Stereoselectivity Control Interplay in Racemic Lactide Polymerization by Achiral Al-Salen Complexes.

The origin of stereocontrol in ring opening polymerization (ROP) of racemic lactide (rac-LA) promoted by achiral aluminium-based catalysts has been explained through DFT calculations combined with a molecular descriptor (%V) and the activation strain model (ASM-NEDA) analysis. The proposed chain end control (CEC) model suggests that the ligand framework adopts a chiral configuration mimicking the enantiomorphic site control (ESC) while also incorporating control of the last inserted monomer unit. It is found that the ligand wrapping mode around the aluminium centre is dictated by the monomer configuration (R,R-LA and S,S-LA).

Synthesis of pyrrolo[2,3-]pyridazines and pyrrolo[2,3-]pyridines (6-azaindoles). Experimental and theoretical study.

A new synthetic route towards 6-azaindoles (pyrrolo[2,3-]pyridines) and pyrrolo[2,3-]pyridazines starting from 4-aroyl pyrroles is described. This overall protocol involves: (i) the Vilsmeier-Haack reaction to obtain pyrrolo-2,3-dicarbonyles and (ii) condensation with hydrazines or glycine methyl ester. The reaction mechanism between pyrrolo-2,3-dicarbonyl with phenyl hydrazine and glycine methyl ester has been modelled using DFT calculations to prove the formation of one from two possible isomers of condensation.

Mechanistic insights on 1-butene polymerization catalyzed by homogeneous single-site catalysts: a DFT computational study.

Isotactic poly (1-butene) (iPB) is an interesting semi-crystalline thermoplastic material characterized by notable physical and mechanical attributes encompassing superior creep and stress resistance, elevated toughness, stiffness, and thermal endurance. These distinctive features position iPB as a viable candidate for specific applications; however, its widespread utilization is hindered by certain inherent limitations. Indeed, iPB manifests an intricate polymorphic behavior, and the gradual and spontaneous transition of the kinetically favored form II to the thermodynamically favored form I during aging introduces alterations to the material's properties.

Combining Cyclic Units and Unsaturated Pendant Groups by Propene/1,5-Hexadiene Copolymerization Toward Functional Isotactic Polypropylene.

The precise use of a widely available and inexpensive metallocene catalyst enabled the synthesis of isotactic polypropylene copolymers characterized by the copresence of randomly distributed cyclic units in the backbone and unsaturated pendant units employing 1,5-hexadiene as comonomer. Optimization of the polymerization conditions avoided the cross-linking phenomena that negatively affects the material processing and final properties, resulting in good yields of samples featuring high molecular masses and a precisely controlled microstructure. Such polypropylene-based copolymers exhibit a broad spectrum of properties ranging from thermoplastic to surprising elastomeric behavior, with the additional value of being functionalizable by post-polymerization reactions.

Revisiting Stereoselective Propene Polymerization Mechanisms: Insights through the Activation Strain Model.

The stereoelectronic factors responsible for stereoselectivity in propene polymerization with several metallocene and post-metallocene transition metal catalysts have been revisited using a combined approach of DFT calculations, the Activation Strain Model, Natural Energy Decomposition Analysis and a molecular descriptor (%V). There are in most cases two different paths leading to the formation of stereoerrors (SE), and the classical model does not suffice to fully understand stereoregulation. Improving stereoselectivity requires raising the energies of both SE insertion transition states.

Predicting the propene stereoselectivity on transition metal catalysts: A daunting task for density functional theory.

Thanks to recent developments in hardware and software, quantum chemical methods are increasingly used for interpreting the complex mechanisms underlying polymerization reaction by homogeneous catalysis. Unfortunately, the dimensions of even the smallest realistic models are too large to permit the use of state-of-the-art composite wave function methods. Under these circumstances, density functional theory still offers the best compromise between cost and accuracy.

Ring Opening Polymerization of Six- and Eight-Membered Racemic Cyclic Esters for Biodegradable Materials.

