First-principles and Molecular Dynamics simulation studies of functionalization of Au32 golden fullerene with amino acids.

With the growing potential applications of nanoparticles in biomedicine especially the increasing concerns of nanotoxicity of gold nanoparticles, the interaction between protein and nanoparticles is proving to be of fundamental interest for bio-functionalization of materials. The interaction of glycine (Gly) amino acid with Au32 fullerene was first investigated with B3LYP-D3/TZVP model. Several forms of glycine were selected to better understand the trends in binding nature of glycine interacting with the nanocage. We have evaluated various stable configurations of the Gly/Au32 complexes and the calculated adsorption energies and AIM analysis indicate that non-Gly, z-Gly and also tripeptide glycine can form stable bindings with Au32 at aqueous solution via their amino nitrogen (N) and/or carbonyl/carboxyl oxygen (O) active sites. Furthermore, cysteine, tyrosine, histidine and phenylalanine amino acids bound also strongly to the Au32 nanocage. Electronic structures and quantum molecular descriptors calculations also demonstrate the significant changes in the electronic properties of the nanocage due to the attachment of selected amino acids. DFT based MD simulation for the most stable complex demonstrate that Gly/Au32 complex is quite stable at ambient condition. Our first-principles findings offer fundamental insights into the functionalization of Au32 nanocage and envisage its applicability as novel carrier of the drugs.

DFT/TD-semiempirical study on the structural and electronic properties and absorption spectra of supramolecular fullerene-porphyrine-metalloporphyrine triads based dye-sensitized solar cells.

In the present work density functional theory (DFT) and time-dependent semiempirical ZNIDO/S (TD-ZNIDO/S) methods have been used to investigate the ground state geometries, electronic structures and excited state properties of triad systems. The influences of the type of metal in the porphyrin ring, change in bridge position and porphyrine-ZnP duplicate on the energies of frontier molecular orbital and UV-Vis spectra has been studied. Geometry optimization, the energy levels and electron density of the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), chemical hardness (η), electrophilicity index (ω), electron accepting power (ω+) were calculated using ZINDO/S method to predict which molecule is the most efficient with a great capability to be used as a triad molecule in solar industry. Moreover the light harvesting efficiency (LHE) was calculated by means of the oscillator strengths which are obtained by TD-ZINDO/S calculation. Theoretical studies of the electronic spectra by ZINDO/S method were helpful in interpreting the observed electronic transitions. This aspect was systematically explored in a series of C60-Porphyrine-Metalloporphyrine (C60-P-Mp) triad system with M being Fe, Co, Ni, Ti, and Zn. Generally, transition metal coordination compounds are used as effective sensitizers, due to their intense charge-transfer absorption over the whole visible range and highly efficient metal-to-ligand charge transfer. We aim to optimize the performance of the title solar cells by altering the frontier orbital energy gaps. The results reveal that cell efficiency can be enhanced by metal functionalization of the free base porphyrin. Ti-porphyrin was found to be the most efficient dye sensitizer for dye sensitized solar cells (DSSCs) based on C60-P-Mptriad system due to C60-Por-TiP complex has lower chemical hardness, gap energy and chemical potential as well as higher electron accepting power among other complexes. In addition, the performance of solar cells favors better with doubly and increasing the π conjugated of the bridge.

Synthesis, spectral and luminescence study, crystal structure determination and DFT calculation of binuclear palladium(II) complexes.

Binuclear palladium(II) complexes with metal-metal (d8-d8) bonding interaction were synthesized by reactions of the 1-methyl-1H-1,2,3,4-tetrazole-5-thiol (Hmtzt) or a mixture of Hmtzt and 1,3-propanediamine (1,3-pda) ligands. Complex [Pd2(µ-mtzt)4]·2CH3CN (1) was synthesized by the reaction of Pd(OAc)2 with Hmtzt dissolved in acetonitrile and complex [Pd2(µ-mtzt)2(mtzt)2(1,3-pda)] (2) was synthesized by reaction of a mixture of Hmtzt and 1,3-propanediamine (dissolved in methanol) with PdCl2 (dissolved in acetonitrile) and were identified through elemental analysis, IR, UV-Vis, 1H NMR, luminescence spectroscopy as well as single-crystal X-ray diffraction method. A single-crystal of complex 1 shows that two Pd(II) centers are linked together by four bridging tetrazole ligands providing a paddle wheel-like arrangement. Also a crystal structure of complex 2 shows that this complex possesses a symmetric structure in which one Pd atom is tetra-coordinated by four sulfur atoms to forms PdS4 and other Pd atom is tetra-coordinated by four nitrogen to forms PdN4 coordination sphere. Density functional theory (DFT) was performed in this study for the Hmtzt ligand and binuclear palladium(II) complexes (1) and (2). The DFT calculation shows PdII-PdII bond lengths of 2.831 and 3.086Å in complex 1 and 2, respectively which are close to the observed bond lengths of 2.802(11) and 3.0911(17)Å from single-crystal X-ray structure. The optimized geometry of the complexes is shown good agreement by X-ray data. Structural properties and molecular descriptors including bond lengths, bond angles, chemical hardness, dipole moment, HOMO-LUMO energy levels, electron transfer were analyzed. The IR spectroscopy was performed using VEDA4 software and UV-Vis spectra were analyzed using time-dependent density functional theory (TD-DFT) method. The theoretical and experimental data were also compared with each other.

