Molecular Weight Samples Research Articles

Understanding the enhanced aqueous solubility of styrene by terrestrial dissolved organic matter using stable isotope mass balance and FTIR

We present a new stable isotope mass balance method for measuring the enhanced aqueous solubility of specific organic compounds in the presence of natural dissolved organic matter (DOM). It involves interfacing a standard dissolved organic carbon (DOC) analyzer with a stable isotope ratio monitoring system, is applicable to a wide range of model organic compounds and can be tuned to provide maximum precision for a given range of compound solubility and initial natural DOC concentration. Using 13C-labeled styrene as a model compound, we applied the method to investigate the reactivity of Dismal Swamp DOM as a function of season, nominal molecular size and chemical composition as determined using Fourier Transform Infrared Spectroscopy (FTIR). The solubility enhancement of styrene ranged from 23% to 118% relative to deionized water, while DOC-normalized enhancements varied from about 0.04 to 0.35 μM styrene/μM DOC as a function of season and nominal molecular weight. Statistical analysis of FTIR spectra reveals a strong positive correlation between the styrene concentration and the carboxyl content of the natural DOM. Reactivity differences between high molecular weight (HMW), low molecular weight (LMW) and total DOM samples are consistent with potential variations in their higher order structures.

Novel Biodegradable Polyester Poly(Propylene Succinate): Synthesis and Application in the Preparation of Solid Dispersions and Nanoparticles of a Water-Soluble Drug

Poly(propylene succinate) (PPSu) polymers of average molecular weights from 2,800 to 13,100 g/mol were synthesized and characterized with regard to crystallinity, thermal properties, and cytocompatibility. Higher molecular weight samples exhibited lower degree of crystallinity and melted at lower temperatures. Melting of the polymer appeared to begin at 38 degrees C. PPSu cytocompatibility was investigated based on human umbilical vein endothelial cells viability in the presence of increasing concentrations of polymer, and it was found that PPSu exhibited comparable cytocompatibility with poly(DL-lactide). The feasibility of applying PPSu as a drug carrier was shown for the first time, as solid dispersions and nanoparticles of sodium fluvastatin based in PPSu were prepared. Drug release rates decreased with increasing the molecular weight of PPSu in both solid dispersions and nanoparticles. For dispersions prepared from PPSu of the same molecular weight, drug release rates increased with drug loading. It appears that PPSu applicability as a drug carrier warrants further consideration.

Interaction between Poly(9,9-bis(6′-N,N,N-trimethylammonium)hexyl)fluorene phenylene) Bromide and DNA as Seen by Spectroscopy, Viscosity, and Conductivity: Effect of Molecular Weights and DNA Secondary Structure

The interaction between three poly(9,9-bis(6-N,N,N-trimethylammonium)hexyl)fluorene phenylene) bromide (HTMA-PFP) samples of different molecular weights (Mn=14.5, 30.1 and 61.3 kg/mol) and both dsDNA and ssDNA secondary structures has been studied using UV-visible absorption and fluorescence spectroscopies (including steady-state, time-resolved, and anisotropy measurements for the latter), viscosity, and electrical conductivity in 4% (v/v) DMSO-water mixtures. At low nucleic acid concentrations, formation of a 1:1 complex in terms of HTMA-PFP repeat units and DNA bases occurs. This interaction results in quenching of polymer emission. For higher molar ratios of DNA to HTMA-PFP, corresponding to charge neutralization, a second process is observed that is attributed to aggregate formation. From the changes in the absorption spectra, the polymer aggregation constant and the aggregate absorption spectra were calculated by applying an iterative method. Polymer aggregation dramatically quenches HTMA-PFP fluorescence in the region of the electroneutrality point. Under these conditions, the ratio of the emission intensity at 412 nm (maximum) to that at 434 nm (I412/I434) reaches a minimum, the electrical conductivity decreases, and the viscosity of the solution remains constant, showing that the DNA concentration can be determined through various HTMA-PFP physicochemical properties. With respect to the photophysical parameters (emission quantum yield, shape and shift of emission spectra), no significant differences were observed between dsDNA and ssDNA or with conjugated polymer or DNA molecular weight. The two short-lived components in the fluorescence decays are attributed to the presence of aggregates. Aggregates are also suggested to be responsible for the decrease in the fluorescence anisotropy through interchain exciton migration.

