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Systematic functionalization of perfluoroaryl azides with chelating agents capable of complexing transition metals produces a new class of bifunctional photolabile chelating agents (BFPCAs). The strategy to shield the azide functionality from the electronic and steric influence of the electron-rich metal Pd through ester and amide bridges raised CH insertion efficiency to unprecedented levels (>92%) in a model solvent (cyclohexane). In contrast, perfluoroaryl azides attached to chelating agents via hydrazones show no significant CH insertion in cyclohexane upon photolysis. Measurements of the lifetimes of the singlet nitrenes derived from these agents by flash photolysis techniques correlate well with the efficiency of CH insertion by demonstrating longer lifetimes (10−50 times) for singlet nitrenes derived from azidotetrafluorinated esters and amides compared with the related hydrazones, which failed to yield significant CH insertion. A representative BFPCA 12 is chelated to diagnostic radionuclide 99mTc...

Synthesis of a new photo cross-linking agent incorporating chromogenicity, cleavability, and water solubility is described. The high efficiency of nitrene insertion observed upon photolysis of perfluoroaryl azides into organic solvents and proteins is extended to the design and synthesis of new multifunctional cross-linking agents useful for protein–protein interactions. The new cross-linker sulfosuccinimidyl (perfluorobenzamido)-ethyl-1,3′-dithiopropionate (SFAD) 10 was conjugated to IgG and cross-linked to horseradish peroxidase (HRP). The analysis of the cross-linked product using ELISA assays leads to a higher yield of IgG–HRP cross-linked product than that seen with a similar nonfluorinated analog. The efficiency of photo cross-linking by SFAD is also extended to small molecule biotin via CH insertion and checked for the retention of binding affinity of the cross-linked product.

The photoreduction of acetylene is catalyzed by Mo 2 O 4 (dedtc) 2 (dedtc, diethyldithiocarbamate) in the presence of 5–8 nm diameter colloidal TiO 2 . This photocatalytic process exhibits optimum activity at pH 6 and a loading of 30 catalyst molecules per TiO 2 particle. The same catalytic site(s) are responsible for C 2 H 2 reduction to C 2 H 4 and C 2 H 6 and H + reduction to H 2 . The overall photonic efficiency is 1.3% for the transfer of reducing equivalents to products at full lamp intensity, and increases with decreasing intensity. The effects of pH, temperature, intensity and loading on the catalytic process are consistent with a mechanism in which the catalytic site associated with the TiO 2 surface promotes the transfer of H atoms or electrons to the bound substrate. The photocatalytic properties of this neutral molecular complex are compared with those observed for other Mo-containing catalysts.

Synthesis and evaluation of a new class of photochemically activated heterobifunctional chelating agents for protein modification is described. Selective functionalization of perfluoroaryl azides by versatile phosphorus hydrazide ligating systems 2 and 3 for the complexation of transition metals and analogous radiometals form the basis for these new agents. The utility of the photogenerated precursors from these bifunctional agents to form covalent attachments is demonstrated through examination of C-H bond insertion on cyclohexane. Representative amide-coupled phosphorus hydrazides 5 and 6 provide78% insertion of the probe into unactivated C-H bonds of cyclohexane with short photolysis times. Photoconjugation of the photoactivable heterobifunctional chelating agent 6 and its Pd metalated analog 7 with HSA is also evaluated. The uncomplexed chelate appears to add to HSA with high efficiency, consistent with the observed 82% bond insertion into model solvents. Covalent attachment of 7, evaluated through the use of (109)Pd, was estimated to be between 49% and 74% with the uncertainty arising because of prephotolysis association of the (109)Pd complex with HSA. The application of in situ (19)F NMR to distinguish between bond insertion and noninsertion processes is demonstrated. These results suggest that functionalized perfluoroaryl azido phosphorus hydrazides may find utility as heterobifunctional photolabeling agents for attaching radionuclides to proteins and antibodies.

The synthesis and biological activity of functionalized lisinopril, a potent angiotensin converting enzyme (ACE) inhibitor is described. Selective functionalization of lisinopril is achieved at the secondary amino position by a photochemical method, whereas esterfication of the carboxylic groups and modification at the primary amino group is achieved by chemical methods. Autoradiographic investigations using competitive 125 I radioactive binding assays with the modified lisinopril reveal that the terminal amino group modification enhanced the binding to ACE, whereas the secondary amino group functionalization did not differ significantly from the binding properties of native lisinopril. However, esterification of the carboxyl groups reduced the inhibitory potentency from n M to μ M . These results suggest that lisinopril can be derivatized with preservation of inhibition potency toward ACE. These modifications may find utility in the development of photoaffinity labeling agents for ACE or to incorporate bifunctional chelating agents carrying diagnostic radiometals for the development of cardiac imaging agents.