Molecular origin of drug release by water boiling inside carbon nanotubes from reactive molecular dynamics simulation and DFT perspectives.

Owing to their nanosized hollow cylindrical structure, CNTs hold the promise to be utilized as desired materials for encapsulating molecules which demonstrate wide inferences in drug delivery. Here we evaluate the possibility of drug release from the CNTs with various types and edge chemistry by reactive MD simulation to explain the scientifically reliable relations for proposed process. It was shown that heating of CNTs (up to 750 K) cannot be used for release of incorporated drug (phenylalanine) into water and even carbonated water solvent with very low boiling temperature. This is due to the strong physisorption (π-stacking interaction) between the aromatic of encapsulated drug and CNT sidewall which causes the drug to bind the nanotube sidewall. We have further investigated the interaction nature and release mechanism of water and drug confined/released within/from the CNTs by DFT calculations and the results confirmed our MD simulation findings. The accuracy of DFT method was also validated against the experimental and theoretical values at MP2/CCSD level. Therefore, we find that boiling of water/carbonated water confined within the CNTs could not be a suitable technique for efficient drug release. Our atomistic simulations provide a well-grounded understanding for the release of drug molecules confined within CNTs.

Tunable phenol remediation from wastewater using SWCNT-based, sub-nanometer porous membranes: reactive molecular dynamics simulations and DFT calculations.

The importance and impact of the application of CNT membranes with sub-nanometer pores for effective water purification are marvelous. Here we demonstrate, by reactive MD simulations, that CNT membranes can efficiently reject phenol due to molecular size exclusion effects and yield high permeability of water. The water flux in armchair CNTs with a pore diameter of about 7 Å is 1.3 orders of magnitude greater than that of the zigzag counterparts, and pore chemistry plays an important role in moderating the water flux. Nanotubes with H-capped atoms on their rims lead to higher fluxes (50 times) than that of the C-passive counterpart. In nanotubes of larger diameters (8 Å), the pore size is large enough to permit phenol molecules to permeate without any restraint. A series of evidence-based investigations on the interaction nature of the systems under consideration was performed to explain the specific molecular factors as well as systematically reliable relationships for water molecules penetrating through various nanotubes. DFT calculations were also performed to evaluate the validity of the reactive potential employed here. We expect these findings to establish a basis for the design of novel energy-efficient nanotube based membranes as an economical means for the removal of organic contaminants from water, and they can be a benchmark for directing experimental efforts, which are presently restricted by the difficulty associated with creating sub-nanometer pores of a specific size for water treatments.

Computational studies on the interactions of glycine amino acid with graphene, h-BN and h-SiC monolayers.

In the present work, the adsorption of glycine amino acid and its zwitterionic form onto three different hexagonal sheets, namely graphene, boron-nitride (h-BN) and silicon carbide (h-SiC), has been investigated within the framework of Density Functional Theory (DFT) calculations. The energetics and geometrical parameters of the considered systems have been explored at the GGA-PBE level in combination with Grimme's empirical dispersion corrections with Becke-Johnson damping, the DFT-D3(BJ) method. Based on the obtained results, we found that both the glycine molecule and its zwitterionic conformation tend to be chemisorbed onto the surface of h-SiC (Eads ranges from -1.01 to -1.319 eV) while the types of interactions are recognized to be of non-covalent nature for the case of graphene (Eads ranges from -0.121 to -0.345 eV) and h-BN (Eads ranges from -0.103 eV to -0.325 eV) systems. Moreover, the empirical dispersion corrections applied in these calculations significantly improved the results and confirmed the crucial role of dispersion corrections in obtaining reliable geometries and adsorption energies. Our findings revealed that the electronic properties of the considered systems did not change during the adsorption process and these monolayers preserve their inherent electronic properties as they interact with the glycine molecule. Using the SMD implicit solvation model, the effect of solvation has also been evaluated by re-optimizing the structures within a medium with a dielectric constant of 78.39 (liquid water) and it has been shown that the strength of the interaction between the glycine conformers and hexagonal sheets has decreased. The accuracy of the obtained values has been evaluated by some benchmark calculations at the hybrid PW6B95 level of theory and reasonable consistency is found between the results of the PBE-D3 method and our benchmark system. In summary, h-SiC exhibited the highest affinity toward glycine conformers and gained an important edge over other monolayers. Our findings would actively encourage experimentalists to explore the potential applications of these materials in drug delivery, biofunctionalization of nanostructured monolayers as well as electronic and nanosensor devices.

