Development in the area of UV-crosslinkable solvent-based pressure-sensitive adhesives with excellent shrinkage resistance

Solvent-based UV-crosslinkable pressure-sensitive adhesives (PSA) present a new class of products that offers the potential to produce a novel generation of ultraviolet cured self-adhesive products with excellent shrinkage resistance. A variety of solvent-based pressure-sensitive adhesives were prepared by synthesis in ethyl acetate with solid content on 50 wt.% with 2-ethylhexyl acrylate, methyl acrylate, acrylic acid, N-vinyl caprolactam and unsaturated photoinitiators: 4-acryloyloxy benzophenone, allyl benzoine and phenyl-(1-acryloyloxy)-cyclohexyl ketone. The main emphasis is given to the influence of viscosity and molecular mass of synthesized adhesive on their shrinkage. Further trials show the effect of the UV-crosslinking process with UV-lamp and comparison with acrylics PSA crosslinked with metal chelates aluminium acetylacetonate and titanium acetylacetonate on shrinkage. Further examinations describe the influence of various factors such as UV exposure time and UV dose on very relevant PSA performance such as shrinkage on coated PVC carrier.     

Molecular modeling of cytochrome P450 3A4

The three-dimensional structure of human cytochrome P450 3A4 was modeled based on crystallographic coordinates of four bacterial P450s: P450 BM-3, P450cam, P450terp, and P450eryF. The P450 3A4 sequence was aligned to those of the known proteins using a structure-based alignment of P450 BM-3, P450cam, P450terp, and P450eryF. The coordinates of the model were then calculated using a consensus strategy, and the final structure was optimized in the presence of water. The P450 3A4 model resembles P450 BM-3 the most, but the B helix is similar to that of P450eryF, which leads to an enlarged active site when compared with P450 BM-3, P450cam, and P450terp. The 3A4 residues equivalent to known substrate contact residues of the bacterial proteins and key residues of rat P450 2B1 are located in the active site or the substrate access channel. Docking of progesterone into the P450 3A4 model demonstrated that the substrate bound in a 6-orientation can interact with a number of active site residues, such as 114, 119, 301, 304, 305, 309, 370, 373, and 479, through hydrophobic interactions. The active site of the enzyme can also accommodate erythromycin, which, in addition to the residues listed for progesterone, also contacts residues 101, 104, 105, 214, 215, 217, 218, 374, and 478. The majority of 3A4 residues which interact with progesterone and/or erythromycin possess their equivalents in key residues of P450 2B enzymes, except for residues 297, 480 and 482, which do not contact either substrate in P450 3A4. The results from docking of progesterone and erythromycin into the enzyme model make it possible to pinpoint residues which may be important for 3A4 function and to target them for site-directed mutagenesis.     

The solvation of Li and Na in acetonitrile from ab initio-derived many-body ion–solvent potentials

Several Li⁺- and Na⁺-acetonitrile models were derived from ab initio calculations at the counterpoise-corrected MP2/TZV++(d,p) level for distorted ion-(MeCN)_n clusters with n=1, 4 and 6. Two different many-body ion-acetonitrile models were constructed: an effective three-body potential for use with the six-site effective pair model of Böhm et al., and an effective polarizable many-body model. The polarizable acetonitrile model used in the latter model is a new empirical model which was also derived in the present paper. Mainly for comparative purposes, two ion-acetonitrile pair potentials were also constructed from the ab initio cluster calculations: one pure pair potential and one effective pair potential. Using all these potential models, MD simulations in the NPT ensemble were performed for the pure acetonitrile liquid and for Li⁺(MeCN) and Na⁺(MeCN) solutions with 1 ion in 512 solvent molecules and with a simulation time of at least 120 ps per system. Thermodynamic properties, solvation-shell structure and the self-diffusion coefficient of the ions and of the solvent molecules were calculated and compared between the different models and with experimental data, where available. The Li⁺ ion is found to be four-coordinated when the new many-body potentials are used, in contrast to the six-coordinated structure obtained for the pure pair and effective pair potentials. The coordination number of Na⁺ is close to six for all the models derived here, although the coordination number becomes slightly smaller with the many-body potentials. For both ions, the solvent molecules in the first shell point their nitrogen ends towards the cation, while in the second shell the opposite orientation is the most common.     

Synthesis and network structure of ionic poly(N,N-dimethylacrylamide-co-acrylamide) hydrogels: Comparison of swelling degree with theory

At four different charge densities, ionic hydrogels based on N,N-dimethylacrylamide (DMAAm), acrylamide (AAm), and itaconic acid (IA) were synthesized by free-radical cross-linking copolymerization in water with N,N-methylenebis(acrylamide) (BAAm) as the cross-linker, ammonium persulfate (APS) as the initiator, and N,N,N′,N′-tetramethylenediamine (TEMED) as the activator. The swelling behaviors of these hydrogels were analyzed in buffer solutions at various pH. It was observed that the swelling behavior of cross-linked ionic poly(N,N-dimethylacrylamide-co-acrylamide) [P(DMAAm-co-AAm)] hydrogels at different pHs agreed with the modified Flory-Rehner equation based both on the phantom network and affine network models and the ideal Donnan theory. In addition, the kinetics of swelling of the hydrogels was studied in pH 2, 5 and 9 buffer solutions. The swelling curves exhibited the characteristic features of transport process, apparently the Fickian diffusion of fast rates.     