Preparation and Characterization of Enzyme-Modified Konjac Glucomannan/Xanthan Blend Films

Enzyme-modified konjac glucomannan (KGM) and xanthan blend films have been prepared and characterized. Enzymatic hydrolysis of purified KGM by β-mannanase yielded samples of various weight-average molecular weight (M w) that were determined by size-exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALLS) and calculated using the established Mark–Houwink–Sakurada equation [η] = 4.07 × 10−4 M w 0.733. KGM degradation products were blended with xanthan for preparation of films that were used in orthogonal-designed experiments. These films were characterized in terms of their structures, thermal stability, crystallinities and mechanical properties. The results of Fourier transform infrared spectroscopy indicated that, after blending, there was strong intermolecular interaction caused by hydrogen bonds between xanthan and KGM hydrolysates. This phenomenon was more marked at lower M w of KGM. The thermal stability of the blend films determined by differential scanning calorimetry was higher with increasing KGM molecular weight. The degrees of crystallinity characterized by X-ray diffraction (XRD) decreased with the increasing content of non-degraded KGM. Mechanical properties of the polymer blends including the tensile strength and elongation rate were also correlated to M w of KGM. The tensile strength achieved a maximum at 10.25 MPa with KGM of M w = 4.25 × 105 and the elongation rate reached a maximum value of 89.5% with KGM of M w = 8.95 × 105. These results were directly attributed to intermolecular interactions between xanthan and KGM, and this synergistic behavior led to good physicochemical and mechanical performance of the blended films.

A method for measuring the degree of anionicity of polyacrylamide-based flocculants

A simple procedure was described for routine measurements of the degree of anionicity of polyacrylamide-based flocculants. The method relies on determining the total organic carbon content and assaying ion concentrations in a dilute solution (in distilled water at natural pH) of the tested flocculant. While the total carbon content in solution gives the total number of acrylic and acrylamide units in the polymer, the concentration of the counter-cation provides a measure of the number of acrylic units only. Thus a degree of anionicity can also be obtained from a simple equation. Five commercial flocculant samples of similar molecular weights but of different degrees of anionicity were then used for evaluating the proposed procedure, and the obtained degrees of anionicity were in excellent agreement with the data provided by the manufacturer of the flocculants. Potential advantages and limitations of the method were also discussed.

In vitro hydrolytic degradation of poly(para-dioxanone) with high molecular weight

The in vitro hydrolytic degradation of high molecular weight poly (para-dioxanone) was studied by examining the changes of weight retention, water absorption, pH value, tensile strength, break elongation, thermal properties, and morphology of high molecular weight PPDO in phosphate buffered saline (PBS) (pH 7.44) at 37°C for 8 weeks. During the degradation, all samples’ weight retention decreased and water absorption increased significantly, whereas hydrolysis rate of PPDO bars varied with molecular weight. Compared with lower molecular weight samples, higher molecular weight PPDO samples exhibited higher hydrolysis rate. The samples’ glass transition temperature (Tg) decreased notably, while the degrees of crystallinity (Dc) increased. The samples almost totally lost their tensile strengths and breaking elongation after 4 weeks of degradation. The results suggested that the stability of PPDO in vitro hydrolytic degradation increased with the increase of molecular weight.

Measurement of Supercritical CO2 Plasticization of Poly(tetrafluoroethylene) Using a Linear Variable Differential Transformer

From measurements utilizing a linear variable differential transformer (LVDT), poly(tetrafluoroethylene) is found to undergo unusually high linear dilation in CO2 at high temperatures and pressures. The extent of dilation and the dilational profiles are shown to depend strongly on molecular weight and crystallinity. It is also shown that the conditions at which melting and sintering occur can be identified from LVDT measurements. After the first heating cycle in CO2, unsintered samples (PTFE-230, -600, -1000, and U-PTFE) show a Tm identical to PTFE (327 °C) instead of the higher pre-CO2 Tm. This observation indicates that these samples were sintered during the LVDT measurements. ΔHf was constant for pre-CO2 PTFE-230, -600, and -1000, but after sintering, crystallinity decreased with increasing molecular weight. In contrast to the precipitous drop for U-PTFE, ΔHf for PTFE-230, -600, and -1000 remained above 70 J/g. Chain entanglement effects on crystallization are modest for these low molecular weight materials. For lower molecular weight samples (PTFE-230, -600, and -1000), Tm depression and melt flow were observed. For the high molecular weight samples (PTFE and U-PTFE), Tm depression in CO2 also occurs, but exceptionally high molecular weight and chain entanglement preclude melt flow. Both PTFE and U-PTFE are unusual in that melting is signaled by an increase in dilation rather than the usual loss of shape or “slumping” due to melt flow. Despite the hydrostatic pressure effect, PTFE melting point depression in supercritical CO2 was found to be approximately 30 °C.

