Kinetics and growth mechanism of the photoinduced synthesis of silver nanoparticles stabilized with lysozyme.

A fast and single-step procedure is reported for the preparation of stable solutions of spherical-shaped silver nanoparticles (AgNPs) coated with lysozyme (LZ). The preparation of the AgNP@LZ nanocomposites was based on the reduction of Ag+ with ketyl radicals photo-generated by the UVA-photolysis of the benzoin I-2959. Both reaction precursors bind to LZ, modifying its superficial charge and conformational structure. The photo-induced kinetics of formation of the AgNPs as a function of the LZ concentration was monitored in-situ by UV-vis absorption spectroscopy. The multivariate curve resolution-alternating least square (MCR-ALS) method was used for the deconvolution of the kinetic curves for each transient species formed before the growth of the final AgNPs colloids. The Kolmogorov-Johnson-Mehl-Avrami (KJMA) model to describe the formation of the AgNPs was used, and the respective first-order rate constants for the growth of the AgNPs as a function of the lysozyme concentration were calculated and the role of the protein capping in the growth kinetics was evaluated. Despite the protein being partially oxidized by the photo-generated radicals, it was strongly adsorbed onto the silver surface forming a tight coating shell around the AgNPs of approximately 30-60 protein molecules. As a result of the partial denaturation and crowded packing, its intrinsic lytic activity was strongly reduced.

Reorganization of Hydration Water of DPPC Multilamellar Vesicles Induced by l-Cysteine Interaction.

The aim of this study is to analyze the consequences of water redistribution on the structure and stability of phospholipid bilayers induced by cysteine (Cys). This interaction is studied with 1,2-dipalmitoyl- sn-glycero-3-phosphatidylcholine (DPPC) multilamellar vesicles in gel (30 °C) and liquid crystalline (50 °C) state; experimental studies were performed by means of Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and differential scanning calorimetry (DSC). The polar head sites of the lipid molecules to which water can bind are identified by competition with compounds that form hydrogen bonds, such as Cys. FTIR spectroscopy results revealed that there is a Cys interaction with the phospholipid head groups in the gel and liquid crystalline phases. Raman spectra were measured in the gel state. They were dominated by vibrations of the fatty acyl chains, with superposition of a few bands from the head group, and clearly showed that the S-H stretching band of Cys shifted to lower frequencies with a decrease in its force constant. DSC disclosed an overview of the behavior of the multilamellar vesicles in the working temperature range (30-50 °C) and showed how the increase of the molar ratios modified the environment of the polar head and the hydrocarbon chains. A loss of the pretransition ( TP) and an increase in the temperature of main transition ( Tm) with increasing Cys/DPPC molar ratio were observed.

Molecular view of the interaction of S-methyl methanethiosulfonate with DPPC bilayer.

We present molecular dynamics (MD) simulation studies of the interaction of a chemo preventive and protective agent, S-methyl methanethiosulfonate (MMTS), with a model bilayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). We analyzed and compared its diffusion mechanisms with the related molecule dimethyl sulfoxide (DMSO). We obtained spatially resolved free energy profiles of MMTS partition into a DPPC bilayer in the liquid-crystalline phase through potential of mean force (PMF) calculations using an umbrella sampling technique. These profiles showed a minimum for MMTS close to the carbonyl region of DPPC. The location of MMTS molecules in the DPPC bilayer observed in the MD was confirmed by previous SERS studies. We decomposed PMF profiles into entropic and enthalpic contributions. These results showed that the driving force for the partitioning of MMTS into the upper region of DPPC is driven by a favorable entropy change while partitioning into the acyl chains is driven by enthalpy. On the other hand, the partition of DMSO into the membrane is not favored, and is driven by entropy instead of enthalpy. Free diffusion MD simulations using all atom and coarse grained (CG) models of DPPC in presence of MMTS were used to analyze the effect of DPPC-MMTS interaction. Density profiles showed that MMTS locates preferentially in the carbonyl region, as expected according to the PMF profile and the experimental evidence. MMTS presented two differential effects over the packing of DPPC hydrocarbonate chains at low or at high molar ratios. An ordering effect was observed when a CG MMTS model was used. Finally, free diffusion MD and PMF decomposition for DMSO were used for comparison.

Gas-phase structure of 2,2,2-trichloroethyl chloroformate studied by electron diffraction and quantum-chemical calculations.

The molecular structure and conformational properties of 2,2,2-trichloroethyl chloroformate, ClC(O)OCH2CCl3 were determined experimentally using gas-phase electron diffraction (GED) and theoretically based on quantum-chemical calculations at the MP2 and DFT levels of theory. Further experimental measurements such as UV-visible, IR and Raman spectroscopy were complemented with the corresponding theoretical studies. All experimental results and calculations confirm the presence of two conformers namely anti-gauche (C1 symmetry) and anti-anti (Cs symmetry). The conformational preference was rationalised by NBO and AIM analyses. Molecular properties such as ionisation potential, electronegativity, chemical potential, chemical hardness and softness were deduced from HOMO-LUMO analyses. The TD-DFT approach was applied to assign the electronic transitions observed in the UV-visible spectrum. A detailed interpretation of the infrared and Raman spectra of the title compound are reported. Using calculated frequencies as a guide, IR and Raman spectra also provide evidence for the presence of both C1 and Cs conformers.

DFT calculations of structure and vibrational properties of 2,2,2-trichloroethylacetate, CH(3)CO(2)CH(2)CCl(3).

