Improved staining of proteins in polyacrylamide gels including isoelectric focusing gels with clear background at nanogram sensitivity using Coomassie Brilliant Blue G-250 and R-250

An improved procedure for staining of proteins following separation in polyacrylamide gels is described which utilizes the colloidal properties of Coomassie Brilliant Blue G-250 and R-250. The new method is based on addition of 20% v/v methanol and higher concentrations of ammonium sulfate to the staining solution previously described. The method combines the advantage of much shorter staining time with high sensitivity, a clear background not requiring destaining, stepwise staining, and stable fixation after staining. The method has been applied to staining of polyacrylamide gels after sodium dodecyl sulfate-electrophoresis and isoelectric focusing in carrier ampholyte-generated pH gradients.     

Cooperative ligation,back-bonding,and possible pyridine-pyridine interactions in tetrapyridine-vanadium(II): a visible and X-ray spectroscopic study

The binding of pyridine by V(II) in aqueous solution shows evidence for the late onset of cooperativity. The K(1) governing formation of [V(py)](2+) (lambda(max) = 404 nm, epsilon(max) = 1.43 +/- 0.3 M(-1) cm(-1)) was determined spectrophotometrically to be 11.0 +/- 0.3 M(-)(1), while K(1) for isonicotinamide was found to be 5.0 +/- 0.1 M(-1). These values are in the low range for 3d M(2+) ions and indicate that V(II).py back-bonding is not significant in the formation of the 1:1 complex. Titration of 10.5 mM V(II) with pyridine in aqueous solution showed an absorption plateau at about 1 M added pyridine, indicating a reaction terminus. Vanadium K-edge EXAFS analysis of 63 mM V(II) in 2 M pyridine solution revealed six first-shell N/O ligands at 2.14 A and 4 +/- 1 pyridine ligands per V(II). UV/vis absorption spectroscopy indicated that the same terminal V(II) species was present in both experiments. Model calculations showed that in the absence of back-bonding only 2.0 +/- 0.2 and 2.4 +/- 0.2 pyridine ligands would be present, respectively. Cooperativity in multistage binding of pyridine by [V(aq)](2+) is thus indicated. XAS K-edge spectroscopy of crystalline [V(O(3)SCF(3))(2)(py)(4)] and of V(II) in 2 M pyridine solution each exhibited the analogous 1s --> (5)E(g) and 1s --> (5)T(2g) transitions, at 5465.5 and 5467.5 eV, and 5465.2 and 5467.4 eV, respectively, consistent with the EXAFS analysis. In contrast, [V(py)(6)](PF(6))(2) and [V(H(2)O)(6)]SO(4) show four 1s --> 3d XAS transitions suggestive of a Jahn-Teller distorted excited state. Comparison of the M(II)[bond]N(py) bond lengths in V(II) and Fe(II) tetrapyridines shows that the V(II)[bond]N(py) distances are about 0.06 A shorter than predicted from ionic radii. For [VX(2)(R-py)(4)] (X = Cl(-), CF(3)SO(3)(-); R = 4-Et, H, 3-EtOOC), the E(1/2) values of the V(II)/V(III) couples correlate linearly with the Hammett sigma values of the R group. These findings indicate that pi back-bonding is important in [V(py)(4)](2+) even though absent in [V(py)](2+). The paramagnetism of [V(O(3)SCF(3))(2)(py)(4)] in CHCl(3), 3.8 +/- 0.2 mu(B), revealed that the onset of back-bonding is not accompanied by a spin change. Analysis of the geometries of V(II) and Fe(II) tetrapyridines indicates that the ubiquitous propeller motif accompanying tetrapyridine ligation may be due to eight dipole interactions arising from the juxtaposed C-H edges and pi clouds of adjoining ligands, worth about -6 kJ each. However, this is not the source of the cooperativity in the binding of multiple pyridines by V(II) because the same interactions are present in the Fe(II)-tetrapyridines, which do not show cooperative ligand binding. Cooperativity in the binding of pyridine by V(II) is then assigned by default to V(II)-pyridine back-bonding, which emerges only after the first pyridine is bound.     

