Preparation, spectral characterization, cytotoxic and thermal studies of platinum (IV) thiohydrazone complexes

Platinum (IV) complexes of type [Pt(L)₂Cl₂] [where, L=benzaldehyde-N,N-diphenyl-N-thiohydrazone (L¹), salicylaldehyde-N,N-diphenyl-N-thiohydrazone (L²), acetaphenone-N,N-diphenyl-N-thiohydrazone (L³) and cyclohexanone-N,N-diphenyl-N-thiohydrazone (L⁴)] have been synthesized. The thiohydrazones can exist as thione–thiol tautomer and coordinates as a bidentate N–S ligand. The ligands found to act in monobasic bidentate fashion. Analytical data reveals that metal to ligand stoichiometry is 1:2. The complexes have been characterized by elemental analysis, IR, mass, electronic, ¹H NMR spectroscopic studies, and TG/DTA study. Various kinetic and thermodynamic parameters like order of reaction (n), activation energy (E_a), apparent activation entropy (S^#) and heat of reaction (ΔH) have also been carried out for one complex. Cytotoxic study has also been carried out for one complex.     

Synthesis and spectroscopic properties of reconstituted zinc-myoglobin appending a DNA-binding platinum(II) complex

A reconstituted zinc-myoglobin (ZnMb) dyad, ZnMb-[Pt(bpy)(en)]2+, has been prepared by incorporating chemically-modified zinc-porphyrin, being capable of DNA-binding of the Pt complex, [Pt(bpy)(en)]2+, where bpy and en are 2,2'-bipyridine and ethylenediamine, respectively. The steady-state fluorescence of the cofactor, [Pt(bpy)(mu-enPP)Zn]Cl2, in MeOH indicates that the excited singlet state of zinc--porphyrin was almost quenched, probably because of the strong hydrophobic and pi-pi stacking interactions between the [Pt(bpy)(mu-enPP)Zn]2+ ions. In the reconstituted ZnMb-[Pt(bpy)(en)]2+, the quenching reaction of 1(ZnMb)* with the [Pt(bpy)(en)]2+ moiety does not occur, indicating apo-Mb matrix is essential. On the other hand, when the [Pt(bpy)(en)]2+ moiety was excited, the enhancement of the fluorescence from ZnMb unit was observed. It is suggested that the energy transfer from (1)([Pt(bpy)(en)]2+)* to ZnMb occurs. The spectroscopic changes of ZnMb-[Pt(bpy)(en)]2+ in the presence of calf-thymus DNA were also provided. Soret band at 428 nm gradually decreased, and isosbestic points at 321, 414, and 432 nm were observed with increasing the DNA concentration. When the Pt(II) moiety was excited at lambda(ex) 321 nm, the fluorescence signal around 600 nm similarly decreased. The synthetic manipulation of ZnMb by using a DNA-binding Pt(II) complex demonstrates sensitive fluorescent signal for DNA and valuable information to study photoinduced electron transfer within a Mb-DNA complex.     

Synthesis, thermal and photophysical properties of phenoxy-substituted dendrimeric cyclic phosphazenes

In the present study, we describe the synthesis of a hydroxyl substituted bridged phenoxycyclotriphosphazene (5), [N₃P₃(OPh)₅OPhO(OPh)₅N₃P₃OPhOH], as a side group and its use for preparation of dendrimeric cyclic phosphazenes. For this purposes, compound 5 is synthesised in five steps from the reactions of cyclotriphosphazene with phenol derivatives. The dendrimeric compounds 6 and 7 have been prepared by the reactions of compound 5 with hexachlorocyclotriphosphazene, N₃P₃Cl₆, or octachlorocyclotetraphosphazene, N₄P₄Cl₈, respectively. Newly synthesized compounds have been fully characterized by elemental analysis, MALDI-TOF mass spectrometry, FT-IR, ¹H, ¹³C and ³¹P NMR spectroscopy. The thermal stability and fluorescence spectral properties of dendrimeric compounds 6 and 7 are investigated and compared with that of the previously reported cyclic compounds (I-II). Fluorescence quantum yields and lifetimes of dendrimeric compounds and their quenching behaviour by 1,4-benzoquinone are studied in dichloromethane.     