The low percentage of recyclability of the polymeric materials obtained by olefin transition metal (TM) polymerization catalysis has increased the interest in their substitution with more eco-friendly materials with reliable physical and mechanical properties. Among the variety of known biodegradable polymers, linear aliphatic polyesters produced by ring-opening polymerization (ROP) of cyclic esters occupy a prominent position. The polymer properties are highly dependent on the macromolecule microstructure, and the control of stereoselectivity is necessary for providing materials with precise and finely tuned properties.

Mechanism of Alternating Poly(lactic--glycolic acid) Formation by Polymerization of ()- and ()-3-Methyl Glycolide Using an Enantiopure Aluminum Complex.

The mechanism(s) of alternating PLGA synthesis by ring-opening polymerization of ()- and ()-3-methyl glycolide promoted by enantiopure aluminum complexes have been rationalized by density functional theory (DFT) calculations. The high regioselectivity of the ()-MeG polymerization is obtained by repetitive ring opening at the glycolyl site by the ()-catalyst whereas a lower regioselectivity is predicted by the ROP of ()-MeG. The behavior of the two monomers is rationalized by unveiling the active site fluxionality of the enantiopure catalyst, identifying the rate-limiting steps that encode a preference at the glycolyl site versus the lactyl site, and revealing selection of the opposite monomer enantioface.

A Computational Evaluation of the Steric and Electronic Contributions in Stereoselective Olefin Polymerization with Pyridylamido-Type Catalysts.

A density functional theory (DFT) study combined with the steric maps of buried volume (%) as molecular descriptors and an energy decomposition analysis through the ASM (activation strain model)-NEDA (natural energy decomposition analysis) approach were applied to investigate the origins of stereoselectivity for propene polymerization promoted by pyridylamido-type nonmetallocene systems. The relationships between the fine tuning of the ligand and the propene stereoregularity were rationalized (e.g.

Calcified coronary lesions.

The treatment of calcific coronary lesions is still a major interventional issue in haemodynamics laboratories. The prevalence of the disease is even increasing, considering the general ageing of the population undergoing coronarography, as well as the often associated comorbidities. In recent years, new devices have been developed that allow both better identification and also better treatment of these lesions.

Crystallization Behavior of Isotactic Propene-Octene Random Copolymers.

The crystallization behavior of random propene-octene isotactic copolymers (iPPC8) prepared with a homogeneous metallocene catalyst has been studied. Samples of iPPC8 with low octene content up to about 7 mol% were isothermally crystallized from the melt at various crystallization temperatures. The samples crystallize in mixtures of the α and γ forms of isotactic polypropylene (iPP).

Design of the PERSEO Registry on the management of patients treated with oral anticoagulants and coronary stent.

Aim: Percutaneous coronary intervention with stent implantation (PCI-S) in patients requiring chronic oral anticoagulant therapy (OAC) is associated with an increased risk of bleeding and ischemic complications. Different randomized studies showed a significant advantage of a double antithrombotic therapy and superiority of direct oral anticoagulant (DOAC) compared with warfarin, but real-world data are limited. Aim is to evaluate the antithrombotic management and clinical outcome of patients with an indication for OAC who undergo PCI-S in a 'real-world' setting.

Melt-Crystallizations of α and γ Forms of Isotactic Polypropylene in Propene-Butene Copolymers.

Random isotactic propene-butene copolymers (iPPC4) of different stereoregularity have been synthesized with three different homogeneous single center metallocene catalysts having different stereoselectivity. All samples crystallize from the polymerization solution in mixtures of α and γ forms, and the relative amount of γ form increases with increasing concentrations of butene and of stereodefects. All samples crystallize from the melt in mixtures of α and γ forms and the fraction of γ form increases with decreasing cooling rate.

Unconventional Stereoerror Formation Mechanisms in Nonmetallocene Propene Polymerization Systems Revealed by DFT Calculations.

An unconventional mechanism for the stereoerror formation in propene polymerization catalyzed by -symmetric salalen-M systems (M = Zr, Hf) is suggested by DFT calculations. While propagation happens with the ligand in its conformation, a change of ligand wrapping mode from to is the main source of the lower stereoselectivities obtained with Zr and Hf. This is different for the Ti analogues, where the ligand - wrapping mode does not play a role.