Effects of Film Thickness and Molecular Weight on the Interfacial Dynamics of Atactic Poly(methyl methacrylate)

We have investigated the surface vibrational dynamics at the polymer-vacuum interface of atactic poly(methyl methacrylate) thin films supported on SiO(x)/Si(100) as a function of film thickness and molecular weight. The highly surface-sensitive and nondestructive technique of inelastic helium atom scattering probes the vibrational dynamics at the true polymer-vacuum interface due to the lack of helium atom penetration into the film. For higher molecular weight samples (350 kg/mol), scattering spectra differ between films of thicknesses of fractions of the bulk radius of gyration compared with thicker films due to substrate interactions. A difference in the line shape of the scattering spectra is also present for lower molecular weight samples (60 kg/mol) compared with the thick, higher molecular weight samples. The differences in scattering spectra indicate a reduction of interfacial surface vibrational motion for both the thin, high molecular weight, and low molecular weight films as compared to thick, high molecular weight films. Our experiments demonstrate that dynamics at the interface of polymer thin films are unchanging until the films are thin enough for substrate interactions to influence vibrations at the true interface.

Step-like melting mechanisms of isothermally crystallized isotactic polypropylene

The complex melting behavior of isotactic polypropylene, after isothermal crystallization, was studied within the context of step-like melting mechanisms which were previously proposed for high temperature polymers. The morphological characteristics of the melting process were also studied as a function of molecular weight, and close similarities were observed with respect to high temperature polymers. Positive birefringence crystals of low molecular weight samples developed double melting behavior in three steps. The first melting step was assigned to continuous melting of secondary crosshatch reversing lamellae, together with recrystallization of the remaining isothermal crystals. In the second melting step (first melting endotherm), crystals tended to lose their original coarse negative birefringence due to melting of secondary reversing branching. This effect rendered new, finer texture, but still negative birefringence crystals. In the third melting step (second melting endotherm), there was a combination of melting of two crystal populations, one consisting of the remaining fraction of reversing primary crystals, and the other consisting of nonreversing primary crystals. A crosshatch secondary branching model was therefore proposed to explain the overall results. Mixed birefringence spherulites of high molecular weight samples displayed similar, although proportional, behavior under identical crystallization and melting conditions corroborating the proposed melting mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2188–2200, 2008

Production of Sophorolipid Biosurfactant byPichia anomala

Biosurfactant production by Pichia anomala PY1, a thermotorelant strain isolated from fermented food, was examined as grown in media containing various carbon and nitrogen sources. The optimal conditions for biosurfactant production included 4% soybean oil as carbon source at pH 5.5 at 30 degrees C for 7 d. Under these conditions, the surface tension of the medium decreased to 28 mN/m with oil displacement measured at 69.43 cm(2). Comparative studies of biosurfactant production in media containing glucose or soybean oil were performed. The biosurfactants obtained were isolated and purified by chromatographic methods. The molecular weights of samples were further investigated by mass spectrometry. In medium containing glucose, biosurfactants of molecular weights of 675, 691, and 707 were obtained, while those isolated from medium containing soybean oil were of molecular weights of 658, 675, and 691. These results reveal that sophorolipid compounds containing fatty acids of C20 and C18:1 were produced from both media.

Fluorescence Excitation and Emission Spectroscopy on Single MEH-PPV Chains at Low Temperature

Fluorescence emission and excitation spectra of single MEH-PPV polymer molecules dispersed in thin PMMA films have been recorded at 1.2 and 20 K. We observe single as well as multichromophore emission in single chain emission spectra, whereby the relative fractions depend on the two different molecular weights (50 and 350 kDa) studied. The molecular weight also affects the distribution of peak emission maxima, which is monomodal (bimodal) for the low (high) molecular weight. The appearance of an additional "red" subpopulation for the high molecular weight sample is attributed to interactions of multiple chromophores from a sufficiently flexible single chain. The comparison of emission spectra appearing in the "blue" as well as "red" subpopulations suggests that these intrachain interactions rather lead to ground-state aggregates than excimers. Independent of the molecular weight, large variations in spectral shape and apparent line width in the emission spectra have been observed. Occasionally, we find very narrow purely electronic zero-phonon lines both in emission and in excitation spectra, with line widths down to the instrumental resolution. In accordance with earlier literature data it is argued that linear electron-phonon coupling should be quite strong for MEH-PPV in PMMA, leading to only a small fraction of chromophores exhibiting zero-phonon lines. In addition, spectral diffusion, which manifests itself by several time-dependent line shifting and broadening phenomena, contributes to the substantial variations of spectral shapes. Excitation experiments with particularly stable chromophores provide an upper limit for the optical line width (approximately 0.1 cm(-1)), which at 1.2 K can actually approach the lifetime-limited homogeneous width. Raising the temperature to 20 K leads to line broadening and typically, to disappearance of zero-phonon lines. The failure to observe zero-phonon lines of chromophores supposedly serving as donors in intramolecular energy transfer is tentatively attributed to fast transfer rates, resulting in strongly broadened lines which escape detection even at 1.2 K.

