Two-Layer Model of Colloidal Gold Bioconjugates and Its Application to the Optimization of Nanosensors

An optical model of the conjugates of colloidal gold nanoparticles with biopolymers is analyzed in terms of two-layer spherical particle with the gold core and dielectric coating. The Mie theory was used to study the dependence of variations (caused by the adsorption of a biopolymer on the particle surface) in the extinction and light scattering (at 90°) spectra on the gold core diameter (d = 5–200 nm), the shell refractive index and thickness s (ratio s/d = 0–1). Some theoretical results by Templeton et al. (J. Phys. Chem. B, 2000, vol. 104, pp. 564–570) on the two-layer dipole model were corrected. It is shown that the dependence of spectral shifts of the extinction and scattering peaks on the conjugate structure is adequately described by the dipole approximation. In particular, we found the universal dependence of the normalized spectral shift of extinction maximum on the s/d ratio. Having in mind the optimization of conjugate–nanosensors, we studied the problem of what particle size is optimal for the transformation of biopolymer adsorption event into the variations in the spectral parameters of extinction and light scattering. Based on the calculations of extinction maximum values and positions, as well as on calculated differential extinction spectra, we concluded that a maximal conjugate efficiency corresponds to the core diameters of 40–80 nm. We also discussed the principles of conjugate–nanosensors optimization for the polymer shell structure.     

Indexing Non-merohedrally Twinned Crystals by Bruker'sAPEX2 and Agilent's CrysAlis~(PRO), an Example of a Crystal Structure That Can Be Refined through Either the PLATONRoute or the ‘HKLF 5' Route,and, Simultaneous Data Collection of Two Crystals in a Tw

The first part of this report describes the data reduction of non-merohedrally twinned crystals measured on Bruker and Agilent area-detector diffractometers. The image frames of methyl-2-aminopyrazine-3-carboxylate were processed with APEX2 to furnish a set of overlapping diffraction indices that were used for solution and refinement. CrysAlisPRO was used for processing the frames of bis(diethyldicarbamato)nickel, which exists in monoclinic and tetragonal polymorphs, and in untwinned and twinned forms. In the second part, the crystal structure of [(3-formyl-4- hydroxyphenyl)methyl]triphenylphosphanium chloride was refined through the ‘HKLF 5'(based on a combined set of diffraction indices) and PLATON(based on one set of diffraction indices) routes to give identical outcomes because the amount of overlap of the twin domains is small. For the third part, in a proof-of-concept investigation, the diffraction pattern of untwinned and twinned 4-{(E)-(4-aminophenyl)diazenyl]phenylamine was recorded simultaneously in one run; the three domains could be indexed and the crystal structure satisfactorily refined. The refinement was identical to those derived from independent measurements; the crystal structure features two independent centrosymmetric molecules, one of which is ordered and the other whole-molecule-disordered. This two-in-one run opens up the possibility that two or more crystals having different atomic compositions can be measured simultaneously if their reciprocal lattices do not overlap significantly.     

Dimethyltin Dichloride-Dibenzyl Sulfoxide, a Compound Crystallizing with Seven Molecules in the Asymmetric Unit

Dimethyltin dichloride-dibenzyl sulfoxide,((CH3)2SnCl2·O=S(CH2C6H5)2),crystallizes in the orthorhombic space group P212121 with a superstructure of dimensions a = 11.9290(1),b = 19.50490(1),c = 55.7390(6) ; Z = 28. The geometry of the five-coordinated tin atom in each of the seven independent adduct molecules is a square pyramid that is displaced towards a cis-trigonal bipyramid; the extent of displacement along the Berry pseudorotation pathway ranges from 20 to 45%.     