The molecular structure and conformational properties of 2,2,2-trichloroethylacetate, CH(3)CO(2)CH(2)CCl(3), were determined by ab initio (MP2) and DFT quantum chemical calculations at different levels of theory. The theoretical study was complemented with experimental measurements such as IR and Raman spectroscopy. The experimental and calculations confirm the presence of two conformers, one with anti, gauche conformation (C1 symmetry) and another with anti, anti form (Cs symmetry). The conformational preference was studied using the total energy scheme, NBO and AIM analysis. The infrared spectra of CH(3)CO(2)CH(2)CCl(3) are reported in the liquid and solid phases and the Raman spectrum in liquid phase. Using calculated frequencies as a guide, evidence for both C1 and Cs conformers is obtained in the IR and Raman spectra.

Layered crystal structure, conformational and vibrational properties of 2,2,2-trichloroethoxysulfonamide: an experimental and theoretical study.

The molecular structure of 2,2,2-trichloroethoxysulfonamide, CCl3CH2OSO2NH2, has been determined in the solid state by X-ray diffraction data and in the gas phase by ab initio (MP2) and DFT calculations. The substance crystallizes in the monoclinic P21/c space group with a = 9.969(3)Å, b = 22.914(6)Å, c = 7.349(2)Å, ß = 91.06(3)°, and Z = 8 molecules per unit cell. There are two independent, but closely related molecular conformers in the crystal asymmetric unit. They only differ in the angular orientation of the sulfonamide (SO2NH2) group. The conformers are arranged in the lattice as center-symmetric NH · · · O(sulf)-bonded dimers. Neighboring dimers are linked through further NH · · · O(sulf) bonds giving rise to a crystal layered structure. The solid state infrared and Raman spectra have been recorded and the observed bands assigned to the molecular vibration modes. Also, the thermal behavior of the substance was investigated by TG-DT analysis. The stability of the molecule arising from hyper-conjugative interactions and charge delocalization has been analyzed using natural bond (NBO) analysis.

Interaction of S-methyl methanethiosulfonate with DPPC bilayer.

The present study is a first step towards the investigation of S-methyl methanethiosulfonate (MMTS) interaction with membrane model systems like liposomes. In this paper, the interaction of MMTS with dipalmitoylphosphatidylcholine (DPPC) bilayers was studied by FTIR and SERS spectroscopy. Lysolipid effect on vesicle stability was studied. The results show that MMTS interacts to different extents with the phosphate and carbonyl groups of membranes in the gel and the liquid crystalline states. To gain a deeper insight into MMTS properties that may be potentially helpful in the design of new drugs with therapeutic effects, we performed theoretical studies that may be the basis for the design of their mode of action.

Conformational and vibrational analysis of methyl methanesulfonate, CH3SO2OCH3.

The molecular structure of methyl methanesulfonate, CH(3)SO(2)OCH(3), has been optimized by using methods based on density functional theory, coupled cluster, and Moller-Plesset second order perturbation theory (MP2). With regard to CH(3)SO(2)OCH(3), two populated conformations with symmetries C(s) and C(1) are obtained, the former being more stable than the latter. The theoretical data indicate that although both anti and gauche conformers are possible by rotation about the S-O bond, the preferred conformation is anti. The total energy as a function of the CSOC dihedral angle has been calculated using the MP2 method with the 6-31G(d) and cc-pVDZ basis sets and the hybrid functional B3LYP using 6-31G(d), 6-311G(d,p), and 6-311++G(d,p) basis sets. A natural bond orbital analysis showed that the lone pair --> sigma* hyperconjugative interactions favor the anti conformation. Furthermore, the infrared spectra for the liquid and solid phases, the Raman spectrum for the liquid one, and the inelastic neutron scattering spectrum of the solid phase have been recorded, and the observed bands have been assigned to the vibrational modes. The experimental vibrational data, along with calculated theoretical force constants, were used to define a scaled quantum mechanical force field for the target system that enabled us to fit the measured frequencies with a final root-mean-square deviation of 10 cm(-1).

Gas-phase structure, rotational barrier, and vibrational properties of methyl methanethiosulfonate, CH3SO2SCH3: an experimental and computational study.

The molecular structure of methyl methanethiosulfonate, CH3SO2SCH3, has been determined in the gas phase from electron-diffraction data supplemented by ab initio (HF, MP2) and density functional theory (DFT) calculations using 6-31G(d), 6-311++G(d,p), and 6-311G(3df,3pd) basis sets. Both experimental and theoretical data indicate that although both anti and gauche conformers are possible by rotating about the S-S bond, the preferred conformation is gauche. The barrier to internal rotation in the CSSC skeleton has been calculated using the RHF/6-31G(d), MP2/6-31G(d), and B3LYP/6-31G(d) methods as well as MP2 with a 6-31G(3df) basis set on sulfur and 6-31G(d) on C, H, and O. A 6-fold decomposition of the rotational barrier has been performed in terms of a Fourier-type expansion, enabling us to analyze the nature of the potential function, showing that the coefficients V1 and V2 are the dominant terms; V1 is associated with nonbonding interactions, and V2 is associated with hyperconjugative interactions. A natural bond orbital analysis showed that the lone pair --> sigma* hyperconjugative interactions favor the gauche conformation. Furthermore, the infrared spectra for the liquid and solid phases and the Raman spectrum for the liquid have been recorded, and the observed bands have been assigned to the vibrational normal modes. The experimental vibrational data, along with calculated theoretical force constants, were used to define a scaled quantum mechanical force field for the target system that enabled us to estimate the measured frequencies with a final root-mean-square deviation of 6 cm-1.