Electropolymerized Pyrrole‐Substituted Manganese Phthalocyanine Films for the Electroassisted Biomimetic Catalytic Reduction of Molecular Oxygen

We report for the first time on the electroassisted biomimetic activation of molecular oxygen by a newly prepared electropolymerized polypyrrole‐manganese phthalocyanine film. The prepared films and their intervention in the electroassisted catalytic reduction of molecular oxygen were analyzed by cyclic voltammetry and UV‐visible spectrophotometry on optically transparent electrodes. The obtained results demonstrate the probable existence of the key‐steps responsible for the suggested formation of the highly reactive manganese oxo intermediate.     

DNAzyme amplification of molecular beacon signal

This paper reports an improved catalytic molecular beacon. Addition of the target oligonucleotide activates a DNA enzyme (DNAzyme), which, in turn, activates multiple copies of molecular beacons (MB) and gives rise to a strong fluorescence signal. In a previous design, the activated DNAzyme could oligomerize, especially dimerize, and result in inactivation of the DNAzyme. The current design avoids this problem, upon activated by the target DNA, the DNAzyme will stay constantly active. With the improved method, a detection of 10 pM DNA has been demonstrated, which is 1000 times more sensitive than the method previously reported.     

Functionality map analysis of the active site cleft of human thrombin

Summary The Multiple Copy Simultaneous Search methodology has been used to construct functionality maps for an extended region of human thrombin, including the active site. This method allows the determination of energetically favorable positions and orientations for functional groups defined by the user on the three-dimensional surface of a protein. The positions of 10 functional group sites are compared with those of corresponding groups of four thrombin-inhibitor complexes. Many, but not all features, of known thrombin inhibitors are reproduced by the method. The results indicate that certain aspects of the binding modes of these inhibitors are not optimal. In addition, suggestions are made for improving binding by interaction with functional group sites on the thrombin surface that are not used by the thrombin inhibitors. Abbreviations: MCSS, multiple copy simultaneous search; PPACK, d-phenylalanyl-l-propyl-l-arginine chloromethane; NAPAP, N -(2-naphthylsulfonylglycyl)-d-para-amidinophenylalanylpiperidine; argatroban, (2R,4R)-4-methyl-1-[N -(3-methyl-1,2,3,4-tetrahydro-8-quinolinylsulfonyl)-l-arginyl]-2-piperidine carboxylic acid; rms, root mean square. The thrombin residues are numbered according to the chymotrypsin-based numbering by Bode et al. [8]. P1, P2, P3, etc., denote the peptide inhibitor residues on the amino-terminal side of the scissile peptide bond, and S1, S2, S3, etc., the corresponding subsites of thrombin     

Molecular mechanics (MM2) calculations and cone angles of phosphine ligands

Molecular mechanics (MM2) calculations were performed on 54 conformations of 18 phosphines (PH₃; PH_3−nR_n, where n = 1,…3, and R = Me and Et, n = 1 or 2 and R =ⁱPr, and n = 1 and R =^tBu, PMe₂Et, PMeEt₂, and PPhMe₂, and PPh₂R where R = Me, Et, ⁱPr, ^tBu and Ph). The results are compared to those previously obtained from MINDO/3 and MNDO calculations, and to experimental data. Single conformer cone angles and weighted average cone angles were calculated from MM2 optimized geometries employing Tolman's general definition, and they are compared to Tolman's values, MINDO/3 results, and T.L. Brown's E_R values. Of the cone angle definitions used, the weighted average values are suggested as the best single representation of phosphine ligand sizes. The steric parameters (cone angle and E_R values) alone, and in conjunction with electronic parameters, are correlated with experimental data.     

A molecular mechanics approach for analyzing tensile nonlinear deformation behavior of single-walled carbon nanotubes

In this paper, by capturing the atomic information and reflecting the behaviour governed by the nonlinear potential function, an analytical molecular mechanics approach is proposed. A constitutive relation for single-walled carbon nanotubes (SWCNT’s) is established to describe the nonlinear stress-strain curve of SWCNT’s and to predict both the elastic properties and breaking strain of SWCNT’s during tensile deformation. An analysis based on the virtual internal bond (VIB) model proposed by P. Zhang et al. is also presented for comparison. The results indicate that the proposed molecular mechanics approach is indeed an acceptable analytical method for analyzing the mechanical behavior of SWCNT’s. The project supported by the National Natural Science Foundation of China (10121202, 90305015 and 10328203), the Key Grant Project of Chinese Ministry of Education (0306) and the Research Grants Council of the Hong Kong Special Administrative Region, China (HKU 7195/04E).     

Ion beam mixing of α-MoSi2

Abstract

Using molecular dynamics simulation, we study the mixing of an α-MoSi₂ crystal by 1 keV Ar ions. The observed order of magnitude of the mixing is compatible with a spike model of ion beam mixing. The influence of the target surface and of chemical effects are discussed.