A comparative study of the complexes Mo 2 O x S y (cys) 2 2- (x = 4, 3, 2; y = 4 - x) as catalysts for electron transfer from irradiated TiO 2 to acetylene is reported. These catalytic species all show similar behavior with respect to variations in intensity, loading, and pH. Their ability to facilitate electron transfer from TiO 2 to substrate increases in the order Mo 2 O 2 S 2 (cys) 2 2- > Mo 2 O 3 S(cys) 2 2- > Mo 2 O 4 (cys) 2 2- . At high light intensity, efficiencies for electron transfer from the colloidal TiO2 surface are comparable to those obtained with Pt under similar conditions. Efficiencies increase with decreased light intensity, giving product yields which account for 7-9% of the incident light at the lowest intensities studied. All three catalysts produce H 2 in N 2 - or C 2 H 4 -saturated solutions, but only Mo 2 O 2 S 2 (cys) 2 2- produces H 2 in the presence of C 2 H 2 . The effects of pH, temperature, intensity, and loading on the catalytic process are consistent with a proposed mechanism in which the catalytic site associated with the TiO 2 surface promotes the transfer of electrons to the bound substrate. For each complex, a single catalytic site appears to be responsible for all reduction processes. A comparison of the photocatalytic properties of species containing the Mo(V) 2 core is included.

Achieving high efficiency covalent attachment of molecular probes to biomolecules by photolabeling techniques remains an elusive goal of chemists and biologists. Developments in the understanding of the fundamental photochemistry of perfluoroaryl azides suggest a new means of attaching diagnostic and therapeutic radionuclei to proteins and antibodies through heterobifunctional chelating agents containing a photoactive terminus. Such an approach requires establishment of the coordination chemistry of ligating systems, appropriate molecular design of the photolabel, analytical method development for critical analysis of photolabeled products and retention of immunoreactivity of antibodies in the postlabeling stage. In this review, we summarize recent developments in photolabeling technology and discuss new challenges for application of the technology in the field of nuclear medicine.

The competitive photocatalytic reduction of H + and C 2 H 2 at catalytic sites formed when Mo 2 S 4 (S 2 C 2 H 4 ) 2− 2 is photoreduced on colloidal TiO 2 in the presence of a sacrificial electron donor was studied. Comparisons of the total number of electrons transferred to both substrates as a function of pH suggest that the substrates compete for a common catalytic site. Based on analogies with homogeneous solution studies, a mechanism involving an Mo(IV) dimeric species as the catalytic site is suggested. The efficiency for conversion of incident light to reduced products increases with decreasing light intensity and maximizes at about seven electrons transferred per 100 photons absorbed.

The photocatalytic of molecular hydrogen from aqueous suspensions of colloidal TiO2 loaded with MoS2−4 and Mo2S4(S2C2H4)2−2 was studied as a function of pH, loading and light intensity. The efficiency of these systems, in which polyvinyl alcohol and ethylenediamine tetraacetic acid (EDTA) were utilized as sacrificial electron donors, was compared with the well-studied systems utilizing platinum as an electron transfer catalyst. Optimum loading levels were 20 ions per particle for tetrathiomolybdate and 6 ions per particle for the thio dimer. Both of the Mo-S systems were only about 40% as efficient as platinum. Quantum yields of molecular hydrogen approximately doubled as the intensity was decreased by a factor of 10 and increased about twofold when the more efficient hole scavenger, EDTA, was added to the mixture. The highest yield obtained, in terms of the percentage utilization of the photoproduced electrons, was 11.5% compared with 28.2% for platinum. Except for differences in optimum loading levels, both catalysts gave similar results.

Photoreduction of Mo(V) aquo dimers and Mo(IV) aquo trimers onto colloidal TiO 2 in the presence of a sacrificial electron donor (PVA) produces catalytic sites for the photoreduction of acetylene to ethane and ethylene during band gap irradiation. The Mo 2 site assists in production of both ethylene and ethane while the Mo 3 enhances only the ethane production

Coupling of the TMS derivative of triphenylphosphinimine with 4-azido-2,3,5,6-tetrafluorobenzonitrile give substitution exclusively at the ortho position. The resulting bifunctional molecule has a photoprobe at one terminus and contains a chelating moiety, which readily complexes Pd. Substitution shifts the λmax to 350 nm, which is beyond the absorption limit of most biomolecules and permits photoactivation without damaging the biomolecule.