An azomethin-zinc complex for organic electroluminescence: Crystal structure, thermal stability and optoelectronic properties

An azomethin-zinc complex, bis[salicylidene(4-dimethylamino)aniline]zinc(II) (Zn(sada)₂) was synthesized and structurally characterized by single-crystal X-ray crystallography. Crystal data for Zn(C₁₅H₁₅N₂O)₂ was determined as follows: space group, triclinic, ; a = 10.2791(9) Å, b = 16.5008(14) Å, c = 17.5984(15) Å, α = 114.830(2)°, β = 96.579(2)°, γ = 97.674(2)°, Z = 4. Through thermal analysis characterization and FT-IR spectra, this complex was proved to have good thermal stability. The vapor-deposited films exhibited uniform and environment-stable morphology. The light emission and charge transporting performance of Zn(sada)₂ in organic light emitting diodes (OLEDs) were investigated preliminarily, and the results indicated the superior electron transporting property of this complex. Compared with the typical bilayer device of N,N′-diphenyl-N,N′-bis(1-naphthyl)-benzidine (NPB)/tris-(8-hydroxyquinoline)aluminum (Alq₃), the device with Zn(sada)₂ as the electron transporting layer exhibited a much lower turn-on voltage of 2.5 V (it is usually 3.5 V for an NPB/Alq₃ device).     

Predicting sequence-dependent melting stability of short duplex DNA oligomers

Many important applications of DNA sequence-dependent hybridization reactions have recently emerged. This has sparked a renewed interest in analytical calculations of sequence-dependent melting stability of duplex DNA. In particular, for many applications it is often desirable to accurately predict the transition temperature, or t_m, of short duplex DNA oligomers (∼ 20 base pairs or less) from their sequence and concentration. The thermodynamic analytical method underlying these predictive calculations is based on the nearest-neighbor model. At least 11 sets of nearest-neighbor sequence-dependent thermodynamic parameters for DNA have been published. These sets are compared. Use of the nearest-neighbor sets in predicting t_m from the DNA sequence is demonstrated, and the ability of the nearest-neighbor parameters to provide accurate predictions of experimental t_m's of short duplex DNA oligomers is assessed. © 1998 John Wiley & Sons, Inc. Biopoly 44: 217–239, 1997     

Preparation, structural, magnetic and thermal properties of two heterobimetallic cyano-bridged nickel(II)-copper(II)/platinum(II) coordination polymers

Two unique bimetalic Pt(II) coordination polymers of composition [Ni(hydeten)₂Pt(CN)₄] (Ni-Pt) and [Cu(hydeten)₂Pt(CN)₄] (Cu-Pt) [hydeten = N-(2-hydroxyethyl-ethylenediamine) or 2-(2-aminoethylamino)ethanol] have been synthesized and structurally characterized by various methods in this study. The crystal structure of Cu-Pt was determined by single-crystal X-ray diffraction analysis. The structure of Cu-Pt forms of infinite 2,2-TT type [-Cu(hydeten)₂-NC-Pt(CN)₂-CN-] chains containing paramagnetic copper atoms bridged by tetracyanoplatinate species. In this complex, Cu(II) centers display an axially elongated octahedron with two chelating hydeten molecules in the equatorial positions and N-bonded bridging cyano groups in the axial positions, whereas Pt(II) centers are four coordinate with four cyanide-carbon atoms in a square-planar arrangement. The decrease of the moments of these complexes in temperature range of 50 305 K can assigned to the antiferromagnetic interactions in the structures. The thermal decomposition of Cu-Pt comprise of five distinguished stages, while the thermal decomposition of Ni-Pt take place four different stages.     

Thermal stability of triple helical DNAs containing 2'-deoxyinosine and 2'-deoxyxanthosine

In this paper, we describe the synthesis and thermal stabilities of the triplexes containing either 2′-deoxyinosine (1) or 2′-deoxyxanthosine (3) in their second strands. It was found that the triplexes with the 2′-deoxy-5-methylcytidine(dM)•1:dC and dM•1:dA base triplets are thermally stable, but those containing the dM•1:T and dM•1:dG base triplets are unstable under both neutral and slightly acidic conditions. On the other hand, it was found that the oligonucleotide containing 3 could form thermally stable triplexes with the oligonucleotides that involve four natural bases opposite the sites of 3. The rank of the thermal stabilities of the triplexes was as follows: the triplex containing the dM•3:dC base triplet > that containing the dM•3:dA base triplet > that containing the dM•3:T base triplet > that containing the dM•3:dG base triplet.     

Synthesis, thermal stability and photoluminescence of new cadmium sulfide/organic composite hollow sphere nanostructures

Novel cadmium sulfide/organic composite hollow spheres composed of sword-like nanorods were synthesized via a simple reaction between cadmium salts and thioglycolic acid (TGA) at room temperature. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SEAD) and Fourier transform infrared (FT-IR) spectra. Thermal stability of the organic composite was investigated. CdS/organic composite would decompose into pure wurtzite CdS through hydrothermal treatment. Effect of the cadmium source on the formation of the CdS/organic composite was investigated. Photoluminescence (PL) was used to study the optical properties of CdS/organic composite and pure CdS.     