Theoretical insight into hydrogen adsorption onto graphene: a first-principles B3LYP-D3 study.

This work investigates hydrogen adsorption onto various graphene flakes such as coronene and coronene-like as suitable models of graphene within the framework of the DFT-B3LYP method. The non-local van der Waals (vdW) density functional (B3LYP-D3) method is used for both structural geometry optimization and total energy estimations. Calculations were carried out for a hydrogen molecule above a coronene surface with both conventional and vdW corrected DFT to investigate how these approaches perform in the case of hydrogen adsorption on a graphene surface. Our first-principles results within the B3LYP-D3/def2-TZVPP model show that hydrogen physisorbs on a coronene surface with an adsorption energy of -5.013 (kJ mol(-1)) which is in good agreement with the experimental value. The influence of the basis set and graphene flake size were also evaluated and the results indicate that these slightly affect the adsorption properties. We found also that it is crucial to use non-local dispersion interactions to get accurate results for hydrogen adsorption on a graphene surface. Furthermore, the co-adsorption of H2 molecules onto the graphene surface was investigated. The results obtained at the B3LYP-D3/def2-TZVP level show that H2 molecules can be physisorbed on both sides of the graphene layer with adsorption properties similar to those for a single surface. Finally, we showed that H2 molecules might be bound to the graphene surface via a bilayer adsorption scheme with weak adsorption energy. Charge population and electron density analysis confirm the weak binding nature of the system under consideration.

Simulations on the possibility of formation of complexes between fluorouracil drug and cucurbit[n]urils: ab initio van der Waals DFT study.

The binding geometry of fluorouracil/cucurbit[n]urils (CB[n]s) complexes with n = 5-8 is investigated using the first-principles van der Waals density functional (vdW-DF) method, involving full geometry optimization. Such host-guest complexes are typically calculated using conventional DFT method, which significantly underestimates non-local dispersion forces (or vdW contributions) and therefore affects interactions between respected entities. We address here the role of vdW forces for the fluorouracil and CB[n]s molecules which can form directional hydrogen bonds with each other. It was found that the inclusion of dispersion interactions significantly affects the host-guest binding properties and the hydrogen bonding between the molecules provides the main binding mechanism, while results in the same geometries for the considered complexes. The 0.84 eV binding energy, for the thermodynamically favorable state, reveals that the interaction of fluorouracil with CB[n]s is an exothermic interaction and typical for strong hydrogen bonding. Furthermore, we have investigated the binding nature of these host-guest systems in aqueous solution with ab initio MD simulations adopting vdW-DF method. These findings afford evidence for the applicability of the vdW-DF approach and provide a realistic benchmark for the investigation of the host-guest complexes.

Necessity of Routine Forearm Radiography before Arterio Venous Fistula Creation in Diabetics & Old Patients

AVF loss and recurrent requirement of AVF constitution increase with HD vintage. Studies in different regions shows different results in the impact of presence of DM on AVF survival. This study showed that age and DM had significant relation with arterial calcification in Iranian patients who had renal failure.

The outcome of induction therapy with monoclonal antibodies in kidney transplantation among Iranian patients: a prospective study.

INTRODUCTION: The administration of interlukin-2 receptor antagonists for induction therapy has reduced the incidence of acute rejection episodes in kidney transplantation. Although some studies have investigated the efficacy of these monoclonal antibodies, there is little experience among Iranian kidney transplant recipients. MATERIALS AND METHODS: Forty-three patients randomly divided into 2 groups were prospectively followed for 3.4 years. Eighteen patients received 2 doses of basiliximab (group I) and another 25 patients received 5 doses of daclizumab (group II). The posttransplantation complications, last serum creatinine level, as well as graft and patient survival rates were compared to investigate the efficacy of these therapies. RESULTS: Among 43 patients, 11.6% experienced acute rejection episodes: 22.2% in group I and 4% in group II (P > .05). In this study, 4.6% of recipients underwent graft nephrectomy: 11.1% in group I and 4% in group II (P > .05). The mortality rate was 4.6%: 5.5% in group I and 4% in group II (P > .05). The mean serum creatinine level was 1.47 +/- 0.7 mg/dL. Although it was lower in group I, the difference was not significant. The 1-year graft and patient survival rates were 90.6% and 95.3%, respectively, with no significant differences between the groups. DISCUSSION: Although induction therapy with monoclonal antibodies may reduce the incidence of acute rejection episodes, graft and patient survival rates were unchanged compared with conventional therapies. Also, there were no significant differences between the results of induction therapy with basiliximab and daclizumab.

