Practical Synthesis of Phosphinic Dipeptides by Tandem Esterification of Aminophosphinic and Acrylic Acids under Silylating Conditions

In this report, a synthetic protocol for the preparation of phosphinic dipeptides of type 5 is presented. These compounds serve as valuable building blocks for the development of highly potent phosphinopeptidic inhibitors of medicinally relevant Zn-metalloproteases and aspartyl proteases. The proposed method is based on the tandem esterification of α-aminophosphinic and acrylic acids under silylating conditions in order to subsequently participate in a P-Michael reaction. The scope of the transformation was investigated by using a diverse set of readily available acrylic acids and (R)-α-aminophosphinic acids, and high yields were achieved in all cases. In most examples reported herein, the isolation of biologically relevant (R,S)-diastereoisomers became possible by simple crystallization from the crude products, thus enhancing the operational simplicity of the proposed method. Finally, functional groups corresponding to acidic or basic natural amino acids are also compatible with the reaction conditions. Based on the above, we expect that the practicality of the proposed protocol will facilitate the discovery of pharmacologically useful bioactive phosphinic peptides.     

First Hitting Time of Brownian Motion on Simple Graph with Skew Semiaxes

Consider a stochastic process that lives on n-semiaxes emanating from a common origin. On each semiaxis it behaves as a Brownian motion and at the origin it chooses a semiaxis randomly. In this paper we study the first hitting time of the process. We derive the Laplace transform of the first hitting time, and provide the explicit expressions for its density and distribution functions. Numerical examples are presented to illustrate the application of our results.

     

Short-time vibrational dynamics of metaphosphate glasses

In this paper we present the picosecond vibrational dynamics of a series of binary metaphosphate glasses, namely Na₂O–P₂O₅, MO–P₂O₅ (M=Ba, Sr, Ca, Mg) and Al₂O₃–3P₂O₅ by means of Raman spectroscopy. We studied the vibrational dephasing and vibrational frequency modulation by calculating time correlation functions of vibrational relaxation by fits in the frequency domain. The fitting method used enables one to model the real line profiles intermediate between Lorentzian and Gaussian by an analytical function, which has an analytical counterpart in the time domain. The symmetric stretching modes ν_s(PO₂^?) and ν_s(P–O–P) of the PO₂^? entity of PØ₂O₂^? units and of P–O–P bridges in metaphosphate arrangements have been investigated by Raman spectroscopy and we used them as probes of the dynamics of these glasses. The vibrational time correlation functions of both modes studied are rather adequately interpreted within the assumption of exponential modulation function in the context of Kubo–Rothschield theory and indicate that the system experiences an intermediate dynamical regime that gets only slower with an increase in the ionic radius of the cation-modifier. We found that the vibrational correlation functions of all glasses studied comply with the Rothschild approach assuming that the environmental modulation is described by a stretched exponential decay. The evolution of the dispersion parameter α with increasing ionic radius of the cation indicates the deviation from the model simple liquid indicating the reduction of the coherence decay in the perturbation potential as a result of local short lived aggregates. The results are discussed in the framework of the current phenomenological status of the field.     

Theory of gold on ceria

The great promise of ceria-supported gold clusters as catalysts of the future for important industrial processes, such as the water gas shift reaction, has prompted a flurry of activity aimed at understanding the molecular-level details of their operation. Much of this activity has focused on experimental and theoretical studies of the structure of perfect and defective ceria surfaces, with and without gold clusters of various sizes. The complicated electronic structure of ceria, particularly in its reduced form, means that at present it is highly challenging to carry out accurate electronic structure simulations of such systems. To overcome the challenges, the majority of recent theoretical studies have adopted a pragmatic and often controversial approach, applying the so-called DFT + U technique. Here we will briefly discuss some recent studies of Au on CeO(2){111} that mainly use this methodology. We will show that considerable insight has been obtained into these systems, particularly with regard to Au adsorbates and Au cluster reactivity. We will also briefly discuss the need for improved electronic structure methods, which would enable more rigorous and robust studies in the future.     