Role of weak interactions in thermal stability of proteins

A database analysis was done to study the role of weak interactions such as CHcdots, three dots, centeredO, CHcdots, three dots, centeredPI(m) and NHcdots, three dots, centeredPI(m) in the thermal stability of proteins. The CHcdots, three dots, centeredO and CHcdots, three dots, centeredPI(m) interactions are more in the case of thermophilic proteins as compared to mesophiles. Amino acid analysis showed that hydrophobic amino acids like Val and Ile, and Cys contribute more to CHcdots, three dots, centeredO hydrogen bonds where as Pro and Gly contribute more to CHcdots, three dots, centeredPI(m) interactions. Though NHcdots, three dots, centeredPI(m) interactions are dominated by Lys and Arg in thermophiles and mesophiles, the Arg contribution is significantly higher in thermophiles. Interestingly, Glycine is a predominant contributor to all the weak interactions. The number of aromatic amino acids in the thermophiles is more and hence a large number of aromatic clusters were observed in this class. Thus, a cumulative effect of weak interactions seems to be important in thermal stability of proteins. The study also shows that introduction of Gly, Arg, Phe, Pro, and Tyr may enhance the thermal stability.     

Thermal stability of Artemia HGPRT: effect of substrates on inactivation kinetics

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT, E.C. 2.4.2.8) from Artemia cysts exhibits maximum activity at 70°C. Its thermal stability has been examined following enzymatic activity as a function of temperature. Cold-induced renaturation experiments of samples heated at increasing temperatures showed that reversibility of thermal inactivation depends on the incubation time and final temperature. Prolonged incubation of the thermoinactivated enzyme at 0°C did not afford any further increase of the catalytic activity at 37°C. The complex substrate PRPP:Mg protects HGPRT from thermal inactivation. However, incubations with hypoxanthine rendered a less thermostable enzyme at any temperature tested. The irreversible inactivation of HGPRT proceeds in two exponential steps. The analysis of the apparent rate constants for the fast and the slow phases, λ₁ and λ₂ as per the Lumry and Eyring model suggests the existence of more than three states in the thermal denaturation pathway of the free enzyme. In the presence of PRPP:Mg the irreversible process follows a single exponential and proceeds very slowly below 70°C. PRPP:Mg also protects the enzyme from inactivation by NEM and pCMB, suggesting that -SH groups may be in the vicinity of the active site     

Effect of phosphorylation on the thermal and light stability of the thylakoid membranes

Higher plant thylakoid membranes contain a protein kinase that phosphorylates certain threonine residues of light-harvesting complex II (LHCII), the main light-harvesting antenna complexes of photosystem II (PSII) and some other phosphoproteins (Allen, Biochim Biophys Acta 1098:275, 1992). While it has been established that phosphorylation induces a conformational change of LHCII and also brings about changes in the lateral organization of the thylakoid membrane, it is not clear how phosphorylation affects the dynamic architecture of the thylakoid membranes. In order to contribute to the elucidation of this complex question, we have investigated the effect of duroquinol-induced phosphorylation on the membrane ultrastructure and the thermal and light stability of the chiral macrodomains and of the trimeric organization of LHCII. As shown by small angle neutron scattering on thylakoid membranes, duroquinol treatment induced a moderate (~10%) increase in the repeat distance of stroma membranes, and phosphorylation caused an additional loss of the scattering intensity, which is probably associated with the partial unstacking of the granum membranes. Circular dichroism (CD) measurements also revealed only minor changes in the chiral macro-organization of the complexes and in the oligomerization state of LHCII. However, temperature dependences of characteristic CD bands showed that phosphorylation significantly decreased the thermal stability of the chiral macrodomains in phosphorylated compared to the non-phosphorylated samples (in leaves and isolated thylakoid membranes, from 48.3°C to 42.6°C and from 47.5°C to 44.3°C, respectively). As shown by non-denaturing PAGE of thylakoid membranes and CD spectroscopy on EDTA washed membranes, phosphorylation decreased by about 5°C, the trimer-to-monomer transition temperature of LHCII. It also enhanced the light-induced disassembly of the chiral macrodomains and the monomerization of the LHCII trimers at 25°C. These data strongly suggest that phosphorylation of the membranes considerably facilitates the heat- and light-inducible reorganizations in the thylakoid membranes and thus enhances the structural flexibility of the membrane architecture.     