Functionalization of perfluoro aryl azides by bifunctional chelating agents (BFCAs) capable of forming high specific activity complexes with (99m)Tc (for gamma-imaging) and (188)Re (for radiotherapy) is described. The synthesis of multidonor BFCAs containing N(2)S(2), N(4), and N(3)S donor groups containing imidazole, pyridine, and pyrazine functionalities that may be important for tuning the pharmacokinetic parameters is also described. Functionalization of perfluoro aryl azides at various sites on BFCAs yields novel bifunctional photolabile chelating agents (BFPCAs) that are useful for covalent attachment to biomolecules. A representative Re-BFPCA 8a in a model solvent, diethylamine, proceeded to give a high yield of intermolecular NH insertion product without the decomplexation of the metal ion from 8a. All products originated from the photolysis of 8a in diethylamine are characterized by analytical techniques, and a plausible mechanism of formation of different photolytic products is suggested. The high yield of intermolecular NH insertion of Re-BFPCA 8a is extended to labeling of human serum albumin (HSA) and Fab fragments under aqueous conditions. The photolabeling technology developed here offers a new way to attach diagnostically and therapeutically useful radiotracers (e.g., (99m)Tc, (188)Re) to Fab fragments for potential noninvasive imaging and therapy of cancer.

The efficiency of photolabeling of HSA and IgG with [14C]methyl 4-azido-2,3,5,6-tetrafluorobenzoate has been studied using size exclusion chromatography in conjunction with liquid scintillation counting. Labeling efficiencies of 78% for HSA and 82% for IgG have been determined. The extent of bond insertion into proteins exceeds the C-H insertion efficiency in cyclohexane with less wastage into anilinium and azo side products. These results suggest that the photoprobe accesses hydrophobic regions of both proteins prior to photolysis.

This report discusses activities and progress that has occurred since initiation of this project on September 1, 1989. We have synthesized ethyl N,N{prime}-bis(benzoylmercaptoacetyl)-2,3-diaminopropanoate, a ligand to be used as a bifunctional chelating agent (BFCA), to form {sup 186}Re or {sup 188}Re ({sup 186}Re/{sup 188}Re) complexes. {sup 186}Re/{sup 188}Re, in reducing media, reacts with this ligand to form {sup 186}Re/{sup 188}Re-CO{sub 2}DADS chelates that will be used to formulate new radiolabeled photoaffinity labels (RPALs). Initial steps have been taken to synthesize R-As-dithiol compounds. This approach will be used to produce {sup 77}As-RPALs or covalently link {sup 77}As directly to monoclonal antibodies (MAbs). The R group will contain a group that can be used for conjugation reactions. Spectral and photochemical properties of various types of photoaffinity labels (PALs) have been studied. Acrylo-azido compounds and 9-azido acridine have been studied as well as several other photoprobes. The binding characteristics of the azido-based PALs to HSA have been studied and progress has been made on developing techniques for efficiently separating of non-covalently sound PALs. The Nd-YAG laser was purchased and arrived in 1990. It has been assembled and tested and is now operational.

Photolysis of 4-azido-tetrafluorobenzonitrile results in the highest yield reported to date, (75–80% as estimated from 19F NMR spectroscopy) for nitrene insertion into the unactivated C–H bond of cyclohexane; the photochemical adduct is characterized by 1H and 13C NMR spectroscopy and the structure is confirmed by X-ray crystallography for the first time.

The phosphorus hydrazide PhP(S)(NMeNH2)21 reacted with the azido functionalized aldehyde 4-N3C6F4CHO to give a mixture of Schiff-base adducts with one or two perfluoroaryl azido substituents on 1. However, the reaction with R′CHO (R = 4-O2NC6H4, 3-O2NC6H4 or 2,4-Me2C6H3) resulted in a considerable selectivity of incorporating one aromatic substituent in the terminal hydrazide unit of 1via Schiff-base coupling to produce PhP(S)(NMeNH2)(NMeNCHR′)(R′= 4-O2NC6H43, 3-O2NC6H44 or 2,4-Me2C6H35). These mono-Schiff-base adducts 3–5 undergo further Schiff-base coupling with azidotetrafluorobenzaldehyde to produce the azido-functionalized phosphorus hydrazides PhP(S)-(NMeNCHC6F4N3)(NMeNCHR′)(R′= 4-O2NC6H47, 3-O2NC6H48 or 2,4-Me2C6H39). The ligating properties of the representative phosphorus hydrazides 2 and 9 with palladium (II) were investigated. The crystal structure of the complex [PdCl2{PhP(S)(NMeNH2)(NMeNCHC6F4N3-4)}] reveals that the palladium(II) is bound in a chelating cis arrangement to the phosphorus chalcogenide and the hydrazine nitrogen via a five-membered metallacyclic framework: monoclinic, space group P21/n, a= 7.826(10), b= 18.051 (20), c= 18.330(3)A, β= 98.196(7)°, Z= 4, R= 0.038 and R′= 0.053.