Microphase Separation and Shear Alignment of Gradient Copolymers: Melt Rheology and Small-Angle X-Ray Scattering Analysis

The degree of microphase or nanophase segregation in gradient copolymers with compositions varying across the whole copolymer backbone is studied via low-amplitude oscillatory shear (LAOS) measurements and small-angle X-ray scattering (SAXS). Studies are done as a function of comonomer segregation strength, molecular weight (MW), gradient architecture and temperature. Controlled radical polymerization is used to synthesize strongly segregating styrene/4-acetoxystyrene (S/AS) and the more weakly segregating S/n-butyl acrylate (S/nBA) gradient copolymers. Results are compared to those from S/AS and S/nBA random and block copolymers. The higher MW S/AS gradient copolymer exhibits LAOS behavior similar to the highly microphase segregated S/AS block copolymer, while the lower MW S/AS gradient copolymer exhibits complex, nonterminal behavior indicative of a lower degree of microphase segregation. The S/nBA gradient copolymers demonstrate more liquidlike behavior, with the lower MW sample exhibiting near-Newtonian behavior, indicative of a weakly segregating structure, while the higher MW, steeper gradient sample shows behavior ranging from solidlike to more liquidlike with increasing temperature. With the exception of the lower MW S/nBA case, the gradient copolymers exhibit temperature-dependent LAOS behavior over a wide temperature range, reflecting their temperature-dependent nanodomain composition amplitudes. The S/AS samples have SAXS results consistent with the degree of microphase segregation observed via rheology. Shear alignment studies are done on the higher MW S/AS gradient copolymer, which is the most highly microphase segregated gradient copolymer. Rheology and SAXS provide evidence of shear alignment, despite the gradual variation in composition profile across the nanodomains of such gradient copolymers. A short review of the nomenclature and behavior of linear copolymer architectures is also provided.

Chain Dynamics and Viscoelastic Properties of Poly(ethylene oxide)

The chain dynamics and viscoelastic properties of poly(ethylene oxide) (PEO) were studied covering a wide range of molecular weights and temperatures. Two experimental techniques were used: rheology, in order to study the large scale viscoelastic properties, and neutron spin−echo (NSE) spectroscopy, to investigate the chain dynamics at the molecular level. We aimed to explore the characteristic dynamical parameters of the pure homopolymer system and describe its dependence on the polymer molecular weight and temperature. We will show that, after accounting for the molecular weigth dependence of the glass transition temperature, the dynamics observed for the different molecular weight samples can be consistently described by the Vogel−Tammann−Fulcher (VTF) temperature dependence.

Linear and nonlinear shear flow behavior of monodisperse polyisoprene melts with a large range of molecular weights

Shear rheological data for a wide range of nearly monodisperse linear polyisoprene melts are reported herein using the results of linear and nonlinear measurements. The number of entanglements per chain ranges from about 0.5 to 230. In order to extend the range of available frequencies and shear rates the procedure of time-temperature superposition is improved and validated in both the linear and the nonlinear regime. In the linear flow regime a detailed comparison with the tube theory by Likhtman and McLeish [Macromolecules 35, 6332–6343 (2002)] was performed. The overall agreement was found to be satisfactory but several minor disagreements, e.g., at the crossover regime and for the steady-state compliance, were observed and have been discussed. Until now, most nonlinear models for entangled polymers were compared with shear data on solutions. However, the equivalence between solutions and melts is not well established. In this paper the results of a series of nonlinear start-up shear experiments are compared with those predicted by the tube model [Graham et al., J. Rheol. 47, 1117–1200 (2003)] and with several literature datasets on entangled solutions having similar numbers of entanglements. The melts were found to behave in a very similar manner to the previously studied solutions and agree well with the tube theory. Disagreements are observed when the shear rate exceeds the Rouse time of one entanglement and also for chains with very small number of entanglements. For the high molecular weight samples possible instabilities and edge fracture can occur at high strains and the results are discussed in light of these effects. The extensive dataset presented here could serve as a test for future theories and models of entangled melts.

