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991.
992.
Jonas Boström Valera Veryazov Francesco Aquilante Thomas Bondo Pedersen Roland Lindh 《International journal of quantum chemistry》2014,114(5):321-327
An algorithm for computing analytical gradients of the second‐order Møller–Plesset (MP2) energy using density fitting (DF) is presented. The algorithm assumes that the underlying canonical Hartree–Fock reference is obtained with the same auxiliary basis set, which we obtain by Cholesky decomposition (CD) of atomic electron repulsion integrals. CD is also used for the negative semidefinite MP2 amplitude matrix. Test calculations on the weakly interacting dimers of the S22 test set (Jure?ka et al., Phys. Chem. Chem. Phys. 2006, 8, 1985) show that the geometry errors due to the auxiliary basis set are negligible. With double‐zeta basis sets, the error due to the DF approximation in intermolecular bond lengths is better than 0.1 pm. The computational time is typically reduced by a factor of 6–7. © 2013 Wiley Periodicals, Inc. 相似文献
993.
Functionalization of Quinazolin‐4‐ones Part 1: Synthesis of Novel 7‐Substituted‐2‐thioxo Quinazolin‐4‐ones from 4‐Substituted‐2‐Aminobenzoic Acids and PPh3(SCN)2 下载免费PDF全文
4‐(Nitro, amino, acetylamino)‐2‐aminobenzoic acid were allowed to react with PPh3(SCN)2 and gave the crossholding 7‐nitro, 7‐acetylamino‐ and 7‐amino‐2‐thioxo quinazolin‐4‐ones respectively. The nature of the substituent at position 4 of the 2‐aminobenzoic acids has significant influence on the outcome of the cyclisation reaction with PPh3(SCN)2. Similarly, the nature of the substituent at position 7 of the 2‐substituted quinazolin‐4‐ones significantly affected the ease with which alkylation reactions could be performed. The alkylation selectivity of the 7‐ substiuted‐2‐thioxo quinazolin‐4‐ones was found to depend on the nature of the alkyl halide and the nature of the substituent at position 2. 相似文献
994.
995.
The synthesis of a new derivative of tryptophan Fmoc-Trp(Boc-Sar-Sar)-OH is described. Fmoc-Trp(Boc-Sar-Sar)-OH is introduced into peptides by solid-phase peptide synthesis and during treatment with TFA at the end of the synthesis, the Boc group is cleaved and the peptide is obtained with the indole nucleus modified with the sarcosinyl-sarcosinyl (Sar-Sar) moiety. This modification will introduce a cationic charge that improves the solubility of the peptide during HPLC purification. The Sar-Sar moiety is cleaved upon exposure to physiological pH. The Boc-Sar-Sar group might, therefore, also find use in the design of pro-drugs of indole-containing compounds. 相似文献
996.
Reaction of thiophene-2-methylamine with one or two equivalents of PPh2Cl in the presence of NEt3, proceeds in thf to give thiophene-2-(N-diphenylphosphino)methylamine, 1a and thiophene-2-(N,N-bis(diphenylphosphino))methylamine, 2a respectively, under anaerobic conditions. Oxidations of 1a and 2a with aqueous hydrogen peroxide, elemental sulfur or gray selenium in thf gives the corresponding oxides, sulfides and selenides [Ph2P(E)NHCH2-C4H3S] (E: O 1b, S 1c, Se 1d) and [(Ph2P(E))2NCH2-C4H3S], (E: O 2b, S 2c, Se 2d) respectively, in high yield. Furthermore, two novel Ru(II) complexes with the P-N ligands 1a and 2a were synthesized starting with the complex [Ru(η6-p-cymene)(μ-Cl)Cl]2. The complexes were fully characterized by analytical and spectroscopic methods. 31P-{1H} NMR, DEPT, 1H-13C HETCOR or 1H-1H COSY correlation experiments were used to confirm the spectral assignments. The molecular structure of thiophene-2-(N-diphenylthiophosphino)methylamine was also elucidated by single-crystal X-ray crystallography. Following activation by NaOH, compounds 3 and 4 catalyze the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of iso-PrOH as the hydrogen source. [Ru(Ph2PNHCH2-C4H3S)(η6-p-cymene)Cl2], 3 and [Ru((PPh2)2NCH2-C4H3S)(η6-p-cymene)Cl]Cl, 4 complexes are suitable catalyst precursors for the transfer hydrogenation of acetophenone derivatives in 0.1 M iso-PrOH solution. Notably 4 acts as an excellent catalyst giving the corresponding alcohols in excellent conversions up to 99% (TOF ? 744 h−1). This transfer hydrogenation is characterized by low reversibility under the experimental conditions. 相似文献
997.