Transglutaminase-catalyzed synthesis of trypsin-cyclodextrin conjugates: kinetics and stability properties

Bovine pancreatic trypsin was modified by the mono-6-amino-6-deoxy derivatives of alpha-, beta-, and gamma-cyclodextrin through a transglutaminase-catalyzed reaction. The trypsin-cyclodextrin conjugates, containing about 3 mol of oligosaccharide per mole of protein, were tested for their catalytic and stability properties. The specific esterolytic activity and the kinetics constants of trypsin were significantly improved following the transglutaminase-induced structural modifications. Trypsin-cyclodextrin conjugates were also found markedly (sixfold) more resistant to autolytic degradation at alkaline pH, and their thermal stability profile was improved by about 16 degrees C. Moreover, they were particularly resistant to heat inactivation when treated at different temperatures ranging from 45 degrees C to 70 degrees C for different periods of time.     

Calibration of the change in thermal stability of DNA duplexes and degree of base pair mismatch

Summary One method of determining the degree of base pair divergence between two sources of DNA (different strains, species, etc.) is to determine the decrease in thermal stability of hybrid duplex DNA due to mismatching of base pairs. Attempts to calibrate the change in median melting temperature (T_m) to base pair mismatch have led to conflicting results. We have studied the T_m between DNAs of known sequence over a range of from 0.55% to 7.2% base pair mismatch. The relationship of T_m and percent base pair mismatch is remarkably linear over this range with a correlation coefficient >0.98. A T_m of 1°C corresponds to 1.7% base pair mismatch. This conversion is higher than that usually assumed and, therefore, rates of DNA evolution estimated by DNA-DNA hybridization studies are likely faster than previously thought.     

近交系小鼠双色荧光正相杂交芯片技术体系的建立和优化

目的探讨采用单核苷酸多态性（SNP）检测方法-双色荧光正相杂交芯片技术对近交系小鼠遗传质量监测及相关影响因素。方法运用基于芯片的双色荧光正相杂交检测SNP技术,进行芯片杂交动力学研究,考察信号值（Cy3,Cy5）和ratio值（Cy5/Cy3）与PCR产物点样浓度、PCR产物长度和荧光标记探针长度之间的关系,研究PCR产物点样浓度、PCR产物长度和荧光标记探针长度对SNP分型的影响。结果采用正反标记实验后,Ratio值随着PCR产物点样浓度的增加呈稳定趋势;PCR双链产物长度对信号值影响比较大,点样时其长度不宜太长,最好不超过450 bp;随荧光标记探针长度的增加,基因分型能力明显下降,长度为15 bp最佳,长度超过20 bp时,已基本没有区分能力。结论PCR产物点样浓度、PCR产物长度和荧光标记探针长度是双色荧光正相杂交SNP分型系统的重要影响因素,采取适当的PCR产物点样浓度、PCR产物长度和荧光标记探针长度,并采用正反标记实验,可以取得稳定、准确的基因分型效果。为进一步进行近交系小鼠遗传质量监测的研究奠定基础。     

Enhancing the thermal stability of lipases through mutagenesis and immobilization on zeolites

The hydrolysis reaction of p-nitrophenyl butyrate catalyzed by lipases was followed with in situ UV/vis diode array spectrophotometry. Five enzymes - Candida antarctica lipase B and Fusarium solani pisi cutinase wild-type and three single-mutation variants - were tested as catalysts in homogeneous conditions and immobilized on zeolite NaY, on a polyacrylate support and as cross-linked aggregates. Using deconvolution techniques and kinetic modeling, the thermal stability of the different biocatalysts was compared in operational conditions and the results were supported by steady-state enzyme fluorescence measurements. We concluded that both the mutagenesis and the immobilization on zeolite NaY had a positive effect on the thermal stability of F. solani pisi cutinase.     