Effects of molecular weight distribution on the flow-enhanced crystallization of poly(1-butene)

In this paper we analyze the crystallization kinetics under steady shear flow conditions of different samples obtained by blending two isotactic poly(1-butene)s with different average molecular weights. It is observed that the addition of a small amount of high molecular weight (MW) polymer (<6wt%) to a low MW sample does not produce any appreciable effect upon the crystallization kinetics under both quiescent and shear flow conditions. When more elevated amounts of high MW polymer are added, only mild effects upon the crystallization kinetics, under both quiescent and shear conditions, are observed. This behavior can be attributed to constraint release of high MW chains due to the relaxation of the shorter chains. Such a physical phenomenon can be described by the double reptation theory, which, indeed, allows for good quantitative predictions of the experimental results by using the relaxation times of the two blend components as the only fitting parameters.

Direct detection of N−H⋯N hydrogen bonds in biomolecules by NMR spectroscopy

A nuclear magnetic resonance (NMR) experiment is described for the direct detection of N-H[...]N hydrogen bonds (H-bonds) in 15N isotope-labeled biomolecules. This quantitative HNN-COSY (correlation spectroscopy) experiment detects and quantifies electron-mediated scalar couplings across the H-bond (H-bond scalar couplings), which connect magnetically active (15)N nuclei of the H-bond donor and acceptor. Detectable H-bonds comprise the imino H-bonds in canonical Watson-Crick base pairs, many H-bonds in unusual nucleic acid base pairs and H-bonds between protein backbone or side-chain N-H donor and N acceptor moieties. Unlike other NMR observables, which provide only indirect evidence of the presence of H-bonds, the H-bond scalar couplings identify all partners of the H-bond, the donor, the donor proton and the acceptor in a single experiment. The size of the scalar couplings can be related to H-bond geometries and as a time average to H-bond dynamics. The time required to detect the H-bonds is typically less than 1 d at millimolar concentrations for samples of molecular weight < or = approximately 25 kDa. A C15N/13C-labeled potato spindle tuber viroid T1 RNA domain is used as an example to illustrate this procedure.

RHEOLOGICAL PROPERTIES OF POLY(VINYLIDENE FLUORIDE) IN MOLTEN STATE

The rheological behavior of poly(vinylidene fluoride) (PVDF) samples of different molecular weights was investigated by means of high pressure capillary rheometer and rotational rheometer. Information on the rheological properties of such materials above melt temperatures is of interest as this can lead to an improved understanding of polymer behavior in processing and fabrication technologies. Shift factors derived from time-temperature superposition showed good fit to the Arrhenius equation with a flow activation energy E of almost 74 kJ/mol, which was essentially independent of polymer molecular weight suggesting the unit of flow was a collective motion of chain segments rather than the whole chain itself.

Chitosan Derivatives/Calcium Carbonate Composite Capsules Prepared by the Layer‐by‐Layer Deposition Method

Core/shell capsules composed of calcium carbonate whisker core (rod‐like shape) and chitosan/chitosansulfate shell were prepared by the layer‐by‐layer deposition technique. Two chitosan samples of different molecular weights (Mw = 9.7 × 104 and 1.09 × 106g · mol−1) were used as original materials. Hollow capsules were also obtained by dissolution of the core in hydrochloric acid. Electron microscopy revealed that the surface of the shell is rather ragged associated with some agglomerates. The shell thickness l obeys a linear relation with respect to the number of deposited layers m as l = md + a(a &gt; 0). The values of d (thickness per layer) were 4.0 and 1.0 nm for the higher and lower Mw chitosan materials, respectively, both of which are greater than the thickness of the monolayer. The results suggest that the feature of the deposition does not obey an ideal homogeneous monolayer‐by‐monolayer deposition mechanism. Shell crosslinked capsules were also prepared via photodimerization reaction of cinnamoyl groups after a deposition of cinnamoyl chitosan to the calcium carbonate whisker core. The degree of crosslink was not enough to stabilize the shell structure, and hollow capsule was not obtained.