Circulating Ligands of the Receptor for Advanced Glycation End Products and the Soluble Form of the Receptor Modulate Cardiovascular Cell Apoptosis in Diabetes

We determined whether plasma concentrations of the receptor for advanced glycation end products (RAGE) and the soluble (s) form of RAGE (sRAGE) in healthy individuals and patients with type 2 diabetes (T2D) modulate vascular remodeling. Healthy individuals and patients with T2D were divided into two age groups: young = <35 years old or middle-aged (36–64 years old) and stratified based on normal glucose tolerance (NGT), impaired (IGT), and T2D. Plasma titers of sRAGE, the RAGE ligands, AGEs, S100B, S100A1, S100A6, and the apoptotic marker Fas ligand Fas(L) were measured by enzyme-linked immunosorbent assay (ELISA). The apoptotic potential of the above RAGE ligands and sRAGE were assessed in cultured adult rat aortic smooth muscle cells (ASMC). In NGT individuals, aging increased the circulating levels of AGEs and S100B and decreased sRAGE, S100A1 and S100A6. Middle-aged patients with T2D presented higher levels of circulating S100B, AGEs and FasL, but lower levels of sRAGE, S100A1 and S100A6 than individuals with NGT or IGT. Treatment of ASMC with either AGEs or S100B at concentrations detected in T2D patients increased markers of inflammation and apoptosis. Responses attenuated by concomitant administration of sRAGE. In middle-aged patients with T2D, lower circulating plasma levels of sRAGE may limit decoy and exogenous trapping of deleterious pro-apoptotic/pro-inflammatory RAGE ligands AGEs and S100B, increasing the risk for diabetic complications.     

Hydrogen bonds and van der waals forces in ice at ambient and high pressures

The first principles methods, density-functional theory and quantum Monte Carlo, have been used to examine the balance between van der Waals (vdW) forces and hydrogen bonding in ambient and high-pressure phases of ice. At higher pressure, the contribution to the lattice energy from vdW increases and that from hydrogen bonding decreases, leading vdW to have a substantial effect on the transition pressures between the crystalline ice phases. An important consequence, likely to be of relevance to molecular crystals in general, is that transition pressures obtained from density-functional theory exchange-correlation functionals which neglect vdW forces are greatly overestimated.     

Visualization of hydrogen bonding and associated chirality in methanol hexamers

Using a combination of scanning tunneling microscopy (STM) and density functional theory the hydrogen bond directionality and associated chirality of enantiopure clusters is visualized and controlled. This is demonstrated with methanol hexamers adsorbed on Au(111), which depending on their chirality, adopt two distinct molecular footprints on the surface. Controlled STM tip manipulations were used to interconvert the chirality of entire clusters and to break up metastable chain structures into hexamers.     

Determination of fenthion and oxidation products in personal protection equipment by gas chromatography

A method for the co-extraction and simultaneous chromatographic determination of fenthion and its five oxidation products (or metabolites) fenoxon, fenoxon-sulfoxide, fenoxon-sulfone, fenthion-sulfoxide, and fenthion-sulfone in personal protection equipment (PPE) of pesticide applicators was developed and validated. Capillary gas chromatography-nitrogen-phosphorus detection was used for the analytical determination of all the aforementioned compounds over the concentration range of 0.1-0.5 microg/mL. All necessary validation criteria of the method were met. The method was found to be highly selective, accurate, and precise, gave satisfactory recovery (>70%) and RSD values (<20%) for fenthion and its metabolites in all tested specimens of personal protection equipment and in air samplers. The limit of quantification (LOQ) and linearity were determined for the most relevant PPE (i.e. inner coverall) for the parent compound and for the metabolites. The LOQ values ranged from 0.05 to 0.1 ppb while the linearity in the tested range of 0.1-0.5 ppm had r(2)>0.994 for all analytes.