Molecular volume calculation using AM1 semi-empirical method toward diffusion coefficients and electrophoretic mobility estimates in aqueous solution

Diffusion coefficients and electrophoretic mobility are two important physicochemical parameters used in mass transport phenomenon studies. The volume of the solute is required to determine or estimate these parameters. Classical methods, such as the LeBas method are commonly used. However, although valid, this method may represent a boring and time-consuming task, depending on the nature and number of compounds to be calculated. In this study, the volumes of a series of neutral and charged substances of the main functional groups present in organic molecules, amino acids, drugs and diverse compounds, such as cytosine and glucose, were calculated according to the LeBas method (V_M) and the AM1 semi-empirical method, V_W(AM1). The latter showed to be statistically coincident with the former. Employed as a pure value or corrected by the LeBas molar volume, the AM1 molecular volume was also demonstrated to estimate the diffusion coefficients in infinite aqueous dilution within an acceptable average error, according to the Othmer–Thakar, Wilke–Chang and Hayduk–Laudie methods, as well as the electrophoretic mobility of charged substances, such as carboxylates and protonated amines. According to these results, the AM1 method was seen to be statistically valid to calculate molecular volume. Many advantages in the construction of most diverse structures were noted, as well as a reduction in time and an increase in the quality of the information, when run on molecular modeling software.     

Downfalls of Chemical Probes Acting at the Kinase ATP-Site: CK2 as a Case Study

Protein kinases are a large class of enzymes with numerous biological roles and many have been implicated in a vast array of diseases, including cancer and the novel coronavirus infection COVID-19. Thus, the development of chemical probes to selectively target each kinase is of great interest. Inhibition of protein kinases with ATP-competitive inhibitors has historically been the most widely used method. However, due to the highly conserved structures of ATP-sites, the identification of truly selective chemical probes is challenging. In this review, we use the Ser/Thr kinase CK2 as an example to highlight the historical challenges in effective and selective chemical probe development, alongside recent advances in the field and alternative strategies aiming to overcome these problems. The methods utilised for CK2 can be applied to an array of protein kinases to aid in the discovery of chemical probes to further understand each kinase’s biology, with wide-reaching implications for drug development.     

Structural characterization of cardiolipin by tandem quadrupole and multiple-stage quadrupole ion-trap mass spectrometry with electrospray ionization

We report negative-ion electrospray tandem mass spectrometric methods for structural characterization of cardiolipin (CL), a four-acyl-chain phospholipid containing two distinct phosphatidyl moieties, of which structural assignment of the fatty acid residues attached to the glycerol backbones performed by low-energy CAD tandem mass spectrometry has not been previously described. The low-energy MS2-spectra of the [M - H]- and [M - 2H]2- ions obtained with ion-trap or with tandem quadrupole instrument combined with ion-trap MS3-spectra or with source CAD product-ion spectra provide complete structural information for CL characterization. The MS2-spectra of the [M - H]- ions contain two sets of prominent fragment ions that comprise a phosphatidic acid, a dehydrated phosphatidylglycerol, and a (phosphatidic acid + 136) anion. The substantial differences in the abundances of the two distinct phosphatidic anions observed in the MS2-spectra of the [M -H]- ions lead to the assignment of the phosphatidyl moieties attached to the 1' or 3' position of central glycerol. Upon further collisional dissociation, the MS3-spectra of the phosphatidic anions provide information to identify the fatty acyl substituents and their position in the glycerol backbone. The MS2-spectra of the [M - 2H]2- ions obtained with TSQ or ITMS contain complementary information to confirm structural assignment. The applications of the above methods in the differentiation of cardiolipin isomers and in the identification of complex cardiolipin species consisting of multiple molecular structures are also demonstrated.     

Kinetic study of the thermal and thermo-oxidative degradations of polylactide-modified films for food packaging

In this study, the thermal degradations of some commercial polylactide (PLA) films, pure and subjected to various superficial treatments, were investigated in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Degradations were carried out in a thermobalance, in the scanning mode, at various heating rates, and the obtained thermogravimetric curves were discussed and interpreted. Experiments, performed in the temperature range of 35–700 °C, showed similar behavior in both the atmospheres used. The initial decomposition temperature (T _i) and the apparent activation energy (E _a) of degradation of the differently treated PLA films were determined and compared with each other and with those of untreated PLA. The E _a of degradation was obtained by Kissinger’s method, and the values were found increased linearly as a function of crystallinity percentage (%c) as well as the T _i values. The glass transition temperature (T _g) was also determined by differential scanning calorimetry. All the investigated parameters showed dependence on different treatments made to the films. The results obtained for the degradations of PLA films were compared with each other, and a classification of thermal stability in the studied environments were made.     

SILYL- AND GERMYL-DIAZADIPHOSPHETIDINES

Abstract

Reaction of the 1,3,2,4-diazadiphosphetidine, trans-[C₆H₅N(H)P(S)NC₆H₅]₂ with LiR (R = Me, n-Bu) followed by treatment of the resulting dianions with Me₃SiCl and Me₃GeBr produced trans-[C₆H₅N(R)P(S)NC₆H₅]₂(R = Me₃Si, 2; Me₃Ge, 3). Substitution occurs without cis-trans isomerization or significant cleavage of the 1,3,2,4-diazadiphosphetidine ring. 2 and 3 have been characterized by spectral (¹H and ³¹P NMR, IR, and MS) and elemental analytical data. Analogous reactions involving Me₃SnCl yield mixtures containing [C₆H₅N(SnMe₃)P(S)NC₆H₅]₂ which could not be isolated or completely characterized.     

Synthesis and application of cinnamate-functionalized rubber for the preparation of UV-curable films

A butyl rubber derivative that can be cured upon exposure to UV light in the absence of additional chemical additives was developed. This polymer was prepared by the reaction of hydroxyl-functionalized butyl rubber with cinnamoyl chloride to provide a cinnamate functionalized rubber. The cinnamate content was varied by starting with derivatives prepared from butyl rubber containing either 2 or 7 mol% isoprene. The kinetics of the cross-linking was studied by UV–visible spectroscopy and it was found to vary according to the film thickness. The changes in gel content and volume swelling ratio with irradiation time were dependent on the cinnamate content. Toxicity studies suggested that the cross-linked materials do not leach toxic molecules. The approach was also applied to obtain cross-linked films of butyl rubber-poly(ethylene oxide) graft copolymers, leading to surfaces that resisted the adhesion and growth of cells. Thus the approach is versatile and is of particular interest when non-leaching coatings of cross-linked butyl rubber are desired for biomedical or other applications.     

Fluorinated polymerizable phosphonium salts from PH3: Surface properties of photopolymerized films

An array of highly fluorinated polymerizable phosphonium salts (HFPPS) were synthesized from PH₃ and utilized in UV‐curable formulations. Inclusion of these salts at very low loading (0.1–1 wt %) into hexanediol diacrylate (HDDA) resulted in hydrophobic surfaces. The water repellency was achieved with short C₄F₉ fluorocarbon appendages in the monomer as opposed to the bioaccumulative C₈F₁₇ appended polymers. The physical properties of these new monomers were also characterized. The molecular architecture of the monomers had a pronounced effect on both their physical properties along with the degree of hydrophobicity imparted in the polymer. Salts utilizing the bis(trifluoromethylsulfonyl)imide anion displayed excellent compatibility with HDDA, while the chloride salts were insoluble. Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) confirmed the presence of the HFPPS at the surface of the polymer coating. For the first time this demonstrates how these salts may be used to functionalize the surface of a UV‐cured film with ionic species. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2782–2792