To inform prospective design rules for controlling aza-arene
photochemistry,
we studied hydrogen-bonded complexes of 2,5,8-tris(4-methoxyphenyl)-1,3,4,6,7,9,9b-heptaazaphenalene
(TAHz), a molecular photocatalyst chemically related to graphitic
carbon nitride, with a variety of phenol derivatives. We have focused
on excited state proton-coupled electron transfer (ES-PCET) reactions
of heptazines because the excited state properties governing this
process remain conceptually opaque compared to proton reduction reactions
for these materials. We used ground-state absorption, time-resolved
photoluminescence, and ab initio quantum chemical calculations to
analyze TAHz reactivity toward a series of six para-substituted phenol
derivatives. We determined association constants (K
A), excited-state quenching rate constants (k
Q), kinetic isotope effects, and transition-state barriers
(ΔE
⧧). From this data, we
provide a generalizable picture of hydrogen bond formation and excited
state reactivity of heptazine-based materials with hydrogen-atom donating
solvents. These results provide important insights into strategies
to tune charge transfer state energies and increase ES-PCET rates.
Multiple morphological abnormalities of flagella (MMAF) is one kind of severe teratozoospermia. Gene mutations reported in previous works only revealed the pathogenesis of approximately half of the MMAF cases, and more genetic defects in MMAF need to be explored. In the present study, we performed a genetic analysis on Han Chinese men with MMAF using whole‐exome sequencing. After filtering out the cases with known gene mutations, we identified five novel mutation sites in the DNAH2 gene in three cases from three families. These mutations were validated through Sanger sequencing and absent in all control individuals. In silico analysis revealed that these DNAH2 variations are deleterious. The spermatozoa with DNAH2 mutations showed severely disarranged axonemal structures with mitochondrial sheath defection. The DNAH2 protein level was significantly decreased and inner dynein arms were absent in the spermatozoa of patients. ICSI treatment was performed for two MMAF patients with DNAH2 mutations and the associated couples successfully achieved pregnancy, indicating good nuclear quality of the sperm from the DNAH2 mutant patients. Together, these data suggest that the DNAH2 mutation can cause severe sperm flagella defects that damage sperm motility. These results provide a novel genetic pathogeny for the human MMAF phenotype.
It has recently been shown that cycl[3.3.3]azine and heptazine (1,3,4,6,7,9,9b-heptaazaphenalene) as well as related azaphenalenes exhibit inverted singlet and triplet states, that is, the energy of the lowest singlet excited...
Recently,
a derivative of the heptazine (tris-triazine) molecule,
trianisole-heptazine (TAHz), was synthesized and was shown to catalyze
the oxidation of water to hydroxyl radicals under 365 nm LED light
in a homogeneous reaction (E. J. Rabe et al., J. Phys. Chem. Lett2018962576261). The possibility of water photo-oxidation
with a precisely defined molecular catalyst in neat solvents opens
new perspectives for clarifying the fundamental reaction mechanisms
involved in water oxidation photocatalysis. In the present work, the
effects of chemical substituents on the three CH positions of Hz on
the photocatalytic reactivity were explored with wave function-based ab initio electronic-structure calculations for hydrogen-bonded
complexes of Hz and three selected Hz derivatives (TAHz, trichloro-Hz,
and tricyano-Hz) with a water molecule. While anisole is an electron-donating
substituent, Cl is a weakly electron-withdrawing substituent and CN
is a strongly electron-withdrawing substituent. It is shown that the
barrier for the photoinduced abstraction of an H atom from the water
molecule is raised (lowered) by electron-donating (electron-withdrawing)
substituents. The highly mobile and reactive hydroxyl radicals generated
by water oxidation can recombine with the reduced chromophore radicals
to yield photohydrates. The effect of substituents on the thermodynamics
of the photohydration reaction was computed. Among the four chromophores
studied, TAHz stands out on account of the metastability of its photohydrate,
which suggests self-healing of the photocatalyst after oxidation of
TAHzH radicals by OH radicals. In addition, the effect of substituents
on the H atom photodetachment reaction from the reduced chromophores,
which closes the catalytic cycle, has been investigated. The energy
of the repulsive 2πσ* state, which drives the
photodetachment reaction is lowered (raised) by electron-donating
(electron withdrawing) substituents. All four chromophores exhibit
inverted S1/T1 gaps. This feature eliminates
long-lived triplet states and thus avoids the activation of molecular
oxygen to highly reactive singlet oxygen.
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