用宇宙线大气簇射N_e-M_μ关系研究“膝”区原初成分

用梁王山宇宙线观测站获得的宇宙线大气簇射μ子数据,与假设原初分别为质子、氦核、中等核(Z=15)和铁核的Monte-Carlo模拟结果进行比较,结果显示宇宙线膝区原初成分无明显变化且以轻核为主．     

A new spectral resonance of metallic nanorods

The extinction, integrated scattering, and absorption spectra of gold and silver nanorods with random and regular orientation are studied. The calculations are performed for spheroids, circular cylinders, circular cylinders with hemispherical ends (T-matrix method), and rectangular prisms (discrete dipole approximation). A new quadrupole resonance is discovered that arises between the usual plasmon dipole resonances excited by a field longitudinal or transverse with respect to the symmetry axis. The new resonance can be excited only by a TM incident wave and is the greatest for orientation of the symmetry axis of the particle at an angle of 54° with respect to the light beam.     

On the measurement of gold nanoparticle sizes by the dynamic light scattering method

The application of the dynamic light scattering (DLS) method for determining the size distribution of colloidal gold nanoparticles in a range of 1–100 nm is discussed. It is shown that rotational diffusion of nonspherical strongly scattering particles with sizes of larger than 30–40 nm results in the appearance of a false peak in a size range of about 5–10 nm. In this case, the uncritical application of the DLS method may yield particle volume or number size distributions different from those obtained by transmission electron microscopy. For weakly scattering particles with diameters of smaller that 20 nm, the DLS method demonstrates an additional peak of intensity distribution in the region of large sizes that is related to particle aggregates or byproduct particles rather than individual nanoparticles. Practical methods for solving the problem of false peaks are discussed. It is established that the width of the DLS distribution does not correspond to transmission electron microscopy data and is overestimated. The advantages and drawbacks of the methods are compared and it is noted that, at present, the DLS method is the only instrument suitable for nonperturbative and sensitive diagnostics of relatively slow aggregation processes with characteristic times on the order of 1 min. In particular, this method can be used to diagnose gold nanoparticle conjugate aggregation initiated by biospecific interactions on their surface.     

以邻菲咯啉衍生物及1，3-间苯二甲酸为配体的一维链状Cd(Ⅱ)配位聚合物的合成及结构

在水热条件下,我们利用邻菲咯啉衍生物配体(L=2-(3-fluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline)和1,3-间苯二甲酸(1,3-H2BDC)反应得到了一维配位聚合物[Cd2(L)2(1,3-BDC)2]n,并对该化合物进行了元素分析、红外和单晶X-射线表征。该化合物属于三斜晶系,空间群Pī,晶胞参数a=1.080 8(4)nm,b=1.149 5(4)nm,c=1.924 8(7)nm,α=106.482(5)°,β=99.436(6)°,γ=93.093(6)°,V=2 249.2(14)nm3,Z=4,C27H15CdFN4O4,Mr=590.83,Dc=1.745 g.cm-3,F(000)=1 176,μ(Mo Kα)=1.024 mm-1,R=0.044 5和wR=0.111 7。该化合物为一维链状结构,链与链之间又进一步地通过CH-π相互作用形成二维层状超分子结构。     

Can the light scattering depolarization ratio of small particles be greater than 1/3?

According to the theory of light scattering by small randomly oriented particles, the depolarized ratio of the scattered intensities, I(vh)/I(vv), cannot exceed 1/3. Here we show that this conclusion does not hold for nonspherical plasmon resonant metal particles. Our analysis is based on the Rayleigh approximation and the exact T-matrix method as applied to spheroids and circular cylinders with semispherical ends. For small particles, the condition I(vh)/I(vv) >1/3 can be satisfied within the upper left quadrant of the complex relative dielectric permeability Real(eps) < -2 (rods) and within the upper unit semicircle centered at Real(eps) = -1 (disks). For gold nanorods with the axis ratio exceeding 2, the maximal theoretical values I(vh)/I(vv) lie between 1/3 and 3/4 at wavelengths of 550-650 nm. The extinction and static light scattering spectra (450-850 nm, at 90 degrees degrees) as well as the depolarized ratio of He-Ne laser light scattering were measured with gold nanospheres (the average diameters of 21, 29, and 46 nm) and nanorods (the longitudinal plasmon resonance peak positions at 655, 692, and 900 nm). The measured depolarization ratios of nanospheres (0.07-0.16) and nanorods (0.3-0.48) are in good agreement with theoretical calculations based on estimations of the average particle size and shape.