金属配合物间的电子传递—历史的回顾

美国Stanford大学的H. Taube教授由于在无机化学方面的贡献而荣获1983年度诺贝尔奖金。这里我们将他的“诺贝尔演讲词”译出,供国内同志参考。历史给人以智慧。从中不仅可以知道当前无机化学的一个发展方向,而且可以了解一个新的领城是如何开发和形成的。     

Application of ultra-performance liquid chromatography/tandem mass spectrometry for the measurement of vitamin D in foods and nutritional supplements

Ultra-performance liquid chromatography (UPLC)/MS/MS was applied to measure vitamin D in various foods and nutritional supplements. The run-time of the chromatographic separation was cut from 20 min in HPLC/MS/MS to 10 min in UPLC/MS/MS, while equal or better separation efficiency was achieved to deal with complex food matrixes. Under the optimized conditions, all the previtamins of vitamin D3, D2, and isotope-labeled vitamin D3 were baseline-separated from their corresponding vitamins. It was also demonstrated that many sterol isomers in complex food matrixes that interfere in the analysis could be well-separated from the analytes. Accuracy of this method was evaluated by analysis of NIST SRM 1849 infant formula reference material. With eight replicates, the average vitamin D3 concentration was 0.251 +/- 0.012 mg/kg, an excellent agreement with the certified value of 0.251 +/- 0.027 mg/kg. In addition, spike recovery from a commercial infant formula matrix was in the range of 100 to 108% for both vitamins D3 and D2 at three spike concentration levels. The spike recovery for an even more complex matrix, pet food, was 101-105%. LOQ values were 0.026 and 0.033 IU/g, or 0.086 and 0.11 IU/mL in solution, for vitamins D3 and D2, respectively. The dynamic range had three orders of magnitude, which made the method flexible and useful to deal with the wide concentration range of vitamin D in various samples. The method was robust based on the results of changing the parameters of LC separation and MS measurement. This accurate and reliable vitamin D method increased instrument efficiency and analysis productivity significantly.     

Frozen natural orbital coupled-cluster theory: forces and application to decomposition of nitroethane

The frozen natural orbital (FNO) coupled-cluster method increases the speed of coupled-cluster (CC) calculations by an order of magnitude with no consequential error along a potential energy surface. This method allows the virtual space of a correlated calculation to be reduced by about half, significantly reducing the time spent performing the coupled-cluster (CC) calculation. This paper reports the derivation and implementation of analytical gradients for FNO-CC, including all orbital relaxation for both noncanonical and semicanonical perturbed orbitals. These derivatives introduce several new orbital relaxation contributions to the CC density matrices. FNO-CCSD(T) and FNO-LambdaCCSD(T) are applied to a test set of equilibrium structures, verifying that these methods are capable of reproducing geometries and vibrational frequencies accurately, as well as energies. Several decomposition pathways of nitroethane are investigated using CCSD(T) and LambdaCCSD(T) with 60% of the FNO virtual orbitals in a cc-pVTZ basis, and find differences on the order of 5 kcalmol with reordering of the transition state energies when compared to B3LYP 6-311 + G(3df, 2p).     

Generalizations of Polya's urn Problem

We consider generalizations of the classical Polya urn problem: Given finitely many bins each containing one ball, suppose that additional balls arrive one at a time. For each new ball, with probability p, create a new bin and place the ball in that bin; with probability 1–p, place the ball in an existing bin, such that the probability that the ball is placed in a bin is proportional to $ m^\gamma $, where m is the number of balls in that bin. For p=0, the number of bins is fixed and finite, and the behavior of the process depends on whether is greater than, equal to, or less than 1. We survey the known results and give new proofs for all three cases. We then consider the case p>0. When =1, this is equivalent to the so-called preferential attachment scheme which leads to power law distribution for bin sizes. When >1, we prove that a single bin dominates, i.e., as the number of balls goes to infinity, the probability that any new ball either goes into that bin or creates a new bin converges to 1. When p > 0 and < 1, we show that under the assumption that certain limits exist, the fraction of bins having m balls shrinks exponentially as a function of m. We then discuss further generalizations and pose several open problems.AMS Subject Classification: 05D40, 60C05, 60G20, 68R10, 91C99.     

Homologous non-isotopic symplectic surfaces of higher genus

We construct an infinite family of homologous, non-isotopic, symplectic surfaces of any genus greater than one in a certain class of closed, simply connected, symplectic four-manifolds. Our construction is the first example of this phenomenon for surfaces of genus greater than one.