Sami-Pekka Hirvonen Mikko Mänttäri Valter Wigren Mikko Salomäki Carita Kvarnström Heikki Tenhu 《Colloid and polymer science》2011,289(9):1065-1072
Poly(benzimidazobenzophenanthroline) (BBL) was prepared according to literature method and modified with poly(ethylene oxide)
in a one pot synthesis. After precipitation in aqueous sodium carbonate solution and subsequent purification, aqueous dispersions
were prepared by ultrasonication. Particle sizes in the dispersions ranged from few tens of nanometers to several micrometers
and most of the particles had sizes of 50–250 nm. Further studies indicated that the colloidal stability is a combined result
of steric stabilization caused by excluded volume interactions of PEO chains on particle surface and electrostatic stabilization
by the dissociated carboxylic acid groups on the particle surface. The product could be processed into uniform films 20–30 nm
in thickness by spin coating onto gold-plated silicon substrates having aminethiol monolayer as the top most layer. 相似文献
998.
Fall AB Lindström SB Sundman O Ödberg L Wågberg L 《Langmuir : the ACS journal of surfaces and colloids》2011,27(18):11332-11338
Cellulose nanofibrils constitute an attractive raw material for carbon-neutral, biodegradable, nanostructured materials. Aqueous suspensions of these nanofibrils are stabilized by electrostatic repulsion arising from deprotonated carboxyl groups at the fibril surface. In the present work, a new model is developed for predicting colloidal stability by considering deprotonation and electrostatic screening. This model predicts the fibril-fibril interaction potential at a given pH in a given ionic strength environment. Experiments support the model predictions that aggregation is induced by decreasing the pH, thus reducing the surface charge, or by increasing the salt concentration. It is shown that the primary mechanism for aggregation upon the addition of salt is the surface charge reduction through specific interactions of counterions with the deprotonated carboxyl groups, and the screening effect of the salt is of secondary importance. 相似文献
999.
Salis A Boström M Medda L Cugia F Barse B Parsons DF Ninham BW Monduzzi M 《Langmuir : the ACS journal of surfaces and colloids》2011,27(18):11597-11604
The points of zero charge/potential of proteins depend not only on pH but also on how they are measured. They depend also on background salt solution type and concentration. The protein isoelectric point (IEP) is determined by electrokinetical measurements, whereas the isoionic point (IIP) is determined by potentiometric titrations. Here we use potentiometric titration and zeta potential (ζ) measurements at different NaCl concentrations to study systematically the effect of ionic strength on the IEP and IIP of bovine serum albumin (BSA) aqueous solutions. It is found that high ionic strengths produce a shift of both points toward lower (IEP) and higher (IIP) pH values. This result was already reported more than 60 years ago. At that time, the only available theory was the purely electrostatic Debye-Hu?ckel theory. It was not able to predict the opposite trends of IIP and IEP with ionic strength increase. Here, we extend that theory to admit both electrostatic and nonelectrostatic (NES) dispersion interactions. The use of a modified Poisson-Boltzmann equation for a simple model system (a charge regulated spherical colloidal particle in NaCl salt solutions), that includes these ion specific interactions, allows us to explain the opposite trends observed for isoelectric point (zero zeta potential) and isoionic point (zero protein charge) of BSA. At higher concentrations, an excess of the anion (with stronger NES interactions than the cation) is adsorbed at the surface due to an attractive ionic NES potential. This makes the potential relatively more negative. Consequently, the IEP is pushed toward lower pH. But the charge regulation condition means that the surface charge becomes relatively more positive as the surface potential becomes more negative. Consequently, the IIP (measuring charge) shifts toward higher pH as concentration increases, in the opposite direction from the IEP (measuring potential). 相似文献
1000.
Sarı MM Armutcu C Bereli N Uzun L Denizli A 《Colloids and surfaces. B, Biointerfaces》2011,84(1):140-147
Affinity adsorption technique is increasingly used for protein purification, separation and other biochemical applications. Therapeutic molecules such as antibodies, cytokines, therapeutic DNA and plasma proteins must be purified before characterization and utilization. The aim of this study was to prepare micronsized spherical polymeric beads and to investigate the extent of their human insulin adsorption capability. Monosize poly(ethylene glycol dimethacrylate-N-methacryloyl-(L)-histidine) [poly(EDMA-MAH)] beads were prepared by modified suspension copolymerization. Functional monomer (MAH) was synthesized using methacryloyl chloride and L-histidine. The beads were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, swelling test and elemental analysis. MAH incorporation into monosize polymeric beads, having an average size around 2-3 μm, was estimated as 55.3 μmol MAH/g bead. Equilibrium swelling ratios of poly(EDMA-MAH) and poly(EDMA) beads were 65% and 55%, respectively. Adsorption experiments were performed under different conditions (i.e., pH, temperature, protein concentration and ionic strength). It was found that adsorption characteristics are strongly depend on these conditions. Maximum insulin adsorption capacity was achieved as 24.7 mg insulin/g poly(EDMA-MAH) beads. Results were well fitted to the Langmuir isotherm model. Compared with poly(EDMA-MAH), nonspecific insulin adsorption onto poly(EDMA) beads was very low (0.61 mg insulin/g bead) and can be negligible. It was observed that insulin could be repeatedly adsorbed and desorbed (at least 10 times) without significant loss in adsorption capacity. 相似文献