to the carrier-envelope phase dependent double ionization yields of methyl iodide. This observation provides a new way for monitoring the absolute CEPs of few-cycle pulses by observing the ion momentum distributions.

Ionization of HCCI Neutral and Cations by Strong Laser Fields Simulated With Time Dependent Configuration Interaction.

Strong field ionization of neutral iodoacetylene (HCCI) can produce a coherent superposition of the X and A cations. This superposition results in charge migration between the CC orbital and the iodine -type lone pair which can be monitored by strong field ionization with short, intense probe pulses. Strong field ionization of the X and A states of HCCI cation was simulated with time-dependent configuration interaction using singly ionized configurations and singly excited, singly ionized configurations (TD-CISD-IP) and an absorbing boundary.

Stereoselective 1,2- Furanosylations Catalyzed by Phenanthroline.

Stereoselective formation of the 1,2- furanosidic linkage, a motif of many biologically relevant oligosaccharides and polysaccharides, remains an important synthetic challenge. We herein report a new stereoselective 1,2- furanosylation method promoted by phenanthroline catalysts under mild and operationally simple conditions. NMR experiments and density functional theory calculations support an associative mechanism in which the rate-determining step occurs from an inverted displacement of the faster-reacting phenanthrolinium ion intermediate with an alcohol nucleophile.

Distinct Bimetallic Cooperativity Among Water Reduction Catalysts Containing [Co Co ], [Ni Ni ], and [Zn Zn ] Cores.

Three binuclear species [LCo (μ-Pz) ](ClO ) (1), [LNi (CH OH) Cl ]ClO (2), and [LZn Cl ]PF (3) supported by the deprotonated form of the ligand 2,6-bis[bis(2-pyridylmethyl) amino-methyl]-4-methylphenol were synthesized, structurally characterized as solids and in solution, and had their electrochemical and spectroscopic behavior established. Species 1-3 had their water reduction ability studied aiming to interrogate the possible cooperative catalytic activity between two neighboring metal centers. Species 1 and 2 reduced H O to H effectively at an applied potential of -1.

Calculations of p Values for a Series of Naturally Occurring Modified Nucleobases.

Modified nucleobases are found in functionally important regions of RNA and are often responsible for essential structural roles. Many of these nucleobase modifications are dynamically regulated in nature, with each modification having a different biological role in RNA. Despite the high abundance of modifications, many of their characteristics are still poorly understood.

Mechanism of Orbital Interactions in the Sharpless Epoxidation with Ti(IV) Peroxides: A DFT Study.

The M06-2X DFT functional has been employed to examine monomeric titanium(IV) hydroperoxo catalysts that model the individual steps in the dimeric titanium(IV)-catalyzed Sharpless reaction. This is the first example of a transition structure for titanium(IV) -butyl hydroperoxide-catalyzed epoxidation that describes the molecular motion required for oxygen atom transfer. These epoxidation catalysts have been examined for both bimolecular reactions with E-2-butene and the intramolecular epoxidation of allyl alcohol.

Ellipticity controlled dissociative double ionization of ethane by strong fields.

The yields of all dissociation channels of ethane dications produced by strong field double ionization were measured. It was found that the branching ratios can be controlled by varying the ellipticity of laser pulses. The CH formation and H formation channels show a clear competition, producing the highest and lowest branching ratios at ellipticity of ∼0.

Ab Initio Direct Dynamics.

The reactivity and dynamics of molecular systems can be explored computationally by classical trajectory calculations. The traditional approach involves fitting a functional form of a potential energy surface (PES) to the energies from a large number of electronic structure calculations and then integrating numerous trajectories on this fitted PES to model the molecular dynamics. The ever-decreasing cost of computing and continuing advances in computational chemistry software have made it possible to use electronic structure calculations directly in molecular dynamics simulations without first having to construct a fitted PES.

Sequential double ionization of molecules by strong laser fields simulated with time-dependent configuration interaction.

A new time-dependent configuration interaction method has been developed for simulating strong field sequential double ionization of molecular systems. Ionization of the neutral is simulated by time-dependent configuration interaction with single excitations (TD-CIS) and an absorbing boundary. At each time step, the ionized part of the wavefunction from the TD-CIS calculation is transferred to a second time-dependent configuration interaction simulation for ionization of the cation to the dication.

Alkyl Radical-Free Cu(I) Photocatalytic Cross-Coupling: A Theoretical Study of Anomerically Specific Photocatalyzed Glycosylation of Pyranosyl Bromide.

Previously, we reported a visible light-activated Cu(I) photocatalyst capable of facilitating C-O bond formation of glycosyl bromides and aliphatic alcohols with a high degree of diastereoselectivity. This catalyst functions equally well in the presence of radical traps, suggesting an entirely inner sphere mechanism atypical for heteroleptic Cu photocatalysis. Further, experimental estimates put the chromophore reducing power at -1.