The complex dielectric constant ϵ = ϵ′– jϵ″ of single crystals of squaric acid C4H2O4(H2SQ) was examined at around 100 MHz and between 2 and 8 GHz as a function of temperature. In the GHz range the imaginary part ϵ″ can be well described by the beginning of a monodispersive relaxation, whose relaxation frequency slows down to about 55 GHz in the high temperature phase near Tc. The real part ϵ, however, shows marked deviations from the Debye formula. The results are discussed with respect to the dynamics of the sublattice polarizations related to antiferro-electricity in this substance. Im Bereich um 100 MHz und zwischen 2 und 8 GHz wurde die temperaturabhangige komplexe Dielektrizitatskonstante ϵ = ϵ′– jϵ″ von Quadratsaureeinkristallen C4H2O4(H2SQ) untersucht. Im GHz-Gebiet kann der Imaginarteil ϵ″ gut durch den Anfang einer monodispersiven Relaxation beschrieben werden, deren Relaxationsfrequenz auf etwa 55 GHz in der Hochtemperaturphase nahe Tc absinkt. Der Realteil dagegen zeigt deutliche Abweichungen vom Debye-Verhalten. Die Resultate werden im Zusammenhang mit der Dynamik der Untergitterpolarisationen diskutiert, die zur Antiferroelektrizitat in dieser Substanz beitragen.

Using the method of flash photolysis, the triplet of the single indole side chain of human serum albumin was detected at room temperature. In a nitrogen saturated solution, this species was found to decay exponentially for over a factor of ten with a lifetime τ 0.5 ms. Analogous experiments, reported here, with bovine serum albumin yield a non-exponential decay which may be decomposed into two components. The yield of the longer lived triplet, with an average τ of ∼6 ms, is significantly enhanced by addition of a 20 fold excess of sodium dodecyl sulfate or 1 M Br-. The yield of the shorter lived triplet, τ 0.4 ms, is unaffected by these treatments as was previously observed for the single indole in HSA. Thus, the short lived triplet may be assigned to the indole in BSA which is homologous to the one in HSA. The longer lived triplet may be assigned to the remaining indole of BSA. On the bases of wavelength dependence studies, two additional transients may be identified; the electron adduct of the disulfide bond, λ; 420 with a τ 30 ms, and the neutral indole radical,λ; 520 nm with τ ls. These results suggest that the triplet, because of its long τ, will be a valuable intrinsic reporter group for the study of the structure and dynamics of proteins in solution at room temperature.

— The initial yields of the cation and neutral radicals and the triplet are greatly enhanced when high concentrations of Br- are present during the flash photolysis of aqueous solutions containing either tryptophan or N-acetyl-L-trytophanamide. The present study is an attempt to elucidate the mechanism by which Br- induces these effects. The results obtained indicate that the initial event involves an interaction between the fluorescent state and Br- to promote the formation of a long-lived radical precursor that may be the triplet. It is shown that all of the Br--induced neutral and cation radical formation originate from this long-lived state. Furthermore, it was found that the mechanism of radical production from the Br--induced long-lived precursor does not involve hydrated electron formation.

— The flash photolysis of N-acetyl-L-tryptophanamide (NATA) in the presence of the fluorescence quenchers, imidazole, acrylamide and trichloroethanol, has been investigated. Imadazole and acrylamide induce a decrease in the NATA radical yield which correlates with their NATA fluorescence quenching action. These observations suggest that the fluorescent state is primarily responsible for the monophotonic photoionization processes. The acrylamide data also suggest that 40–65% of the NATA radicals arise from a long-lived state (τ˜μs) which must originate from the fluorescent state. Unlike imidazole and acrylamide, trichloroethanol enhances the radical yield by reaction with excited state precursors. Mechanisms for the quenching of fluorescence and the long-lived states are discussed.

The reaction of the p-aminophenylthiyl radical (RS) with galvinoxyl has been used to determine the extinction coefficient of RS in several solvents. Values of ϵRS range from 11 000 M−1 cm−1 in cyclohexane to 19 000 M−1 cm−1 in acetonitrile. The addition of RS to galvinoxyl and the second-order recombination of RS both proceed at nearly diffusion-controlled rates with rate constants of (1.1 − 2) × 109 M−1 s−1. Rates of addition of RS to styrene have been determined to elucidate ground state radical solvation effects. In cyclohexane RS adds to styrene with a rate constant of 1.7 × 105 M−1 s−1. Increasing the polarity of the solvent lowers this rate constant to a limiting value of 4.8 X 103 M−1 s−1 in acetone and more polar solvents.