Synthesis and antiviral properties of biomimetic iminosugar-based nucleosides.

Herein we report the synthesis, conformational analysis and the evaluation of the antiviral activity of six-membered nucleoside analogues having a piperidine ring as the preorganized (deoxy)ribose bioisostere. Mutagenic nucleobase-containing nucleosides 1 and 2 were obtained by appropriate manipulation of the well-known glycomimetic agent deoxynojirimycin as easily accessible starting material. In vitro assays revealed activity of 5-iododeoxyuridine analogue 1 against all DNA viruses tested.

Ring-Opening Polymerization of -Lactide Catalyzed by Potassium-Based Complexes: Mechanistic Studies.

Two non-toxic potassium compounds, and , with a commercial oximate ligand have been prepared and fully spectroscopically characterized. Their activity as catalysts for the ring-opening polymerization (ROP) process of LLA has been studied, showing that they are extremely active and able to polymerize the monomer in a few minutes. For derivative , the presence of a crown ether in the potassium coordination sphere affects the nuclearity of the compound and consequently its solubility, with both aspects having an influence in the polymerization process.

Modeling the spectral properties of poly(x-phenylenediamine) conducting polymers using a combined TD-DFT and electrostatic embedding approach.

The absorption spectra of polymers derived from ortho, meta and para phenylenediamines (o-PDA, m-PDA and p-PDA) have been simulated combining periodic density functional theory (DFT) calculations with time-dependent DFT simulations. These latter have been carried out on finite clusters embedded in a set of point charges devised to exactly reproduce the electrostatic potential of the periodic chains. The results are compared with those obtained for solvated o-PDA, m-PDA and p-PDA oligomers of increasing sizes extracted from the periodic structures.

Structure and Morphology of Crystalline Syndiotactic Polypropylene-Polyethylene Block Copolymers.

A study of the structure and morphology of diblock copolymers composed of crystallizable blocks of polyethylene (PE) and syndiotactic polypropylene (sPP) having different lengths is reported. In both analyzed samples, the PE block crystallizes first by cooling from the melt (at 130 °C) and the sPP block crystallizes after at a lower temperature. Small angle X-ray scattering (SAXS) recorded during cooling showed three correlation peaks at values of the scattering vector, = 0.

Double Crystallization and Phase Separation in Polyethylene-Syndiotactic Polypropylene Di-Block Copolymers.

Crystallization and phase separation in the melt in semicrystalline block copolymers (BCPs) compete in defining the final solid state structure and morphology. In crystalline-crystalline di-block copolymers the sequence of crystallization of the two blocks plays a definitive role. In this work we show that the use of epitaxial crystallization on selected crystalline substrates allows achieving of a control over the crystallization of the blocks by inducing crystal orientations of the different crystalline phases and a final control over the global morphology.

Mechanistic Aspects of the Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling Reaction.

The story of C-C bond formation includes several reactions, and surely Suzuki-Miyaura is among the most outstanding ones. Herein, a brief historical overview of insights regarding the reaction mechanism is provided. In particular, the formation of the catalytically active species is probably the main concern, thus the preactivation is in competition with, or even assumes the role of the rate determining step (rds) of the overall reaction.

Syndiotactic PLA from meso-LA polymerization at the Al-chiral complex: a probe of DFT mechanistic insights.

The mechanism(s) for the formation of syndiotactic PLA by the ROP of meso-LA by a chiral-Al-complex are disclosed by DFT calculations. The contributions toward stereoselectivity have been analyzed confirming the peculiar chiral recognition for stereocontrolled ROP polymerization.

Allyl Monitorization of the Regioselective Pd-Catalyzed Annulation of Alkylnyl Aryl Ethers Leading to Bismethylenechromanes.

The mechanism for the synthesis of 2,3-bismethylenechromanes obtained by the reaction between silylethynyloxyarenes and allylic pivalates and catalyzed by a palladium complex has been investigated using computational methods rooted in density functional theory. The reaction is promoted by a C-H bond activation and the consequent bond cleavage of both substrates, followed by a novel annulation. The whole mechanism of this reaction is described together with the drawbacks that could block it.