Microspectroscopic analysis of green fluorescent proteins infiltrated into mesoporous silica nanochannels

The infiltration of enhanced green fluorescent protein (EGFP) into nanochannels of different diameters in mesoporous silica particles was studied in detail by fluorescence microspectroscopy at room temperature. Silica particles from the MCM-41, ASNCs and SBA-15 families possessing nanometer-sized (3-8 nm in diameter) channels, comparable to the dimensions of the infiltrated guest protein EGFP (barrel structure with dimensions of 2.4 nm × 4.2 nm), were used as hosts. We found that it is necessary to first functionalize the surfaces of the silica particles with an amino-silane for effective encapsulation of EGFP. We demonstrated successful infiltration of the protein into the nanochannels based on fluorescence microspectroscopy and loading capacity calculations, even for nanochannel diameters approaching the protein dimensions. We studied the spatial distributions of the EGFPs within the silica particles by confocal laser scanning microscopy (CLSM) and multimode microscopy. Upon infiltration, the fluorescence lifetime drops as expected for an emitter embedded in a high refractive index medium. Further, the spectral properties of EGFP are preserved, confirming the structural integrity of the infiltrated protein. This inorganic-protein host-guest system is an example of a nanobiophotonic hybrid system that may lead to composite materials with novel optical properties.     

Resistivity,thermopower and single-particle tunneling studies on some zinc-doped yttrium barium copper oxide superconductors

Abstract

Resistance and thermopower measurements have been made on a series of compounds, YBa₂Cu₃- _x Zn _x O_7-y, with x = 0.025, 0.05, 0.1, 0.15 and 0.2. The superconducting transition temperature decreases as the zinc concentration increases. In a range of temperatures below T_M , the mid point of the transition, the resistance shows an exponential temperature dependence fitting the phenomenological formula proposed by Ausloos et al. From the plot of logarithm of resistivity vs. (T_M ? T) ^1/2/T, one deduces a value of the average dimension of the Josephson junction to be a few tens of Å, suggesting the microtwin boundaries to be the location of the junctions. The thermopower shows a peak always just above T_c . This conclusively shows that phonon drag is not the cause of the peak. The temperature dependence of the thermopower appears to resemble closely the earlier observations of Srinivasan et al. on yttrium barium copper oxide. Single-particle tunneling measurements carried out for two concentrations, x = 0 and 0.05, appear to indicate that the energy gap parameter scales with T_c , and 2Δ/kT_c has an approximate value of 5.5.     

Parabolic subgroups and automorphism groups of Schubert varieties

Let G be a simple algebraic group of adjoint type over the field $\mathbb{C}$ of complex numbers, B be a Borel subgroup of G containing a maximal torus T of G. Let w be an element of the Weyl group W and $X(w)$ be the Schubert variety in $G/B$ corresponding to w. In this article we show that given any parabolic subgroup P of G containing B properly, there is an element $w\in W$ such that P is the connected component, containing the identity element of the group of all algebraic automorphisms of $X(w)$.     

Studies on biochemical markers in cryoinfarction in rats

Cryoinfarction in rats was carried out by placing the cooled probe directly on the midway of left anterior descending coronary artery. This caused damage to the blood vessel, hindering blood flow to the distal part of the left ventricle. Gross pathology showed around 26% infarction at 24 h. Histopathology revealed death of cardiomyocytes with blood vessel congestion at the end of 24 h, inflammatory infiltrate at 48 h, fibrotic scar by 96 h and collagen deposition by 192 h. Acute myocardial infarction biomarkers such as Cardiac Troponin T, Creatine Kinase MB and NT pro BNP were shown to be elevated by 4 h. ECG showed an ST segment elevation by 96 h. This cryoinfarction model was suitable to study changes taking place during acute myocardial infarction in humans.     

Resonance CARS study of the structure of "green" and "red" chromophores within the red fluorescent protein DsRed

Vibrational spectra of red fluorescent protein DsRed have been studied for the first time by polarization-sensitive multiplex coherent anti-Stokes Raman scattering at two excitation wavelengths, 545 and 583 nm, in resonance with the absorption bands of the immature "green" and mature "red" protein chromophores. Overall vibrational patterns of both DsRed chromophores were found to be similar to each other and to differ from that of S65T-GFP at pH8. The combined analysis of our CARS data and published structural information suggest that both "green" and "red" DsRed species possess an extended chromophore structure. Consequently, our data suggest that pi-bonding system extension during isomerization around the cis peptide bond between Phe 65 and Gln 66 is a necessary but not sufficient step in DsRed chromophore maturation.     

F bands in KCl-KBr mixed crystals

Gamma ray-induced F bands in melt grown mixed crystals of KCl and KBr are studied at room temperature. The effect of dislocations on F-centre density in mixed crystals has been discussed. In addition, the influence of composition of mixed crystals on F band parameters has been studied. The behaviour of observed F bands is correlated to local strained regions and to the configuration of F centre in mixed crystals.     

Copper uptake by silica and iron oxide under high surface coverage conditions: surface charge and sorption equilibrium modeling

A sorption modeling approach based on surface complexation concepts was applied to predict copper uptake and its effects on the surface electrostatic potential of ferric oxide and silica colloids. Equilibrium modeling of copper uptake by ferric oxide using the traditional surface complexation model (SCM) was reasonably successful with some discrepancies especially in the acidic pH ranges and high colloid concentration cases. Good predictions of the ferric oxide charge reversals during uptake were obtained from the modeling. Based on the SCM predictions, copper removal from solution is due to the outer-sphere complexation of the first hydrolysis product, resulting in the surface-metal complex SO(-)CuOH(+). The SCM was found to be insufficient to describe copper uptake by silica particles. To address discrepancies between experimental data and SCM predictions, the SCM was modified to include attributes of the surface polymer model (SPM), which incorporates sorption of the dimeric copper species Cu(2)(OH)(2)(2+). The continuum model (CM) was also studied as a second modification to the SCM to include formation of surface precipitates. Both the SPM and the CM were successful in modeling copper uptake and zeta potential variations as a function of pH at various solution conditions and colloid concentrations. From the SPM and CM predictions, it was concluded that for systems with high surface loadings, copper removal from solution occurs due to the formation of both monomeric and dimeric surface complexes, as well as through precipitation mechanisms.     

Multifractality and conformal invariance at 2D metal-insulator transition in the spin-orbit symmetry class

We study the multifractality (MF) of critical wave functions at boundaries and corners at the metal-insulator transition (MIT) for noninteracting electrons in the two-dimensional (2D) spin-orbit (symplectic) universality class. We find that the MF exponents near a boundary are different from those in the bulk. The exponents at a corner are found to be directly related to those at a straight boundary through a relation arising from conformal invariance. This provides direct numerical evidence for conformal invariance at the 2D spin-orbit MIT. The presence of boundaries modifies the MF of the whole sample even in the thermodynamic limit.