The kinetics of the addition of p-aminophenylthiyl radicals to vinyl monomers were studied in cyclohexane. Thiyl radicals, generated by flash photolysis of the p-aminophenyldisulfide, react with monomers in a reversible fashion. These addition rates show a good correlation with the electron density of the monomer double bond and with stability parameters of the resulting adduct.

A simple analytical method for aldehyde determinations in ambient air is described. The method involved trapping the aldehydes as their DNPH derivatives in acetonitrile solution and then direct injection and analysis of the resulting solution on a reversed phase HPLC column with simultaneous detection at 254 and 360 nm. Several comparison studies are described.

The rate constant for the combination of trichloromethyl radicals in the gas phase has been measured by applying the rotating sector technique to the gas phase carbon tetrachloride–cyclohexane photochemical system. A temperature-independent rate constant, k5, of 3.9 ± 1.0 × 1012 cc mole−1 sec−1 was found. Arrhenius parameters for the reaction were found to be given by the expression log k4 = 11.79 – (10,700/2.3 RT).

The rate constant for the combination of 1,1-dichloro-2,2,2-trifluoroethyl radicals in the gas phase has been measured by applying the rotating sector technique to the 1,1,1-trichloro-2,2,2-trifluoroethane–cyclohexane photochemical system. The combination rate constant, k5, was found to be 6.6 × 1012 cc mole−1 sec−1. Arrhenius parameters for the reaction, are given by the expression log k4 = 11.81 – (9700/2.3RT).

Radioiodine scavenging methods were employed in the radiolysis of liquid hydrocarbons to examine details of the production and reaction of methyl radicals. Carrierfree chromatographic separation of the radio-methyl iodide enabled studies to be carried out at iodine concentrations down to 5 x 10/sup -7/ M. In the radiolysis of 2,2,4trimethylpentaneiodine solutions at room temperature the methyl iodide yield is shown to be independent of iodine concentration above 10/ sup -5/ M. Competition between the scavenging reaction and abstraction of hydrogen from the solvent by the methyl radicals was observed in the region of 10/ sup -6/ M. In the absence of iodine the methane yield is shown to be dependent on absorbed dose rate in the region of 10/sup 7/ rads/hr. At this dose rate the abstraction process competes effectively with the reaction between methyl radicals and other alkyl radicals. Measurement of the competition rates of the above reactions, together with rate information from paramagnetic resonance experiments, allows an estimate of 3 x 10/sup 8/ liters mole/sup -1/ sec/sup -1/ to be made for the absolute second-order rate constant for the reaction of methyl radicals with molecular iodine in liquid 2,2,4-trimethylpentane. The efficiency of reaction per encounter is shown tomore » be close to unity with little or no activation energy involved. A survey of methyl radical production from various hydrocarbons showed that carbon-methyl bond rupture deviates substantially from that predicted by a simple model involving only a statistical consideration of the number of methyl groups in the molecule. The yields were found to be very markedly dependent on specific details of the structure of the species being irradiated. For individual homologous series the methyl radical yields were observed to be decreasing monotonic functions of the chain length of the hydrocarbon. For the paraffins and isoparaffins the yield was proportional to the inverse square of the number of carboncarbon bonds in the molecule. By a generalization of this relationship, an empirical rule was developed which allows reasonable quantitative estimates to be made for the methyl radical yields from even highly branched hydrocarbons. (auth)« less

The thermal decomposition of hexachloroethane in the presence of chlorine has been studied over the temperature range 340-400°C and a pressure range of 0.5°2.5 atm. The rate of the unimolecular CC bond spliting reaction can be described by the Arrhenius equation Comparison of these rate data with thermodynamic data suggests a combination rate for CCl3 radicals which is consistent with earlier measurements.

The rates of hydrated electron reactions with cysteamine, cysteine, thioglycol, α-mercaptopropionic acid, β-mercaptopropionic acid, and penicillamine have been studied in the pH 1-3 region. Hydrogen yields, which are a function of pH in this region, were used to monitor the competition between H+ and RSH for hydrated electrons. Corrections were applied to the observed rate constants to account for dissociation of the COOH group and the ionic strength effect on hydrated electron reactions. In the cases of cysteine and penicillamine, the rate constants for reaction with protonated amino acids at infinite dilution were greater by a factor of 3-5 than those for reaction with the zwitterion. Uncharged species show no pH dependence of the rate constant within this region. All rate constants measured were of comparable magnitude and approached the diffusion controlled limit.