Comparison of family 12 glycoside hydrolases and recruited substitutions important for thermal stability

As part of a program to discover improved glycoside hydrolase family 12 (GH 12) endoglucanases, we have studied the biochemical diversity of several GH 12 homologs. The H. schweinitzii Cel12A enzyme differs from the T. reesei Cel12A enzyme by only 14 amino acids (93% sequence identity), but is much less thermally stable. The bacterial Cel12A enzyme from S. sp. 11AG8 shares only 28% sequence identity to the T. reesei enzyme, and is much more thermally stable. Each of the 14 sequence differences from H. schweinitzii Cel12A were introduced in T. reesei Cel12A to determine the effect of these amino acid substitutions on enzyme stability. Several of the T. reesei Cel12A variants were found to have increased stability, and the differences in apparent midpoint of thermal denaturation (T(m)) ranged from a 2.5 degrees C increase to a 4.0 degrees C decrease. The least stable recruitment from H. schweinitzii Cel12A was A35S. Consequently, the A35V substitution was recruited from the more stable S. sp. 11AG8 Cel12A and this T. reesei Cel12A variant was found to have a T(m) 7.7 degrees C higher than wild type. Thus, the buried residue at position 35 was shown to be of critical importance for thermal stability in this structural family. There was a ninefold range in the specific activities of the Cel12 homologs on o-NPC. The most and least stable T. reesei Cel12A variants, A35V and A35S, respectively, were fully active. Because of their thermal tolerance, S. sp. 11AG8 Cel12A and T. reesei Cel12A variant A35V showed a continual increase in activity over the temperature range of 25 degrees C to 60 degrees C, whereas the less stable enzymes T. reesei Cel12A wild type and the destabilized A35S variant, and H. schweinitzii Cel12A showed a decrease in activity at the highest temperatures. The crystal structures of the H. schweinitzii, S. sp. 11AG8, and T. reesei A35V Cel12A enzymes have been determined and compared with the wild-type T. reesei Cel12A enzyme. All of the structures have similar Calpha traces, but provide detailed insight into the nature of the stability differences. These results are an example of the power of homolog recruitment as a method for identifying residues important for stability.     

Respective importance of protein folding and glycosylation in the thermal stability of recombinant feruloyl esterase A

The thermal stability of four molecular forms (native, refolded, glycosylated, non-glycosylated) of feruloyl esterase A (FAEA) was studied. From the most to the least thermo-resistant, the four molecular species ranked as follows: (i) glycosylated form produced native, (ii) non-glycosylated form produced native, (iii) non-glycosylated form produced as inclusion bodies and refolded, and (iv) glycosylated form produced native chemically denatured and then refolded. On the basis of these results and of crystal structure data, we discuss the respective importance of protein folding and glycosylation in the thermal stability of recombinant FAEA.     

Biofabrication of platinum nanoparticles using Fumariae herba extract and their catalytic properties

Due to the increasing popularity of using plant extract in the synthesis of nanoparticles, this study presented the synthesis of platinum nanoparticles using Fumariae herba extract. The formation of platinum nanoparticles was confirmed by UV–visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with EDS profile. Transmission electron micrograph presented the hexagonal and pentagonal shape of the synthesized nanoparticles sized about 30 nm. Moreover, platinum nanoparticles presented good catalytic properties in the reduction of methylene blue and crystal violet.     

Platinum allenylidene complexes and formation of platinum and palladium acetonitrile alkynyl complexes

The platinum(0) complex [Pt(PPh₃)₄] reacts with brominated propargylic amides and esters in benzene by oxidative addition to give trans-[Br(PPh₃)₂Pt-CC-C(O)R] complexes whereas no reaction occurs when halogenated solvents (CH₂Cl₂, CHCl₃) are used. The cis-ligands PPh₃ can be replaced by P(ⁱPr)₃ and the bromide by trifluoroacetate. O-Alkylation of those trans-[X(PR′₃)₂Pt-CC-C(O)R] complexes (X = Br, CF₃COO; R′ = Ph, ⁱPr) derived from propargylic amides with MeOTf or [Me₃O]BF₄ in CH₂Cl₂ gives the first cationic monoallenylidene complexes of platinum, trans-[X(PR′₃)₂PtCCC(OMe)NR₂]⁺Y⁻ (Y = OTf, BF₄). In contrast, trans-[Br(PPh₃)₂Pt-CC-C(O)OMenthyl] derived from a propargylic ester does not react with MeOTf in CH₂Cl₂. However, in acetonitrile instead of O-methylation the substitution of acetonitrile for the bromide ligand to yield the cationic acetonitrile alkynyl platinum complex trans-[MeCN(PPh₃)₂Pt-CC-C(O)OMenthyl]⁺OTf⁻ is observed. The related palladium complexes trans-[X(PR′₃)₂Pd-CC-C(O)OR] (X = Br, CF₃COO; R′ = Ph, ⁱPr, R = menthyl, Et) react with MeOTf or [Et₃O]BF₄ analogously affording trans-[MeCN(PR′₃)₂Pd-CC-C(O)OR]⁺Y⁻ (Y = OTf, BF₄).