Chronic kidney disease after hematopoietic cell transplantation: frequency, risk factors, and outcomes.

BACKGROUND: Occurrence of chronic kidney disease (CKD) after hematopoietic cell transplantation (HCT) is rare with relatively few reported cases. The aim of this study was to evaluate the frequency of CKD among patients who received HCT for hematologic and nonhematologic disorders. OBJECTIVE: We performed a prospective study to evaluate the frequency of CKD and its risk factors. Between 1997 and 2006 there were 1693 patients engrafted at the Bone Marrow Transplant Research Center. METHOD: CKD was defined as a doubling of serum creatinine level from the baseline and after 1 year from receiving a transplantation. The risk of CKD in relation to a non-based total body irradiation conditioning regimen, the type of graft (allograft autograft), and the incidences of graft-versus-host disease (GVHD), drug toxicity, and veno occlusive disease (VOD) were examined in 1963 HCT patients. RESULTS: Kidney involvement developed in 66 patients (4%). By 6-12 months after HCT, approximately 33% of these patients developed CKD (23 patients: 19 allograft and 4 autograft). In most CKD patients, the cause was idiopathic. In 23 patients who developed CKD, 5 patients had acute kidney injury during the transplantation period with GVHD. Other renal involvements were as follows: hypertension (17%), proteinuria (15%), hydronephrosis (2%), hematuria (18%), and diabetes (3%). CONCLUSION: The frequency of CKD in this study seems to be high. It is important to know the specific type of kidney damage, to determine when to be aware of the time of occurrence of renal complications and to understand the best methods to treat patients with renal injury secondary to nephrotic syndrome and idiopathic CKD.

Benign and malignant skin lesions in renal transplant recipients.

BACKGROUND: Skin lesions - benign and malignant - occur frequently in organ transplant recipients receiving long-term immunosuppressive therapy. These patients are at greater risk of skin cancers. AIMS: To study dermatologic problems in renal transplant recipients (RTRs). METHODS: One hundred patients (53 men and 47 women) were consecutively examined for benign and malignant skin complications since transplantation in Razi Hospital in Tehran Medical University. The main immunosuppressive therapy regimen in these patients was a combination of prednisolone, azathioprine, and cyclosporine. RESULTS: The early and most common complication was cosmetic side effects that occurred in 98% patients. Skin infections occurred in 83% of the patients and most of them were viral infections (65%), especially of human papilloma viruses (HPVs) in 40% of the patients. We found six cases of malignancy in these patients in that four cases were skin cancers, including one case of SCC, one BCC, and two cases of Kaposi's sarcoma. Dermatologic problems occur most frequently in RTRs, especially skin cancers which have higher frequency in these patients than general population, particularly, Kaposi sarcoma. Sun exposure has an important role in developing epithelial skin cancers following transplantation. The age of developing skin cancer in these patients was early than normal population. CONCLUSION: Our results emphasize the importance of dermatologic examinations and monitoring RTRs to obtain an early diagnosis and treatment of cutaneous manifestations.

Behavior of a single nitrogen molecule on the pentagon at a carbon nanotube tip: a first-principles study.

Density functional theory (DFT) is used to investigate the adsorption properties of nitrogen on the pentagon at the tip of a capped (5, 5) single-walled carbon nanotube. The adsorption of N(2) outside the carbon nanotube with a parallel orientation with respect to the plane of the pentagon is found to be the most stable state of adsorption. Its binding energy of -0.318 eV is very small, with a large C-N equilibrium distance of 2.94 Å. We have also investigated the number and the position of adsorption sites in the pentagon for the parallel configuration. This knowledge can lead to the precise control of adsorption states, and consequently may bring about a novel multistate monomolecular device. We find two stable configurations of the molecule that have only a small difference in energy, while the other configurations are energetically unfavorable. Our results support previous experimental predictions that the nitrogen molecule transits between two states with a small current pulse. The predicted position sites for the transient states are in reasonable agreement with experimental observations.

Association of hyperglycemia on allograft function in the early period after renal transplantation.

Hyperglycemia is common following renal transplantation. This study was conducted to evaluate the relationship of perioperative serum glucose levels and acute rejection in 100 nondiabetic patients who underwent renal transplantation. Blood glucose was measured immediately following surgery and every 6 hours during the first 48 hours posttransplant as well as for 1 month to evaluate occurrence of acute rejection episodes (ARE). The rate of ARE was 33%. The mean blood glucose level immediately after surgery in patients with versus without ARE was 249.67 +/- 61.78 and 184.82 +/- 73.35 mg/dL, respectively (P=.000). There was no significant correlation between ARE and donor or recipient age or sex, delayed graft function, type of donor, or treatment. This study suggested a correlation between immediate blood glucose and ARE. In this regard, blood glucose monitoring and control during operation and immediate postoperatively may reduce the acute rejection rate.