THERMOSENSITIVITY OF NARROW-DISPERSED POLY(N-n-PROPYLACRYLAMIDE) PREPARED BY ATOM TRANSFER RADICAL POLYMERIZATION

Controlled polymerization of N-n-propylacrylamide was achieved by atom transfer radical polymerization (ATRP) in a N,N-dimethylformamide-water mixture (50 vol%) at room temperature with methyl 2-chloropropinonate as initiator and CuCl/tris(2-dimethylaminoethyl)amine as the catalytic system in a ratio of 1:1:1. High molecular weight homopolymers (up to 3.7 × 104) with narrow molecular weight distribution (less than 1.2) were obtained. The living character of the polymerization was further demonstrated by self-blocking experiment. An inverse molecular weight dependence of the cloud point of narrow-dispersed poly(N-n-propylacrylamide) aqueous solution was determined by turbidimetry and differential scanning calorimetry, especially for the low molecular weight samples.

Influence of Silver Salt Types on Formation of Silver Cluster Ions in MALDI with DHB as Matrix

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a soft ionization technique used for the analysis of large nonvolatile molecules such as biopolymers and synthetic polymers. The goal of sample preparation in MALDI analysis is homogeneous cocrystallization of analyte and matrix molecules. The role of the matrix is very crucial in MALDI and many researchers have studied on what is a good matrix. Macha and Limbach discussed about the role of matrix in MALDI analysis. Matrix compounds are still discovered through trial and error because there has not been enough research to investigate what are the factors that affect the functioning of such compounds in MALDI process. The matrix dilutes and isolates polymers in the sample preparation step and plays a role in the analyte desorption and ionization process by absorbing the laser energy at the wavelength used. The ratio of the analyte to the matrix depends on the molecular weight and chemical properties of the analyte. The ratio increases when higher molecular weight sample is analyzed. In general, the molar ratio of the analyte to the matrix ranges from 1:10 to 1:10. Dihydroxybenzoic acid has many isomers such as 2,3-, 2,4-, 2,5-, 2,6-, and 3,4-dihydroxybenzoic acids. Among them, 2,5-dihydroxybenzoic acid has the most absorption coefficient at a wavelength of 337 nm. 2,5-Dihydroxybenzoic acid (DHB) is commonly used for the analysis of synthetic polymers as well as biopolymers. Some polar matrices such as 4-hydroxy-3,5-dimethoxy-cinnamic acid, α-cyano-4-hydroxy-cinnamic acid, and methyl salicyclic acid interact well with biopolymers while some polar matrices such as 2-(4-hydroxyphenylazo)-benzoic acid (HABA), all-trans-retinoic acid (RTA), and dithranol work for synthetic polymers. Nonpolar matrices such as anthracene, pyrene, acenaphthene, and terthiophene are suitable for nonpolar samples. In a MALDI mass spectrum, the protonated molecule and cation adduct of an analyte give an important information about the molecular ion mass. Some researchers reported that sliver clusters can be effectively produced under MALDI conditions from sliver salts in the presence of matrices. During the analysis of organic molecules when Ag is used as the cationizing agent, it can be recognized that besides the desired adduct ions, [M + Ag], an additional silver cluster ions, Agn . Study on metal cluster formation in gas-phase by mass spectrometry provides valuable information on the stability and electronic properties of the metal clusters depending on the sizes and this information can be utilized when the clusters are immersed into a liquid or solid environment. One of useful methods to generate silver cluster ions is MALDI using silver salts and matrices. Keki and coworkers studied the matrix effect on the formation of the silver cluster ions under MALDI conditions using reductive polar organic matrices and silver trifluoroacetate (AgTFA) and reported that the silver cluster ions were effectively produced and the matrix greatly influenced the resulting cluster ion abundances. Properties of metal salts are depending on the kind of the counter anions as well as the metal types. It can be expected that the formation of the silver cluster ions in MALDI will be affected by the counter anions of silver salts. However, this investigation has not been sufficiently carried out. In the present work, we investigated the influence of the silver salt types on the formation of silver clusters in MALDI conditions and experimental results were explained with the interactions and reactions between the silver salt and the matrix, DHB. The MALDI mass spectrum of the AgBz shows the silver cluster ion intensity distribution with an odd-even alternation pattern as shown in Figure 1. The intensity of the oddnumber cluster ions tends to be stronger than that of the neighboring even-number cluster ions. The mass spectrum also shows the clear magic numbers of n = 21 and 35 of Agn . The magic number of n = 21 is in good agreement